chapter
stringlengths 1.97k
1.53M
| path
stringlengths 47
241
|
|---|---|
Thumbnail: Space-filling model of a section of the polyethylene terephthalate polymer, also known as PET and PETE, a polyester used in most plastic bottles. Color code: Carbon, C (black), Hydrogen, H (white), and Oxygen, O (red). (Public Domain; Jynto(opens in new window)).
10: Polymers
Learning Objectives
• Define the terms monomer and polymer.
• Know the different types of natural polymers.
A polymer is a large molecule, or macromolecule, composed of many repeated subunits.The term "polymer" derives from the Greek word polus (meaning "many, much") and meros (meaning "part"), and refers to a molecule whose structure is composed of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant properties. As shown schematically in Figure \(1\).
Due to their broad range of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals. The terms polymer and resin are often synonymous with plastic.
Natural Polymers
Some very important biological materials are polymers. Of the three major food groups, polymers are represented in two: proteins and carbohydrates. Proteins are polymers of amino acids, which are monomers that have an amine functional group and a carboxylic acid functional group. Proteins play a crucial role in living organisms.
Linking hundreds of glucose molecules together makes a relatively common material known as starch:
Starch is an important source of energy in the human diet. Note how individual glucose units are joined together. They can also be joined together in another way, like this:
This polymer is known as cellulose. Cellulose is a major component in the cell walls of plants. Curiously, despite the similarity in the building blocks, some animals (such as humans) cannot digest cellulose; those animals that can digest cellulose typically rely on symbiotic bacteria in the digestive tract for the actual digestion. Animals do not have the proper enzymes to break apart the glucose units in cellulose, so it passes through the digestive tract and is considered dietary fiber.
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are also polymers, composed of long, three-part chains consisting of phosphate groups, sugars with 5 C atoms (ribose or deoxyribose), and N-containing rings referred to as bases. Each combination of the three parts is called a nucleotide; DNA and RNA are essentially polymers of nucleotides that have rather complicated but intriguing structures (Figure \(2\) - Nucleotides). DNA is the fundamental material in chromosomes and is directly responsible for heredity, while RNA is an essential substance in protein synthesis.
The DNA in our cells is a polymer of nucleotides, each of which is composed of a phosphate group, a sugar, and a N-containing base
The above mentioned biopolymers (polymers produced by living organisms) are discussed further in Chapter 16.
Celluloid: Billiard Balls
Celluloids are a class of compounds created from nitrocellulose (partially nitrated cellulose) and camphor, with added dyes and other agents. Generally considered the first thermoplastic, it was first created as Parkesinein (by Alexander Parkes of Birmingham England) in 1856 and as Xylonite in 1869. In the 1860s, an American, John Wesley Hyatt, acquired Parkes's patent and began experimenting with cellulose nitrate with the intention of manufacturing billiard balls, which until that time were made from ivory. In the 1870s the modified plastic was registered as "celluloid".
The main use was in movie and photography film industries, which used only celluloid film stock prior to the adoption of acetate safety film in the 1950s. Celluloid is highly flammable, difficult and expensive to produce and no longer widely used; its most common uses today are in table tennis balls, musical instruments, and guitar picks.
Bakelite (sometimes spelled Baekelite) or polyoxybenzylmethylenglycolanhydride was the first plastic made from synthetic components. It is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde. It was developed by the Belgian-American chemist Leo Baekeland in Yonkers, New York, in 1907.
Bakelite was patented on December 7, 1909. The creation of a synthetic plastic was revolutionary for its electrical non conductivity and heat-resistant properties in electrical insulators, radio and telephone casings and such diverse products as kitchenware, jewelry, pipe stems, children's toys, and firearms.
Polymers
Video \(2\) Polymers Crash Course
Summary
• Polymers are giant molecules that consist of long chains of units called monomers connected by covalent bonds.
• Polymerization is the process of linking monomers together to form a polymer.
• Plastic is the general term for polymers made from synthetic materials.
• Several important biological polymers include proteins, starch, cellulose, DNA and RNA.
Contributors and Attributions
• Joshua Halpern, Scott Sinex and Scott Johnson
• TextMap: Beginning Chemistry (Ball et al.)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.01%3A_Polymerization_-_Making_Big_Ones_Out_of_Little_Ones.txt |
Learning Objectives
• List the different types of polyethylene.
• Differentiate between thermolastic and thermosetting polymers.
Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898. Industrial production of low-density polyethylene (LDPE) began in 1939 in England. Because polyethylene was found to have very low-loss properties at very high frequency radio waves, commercial distribution in Britain was suspended on the outbreak of World War II in order to produce insulation for UHF (ultra high frequency) and SHF (super high frequency) cables of radar sets.
Polyethylene or polythene is the most common plastic. As of 2017, over 100 million tonnes of polyethylene resins are produced annually, accounting for 34% of the total plastics market. Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, with most having the chemical formula (C2H4)n. PE is usually a mixture of similar polymers of ethylene with various values of n.
Polymers based on skeletons with only carbon are all synthetic. Let's begin by looking at polyethylene Figure \(1\) . It is the simplest polymer, consisting of random-length (but generally very long) chains made up of two-carbon units.
You will notice some "fuzziness" in the way that the polyethylene structures are represented above. The squiggly lines at the ends of the long structure indicate that the same pattern extends indefinitely. The more compact notation on the right shows the minimal repeating unit enclosed in brackets overprinted with a dash; this means the same thing and is the preferred way of depicting polymer structures.
Types of Polyethylene
Most of synthetic polymers are formed from ethylene. The relative lengths of the chains and any branches control the properties of polyethylene. The most important polymer grades with regard to volume are High density polyethylene (HDPE) Low density polyethylene (LDPE), and Linear low density polyethylene (LLDPE).
HDPE (High density polyethylene) is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching. The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers. HDPE has high tensile strength. It is used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and water pipes. One-third of all toys are manufactured from HDPE. In 2007, the global HDPE consumption reached a volume of more than 30 million tons.
LDPE (Low density polyethylene) is defined by a density range of 0.910–0.940 g/cm3. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap. In 2013, the global LDPE market had a volume of almost US\$33 billion.
LLDPE (Linear low density polyethylene) is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches. LLDPE has higher tensile strength than LDPE, and it exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown, compared with LDPE, with better environmental stress-cracking resistance, but is not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. It is used for cable coverings, toys, lids, buckets, containers, and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility, and relative transparency. Product examples range from agricultural films, Saran wrap, and bubble wrap, to multilayer and composite films. In 2013, the world LLDPE market reached a volume of US\$40 billion.
Polyethylene Production
Video \(1\) The commercial production of Polyethylene (polyethene). from the Royal Society of Chemistry
Thermoplastic and Thermosetting Polymers
Polymers can be classified by their physical response to heating. Polyethylene is a thermoplastic; however, it can become a thermoset plastic when modified (such as cross-linked polyethylene). Thermoplastics are plastics that soften when heated and become firm again when cooled. This is the more popular type of plastic because the heating and cooling may be repeated and the thermoplastic may be reformed.
Thermosets are plastics that soften when heated and can be molded, but harden permanently. They will decompose when reheated. An example is Bakelite, which is used in toasters, handles for pots and pans, dishes, electrical outlets and billiard balls.
Summary
Polyethylene is the long chain polymer formed from ethylene (ethene) monomers.
Polyethylene can be classified as HDPE, LDPE, and LLDPE based on how close the polymer chains pack together affecting its density.
Polymers can be classified as thermoplastics (can be reformed after repeated heating) or thermosets (harden permanently) based on their physical response to heating. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.02%3A_Polyethylene_-_From_the_Battle_of_Britain_to_Bread_Bags.txt |
Learning Objectives
• Define addition polymerization.
• Draw the structure of a polymer from its monomer.
• Know the uses/applications of common polymers.
Addition polymerization and condensation polymerization are two modes of polymerization reactions in the formation of polymers. In addition polymerization, the monomer molecules bond to each other without the loss of any other atoms. Addition polymers from alkene monomers or substituted alkene monomers are the biggest groups of polymers in this class. Ring opening polymerization can occur without the loss of any small molecules. Whereas, in condensation polymerization (Section 10.5) two different monomers combine with the loss of a small molecule, usually water. Most polyesters and polyamides (nylon) are in this class of polymers.
Addition or chain-growth polymerization involves the rearrangement of bonds within the monomer in such a way that the monomers link up directly with each other:
In order to make this happen, a chemically active molecule (called an initiator) is needed to start what is known as a chain reaction. The manufacture of polyethylene is a very common example of such a process. It employs a free-radical initiator that donates its unpaired electron to the monomer, making the latter highly reactive and able to form a bond with another monomer at this site.
In theory, only a single chain-initiation process needs to take place, and the chain-propagation step then repeats itself indefinitely, but in practice multiple initiation steps are required, and eventually two radicals react (chain termination) to bring the polymerization to a halt.
As with all polymerizations, chains having a range of molecular weights are produced, and this range can be altered by controlling the pressure and temperature of the process.
Polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.Phillips Petroleum chemists J. Paul Hogan and Robert Banks first polymerized propylene in 1951. Propylene was first polymerized to a crystalline isotactic polymer by Giulio Natta as well as by the German chemist Karl Rehn in March 1954. Polypropylene is used alone or as a copolymer, usually with with ethylene. These polymers have an exceptionally wide range of uses — rope, binder covers, plastic bottles, staple yarns, non-woven fabrics, electric kettles. When uncolored, it is translucent but not transparent. Its resistance to fatigue makes it useful for food containers and their lids, and flip-top lids on bottled products such as ketchup.
After polyethylene, polypropylene is the most profitable plastic with revenues expected to exceed US\$145 billion by 2019. The sales of this material are forecast to grow at a rate of 5.8% per year until 2021. Polypropylene is produced by the chain-growth polymerization of propylene:
Polystyrene
Polystyrene was discovered in 1839 by Eduard Simon, an apothecary from Berlin.In 1941, Dow Chemical invented a Styrofoam process. Polystyrene is transparent but rather brittle, and yellows under uv light. Widely used for inexpensive packaging materials and "take-out trays", foam "packaging peanuts", CD cases, foam-walled drink cups, and other thin-walled and moldable parts.
Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam with a normal density range of 11 to 32 kg/m3. It is usually white and made of pre-expanded polystyrene beads. EPS is used for food containers, molded sheets for building insulation, and packing material either as solid blocks formed to accommodate the item being protected or as loose-fill "peanuts" cushioning fragile items inside boxes. EPS is colloquially called "styrofoam" in the United States and Canada, an incorrectly applied genericization of Dow Chemical's brand of extruded polystyrene.
Polystyrene results when styrene monomers interconnect. In the polymerisation, the carbon–carbon π bond of the vinyl group is broken and a new carbon–carbon σ bond is formed, attaching to the carbon of another styrene monomer to the chain.
Polyvinyl Chloride
PVC was accidentally synthesized in 1872 by German chemist Eugen Baumann.. The polymer appeared as a white solid inside a flask of vinyl chloride that had been left exposed to sunlight. Polyvinyl chloride (PVC) is the world's third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene. About 40 million tonnes are produced per year. Polyvinyl chloride is one of the world's most widely used polymers. By itself it is quite rigid and used in construction materials such as pipes, house siding, flooring. Addition of plasticizers make it soft and flexible for use in upholstery, electrical insulation, shower curtains and waterproof fabrics. There is some effort being made to phase out this polymer owing to environmental concerns.
Polytetrafluorehtylene (PTFE): The Nonstick Coating
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best-known brand name of PTFE-based formulas is Teflon (Figure \(1\)) Aldehydby Chemours. Chemours is a spin-off of DuPont, which originally discovered the compound in 1938. This highly-crystalline fluorocarbon is exceptionally inert to chemicals and solvents. Water and oils do not wet it, which accounts for its use in cooking ware and other anti-stick applications, including personal care products.
These properties — non-adhesion to other materials, non-wetability, and very low coefficient of friction ("slipperyness") — have their origin in the highly electronegative nature of fluorine whose atoms partly shield the carbon chain. Fluorine's outer electrons are so strongly attracted to its nucleus that they are less available to participate in London (dispersion force) interactions.
Some common addition polymers are listed in Tables \(1\) and \(2\). Note that all the monomers have carbon-to-carbon double bonds. Many polymers are mundane (e.g., plastic bags, food wrap, toys, and tableware), but there are also polymers that conduct electricity, have amazing adhesive properties, or are stronger than steel but much lighter in weight.
Table \(1\) Some Addition Polymers.
Figure \(2\)
Table \(2\) Other Polymers and their Uses.
Monomer Polymer Name Trade Name(s) Uses
H2C=CCl2 polyvinylidene dichloride Saran Clinging food wrap
H2C=CH(CN) polyacrylonitrile Orlon, Acrilan, Creslan Fibers for textiles, carpets, upholstery
H2C=CH(OCOCH3) polyvinyl acetate Elmer's glue - Silly Putty Demo
H2C=CH(OH) polyvinyl alcohol Ghostbusters Demo
H2C=C(CH3)COOCH3 polymethyl methacrylate Plexiglass, Lucite Stiff, clear, plastic sheets, blocks, tubing, and other shapes
H2C=CH-C(CH3)=CH2 polyisoprene natural or some synthetic rubber applications similar to natural rubber
H2C=CH-CH=CH2 polybutadiene polybutadiene synthetic rubber select synthetic rubber applications
H2C=CH-CCl=CH2 polychloroprene Neoprene chemically-resistant rubber
Processing Polymers
Molding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. This itself may have been made using a pattern or model of the final object. Compression molding is a forming process in which a plastic material is placed directly into a heated metal mold then is softened by the heat and therefore forced to conform to the shape of the mold, as the mold closes. Transfer molding (BrE moulding) is a manufacturing process where casting material is forced into a mold. Transfer molding is different from compression molding in that the mold is enclosed [Hayward] rather than open to the fill plunger resulting in higher dimensional tolerances and less environmental impact.
Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting), glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. Drawing is a similar process, which uses the tensile strength of the material to pull it through the die. This limits the amount of change which can be performed in one step, so it is limited to simpler shapes, and multiple stages are usually needed. Drawing is the main way to produce wire. Metal bars and tubes are also often drawn.
Example \(1\)
Draw the polymer that results from the polymerization of tetrafluoroethylene.
Solution
In the case of this monomer, the double bond opens up and joins to other monomers, just as with ethylene. The polymer that is made has this structure:
Exercise \(1\)
Draw the polymer that results from the polymerization of the following monomers:
a.
b.
Summary
• Addition polymerization is when the monomer molecules bond to each other without the loss of any other atoms.
• Examples of addition polymers include polyethylene, polypropylene, polystyrene, polyvinylchloride, polytetrafluoroethylene, etc.
• Many objects in daily use from packing, wrapping, and building materials include half of all polymers synthesized. Other uses include textiles, many electronic appliance casings, CD's, automobile parts, and many others are made from polymers. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.03%3A_Addition_Polymerization_-_One__One__One__..._Gives_One.txt |
Learning Objectives
• Know the properties of rubber.
• Describe the process of vulcanization.
Natural rubber, also called India rubber or caoutchouc, as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water. Thailand and Indonesia are two of the leading rubber producers. Forms of polyisoprene that are used as natural rubbers are classified as elastomers.
Isoprene Polyisoprene (rubber)
Currently, rubber is harvested mainly in the form of the latex from the rubber tree or others. The latex is a sticky, milky colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into rubber ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for marketing.
Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio and high resilience, and is extremely waterproof.
Vulcanization
In 1832–1834 Nathaniel Hayward and Friedrich Ludersdorf discovered that rubber treated with sulfur lost its stickiness. It is likely Hayward shared his discovery with Charles Goodyear, possibly inspiring him to make the discovery of vulcanization. Thomas Hancock (1786–1865), a scientist and engineer, was the first to patent vulcanization of rubber. He was awarded a British patent on May 21, 1845. Three weeks later, on June 15, 1845, Charles Goodyear was awarded a patent in the United States. It was Hancock's friend William Brockedon who coined term 'vulcanization'. Goodyear claimed that he had discovered vulcanization earlier, in 1839.
Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by heating them with sulfur or other equivalent curatives or accelerators. Sulfur forms cross-links (bridges) between sections of polymer chain which results in increased rigidity and durability, as well as other changes in the mechanical and electronic properties of the material. A vast array of products are made with vulcanized rubber, including tires, shoe soles, hoses, and conveyor belts. The term vulcanization is derived from Vulcan, the Roman god of fire.
Synthetic Rubber
The expanded use of bicycles, and particularly their pneumatic tires, starting in the 1880s, created increased demand for rubber. In 1909 a team headed by Fritz Hofmann, working at the Bayer laboratory in Germany, succeeded in polymerizing isoprene, the first synthetic rubber. A synthetic rubber is any artifiical elastomer. These are mainly polymers synthesized from petroleum by products.
Polybutadiene rubber is a polymer formed from the polymerization of the monomer 1,3-butadiene. Polybutadiene has a high resistance to wear and is used especially in the manufacture of tires, which consumes about 70% of the production. Another 25% is used as an additive to improve the toughness (impact resistance) of plastics such as polystyrene and acrylonitrile butadiene styrene (ABS). Polybutadiene rubber accounted for about a quarter of total global consumption of synthetic rubbers in 2012. It is also used to manufacture golf balls, various elastic objects and to coat or encapsulate electronic assemblies, offering high electrical resistivity.
Neoprene (also polychloroprene or pc-rubber) is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene exhibits good chemical stability and maintains flexibility over a wide temperature range. Neoprene is sold either as solid rubber or in latex form and is used in a wide variety of applications, such as laptop sleeves, orthopaedic braces (wrist, knee, etc.), electrical insulation, liquid and sheet applied elastomeric membranes or flashings, and automotive fan belts.Neoprene is produced by free-radical polymerization of chloroprene. In commercial production, this polymer is prepared by free radical emulsion polymerization. Polymerization is initiated using potassium persulfate. Bifunctional nucleophiles, metal oxides (e.g. zinc oxide), and thioureas are used to crosslink individual polymer strands.
Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene (the version developed by Goodyear is called Neolite). These materials have good abrasion resistance and good aging stability when protected by additives. In 2012, more than 5.4 million tonnes of SBR were processed worldwide. About 50% of car tires are made from various types of SBR.
It is a commodity material which competes with natural rubber. The elastomer is used widely in pneumatic tires. Other uses include shoe heels and soles, gaskets, and even chewing gum.
Polymers in Paints
Polymers are one of the key components of modern paints that function as binders. The binder is the film-forming component of paint. It is the only component that is always present among all the various types of formulations. The binder imparts properties such as gloss, durability, flexibility, and toughness. Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, or siloxanes or oils.
Summary
The many uses of natural rubber has led to development and manufacture of synthetic rubber.
Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by heating them with sulfur or other equivalent curatives or accelerators.
Three examples of synthetic rubber used in various applications are polybutadiene, polychloroprene (Neoprene), and styrene-butadiene rubber (SBR)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.04%3A_Rubber_and_Other_Elastomers.txt |
Learning Objectives
• Know the difference between addition and condensation polymerization.
• Know the properties and uses of common synthetic condensation polymers.
A large number of important and useful polymeric materials are not formed by addition polymerizaiton, but proceed instead by conventional functional group transformations of polyfunctional reactants. These polymerizations often (but not always) occur with loss of a small byproduct, such as water, and generally (but not always) combine two different components in an alternating structure. The polyester Dacron and the polyamide Nylon 66, shown here, are two examples of synthetic condensation polymers, also known as step-growth polymers. In contrast to addition polymerizaion, most of which grow by carbon-carbon bond formation, step-growth polymers generally grow by carbon-heteroatom bond formation (C-O & C-N in Dacron & Nylon respectively). Although polymers of this kind might be considered to be alternating copolymers, the repeating monomeric unit is usually defined as a combined moiety.
Examples of naturally occurring condensation polymers are cellulose, starch, the polypeptide chains of proteins, and poly(β-hydroxybutyric acid), a polyester synthesized in large quantity by certain soil and water bacteria.
Nylon and Other Polyamides
Condensation polymerization (also known as step-growth) requires that the monomers possess two or more kinds of functional groups that are able to react with each other in such a way that parts of these groups combine to form a small molecule (often H2O) which is eliminated from the two pieces. The now-empty bonding positions on the two monomers can then join together .
One important class of condensation polymers are polyamides. They arise from the reaction of carboxylic acid and an amine. Examples include nylons and proteins.
When prepared from diamines and dicarboxylic acids, e.g. the production of nylon 66, the polymerization produces two molecules of water per repeat unit:
n H2N-X-NH2 + n HO2C-Y-CO2H → [HN-X-NHC(O)-Y-C(O)]n + 2n H2O
Note that the monomeric units that make up the polymer are not identical with the starting components.
Nylon is a thermoplastic silky material that can be melt-processed into fibers, films, or shapes.:2 It is made of repeating units linked by amide links similar to the peptide bonds in proteins. Nylon polymers can be mixed with a wide variety of additives to achieve many different property variations. Nylon polymers have found significant commercial applications in fabric and fibers (apparel, flooring and rubber reinforcement), in shapes (molded parts for cars, electrical equipment, etc.), and in films (mostly for food packaging).
Nylon was the first commercially successful synthetic thermoplastic polymer. DuPont began its research project in 1927. The first example of nylon (nylon 6,6) was produced using diamines on February 28, 1935, by Wallace Hume Carothers (Figure \(1\)) at DuPont's research facility at the DuPont Experimental Station. In response to Carothers' work, Paul Schlack at IG Farben developed nylon 6, a different molecule based on caprolactam, on January 29, 1938.:10
Nylon was first used commercially in a nylon-bristled toothbrush in 1938, followed more famously in women's stockings or "nylons" which were shown at the 1939 New York World's Fair and first sold commercially in 1940. During World War II, almost all nylon production was diverted to the military for use in parachutesand parachute cord. Wartime uses of nylon and other plastics greatly increased the market for the new materials.
Other polyamides of practical use include nylon 6 and kevlar. Nylon-6 is made from a monomer called caprolactam.
Notice that this already contains an amide link. When this molecule polymerizes, the ring opens, and the molecules join up in a continuous chain. Nylon 6 fibers are tough, possessing high tensile strength, as well as elasticity and lustre. They are wrinkleproof and highly resistant to abrasion and chemicals such as acids and alkalis. The fibers can absorb up to 2.4% of water, although this lowers tensile strength.
Kevlar is similar in structure to nylon-6,6 except that instead of the amide links joining chains of carbon atoms together, they join benzene rings. The two monomers are benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene.
If you line these up and remove water between the -COOH and -NH2 groups in the same way as we did with nylon-6,6, you get the structure of Kevlar:
Kevlar is a very strong material - about five times as strong as steel, weight for weight. It is used in bulletproof vests, in composites for boat construction, in lightweight mountaineering ropes, and for lightweight skis and racquets - amongst many other things.
Polyethylene Terephthalate and Other Polyesters
One important class of condensation polymers are polyesters. They arise from the reaction of carboxylic acid and an alcohol. Examples include polyesters, e.g. polyethyleneterephthalate:
n HO-X-OH + n HO2C-Y-CO2H → [O-X-O2C-Y-C(O)]n + (3n-2) H2O
Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins.
It may also be referred to by the brand names Terylene in the UK, Lavsan in Russia and the former Soviet Union, and Dacron in the US.
The majority of the world's PET production is for synthetic fibres (in excess of 60%), with bottle production accounting for about 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. Polyester makes up about 18% of world polymer production and is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).
Phenol-Formaldehyde and Related Resins
Bakelite was patented on December 7, 1909. The creation of a synthetic plastic was revolutionary for its electrical nonconductivity and heat-resistant properties in electrical insulators, radio and telephone casings and such diverse products as kitchenware, jewelry, pipe stems, children's toys, and firearms.
In recent years the "retro" appeal of old Bakelite products has made them collectible.
Bakelite was designated a National Historic Chemical Landmark on November 9, 1993, by the American Chemical Society in recognition of its significance as the world's first synthetic plastic.
Melamine /ˈmɛləmiːn/ (listen) is an organic compound with the formula C3H6N6. This white solid is a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire retardant properties due to its release of nitrogen gas when burned or charred. Melamine can be combined with formaldehyde and other agents to produce melamine resins. Such resins are characteristically durable thermosetting plastic used in high pressure decorative laminates such as Formica, melamine dinnerware, laminate flooring, and dry erase boards. Melamine foam is used as insulation, soundproofing material and in polymeric cleaning products, such as Magic Eraser.
Other Condensation Polymers
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily worked, molded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates received their name because they are polymers containing carbonate groups (−O−(C=O)−O−). A balance of useful features, including temperature resistance, impact resistance and optical properties, positions polycarbonates between commodity plastics and engineering plastics.
The main polycarbonate material is produced by the reaction of bisphenol A (BPA) and phosgene COCl2. The overall reaction can be written as follows:
Polycarbonate is mainly used for electronic applications that capitalize on its collective safety features. Being a good electrical insulator and having heat-resistant and flame-retardant properties. The second largest consumer of polycarbonates is the construction industry, e.g. for domelights, flat or curved glazing, and sound walls, which all use extruded flat solid or multiwall sheet, or corrugated sheet. A major application of polycarbonate is the production of Compact Discs, DVDs, and Blu-ray Discs.
Polyurethane (PUR and PU) is a polymer composed of organic units joined by carbamate (urethane) links. While most polyurethanes are thermosetting polymers that do not melt when heated, thermoplastic polyurethanes are also available.
Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics. Polyurethanes are produced by reacting an isocyanate containing two or more isocyanate groups per molecule (R−(N=C=O)n) with a polyol containing on average two or more hydroxyl groups per molecule (R′−(OH)n) in the presence of a catalyst or by activation with ultraviolet light.
Polyurethanes are used in the manufacture of high-resilience foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires (such as roller coaster, escalator, shopping cart, elevator, and skateboard wheels), automotive suspension bushings, electrical potting compounds, high performance adhesives, surface coatings and surface sealants, synthetic fibers (e.g., Spandex), carpet underlay, hard-plastic parts (e.g., for electronic instruments), condoms, and hoses.
Health and Safety
Fully reacted polyurethane polymer is chemically inert. No exposure limits have been established in the U.S. by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity.
Polyurethane polymer is a combustible solid and can be ignited if exposed to an open flame. Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.Because of the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful. California later issued Technical Bulletin 117 2013 which allowed most polyurethane foam to pass flammability tests without the use of flame retardants. Green Science Policy Institute states: "Although the new standard can be met without flame retardants, it does NOT ban their use. Consumers who wish to reduce household exposure to flame retardants can look for a TB117-2013 tag on furniture, and verify with retailers that products do not contain flame retardants."
Liquid resin blends and isocyanates may contain hazardous or regulated components. Isocyanates are known skin and respiratory sensitizers. Additionally, amines, glycols, and phosphate present in spray polyurethane foams present risks.
Exposure to chemicals that may be emitted during or after application of polyurethane spray foam (such as isocyanates) are harmful to human health and therefore special precautions are required during and after this process.
In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment). In Europe, health and safety information is available from ISOPA, the European Diisocyanate and Polyol Producers Association.
Epoxy is either any of the basic components or the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups.
Epoxy resins may be reacted (cross-linked) either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols (usually called mercaptans). These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. The structure of bisphenol-A diglycidyl ether epoxy resin is shown below: n denotes the number of polymerized subunits and is typically in the range from 0 to 25
Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has a wide range of applications, including metal coatings, use in electronics/electrical components/LEDs, high tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials and structural adhesives. Epoxy is sometimes used as a glue (see image at right).
Composite Materials
A composite material (also called a composition material or shortened to composite, which is the common name) is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. Composite materials are generally used for buildings, bridges, and structures such as boat hulls, swimming pool panels, racing car bodies, shower stalls, bathtubs, storage tanks, imitation granite and cultured marble sinks and countertops.
Composites are made up of individual materials referred to as constituent materials. There are two main categories of constituent materials: matrix (binder) and reinforcement. At least one portion of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the product or structure to choose an optimum combination. Many commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, PEEK (polyether ether ketone), and others. Common fibres used for reinforcement include glass fibres, carbon fibres, cellulose (wood/paper fibre and straw) and high strength polymers for example aramid. Silicon carbide fibers are used for some high temperature applications.
One of the most common and familiar composite is fibreglass, in which small glass fibre are embedded within a polymeric material (normally an epoxy or polyester). The glass e is relatively strong and stiff (but also brittle), whereas the polymer is ductile (but also weak and flexible). Thus the resulting fibreglass is relatively stiff, strong, flexible, and ductile.
Figure \(6\) Glass reinforcements used for fiberglass are supplied in different physical forms, microspheres, chopped or woven.
Silicones
Silicones, also known as polysiloxanes, are polymers that include any synthetic compound made up of repeating units of siloxane. Silicones consist of an inorganic silicon-oxygen backbone chain (⋯–Si–O–Si–O–Si–O–⋯) with organic side groups attached to the silicon atoms. Silicones have in general the chemical formula [R2SiO]n, where R is an organic group such as an alkyl (methyl, ethyl) or phenyl group. A silicone polymer tha consist of repeated units of dimethyl silicone is shown below.
They are typically heat-resistant and either liquid or rubber-like. Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical (e.g., insulation), electronics (e.g., coatings), household (e.g., sealants and cooking utensils), automobile (e.g., gaskets), aeroplane (e.g., seals), office machines (e.g., keyboard pads), medicine and dentistry (e.g., tooth impression molds), textiles and paper (e.g., coatings). For these applications, an estimated 400,000 tonnes of silicones were produced in 1991.
Silicone vs Silicon
Silicone is often confused with silicon, but they are distinct substances. Silicon is a chemical element, a hard dark-grey semiconducting metalloid which in its crystalline form is used to make integrated circuits ("electronic chips") and solar cells. Silicones are compounds that contain silicon, carbon, hydrogen, oxygen, and perhaps other kinds of atoms as well, and have very different physical and chemical properties.
Summary
• Condensation polymerization (also known as step-growth) requires that the monomers possess two or more kinds of functional groups that are able to react with each other in such a way that parts of these groups combine to form a small molecule (often H2O) which is eliminated from the two pieces. The now-empty bonding positions on the two monomers can then join together .
• Examples of natural condensation polymers include cellulose, starch, and polypeptide chains of proteins.
• Several synthetic condensation polymers discussed include nylon, kevlar, polyester, Bakelite, Melamine, polycarbonates, polyurethanes, epoxies.
• Synthetic condensation polymers have a wide array of household, industrial, commercial, and medical uses and applications. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.05%3A_Condensation_Polymers.txt |
Learning Objectives
• Know the properties of polymers based on their molecular and intermolecular structures.
• Know the relationship between degree of crystallinity to physical properties of polymers.
The physical properties of a polymer such as its strength and flexibility depend on:
• chain length - in general, the longer the chains the stronger the polymer;
• side groups - polar side groups (including those that lead to hydrogen bonding) give stronger attraction between polymer chains, making the polymer stronger;
• branching - straight, unbranched chains can pack together more closely than highly branched chains, giving polymers that have higher density, are more crystalline and therefore stronger;
• cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.
Crystalline and Amorphous Polymers
When applied to polymers, the term crystalline has a somewhat ambiguous usage. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding and/or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers.Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, reduced crystallinity may also be associated with increased transparency.
.
Figure \(1\) The crystalline parts of this polymer are shown in blue.
Depending on the degree of crystallinity, there will be a higher temperature, the melting point tm , at which the crystalline regions come apart and the material becomes a viscous liquid. Such liquids can easily be injected into molds to manufacture objects of various shapes, or extruded into sheets or fibers. Other polymers (generally those that are highly cross-linked) do not melt at all; these are known as thermosets. If they are to be made into molded objects, the polymerization reaction must take place within the molds — a far more complicated process. About 20% of the commercially-produced polymers are thermosets; the remainder are thermoplastics.
The Glass Transition Temperature
In some polymers (known as thermoplastics) there is a fairly definite softening point that is observed when the thermal kinetic energy becomes high enough to allow internal rotation to occur within the bonds and to allow the individual molecules to slide independently of their neighbors, thus rendering them more flexible and deformable. This defines the glass transition temperature tg . Hard plastics like polystyrene and poly(methyl methacrylate) are used well below their glass transition temperatures, i.e., when they are in their glassy state. Their Tg values are well above room temperature, both at around 100 °C (212 °F). Rubber elastomers like polyisoprene and polyisobutylene are used above their Tg, that is, in the rubbery state, where they are soft and flexible.
Fiber Formation
Bill Pittendreigh, DuPont, and other individuals and corporations worked diligently during the first few months of World War II to find a way to replace Asian silk and hemp with nylon in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a high-grade paper for U.S. currency. At the outset of the war, cotton accounted for more than 80% of all fibers used and manufactured, and wool fibers accounted for nearly all of the rest. By August 1945, manufactured fibers had taken a market share of 25%, at the expense of n. After the war, e of shortages of both silk and nylon, nylon parachute material was sometimes repurposed to make dresses.Nylon 6 and 66 fibers are used in carpet manufacture. Nylon is one kind of fibers used in tire cord. Herman E. Schroeder pioneered application of nylon in tires.
Fabrics woven or knitted from polyester thread or yarn are used extensively in apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets, upholstered ure and computer mouse mats. Industrial polyester fibers, yarns and ropes are used in car tire reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high-energy absorption. Polyester fiber is used as cushioning and insulating material in pillows, comforters and upholstery padding. Polyester fabrics are highly stain-resistant—in fact, the only class of dyes which can be used to alter the color of polyester fabric are what are known as disperse dyes.
Acrylic fibers are synthetic fibers made from a polymer (polyacrylonitrile) with an average molecular weight of -100,000, about 1900 monomer units. For a fiber to be called "acrylic" in the US, the polymer must contain at least 85% acrylonitrile monomer. Typical comonomers are vinyl acetate or methyl acrylate. DuPont created the first acrylic fibers in 1941 and trademarked them under the name Orlon. It was first developed in the mid-1940s but was not produced in large quantities until the 1950s. Strong and warm, acrylic fiber is often used for sweaters and tracksuits and as linings for boots and gloves, as well as in furnishing fabrics and carpets. It is manufactured as a filament, then cut into short staple lengths similar to wool hairs, and spun into yarn.
Modacrylic is a modified acrylic fiber that contains at least 35% and at most 85% acrylonitrile monomer. The comonomers vinyl chloride, vinylidene chloride or vinyl bromide used in modacrylic give the fiber flame retardant properties. End-uses of modacrylic include faux fur, wigs, hair extensions and protective clothing.
Microfiber (or microfibre) is synthetic fiber finer than one denier or decitex/thread, having a diameter of less than ten micrometres. This is smaller than the diameter of a strand of silk (which is approximately one denier), which is itself about 1/5 the diameter of a human hair.
The most common types of microfibers are made from polyesters, polyamides (e.g., nylon, Kevlar, Nomex, trogamide), or a conjugation of polyester, polyamide, and polypropylene. Microfiber is used to make mats, knits, and weaves for apparel, upholstery, industrial filters, and cleaning products. The shape, size, and combinations of synthetic fibers are selected for specific characteristics, including softness, toughness, absorption, water repellency, electrostatics, and filtering capabilities.
Environmental and Safety Issues
Microfiber textiles tend to be flammable if manufactured from hydrocarbons (polyester) or carbohydrates (cellulose) and emit toxic gases when burning, more so if aromatic (PET, PS, ABS) or treated with halogenatedflame retardants and azo dyes. Their polyester and nylon stock are made from petrochemicals, which are not a renewable resource and are not biodegradable. However, if made out of polypropylene, they are recyclable (Prolen).
For most cleaning applications they are designed for repeated use rather than being discarded after use. An exception to this is the precise cleaning of optical components where a wet cloth is drawn once across the object and must not be used again as the debris collected are now embedded in the cloth and may scratch the optical surface.
Microfiber that is made from petrochemicals includes polyester and nylon which are not biodegradable. However, microfiber made from polypropylene can be recyclable. Microfiber products may also have the potential of entering the oceanic water supply and food chain similar to other microplastics. Synthetic clothing made of microfibers that are washed can release materials and travel to local wastewater treatment plants, contributing to plastic pollution in water. Fibers retained in wastewater treatment sludge (biosolids) that are land-applied can persist in soils.
There are environmental concerns about this product entering the oceanic food chain similar to other microplastics. A study by the clothing brand Patagonia and University of California, Santa Barbara, found that when synthetic jackets made of microfibers are washed, on average 1.7 grams (0.060 oz) of microfibers are released from the washing machine. These microfibers then travel to local wastewater treatment plants, where up to 40% of them enter into rivers, lakes, and oceans where they contribute to the overall plastic pollution. Microfibers account for 85% of man-made debris found on shorelines worldwide.
However, no pesticides are used for producing synthetic fibers (in comparison to cotton). If these products are made of polypropylene yarn, the yarn is dope-dyed; i.e. no water is used for dyeing (as with cotton, where thousands of liters of water become contaminated).
Summary
• The physical properties of a polymer such as its strength and flexibility depend on chain length, side groups present, branching, and cross-linking.
• Synthetic polymers may consist of both crystalline (more ordered, crystal-like) and amorphous (less ordered) regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material.
• The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers.
• Due to their chemical structure, nylon, polyester, and acrylic fibers have physical properties that are comparable or even superior to natural fibers Thus, many of these fibers have a variety of uses and have replaced natural fibers in various products. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.06%3A_Properties_of_Polymers.txt |
Learning Objectives
• Know the problems associated with plastics.
• Identify the type of polymer associated with each recycling number.
• Know the different plastic recycling processes.
Problems with Plastics
Due to their low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in a multitude of products of different scale, including paper clips and spacecraft. They have prevailed over traditional materials, such as wood, stone, horn and bone, leather, metal, glass, and ceramic, in some products previously left to natural materials. However, there are numerous problems encountered with plastic use.
Small-molecule release
Many kinds of polymers contain small molecules — either unreacted monomers, or substances specifically added (plasticizers, uv absorbers, flame retardants, etc.) to modify their properties. Many of these smaller molecules are able to diffuse through the material and be released into any liquid or air in contact with the plastic — and eventually into the aquatic environment. Those that are used for building materials (in mobile homes, for example) can build up in closed environments and contribute to indoor air pollution.
Residual monomer
Formation of long polymer chains is a complicated and somewhat random process that is never perfectly stoichiometric. It is therefore not uncommon for some unreacted monomer to remain in the finished product. Some of these monomers, such as formaldehyde, styrene (from polystyrene, including polystyrene foam food take-out containers), vinyl chloride, and bisphenol-A (from polycarbonates) are known carcinogens. Although there is little evidence that the small quantities that diffuse into the air or leach out into fluids pose a quantifiable health risk, people are understandably reluctant to tolerate these exposures, and public policy is gradually beginning to regulate them.
Perfluorooctanoic acid (PFOA), the monomer from which Teflon is made, has been the subject of a 2004 lawsuit against a DuPont factory that contaminated groundwater. Small amounts of PFOA have been detected in gaseous emissions from hot fluorocarbon products.
Decomposition products
Most commonly-used polymers are not readily biodegradable, particularly under the anaerobic conditions of most landfills. And what decomposition does occur will combine with rainwater to form leachates that can contaminate nearby streams and groundwater supplies. Partial photodecomposition, initiated by exposure to sunlight, is a more likely long-term fate for exposed plastics, resulting in tiny broken-up fragments. Many of these materials are less dense than seawater, and once they enter the oceans through coastal sewage outfalls or from marine vessel wastes, they tend to remain there indefinitely.
Open burning of polymeric materials containing chlorine (polyvinyl chloride, for example) is known to release compounds such as dioxins that persist in the environment. Incineration under the right conditions can effectively eliminate this hazard. Disposed products containing fluorocarbons (Teflon-coated ware, some personal-care, waterproofing and anti-stick materials) break down into perfluorooctane sulfonate which has been shown to damage aquatic animals.
Hazards to animals
There are two general types of hazards that polymers can introduce into the aquatic environment. One of these relates to the release of small molecules that act as hormone disrupters as described above. It is well established that small aquatic animals such as fish are being seriously affected by such substances in many rivers and estuarine systems, but details of the sources and identities of these molecules have not been identified. One confounding factor is the release of sewage water containing human birth-control drugs (which have a feminizing effect on sexual development) into many waterways.
The other hazard relates to pieces of plastic waste that aquatic animals mistake for food or become entangled in (Figure \(1\)) .
These dangers occur throughout the ocean, but are greatly accentuated in regions known as gyres. These are regions of the ocean in which a combination of ocean currents drives permanent vortices that tend to collect and concentrate floating materials. The most notorious of these are the Great Pacific Gyres that have accumulated astounding quantities of plastic waste.
.
Recycling
The huge quantity (one estimate is 108 metric tons per year) of plastic materials produced for consumer and industrial use has created a gigantic problem of what to do with plastic waste which is difficult to incinerate safely and which, being largely non-biodegradable, threatens to overwhelm the capacity of landfills. An additional consideration is that de novo production most of the major polymers consumes non-renewable hydrocarbon resources.
Plastics recycling has become a major industry, greatly aided by enlightened trash management policies in the major developed nations. However, it is plagued with some special problems of its own:
• Recycling is only profitable when there is a market for the regenerated material. Such markets vary with the economic cycle (they practically disappeared during the recession that commenced in 2008.)
• The energy-related costs of collecting and transporting plastic waste, and especially of processing it for re-use, are frequently the deciding factor in assessing the practicability of recycling.
• Collection of plastic wastes from diverse sources and locations and their transport to processing centers consumes energy and presents numerous operational problems.
• Most recycling processes are optimized for particular classes of polymers. The diversity of plastic types necessitates their separation into different waste streams — usually requiring manual (i.e., low-cost) labor. This in turn encourages shipment of these wastes to low-wage countries, thus reducing the availability of recycled materials in the countries in which the plastics originated.
Some of the major recycling processes include
• Thermal decomposition processes that can accommodate mixed kinds of plastics and render them into fuel oil, but the large inputs of energy they require have been a problem.
• A very small number of condensation polymers can be depolymerized so that the monomers can be recovered and re-used.
• Thermopolymers can be melted and pelletized, but those of widely differing types must be treated separately to avoid incompatability problems.
• Thermosets are usually shredded and used as filler material in recycled thermopolymers.
Other processes
A process has also been developed in which many kinds of plastic can be used as a carbon source in the recycling of
scrap steel. There is also a possibility of mixed recycling of different plastics, which does not require their separation. It is called compatibilization and requires use of special chemical bridging agents compatibilizers. It can help to keep the quality of recycled material and to skip often expensive and inefficient preliminary scanning of waste plastics streams and their separation/purification.
Recycled Plastics
Seven groups of plastic polymers, each with specific properties, are used worldwide for packaging applications (see Table \(1\)). Each group of plastic polymer can be identified by its plastic identification code (PIC), usually a number or a letter abbreviation. For instance, low-density polyethylene can be identified by the number "4" or the letters "LDPE". The PIC appears inside a three-chasing-arrow recycling symbol. The symbol is used to indicate whether the plastic can be recycled into new products.
The PIC was introduced by the Society of the Plastics Industry, Inc., to provide a uniform system for the identification of various polymer types and to help recycling companies separate various plastics for reprocessing. Manufacturers of plastic products are required to use PIC labels in some countries/regions and can voluntarily mark their products with the PIC where there are no requirements. Consumers can identify the plastic types based on the codes usually found at the base or at the side of the plastic products, including food/chemical packaging and containers.
Not all categories are accepted by all local recycling authorities, so residents need to be informed about which kinds should be placed in recycling containers and which should be combined with ordinary trash.
Table \(1\) The Major Groups of Plastic Polymers. Source: Wikipedia
Plastic identification code Type of plastic polymer Properties Common packaging applications Melting temperatures (°C)
Polyethylene terephthalate(PET, PETE) Clarity, strength, toughness, barrier to gas and moisture. Soft drink, water and salad dressing bottles; peanut butter and jam jars; ice cream cone lids; small consumer electronics Tm = 250
High-density polyethylene(HDPE) Stiffness, strength, toughness, resistance to moisture, permeability to gas Water pipes, Gas & Fire Pipelines, Electrical & Communications conduit, hula hoop rings, five gallon buckets, milk, juice and water bottles; grocery bags, some shampoo/toiletry bottles Tm = 130
Polyvinyl chloride(PVC) Versatility, ease of blending, strength, toughness. Blister packaging for non-food items; cling films for non-food use. May be used for food packaging with the addition of the plasticisers needed to make natively rigid PVC flexible. Non-packaging uses are electrical cable insulation; rigid piping; vinyl records. Tm = 240
Low-density polyethylene(LDPE) Ease of processing, strength, toughness, flexibility, ease of sealing, barrier to moisture Frozen food bags; squeezable bottles, e.g. honey, mustard; cling films; flexible container lids Tm = 120
Polypropylene(PP) Strength, toughness, resistance to heat, chemicals, grease and oil, versatile, barrier to moisture. Reusable microwaveable ware; kitchenware; yogurt containers; margarine tubs; microwaveable disposable take-away containers; disposable cups; soft drink bottle caps; plates. Tm = 173
Polystyrene(PS) Versatility, clarity, easily formed Egg cartons; packing peanuts; disposable cups, plates, trays and cutlery; disposable take-away containers Tm = 240
Other (often polycarbonateor ABS) Dependent on polymers or combination of polymers Beverage bottles, baby milk bottles. Non-packaging uses for polycarbonate, compact discs, "unbreakable" glazing, electronic apparatus housing, lenses (including sunglasses), prescription glasses, automotive headlamps, riot shields, instrument panels.
Polycarbonate:
Tm = 225
Tire Recycling
The large number of rubber tires that are disposed of, together with the increasing reluctance of landfills to accept them, has stimulated considerable innovation in the re-use of this material, especially in the construction industry.
Plastics and Fire Hazards
The term fire (or flame)-retardant as applied to organic (i.e., containing carbon) materials, is intended to refer to reduced fire hazard, as all will burn under certain circumstances. Fabric flammability is an important textile issue, especially for stage drapery that will be used in a public space such as a school, theatre or special event venue. In the United States, Federal regulations require that drapery fabrics used in such spaces be certified as flame or fire-retardant. For draperies and other fabrics used in public places, this is known as the NFPA 701 Test, which follows standards developed by the National Fire Protection Association (NFPA). Although all fabrics will burn, some are naturally more resistant to fire than others. Those that are more flammable can have their fire resistance drastically improved by treatment with fire-retardant chemicals. Inherently flame-retardant fabrics such as polyester are commonly used for flame retardant curtain fabrics.
The deaths in fiery crashes of race car drivers Fireball Roberts at Charlotte, and Eddie Sachs and Dave MacDonald at Indianapolis in 1964 led to the use of flame-resistant ics such as Nomex. Nomex and related aramid polymers are related to nylon, but have aromatic backbones, and hence are more rigid and more durable. Nomex is an example of a meta variant of the aramids (Kevlar is a para aramid). Unlike Kevlar, Nomex strands cannot align during filament polymerization and has less strength. However, it has excellent thermal, chemical, and radiation resistance for a polymer material.
A Nomex hood is a common piece of racing and firefighting equipment. It is placed on the head on top of a firefighter's face mask. The hood protects the portions of the head not covered by the helmet and face mask from the intense heat of the fire.
Wildland firefighters wear Nomex shirts and trousers as part of their personal protective equipment during wildfire suppression activities.
Racing car drivers wear driving suits constructed of Nomex and or other fire retardant materials, along with Nomex gloves, long underwear, balaclavas, socks, helmet lining and shoes, to protect them in the event of a fire.
Military pilots and aircrew wear flight suits made of over 92 percent Nomex to protect them from the possibility of cockpit fires and other mishaps. Recently, troops riding in ground vehicles have also begun wearing Nomex. Kevlar thread is often used to hold the fabric together at seams.
Military tank drivers also typically use Nomex hoods as protection against fire.
Plasticizers and Pollution
Plasticizers (UK: plasticisers) or dispersants are additives that increase the plasticity or decrease the viscosity of a material. These substances are compounded into certain types of plastics to render them more flexible by lowering the glass transition temperature. They accomplish this by taking up space between the polymer chains and acting as lubricants to enable the chains to more readily slip over each other. Many (but not all) are small enough to be diffusible and a potential source of health problems.
Polyvinyl chloride polymers are one of the most widely-plasticized types, and the odors often associated with flexible vinyl materials such as garden hoses, waterbeds, cheap shower curtains, raincoats and upholstery are testament to their ability to migrate into the environment.
The well-known "new car smell" is largely due to plasticizer release from upholstery and internal trim.
According to 2014 data, the total global market for plasticizers was 8.4 million metric tonnes including 1.3 million metric tonnes in Europe.
Substantial concerns have been expressed over the safety of some plasticizers, especially because some low molecular weight ortho-phthalates have been classified as potential endocrine disruptors with some developmental toxicity reported.
Summary
• Plastics are found everywhere due to its low cost, versatility, ease of use etc.
• Plastics pose a threat to the environment due to residual or degradation products that contribute to air and water pollution.
• Plastics hazards to animals and marine life as these living creatures mistake them for food.
• Plastic polymers are classified into seven groups for recycling purposes. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/10%3A_Polymers/10.07%3A_Plastics_and_the_Environment.txt |
Learning Objectives
• Know the different sources of background radiation.
• Describe the biological impact of ionizing radiation
• List common sources of radiation exposure in the US.
Background Radiation
We are all exposed to a small amount of radiation in our daily lives. This background radiation comes from naturally occurring sources and from human-produced radiation. Exposure to x-rays and nuclear medicine isotopes, ground sources, and cosmic radiation account for almost half of the background exposure of the average American. Radon gas, formed from the decay of uranium and thorium isotopes, is responsible for a little over half the total amount of background radiation. See the table below for background sources.
Table \(1\) Sources of Background Radiation
radon \(54\%\)
consumer products \(3\%\)
nuclear medicine \(4\%\)
cosmic radiation \(8\%\)
terrestrial \(8\%\)
internal \(11\%\)
x-rays \(11\%\)
other \(1\%\)
The Problem of Radon
For many people, one of the largest sources of exposure to radiation is from radon gas (Rn-222). Radon-222 is an α emitter with a half–life of 3.82 days. It is one of the products of the radioactive decay series of U-238, which is found in trace amounts in soil and rocks. The radon gas that is produced slowly escapes from the ground and gradually seeps into homes and other structures above. Since it is about eight times more dense than air, radon gas accumulates in basements and lower floors, and slowly diffuses throughout buildings (Figure \(1\)).
Radon is found in buildings across the country, with amounts depending on where you live. The average concentration of radon inside houses in the US (1.25 pCi/L) is about three times the levels found in outside air, and about one in six houses have radon levels high enough that remediation efforts to reduce the radon concentration are recommended. Exposure to radon increases one’s risk of getting cancer (especially lung cancer), and high radon levels can be as bad for health as smoking a carton of cigarettes a day. Radon is the number one cause of lung cancer in nonsmokers and the second leading cause of lung cancer overall. Radon exposure is believed to cause over 20,000 deaths in the US per year.
Measuring Radiation Exposure
Several different devices are used to detect and measure radiation, including Geiger counters, scintillation counters (scintillators), and radiation dosimeters (Figure \(2\)). Probably the best-known radiation instrument, the Geiger counter (also called the Geiger-Müller counter) detects and measures radiation. Radiation causes the ionization of the gas in a Geiger-Müller tube. The rate of ionization is proportional to the amount of radiation. A scintillation counter contains a scintillator—a material that emits light (luminesces) when excited by ionizing radiation—and a sensor that converts the light into an electric signal. Radiation dosimeters also measure ionizing radiation and are often used to determine personal radiation exposure. Commonly used types are electronic, film badge, thermoluminescent, and quartz fiber dosimeters.
Radiation Damage to Cells
The increased use of radioisotopes has led to increased concerns over the effects of these materials on biological systems (such as humans). All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break chemical bonds, or ionize molecules. The most serious biological damage results when these radioactive emissions fragment or ionize molecules. For example, alpha and beta particles emitted from nuclear decay reactions possess much higher energies than ordinary chemical bond energies. When these particles strike and penetrate matter, they produce ions and molecular fragments that are extremely reactive. The damage this does to biomolecules in living organisms can cause serious malfunctions in normal cell processes, taxing the organism’s repair mechanisms and possibly causing illness or even death (Figure \(3\)).
Radiation can harm either the whole body (somatic damage) or eggs and sperm (genetic damage). Its effects are more pronounced in cells that reproduce rapidly, such as the stomach lining, hair follicles, bone marrow, and embryos. This is why patients undergoing radiation therapy often feel nauseous or sick to their stomach, lose hair, have bone aches, and so on, and why particular care must be taken when undergoing radiation therapy during pregnancy.
Ionizing vs. Nonionizing Radiation
There is a large difference in the magnitude of the biological effects of nonionizing radiation (for example, light and microwaves) and ionizing radiation, emissions energetic enough to knock electrons out of molecules (for example, α and β particles, γ rays, X-rays, and high-energy ultraviolet radiation) (Figure \(4\)).
Energy absorbed from nonionizing radiation speeds up the movement of atoms and molecules, which is equivalent to heating the sample. Although biological systems are sensitive to heat (as we might know from touching a hot stove or spending a day at the beach in the sun), a large amount of nonionizing radiation is necessary before dangerous levels are reached. Ionizing radiation, however, may cause much more severe damage by breaking bonds or removing electrons in biological molecules, disrupting their structure and function. The damage can also be done indirectly, by first ionizing H2O (the most abundant molecule in living organisms), which forms a H2O+ ion that reacts with water, forming a hydronium ion and a hydroxyl radical:
Effects of Long-term Radiation Exposure on the Human Body
The effects of radiation depend on the type, energy, and location of the radiation source, and the length of exposure. As shown in Figure \(6\), the average person is exposed to background radiation, including cosmic rays from the sun and radon from uranium in the ground; radiation from medical exposure, including CAT scans, radioisotope tests, X-rays, and so on; and small amounts of radiation from other human activities, such as airplane flights (which are bombarded by increased numbers of cosmic rays in the upper atmosphere), radioactivity from consumer products, and a variety of radionuclides that enter our bodies when we breathe (for example, carbon-14) or through the food chain (for example, potassium-40, strontium-90, and iodine-131).
A short-term, sudden dose of a large amount of radiation can cause a wide range of health effects, from changes in blood chemistry to death. Short-term exposure to tens of rems of radiation will likely cause very noticeable symptoms or illness; a dose of about 500 rems is estimated to have a 50% probability of causing the death of the victim within 30 days of exposure. Exposure to radioactive emissions has a cumulative effect on the body during a person’s lifetime, which is another reason why it is important to avoid any unnecessary exposure to radiation. Health effects of short-term exposure to radiation are shown in Table \(2\).
Table \(2\) Health Effects of Radiation
Exposure (rem) Health Effect Time to Onset (without treatment)
5–10 changes in blood chemistry
50 nausea hours
55 fatigue
70 vomiting
75 hair loss 2–3 weeks
90 diarrhea
100 hemorrhage
400 possible death within 2 months
1000 destruction of intestinal lining
internal bleeding
death 1–2 weeks
2000 damage to central nervous system
loss of consciousness; minutes
death hours to days
It is impossible to avoid some exposure to ionizing radiation. We are constantly exposed to background radiation from a variety of natural sources, including cosmic radiation, rocks, medical procedures, consumer products, and even our own atoms. We can minimize our exposure by blocking or shielding the radiation, moving farther from the source, and limiting the time of exposure.
Summary
• Background radiation is defined and different sources of background radiation are listed.
• We are constantly exposed to radiation from a variety of naturally occurring and human-produced sources.
• Various devices, including Geiger counters, scintillators, and dosimeters, are used to detect and measure radiation, and monitor radiation exposure.
• Ionizing radiation is the most harmful because it can ionize molecules or break chemical bonds, which damages the molecule and causes malfunctions in cell processes. It can also create reactive hydroxyl radicals that damage biological molecules and disrupt physiological processes. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.01%3A_Natural_Radioactivity.txt |
Learning Objectives
• Identify common particles and energies involved in nuclear reactions.
• Write and balance nuclear equations.
Changes of nuclei that result in changes in their atomic numbers, mass numbers, or energy states are nuclear reactions. To describe a nuclear reaction, we use an equation that identifies the nuclides involved in the reaction, their mass numbers and atomic numbers, and the other particles involved in the reaction.
Types of Particles in Nuclear Reactions
Many entities can be involved in nuclear reactions. The most common are protons, neutrons, alpha particles, beta particles, positrons, and gamma rays, as shown in Table $1$.
Table $1$ A Summary of the Names, Symbols, Representations, and Descriptions of the Most Common Particles in Nuclear Reactions.
Balancing Nuclear Reactions
A balanced chemical reaction equation reflects the fact that during a chemical reaction, bonds break and form, and atoms are rearranged, but the total numbers of atoms of each element are conserved and do not change. A balanced nuclear reaction equation indicates that there is a rearrangement during a nuclear reaction, but of subatomic particles rather than atoms. Nuclear reactions also follow conservation laws, and they are balanced in two ways:
1. The sum of the mass numbers of the reactants equals the sum of the mass numbers of the products.
2. The sum of the charges of the reactants equals the sum of the charges of the products.
If the atomic number and the mass number of all but one of the particles in a nuclear reaction are known, we can identify the particle by balancing the reaction. For instance, we could determine that $\ce{^{17}_8O}$ is a product of the nuclear reaction of $\ce{^{14}_7N}$ and $\ce{^4_2He}$ if we knew that a proton, $\ce{^1_1H}$, was one of the two products. Example $1$ shows how we can identify a nuclide by balancing the nuclear reaction.
Nuclear Decay Processes
Radioactive decay involves the emission of a particle and/or energy as one atom changes into another. In most instances, the atom changes its identity to become a new element. There are four different types of emissions that occur.
Alpha Emission
Alpha $\left( \alpha \right)$ decay involves the release of helium ions from the nucleus of an atom. This ion consists of two protons and two neutrons and has a $2+$ charge. Release of an $\alpha$-particle produces a new atom that has an atomic number two less than the original atom and an atomic weight that is four less. A typical alpha decay reaction is the conversion of uranium-238 to thorium:
$\ce{^{238}_{92}U} \rightarrow \ce{^{234}_{90}Th} + \ce{^4_2 \alpha}^+ \nonumber$
We see a decrease of two in the atomic number (uranium to thorium) and a decrease of four in the atomic weight (238 to 234). Usually the emission is not written with atomic number and weight indicated since it is a common particle whose properties should be memorized. Quite often the alpha emission is accompanied by gamma $\left( \gamma \right)$ radiation, a form of energy release. Many of the largest elements in the periodic table are alpha-emitters.
Chemists often use the names parent isotope and daughter isotope to represent the original atom and the product other than the alpha particle. In the previous example, $_{92}^{238}\textrm{U} \nonumber$ is the parent isotope, and $_{90}^{234}\textrm{Th} \nonumber$ is the daughter isotope. When one element changes into another in this manner, it undergoes radioactive decay.
Example $1$
Write the nuclear equation that represents the radioactive decay of radon-222 by alpha particle emission and identify the daughter isotope.
Solution
Radon has an atomic number of 86, so the parent isotope is represented as $_{86}^{222}\textrm{Rn} \nonumber$
We represent the alpha particle as
$_{2}^{4}\textrm{He} \nonumber$
Use subtraction (222 − 4 = 218 and 86 − 2 = 84) to identify the daughter isotope as polonium:
$_{86}^{222}\textrm{Rn}\rightarrow \; _{2}^{4}\textrm{He}+\: _{84}^{218}\textrm{Th} \nonumber$
Exercise $1$
Write the nuclear equation that represents radioactive decay of polonium-208 by alpha particle emission and identify the daughter isotope.
Answer
$_{80}^{208}\textrm{Po}\rightarrow \; _{2}^{4}\textrm{He}+\: _{82}^{204}\textrm{Pb} \nonumber$
$_{82}^{204}\textrm{Pb} \nonumber$
Beta Emission
Beta $\left( \beta \right)$ decay is a more complicated process. Unlike the $\alpha$-emission, which simply expels a particle, the $\beta$-emission involves the transformation of a neutron in the nucleus to a proton and an electron. The electron is then ejected from the nucleus. In the process,the atomic number increases by one while the atomic weight stays the same. As is the case with $\alpha$-emissions, $\beta$-emissions are often accompanied by $\gamma$-radiation.
A typical beta decay process involves carbon-14, often used in radioactive dating techniques. The reaction forms nitrogen-14 and an electron:
$\ce{^{14}_6C} \rightarrow \ce{^{14}_7N} + \ce{^0_{-1}e} \nonumber$
Again, the beta emission is usually simply indicated by the Greek letter $\beta$; memorization of the process is necessary in order to follow nuclear calculations in which the Greek letter $\beta$ appears without further notation.
Example $2$
Write the nuclear equation that represents the radioactive decay of boron-12 by beta particle emission and identify the daughter isotope. A gamma ray is emitted simultaneously with the beta particle.
Solution
The parent isotope is \[B512," id="MathJax-Element-16-Frame" role="presentation" style="position:relative;" tabindex="0"> | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.02%3A_Nuclear_Equations.txt |
Learning Objectives
• Define half-life.
• Determine the amount of radioactive substance remaining after a given number of half-lives.
• Define a radioactive decay series.
Whether or not a given isotope is radioactive is a characteristic of that particular isotope. Some isotopes are stable indefinitely, while others are radioactive and decay through a characteristic form of emission. As time passes, less and less of the radioactive isotope will be present, and the level of radioactivity decreases. An interesting and useful aspect of radioactive decay is half life. which is the amount of time it takes for one-half of a radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by conditions and is independent of the initial amount of that isotope.
For example, cobalt-60, an isotope that emits gamma rays used to treat cancer, has a half-life of 5.27 years (Figure $1$). In a given cobalt-60 source, since half of the $\ce{^{60}_{27}Co}$ nuclei decay every 5.27 years, both the amount of material and the intensity of the radiation emitted is cut in half every 5.27 years. (Note that for a given substance, the intensity of radiation that it produces is directly proportional to the rate of decay of the substance and the amount of the substance.) This is as expected for a process following first-order kinetics. Thus, a cobalt-60 source that is used for cancer treatment must be replaced regularly to continue to be effective.
We can determine the amount of a radioactive isotope remaining after a given number half-lives by using the following expression:
$amount\; \: remaining\: =\: initial\:amount\times \left ( \frac{1}{2} \right )^{n} \nonumber$
where n is the number of half-lives. This expression works even if the number of half-lives is not a whole number.
Example $1$:
The half-life of fluorine-20 is 11.0 s. If a sample initially contains 5.00 g of fluorine-20, how much remains after 44.0 s?
Solution
If we compare the time that has passed to the isotope's half-life, we note that 44.0 s is exactly 4 half-lives, so using the previous expression, n = 4. Substituting and solving results in the following:
$amount\; \: remaining\: =\: 5.00g\times \left ( \frac{1}{2} \right )^{4}\ amount\; \: remaining\: =\: 5.00g\times \left ( \frac{1}{16} \right )\ amount\; \: remaining\: =\: 0.313g \nonumber$
Less than one-third of a gram of fluorine-20 remains.
Exercise $1$
The half-life of titanium-44 is 60.0 y. A sample of titanium contains 0.600 g of titanium-44. How much remains after 240.0 y?
Answer
0.0375 g
Example $2$
If there are 60 grams of $\ce{Np}$-240 present, how much $\ce{Np}$-240 will remain after 4 hours? ($\ce{Np}$-240 has a half-life of 1 hour)
Solution
$\ce{Np}$-240 with a half life of only 1 hour.
After 4 hours, only $3.75 \: \text{g}$ of our original $60 \: \text{g}$ sample would remain the radioactive isotope $\ce{Np}$-240.
Exercise $2$
A sample of $\ce{Ac}$-225 originally contained 80 grams and after 50 days only 2.55 grams of the original $\ce{Ac}$-225 remain. What is the half life of $\ce{Ac}$-225?
Answer
10 days.
The half-lives of many radioactive isotopes have been determined and they have been found to range from extremely long half-lives of 10 billion years to extremely short half-lives of fractions of a second. For example: the half-life of $\ce{^{209}_{83}Bi}$ is 1.9 × 1019 years; $\ce{^{239}_{94}Ra}$ is 24,000 years; $\ce{^{222}_{86}Rn}$ is 3.82 days; and element-111 (Rg for roentgenium) is 1.5 × 10–3 seconds. The table below illustrates half-lives for several selected elements.
Table $1$: Table of Selected Half-lives
Element Mass Number (A) Half-life Element Mass Number (A) Half Life
Uranium 238 4.5 Billion years Californium 251 800 years
Neptunium 240 1 hour Nobelium 254 3 seconds
Plutonium 243 5 hours Carbon 14 5730 years
Americium 245 25 minutes Carbon 16 740 milliseconds
Uranium Decay Series
The naturally occurring radioactive isotopes of the heaviest elements fall into chains of successive disintegrations, or decays, and all the species in one chain constitute a radioactive family, or radioactive decay series. Three of these series include most of the naturally radioactive elements of the periodic table. They are the uranium series, the actinide series, and the thorium series. (Figure $2$). In all three series, the end-product is a stable isotope of lead.
Radioactive Dating
Radioactive dating is a process by which the approximate age of an object is determined through the use of certain radioactive nuclides. For example, carbon-14 has a half-life of 5,730 years and is used to measure the age of organic material. The ratio of carbon-14 to carbon-12 in living things remains constant while the organism is alive because fresh carbon-14 is entering the organism whenever it consumes nutrients. When the organism dies, this consumption stops, and no new carbon-14 is added to the organism. As time goes by, the ratio of carbon-14 to carbon-12 in the organism gradually declines, because carbon-14 radioactively decays while carbon-12 is stable. Analysis of this ratio allows archaeologists to estimate the age of organisms that were alive many thousands of years ago. For example, with the half-life of $\ce{^{14}_6C}$ being 5730 years, if the $\ce{^{14}_6C : ^{12}_6C}$ ratio in a wooden object found in an archaeological dig is half what it is in a living tree, this indicates that the wooden object is 5730 years old.
C-14 dating does have limitations. For example, a sample can be C-14 dating if it is approximately 100 to 50,000 years old. Before or after this range, there is too little of the isotope to be detected. Substances must have obtained C-14 from the atmosphere. For this reason, aquatic samples cannot be effectively C-14 dated. Lastly, accuracy of C-14 dating has been affected by atmosphere nuclear weapons testing. Fission bombs ignite to produce more C-14 artificially. Samples tested during and after this period must be checked against another method of dating (isotopic or tree rings).
To calculate the age of a substance using isotopic dating, use the equation below:
$\text{how old (time)} = n \times t_{1/2} \nonumber$
where $n$ is the number of half-lives and $t_{1/2}$ is the half-life (in time).
Example $3$
How long will it take for 18.0 grams of Ra-226 to decay to leave a total of 2.25 grams? Ra-226 has a half-life of 1600 years.
Solution
18.0g ⇒ 9.0g ⇒ 4.5g ⇒ 2.25g, this is three half-lives
$\text{how old (time)} = 3 \times 1600\, years \nonumber$
This decay process takes 4800 years to occur.
Willard Libby
A National Historic Chemical Landmark -American Chemical Society
Dedicated at the University of Chicago on October 10, 2016.
In 1946, Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon-14, a newly discovered radioactive isotope of carbon. Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms. The “radiocarbon revolution” made possible by Libby’s discovery greatly benefited the fields of archaeology and geology by allowing practitioners to develop more precise historical chronologies across geography and cultures.
Willard F. Libby (right), the physical chemist who conceived of radiocarbon dating, with graduate student Ernest Anderson.
University of Chicago Photographic Archive, apf1-03868, Special Collections Research Center, University of Chicago Library.
Go to Link below for more details
www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html
Radioactive Dating Using Nuclides Other than Carbon-14
Radioactive dating can also use other radioactive nuclides with longer half-lives to date older events. An ingenious application of half-life studies established a new science of determining ages of materials by half-life calculations. For geological dating, the decay of $\ce{U}$-238 can be used. The half-life of $\ce{U}$-238 is $4.5 \times 10^9$ years. The end product of the decay of $\ce{U}$-238 is $\ce{Pb}$-206. After one half-life, a 1.00 gram sample of uranium will have decayed to 0.50 grams of $\ce{U}$-238 and 0.43 grams of $\ce{Pb}$-206. By comparing the amount of $\ce{U}$-238 to the amount of $\ce{Pb}$-206 in a sample of uranium mineral, the age of the mineral can be estimated. Present day estimates for the age of the Earth's crust from this method is at 4 billion years. This radioactivity approach can be used to detecting fake wine vintages too.
Isotopes with shorter half-lives are used to date more recent samples. For example, tritium (t1/2 =12.3 years) can date samples within an age range of 1-100 years. Chemists and geologists use tritium dating to determine the age of water (ocean and fresh). In addition, tritium dating can be useful in determining the age of wines and brandies.
K-40 decays by positron emission and electron capture to form Ar-40 with a half-life of 1.25 billion years. If a rock sample is crushed and the amount of Ar-40 gas that escapes is measured, determination of the Ar-40:K-40 ratio yields the age of the rock. Other methods, such as rubidium-strontium dating (Rb-87 decays into Sr-87 with a half-life of 48.8 billion years), operate on the same principle. To estimate the lower limit for the earth’s age, scientists determine the age of various rocks and minerals, making the assumption that the earth is older than the oldest rocks and minerals in its crust. As of 2014, the oldest known rocks on earth are the Jack Hills zircons from Australia, found by uranium-lead dating to be almost 4.4 billion years old.
Summary
• Natural radioactive processes are characterized by a half-life, the time it takes for half of the material to decay radioactively.
• The amount of material left over after a certain number of half-lives can be determined using the following expression:
$amount\; \: remaining\: =\: initial\:amount\times \left ( \frac{1}{2} \right )^{n} \nonumber$
where n is the number of half-lives.
• $\ce{C}$-14 dating procedures have been used to determine the age of organic artifacts. Its half-life is approximately 5700 years. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.03%3A_Half-Life_and_Radioisotopic_Dating.txt |
Learning Objective
• Describe the synthesis of transuranium nuclides.
After the discovery of radioactivity, the field of nuclear chemistry was created and developed rapidly during the early twentieth century. A slew of new discoveries in the 1930s and 1940s, along with World War II, combined to usher in the Nuclear Age in the mid-twentieth century. Science learned how to create new substances, and certain isotopes of certain elements were found to possess the capacity to produce unprecedented amounts of energy, with the potential to cause tremendous damage during war, as well as produce enormous amounts of power for society’s needs during peace.
Synthesis of Nuclides
Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen atoms with high-speed α particles from a natural radioactive isotope of radium and observed protons resulting from the reaction:
$\ce{^{14}_7N + ^4_2He ⟶ ^{17}_8O + ^1_1H} \nonumber$
The $\ce{^{17}_8O}$ and $\ce{^1_1H}$ nuclei that are produced are stable, so no further (nuclear) changes occur.
To reach the kinetic energies necessary to produce transmutation reactions, devices called particle accelerators are used. These devices use magnetic and electric fields to increase the speeds of nuclear particles. In all accelerators, the particles move in a vacuum to avoid collisions with gas molecules. When neutrons are required for transmutation reactions, they are usually obtained from radioactive decay reactions or from various nuclear reactions occurring in nuclear reactors. The Chemistry in Everyday Life feature that follows discusses a famous particle accelerator that made worldwide news.
CERN Particle Accelerator
Located near Geneva, the CERN (“Conseil Européen pour la Recherche Nucléaire,” or European Council for Nuclear Research) Laboratory is the world’s premier center for the investigations of the fundamental particles that make up matter. It contains the 27-kilometer (17 mile) long, circular Large Hadron Collider (LHC), the largest particle accelerator in the world (Figure $1$). In the LHC, particles are boosted to high energies and are then made to collide with each other or with stationary targets at nearly the speed of light. Superconducting electromagnets are used to produce a strong magnetic field that guides the particles around the ring. Specialized, purpose-built detectors observe and record the results of these collisions, which are then analyzed by CERN scientists using powerful computers.
In 2012, CERN announced that experiments at the LHC showed the first observations of the Higgs boson, an elementary particle that helps explain the origin of mass in fundamental particles. This long-anticipated discovery made worldwide news and resulted in the awarding of the 2013 Nobel Prize in Physics to François Englert and Peter Higgs, who had predicted the existence of this particle almost 50 years previously.
Prior to 1940, the heaviest-known element was uranium, whose atomic number is 92. Now, many artificial elements have been synthesized and isolated, including several on such a large scale that they have had a profound effect on society. One of these—element 93, neptunium (Np)—was first made in 1940 by McMillan and Abelson by bombarding uranium-238 with neutrons. The reaction creates unstable uranium-239, with a half-life of 23.5 minutes, which then decays into neptunium-239. Neptunium-239 is also radioactive, with a half-life of 2.36 days, and it decays into plutonium-239. The nuclear reactions are:
\begin{align} &\ce{^{238}_{92}U + ^1_0n⟶ ^{239}_{92}U} &&\ &\ce{^{239}_{92}U⟶ ^{239}_{93}Np + ^0_{−1}e \,\,\,\mathit{t}_{1/2}} &&\textrm{half-life}=\mathrm{23.5\: min}\ &\ce{^{239}_{93}Np⟶ ^{239}_{94}Pu + ^0_{−1}e\,\,\, \mathit{t}_{1/2}} &&\textrm{half-life}=\mathrm{2.36\: days} \end{align} \nonumber
Plutonium is now mostly formed in nuclear reactors as a byproduct during the decay of uranium. Some of the neutrons that are released during U-235 decay combine with U-238 nuclei to form uranium-239; this undergoes β decay to form neptunium-239, which in turn undergoes β decay to form plutonium-239 as illustrated in the preceding three equations. It is possible to summarize these equations as:
$\mathrm{\ce{^{238}_{92}U} + {^1_0n}⟶ \ce{^{239}_{92}U} \xrightarrow{β^-} \ce{^{239}_{93}Np} \xrightarrow{β^-} \ce{^{239}_{94}Pu}} \nonumber$
Heavier isotopes of plutonium—Pu-240, Pu-241, and Pu-242—are also produced when lighter plutonium nuclei capture neutrons. Some of this highly radioactive plutonium is used to produce military weapons, and the rest presents a serious storage problem because they have half-lives from thousands to hundreds of thousands of years.
Although they have not been prepared in the same quantity as plutonium, many other synthetic nuclei have been produced. Nuclear medicine has developed from the ability to convert atoms of one type into other types of atoms. Radioactive isotopes of several dozen elements are currently used for medical applications. The radiation produced by their decay is used to image or treat various organs or portions of the body, among other uses.
The elements beyond element 92 (uranium) are called transuranium elements. As of this writing, 22 transuranium elements have been produced and officially recognized by IUPAC; several other elements have formation claims that are waiting for approval. Some of these elements are shown in Table $1$.
Table $1$ Preparation of Some of the Transuranium Elements
Name Symbol Atomic Number Reaction
americium Am 95 $\ce{^{239}_{94}Pu + ^1_0n ⟶ ^{240}_{95}Am + ^0_{−1}e}$
curium Cm 96 $\ce{^{239}_{94}Pu + ^4_2He ⟶ ^{242}_{96}Cm + ^1_0n}$
californium Cf 98 $\ce{^{242}_{96}Cm + ^4_2He⟶ ^{245}_{98}Cf + ^1_0n}$
einsteinium Es 99 $\ce{^{238}_{92}U + 15^1_0n⟶ ^{253}_{99}Es + 7^0_{−1}e}$
mendelevium Md 101 $\ce{^{253}_{99}Es + ^4_2He ⟶ ^{256}_{101}Md + ^1_0n}$
nobelium No 102 $\ce{^{246}_{96}Cm + ^{12}_6C ⟶ ^{254}_{102}No + 4 ^1_0n}$
rutherfordium Rf 104 $\ce{^{249}_{98}Cf + ^{12}_6C⟶ ^{257}_{104}Rf + 4 ^1_0n}$
seaborgium Sg 106
$\ce{^{206}_{82}Pb + ^{54}_{24}Cr ⟶ ^{257}_{106}Sg + 3 ^1_0n}$
$\ce{^{249}_{98}Cf + ^{18}_8O ⟶ ^{263}_{106}Sg + 4 ^1_0n}$
meitnerium Mt 107 $\ce{^{209}_{83}Bi + ^{58}_{26}Fe ⟶ ^{266}_{109}Mt + ^1_0n}$
Summary
• It is possible to produce new atoms by bombarding other atoms with nuclei or high-speed particles.
• The products of transmutation reactions can be stable or radioactive.
• A number of artificial elements, including technetium, astatine, and the transuranium elements, have been produced in this way. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.04%3A_Artificial_Transmutation.txt |
Learning Objectives
• Understand how radiation is used in agriculture and various industries.
• Understand the difference between diagnostic and therapeutic radiation.
Radioactive isotopes have the same chemical properties as stable isotopes of the same element, but they emit radiation, which can be detected. If we replace one (or more) atom(s) with radioisotope(s) in a compound, we can track them by monitoring their radioactive emissions. This type of compound is called a radioactive tracer (or radioactive label). Radioisotopes are used to follow the paths of biochemical reactions or to determine how a substance is distributed within an organism.
Radioisotopes in Industry and Agriculture
Radioisotopes (radioactive isotopes or radionuclides or radioactive nulcides) are used in two major ways: either for their radiation alone (irradiation, nuclear batteries) or for the combination of chemical properties and their radiation (tracers, biopharmaceuticals).
Tracer Applications
Radioactive isotopes are effective tracers because their radioactivity is easy to detect. A tracer is a substance that can be used to follow the pathway of that substance through some structure. For instance, leaks in underground water pipes can be discovered by running some tritium (H-3)-containing water through the pipes and then using a Geiger counter to locate any radioactive tritium subsequently present in the ground around the pipes. (Recall that tritium is a radioactive isotope of hydrogen.)
Tracers are used in diverse ways to study the mechanisms of chemical reactions in plants and animals. These include labeling fertilizers in studies of nutrient uptake by plants and crop growth, investigations of digestive and milk-producing processes in cows, and studies on the growth and metabolism of animals and plants.
For example, the radioisotope C-14 was used to elucidate the details of how photosynthesis occurs. The overall reaction is:
$\ce{6CO2}(g)+\ce{6H2O}(l)⟶\ce{C6H12O6}(s)+\ce{6O2}(g), \nonumber$
but the process is much more complex, proceeding through a series of steps in which various organic compounds are produced. In studies of the pathway of this reaction, plants were exposed to CO2 containing a high concentration of $\ce{^{14}_6C}$. At regular intervals, the plants were analyzed to determine which organic compounds contained carbon-14 and how much of each compound was present. From the time sequence in which the compounds appeared and the amount of each present at given time intervals, scientists learned more about the pathway of the reaction.
Phosphorus-32 is used in plant sciences for tracking a plant's uptake of fertilizer from the roots to the leaves. The phosphorus-32-labelled fertilizer is given to the plant hydroponically or via water in the soil and the usage of the phosphorus can be mapped from the emitted beta radiation. The information gathered by mapping the fertilizer uptake show how the plant takes up and uses the phosphorus from fertilizer.
Irradiation of Food and Mail
Co-60 (gamma source) and x-rays are use to irradiate many foods in the United States. Ionizing radiation can be used to kill food borne illnesses like salmonella and e coli. Irradiating food can also prolong shelf-life, delay ripening, and destroy insects. In addition, gamma/x-ray can sterilize foods making refrigeration unnecessary. Often, sterilized food is served to hospital patients who have impaired immune systems.
In the United States, irradiation of food is regulated by the FDA (Food and Drug Administration). Foods that have been irradiated must display the symbol called the radura on their packaging. Some foods that could display this symbol are: meats (beef, pork, chicken), shrimp, lobster, fruits, vegetables, shellfish, and spices. Contrary to the belief of some people, irradiation of food does not make the food itself radioactive.
In the fall of 2001, anthrax laced letters (Figure $2$) were sent to various new agencies and two United States senators. Anthrax is an infectious disease caused by bacteria. It exists naturally in some soils and can be isolated in a laboratory.
To combat this form of bioterrorism, the United States Postal Service(USPS)and the Federal Bureau of Investigation (FBI) installed x-ray generators to irradiate suspicious looking mail sent to some governmental facilities. X-rays will kill the majority of this bacteria and some viruses as well. Once irradiated, mail (packages and letters) might change in color, texture, and smell. This ionizing radiation chemically alters the composition of the mail's paper component. The x-rays do not leave the mail radioactive.
Smoke Detectors
Americium-241, an α emitter with a half-life of 458 years, is used in tiny amounts in ionization-type smoke detectors (Figure $3$). The α emissions from Am-241 ionize the air between two electrode plates in the ionizing chamber. A battery supplies a potential that causes movement of the ions, thus creating a small electric current. When smoke enters the chamber, the movement of the ions is impeded, reducing the conductivity of the air. This causes a marked drop in the current, triggering an alarm.
Other Applications
Commercial applications of radioactive materials are equally diverse . They include determining the thickness of films, paper, and thin metal sheets by exploiting the penetration power of various types of radiation(Figure $4$). Flaws in metals used for structural purposes can be detected using high-energy gamma rays from cobalt-60 in a fashion similar to the way X-rays are used to examine the human body. In one form of pest control, flies are controlled by sterilizing male flies with γ radiation so that females breeding with them do not produce offspring.
Radioisotopes in Medicine
Radioactive tracers are also used in many medical applications, including both diagnosis and treatment. They are used to measure engine wear, analyze the geological formation around oil wells, and much more.
Radioisotopes have revolutionized medical practice, where they are used extensively. Over 10 million nuclear medicine procedures and more than 100 million nuclear medicine tests are performed annually in the United States.
Diagnostic Medical Applications
Diagnostic medical applications involve testing for a disease or condition. In nuclear medicine, this could involve using PET scans, or isotopic studies. The radiation involved for each of these types of tools will vary in mrem or mSv amounts.
PET Scanning
Positron Emission Tomography or PET scan is a type of nuclear medicine imaging. Depending on the area of the body being imaged, a radioactive isotope is either injected into a vein, swallowed by mouth, or inhaled as a gas. When the radioisotope is collected in the appropriate area of the body, the gamma ray emissions are detected by a PET scanner (often called a gamma camera) which works together with a computer to generate special pictures, providing details on both the structure and function of various organs. Watch this informational video on how this technique works.
PET Scan
Video $1$ PET scans: What to expect.
PET scans are used to:
• Detect cancer
• Determine the amount of cancer spread
• Assess the effectiveness of treatment plans
• Determine blood flow to the heart muscle
• Determine the effects of a heart attack
• Evaluate brain abnormalities such as tumors and memory disorders
• Map brain and heart function
PET Scanning, is used to image the physiological aspects of the body rather than the anatomy (Figures $5$ and $6$). It images the function of the body rather than the form, such as where tagged molecules go and how they are used. For instance, if you were to image the brain of a deceased person, nothing would show up on a PET scan opposed to a CAT scan, as the brain is no longer functional. Pet Scanning is very useful in imaging tumors, which can be done when patients are injected with certain tracers. Often times PET scanners are used in collaboration with CAT scanners to create a composite image that shows both the function and form of the body. The animation below is a whole-body PET scan using the radioisotope of 18F (t1/2 = 110 min). Using this tracer, doctors can determine if cancer has metastasized by looking at the metabolic activity of glucose.
Other Isotopic Tests
Radioisotopes have revolutionized medical practice, where they are used extensively. Over 10 million nuclear medicine procedures and more than 100 million nuclear medicine tests are performed annually in the United States. Four typical examples of radioactive tracers used in medicine are technetium-99 $\ce{(^{99}_{43}Tc)}$, thallium-201 $\ce{(^{201}_{81}Tl)}$, iodine-131 $\ce{(^{131}_{53}I)}$, and sodium-24 $\ce{(^{24}_{11}Na)}$. Damaged tissues in the heart, liver, and lungs absorb certain compounds of technetium-99 preferentially. After it is injected, the location of the technetium compound, and hence the damaged tissue, can be determined by detecting the γ rays emitted by the Tc-99 isotope. Thallium-201 (Figure $7$) becomes concentrated in healthy heart tissue, so the two isotopes, Tc-99 and Tl-201, are used together to study heart tissue. Iodine-131 concentrates in the thyroid gland, the liver, and some parts of the brain. It can therefore be used to monitor goiter and treat thyroid conditions, such as Grave’s disease, as well as liver and brain tumors. Salt solutions containing compounds of sodium-24 are injected into the bloodstream to help locate obstructions to the flow of blood.
Small doses of $\ce{I}$-131 (too small to kill cells) are used for purposes of imaging the thyroid. Once the iodine is concentrated in the thyroid, the patient lays down on a sheet of film and the radiation from the $\ce{I}$-131 makes a picture of the thyroid on the film. The half-life of iodine-131 is approximately 8 days so after a few weeks, virtually all of the radioactive iodine is out of the patient's system. During that time, they are advised that they will set off radiation detectors in airports and will need to get special permission to fly on commercial flights.
Some isotopes that are used to diagnose diseases are shown in Table $1$. All of these nuclear isotopes release one form of ionizing radiation (either/add particle or ray). In addition, each isotopic application would involve a specific amount of mrem/mSv radiation.
Table $1$ Selected Radioisotopes Used in Diagnostic Nuclear Medicine
Symbol-mass Half-Life (t1/2) Application
Xe-133 5.27 days Lung imaging
H-3 12.26 years Analyzing total body water
Tl-201 73 hours Stress tests for heart problems
Fe-59 44.5 days Detection of anemia
Gd-153 242 days Analyzing bone density
Cr-51 27.8 days Determining blood volume
C-11 20.4 minutes Brain scans
Tc-99m 6.0 hours Heart, lung, kidney, bone marrow, brain, or bone marrow imaging
Pu-238 86 years Powering pacemakers
I-131 8.0 days Imaging Thyroid
The “m” in Tc-99m stands for “metastable,” indicating that this is an unstable, high-energy state of Tc-99. Metastable isotopes emit $γ$ radiation to rid themselves of excess energy and become (more) stable.
Keep in mind that x-rays, CT scans, PET scans, and isotopic studies involve ionizing radiation. In contrast, MRI (magnetic resonance imaging) and ultrasounds do not utilize ionizing forms of radiation.
Therapeutic Radiation
There are many techniques used to treat cancer. Surgery can be used to remove cancerous tumors inside or on the body. With chemotherapy, ingested or injected chemicals are used to kill rapidly dividing cells (cancerous and noncancerous). Other cancer treatment methods include immunotherapy, stem cell replacement, hormone therapy, and targeted therapy.
Radiation therapy and Chemotherapy: Two different treatment procedures
Patients diagnosed with cancer might be required to do chemotherapy or radiation therapy. Sometimes, both of these methods are used for a patient. In this picture, a female patient is receiving chemotherapy through an IV. She is participating in cooling therapy while receiving her treatment. By placing her hands and feet in cooling devices, this will lower her chances of losing her finger and toenails. Cold cap therapy is also now available for chemotherapy patients. Wearing this type of device could enable a patient to keep his/her hair during chemotherapy.
Current therapeutic radiation applications involve the use of gamma, x-rays, or protons. Recently, some research facilities are investigating the use of alpha and beta tagged molecules to kill cancer cells. These radioisotopes will first locate a cancer related molecule on a tumor cell. Then, the alpha or beta tagged species will inject its radiation into the tumor. Sr-89 (beta emitter) and Ra-223 (alpha emitter) have been used in clinical research trials of certain types of bone cancers.
Radiation Therapy is used as a treatment to control malignant cells within cancer patients. Oncologists (specialists that deal with cancer) utilize radiation frequently to help slow or cure the spread of cancer within individuals. Radiation is specifically applied to malignant tumors in order to shrink them in size. Medical professionals, mainly radiation oncologists, administer a variety of dosages to patient, contingent to the patients current health, as well as other treatments such as chemotherapy, success of surgery, etc.
External Beam Therapy (Photon and Proton Therapy)
External Beam Therapy (EBT) is a method of delivering a high energy beam of radiation to the precise location of a patient's tumor. These beams can destroy cancer cells and with careful planning, NOT kill surrounding cells. The concept is to have several beams of radiation, each of which is sub-lethal, enter the body from different directions. The only place in the body where the beam would be lethal is at the point where all the beams intersect. Before the EBT process, the patient is three-dimensionally mapped using CT scans and x-rays. The patient receives small tattoos to allow the therapist to line up the beams exactly. Alignment lasers are used to precisely locate the target. The radiation beam is usually generated with a linear accelerator. The video below illustrates the basic preparation and administration of external beam therapy.
Radiation Therapy
Video $2$ Targeting cancer - Radiation therapy treatment process.
Photon EBT utilizes either x-ray or gamma rays. An x-ray source would require a linear accelerator to produce high energy electrons. In contrast, a gamma source incorporates a radioactive isotope (like Co-60). Keep in mind both of these technologies use ionizing radiation. As a result, cancer patients must be monitored throughout their life to ensure they do not develop other cancers, like leukemia. EBT is used to treat the following diseases as well as others:
• Breast cancer
• Colorectal cancer
• Head and neck cancer
• Lung cancer
• Prostate cancer
The majority of radiation patients receive photon EBT. The smaller size of this machine makes this therapy an option for all sizes of hospitals and cancer treatment centers. Photon EBT equipment costs approximately three million dollars. The size and the price of this technology enables smaller facilities to keep their patients closer to home during treatment
Another method of radiation treatment involving protons is not as commonly used in the United States. Photon therapy requires a cyclotron to generate proton beams (recall, a proton is an ionized H-1 isotope). Unlike x-ray or gamma rays (photon therapy), protons are extremely heavy.
At this time, research facilities are working on miniaturizing proton generators. An ideal technology would reduce the cost from hundreds of millions of dollars to about twenty to thirty million per device. This would make proton therapy more available and convenient for patients.
Proton Therapy vs Radiation Therapy
Video$3$ Proton therapy versus radiation therapy
There are many advantages to choosing proton therapy over photon therapy. Unlike photon radiation, proton beams will only penetrate to the depth of the tumor and not pass through the entire body. This reduces the overall toxicity dose. In addition, fewer treatments are required for proton therapy patients than photon therapy.Unfortunately, proton therapy is more expensive than photon therapy and less common. Once approved by a facility and medical insurance, a patient may have to move temporarily to a larger city to receive treatment. Some forms of cancer have never been clinically treated with proton therapy (namely, breast cancer). Patients desiring proton therapy might not be able to receive type of therapy due to lack of research.
Brachtherapy
Brachytherapy involves placing ionizing pellets(seeds) or rods directly at the tumor. Photons (in the form of x-ray or gamma ray) are produced inside the body and will penetrate throughout this particular area localizing the radiation. Pellets are surgically implanted while rods can be temporarily inserted to produce radiation internally. With pellets/seeds, the patient will remain radioactive as long as these devices remain inside the body. People undergoing this type of radiotherapy need to be aware of their constant emission of radiation. Radiation that is administered through rods connected to a photon device will disperse energy immediately and not leave the patient radioactive.
Brachytherapy is widely used in the treatment of cancers involving reproductive organs. Because the radiation is isolated internally, patients are less likely to experience side effects when receiving this type of treatment. Cancers that have been treated with brachytherapy are shown below:
• Prostate
• Breast
• Esophageal
• Lung
• Uterine
• Anal/Rectal
• Sarcomas
• Head and neck
Table $2$ list commonly used radionuclides for brachtherapy. Table $2$ Commonly Used Radiation Sources (radionuclides) for Brachytherapy.
Radionuclide Type Half-life
Cesium-131 (131Cs) Electron Capture, ε 9.7 days
Cesium-137 (137Cs) β- particles, γ-rays 30.17 years
Cobalt-60 (60Co) β- particles, γ-rays 5.26 years
Iridium-192 (192Ir) γ-rays 73.8 days
Iodine-125 (125I) Electron Capture, ε 59.6 days
Palladium-103 (103Pd) Electron Capture, ε 17.0 days
Ruthenium-106 (106Ru) β- particles 1.02 years
Radium-226 (226Ra) β- particles 1599 years
Side Effects of Radiation Therapy
Patients receiving radiation therapy can experience a variety of side effects. For example, sterility could occur if reproductive organs are irradiated. Skin that has been irradiated can appear dry and feel itchy. Some patients will loose sensation in the irradiated area. Radiation can affect the production of white and red blood cells. A reduction of white blood cells results in immunity disorders. Red blood cell lose causes anemia. Gastrointestinal issues such as diarrhea and nausea are common during radiation therapy. Some patients will lose hair as well. Lastly, dry mouth and tooth decay are prevalent during radiation treatments.
Medications are available to alleviate symptoms of radiation therapy. Narcotics can be prescribed to help alleviate intense pain. Prescription medications like zofran (Figure $10$) and phenergan can help with nausea. Special mouthwashes have been formulated to reduce dry mouth and cavities.
Hair loss is a side effect of radiation, but only locally
Radiation therapy can cause hair loss, but hair is only lost in the area being treated. For instance, radiation to your head may cause you to lose some or all the hair on your head (even eyebrows and lashes), but if you get treatment to your hip, you won’t lose the hair on your head.
Summary
• Compounds known as radioactive tracers can be used to follow reactions, track the distribution of a substance, diagnose and treat medical conditions, and much more.
• Other radioactive substances are helpful for controlling pests, visualizing structures, providing fire warnings, and for many other applications.
• Hundreds of millions of nuclear medicine tests and procedures, using a wide variety of radioisotopes with relatively short half-lives, are performed every year in the US.
• Radiation therapy uses high-energy radiation to kill cancer cells by damaging their DNA. The radiation used for this treatment may be delivered externally or internally. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.05%3A_Uses_of_Radioisotopes.txt |
Learning Objective
• Compare qualitatively the ionizing and penetration power of alpha particles $\left( \alpha \right)$, beta particles $\left( \beta \right)$, and gamma rays $\left( \gamma \right)$.
With all the radiation from natural and man-made sources, we should quite reasonably be concerned about how all the radiation might affect our health. The damage to living systems is done by radioactive emissions when the particles or rays strike tissue, cells, or molecules and alter them. These interactions can alter molecular structure and function; cells no longer carry out their proper function and molecules, such as DNA, no longer carry the appropriate information. Large amounts of radiation are very dangerous, even deadly. In most cases, radiation will damage a single (or very small number) of cells by breaking the cell wall or otherwise preventing a cell from reproducing.
The ability of radiation to damage molecules is analyzed in terms of what is called ionizing power. When a radiation particle interacts with atoms, the interaction can cause the atom to lose electrons and thus become ionized. The greater the likelihood that damage will occur by an interaction is the ionizing power of the radiation.
Much of the threat from radiation is involved with the ease or difficulty of protecting oneself from the particles. How thick of wall do you need to hide behind to be safe? The ability of each type of radiation to pass through matter is expressed in terms of penetration power. The more material the radiation can pass through, the greater the penetration power and the more dangerous they are. In general, the greater mass present the greater the ionizing power and the lower the penetration power.
Comparing only the three common types of ionizing radiation, alpha particles have the greatest mass. Because of the large mass of the alpha particle, it has the highest ionizing power and the greatest ability to damage tissue. That same large size of alpha particles, however, makes them less able to penetrate matter. Alpha particles have the least penetration power and can be stopped by a thick sheet of paper or even a layer of clothes. They are also stopped by the outer layer of dead skin on people. This may seem to remove the threat from alpha particles but only from external sources. In a situation like a nuclear explosion or some sort of nuclear accident where radioactive emitters are spread around in the environment, the emitters can be inhaled or taken in with food or water and once the alpha emitter is inside you, you have no protection at all.
Beta particles are much smaller than alpha particles and therefore, have much less ionizing power (less ability to damage tissue), but their small size gives them much greater penetration power. Most resources say that beta particles can be stopped by a one-quarter inch thick sheet of aluminum. Once again, however, the greatest danger occurs when the beta emitting source gets inside of you.
Gamma rays are not particles but a high energy form of electromagnetic radiation (like x-rays except more powerful). Gamma rays are energy that has no mass or charge. Gamma rays have tremendous penetration power and require several inches of dense material (like lead) to shield them. Gamma rays may pass all the way through a human body without striking anything. They are considered to have the least ionizing power and the greatest penetration power.
A comparison of Alpha particles, beta particles and gamma rays is given in Table $1$.
Table $1$ Comparison of Penetrating Power,Ionizing Power and Shielding of Alpha and Beta Particles, and Gamma Rays.
Particle Symbol Mass Penetrating Power Ionizing Power Shielding
Alpha $\alpha$ $4 \mathrm{amu}$ Very Low Very High Paper Skin
Beta $\beta$ $1 / 2000 \mathrm{amu}$ Intermediate Intermediate Aluminum
Gamma $\gamma$ 0 (energy only) Very High Very Low 2 inches lead
The safest amount of radiation to the human body is zero. It isn't possible to be exposed to no ionizing radiation so the next best goal is to be exposed to as little as possible. The two best ways to minimize exposure is to limit time of exposure and to increase distance from the source.
Summary
• Types of radiation differ in their ability to penetrate material and damage tissue, with alpha particles the least penetrating but potentially most damaging and gamma rays the most penetrating.
• The two best ways to minimize exposure is to limit time of exposure and to increase distance from the source. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.06%3A_Penetrating_Power_of_Radiation.txt |
Learning Objectives
• Explain where nuclear energy comes from.
• Describe the difference between fission and fusion.
• Know key examples of nuclear fission and nuclear fusion.
A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as fission and fusion. Some early evidence for nuclear fission was the formation of a short-lived radioisotope of barium which was isolated from neutron irradiated uranium (139Ba, with a half-life of 83 minutes and 140Ba, with a half-life of 12.8 days, are major fission products of uranium). Nuclear fission is the splitting of an atomic nucleus. In nuclear weapons and reactors, neutrons hit unstable nuclei to form smaller atoms. Nuclear Fusion is the bringing together of two atomic nuclei to form a larger atom. Figure $1$ illustrates the difference between nuclear fission and nuclear fusion.
Einstein and the Equivalence of Mass and Energy
Nuclear changes occur with a simultaneous release of energy. Where does this energy come from? If we could precisely measure the masses of the reactants and products of a nuclear reaction, we would notice that the amount of mass drops slightly in the conversion from reactants to products. Consider the following nuclear equation, in which the molar mass of each species is indicated to four decimal places:
$_{235.0439}^{235}\textrm{U}\rightarrow _{138.9088}^{139}\textrm{Ba}+_{93.9343}^{94}\textrm{Kr}+_{2\times 1.0087}^{2^{1}}\textrm{n} \nonumber$
If we compare the mass of the reactant (235.0439) to the masses of the products (sum=234.8605) we notice a mass difference of -0.1834 g or -0.0001834 kg. Where did this mass go?
According to Albert Einstein's theory of relativity, energy (E) and mass (m) are related by the following equation:
$E = mc^2 \nonumber$
where c is the speed of light, or $c=3.00\times 10^{8}\, m/s \nonumber$
In the course of the chemical reaction for uranium, the mass difference is converted to energy, which is given off by the reaction:
$E=(-0.0001834\, kg)(3.00\times 10^{8}\, m/s)^{2}=-1.65\times 10^{13}J=-1.65\times 10^{10}kJ \nonumber$
(For the units to work out, mass must be expressed in units of kilograms.) That is, 16.5 billion kJ of energy is given off every time 1 mol of uranium-235 undergoes this nuclear reaction. This is an extraordinary amount of energy. Compare it to combustion reactions of hydrocarbons, which give off about 650kJ/mol of energy for every CH2 unit in the hydrocarbon-on the order of hundreds of kilojoules per mole. Nuclear reactions give off billions of kilojoules per mole.
If this energy could be properly harvested, it would be a significant source of energy for our society. Nuclear energy involves the controlled harvesting of energy from fission reactions. The reaction can be controlled because the fission of uranium-235 (and a few other isotopes, such as plutonium-239) can be artificially initiated by injecting a neutron into a uranium nucleus. The overall nuclear equation, with energy included as a product, is then as follows:
$_{}^{235}\textrm{U}\: +\: _{ }^{1}\textrm{n}\rightarrow \: _{ }^{139}\textrm{Ba}\: +\: _{ }^{94}\textrm{Kr}\: +\: 3_{ }^{1}\textrm{n} \nonumber$
Thus by the careful addition of extra neutrons into a sample of uranium, we can control the fission process and obtain energy that can be used for other purposes. (Artificial or induced radioactivity, in which neutrons are injected into a sample of matter that subsequently cause fission, was first demonstrated in 1934 by Irène Joliot-Curie and Frédéric Joliot, the daughter and son-in-law of Marie Curie.)
Binding Energy
The forces that bind nucleons together in an atomic nucleus are much greater than those that bind an electron to an atom through electrostatic attraction. This is evident by the relative sizes of the atomic nucleus and the atom ($10^{-15}$ and $10^{-10}$m, respectively). The energy required to pry a nucleon from the nucleus is therefore much larger than that required to remove (or ionize) an electron in an atom. In general, all nuclear changes involve large amounts of energy per particle undergoing the reaction. This has numerous practical applications.
As shown in figure $2$, energy is put into the system to break apart the nucleus. The amount of energy required is called the total binding energy (BE), $E_b$. The binding energy is equal to the amount of energy released in forming the nucleus, and is therefore given by
$E_b = (\Delta m)c^2. \label{BE}$
In nuclear physics, one of the most important experimental quantities is the binding energy per nucleon (BEN), which is defined by
$BEN = \dfrac{E_b}{A} \label{BEN}$
This quantity is the average energy required to remove an individual nucleon (proton or neutron) from a nucleus—analogous to the ionization energy of an electron in an atom. If the BEN is relatively large, the nucleus is relatively stable. BEN values are estimated from nuclear scattering experiments.
Figure $3$ shows the relative binding energies for various isotopes. Of these elements, fission requires heavy, unstable nuclei. This means selected atoms would have low binding energies and would have large atomic masses. Nuclei that are larger than Fe-56 may undergo fission. Uranium-238 and uranium-235 both have lower binding energies with heavy masses-.
These two isotopes would be suitable for splitting based on these requirements. Of these two isotopes, only uranium-235 is readily fissionable. This is due to odd neutron count contributing to additional instability. Another fissionable isotope not shown in Figure $3$ is plutonium-239. This is a synthetic isotope produced by transmutation and decay reactions. Like uranium-235, it has low binding energy, high mass, and an odd number of neutrons. U-235 and Pu-239 are used in atomic bombs (fission based) and nuclear reactors.
Positively charged centers of atoms make nuclear fusion extremely difficult. For this reason, smaller atoms are suitable for fusion reactions. In addition, these particular isotopes need to have low binding energies in order to undergo fusion. Atoms that possess these two qualities are H-2 and H-3. For fusion to occur, extreme temperatures are required to fuse these deuterium and tritium together.
As we will see, the BEN-versus-A graph implies that nuclei divided or combined release an enormous amount of energy. This is the basis for a wide range of phenomena, from the production of electricity at a nuclear power plant to sunlight.
Nuclear Fission
In both fission and fusion, large amounts of energy are given off in the form of heat, light, and gamma radiation. Italian physicist, Enrico Fermi, performed the first fission reaction in 1934. He was unaware that he had split a uranium atom into two smaller nuclei. Nuclear fission of heavy elements was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner (Figure $4$) and her nephew Otto Robert Frisch. Frisch named the process "fission" by analogy with biological fission of living cells.
Image take from: https://upload.wikimedia.org/wikiped...ner12crop2.J
Since then, fission has been observed in many other isotopes, including most actinide isotopes that have an odd number of neutrons. A typical nuclear fission reaction is shown in Figure $5$.
Among the products of Meitner, Hahn, and Strassman’s fission reaction were barium, krypton, lanthanum, and cerium, all of which have nuclei that are more stable than uranium-235. Since then, hundreds of different isotopes have been observed among the products of fissionable substances.
Fission has been used in nuclear weapons and powers all nuclear reactors. Approximately fifty-five countries worldwide possess fission technology in the form of research or energy reactors. Less than ten of these countries have fission weapons.
A tremendous amount of energy is produced by the fission of heavy elements. For instance, when one mole of U-235 undergoes fission, the products weigh about 0.2 grams less than the reactants; this “lost” mass is converted into a very large amount of energy, about 1.8 × 1010 kJ per mole of U-235. Nuclear fission reactions produce incredibly large amounts of energy compared to chemical reactions. The fission of 1 kilogram of uranium-235, for example, produces about 2.5 million times as much energy as is produced by burning 1 kilogram of coal.
Nuclear Chain Reaction
As described earlier, when undergoing fission U-235 produces two “medium-sized” nuclei, and two or three neutrons. These neutrons may then cause the fission of other uranium-235 atoms, which in turn provide more neutrons that can cause fission of even more nuclei, and so on. If this occurs, we have a nuclear chain reaction (Figure $6$). On the other hand, if too many neutrons escape the bulk material without interacting with a nucleus, then no chain reaction will occur.
Material that can sustain a nuclear fission chain reaction is said to be fissile or fissionable. (Technically, fissile material can undergo fission with neutrons of any energy, whereas fissionable material requires high-energy neutrons.) Nuclear fission becomes self-sustaining when the number of neutrons produced by fission equals or exceeds the number of neutrons absorbed by splitting nuclei plus the number that escape into the surroundings. The amount of a fissionable material that will support a self-sustaining chain reaction is a critical mass. An amount of fissionable material that cannot sustain a chain reaction is a subcritical mass. An amount of material in which there is an increasing rate of fission is known as a supercritical mass. The critical mass depends on the type of material: its purity, the temperature, the shape of the sample, and how the neutron reactions are controlled (Figure $7$).
Thermonuclear Reactions
Thermonuclear fusion is a way to achieve nuclear fusion by using extremely high temperatures. There are two forms of thermonuclear fusion: uncontrolled, in which the resulting energy is released in an uncontrolled manner, as it is in thermonuclear weapons ("hydrogen bombs") and in most stars; and controlled, where the fusion reactions take place in an environment allowing some or all of the energy released to be harnessed for constructive purposes. The discussion below is limited to the fusion process that powers the sun and the stars.
The prime energy producer in the sun is the fusion of hydrogen to form helium, which occurs at a solar-core temperature of 14 million kelvin. The net result is the fusion of four protons into one alpha particle, with the release of two positrons, two neutrinos (which changes two of the protons into neutrons), and energy (Figure $8$).
This is a net reaction of a more complicated series of events:
$\ce{4^1_1H ⟶ ^4_2He + 2 ^1_{0}n} \nonumber$
A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about 3.6 × 1011 kJ of energy per mole of $\ce{^4_2He}$ produced. This is somewhat larger than the energy produced by the nuclear fission of one mole of U-235 (1.8 × 1010 kJ), and over 3 million times larger than the energy produced by the (chemical) combustion of one mole of octane (5471 kJ).
Summary
• Nuclear energy comes from tiny mass changes in nuclei as radioactive processes occur.
• In fission, large nuclei break apart and release energy; in fusion, small nuclei merge together and release energy.
• The continues process whereby neutrons produced from the initial fission of a large nucleus like U-235 cause further fission of another nucleus.
• In a critical mass, a large enough number of neutrons in the fissile material induce fission to create a chain reaction.
• The most important fusion process in nature is the one that powers the stars. The net result is the fusion of four protons into one alpha particle, with the release of two positrons, two neutrinos (which changes two of the protons into neutrons), and energy | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.07%3A_Energy_from_the_Nucleus.txt |
Learning Objectives
• Describe the key features of an atomic bomb.
• Define nuclear fallout.
World war two brought about many advances in weaponry. The Nazis used the immense science ability of their newly conquered countries to attempt to create super weapons to keep the new territory. The weapons included new tanks like the feared Tiger Tank, or the highly advanced Luftwaffe air force. However, the one weapon the Nazi's really wanted to hold was the atomic bomb. The problem that the Nazi's began to have though was that many of the great minds they once had left the country and came to the United States. Also, in the end Allied troops got to Hitler and his scientists just before they could complete any atomic bombs. The U.S. also wanted to create an atom bomb, and for the same reasons. The Manhattan Project was started to form this new weapon.
The Manhattan Project was successful in the United States because of the vast resources that could be pulled together for the project. The great minds worked under the University of Chicago football field to try and create fission. A plant in Tennessee had the sole purpose of producing enough uranium for atomic bomb testing. Finally, New Mexico was the epicenter of the whole operation. This is where the bombs were constructed and tested. The resources needed were immense. There had to be enough fuel for the bomb, and everything required to make it. There had to be housing and food for all the scientists. Maybe most importantly, there had to be enough money to support the project. The Unites States was able to effectively use all of these resources, while the Germans did not have the resources, and didn't use them as effectively. Finally, after years of hard work an atomic bomb test took place of July 16, 1945. The bomb was held together in some parts by just tape, yet it was a huge success. The problem was that the war in Europe was already over, so President Truman had to decide whether or not to use the bomb on Japan.
The war in the Pacific was a lot different than the war in Europe. In Europe, you landed once and fought your way through to Berlin to defeat the Nazi's. However, in the Pacific Japan controlled hundreds of Islands before you got to the mainland. The invasion would have cost huge amounts of American lives and resources. As a result, when the bomb had a successful test President Truman said he hardly hesitated to approve of the usage of the atomic bomb on Japan.
The first atomic bomb was dropped on Hiroshima on August 6, 1945 by the Enola Gay. The bomb destroyed the city, killing almost 100,000 people. The city of Hiroshima was essentially leveled. Following this attack, on August 9, 1945 another atomic bomb was dropped on Nagasaki. The same effects were felt in this city. The United States was ready to drop another atomic bomb in the third week of August, 3 more in September, and 3 more in October if necessary. However, on August 15 Japan surrendered to the allies and World War Two was officially over.
The Workings of the Atomic Bomb
A crucial feature of the fission of uranium without which an atom bomb is impossible is that fission produces more neutrons than it consumes. As can be seen from Eqs. (1), for every neutron captured by a $\ce{^{235}_{92}U}$ nucleus, between two and four neutrons are produced. Suppose now that we have a very large sample of the pure $\ce{^{235}_{92}U}$ isotope and a stray neutron enters this sample. As soon as it hits a $\ce{^{235}_{92}U}$ nucleus, fission will take place and about three neutrons will be produced. These in turn will fission three more 235U nuclei, producing a total of nine neutrons. A third repetition will produce 27 neutrons. a fourth 81. and so on. This process (which is called a chain reaction) escalates very rapidly. Within a few microseconds a very large number of nuclei fission, with the release of a tremendous amount of energy, and an atomic explosion results.
)
There are two reasons why a normal sample of uranium metal does not spontaneously explode in this way. In the first place natural uranium consists mainly of the isotope $\ce{^{238}_{92}U}$, while the fissionable isotope $\ce{^{235}_{92}U}$ comprises only 0.7 percent of the total. Most of the neutrons produced in a given fission process are captured by $\ce{^{238}_{92}U}$ nuclei without any further production of neutrons. The escalation of the fission process thus becomes impossible. However, even a sample of pure 235U will not always explode spontaneously. If it is sufficiently small, many of the neutrons will escape into the surroundings without causing further fission. The sample must exceed a critical mass before an explosion results. In an atomic bomb several pieces of fissionable material, all of which are below the critical mass, are held sufficiently far apart for no chain reaction to occur. When these are suddenly brought together, an atomic explosion results immediately.
Two types of atomic bombs were developed concurrently during the war: a relatively simple and a more complex . The gun-type design proved impractical to use with , and therefore a simpler gun-type called was developed that used , an that makes up only 0.7 percent of natural . Chemically identical to the most common isotope, , and with almost the same mass, it proved difficult to separate the two.
In parallel with the work on uranium was an effort to produce , which was discovered at the in 1940. After the feasibility of the world's first artificial nuclear reactor, the , was demonstrated in 1942 at the in the , the Project designed the at Oak Ridge and the production reactors at the in , in which uranium was irradiated and into plutonium. The plutonium was then chemically separated from the uranium, using the . The plutonium implosion-type weapon was developed in a concerted design and development effort by the Los Alamos Laboratory.
Isotopic Enrichment
A great deal of the five years of the Manhattan Project was spent in separating the 0.7 percent of 235U from the more abundant 238U. Most of this work was performed at the at . This was done by preparing the gaseous compound UF6 and allowing it to effuse through a porous screen. Each effusion resulted in a gas which was slightly richer in the lighter isotope. Repeating this process eventually produced a compound rich enough in 235U for the purposes of bomb manufacture.
Synthesis of Plutonium
In parallel with the work on uranium was an effort to produce , which was discovered at the in 1940. Only the first bomb dropped on Japan used uranium. The second bomb used the artificial element plutonium, produced by the neutron bombardment of 238U:
$\ce{^{235}_{92} U + ^{1}_0n \rightarrow ^{239}_{94}Pu + 2 ^{0}_{-1}\beta } \nonumber$
Fission of Pu-239 occurs in much the same way as for U-235, giving a variety of products; for example,
$\ce{^{239}_{94} Pu + ^{1}_0n \rightarrow ^{90}_{38}Pu + ^{147}_{56}Ba + 3 ^{1}_{0}n } \nonumber$
Again this is a highly exothermic reaction yielding about the same energy per mole (20 000 GJ mol–1) as 235U.
This immense amount of energy released is the reason why plutonium and uranium were used. By comparison, 1 ton of TNT yields about 4 GJ mol–1 of energy. This means that the atomic bombs had about 5,000 times more energy than 1 ton of TNT, that is a huge amount of energy, and explains why the bomb was so effective and destructive.
Nuclear explosion
Video $1$ Nuclear explosion power comparison.
Although the Fat Man atomic bomb was extremely powerful and destructive, it is not even close to the power of subsequent nuclear bombs. The atomic age was set forth by the United States on those two fateful days in August. In the subsequent years many other countries harnessed the power of nuclear weapons, including Russia, China, Britain, and France. The "high point" of the atomic age came with the explosion of the Tsar Bomba by Russia. This bomb was equal to 50 megatons of TNT, or 2,500 times more powerful than the Fat Man bomb. It was said that when the bomb was detonated the shock wave in the ground could be felt over 600 miles away (the bomb wasn't even detonated on the ground either, but rather in mid air!). The advance and use of nuclear weapons seemed to be growing at an extraordinarily fast pace. However, countries stepped up and signed various treaties, including the Nuclear Non-Proliferation Treaty, to stop the increase in nuclear weapons and hopefully the use of any more in the future.
Bomb Construction
At Los Alamos, New Mexico, J. Robert Oppenheimer, and his research group were given the task of assembling and testing the fission bomb. Both types of fuel that were manufactured (U-235 and Pu-239) would be placed separately into two different bomb designs. The smaller of the two bombs would contain U-235 and was code-named "Little Boy." The larger bomb, which housed Pu-239, was named "Fat Man." Of the two, only the Pu-239 bomb would be tested before it was dropped in wartime.
The basic design of the U-235 bomb is shown in the figure below. To prevent the spontaneous detonation of an atomic bomb, the fissile U-235 is kept in a subcritical configuration. It is then rapidly assembled into a supercritical mass using conventional explosives. Once the bomb has achieved this mass, any neutron introduced into it will be likely to initiate a chain reaction. The mechanism for "Little Boy" was a gun that fired one subcritical piece of U-235 into another to form a supercritical mass (Figure $2$). The pieces had to be assembled within a time less than the average time between appearances of spontaneous neutrons from either U-235 or cosmic radiation. A conventional explosive in an artillery barrel could fire the U-235 mass at speeds of a few millimeters per second, fast enough to prevent a fizzle caused by a spontaneous neutron setting off a premature chain reaction.
Originally, the gun-type mechanism was planned for both the U-235 and Pu-239 weapons. However, a problem arose with the Pu-239 bomb that required a different assembly mechanism because of the small amount of Pu-240 that is produced with the Pu-239 in the reactor. Pu-240 emits large numbers of neutrons spontaneously: 1,030 neutrons per gram per second compared with 0.0004 neutrons per gram per second for U-235. Even at a concentration of 1% Pu-240 in the fissile Pu-239, the required mass of Pu emits 52,000 neutrons per second or one neutron every 20 microseconds. Thus, it is very probable that a neutron from Pu-240 will initiate a premature chain reaction during the critical last 100 microseconds of the critical mass in a gun-type assembly. This problem was discovered in mid-1944, well after the start of the construction of the massive Hanford plutonium production facilities.
The removal of the Pu-240 was impractical. So the scientists and engineers looked for a faster method of assembling the plutonium. A mechanism based on implosion provided the solution to this problem. In this design, the fissile material is shaped into a single sphere with a mass slightly less than critical (Figure $3$). Layers of carefully shaped high explosives surround the sphere. When the explosives are detonated, the force of the shock wave compresses the fissile material into a smaller volume, forming a supercritical mass. This method of assembly is much faster than the gun-type mechanism and thus eliminates the problems resulting from spontaneous neutron emission of Pu-240. The spherical mass resulted in a pumpkin-shaped weapon called "Fat Man".
Example $1$
Watch the from the 23-minute mark through the 32-minute mark of the third installment of the History Channel's Manhattan Project and answer the questions below.
1. What were the problems with the two different types of fuel that were to be used in the fission weapons?
2. What was the configuration or set-up of the Pu-239 bomb?
3. The combination of electromagnetic separation and gaseous diffusion enriched enough U-235 to produce how many bombs?
4. Why was the U-235 bomb never tested?
5. When was the construction of the U-235 completed?
6. How much did Truman know about the nuclear bombs when FDR was alive?
7. Who was selected to pilot the plane for the nuclear weapons?
8. What island would serve as a base to house the nuclear bombs before delivering them to their targets?
In July 1945, the United States had enough fissile material for one uranium and two plutonium weapons. The scientists and engineers felt confident that the gun-type assembly mechanism for Little Boy would function properly. Besides, they did not have the material for a test device. They were less confident about the implosion mechanism on the plutonium weapon and felt that a test was necessary. On July 16, 1945, the first nuclear device, known as "The Gadget", was placed on a 100-foot tower and successfully detonated in the Alamogordo Desert, 200 miles south of Los Alamos (Figure $4$).
As the war with Japan continued and a costly allied invasion loomed as a real possibility, President Truman approved the use of nuclear weapons against selected Japanese targets. The U.S. Army Air Force received orders to use these weapons anytime after August 3, 1945. On August 6, "Little Boy" was dropped on Hiroshima (Figure $5$).
Little Boy was a uranium weapon containing 141.4 pounds of fissionable material containing 82.7% U-235. Only about two pounds fissioned, releasing an energy equivalent to 15-16,000 tons of TNT. The immediate effects of the blast killed an estimated 70,000 people, and by the end of 1945 an additional 20,000 to 70,000 deaths occurred, many due to lack of adequate medical resources.
Three days later, "Fat Man" destroyed a large part of Nagasaki (Figure $6$). Fat Man contained 13.6 pounds of Pu-239, of which only 2 pounds underwent fission. The explosive yield was equivalent to about 22,000 tons of TNT. Fat man resulted in 35,000 immediate deaths. By the end of 1945, at least 70,000 people perished in this event.
Figure $6$: Fat Man – One of many Pu-239 nuclear weapons constructed during WWII. Courtesy of the U.S. Department of Defense
Example $2$
Start the video below at the 23:20 mark and stop it at the 29-minute setting. Then, answer the questions below:
1. When and where was the first nuclear bomb tested?
2. Was the bomb placed on the ground?
3. What were scientists afraid the first nuclear bomb would do?
4. What did Edward Teller (father of the fusion bomb) apply to his skin before the bomb was ignited? Why did he do this?
5. What did the bomb do to the tower and the surrounding sand?
6. In the photograph, where did General Grove focus his attention?
Nuclear Fallout
Nuclear fallout refers to the radioactive material that "falls out" of the atmosphere after a nuclear explosion (reactor or bomb). It consists of dust and radioactive particles that can contaminate an area with radioactivity and pose a huge health hazard to biological organisms. It can contaminate the animal food chain which can have drastic effects on the affected region. Weather has a huge impact on fallout, wind currents can spread radioactive fallout either over a large area, such as in the case of Castle Bravo, or not.
In regards to nuclear reactions, fission produces more fallout products that fusion. Intense heat of the latter type of reactions reduces the amount and type of radioisotopes produced. Although more powerful, fusion is a "cleaner" type of nuclear reaction. By increasing the fission component of a fusion weapon, bombs can be designed to generate more fallout products.Of the different types of isotopes that fission produces, the most worrisome are Sr-90, Cs-137,and I-131. The first of these isotopes has a half-life of 28.8 years and decays by gamma and beta emission. Once ingested or inhaled, Sr-90 deposits in teeth, bone,and bone marrow. Sr-90 exposure can lead to bone cancer and/or leukemia. Cs-137 (t1/2 = 30.17 years) emits beta and gamma radiation. This ionizing radiation deposits in soft tissues of the body. In addition, this particular radioisotope is water soluble and can easily contaminant food and water supplies. I-131 had a half-life over 8.1 days and undergoes gamma/beta decay. Once this fallout product enters the body, it attacks the thyroid gland. Extensive damage could affect heart rate, blood pressure, body temperature, and childhood growth. In addition, I-131 exposure could result in thyroid cancer.
Nuclear Fallout
Watch the fallout video and then answer the questions below:
Summary
• In an atomic bomb several pieces of fissionable material are held sufficiently far apart for no chain reaction to occur. When these are suddenly brought together, the critical mass is reached and an atomic explosion results immediately.
• The two fission bombs assembled at Los Alamos, New Mexico, by J. Robert Oppenheimer, and his research group were manufactured with two types of fuel namely, U-235 and Pu-239.
• The smaller of the two bombs would contain U-235 and was code-named "Little Boy." This bomb was dropped in Hirsohima, Japan on Aug.6, 1945.
• The larger bomb, which housed Pu-239, was named "Fat Man." This bomb was dropped in Nagazaki, Japan on Aug.9, 1945.
• Nuclear fallout refers to the radioactive material that "falls out" of the atmosphere after a nuclear explosion (reactor or bomb).
Contributors and Attributions
• Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/[email protected]).
• Ed Vitz (Kutztown University), John W. Moore (UW-Madison), Justin Shorb (Hope College), Xavier Prat-Resina (University of Minnesota Rochester), Tim Wendorff, and Adam Hahn.
• Frank A. Settle (Washington and Lee University)
• Muneeba Ali (Furman University) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.08%3A_Nuclear_Bombs.txt |
Learning Objective
• Know the benefits and consequences of nuclear energy.
Nuclear Power Generation
The generation of electricity is critical for operation of businesses, health care delivery, schools, homes, and other areas requiring the use of electrical power. According to 2011 statistics, coal is used for \(42\%\) of the total power generated, with natural gas being employed for another \(25\%\). Nuclear power plants are employed in about \(19\%\) of the cases, with renewable energy sources supplying the last \(13\%\). All of these fuels are used to heat water to generate steam. The steam then turns a turbine to generate electricity.
Nuclear power plants use the energy from nuclear fission to produce electricity. U-235 is the preferred nuclear fuel because when its atoms are split (fissioned), they not only emit heat and high energy radiation but also enough neutrons to maintain a chain reaction and provide energy to power a nuclear power plant. Uranium is found in rocks all over the world but is relatively rare and the supply is finite making it a nonrenewable energy source.
Uranium usually occurs in combination with small amounts of other elements and once it is mined, the U-235 must be extracted and processed before it can be used as a fuel in a nuclear power plant to generate electricity. The processed uranium is formed into fuel rods and then bundled into fuel assemblies. Fuel assemblies are stored onsite until they are needed by the reactor operators. At this stage, the uranium is only mildly radioactive, and essentially all radiation is contained within the metal tubes. When needed, the fuel is loaded into a reactor core (Figure \(1\)). Typically, about one third of the reactor core (40 to 90 fuel assemblies) is changed out every 12 to 24 months.
The most common type of reactors are the pressurized water reactors (PWR) (Figure \(1\)) in which water is pumped through the reactor core and heated by the fission process. The water is kept under high pressure inside the reactor so it does not boil. The heated water from the reactor passes through tubes inside the steam generator where the heat is transferred to water flowing around the tubes in the steam generator. The water in the steam generator boils and turns to steam. The steam is piped to the turbines. The force of the expanding steam drives the turbines, which spin a magnet in coil of wire – the generator– to produce electricity.
After passing through the turbines, the steam is converted back to water by circulating it around tubes carrying cooling water in the condenser. The condensed steam – now water – is returned to the steam generators to repeat the cycle.
The three water systems (condenser, steam generator, and reactor) are separate from each other and are not permitted to mix. Water in the reactor is radioactive and is contained within the containment structure whereas water in the steam generator and condenser is nonradioactive.
Benefits of Nuclear Energy
By using fission, nuclear power plants generate electricity without emitting air pollutants like those emitted by fossil fuel-fired power plants. This means that financial costs related to chronic health problems caused by air pollutants such as particulate material, carbon monoxide, nitrogen oxides and ozone among others are significantly reduced. In addition nuclear reactors do not produce carbon dioxide while operating which means that nuclear energy does not contribute to the global warming problem.
Another benefit of nuclear energy over fossil fuels especially coal is that uranium generates far more power per unit weight or volume. This means that less of it needs to be mined and consequently the damage to the landscapes is less especially when compared to the damage that results from coal mining such as mountaintop removal.
Nuclear power is also used to propel ships. The turbine can be connected to a propeller system. The rotating turbine shaft will turn the propeller to move the ship.
The Drawbacks of Nuclear Energy
The main environmental concern related to nuclear power is the creation of radioactive wastes such as uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. These materials can remain radioactive and dangerous to human health for thousands of years. Radioactive wastes are classified as low-level and high-level. By volume, most of the waste related to the nuclear power industry has a relatively low-level of radioactivity. Uranium mill tailings contain the radioactive element radium, which decays to produce radon, a radioactive gas. Most uranium mill tailings are placed near the processing facility or mill where they come from. Uranium mill tailings are covered with a barrier of material such as clay to prevent radon from escaping into the atmosphere, and they are then covered by a layer of soil, rocks, or other materials to prevent erosion of the sealing barrier.
Spent fuel rods contain a variety of products, consisting of unstable nuclei ranging in atomic number from 25 to 60, some transuranium elements, including plutonium and americium, and unreacted uranium isotopes. The unstable nuclei and the transuranium isotopes give the spent fuel a dangerously high level of radioactivity. The long-lived isotopes require thousands of years to decay to a safe level. The ultimate fate of the nuclear reactor as a significant source of energy in the United States probably rests on whether or not a politically and scientifically satisfactory technique for processing and storing the components of spent fuel rods can be developed.
The other types of low-level radioactive waste are the tools, protective clothing, wiping cloths, and other disposable items that get contaminated with small amounts of radioactive dust or particles at nuclear fuel processing facilities and power plants. These materials are subject to special regulations that govern their handling, storage, and disposal so they will not come in contact with the outside environment.
High-level radioactive waste consists of spent nuclear reactor fuel (i.e., fuel that is no longer useful for producing electricity). The spent reactor fuel is in a solid form consisting of small fuel pellets in long metal tubes called rods. Spent reactor fuel assemblies are initially stored in specially designed pools of water, where the water cools the fuel and acts as a radiation shield. Spent reactor fuel assemblies can also be stored in specially designed dry storage containers. An increasing number of reactor operators now store their older spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling. There is currently no permanent disposal facility in the United States for high-level nuclear waste.
When a nuclear reactor stops operating, it must be decommissioned. This involves safely removing the reactor and all equipment that has become radioactive from service and reducing radioactivity to a level that permits other uses of the property. The U.S. Nuclear Regulatory Commission has strict rules governing nuclear power plant decommissioning that involve cleanup of radioactively contaminated plant systems and structures, and removal of the radioactive fuel.
A nuclear meltdown, or uncontrolled nuclear reaction in a nuclear reactor, can potentially result in widespread contamination of air and water. Some serious nuclear and radiation accidents have occurred worldwide. The most severe accident was the Chernobyl accident of 1986 in the then Soviet Union (now Ukraine) which killed 31 people directly and sickened or caused cancer in thousands more. The Fukushima Daiichi nuclear disaster (2011) in Japan (Figure \(3\)) was caused by a 9.0 magnitude earthquake that shut down power supply and a tsunami that flooded the plant’s emergency power supply. This resulted in the release of radioactivity although it did not directly result in any deaths at the time of the disaster. Another nuclear accident was the Three Mile Island accident (1979) in Pennsylvania, USA. This accident resulted in a near disastrous core meltdown that was due to a combination of human error and mechanical failure but did not result in any deaths and no cancers or otherwise have been found in follow up studies of this accident. While there are potentially devastating consequences to a nuclear meltdown, the likelihood of one occurring is extremely small. After every meltdown, including the 2011 Fukushima Daiichi disaster, new international regulations were put in place to prevent such an event from occurring again.
The processes for mining and refining uranium ore and making reactor fuel require large amounts of energy. Nuclear power plants have large amounts of metal and concrete, which also require large amounts of energy to manufacture. If fossil fuels are used for mining and refining uranium ore or in constructing the nuclear plant, then the emissions from burning those fuels could be associated with the electricity that nuclear power plants generate.
Nuclear Reactor Design and Operation
Video \(1\) The design and safe operation of a nuclear reactor.
Summary
• The importance of nuclear power in generating electricity is described.
• The operation of a nuclear power plant is described.
• The drawbacks of nuclear energy is described. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/11%3A_Nuclear_Chemistry/11.09%3A_Uses_and_Consequences_of_Nuclear_Energy.txt |
Thumbnail: Nutrient pollution caused by Surface runoff of soil and fertilizer during a rain storm. (Public Domain; Lynn Betts via ).
12: Chemistry of Earth
Learning Objective
• Describe the chemical composition and structure of Earth.
The layers found inside Earth are divided by composition into core, mantle, and crust or by mechanical properties into lithosphere and asthenosphere. Scientists use information from earthquakes and computer modeling to learn about Earth’s interior.
THE EARTH’S LAYERS
The layers scientists recognize are pictured in Figure \(1\).
Core, mantle, and crust are divisions based on chemical composition:
Crust: The Earth's surface is the crust. Generally speaking, the crust is predominately silicon oxide and aluminum oxide. Continental crust is thicker and less dense than oceanic crust. Earth’s crust varies in thickness from less than 5 km (under mid-ocean spreading ridges) to more than 70 km (beneath the highest mountain range).
Mantle: The next layer down chemically is the mantle. The mantle has an ultramafic composition – it contains more iron, magnesium, less aluminum and somewhat less silicon than the crust. The mantle is roughly 2,900 km thick. In terms of volume, the mantle is the largest of earth’s three chemical layers.
Core:The final layer is the core, which is mostly iron and nickel. The core is about 3,500 km thick.
Table \(1\) summarizes the chemical layers of the earth.
Table \(1\) Chemical Layers of Earth.
Crust Mantle Core
composition: high Si, Al, & O composition: moderate Si, high Mg & Fe composition: Fe & Ni
thickness: 5 to 70 km thickness: 2,900 km thickness: 3,500 km
Table \(2\) provides the elemental composition of the Earth's crust.
Table \(2\) The Elements of Earth's Crust. Source: Wikipedia
Most Abundant Elements of Earth's Crust Approximate % by weight
O 46.6
Si 27.7
Al 8.1
Fe 5.0
Ca 3.6
Na 2.8
K 2.6
Mg 1.5
Lithosphere and asthenosphere are divisions based on mechanical properties:
1. The lithosphere is composed of both the crust and the portion of the upper mantle that behaves as a brittle, rigid solid.
2. The asthenosphere is partially molten upper mantle material that behaves plastically and can flow.
Compositional and Mechanical Layers of the Earth
https://www.khanacademy.org/science/cosmology-and-astronomy/earth-history-topic/plate-techtonics/v/compositional-and-mechanical-layers-of-the-earth
Video \(1\) A comparison of the compositional and mechanical layers of the earth.
Crust and Lithosphere
Earth’s outer surface is its crust; a cold, thin, brittle outer shell made of rock. The crust is very thin, relative to the radius of the planet. There are two very different types of crust, each with its own distinctive physical and chemical properties, which are summarized in Table \(3\).
Table \(3\) The Physical and Chemical Properties of Oceanic and Continental Crust.
Crust Thickness Density Composition Rock types
Oceanic 5-12 km (3-8 mi) 3.0 g/cm3 Mafic Basalt and gabbro
Continental Avg. 35 km (22 mi) 2.7 g/cm3 Felsic All types
Oceanic crust is composed of mafic magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbro (Figure \(2\)).
Sediments, primarily muds and the shells of tiny sea creatures, coat the sea floor. Sediment is thickest near the shore where it comes off the continents in rivers and on wind currents.
Continental crust is made up of many different types of igneous, metamorphic, and sedimentary rocks. The average composition is granite, which is much less dense than the mafic rocks of the oceanic crust (Figure \(3\)). Because it is thick and has relatively low density, continental crust rises higher on the mantle than oceanic crust, which sinks into the mantle to form basins. When filled with water, these basins form the planet’s oceans.
The lithosphere is the outermost mechanical layer, which behaves as a brittle, rigid solid. The lithosphere is about 100 kilometers thick. Look at Figure \(1\). Can you find where the crust and the lithosphere are located? How are they different from each other?
The definition of the lithosphere is based on how earth materials behave, so it includes the crust and the uppermost mantle, which are both brittle. Since it is rigid and brittle, when stresses act on the lithosphere, it breaks. This is what we experience as an earthquake.
Mantle
The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. Scientists know that the mantle is made of rock based on evidence from seismic waves, heat flow, and meteorites.
The properties fit the ultramafic rock peridotite, which is made of the iron- and magnesium-rich silicate minerals (Figure \(4\)). Peridotite is rarely found at Earth’s surface.
Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties.
Core
At the planet’s center lies a dense metallic core. Scientists know that the core is metal because:
1. The density of Earth’s surface layers is much less than the overall density of the planet, as calculated from the planet’s rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85% iron metal with nickel metal making up much of the remaining 15%.
2. Metallic meteorites are thought to be representative of the core. The 85% iron/15% nickel calculation above is also seen in metallic meteorites (Figure \(5\)).
Figure \(5\) An iron meteorite is the closest thing to the Earth’s core that we can hold in our hands.
If Earth’s core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not.
Summary
• The core, mantle, and crust are divisions of Earth based on chemical composition.
• The lithosphere and asthenosphere are divisions of Earth based on mechanical properties.
• The three most abundant elements of Earth's crust are oxygen (46.6% by weight), silicon (27.7%), and aluminum (8.1%).
Contributors
Libretext: Fundamentals of Geology (Schulte)
Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/12%3A_Chemistry_of_Earth/12.01%3A_Spaceship_Earth-_Structure_and_Composition.txt |
Learning Objective
• Describe different types of silicate based minerals.
The silicates are the largest, the most interesting and the most complicated class of minerals than any other minerals. Approximately 30% of all minerals are silicates and some geologists estimate that 90% of the Earth's crust is made up of silicates, SiO44- based material. Thus, oxygen and silicon are the two most abundant elements in the earth's crust.
The building block of all of these minerals is the silica tetrahedron, a combination of four oxygen atoms and one silicon atom. As we’ve seen, it’s called a tetrahedron because planes drawn through the oxygen atoms form a shape with 4 surfaces (Figure \(1\)). Since the silicon ion has a charge of 4 and each of the four oxygen ions has a charge of −2, the silica tetrahedron has a net charge of −4.
In silicate minerals, these tetrahedra are arranged and linked together in a variety of ways, from single units to complex frameworks (Table \(1\)).
Table \(1\) Silicate Mineral Configurations (The triangles represent silica tetrahedra).
Tetrahedron Configuration Picture Tetrahedron Configuration Name Example Minerals
Isolated (nesosilicates) Olivine, garnet, zircon, kyanite
Pairs (sorosilicates) Epidote, zoisite
Rings (cyclosilicates) Tourmaline
Single chains (inosilicates) Pyroxenes, wollastonite
Double chains (inosilicates) Amphiboles
Sheets (phyllosilicates) Micas, clay minerals, serpentine, chlorite
3-dimensional structure Framework (tectosilicates) Feldspars, quartz, zeolite
In the extreme case, the tetrahedra are arranged in a regular, orderly fashion forming a three-dimensional network. Quartz is such a structure (Figure \(2\)), and its formula is SiO2. If silica in the molten state is cooled very slowly it crystallizes at the freezing point. But if molten silica is cooled more rapidly, the resulting solid is a disorderly arrangement which is called glass, often also called quartz.
Note:
Silicates are extremely important materials, both natural (such as granite, gravel, and garnet) and artificial (such as Portland cement, ceramics, glass, and waterglass), for all sorts of technological and artistic activities. Source: Wikipedia
Glasses
Glass is a non-crystalline, often transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, optics, and optoelectronics. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide (CaO), also called lime, and several minor additives.
Table \(2\) list the more common types of silicate glasses and their ingredients, properties, and applications. Figure \(3\) are examples of silicate glasses.
Table \(2\) Common Types of Silicate Glasses.
Type and Properties Key Ingredients Applications
Fused quartz has very low thermal expansion and excellent resistance to thermal shock, being able to survive immersion in water while red hot, resists high temperatures (1000–1500 °C) and chemical weathering, and is very hard. Chemically pure silica (silicon dioxide) Used for high-temperature applications such as furnace tubes, lighting tubes, melting crucibles, etc.
Soda-lime-silica glass is transparent, easily formed, and most suitable for window glass and tableware.[68] However, it has a high thermal expansion and poor resistance to heat. (Na2O) + lime (CaO) + magnesia (MgO) + alumina (Al2O3) account for over 75% of manufactured glass, containing about 70 to 74% silica by weight Typically used for windows, bottles, light bulbs, and jars.[
Sodium borosilicate glasses have fairly low coefficients of thermal expansion (7740 Pyrex CTE is 3.25×10−6/°C[69] as compared to about 9×10−6/°C for a typical soda-lime glass[70]). They are, therefore, less subject to stress caused by thermal expansion and thus less vulnerable to cracking from thermal shock. 5–13% boron trioxide (B2O3) Commonly used for e.g. labware (e.g. Pyrex, Duran), household cookware, and sealed beam car head lamps.[
Lead-oxide glass, crystal glass, lead glass has high density which results in a high electron density, and hence high refractive index, making the look of glassware more brilliant and causing noticeably more specular reflection and increased optical dispersion.[61][72] Lead glass has a high elasticity, making the glassware more workable and giving rise to a clear "ring" sound when struck. silica + lead oxide (PbO) + potassium oxide (K2O) + soda (Na2O) + zinc oxide (ZnO) + alumina Used for tableware, art objects, optical glass.
Aluminosilicate glass tends to be more difficult to melt and shape compared to borosilicate compositions, but has excellent thermal resistance and durability. alumina and silica Extensively used for fiberglass, used for making glass-reinforced plastics (boats, fishing rods, etc.), top-of-stove cookware, and halogen bulb glass.
Germanium-oxide glass is an extremely clear glass. Light loses only 5% of its intensity through 1 km of glass fiber. alumina + germanium dioxide (GeO2). Used for fiber-optic waveguides in communication networks.
Colored glass is clear glass with oxides added . Different oxide additives produce the different colors in glass: turquoise (copper(II) oxide),[121] purple (manganese dioxide), red (cadmium sulfide), blue (cobalt oxide) and green (Iron(II) oxide and chromium(III) oxide). Used for tableware and decorative glassware.
a. b. c.
Figure \(3\) Examples of silicate glasses: a. Pyrex measuring cup, b. red glass bottle with yellow glass overlay, and c. four-color Roman glass bowl, manufactured circa 1st century B.C..
Asbestos
Asbestos is the name applied to six naturally occurring minerals that are mined from the earth. The different types of asbestos are:
• Amosite
• Chrysotile
• Tremolite
• ActinoliteUnlink
• Anthophyllite
• Crocidolite
Of these six, three are used more commonly. Chrysotile (white) is the most common, but it is not unusual to encounter. Amosite (brown / off-white), or Crocidolite (blue) as well. Asbestos are noncombustable fibrous material, and they have been used for terminal insulation material, brake linings, construction material, and filters. When mixed with cement, it reinforce the mechanical strength of concrete. It decomposes due to loss of water, and forms forsterite and silica at high temperature.
Ceramics
A ceramic is a solid material comprising an inorganic compound of metal, non-metal or ionic and covalent bonds. Common examples are earthenware, porcelain, and brick.
Varying crystallinity and electron composition in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators (extensively researched in ceramic engineering). With such a large range of possible options for the composition/structure of a ceramic (e.g. nearly all of the elements, nearly all types of bonding, and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (e.g. hardness, toughness, electrical conductivity, etc.) are difficult to specify for the group as a whole. General properties such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance and low ductility are the norm,[1] with known exceptions to each of these rules (e.g. piezoelectric ceramics, glass transition temperature, superconductive ceramics, etc.).
Cement and Concrete
A cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Cement is the most widely used material in existence and is only behind water as the planet's most-consumed resource.[1]
Cements used in construction are usually inorganic, often lime or calcium silicate based.
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens over time—most frequently in the past a lime-based cement binder, such as lime putty, but sometimes with other hydraulic cements, such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (for its visual resemblance to Portland stone).[2][3] Many other non-cementitious types of concrete exist with different methods of binding aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces, and polymer concretes that use polymers as a binder.
Summary
• The silicates are the largest, the most interesting and the most complicated class of minerals than any other minerals. Approximately 90% of the Earth's crust is made up of silicates, SiO44- based material.
• Silicates are extremely important materials, both natural (such as granite, gravel, and garnet) and artificial (such as Portland cement, ceramics, glass, and waterglass), for all sorts of technological and artistic activities
Contributors and Attributions
• Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)
• Libretext: Physical Geology (Earle)
• Libretext: Inorganic Chemistry
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/12%3A_Chemistry_of_Earth/12.02%3A_Silicates_and_the_Shapes_of_Things.txt |
Learning Objectives
• Identify important metals and describe their extraction from their main ores.
• List different metals, their uses, and their alloys.
• Describe the environmental impact of metal production.
Most metals are found as types of rock in the Earth's crust. These ores contain sufficient minerals with important elements including metals that can be economically extracted from the rock. Metal ores are generally oxides, sulfides, silicates (Table $1$) or "native" metals (such as native copper) that are not commonly concentrated in the Earth's crust, or "noble" metals (not usually forming compounds) such as gold (Figure $1$). The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals.
Alloys
An alloy is a mixture composed of two or more elements, at least one of which is a metal. You are probably familiar with some alloys of copper (such as brass and bronze) and iron (steel) . Alloys can be one of two general types. In one type, called a substitutional alloy, the various atoms simply replace each other in the crystal structure. In another type, called an interstitial alloy, the smaller atoms such as carbon fit in between the larger atoms in the crystal packing arrangement.
Steels are a very important class of alloys. The many types of steels are primarily composed of iron, with various amounts of the elements carbon, chromium, manganese, nickel, molybdenum, and boron. Steels are widely used in building construction because of their strength, hardness, and resistance to corrosion. Most large modern structures like skyscrapers and stadiums are supported by a steel skeleton (see figure below).
Copper,Brass, and Bronze
Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity and as a building material.
Copper is one of the few metals that can occur in nature in a directly usable metallic form (native metals). This led to very early human use in several regions, from c. 8000 BC. Thousands of years later, it was the first metal to be smelted from sulfide ores, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3500 BC.
Most commercial ores are sulfides, especially chalcopyrite (CuFeS2), bornite (Cu5FeS4) and, to a lesser extent, covellite (CuS) and chalcocite (Cu2S).
Cu2S, is converted into oxides:
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
The cuprous oxide is then converted to copper upon heating:
2 Cu2O → 4 Cu + O2
Copper is a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement. Bronze, an alloy of copper and tin has been in use since ancient times. The Bronze Age saw the increased use of metals rather than stone for weapons, tools, and decorative objects. Brass, an alloy of copper and zinc, is widely used in musical instruments like the trumpet and trombone. Alloys are commonly used in manufactured items because the properties of these metal mixtures are often superior to a pure metal. Bronze is harder than copper and more easily cast. Brass is very malleable and its acoustic properties make it useful for musical instruments (Figure $1$).
Iron and Steel
The early application of iron to the manufacture of tools and weapons was possible because of the wide distribution of iron ores and the ease with which iron compounds in the ores could be reduced by carbon. Iron ore is reduced with coke in a blast furnace (Figure $1$). The blast furnace is loaded with iron ores, usually hematite Fe2O3 or magnetite Fe3O4, together with coke (coal that has been separately baked to remove volatile components). Air pre-heated to 900 °C is blown through the mixture, in sufficient amount to turn the carbon into carbon monoxide:
2 C + O2 → 2 CO
This reaction raises the temperature to about 2000 °C The carbon monoxide reduces the iron ore to metallic iron[112]
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Some iron in the high-temperature lower region of the furnace reacts directly with the coke:[112]
2 Fe2O3 + 3 C → 4 Fe + 3 CO2
Much of the iron produced is refined and converted into steel. Steel is made from iron by removing impurities and adding substances such as manganese, chromium, nickel, tungsten, molybdenum, and vanadium to produce alloys with properties that make the material suitable for specific uses. Most steels also contain small but definite percentages of carbon (0.04%–2.5%). However, a large part of the carbon contained in iron must be removed in the manufacture of steel; otherwise, the excess carbon would make the iron brittle. However, there is not just one substance called steel - they are a family of alloys of iron with carbon or various metals.
Impurities in the iron from the Blast Furnace include carbon, sulfur, phosphorus and silicon, which have to be removed.
• Removal of sulfur: Sulfur has to be removed first in a separate process. Magnesium powder is blown through the molten iron and the sulfur reacts with it to form magnesium sulfide. This forms a slag on top of the iron and can be removed. $Mg + S \rightarrow MgS \label{127}$
• Removal of carbon: The still impure molten iron is mixed with scrap iron (from recycling) and oxygen is blown on to the mixture. The oxygen reacts with the remaining impurities to form various oxides. The carbon forms carbon monoxide. Since this is a gas it removes itself from the iron! This carbon monoxide can be cleaned and used as a fuel gas.
• Removal of other elements: Elements like phosphorus and silicon react with the oxygen to form acidic oxides. These are removed using quicklime (calcium oxide) which is added to the furnace during the oxygen blow. They react to form compounds such as calcium silicate or calcium phosphate which form a slag on top of the iron.
Cast iron has already been mentioned above. This section deals with the types of iron and steel which are produced as a result of the steel-making process.
• Wrought iron: If all the carbon is removed from the iron to give high purity iron, it is known as wrought iron. Wrought iron is quite soft and easily worked and has little structural strength. It was once used to make decorative gates and railings, but these days mild steel is normally used instead.
• Mild steel: Mild steel is iron containing up to about 0.25% of carbon. The presence of the carbon makes the steel stronger and harder than pure iron. The higher the percentage of carbon, the harder the steel becomes. Mild steel is used for lots of things - nails, wire, car bodies, ship building, girders and bridges amongst others.
• High carbon steel: High carbon steel contains up to about 1.5% of carbon. The presence of the extra carbon makes it very hard, but it also makes it more brittle. High carbon steel is used for cutting tools and masonry nails (nails designed to be driven into concrete blocks or brickwork without bending). High carbon steel tends to fracture rather than bend if mistreated.
• Special steels: These are iron alloyed with other metals (Table $1$).
Table $1$ Special Steels
Iron mixed with Special properties Uses include
stainless steel chromium and nickel resists corrosion cutlery, cooking utensils, kitchen sinks, industrial equipment for food and drink processing
titanium steel titanium withstands high temperatures gas turbines, spacecraft
manganese steel manganese very hard rock-breaking machinery, some railway track (e.g. points), military helmets
Steelmaking Animation
Video $1$ The process of steelmaking.
Aluminum
Aluminum is too high in the electrochemical series (reactivity series) to extract it from its ore using carbon reduction. The temperatures needed are too high to be economic. Instead, it is extracted by electrolysis. The ore is first converted into pure aluminum oxide by the Bayer Process, and this is then electrolyzed in solution in molten cryolite - another aluminum compound. The aluminum oxide has too high a melting point to electrolyse on its own. The usual aluminum ore is bauxite. Bauxite is essentially an impure aluminum oxide. The major impurities include iron oxides, silicon dioxide and titanium dioxide.
Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The concentration, temperature and pressure used depend on the source of the bauxite and exactly what form of aluminum oxide it contains. Temperatures are typically from 140°C to 240°C; pressures can be up to about 35 atmospheres. With hot concentrated sodium hydroxide solution, aluminum oxide reacts to give a solution of sodium tetrahydroxoaluminate.
$Al_2O_3 + 2NaOH + 3H_2O \longrightarrow 2NaAl(OH)_4 \nonumber$
The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminum hydroxide. This provides something for the new aluminum hydroxide to precipitate around.
$NaAl(OH)_4 \longrightarrow Al(OH)_3 + NaOH \nonumber$
Aluminum oxide (sometimes known as alumina) is made by heating the aluminum hydroxide to a temperature of about 1100 - 1200°C.
$2Al(OH)_3 \longrightarrow Al_2O_3 + 3H_2O \nonumber$
The aluminum oxide is electrolyzed in solution in molten cryolite, Na3AlF6. Cryolite is another aluminum ore, but is rare and expensive, and most is now made chemically.
Uses of Aluminum
Aluminum is usually alloyed with other elements such as silicon, copper or magnesium. Pure aluminum isn't very strong, and alloying it adds to it strength. Aluminum is especially useful because it
• has a low density;
• is strong when alloyed;
• is a good conductor of electricity;
• has a good appearance;
• resists corrosion because of the strong thin layer of aluminum oxide on its surface. This layer can be strengthened further by anodizing the aluminum.
Anodizing essentially involves etching the aluminum with sodium hydroxide solution to remove the existing oxide layer, and then making the aluminum article the anode in an electrolysis of dilute sulfuric acid. The oxygen given of at the anode reacts with the aluminum surface, to build up a film of oxide up to about 0.02 mm thick. As well as increasing the corrosion resistance of the aluminum, this film is porous at this stage and will also take up dyes. (It is further treated to make it completely non-porous afterwards.) That means that you can make aluminum articles with the colour built into the surface.
Some uses include:
Aluminum is used for because
aircraft light, strong, resists corrosion
other transport such as ships' superstructures, container vehicle bodies, tube trains (metro trains) light, strong, resists corrosion
overhead power cables (with a steel core to strengthen them) light, resists corrosion, good conductor of electricity
saucepans light, resists corrosion, good appearance, good conductor of heat
Recycling
Aluminum is an infinitely recyclable material, and it takes up to 95 percent less energy to recycle it than to produce primary aluminum, which also limits emissions, including greenhouse gases. Today, about 75 percent of all aluminum produced in history, nearly a billion tons, is still in use.[6]
The recycling of aluminum generally produces significant cost savings over the production of new aluminum, even when the cost of collection, separation and recycling are taken into account.[7] Over the long term, even larger national savings are made when the reduction in the capital costs associated with landfills, mines, and international shipping of raw aluminum are considered.
Environmental Impact of Steel and Aluminum Production
The impact of steel and aluminum production on the environment can be traced back from the mining of the ores to the production of the final commercial products (i.e. steel and aluminum). The main sources of emissions during the different phases of manufacture include the products of combustion such as nitrous oxide, carbon dioxide, carbon monoxide, and sulfur dioxide and fugitive dust from the operation of equipment. The effect of the different emissions on air quality (i.e. smog formation, greenhouse effect, acid rain etc.) will be discussed in more detail in Chapter 13.
Sulfuric acid is created when water and oxygen interact with sulfur bearing minerals and chemicals in rocks. Many metals become mobile as water becomes more acidic and at high concentrations these metals become toxic to most life forms. There is also production of enormous amounts of wastewater contaminants, hazardous wastes, and solid wastes.
Summary
• Metal ores contain sufficient minerals with important elements including metals that can be economically extracted from the rock. The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals.
• Alloys are mixtures of materials, at least one of which is a metal.
• Bronze alloys were widely used in weapons.
• Brass alloys have long been employed in musical instruments.
• Steel alloys are strong and durable.
• Aluminum alloys are widely used due to its durability, resistance to corrosion, and good conductivity.
Contributors and Attributions
• TextMap: General Chemistry: General Chemistry (Petrucci et al.)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/12%3A_Chemistry_of_Earth/12.03%3A_Metals_and_Ores.txt |
Learning Objectives
• Describe the composition and classification of solid waste.
• List the 3R's of Garbage and its benefits.
Land Pollution: Solid Wastes
Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste, as in a garbage disposal; the two are sometimes collected separately. In the European Union, the semantic definition is 'mixed municipal waste,' given waste code 20 03 01 in the European Waste Catalog. Although the waste may originate from a number of sources that has nothing to do with a municipality, the traditional role of municipalities in collecting and managing these kinds of waste have produced the particular etymology 'municipal.'
The composition of municipal solid waste varies greatly from municipality to municipality,[1] and it changes significantly with time. In municipalities which have a well developed waste recycling system, the waste stream mainly consists of intractable wastes such as plastic film and non-recyclable packaging materials. At the start of the 20th century, the majority of domestic waste (53%) in the UK consisted of coal ash from open fires.[2] In developed areas without significant recycling activity it predominantly includes food wastes, market wastes, yard wastes, plastic containers and product packaging materials, and other miscellaneous solid wastes from residential, commercial, institutional, and industrial sources.[3] Most definitions of municipal solid waste do not include industrial wastes, agricultural wastes, medical waste, radioactive waste or sewage sludge.[4] Waste collection is performed by the municipality within a given area. The term residual waste relates to waste left from household sources containing materials that have not been separated out or sent for processing.[5] Waste can be classified in several ways but the following list represents a typical classification:
• Biodegradable waste: food and kitchen waste, green waste, paper (most can be recycled, although some difficult to compost plant material may be excluded[6])
• Recyclable materials: paper, cardboard, glass, bottles, jars, tin cans, aluminum cans, aluminium foil, metals, certain plastics, textiles, clothing, tires, batteries, etc.
• Inert waste: construction and demolition waste, dirt, rocks, debris
• Electrical and electronic waste (WEEE) - electrical appliances, light bulbs, washing machines, TVs, computers, screens, mobile phones, alarm clocks, watches, etc.
• Composite wastes: waste clothing, Tetra Pack food and drink cartons, waste plastics such as toys and plastic garden furniture
• Hazardous waste including most paints, chemicals, tires, batteries, light bulbs, electrical appliances, fluorescent lamps, aerosol spray cans, and fertilizers
• Toxic waste including pesticides, herbicides, and fungicides
• Biomedical waste, expired pharmaceutical drugs, etc.
For example, typical municipal solid waste in China is composed of 55.9% food residue, 8.5% paper, 11.2% plastics, 3.2% textiles, 2.9% wood waste, 0.8% rubber, and 18.4% non-combustibles. The breakdown of municipal waste by material is shown below (Figure \(1\)).
The Three R's of Garbage: Reduce, Reuse and Recyle
Reducing and Reusing Basics
The most effective way to reduce waste is to not create it in the first place. Making a new product requires a lot of materials and energy - raw materials must be extracted from the earth, and the product must be fabricated then transported to wherever it will be sold. As a result, reduction and reuse are the most effective ways you can save natural resources, protect the environment and save money.
Benefits of Reducing and Reusing
• Prevents pollution caused by reducing the need to harvest new raw materials
• Saves energy
• Reduces greenhouse gas emissions that contribute to global climate change
• Helps sustain the environment for future generations
• Saves money
• Reduces the amount of waste that will need to be recycled or sent to landfills and incinerators
• Allows products to be used to their fullest extent
Ideas on How to Reduce and Reuse
• Buy used. You can find everything from clothes to building materials at specialized reuse centers and consignment shops. Often, used items are less expensive and just as good as new.
• Look for products that use less packaging. When manufacturers make their products with less packaging, they use less raw material. This reduces waste and costs. These extra savings can be passed along to the consumer. Buying in bulk, for example, can reduce packaging and save money.
• Buy reusable over disposable items. Look for items that can be reused; the little things can add up. For example, you can bring your own silverware and cup to work, rather than using disposable items.
• Maintain and repair products, like clothing, tires and appliances, so that they won't have to be thrown out and replaced as frequently.
• Borrow, rent or share items that are used infrequently, like party decorations, tools or furniture.
Recycling Basics
Recycling is the process of collecting and processing materials that would otherwise be thrown away as trash and turning them into new products. Recycling can benefit your community and the environment.
Benefits of Recycling
• Reduces the amount of waste sent to landfills and incinerators
• Conserves natural resources such as timber, water and minerals
• Increases economic security by tapping a domestic source of materials
• Prevents pollution by reducing the need to collect new raw materials
• Saves energy
• Supports American manufacturing and conserves valuable resources
• Helps create jobs in the recycling and manufacturing industries in the United States
Recycling Creates Jobs
EPA released significant findings on the economic benefits of the recycling industry with an update to the national Recycling Economic Information (REI) Study in 2016. This study analyzes the numbers of jobs, wages and tax revenues attributed to recycling. The study found that in a single year, recycling and reuse activities in the United States accounted for:
• 757,000 jobs
• \$36.6 billion in wages; and
• \$6.7 billion in tax revenues.
This equates to 1.57 jobs, \$76,000 in wages, and \$14,101 in tax revenues for every 1,000 tons of materials recycled.
Summary
• Municipal solid waste (MSW), (i.e. trash or garbage in the United States and rubbish in Britain), is a type of waste consisting of everyday items that are discarded by the public.
• Most definitions of municipal solid waste do not include industrial wastes, agricultural wastes, medical waste, radioactive waste or sewage sludge.
• Typical classification of waste includes biodegradable wastes, recyclable materials, inert waste, electrical and electronic waste, composite wastes, hazardous wastes, toxic waste, and biomedical wastes.
• Reducing, reusing, and recycling solid wastes reduces the amount of waste in landfills and incinerators and promotes safer and cleaner environment.
Contributors and Attributions
US EPA (Environmental Protection Agency)
Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/12%3A_Chemistry_of_Earth/12.04%3A_Earth%27s_Dwindling_Resources.txt |
Learning Objectives
• Describe the different layers of the atmosphere.
• Know the composition of air.
The Earth's atmosphere is composed of several layers (Figure \(1\)). The lowest layer, the troposphere, extends from the Earth's surface up to about 6 miles or 10 kilometers (km) in altitude. Virtually all human activities occur in the troposphere. Mt. Everest, the tallest mountain on the planet, is only about 5.6 miles (9 km) high. The next layer, the stratosphere, continues from 6 miles (10 km) to about 31 miles (50 km). Most commercial airplanes fly in the lower part of the stratosphere.
Most atmospheric ozone is concentrated in a layer in the stratosphere, about 9 to 18 miles (15 to 30 km) above the Earth's surface (see the figure below). Ozone is a molecule that contains three oxygen atoms. At any given time, ozone molecules are constantly formed and destroyed in the stratosphere. The total amount has remained relatively stable during the decades that it has been measured.
The ozone layer in the stratosphere absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface. Most importantly, it absorbs the portion of UV light called UVB. UVB has been linked to many harmful effects, including skin cancers, cataracts, xand harm to some crops and marine life.
The mesosphere starts just above the stratosphere and extends to 85 kilometers (53 miles) high. Meteors burn up in this layer
The thermosphere starts just above the mesosphere and extends to 600 kilometers (372 miles) high. Aurora and satellites occur in this layer. The ionosphere is an abundant layer of electrons and ionized atoms and molecules that stretches from about 48 kilometers (30 miles) above the surface to the edge of space at about 965 km (600 mi), overlapping into the mesosphere and thermosphere. This dynamic region grows and shrinks based on solar conditions and divides further into the sub-regions: D, E and F; based on what wavelength of solar vvradiation is absorbed. The ionosphere is a critical link in the chain of Sun-Earth interactions. This region is what makes radio communications possible. The exosphere is is the upper limit of the atmosphere. It extends from the top of the thermosphere up to 10,000 km (6,200 mi).
Figure \(1\) The Earth's atmosphere Credit: NASA/Goddard
Composition of the Atmosphere
Except for water vapor, whose atmospheric abundance varies from practically zero up to 4%, the fractions of the major atmospheric components N2, O2, and Ar are remarkably uniform below about 100 km (Table \(1\)). At greater heights, diffusion becomes the principal transport process, and the lighter gases become relatively more abundant. In addition, photochemical processes result in the formation of new species whose high reactivities would preclude their existence in significant concentrations at the higher pressures found at lower elevations.
The atmospheric gases fall into three abundance categories: major, minor, and trace. Nitrogen, the most abundant component, has accumulated over time as a result of its geochemical inertness; a very small fraction of it passes into the other phases as a result of biological activity and natural fixation by lightning. It is believed that denitrifying bacteria in marine sediments may provide the major route for the return of N2 to the atmosphere. Oxygen is almost entirely of biological origin, and cycles through the hydrosphere, the biosphere, and sedimentary rocks. Argon consists mainly of Ar40 which is a decay product of K40 in the mantle and crust.
Table \(1\) The Major Components of Clean Dry Air in the Lower Atmosphere
nitrogen N2 78.08 %
oxygen O2 20.95 %
argon Ar 0.93 %
The most abundant of the minor gases aside from water vapor is carbon dioxide (Table \(2\)). Next in abundance are neon and helium. Helium is a decay product of radioactive elements in the earth, but neon and the other inert gases are primordial, and have probably been present in their present relative abundances since the earth’s formation. Two of the minor gases, ozone and carbon monoxide, have abundances that vary with time and location. A variable abundance implies an imbalance between the rates of formation and removal. In the case of carbon monoxide, whose major source is anthropogenic (a small amount is produced by biological action), the variance is probably due largely to localized differences in fuel consumption, particularly in internal combustion engines. The nature of the carbon monoxide sink (removal mechanism) is not entirely clear; it may be partly microbial.
Table \(2\) The Minor Components of Air in the Lower Atmosphere.
water H2O 0-4 %
carbon dioxide CO2 325 ppm
neon Ne 18 ppm
helium He 5 ppm
methane CH4 2 ppm
krypton Kr 1 ppm
hydrogen H2 0.5 ppm
nitrous oxide N2O 0.3 ppm
carbon monoxide CO 0.05-0.2 ppm
ozone O3 0.02 - 10 ppm
xenon Xe 0.08 ppm
Summary
• The layers of the atmosphere include the trophosphere, stratosphere, mesosphere, thermosphere, and exosphere.
• The major components of dry clean air are N2, O2, and Ar.
• The most abundant of the minor gases are water vapor and CO2 | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.02%3A_Earth%27s_Atmosphere-_Divisions_and_Composition.txt |
Learning Objectives
• Describe the nitrogen cycle.
• Describe the oxygen cycle.
• Describe the conditions for temperature inversion.
The mix of gases in the atmosphere forms a complex system organized into layers that together support life on Earth. Although there are numerous gases, as shown in Table 13.1.1, the top four gases make up 99.998 % of the volume of clean dry air (unpolluted air that does not contain water vapor). Of this dry composition of the atmosphere nitrogen, by far, is the most common (78%). Nitrogen dilutes oxygen and prevents rapid or instantaneous burning at the Earth's surface, as oxygen gas is a necessary reactant of the combustion process. Nitrogen is also needed and used by living things to make proteins, though as nitrogen gas, N2, it is unavailable to most living things. Oxygen is used by all living things to make molecules that are essential for life. It is also essential for aerobic respiration as well as combustion or burning.
Nitrogen Cycle
All life requires nitrogen-compounds, e.g., proteins and nucleic acids. Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen. But most organisms cannot use nitrogen in this form. Figure $1$ illustrates the entire nitrogen cycle. Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as: nitrate ions (NO3), ammonium ions (NH4+) and urea (NH2)2CO. Animals secure their nitrogen (and all other) compounds from plants (or animals that have fed on plants).
Four processes participate in the cycling of nitrogen through the biosphere: (1) nitrogen fixation, (2) decay, (3) nitrification, and (4) denitrification. Microorganisms play major roles in all four of these.
Nitrogen Fixation
The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy. Three processes are responsible for most of the nitrogen fixation in the biosphere:
• atmospheric fixation by lightning
• biological fixation by certain microbes alone or in a symbiotic relationship with some plants and animals
• industrial fixation
Atmospheric Fixation
The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to the earth. Atmospheric nitrogen fixation probably contributes some 5– 8% of the total nitrogen fixed.
Industrial Fixation
Under great pressure, at a temperature of 600°C, and with the use of a catalyst, atmospheric nitrogen and hydrogen (usually derived from natural gas or petroleum) can be combined to form ammonia (NH3). Ammonia can be used directly as fertilizer, but most of its is further processed to urea and ammonium nitrate (NH4NO3).
Biological Fixation
The ability to fix nitrogen in the soil (Figure $2$ ) only in certain bacteria and archaea.
• Some live in a symbiotic relationship with plants of the legume family (e.g., soybeans, alfalfa).
• Some establish symbiotic relationships with plants other than legumes (e.g., alders).
• Some establish symbiotic relationships with animals, e.g., termites and "shipworms" (wood-eating bivalves).
• Some nitrogen-fixing bacteria live free in the soil.
• Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies.
Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP. Although the first stable product of the process is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.
Decay
The proteins made by plants enter and pass through food webs just as carbohydrates do. At each trophic level, their metabolism produces organic nitrogen compounds that return to the environment, chiefly in excretions. The final beneficiaries of these materials are microorganisms of decay. They break down the molecules in excretions and dead organisms into ammonia.
Nitrification
Ammonia can be taken up directly by plants — usually through their roots. However, most of the ammonia produced by decay is converted into nitrates. Until recently this was thought always to be accomplished in two steps:
1. Bacteria of the genus Nitrosomonas oxidize $\ce{NH3}$ to nitrites ($\ce{NO2^{−}}$).
2. Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates ($\ce{NO3^{−}}$).
These two groups of autotrophic bacteria are called nitrifying bacteria. Through their activities (which supply them with all their energy needs), nitrogen is made available to the roots of plants. However, in 2015, two groups reported finding that bacteria in the genus Nitrospira were able to carry out both steps: ammonia to nitrite and nitrite to nitrate. This ability is called "comammox" (for complete ammonia oxidation).
In addition, both soil and the ocean contain archaeal microbes, assigned to the Crenarchaeota, that convert ammonia to nitrites. They are more abundant than the nitrifying bacteria and may turn out to play an important role in the nitrogen cycle.
Many legumes, in addition to fixing atmospheric nitrogen, also perform nitrification - converting some of their organic nitrogen to nitrites and nitrates. These reach the soil when they shed their leaves.
Denitrification
The three processes above remove nitrogen from the atmosphere and pass it through ecosystems. Denitrification reduces nitrates and nitrites to nitrogen gas, thus replenishing the atmosphere. In the process several intermediates are formed:
• nitric oxide (NO)
• nitrous oxide (N2O)(a greenhouse gas 300 times as potent as CO2)
• nitrous acid (HONO)
Once again, bacteria are the agents. They live deep in soil and in aquatic sediments where conditions are anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in their respiration.
Anammox (anaerobic ammonia oxidation)
Under anaerobic conditions in marine and freshwater sediments, other species of bacteria are able to oxidize ammonia (with $\ce{NO2^{−}}$) forming nitrogen gas.
$\ce{NH4^{+} + NO2^{−} → N2 + 2H2O} \nonumber$
The anammox reaction may account for as much as 50% of the denitrification occurring in the oceans. All of these processes participate in closing the nitrogen cycle.
Are the denitrifiers keeping up?
Agriculture may now be responsible for one-half of the nitrogen fixation on earth through the use of fertilizers produced by industrial fixation and the the growing of legumes like soybeans and alfalfa. This is a remarkable influence on a natural cycle. Are the denitrifiers keeping up the nitrogen cycle in balance? Probably not. Certainly, there are examples of nitrogen enrichment in ecosystems. One troubling example: the "blooms" of algae in lakes and rivers as nitrogen fertilizers leach from the soil of adjacent farms (and lawns). The accumulation of dissolved nutrients in a body of water is called eutrophication.
Oxygen Cycle
Oxygen is the most abundant element on the earth’s crust. The earth’s surface is composed of the crust, atmosphere, and hydrosphere. About 50% of the mass of the earth’s crust consists of oxygen (combined with other elements, principally silicon). Oxygen occurs as O2 molecules and, to a limited extent, as O3 (ozone) molecules in air. It forms about 20% of the mass of the air. About 89% of water by mass consists of combined oxygen. In combination with carbon, hydrogen, and nitrogen, oxygen is a large part of plants and animals.
Oxygen is a colorless, odorless, and tasteless gas at ordinary temperatures. It is slightly denser than air. Although it is only slightly soluble in water (49 mL of gas dissolves in 1 L at STP), oxygen’s solubility is very important to aquatic life.
Oxygen is essential in combustion processes such as the burning of fuels. Plants and animals use the oxygen from the air in respiration (Figure $4$). The main way free oxygen is lost from the atmosphere is via and , mechanisms in which life and consume oxygen and release carbon dioxide.
The respiration process is represented as:
$\ce{6O2+C6H12O6→6CO2+6H2O} \nonumber$
Green plants continually replenish the oxygen in the atmosphere by a process called photosynthesis (Figure $3$) . The products of photosynthesis may vary, but, in general, the process converts carbon dioxide and water into glucose (a sugar) and oxygen using the energy of light:
\begin{alignat}{3} &\ce{6CO2}(g) \:+\: &&\ce{6H2O}(l) \:\mathrm{\underset{light}{\xrightarrow{chlorophyll}}}\: &&\ce{C6H12O6}(aq) \:+\: &&\ce{6O2}(g)\ &\mathrm{carbon\ dioxide} &&\ce{water} &&\ce{glucose} &&\ce{oxygen} \end{alignat} \nonumber
Overview of and photosynthesis (green) and respiration (red).
Water (at right), together with carbon dioxide (CO2), form oxygen and organic compounds (at left),
which can be respired to water and (CO2). Source: Wikipedia
Thus, the oxygen that became carbon dioxide and water by the metabolic processes in plants and animals returns to the atmosphere by photosynthesis. Photosynthesizing organisms include the plant life of the land areas as well as the of the oceans. The tiny marine was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean.
Oxygen is a key reactant in various oxidation reactions mentioned in section 8.5. Atmospheric free oxygen is also consumed by chemical weathering and surface reactions. An example of surface weathering is formation of rust:
Ozone forms naturally in the upper atmosphere by the action of ultraviolet light from the sun on the oxygen there. Most atmospheric ozone occurs in the stratosphere, a layer of the atmosphere extending from about 10 to 50 kilometers above the earth’s surface. This ozone acts as a barrier to harmful ultraviolet light from the sun by absorbing it via a chemical decomposition reaction:
$\ce{O3}(g)\xrightarrow{\ce{ultraviolet\: light}}\ce{O}(g)+\ce{O2}(g) \nonumber$
Temperature Inversions
In meteorology, an inversion, also known as a temperature inversion, is a deviation from the normal change of an amospheric property with altitude. It almost always refers to an inversion of the thermal lapse rate. Normally, air temperature decreases with an increase in altitude. During an inversion, warmer air is held above cooler air; the normal temperature profile with altitude is inverted.
An inversion traps air pollution, such as smog, close to the ground. An inversion can also suppress convection by acting as a "cap". If this cap is broken for any of several reasons, convection of any moisture present can then erupt into violent thunderstorms Temperature inversion can notoriously result in freezing rain in cold climates.
Summary
• The different forms of nitrogen that can be used in metabolism are produced through the process of nitrogen fixation.
• Bacteria in the soil carry out a process known as denitrification which converts nitrates back to nitrogen gas.
• Oxygen is produced mainly through photosynthesis. An additional source of atmospheric free oxygen comes from , whereby high-energy radiation breaks down atmospheric water and nitrous oxide.
• Oxygen is utilized during cellular respiration and decay. As well as during chemical weathering and various oxidation reactions.
• Temperature inversion is when a layer of cool air is trapped under a layer of warmer air. The cool dense air can trap and accumulate air pollutants. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.03%3A_Chemistry_of_the_Atmosphere.txt |
Learning Objectives
• Define air pollution.
• Know the sources and effects of major outdoor pollutants
Air pollution refers to the introduction, into the atmosphere, of substances that have harmful effects on humans, other living organisms, and the environment either as solid particles, liquid droplets or gases. Air pollution can result from natural processes such as dust storms, forest fires, and volcanic eruptions, or from human activities such as biomass burning, vehicular emissions, mining, agriculture, and industrial processes. Improved technology and government policies have helped reduce most types of outdoor air pollution in many industrialized countries including the United States, in recent decades. However, outdoor air quality is still a problem in less industrialized nations, especially in megacities of rapidly industrializing nations such as China and India.
Outdoor pollutants can come from stationary (point) sources or mobile (nonpoint) sources (Figure $1$). Stationary sources have a fixed location, for example power plant smokestacks, burning, construction sites, farmlands and surface mines among others. Mobile sources of air pollutants move from place to place while emitting pollutants. Examples of mobile sources include vehicles, aircrafts, ships, and trains.
Pollutants are categorized into two major types based on how they originated namely primary and secondary pollutants. Primary pollutants are those released directly from the source into the air in a harmful form. The primary pollutants that account for nearly all air pollution problems are carbon monoxide (58%), volatile organic compounds (VOCs, 11%), nitrogen oxides (15%), sulfur dioxides (13%), and particulate material (3%). Secondary pollutants are produced through reactions between primary pollutants and normal atmospheric compounds. For example, ground-level ozone forms over urban areas through reactions, powered by sunlight, between primary pollutants (oxides of nitrogen) and other atmospheric gases such as VOCs.
Criteria pollutants
Under the Clean Air Act, the Environmental Protection Agency (EPA) establishes air quality standards to protect public health and the environment. EPA has set national air quality standards for six common air pollutants namely: 1) carbon monoxide; 2) ground-level ozone; 3) nitrogen dioxide; 4) Sulfur dioxide; 5) lead; and 6) particulate matter (also known as particle pollution). Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats. EPA calls these pollutants "criteria" air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels. The set of limits based on human health is called primary standards. Another set of limits intended to prevent environmental and property damage is called secondary standards.
1. Carbon Monoxide (CO): is a colorless, odorless gas emitted from combustion processes, specifically, the incomplete combustion of fuel. Nationally and, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.
2. Ground-level ozone (O3): is a colorless gas with a slightly sweet odor that is not emitted directly into the air, but is created by the interaction of sunlight, heat, oxides of nitrogen (NOx) and volatile organic compounds (VOCs). Ozone is likely to reach unhealthy levels on hot sunny days in urban environments. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOCs.
3. Nitrogen dioxide (NO2): is one of a group of highly reactive gasses known as "oxides of nitrogen," or "nitrogen oxides (NOx)." Other nitrogen oxides include nitrous acid and nitric acid. NO2 is a yellowish-brown to reddish-brown foul-smelling gas that is a major contributor to smog and acid rain. Nitrogen oxides result when atmospheric nitrogen and oxygen react at the high temperatures created by combustion engines. Most emissions in the U.S. result from combustion in vehicle engines, electrical utility, and industrial combustion.
4. Sulfur dioxide (SO2): Sulfur dioxide is one of a group of highly reactive gasses known as “oxides of sulfur.” The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metals from their ores, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment.
5. Lead (Pb): is a metal found naturally in the environment as well as in manufactured products. The major sources of lead emissions have historically been from fuels in motor vehicles (such as cars and trucks) and industrial sources. As a result of EPA's regulatory efforts to remove lead from gasoline, emissions of lead from the transportation sector dramatically declined by 95 percent between 1980 and 1999, and levels of lead in the air decreased by 94 percent during that time period. The major sources of lead emissions today are ore and metal processing and piston-engine aircraft operating on leaded aviation gasoline. Today, the highest levels of lead in air are usually found near lead smelters.
6. Particulate material (PM), sometimes known simply as “particulates” refers to solid particles and liquid droplets suspended in the air we breathe. Particulate pollution is made up of a variety of components, including acids (nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (pollen and mold spores). The size of the particles in directly linked to their potential for causing health problems. Particles that are 10 micrometers in diameter or smaller generally pass through the throat and nose and enter the lungs. EPA groups these into two types: "inhalable coarse particles," with diameters larger than 2.5 micrometers and smaller than 10 micrometers and "fine particles," with diameters that are 2.5 micrometers and smaller. How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle (Figure $2$). Our respiratory systems are equipped to filter larger particles out of the air once it is inhaled. However, the lungs are vulnerable to both coarse particles (PM10), and fine particles (PM2.5). These can slip past the respiratory system's natural defenses and get deep into the lungs and some may even get into the bloodstream. Coarse particles come from road dust while fine particles come from combustion processes.
Volatile Organic Compounds
Volatile organic compounds (VOCs) are carbon-containing chemicals emitted as gases from natural and human-made sources. Natural sources of VOCs include plants, the largest source, and bacteria in the guts of termites and ruminant animals. These compounds are generally oxidized to carbon monoxide and carbon dioxide in the atmosphere. VOCs are of great concern because they are precursors for the formation of ozone, a secondary air pollutant.
A large number of synthetic organic chemicals such as benzene, toluene, formaldehyde, vinyl chloride, chloroform, and phenols are widely used as ingredients in countless household products. Paints, paint strippers, varnishes, many cleaning, disinfecting, cosmetic, degreasing, and hobby products all contain VOCs. Fuels are also made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored. The “new car smell” characteristic of new cars is from a complex mix of dozens of VOC. Also, concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. They are often held responsible for sick building syndrome, an illness resulting from indoor pollution in which the specific cause is not identified.
Smog
Smog is a mixture of air pollutants (sulfur dioxide, nitrogen oxides, ozone, and particulates) that often form over urban areas as a result of fossil fuel combustion. The term was coined from the terms “smoke” and “fog” referring to a brownish haze that pollutes the air, greatly reducing visibility and making it difficult for some people to breathe (Figure $3$ and $4$). There are two main types of smog: industrial and photochemical smog. Industrial smog is produced primarily by the burning of fossil fuels which produces carbon dioxide (from complete combustion), carbon monoxides (from partial combustion), sulfur, and mercury. The sulfur reacts with other chemicals in the atmosphere producing several sulfur compounds including sulfur dioxide. These compounds along with particulate material make up industrial smog. Photochemical smog is formed when sunlight drives chemical reactions between primary pollutants from automobiles and normal atmospheric compounds. The product is a mix of over 100 different chemicals with the most abundant being ground-level ozone. This type of smog will be discussed in more detail in section 13.5.
Figure $3$: Smog over Almaty city, Kazakhstan. Photo by Igors Jefimovs. Source: Wikicommons commons.wikimedia.org/wiki/C...dia/File:Smog_ over_Almaty.jpg
Industrial Smog
Industrial smog or London-type smog is mainly a product of burning large amounts of high sulfur coal. Clean air laws passed in 1956 have greatly reduced smog formation in the United Kingdom; however, in other parts of the world London-type smog is still very prevalent. The main constituent of London-type smog is soot; however, these smogs also contain large quantities of fly ash, sulfur dioxide, sodium chloride and calcium sulfate particles. If concentrations are high enough, sulfur dioxide can react with atmospheric hydroxide to produce sulfuric acid, which will precipitate as acid rain.
$SO_2 + OH \rightarrow HOSO_2 \label{1}$
$HOSO_2 + O_2 \rightarrow HO_2 + SO_3 \label{2}$
$SO_3 + H_2O \rightarrow H_2SO_4 \label{3}$
Concerns about the harmful effects of acid rain have led to strong pressure on industry to minimize the release of SO2 and NO. For example, coal-burning power plants now use SO2 “scrubbers,” which trap SO2 by its reaction with lime (CaO) to produce calcium sulfite dihydrate (CaSO3·2H2O; Figure $5$).
Toxic pollutants
Toxic air pollutants, also known as hazardous air pollutants, are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. Examples of toxic air pollutants include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; methylene chloride, which is used as a solvent and paint stripper by a number of industries; and others such as dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds.
Most air toxics originate from human-made sources, including mobile sources (e.g., cars, trucks, buses) and stationary sources (e.g., factories, refineries, power plants), as well as indoor sources (e.g., some building materials and cleaning solvents). Some air toxics are also released from natural sources such as volcanic eruptions and forest fires. Exposure to air toxics is mainly through breathing but some toxic air pollutants such as mercury can deposit onto soils or surface waters, where they are taken up by plants and ingested by animals and are eventually magnified up through the food chain. Like humans, animals may experience health problems if exposed to sufficiently high quantities of air toxics over time.
Effects of Air Pollution on Human Health
The World Health Organization (WHO) and other international agencies recognize air pollution as a major threat to human health. Numerous scientific studies have linked air pollution to a variety of health problems (Table $1$) including: aggravation of respiratory and cardiovascular diseases; decreased lung function; increased frequency and severity of respiratory symptoms such as difficulty breathing and coughing; increased susceptibility to respiratory infections; effects on the nervous system, including the brain, such as IQ loss and impacts on learning, memory, and behavior; cancer; and premature death. Immediate effects of air pollution may show up after a single exposure or repeated exposures. Other health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure.
Immediate effects of air pollution include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever , may also show up soon after exposure to some indoor air pollutants.
Table $1$: Sources and health effects of criteria pollutants
Pollutant Sources Health Effects
Ground-level Ozone (O3) Secondary pollutant typically formed by chemical reaction of volatile organic compounds (VOCs) and NOx in the presence of sunlight. Decreases lung function and causes respiratory symptoms, such as coughing and shortness of breath; aggravates asthma and other lung diseases leading to increased medication use, hospital admissions, emergency department (ED) visits, and premature mortality.
Particulate Matter (PM) Emitted or formed through chemical reactions; fuel combustion (e.g., burning coal, wood, diesel); industrial processes; agriculture (plowing, field burning); and unpaved roads. Short-term exposures can aggravate heart or lung diseases leading to respiratory symptoms, increased medication use, hospital admissions, ED visits, and premature mortality; long-term exposures can lead to the development of heart or lung disease and premature mortality.
Lead Smelters (metal refineries) and other metal industries; combustion of leaded gasoline in piston engine aircraft; waste incinerators; and battery manufacturing. Damages the developing nervous system, resulting in IQ loss and impacts on learning, memory, and behavior in children. Cardiovascular and renal effects in adults and early effects related to anemia.
Oxides of Nitrogen (NOx) Fuel combustion (e.g., electric utilities, industrial boilers, and vehicles) and wood burning. Aggravate lung diseases leading to respiratory symptoms, hospital admissions, and ED visits; increased susceptibility to respiratory infection.
Carbon Monoxide (CO) Fuel combustion (especially vehicles), industrial processes, fires, waste combustion, and residential wood burning. Reduces the amount of oxygen reaching the body’s organs and tissues; aggravates heart disease, resulting in chest pain and other symptoms leading to hospital admissions and ED visits.
Sulfur Dioxide (SO2) Fuel combustion (especially high-sulfur coal); electric utilities and industrial processes; and natural sources such as volcanoes. Aggravates asthma and increased respiratory symptoms. Contributes to particle formation with associated health effects.
Source: www.epa.gov
The likelihood of immediate reactions to air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. Some sensitive individuals appear to be at greater risk for air pollution-related health effects, for example, those with pre-existing heart and lung diseases (e.g., heart failure/ischemic heart disease, asthma, emphysema, and chronic bronchitis), diabetics, older adults, and children. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.
Summary
• Air pollution refers to the introduction, into the atmosphere, of substances that have harmful effects on humans, other living organisms, and the environment either as solid particles, liquid droplets or gases.
• Major sources of air pollution are gas emissions from fossil fueled vehicles and their reaction products (CO, NOx, Ozone) as well as particulate matter, SO2, and VOCs.
• Examples of toxic air pollutants include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; methylene chloride, which is used as a solvent and paint stripper by a number of industries; and others such as dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds.
• Smog is a mixture of air pollutants (sulfur dioxide, nitrogen oxides, ozone, and particulates) that often form over urban areas as a result of fossil fuel combustion. The term was coined from the terms “smoke” and “fog” referring to a brownish haze that pollutes the air, greatly reducing visibility and making it difficult for some people to breathe.
• Numerous scientific studies have linked air pollution to a variety of health problems.
Contributors and Attributions
• Libretext: Introduction to Environmental Science (Zendher et al.)
• TextMap: General CHemistry (Averill and Eldredge)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.04%3A_Outdoor_Air_Pollution.txt |
Learning Objective
• Identify the different pollutant gases in automobile emissions.
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel fuel, fuel oil, or coal. It is a major component of motor vehicle emissions (and from stationary internal combustion engines), which can also include:
• Crankcase blow-by
• Evaporation of unused gasoline
Motor vehicle emissions contribute to air pollution and are a major ingredient in the creation of smog in some large cities. A 2013 study by MIT indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions.
Carbon monoxide and nitrogen oxides are the two main pollutant gases from automobile emissions. Ozone is a result of the reaction between nitrogen oxides and volatile organic compounds (VOCs).
Carbon Monoxide
Carbon Monoxide (CO) is a colorless, odorless gas that can be harmful when inhaled in large amounts. CO is released when something is burned. The greatest sources of CO to outdoor air are cars, trucks and other vehicles or machinery that burn fossil fuels. A variety of items in your home such as unvented kerosene and gas space heaters, leaking chimneys and furnaces, and gas stoves also release CO and can affect air quality indoors.
Harmful effects
Breathing air with a high concentration of CO reduces the amount of oxygen that can be transported in the blood stream to critical organs like the heart and brain.
At very high levels, which are possible indoors or in other enclosed environments, CO can cause dizziness, confusion, unconsciousness and death.
Very high levels of CO are not likely to occur outdoors. However, when CO levels are elevated outdoors, they can be of particular concern for people with some types of heart disease. These people already have a reduced ability for getting oxygenated blood to their hearts in situations where the heart needs more oxygen than usual. They are especially vulnerable to the effects of CO when exercising or under increased stress. In these situations, short-term exposure to elevated CO may result in reduced oxygen to the heart accompanied by chest pain also known as angina.
Nitrogen Oxides
Nitrogen dioxide (NO2) is one of a group of highly reactive gasses known as "oxides of nitrogen," or "nitrogen oxides (NOx)." Other nitrogen oxides include nitrous acid and nitric acid. NO2 is a yellowish-brown to reddish-brown foul-smelling gas that is a major contributor to smog and acid rain. Nitrogen oxides result when atmospheric nitrogen and oxygen react at the high temperatures created by combustion engines. Most emissions in the U.S. result from combustion in vehicle engines, electrical utility, and industrial combustion.
NO2 primarily gets in the air from the burning of fuel. NO2 forms from emissions from cars, trucks and buses, power plants, and off-road equipment.
Health effects
Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing), hospital admissions and visits to emergency rooms. Longer exposures to elevated concentrations of NO2 may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. People with asthma, as well as children and the elderly are generally at greater risk for the health effects of NO2.
NO2 along with other NOx reacts with other chemicals in the air to form both particulate matter and ozone. Both of these are also harmful when inhaled due to effects on the respiratory system.
Environmental effects
NO2 and other NOx interact with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain harms sensitive ecosystems such as lakes and forests.
The nitrate particles that result from NOx make the air hazy and difficult to see though. This affects the many national parks that we visit for the view. NOx in the atmosphere contributes to nutrient pollution in coastal waters.
Ozone
Ground-level ozone (O3) is a colorless gas with a slightly sweet odor that is not emitted directly into the air, but is created by the interaction of sunlight, heat, oxides of nitrogen (NOx) and volatile organic compounds (VOCs). Ozone is likely to reach unhealthy levels on hot sunny days in urban environments. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOCs.
Ozone is a gas composed of three atoms of oxygen (O3). Ozone occurs both in the Earth's upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found.
Called stratospheric ozone, good ozone occurs naturally in the upper atmosphere, where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. This beneficial ozone has been partially destroyed by manmade chemicals, causing what is sometimes called a "hole in the ozone." The good news is, this hole is diminishing.
Ozone at ground level is a harmful air pollutant, because of its effects on people and the environment, and it is the main ingredient in “smog."
How does ground-level ozone form?
Tropospheric, or ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight.
Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months. Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels.
Health effects
Ozone in the air we breathe can harm our health especially on hot sunny days when ozone can reach unhealthy levels. People most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers.
Environmental effects
Ozone affects sensitive vegetation and ecosystems, including forests, parks, wildlife refuges and wilderness areas. In particular, ozone harms sensitive vegetation during the growing season.
Summary
• Carbon monoxide and nitrogen oxides are the two main compounds from automobile emissions.
• Ozone but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC).
• Different levels of exposure to automobile emissions and ozone can lead to various health problems.
Contributor
• US Environmental Protection Agency | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.05%3A_13.4__Automobile_Emissions.txt |
Learning Objectives
• Describe photochemical smog.
• List different means to address photochemical smog.
Photochemical smog is a type of air pollution due to the reaction of solar radiation with airborne pollutant mixtures of nitrogen oxides (NOx) and volatile organic compounds (hydrocarbons). Smog is a byproduct of modern industrialization. Due to industry and the number of motor vehicles, this is more of a problem in large cities that have a warm, sunny and dry climate.
• Oxidation: Photochemical smog is also referred to as oxidizing smog. Oxidation reactions have been defined several ways. In terms of oxygen transfer, oxidation is a gain of oxygen. Oxidation can also be defined as a loss of hydrogen. The most important use of oxidation is described in terms of electron transfer. Oxidation can be described as an increase in oxidation number or loss of electrons. Oxidation numbers represents a distribution of charge. In other words, oxidation numbers represent the charge of the atom if the compound was composed of ions.
• Reduction: Reduction can involve the gain of hydrogen or loss of oxygen. Reduction can refer to the gain of electrons, which results in a decrease in oxidation number.
Formation of Photochemical Smog
The different reactions involved in the formation of photochemical smog are given below.
Step 1: People begin driving in the morning, nitrogen is burned or oxidized
$N_2 + O_2 \rightarrow 2NO \nonumber$
• Oxidation number of N2 is 0. The nitrogen in NO has acquired an oxidation number of +2.
Step 2: After a few hours, NO combines with O2, in another oxidation reaction
$2NO + O_2 \rightarrow 2NO_2 \nonumber$
• The nitrogen in NO has an oxidation number of +2. The nitrogen in NO2 has an oxidation number of +4.
Step 3: Nitrogen dioxide absorbs light energy, resulting in a reduction reaction
$NO_2 \rightarrow NO + O \nonumber$
• The nitrogen in NO2 has an oxidation number of +4 and the nitrogen in NO is +2.
Step 4: In sunlight, atomic oxygen combines with oxygen gas to form ozone
$O + O_2 \rightarrow O_3 \nonumber$
Step 5: Reaction is temperature and sunlight dependent
$O_3 + NO \rightleftharpoons NO_2 + O_2 \nonumber$
Alternative Reactions
NO and NO2 can also react with the hydrocarbons instead of ozone to form other volatile compounds known as PAN (peroxyacetyl nitrate) as shown in Figure . The accumulation of ozone and volatile organic compounds along with the energy from the sun forms the brown, photochemical smog seen on hot, sunny days. Panoramic view of Santiago covered by a layer of smog on May 10, 2006. The Metropolitan Region of Santiago facing the driest autumn last 28 years due to lack of rainfall, which coupled with poor air circulation, causes an increase in smog.
Health Hazards
Because ozone is highly reactive, it has the ability to oxidize and destroy lung tissue. Short term exposures to elevated levels of ozone (above .75 ppm) have been linked to a host of respiratory irritations including coughing, wheezing, substernal soreness, pharyngitis, and dyspnea. Prolonged exposure to the molecule has been proven to cause a permanent reduction in lung function, as well as elevate the risk of developing asthma. Sulfur dioxide is a common component of London smog. Epidemiological studies have linked short term sulfur dioxide exposure to respiratory irritations including coughing, wheezing, and pharyngitis.
Other Harmful Effects of Smog
Plants are harmed by exposure to nitrogen oxides, ozone, and peroxyacetyl nitrate (PAN, see above), all oxidants present in a smoggy atmosphere. PAN is the most harmful of these constituents, damaging younger plant leaves, especially. Ozone exposure causes formation of yellow spots on leaves, a condition called chlorotic stippling. Some plant species, including sword-leaf lettuce, black nightshade, quickweed, and double-fortune tomato, are extremely susceptible to damage by oxidant species in smog and are used as bioindicators of the presence of smog. Costs of crop and orchard damage by smog run into millions of dollars per year in areas prone to this kind of air pollution, such as southern California.
Materials that are adversely affected by smog are generally those that are attacked by oxidants. The best example of such a material is rubber, especially natural rubber, which is attacked by ozone. Indeed, the hardening and cracking of natural rubber has been used as a test for atmospheric ozone.
Visibility-reducing atmospheric aerosol particles are the most common manifestation of the harm done to atmospheric quality by smog. The smog-forming process occurs by the oxidation of organic materials in the atmosphere, and carbon-containing organic materials are the most common constituents of the aerosol particles in an atmosphere afflicted by smog. Conifer trees(pine and cypress) and citrus trees are major contributors to the organic hydrocarbons that are precursors to organic particle formation in smog.
Controlling Photochemical Smog
Every new vehicle sold in the United States must include a catalytic converter to reduce photochemical emissions. Catalytic converters force CO and incompletely combusted hydrocarbons to react with a metal catalyst, typically platinum, to produce CO2 and H2O. Additionally, catalytic converters reduce nitrogen oxides from exhaust gases into O2 and N2, eliminating the cycle of ozone formation. Many scientists have suggested that pumping gas at night could reduce photochemical ozone formation by limiting the amount of exposure VOCs have with sunlight.
Preventing Smog with Green Chemistry
Smog is basically a chemical problem, which would indicate that it should be amenable to chemical solutions. Indeed, the practice of green chemistry and the application of the principles of industrial ecology can help to reduce smog. This is due in large part to the fact that a basic premise of green chemistry is to avoid the generation and release of chemical species with the potential to harm the environment. The best way to prevent smog formation is to avoid the release of nitrogen oxides and organic vapors that enable smog to form. At an even more fundamental level, measures can be taken to avoid the use of technologies likely to release such substances, for example, by using alternatives to polluting automobiles for transportation.
The evolution of automotive pollution control devices to reduce smog provides an example of how green chemistry can be used to reduce pollution. The first measures taken to reduce hydrocarbon and nitrogen oxide emissions from automobiles were very much command-and-control and “end-of-pipe” measures. These primitive measures implemented in the early 1970s did reduce emissions, but with a steep penalty in fuel consumption and in driving performance of vehicles. However, over the last three decades, the internal combustion automobile engine has evolved into a highly sophisticated computer-controlled machine that generally performs well, emits few air pollutants, and is highly efficient. (And it would be much more efficient if those drivers who feel that they must drive “sport utility” behemoths would switch to vehicles of a more sensible size.) This change has required an integrated approach involving reformulation of gasoline. The first major change was elimination from gasoline of tetraethyllead, an organometallic compound that poisoned automotive exhaust catalysts (and certainly was not good for people). Gasoline was also reformulated to eliminate excessively volatile hydrocarbons and unsaturated hydrocarbons (those with double bonds between carbon atoms) that are especially reactive in forming photochemical smog.
An even more drastic approach to eliminating smog-forming emissions is the use of electric automobiles that do not burn gasoline. These vehicles certainly do not pollute as they are being driven, but they suffer from the probably unsolvable problem of a very limited range between charges and the need for relatively heavy batteries. However, hybrid automobiles using a small gasoline or diesel engine that provides electricity to drive electric motors propelling the automobile and to recharge relatively smaller batteries can largely remedy the emission and fuel economy problems with automobiles. The internal combustion engine on these vehicles runs only as it is needed to provide power and, in so doing, can run at a relatively uniform speed that provides maximum economy with minimum emissions.
Another approach that is being used on vehicles as large as buses that have convenient and frequent access to refueling stations is the use of fuel cells that can generate electricity directly from the catalytic combination of elemental hydrogen and oxygen, producing only harmless water as a product . There are also catalytic process that can generate hydrogen from liquid fuels, such as methanol, so that vehicles carrying such a fuel can be powered by electricity generated in fuel cells.
Green chemistry can be applied to devices and processes other than automobiles to reduce smog-forming emissions. This is especially true in the area of organic solvents used for parts cleaning and other industrial operations, vapors of which are often released to the atmosphere. The substitution of water with proper additives or even the use of supercritical carbon dioxide fluid can eliminate such emissions.
Summary
• Photochemical smog is a mixture of pollutants that are formed (mostly during the hot summer months) when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities.
• Photochemical smog is formed from the reactions of natural and man-made emissions of nitrogen oxides and VOCs.
• Smog is a serious problem in many cities and continues to harm human health and are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma.
• Catalytic converters in gas powered vehicles help reduce photochemical emissions.
• The practice of green chemistry and the application of the principles of industrial ecology can help to reduce smog.
Contributors and Attributions
• Ed Vitz (Kutztown University), John W. Moore (UW-Madison), Justin Shorb (Hope College), Xavier Prat-Resina (University of Minnesota Rochester), Tim Wendorff, and Adam Hahn.
• Stanley Manahan (University of Missouri)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.06%3A_Photochemical_Smog-_Making_Haze_While_the_Sun_Shines.txt |
Learning Objective
• Describe acid rain and its effects.
Acid rain is a term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere (Figure $1$) containing higher than normal amounts of nitric and sulfuric acids. The precursors, or chemical forerunners, of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. The result is a mild solution of sulfuric acid and nitric acid.
$SO_2 + HOH \rightarrow H_2SO_3 \label{1}$
$2 NO_2 + HOH \rightarrow HNO_2 + HNO_3 \label{2}$
When sulfur dioxide and nitrogen oxides are released from power plants and other sources, prevailing winds blow these compounds across state and national borders, sometimes over hundreds of miles.
Acid rain is measured using a scale called “pH.” The lower a substance’s pH, the more acidic it is. Pure water has a pH of 7.0. However, normal rain is slightly acidic because carbon dioxide (CO2) dissolves into it forming weak carbonic acid, giving the resulting mixture a pH of approximately 5.6 at typical atmospheric concentrations of CO2. As of 2000, the most acidic rain falling in the U.S. has a pH of about 4.3.
Effects of Acid Rain
Acid rain causes acidification of lakes and streams and contributes to the damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation’s cultural heritage. Prior to falling to the earth, sulfur dioxide (SO2) and nitrogen oxide (NOx) gases and their particulate matter derivatives—sulfates and nitrates—contribute to visibility degradation and harm public health.
The ecological effects of acid rain are most clearly seen in the aquatic, or water, environments, such as streams, lakes, and marshes. Most lakes and streams have a pH between 6 and 8, although some lakes are naturally acidic even without the effects of acid rain. Acid rain primarily affects sensitive bodies of water, which are located in watersheds whose soils have a limited ability to neutralize acidic compounds (called “buffering capacity”). Lakes and streams become acidic (i.e., the pH value goes down) when the water itself and its surrounding soil cannot buffer the acid rain enough to neutralize it. In areas where buffering capacity is low, acid rain releases aluminum from soils into lakes and streams; aluminum is highly toxic to many species of aquatic organisms. Acid rain causes slower growth, injury, or death of forests as shown in Figure $2$. Of course, acid rain is not the only cause of such conditions. Other factors contribute to the overall stress of these areas, including air pollutants, insects, disease, drought, or very cold weather. In most cases, in fact, the impacts of acid rain on trees are due to the combined effects of acid rain and these other environmental stressors.
Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals(such as bronze).
The damage that acid rain does to limestone and marble buildings and sculptures is due to a classic acid–base reaction. Marble and limestone both consist of calcium carbonate (CaCO3), a salt derived from the weak acid H2CO3. The reaction of a strong acid with a salt of a weak acid goes to completion. Thus we can write the reaction of limestone or marble with dilute sulfuric acid as follows:
$CaCO_{3(s)} + H_2SO_{4(aq)} \rightarrow CaSO_{4(s)} + H_2O_{(l)} + CO_{2(g)} \label{3}$
Because CaSO4 is sparingly soluble in water, the net result of this reaction is to dissolve the marble or limestone.
These effects significantly reduce the societal value of buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and cars (Figure $3$).
Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions contribute to visibility impairment, meaning we cannot see as far or as clearly through the air. The pollutants that cause acid rain—sulfur dioxide (SO2) and nitrogen oxides (NOx)—damage human health. These gases interact in the atmosphere to form fine sulfate and nitrate particles that can be transported long distances by winds and inhaled deep into people’s lungs. Fine particles can also penetrate indoors. Many scientific studies have identified a relationship between elevated levels of fine particles and increased illness and premature death from heart and lung disorders, such as asthma and bronchitis.
Summary
• Acid rain is a term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids.
• Acidic rain water in the soil, streams, lakes, and marshes (and other bodies of water) can be harmful to trees, plants, animals, especially aquatic plants and animals.
• Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals(such as bronze) and the deterioration of paint and stone (such as marble and limestone). | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.07%3A_Acid_Rain-_Air_Pollution_Water_Pollution.txt |
Learning Objectives
• Name the different indoor pollutants and their sources.
• Know the harmful effects of indoor pollutants.
In both developed and developing nations, indoor air pollution poses a greater health risk than outdoor air pollution. According to the World Health Organization (WHO) and other agencies such as the Environmental Protection Agency (EPA), indoor air generally contains higher concentrations of toxic pollutants than outdoor air. Additionally, people generally spend more time indoors than outdoors, hence, the health effects from indoor air pollution in workplaces, schools, and homes are far greater than outdoor. Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home.
Outdoor air enters and leaves a building by infiltration, natural ventilation, and mechanical ventilation. In infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase. High temperature and humidity levels can also increase concentrations of some pollutants.
There are many sources of indoor air pollution in any home (Figure \(1\)). These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices. Pollutants causing indoor air pollution can also originate from outside sources such as radon, pesticides, and outdoor air pollution. Radon is a naturally occurring radioactive gas produced from the decay of uranium in rock. If a building/home is constructed in an area with uranium containing rock, the gas can seep through the foundations and accumulate in basements. Exposure to radon can cause lung cancer.
The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted. Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in house-keeping. High pollutant concentrations can remain in the air for long periods after some of these activities.
Risks from indoor air pollution differ between less industrialized and industrialized nations. Indoor pollution has a greater impact in less industrialized nations where many people use cheaper sources of fuel such as wood, charcoal, and crop waste among others for cooking and heating, often with little or no ventilation. The most significant indoor pollutant, therefore, is soot and carbon monoxide. In industrialized nations, the primary indoor air health risks are cigarette smoke and radon.
Combustion Pollutants
Combustion pollutants are gases or particles that come from burning materials. In homes, the major source of combustion pollutants are improperly vented or unvented fuel-burning appliances such as space heaters, wood stoves, gas stoves, water heaters, dryers, and fireplaces. The types and amounts of pollutants produced depends on the type of appliance, how well the appliance is installed, maintained and vented and the kind of fuel it uses. Common combustion pollutants include:
Carbon monoxide (CO) which is a colorless, odorless gas that interferes with the delivery of oxygen throughout the body. Carbon monoxide causes headaches, dizziness, weakness, nausea and even death. Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher.
Nitrogen dioxide (NO2) which is a colorless, odorless gas that causes eye, nose and throat irritation, shortness of breath, and an increased risk of respiratory infection. Average level in homes without combustion appliances is about half that of outdoors. In homes with gas stoves, kerosene heaters or un-vented gas space heaters, indoor levels often exceed outdoor levels.
Particulate Matter (PM) which refers to fine particles that forms in smoke when wood or other organic matter burns.
Other pollutants from wood smoke In addition to particle pollution, wood smoke contains several toxic harmful air pollutants including benzene, formaldehyde, acrolein, and polycyclic aromatic hydrocarbons (PAHs).
Secondhand Smoke
Secondhand smoke is a mixture of the smoke given off by the burning of tobacco products, such as cigarettes, cigars or pipes and the smoke exhaled by smokers. Secondhand smoke is also called environmental tobacco smoke (ETS). Exposure to secondhand smoke is sometimes called involuntary or passive smoking. Secondhand smoke, classified by EPA as a Group A carcinogen, contains more than 7,000 substances. Secondhand smoke exposure commonly occurs indoors, particularly in homes and cars. Secondhand smoke can move between rooms of a home and between apartment units. Opening a window or increasing ventilation in a home or car is not protective from secondhand smoke.
Radon
Radon is a radioactive gas that results from the natural decay of uranium and radiumfound in nearly all rocks and soils. Elevated radon levels have been found in every state. Radon is in the atmosphere and can also be found in ground water. The national average for radon in outdoor air is 0.4 picocuries per liter (pCi/L), while the average for indoor air is 1.3 pCi/L.
Any building can have high levels of radon, including new and old homes, well-sealed and drafty homes, office buildings and schools, and homes with or without basements. Radon gas can get into buildings through cracks in solid floors and walls, construction joints, gaps in suspended floors and around service pipes, cavities inside walls, the water supply and building materials. Testing is the only way to know if your home has elevated radon levels.EPA recommends fixing your home when the radon level is at or above 4 pCi/L.
Figure \(2\): Sources of Radon. Image source: EPAhttps://www.epa.gov/radiation/radionuclide-basics-radon
EPA estimates that about 21,000 lung cancer deaths each year in the U.S. are radon-related. Exposure to radon is the second leading cause of lung cancer after smoking. For most people, radon is the single greatest environmental source of radiation exposure. EPA recommends that all homes and schools be tested for radon. For smokers, the risk of lung cancer is heightened due to the combined effects of radon and smoking.
Other Indoor Pollutants
Molds are usually not a problem indoors, unless mold spores land on a wet or damp spot and begin growing. Molds have the potential to cause health problems. Molds produce allergens (substances that can cause allergic reactions) and irritants. Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash.
Allergic reactions to mold are common. They can be immediate or delayed. Molds can also cause asthma attacks in people with asthma who are allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people. Symptoms other than the allergic and irritant types are not commonly reported as a result of inhaling mold.
Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands.
Organic chemicals are widely used as ingredients in household products. Paints, varnishes and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored.
EPA's Office of Research and Development's "Total Exposure Assessment Methodology (TEAM) Study" (Volumes I through IV, completed in 1985) found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas. TEAM studies indicated that while people are using products containing organic chemicals, they can expose themselves and others to very high pollutant levels, and elevated concentrations can persist in the air long after the activity is completed.
VOCs are emitted by a wide array of products used in homes including paints and lacquers, paint strippers, cleaning supplies, varnishes and waxes, pesticides, building materials and furnishings, office equipment, moth repellents, air fresheners, and dry-cleaned clothing. VOCs evaporate into the air when these products are used or sometimes even when they are stored.
Volatile organic compounds irritate the eyes, nose and throat, and cause headaches, nausea, and damage to the liver, kidneys and central nervous system. Some of them can cause cancer.
Asbestos is a mineral fiber that occurs in rock and soil. Because of its fiber strength and heat resistance asbestos has been used in a variety of building construction materials for insulation and as a fire retardant. Asbestos has also been used in a wide range of manufactured goods, mostly in building materials (roofing shingles, ceiling and floor tiles, paper products, and asbestos cement products), friction products (automobile clutch, brake, and transmission parts), heat-resistant fabrics, packaging, gaskets, and coatings.
Asbestos fibers may be released into the air by the disturbance of asbestos-containing material during product use, demolition work, building or home maintenance, repair, and remodeling. In general, exposure may occur only when the asbestos-containing material is disturbed or damaged in some way to release particles and fibers into the air.
Three of the major health effects associated with asbestos exposure are:
· lung cancer
· mesothelioma, a rare form of cancer that is found in the thin lining of the lung, chest and the abdomen and heart
· asbestosis, a serious progressive, long-term, non-cancer disease of the lungs
Improving Your Indoor Air Quality
Take steps to help improve your air quality and reduce your IAQ-related health risks at little or no cost by:
Controlling the sources of pollution: Usually the most effective way to improve indoor air is to eliminate individual sources or reduce their emissions.
Ventilating: Increasing the amount of fresh air brought indoors helps reduce pollutants inside. When weather permits, open windows and doors, or run an air conditioner with the vent control open. Bathroom and kitchen fans that exhaust to the outdoors also increase ventilation and help remove pollutants.
Always ventilate and follow manufacturers’ instructions when you use products or appliances that may release pollutants into the indoor air.
Changing filters regularly: Central heaters and air conditioners have filters to trap dust and other pollutants in the air. Make sure to change or clean the filters regularly, following the instructions on the package.
Adjusting humidity:The humidity inside can affect the concentrations of some indoor air pollutants. For example, high humidity keeps the air moist and increases the likelihood of mold.
Keep indoor humidity between 30 and 50 percent. Use a moisture or humidity gauge, available at most hardware stores, to see if the humidity in your home is at a good level. To increase humidity, use a vaporizer or humidifier. To decrease humidity, open the windows if it is not humid outdoors. If it is warm, turn on the air conditioner or adjust the humidity setting on the humid
Get a quick glimpse of some of the most important ways to protect the air in your home by touring the Indoor Air Quality (IAQ) House. Room-by-room, you'll learn about the key pollutants and how to address them.
Interactive Version
https://www.epa.gov/indoor-air-quality-iaq/interactive-tour-indoor-air-quality-demo-house#mainHouse
Text Version
https://www.epa.gov/indoor-air-quality-iaq/text-version-indoor-air-quality-house-tour
Summary
• Indoor pollutants include combustion pollutants (from burning of oil, gas, kerosene, coal, wood, and tobacco products); building materials and furnishings products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices.
• Pollutants causing indoor air pollution can also originate from outside sources such as radon, pesticides, and outdoor air pollution.
• Indoor pollutants can cause serious health problems to sensitive groups.
• Several suggestions were provided to improve indoor air quality.
Contributors and Attributions
US Environmental Protection Agency | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.08%3A_Indoor_Air_Pollution.txt |
Learning Objectives
• Describe the depletion of the ozone layer.
• Explain how chlorine and bromine atoms react with ozone that leads to the depletion of the ozone layer.
The earth's stratospheric ozone layer plays a critical role in absorbing ultraviolet radiation emitted by the sun. In the last thirty years, it has been discovered that stratospheric ozone is depleting as a result of anthropogenic pollutants. There are a number of chemical reactions that can deplete stratospheric ozone; however, some of the most significant of these involves the catalytic destruction of ozone by halogen radicals such as chlorine and bromine.
Introduction
The atmosphere of the Earth is divided into five layers. In order of closest and thickest to farthest and thinnest the layers are listed as follows: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The majority of the ozone in the atmosphere resides in the stratosphere, which extends from six miles above the Earth’s surface to 31 miles. Humans rely heavily on the absorption of ultraviolet B rays by the ozone layer because UV-B radiation causes skin cancer and can lead to genetic damage. The ozone layer has historically protected the Earth from the harmful UV rays, although in recent decades this protection has diminished due to stratospheric ozone depletion.
Ozone depletion is largely a result of man-made substances. Humans have introduced gases and chemicals into the atmosphere that have rapidly depleted the ozone layer in the last century. This depletion makes humans more vulnerable to the UV-B rays which are known to cause skin cancer as well as other genetic deformities. The possibility of ozone depletion was first introduced by scientists in the late 1960's as dreams of super sonic transport began to become a reality. Scientists had long been aware that nitric oxide (NO) can catalytically react with ozone ($O_3$) to produce $O_2$ molecules; however, $NO$ molecules produced at ground level have a half life far too short to make it into the stratosphere. It was not until the advent of commercial super sonic jets (which fly in the stratosphere and at an altitude much higher then conventional jets) that the potential for $NO$ to react with stratospheric ozone became a possibility. The threat of ozone depletion from commercial super sonic transport was so great that it is often cited as the main reason why the US federal government pulled support for its development in 1971. Fear of ozone depletion was abated until 1974 when Sherwood Rowland and Mario Molina discovered that chlorofluorocarbons could be photolyzed by high energy photons in the stratosphere. They discovered that this process could releasing chlorine radicals that would catalytically react with $O_3$ and destroy the molecule. This process is called the Rowland-Molina theory of $O_3$ depletion.
The Chapman Cycle
The stratosphere is in a constant cycle with oxygen molecules and their interaction with ultraviolet rays. This process is considered a cycle because of its constant conversion between different molecules of oxygen. The ozone layer is created when ultraviolet rays react with oxygen molecules (O2) to create ozone (O3) and atomic oxygen (O). This process is called the Chapman cycle.
Step 1: An oxygen molecules is photolyzed by solar radiation, creating two oxygen radicals:
$h\nu + O_2 \rightarrow 2O^. \nonumber$
Step 2: Oxygen radicals then react with molecular oxygen to produce ozone:
$O_2 + O^. \rightarrow O_3 \nonumber$
Step 3: Ozone then reacts with an additional oxygen radical to form molecular oxygen:
$O_3 + O^. \rightarrow 2O_2 \nonumber$
Step 4: Ozone can also be recycled into molecular oxygen by reacting with a photon:
$O_3 + h\nu \rightarrow O_2 + O^. \nonumber$
It is important to keep in mind that ozone is constantly being created and destroyed by the Chapman cycle and that these reactions are natural processes, which have been taking place for millions of years. Because of this, the thickness the ozone layer at any particular time can vary greatly. It is also important to know that O2 is constantly being introduced into the atmosphere through photosynthesis, so the ozone layer has the capability of regenerating itself.
Chemistry of Ozone Depletion
CFC molecules are made up of chlorine, fluorine and carbon atoms and are extremely stable. This extreme stability allows CFC's to slowly make their way into the stratosphere (most molecules decompose before they can cross into the stratosphere from the troposphere). This prolonged life in the atmosphere allows them to reach great altitudes where photons are more energetic. When the CFC's come into contact with these high energy photons, their individual components are freed from the whole. The following reaction displays how Cl atoms have an ozone destroying cycle:
$Cl + O_3 \rightarrow ClO + O_2 \tag{step 1}$
$ClO + O^. \rightarrow Cl + O_2 \tag{step 2}$
$O_3 + O^. \rightarrow 2O_2 \tag{Overall reaction}$
Chlorine is able to destroy so much of the ozone because it acts as a catalyst. Chlorine initiates the breakdown of ozone and combines with a freed oxygen to create two oxygen molecules. After each reaction, chlorine begins the destructive cycle again with another ozone molecule. One chlorine atom can thereby destroy thousands of ozone molecules. Because ozone molecules are being broken down they are unable to absorb any ultraviolet light so we experience more intense UV radiation at the earths surface.
From 1985 to 1988, researchers studying atmospheric properties over the south pole continually noticed significantly reduced concentrations of ozone directly over the continent of Antarctica. For three years it was assumed that the ozone data was incorrect and was due to some type of instrument malfunction. In 1988, researchers finally realized their error and concluded that an enormous hole in the ozone layer had indeed developed over Antarctica. Examination of NASA satellite data later showed that the hole had begun to develop in the mid 1970's.
The ozone hole over Antarctica is formed by a slew of unique atmospheric conditions over the continent that combine to create an ideal environment for ozone destruction.
• Because Antarctica is surrounded by water, winds over the continent blow in a unique clockwise direction creating a so called "polar vortex" that effectively contains a single static air mass over the continent. As a result, air over Antarctica does not mix with air in the rest of the earth's atmosphere.
• Antarctica has the coldest winter temperatures on earth, often reaching -110 F. These chilling temperatures result in the formation of polar stratospheric clouds (PSC's) which are a conglomeration of frozen H2O and HNO3. Due to their extremely cold temperatures, PSC's form an electrostatic attraction with CFC molecules as well as other halogenated compounds
As spring comes to Antarctica, the PSC's melt in the stratosphere and release all of the halogenated compounds that were previously absorbed to the cloud. In the antarctic summer, high energy photons are able to photolyze the halogenated compounds, freeing halogen radicals that then catalytically destroy O3. Because Antarctica is constantly surrounded by a polar vortex, radical halogens are not able to be diluted over the entire globe. The ozone hole develops as result of this process.
Resent research suggests that the strength of the polar vortex from any given year is directly correlated to the size of the ozone hole. In years with a strong polar vortex, the ozone hole is seen to expand in diameter, whereas in years with a weaker polar vortex, the ozone hole is noted to shrink
Ozone Depleting Substances
The following substances are listed as ozone depleting substances under Title VI of the United State Clean Air Act:
Table $1$: Ozone Depleting Substances And Their Ozone-Depletion Potential. Taken directly from the Clean Air Act, as of June 2010.
Substance Ozone- depletion potential
chlorofluorocarbon-11 (CFC–11) 1.0
chlorofluorocarbon-12 (CFC–12) 1.0
chlorofluorocarbon-13 (CFC–13) 1.0
chlorofluorocarbon-111 (CFC–111) 1.0
chlorofluorocarbon-112 (CFC–112) 1.0
chlorofluorocarbon-113 (CFC–113) 0.8
chlorofluorocarbon-114 (CFC–114) 1.0
chlorofluorocarbon-115 (CFC–115) 0.6
chlorofluorocarbon-211 (CFC–211) 1.0
chlorofluorocarbon-212 (CFC–212) 1.0
chlorofluorocarbon-213 (CFC–213) 1.0
chlorofluorocarbon-214 (CFC–214) 1.0
chlorofluorocarbon-215 (CFC–215) 1.0
chlorofluorocarbon-216 (CFC–216) 1.0
chlorofluorocarbon-217 (CFC–217) 1.0
halon-1211 3.0
halon-1301 10.0
halon-2402 6.0
carbon tetrachloride 1.1
methyl chloroform 0.1
hydrochlorofluorocarbon-22 (HCFC–22) 0.05
hydrochlorofluorocarbon-123 (HCFC–123) 0.02
hydrochlorofluorocarbon-124 (HCFC–124) 0.02
hydrochlorofluorocarbon-141(b) (HCFC–141(b)) 0.1
hydrochlorofluorocarbon-142(b) (HCFC–142(b)) 0.06
Summary
• Any disruption of the balance that results in a higher rate of ozone destruction than ozone creation would result in depletion of ozone.
• Some compounds that release chlorine or bromine when they are exposed to intense UV light in the stratosphere contribute to ozone depletion, and are called ozone-depleting substances (ODS)
• The Montreal Protocol is an international agreement that committed all parties (signatory nations) to a schedule for phasing out the production and use of CFCs and other substances known to be harmful to the ozone layer.
Contributors and Attributions
• Libretext: Supplemental Module, Physical and Theoretical Chemistry | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.08%3A_Stratospheric_Ozone-_Earth%27s_Vital_Shield.txt |
Learning Objectives
• Define global warming, climate change, the greenhouse effect, and greenhouse gases.
• Discuss strategies for reducing the intensity of the human influence on the greenhouse effect.
Global warming refers to the increase in the average temperature of the Earth’s atmosphere due to elevated greenhouse gas concentrations, heightening the greenhouse effect. Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
The largest driver of warming is the emission of gases that create a greenhouse effect, of which more than 90% are carbon dioxide (CO
2) and methane. Fossil fuel burning (coal, oil, and natural gas) for energy consumption is the main source of these emissions, with additional contributions from agriculture, deforestation, and manufacturing. The human cause of climate change is not disputed by any scientific body of national or international standing. Temperature rise is accelerated or tempered by climate feedbacks, such as loss of sunlight-reflecting snow and ice cover, increased water vapour (a greenhouse gas itself), and changes to land and ocean carbon sinks.
The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere (Figure $2$). Radiatively active gases (i.e. greenhouse gases) in a planet's atmosphere radiate energy in all directions. Part of this radiation is directed towards the surface, thus warming it. The intensity of downward radiation – that is, the strength of the greenhouse effect – depends on the amount of greenhouse gases that the atmosphere contains. The temperature rises until the intensity of upward radiation from the surface, thus cooling it, balances the downward flow of energy.
Earth's natural greenhouse effect is critical to supporting life and initially was a precursor to life moving out of the ocean onto land. Human activities, mainly the burning of fossil fuels and clear cutting of forests, have increased the greenhouse effect and caused global warming.
The term greenhouse effect is a slight misnomer in the sense that physical greenhouses warm via a different mechanism. The greenhouse effect as an atmospheric mechanism functions through radiative heat loss while a traditional greenhouse as a built structure blocks convective heat loss. The result, however, is an increase in temperature in both cases.
Figure $2$ The greenhouse effect of solar radiation on the Earth's surface caused by emission of greenhouse gases. Source: Wikipedia
Greenhouse Gases and Global Warming
A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. It’s important to realize that water vapor (H2O) is also a greenhouse gas. While humans have little direct impact on water vapor concentrations in the atmosphere, it is still an essential component of the natural greenhouse effect that occurs in our atmosphere. The four major categories of greenhouse gases that have been impacted by humans the most will be discussed in detail below. See Table $1$ for a numeric comparison of these greenhouse gases.
• Carbon dioxide, CO2
• Methane, CH4
• Nitrous oxide, N2O
• Synthetic fluorinated gases, including hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)
Carbon dioxide (CO2) is the greenhouse gas responsible for most of the human-caused climate change in our atmosphere. It has the highest concentration in the atmosphere of any of the greenhouse gases that we’ll discuss here. Remember that CO2 is a direct product of both combustion and cellular respiration, causing it to be produced in great quantities both naturally and anthropogenically. Any time biomass or fossil fuels are burned, CO2 is released. Major anthropogenic sources include: electricity production from coal-fired and natural gas power plants, transportation, and industry (Chapter 4). To get an idea of how CO2 concentration has changed over time, watch this video compiled by the National Oceanic and Atmospheric Administration (NOAA): http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html. This video contains atmospheric CO2 concentrations measured directly, dating back to 1958, as well as atmospheric CO2 concentrations measured indirectly from ice core data, dating back to 800,000 BCE. By 1990, a quantity of over seven billion tons of carbon (equivalent to 26 billion tons of carbon dioxide when the weight of the oxygen atoms are also considered) was being emitted into the atmosphere every year, much of it from industrialized nations. Similar to the action of the naturally existing greenhouse gases, any additional greenhouse gases leads to an increase in the surface temperature of the Earth.
While CO2 is produced by aerobic cellular respiration, gases such as CH4 and N2O are often the products of anaerobic metabolisms. Agriculture is a major contributor to CH4 emissions. In addition to anaerobic bacteria, methane is also a significant component of natural gas, and is commonly emitted through the mining and use of natural gas and petroleum, in addition to coal mining. Finally, landfills contribute significantly to CH4 emissions, as the waste put into the landfill largely undergoes anaerobic decomposition as it is buried under many layers of trash and soil. Natural sources of CH4 include swamps and wetlands, and volcanoes.
The vast majority of N2O production by humans comes from agricultural land management. While some N2O is naturally emitted to the atmosphere from soil as part of the nitrogen cycle, human changes in land management, largely due to agricultural practices, have greatly increased N2O emissions. Some N2O is also emitted from transportation and industry.
Due to their relatively high concentrations in the atmosphere compared to synthetic gases, CO2, CH4, and N2O, are responsible for most of the human-caused global climate change over the past century. Figure $2$ shows the increases in all three gases since 1750. Ice core data shows us that the atmospheric CO2 concentration never exceeded 300 ppm before the industrial revolution. As of early 2015, the current atmospheric CO2 concentration is 400 ppm.
One class of greenhouse gas chemicals that has no natural sources is the fluorinated gases. These include HFCs, PFCs, and SF6, among others. Because these are synthetic chemicals that are only created by humans, these gases were essentially non-existent before the industrial revolution. These synthetic gases are used for a wide variety of applications, from refrigerants to semiconductor manufacturing, and propellants to fire retardants. They tend to have a long lifetime in the atmosphere, as seen in Table $1$. Some of these chemicals, as well as the older chlorofluorocarbons (CFCs), have been phased out by international environmental legislation under the Montreal Protocol. Due to their long lifespan, many of these now banned CFCs remain in the atmosphere. Newer chemical replacements, such as HFCs, provide many of the same industrial applications, but unfortunately have their own environmental consequences.
Just as greenhouse gases differ in their sources and their residence time in the atmosphere, they also differ in their ability to produce the greenhouse effect. This is measured by the global warming potential, or GWP, of each greenhouse gas. The GWP of a greenhouse gas is based on its ability to absorb and scatter energy, as well as its lifetime in the atmosphere. Since CO2 is the most prevalent greenhouse gas, all other greenhouse gases are measured relative to it. As the reference point, CO2 always has a GWP of 1. Note the very high GWP values of the synthetic fluorinated gases in Table $1$. This is largely due to their very long residence time in the atmosphere. Also note the higher GWP values for CH4 and N2O compared to CO2.
Table $1$. Comparision of Greenhouse Gases.
Greenhouse gas Chemical formula or abbreviation Lifetime in atmosphere Global warming potential (100-year)
Carbon dioxide CO2 Variable 1
Methane CH4 12 years 28-36
Nitrous oxide N2O 114 years 298
Hydrofluorocarbons Abbreviation: HFCs 1-270 years 12-14,800
Perfluorocarbons Abbreviation: PFCs 2,600-50,000 years 7,390
Sulfur hexafluoride SF6 3,200 years 22,800
Other climate influencers
In addition to greenhouse gases, other manmade changes may be forcing climate change. Increases in near-surface ozone from internal combustion engines, aerosols such as carbon black, mineral dust and aviation-induced exhaust are acting to raise the surface temperature. This primarily occurs due to a decrease in the albedo of light-colored surfaces by the darker-colored carbon black, soot, dust, or particulate matter. As you know, it is more comfortable to wear a white shirt on a hot summer day than a black shirt. Why is this? Because the lighter-colored material bounces more solar radiation back toward space than the darker-colored material does, allowing it to stay cooler. The darker-colored material absorbs more solar radiation, increasing its temperature. Just as the white shirt has a higher albedo than the black shirt, light-colored objects in nature (such as snow) have a higher albedo than dark-colored objects (such as soot or dust). As humans increase the amount of carbon black, soot, dust, and particulates in the atmosphere, we decrease the albedo of light-colored surfaces, causing them to absorb more solar radiation and become warmer than they would without human influence. An example of this can be seen in the snow on Figure $3$.
Consequences of Climate Change
We will only discuss some of the consequences of climate change in this section, including changes in temperature, precipitation, ocean level, and ocean acidity. There are many more changes that have been seen, and are projected to continue in the future. These include: changes in the amount and distribution of ice and snow, changes in seasonality, ecosystem shift, and habitat changes of plant and animal populations, in addition to others. For more information about these consequence of climate change, visit this site: http://www.epa.gov/climatechange/sci...ors/index.html.
Temperature and precipitation
Temperature and precipitation are the two most direct impacts on the Earth’s climate due to climate change. By now, you should already understand why an increase in greenhouse gas levels in the atmosphere causes an increase in temperature. But why does it also impact precipitation patterns? As you already know, water vapor is an important component of the Earth’s atmosphere . As the air in the troposphere warms and cools, the amount of water vapor that it holds changes dramatically. Here in Georgia, we have very hot and humid summers. The high summer humidity in this region is possible due to the increased capability warm air has to hold water vapor. Simply put, warmer air can hold more water than cooler air. As air cools, its ability to hold water vapor decreases, and any excess water will leave the air as liquid water. A great example of this is the formation of dew on surfaces overnight. During the day, the temperature is warmer than it is at night, and the air has a relatively high holding capacity for water vapor. When the sun sets, the air cools, decreasing its capacity to hold water vapor. That extra water must go somewhere, and it does that by accumulating on surfaces. Similarly, when warm and cool air fronts collide, the chances for rain and thunderstorms increase. Furthermore, an increase in temperature enhances evaporation occurring at the Earth’s surface. This increased evaporation leads to greater concentrations of water vapor in the atmosphere which can lead to increased precipitation.
The change in temperature that we have already seen in the Earth’s average atmospheric temperature is relatively small (about1.2 °C, according to Figure 7.5.1). However, as with many of the aspects of climate change, the potential for greater changes increases dramatically as time progresses in the future. This can be seen in Figure $4$, which displays a model of the predicted temperature increase. Notice that these changes occur relatively rapidly, and are not uniform across the globe. What might be some of the reasons for this?
Changes in precipitation occur due to a variety of factors, including changes in atmospheric water vapor content due to changing temperature, as discussed above. Also at play is the heightened evaporation rate of water on Earth’s surface under warmer temperatures. More evaporation leads to more precipitation. Finally, shifts in wind patterns impact the distribution of precipitation events. As you can see in Figure $5$, there are some areas of the globe that are expected to have an increase in precipitation, while others are expected to have a dramatic decrease. Some major population centers projected to have a moderate to severe precipitation increase include (population estimates of the metropolitan area given in parentheses): New York, United States (20.1 million); Bogotá, Colombia (12.1 m.); and Manila, Philippines (11.9 m.). What sort of challenges might these cities face in the future as they deal with this change in their climate?
In contrast, many more major metropolitan areas are projected to have a moderate to severe precipitation decrease (droughts) by the end of the 21st century. These include Delhi, India (21.8 m.); Lagos, Nigeria (21 m.); São Paulo, Brazil (20.9 m.); Kolkata, India (14.6 m.); Istanbul, Turkey (14.4 m.); Los Angeles, United States (13.3 m.); Rio de Janeiro, Brazil (12 m.); Paris, France (12 m.); and Lahore, Pakistan (11.3 m.). The largest challenge that these areas are likely to face is a dwindling water supply for drinking and agriculture. See Chapter 8 for more detail on challenges faced by societies to supply clean, reliable water to their populations and farms.
Additional challenges may be felt by all areas of the world with regard to changes in the seasonality or timing of precipitation, as well the form in which precipitation falls (e.g., mist or downpour; rain, ice, or snow). All of these factors affect the availability of soil water for plants, the flow of rivers and streams, and the overall accessibility of water worldwide. Furthermore, scientists predict an increase in the number and severity of storms as climate change progresses. For a full discussion of the potential impacts of this, see the assigned article.
Sea level rise While we know that water continuously cycles around the world, and that the overall quantity of water on Earth will not change due to global climate change, the distribution of this water is changing. In particular, oceans are increasing in volume while land ice stores (such as glaciers) are decreasing. This contributes to an increase in sea level worldwide (Figure $6$).
From the data in Figure $6$, we see that sea level has increased at an average of 0.06 inches (0.15 cm) per year over the time period shown above. Most of this rise, however, has occurred within the most recent decades. The rate of increase has gone up to between 0.11 to 0.14 inches (0.28 to 0.36 cm) per year since 1993. There are two forces causing sea level to rise, both caused by climate change. First, the increased global temperature has caused increased ice melting in many regions of the globe. Melting land ice (such as the glacier shown in Figure $7$) contributes to sea level rise because water that used to be stored in ice sitting on top of land becomes running water which reaches the ocean through runoff. We also observe sea ice melting (see http://www.epa.gov/climatechange/sci ence/indicators/index.html for data and figures). Sea ice, such as the ice that covers the arctic regions of the Northern Hemisphere, has no land underneath it. When it melts, the water stays in the same locations, and the overall sea level does not change.
The second factor that influences sea level rise is a phenomenon called thermal expansion. Due to the physical properties of water, as water warms, its density decreases. A less dense substance will have fewer molecules in a given area than a more dense substance (see Chapter 1 supplemental material). This means that as the overall temperature of the oceans increases due to global climate change, the same amount of water molecules will now occupy a slightly larger volume. This may not seem significant, but considering the 1.3 billion trillion liters (264 billion gallons) of water in the ocean, even a small change in density can have large effects on sea level as a whole.
Scientists have already documented sea level rise in some areas of the world, including one familiar to most of us: the Southeastern United States. Figure $8$ depicts the measured land area lost due to increasing sea level since 1996. Note that the Southeast (defined here as the Atlantic coast of North Carolina south to Florida) is particularly susceptible to land area loss due to the gently sloping nature of our coastline. Moving northward into the Mid-Atlantic States (defined here as Virginia north to Long Island, New York), coastal habitats tend to have a steeper geography, which protects against some losses.
While the ecological effects of sea level rise remain in the United States, we don’t project any catastrophic loss of life, property, or livelihood for some time. This is, in part, due to large investments that we have made in infrastructure to protect our cities and farmlands. This is not the case in many areas of the world. For a discussion of the impacts of sea level rise on less industrialized nations of Bangladesh, Maldives, Kiribati, and Fiji, review the required article reading.
Ocean acidification
Dissolved CO2 is essential for many organisms, including shell-building animals and other organisms that form a hard coating on their exterior (e.g., shellfish, corals, Haptophyte algae). This hard coating is built out of aragonite, a mineral form of the molecule calcium carbonate, CaCO3. These organisms rely on the formation of carbonate ions (see Chapter 1 supplemental material for information on ions), CO3 2-, from dissolved CO2, through a natural, chemical reaction that occurs. This takes place through a chain-reaction equation, where bicarbonate (HCO3- ) is formed as an intermediate, and hydrogen ions (H+ ) are generated (equations $1$ and $2$).
$CO_{2} + H_{2}O \leftrightarrow H^{+} + HCO_{3}^{-} \nonumber$
$HCO_{3}^{-} \leftrightarrow H^{+} + CO_{3}^{2-} \nonumber$
To have a better visualization of this process, follow along with the interactive graphic at: http://www.whoi.edu/home/oceanus_ima...ification.html.
As you can see, both equations $1$ and $2$ each produce one H+ . This is significant to water chemistry because an increase in H+ concentration means a decrease in the pH of the water. You can see in Figure $9$ that a lower pH means that the liquid is more acidic. As shown in the interactive graphic, an increase in CO2 in the atmosphere causes additional CO2 to be dissolved in the ocean. This means that more CO2 in the atmosphere leads to more acidic ocean environments.
Unfortunately for shell-building animals, the buildup of H+ in the more acidic ocean environment blocks the absorption of calcium and CO32-, and makes the formation of aragonite more difficult. An aragonite deficit is already being documented in many of the world’s oceans, as shown in Figure $10$.
The increasing acidity of the world’s oceans is resulting in habitat changes across the globe. This is only expected to worsen as atmospheric CO2 levels continue to increase. Many organisms, including the corals that are the foundation species of the beautiful coral reefs, are very sensitive to changes in ocean pH. Scientists have documented cases of ecosystem destruction through coral bleaching, caused by the effects of climate change including ocean acidification and increased temperature. For more information, visit the NOAA Coral Reef Conservation Program website: coralreef.noaa.gov/threats/climate/.
Climate Strategies
While the situation surrounding global climate change is in serious need of our attention, it is important to realize that many scientists, leaders, and concerned citizens are making solutions to climate change part of their life’s work. The two solutions to the problems caused by climate change are mitigation and adaptation, and we will likely need a combination of both in order to prosper in the future.
Adaptation strategies
We know that climate change is already occurring, as we can see and feel the effects of it. For this reason, it is essential to also adapt to our changing environment. This means that we must change our behaviors in response to the changing environment around us. Some adaptation strategies are discussed in the required article reading.
Adaption strategies will vary greatly by region, depending on the largest specific impacts in that area. For example, in the city of Delhi, India, a dramatic decrease in rainfall is projected over the next century (Figure 7.6.2). This city will likely need to implement policies and practices relating to conservation of water, for example: rainwater harvesting, water re-use, and increased irrigation efficiency. Rain-limited cities near oceans, such as Los Angeles, California may choose to use desalination to provide drinking water to their citizens. Desalination involves taking the salt out of seawater to make it potable (Chapter 14).
Cities with low elevations near oceans may need to implement adaptation strategies to rising sea levels, from seawalls and levees to relocation of citizens. One adaptations strategy gaining use is the creation or conservation of wetlands, which provide natural protection against storm surges and flooding.
Mitigation strategies
In general, a strategy to mitigate climate change is one that reduces the amount of greenhouse gases in the atmosphere or prevents additional emissions. Mitigations strategies attempt to “fix” the problems caused by climate change. Governmental regulations regarding fuel efficiency of vehicles is one example of an institutionalized mitigation strategy already in place in the United States and in many other countries around the world. Unlike some other countries, there are no carbon taxes or charges on burning fossil fuels in the United States. This is another governmental mitigation strategy that has been shown to be effective in many countries including India, Japan, France, Costa Rica, Canada, and the United Kingdom.
In addition to government measures and incentives, technology can also be harnessed to mitigate climate change. One strategy for this is the use of carbon capture and sequestration (CCS). Through CCS, 80-90% of the CO2 that would have been emitted to the atmosphere from sources such as a coal-fired power plant is instead captured and then stored deep beneath the Earth’s surface. The CO2 is often injected and sequestered hundreds of miles underground into porous rock formations sealed below an impermeable layer, where it is stored permanently (Figure $11$).
Scientists are also looking into the use of soils and vegetation for carbon storage potential. Proper management of soil and forest ecosystems has been shown to create additional carbon sinks for atmospheric carbon, reducing the overall atmospheric CO2 burden. Increasing soil carbon further benefits communities by providing better-quality soil for agriculture and cultivation.
Technologies related to alternative energy sources (Chapter 15) mitigate climate change by providing people with energy not derived from the combustion of fossil fuels. Finally, simple activities such as energy conservation, choosing to walk or bike instead of driving, and disposing of waste properly are activities that, when done by large numbers of people, actively mitigate climate change by preventing carbon emissions.
Take a moment to identify ways that you personally can be involved in the mitigation of or adaptation to climate change. What changes can you make in your own life to prevent excess carbon emissions? Similar to your ecological footprint, which you should have already calculated in lab, you can also calculate your carbon footprint. Use the EPA’s carbon footprint calculator to do so, and investigate the Reduce Your Emissions section to find ways to decrease your carbon footprint.
Recommendations from the US Environmental Protection Agency
Figure $12$ list various technologies and approaches that companies and individuals can adapt to reduce greenhouse gases. Technologies related to alternative energy sources mitigate climate change by providing people with energy not derived from the combustion of fossil fuels. Finally, simple activities such as energy conservation, choosing to walk or bike instead of driving, and disposing of waste properly are activities that, when done by large numbers of people, actively mitigate climate change by preventing carbon emissions.
Solutions for Transportation Air Pollution
Solutions for transportation air pollution, emission reductions, can lead to cleaner air and better health.
• Catalytic converters in conjunction with unleaded gasoline and low sulfur levels significantly reduce hydrocarbon and nitrogen oxide emissions.
• Fuel standards reduce exposure to pollutants like lead and benzene. Renewable fuels reduce CO2 emissions.
• Engine technologies like computer controls, variable valve timing, multi-valve engines, turbo charging and gasoline direct injection improve fuel economy and reduce CO2 emissions.
• Transmission technologies like 7+ speeds, dual clutch transmissions, (DCTs), and continuously variable transmissions (CVTs) improve fuel economy and reduce CO2 emissions.
• Diesel filters reduce particulate matter from on road and off road diesel engines. Alternative vehicle technologies like plug-in electric vehicles and fuel cells equals zero tailpipe emissions.
• Better transportation planning for passengers and freight reduce emissions and fuel use.
Summary
• Gases that trap heat in the atmosphere are called greenhouse gases.
• The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.
• Global warming refers to the increase in the average temperature of the Earth’s atmosphere due to elevated greenhouse gas concentrations, heightening the greenhouse effect.
• Climate change includes both global warming driven by human-induced emissions of greenhouse gasesand the resulting large-scale shifts in weather patterns.
• Greenhouse gases differ in their ability to produce the greenhouse effect as measured by the global warming potential, or GWP. A molecule of CH4 is about 28 times more effective than one of CO2 at absorbing infrared radiation, while N2O is 298 times more effective . The synthetic fluorinated gases are evn much higher (in the thousands). This is largely due to their very long residence time in the atmosphere.
• Different technologies and approaches recommended by the US EPA to to reduce human greenhouse emmissions were provided.
Contributors and Attributions
• Libretext: Introduction to Environmental Science (Zendher et al.)
• US EPA
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.09%3A_Carbon_Dioxide_and_Climate_Change.txt |
Learning Objectives
• Know the EPA standards for criteria air pollutants.
• Know the sources, health, and environmental effects of criteria air pollutants.
The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for pollutants considered harmful to public health and the environment. The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.
The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" air pollutants. Periodically, the standards are reviewed and may be revised. The current standards are listed in Table \(1\). Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3).
Table \(1\) National Ambient Air Quality Standards for Criteria Air Pollutants.
Pollutant
[links to historical tables of NAAQS reviews]
Primary/
Secondary
Averaging Time Level Form
Carbon Monoxide (CO) primary 8 hours 9 ppm Not to be exceeded more than once per year
1 hour 35 ppm
Lead (Pb) primary and
secondary
Rolling 3 month average 0.15 μg/m3 (1) Not to be exceeded
Nitrogen Dioxide (NO2) primary 1 hour 100 ppb 98th percentile of 1-hour daily maximum concentrations, averaged over 3 years
primary and
secondary
1 year 53 ppb (2) Annual Mean
Ozone (O3) primary and
secondary
8 hours 0.070 ppm (3) Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years
Particle Pollution (PM) PM2.5 primary 1 year 12.0 μg/m3 annual mean, averaged over 3 years
secondary 1 year 15.0 μg/m3 annual mean, averaged over 3 years
primary and
secondary
24 hours 35 μg/m3 98th percentile, averaged over 3 years
PM10 primary and
secondary
24 hours 150 μg/m3 Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide (SO2) primary 1 hour 75 ppb (4) 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
secondary 3 hours 0.5 ppm Not to be exceeded more than once per year
(1) In areas designated nonattainment for the Pb standards prior to the promulgation of the current (2008) standards, and for which implementation plans to attain or maintain the current (2008) standards have not been submitted and approved, the previous standards (1.5 µg/m3 as a calendar quarter average) also remain in effect.
(2) The level of the annual NO2 standard is 0.053 ppm. It is shown here in terms of ppb for the purposes of clearer comparison to the 1-hour standard level.
(3) Final rule signed October 1, 2015, and effective December 28, 2015. The previous (2008) O3 standards additionally remain in effect in some areas. Revocation of the previous (2008) O3 standards and transitioning to the current (2015) standards will be addressed in the implementation rule for the current standards.
(4) The previous SO2 standards (0.14 ppm 24-hour and 0.03 ppm annual) will additionally remain in effect in certain areas: (1) any area for which it is not yet 1 year since the effective date of designation under the current (2010) standards, and (2)any area for which an implementation plan providing for attainment of the current (2010) standard has not been submitted and approved and which is designated nonattainment under the previous SO2 standards or is not meeting the requirements of a SIP call under the previous SO2 standards (40 CFR 50.4(3)). A SIP call is an EPA action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the required NAAQS.
Table \(2\) list the sources and harmful effects of criteria pollutants.
Table \(2\) Sources, Health and Environmental Effects of Criteria Pollutants.
Pollutant Sources Health Effects Environmental Effects
Ground-level Ozone (O3) Secondary pollutant typically formed by chemical reaction of volatile organic compounds (VOCs) and NOx in the presence of sunlight. Decreases lung function and causes respiratory symptoms, such as coughing and shortness of breath; aggravates asthma and other lung diseases leading to increased medication use, hospital admissions, emergency department (ED) visits, and premature mortality. Ozone affects sensitive vegetation and ecosystems, including forests, parks, wildlife refuges and wilderness areas. In particular, ozone harms sensitive vegetation during the growing season.
Particulate Matter (PM) Emitted or formed through chemical reactions; fuel combustion (e.g., burning coal, wood, diesel); industrial processes; agriculture (plowing, field burning); and unpaved roads. Short-term exposures can aggravate heart or lung diseases leading to respiratory symptoms, increased medication use, hospital admissions, ED visits, and premature mortality; long-term exposures can lead to the development of heart or lung disease and premature mortality.
Visibility impairment
Fine particles (PM2.5) are the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.
Environmental damage
Particles can be carried over long distances by wind and then settle on ground or water. Depending on their chemical composition, the effects of this settling may include:
· making lakes and streams acidic
· changing the nutrient balance in coastal waters and large river basins
· depleting the nutrients in soil
· damaging sensitive forests and farm crops
· affecting the diversity of ecosystems
· contributing to acid rain effects.
Materials damage
PM can stain and damage stone and other materials, including culturally important objects such as statues and monuments. Some of these effects are related to acid rain effects on materials.
Lead Smelters (metal refineries) and other metal industries; combustion of leaded gasoline in piston engine aircraft; waste incinerators; and battery manufacturing. Damages the developing nervous system, resulting in IQ loss and impacts on learning, memory, and behavior in children. Cardiovascular and renal effects in adults and early effects related to anemia. Lead is persistent in the environment and can be added to soils and sediments through deposition from sources of lead air pollution. Other sources of lead to ecosystems include direct discharge of waste streams to water bodies and mining. Elevated lead in the environment can result in decreased growth and reproductive rates in plants and animals, and neurological effects in vertebrates.
Oxides of Nitrogen (NOx) Fuel combustion (e.g., electric utilities, industrial boilers, and vehicles) and wood burning. Aggravate lung diseases leading to respiratory symptoms, hospital admissions, and ED visits; increased susceptibility to respiratory infection.
NO2 and other NOx interact with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain harms sensitive ecosystems such as lakes and forests.
NOx in the atmosphere contributes to nutrient pollution in coastal waters.
Carbon Monoxide (CO) Fuel combustion (especially vehicles), industrial processes, fires, waste combustion, and residential wood burning. Reduces the amount of oxygen reaching the body’s organs and tissues; aggravates heart disease, resulting in chest pain and other symptoms leading to hospital admissions and ED visits.
Sulfur Dioxide (SO2) Fuel combustion (especially high-sulfur coal); electric utilities and industrial processes; and natural sources such as volcanoes. Aggravates asthma and increased respiratory symptoms. Contributes to particle formation with associated health effects.
At high concentrations, gaseous SOx can harm trees and plants by damaging foliage and decreasing growth.
SO2 and other sulfur oxides can contribute to acid rain which can harm sensitive ecosystems.
Source: www.epa.gov
The likelihood of immediate reactions to air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. Some sensitive individuals appear to be at greater risk for air pollution-related health effects, for example, those with pre-existing heart and lung diseases (e.g., heart failure/ischemic heart disease, asthma, emphysema, and chronic bronchitis), diabetics, older adults, and children. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.
Paying the Price
Pollution has a cost. Manufacturing activities that cause air pollution impose health and clean-up costs on the whole of society, whereas the neighbors of an individual who chooses to fire-proof his home may benefit from a reduced risk of a fire spreading to their own homes. A manufacturing activity that causes air pollution is an example of a negative externality in production. A negative externality in production occurs “when a firm’s production reduces the well-being of others who are not compensated by the firm." For example, if a laundry firm exists near a polluting steel manufacturing firm, there will be increased costs for the laundry firm because of the dirt and smoke produced by the steel manufacturing firm. If external costs exist, such as those created by pollution, the manufacturer will choose to produce more of the product than would be produced if the manufacturer were required to pay all associated environmental costs. Because responsibility or consequence for self-directed action lies partly outside the self, an element of externalization is involved. If there are external benefits, such as in public safety, less of the good may be produced than would be the case if the producer were to receive payment for the external benefits to others. However, goods and services that involve negative externalities in production, such as those that produce pollution, tend to be over-produced and underpriced since the externality is not being priced into the market.
Pollution can also create costs for the firms producing the pollution. Sometimes firms choose, or are forced by regulation, to reduce the amount of pollution that they are producing. The associated costs of doing this are called abatement costs, or marginal abatement costs if measured by each additional unit. In 2005 pollution abatement capital expenditures and operating costs in the US amounted to nearly \$27 billion.
Summary
• The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" air pollutants.
• The six criteria pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide.
• The key air pollutants can cause various environmental and health problems that could affect the respiratory, nervous, and cardiovascular systems.
• US EPA
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/13%3A_Air/13.10%3A__Who_Pollutes_Who_Pays.txt |
Thumbnail: Acid mine drainage in the Rio Tinto River. (Public Domain; Carol Stoker @ NASA via ).
14: Water
LEARNING OBJECTIVE
Describe the different properties of water as it relates to its polarity and ability to form hydrogen bonds.
Looking Closer: Water, the Most Important Liquid
Earth is the only known body in our solar system that has liquid water existing freely on its surface. That is a good thing because life on Earth would not be possible without the presence of liquid water. Water is a simple molecule consisting of one oxygen atom bonded to two different hydrogen atoms (Figure $1$). Because of the higher electronegativity of the oxygen atom, the bonds are polar covalent (polar bonds). The oxygen atom attracts the shared electrons of the covalent bonds to a significantly greater extent than the hydrogen atoms. As a result, the oxygen atom requires a partial negative charge $\left( \delta - \right)$, while the hydrogen atoms each acquire a partial positive charge $\left( \delta + \right)$. The molecule adopts a bent structure because of the two lone pairs of electrons on the oxygen atom. The $\ce{H-O-H}$ bond angle is about $105^\text{o}$, slightly smaller than the ideal $109.5^\text{o}$ of an $sp^3$ hybridized atomic orbital.The bent shape of the water molecule is critical because the polar $\ce{O-H}$ bonds do not cancel one another and the molecule as a whole is polar.
Hydrogen Bonds
Due to water’s polarity, each water molecule attracts other water molecules as oppositely charged ends of the molecules attract each other. When this happens, a weak interaction occurs between the positive hydrogen end from one molecule and the negative oxygen end of another molecule. This interaction is called a hydrogen bond. This hydrogen bonding contributes to the following water’s unique properties.
1. Water is the universal solvent
2. Exists in nature as a solid, liquid, and gas
3. The density of ice is less than liquid water
4. Water has a high heat capacity
5. Water has a high heat of vaporization
6. Water exists as a liquid at room temperature It is important to note here that even we are only focusing on water in this text book, hydrogen bonding also occurs in other substances that have polar molecules.
Density of Water
Liquid water is a fluid. The hydrogen bonds in liquid water constantly break and reform as the water molecules tumble past one another. As water cools, its molecular motion slows and the molecules move gradually closer to one another. The density of any liquid increases as its temperature decreases. For most liquids, this continues as the liquid freezes and the solid state is denser than the liquid state. However, water behaves differently (Table $1$) . It actually reaches its highest density at about $4^\text{o} \text{C}$.
Temperature $\left( ^\text{o} \text{C} \right)$ Density $\left( \text{g/cm}^3 \right)$
Table $1$ Density of Water and Ice
100 (liquid) 0.9584
50 0.9881
25 0.9971
10 0.9997
4 1.0000
0 (liquid) 0.9998
0 (solid) 0.9168
Between $4^\text{o} \text{C}$ and $0^\text{o} \text{C}$, the density gradually decreases as the hydrogen bonds begin to form a network characterized by a generally hexagonal structure with open spaces in the middle of the hexagons (Figure $2$ ).
Ice is less dense than liquid water and so it floats. Ponds or lakes begin to freeze at the surface, closer to the cold air. A layer of ice forms, but does not sink as it would if water did not have this unique structure dictated by its shape, polarity, and hydrogen bonding. If the ice were to sink as it froze, entire lakes would freeze solid. Since the ice does not sink, liquid water remains under the ice all winter long. This is important, as fish and other organisms are capable of surviving through winter. Ice is one of only a very few solids that is less dense than its liquid form.
Solvation Ability of Water
Water typically dissolves many ionic compounds and polar molecules. Nonpolar molecules such as those found in grease or oil do not dissolve in water. We will first examine the process that occurs when an ionic compound such as table salt (sodium chloride) dissolves in water.
Water is attracted to the sodium chloride crystal because water is polar and has both a positive and a negative end. The positively charged sodium ions in the crystal attract the oxygen end of the water molecules because they are partially negative. The negatively charged chloride ions in the crystal attract the hydrogen end of the water molecules because they are partially positive. The action of the polar water molecules takes the crystal lattice apart (see Figure $3$) .
After coming apart from the crystal, the individual ions are then surrounded by solvent particles in a process called solvation. Note that the individual $\ce{Na^+}$ ions are surrounded by water molecules with the oxygen atom oriented near the positive ion. Likewise, the chloride ions are surrounded by water molecules with the opposite orientation. Hydration is the process of solute particles being surrounded by water molecules arranged in a specific manner. Hydration helps to stabilize aqueous solutions by preventing the positive and negative ions from coming back together and forming a precipitate.
Table sugar is sucrose $\left( \ce{C_{12}H_{22}O_{11}} \right)$ and is an example of a molecular compound. Solid sugar consists of individual sugar molecules held together by intermolecular attractive forces. When water dissolves sugar, it separates the individual sugar molecules by disrupting the attractive forces, but does not break the covalent bonds between the carbon, hydrogen, and oxygen atoms. Dissolved sugar molecules are also hydrated, but without as distinct an orientation to the water molecules as in the case of the ions. The sugar molecules contain many $\ce{-OH}$ groups that can form hydrogen bonds with the water molecules, helping form the sucrose solution.
The Amphoteric Nature of Water
Water is amphoteric: it has the ability to act as either an acid or a base in chemical reactions. According to the Brønsted-Lowry definition, an acid is a proton (H+) donor and a base is a proton acceptor. When reacting with a stronger acid, water acts as a base; when reacting with a stronger base, it acts as an acid. For instance, water receives an H+ ion from HCl when hydrochloric acid is formed:
HCl(acid) + H2O(base) ⇌ H3O+ + Cl
In the reaction with ammonia, NH3, water donates a H+ ion, and is thus acting as an acid:
NH3(base) + H2O(acid) ⇌ NH+4 + OH
High Heat Capacity and Specific Heat of Water
Different substances respond to heat in different ways. If a metal chair sits in the bright sun on a hot day, it may become quite hot to the touch. An equal mass of water in the same sun will not become nearly as hot. Table $2$ list specific heats of various substances compared to water.Water has the highest specific heat capacity of any liquid. Water’s high heat capacity is a property caused by hydrogen bonding among the water molecules. Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius. For water, this amount is 1 cal/goC. The units for specific heat can either be in the SI units of joules per gram per degree $\left( \text{J/g}^\text{o} \text{C} \right)$ or calories per gram per degree $\left( \text{cal/g}^\text{o} \text{C} \right)$. This text will use $\text{J/g}^\text{o} \text{C}$ for specific heat.
It takes water a long time to heat up and a long time to cool down. In fact, the specific heat capacity of water is about five times more than that of sand. This explains why land cools faster than the sea. Coastal climates are much more moderate than inland climates because of the presence of the ocean. Water in lakes or oceans absorbs heat from the air on hot days and releases it back into the air on cool days. Water is used as a coolant for machinery because it is able to absorb large quantities of heat (Figure $4$). Due to its high heat capacity, warm-blooded animals use water to disperse heat more evenly and maintain temperature in their bodies: it acts in a similar manner to a car’s cooling system, transporting heat from warm places to cool places, causing the body to maintain a more even temperature.
Substance Specific Heat $\left( \text{J/g}^\text{o} \text{C} \right)$
Table $2$ Specific Heats of Some Common Substances
Water (l) 4.18
Water (s) 2.06
Water (g) 1.87
Ammonia (g) 2.09
Ethanol (l) 2.44
Aluminum (s) 0.897
Carbon, graphite (s) 0.709
Copper (s) 0.385
Gold (s) 0.129
Iron (s) 0.449
Lead (s) 0.129
Mercury (l) 0.140
Silver (s) 0.233
High Heat of Vaporization of Water
Water in its liquid form has an unusually high boiling point temperature, a value close to 100°C. As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, an energy requirement called the heat of vaporization. Water has a heat of vaporization value of 40.65 kJ/mol. A considerable amount of heat energy (586 calories) is required to accomplish this change in water. This process occurs on the surface of water. As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other, which is required for it to enter its gaseous phase (steam). As a result, water acts as a heat sink, or heat reservoir, and requires much more heat to boil than does a liquid such as ethanol (grain alcohol), whose hydrogen bonding with other ethanol molecules is weaker than water’s hydrogen bonding.
The fact that hydrogen bonds need to be broken for water to evaporate means that a substantial amount of energy is used in the process. As the water evaporates, energy is taken up by the process, cooling the environment where the evaporation is taking place. In many living organisms, including humans, the evaporation of sweat, which is 90 percent water, allows the organism to cool so that homeostasis of body temperature can be maintained.
Summary
• The polarity of water and its ability to hydrogen bond contributes to its unique properties.
• Ionic solute molecules are hydrated (surrounded by solvent molecules in a specific orientation).
• Ice is less dense than liquid water due to spaces in the intermolecular structure of ice not present in water.
• Heat capacity is the amount of heat required to raise the temperature of an object by $1^\text{o} \text{C}$).
• The specific heat of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by $1^\text{o} \text{C}$.
• The dissociation of liquid water molecules, which changes the substance to a gas, requires a lot of energy.
Contributors and Attributions
• Boundless: The Chemical Foundation of Life
• Libretext: Introduction to Environmental Science (Zendher et al.)
• TextMap: Introductory Chemistry (Tro) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.01%3A_Water_-_Some_Unique_Properties.txt |
Learning Objectives
• Know the distribution of earth's water.
• Describe the water (hydrologic) cycle.
• Know the different natural water contaminants
Water 's influence on the world around us is affected by its unique properties some of which where discussed in the previous section. Without water, life might not be able to exist on Earth, and it certainly would not have the tremendous complexity and diversity that we see.
Distribution of Earth's Water
Earth’s oceans contain 97% of the planet’s water, so just 3% is fresh water, water with low concentrations of salts (Figure $1$). The majority of the Earth's water can be classified as being saline (or salt containing). Most freshwater is trapped as ice in the vast glaciers and ice sheets of Greenland. A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir.
The Water (Hydrologic) Cycle and Natural Contaminants
Because Earth’s water is present in all three states, it can get into a variety of environments around the planet. The movement of water around Earth’s surface is the water cycle (Figure $2$).
Water changes from a liquid to a gas by evaporation to become water vapor. The Sun’s energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a freshwater reservoir. The water vapor remains in the atmosphere until it undergoes condensation and then precipitation. Precipitation can be rain, sleet, hail, or snow. At the surface, water or melted water, may eventually evaporate and reenter the atmosphere. A significant amount of water infiltrates into the ground. Water may seep through dirt and rock below the soil through pores infiltrating the ground to go into Earth’s groundwater system (Figure $\PageIndex3}$). Groundwater enters aquifers which are bodies of rock or sediment that store (and yield) large amounts of usable water in their pores. Alternatively, the water may come to the surface through springs or find its way back to the oceans.
Substances Present in Natural Waters
The amounts of water present in the atmosphere and on land (as surface runoff, lakes and streams) is great enough to make it a significant agent in transporting substances between the lithosphere (the rigid surface of the earth) and the oceans. Water interacts with both the atmosphere and the lithosphere (the rigid surface of the earth) acquiring solutes from each, and thus provides the major chemical link between these two realms. The various transformations undergone by water through the different stages of the hydrologic cycle act to transport both dissolved and particulate substances between different geographic locations.
The Safe Drinking Water Act defines the term "contaminant" as meaning any physical, chemical, biological, or radiological substance or matter in water. Therefore, the law defines "contaminant" very broadly as being anything other than water molecules.
Gases
The carbon dioxide in natural water creates an interesting phenomenon. Rainwater is saturated with CO2, and it dissolves limestones. When CO2 is lost due to temperature changes or escaping from water drops, the reverse reaction takes place. The solid formed, however, may be a less stable phase called aragonite, which has the same chemical formula as, but a different crystal structure than that of calcite.
The rain dissolves calcium carbonate by the two reactions shown above. The water carries the ions with it, sips through the crack of the rocks. When it reached the ceiling of a cave, the drop dangles there for a long time before fallen. During this time, the carbon dioxide escapes and the pH of the water increases. Calcium carbonate crystals begin to appear. Calcite, aragonite, stalactite, and stalagmite are four common solids found in the formation of caves.
Dissolved Minerals
Table $1$ list the major ions present in seawater. The composition does vary, depending on region, depth, latitude, and water temperature. Waters at the river mouths contain less salt. If the ions are utilized by living organism, its contents vary according to the populations of organisms.
Dust particles and ions present in the air are nucleation center of water drops. Thus, waters from rain and snow also contain such ions: Ca2+, Mg2+, Na+, K+, NH4+. These cations are balanced by anions, HCO3-, SO4-, NO2-, Cl-, and NO3-. The pH of rain is between 5.5 and 5.6. Rain and snow waters eventually become river or lake waters. When the rain or snow waters fall, they interact with vegetation, top soil, bed rock, river bed and lake bed, dissolving whatever is soluble. Bacteria, algae, and water insects also thrive. Solubilities of inorganic salts are governed by the kinetics and equilibria of dissolution. The most common ions in lake and river waters are the same as those present in rainwater, but at higher concentrations. The pH of these waters depends on the river bed and lake bed. Natural waters contain dissolved minerals. Waters containing Ca2+ and Mg2+ ions are usually called hard water.
cations
g/kg
anions
g/kg
Table 1 Major Ions in Seawater (These values, expressed in parts per thousand, are for seawater of 35% salinity).
Na+
10.77
Cl
19.354
Mg2+
1.29
SO42–
2.712
Ca2+
0.412
Br
0.087
K+
0.399
Sr2+
0.0079
Al3+
0.005
Note
Although most elements are found in seawater only at trace levels, marine organisms may selectively absorb them and make them more detectable. Iodine, for example, was discovered in marine algae (seaweeds) 14 years before it was found in seawater. Other elements that were not detected in seawater until after they were found in marine organisms include barium, cobalt, copper, lead, nickel, silver and zinc. Si-32, presumably deriving from cosmic ray bombardment of Ar, has been discovered in marine sponges.
Hard Water
Minerals usually dissolve in natural water bodies such as lakes, rivers, springs, and underground waterways (ground waters). Calcium carbonate, CaCO3, is one of the most common inorganic compounds in the Earth crust. It is the ingredient for both calcite and aragonite. These two minerals have different crystal structures and appearance. This photograph shows crystals of typical Calcite.
Calcium-carbonate minerals dissolve in water, with a solubility product as shown below.
$CaCO_3 \rightleftharpoons Ca^{2+} + CO_3^{2-} \;\;\; K_{sp} = 5 \times 10^{-9} \nonumber$
From the solubility product, we can (see example 1) evaluate the molar solubility to be 7.1x10-5 M or 7.1 mg/L (7.1 ppm of CaCO3 in water). The solubility increases as the pH decrease (increase acidity). This is compounded when the water is saturated with carbon dioxide, CO2. Saturated CO2 solution contains carbonic acid, which help the dissolution due to the reaction:
$H_2O + CO_2 \rightleftharpoons H_2CO_3 \nonumber$
$CaCO_3 + H_2CO_3 \rightleftharpoons Ca^{2+} + 2 HCO_3^- \nonumber$
Because of these reactions, some natural waters contain more than 300 ppm calcium carbonates or its equivalents.
The composition of the ocean has attracted the attention of some of the more famous names in science, including Robert Boyle, Antoine Lavoisier and Edmund Halley. Their early investigations tended to be difficult to reproduce, owing to the different conditions under which they crystallized the various salts. As many as 54 salts, double salts and hydrated salts can be obtained by evaporating seawater to dryness. At least 73 elements are now known to be present in seawater.
Organic Matter
Most of the organic carbon in seawater is present as dissolved material, with only about 1-2% in particulates. The total organic carbon content ranges between 0.5 mg/L in deep water to 1.5 mg/L near the surface. There is still considerable disagreement about the composition of the dissolved organic matter; much of it appears to be of high molecular weight, and may be polymeric. Substances qualitatively similar to the humic acids found in soils can be isolated. The greenish color that is often associated with coastal waters is due to a mixture of fluorescent, high molecular weight substances of undetermined composition known as “Gelbstoffe”. It is likely that the significance of the organic fraction of seawater may be much greater than its low abundance would suggest. For one thing, many of these substances are lipid-like and tend to adsorb onto surfaces. It has been shown that any particle entering the ocean is quickly coated with an organic surface film that may influence the rate and extent of its dissolution or decomposition. Certain inorganic ions may be strongly complexed by humic-like substances. The surface of the ocean is mostly covered with an organic film, only a few molecular layers thick. This is believed to consist of hydrocarbons, lipids, and the like, but glycoproteins and proteoglycans have been reported. If this film is carefully removed from a container of seawater, it will quickly be reconstituted. How significant this film is in its effects on gas exchange with the atmosphere is not known.
Summary
• The water (hydrologic) cycle describes the continuous movement of water on, above and below the surface of the Earth. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, surface runoff, and subsurface flow. In doing so, the water goes through different forms: liquid, solid (ice) and capor.
• Different substances that can be found in natural waters include dissolved minerals, dissolved gases, and organic matter. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.02%3A_Water_in_Nature.txt |
Learning Objective
• Describe the impact of human activities on water quality.
The global water crisis also involves water pollution. For water to be useful for drinking and irrigation, it must not be polluted beyond certain thresholds. According to the World Health Organization, in 2008 approximately 880 million people in the world (or 13% of world population) did not have access to safe drinking water. At the same time, about 2.6 billion people (or 40% of world population) lived without improved sanitation, which is defined as having access to a public sewage system, septic tank, or even a simple pit latrine. Each year approximately 1.7 million people die from diarrheal diseases associated with unsafe drinking water, inadequate sanitation, and poor hygiene. Almost all of these deaths are in developing countries, and around 90% of them occur among children under the age of 5 (Figure 1). Compounding the water crisis is the issue of social justice; poor people more commonly lack clean water and sanitation than wealthy people in similar areas. Globally, improving water safety, sanitation, and hygiene could prevent up to 9% of all disease and 6% of all deaths.
In addition to the global waterborne disease crisis, chemical pollution from agriculture, industry, cities, and mining threatens global water quality. In Gallup public polls conducted over the past decade Americans consistently put water pollution and water supply as the top environmental concerns over issues such as air pollution, deforestation, species extinction, and global warming.
Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and/or the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical, or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes can cause water pollution, most pollution is derived from human, land-based activities. Water pollutants can move through different water reservoirs, as the water carrying them progresses through stages of the water cycle.
Pollutants enter water supplies from point sources, which are readily identifiable and relatively small locations, or nonpoint sources, which are large and more diffuse areas (Figure $1$) . Point sources of pollution include animal factory farms that raise a large number and high density of livestock such as cows, pigs, and chickens. Also, pipes included are pipes from a factories or sewage treatment plants. Combined sewer systems that have a single set of underground pipes to collect both sewage and storm water runoff from streets for wastewater treatment can be major point sources of pollutants. During heavy rain, storm water runoff may exceed sewer capacity, causing it to back up and spilling untreated sewage directly into surface waters.
This section and the next will focus on how human activities affect water quality.
Too Much Organic Matter Means Too Little Oxygen
Oxygen-demanding waste is an extremely important pollutant to ecosystems. Most surface water in contact with the atmosphere has a small amount of dissolved oxygen, which is needed by aquatic organisms for cellular respiration. Bacteria decompose dead organic matter and remove dissolved oxygen (O2) according to the following reaction:
$\text{organic matter} + O_{2} \rightarrow CO_{2} + H_{2} O \nonumber$
Too much decaying organic matter in water is a pollutant because it removes oxygen from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen used by aerobic (in the presence of oxygen) bacterial decomposition of organic matter is called biochemical oxygen demand (BOD). The major source of dead organic matter in many natural waters is sewage; grass and leaves are smaller sources. An unpolluted water body with respect to BOD is a turbulent river that flows through a natural forest. Turbulence continually brings water in contact with the atmosphere where the O2 content is restored. The dissolved oxygen content in such a river ranges from 10 to 14 ppm O2, BOD is low, and clean-water fish such as trout. A polluted water body with respect to oxygen is a stagnant deep lake in an urban setting with a combined sewer system. This system favors a high input of dead organic carbon from sewage overflows and limited chance for water circulation and contact with the atmosphere. In such a lake, the dissolved O2 content is ≤5 ppm O2, BOD is high, and low O2-tolerant fish, such as carp and catfish dominate.
Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients for growth, most of which are plentiful in water. N and P are called limiting nutrients, however, because they usually are present in water at low concentrations and therefore restrict the total amount of plant growth. This explains why N and P are major ingredients in most fertilizer. High concentrations of N and P from human sources (mostly agricultural and urban runoff including fertilizer, sewage, and phosphorus-based detergent) can cause cultural eutrophication, which leads to the rapid growth of aquatic producers, particularly algae. Thick mats of floating algae or rooted plants lead to a form of water pollution that damages the ecosystem by clogging fish gills and blocking sunlight. A small percentage of algal species produce toxins that can kill animals, including humans. Exponential growths of these algae are called harmful algal blooms. When the prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low O2 concentrations in the water (< 2 ppm O2), a condition called hypoxia. This results in a dead zone because it causes death from asphyxiation to organisms that are unable to leave that environment. An estimated 50% of lakes in North America, Europe, and Asia are negatively impacted by cultural eutrophication. In addition, the size and number of marine hypoxic zones have grown dramatically over the past 50 years including a very large dead zone located offshore Louisiana in the Gulf of Mexico. Cultural eutrophication and hypoxia are difficult to combat, because they are caused primarily by nonpoint source pollution, which is difficult to regulate, and N and P, which are difficult to remove from wastewater.
Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.
Chemical Pollution from Waste
Since the 1990s, water contamination by pharmaceuticals has been an environmental issue of concern. In addition, it is important to note that many public health professionals in the United States began writing reports of pharmaceutical contamination in waterways in the 1970s.” Most pharmaceuticals are deposited in the environment through human consumption and excretion, and are often filtered ineffectively by municipal sewage treatment plants which are not designed to manage them (Figure $2$) . Once in the water, they can have diverse, subtle effects on organisms, although research is still limited. Pharmaceuticals may also be deposited in the environment through improper disposal, runoff from sludge fertilizer and reclaimed wastewater irrigation, and leaky sewer pipes. In 2009, an investigative report by Associated Press concluded that U.S. manufacturers had legally released 271 million pounds of compounds used as drugs into the environment, 92% of which was the industrial chemicals phenol and hydrogen peroxide, which are also used as antiseptics. It could not distinguish between drugs released by manufacturers as opposed to the pharmaceutical industry. It also found that an estimated 250 million pounds of pharmaceuticals and contaminated packaging were discarded by hospitals and long-term care facilities.
The use of pharmaceuticals and personal care products (PPCPs) is on the rise with an estimated increase from 2 billion to 3.9 billion annual prescriptions between 1999 and 2009 in the United States alone. Figure $3$ illustrates how PPCPs enter into the environment through individual human activity and as residues from manufacturing, agribusiness, veterinary use, and hospital and community use. In Europe, the input of pharmaceutical residues via domestic waste water is estimated to be around 80% whereas 20% is coming from hospitals. Individuals may add PPCPs to the environment through waste excretion and bathing as well as by directly disposing of unused medications to septic tanks, sewers, or trash. Because PPCPs tend to dissolve relatively easily and do not evaporate at normal temperatures, they often end up in soil and water bodies.
Some PPCPs are broken down or processed easily by a human or animal body and/or degrade quickly in the environment . However, others do not break down or degrade easily. The likelihood or ease with which an individual substance will break down depends on its chemical makeup and the metabolic pathway of the compound.
While the full effects of most PPCPs on the environment are not understood, there is concern about the potential they have for harm because they may act unpredictably when mixed with other chemicals from the environment or concentrate in the food chain. Additionally, some PPCPs are active at very low concentrations, and are often released continuously in large or widespread quantities.
Because of the high solubility of most PPCPs, aquatic organisms are especially vulnerable to their effects. The increased presence of estrogen and other synthetic hormones in waste water due to birth control and hormonal therapies has been linked to increased feminization of exposed fish and other aquatic organisms. The chemicals within these PPCP products could either affect the feminization or masculinization of different fishes, therefore affecting their reproductive rates.
The major route for pharmaceutical residues to reach the aquatic environment is most probably by excretion from patients undergoing pharma treatment. Since many pharmaceutical substances are not metabolized in the body they may be excreted in biologically active form, usually via the urine. Furthermore, many pharmaceutical substances are not fully taken up from the intestine (following oral administration in patients) into their blood stream. The fraction not taken up into the blood stream will remain in the gut and eventually be excreted via the faeces. Hence, both urine and faeces from treated patients contain pharmaceutical residues. Between 30 and 90% of the orally administered dose is generally excreted as active substance in the urine.
An additional source to environmental pollution with pharmaceuticals is improper disposal of unused or expired drug residues. In European countries take-back systems for such residues are usually in place (although not always utilized to full extent) while in e.g. the US only voluntary initiatives on a local basis exist. Though most of the waste goes to incineration and people are asked to throw unused or expired pharmaceuticals into the household waste investigations in Germany showed that up to 24% of liquid pharmaceuticals and 7% of tablets or ointments are disposed always or at least “rarely” via the toilet or sink.
Proper destruction of pharma residues should yield rest products without any pharmaceutical or ecotoxic activity. Furthermore, the residues should not act as components in the environmental formation of new such products. Incineration at a high temperature (>1000 degrees Celsius) is considered to fulfill the requirements, but even following such incineration residual ashes from the incineration should be properly taken care of.
Pharmaceuticals used in veterinary medicine, or as additives to animal food, pose a different problem, since they are excreted into soil or possibly open surface waters. It is well known that such excretions may affect terrestrial organisms directly, leading to extinction of exposed species (e.g. dung-beetles). Lipid-soluble pharma residues from veterinary use may bind strongly to soil particles, with little tendency to leak out to ground water or to local surface waters. More water-soluble residues may be washed out with rain or melting snow and reach both ground water and surface water streams.
Water Borne Diseases
Waterborne diseases are conditions caused by pathogenic micro-organisms that are transmitted in water. These diseases can be spread while bathing, washing, drinking water, or by eating food exposed to contaminated water. While diarrhea and vomiting are the most commonly reported symptoms of waterborne illness, other symptoms can include skin, ear, respiratory, or eye problems. Waterborne diseases are impacted by a country's economy and also impact the economy by being costly to deal with.
Microorganisms causing diseases that characteristically are waterborne prominently include protozoa and bacteria, many of which are intestinal parasites, or invade the tissues or circulatory system through walls of the digestive tract. Various other waterborne diseases are caused by viruses. (In spite of philosophical difficulties associated with defining viruses as "organisms", it is practical and convenient to regard them as microorganisms in this connection.)
Yet other important classes of water-borne diseases are caused by metazoan parasites. Typical examples include certain Nematoda, that is to say "roundworms". As an example of water-borne Nematode infections, one important waterborne nematode disease is Dracunculiasis. It is acquired by swallowing water in which certain copepoda occur that act as vectors for the Nematoda. Anyone swallowing a copepod that happens to be infected with Nematode larvae in the genus Dracunculus, becomes liable to infection. The larvae cause guinea worm disease.
Another class of waterborne metazoan pathogens are certain members of the Schistosomatidae, a family of blood flukes. They usually infect victims that make skin contact with the water. Blood flukes are pathogens that cause Schistosomiasis of various forms, more or less seriously affecting hundreds of millions of people worldwide.
Video $1$ The Coalition for Global Community Health is working within existing social structures in Belén, Iquitos, Peru to uphold the human rights of the community members. We speak directly with community members in an open forum to learn about their needs, desires, and ideas for creating an opportunity to change their communities for the better
The table below shows water-borne diseases that can result from viruses, bacteria, and parasites. In some cases, vaccines are available. When eating, drinking, or swimming, it is important to be aware of how you could be affected by these pathogens. Sanitation of drinking water with chlorine-based compounds reduces the power of these pathogens. In addition, proper handling of foods and beverages could reduce your risk of developing one or more of the following health problems.
Table $1$ Pathogens That Cause Waterborne Illnesses.
Pathogen Name Pathogen Type Source Health problem Prevention/Treatment
Giardia Parasite Fecal contamination and uncooked food Vomiting, diarrhea, and cramps Medication afterward
Cryptosporidium Parasite Fecal contamination Vomiting, diarrhea, fever, and cramps Medication afterward
Typhoid Bacteria Fecal contamination High fever, stomach pains, headache, and rash Vaccination/Antibiotics
E. coli Bacteria Fecal contamination Diarrhea and cramps Fluids
Legionella Bacteria Found naturally in heated water Causes Legionnaires (a type of pneumonia) Medications afterward
Cholera Bacteria Related to fecal contamination or undercooked or raw shellfish Diarrhea Vaccine/Rehydration, antibiotics, and Zinc
Hepatitis A Virus Contaminated food and water Vomiting, dark urine, and yellowing of the eyes. Vaccination/Fluids
Polio Virus Fecal contamination Flu symptoms, paralysis Vaccination
(Figure $4$) shows how a person might contract Giardiasis from giardia, a parasite. This particular pathogen can live in a body up to six months. Once detected through a stool sample, a patient can be prescribed specific antibiotics like Flagyl to treat the infection. Unfortunately, there is no vaccine for preventing Giardiasis.
Acidic Waters
Water can become contaminated at any part of the water cycle. Air pollution can affect water vapor and water liquid. Combustion sources like vehicles and power plants generate compounds like $\ce{NO_xs}$, $\ce{SO_xs}$, $\ce{CO}$, $\ce{CO2}$, and other various inorganic and organic volatile organic compounds (VOC) species (Table $2$). Some of these compounds can become soluble in water. This could affect pH (or acidity) level of water surface water. Normally, the pH of water is a neutral value (or pH= 7). When $\ce{NO_xs}$, $\ce{SO_xs}$, $\ce{CO}$, $\ce{CO2}$ enter the water cycle, then the pH level is lowered below 7.0. If these gases are absorbed in rain clouds, then acid rain results. Specific acids involved in acid rain are sulfuric, nitric, and carbonic. This environmental problem affects living organisms and building materials. Acid solutions can corrode metals and make them soluble as well.
Table $2$: Source of Water Contamination (Due to Acid Rain) in the United States
Combustion products Sources
CO2 and CO Combustion of any material (any fuel or tree)
NOX (NO2 and NO3) High-temperature combustion of any fuel ( gas, diesel, or coal), a product of lightning
SOx (SO2 and SO3) Combustion of sulfur-based fuels (diesel and coal), volcanic release
VOC (volatile organic compound) Combustion of any carbon-based fuel (gas, diesel, or coal), fumes from paints or solvents
In the United States, the northeast has the most problems with acid rain. Concentrated populations that use electrical energy and vehicles contribute greatly to the pH reduction of rainwater. Reducing gaseous output requires capping combustion sources (vehicles and power plants). Acidity in rain is measured by collecting samples of rain and measuring its pH. To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at sites all over the country (Figure $5$). The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by a large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain.
Summary
• Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and/or the ecosystem.
• Pollutants enter water supplies from point sources, which are readily identifiable and relatively small locations, or nonpoint sources, which are large and more diffuse areas
• Organic matter as well as phosphates and nitrates from human and farm animal waste support the growth of algae and microorganisms, including bacteria.
• Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.
• Acid rain (formed as a consequence of air pollution) could affect building materials and living organisms on land and various bodies of water. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.03%3A_Chemical_and_Biological_Contamination.txt |
Learning Objective
• Define groundwater contamination.
• List other groundwater contaminants and their sources.
Ground water contamination (also called groundwater pollution) occurs when pollutants are released to the ground and make their way down into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution.
How Does Groundwater Become Contaminated?
The pollutant often creates a contaminant plume within an aquifer. Movement of water and dispersion within the aquifer spreads the pollutant over a wider area. Its advancing boundary, often called a plume edge, can intersect with groundwater wells or daylight into surface water such as seeps and springs, making the water supplies unsafe for humans and wildlife. The movement of the plume, called a plume front, may be analyzed through a hydrological transport model or groundwater model. Analysis of groundwater pollution may focus on soil characteristics and site geology, hydrogeology, hydrology, and the nature of the contaminants.
Pollution can occur from on-site sanitation systems, landfills, effluent from wastewater treatment plants, leaking sewers, petrol filling stations or from over application of fertilizers in agriculture. Pollution (or contamination) can also occur from naturally occurring contaminants, such as arsenic or fluoride. Using polluted groundwater causes hazards to public health through poisoning or the spread of disease.
Different mechanisms have influence on the transport of pollutants, e.g. diffusion, adsorption, precipitation, decay, in the groundwater. The interaction of groundwater contamination with surface waters is analyzed by use of hydrology transport models.
Pollutant types
Contaminants found in groundwater cover a broad range of physical, inorganic chemical, organic chemical, bacteriological, and radioactive parameters. Principally, many of the same pollutants that play a role in surface water pollution may also be found in polluted groundwater, although their respective importance may differ.
Arsenic and fluoride
Arsenic and fluoride have been recognized by the World Health Organization (WHO) as the most serious inorganic contaminants in drinking-water on a worldwide basis.
Inorganic arsenic is the most common type of arsenic in soil and water. The metalloid arsenic can occur naturally in groundwater, as seen most frequently in Asia, including in China, India and Bangladesh. In the Ganges Plain of northern India and Bangladesh severe contamination of groundwater by naturally occurring arsenic affects 25% of water wells in the shallower of two regional aquifers. Groundwater in these areas is also contaminated by the use of arsenic-based pesticides.
Arsenic in groundwater can also be present where there are mining operations or mine waste dumps that will leach arsenic.
Natural fluoride in groundwater is of growing concern as deeper groundwater is being used, "with more than 200 million people at risk of drinking water with elevated concentrations." Fluoride can especially be released from acidic volcanic rocks and dispersed volcanic ash when water hardness is low. High levels of fluoride in groundwater is a serious problem in the Argentinean Pampas, Chile, Mexico, India, Pakistan, the East African Rift, and some volcanic islands (Tenerife)
In areas that have naturally occurring high levels of fluoride in groundwater which is used for drinking water, both dental and skeletal fluorosis can be prevalent and severe.
Pathogens
Waterborne diseases can be spread via a groundwater well which is contaminated with fecal pathogens from pit latrines
The lack of proper sanitation measures, as well as improperly placed wells, can lead to drinking water contaminated with pathogens carried in feces and urine. Such fecal-oral transmitted diseases include typhoid, cholera and diarrhea. Of the four pathogen types that are present in feces (bacteria, viruses, protozoa, and helminths or helminth eggs), the first three can be commonly found in polluted groundwater, whereas the relatively large helminth eggs are usually filtered out by the soil matrix.
Deep, confined aquifers are usually considered the safest source of drinking water with respect to pathogens. Pathogens from treated or untreated wastewater can contaminate certain, especially shallow, aquifers.
Nitrate
Nitrate is the most common chemical contaminant in the world's groundwater and aquifers. In some low-income countries, nitrate levels in groundwater are extremely high, causing significant health problems. It is also stable (it does not degrade) under high oxygen conditions.
Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause "blue baby syndrome" (acquired methemoglobinemia). Drinking water quality standards in the European Union stipulate less than 50 mg/L for nitrate in drinking water.
However, the linkages between nitrates in drinking water and blue baby syndrome have been disputed in other studies. The syndrome outbreaks might be due to other factors than elevated nitrate concentrations in drinking water.
Elevated nitrate levels in groundwater can be caused by on-site sanitation, sewage sludge disposal and agricultural activities. It can therefore have an urban or agricultural origin.
Organic compounds
Volatile organic compounds (VOCs) are a dangerous contaminant of groundwater. They are generally introduced to the environment through careless industrial practices. Many of these compounds were not known to be harmful until the late 1960s and it was some time before regular testing of groundwater identified these substances in drinking water sources.
Primary VOC pollutants found in groundwater include aromatic hydrocarbons such as BTEX compounds ( benzene, toluene, ethylbenzene and xylenes), and chlorinated solvents including tetrachloroethylene (PCE), trichloroethylene (TCE), and vinyl chloride (VC). BTEX are important components of gasoline. PCE and TCE are industrial solvents historically used in dry cleaning processes and as a metal degreaser, respectively.
Other organic pollutants present in groundwater and derived from industrial operations are the polycyclic aromatic hydrocarbons (PAHs). Due to its molecular weight, Naphthalene is the most soluble and mobile PAH found in groundwater, whereas benzo(a)pyrene is the most toxic one. PAHs are generally produced as byproducts by incomplete combustion of organic matter.
Organic pollutants can also be found in groundwater as insecticides and herbicides. As many other synthetic organic compounds, most pesticides have very complex molecular structures. This complexity determines the water solubility, adsorption capacity, and mobility of pesticides in the groundwater system. Thus, some types of pesticides are more mobile than others so they can more easily reach a drinking-water source.
Metals
Several trace metals occur naturally in certain rock formations and can enter in the environment from natural processes such as weathering. However, industrial activities such as mining, metallurgy, solid waste disposal, paint and enamel works, etc. can lead to elevated concentrations of toxic metals including lead, cadmium and chromium. These contaminants have the potential to make their way into groundwater.
The migration of metals (and metalloids) in groundwater will be affected by several factors, in particular by chemical reactions which determine the partitioning of contaminants among different phases and species. Thus, the mobility of metals primarily depends on the pH and redox state of groundwater.
Pharmaceuticals
Trace amounts of pharmaceuticals from treated wastewater infiltrating into the aquifer are among emerging ground-water contaminants being studied throughout the United States. Popular pharmaceuticals such as antibiotics, anti-inflammatories, antidepressants, decongestants, tranquilizers, etc. are normally found in treated wastewater. This wastewater is discharged from the treatment facility, and often makes its way into the aquifer or source of surface water used for drinking water.
Trace amounts of pharmaceuticals in both groundwater and surface water are far below what is considered dangerous or of concern in most areas, but it could be an increasing problem as population grows and more reclaimed wastewater is utilized for municipal water supplies.
Others
Other organic pollutants include a range of organohalides and other chemical compounds, petroleum hydrocarbons, various chemical compounds found in personal hygiene and cosmetic products, drug pollution involving pharmaceutical drugs and their metabolites. Inorganic pollutants might include other nutrients such as ammonia and phosphate, and radionuclides such as uranium (U) or radon (Rn) naturally present in some geological formations. Saltwater intrusion is also an example of natural contamination, but is very often intensified by human activities.
Groundwater pollution is a worldwide issue. A study of the groundwater quality of the principal aquifers of the United States conducted between 1991 and 2004, showed that 23% of domestic wells had contaminants at levels greater than human-health benchmarks. Another study suggested that the major groundwater pollution problems in Africa, considering the order of importance are: (1) nitrate pollution, (2) pathogenic agents, (3) organic pollution, (4) salinization, and (5) acid mine drainage.
Potential Health and Other Effects of Groundwater Contaminants
The United States Geological Survey provides an extensive list of groundwater contaminants with their potential health and other effects.
https://www.epa.gov/sites/production/files/2015-08/documents/mgwc-gwc1.pdf
Summary
• Ground water contamination (also called groundwater pollution) occurs when pollutants are released to the ground and make their way down into groundwater.
• Contaminants found in groundwater cover a broad range of physical, inorganic chemical, organic chemical, bacteriological, and radioactive parameters.
• The United States Geological Survey developed an extensive list of groundwater contaminants with their potential health and other effects.
Contributors and Attributions
• Wikipedia
• US Geological Survey (USGS) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.04%3A_Groundwater_Contamination_to_Tainted_Tap_Water.txt |
Learning Objective
• List the end uses of water in residential and non residential areas.
Water in Daily Life
Residential water use (also called domestic use, household use, or tap water use) includes all indoor and outdoor uses of drinking quality water at single-family and multifamily dwellings. These uses include a number of defined purposes (or water end uses) such as flushing toilets, washing clothes and dishes, showering and bathing, drinking, food preparation, watering lawns and gardens, and maintaining swimming pools. Some of these end uses are detectable (and measurable) while others are more difficult to gauge.
Indoor water use includes water flows through fixtures and appliances inside the house. Because the distribution of indoor use in the sample of homes measured is positively skewed, a more appropriate measure of central tendency is the median, which is about 125 gphd (gallons per household per day) or 472 lphd, liters per household per day). Toilet flushing is the largest indoor use of water, followed by flows through kitchen and bathroom faucets, showers, clothes washers, leaks, bathtubs, other/miscellaneous uses, and dishwashers. Since the late 1990s, total indoor use has decreased by 22 percent, primarily due to the improved water efficiency of clothes washers and toilets, among other low-flow fixtures.
The outdoor residential water use includes landscape irrigation, filling and back washing swimming pools, water used through outdoor faucets (hose bibs) for washing pavement and cars, and other outdoor uses. Annual outdoor use in North American cities differs by climatic region and ranged from 13,000 gallons in Waterloo, Canada to 120,400 gallons in Scottsdale, Arizona. The average outdoor use across 9 sampled cities in the Water Research Foundation study was 50,500 gallons per household per year or 138 gallons per day (524 liters per day). Nearly 17 percent of homes irrigate their landscapes in excess of theoretical irrigation requirement. If excess irrigation could be eliminated, the average outdoor use would drop by 8,200 gallons per house, or by 16 percent.
Commercial, Industrial, Agricultural & Electricity Water Use
It’s easy to forget that we also use water in ways we don't see every day (Figure \(2\)). Water is used to grow our food, manufacture our favorite goods, and keep our businesses running smoothly. We also use a significant amount of water to meet the nation's energy needs.
Figure \(2\) U.S. freshwater withdrawals.
Water Footprint
A water footprint shows the extent of water use in relation to consumption by people. The water footprint of an individual, community or business is defined as the total volume of fresh water used to produce the goods and services consumed by the individual or community or produced by the business. Water use is measured in water volume consumed (evaporated) and/or polluted per unit of time. A water footprint can be calculated for any well-defined group of consumers (e.g., an individual, family, village, city, province, state or nation) or producers (e.g., a public organization, private enterprise or economic sector), for a single process (such as growing rice) or for any product or service.
Traditionally, water use has been approached from the production side, by quantifying the following three columns of water use: water withdrawals in the agricultural, industrial, and domestic sector. While this does provide valuable data, it is a limited way of looking at water use in a globalized world, in which products are not always consumed in their country of origin. International trade of agricultural and industrial products in effect creates a global flow of virtual water, or embodied water (akin to the concept of embodied energy).
In 2002, the water footprint concept was introduced in order to have a consumption-based indicator of water use, that could provide useful information in addition to the traditional production-sector-based indicators of water use. It is analogous to the ecological footprint concept introduced in the 1990s. The water footprint is a geographically explicit indicator, not only showing volumes of water use and pollution, but also the locations. Thus, it gives a grasp on how economic choices and processes influence the availability of adequate water resources and other ecological realities across the globe (and vice versa).
The water footprint of a product is the total volume of freshwater used to produce the product, summed over the various steps of the production chain. The water footprints involved in various diets vary greatly, and much of the variation tends to be associated with levels of meat consumption. The following table gives examples of estimated global average water footprints of popular agricultural products.
Table \(3\) Global average water footprints of some agricultural products.
Product Global average water footprint, L/kg
almonds, shelled 16,194
beef 15,415
chocolate 17,196
cotton lint 9,114
lettuce 238
milk 1,021
olive oil 14,430
tomatoes, fresh 214
tomatoes, dried 4,275
vanilla beans 126,505
wheat bread 1,608
(For more product water footprints: see the Product Gallery of the Water Footprint Network)
Summary
• The average American family daily indoor water use is approximately 125 gallons per household per day.
• The water footprint is a geographically explicit indicator, not only showing volumes of water use and pollution, but also the locations.
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.05%3A_Water_Who_Uses_It_and_How_Much.txt |
Learning Objectives
• Know the primary standards for various contaminants in drinking water.
• Describe the importance of the different steps in water treatment.
Public Water Systems Fast Facts from US CDC
• Of the approximately 155,693 public water systems in the United States, 52,110 (33.5%) are community systems and 103,583 (66.5%) are noncommunity systems, including 84,744 transient systems and 18,839 nontransient systems 1.
• Over 286 million Americans get their tap water from a community water system 1.
• 8% of U.S. community water systems provide water to 82% of the U.S. population through large municipal water systems 1.
• Although the majority of community water systems (78%) are supplied by ground water, more people (68%) are supplied year-round by community water systems that use surface water .
Note: EPA. Factoids: drinking water and ground water statistics for 2007. March 2008, April 2008.
Safe Drinking Water Act
Up until 1974, public drinking water supplies in the United States were monitored and regulated by state and local authorities. Lists of contaminants with their various concentrations could vary from state to state. As the chemical industry grew, these same state agencies noted the increased presence of existing and new organic chemicals in public water systems. In order to standardize drinking water across the country, the Environmental Protection Agency (EPA) enacted the Safe Water Drinking Act of 1974.
The 1974 act enabled the EPA to monitor and regulate public water systems that serve over 25 people. Implementation and enforcement of drinking water standards would still be performed by each state. Regarding drinking water sources (surface and ground), the EPA and state agencies protect and monitor these as well. Levels of contaminants would be defined using the concentration terms Maximum Contaminant Level (MCL) and Treatment Technique (TT)
National Primary Standards for Drinking Water
The first set of drinking water standards included only 22 chemicals and/or pathogens. EPA established two major types of contaminants: primary and secondary. The first of these types (primary) contaminants are substances (examples could include Hg, As, and U) that can be toxic in small amounts. On the other hand, secondary contaminants are less toxic species (Fe and Zn) and would include cosmetic issues (color, taste, and odor) of drinking water.
All primary contaminants have enforceable concentration values. For the majority of these pollutants, EPA lists concentration limits by using the term Maximum Contaminant Level (MCL). If a water supplier exceeds a given MCL for a toxin, then fines and penalties could by imposed by the EPA. A few pathogens (Giardia Lamblia and Legionella) use Treatment Technique (TT) notation rather than numerical MCL concentrations. Water that contains any amount of these pathogens must be sanitized immediately with a standardized EPA procedure.
A detailed list of acceptable levels of different contaminants by EPA classification can be found on the the link below.
https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
The complete table of standards is given below.
https://www.epa.gov/sites/production/files/2016-06/documents/npwdr_complete_table.pdf
Table $1$ Table $1$ Standards for Various Contaminants in Drinking Water.
Contaminant MCLG1(mg/L)2 MCL or TT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Microorganisms-
Cryptosporidium
zero TT3 Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Microorganisms-
Giardia lamblia
zero TT Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Microorganisms-
Total Coliforms (including fecal coliform and E. Coli)
zero 5.0% Not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present5 Coliforms are naturally present in the environment; as well as feces; fecal coliforms and E. coli only come from human and animal fecal waste.
Viruses (enteric) zero TT Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Inorganic Chemicals-
Antimony
0.006 0.006 Increase in blood cholesterol; decrease in blood sugar Discharge from petroleum refineries; fire retardants; ceramics; electronics; solder
Inorganic Chemicals-
Chromium (total)
0.1 0.1 Allergic dermatitis Discharge from steel and pulp mills; erosion of natural deposits
Inorganic Chemicals-
Nitrate (measured as Nitrogen)
10 10 Infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome. Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits
Organic Chemicals-
Benzene
zero 0.005 Anemia; decrease in blood platelets; increased risk of cancer Discharge from factories; leaching from gas storage tanks and landfills
Organic Chemicals-
Carbon tetrachloride
zero 0.005 Liver problems; increased risk of cancer Discharge from chemical plants and other industrial activities
Organic Chemicals-
Styrene
0.1 0.1 Liver, kidney, or circulatory system problems Discharge from rubber and plastic factories; leaching from landfills
Radionuclides
Alpha particles
none ---------- zero 15 picocuries per Liter (pCi/L) Increased risk of cancer Erosion of natural deposits of certain minerals that are radioactive and may emit a form of radiation known as alpha radiation
Notes
1Definitions:
• Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.
• Maximum Contaminant Level (MCL) - The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.
• Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.
• Treatment Technique (TT) - A required process intended to reduce the level of a contaminant in drinking water.
• Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.
2 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million (PPM).
Calculations of Parts per Million and Parts per Billion
In addition to percentage units, the units for expressing the concentration of extremely dilute solutions are parts per million (ppm) and parts per billion (ppb). Both of these units are mass based and are defined as follows:
$\mathrm{ppm=\dfrac{mass\: of\: solute}{mass\: of\: solution}\times1,000,000} \nonumber$
$\mathrm{ppb=\dfrac{mass\: of\: solute}{mass\: of\: solution}\times1,000,000,000} \nonumber$
Similar to parts per million and parts per billion, related units include parts per thousand (ppth) and parts per trillion (ppt).
Concentrations of trace elements in the body—elements that are present in extremely low concentrations but are nonetheless necessary for life—are commonly expressed in parts per million or parts per billion. Concentrations of poisons, contaminants, and pollutants are also described in these units. For example, cobalt is present in the body at a concentration of 21 ppb, while the State of Oregon’s Department of Agriculture limits the concentration of arsenic in fertilizers to 9 ppm.
ppm and ppb
In aqueous solutions, 1 ppm is essentially equal to 1 mg/L, and 1 ppb is equivalent to 1 µg/L.
$\text{1 ppm}= \dfrac{\text{1 mg Solute}}{\text{1 L Solution}} \nonumber$
$\text{1 ppb} = \dfrac{1\; \mu \text{g Solute}}{\text{1 L Solution}} \nonumber$
Amendment SDWA of 1986
This change to the Safe Drinking Water Act established MCLGs and increased the total of regulated contaminants to 83. The EPA would also install more monitoring devices to detect organic contaminants. Research was done to detect pathogens more effectively to reduce disease. Lastly, public notifications from water systems to the consumers would be made announced if severe water issues occurred.
Amendment of SDWA of 1996
This particular legislation provided more protection and assessment of water sources (lakes, river, streams). In addition, water companies were required to provide consumers with a water quality report. States could seek federal money for upgrading their water quality processes. Cost benefit analysis would be done to determine risk and reward of lowering the concentration of a contaminant. For small regulated water companies, more financial and technical assistance would be offered to help them maintain drinking water standards.
Water Treatment (US CDC)
Drinking water supplies in the United States are among the safest in the world. However, even in the U.S., drinking water sources can become contaminated, causing sickness and disease from waterborne germs, such as Cryptosporidium, E. coli, Hepatitis A, Giardia intestinalis, and other pathogens.
Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use various methods of water treatment to provide safe drinking water for their communities. Today, the most common steps in water treatment (Figure $1$) used by community water systems (mainly surface water treatment) include:
Coagulation and Flocculation
Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc. Historically, dirty water is cleaned by treating with alum, Al2(SO4)3.12 H2O, and lime, Ca(OH)2. These electrolytes cause the pH of the water to change due to the following reactions:
Al2(SO4)3.12 H2O, -> Al3+(aq) + 3 SO42-(aq) + 12 H2O
SO42-(aq) + H2O -> HSO4-(aq) + OH- (causing pH change)
Ca(OH)2 -> Ca2+(aq) + 2 OH- (causing pH change)
The slightly basic water causes Al(OH)3, Fe(OH)3 and Fe(OH)2 to precipitate, bringing the small particulates with them and the water becomes clear. Some records have been found that Egyptians and Romans used these techniques as early as 2000 BC.
Suspension of iron oxide particulates and humic organic matter in water gives water the yellow muddy appearance. Both iron oxide particulates and organic matter can be removed from coagulation and flocculation. The description given here is oversimplified, and many more techniques have been applied in the treatment of water. Coagulation is a major application of lime in the treatment of wastewater.
Other salts such as iron sulfates Fe2(SO4)3 and FeSO4, chromium sulfate Cr2(SO4)3, and some special polymers are also useful. Other ions such as sodium, chloride, calcium, magnesium, and potassium also affect the coagulation process. So do temperature, pH, and concentration.
Disposal of coagulation sludge is a concern, however.
Sedimentation
During sedimentation, floc settles to the bottom of the water supply, due to its weight. This settling process is called sedimentation. The floc particles are then removed from the bottom of the basins.
Aeration
Bringing air into intimate contact with water for the purpose of exchanging certain components between the two phases is called aeration. Oxygenation is one of the purposes of aeration. Others are removal of volatile organic substances, hydrogen sulfide, ammonia, and volatile organic compounds
Filtration
Once the floc has settled to the bottom of the water supply, the clear water on top will pass through filters of varying compositions (sand, gravel, and charcoal) and pore sizes, in order to remove dissolved particles, such as dust, parasites, bacteria, viruses, and chemicals.
Treatment with Chlorine and/or Chloramine
Most communities use either chlorine or chloramines. Some communities switch back and forth between chlorine and chloramines at different times of the year or for other operational reasons. Less commonly, utilities use other disinfectants, such as chlorine dioxide. Some water systems that use water from a groundwater source (like community wells) do not have to add a disinfectant at all.
Ozone Disinfection
Ozone disinfection, or ozonation, is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe and in a few municipalities in the United States and Canada. It is an effective method to inactivate harmful protozoa that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-products and the absence of taste and odor problems (in comparison to ). No residual ozone is left in the water. In the absence of a residual disinfectant in the water, chlorine or chloramine may be added throughout a distribution system to remove any potential pathogens in the distribution piping.
Ultraviolet Disinfection
Ultraviolet disinfection of water is a purely physical, chemical-free process. Even parasites such as Cryptosporidium or Giardia, which are extremely resistant to chemical disinfectants, are efficiently reduced. UV can also be used to remove chlorine and chloramine species from water; this process is called photolysis, and requires a higher dose than normal disinfection. The dead microorganisms are not removed from the water. UV disinfection does not remove dissolved organics, inorganic compounds or particles in the water. The world's largest water disinfection plant treats drinking water for New York city. The Catskill-Delaware Water Ultraviolet Disinfection Facility, commissioned on 8 October 2013, incorporates a total of 56 energy-efficient UV reactors treating up to 2.2 billion US gallons (8,300,000 m3) a day.
Ultraviolet can also be combined with ozone or hydrogen peroxide to produce hydroxyl radicals to break down trace contaminants through an advanced oxidation process.
Fluoridation (US CDC)
The mineral fluoride occurs naturally on earth and is released from rocks into the soil, water, and air. All water contains some fluoride. Usually, the fluoride level in water is not enough to prevent tooth decay; however, some groundwater and natural springs can have naturally high levels of fluoride.
Fluoride has been proven to protect teeth from decay. Bacteria in the mouth produce acid when a person eats sugary foods. This acid eats away minerals from the tooth’s surface, making the tooth weaker and increasing the chance of developing cavities. Fluoride helps to rebuild and strengthen the tooth’s surface, or enamel. Water fluoridation prevents tooth decay by providing frequent and consistent contact with low levels of fluoride. By keeping the tooth strong and solid, fluoride stops cavities from forming and can even rebuild the tooth’s surface.
Community water fluoridation is the process of adjusting the amount of fluoride found in water to achieve optimal prevention of tooth decay.
Although other fluoride-containing products, such as toothpaste, mouth rinses, and dietary supplements are available and contribute to the prevention and control of tooth decay, community water fluoridation has been identified as the most cost-effective method of delivering fluoride to all, reducing tooth decay by 25% in children and adults.1
Benefits: Strong Teeth (US CDC)
Fluoride benefits children and adults throughout their lives. For children younger than age 8, fluoride helps strengthen the adult (permanent) teeth that are developing under the gums. For adults, drinking water with fluoride supports tooth enamel, keeping teeth strong and healthy. The health benefits of fluoride include having:
• Fewer cavities.
• Less severe cavities.
• Less need for fillings and removing teeth.
• Less pain and suffering because of tooth decay.
Fluoride in the Water Today
In 2012, more than 210 million people, or 75% of the US population, were served by community water systems that contain enough fluoride to protect their teeth.5 However, approximately 100 million Americans still do not have access to water with fluoride. Because it is so beneficial, the United States has a national goal for 80% of Americans to have water with enough fluoride to prevent tooth decay by 2020.
https://www.youtube.com/watch?v=0_ZcCqqpS2o&feature=youtu.be
Summary
• The Safe Drinking Water Act (SDWA) (originally passed by Congress in 1974) protects public health by regulating the nation's public drinking water supply.
• The different steps in water treatment include floculation, sedimentation, filtration, aeration, and disinfection or combinations thereof. Fluoride is also added to municipal water systems for prevention of tooth decay.
Contributors and Attributions
• Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)
• US EPA
• Center for Disease Control (CDC)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.06%3A_Making_Water_Fit_to_Drink.txt |
Learning Objectives
• Explain the major steps in wastewater treatment.
• List the different uses of reclaimed water.
Wastewater and sewage is treated in three phases: primary (solid removal), secondary (bacterial decomposition), and tertiary (extra filtration).
Sewage is generated by residential and industrial establishments. It includes household waste liquid from toilets, baths, showers, kitchens, sinks, and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world. Greywater is water generated from domestic activities such as laundry, dishwashing, and bathing, and can be reused more readily. Blackwater comes from toilets and contains human waste.
Figure \(1\) Diagram of Sewage Treatment Process: Sewage passes through primary, secondary, and tertiary treatment.
Primary Treatment
In primary treatment, sewage is stored in a basin where solids (sludge) can settle to the bottom and oil and lighter substances can rise to the top. These layers are then removed and then the remaining liquid can be sent to secondary treatment. Sewage sludge is treated in a separate process called sludge digestion.
Secondary Treatment
Secondary treatment removes dissolved and suspended biological matter, often using microorganisms in a controlled environment. Most secondary treatment systems use aerobic bacteria, which consume the organic components of the sewage (sugar, fat, and so on). Some systems use fixed film systems, where the bacteria grow on filters, and the water passes through them. Suspended growth systems use “activated” sludge, where decomposing bacteria are mixed directly into the sewage. Because oxygen is critical to bacterial growth, the sewage is often mixed with air to facilitate decomposition.
Tertiary Treatment
Tertiary treatment (sometimes called “effluent polishing”) is used to further clean water when it is being discharged into a sensitive ecosystem.
Several methods can be used to further disinfect and purify sewage beyond primary and secondary treatment.
Sand filtration, where water is passed through a sand filter, can be used to remove particulate matter.
Wastewater may still have high levels of nutrients such as nitrogen and phosphorus. These can disrupt the nutrient balance of aquatic ecosystems and cause algae blooms and excessive weed growth. Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulate organisms that store phosphate in their tissue. When the biomass accumulated in these bacteria is separated from the treated water, these biosolids have a high fertilizer value. Nitrogen can also be removed using nitrifying bacteria.
Lagooning is another method for removing nutrients and waste from sewage. Water is stored in a lagoon and native plants, bacteria, algae, and small zooplankton filter nutrients and small particles from the water.
Treatment by activated carbon is mostly due to adsorption or absorption. When a chemical species is adhered to the surface of a solid, it is an adsorption. When partial chemical bonds are formed between adsorbed species or when the absorbate got into the channels of the solids, we call it absorption. However, these two terms are often used to mean the same, because to distinguish one from type from the other is very difficult.
Application of activated charcoal for the removal of undesirable order and taste in drinking water has been recognized at the dawn of civilization. Using bone char and charred vegetation, gravel, and sand for the filtration of water for domestic application has been practised for thousands of years. Charcoal absorbs many substances, ranging from colored organic particulates to inorganic metal ions. Charcoal has been used to remove the colour of raw sugar from various sources.
Filtration is the process of removing solids from a fluid by passing it through a porous medium. Coarse, medium, and fine porous media have been used depending on the requirement. The filter media are artificial membranes, nets, sand filter, and high technological filter systems. The choice of filters depends on the required filtering speed and the cleanness requirement. The flow required for filtration can be achieved using gravity or pressure. In pressure filtration, one side of the filter medium is at higher pressure than that of the other so that the filter plane has a pressure drop. Some portion of this filter type must be enclosed in a container.
When a compartment containing a dilute solution is connected to another compartment containing a concentrated solution by a semipermeable membrane, water molecules move from the dilute solution to concentrated solution. This phenomenon is called osmosis. By applying pressure in the higher concentration solution, water molecules migrate from a high concentration solution to a low concentration solution through a semipermeable membrane. This method is called reverse osmosis water filter system. In this technique, the membrane must be able to tolerate the high pressure, and prevent solute molecules to pass through. This technology certainly works, and it has been used to convert salt (ocean or sea) water into fresh water. With this technique, the water with higher concentration is discharged. Thus, this technology is costly in regions where the water cost is high.
Sludge Digestion
Sewage sludge scraped off the bottom of the settling tank during primary treatment is treated separately from wastewater. Sludge can be disposed of in several ways. First, it can be digested using bacteria; bacterial digestion can sometimes produce methane biogas, which can be used to generate electricity. Sludge can also be incinerated, or condensed, heated to disinfect it, and reused as fertilizer.
Uses of Reclaimed Wastewater
Water reclamation (also called wastewater reuse) is the process of converting wastewater into water that can be reused for other purposes. Reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater (i.e., groundwater recharge). Reused water may also be directed toward fulfilling certain needs in residences (e.g. toilet flushing), businesses, and industry, and could even be treated to reach drinking water standards. This last option is called either "direct potable reuse" or "indirect potable" reuse, depending on the approach used.
Reclaiming water for reuse applications instead of using freshwater supplies can be a water-saving measure. When used water is eventually discharged back into natural water sources, it can still have benefits to ecosystems, improving streamflow, nourishing plant life and recharging aquifers, as part of the natural water cycle.
Wastewater reuse is a long-established practice used for irrigation, especially in arid countries. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities. This can reduce scarcity and alleviate pressures on groundwater and other natural water bodies. Another potentially positive aspect is the nutrient content in the wastewater, which might reduce the need of other fertilizers.
Drawbacks or risks often mentioned include the content of potentially harmful substances such as bacteria, heavy metals or organic pollutants (including pharmaceuticals, personal care products and pesticides). Irrigation with wastewater can have both positive and negative effects on soil and plants, depending on the composition of the wastewater and on the soil or plant characteristics.
Most of the uses of water reclamation are non potable uses such as washing cars, flushing toilets, cooling water for power plants, concrete mixing, artificial lakes, irrigation for golf courses and public parks, and for hydraulic fracturing. Where applicable, systems run a dual piping system to keep the recycled water separate from the potable water.
The main reclaimed water applications in the world are shown below:
Table \(1\) Uses of Reclaimed Water
Categories of use Uses
Urban uses Irrigation of public parks, sporting facilities, private gardens, roadsides; Street cleaning; Fire protection systems; Vehicle washing; Toilet flushing; Air conditioners; Dust control.
Agricultural uses Food crops not commercially processed; Food crops commercially processed; Pasture for milking animals; Fodder; Fibre; Seed crops; Ornamental flowers; Orchards; Hydroponic culture; Aquaculture; Greenhouses; Viticulture.
Industrial uses Processing water; Cooling water; Recirculating cooling towers; Washdown water; Washing aggregate; Making concrete; Soil compaction; Dust control.
Recreational uses Golf course irrigation; Recreational impoundments with/without public access (e.g. fishing, boating, bathing); Aesthetic impoundments without public access; Snowmaking.
Environmental uses Aquifer recharge; Wetlands; Marshes; Stream augmentation; Wildlife habitat; Silviculture.
Potable uses Aquifer recharge for drinking water use; Augmentation of surface drinking water supplies; Treatment until drinking water quality.
If it's good enough for astronauts...
Astronauts aboard the International Space Station drink reclaimed urine. (Credit: NASA)
In outer space, as on the International Space Station, water is at a premium and not a drop is to be wasted. Astronauts aboard the station must drink recycled water. Water from humidity in the air is condensed and used as drinking water, but American astronauts also drink recycled urine! You can imagine the urine, which is of course almost all water, would go through a rigorous purification process, but this just shows if the need exists, that the same water can serve valuable purposes over and over again.
Summary
• Wastewater treatment is a process used to remove from or and convert it into an that can be returned to the with minimum impact on the environment, or directly reused.
• In a wastewater treatment plant wastewater or sewage undergo primary,secondary, as well as tertiary treatments depending on the end use.
• Most of the uses of water reclamation are non potable uses such as washing cars, flushing toilets, cooling water for power plants, concrete mixing, artificial lakes, irrigation for golf courses and public parks, and for hydraulic fracturing
Contributors and Attributions
• Libretexts: Microbioloy (Boundless)
• USGS
• Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14%3A_Water/14.08%3A_Wastewater_Treatment.txt |
It takes energy to launch a spaceship into space. If it takes 1 energy unit to warm 0.25 g of water by 1°C, then it takes over 15,100 energy units to put that 0.25 g of water into earth orbit. The most powerful engines designed to lift rockets into space were part of the Saturn V rocket, that was built by the National Aeronautics and Space Administration (NASA). The rocket had three stages, with the first stage having the capability of launching about 3.5 million kg of mass. About 2.3 million kg was the actual fuel for the first stage; rockets in space have the unpleasant task of having to take their own chemicals with them to provide thrust.
Having to carry its own fuel puts a lot of mass burden on an engine in space. This is why NASA is developing other types of engines to minimize fuel mass. An ion thruster uses xenon atoms that have had at least one electron removed from their atoms. The resulting ions can be accelerated by electric fields, causing a thrust. Because xenon atoms are very large for atoms, the thrusting efficiency is high even though the actual thrust is low. Because of this, ion engines are useful only in space.
Energy is a very important quantity in science and the world around us. Although most of our energy ultimately comes from the sun, much of the energy we use on a daily basis is rooted in chemical reactions. The gasoline in your car, the electricity in your house, the food in your diet-all provide substances for chemical reactions to provide energy (gasoline, food) or are produced from chemical reactions (electricity, about 50% of which is generated by burning coal). As such, it is only natural that the study of chemistry involves energy.
15: Energy
Learning Objectives
• Define energy and distinguish between kinetic and potential enregy.
• Describe photosynthesis
• Perform calculations involving power and energy.
The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result. Sunlight at the top of Earth's atmosphere is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light.[46] The atmosphere in particular filters out over 70% of solar ultraviolet, especially at the shorter wavelengths.[47] Solar ultraviolet radiation ionizes Earth's dayside upper atmosphere, creating the electrically conducting ionosphere.[48]The energy of sunlight supports almost all life[c] on Earth by photosynthesis,[37] and drives Earth's climate and weather.
Energy can be defined as the capacity to supply heat or do work. One type of work (w) is the process of causing matter to move against an opposing force. For example, we do work when we inflate a bicycle tire—we move matter (the air in the pump) against the opposing force of the air surrounding the tire. Energy is measured in SI units, in joules (J). The Joule (= 1 Newton-meter) is a very small unit, however it is equivalent to the amount of work of lifting a small apple (98 grams) vertically up one meter. In terms of heat,
$\mathrm{1\: cal = 4.184\: J}$
The rate of work done or energy transfer is called power, and its unit is watt.
$\mathrm{1\: watt = 1\: J/s}$
Your calculator may consume some milliwatt, and a computer consumes about 100 watt, as does a 100-W light bulb. The kilowatt (kW) is equal to one thousand (103) watts. This unit is typically used to express the output power of engines and the power of electric motors, tools, machines, and heaters. It is also a common unit used to express the electromagnetic power output of broadcast radio and television transmitters. Different examples of power are given in Table $1$.
One kilowatt is approximately equal to 1.34 horsepower. A small electric heater with one heating element can use 1.0 kilowatt. The average electric power consumption of a household in the United States is about one kilowatt.
Table $1$ Power in Kilowatts of Various Objects or Phenomenon.
Object or Phenomenon Power in kilowatts (kW)
Supernova (at peak) $5 \times 10^{34}$
Milky Way galaxy $10^{34}$
Crab Nebula pulsar $10^{25}$
The Sun $4 \times 10^{23}$
Volcanic eruption (maximum) $4 \times 10^{12}$
Lightning bolt $2 \times 10^{9}$
Nuclear power plant (total electric and heat transfer) $3 \times 10^6$
Aircraft carrier (total useful and heat transfer) $10^5$
Dragster (total useful and heat transfer) $2 \times 10^3$
Car (total useful and heat transfer) $8 \times 10^1$
Football player (total useful and heat transfer) $5$
Clothes dryer $4$
Typical incandescent light bulb (total useful and heat transfer) (60W) $0.06$
Electric clock $0.003$
Pocket calculator $10^{-6}$
Example $1$ Power and Energy Conversion
Calculate the electrical energy, in joules (J) , that is used by a 20W LED bulb that was left "on" for 3.0 hours.
Solution
1. Since 1 W = 1 J/s then 20W = 20 J/s.
2. Convert 3 h to s.
3. Calculate the amount in J for 10,800 s.
Exercise $1$
Calculate the electrical energy, in joules (J) , that is used by a 100W incandescent bulb that was left "on" for 2 hours.
Answer
720,000 J
Energy and the Life-Support System
Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, which are then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago.
Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates (Figure $1$). After the process is complete, it releases oxygen and produces simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.
The chemical equation for photosynthesis is given in Figure $2$. Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. In reality, the process takes place in many steps involving intermediate reactants and products.
Kinetic and Potential Energy
Like matter, energy comes in different types. One scheme classifies energy into two types: potential energy, the energy an object has because of its relative position, composition, or condition, and kinetic energy, the energy that an object possesses because of its motion. Water at the top of a waterfall or dam has potential energy because of its position; when it flows downward through generators, it has kinetic energy that can be used to do work and produce electricity in a hydroelectric plant (Figure $3$). A battery has potential energy because the chemicals within it can produce electricity that can do work.
Potential energy is not only associated with the location of matter, but also with the structure of matter. Even a spring on the ground has potential energy if it is compressed; so does a rubber band that is pulled taut. On a molecular level, the bonds that hold the atoms of molecules together exist in a particular structure that has potential energy. The fact that energy can be released by the breakdown of certain chemical bonds implies that those bonds have potential energy. In fact, there is potential energy stored within the bonds of all the food molecules we eat, which is harnessed for use. The type of potential energy that exists within chemical bonds, and is released when those bonds are broken, is called chemical energy. Chemical energy is responsible for providing living cells with energy from food. The release of energy occurs when the molecular bonds within food molecules are broken.
Summary
• Energy can be defined as the capacity to supply heat or do work and is measured in SI units, in joules (J)
• Photosynthesis is essential to all life on earth and it is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism.
• Energy comes in two fundamentally different forms – kinetic energy and potential energy.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy that depends on the position of an object relative to another object.
Contributors and Attributions
• Adelaide E. Clark, Oregon Institute of Technology
• Wikipedia
• General Biology OpenStax
• University Physics OpenStax
• Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/[email protected]). | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.01%3A_Our_Sun_a_Giant_Nuclear_Power_Plant.txt |
Learning Objectives
• Define endothermic and exothermic reactions.
• Determine whether a reaction is endothermic or exothermic through observations, temperature changes, or an energy diagram.
• Describe the calculation of heat of reaction using bond energies.
When physical or chemical changes occur, they are generally accompanied by a transfer of energy. The law of conservation of energy states that in any physical or chemical process, energy is neither created nor destroyed. In other words, the entire energy in the universe is conserved. In order to better understand the energy changes taking place during a reaction, we need to define two parts of the universe, called the system and the surroundings. The system is the specific portion of matter in a given space that is being studied during an experiment or an observation. The surroundings is everything in the universe that is not part of the system. In practical terms for a laboratory chemist, the system is the particular chemicals being reacted, while the surroundings is the immediate vicinity within the room. During most processes, energy is exchanged between the system and the surroundings.
In the course of an endothermic process, the system gains heat from the surroundings and so the temperature of the surroundings decreases. A chemical reaction or physical change is exothermic if heat is released by the system into the surroundings. Because the surroundings is gaining heat from the system, the temperature of the surroundings increases (Figure $1$). Exothermic and endothermic reactions can be thought of as having energy as either a product of the reaction or a reactant. Exothermic reactions give off energy, so energy is a product. Endothermic reactions require energy, so energy is a reactant.
Phase changes, discussed in the previous section 7.3, are also classified in a similar way. The change from gas to liquid (condensation) and liquid to solid (freezing) are exothermic. The change from solid to liquid (melting), and liquid to gas (evaporation and boiling) are endothermic. The exothermic processes release heat to the surroundings while the endothermic processes absorb heat from the surroundings.
When methane gas is combusted, heat is released, making the reaction exothermic. Specifically, the combustion of $1 \: \text{mol}$ of methane releases 890.4 kilojoules of heat energy. This information can be shown as part of the balanced equation.
$\ce{CH_4} \left( g \right) + 2 \ce{O_2} \left( g \right) \rightarrow \ce{CO_2} \left( g \right) + 2 \ce{H_2O} \left( l \right) + 890.4 \: \text{kJ} \nonumber$
The process in the above thermochemical equation can be shown visually in the figure below.
In the combustion of methane example, the enthalpy change is negative because heat is being released by the system. Therefore, the overall enthalpy of the system decreases. The heat of reaction is the enthalpy change for a chemical reaction. In the case above, the heat of reaction is $-890.4 \: \text{kJ}$. The thermochemical reaction can also be written in this way:
$\ce{CH_4} \left( g \right) + 2 \ce{O_2} \left( g \right) \rightarrow \ce{CO_2} \left( g \right) + 2 \ce{H_2O} \left( l \right) \: \: \: \: \: \Delta H = -890.4 \: \text{kJ} \nonumber$
Endothermic reactions absorb energy from the surroundings as the reaction occurs. When $1 \: \text{mol}$ of calcium carbonate decomposes into $1 \: \text{mol}$ of calcium oxide and $1 \: \text{mol}$ of carbon dioxide, $177.8 \: \text{kJ}$ of heat is absorbed. The process is shown visually in the figure above (B). The thermochemical reaction is shown below.
$\ce{CaCO_3} \left( s \right) + 177.8 \: \text{kJ} \rightarrow \ce{CaO} \left( s \right) + \ce{CO_2} \left( g \right) \nonumber$
Because the heat is absorbed by the system, the $177.8 \: \text{kJ}$ is written as a reactant. The heat of reaction is positive for an endothermic reaction.
Example $1$
Label each of the following processes as endothermic or exothermic.
1. water boiling
2. gasoline burning
3. ice forming on a pond
Solution
1. endothermic - you must put a pan of water on the stove and give it heat in order to get water to boil. Because you are adding heat/energy, the reaction is endothermic.
2. exothermic - when you burn something, it feels hot to you because it is giving off heat into the surroundings.
3. exothermic - think of ice forming in your freezer instead. You put water into the freezer, which takes heat out of the water, to get it to freeze. Because heat is being pulled out of the water, it is exothermic. Heat is leaving.
Exercise $1$
Label each of the following processes as endothermic or exothermic.
1. water vapor condensing
2. gold melting
Answer (a)
exothermic
Answer (b)
endothermic
Example $2$
Is each chemical reaction exothermic or endothermic?
1. 2H2(g) + O2(g) → 2H2O(ℓ) + 135 kcal
2. N2(g) + O2(g) + 45 kcal → 2NO(g)
Solution
1. Because energy is a product, energy is given off by the reaction. Therefore, this reaction is exothermic.
2. Because energy is a reactant, energy is absorbed by the reaction. Therefore, this reaction is endothermic.
Exercise $2$
Is each chemical reaction exothermic or endothermic?
1. H2(g) + F2(g) → 2HF (g) + 130 kcal
2. 2C(s) + H2(g) + 5.3 kcal → C2H2(g)
Answer
a. The energy (130 kcal) is produced, hence the reaction is exothermic
b. The energy (5.3 kcal) is supplied or absorbed to react, hence, the reaction is endothermic
Bond Energy
Atoms bond together to form compounds because in doing so they attain lower energies than they possess as individual atoms. A quantity of energy, equal to the difference between the energies of the bonded atoms and the energies of the separated atoms, is released, usually as heat. That is, the bonded atoms have a lower energy than the individual atoms do. When atoms combine to make a compound, energy is always given off, and the compound has a lower overall energy.
When a chemical reaction occurs, molecular bonds are broken and other bonds are formed to make different molecules. For example, the bonds of two water molecules are broken to form hydrogen and oxygen.
$2H_2O \rightarrow 2H_2 + O_2 \nonumber$
Energy is always required to break a bond, which is known as bond energy. While the concept may seem simple, bond energy serves a very important purpose in describing the structure and characteristics of a molecule.
Energy is always required to break a bond. Energy is released when a bond is made.
Table $1$ Approximate Bond Energies
Bond Bond Energy (kJ/mol)
C–H 413
C–O 358
C=O* 745
C–N 305
C–C 347
C=C 614
C≡C 839
N–H 391
O—H 467
H–H 432
H—Cl 427
H—I 295
*C = O(CO2) = 799
When a chemical reaction occurs, the atoms in the reactants rearrange their chemical bonds to make products. The new arrangement of bonds does not have the same total energy as the bonds in the reactants. Therefore, when chemical reactions occur, there will always be an accompanying energy change. The enthalpy change, for a given reaction can be calculated using the bond energy values from Table $1$.
In this process, one adds energy to the reaction to break bonds, and extracts energy for the bonds that are formed.
$\text{enthalpy change} = \sum (\text{bonds broken}) - \sum (\text{bonds formed}) \nonumber$
Example $3$: Generation of Hydrogen Iodide
What is the enthalpy change for this reaction and is it endothermic or exothermic?
$H_2(g)+I_2(g) \rightarrow 2HI(g) \nonumber$
Solution
First look at the equation and identify which bonds exist on in the reactants.
• one H-H bond and
• one I-I bond
Now do the same for the products
• two H-I bonds
Then identify the bond energies of these bonds from the table above:
• H-H bonds: 436 kJ/mol
• I-I bonds: 151 kJ/mol
The sum of enthalpies on the reaction side is:
436 kJ/mole + 151 kJ/mole = 587 kJ/mol.
This is how much energy is needed to break the bonds on the reactant side. Then we look at the bond formation which is on the product side:
• 2 mol H-I bonds: 297 kJ/mol
The sum of enthalpies on the product side is:
2 x 297 kJ/mol= 594 kJ/mol
This is how much energy is released when the bonds on the product side are formed. The net change of the reaction is therefore
587 kJ/mol -594 kJ/mol= -7 kJ/mol.
Since this is negative, the reaction is exothermic.
Exercise $3$: Decomposition of Water
Using the bond energies given in the chart above, find the enthalpy change for the thermal decomposition of water:
$2H_2O (g) \rightarrow 2H_2 + O_2 (g) \nonumber$
Is the reaction written above exothermic or endothermic? Explain.
Solution
The enthalpy change deals with breaking two mole of O-H bonds and the formation of 1 mole of O-O bonds and two moles of H-H bonds (Table $1$).
• The sum of the energies required to break the bonds on the reactants side is 4 x 460 kJ/mol = 1840 kJ/mol.
• The sum of the energies released to form the bonds on the products side is
• 2 moles of H-H bonds = 2 x 436.4 kJ/mol = 872.8 kJ/mol
• 1 moles of O=O bond = 1 x 498.7 kJ/mil = 498.7 kJ/mol
which is an output (released) energy = 872.8 kJ/mol + 498.7 kJ/mol = 1371.5 kJ/mol.
Total energy difference is 1840 kJ/mol – 1371.5 kJ/mol = 469 kJ/mol, which indicates that the reaction is endothermic and that 469 kJ of heat is needed to be supplied to carry out this reaction.
This reaction is endothermic since it requires energy in order to create bonds.
Summary
• Chemical processes are labeled as exothermic or endothermic based on whether they give off or absorb energy, respectively.
• Atoms are held together by a certain amount of energy called bond energy.
• Energy is released to generate bonds, which is why the enthalpy change for breaking bonds is positive. Energy is required to break bonds. Atoms are much happier when they are "married" and release energy because it is easier and more stable to be in a relationship (e.g., to generate octet electronic configurations). The enthalpy change is negative because the system is releasing energy when forming bond.
Contributors and Attributions
• Libretext: Introductory Chemistry (Tro)
• Libretext: Fundamentals of General Organic and Biological Chemistry (McMurry et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.02%3A_Energy_and_Chemical_Reactions.txt |
Learning Objectives
• Define chemical reaction rate.
• Describe the effects of temperature, concentration, surface area, and catalysis on reaction rates.
The lizard in the photograph is not simply enjoying the sunshine or working on its tan. The heat from the sun’s rays is critical to the lizard’s survival. A warm lizard can move faster than a cold one because the chemical reactions that allow its muscles to move occur more rapidly at higher temperatures. In the absence of warmth, the lizard is an easy meal for predators.
From baking a cake to determining the useful lifespan of a bridge, rates of chemical reactions play important roles in our understanding of processes that involve chemical changes.
A rate is a measure of how some property varies with time. Speed is a familiar rate that expresses the distance traveled by an object in a given amount of time. Wage is a rate that represents the amount of money earned by a person working for a given amount of time. Likewise, the rate of a chemical reaction is a measure of how much reactant is consumed, or how much product is produced, by the reaction in a given amount of time.
The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts. Rates of reactions that consume or produce gaseous substances, for example, are conveniently determined by measuring changes in volume or pressure. For reactions involving one or more colored substances, rates may be monitored via measurements of light absorption. For reactions involving aqueous electrolytes, rates may be measured via changes in a solution’s conductivity.
For reactants and products in solution, their relative amounts (concentrations) are conveniently used for purposes of expressing reaction rates. If we measure the concentration of hydrogen peroxide, H2O2, in an aqueous solution, we find that it changes slowly over time as the H2O2 decomposes, according to the equation:
$\ce{2H2O2}(aq)⟶\ce{2H2O}(l)+\ce{O2}(g) \nonumber$
The rate at which the hydrogen peroxide decomposes can be expressed in terms of the rate of change of its concentration, as shown here:
\begin{align*} \ce{rate\: of\: decomposition\: of\: H_2O_2} &=\mathrm{−\dfrac{change\: in\: concentration\: of\: reactant}{time\: interval}}\[4pt] \end{align*} \nonumber
Factors Affecting Reaction Rates
By their nature, some reactions occur very quickly, while others are very slow. However, certain changes in the reacting conditions can have an effect on the rate of a given chemical reaction.
Concentration
The rates of many reactions depend on the concentrations of the reactants. Rates usually increase when the concentration of one or more of the reactants increases. In a polluted atmosphere where the concentration of sulfur dioxide is high, calcium carbonate deteriorates more rapidly than in less polluted air. Similarly, phosphorus burns much more rapidly in an atmosphere of pure oxygen than in air, which is only about 20% oxygen.
Phosphorus Burning
Video $1$ Phosphorous burns rapidly in air, but it will burn even more rapidly if the concentration of oxygen in is higher.
Surface Area
A large log placed in a fire will burn relatively slowly. If the same mass of wood were added to the fire in the form of small twigs, they would burn much more quickly. This is because the twigs provide a greater surface area than the log does. An increase in the surface area of a reactant increases the rate of a reaction. Surface area is larger when a given amount of a solid is present as smaller particles. A powdered reactant has a greater surface area than the same reactant as a solid chunk. In order to increase the surface area of a substance, it may be ground into smaller particles or dissolved into a liquid. In solution, the dissolved particles are separated from each other and will react more quickly with other reactants.
Temperature
Chemical reactions typically occur faster at higher temperatures. Food can spoil quickly when left on the kitchen counter. However, the lower temperature inside of a refrigerator slows that process so that the same food remains fresh for days. We use a burner or a hot plate in the laboratory to increase the speed of reactions that proceed slowly at ordinary temperatures. In many cases, an increase in temperature of only 10 °C will approximately double the rate of a reaction in a homogeneous system.
The Presence of a Catalyst
Hydrogen peroxide solutions foam when poured onto an open wound because substances in the exposed tissues act as catalysts, increasing the rate of hydrogen peroxide’s decomposition. However, in the absence of these catalysts (for example, in the bottle in the medicine cabinet) complete decomposition can take months. A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative pathway or mechanism for the reaction to follow.
Summary
• The reaction rate indicates how fast the reaction proceeds.
• Factors affecting reaction rate are:
• Concentration of reactants
• Surface area
• Temperature
• Presence of catalysts | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.03%3A_Reaction_Rates.txt |
Learning Objective
• Explain the first and second laws of thermodynamics
Thermodynamics refers to the study of energy and energy transfer involving physical matter. The matter and its environment relevant to a particular case of energy transfer are classified as a system, and everything outside of that system is called the surroundings. For instance, when heating a pot of water on the stove, the system includes the stove, the pot, and the water. Energy is transferred within the system (between the stove, pot, and water). There are two types of systems: open and closed. An open system is one in which energy can be transferred between the system and its surroundings. The stovetop system is open because heat can be lost into the air. A closed system is one that cannot transfer energy to its surroundings.
Biological organisms are open systems. Energy is exchanged between them and their surroundings, as they consume energy-storing molecules and release energy to the environment by doing work. Like all things in the physical world, energy is subject to the laws of physics. The laws of thermodynamics govern the transfer of energy in and among all systems in the universe.
The First Law of Thermodynamics
The first law of thermodynamics deals with the total amount of energy in the universe. It states that this total amount of energy is constant. In other words, there has always been, and always will be, exactly the same amount of energy in the universe. Energy exists in many different forms. According to the first law of thermodynamics, energy may be transferred from place to place or transformed into different forms, but it cannot be created or destroyed. The transfers and transformations of energy take place around us all the time. Light bulbs transform electrical energy into light energy. Gas stoves transform chemical energy from natural gas into heat energy. Plants, during photosynthesis perform one of the most biologically useful energy transformations on earth: that of converting the energy of sunlight into the chemical energy stored within organic molecules. Some examples of energy transformations are shown in Figure \(1\).
The challenge for all living organisms is to obtain energy from their surroundings in forms that they can transfer or transform into usable energy to do work. Living cells have evolved to meet this challenge very well. Chemical energy stored within organic molecules such as sugars and fats is transformed through a series of cellular chemical reactions into energy within molecules of ATP (Adenosine triphosphate). Energy in ATP molecules is easily accessible to do work. Examples of the types of work that cells need to do include building complex molecules, transporting materials, powering the beating motion of cilia or flagella, contracting muscle fibers to create movement, and reproduction.
The Second Law of Thermodynamics
An important concept in physical systems is that of order and disorder (also known as randomness). The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy (Figure \(2\)). To better understand entropy, think of a student’s bedroom. If no energy or work were put into it, the room would quickly become messy. It would exist in a very disordered state, one of high entropy. Energy must be put into the system, in the form of the student doing work and putting everything away, in order to bring the room back to a state of cleanliness and order. This state is one of low entropy. Similarly, a car or house must be constantly maintained with work in order to keep it in an ordered state. Left alone, the entropy of the house or car gradually increases through rust and degradation. Molecules and chemical reactions have varying amounts of entropy as well. For example, as chemical reactions reach a state of equilibrium, entropy increases, and as molecules at a high concentration in one place diffuse and spread out, entropy also increases.
All physical systems can be thought of in this way: Living things are highly ordered, requiring constant energy input to be maintained in a state of low entropy. As living systems take in energy-storing molecules and transform them through chemical reactions, they lose some amount of usable energy in the process, because no reaction is completely efficient. They also produce waste and by-products that aren’t useful energy sources. This process increases the entropy of the system’s surroundings. Since all energy transfers result in the loss of some usable energy, the second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe. Even though living things are highly ordered and maintain a state of low entropy, the entropy of the universe in total is constantly increasing due to the loss of usable energy with each energy transfer that occurs. Essentially, living things are in a continuous uphill battle against this constant increase in universal entropy.
Summary
• The first law states that the total amount of energy in the universe is constant. This means that energy can’t be created or destroyed, only transferred or transformed.
• The second law of thermodynamics states that every energy transfer involves some loss of energy in an unusable form, such as heat energy, resulting in a more disordered system. In other words, no energy transfer is completely efficient and tends toward disorder.
Contributors and Attributions
Template:ContribOpenSTAXBio | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.04%3A_The_Laws_of_Thermodynamics.txt |
Learning Objective
• Describe the different fossil fuels.
Fossil fuels is the term given to energy sources with a high hydrocarbon content (see Chapter 1 for a review of hydrocarbon molecules) found in the Earth’s crust that formed in the geologic past and can be burned to release their energy. They were formed from prehistoric plants and animals that lived hundreds of millions of years ago (100 – 500 million years ago). When these ancient living organisms died they were quickly buried and subjected to immense pressure from overlying earth materials including layers of mud, rock, sand, and sometimes surface water bodies such as oceans and lakes.
During the millions of years that passed, the dead plants and animals slowly decomposed in anaerobic (very low to no oxygen) conditions and their chemical energy became concentrated. The organic compounds that once made up tissues of these organisms were chemically changed under high pressures and temperatures. While some fossil fuels may be in the process of formation today, the amount of time required for usable quantities to form is measured in millions of years, so these fuels will never be available for us. Thus for all practical purposes we consider fossil fuels to be finite and non-renewable.
Fossil Fuel Types and Formation
There are three main types of fossil fuels – natural gas, oil, and coal – and the specific type formed depends on the combination of organic matter that was present, how long it was buried and what temperature and pressure conditions existed when they were decomposing. Oil and natural gas were created from organisms that lived in water and were buried under ocean or river sediments. Long after the great prehistoric seas and rivers vanished, heat, pressure, and bacteria combined to compress and transform the organic material under layers of silt or shale rock (Figure \(1\)). In most areas, a thick liquid called oil formed first, but in deeper, hot regions underground, the transformation process continued until natural gas was formed. Over time, some of this oil and natural gas began working its way upward through the earth’s crust until they ran into rock formations called “caprocks” that are dense enough to prevent them from seeping to the surface. It is from under these caprocks that most oil and natural gas is retrieved today.
Coal is a fossil fuel that formed from the remains of trees, ferns, and other plants that lived 300 to 400 million years ago (Figure \(2\)). In some areas, such as portions of what is now the eastern United States, coal was formed from swamps covered by sea water. The sea water contained a large amount of sulfur, and as the seas dried up, the sulfur was left behind in the coal. Scientists are working on ways to take the sulfur out of coal because when coal burns, the sulfur is released in to the atmosphere as an air pollutant (see Chapter 6). Some coal deposits, however, were formed from freshwater swamps which had very little sulfur in them. These coal deposits, located largely in the western part of the United States, have much less sulfur in them.
Consumption and Production
Historically, human prosperity has been directly correlated with energy use. The health and vitality of world societies critically depends on energy, most of which comes from fossil fuels (Figure \(3\)). Energy resources, however, are unevenly distributed throughout the world, and so are the consumption rates. Developed regions generally consume far more energy than the developing regions. For example, the United States has only about 5% of the world’s population but constitutes over 20% of the world’s energy consumption. Additionally, developing countries devote a larger proportion of energy consumption to subsistence activities such as growing and preparing food, and heating homes. Industrialized nations rely more on mechanized equipment and technology and, therefore, a greater proportion of their energy consumption goes to transportation and industry.
Fossil fuels can be utilized without being converted or transformed to another form of energy, this is referred to as primary energy consumption. In their primary form, fossil fuels can be used for transportation, heating and cooking, or used to generate electricity. The use of electricity is a form of secondary energy consumption. Transforming fossil fuel energy into electricity allows for easier transportation over long distances and application to a variety of uses. Additionally, as shown in Figure \(4\), there are four major sectors that consume energy: 1) The industrial sector which includes facilities and equipment used for manufacturing, agriculture, mining, and construction; 2) The transportation sector includes vehicles that transport people or goods including cars, trucks, buses, motorcycles, trains, aircraft, boats, barges, and ships; 3) The residential sector consists of homes and apartments; 4) The commercial sector includes offices, malls, stores, schools, hospitals, hotels, warehouses, restaurants, places of worship, and more. Each of these sectors also consumes electricity produced by the electric power sector.
In 2019, U.S. energy production exceeded U.S. energy consumption on an annual basis for the first time since 1957. The United States produced 101.0 quads of energy and consumed 100.2 quads. After record high energy production and consumption in 2018, U.S. energy production grew 5.7% and energy consumption decreased by 0.9% in 2019.
Fossil fuels—petroleum, natural gas, and coal—accounted for about 80% of total U.S. primary energy production in 2019 see Figure \(5\).
Summary
• Fossil fuels are energy sources from the Earth’s crust (that formed in the geologic past) with a high hydrocarbon content and can be burned to release their energy.
• The three main types of fossil fuels that were discussed are natural gas, oil, and coal.
Contributors and Attributions
• U.S. Energy Information Administration
• Libretext: Introduction to Environmental Science (Zendher et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.05%3A_Power-_People_Horses_and_Fossils.txt |
Learning Objectives
• Describe coal and its processing.
• List the products of coal burning that promotes pollution.
Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures. It is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified into four main types, or ranks depending on the types and amounts of carbon present and on the amount of heat energy the coal can produce, including anthracite, bituminous, subbituminous, and lignite (highest to lowest ranked, pictured in Figure \(1\).
There are four distinct classes of coal (Table \(1\)); their hydrogen and oxygen contents depend on the length of time the coal has been buried and the pressures and temperatures to which it has been subjected. The most abundant form in the United States is bituminous coal, which has a high sulfur content becauseof the presence of small particles of pyrite (FeS2). The combustion of coal releases the sulfur in FeS2 as SO2, which is a major contributor to acid rain.
Table \(1\) Properties of Different Types of Coal.
Type % Carbon Hydrogen:Carbon Mole Ratio % Oxygen % Sulfur US Deposits
anthracite 92 0.5 3 1 Pennsylvania, New York
bituminous 80 0.6 8 5 Appalachia, Midwest, Utah
subbituminous 77 0.9 16 1 Rocky Mountains
lignite 71 1.0 23 1 Montana
Peat, a precursor to coal, is the partially decayed remains of plants that grow in swampy areas. It is removed from the ground in the form of soggy bricks of mud that will not burn until they have been dried. If a peat bog were buried under many layers of sediment for a few million years, the peat could eventually be compressed and heated enough to become lignite, the lowest grade of coal; given enough time and heat, lignite would eventually become anthracite, a much better fuel.
For us to use the potential energy stored in coal, it first must be mined from the ground. This process in itself uses a great deal of resources and has its own environmental impacts. Coal then typically undergoes processing to make it suitable for use in coal-fire power plants. Finally, the processed coal is burned in these power plants, and the kinetic energy released from its combustion is harnessed for electricity generation or other purposes. Figure \(2\) below is a schematic diagram showing a typical layout of a coal-fire power plant. You can also watch a short video of a virtual tour of a coal power plant at the URL provided below.
Power Plant Virtual Tour
Video \(1\) Coal-Fueled Power Plant Virtual Tour Video
The Global Carbon Cycle
Figure \(3\) illustrates the global carbon cycle, the distribution and flow of carbon on Earth. Normally, the fate of atmospheric CO2 is to either (1) dissolve in the oceans and eventually precipitate as carbonate rocks or (2) be taken up by plants. The rate of uptake of CO2 by the ocean is limited by its surface area and the rate at which gases dissolve, which are approximately constant. The rate of uptake of CO2 by plants, representing about 60 billion metric tons of carbon per year, partly depends on how much of Earth’s surface is covered by vegetation. Unfortunately, the rapid deforestation for agriculture is reducing the overall amount of vegetation, and about 60 billion metric tons of carbon are released annually as CO2 from animal respiration and plant decay. The amount of carbon released as CO2 every year by fossil fuel combustion is estimated to be about 5.5 billion metric tons. The net result is a system that is slightly out of balance, experiencing a slow but steady increase in atmospheric CO2 levels. As a result, average CO2 levels have increased by about 30% since 1850.
Most of Earth’s carbon is found in the crust, where it is stored as calcium and magnesium carbonate in sedimentary rocks. The oceans also contain a large reservoir of carbon, primarily as the bicarbonate ion (HCO3). Green plants consume about 60 billion metric tons of carbon per year as CO2 during photosynthesis, and about the same amount of carbon is released as CO2 annually from animal and plant respiration and decay. The combustion of fossil fuels releases about 5.5 billion metric tons of carbon per year as CO2.
Pollution from Coal Burning
In the United States and most of the world, most of the coal consumed is used as a fuel to generate electricity. Burning coal produces emissions such as sulfur dioxide (SO2) and nitrogen oxides (NOx) that are associated with acid rain (more on this in chapter 6). Carbon dioxide (CO2), another emission resulting from burning coal, is a major greenhouse gas that is associated with global warming (see Chapter 13 ). Burning of coal is classified as incomplete combustion, since the reaction of carbon (in coal) with oxygen produces carbon monoxide and/or carbon (soot) in addition to carbon dioxide.
Burning coal produces emissions that also impact human health. Emissions such as sulfur dioxide (SO2), nitrogen oxides (NOx) and particulates contribute to respiratory illnesses. Particulates also contribute to a condition among coal miners and other coal workers known as coal workers' pneumoconiosis (CWP) or black lung disease, which results from long exposure to coal dust. Inhaled coal dust progressively builds up in the lungs and is unable to be removed by the body; this leads to inflammation, fibrosis, and in worse cases, tissue death (necrosis).
Coal is the largest source of mercury and also a source of other heavy metals, many of which have been linked to both neurological and developmental problems in humans and other animals. Mercury concentrations in the air usually are low and of little direct concern. However, when mercury enters water, either directly or through deposition from the air, biological processes transform it into methylmercury, a highly toxic chemical that accumulates in fish and the animals (including humans) that eat fish.
Reducing the Environmental Impacts of Coal Use
Regulations such as the Clean Air Act and the Clean Water Act require industries to reduce pollutants released into the air and water. Below are some actions that have been taken to reduce the negative impacts of coal on human and environmental health:
Clean coal technology: Industry has found several ways to reduce sulfur, NOx, and other impurities from coal before burning.
• Coal consumers have shifted toward greater use of low sulfur coal.
• Power plants use scrubbers, to clean SO2, NOx, particulate matter, and mercury from the smoke before it leaves their smokestacks. In addition, industry and the U.S. government have cooperated to develop technologies that make coal more energy-efficient so less needs to be burned.
• Research is underway to address emissions of carbon dioxide from coal combustion. Carbon capture & sequestration separates CO2 from emissions sources and recovers it in a concentrated stream. The CO2 can then be sequestered, which puts CO2 into storage, possibly underground, where it will remain permanently.
• Reuse and recycling can also reduce coal’s environmental impact. Land that was previously used for coal mining can be reclaimed and used for airports, landfills, and golf courses. Waste products captured by scrubbers can be used to produce products like cement and synthetic gypsum for wallboard.
Summary
• Coal is a complex solid material derived primarily from plants that died and were buried hundreds of millions of years ago and were subsequently subjected to high temperatures and pressures.
• Coal is classified into four main types, depending on the types and amounts of carbon present and on the amount of heat energy the coal can produce, including anthracite, bituminous, subbituminous, and lignite.
• The processing of coal is described as well as the environmental and health impacts of its use.
• Research is underway and various approaches are implemented (clean coal technology, use of low sulfur coal, use of scrubbers etc.) to reduce the environmental impacts of coal use.
Contributors and Attributions
Libretext: Introduction to Environmental Science (Zendher et al.)
Libretext: General Chemistry (Petrucci et al.)
Anne Marie Helmenstine, Ph.D. “What Is a Combustion Reaction?” ThoughtCo, www.thoughtco.com/combustion-reactions-604030. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.06%3A_Coal_-_The_Carbon_Rock_of_Ages.txt |
Learning Objectives
• Describe the nature and processing of natural gas, petroleum, and gasoline.
• List different alternative fuels.
Crude oil is frequently found in reservoirs along with natural gas. In the past, natural gas was either burned or allowed to escape into the atmosphere. Now, technology has been developed to capture the natural gas and either reinject it into the well or compress it into liquid natural gas (LNG).
Natural Gas
Natural gas is predominately composed of methane (CH4). Some of the gases that are produced along with methane, such as butane and propane (by-products), are separated and cleaned at a gas processing plant. The by-products, once removed, are used in a number of ways. For example, propane can be used for cooking on gas grills. Natural gas withdrawn from a well may contain liquid hydrocarbons and non-hydrocarbon gases. This is called "wet" natural gas. The natural gas is separated from these components near the site of the well or at a processing plant. The gas is then considered "dry" and is sent through pipelines to a local distribution company, and, ultimately, to the consumer.
Most of the natural gas consumed in the United States is produced in the United States. Some is imported from Canada and shipped to the United States in pipelines. A small amount of natural gas is shipped to the United States as LNG.
Fracking for Gas
Conventional natural gas is found in permeable reservoirs, typically composed of sandstone or limestone, where extraction is relatively straightforward because the gas generally flows freely. Unconventional gas is found in rocks with extremely low permeability, which makes extracting it much more difficult. Such gas is extracted by employing so-called “unconventional” techniques such as hydraulic fracturing (fracking), which has been in use since the late 1940s. In recent decades, fracking technology has greatly improved, and its use has been expanded. The process of fracking for gas is very similar to that of fracking for oil, and the environmental impacts are similar also.
Petroleum
Petroleum Oil is currently the most widely used fossil fuel and accounts for about one third of global energy consumption. Unlike coal, which is primarily used as a fuel for electricity generation, oil is primarily used as a fuel for transportation. Oil is also used to manufacture plastics and other synthetic compounds ubiquitous to our everyday life. Crude (unprocessed) oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish, reddish, or even greenish). In the reservoir it is usually found in association with natural gas, which being lighter forms a gas cap over the oil.
Oil is made up of hydrocarbons which are molecules that contain hydrogen and carbon in various lengths and structures, from straight chains to branching chains to rings. Hydrocarbons contain a lot of energy and many of the things derived from crude oil like gasoline, diesel fuel, paraffin wax and so on take advantage of this energy.
Extraction
Oil is mainly obtained by drilling either on land (onshore) or in the ocean (offshore). Early offshore drilling was generally limited to areas where the water was less than 300 feet deep. Oil and natural gas drilling rigs now operate in water as deep as two miles. Offshore oil producers are required to take precautions to prevent pollution, spills, and significant changes to the ocean environment. Offshore rigs are designed to withstand hurricanes. Offshore production is much more expensive than land-based production. When offshore oil wells are no longer productive enough to be economical, they are sealed and abandoned according to applicable regulations.
Processing and Refining
When extracted, crude oil consists of many types of hydrocarbons as well as some unwanted substances such as sulfur, nitrogen, oxygen, dissolved metals, and water all mixed together. Unprocessed crude oil is therefore, not generally useful in industrial applications and must first be separated into different useable products at a refinery (Figure \(1\)). All refineries perform three basic steps: separation, conversion, and treatment in the processing and refining of crude oil.
During separation, the various products (hydrocarbons) are separated in to different components (called fractions), by taking advantage of the differences in boiling temperature of the components. This process is called fractional distillation and involves heating up the crude, letting it vaporize and then condensing the vapor. The lightest components have the lowest boiling temperature and rise to the top while the heaviest which also have the highest boiling temperature remain at the bottom.
Conversion is the chemical processing in which some of the fractions are transformed in to other products, for example, a refinery can turn diesel fuel into gasoline depending on the demand for gasoline. Conversion can involve breaking larger hydrocarbon chains into smaller ones (cracking), combining smaller chains into larger ones (unification) or rearranging the molecules to created desired products (alteration).
Treatment is done to the fractions to remove impurities such as sulfur, nitrogen and water among others. Refineries also combine the various fractions (processed and unprocessed) into mixtures to make desired products. For example, different mixtures of hydrocarbon chains can create gasolines with different octane ratings, with and without additives, lubricating oils of various weights and grades (e.g., WD-40, 10W-40, 5W-30, etc.), heating oil and many others. The products are stored on-site until they can be delivered to various markets such as gas stations, airports and chemical plants.
A 42 U.S. gallon barrel of crude oil yields about 45 gallons of petroleum products because of refinery processing gain. This increase in volume is similar to what happens to popcorn when it is popped. Gasoline makes up the largest fraction of all petroleum products obtained (Figure \(2\)). Other products include diesel fuel and heating oil, jet fuel, petrochemical feedstocks, waxes, lubricating oils, and asphalt.
Fracking for oil
Hydraulic fracturing, informally referred to as “fracking,” is an oil well development process that typically involves injecting water, sand, and chemicals under high pressure into a bedrock formation via the well. This process is intended to create new fractures in the rock as well as increase the size, extent, and connectivity of existing fractures. Hydraulic fracturing is a well-stimulation technique used commonly in low-permeability rocks like tight sandstone, shale, and some coal beds to increase oil flow to a well from petroleum-bearing rock formations.
There are concerns regarding the potential contamination of fresh groundwater resources from oil and gas extraction wells that use hydraulic fracturing; either from the petroleum resource being produced or from the chemicals introduced in the fracturing process. Fracking fluid flowback – the fluid pumped out of the well and separated from oil and gas – not only contains the chemical additives used in the drilling process but also contains heavy metals, radioactive materials, volatile organic compounds (VOCs) and hazardous air pollutants such as benzene, toluene, ethylbenzene and xylene. In some cases, this contaminated water is sent to water treatment plants that are not equipped to deal with some of these classes of contamination.
Gasoline
Petroleum is converted to useful products such as gasoline in three steps: distillation, cracking, and reforming. Part (a) in Figure \(3\ shows a cutaway drawing of a column used in the petroleum industry for separating the components of crude oil. The petroleum is heated to approximately 400°C (750°F), at which temperature it has become a mixture of liquid and vapor. This mixture, called the feedstock, is introduced into the refining tower. The most volatile components (those with the lowest boiling points) condense at the top of the column where it is cooler, while the less volatile components condense nearer the bottom. Some materials are so nonvolatile that they collect at the bottom without evaporating at all. Thus the composition of the liquid condensing at each level is different. These different fractions, each of which usually consists of a mixture of compounds with similar numbers of carbon atoms, are drawn off separately. Part (b) Figure \(3\ shows the typical fractions collected at refineries, the number of carbon atoms they contain, their boiling points, and their ultimate uses. These products range from gases used in natural and bottled gas to liquids used in fuels and lubricants to gummy solids used as tar on roads and roofs.
Figure \(3\) The Distillation of Petroleum. (a) This is a diagram of a distillation column used for separating petroleum fractions. (b) Petroleum fractions condense at different temperatures, depending on the number of carbon atoms in the molecules, and are drawn off from the column. The most volatile components (those with the lowest boiling points) condense at the top of the column, and the least volatile (those with the highest boiling points) condense at the bottom.
Octane Ratings of Gasolines
The quality of a fuel is indicated by its octane rating, which is a measure of its ability to burn in a combustion engine without knocking or pinging. Knocking and pinging signal premature combustion (Figure \(4\)) which can be caused either by an engine malfunction or by a fuel that burns too fast. In either case, the gasoline-air mixture detonates at the wrong point in the engine cycle, which reduces the power output and can damage valves, pistons, bearings, and other engine components. The various gasoline formulations are designed to provide the mix of hydrocarbons least likely to cause knocking or pinging in a given type of engine performing at a particular level.
The octane scale was established in 1927 using a standard test engine and two pure compounds: n-heptane and isooctane (2,2,4-trimethylpentane). n-Heptane, which causes a great deal of knocking on combustion, was assigned an octane rating of 0, whereas isooctane, a very smooth-burning fuel, was assigned an octane rating of 100. Chemists assign octane ratings to different blends of gasoline by burning a sample of each in a test engine and comparing the observed knocking with the amount of knocking caused by specific mixtures of n-heptane and isooctane. For example, the octane rating of a blend of 89% isooctane and 11% n-heptane is simply the average of the octane ratings of the components weighted by the relative amounts of each in the blend. Converting percentages to decimals, we obtain the octane rating of the mixture:
\[0.89(100) + 0.11(0) = 89 \tag{3.8.1} \]
As given in Table \(1\, many compounds that are now available have octane ratings greater than 100, which means they are better fuels than pure isooctane. In addition, antiknock agents, also called octane enhancers, have been developed. One of the most widely used for many years was tetraethyllead [(C2H5)4Pb], which at approximately 3 g/gal gives a 10–15-point increase in octane rating. Since 1975, however, lead compounds have been phased out as gasoline additives because they are highly toxic. Other enhancers, such as methyl t-butyl ether (MTBE), have been developed to take their place. They combine a high octane rating with minimal corrosion to engine and fuel system parts. Unfortunately, when gasoline containing MTBE leaks from underground storage tanks, the result has been contamination of the groundwater in some locations, resulting in limitations or outright bans on the use of MTBE in certain areas. As a result, the use of alternative octane enhancers such as ethanol, which can be obtained from renewable resources such as corn, sugar cane, and, eventually, corn stalks and grasses, is increasing.
Table \(1\) The Octane Ratings of Some Hydrocarbons and Common Additives.
Alternative Fuels
Alternative means to power vehicles is a hot topic in environmental chemistry. Hybrid vehicles, ethanol, biodiesel (Figure \(5\)), natural gas, and hydrogen fuel cells are all options for powering vehicles that reduce the environmental impact of greenhouse gases in the environment. The main concern for these alternative fuels is their efficiency vs. cost when compared to fossil fuels. Table \(2\) shows the chemical structure for several fuels, as well as the energy content of each.
Table \(2\) Energy Content of Fuels*.
Gasoline No. 2 Diesel Biodiesel Ethanol Hydrogen Liquefied Natural Gas (LNG) Liquefied Petroleum Gas
Chemical Structure C4 to C12 C8 to C25 Methyl esters of C12 to C22 fatty acids CH3CH2OH H2 CH4 C3H8 (majority) and C4H10 (minority)
Energy Content (Higher Heat Value) 124,340 Btu/gal (g) 137,380 Btu/gal (g) 127,960 Btu/gal for B100 (g) 84,530 Btu/gal for E100 (g) 61,013 Btu/lb (g) 84,820 Btu/gal (g) 91,410 Btu/gal (g
Energy Contained in Various Alternative Fuels as Compared to One Gallon of Gasoline 100% 113% 103% 77% 100% 64% 73%
*Table created at: http://www.afdc.energy.gov/afdc/fuels/properties.html
Ethanol
Ethanol can be used in varying percent grades by vehicles. Gasohol is 10% ethanol, produces less carbon emissions than typical gasoline, but decreases the miles per gallon (MPG) of the vehicle slightly. E85 is up to 85% ethanol, can be less expensive depending upon where you live, but lowers the MPG up to 30% compared to typical gasoline. Let’s look at the bond enthalpy change for the burning of fossil fuels vs. the burning of E85 to understand the drop in MPG.
Summary
• The extraction and processing of natural gas (mainly methane) and petroleum oil were discussed.
• Petroleum is converted to useful products such as gasoline by distillation, cracking, and reforming.
• Alternative means to power vehicles and reduce the effect of greenhouse gases in the environment include hybrid vehicles, ethanol, biodiesel , natural gas, and hydrogen fuel cells.
15.08: Convenient Energy
Learning Objective
• Describe the gasification and liquefaction of coal and the interest in its conversion.
Oil and natural gas resources are limited. Current estimates suggest that the known reserves of petroleum will be exhausted in about 60 years, and supplies of natural gas are estimated to run out in about 120 years. Coal, on the other hand, is relatively abundant, making up more than 90% of the world’s fossil fuel reserves. As a solid, coal is much more difficult to mine and ship than petroleum (a liquid) or natural gas.
Coal Gasification and Liquefaction
A great deal of current research focuses on developing methods to convert coal to gaseous fuels (coal gasification) or liquid fuels (coal liquefaction). In the most common approach to coal gasification, coal reacts with steam to produce a mixture of CO and H2 known as synthesis gas, or syngas:Because coal is 70%–90% carbon by mass, it is approximated as C in Equation $\ref{15.8.1}$.
$\mathrm{C_{(s)} +H_2O_{(g)} → CO_{(g)}+H_{2(g)}} \;\;\; ΔH= \mathrm{131\: kJ} \label{15.8.1}$
Converting coal to syngas removes any sulfur present and produces a clean-burning mixture of gases.
Syngas is also used as a reactant to produce methane and methanol. A promising approach is to convert coal directly to methane through a series of reactions:
$\mathrm{2C(s)+2H_2O(g)→\cancel{2CO(g)}+\cancel{2H_2(g)}}\hspace{20px}ΔH_1= \mathrm{262\: kJ}\ \mathrm{\cancel{CO(g)}+\cancel{H_2O(g)}→CO_2(g)+\cancel{H_2(g)}}\hspace{20px}ΔH_2=\mathrm{−41\: kJ}\ \mathrm{\cancel{CO(g)}+\cancel{3H_2(g)}→CH_4(g)+\cancel{H_2O(g)}}\hspace{20px}ΔH_3=\mathrm{−206\: kJ}\ \overline{\mathrm{Overall:\hspace{10px}2C(s)+2H_2O(g)→CH_4(g)+CO_2(g)}\hspace{20px}ΔH_\ce{comb}= \mathrm{15\: kJ}}\hspace{40px}\label{15.8.2}$
Burning a small amount of coal or methane provides the energy consumed by these reactions. Unfortunately, methane produced by this process is currently significantly more expensive than natural gas. As supplies of natural gas become depleted, however, this coal-based process may well become competitive in cost.
Similarly, the techniques available for converting coal to liquid fuels are not yet economically competitive with the production of liquid fuels from petroleum. Current approaches to coal liquefaction use a catalyst to break the complex network structure of coal into more manageable fragments. The products are then treated with hydrogen (from syngas or other sources) under high pressure to produce a liquid more like petroleum. Subsequent distillation, cracking, and reforming can be used to create products similar to those obtained from petroleum. The total yield of liquid fuels is about 5.5 bbl of crude liquid per ton of coal (1 bbl is 42 gal or 160 L). Although the economics of coal liquefaction are currently even less attractive than for coal gasification, liquid fuels based on coal are likely to become economically competitive as supplies of petroleum are consumed.
Summary
• There is great interest in developing methods to convert coal to gaseous fuels (coal gasification) or liquid fuels (coal liquefaction) as it is more convenient to mine and transport gas and liquid fuels.
• Converting coal to syngas (synthesis gas) removes any sulfur present and produces a clean-burning mixture of gases.
Contributors and Attributions
• Libretext: General Chemistry (Petrucci et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.07%3A_Natural_Gas_and_Petroleum.txt |
Learning Objective
• List the benefits and problems with nuclear energy.
Nuclear power is the use of nuclear reactions that release nuclear energy to generate heat, which most frequently is then used in steam turbines to produce electricity in a nuclear power plant. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators. Generating electricity from fusion power remains at the focus of international research.
Civilian nuclear power supplied 2,563 terawatt hours (TWh) of electricity in 2018, equivalent to about 10% of global electricity generation, and was the second largest low-carbon power source after hydroelectricity. As of December 2019, there are 443 civilian fission reactors in the world, with a combined electrical capacity of 395 gigawatt (GW). There are also 56 nuclear power reactors under construction and 109 reactors planned, with a combined capacity of 60 GW and 120 GW, respectively. The United States has the largest fleet of nuclear reactors, generating over 800 TWh zero-emissions electricity per year with an average capacity factor of 92%. Most reactors under construction are generation III reactors in Asia.
Nuclear power has one of the lowest levels of fatalities per unit of energy generated compared to other energy sources. Coal, petroleum, natural gas and hydroelectricity each have caused more fatalities per unit of energy due to air pollution and accidents.[10] Since its commercialization in the 1970s, nuclear power has prevented about 1.84 million air pollution-related deaths and the emission of about 64 billion tonnes of carbon dioxide equivalent that would have otherwise resulted from the burning of fossil fuels.
There is a debate about nuclear power. Proponents, such as the World Nuclear Association and Environmentalists for Nuclear Energy, contend that nuclear power is safe and it reduces carbon emissions. Nuclear power opponents, such as Greenpeace and NIRS, contend that nuclear power poses many threats to people and the environment.
There are over thirty countries that use nuclear power to generate electricity (see Table $1$. There were about 450 nuclear power reactors worldwide, producing close to 400,000 MW (MegaWatts) of electrical capacity. Commercial nuclear reactors can be found in North and South America, Europe, Africa, and Asia. The United States has the most reactors of any other countries. There are around ninety-eight reactors in the United States that provide around twenty percent of the electrical energy in the United States. Other countries, like France, employ around sixty nuclear reactors to produce 70% of their electrical power.
Table $1$: Nuclear Share of Electricity Generation and Number of Operated Reactors in 2019. Source: International Atomic Energy Agency (IAEA)
Country Number of Operated Reactors Total Net Electrical Capacity
[MW]
Nuclear Electricity Supplied
[GW.h]
Nuclear Share
[%]
UNITED STATES OF AMERICA 98 99648 809358.57 19.7
UNITED KINGDOM 15 8923 51032.09 15.6
UKRAINE 15 13107 78144.26 53.9
SWITZERLAND 5 3333 25369.65 23.9
SWEDEN 8 8592 64428.86 34.0
SPAIN 7 7121 55856.07 21.4
SOUTH AFRICA 2 1860 13602.57 6.7
SLOVENIA 1 688 5532.98 37.0
SLOVAKIA 4 1814 14282.25 53.9
RUSSIA 39 28448 195535.15 19.7
ROMANIA 2 1300 10368.21 18.5
PAKISTAN 5 1318 9065.80 6.6
NETHERLANDS 1 482 3700.71 3.2
MEXICO 2 1552 10880.73 4.5
KOREA, REPUBLIC OF 25 23833 138809.35 26.2
JAPAN 38 36476 65681.92 7.5
IRAN, ISLAMIC REPUBLIC OF 1 915 5865.73 1.8
INDIA 22 6255 40740.49 3.2
HUNGARY 4 1902 15414.83 49.2
FRANCE 58 63130 382402.75 70.6
FINLAND 4 2794 22914.88 34.7
CZECH REPUBLIC 6 3932 28581.12 35.2
CHINA 48 45518 330122.19 4.9
CANADA 19 13554 94853.85 14.9
BULGARIA 2 2006 15868.88 37.5
BRAZIL 2 1884 15224.11 2.7
BELGIUM 7 5930 41421.66 47.6
ARMENIA 1 375 2028.96 27.8
ARGENTINA 3 1641 7926.96 5.9
Total 449 392779 2586163.02 N
Nuclear Power Plants
After fabrication, fuel assemblies are transported to nuclear power plants where they are used as a source of energy for generating electricity. They are stored onsite until they are needed by the reactor operators. At this stage, the uranium is only mildly radioactive, and essentially all radiation is contained within the metal tubes. When needed, the fuel is loaded into a reactor core (Figure $2$). Typically, about one third of the reactor core (40 to 90 fuel assemblies) is changed out every 12 to 24 months.
The most common type of reactors are the pressurized water reactors (PWR) (Figure $2$) in which water is pumped through the reactor core and heated by the fission process. The water is kept under high pressure inside the reactor so it does not boil. The heated water from the reactor passes through tubes inside the steam generator where the heat is transferred to water flowing around the tubes in the steam generator. The water in the steam generator boils and turns to steam. The steam is piped to the turbines. The force of the expanding steam drives the turbines, which spin a magnet in coil of wire – the generator– to produce electricity.
After passing through the turbines, the steam is converted back to water by circulating it around tubes carrying cooling water in the condenser. The condensed steam – now water – is returned to the steam generators to repeat the cycle.
The three water systems (condenser, steam generator, and reactor) are separate from each other and are not permitted to mix. Water in the reactor is radioactive and is contained within the containment structure whereas water in the steam generator and condenser is nonradioactive.
The Nuclear Advantage: Minimal Air Pollution
By using fission, nuclear power plants generate electricity without emitting air pollutants like those emitted by fossil fuel-fired power plants. This means that financial costs related to chronic health problems caused by air pollutants such as particulate material, carbon monoxide, nitrogen oxides and ozone among others are significantly reduced. In addition nuclear reactors do not produce carbon dioxide while operating which means that nuclear energy does not contribute to the global warming problem.
Another benefit of nuclear energy over fossil fuels especially coal is that uranium generates far more power per unit weight or volume. This means that less of it needs to be mined and consequently the damage to the landscapes is less especially when compared to the damage that results from coal mining such as mountaintop removal.
Problems with Nuclear Power
The main environmental concern related to nuclear power is the creation of radioactive wastes such as uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. These materials can remain radioactive and dangerous to human health for thousands of years. Radioactive wastes are classified as low-level and high-level. By volume, most of the waste related to the nuclear power industry has a relatively low-level of radioactivity. Uranium mill tailings contain the radioactive element radium, which decays to produce radon, a radioactive gas. Most uranium mill tailings are placed near the processing facility or mill where they come from. Uranium mill tailings are covered with a barrier of material such as clay to prevent radon from escaping into the atmosphere, and they are then covered by a layer of soil, rocks, or other materials to prevent erosion of the sealing barrier.
The other types of low-level radioactive waste are the tools, protective clothing, wiping cloths, and other disposable items that get contaminated with small amounts of radioactive dust or particles at nuclear fuel processing facilities and power plants. These materials are subject to special regulations that govern their handling, storage, and disposal so they will not come in contact with the outside environment.
High-level radioactive waste consists of spent nuclear reactor fuel (i.e., fuel that is no longer useful for producing electricity). The spent reactor fuel is in a solid form consisting of small fuel pellets in long metal tubes called rods. Spent reactor fuel assemblies are initially stored in specially designed pools of water, where the water cools the fuel and acts as a radiation shield. Spent reactor fuel assemblies can also be stored in specially designed dry storage containers. An increasing number of reactor operators now store their older spent fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling. There is currently no permanent disposal facility in the United States for high-level nuclear waste.
When a nuclear reactor stops operating, it must be decommissioned. This involves safely removing the reactor and all equipment that has become radioactive from service and reducing radioactivity to a level that permits other uses of the property. The U.S. Nuclear Regulatory Commission has strict rules governing nuclear power plant decommissioning that involve cleanup of radioactively contaminated plant systems and structures, and removal of the radioactive fuel.
The processes for mining and refining uranium ore and making reactor fuel require large amounts of energy. Nuclear power plants have large amounts of metal and concrete, which also require large amounts of energy to manufacture. If fossil fuels are used for mining and refining uranium ore or in constructing the nuclear plant, then the emissions from burning those fuels could be associated with the electricity that nuclear power plants generate.
Nuclear Accidents
A nuclear meltdown, or uncontrolled nuclear reaction in a nuclear reactor, can potentially result in widespread contamination of air and water. Some serious nuclear and radiation accidents have occurred worldwide. The most severe accident was the Chernobyl accident of 1986 in the then Soviet Union (now Ukraine) which killed 31 people directly and sickened or caused cancer in thousands more. The Fukushima Daiichi nuclear disaster (2011) in Japan was caused by a 9.0 magnitude earthquake that shut down power supply and a tsunami that flooded the plant’s emergency power supply. This resulted in the release of radioactivity although it did not directly result in any deaths at the time of the disaster. Another nuclear accident was the Three Mile Island accident (1979) in Pennsylvania, USA. This accident resulted in a near disastrous core meltdown that was due to a combination of human error and mechanical failure but did not result in any deaths and no cancers or otherwise have been found in follow up studies of this accident. While there are potentially devastating consequences to a nuclear meltdown, the likelihood of one occurring is extremely small. After every meltdown, including the 2011 Fukushima Daiichi disaster, new international regulations were put in place to prevent such an event from occurring again.
Breeder Reactors: Making More Fuel Than They Burn
Because $\ce{_{92}^{235}U}$ is only 0.7 percent of naturally occurring uranium, its supply is fairly limited and could well only last for about 50 years of full-scale use. The other 99 percent of the uranium can also be utilized if it is first converted into plutonium by neutron bombardment:
$\ce{_{92}^{238}U + _{0}^{1}n -> _{94}^{239}Pu + 2 _{-1}^{0}e} \nonumber$
$\ce{_{94}^{239}Pu}$ is also fissionable, and so it could be used in a nuclear reactor as well as $\ce{_{92}^{235}U}$.
The production of plutonium can be carried out in a breeder reactor which not only produces energy like other reactors but is designed to allow some of the fast neutrons to bombard the $\ce{_{92}^{235}U}$, producing plutonium at the same time. More fuel is then produced than is consumed.
Breeder reactors present additional safety hazards to those already outlined. They operate at higher temperatures and use very reactive liquid metals such as sodium in their cooling systems, and so the possibility of a serious accident is higher. In addition the large quantities of plutonium which would be produced in a breeder economy would have to be carefully safeguarded. Plutonium is an α emitter and is very dangerous if taken internally. Its half-life is 24,000 years, and so it will remain in the environment for a long time if dispersed. Moreover, $\ce{_{94}^{239} Pu}$ can be separated chemically (not by the much more expensive gaseous diffusion used to concentrate $\ce{_{92}^{ 235}U}$ from fission products and used to make bombs. Such a material will obviously be attractive to terrorist groups, as well as to countries which are not currently capable of producing their own atomic weapons.
Today many nations are considering an expanded role for nuclear power in their energy portfolios. This expansion is driven by concerns about global warming, growth in energy demand, and relative costs of alternative energy sources. In 2008, 435 nuclear reactors in 30 countries provided 16% of the world’s electricity. In January 2009, 43 reactors were under construction in 11 countries, with several hundred more projected to come on line globally by 2030.
Nuclear Fusion
The most important fusion process in nature is the one that powers stars. The fusion of hydrogen and helium, which is the primary energy producer in the sun has been discussed in Chapter 11. This section briefly discusses harnessing energy from nuclear fusion to generate electricity.
The fusion reaction of great interest is known as deuterium–tritium fusion (D–T fusion) wherein a deuterium atom and a tritium atom fuse to produce helium-4 (Figure $3$).
$_1^2\textrm H+\,_1^3\textrm H\rightarrow \,_2^4\textrm{He}+\,_0^1\textrm n \tag{21.6.13}$
Fusion power has the potential to provide sufficient energy to satisfy mounting demand, and to do so sustainably, with a relatively small impact on the environment. Nuclear fusion has many potential attractions. Firstly, its hydrogen isotope fuels are relatively abundant – one of the necessary isotopes, deuterium, can be extracted from seawater, while the other fuel, tritium, would be bred from a lithium blanket using neutrons produced in the fusion reaction itself. Furthermore, a fusion reactor would produce virtually no CO2 or atmospheric pollutants, and its radioactive waste products would mostly be very short-lived compared to those produced by conventional nuclear reactors (fission reactors).
Useful fusion reactions require very high temperatures for their initiation—about 15,000,000 K or more. At these temperatures, all molecules dissociate into atoms, and the atoms ionize, forming plasma. These conditions occur in an extremely large number of locations throughout the universe—stars are powered by fusion. Humans have already figured out how to create temperatures high enough to achieve fusion on a large scale in thermonuclear weapons. A thermonuclear weapon such as a hydrogen bomb contains a nuclear fission bomb that, when exploded, gives off enough energy to produce the extremely high temperatures necessary for fusion to occur.
Another much more beneficial way to create fusion reactions is in a fusion reactor, a nuclear reactor in which fusion reactions of light nuclei are controlled. Because no solid materials are stable at such high temperatures, mechanical devices cannot contain the plasma in which fusion reactions occur. Two techniques to contain plasma at the density and temperature necessary for a fusion reaction are currently the focus of intensive research efforts: containment by a magnetic field and by the use of focused laser beams (Figure $3$). A number of large projects are working to attain one of the biggest goals in science: getting hydrogen fuel to ignite and produce more energy than the amount supplied to achieve the extremely high temperatures and pressures that are required for fusion. The US Department of Energy is funding several sites conducting fusion research as given on the link https://www.usiter.org/fusion/us-fusion-research-sites. One of the research sites is features in the video below Video $1$.
Summary
• There is still ongoing debate about nuclear power.
• Proponents, such as the World Nuclear Association and Environmentalists for Nuclear Energy, contend that nuclear power is a safe, energy source that reduces carbon emissions.
• Nuclear power opponents, such as Greenpeace and NIRS, contend that nuclear power poses many threats to people and the environment.
• There are over thirty countries that use nuclear power to generate electricity.
Contributor
• Libretext: Introduction to Environmental Science (Zendher et al.) (CC BY-NC-SA)
• Wikipedia (CC BY-SA)
• Libretext: Chemistry of Global Awareness (Gordon) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.09%3A_Nuclear_Energy.txt |
Learning Objectives
• Describe the different renewable energy sources.
• List any impacts it may have on the environment.
Energy sources that are more or less continuously made available in a time frame useful to people are called renewable energy. Renewable energy sources are often considered alternative sources because, in general, most industrialized countries do not rely on them as their main energy source. Instead, they tend to rely on the conventional energy sources such as fossil fuels or nuclear power that are non-renewable. Because of the energy crisis in the United States during the 1970s, dwindling supplies of fossil fuels and hazards associated with nuclear power, use of renewable energy sources such as solar energy, hydroelectric, wind, biomass, and geothermal has grown. Renewable energy comes from the sun (considered an "unlimited" supply) or other sources that can theoretically be renewed at least as quickly as they are consumed. If used at a sustainable rate, these sources will be available for consumption for thousands of years or longer. Renewable alternatives derive from wind, water, solar or biomass (Figure \(1\)). Note that wind, water and biomass energy sources are indirect sources of solar energy. One limitation currently associated with most forms of renewable energy is that the energy is not concentrated and not easily portable.
Energy is an important ingredient in all phases of society. We live in a very interdependent world, and access to adequate and reliable energy resources is crucial for economic growth and for maintaining the quality of our lives. The principal energy resources used in the world are shown in Figure \(2\). With the rapid growth of electricity generation, renewables—including solar, wind, and hydroelectric power—are the fastest-growing energy source between 2018 and 2050, surpassing petroleum and other liquids to become the most used energy source in the Reference case. Worldwide renewable energy consumption increases by 3.1% per year between 2018 and 2050, compared with 0.6% annual growth in petroleum and other liquids, 0.4% growth in coal, and 1.1% annual growth in natural gas consumption.
Global natural gas consumption increases more than 40% between 2018 and 2050, and total consumption reaches nearly 200 quadrillion Btu by 2050. In addition to the natural gas used in electricity generation, natural gas consumption increases in the industrial sector. Chemical and primary metals manufacturing, as well as oil and natural gas extraction, account for most of the growing industrial demand.
Global liquid fuels consumption increases more than 20% between 2018 and 2050, and total consumption reaches more than 240 quadrillion Btu in 2050. Demand in OECD (Organisation for Economic Cooperation and Development) countries remains relatively stable during the projection period, but non-OECD demand increases by about 45%.
Why Use Renewable Energy Sources?
Majority of renewable energy sources including solar, wind, water, and biomass can be directly or indirectly attributed to the sun. The fact that the sun will continue burning for another 4-5 billion years makes it inexhaustible as an energy source for human civilization. With appropriate technology, renewable energy sources allow for local, decentralized control over power. Homes, businesses, and isolated communities can use sources such as solar to produce electricity without being near a power plant or being connected to a grid. This eliminates problems such as spills associated with extraction and transportation of fossil fuels that is needed in order to supply these fossil fuels to those areas that are lacking. Most renewable energy sources do not pollute the air with greenhouse gas emissions and other air pollutants associated with fossil fuels. This is especially important in combating climate change.
Solar Energy
Solar energy is the ultimate energy source driving life on earth and many human activities. Though only one billionth of the energy that leaves the sun (Figure \(3\)) actually reaches the earth's surface, this is more than enough to meet the world’s energy requirement. In fact, all other sources of energy, renewable and non-renewable, are actually stored forms of solar energy. The process of directly converting solar energy to heat or electricity is considered a renewable energy source. Solar energy represents an essentially unlimited supply of energy as the sun will long outlast human civilization on earth. The difficulties lie in harnessing the energy. Solar energy has been used for centuries to heat homes and water, and modern technology (photovoltaic cells) has provided a way to produce electricity from sunlight. There are two basic forms of solar energy collectors are passive and active.
Solar photovoltaic (PV) devices, or solar cells, change sunlight directly into electricity. PV uses semiconducting materials such as silicon to produce electricity from sunlight: when light hits the cells, the material produces free electrons that migrate across the cell, creating an electric current. Small PV cells can power calculators, watches, and other small electronic devices. Arrangements of many solar cells in PV panels and arrangements of multiple PV panels in PV arrays can produce electricity for an entire house or building (Figure \(4\)a). Some PV power plants have large arrays that cover many acres to produce electricity for thousands of homes.
Hundreds of thousands of houses and buildings around the world have PV systems on their roofs. Many multi-megawatt PV power plants have also been built. Covering 4% of the world's desert areas with photovoltaics could supply the equivalent of all of the world's electricity. The Gobi Desert alone could supply almost all of the world's total electricity demand.
Solar thermal power plants, like the one in Figure \(4\)b use concentrating solar collector systems to collect and concentrate sunlight to produce the high temperature heat needed to generate electricity.
Solar power has minimal impact on the environment, depending on where it is placed. The manufacturing of photovoltaic (PV) cells generates some hazardous waste from the chemicals and solvents used in processing. Often solar arrays are placed on roofs of buildings or over parking lots or integrated into construction in other ways. However, large systems may be placed on land and particularly in deserts where those fragile ecosystems could be damaged if care is not taken. Some solar thermal systems use potentially hazardous fluids (to transfer heat) that require proper handling and disposal. Concentrated solar systems may need to be cleaned regularly with water, which is also needed for cooling the turbine-generator. Using water from underground wells may affect the ecosystem in some arid locations.
Biomass Energy
Biomass energy is from the energy stored in materials of biological origin such as plants and animals. Biomass energy is the oldest energy source used by humans. Until the Industrial Revolution prompted a shift to fossil fuels in the mid-18th century, biomass energy was the world's dominant fuel source. Currently, about 12 percent of the world's energy comes from biomass. Biomass is most frequently used as a fuel source in many developing nations, but with the decline of fossil fuel availability and the increase in fossil fuel prices, biomass is increasingly being used as a fuel source even in developed nations.
Direct combustion of solid biomass. The most common source for direct combustion is wood, but energy can also be generated by burning animal manure (dung), herbaceous plant material (non-wood), peat (partially decomposed plant and animal tissues), or converted biomass such as charcoal (wood that has been partially burned to produce a coal-like substance). Using wood and charcoal made from wood, for heating and cooking can replace fossil fuels and may result in lower CO2 emissions. If wood is harvested from forests or woodlots that have to be thinned or from urban trees that fall down or needed be cut down anyway, then using it for biomass does not impact those ecosystems.
Biomass is also being used on a larger scale, where small power plants are powered by biomass such as woodchips (Figure \(5\)). For instance, Central State Hospital, Milledgeville, GA has a woodchip burning plant that was the most advanced system available for its time and operating today. Colgate University in Hamilton, New York, has had a wood-burning boiler since the mid-1980's that processes about 20,000 tons of locally and sustainably harvested wood chips, the equivalent of 1.17 million gallons (4.43 million liters) of fuel oil, avoiding 13,757 tons of emissions, and saving the university over \$1.8 million in heating costs. The University's steam-generating wood-burning facility now satisfies more than 75 percent of the campus's heat and domestic hot water needs. For more information about this, click here Colgate University.
Gaseous Biomass. Organic material can be converted to methane, the main component of natural gas, by anaerobic decomposition or fermentation, a process that utilizes anaerobic bacteria. Methane is a relatively clean fuel that burns efficiently. It can be generated from any kind of organic waste such as municipal sewage and garbage, livestock manure, kitchen, and garden scraps. In fact, municipal landfills are active sites of methane production contributing annually to methane in the atmosphere and to global warming. This gas can and is currently being captured by numerous landfills around the United States that burn it to generate electricity at power plants or supply it to homes for heating.
Liquid Biofuels. Biofuels are transportation fuels produced from plant sources and used to power vehicles. The most common ones are ethanol and biodiesel.
• Ethanol, also known as ethyl alcohol or grain alcohol, is produced by fermenting crops such as corn, sugarcane, and other crops and then mixed with conventional gasoline. As an additive, ethanol lowers reliance on conventional oil and increases the combustion efficiency of gasoline, reducing pollutant emissions.
• Biodiesel which is essentially vegetable oil, can also be derived from a wide range of plant sources, including rapeseed, sunflowers, and soybeans, and can be used in most conventional diesel engines. Biodiesel can also be made from used vegetable oil and has been produced on a very local basis. Because it burns more cleanly than its petroleum-based counterpart, biodiesel can reduce pollution from heavy-duty vehicles such as trucks and buses. Compared to petroleum diesel, biodiesel combustion produces less sulfur oxides, particulate matter, carbon monoxide, and unburned and other hydrocarbons, but more nitrogen oxide.
Environmental Impacts of Biomass Energy
A major challenge of biomass is determining if it is really a more sustainable option. The energy content of some biomass energy sources may not be as high as fossil fuels so more must be burned to generate the same energy. It often takes energy to make energy and biomass is one example where the processing to make it may not be offset by the energy it produces. If traditional monoculture crops like corn or soybeans are used, they require major quantities of fossil fuel to manufacture fertilizer, run farm machines, and ship the fuel to markets, so these biofuels do not always offer significant net energy savings over gasoline and diesel fuel. In such instances, biofuels may not be carbon-neutral because the process of producing the biofuels results in more CO2 added to the atmosphere than that removed by the growing crops.
Burning biomass directly (wood, manure, etc.) produces high particulate material pollution (see chapter 13 on Air Pollution), produces CO2 and deprives the soil of nutrients it normally would have received from the decomposition of the organic matter. Each type of biomass energy source, therefore, must be evaluated for its full life-cycle impact in order to determine if it is really advancing sustainability and reducing environmental impacts.
Hydrogen: Light and Powerful
Hydrogen gas may be an important clean fuel of the future. Hydrogen is considered an energy carrier, like electricity and batteries, it carries energy that can be converted for use later. Hydrogen gas does not tend to exist freely but rather hydrogen atoms bind to other atoms and molecules becoming incorporated in everything from water to organic compounds. Therefore, to obtain hydrogen gas for fuel, energy is needed to force these substances to release their hydrogen atoms. One such procedure is known as electrolysis in which an electric current is passed through water to decompose the water molecule into oxygen and hydrogen (Figure \(6\)). Hydrogen can also be produced from hydrocarbons such as natural gas and coal, fermentation of plant waste material, and using algae.
Fuel cells are highly efficient power plants that produce electricity using hydrogen fuel in a chemical reaction that is a reverse of the electrolysis process that produced the hydrogen fuel (Figure \(7\)). Energy is released by an exothermic electrochemical reaction that combines hydrogen and oxygen ions through an electrolyte material to generate electricity and heat. Experimental fuel cells that can power automobiles have been developed (Figure \(2\)).
Challenges of Hydrogen
Currently, the infrastructure for using hydrogen fuel is lacking and converting a nation such as the United States to hydrogen would require massive and costly development of facilities to produce, store, transport, and provide the fuel. The environmental impact of hydrogen production itself depends on the source of material used to supply the hydrogen. For example, biomass and fossil fuel sources result in carbon-based emissions. Some research suggests that leakage of hydrogen from its production, transport, and use could potentially deplete stratospheric ozone. Research into this is still ongoing.
Other Renewable Sources
Wind Power
Wind is a renewable energy source that uses the power of moving air to generate electricity. Wind turbines use blades to collect the wind’s kinetic energy. Wind flows over the blades creating lift (similar to the effect on airplane wings), which causes the blades to turn. The blades are connected to a drive shaft that turns an electric generator, which produces electricity (Figure \(8\)). Wind turbines are becoming a more prominent sight across the United States, even in regions that are considered to have less wind potential. Wind turbines (often called windmills) do not release emissions that pollute the air or water (with rare exceptions), and they do not require water for cooling. The U.S. wind industry had 40,181 MW of wind power capacity installed at the end of 2010, with 5,116 MW installed in 2010 alone, providing more than 20 % of installed wind power around the globe. According to the American Wind Energy Association, over 35 % of all new electrical generating capacity in the United States since 2006 was due to wind, surpassed only by natural gas.
Most windmills generate about 1kW of electricity, which is only practical for decentralized power generation. California has about 17,000 windmills with a capacity of about 1,400 MW. This is about 80% of all windmills in the U.S. In West Europe windmill generators are quite common. Since a wind turbine has a small physical footprint relative to the amount of electricity it produces, many wind farms are located on crop, pasture, forest land, or coastal areas. They contribute to economic sustainability by providing extra income to farmers and ranchers, allowing them to stay in business and keep their property from being developed for other uses. For example, energy can be produced by installing wind turbines in the Appalachian Mountains of the United States instead of engaging in mountain top removal for coal mining.
Offshore wind turbines on lakes or the ocean may have smaller environmental impacts than turbines on land. Wind turbines do have a few environmental challenges. There are aesthetic concerns to some people when they see them on the landscape. A few wind turbines have caught on fire, and some have leaked lubricating fluids, though this is relatively rare. Some people do not like the sound that wind turbine blades make. Turbines have been found to cause bird and bat deaths particularly if they are located along their migratory path. This is of particular concern if these are threatened or endangered species. There are ways to mitigate that impact and it is currently being researched. There are some small impacts from the construction of wind projects or farms, such as the construction of service roads, the production of the turbines themselves, and the concrete for the foundations. However, overall life cycle analysis has found that turbines make much more energy than the amount used to make and install them.
Geothermal Energy
Geothermal energy uses heat from the Earth's internal geologic processes in order to produce electricity or provide heating. The subsurface temperature of the Earth provides an endless energy resource. One source of geothermal energy is steam. Groundwater percolates down through cracks in the subsurface rocks until it reaches rocks heated by underlying magma, and the heat converts the water to steam. Sometimes this steam makes its way back to the surface in the form of a geyser or hot spring. Wells can be dug to tap the steam reservoir and bring it to the surface, to drive generating turbines and produce electricity (Figure \(9\)a). Hot water can be circulated to heat buildings. Regions near tectonic plate boundaries have the best potential for geothermal activity.
The environmental impact of geothermal energy depends on how it is being used. Direct use and heating applications have almost no negative impact on the environment. Geothermally heated water can release dissolved gases, including carbon dioxide, methane, ammonia and hydrogen sulfide, although these are usually in very small quantities when compared to those released from fossil fuel plants. In addition, geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. They emit 97 % less acid rain-causing sulfur compounds than are emitted by fossil fuel plants.
Hydroelectric Power (Hydropower)
This is the second largest source of renewable energy used, next to biomass energy. The majority of hydropower currently comes from dams built across a river to block the flow of river water. The water stored behind the dam contains potential energy and when released, the potential energy is converted to kinetic energy as the water rushes down. This energy is used to turn blades of turbines and causing a generator to generate electricity. Electricity generated in the powerhouse of a dam is transmitted to the electric grid by transmission lines while the water flows into the riverbed below the dam and continues down river. An alternative approach considered less disruptive involves diverting a portion of the river’s water through a pipe or channel and passed through a powerhouse to generate electricity and returned to the river. Another approach involves pumping water from a lower reservoir to a higher reservoir and then allowed to flow downhill through a turbine, generating electricity. This approach, however, requires energy input to pump the water. Figure \(10\) show a hydroelectric facility (a) and also illustrates the generation of electricity (b).
Hydropower (hydro-electric) is considered a clean and renewable source of energy since it does not directly produce emissions of air pollutants and the source of power is regenerated. However, hydropower dams, reservoirs, and the operation of generators can have serious environmental impacts. A dam that is used to create a reservoir or to divert water to a run-ofriver hydropower plant can obstruct migration of fish to their upstream spawning areas in areas where salmon must travel upstream to spawn, such as along the Columbia River in Washington and Oregon. Hydro turbines kill and injure some of the fish that pass through the turbine although there are ways to reduce that effect. This problem can be partially alleviated by using ‘fish ladders’ that help the salmon get up the dams.
A reservoir and operation of the dam can affect the natural water habitat due to changes in water temperatures, chemistry, flow characteristics, and silt loads, all of which can lead to significant changes in the ecology and physical characteristics of the river upstream and downstream.
Potential of Tidal Power
Tidal power involves placing turbines in zones of the ocean with significant tides and currents, and using the power of flowing water to turn the blades of a turbine to generate electricity. Ocean power systems are still being researched and currently still experimental. For example, the Bay of Fundy, which has a 15 m tide, a dam constructed across the estuary would let water enter on the incoming tide, then release the water through turbines at low tide. The energy potential is great http://www.ialtenergy.com/tidal-power-news.html , and so is the environmental cost. Tapping tidal energy resources involves building major dams on inlets and estuaries that are prized for other purposes, so few tidal energy facilities have been developed. Harnessing waves and currents on a significant scale will involve designing turbine structures that are large, inexpensive, and can operate for long periods under the physical stresses and corrosive forces of ocean environments. Though proposed, a tidal power plant has not been constructed at Fundy. There is a 240,000 kW tidal plant at La Rance, France.
Summary
• Renewable sources of energy are derived from wind, water, solar or biomass.
• One limitation currently associated with most forms of renewable energy is that the energy is not concentrated and not easily portable.
• There is a projected increase from 15% (2018) to 28% of global renewable energy consumption.
Contributor
US Energy Information Administration
Libretext: Introduction to Environmental Science (Zendher et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/15%3A_Energy/15.10%3A_Renewable_Energy_Sources.txt |
Thumbnail: DNA double helix. (public domain; NIH - Genome Research Institute).
16: Biochemistry
Learning Objective
• Know the similarities and differences between plant and animal cells.
• Know the functions of the major parts of plant and animal cells.
Biochemistry, sometimes called biological chemistry, is the study of chemical processes within and relating to living organisms. Biochemical processes give rise to the complexity of life. Biochemistry focuses on understanding how biological molecules give rise to the processes that occur within living cells and between cells, which in turn relates greatly to the study and understanding of tissues, organs, and organism structure and function. Much of biochemistry deals with the structures, functions and interactions of biological macromolecules, such as proteins, nucleic acids, carbohydrates and lipids, which provide the structure of cells and perform many of the functions associated with life. The mechanisms by which cells harness energy from their environment via chemical reactions are known as metabolism. The findings of biochemistry are applied primarily in medicine, nutrition, and agriculture. In medicine, biochemists investigate the causes and cures of diseases. In nutrition, they study how to maintain health wellness and study the effects of nutritional deficiencies. In agriculture, biochemists investigate soil and fertilizers, and try to discover ways to improve crop cultivation, crop storage and pest control.
The major parts of plant and animal cells (Figure $1$) include the plasma membrane, nucleus, ribosomes, and mitochondria.
The plasma membrane is made up of a phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment. A phospholipid is a lipid molecule composed of two fatty acid chains, a glycerol backbone, and a phosphate group. The plasma membrane regulates the passage of some substances, such as organic molecules, ions, and water, preventing the passage of some to maintain internal conditions, while actively bringing in or removing others. Other compounds move passively across the membrane.
Nucleus
Typically, the nucleus is the most prominent organelle in a cell . The nucleus (plural = nuclei) houses the cell’s DNA in the form of chromatin and directs the synthesis of ribosomes and proteins.
Ribosomes
Ribosomes are the cellular structures responsible for protein synthesis. When viewed through an electron microscope, free ribosomes appear as either clusters or single tiny dots floating freely in the cytoplasm. Ribosomes may be attached to either the cytoplasmic side of the plasma membrane or the cytoplasmic side of the endoplasmic reticulum. Electron microscopy has shown that ribosomes consist of large and small subunits. Ribosomes are enzyme complexes that are responsible for protein synthesis.
Because protein synthesis is essential for all cells, ribosomes are found in practically every cell, although they are smaller in prokaryotic cells. They are particularly abundant in immature red blood cells for the synthesis of hemoglobin, which functions in the transport of oxygen throughout the body.
Mitochondria
Mitochondria (singular = mitochondrion) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. The formation of ATP from the breakdown of glucose is known as cellular respiration. In keeping with our theme of form following function, it is important to point out that muscle cells have a very high concentration of mitochondria because muscle cells need a lot of energy to contract.
Figure $1$: This figure shows (a) a typical animal cell and (b) a typical plant cell.
Animal Cells versus Plant Cells
Despite their fundamental similarities, there are some striking differences between animal and plant cells. Animal cells have centrioles, centrosomes (discussed under the cytoskeleton), and lysosomes, whereas plant cells do not. Plant cells have a cell wall (made of cellulose), chloroplasts, plasmodesmata, and plastids used for storage, and a large central vacuole, whereas animal cells do not.
Energy in Biological Systems
Green plants are capable of synthesizing glucose (C6H12O6) from carbon dioxide (CO2) and water (H2O) by using solar energy in the process known as photosynthesis:
$\ce{6CO_2 + 6H_2O} + \text{686 kcal} \rightarrow \ce{C_6H_{12}O_6 + 6O_2} \label{$1$}$
(The 686 kcal come from solar energy.) Chloroplasts function in photosynthesis and can be found in cells of plants and algae. The chloroplasts contain a green pigment called chlorophyll, which captures the energy of sunlight for photosynthesis. Plants can use the glucose for energy or convert it to larger carbohydrates, such as starch or cellulose. Starch provides energy for later use, perhaps as nourishment for a plant’s seeds, while cellulose is the structural material of plants. We can gather and eat the parts of a plant that store energy—seeds, roots, tubers, and fruits—and use some of that energy ourselves. Carbohydrates are also needed for the synthesis of nucleic acids and many proteins and lipids. This is the major difference between plants and animals: Plants are able to make their own food, like glucose, whereas animals must rely on other organisms for their organic compounds or food source.
Summary
The major parts of plant and animal cells (Figure $1$) include the plasma membrane, nucleus, ribosomes, and mitochondria.
Animal cells have centrioles, centrosomes (discussed under the cytoskeleton), and lysosomes, whereas plant cells do not.
Plant cells have a cell wall (made of cellulose), chloroplasts, plasmodesmata, and plastids used for storage, and a large central vacuole, whereas animal cells do not.
Green plants are capable of synthesizing glucose (C6H12O6) from carbon dioxide (CO2) and water (H2O) by using solar energy in the process known as photosynthesis. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.01%3A_Energy_and_the_Living_Cell.txt |
Learning Objective
• Know the difference between starch, cellulose and glycogen.
• List the key steps in carbohydrate digestion.
All carbohydrates consist of carbon, hydrogen, and oxygen atoms and are polyhydroxy aldehydes or ketones or are compounds that can be broken down to form such compounds. Examples of carbohydrates include starch, fiber, the sweet-tasting compounds called sugars, and structural materials such as cellulose. Different carbohydrates that will be discussed below include the simple sugars, oligosaccharides and polysaccharides (Figure \(1\).
Example \(1\)
Which compounds would be classified as carbohydrates?
a. b. c. d.
Solution
1. This is a carbohydrate because the molecule contains an aldehyde functional group with OH groups on the other two carbon atoms.
2. This is not a carbohydrate because the molecule does not contain an aldehyde or a ketone functional group.
3. This is a carbohydrate because the molecule contains a ketone functional group with OH groups on the other two carbon atoms.
4. This is not a carbohydrate; although it has a ketone functional group, one of the other carbons atoms does not have an OH group attached.
Exercise \(1\)
Which compounds would be classified as carbohydrates?
1. 2. 3. 4.
Some Simple Sugars
The naturally occurring monosaccharides contain three to seven carbon atoms per molecule (one sugar unit) . Monosaccharides (or simple sugars) of specific sizes may be indicated by names composed of a stem denoting the number of carbon atoms and the suffix -ose. For example, the terms triose, tetrose, pentose, and hexose signify monosaccharides with, respectively, three, four, five, and six carbon atoms. Monosaccharides are also classified as aldoses or ketoses. Those monosaccharides that contain an aldehyde functional group are called aldoses; those containing a ketone functional group on the second carbon atom are ketoses. Combining these classification systems gives general names that indicate both the type of carbonyl group and the number of carbon atoms in a molecule. Thus, monosaccharides are described as aldotetroses, aldopentoses, ketopentoses, ketoheptoses, and so forth.
Although a variety of monosaccharides are found in living organisms, three hexoses are particularly abundant: D-glucose, D-galactose, and D-fructose (Figure \(2\)). Glucose and galactose are both aldohexoses, while fructose is a ketohexose.
In aqueous solution, the predominant forms are not the straight-chain structure shown above. Rather, they adopt a cyclic structure. The representative ring structures of glucose, fructose, and galactose are shown in Figure \(3\). Notice that all are 6-carbon sugars (hexoses). However, fructose has a five member ring, while glucose and galactose have 6 member rings. Also notice that the only structural difference between glucose and galactose is the position of the alcohol (OH) group that is shown in red.
A disaccharide contains two monosaccharides joined together. Examples include and . They are composed of two monosaccharide units bound together by a bond known as a formed via a , resulting in the loss of a atom from one monosaccharide and a from the other. The of unmodified disaccharides is C12H22O11. Although there are numerous kinds of disaccharides, a handful of disaccharides are particularly notable.
Sucrose, which may be obtained by condensing a molecule of α-glucose with one of the cyclic forms of fructose called β-fructose. The structure of sucrose is shown in Figure \(4\).
Other, less familiar, examples of disaccharides are lactose, which occurs in milk, and maltose, which are shown in Figure \(5\). In order to digest a disaccharide like sucrose or lactose, the human body must have an enzyme which can catalyze hydrolysis of the linkage between the two monosaccharide units. Many Asians, Africans, and American Indians are incapable of synthesizing lactase, the enzyme that speeds hydrolysis of lactose. If such persons drink milk, the undigested lactose makes them sick.
The polysaccharides are the most abundant carbohydrates in nature and serve a variety of functions, such as energy storage or as components of plant cell walls. Polysaccharides are very large polymers composed of tens to thousands of monosaccharides joined together by glycosidic linkages. The three most abundant polysaccharides are starch, glycogen, and cellulose. These three are referred to as homopolymers because each yields only one type of monosaccharide (glucose) after complete hydrolysis. Heteropolymers may contain sugar acids, amino sugars, or noncarbohydrate substances in addition to monosaccharides. Heteropolymers are common in nature (gums, pectins, and other substances) but will not be discussed further in this textbook. The polysaccharides are nonreducing carbohydrates, are not sweet tasting, and do not undergo mutarotation.
Starch
Starch is the most important source of carbohydrates in the human diet and accounts for more than 50% of our carbohydrate intake. It occurs in plants in the form of granules, and these are particularly abundant in seeds (especially the cereal grains) and tubers, where they serve as a storage form of carbohydrates. The breakdown of starch to glucose nourishes the plant during periods of reduced photosynthetic activity. We often think of potatoes as a “starchy” food, yet other plants contain a much greater percentage of starch (potatoes 15%, wheat 55%, corn 65%, and rice 75%). Commercial starch is a white powder.
Starch is a mixture of two polymers: amylose and amylopectin. Natural starches consist of about 10%–30% amylose and 70%–90% amylopectin. Amylose is a linear polysaccharide composed entirely of D-glucose units joined by the α-1,4-glycosidic linkages we saw in maltose (part (a) of Figure \(6\)). Experimental evidence indicates that amylose is not a straight chain of glucose units but instead is coiled like a spring, with six glucose monomers per turn (part (b) of Figure \(6\)). When coiled in this fashion, amylose has just enough room in its core to accommodate an iodine molecule. The characteristic blue-violet color that appears when starch is treated with iodine is due to the formation of the amylose-iodine complex. This color test is sensitive enough to detect even minute amounts of starch in solution.
Amylopectin is a branched-chain polysaccharide composed of glucose units linked primarily by α-1,4-glycosidic bonds but with occasional α-1,6-glycosidic bonds, which are responsible for the branching. A molecule of amylopectin may contain many thousands of glucose units with branch points occurring about every 25–30 units (Figure \(7\)). The helical structure of amylopectin is disrupted by the branching of the chain, so instead of the deep blue-violet color amylose gives with iodine, amylopectin produces a less intense reddish brown.
Dextrins are glucose polysaccharides of intermediate size. The shine and stiffness imparted to clothing by starch are due to the presence of dextrins formed when clothing is ironed. Because of their characteristic stickiness with wetting, dextrins are used as adhesives on stamps, envelopes, and labels; as binders to hold pills and tablets together; and as pastes. Dextrins are more easily digested than starch and are therefore used extensively in the commercial preparation of infant foods.
The complete hydrolysis of starch yields, in successive stages, glucose:
starch → dextrins → maltose → glucose
In the human body, several enzymes known collectively as amylases degrade starch sequentially into usable glucose units.
Glycogen
Glycogen is the energy reserve carbohydrate of animals. Practically all mammalian cells contain some stored carbohydrates in the form of glycogen, but it is especially abundant in the liver (4%–8% by weight of tissue) and in skeletal muscle cells (0.5%–1.0%). Like starch in plants, glycogen is found as granules in liver and muscle cells. When fasting, animals draw on these glycogen reserves during the first day without food to obtain the glucose needed to maintain metabolic balance.
Glycogen is structurally quite similar to amylopectin, although glycogen is more highly branched (8–12 glucose units between branches) and the branches are shorter. When treated with iodine, glycogen gives a reddish brown color. Glycogen can be broken down into its D-glucose subunits by acid hydrolysis or by the same enzymes that catalyze the breakdown of starch. In animals, the enzyme phosphorylase catalyzes the breakdown of glycogen to phosphate esters of glucose.
About 70% of the total glycogen in the body is stored in muscle cells. Although the percentage of glycogen (by weight) is higher in the liver, the much greater mass of skeletal muscle stores a greater total amount of glycogen.
Cellulose
Cellulose, a fibrous carbohydrate found in all plants, is the structural component of plant cell walls. Because the earth is covered with vegetation, cellulose is the most abundant of all carbohydrates, accounting for over 50% of all the carbon found in the vegetable kingdom. Cotton fibrils and filter paper are almost entirely cellulose (about 95%), wood is about 50% cellulose, and the dry weight of leaves is about 10%–20% cellulose. The largest use of cellulose is in the manufacture of paper and paper products. Although the use of noncellulose synthetic fibers is increasing, rayon (made from cellulose) and cotton still account for over 70% of textile production.
Like amylose, cellulose is a linear polymer of glucose. It differs, however, in that the glucose units are joined by β-1,4-glycosidic linkages, producing a more extended structure than amylose (part (a) of Figure \(8\)). This extreme linearity allows a great deal of hydrogen bonding between OH groups on adjacent chains, causing them to pack closely into fibers (part (b) of Figure \(8\)). As a result, cellulose exhibits little interaction with water or any other solvent. Cotton and wood, for example, are completely insoluble in water and have considerable mechanical strength. Because cellulose does not have a helical structure, it does not bind to iodine to form a colored product.
Cellulose yields D-glucose after complete acid hydrolysis, yet humans are unable to metabolize cellulose as a source of glucose. Our digestive juices lack enzymes that can hydrolyze the β-glycosidic linkages found in cellulose, so although we can eat potatoes, we cannot eat grass. However, certain microorganisms can digest cellulose because they make the enzyme cellulase, which catalyzes the hydrolysis of cellulose. The presence of these microorganisms in the digestive tracts of herbivorous animals (such as cows, horses, and sheep) allows these animals to degrade the cellulose from plant material into glucose for energy. Termites also contain cellulase-secreting microorganisms and thus can subsist on a wood diet. This example once again demonstrates the extreme stereospecificity of biochemical processes.
Summary
• Starch is a storage form of energy in plants. It contains two polymers composed of glucose units: amylose (linear) and amylopectin (branched).
• Glycogen is a storage form of energy in animals. It is a branched polymer composed of glucose units. It is more highly branched than amylopectin.
• Cellulose is a structural polymer of glucose units found in plants. It is a linear polymer with the glucose units linked through β-1,4-glycosidic bonds.
Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.02%3A_Carbohydrates-_A_Storehouse_of_Energy.txt |
Learning Objectives
• Recognize the structures of common fatty acids.
• Describe the structure of fats and oils and classify them as saturated, monounsaturated, or polyunsaturated.
Fats and oils, found in many of the foods we eat, belong to a class of biomolecules known as lipids. Gram for gram, they pack more than twice the caloric content of carbohydrates: the oxidation of fats and oils supplies about 9 kcal of energy for every gram oxidized, whereas the oxidation of carbohydrates supplies only 4 kcal/g. Although the high caloric content of fats may be bad news for the dieter, it says something about the efficiency of nature’s designs. Our bodies use carbohydrates, primarily in the form of glucose, for our immediate energy needs. Our capacity for storing carbohydrates for later use is limited to tucking away a bit of glycogen in the liver or in muscle tissue. We store our reserve energy in lipid form, which requires far less space than the same amount of energy stored in carbohydrate form. Lipids have other biological functions besides energy storage. They are a major component of the membranes of the 10 trillion cells in our bodies. They serve as protective padding and insulation for vital organs. Furthermore, without lipids in our diets, we would be deficient in the fat-soluble vitamins A, D, E, and K.
Lipids are not defined by the presence of specific functional groups, as carbohydrates are, but by a physical property—solubility. Compounds isolated from body tissues are classified as lipids if they are more soluble in organic solvents, such as dichloromethane, than in water. By this criterion, the lipid category includes not only fats and oils, which are esters of the trihydroxy alcohol glycerol and fatty acids, but also compounds that incorporate functional groups derived from phosphoric acid, carbohydrates, or amino alcohols, as well as steroid compounds such as cholesterol (Figure \(1\) presents one scheme for classifying the various kinds of lipids). We will discuss the various kinds of lipids by considering one subclass at a time and pointing out structural similarities and differences as we go.
Fatty Acids
Fatty acids are carboxylic acids that are structural components of fats, oils, and all other categories of lipids, except steroids. More than 70 have been identified in nature. They usually contain an even number of carbon atoms (typically 12–20), are generally unbranched, and can be classified by the presence and number of carbon-to-carbon double bonds. Thus, saturated fatty acids contain no carbon-to-carbon double bonds, monounsaturated fatty acids contain one carbon-to-carbon double bond, and polyunsaturated fatty acids contain two or more carbon-to-carbon double bonds.
Table \(1\) lists some common fatty acids and one important source for each. The atoms or groups around the double bonds in unsaturated fatty acids can be arranged in either the cis or trans isomeric form. Naturally occurring fatty acids are generally in the cis configuration. Table \(1\) Some Common Fatty Acids Found in Natural Fats.
Name Abbreviated Structural Formula Condensed Structural Formula Melting Point (°C) Source
lauric acid C11H23COOH CH3(CH2)10COOH 44 palm kernel oil
myristic acid C13H27COOH CH3(CH2)12COOH 58 oil of nutmeg
palmitic acid C15H31COOH CH3(CH2)14COOH 63 palm oil
palmitoleic acid C15H29COOH CH3(CH2)5CH=CH(CH2)7COOH 0.5 macadamia oil
stearic acid C17H35COOH CH3(CH2)16COOH 70 cocoa butter
oleic acid C17H33COOH CH3(CH2)7CH=CH(CH2)7COOH 16 olive oil
linoleic acid C17H31COOH CH3(CH2)3(CH2CH=CH)2(CH2)7COOH −5 canola oil
α-linolenic acid C17H29COOH CH3(CH2CH=CH)3(CH2)7COOH −11 flaxseed
arachidonic acid C19H31COOH CH3(CH2)4(CH2CH=CH)4(CH2)2COOH −50 liver
Two polyunsaturated fatty acids—linoleic and α-linolenic acids—are termed essential fatty acids because humans must obtain them from their diets. Both substances are required for normal growth and development, but the human body does not synthesize them. The body uses linoleic acid to synthesize many of the other unsaturated fatty acids, such as arachidonic acid, a precursor for the synthesis of prostaglandins. In addition, the essential fatty acids are necessary for the efficient transport and metabolism of cholesterol. The average daily diet should contain about 4–6 g of the essential fatty acids.
Fats and oils are the most abundant lipids in nature. They provide energy for living organisms, insulate body organs, and transport fat-soluble vitamins through the blood. Although we often draw the carbon atoms in a straight line, they actually have more of a zigzag configuration (Figure \(\PageIndex{2a}\)). Viewed as a whole, however, the saturated fatty acid molecule is relatively straight (Figure \(\PageIndex{2b}\)). Such molecules pack closely together into a crystal lattice, maximizing the strength of dispersion forces and causing fatty acids and the fats derived from them to have relatively high melting points. In contrast, each cis carbon-to-carbon double bond in an unsaturated fatty acid produces a pronounced bend in the molecule, so that these molecules do not stack neatly. As a result, the intermolecular attractions of unsaturated fatty acids (and unsaturated fats) are weaker, causing these substances to have lower melting points. Most are liquids at room temperature.
Structures of Fats and Oils
Fats and oils are called triglycerides (or triacylcylgerols) because they are esters composed of three fatty acid units joined to glycerol, a trihydroxy alcohol:
If all three OH groups on the glycerol molecule are esterified with the same fatty acid, the resulting ester is called a simple triglyceride. Although simple triglycerides have been synthesized in the laboratory, they rarely occur in nature. Instead, a typical triglyceride obtained from naturally occurring fats and oils contains two or three different fatty acid components and is thus termed a mixed triglyceride.
A triglyceride is called a fat if it is a solid at 25°C; it is called an oil if it is a liquid at that temperature. These differences in melting points reflect differences in the degree of unsaturation and number of carbon atoms in the constituent fatty acids. Triglycerides obtained from animal sources are usually solids, while those of plant origin are generally oils. Therefore, we commonly speak of animal fats and vegetable oils.
No single formula can be written to represent the naturally occurring fats and oils because they are highly complex mixtures of triglycerides in which many different fatty acids are represented. Table \(2\) shows the fatty acid compositions of some common fats and oils. The composition of any given fat or oil can vary depending on the plant or animal species it comes from as well as on dietetic and climatic factors. To cite just one example, lard from corn-fed hogs is more highly saturated than lard from peanut-fed hogs. Palmitic acid is the most abundant of the saturated fatty acids, while oleic acid is the most abundant unsaturated fatty acid.
Table \(2\) Average Fatty Acid Composition of Some Common Fats and Oils (%)*.
Lauric Myristic Palmitic Stearic Oleic Linoleic Linolenic
Fats
butter (cow) 3 11 27 12 29 2 1
tallow 3 24 19 43 3 1
lard 2 26 14 44 10
Oils
canola oil 4 2 62 22 10
coconut oil 47 18 9 3 6 2
corn oil 11 2 28 58 1
olive oil 13 3 71 10 1
peanut oil 11 2 48 32
soybean oil 11 4 24 54 7
*Totals less than 100% indicate the presence of fatty acids with fewer than 12 carbon atoms or more than 18 carbon atoms.
Coconut oil is highly saturated. It contains an unusually high percentage of the low-melting C8, C10, and C12 saturated fatty acids.
Terms such as saturated fat or unsaturated oil are often used to describe the fats or oils obtained from foods. Saturated fats contain a high proportion of saturated fatty acids, while unsaturated oils contain a high proportion of unsaturated fatty acids. The high consumption of saturated fats is a factor, along with the high consumption of cholesterol, in increased risks of heart disease.
Physical Properties of Fats and Oils
Contrary to what you might expect, pure fats and oils are colorless, odorless, and tasteless. The characteristic colors, odors, and flavors that we associate with some of them are imparted by foreign substances that are lipid soluble and have been absorbed by these lipids. For example, the yellow color of butter is due to the presence of the pigment carotene; the taste of butter comes from two compounds—diacetyl and 3-hydroxy-2-butanone—produced by bacteria in the ripening cream from which the butter is made.
Fats and oils are lighter than water, having densities of about 0.8 g/cm3. They are poor conductors of heat and electricity and therefore serve as excellent insulators for the body, slowing the loss of heat through the skin.
Chemical Reactions of Fats and Oils
Fats and oils can participate in a variety of chemical reactions—for example, because triglycerides are esters, they can be hydrolyzed in the presence of an acid, a base, or specific enzymes known as lipases. The hydrolysis of fats and oils in the presence of a base is used to make soap and is called saponification. Today most soaps are prepared through the hydrolysis of triglycerides (often from tallow, coconut oil, or both) using water under high pressure and temperature [700 lb/in2 (∼50 atm or 5,000 kPa) and 200°C]. Sodium carbonate or sodium hydroxide is then used to convert the fatty acids to their sodium salts (soap molecules):
Iodine Value
The iodine value (or iodine adsorption value or iodine number or iodine index, commonly abbreviated as IV) in chemistry is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. Iodine numbers are often used to determine the amount of unsaturation in fats, oils and waxes. In fatty acids, unsaturation occurs mainly as double bonds which are very reactive towards halogens, the iodine in this case. Thus, the higher the iodine value, the more unsaturations are present in the fat. It can be seen from the table that coconut oil is very saturated, which means it is good for making soap. On the other hand, linseed oil is highly unsaturated, which makes it a drying oil, well suited for making oil paints.
Table \(1\) Iodine Numbers of Common Fats and Oils. Source Wikipedia
Fat Iodine Value (g/100g)
Beef tallow 42-48
Butter 25-42
Canola Oil 110-126
Coconut Oil 6-11
Fish oil 190-205
Linseed Oil 170-204
Olive Oil 75-94
Safflower Oil 135-150
Walnut Oil 132-162
Looking Closer: Soaps
Ordinary soap is a mixture of the sodium salts of various fatty acids, produced in one of the oldest organic syntheses practiced by humans (second only to the fermentation of sugars to produce ethyl alcohol). Both the Phoenicians (600 BCE) and the Romans made soap from animal fat and wood ash. Even so, the widespread production of soap did not begin until the 1700s. Soap was traditionally made by treating molten lard or tallow with a slight excess of alkali in large open vats. The mixture was heated, and steam was bubbled through it. After saponification was completed, the soap was precipitated from the mixture by the addition of sodium chloride (NaCl), removed by filtration, and washed several times with water. It was then dissolved in water and reprecipitated by the addition of more NaCl. The glycerol produced in the reaction was also recovered from the aqueous wash solutions.
Pumice or sand is added to produce scouring soap, while ingredients such as perfumes or dyes are added to produce fragrant, colored soaps. Blowing air through molten soap produces a floating soap. Soft soaps, made with potassium salts, are more expensive but produce a finer lather and are more soluble. They are used in liquid soaps, shampoos, and shaving creams.
Dirt and grime usually adhere to skin, clothing, and other surfaces by combining with body oils, cooking fats, lubricating greases, and similar substances that act like glues. Because these substances are not miscible in water, washing with water alone does little to remove them. Soap removes them, however, because soap molecules have a dual nature. One end, called the head, carries an ionic charge (a carboxylate anion) and therefore dissolves in water; the other end, the tail, has a hydrocarbon structure and dissolves in oils. The hydrocarbon tails dissolve in the soil; the ionic heads remain in the aqueous phase, and the soap breaks the oil into tiny soap-enclosed droplets called micelles, which disperse throughout the solution. The droplets repel each other because of their charged surfaces and do not coalesce. With the oil no longer “gluing” the dirt to the soiled surface (skin, cloth, dish), the soap-enclosed dirt can easily be rinsed away.
Summary
• Fatty acids are carboxylic acids that are the structural components of many lipids.
• Saturated fatty acids contain no carbon-to-carbon double bonds, monounsaturated fatty acids contain one carbon-to-carbon double bond, and polyunsaturated fatty acids contain two or more carbon-to-carbon double bonds.
• Fats and oils are composed of molecules known as triglycerides, which are esters composed of three fatty acid units linked to glycerol.
• Fats and oils can participate in a variety of chemical reactions—for example, because triglycerides are esters, they can be hydrolyzed in the presence of an acid, a base, or specific enzymes known as lipases.
• The hydrolysis of fats and oils in the presence of a base is used to make soap and is called saponification.
• Animal fats and oils which are made up mostly of saturated fatty acids have low iodine values (numbers), while those oils with high degree of unsaturation (with more C=C bonds) have high iodine values.
Contributors and Attributions
• Libretext: The Basics od GOB Chemistry (Ball et al.)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.03%3A_Fats_and_Other_Lipids.txt |
Learning Objectives
• Identify different amino acids.
• Describe how short chain proteins (polypeptides) are formed from amino acids.
Proteins may be defined as compounds of high molar mass consisting largely or entirely of chains of amino acids. Their masses range from several thousand to several million daltons (Da). In addition to carbon, hydrogen, and oxygen atoms, all proteins contain nitrogen and sulfur atoms, and many also contain phosphorus atoms and traces of other elements. Proteins serve a variety of roles in living organisms and are often classified by these biological roles. Muscle tissue is largely protein, as are skin and hair. Proteins are present in the blood, in the brain, and even in tooth enamel. Each type of cell in our bodies makes its own specialized proteins, as well as proteins common to all or most cells. We begin our study of proteins by looking at the properties and reactions of amino acids, which is followed by a discussion of how amino acids link covalently to form peptides and proteins. We end the chapter with a discussion of enzymes—the proteins that act as catalysts in the body.
The proteins in all living species, from bacteria to humans, are constructed from the same set of 20 amino acids, so called because each contains an amino group attached to a carboxylic acid. The amino acids in proteins are α-amino acids, which means the amino group is attached to the α-carbon of the carboxylic acid. Humans can synthesize only about half of the needed amino acids; the remainder must be obtained from the diet and are known as essential amino acids. However, two additional amino acids have been found in limited quantities in proteins: Selenocysteine was discovered in 1986, while pyrrolysine was discovered in 2002.
The amino acids are colorless, nonvolatile, crystalline solids, melting and decomposing at temperatures above 200°C. These melting temperatures are more like those of inorganic salts than those of amines or organic acids and indicate that the structures of the amino acids in the solid state and in neutral solution are best represented as having both a negatively charged group and a positively charged group. Such a species is known as a zwitterion.
Classification
In addition to the amino and carboxyl groups, amino acids have a side chain or R group attached to the α-carbon. Each amino acid has unique characteristics arising from the size, shape, solubility, and ionization properties of its R group. As a result, the side chains of amino acids exert a profound effect on the structure and biological activity of proteins. Although amino acids can be classified in various ways, one common approach is to classify them according to whether the functional group on the side chain at neutral pH is nonpolar, polar but uncharged, negatively charged, or positively charged. The structures and names of the 20 amino acids, their one- and three-letter abbreviations, and some of their distinctive features are given in Table \(1\).
Table \(1\): Common Amino Acids Found in Proteins
Common Name Abbreviation Structural Formula (at pH 6) Molar Mass Distinctive Feature
Amino acids with a nonpolar R group
glycine gly (G) 75 the only amino acid lacking a chiral carbon
alanine ala (A) 89
valine val (V) 117 a branched-chain amino acid
leucine leu (L) 131 a branched-chain amino acid
isoleucine ile (I) 131 an essential amino acid because most animals cannot synthesize branched-chain amino acids
phenylalanine phe (F) 165 also classified as an aromatic amino acid
tryptophan trp (W) 204 also classified as an aromatic amino acid
methionine met (M) 149 side chain functions as a methyl group donor
proline pro (P) 115 contains a secondary amine group; referred to as an α-imino acid
Amino acids with a polar but neutral R group
serine ser (S) 105 found at the active site of many enzymes
threonine thr (T) 119 named for its similarity to the sugar threose
cysteine cys (C) 121 oxidation of two cysteine molecules yields cystine
tyrosine tyr (Y) 181 also classified as an aromatic amino acid
asparagine asn (N) 132 the amide of aspartic acid
glutamine gln (Q) 146 the amide of glutamic acid
Amino acids with a negatively charged R group
aspartic acid asp (D) 132 carboxyl groups are ionized at physiological pH; also known as aspartate
glutamic acid glu (E) 146 carboxyl groups are ionized at physiological pH; also known as glutamate
Amino acids with a positively charged R group
histidine his (H) 155 the only amino acid whose R group has a pKa (6.0) near physiological pH
lysine lys (K) 147
arginine arg (R) 175 almost as strong a base as sodium hydroxide
The first amino acid to be isolated was asparagine in 1806. It was obtained from protein found in asparagus juice (hence the name). Glycine, the major amino acid found in gelatin, was named for its sweet taste (Greek glykys, meaning “sweet”). In some cases an amino acid found in a protein is actually a derivative of one of the common 20 amino acids (one such derivative is hydroxyproline). The modification occurs after the amino acid has been assembled into a protein.
Zwitterions
The structure of an amino acid allows it to act as both an acid and a base. An amino acid has this ability because at a certain pH value (different for each amino acid) nearly all the amino acid molecules exist as zwitterions. If acid is added to a solution containing the zwitterion, the carboxylate group captures a hydrogen (H+) ion, and the amino acid becomes positively charged. If base is added, ion removal of the H+ ion from the amino group of the zwitterion produces a negatively charged amino acid. In both circumstances, the amino acid acts to maintain the pH of the system—that is, to remove the added acid (H+) or base (OH) from solution.
The Peptide Bond: Peptides and Proteins
Two or more amino acids can join together into chains called peptides. Previously, we discussed the reaction between ammonia and a carboxylic acid to form an amide. In a similar reaction, the amino group on one amino acid molecule reacts with the carboxyl group on another, releasing a molecule of water and forming an amide linkage as shown in Figure \(1\)
An amide bond joining two amino acid units is called a peptide bond. Note that the product molecule still has a reactive amino group on the left and a reactive carboxyl group on the right. These can react with additional amino acids to lengthen the peptide. The process can continue until thousands of units have joined, resulting in large proteins.
A chain consisting of only two amino acid units is called a dipeptide; a chain consisting of three is a tripeptide. By convention, peptide and protein structures are depicted with the amino acid whose amino group is free (the N-terminal end) on the left and the amino acid with a free carboxyl group (the C-terminal end) to the right.
The general term peptide refers to an amino acid chain of unspecified length. However, chains of about 50 amino acids or more are usually called proteins or polypeptides. In its physiologically active form, a protein may be composed of one or more polypeptide chains.
Peptide cells in our bodies have an intricate mechanism for the manufacture of proteins. Humans have to use other techniques in order to synthesize the same proteins in a lab. The chemistry of peptide synthesis is complicated. Both active groups on an amino acid can react and the amino acid sequence must be a specific one in order for the protein to function. Robert Merrifield developed the first synthetic approach for making proteins in the lab, a manual approach which was lengthy and tedious (and, he won the Nobel Prize in Chemistry in 1984 for his work). Today, however, automated systems can crank out a peptide in a very short period of time.
The Sequence of Amino Acids
The particular sequence of amino acids in a longer chain is called an amino acid sequence. By convention, the amino acid sequence is listed in the order such that the free amine group is on the left end of the molecule and the free carboxyl group is on the right end of the molecule.
For example, suppose that a sequence of the amino acids glycine, tryptophan, and alanine is formed with the free amine group as part of the glycine and the free carboxyl group as part of the alanine. The amino acid sequence can be easily written using the abbreviations as Gly-Trp-Ala. This is a different sequence from Ala-Trp-Gly because the free amine and carboxyl groups would be on different amino acids in that case.
Bradykinin
Just as millions of different words are spelled with our 26-letter English alphabet, millions of different proteins are made with the 20 common amino acids. However, just as the English alphabet can be used to write gibberish, amino acids can be put together in the wrong sequence to produce nonfunctional proteins. Although the correct sequence is ordinarily of utmost importance, it is not always absolutely required. Just as you can sometimes make sense of incorrectly spelled English words, a protein with a small percentage of “incorrect” amino acids may continue to function. However, it rarely functions as well as a protein having the correct sequence. There are also instances in which seemingly minor errors of sequence have disastrous effects. For example, in some people, every molecule of hemoglobin (a protein in the blood that transports oxygen) has a single incorrect amino acid unit out of about 300 (a single valine replaces a glutamic acid). That “minor” error is responsible for sickle cell anemia, an inherited condition that usually is fatal.
Example \(1\)
Draw the polypeptide Asp-Val-Ser.
Solution
1. Identify the structures of each of the three given amino acids and draw them in the same order as given in the name.
2. Leaving the order the same, connect the amino acids to one another by forming peptide bonds. Note that the order given in the name is the same way the amino acids are connected in the molecule. The first one listed is always the \(\ce{N}\)-terminus of the polypeptide.
Example \(2\)
List all of the possible polypeptides that can be formed from cysteine (Cys), leucine (Leu), and arginine (Arg).
Solution
Although there are only three amino acids, the order in which they are bonded changes the identity, properties, and function of the resulting polypeptide. There are six possible polypeptides formed from these three amino acids.
Cys-Leu-Arg
Cys-Arg-Leu
Leu-Cys-Arg
Leu-Arg-Cys
Arg-Cys-Leu
Arg-Leu-Cys
Exercise \(1\)
Draw the structure for each peptide.
1. gly-val
2. val-gly
Answers
a.
b.
Summary
• The amino group of one amino acid can react with the carboxyl group on another amino acid to form a peptide bond that links the two amino acids together.
• Additional amino acids can be added on through the formation of addition peptide (amide) bonds.
• A chain consisting of only two amino acid units is called a dipeptide; a chain consisting of three is a tripeptide.
• Chains of about 50 amino acids or more are usually called proteins or polypeptides.
• A sequence of amino acids in a peptide or protein is written with the N-terminal amino acid first and the C-terminal amino acid at the end (writing left to right).
• The order, or sequence, in which the amino acids are connected is also of critical importance in order for a peptide or protein to be physiologically active.
Contributors and Attributions
• Libretext: The Basics of GOB Chemistry (Ball et al.)
• Allison Soult, Ph.D. (Department of Chemistry, University of Kentucky) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.04%3A_Proteins-_Polymers_of_Amino_Acids.txt |
Learning Objectives
• Describe the four levels of protein structure.
• Identify the types of attractive interactions that hold proteins in their most stable three-dimensional structure
• Explain the role of an enzyme in the body.
Each of the thousands of naturally occurring proteins has its own characteristic amino acid composition and sequence that result in a unique three-dimensional shape. Since the 1950s, scientists have determined the amino acid sequences and three-dimensional conformation of numerous proteins and thus obtained important clues on how each protein performs its specific function in the body.
Proteins are compounds of high molar mass consisting largely or entirely of chains of amino acids. Because of their great complexity, protein molecules cannot be classified on the basis of specific structural similarities, as carbohydrates and lipids are categorized. The two major structural classifications of proteins are based on far more general qualities: whether the protein is (1) fiberlike and insoluble or (2) globular and soluble. Some proteins, such as those that compose hair, skin, muscles, and connective tissue, are fiberlike. These fibrous proteins are insoluble in water and usually serve structural, connective, and protective functions. Examples of fibrous proteins are keratins, collagens, myosins, and elastins. Hair and the outer layer of skin are composed of keratin. Connective tissues contain collagen. Myosins are muscle proteins and are capable of contraction and extension. Elastins are found in ligaments and the elastic tissue of artery walls.
Globular proteins, the other major class, are soluble in aqueous media. In these proteins, the chains are folded so that the molecule as a whole is roughly spherical. Familiar examples include egg albumin from egg whites and serum albumin in blood. Serum albumin plays a major role in transporting fatty acids and maintaining a proper balance of osmotic pressures in the body. Hemoglobin and myoglobin, which are important for binding oxygen, are also globular proteins.
Levels of Protein Structure
The structure of proteins is generally described as having four organizational levels. The first of these is the primary structure, which is the number and sequence of amino acids in a protein’s polypeptide chain or chains, beginning with the free amino group and maintained by the peptide bonds connecting each amino acid to the next. The primary structure of insulin, composed of 51 amino acids, is shown in Figure $1$.
A protein molecule is not a random tangle of polypeptide chains. Instead, the chains are arranged in unique but specific conformations. The term secondary structure refers to the fixed arrangement of the polypeptide backbone. On the basis of X ray studies, Linus Pauling and Robert Corey postulated that certain proteins or portions of proteins twist into a spiral or a helix. This helix is stabilized by intrachain hydrogen bonding between the carbonyl oxygen atom of one amino acid and the amide hydrogen atom four amino acids up the chain (located on the next turn of the helix) and is known as a right-handed α-helix. X ray data indicate that this helix makes one turn for every 3.6 amino acids, and the side chains of these amino acids project outward from the coiled backbone (Figure $2$). The α-keratins, found in hair and wool, are exclusively α-helical in conformation. Some proteins, such as gamma globulin, chymotrypsin, and cytochrome c, have little or no helical structure. Others, such as hemoglobin and myoglobin, are helical in certain regions but not in others.
Another common type of secondary structure, called the β-pleated sheet conformation, is a sheetlike arrangement in which two or more extended polypeptide chains (or separate regions on the same chain) are aligned side by side. The aligned segments can run either parallel or antiparallel—that is, the N-terminals can face in the same direction on adjacent chains or in different directions—and are connected by interchain hydrogen bonding (Figure $3$). The β-pleated sheet is particularly important in structural proteins, such as silk fibroin. It is also seen in portions of many enzymes, such as carboxypeptidase A and lysozyme.
Tertiary structure refers to the unique three-dimensional shape of the protein as a whole, which results from the folding and bending of the protein backbone. The tertiary structure is intimately tied to the proper biochemical functioning of the protein. Figure $4$ shows a depiction of the three-dimensional structure of insulin.
Four major types of attractive interactions determine the shape and stability of the tertiary structure of proteins.
You studied several of them previously.
1. Ionic bonding. Ionic bonds result from electrostatic attractions between positively and negatively charged side chains of amino acids. For example, the mutual attraction between an aspartic acid carboxylate ion and a lysine ammonium ion helps to maintain a particular folded area of a protein (part (a) of Figure $5$).
2. Hydrogen bonding. Hydrogen bonding forms between a highly electronegative oxygen atom or a nitrogen atom and a hydrogen atom attached to another oxygen atom or a nitrogen atom, such as those found in polar amino acid side chains. Hydrogen bonding (as well as ionic attractions) is extremely important in both the intra- and intermolecular interactions of proteins (part (b) of Figure $5$).
3. Disulfide linkages. Two cysteine amino acid units may be brought close together as the protein molecule folds. Subsequent oxidation and linkage of the sulfur atoms in the highly reactive sulfhydryl (SH) groups leads to the formation of cystine (part (c) of Figure $5$). Intrachain disulfide linkages are found in many proteins, including insulin (yellow bars in Figure $1$) and have a strong stabilizing effect on the tertiary structure.
1. Dispersion forces. Dispersion forces arise when a normally nonpolar atom becomes momentarily polar due to an uneven distribution of electrons, leading to an instantaneous dipole that induces a shift of electrons in a neighboring nonpolar atom. Dispersion forces are weak but can be important when other types of interactions are either missing or minimal (part (d) of Figure $5$). This is the case with fibroin, the major protein in silk, in which a high proportion of amino acids in the protein have nonpolar side chains. The term hydrophobic interaction is often misused as a synonym for dispersion forces. Hydrophobic interactions arise because water molecules engage in hydrogen bonding with other water molecules (or groups in proteins capable of hydrogen bonding). Because nonpolar groups cannot engage in hydrogen bonding, the protein folds in such a way that these groups are buried in the interior part of the protein structure, minimizing their contact with water.
When a protein contains more than one polypeptide chain, each chain is called a subunit. The arrangement of multiple subunits represents a fourth level of structure, the quaternary structure of a protein. Hemoglobin, with four polypeptide chains or subunits, is the most frequently cited example of a protein having quaternary structure (Figure $6$). The quaternary structure of a protein is produced and stabilized by the same kinds of interactions that produce and maintain the tertiary structure. A schematic representation of the four levels of protein structure is in Figure $7$.
The primary structure consists of the specific amino acid sequence. The resulting peptide chain can twist into an α-helix, which is one type of secondary structure. This helical segment is incorporated into the tertiary structure of the folded polypeptide chain. The single polypeptide chain is a subunit that constitutes the quaternary structure of a protein, such as hemoglobin that has four polypeptide chains.
Globular and Fibrous Proteins
Once proteins form and have developed all levels of their structure, they can be classified as either fibrous or globular. These classifications give the basic shape of the entire protein molecule. While many proteins are globular proteins (see figure below), keratin proteins are fibrous (see figure below) and make up the hair, nails, and the outer layer of skin.
Enzymes: Exquisite Precision Machines
The first enzyme to be isolated was discovered in 1926 by American chemist James Sumner, who crystallized the protein. The enzyme was urease, which catalyzes the hydrolytic decomposition of urea, a component of urine, into ammonia and carbon dioxide.
$\ce{H_2NCON_2} \left( aq \right) + \ce{H_2O} \left( l \right) \overset{\text{urease}}{\rightarrow} 2 \ce{NH_3} \left( g \right) + \ce{CO_2} \left( g \right) \nonumber$
His discovery was ridiculed at first because nobody believed that enzymes would behave the same way that other chemicals did. Sumner was eventually proven right and won the Nobel Prize in Chemistry in 1946.
Enzymes and Biochemical Reactions
Most chemical reactions within organisms would be impossible under the conditions in cells. For example, the body temperature of most organisms is too low for reactions to occur quickly enough to carry out life processes. Reactants may also be present in such low concentrations that it is unlikely they will meet and collide. Therefore, the rate of most biochemical reactions must be increased by a catalyst. A catalyst is a chemical that speeds up chemical reactions. In organisms, catalysts are called enzymes. Essentially, enzymes are biological catalysts.
Like other catalysts, enzymes are not reactants in the reactions they control. They help the reactants interact but are not used up in the reactions. Instead, they may be used over and over again. Unlike other catalysts, enzymes are usually highly specific for particular chemical reactions. They generally catalyze only one or a few types of reactions.
Enzymes are extremely efficient in speeding up reactions. They can catalyze up to several million reactions per second. As a result, the difference in rates of biochemical reactions with and without enzymes may be enormous. A typical biochemical reaction might take hours or even days to occur under normal cellular conditions without an enzyme, but less than a second with an enzyme.
Figure $10$ diagrams a typical enzymatic reaction. A substrate is the molecule or molecules on which the enzyme acts. In the urease catalyzed reaction, urea is the substrate.
The first step in the reaction is that the substrate binds to a specific part of the enzyme molecule, known as the active site. The binding of the substrate is dictated by the shape of each molecule. Side chains on the enzyme interact with the substrate in a specific way, resulting in the making and breaking of bonds. The active site is the place on an enzyme where the substrate binds. An enzyme folds in such a way that it typically has one active site, usually a pocket or crevice formed by the folding pattern of the protein. Because the active site of an enzyme has such a unique shape, only one particular substrate is capable of binding to that enzyme. In other words, each enzyme catalyzes only one chemical reaction with only one substrate. Once the enzyme/substrate complex is formed, the reaction occurs and the substrate is transformed into products. Finally, the product molecule or molecules are released from the active site. Note that the enzyme is left unaffected by the reaction and is now capable of catalyzing the reaction of another substrate molecule.
For many enzymes, the active site follows a lock and key (Figure $\PageIndex{11A}$ ) model where the substrate fits exactly into the active site. The enzyme and substrate must be a perfect match so the enzyme only functions as a catalyst for one reaction. Other enzymes have an induced fit (Figure $\PageIndex{11B}$ ) model. In an induced fit model, the active site can make minor adjustments to accommodate the substrate. This results in an enzyme that is capable of interacting with a small group of similar substrates. Look at the shape of the active site compared to the shape of the substrate in B of the figure below. The active site adjusts to accommodate the substrate.
Inhibitors
An inhibitor is a molecule which interferes with the function of an enzyme, either by slowing or stopping the chemical reaction. Inhibitors can work in a variety of ways, but one of the most common is illustrated in the figure below.
A competitive inhibitor binds competitively at the active site and blocks the substrate from binding. Since no reaction occurs with the inhibitor, the enzyme is prevented from catalyzing the reaction.
A non-competitive inhibitor does not bind at the active site. It attaches at an allosteric site, which is some other site on the enzyme, and changes the shape of the protein. The allosteric site is any site on the enzyme that is not the active site. The attachment of the non-competitive inhibitor to the allosteric site results in a shift in three-dimensional structure that alters the shape of the active site so that the substrate will no longer fit in the active site properly (see figure below).
Cofactors and Coenzymes
Some enzymes require the presence of another substrate as a "helper" molecule in order to function properly. Cofactors and coenzymes serve in this role. Cofactors are inorganic species and coenzymes are small organic molecules. Many vitamins, such as B vitamins, are coenzymes. Some metal ions which function as cofactors for various enzymes include zinc, magnesium, potassium, and iron.
Catalytic Activity of Enzymes
Enzymes generally lower activation energy by reducing the energy needed for reactants to come together and react. One way that enzymes act is to bring reactants (substrates) together so they don't have to expend energy moving about until they collide at random. Enzymes bind both reactant molecules (substrates), tightly and specifically, at a site on the enzyme's active site. Enzymes can also bring molecules to the active site to break them apart. For example, sucrase is the enzyme for the breakdown of sucrose which enters the active site of the enzyme and helps weaken the interactions between the fructose and glucose that make up sucrose. Sucrase is specific to the breakdown of sucrose as are most enzymes. The active site is specific for the reactants of the biochemical reaction the enzyme catalyzes. Similar to puzzle pieces fitting together, the active site can only bind certain substrates. The activities of enzymes also depend on the temperature, concentration, and the pH of the surroudings.
Concentration
As with most reactions, the concentration of the reactant(s) affects the reaction rate. This is also true in enzyme concentration. When either substrate or enzyme concentration is low, the rate of the reaction will be slower than where there are higher concentrations. The two species must interact for a reaction to occur and higher concentrations of one or both will result in more effective interactions between the two.
However, continuing to increase the substrate's concentration will not always increase the reaction rate. This is because at some point, all of the enzymes will be occupied and unavailable to bind with another substrate molecule until the substrate forms a product molecule and is released from the enzyme.
pH
Some enzymes work best at acidic pHs, while others work best in neutral environments. For example, digestive enzymes secreted in the acidic environment (low pH) of the stomach help break down proteins into smaller molecules. The main digestive enzyme in the stomach is pepsin, which works best at a pH of about 1.5. These enzymes would not work optimally at other pHs. Trypsin is another enzyme in the digestive system, which breaks protein chains in food into smaller particles. Trypsin works in the small intestine, which is not an acidic environment. Trypsin's optimum pH is about 8.
Different reactions and different enzymes will achieve their maximum rate at certain pH values. As shown in the figure below, the enzyme achieves a maximum reaction rate at a pH of 4. Notice that the reaction will continue at lower and higher pH values because the enzyme will still function at other pH values but will not be as effective. At very high or very low pH values, denaturation will occur because an enzyme is just a protein with a specific function.
Temperature
As with pH, reactions also have an ideal temperature where the enzyme functions most effectively. It will still function at higher and lower temperatures, but the rate will be less. For many biological reactions, the ideal temperature is at physiological conditions which is around $37^\text{o} \text{C}$ which is normal body temperature. Many enzymes lose function at lower and higher temperatures. At higher temperatures, an enzyme's shape deteriorates. Only when the temperature comes back to normal does the enzyme regain its shape and normal activity unless the temperature was so high that it caused irreversible damage.
Applications of Enzymes
Enzymes are used in the and other industrial applications when extremely specific catalysts are required (Table $1$). Enzymes in general are limited in the number of reactions they have evolved to catalyze and also by their lack of stability in and at high temperatures. As a consequence, is an active area of research and involves attempts to create new enzymes with novel properties, either through rational design or in vitro evolution. These efforts have begun to be successful, and a few enzymes have now been designed "from scratch" to catalyze reactions that do not occur in nature.
Table $1$ Uses of Enzymes in Various Industries. Source: Wikipedia
Application Enzymes used Uses
Biofuel industry Cellulases Break down cellulose into sugars that can be fermented to produce cellulosic ethanol.
Ligninases Pretreatment of biomass for biofuel production.
Biological detergent Proteases, amylases, lipases Remove protein, starch, and fat or oil stains from laundry and dish ware.
Mannanases Remove food stains from the common food additive guar gum.
Brewing industry Amylase, glucanases, proteases Split polysaccharides and proteins in the malt.
Betaglucanases Improve the wort and beer filtration characteristics.
Amyloglucosisdase and pullulanases Make low-calorie beer and adjust fermentability.
Acetolacatate deacrboxylase (ALDC) Increase fermentation efficiency by reducing diacetyl formation.
Culinary uses Papain Tenderize meat for cooking.
Dairy industry Renin Hydrolyze protein in the manufacture of cheese.
Lipases Produce Camembert cheese and blue cheese such as Roquefort.
Food processing Amylases Produce sugars from starch, such as in making high-fructose corn syrup.
Proteases Lower the protein level of flour, as in biscuit-making.
Trypsin Manufacture hypoallergenic baby foods.
Cellulases, pectinases Clarify fruit juices.
Molecular biology Nucleases, DNA ligase, and polymerases Use restriction digestion and the polymerase chain reaction to create recombinant DNA.
Paper industry Xylanases, hemicellulases, and lignin peroxidases Remove lignin from Kraft pulp.
Personal care Proteases Remove proteins on cotact lenses to prevent infections.
Starch industry Amylases Convert starch into glucose and various syrups.
Summary
• Proteins can be divided into two categories: fibrous, which tend to be insoluble in water, and globular, which are more soluble in water. A protein may have up to four levels of structure.
• The primary structure consists of the specific amino acid sequence.
• The resulting peptide chain can form an α-helix or β-pleated sheet (or local structures not as easily categorized), which is known as secondary structure. These segments of secondary structure are incorporated into the tertiary structure of the folded polypeptide chain.
• The quaternary structure describes the arrangements of subunits in a protein that contains more than one subunit. Four major types of attractive interactions determine the shape and stability of the folded protein: ionic bonding, hydrogen bonding, disulfide linkages, and dispersion forces.
• An enzyme is an organic catalyst produced by a living cell. Enzymes are such powerful catalysts that the reactions they promote occur rapidly at body temperature.
• The molecule or molecules on which an enzyme acts are called its substrates.
• An enzyme has an active site where its substrate or substrates bind to form an enzyme-substrate complex.
• The original lock and key model of enzyme and substrate binding pictured a rigid enzyme of unchanging configuration binding to the appropriate substrate. The newer induced fit model describes the enzyme active site as changing its conformation after binding to the substrate.
• Enzymes have numerous applications in the food and dairy industry, biofuel industry, paper industry etc.
Contributors and Attributions
• Libretext: The Basics of GOB Chemistry (Ball et al.)
• Allison Soult, Ph.D. (Department of Chemistry, University of Kentucky)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.05%3A_Structure_and_Function_of_Proteins.txt |
Learning Objectives
• Describe the two types of nucleic acids and the function of each type.
• Describe the secondary structure of DNA and the importance of complementary base pairing.
• Describe how a new copy of DNA is synthesized.
The repeating, or monomer, units that are linked together to form nucleic acids are known as nucleotides. The deoxyribonucleic acid (DNA) of a typical mammalian cell contains about 3 × 109 nucleotides. Nucleotides can be further broken down to phosphoric acid (H3PO4), a pentose sugar (a sugar with five carbon atoms), and a nitrogenous base (a base containing nitrogen atoms).
$\mathrm{nucleic\: acids \underset{down\: into}{\xrightarrow{can\: be\: broken}} nucleotides \underset{down\: into}{\xrightarrow{can\: be\: broken}} H_3PO_4 + nitrogen\: base + pentose\: sugar} \nonumber$
If the pentose sugar is ribose, the nucleotide is more specifically referred to as a ribonucleotide, and the resulting nucleic acid is ribonucleic acid (RNA). If the sugar is 2-deoxyribose, the nucleotide is a deoxyribonucleotide, and the nucleic acid is DNA.
The nitrogenous bases found in nucleotides are classified as pyrimidines or purines. Pyrimidines are heterocyclic amines with two nitrogen atoms in a six-member ring and include uracil, thymine, and cytosine. Purines are heterocyclic amines consisting of a pyrimidine ring fused to a five-member ring with two nitrogen atoms. Adenine and guanine are the major purines found in nucleic acids (Figure $1$).
The formation of a bond between C1′ of the pentose sugar and N1 of the pyrimidine base or N9 of the purine base joins the pentose sugar to the nitrogenous base. In the formation of this bond, a molecule of water is removed. Table $1$ summarizes the similarities and differences in the composition of nucleotides in DNA and RNA.
The numbering convention is that primed numbers designate the atoms of the pentose ring, and unprimed numbers designate the atoms of the purine or pyrimidine ring.
Table $1$ Composition of Nucleotides in DNA and RNA.
Composition DNA RNA
purine bases adenine and guanine adenine and guanine
pyrimidine bases cytosine and thymine cytosine and uracil
pentose sugar 2-deoxyribose ribose
inorganic acid phosphoric acid (H3PO4) H3PO4
The names and structures of the major ribonucleotides and one of the deoxyribonucleotides are given in Figure $2$.
Apart from being the monomer units of DNA and RNA, the nucleotides and some of their derivatives have other functions as well. Adenosine diphosphate (ADP) and adenosine triphosphate (ATP), shown in Figure $3$, have a role in cell metabolism. Moreover, a number of coenzymes, including flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD+), and coenzyme A, contain adenine nucleotides as structural components.
Nucleic acids are large polymers formed by linking nucleotides together and are found in every cell. Deoxyribonucleic acid (DNA) is the nucleic acid that stores genetic information. If all the DNA in a typical mammalian cell were stretched out end to end, it would extend more than 2 m. Ribonucleic acid (RNA) is the nucleic acid responsible for using the genetic information encoded in DNA to produce the thousands of proteins found in living organisms.
Primary Structure of Nucleic Acids
Nucleotides are joined together through the phosphate group of one nucleotide connecting in an ester linkage to the OH group on the third carbon atom of the sugar unit of a second nucleotide. This unit joins to a third nucleotide, and the process is repeated to produce a long nucleic acid chain (Figure $4$). The backbone of the chain consists of alternating phosphate and sugar units (2-deoxyribose in DNA and ribose in RNA). The purine and pyrimidine bases branch off this backbone.
Each phosphate group has one acidic hydrogen atom that is ionized at physiological pH. This is why these compounds are known as nucleic acids.
Like proteins, nucleic acids have a primary structure that is defined as the sequence of their nucleotides. Unlike proteins, which have 20 different kinds of amino acids, there are only 4 different kinds of nucleotides in nucleic acids. For amino acid sequences in proteins, the convention is to write the amino acids in order starting with the N-terminal amino acid. In writing nucleotide sequences for nucleic acids, the convention is to write the nucleotides (usually using the one-letter abbreviations for the bases, shown in Figure $4$) starting with the nucleotide having a free phosphate group, which is known as the 5′ end, and indicate the nucleotides in order. For DNA, a lowercase d is often written in front of the sequence to indicate that the monomers are deoxyribonucleotides. The final nucleotide has a free OH group on the 3′ carbon atom and is called the 3′ end. The sequence of nucleotides in the DNA segment shown in Figure $4$ would be written 5′-dG-dT-dA-dC-3′, which is often further abbreviated to dGTAC or just GTAC.
Secondary Structure of DNA
The three-dimensional structure of DNA was the subject of an intensive research effort in the late 1940s to early 1950s. Initial work revealed that the polymer had a regular repeating structure. In 1950, Erwin Chargaff of Columbia University showed that the molar amount of adenine (A) in DNA was always equal to that of thymine (T). Similarly, he showed that the molar amount of guanine (G) was the same as that of cytosine (C). Chargaff drew no conclusions from his work, but others soon did.
At Cambridge University in 1953, James D. Watson and Francis Crick announced that they had a model for the secondary structure of DNA. Using the information from Chargaff’s experiments (as well as other experiments) and data from the X ray studies of Rosalind Franklin (which involved sophisticated chemistry, physics, and mathematics), Watson and Crick worked with models that were not unlike a child’s construction set and finally concluded that DNA is composed of two nucleic acid chains running antiparallel to one another—that is, side-by-side with the 5′ end of one chain next to the 3′ end of the other. Moreover, as their model showed, the two chains are twisted to form a double helix—a structure that can be compared to a spiral staircase, with the phosphate and sugar groups (the backbone of the nucleic acid polymer) representing the outside edges of the staircase. The purine and pyrimidine bases face the inside of the helix, with guanine always opposite cytosine and adenine always opposite thymine. These specific base pairs, referred to as complementary bases, are the steps, or treads, in our staircase analogy (Figure $5$).
The structure proposed by Watson and Crick provided clues to the mechanisms by which cells are able to divide into two identical, functioning daughter cells; how genetic data are passed to new generations; and even how proteins are built to required specifications. All these abilities depend on the pairing of complementary bases. Figure $6$ shows the two sets of base pairs and illustrates two things. First, a pyrimidine is paired with a purine in each case, so that the long dimensions of both pairs are identical (1.08 nm).
If two pyrimidines were paired or two purines were paired, the two pyrimidines would take up less space than a purine and a pyrimidine, and the two purines would take up more space, as illustrated in Figure $7$. If these pairings were ever to occur, the structure of DNA would be like a staircase made with stairs of different widths. For the two strands of the double helix to fit neatly, a pyrimidine must always be paired with a purine. The second thing you should notice in Figure $6$ is that the correct pairing enables formation of three instances of hydrogen bonding between guanine and cytosine and two between adenine and thymine. The additive contribution of this hydrogen bonding imparts great stability to the DNA double helix.
We previously stated that deoxyribonucleic acid (DNA) stores genetic information, while ribonucleic acid (RNA) is responsible for transmitting or expressing genetic information by directing the synthesis of thousands of proteins found in living organisms. But how do the nucleic acids perform these functions? Three processes are required: (1) replication, in which new copies of DNA are made; (2) transcription, in which a segment of DNA is used to produce RNA; and (3) translation, in which the information in RNA is translated into a protein sequence.
DNA: Self-Replication
New cells are continuously forming in the body through the process of cell division. For this to happen, the DNA in a dividing cell must be copied in a process known as replication. The complementary base pairing of the double helix provides a ready model for how genetic replication occurs. If the two chains of the double helix are pulled apart, disrupting the hydrogen bonding between base pairs, each chain can act as a template, or pattern, for the synthesis of a new complementary DNA chain.
The nucleus contains all the necessary enzymes, proteins, and nucleotides required for this synthesis. A short segment of DNA is “unzipped,” so that the two strands in the segment are separated to serve as templates for new DNA. DNA polymerase, an enzyme, recognizes each base in a template strand and matches it to the complementary base in a free nucleotide. The enzyme then catalyzes the formation of an ester bond between the 5′ phosphate group of the nucleotide and the 3′ OH end of the new, growing DNA chain. In this way, each strand of the original DNA molecule is used to produce a duplicate of its former partner (Figure $8$). Whatever information was encoded in the original DNA double helix is now contained in each replicate helix. When the cell divides, each daughter cell gets one of these replicates and thus all of the information that was originally possessed by the parent cell.
Example $1$
A segment of one strand from a DNA molecule has the sequence 5′‑TCCATGAGTTGA‑3′. What is the sequence of nucleotides in the opposite, or complementary, DNA chain?
Solution
Knowing that the two strands are antiparallel and that T base pairs with A, while C base pairs with G, the sequence of the complementary strand will be 3′‑AGGTACTCAACT‑5′.
Exercise $1$
A segment of one strand from a DNA molecule has the sequence 5′‑CCAGTGAATTGCCTAT‑3′. What is the sequence of nucleotides in the opposite, or complementary, DNA chain?
Answer
3′‑GGTCACTTAACGGATA‑5′.
Summary
• Nucleotides are composed of phosphoric acid, a pentose sugar (ribose or deoxyribose), and a nitrogen-containing base (adenine, cytosine, guanine, thymine, or uracil). Ribonucleotides contain ribose, while deoxyribonucleotides contain deoxyribose.
• DNA is the nucleic acid that stores genetic information. RNA is the nucleic acid responsible for using the genetic information in DNA to produce proteins.
• Nucleic acid sequences are written starting with the nucleotide having a free phosphate group (the 5′ end).
• Two DNA strands link together in an antiparallel direction and are twisted to form a double helix. The nitrogenous bases face the inside of the helix. Guanine is always opposite cytosine, and adenine is always opposite thymine.
• In DNA replication, each strand of the original DNA serves as a template for the synthesis of a complementary strand.
• DNA polymerase is the primary enzyme needed for replication.
Contributors and Attributions
• Libretext: Basics of GOB Chemistry (Ball et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.06%3A_Nucleic_Acids-_Parts_Structure_and_Function.txt |
Learning Objectives
• Describe the human genome project.
• Describe the advances made possible by recombinant DNA technology.
The Human Genome
This collective body of genes is called the human genome and the project to map it is called the Human Genome Project. The original impetus for this project in the U. S. arose because of interest in the damage to human DNA by radiation, such as that from nuclear weapons. But, from the beginning, it was recognized that the project had enormous commercial potential, especially in the pharmaceutical industry, and could be very valuable in human health.
The announcement in 2001 that mapping of the human genome was complete promised great progress in biology, especially in medicine. Genes function by directing the synthesis of specific proteins and the action of most pharmaceuticals is to alter the activities of proteins, the drug’s target. In some cases proteins are made more active and in others their activity is diminished. Knowledge of the human genome enables a better understanding of protein activity and should facilitate the development of more specific drugs, something that has developed only slowly. For example, the gene responsible for cystic fibrosis was discovered in 1989 by examination of family histories of the disease and only in 2010 were two drugs designed to combat that disease in clinical trials.
Recombinant DNA Technology
Recombinant DNA technology: the process of taking a gene from one organism and inserting it into the DNA of another. Recombinant DNA technology is the latest biochemical analysis that came about to satisfy the need for specific DNA segments. In this process, surrounding DNA from an existing cell is clipped in the desired amount of segments so that it can be copied millions of times.
Recombinant DNA technology engineers microbial cells for producing foreign proteins, and its success solely depends on the precise reading of equivalent genes made with the help of bacterial cell machinery. This process has been responsible for fueling many advances related to modern molecular biology. The last two decades of cloned-DNA sequence studies have revealed detailed knowledge about gene structure as well as its organization. It has provided hints to regulatory pathways with the aid of which gene expression in myriad cell types is controlled by the cells, especially in those organisms having body plan with basic vertebrae structure.
Recombinant DNA technology, apart from being an important tool of scientific research, has also played a vital role in the diagnosis and treatment of various diseases, especially those belonging to genetic disorders.
Some of the recent advances made possible by recombinant DNA technology are:
1. Isolating proteins in large quantities: many recombinant products are now available, including follicle stimulating hormone (FSH), Follistim AQ vial, growth hormone, insulin and some other proteins.
2. Making possible mutation identification: due to this technology, people can be easily tested for mutated protein presence that can lead to breast cancer, neurofibromatosis, and retinoblastoma.
3. Hereditary diseases carrier diagnosis: tests now available to determine if a person is carrying the gene for cystic fibrosis, the Tay-Sachs diseases, Huntington’s disease or Duchenne muscular dystrophy.
4. Gene transfer from one organism to other: the advanced gene therapy can benefit people with cystic fibrosis, vascular disease, rheumatoid arthritis and specific types of cancers.
Summary
• This collective body of genes is called the human genome and the project to map it is called the Human Genome Project. Recombinant DNA (rDNA) is widely used in biotechnology, medicine and research. Proteins and other products that result from the use of rDNA technology are found in essentially every western pharmacy, doctor’s or veterinarian’s office, medical testing laboratory, and biological research laboratory.
• Organisms that have been manipulated using recombinant DNA technology, and products derived from those organisms have found their way into many farms, supermarkets, home medicine cabinets, and even pet shops.
• Biochemical products of recombinant DNA technology in medicine and research include: human recombinant insulin, growth hormone, blood clotting factors, hepatitis B vaccine, and diagnosis of HIV infection.
• Biochemical products of recombinant DNA technology in agriculture include: golden rice, herbicide-resistant crops, and insect-resistant crops.
Contributors and Attributions
S. Manahan (University of Missouri)
Libretexts Microbiology (Boundless) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.08%3A_The_Human_Genome.txt |
Learning Objectives
• Describe the characteristics of the genetic code.
• Describe how a protein is synthesized from mRNA.
One of the definitions of a gene is as follows: a segment of deoxyribonucleic acid (DNA) carrying the code for a specific polypeptide. Each molecule of messenger RNA (mRNA) is a transcribed copy of a gene that is used by a cell for synthesizing a polypeptide chain. If a protein contains two or more different polypeptide chains, each chain is coded by a different gene. We turn now to the question of how the sequence of nucleotides in a molecule of ribonucleic acid (RNA) is translated into an amino acid sequence.
How can a molecule containing just 4 different nucleotides specify the sequence of the 20 amino acids that occur in proteins? If each nucleotide coded for 1 amino acid, then obviously the nucleic acids could code for only 4 amino acids. What if amino acids were coded for by groups of 2 nucleotides? There are 42, or 16, different combinations of 2 nucleotides (AA, AU, AC, AG, UU, and so on). Such a code is more extensive but still not adequate to code for 20 amino acids. However, if the nucleotides are arranged in groups of 3, the number of different possible combinations is 43, or 64. Here we have a code that is extensive enough to direct the synthesis of the primary structure of a protein molecule.
Video: NDSU Virtual Cell Animations project animation "Translation". For more information, see http://vcell.ndsu.nodak.edu/animations
The genetic code can therefore be described as the identification of each group of three nucleotides and its particular amino acid. The sequence of these triplet groups in the mRNA dictates the sequence of the amino acids in the protein. Each individual three-nucleotide coding unit, as we have seen, is called a codon.
Protein synthesis is accomplished by orderly interactions between mRNA and the other ribonucleic acids (transfer RNA [tRNA] and ribosomal RNA [rRNA]), the ribosome, and more than 100 enzymes. The mRNA formed in the nucleus during transcription is transported across the nuclear membrane into the cytoplasm to the ribosomes—carrying with it the genetic instructions. The process in which the information encoded in the mRNA is used to direct the sequencing of amino acids and thus ultimately to synthesize a protein is referred to as translation.
Before an amino acid can be incorporated into a polypeptide chain, it must be attached to its unique tRNA. This crucial process requires an enzyme known as aminoacyl-tRNA synthetase (Figure \(1\)). There is a specific aminoacyl-tRNA synthetase for each amino acid. This high degree of specificity is vital to the incorporation of the correct amino acid into a protein. After the amino acid molecule has been bound to its tRNA carrier, protein synthesis can take place. Figure \(2\) depicts a schematic stepwise representation of this all-important process.
Early experimenters were faced with the task of determining which of the 64 possible codons stood for each of the 20 amino acids. The cracking of the genetic code was the joint accomplishment of several well-known geneticists—notably Har Khorana, Marshall Nirenberg, Philip Leder, and Severo Ochoa—from 1961 to 1964. The genetic dictionary they compiled, summarized in Figure \(3\), shows that 61 codons code for amino acids, and 3 codons serve as signals for the termination of polypeptide synthesis (much like the period at the end of a sentence). Notice that only methionine (AUG) and tryptophan (UGG) have single codons. All other amino acids have two or more codons.
Example \(1\): Using the Genetic Code
A portion of an mRNA molecule has the sequence 5′‑AUGCCACGAGUUGAC‑3′. What amino acid sequence does this code for?
Solution
Use Figure \(3\) to determine what amino acid each set of three nucleotides (codon) codes for. Remember that the sequence is read starting from the 5′ end and that a protein is synthesized starting with the N-terminal amino acid. The sequence 5′‑AUGCCACGAGUUGAC‑3′ codes for met-pro-arg-val-asp.
Exercise \(1\)
A portion of an mRNA molecule has the sequence 5′‑AUGCUGAAUUGCGUAGGA‑3′. What amino acid sequence does this code for?
met-leu-asn-cys-val-gly
The Nature of the Genetic Code
Further experimentation threw much light on the nature of the genetic code, as follows:
1. The code is virtually universal; animal, plant, and bacterial cells use the same codons to specify each amino acid (with a few exceptions).
2. The code is “degenerate”; in all but two cases (methionine and tryptophan), more than one triplet codes for a given amino acid.
3. The first two bases of each codon are most significant; the third base often varies. This suggests that a change in the third base by a mutation may still permit the correct incorporation of a given amino acid into a protein. The third base is sometimes called the “wobble” base.
4. The code is continuous and nonoverlapping; there are no nucleotides between codons, and adjacent codons do not overlap.
5. The three termination codons are read by special proteins called release factors, which signal the end of the translation process.
6. The codon AUG codes for methionine and is also the initiation codon. Thus methionine is the first amino acid in each newly synthesized polypeptide. This first amino acid is usually removed enzymatically before the polypeptide chain is completed; the vast majority of polypeptides do not begin with methionine.
Summary
• In transcription, a segment of DNA serves as a template for the synthesis of an RNA sequence.
• RNA polymerase is the primary enzyme needed for transcription.
• In translation, the information in mRNA directs the order of amino acids in protein synthesis. A set of three nucleotides (codon) codes for a specific amino acid.
Contributors and Attributions
• Libretext: The Baiscs of GOB Chemistry (Ball et al.) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/16%3A_Biochemistry/16.7%3A_RNA_Protein_Synthesis_and_the_Genetic_Code.txt |
Learning Objectives
• Describe the metabolism of carbohydrates.
• Know the source and function of common carbohydrates in the diet.
Carbohydrates are sugars and sugar derivatives whose formulas can be written in the general form: Cx(H2O)y. (The subscripts x and y are whole numbers.) Some typical carbohydrates are sucrose (ordinary cane sugar), C12H22O11; glucose (dextrose), C6H12O6; fructose (fruit sugar), C6H12O6; and ribose, C5H10O5. Since the atom ratio H/O is 2/1 in each formula, these compounds were originally thought to be hydrates of carbon, hence their general name.
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar" (in the broad sense), "saccharide", "ose", "glucide", "hydrate of carbon" or "polyhydroxy compounds with aldehyde or ketone". Some of these terms, specially "carbohydrate" and "sugar", are also used with other meanings.
In food science and in many informal contexts, the term "carbohydrate" often means any food that is particularly rich in the complex carbohydrate starch (such as cereals, bread and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts).
Carbohydrates may be classified according to their degree of polymerization, and may be divided initially into three principal groups, namely sugars, oligosaccharides and polysaccharidesas shown in Table \(1\).
Table \(1\) The Major Dietary Carbohydrates. Source: Wikipedia
Class (DP*) Subgroup Components
Sugars (1–2) Monosaccharides Glucose, galactose, fructose, xylose
Disaccharides Sucrose, lactose, maltose, trehalose
Polyols Sorbitol, mannitol
Oligosaccharides (3–9) Malto-oligosaccharides Maltodextrins
Other oligosaccharides Raffinose, stachyose, fructo-oligosaccharides
Polysaccharides (>9) Starch Amylose, amylopectin, modified starches
Non-starch polysaccharides Glycogen, Cellulose, Hemicellulose, Pectins, Hydrocolloids
DP * = Degree of polymerization
Digestion of Carbohydrates
The human body breaks down complex carbohydrates into glucose. Glucose in the blood (often referred to as “blood sugar”) is the primary energy source for the body. Sugars provide calories, or “energy,” for the body. Each gram of sugar provides 4 calories. Glucose can be used immediately or stored in the liver and muscles for later use.
Carbohydrate digestion begins in the mouth (Figure \(1\)) where salivary α-amylase attacks the α-glycosidic linkages in starch, the main carbohydrate ingested by humans. Cleavage of the glycosidic linkages produces a mixture of dextrins, maltose, and glucose. The α-amylase mixed into the food remains active as the food passes through the esophagus, but it is rapidly inactivated in the acidic environment of the stomach.
The primary site of carbohydrate digestion is the small intestine. The secretion of α-amylase in the small intestine converts any remaining starch molecules, as well as the dextrins, to maltose. Maltose is then cleaved into two glucose molecules by maltase. Disaccharides such as sucrose and lactose are not digested until they reach the small intestine, where they are acted on by sucrase and lactase, respectively. The major products of the complete hydrolysis of disaccharides and polysaccharides are three monosaccharide units: glucose, fructose, and galactose. These are absorbed through the wall of the small intestine into the bloodstream.
Fuel for the Brain
The brain is a marvelous organ. And it's a hungry one, too. The major fuel for the brain is the carbohydrate glucose. The average adult brain represents about \(2\%\) of our body's weight, but uses \(25\%\) of the glucose in the body. Moreover, specific areas of the brain use glucose at different rates. If you are concentrating hard (taking a test, for example), certain parts of the brain need a lot of extra glucose while other parts of the brain only use their normal amount. Something to think about.
Some foods that are high in carbohydrates include bread, pasta, and potatoes (Figure \(2\)) . Because carbohydrates are easily digested, athletes often rely on carbohydrate rich foods to enable a high level of performance.
Common Monosaccharides and Disaccharides
Monosaccharides and disaccharides commonly found in our diets are listed in Table \(3\). Although a variety of monosaccharides are found in living organisms, three hexoses are particularly abundant: D-glucose, D-galactose, and D-fructose (Figure \(3\)). Glucose and galactose are both aldohexoses, while fructose is a ketohexose.
Table \(2\) . Monosaccharides and disaccharides. Source: US FDA
Simple sugars (monosaccharides) are small enough to be absorbed directly into the bloodstream. They include: Sugars that contain two molecules of sugar linked together (disaccharides) are broken down in your body into single sugars. They include:
Fructose Sucrose (table sugar ) = glucose + fructose
Galactose Lactose (milk sugar) = glucose + galactose
Glucose Maltose (malt sugar) = glucose + glucose
Figure \(3\) Structures of three important hexoses. Each hexose is pictured with a food source in which it is commonly found. Source: Photos © Thinkstock.
Glucose
D-Glucose, generally referred to as simply glucose, is the most abundant sugar found in nature; most of the carbohydrates we eat are eventually converted to it in a series of biochemical reactions that produce energy for our cells. It is also known by three other names: dextrose, from the fact that it rotates plane-polarized light in a clockwise (dextrorotatory) direction; corn sugar because in the United States cornstarch is used in the commercial process that produces glucose from the hydrolysis of starch; and blood sugar because it is the carbohydrate found in the circulatory system of animals. Normal blood sugar values range from 70 to 105 mg glucose/dL plasma, and normal urine may contain anywhere from a trace to 20 mg glucose/dL urine.
Galactose
D-Galactose does not occur in nature in the uncombined state. It is released when lactose, a disaccharide found in milk, is hydrolyzed. The galactose needed by the human body for the synthesis of lactose is obtained by the metabolic conversion of D-glucose to D-galactose. Galactose is also an important constituent of the glycolipids that occur in the brain and the myelin sheath of nerve cells. For this reason it is also known as brain sugar. The structure of D-galactose is shown in Figure \(3\). Notice that the configuration differs from that of glucose only at the fourth carbon atom.
Fructose
D-Fructose, also shown in Figure \(3\), is the most abundant ketohexose. Note that from the third through the sixth carbon atoms, its structure is the same as that of glucose. It occurs, along with glucose and sucrose, in honey (which is 40% fructose) and sweet fruits. Fructose (from the Latin fructus, meaning “fruit”) is also referred to as levulose because it has a specific rotation that is strongly levorotatory (−92.4°). It is the sweetest sugar, being 1.7 times sweeter than sucrose, although many nonsugars are several hundred or several thousand times as sweet (Table \(1\)).
Sucrose
Sucrose, probably the largest-selling pure organic compound in the world, is known as beet sugar, cane sugar, table sugar, or simply sugar. Most of the sucrose sold commercially is obtained from sugar cane and sugar beets (whose juices are 14%–20% sucrose) by evaporation of the water and recrystallization. The dark brown liquid that remains after the recrystallization of sugar is sold as molasses.
Maltose
Maltose occurs to a limited extent in sprouting grain. It is formed most often by the partial hydrolysis of starch and glycogen. In the manufacture of beer, maltose is liberated by the action of malt (germinating barley) on starch; for this reason, it is often referred to as malt sugar. Maltose is about 30% as sweet as sucrose. The human body is unable to metabolize maltose or any other disaccharide directly from the diet because the molecules are too large to pass through the cell membranes of the intestinal wall. Therefore, an ingested disaccharide must first be broken down by hydrolysis into its two constituent monosaccharide units.
In the body, such hydrolysis reactions are catalyzed by enzymes such as maltase.
Lactose
Lactose is known as milk sugar because it occurs in the milk of humans, cows, and other mammals. In fact, the natural synthesis of lactose occurs only in mammary tissue, whereas most other carbohydrates are plant products. Human milk contains about 7.5% lactose, and cow’s milk contains about 4.5%. This sugar is one of the lowest ranking in terms of sweetness, being about one-sixth as sweet as sucrose. Lactose is produced commercially from whey, a by-product in the manufacture of cheese. It is important as an infant food and in the production of penicillin.
Many adults and some children suffer from a deficiency of lactase. These individuals are said to be lactose intolerant because they cannot digest the lactose found in milk. A more serious problem is the genetic disease galactosemia, which results from the absence of an enzyme needed to convert galactose to glucose. Certain bacteria can metabolize lactose, forming lactic acid as one of the products. This reaction is responsible for the “souring” of milk.
The different disaccharides and the monosaccharides components are illustrated in Figure \(4\) below.
Each of these disaccharides contains glucose and all the reactions are dehydration reactions. Also notice the difference in the bond structures. Maltose and sucrose have alpha-bonds, which are depicted as v-shaped above. You might hear the term glycosidic used in some places to describe bonds between sugars. A glycoside is a sugar, so glycosidic is referring to a sugar bond. Lactose, on the other hand, contains a beta-bond. We need a special enzyme, lactase, to break this bond, and the absence of lactase activity leads to lactose intolerance.
Naturally Occurring and Added Sugars
Sugars are found naturally in many nutritious foods and beverages and are also added to foods and beverages for taste, texture, and preservation.
Naturally occurring sugars are found in a variety of foods, including: Added sugars are often found in foods low in other nutrients, including:
• Dairy products
• Fruit (fresh, frozen, dried, and canned in 100% fruit juice)
• 100% fruit and vegetable juice
• Vegetables
• Dairy desserts (such as ice cream, other frozen desserts, and puddings)
• Grain-based desserts (such as brownies, cakes, cookies, doughnuts, pastries, pies, and sweet rolls)
• Sugar-sweetened beverages (such as energy drinks, flavored waters, fruit drinks, soft drinks, sports drinks, and sweetened coffee and tea)
• Sweets (such as candies, jams, sweet toppings, and syrups)
The relative sweetness of the different sugars previously discussed are given in Table \(3\).
Table \(3\): The Relative Sweetness of Some Sugars (Sucrose = 100)
Compound Relative Sweetness
lactose 16
maltose 32
glucose 74
sucrose 100
fructose 173
High-Fructose Corn Syrup
Opponents claim that high-fructose corn syrup is contributing to the rise in obesity rates. As a result, some manufactures have started releasing products made with natural sugar. You can read about this trend in the following New York Times article in the link below. Also, manufacturers tried to rebrand high-fructose corn syrup as corn sugar to get around the negative perception of the name. But the FDA rejected the Corn Refiners Association request to change the name officially to corn sugar as described in the second link. The last link is a video made by the American Chemical Society that gives some background on how HFCS is produced and how it compares to sucrose.
Links
Sugar is back on labels, this time as a selling point - http://www.nytimes.com/2009/03/21/dining/21sugar.html?_r=1&ref=nutrition
No new name for high-fructose corn syrup - http://well.blogs.nytimes.com/2012/05/31/no-new-name-for-high-fructose-corn-syrup/?_r=0
Video
Sugar vs. High Fructose Corn Syrup - What's the Difference? - https://www.youtube.com/watch?v=fXMvregmU1g
Complex Carbohydrates: Oligosaccharides and Polysaccharides
An oligosaccharide, from the Greek olígos, "a few", and sácchar, "sugar") is a saccharide polymer containing a small number (typically three to ten) of monosaccharides (simple sugars). Oligosaccharides are a component of fiber from plant tissue. Fructoologosaccharides (FOS) and inulin (Figure \(6\)) are present in Jerusalem artichoke, burdock, chicory, leeks, onions, and asparagus. Inulin is a significant part of the daily diet of most of the world’s population. FOS can also be synthesized by enzymes of the fungus Aspergillus niger acting on sucrose. Galatoologosaccharide (GOS) is naturally found in soybeans and can be synthesized from lactose. FOS, GOS, and inulin are also sold as nutritional supplements.[citation needed]
As the name suggests, polysaccharides are substances built up by the condensation of a very large number of monosaccharide units. Cellulose, for example, is a polymer of β-glucose, containing upwards of 3000 glucose units in a chain. Starch is largely a polymer of α-glucose.
These two substances are a classic example of how a minor difference in the monomer can lead to major differences in the macroscopic properties of the polymer. Good-quality cotton and paper are almost pure cellulose, and they give us a good idea of its properties. Cellulose forms strong but flexible fibers and does not dissolve in water. By contrast, starch has no mechanical strength at all, and some forms are water soluble. Part of the molecular structure of cellulose and starch are shown in Fig. \(6\).
Cellulose and starch are different not only in overall structure and macroscopic properties. From a biochemical point of view they behave so differently that it is difficult to believe that they are both polymers of the same monosaccharide. Enzymes which are capable of hydrolyzing starch will not touch cellulose, and vice versa. From a plant’s point of view this is just as well since cellulose makes up structural material while starch serves as a storehouse for energy. If there were not a sharp biochemical distinction between the two, the need for a bit more energy by the plant might result in destruction of cell walls or other necessary structural components.
Starches in Food
Starch is the most common carbohydrate in the human diet and is contained in many staple foods. The major sources of starch intake worldwide are the cereals (rice, wheat, and maize) and the root vegetables (potatoes and cassava). Many other starchy foods are grown, some only in specific climates, including acorns, arrowroot, arracacha, bananas, barley, breadfruit, buckwheat, canna, colocasia, katakuri, kudzu, malanga, millet, oats, oca, polynesian arrowroot, sago, sorghum, sweet potatoes, rye, taro, chestnuts, water chestnuts and yams, and many kinds of beans, such as favas, lentils, mung beans, peas, and chickpeas.
Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta, porridge and tortilla.
Digestive enzymes have problems digesting crystalline structures. Raw starch is digested poorly in the duodenum and small intestine, while bacterial degradation takes place mainly in the colon. When starch is cooked, the digestibility is increased. Starch gelatinization during cake baking can be impaired by sugar competing for water, preventing gelatinization and improving texture.
Before the advent of processed foods, people consumed large amounts of uncooked and unprocessed starch-containing plants, which contained high amounts of resistant starch. Microbes within the large intestine fermented the starch, produced short-chain fatty acids, which are used as energy, and support the maintenance and growth of the microbes. More highly processed foods are more easily digested and release more glucose in the small intestine—less starch reaches the large intestine and more energy is absorbed by the body. It is thought that this shift in energy delivery (as a result of eating more processed foods) may be one of the contributing factors to the development of metabolic disorders of modern life, including obesity and diabetes.
Fibers in Food
Dietary fiber (British spelling fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins, pectins, beta-glucans, and oligosaccharides.
Polysaccharide fiber differs from other polysaccharides in that it contains beta-glycosidic bonds (as opposed to alpha-glycosidic bonds). To illustrate these differences, consider the structural differences between amylose and cellulose (type of fiber) in the figure below. Both are linear chains of glucose, the only difference is that amylose has alpha-glycosidic bonds, while cellulose has beta-glycosidic bonds as shown below. The beta-bonds in fiber cannot be broken down by the digestive enzymes in the small intestine so they continue into the large intestine.
Fiber can be classified by its physical properties. In the past, fibers were commonly referred to as soluble and insoluble. This classification distinguished whether the fiber was soluble in water. However, this classification is being phased out in the nutrition community. Instead, most fibers that would have been classified as insoluble fiber are now referred to as nonfermentable and/or nonviscous and soluble fiber as fermentable, and/or viscous because these better describe the fiber's characteristics. Viscous refers to the capacity of certain fibers to form a thick gel-like consistency.
Fermentable (soluble fiber) dissolves in water and is readily fermented in the colon into gases and physiologically active by-products, such as short-chain fatty acids produced in the colon by gut bacteria;it is viscous, may be called prebiotic fiber, and delays gastric emptying which, in humans, can result in an extended feeling of fullness.
Non-fermentable (insoluble fiber) does not dissolve in water and is inert to digestive enzymes in the upper gastrointestinal tract and provides bulking. Some forms of insoluble fiber, such as resistant starches, can be fermented in the colon. Bulking fibers absorb water as they move through the digestive system, easing defecation.
Table \(4\) lists some of the common types of fiber and provides a brief description about each. Specific sources of the different types of soluble and insoluble fiber as well as the amount of fiber found in common foods are discussed in section 17.4.
Table \(4\) Common Types of Fermentable (Soluble) Fiber and Non-Fermentable (Insoluble) Fiber.
Fermentable
(Soluble) Fiber
Description
Non-Fermentable
(Insoluble Fiber)
Description
Hemicellulose (soluble type) Surround cellulose in plant cell walls Cellulose Main component of plant cell walls
Pectin Found in cell walls and intracellular tissues of fruits and berries
Hemicellulose
(insoluble type)
Surround cellulose in plant cell walls
Beta-glucans Found in cereal brans Lignin Non carbohydrate found within "woody" plat cell walls
Gums Viscous, usually isolated from seeds
Summary
• Carbohydrate digestion begins in the mouth (in the presence of salivary α-amylase) and continues in the small intestine. The major products of the complete hydrolysis of disaccharides and polysaccharides are three monosaccharide units: glucose, fructose, and galactose. These are absorbed through the wall of the small intestine into the bloodstream.
• Simple sugars like glucose, fructose and the disaccharide sucrose function as natural sweeteners.
• More complex carbohydrates (oligosaccharides and polysaccharides) are now significant parts of the daily diet promoting gut health that leads to other health benefits. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.01%3A_Carbohydrates_in_the_Diet.txt |
Learning Objectives
• Describe the digestion of lipids.
• Know the properties and functions of the different types of lipoproteins.
• Know the sources and function of common dietary lipids.
How Does Fat Differ From Lipids? The answer you receive from this question will depend on who you ask, so it is important to have an understanding of lipids and fats from a chemical and nutritional perspective.
To a chemist, lipids consist of triglycerides, fatty acids, phospholipids, waxes, and sterols. These compounds are grouped together because of their structural and physical property similarities. For instance, all lipids have hydrophobic (water-fearing) properties. Chemists further separate lipids into fats and oils based on their physical properties at room temperature:
• Fats are solid at room temperature
• Oils are liquid at room temperature
From a nutritional perspective, the definition of lipids is the same. The definition of a fat differs, however, because nutrition-oriented people define fats based on their caloric contribution rather than whether they are solid at room temperature. Thus, from a nutrition perspective, Fats are triglycerides, fatty acids, and phospholipids that provide 9 kcal/g. The other difference is that from a caloric perspective, an oil is a fat. For example, let's consider olive oil. Clearly, it is an oil according to a chemist definition, but from a caloric standpoint it is a fat because it provides 9 kcal/g.
Digestion of Lipids
Lipid digestion begins in the upper portion of the small intestine (Figure \(1\)). A hormone secreted in this region stimulates the gallbladder to discharge bile into the duodenum. The principal constituents of bile are the bile salts, which emulsify large, water-insoluble lipid droplets, disrupting some of the hydrophobic interactions holding the lipid molecules together and suspending the resulting smaller globules (micelles) in the aqueous digestive medium. These changes greatly increase the surface area of the lipid particles, allowing for more intimate contact with the lipases and thus rapid digestion of the fats. Another hormone promotes the secretion of pancreatic juice, which contains these enzymes.
The lipases in pancreatic juice catalyze the digestion of triglycerides first to diglycerides and then to 2‑monoglycerides and fatty acids:
The monoglycerides and fatty acids cross the intestinal lining into the bloodstream, where they are resynthesized into triglycerides and transported as lipoprotein complexes known as chylomicrons. Phospholipids and cholesteryl esters undergo similar hydrolysis in the small intestine, and their component molecules are also absorbed through the intestinal lining.
Fats, Cholesterol, and Human Health
The primary sterol that we consume is cholesterol. The structure of cholesterol is shown below.
Cholesterol is frequently found in foods as a cholesterol ester, meaning that there is a fatty acid attached to it. The structure of a cholesterol ester is shown below. All sterols have a similar structure to cholesterol. Cholesterol is only found in foods of animal origin. If consumers were more knowledgeable, intentionally misleading practices, such as labeling a banana “cholesterol free”, would not be as widespread as they currently are today.
Function
Although cholesterol has acquired the status of a nutrition "villain", it is a vital component of cell membranes and is used to produce vitamin D, hormones, and bile acids. You can see the similarity between the structures of vitamin D and estradiol, one of the forms of estrogen shown below.
Figure \(3\) Structures of vitamin D3 and estradiol (a form of estrogen)2,3
We do not need to consume any cholesterol from our diets (not essential) because our bodies have the ability to synthesize the required amounts. The figure below gives you an idea of the cholesterol content of a variety of foods.
There is neither bad nor good cholesterol, despite these descriptions being commonly used for LDL and HDL, respectively. Cholesterol is cholesterol. HDL and LDL contain cholesterol but are actually lipoproteins that will be described below.
Too much cholesterol in the blood can combine with other substances to form plaque. Plaque sticks to the walls of the arteries. This buildup of plaque is known as atherosclerosis. It can lead to coronary artery disease, wherein the coronary arteries become narrow or even blocked.
The most common cause of high cholesterol is an unhealthy lifestyle. This can include:
• Unhealthy eating habits, such as eating lots of bad fats. One type, saturated fat, is found in some meats, dairy products, chocolate, baked goods, and deep-fried and processed foods. Another type, trans fat, is in some fried and processed foods. Eating these fats can raise your LDL (bad) cholesterol.
• Lack of physical activity, with lots of sitting and little exercise. This lowers your HDL (good) cholesterol.
• Smoking, which lowers HDL cholesterol, especially in women. It also raises your LDL cholesterol.
Genetics may also cause people to have high cholesterol. For example, familial hypercholesterolemia (FH) is an inherited form of high cholesterol. Other medical conditions and certain medicines may also cause high cholesterol.
HDL, LDL, and VLDL
Lipoproteins, as the name suggests, are complexes of lipids and protein. The proteins within a lipoprotein are called apolipoproteins (aka apoproteins). T
There are a number of lipoproteins in the body. They differ by the apolipoproteins they contain, size (diameter), density, and composition. The table below shows the difference in density and diameter of different lipoproteins. Notice that as diameter decreases, density increases.
Table \(\PageIndex1}\) Properties of different lipoproteins.
Lipoprotein Density (g/dL) Diameter (nm) Purpose
HDL (high-density lipoproteins) 1.063-1.21 5-12 It is sometimes called "good" cholesterol because it carries cholesterol from other parts of your body back to your liver. Your liver then removes the cholesterol from your body.
LDL (low-density lipoproteins) 1.019-1.063 18-25 It is sometimes called "bad" cholesterol because a high LDL level leads to the buildup of plaque in your arteries.
VLDL (very low-density lipoproteins) 0.95-1.006 30-80 Some people also call VLDL a "bad" cholesterol because it too contributes to the buildup of plaque in your arteries. But VLDL and LDL are different; VLDL mainly carries triglycerides and LDL mainly carries cholesterol.
This inverse relationship is a result of the larger lipoproteins being composed of a higher percentage of triglyceride and a lower percentage of protein as shown below.
Protein is more dense than triglyceride (why muscle weighs more than fat), thus the higher protein/lower triglyceride composition, the higher the density of the lipoprotein. Many of the lipoproteins are named based on their densities (i.e. very low-density lipoproteins).
You are probably familiar with HDL and LDL being referred to as "good cholesterol" and "bad cholesterol," respectively. This is an oversimplification to help the public interpret their blood lipid values, because cholesterol is cholesterol; it's not good or bad. LDL and HDL are lipoproteins, and as a result you can't consume good or bad cholesterol, you consume cholesterol. A more appropriate descriptor for these lipoproteins would be HDL "good cholesterol transporter" and LDL "bad cholesterol transporter."
What's so bad about LDL? LDL enters the endothelium where it is oxidized. This oxidized LDL is engulfed by white blood cells (macrophages), leading to the formation of what are known as foam cells. The foam cells eventually accumulate so much LDL that they die and accumulate, forming a fatty streak. From there the fatty streak, which is the beginning stages of a lesion, can continue to grow until it blocks the artery. This can result in a myocardial infarction (heart attack) or a stroke. HDL is good in that it scavenges cholesterol from other lipoproteins or cells and returns it to the liver. The figure below shows the formation of the fatty streak and how this can progress to a point where it greatly alters blood flow.
Web links
The video below does an excellent job of illustrating this process. However, there are two caveats to point out. First, it incorrectly refers to cholesterol (LDL-C etc.), and second, it is clearly made by a drug company, so keep these factors in mind. The link below is the American Heart Association’s simple animation of how atherosclerosis develops.
Video: Atherosclerosis (5:36)
Cholesterol and CAD
Despite what you learned above about HDL, a recent study questions its importance in preventing cardiovascular disease. It found that people who have genetic variations that lead to higher HDL levels were not at decreased risk of developing cardiovascular disease. You can read more about this interesting finding in the first link below. In addition, another recent study is questioning whether saturated fat is associated with an increased risk of cardiovascular disease.
Doubt Cast on the ‘Good’ in ‘Good Cholesterol’
Study Questions Fat and Heart Disease Link
The following video gives a general overview of macronutrient digestion, uptake, and absorption.
Video: Small Intestine (1:29)
Chain Length of Fatty Acids
Fatty acids have different chain lengths, typically between four and 24 carbons, and most contain an even number of carbon atoms. When the carbon chain length is shorter, the melting point of the fatty acid becomes lower (such as fats found in dairy products) and the fatty acid becomes more liquid. Longer chain lengths tend to result in more solid fats, although melting point is also influenced by the degree of saturation.
Degrees of Saturation of Fatty Acids
Fatty acid chains are composed primarily of carbon and hydrogen atoms that are bonded to each other. The term “saturation” refers to whether the carbon atom in a fatty acid chain is filled (or “saturated”) to capacity with hydrogen atoms. In a saturated fatty acid, each carbon is bonded to two hydrogen atoms, with single bonds between the carbons.
Alternatively, fatty acids can have points where hydrogen atoms are missing, because there is a double bond between carbons (C=C). This is referred to as a point of unsaturation, because the carbon is only bonded to one hydrogen atom instead of two. Unsaturated fatty acids have one or more points of unsaturation, or double bonds between the carbons. A monounsaturated fatty acid is a fatty acid with one double bond, and a polyunsaturated fatty acid is a fatty acid with two or more double bonds.
Triglycerides in food contain a mixture of saturated, monounsaturated, and polyunsaturated fatty acids, but some foods are better sources of these types of fatty acids than others (Figure 5.13). For example, coconut oil is very high in saturated fat, but it still contains some monounsaturated and polyunsaturated fatty acids. Peanut oil is often thought of as a good source of monounsaturated fat, because that is the predominant fatty acid in the oil, but peanut oil also contains a fair amount of polyunsaturated fatty acids and even some saturated fatty acids.
Saturated Fatty Acids
Fat sources with a high percentage of saturated fatty acids tend to be solid at room temperature. This is because the lack of double bonds in the carbon chains of saturated fatty acids makes them very straight, so they pack together well (like a box of toothpicks). Fats that have mostly saturated fatty acids, like butter and coconut oil, are solid at room temperature, as are the visible fat layers in a strip of bacon or a cut of beef. Consuming a diet high in saturated fats is associated with an increased risk of heart disease, because such a diet increases blood cholesterol, specifically the LDL (“bad”) cholesterol level. (More on this later.) Food sources of predominately saturated fatty acids include most animal fats (with the exception of poultry and eggs, which contain more unsaturated fatty acids), dairy products, tropical oils (like coconut and palm oil), cocoa butter, and partially or fully hydrogenated oils.
Unsaturated Fatty Acids
Fat sources rich in unsaturated fatty acids tend to be liquid at room temperature, because the C=C double bonds create bends in the carbon chain, making it harder for fatty acids to pack together tightly. Consuming a diet rich in mono- and polyunsaturated fats is associated with a lower LDL cholesterol level and a lower risk of heart disease.
Food sources of predominately monounsaturated fats include nuts and seeds like almonds, pecans, cashews, and peanuts; plant oils like canola, olive, and peanut oils; and avocados. The fat in poultry and eggs is predominantly unsaturated and contains more monounsaturated than polyunsaturated fatty acids.
Food sources of predominately polyunsaturated fats include plant oils (soybean, corn); fish; flaxseed; and some nuts like walnuts and pecans.
Omega-3, Omega-6, and Essential Fatty Acids
In addition to the length of the carbon chain and the number of double bonds, unsaturated fatty acids are also classified by the position of the first double bond relative to the methyl (-CH3) or “omega” end of the carbon chain (the end furthest from the glycerol backbone in a triglyceride). Fatty acids with the first double bond at the third carbon from the omega end are called omega-3 fatty acids. Those with the first double bond at the sixth carbon from the omega end are called omega-6 fatty acids. (There are also omega-9 fatty acids.)
Fatty acids are vital for the normal operation of all body systems, but the body is capable of synthesizing most of the fatty acids it needs. However, there are two fatty acids that the body cannot synthesize: linoleic acid (an omega-6) and alpha-linolenic acid (ALA, an omega-3). These are called essential fatty acids because they must be consumed in the diet. Other fatty acids are called nonessential fatty acids, but that doesn’t mean they’re unimportant; the classification is based solely on the ability of the body to synthesize the fatty acid. Excellent food sources of linoleic fatty acid include plant oils such as corn oil and soybean oil, often found in salad dressings and margarine. Rich food sources of alpha-linolenic acid (ALA) include nuts, flaxseed, whole grains, legumes, and dark green leafy vegetables.
Most Americans easily consume enough linoleic acid and other omega-6 fatty acids, because corn and soybean oil are common ingredients in our food supply. However, sources of ALA and other omega-3 fatty acids are less common in the American diet, and many people could benefit from incorporating more sources of these into their diet. As an added benefit, whole foods rich in ALA come packaged with other healthful nutrients, like fiber, protein, vitamins, minerals, and phytochemicals.
A true essential fatty acid deficiency is rare in the developed world, but it can occur, usually in people who eat very low-fat diets or have impaired fat absorption. Symptoms include dry and scaly skin, poor wound healing, increased vulnerability to infections, and impaired growth in infants and children.1
Omega-3 and omega-6 fatty acids are precursors to a large family of important signaling molecules called eicosanoids (prostaglandins are one type of eicosanoid). Among the many functions of eicosanoids in the body, one of the most important is to regulate inflammation. Without these hormone-like molecules, the body would not be able to heal wounds or fight off infections each time a foreign germ presented itself. In addition to their role in the body’s immune and inflammatory processes, eicosanoids also help to regulate circulation, respiration, and muscle movement.
Eicosanoids derived from omega-6 fatty acids tend to increase blood pressure, blood clotting, immune response, and inflammation. These are necessary functions, but they can be associated with disease when chronically elevated. In contrast, eicosanoids derived from omega-3 fatty acids tend to lower blood pressure, inflammation, and blood clotting, functions that can benefit heart health. Omega-3 and omega-6 fatty acids compete for the same enzymatic pathways in the formation of different eicosanoids, so increasing omega-3 fatty acids in the diet may have anti-inflammatory effects.
Two additional omega-3 fatty acids with important health benefits are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These long-chain polyunsaturated fatty acids have been shown to help lower blood triglycerides and blood pressure, reduce inflammation, and prevent blood clot formation. They also promote normal growth and development in infants, especially in the development of the brain and eyes. Both of these important omega-3 fatty acids can be synthesized in the body from ALA, so they are not considered essential fatty acids. However, the rate of conversion of ALA to these omega-3s is limited, so it is beneficial to consume them regularly in the diet. Fish, shellfish, fish oils, seaweed, and algae are all good sources of EPA and DHA. DHA is also found in human breast milk in quantities dependent on the mother’s own intake of DHA sources.
Fish oil and omega-3 supplements are among the most commonly used dietary supplements in the United States. Researchers have hypothesized that these supplements might decrease risk of cardiovascular disease, be helpful for those with rheumatoid arthritis, and improve infant brain development when taken in pregnancy or in infancy. Some studies have found such benefits of the supplements, but others haven’t. One reason for these inconsistent results may be that studies often don’t measure participants’ baseline omega-3 levels and intake from foods, and those already consuming adequate omega-3s are less likely to benefit from a supplement. The Dietary Guidelines for Americans recommends consuming 8 ounces of a variety of seafood each week, and in general, people who meet this recommendation likely consume enough omega-3 fatty acids already (along with the other healthful nutrients found in fish) and are unlikely to see an added benefit of taking a fish oil supplement. Some doctors may recommend that people at risk of cardiovascular disease take a fish oil or omega-3 supplement, especially if they don’t eat fish regularly.2
A Word About Trans Fats
The carbon-carbon double bond in an unsaturated fatty acid chain can result in different shapes depending on whether the fatty acid is in a cis or trans configuration. When the hydrogen atoms are bonded to the same side of the carbon chain, it is called a cis fatty acid. Because the hydrogen atoms are on the same side (and repelling one another), the carbon chain has a bent structure. Naturally-occurring fatty acids usually have a cis configuration.
In a transfatty acid, the hydrogen atoms are bonded on opposite sides of the carbon chain, resulting in a more linear structure. Unlike cis fatty acids, most trans fatty acids are not found naturally in foods, but instead are a result of an industrial process called hydrogenation. Hydrogenation is the process of adding hydrogen to the carbon-carbon double bonds, thus making the fatty acid saturated (or less unsaturated, in the case of partial hydrogenation).
Hydrogenation creates both saturated and trans fatty acids. Trans fatty acids are actually unsaturated fatty acids, but they have the linear shape of saturated fatty acids. (The carbon chains are not bent like naturally-occurring unsaturated fats.) The trans fatty acids formed through partial hydrogenation have an unusual shape, which makes their properties and actions in the body similar to saturated fatty acids.
Hydrogenation was developed in order to make oils semi-solid at room temperature, enabling production of spreadable margarine and shortening from inexpensive ingredients like corn oil. Hydrogenation also makes oils more stable and less likely to go rancid, so partially hydrogenated oils were favored by fast food restaurants for frying, and manufacturers of processed baked goods like cookies and chips found they gave their products a longer shelf life. And because trans fats are unsaturated, nutrition scientists and the medical community believed that they were a healthier alternative to saturated fats.
But around the 1990s, evidence that trans fats were not healthy—far worse than saturated fats, in fact—began to accumulate. Like saturated fat, trans fats increase LDL (“bad”) cholesterol, but they also have the effect of decreasing HDL (“good”) cholesterol and of increasing inflammatory processes in the body. Researchers found that consuming trans fats, even at low levels (1 to 3 percent of total energy intake), was associated with an increased risk of coronary heart disease. They estimated that eliminating industrial trans fats from the food supply might prevent as many as 19 percent of heart attacks in the U.S. at the time, coming to 228,000 heart attacks averted.3
In 2006, the U.S. Food and Drug Administration (FDA) began requiring food companies to list trans fat information on the Nutrition Facts panel of food labels to keep consumers informed of their intake of these fats. That prompted the food industry to mostly eliminate partially hydrogenated oils from their products, often substituting palm oil and coconut oil in their place (both of which are high in saturated fat and may promote heart disease). In 2013, the FDA determined that trans fats were no longer considered safe in the food supply, and in 2015, the agency issued a ruling requiring that manufactured trans fats no longer be included in the U.S. food supply. A one-year extension was granted in 2018, and foods produced prior to that date were given time to work through the food supply. The final ruling requires all manufactured trans fats to be eliminated from the U.S. food supply by 2021.4
Summary
• Digestion of lipids by lipases in pancreatic juice occurs primarily in the small intestines. The monoglycerides and fatty acids cross the intestinal lining into the bloodstream, where they are resynthesized into triglycerides and transported as chylomicrons. Phospholipids and cholesteryl esters undergo similar hydrolysis in the small intestine, and their component molecules are also absorbed through the intestinal lining.
• Two lipoproteins (composed of a lipid and a protein) of great interest are HDL "good cholesterol transporter" and LDL "bad cholesterol transporter."
• Trans fats are unhealthy fats that form when vegetable oil hardens in a process called hydrogenation. They can raise LDL cholesterol levels in the blood. They can also lower HDL (good) cholesterol levels. Trans fats are under review for their health effects.
• Saturated fats are also considered as unhealthy fats.
• Studies indicate that the consumption of monounsaturated fats and polyunsaturated fats (specifically those with omega-3 fatty acids) have numerous health benefits. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.02%3A_Fats_and_Cholesterol.txt |
Learning Objectives
• Describe the metabolism of proteins.
• Know the importance of essential amino acids.
• Know the sources and function of common proteins in the diet.
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram; in contrast, lipids provide 9 kcal (37 kJ) per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body.
Protein Functions in Human Body
Protein is a nutrient needed by the human body for growth and maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair and skin. Proteins are also used in membranes, such as glycoproteins. When broken down into amino acids, they are used as precursors to nucleic acid, co-enzymes, hormones, immune response, cellular repair, and other molecules essential for life. Additionally, protein is needed to form blood cells.
Protein Metabolism: Essential Amino Acids
Protein digestion begins in the stomach (Figure \(3\)), where the action of gastric juice hydrolyzes about 10% of the peptide bonds. Gastric juice is a mixture of water (more than 99%), inorganic ions, hydrochloric acid, and various enzymes and other proteins.
The pain of a gastric ulcer is at least partially due to irritation of the ulcerated tissue by acidic gastric juice.
The hydrochloric acid (HCl) in gastric juice is secreted by glands in the stomach lining. The pH of freshly secreted gastric juice is about 1.0, but the contents of the stomach may raise the pH to between 1.5 and 2.5. HCl helps to denature food proteins; that is, it unfolds the protein molecules to expose their chains to more efficient enzyme action. The principal digestive component of gastric juice is pepsinogen, an inactive enzyme produced in cells located in the stomach wall. When food enters the stomach after a period of fasting, pepsinogen is converted to its active form—pepsin—in a series of steps initiated by the drop in pH. Pepsin catalyzes the hydrolysis of peptide linkages within protein molecules. It has a fairly broad specificity but acts preferentially on linkages involving the aromatic amino acids tryptophan, tyrosine, and phenylalanine, as well as methionine and leucine.
Protein digestion is completed in the small intestine.
Amino Acids
There are 20 amino acids our body uses to synthesize proteins. These amino acids can be classified as essential, non-essential, or conditionally essential. The table below shows how the 20 amino acids are classified.
Table \(1\): Essential, conditionally essential, and nonessential amino acids
Essential Conditionally Essential Non-essential
Histidine Arginine Alanine
Isoleucine Cysteine Asparagine
Leucine Glutamine Aspartic Acid or Aspartate
Lysine Glycine Glutamic Acid or Glutamate
Methionine Proline Serine
Phenylalanine Tyrosone
Theronine
Tryptophan
Valine
The body cannot synthesize nine amino acids. Thus, it is essential that these are consumed in the diet. As a result these amino acids are known as essential, or indispensable, amino acids.
Non-essential, or dispensable, amino acids can be made in our body, so we do not need to consume them. Conditionally essential amino acids become essential for individuals in certain situations. An example of a condition when an amino acid becomes essential is the disease phenylketonuria (PKU). Individuals with PKU have a mutation in the enzyme phenylalanine hydroxylase, which normally adds an alcohol group (OH) to the amino acid phenylalanine to form tyrosine as shown below.
Since tyrosine cannot be synthesized by people with PKU, it becomes essential for them. Thus, tyrosine is a conditionally essential amino acid. Individuals with PKU have to eat a very low protein diet and avoid the alternative sweetener aspartame, because it can be broken down to phenylalanine. If individuals with PKU consume too much phenylalanine, phenylalanine and its metabolites, can build up and cause brain damage and severe mental retardation. The drug Kuvan was approved for use with PKU patients in 2007 who have low phenylalanine hydroxylase activity levels.
Protein Sources
Protein occurs in a wide range of food. On a worldwide basis, plant protein foods contribute over 60% of the per capita supply of protein. In North America, animal-derived foods contribute about 70% of protein sources. Insects are a source of protein in many parts of the world. In parts of Africa, up to 50% of dietary protein derives from insects. It is estimated that more than 2 billion people eat insects daily.
Meat, dairy, eggs, soy, fish, whole grains, and cereals are sources of protein. Examples of food staples and cereal sources of protein, each with a concentration greater than 7%, are (in no particular order) buckwheat, oats, rye, millet, maize (corn), rice, wheat, sorghum, amaranth, and quinoa. Some research highlights game meat as a protein source.
Vegan sources of proteins include legumes, nuts, seeds and fruits. Vegan foods with protein concentrations greater than 7% include soybeans, lentils, kidney beans, white beans, mung beans, chickpeas, cowpeas, lima beans, pigeon peas, lupines, wing beans, almonds, Brazil nuts, cashews, pecans, walnuts, cotton seeds, pumpkin seeds, hemp seeds, sesame seeds, and sunflower seeds.
People eating a balanced diet do not need protein supplements.
The table below presents food groups as protein sources.
Table \(2\) Density of amino acid in various protein sources.
Protein powders - such as casein, whey, egg, rice, soy, and cricket flour - are processed and manufactured sources of protein.
Complete and Incomplete Proteins
Proteins can be classified as either complete or incomplete. Complete proteins provide adequate amounts of all nine essential amino acids. Animal proteins such as meat, fish, milk, and eggs are good examples of complete proteins. Incomplete proteins do not contain adequate amounts of one or more of the essential amino acids. For example, if a protein doesn't provide enough of the essential amino acid leucine it would be considered incomplete. Leucine would be referred to as the limiting amino acid, because there is not enough of it for the protein to be complete. Most plant foods are incomplete proteins, with a few exceptions such as soy. The table below shows the limiting amino acids in some plant foods.
Table \(3\) Limiting amino acids in some common plant foods.
Food Amino Acid(s)
Beans and Most Legumes Methionine, Tryptophan
Tree Nuts and Seeds Methionine, Lysine
Grains Lysine
Vegetables Methionine, Lysine
Complementary Proteins
Even though most plant foods do not contain complete proteins, it does not mean that they should be sworn off as protein sources. It is possible to pair foods containing incomplete proteins with different limiting amino acids to provide adequate amounts of the essential amino acids. These two proteins are called complementary proteins, because they supply the amino acid(s) missing in the other protein. A simple analogy would be that of a 4 piece puzzle. If one person has 2 pieces of a puzzle, and another person has 2 remaining pieces, neither of them have a complete puzzle. But when they are combined, the two individuals create a complete puzzle.
(Figure \(4\)) Complementary proteins are kind of like puzzle pieces.
Two examples of complementary proteins are shown below.
It should be noted that complementary proteins do not need to be consumed at the same time or meal. It is currently recommended that essential amino acids be met on a daily basis, meaning that if a grain is consumed at one meal, a legume could be consumed at a later meal, and the proteins would still complement one another4.
Measures of Protein Quality
How do you know the quality of the protein in the foods you consume? The protein quality of most foods has been determined by one of the methods below.
• Biological Value (BV) - (grams of nitrogen retained / grams of nitrogen absorbed) x 100
• Protein Efficiency Ratio (PER) - (grams of weight gained / grams of protein consumed)
This method is commonly performed in growing rats.
• Chemical or Amino Acid Score (AAS) - (Test food limiting essential amino acid (mg/g protein) / needs of same essential amino acid (mg/g protein))
• Protein Digestibility Corrected Amino Acid Score (PDCAAS) - (Amino Acid Score x Digestibility)
This is the most widely used method and was preferred by the Food and Agriculture Organization and World Health Organization (WHO) until recently5,6. The following table shows the protein quality measures for some common foods.
Table \(4\) Measures of protein quality
Protein PER Digestibility AA(%) PDCAAS
Egg 3.8 98 121 100*
Milk 3.1 95 127 100*
Beef 2.9 98 94 92
Soy 2.1 95 96 91
Wheat 1.5 91 47 42
*PDCAAS scores are truncated (cut off) at 100. These egg and milk scores are actually 118 and 121 respectively.
The Food and Agricultural Organization (FAO) recently recommended that PDCAAS be replaced with a new measure of protein quality, the Digestible Indispensable Amino Acid Score (DIAAS). “DIAAS is defined as: DIAAS % = 100 x [(mg of digestible dietary indispensable amino acid in 1 g of the dietary protein) / (mg of the same dietary indispensable amino acid in 1g of the reference protein)].” Ileal digestibility should be utilized to determine the digestibility in DIAAS; ideally in humans, but if not possible in growing pigs or rats6.
The main differences between DIAAS and PDCAAS are:
1. DIAAS take into account individual amino acids digestibility rather than protein digestibility.
2. It focus on ileal instead of fecal (total) digestibility.
3. Has three different reference patterns (different age groups, 0-6 months, 6 months- 3 years, 3-10 years old) instead of a single pattern
4. DIAAS scores will not be truncated7
Protein Deficiency in Young and Old
Protein deficiency rarely occurs alone. Instead it is often coupled with insufficient energy intake. As a result, the condition is called protein-energy malnutrition (PEM). This condition is not common in the U.S., but is more prevalent in less developed countries. Kwashiorkor and marasmus are the two forms of protein energy malnutrition. They differ in the severity of energy deficiency as shown in the figure below.
Kwashiorkor is a Ghanaian word that means "the disease that the first child gets when the new child comes39." The characteristic symptom of kwashiorkor is a swollen abdomen. Energy intake could be adequate, but protein consumption is too low.
Figure \(7\): A child suffering from kwashiorkor
Marasmus means "to waste away" or "dying away", and thus occurs in individuals who have inadequate protein and energy intakes.
Summary
• Protein digestion begins in the stomach where hydrolysis of the protein linkages occurs with the action of gastric juices (mainly HCl ) and the active enzyme pepsin. Protein digestion is completed in the small intestine wherein other protein digesting enzymes are involved.
• Essential amino acids cannot be made by the body and must come from food.
• Complete proteins provide adequate amounts of all nine essential amino acids.
• Complementary proteins are made up of two proteins wherein one protein supply the amino acid(s) missing in the other protein.
• Kwashiorkor and marasmus are two forms of protein energy malnutrition that are not common in the U.S., but is more prevalent in less developed countries | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.03%3A_Proteins-_Muscle_and_Much_More.txt |
Learning Objectives
• List reasons why vitamins and minerals are critical to a healthy diet.
• Describe the functional role, intake recommendations and sources of vitamins and major minerals.
• Learn about the importance and sources of dietary fiber.
• Learn about the importance of water.
Vitamins and minerals are essential to human health and can be obtained in our diet from different types of food.
Dietary Minerals
Minerals in food are inorganic compounds that work with other nutrients to ensure the body functions properly. Minerals are abundant in our everyday lives. From the soil in your front yard to the jewelry you wear on your body, we interact with minerals constantly. There are 20 essential minerals that must be consumed in our diets to remain healthy. The amount of each mineral found in our bodies vary greatly and therefore, so does consumption of those minerals. When there is a deficiency in an essential mineral, health problems may arise.
Major minerals (Figure \(1\)) are classified as minerals that are required in the diet each day in amounts larger than 100 milligrams. These include sodium, potassium, chloride, calcium, phosphorus, magnesium, and sulfur. These major minerals can be found in various foods. Consuming a varied diet significantly improves an individual’s ability to meet their nutrient needs. The most common minerals in the body are calcium and phosphorous, both of which are stored in the skeleton and necessary for the hardening of bones. Most minerals are ionized, and their ionic forms are used in physiological processes throughout the body. Sodium and chloride ions are electrolytes in the blood and extracellular tissues, and iron ions are critical to the formation of hemoglobin. There are additional trace minerals that are still important to the body’s functions, but their required quantities are much lower.
Like vitamins, minerals can be consumed in toxic quantities (although it is rare). A healthy diet includes most of the minerals your body requires, so supplements and processed foods can add potentially toxic levels of minerals. Tables \(1\) and \(2\) provide a summary of minerals and their function in the body.
Table \(1\) Major Minerals and their Function in the Body.
Major Minerals
Mineral Sources Recommended daily allowance Function Problems associated with deficiency
Potassium Meats, some fish, fruits, vegetables, legumes, dairy products 4700 mg Nerve and muscle function; acts as an electrolyte Hypokalemia: weakness, fatigue, muscle cramping, gastrointestinal problems, cardiac problems
Sodium Table salt, milk, beets, celery, processed foods 2300 mg Blood pressure, blood volume, muscle and nerve function Rare
Calcium Dairy products, dark green leafy vegetables, blackstrap molasses, nuts, brewer’s yeast, some fish 1000 mg Bone structure and health; nerve and muscle functions, especially cardiac function Slow growth, weak and brittle bones
Phosphorous Meat, milk 700 mg Bone formation, metabolism, ATP production Rare
Magnesium Whole grains, nuts, leafy green vegetables 310–420 mg Enzyme activation, production of energy, regulation of other nutrients Agitation, anxiety, sleep problems, nausea and vomiting, abnormal heart rhythms, low blood pressure, muscular problems
Chloride Most foods, salt, vegetables, especially seaweed, tomatoes, lettuce, celery, olives 2300 mg Balance of body fluids, digestion Loss of appetite, muscle cramps
Table \(2\) Trace Minerals and their Function in the Body.
Trace Minerals
Mineral Sources Recommended daily allowance Function Problems associated with deficiency
Iron Meat, poultry, fish, shellfish, legumes, nuts, seeds, whole grains, dark leafy green vegetables 8–18 mg Transport of oxygen in blood, production of ATP Anemia, weakness, fatigue
Zinc Meat, fish, poultry, cheese, shellfish 8–11 mg Immunity, reproduction, growth, blood clotting, insulin and thyroid function Loss of appetite, poor growth, weight loss, skin problems, hair loss, vision problems, lack of taste or smell
Copper Seafood, organ meats, nuts, legumes, chocolate, enriched breads and cereals, some fruits and vegetables 900 µg Red blood cell production, nerve and immune system function, collagen formation, acts as an antioxidant Anemia, low body temperature, bone fractures, low white blood cell concentration, irregular heartbeat, thyroid problems
Iodine Fish, shellfish, garlic, lima beans, sesame seeds, soybeans, dark leafy green vegetables 150 µg Thyroid function Hypothyroidism: fatigue, weight gain, dry skin, temperature sensitivity
Sulfur Eggs, meat, poultry, fish, legumes None Component of amino acids Protein deficiency
Fluoride Fluoridated water 3–4 mg Maintenance of bone and tooth structure Increased cavities, weak bones and teeth
Manganese Nuts, seeds, whole grains, legumes 1.8–2.3 mg Formation of connective tissue and bones, blood clotting, sex hormone development, metabolism, brain and nerve function Infertility, bone malformation, weakness, seizures
Cobalt Fish, nuts, leafy green vegetables, whole grains None Component of B12 None
Selenium Brewer’s yeast, wheat germ, liver, butter, fish, shellfish, whole grains 55 µg Antioxidant, thyroid function, immune system function Muscle pain
Chromium Whole grains, lean meats, cheese, black pepper, thyme, brewer’s yeast 25–35 µg Insulin function High blood sugar, triglyceride, and cholesterol levels
Molybdenum Legumes, whole grains, nuts 45 µg Cofactor for enzymes Rare
The Vitamins: Vital, but Not All are Amines
In 1747, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease in which collagen is not properly formed, causing poor wound healing, bleeding of the gums, severe pain, and death. In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the British Royal Navy. This led to the nickname limey for British sailors.
In East Asia, where polished white rice was the common staple food of the middle class, beriberi resulting from lack of vitamin B1 was endemic. In 1884, Takaki Kanehiro, a British-trained medical doctor of the Imperial Japanese Navy, observed that beriberi was endemic among low-ranking crew who often ate nothing but rice, but not among officers who consumed a Western-style diet. This convinced Takaki and the Japanese Navy that diet was the cause of beriberi, but they mistakenly believed that sufficient amounts of protein prevented it. That diseases could result from some dietary deficiencies was further investigated by Christiaan Eijkman, who in 1897 discovered that feeding unpolished rice instead of the polished variety to chickens helped to prevent beriberi in the chickens. The following year, Frederick Hopkins postulated that some foods contained "accessory factors" — in addition to proteins, carbohydrates, fats etc. — that are necessary for the functions of the human body. Hopkins and Eijkman were awarded the Nobel Prize for Physiology or Medicine in 1929 for their discoveries.
In 1910, the first vitamin complex was isolated by Japanese scientist Umetaro Suzuki, who succeeded in extracting a water-soluble complex of micronutrients from rice bran and named it aberic acid (later Orizanin). He published this discovery in a Japanese scientific journal. When the article was translated into German, the translation failed to state that it was a newly discovered nutrient, a claim made in the original Japanese article, and hence his discovery failed to gain publicity.In 1912 Polish-born biochemist Casimir Funk, working in London, isolated the same complex of micronutrients and proposed the complex be named "vitamine". It was later to be known as vitamin B3 (niacin), though he described it as "anti-beri-beri-factor" (which would today be called thiamine or vitamin B1). Funk proposed the hypothesis that other diseases, such as rickets, pellagra, coeliac disease, and scurvy could also be cured by vitamins.
Vitamine to Vitamin
Max Nierenstein a friend and reader of Biochemistry at Bristol University reportedly suggested the "vitamine" name (from "vital amine"). The name soon became synonymous with Hopkins' "accessory factors", and, by the time it was shown that not all vitamins are amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped to deemphasize the "amine" reference, after researchers began to suspect that not all "vitamines" (in particular, vitamin A) have an amine component.
Vitamins are organic compounds found in foods and are a necessary part of the biochemical reactions in the body. They are involved in a number of processes, including mineral and bone metabolism, and cell and tissue growth, and they act as cofactors for energy metabolism. The B vitamins play the largest role of any vitamins in metabolism (Tables \(3\) and \(4\))
You get most of your vitamins through your diet, although some can be formed from the precursors absorbed during digestion. For example, the body synthesizes vitamin A from the β-carotene in orange vegetables like carrots and sweet potatoes. Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins A, D, E, and K, are absorbed through the intestinal tract with lipids in chylomicrons. Vitamin D is also synthesized in the skin through exposure to sunlight. Because they are carried in lipids, fat-soluble vitamins can accumulate in the lipids stored in the body. If excess vitamins are retained in the lipid stores in the body, hypervitaminosis can result.
Water-soluble vitamins, including the eight B vitamins and vitamin C, are absorbed with water in the gastrointestinal tract. These vitamins move easily through bodily fluids, which are water based, so they are not stored in the body. Excess water-soluble vitamins are excreted in the urine. Therefore, hypervitaminosis of water-soluble vitamins rarely occurs, except with an excess of vitamin supplements.
Fat Soluble Vitamins
From the structures shown below, it should be clear that these compounds have more than a solubility connection with lipids. VitaminsA is a terpene, and vitamins E and K have long terpene chains attached to an aromatic moiety. The structure of vitamin D can be described as a steroid in which ring B is cut open and the remaining three rings remain unchanged. The precursors of vitamins A and D have been identified as the tetraterpene beta-carotene and the steroid ergosterol, respectively.
Table \(3\) lists the different fat soluble vitamins and its function.
Table \(3\) Fat Soluble Vitamins and Their Function.
Vitamin and alternative name Sources Recommended daily allowance Function Problems associated with deficiency
A
retinal or β-carotene
Yellow and orange fruits and vegetables, dark green leafy vegetables, eggs, milk, liver 700–900 µg Eye and bone development, immune function Night blindness, epithelial changes, immune system deficiency
D
cholecalciferol
Dairy products, egg yolks; also synthesized in the skin from exposure to sunlight 5–15 µg Aids in calcium absorption, promoting bone growth Rickets, bone pain, muscle weakness, increased risk of death from cardiovascular disease, cognitive impairment, asthma in children, cancer
E
tocopherols
Seeds, nuts, vegetable oils, avocados, wheat germ 15 mg Antioxidant Anemia
K
phylloquinone
Dark green leafy vegetables, broccoli, Brussels sprouts, cabbage 90–120 µg Blood clotting, bone health Hemorrhagic disease of newborn in infants; uncommon in adults
Web link
More detailed information on the different fat soluble vitamins can be found on the link below.
https://med.libretexts.org/Bookshelves/Nutrition/Book%3A_Human_Nutrition_(University_of_Hawaii)/9%3A_Vitamins/9.2%3A_Fat-Soluble_Vitamins
Water Soluble Vitamins
All water-soluble vitamins (Table \(4\)) play a different kind of role in energy metabolism; they are required as functional parts of enzymes involved in energy release and storage. Vitamins and minerals that make up part of enzymes are referred to as coenzymes and cofactors, respectively. Coenzymes and cofactors are required by enzymes to catalyze a specific reaction. They assist in converting a substrate to an end-product. Coenzymes and cofactors are essential in catabolic pathways and play a role in many anabolic pathways too. In addition to being essential for metabolism, many vitamins and minerals are required for blood renewal and function. At insufficient levels in the diet these vitamins and minerals impair the health of blood and consequently the delivery of nutrients in and wastes out, amongst its many other functions.
Table \(4\) Water Soluble Vitamins and Their Function.
Vitamin and alternative name Sources Recommended daily allowance Function Problems associated with deficiency
B1
thiamine
Whole grains, enriched bread and cereals, milk, meat 1.1–1.2 mg Carbohydrate metabolism Beriberi, Wernicke-Korsikoff syndrome
B2
riboflavin
Brewer’s yeast, almonds, milk, organ meats, legumes, enriched breads and cereals, broccoli, asparagus 1.1–1.3 mg Synthesis of FAD for metabolism, production of red blood cells Fatigue, slowed growth, digestive problems, light sensitivity, epithelial problems like cracks in the corners of the mouth
B3
niacin
Meat, fish, poultry, enriched breads and cereals, peanuts 14–16 mg Synthesis of NAD, nerve function, cholesterol production Cracked, scaly skin; dementia; diarrhea; also known as pellagra
B5
pantothenic acid
Meat, poultry, potatoes, oats, enriched breads and cereals, tomatoes 5 mg Synthesis of coenzyme A in fatty acid metabolism Rare: symptoms may include fatigue, insomnia, depression, irritability
B6
pyridoxine
Potatoes, bananas, beans, seeds, nuts, meat, poultry, fish, eggs, dark green leafy vegetables, soy, organ meats 1.3–1.5 mg Sodium and potassium balance, red blood cell synthesis, protein metabolism Confusion, irritability, depression, mouth and tongue sores
B7
biotin
Liver, fruits, meats 30 µg Cell growth, metabolism of fatty acids, production of blood cells Rare in developed countries; symptoms include dermatitis, hair loss, loss of muscular coordination
B9
folic acid
Liver, legumes, dark green leafy vegetables, enriched breads and cereals, citrus fruits 400 µg DNA/protein synthesis Poor growth, gingivitis, appetite loss, shortness of breath, gastrointestinal problems, mental deficits
B12
cyanocobalamin
Fish, meat, poultry, dairy products, eggs 2.4 µg Fatty acid oxidation, nerve cell function, red blood cell production Pernicious anemia, leading to nerve cell damage
C
ascorbic acid
Citrus fruits, red berries, peppers, tomatoes, broccoli, dark green leafy vegetables 75–90 mg Necessary to produce collagen for formation of connective tissue and teeth, and for wound healing Dry hair, gingivitis, bleeding gums, dry and scaly skin, slow wound healing, easy bruising, compromised immunity; can lead to scurvy
Web link
More detailed information on the different water soluble vitamins can be found on the link below.
https://med.libretexts.org/Bookshelves/Nutrition/Book%3A_Human_Nutrition_(University_of_Hawaii)/9%3A_Vitamins/9.3%3A_Water-Soluble_Vitamins
Vitamins as Antioxidants
The “big three” vitamin antioxidants are vitamins E, A, and C, although it may be that they are called the “big three” only because they are the most studied. Other antioxidants obtained from the diet are given in Table \(5\). A simplified diagram on the role of antioxidants is shown in Figure \(4\).
Table \(5\) Some Antioxidants Obtained from Diet and Their Related Functions.
Antioxidant Functions Attributed to Antioxidant Capacity
Vitamin A Protects cellular membranes, prevents glutathione depletion, maintains free radical detoxifying enzyme systems, reduces inflammation
Vitamin E Protects cellular membranes, prevents glutathione depletion
Vitamin C Protects DNA, RNA, proteins, and lipids, aids in regenerating vitamin E
Carotenoids Free radical scavengers
Lipoic acid Free radical scavenger, aids in regeneration of vitamins C and E
Phenolic acids Free radical scavengers, protect cellular membranes
Effects of Cooking
The USDA has conducted extensive studies on the percentage losses of various nutrients from different food types and cooking methods. Some vitamins may become more "bio-available" – that is, usable by the body – when foods are cooked. Table \(6\) below shows whether various vitamins are susceptible to loss from heat—such as heat from boiling, steaming, frying, etc. The effect of cutting vegetables can be seen from exposure to air and light. Water-soluble vitamins such as B and C dissolve into the water when a vegetable is boiled, and are then lost when the water is discarded.
Table \(6\) Vitamin Stability Upon Air, Light and Heat Exposure. Source: Wikipedia.
Vitamin Soluble in Water Stable to Air Exposure Stable to Light Exposure Stable to Heat Exposure
Vitamin A no partially partially relatively stable
Vitamin C very unstable yes no no
Vitamin D no no no no
Vitamin E no yes yes no
Vitamin K no no yes no
Thiamine (B1) highly no ? > 100 °C
Riboflavin (B2) slightly no in solution no
Niacin (B3) yes no no no
Pantothenic Acid (B5) quite stable no no yes
Vitamin B6 yes ? yes ?
Biotin (B7) somewhat ? ? no
Folic Acid (B9) yes ? when dry at high temp
Cobalamin (B12) yes ? yes no
Dietary Fiber and Water
Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins, pectins, beta-glucans, and oligosaccharides already mentioned in Section 17.1.
Dietary fibers can act by changing the nature of the contents of the gastrointestinal tract and by changing how other nutrients and chemicals are absorbed. Some types of soluble fiber absorb water to become a gelatinous, viscous substance which may or may not be fermented by bacteria in the digestive tract. Some types of insoluble fiber have bulking action and are not fermented. Lignin, a major dietary insoluble fiber source, may alter the rate and metabolism of soluble fibers. Other types of insoluble fiber, notably resistant starch, are fermented to produce short-chain fatty acids, which are physiologically active and confer health benefits. Health benefit from dietary fiber and whole grains may include a decreased risk of death and lower rates of coronary heart disease, colon cancer, and type 2 diabetes.
Food sources of dietary fiber (Table \(7\) ) have traditionally been divided according to whether they provide soluble or insoluble fiber. Plant foods contain both types of fiber in varying amounts, according to the plant's characteristics of viscosity and fermentability. Advantages of consuming fiber depend upon which type of fiber is consumed and which benefits may result in the gastrointestinal system. Bulking fibers – such as cellulose, hemicellulose and psyllium – absorb and hold water, promoting regularity. Viscous fibers – such as beta-glucan and psyllium – thicken the fecal mass. Fermentable fibers – such as resistant starch and inulin – feed the bacteria and microbiota of the large intestine, and are metabolized to yield short-chain fatty acids, which have diverse roles in gastrointestinal health.
Table \(7\) Types and Sources of Dietary Fiber.
Nutrient Food additive Source/Comments
Water-insoluble dietary fibers
β-glucans (a few of which are water-soluble)
Cellulose E 460 cereals, fruit, vegetables (in all plants in general)
Chitin in fungi, exoskeleton of insects and crustaceans
Hemicellulose cereals, bran, timber, legumes
Hexoses wheat, barley
Pentose rye, oat
Lignin stones of fruits, vegetables (filaments of the garden bean), cereals
Xanthan gum E 415 production with Xanthomonas-bacteria from sugar substrates
Resistant starch Can be starch protected by seed or shell (type RS1), granular starch (type RS2) or retrograded starch (type RS3)
Resistant starch high amylose corn, barley, high amylose wheat, legumes, raw bananas, cooked and cooled pasta and potatoes
Water-soluble dietary fibers
Arabinoxylan (a hemicellulose) psyllium
Fructans replace or complement in some plant taxa the starch as storage carbohydrate
Inulin in diverse plants, e.g. topinambour, chicory, etc.
Polyuronide
Pectin E 440 in the fruit skin (mainly apples, quinces), vegetables
Alginic acids(Alginates) E 400–E 407 in Algae
Sodium alginate E 401
Potassium alginate E 402
Ammonium alginate E 403
Calcium alginate E 404
Propylene glycol alginate (PGA) E 405
agar E 406
carrageen E 407 red algae
Raffinose legumes
Xylose monosacharide, pentose
Polydextrose E 1200 synthetic polymer, ca. 1kcal/g
Lactulose synthetic disaccharide
Fiber Contents in Food
Dietary fibers are found in fruits, vegetables and whole grains. The amount of fiber contained in common foods are in Table \(8\).
Table \(8\) Amount of Fiber in Common Foods. Source Wikipedia
Food group Serving mean Fibermass per serving
Fruit 120 mL (0.5 cup) 1.1 g
Dark green vegetables 120 mL (0.5 cup) 6.4 g
Orange vegetables 120 mL (0.5 cup) 2.1 g
Cooked dry beans (legumes) 120 mL (0.5 cup) 8.0 g
Starchy vegetables 120 mL (0.5 cup) 1.7 g
Other vegetables 120 mL (0.5 cup) 1.1 g
Whole grains 28 g (1 oz) 2.4 g
Meat 28 g (1 oz) 0.1 g
The breakdown of total dietary fiber in terms of the amounts of soluble and insoluble fiber found in five different foods are listed in Table \(9\).
Table \(9\) Total Dietary Fiber , Total Nonfermentable Fiber, and Total Fermentable Fiber (as percent of sample weight) in Five Different Foods.
Food Total Dietary Fiber
Total Insoluble
(Nonfermentable)
Total Soluble
(Fermentable)
Cereal, all bran 30.1 28.0 2.1
Blueberries, fresh 2.7 2.4 0.3
Broccoli, fresh, cooked 3.5 3.1 0.4
Pork and beans, canned 4.4 3.0 1.4
Almonds, with skin 8.8 8.6 0.2
tr = trace amounts
Dietary fiber is found in plants, typically eaten whole, raw or cooked, although fiber can be added to make dietary supplements and fiber-rich processed foods. Grain bran products have the highest fiber contents, such as crude corn bran (79 g per 100 g) and crude wheat bran (43 g per 100 g), which are ingredients for manufactured foods. Medical authorities, such as the Mayo Clinic, recommend adding fiber-rich products to the Standard American Diet (SAD) which is rich in processed and artificially sweetened foods, with minimal intake of vegetables and legumes.
Plant Sources of Fiber
Some plants contain significant amounts of soluble and insoluble fiber. For example, plums and prunes have a thick skin covering a juicy pulp. The skin is a source of insoluble fiber, whereas soluble fiber is in the pulp. Grapes also contain a fair amount of fiber. A listing of other plant sources of fiber is given in the table below.
Table \(10\) Plant Sources of Soluble and Insoluble Fiber.
Sources of Soluble Fiber Sources of Insoluble Fiber
• legumes (peas, soybeans, lupins and other beans)
• oats, rye, chia, and barley
• some fruits (including figs, avocados, plums, prunes, berries, ripe bananas, and the skin of apples, quinces and pears)
• certain vegetables such as broccoli, carrots, and Jerusalem artichokes
• root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber also)
• psyllium seed husks (a mucilage soluble fiber) and flax seeds
• nuts, with almonds being the highest in dietary fiber
• whole grain foods
• wheat and corn bran
• legumes such as beans and peas
• nuts and seeds
• potato skins
• lignans
• vegetables such as green beans, cauliflower, zucchini (courgette), celery, and nopal
• some fruits including avocado, and unripe bananas
• the skins of some fruits, including kiwifruit, grapes and tomatoes
Fiber Supplements
These are a few example forms of fiber that have been sold as supplements or food additives. These may be marketed to consumers for nutritional purposes, treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterol levels, reducing risk of colon cancer, and losing weight.
Soluble fiber supplements may be beneficial for alleviating symptoms of irritable bowel syndrome, such as diarrhea or constipation and abdominal discomfort. Prebiotic soluble fiber products, like those containing inulin or oligosaccharides, may contribute to relief from inflammatory bowel disease, as in Crohn's disease, ulcerative colitis, and Clostridium difficile, due in part to the short-chain fatty acids produced with subsequent anti-inflammatory actions upon the bowel.Fiber supplements may be effective in an overall dietary plan for managing irritable bowel syndrome by modification of food choices.
One insoluble fiber, resistant starch from high-amylose corn, has been used as a supplement and may contribute to improving insulin sensitivity and glycemic management as well as promoting regularity and possibly relief of diarrhea. One preliminary finding indicates that resistant corn starch may reduce symptoms of ulcerative colitis.
Inulin
Chemically defined as oligosaccharides occurring naturally in most plants, inulins have nutritional value as carbohydrates, or more specifically as fructans, a polymer of the natural plant sugar, fructose. Inulin is typically extracted by manufacturers from enriched plant sources such as chicory roots or Jerusalem artichokes for use in prepared foods. Subtly sweet, it can be used to replace sugar, fat, and flour, is often used to improve the flow and mixing qualities of powdered nutritional supplements, and has significant potential health value as a prebiotic fermentable fiber.
Inulin is advantageous because it contains 25–30% the food energy of sugar or other carbohydrates and 10–15% the food energy of fat. As a prebiotic fermentable fiber, its metabolism by gut flora yields short-chain fatty acids (see below) which increase absorption of calcium, magnesium, and iron, resulting from upregulation of mineral-transporting genes and their membrane transport proteins within the colon wall. Among other potential beneficial effects noted above, inulin promotes an increase in the mass and health of intestinal Lactobacillus and Bifidobacterium populations.
Inulin's primary disadvantage is its tolerance. As a soluble fermentable fiber, it is quickly and easily fermented within the intestinal tract, which may cause gas and digestive distress at doses higher than 15 grams/day in most people. Individuals with digestive diseases have benefited from removing fructose and inulin from their diet. While clinical studies have shown changes in the microbiota at lower levels of inulin intake, some of the health effects require higher than 15 grams per day to achieve the benefits.
Vegetable Gums
Vegetable gum fiber supplements are relatively new to the market. Often sold as a powder, vegetable gum fibers dissolve easily with no aftertaste. In preliminary clinical trials, they have proven effective for the treatment of irritable bowel syndrome. Examples of vegetable gum fibers are guar gum and gum arabic.
Water
Add all the ways you use water every day and you still will not come close to the countless uses water has in the human body. Of all the nutrients, water is the most critical as its absence proves lethal within a few days. Organisms have adapted numerous mechanisms for water conservation. Water uses in the human body can be loosely categorized into four basic functions: transportation vehicle, medium for chemical reactions, lubricant/shock absorber, and temperature regulator.
On a typical day, the average adult will take in about 2500 mL (almost 3 quarts) of aqueous fluids. Although most of the intake comes through the digestive tract, about 230 mL (8 ounces) per day is generated metabolically, in the last steps of aerobic respiration. Additionally, each day about the same volume (2500 mL) of water leaves the body by different routes; most of this lost water is removed as urine. The kidneys also can adjust blood volume though mechanisms that draw water out of the filtrate and urine. The kidneys can regulate water levels in the body; they conserve water if you are dehydrated, and they can make urine more dilute to expel excess water if necessary. Water is lost through the skin through evaporation from the skin surface without overt sweating and from air expelled from the lungs. This type of water loss is called insensible water loss because a person is usually unaware of it.
Summary
• Vitamins and minerals are essential parts of the diet. They are needed for the proper function of metabolic pathways in the body.
• Vitamins are not stored in the body, so they must be obtained from the diet or synthesized from precursors available in the diet.
• Minerals are also obtained from the diet, but they are also stored, primarily in skeletal tissues.
• Dietary fibers can act by changing the nature of the contents of the gastrointestinal tract and by changing how other nutrients and chemicals are absorbed.
• Whole grain, legumes, vegetables, and fruits are excellent sources of dietary fiber.
• Health benefit from dietary fiber and whole grains may include a decreased risk of death and lower rates of coronary heart disease, colon cancer, and type 2 diabetes. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.04%3A_Minerals_Vitamins_and_Other_Essentials.txt |
Learning Objectives
• Describe the consequences of fasting, starvation, and malnutrition.
• List the drawbacks of processing on the nutritional quality of foods.
With a typical high-carbohydrate diet, the human body relies on free blood glucose as its primary energy source. Glucose can be obtained directly from dietary sugars and by the breakdown of other carbohydrates. In the absence of dietary sugars and carbohydrates, glucose is obtained from the breakdown of stored glycogen. Glycogen is a readily-accessible storage form of glucose, stored in notable quantities in the liver and skeletal muscle.
After the exhaustion of the glycogen reserve, and for the next 2–3 days, fatty acids become the principal metabolic fuel. After which, the liver begins to synthesize ketone bodies from precursors obtained from fatty acid breakdown. When the fat stores are exhausted, the cells in the body begin to break down protein.
Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left. In a leaner person, the fat reserves are depleted faster, and the protein, sooner, therefore death occurs sooner. Ultimately, the cause of death is in general cardiac arrhythmia or cardiac arrest, brought on by tissue degradation and electrolyte imbalances. Things like metabolic acidosis may also kill starving people.
Symptoms of Starvation
Early symptoms include impulsivity, irritability, and hyperactivity. Atrophy (wasting away) of the stomach weakens the perception of hunger, since the perception is controlled by the volume of the stomach that is empty. Individuals experiencing starvation lose substantial fat (adipose tissue) and muscle mass as the body breaks down these tissues for energy.Catabolysis is the process of a body breaking down its own muscles and other tissues in order to keep vital systems such as the nervous system and heart muscle (myocardium)functioning. The energy deficiency inherent in starvation causes fatigue and renders the victim more apathetic over time. As the starving person becomes too weak to move or even eat, their interaction with the surrounding world diminishes. In females, menstruation ceases when the body fat percentage is too low to support a fetus.
Victims of starvation are often too weak to sense thirst, and therefore become dehydrated. All movements become painful due to muscle atrophy and dry, cracked skin that is caused by severe dehydration. With a weakened body, diseases are commonplace. Fungi, for example, often grow under the esophagus, making swallowing painful. Vitamin deficiency is also a common result of starvation, often leading to anemia, beriberi, pellagra, and scurvy. These diseases collectively can also cause diarrhea, skin rashes, edema, and heart failure. Individuals are often irritable and lethargic as a result.
There is insufficient scientific data on exactly how long people can live without food. Although the length of time varies with an individual's percentage of body fat and general health, one medical study estimates that in adults complete starvation leads to death within 8 to 12 weeks. Starvation begins when an individual has lost about 30%, or about a third, of their normal body weight. Once the loss reaches 40% death is almost inevitable.
Processed Foods Less Nutrition
For many, the word “malnutrition” produces an image of a child in a third-world country with a bloated belly, and skinny arms and legs. However, this image alone is not an accurate representation of the state of malnutrition. For example, someone who is 150 pounds overweight can also be malnourished.
Malnutrition refers to one not receiving proper nutrition and does not distinguish between the consequences of too many nutrients or the lack of nutrients, both of which impair overall health. Undernutrition is characterized by a lack of nutrients and insufficient energy supply, whereas overnutrition is characterized by excessive nutrient and energy intake. Overnutrition can result in obesity, a growing global health threat. Obesity is defined as a metabolic disorder that leads to an over accumulation of fat tissue.
Although not as prevalent in America as it is in developing countries, undernutrition is not uncommon and affects many subpopulations, including the elderly, those with certain diseases, and those in poverty. Many people who live with diseases either have no appetite or may not be able to digest food properly. Some medical causes of malnutrition include cancer, inflammatory bowel syndrome, AIDS, Alzheimer’s disease, illnesses or conditions that cause chronic pain, psychiatric illnesses, such as anorexia nervosa, or as a result of side effects from medications. Overnutrition is an epidemic in the United States and is known to be a risk factor for many diseases, including Type 2 diabetes, cardiovascular disease, inflammatory disorders (such as rheumatoid arthritis), and cancer.
Food processing does have some benefits, such as making food last longer and making products more convenient. However, there are drawbacks to relying on a lot of heavily processed foods that could lead to undernutrition and/or overnutrition. Whole foods and those that are only minimally processed, like frozen vegetables without any sauce, tend to be more healthy. An unhealthy diet high in fat, added sugar and salt, such as one containing a lot of highly-processed foods, can increase the risk for cancer, type 2 diabetes and heart disease, according to the World Health Organization.
Nutrient losses
Processing foods often involves nutrient losses, which can make it harder to meet your needs if these nutrients aren't added back through fortification or enrichment. For example, using high heat during processing can cause vitamin C losses. Another example is refined grains, which have less fiber, vitamins and minerals than whole grains. Eating refined grains, such as those found in many processed foods, instead of whole grains may increase your risk for high cholesterol, diabetes and obesity, according to a study published in "The American Journal of Clinical Nutrition" in December 2007.
New research highlighting the importance to human health of a rich microbial environment in the intestine indicates that abundant food processing (not fermentation of foods) endangers that environment.
Web Link
The USDA conducted a study of nutrient retention in 2004, creating a table of foods, levels of preparation, and nutrition.
https://www.ars.usda.gov/ARSUserFiles/80400525/Data/retn/retn06.pdf
Added Contaminants
Food processing is typically a mechanical process that utilizes extrusion, large mixing, grinding, chopping and emulsifying equipment in the production process. These processes introduce a number of contamination risks. Such contaminants are left over material from a previous operation, animal or human bodily fluids, microorganisms, nonmetallic and metallic fragments. Further processing of these contaminants will result in downstream equipment failure and the risk of ingestion by the consumer.
Added Sodium and Sugar
One of the main sources for sodium in the diet is processed foods. Sodium is added to prevent spoilage, add flavor and improve the texture of these foods. Americans consume an average of 3,436 milligrams of sodium per day, which is higher than the recommended limit of 2,300 milligrams per day for healthy people, and more than twice the limit of 1,500 milligrams per day for those at increased risk for heart disease.
While you don't need to limit the sugars found naturally in whole, unprocessed foods like fresh fruit, eating too much added sugar found in many processed foods can increase your risk for heart disease, obesity, cavities and Type 2 diabetes. The American Heart Association recommends women limit added sugars to no more than 100 calories, or 25 grams, and men limit added sugars to no more than 155 calories, or about 38.75 grams, per day. Currently, Americans consume an average of 355 calories from added sugars each day.
Trans Fats
Foods that have undergone processing, including some commercial baked goods, desserts, margarine, frozen pizza, microwave popcorn and coffee creamers, sometimes contain trans fats. This is the most unhealthy type of fat, and may increase your risk for high cholesterol, heart disease and stroke. The 2010 Dietary Guidelines for Americans recommends keeping your trans fat intake as low as possible.
Other Potential Disadvantages
Processed foods also tend to be more allergenic than whole foods, according to a June 2004 "Current Opinion in Allergy and Clinical Immunology" article. Although the preservatives and other food additives used in many processed foods are generally recognized as safe, a few may cause problems for some individuals, including sulfites, artificial sweeteners, artificial colors and flavors, sodium nitrate, BHA and BHT, olestra, caffeine and monosodium glutamate.
Summary
• The level of blood sugar is tightly regulated; as blood glucose is consumed, glycogen is converted into glucose. Several metabolic adjustments occur during fasting. After the exhaustion of the glycogen reserve fatty acids become the principal metabolic fuel and ketone bodies are produced. After the fat reserves are used up, the cells in the body begin to break down protein.
• Fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal.
• Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body.
• Malnutrition refers to one not receiving proper nutrition and does not distinguish between the consequences of too many nutrients or the lack of nutrients, both of which impair overall health. Undernutrition is characterized by a lack of nutrients and insufficient energy supply, whereas overnutrition is characterized by excessive nutrient and energy intake.
• Heavily processed foods could cause malnutrition due to the effects of processing on the food or the addition of additives like salt or sugar that are above and beyond the daily recommended levels for consumption. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.05%3A_Starvation_Fasting_and_Malnutrition.txt |
Learning Objective
• Know the different types and properties of natural and artificial flavoring ingredients.
Food touches all of the senses. We taste, we smell, we see color and shape, we feel texture and temperature, and we hear sounds as we eat. All of these elements together create a palette with an infinite number of combinations, but the underlying principles that make food taste good are unchanged.
• Variety and diversity in textures and the elements of taste make for interesting food.
• Contrast is as important as harmony; but avoid extremes and imbalance.
Many ingredients are used to enhance the taste of foods. These ingredients can be used to provide both seasoning and flavoring.
• Seasoning means to bring out or intensify the natural flavor of the food without changing it. Seasonings are usually added near the end of the cooking period. The most common seasonings are salt, pepper, and acids (such as lemon juice). When seasonings are used properly, they cannot be tasted; their job is to heighten the flavors of the original ingredients.
• Flavoring refers to something that changes or modifies the original flavor of the food. Flavoring can be used to contrast a taste such as adding liqueur to a dessert where both the added flavor and the original flavor are perceptible. Or flavorings can be used to create a unique flavor in which it is difficult to discern what the separate flavorings are. Spice blends used in pumpkin pies are a good example of this.
Spices, Herbs, and Flavorings
Knowing how to use seasonings and flavorings skillfully provides cooks and bakers with an arsenal with which they can create limitless flavor combinations. Flavoring and seasoning ingredients include wines, spirits, fruit zests, extracts, essences, and oils. However, the main seasoning and flavoring ingredients are classified as herbs and spices (Figure \(1\)).
Knowing the difference between herbs and spices is not as important as knowing how to use seasonings and flavorings skillfully. In general, fresh seasonings are added late in the cooking process while dry ones tend to be added earlier. It is good practice to under-season during the cooking process and then add more seasonings (particularly if you are using fresh ones) just before presentation. This is sometimes referred to as “layering.” When baking, it is difficult to add more seasoning at the end, so testing recipes to ensure the proper amount of spice is included is a critical process.
Spices
The spice trade developed throughout the Indian subcontinent and Middle East by at earliest 2000 BCE with cinnamon and black pepper, and in East Asia with herbs and pepper. The Egyptians used herbs for mummification and their demand for exotic spices and herbs helped stimulate world trade. The word spice comes from the Old French word espice, which became epice, and which came from the Latin root spec, the noun referring to "appearance, sort, kind": species has the same root. By 1000 BCE, medical systems based upon herbs could be found in China, Korea, and India. Early uses were connected with magic, medicine, religion, tradition, and preservation.
Spices are aromatic substances obtained from the dried parts of plants such as the roots, shoots, fruits, bark, and leaves. They are sold as seeds, blends of spices, whole or ground spices, and seasonings. The aromatic substances that give a spice its particular aroma and flavor are the essential oils. The flavor of the essential oil or flavoring compound will vary depending on the quality and freshness of the spice.
The aromas of ground spices are volatile. This means they lose their odor or flavoring when left exposed to the air for extended periods. They should be stored in sealed containers when not in use. Whole beans or unground seeds have a longer shelf life but should also be stored in sealed containers.
Web Links
An A to Z list of spices is provided on the link https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Book%3A_Chemistry_of_Cooking_(Rodriguez-Velazquez)/Understanding_Ingredients%3A_Spices/83%3A_Spices
A complete FDA list of spices and natural seasonings and flavorings that are generally recognized as safe (GRAS) is provided on the link below:
Herbs
Herbs tend to be the leaves of fragrant plants that do not have a woody stem. Herbs are available fresh or dried, with fresh herbs having a more subtle flavor than dried. You need to add a larger quantity of fresh herbs (up to 50% more) than dry herbs to get the same desired flavor. Conversely, if a recipe calls for a certain amount of fresh herb, you would use about one-half of that amount of dry herb.
The most common fresh herbs are basil, coriander, marjoram, oregano, parsley, rosemary, sage, tarragon, and thyme (Figure \(2\)). Fresh herbs should have a clean, fresh fragrance and be free of wilted or brown leaves. They can be kept for about five days if sealed inside an airtight plastic bag. Fresh herbs are usually added near the completion of the cooking process so flavors are not lost due to heat exposure.
Dried herbs lose their power rather quickly if not properly stored in airtight containers. They can last up to six months if properly stored. Dried herbs are usually added at the start of the cooking process as their flavor takes longer to develop than fresh herbs.
Flavorants or Flavorings
Flavor, is the perceptual impression of food or other substances, and is determined primarily by the chemical senses of the gustatory and olfactory system. The "trigeminal senses", which detect chemical irritants in the mouth and throat, as well as temperature and texture, are also important to the overall gestalt of taste perception. The taste of food, can be altered naturally or artificially.
A "flavorant" is defined as a substance that gives another substance taste, altering the characteristics of the solute, causing it to become sweet, sour, tangy, etc. Although both terms, in common language, denote the combined chemical sensations of taste and smell, the same terms are used in the fragrance and flavors industry to refer to edible chemicals and extracts that alter the flavor of food and food products through the sense of smell.
Due to the high cost, or unavailability of natural flavor extracts, most commercial flavorants are "nature-identical", which means that they are the chemical equivalent of natural flavors, but chemically synthesized rather than being extracted from source materials. Identification of components of natural foods, for example a raspberry, may be done using technology such as headspace techniques, so the flavorist can imitate the flavor by using a few of the same chemicals present.
Table \(1\) list the three principal types of flavorings that are used in foods, under definitions agreed in the EU and Australia.
Table \(1\) Three Principal Types of Flavorings Used in Foods (Under Definitions Agreed in the EU and Australia)
Type Description
Natural flavoring substances These flavoring substances are obtained from plant or animal raw materials, by physical, microbiological, or enzymatic processes. They can be either used in their natural state or processed for human consumption, but cannot contain any nature-identical or artificial flavoring substances.
Nature-identical flavoring substances These are obtained by synthesis or isolated through chemical processes, which are chemically and organoleptically identical to flavoring substances naturally present in products intended for human consumption. They cannot contain any artificial flavoring substances.
Artificial flavoring substances These are not identified in a natural product intended for human consumption, whether or not the product is processed. These are typically produced by fractional distillation and additional chemical manipulation of naturally sourced chemicals, crude oil, or coal tar. Although they are chemically different, in sensory characteristics they are the same as natural ones.
Most artificial flavors are specific and often complex mixtures of singular naturally occurring flavor compounds combined together to either imitate or enhance a natural flavor. These mixtures are formulated by flavorists to give a food product a unique flavor and to maintain flavor consistency between different product batches or after recipe changes. The list of known flavoring agents includes thousands of molecular compounds, and the flavor chemist (flavorist) can often mix these together to produce many of the common flavors. Many flavorants consist of esters, which are often described as being "sweet" or "fruity" (see the table below).
Table \(2\) Different Odors Associated with Esters.
Other Plant based and Artificial Sweeteners
A sugar substitute is a food additive that provides a sweet taste like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie (non-nutritive) or low-calorie sweetener. Artificial sweeteners may be derived through manufacturing of plant extracts or processed by chemical synthesis. Sugar alcohols such as erythritol, xylitol, and sorbitol are derived from sugars. In 2017, sucralose was the most common sugar substitute used in the manufacture of foods and beverages; it had 30% of the global market, which was projected to be valued at \$2.8 billion by 2021.
In 1969, cyclamate was banned for sale in the US by the Food and Drug Administration. As of 2018, there is no strong evidence that non-sugar sweeteners are either unsafe or result in improved health outcomes.
When these sweeteners are provided for restaurant customers to add to beverages such as tea and coffee, they are provided in small colored paper packets (see image); in North America, the colors are typically blue for aspartame, pink for saccharin (US) or cyclamate (Canada), yellow for sucralose, orange for monk fruit extract, and green for stevia. These sweeteners are also a fundamental ingredient in diet drinks to sweeten them without adding calories.
Stevia is a sweetener and sugar substitute derived from the leaves of the plant species Stevia rebaudiana, native to Brazil and Paraguay. The active compounds (Figure \(3\)) are steviol glycosides (mainly stevioside and rebaudioside), which have 30 to 150 times the sweetness of sugar, are heat-stable, pH-stable, and not fermentable.The body does not metabolize the glycosides in stevia, so it contains zero calories like some artificial sweeteners. Stevia's taste has a slower onset and longer duration than that of sugar, and some of its extracts may have a bitter or licorice-like aftertaste at high concentrations.
The legal status of stevia as a food additive or dietary supplement varies from country to country. In the United States, high-purity stevia glycoside extracts have been generally recognized as safe (GRAS) since 2008, and are allowed in food products, but stevia leaf and crude extracts do not have GRAS or Food and Drug Administration (FDA) approval for use in food.
Stevia rebaudiana
The plant Stevia rebaudiana has been used for more than 1,500 years by the Guaraní peoples of South America, who called it ka'a he'ê ("sweet herb"). The leaves have been used traditionally for hundreds of years in both Brazil and Paraguay to sweeten local teas and medicines, and as a "sweet treat".The genus was named for Spanish botanist and physician Petrus Jacobus Stevus (Pedro Jaime Esteve 1500–1556), a professor of botany at the University of Valencia.
In 1899, Swiss botanist Moisés Santiago Bertoni, while conducting research in eastern Paraguay, first described the plant and the sweet taste in detail. Only limited research was conducted on the topic until, in 1931, two French chemists isolated the glycosides that give stevia its sweet taste.
Table \(3\) Relative Sweetness of Different Natural and Artificial Sweeteners.
Compound Relative Sweetness
Sucrose 100
Fructose 173
Stevia 300
Aspartame 18,000
Acesulfame K 20,000
Saccharin 30,000
Sucralose 60,000
Artificial Sweeteners
Several other kinds of organic compounds have been synthesized that are far superior as sweetening agents. These so-called high-intensity or artificial sweeteners (Figure \(4\)) are useful for people with diabetes or other medical conditions that require them to control their carbohydrate intake. The synthetic compounds are noncaloric or used in such small quantities that they do not add significantly to the caloric value of food.
The first artificial sweetener—saccharin—was discovered by accident in 1879. It is 300 times sweeter than sucrose, but it passes through the body unchanged and thus adds no calories to the diet. After its discovery, saccharin was used until it was banned in the early 1900s. However, during the sugar-short years of World War I, the ban was lifted and was not reinstated at the war’s end. One drawback to the use of saccharin is its bitter, metallic aftertaste. The initial solution to this problem was to combine saccharin with cyclamate, a second artificial sweetener discovered in 1937.
In the 1960s and 1970s, several clinical tests with laboratory animals implicated both cyclamate and saccharin as carcinogenic (cancer-causing) substances. The results from the cyclamate tests were completed first, and cyclamate was banned in the United States in 1969. Then a major study was released in Canada in 1977 indicating that saccharin increased the incidence of bladder cancer in rats. The US Food and Drug Administration (FDA) proposed a ban on saccharin that raised immediate public opposition because saccharin was the only artificial sweetener still available. In response, Congress passed the Saccharin Study and Labeling Act in 1977, permitting the use of saccharin as long as any product containing it was labeled with a consumer warning regarding the possible elevation of the risk of bladder cancer. Today this warning is no longer required; moreover, the FDA is currently reviewing the ban on cyclamate, as 75 additional studies and years of usage in other countries, such as Canada, have failed to show that it has any carcinogenic effect.
A third artificial sweetener, aspartame, was discovered in 1965. This white crystalline compound is about 180 times sweeter than sucrose and has no aftertaste. It was approved for use in 1981 and is used to sweeten a wide variety of foods because it blends well with other food flavors. Aspartame is not used in baked goods, however, because it is not heat stable.
In the body (or when heated), aspartame is initially hydrolyzed to three molecules: the amino acids aspartic acid and phenylalanine and an alcohol methanol. Repeated controversy regarding the safety of aspartame arises partly from the fact that the body metabolizes the released methanol to formaldehyde. It should be noted, though, that a glass of tomato juice has six times as much methanol as a similar amount of a diet soda containing aspartame. The only documented risk connected to aspartame use is for individuals with the genetic disease phenylketonuria (PKU); these individuals lack the enzyme needed to metabolize the phenylalanine released when aspartame is broken down by the body. Because of the danger to people with PKU, all products containing aspartame must carry a warning label.
Acesulfame K, discovered just two years after aspartame (1967), was approved for use in the United States in 1988. It is 200 times sweeter than sugar and, unlike aspartame, is heat stable. It has no lingering aftertaste.
One of the newest artificial sweeteners to gain FDA approval (April 1998) for use in the United States is sucralose, a white crystalline solid approximately 600 times sweeter than sucrose. Sucralose is synthesized from sucrose and has three chlorine atoms substituted for three OH groups. It is noncaloric because it passes through the body unchanged. It can be used in baking because it is heat stable.
All of the extensive clinical studies completed to date have indicated that these artificial sweeteners approved for use in the United States are safe for consumption by healthy individuals in moderate amounts.
Flavor Enhancers
The US Food and Drug Administration define flavor enhancers as food additives that enhance the flavors already present in foods without providing their own separate flavor. The names of flavor enhancers found on product labels include moosodium glutamate (msg), hydrolyzed soy protein, autolyzed yeast extract, disodium guanylate or inosinate. Umami or "savory" flavorants, more commonly called taste or flavor enhancers, are largely based on amino acids and nucleotides. These are typically used as sodium or calcium salts. Umami flavorants recognized and approved by the European Union are listed in Table \(3\).
Table \(4\) Umami Favorants Recognized and Approved by the European Union.
Acid Salts Description
Glutamic acid salts This amino acid's sodium salt, monosodium glutamate (MSG), is one of the most commonly used flavor enhancers in food processing. Mono- and diglutamate salts are also commonly used.
Glycine salts Simple amino acid salts typically combined with glutamic acid as flavor enhancers
Guanylic acid salts Nucleotide salts typically combined with glutamic acid as flavor enhancers
Inosinic acid salts Nucleotide salts created from the breakdown of AMP, due to high costs of production, typically combined with glutamic acid as flavor enhancers
5'-ribonucleotide salts Nucleotide salts typically combined with other amino acids and nucleotide salts as flavor enhancers
Monosodium glutamate (MSG), also known as sodium glutamate, (Figure \(5\) is the sodium salt of glutamic acid, one of the most abundant naturally occurring non-essential amino acids. Glutamic acid is found naturally in tomatoes, grapes, cheese, mushrooms and other foods.
MSG is used in the food industry as a flavor enhancer with an umami taste that intensifies the meaty, savory flavor of food, as naturally occurring glutamate does in foods such as stews and meat soups. It was first prepared in 1908 by Japanese biochemist Kikunae Ikeda, who was trying to isolate and duplicate the savory taste of kombu, an edible seaweed used as a base for many Japanese soups. MSG as a flavor enhancer balances, blends, and rounds the perception of other tastes.
Figure \(5\) Monosodium glutamate.
Summary
• Many ingredients are used to enhance the taste of foods. These ingredients can be used to provide both seasoning and flavoring.
• Flavoring and seasoning ingredients include wines, spirits, fruit zests, extracts, essences, and oils. However, the main seasoning and flavoring ingredients are classified as herbs and spices.
• Sucrose and fructose are two common natural sweeteners.
• The so-called high-intensity or artificial sweeteners such as saccharin, cyclamates, and aspartame) are useful for people with diabetes or other medical conditions that require them to control their carbohydrate intake
• Flavor enhancers are food additives (largely based on amino acids and nucleotides) that enhance the flavors already present in foods without providing their own separate flavor.
Contributors
• Sorangel Rodriguez-Velazquez (American University). Chemistry of Cooking by Sorangel Rodriguez-Velazquez is licensed under a Creative Commons Attribution-NonCommercial ShareAlike 4.0 International License, except where otherwise noted
• Libretext: The Basics of GOB Chemistry (Ball et al.)
• Wikipedia
• US Food and Drug Administration (US FDA) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.06%3A_Flavorings-_Spicy_and_Sweet.txt |
Learning Objective
• Know the purpose of other ingredients added to food.
For centuries, ingredients have served useful functions in a variety of foods. Our ancestors used salt to preserve meats and fish, added herbs and spices to improve the flavor of foods, preserved fruit with sugar, and pickled cucumbers in a vinegar solution. Today, consumers demand and enjoy a food supply that is flavorful, nutritious, safe, convenient, colorful and affordable. Food additives and advances in technology help make that possible.
There are thousands of ingredients used to make foods. The Food and Drug Administration (FDA) maintains a list of over 3000 ingredients in its data base "Everything Added to Food in the United States", many of which we use at home every day (e.g., sugar, baking soda, salt, vanilla, yeast, spices and colors).
Still, some consumers have concerns about additives because they may see the long, unfamiliar names and think of them as complex chemical compounds. In fact, every food we eat - whether a just-picked strawberry or a homemade cookie - is made up of chemical compounds that determine flavor, color, texture and nutrient value. All food additives are carefully regulated by federal authorities and various international organizations to ensure that foods are safe to eat and are accurately labeled.
Additives perform a variety of useful functions in foods that consumers often take for granted. Some additives could be eliminated if we were willing to grow our own food, harvest and grind it, spend many hours cooking and canning, or accept increased risks of food spoilage. But most consumers today rely on the many technological, aesthetic and convenient benefits that additives provide.
Following are some reasons why ingredients are added to foods:
1. To Maintain or Improve Safety and Freshness: Preservatives slow product spoilage caused by mold, air, bacteria, fungi or yeast. In addition to maintaining the quality of the food, they help control contamination that can cause foodborne illness, including life-threatening botulism. One group of preservatives -- antioxidants -- prevents fats and oils and the foods containing them from becoming rancid or developing an off-flavor. They also prevent cut fresh fruits such as apples from turning brown when exposed to air.
2. To Improve or Maintain Nutritional Value: Vitamins and minerals (and fiber) are added to many foods to make up for those lacking in a person's diet or lost in processing, or to enhance the nutritional quality of a food. Such fortification and enrichment has helped reduce malnutrition in the U.S. and worldwide. All products containing added nutrients must be appropriately labeled.
3. Improve Taste, Texture and Appearance: Spices, natural and artificial flavors, and sweeteners are added to enhance the taste of food. Food colors maintain or improve appearance. Emulsifiers, stabilizers and thickeners give foods the texture and consistency consumers expect. Leavening agents allow baked goods to rise during baking. Some additives help control the acidity and alkalinity of foods, while other ingredients help maintain the taste and appeal of foods with reduced fat content.
Types of Food Ingredients
The following summary lists the types of common food ingredients, why they are used,
and some examples of the names that can be found on product labels. Some additives are
used for more than one purpose.
Types of Ingredients What They Do Examples
of Uses
Names Found
on Product Labels
Preservatives Prevent food spoilage from bacteria, molds, fungi, or yeast (antimicrobials); slow or prevent changes in color, flavor, or texture and delay rancidity (antioxidants); maintain freshness Fruit sauces and jellies, beverages, baked goods, cured meats, oils and margarines, cereals, dressings, snack foods, fruits and vegetables Ascorbic acid, citric acid, sodium benzoate, calcium propionate, sodium erythorbate, sodium nitrite, calcium sorbate, potassium sorbate, BHA, BHT, EDTA, tocopherols (Vitamin E)
Sweeteners Add sweetness with or without the extra calories Beverages, baked goods, confections, table-top sugar, substitutes, many processed foods Sucrose (sugar), glucose, fructose, sorbitol, mannitol, corn syrup, high fructose corn syrup, saccharin, aspartame, sucralose, acesulfame potassium (acesulfame-K), neotame
Color Additives Offset color loss due to exposure to light, air, temperature extremes, moisture and storage conditions; correct natural variations in color; enhance colors that occur naturally; provide color to colorless and "fun" foods Many processed foods, (candies, snack foods margarine, cheese, soft drinks, jams/jellies, gelatins, pudding and pie fillings) FD&C Blue Nos. 1 and 2, FD&C Green No. 3, FD&C Red Nos. 3 and 40, FD&C Yellow Nos. 5 and 6, Orange B, Citrus Red No. 2, annatto extract, beta-carotene, grape skin extract, cochineal extract or carmine, paprika oleoresin, caramel color, fruit and vegetable juices, saffron (Note: Exempt color additives are not required to be declared by name on labels but may be declared simply as colorings or color added)
Flavors and Spices Add specific flavors (natural and synthetic) Pudding and pie fillings, gelatin dessert mixes, cake mixes, salad dressings, candies, soft drinks, ice cream, BBQ sauce Natural flavoring, artificial flavor, and spices
Flavor Enhancers Enhance flavors already present in foods (without providing their own separate flavor) Many processed foods Monosodium glutamate (MSG), hydrolyzed soy protein, autolyzed yeast extract, disodium guanylate or inosinate
Fat Replacers (and components of formulations used to replace fats) Provide expected texture and a creamy "mouth-feel" in reduced-fat foods Baked goods, dressings, frozen desserts, confections, cake and dessert mixes, dairy products Olestra, cellulose gel, carrageenan, polydextrose, modified food starch, microparticulated egg white protein, guar gum, xanthan gum, whey protein concentrate
Nutrients Replace vitamins and minerals lost in processing (enrichment), add nutrients that may be lacking in the diet (fortification) Flour, breads, cereals, rice, macaroni, margarine, salt, milk, fruit beverages, energy bars, instant breakfast drinks Thiamine hydrochloride, riboflavin (Vitamin B2), niacin, niacinamide, folate or folic acid, beta carotene, potassium iodide, iron or ferrous sulfate, alpha tocopherols, ascorbic acid, Vitamin D, amino acids (L-tryptophan, L-lysine, L-leucine, L-methionine)
Emulsifiers Allow smooth mixing of ingredients, prevent separation
Keep emulsified products stable, reduce stickiness, control crystallization, keep ingredients dispersed, and to help products dissolve more easily
Salad dressings, peanut butter, chocolate, margarine, frozen desserts Soy lecithin, mono- and diglycerides, egg yolks, polysorbates, sorbitan monostearate
Stabilizers and Thickeners, Binders, Texturizers Produce uniform texture, improve "mouth-feel" Frozen desserts, dairy products, cakes, pudding and gelatin mixes, dressings, jams and jellies, sauces Gelatin, pectin, guar gum, carrageenan, xanthan gum, whey
pH Control Agents and acidulants Control acidity and alkalinity, prevent spoilage Beverages, frozen desserts, chocolate, low acid canned foods, baking powder Lactic acid, citric acid, ammonium hydroxide, sodium carbonate
Leavening Agents Promote rising of baked goods Breads and other baked goods Baking soda, monocalcium phosphate, calcium carbonate
Anti-caking agents Keep powdered foods free-flowing, prevent moisture absorption Salt, baking powder, confectioner's sugar Calcium silicate, iron ammonium citrate, silicon dioxide
Humectants Retain moisture Shredded coconut, marshmallows, soft candies, confections Glycerin, sorbitol
Yeast Nutrients Promote growth of yeast Breads and other baked goods Calcium sulfate, ammonium phosphate
Dough Strengtheners and Conditioners Produce more stable dough Breads and other baked goods Ammonium sulfate, azodicarbonamide, L-cysteine
Firming Agents Maintain crispness and firmness Processed fruits and vegetables Calcium chloride, calcium lactate
Enzyme Preparations Modify proteins, polysaccharides and fats Cheese, dairy products, meat Enzymes, lactase, papain, rennet, chymosin
Gases Serve as propellant, aerate, or create carbonation Oil cooking spray, whipped cream, carbonated beverages Carbon dioxide, nitrous oxide
Antioxidants: BHA and BHT
Antioxidants are used as food additives to help guard against food deterioration. Exposure to oxygen and sunlight are the two main factors in the oxidation of food, so food is preserved by keeping in the dark and sealing it in containers or even coating it in wax, as with cucumbers. However, as oxygen is also important for plant respiration, storing plant materials in anaerobic conditions produces unpleasant flavors and unappealing colors. Consequently, packaging of fresh fruits and vegetables contains an ~8% oxygen atmosphere. Antioxidants are an especially important class of preservatives as, unlike bacterial or fungal spoilage, oxidation reactions still occur relatively rapidly in frozen or refrigerated food. These preservatives include natural antioxidants such as ascorbic acid (AA) and tocopherols , as well as synthetic antioxidants such as propyl gallate, tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT).
The most common molecules attacked by oxidation are unsaturated fats; oxidation causes them to turn rancid. Since oxidized lipids are often discolored and usually have unpleasant tastes such as metallic or sulfurous flavors, it is important to avoid oxidation in fat-rich foods. Thus, these foods are rarely preserved by drying; instead, they are preserved by smoking, salting or fermenting. Even less fatty foods such as fruits are sprayed with sulfurous antioxidants prior to air drying. Oxidation is often catalyzed by metals, which is why fats such as butter should never be wrapped in aluminium foil or kept in metal containers. Some fatty foods such as olive oil are partially protected from oxidation by their natural content of antioxidants, but remain sensitive to photooxidation.
Color Additives
A color additive is any dye, pigment or substance which when added or applied to a food, drug or cosmetic, or to the human body, is capable (alone or through reactions with other substances) of imparting color. FDA is responsible for regulating all color additives to ensure that foods containing color additives are safe to eat, contain only approved ingredients and are accurately labeled.
Color additives are used in foods for many reasons: 1) to offset color loss due to exposure to light, air, temperature extremes, moisture and storage conditions; 2) to correct natural variations in color; 3) to enhance colors that occur naturally; and 4) to provide color to colorless and "fun" foods. Without color additives, colas wouldn't be brown, margarine wouldn't be yellow and mint ice cream wouldn't be green. Color additives are now recognized as an important part of practically all processed foods we eat.
US FDA's permitted colors are classified as subject to certification or exempt from certification, both of which are subject to rigorous safety standards prior to their approval and listing for use in foods.
• Certified colors are synthetically produced (or human made) and used widely because they impart an intense, uniform color, are less expensive, and blend more easily to create a variety of hues. There are nine certified color additives approved for use in the United States (e.g., FD&C Yellow No. 6. See chart for complete list.). Certified food colors generally do not add undesirable flavors to foods.
• Colors that are exempt from certification include pigments derived from natural sources such as vegetables, minerals or animals. Nature derived color additives are typically more expensive than certified colors and may add unintended flavors to foods. Examples of exempt colors include annatto extract (yellow), dehydrated beets (bluish-red to brown), caramel (yellow to tan), beta-carotene (yellow to orange) and grape skin extract (red, green).
• In the United States, FD&C numbers (which indicate that the FDA has approved the colorant for use in foods, drugs and cosmetics) are given to approved synthetic food dyes that do not exist in nature, while in the European Union, E numbers are used for all additives, both synthetic and natural, that are approved in food applications.
Artificial Food Colors
In the US, the following seven artificial colorings are generally permitted in food (the most common in bold) as of 2016. The lakes of these colorings are also permitted except the lake of Red No. 3.
• FD&C Blue No. 1 – Brilliant Blue FCF, E133 (blue shade)
• FD&C Blue No. 2 – Indigotine, E132 (indigo shade)
• FD&C Green No. 3 – Fast Green FCF, E143 (turquoise shade)
• FD&C Red No. 3 – Erythrosine, E127 (pink shade, commonly used in glacé cherries)
• FD&C Red No. 40 – Allura Red AC, E129 (red shade)
• FD&C Yellow No. 5 – Tartrazine, E102 (yellow shade)
• FD&C Yellow No. 6 – Sunset Yellow FCF, E110 (orange shade)
Two dyes are allowed by the FDA for limited applications:
• Citrus Red 2 (orange shade) - allowed only to color orange peels.
• Orange B (red shade) - allowed only for use in hot dog and sausage casings (not produced after 1978, but never delisted)
Natural food dyes
Carotenoids , chlorophyllin , anthocyanins , and betanin comprise four main categories of plant pigments grown to color food products. Other colorants or specialized derivatives of these core groups include:
• Annatto, a reddish-orange dye made from the seed of the achiote
• Caramel coloring, made from caramelized sugar
• Carmine, a red dye derived from the cochineal insect, Dactylopius coccus
• Elderberry juice
• Lycopene
• Paprika
• Turmeric
Blue colors are especially rare. One feasible blue dye currently in use is derived from spirulina. Some recent research has explored associating anthocyanins with other phenolics or aluminium ions to develop blue colours. However, the inherent problems posed by the nature of the food matrix, and the need for long‐term stability, makes this a very difficult objective. The pigment genipin, present in the fruit of Gardenia jasminoides, can be treated with amino acids to produce the blue pigment gardenia blue, which is approved for use in Japan but not the EU or the USA.
To ensure reproducibility, the colored components of these substances are often provided in highly purified form. For stability and convenience, they can be formulated in suitable carrier materials (solid and liquids). Hexane, acetone, and other solvents break down cell walls in the fruit and vegetables and allow for maximum extraction of the coloring. Traces of these may still remain in the finished colorant, but they do not need to be declared on the product label. These solvents are known as carry-over ingredients.
Summary
• Different ingredients are added to food in order to:
1. maintain or improve safety and freshness,
2. improve or maintain nutritional value, and
3. improve taste, texture, and appearance.
• Common antioxidants added to foods include, ascorbic acid, tocopherols, propyl gallate, BHA, BHT, & TBHQ.
• There are seven artificial colorings that are generally permitted in the US. The most common ones are FD&C Blue No.1, FD&C Red No. 40, FD&C Yellow No.5, and FD&C Yellow No.6.
• US FDA
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.07%3A_Other_Food_Additives-__Beneficial_or_Dangerous.txt |
Learning Objectives
• Identify food substances and cooking processes known to cause cancer.
• Know common food contaminants and their sources.
Food Substances That May Promote Cancer
Several foods increase the risk of cancer. Alcohol is one example and increases the risk of mouth cancer, pharynx (throat), larynx (voice box), esophagus, liver, breast, colon, and rectum. People who drink should limit their alcohol intake to no more than 2 drinks per day for men and one drink per day for women. A drink is defined as 12 ounces of beer, 5 ounces of wine, or 1 1/2 ounces of 80-proof distilled spirits (hard liquor). Recent studies suggest there is no safe level of alcohol intake for women who are at high risk of developing breast cancer.
Scientific studies have shown that people who eat more fruit and vegetable have a lower risk of developing cancer certain cancers. Those individuals that eat less fruit and vegetables may increase their risk of developing cancer. Fruit and vegetables are rich in antioxidants but several studies of antioxidant supplements have not found a lower cancer risk, so the other compounds in fruits and vegetables may confer this protective effect.
Epidemiological studies have linked a high fat intake with higher rates of breast, prostate, colon, and other cancers. Randomized studies have not found that fat intake increases tumor development or lowers cancer risk either. So, at this time, the evidence is unclear and total amount of fat consumed does not appear to be linked to cancer risk.
Consumption of large amounts of processed meats has been associated with an increased risk of colorectal and stomach cancer. The exact mechanism is not known but nitrites, used to maintain color and bacterial growth in lunch meats, hams, and hot dogs, may play a role.
Frying, broiling, or grilling meats, cooking processes that use high heat, form chemicals that may increase cancer risk. These chemicals are polycyclic aromatic hydrocarbons or heterocyclic aromatic amines.
Eating a lot of foods preserved by salting and/or pickling increase one's risk of stomach, nasopharyngeal, and throat cancer. There is very little evidence that the level of salt used in cooking or flavoring foods or added during ng affect cancer risk.
Aflatoxins are poisonous carcinogens that are produced by certain molds (Aspergillus flavus and Aspergillus parasiticus) which grow in soil, decaying vegetation, hay, and grains. They are regularly found in improperly stored staple commodities such as cassava, chili peppers, corn, cottonseed, millet, peanuts, rice, sesame seeds, sorghum, sunflower seeds, tree nuts, wheat, and a variety of spices. When contaminated food is processed, aflatoxins enter the general food supply where they have been found in both pet and human foods, as well as in feedstocks for agricultural animals. Animals fed contaminated food can pass aflatoxin transformation products into eggs, milk products, and meat.
Food As an Anti-Carcinogens
Dietary fiber and calorie restriction are two anti-carcinogen or anti-promoters that decrease the risk of tumor formation. Dietary fiber is both and is inversely associated with cancer, particularly colon cancer. So the more fiber you eat, the less risk you have of developing colon cancer. One mechanism by which fiber acts is hastening bile acid excretion. Fiber also increases the rate of passage of materials through the colon resulting in decreased production and exposure of the colon to cancer-causing agents, ie dilutes the concentration of carcinogens.
Animal studies have shown that restricting caloric intake by 30% reduces tumor growth and increases life span. The mechanism is not known but may be due to less oxidation thus damage to DNA.
Antioxidants can help block the action of initiators or promoters if their mode of action is to damage DNA by oxidation. Vitamin A, C, E, beta-carotene, and selenium are antioxidant nutrients. Some work locally, like vitamin E in the colon, while other work more globally like selenium and vitamin C. Vitamin A appears to work by keeping cells differentiated which slows the growth rate.
Other compounds in food, particularly fruits and vegetables, have been shown to slow tumor formation. Cruciferous vegetables (eg broccoli, cauliflower, cabbage, and Brussel sprouts to name a few) are rich in nutrients, fiber, glucosinolates which are sulfur-containing chemicals, indoles, and isothiocyanates. Animal studies have found these substances inhibit the development of cancer in several organs in rats and mice (Hecht SS. Inhibition of carcinogenesis by isothiocyanates. Drug Metabolism Reviews 2000;32(3-4):395-411; Murillo G, Mehta RG. Cruciferous vegetables and cancer prevention. Nutrition and Cancer 2001;41(1-2):17-28). Indoles and isothiocyanates help protect cells from DNA damage; help inactivate carcinogens; have antiviral and antibacterial effects; have anti-inflammatory effects; induce cell death (apoptosis); and inhibit tumor blood vessel formation (angiogenesis) and tumor cell migration (needed for metastasis) (National Cancer Institute, Cruciferous Vegetables and Cancer Prevention, 2012, https://www.cancer.gov/about-cancer/...les-fact-sheet). Studies in humans, however, have shown mixed results.
Dietary Recommendation for Decreasing Cancer Risk
The American Institute for Cancer Research, American Cancer Society, and National Cancer Institute provide dietary recommendations to reduce cancer risk. These guidelines are remarkably similar and focus on eating more fruits and vegetables, whole grains, and legumes; reducing processed meat and red meat intake; and limit your intake of alcohol. Fruits, vegetables, and whole grains are rich in fiber. Refined grains, such as white rice, are low or devoid of fiber. All types of fibers should be emphasized. Fruits and vegetables contain antioxidants, phytochemicals, and fiber.
These ten recommendations for cancer prevention are drawn from the WCRF/AICR Second Expert Report. Each recommendation links to more details.
1. Be as lean as possible without becoming underweight.
2. Be physically active for at least 30 minutes every day. Limit sedentary habits.
3. Avoid sugary drinks. Limit consumption of energy-dense foods.
4. Eat more of a variety of vegetables, fruits, whole grains and legumes such as beans.
5. Limit consumption of red meats (such as beef, pork, and lamb) and avoid processed meats.
6. If consumed at all, limit alcoholic drinks to 2 for men and 1 for women a day.
7. Limit consumption of salty foods and foods processed with salt (sodium).
8. Don't use supplements to protect against cancer.
9. * It is best for mothers to breastfeed exclusively for up to 6 months and then add other liquids and foods.
10. * After treatment, cancer survivors should follow the recommendations for cancer prevention.
Food Contamination
Food contamination refers to the presence of harmful chemicals and microorganisms in food, which can cause consumer illness.
The impact of chemical contaminants on consumer health and well-being is often apparent only after many years of processing and prolonged exposure at low levels (e.g., cancer). Unlike food-borne pathogens, chemical contaminants present in foods are often unaffected by thermal processing. Two major categories of chemical contaminants according to the source of contamination and the mechanism by which they enter the food product are agrochemicals and environmental contaminants.
Agrochemicals are chemicals used in agricultural practices and animal husbandry with the intent to increase crop yields. Such agents include pesticides (e.g., insecticides, herbicides, rodenticides), plant growth regulators, veterinary drugs (e.g., nitrofuran, fluoroquinolones, malachite green, chloramphenicol), and bovine somatotropin (rBST).
Environmental contaminants are chemicals that are present in the environment in which the food is grown, harvested, transported, stored, packaged, processed, and consumed. The physical contact of the food with its environment results in its contamination. Possible sources of contamination and contaminants common to that vector include:
• Air: radionuclides (caesium-137, strontium-90), polycyclic aromatic hydrocarbons (PAH)
• Water: arsenic, mercury
• Soil: cadmium, nitrates, perchlorates
• Packaging materials: antimony, tin, lead, perfluorooctanoic acid (PFOA), semicarbazide, benzophenone, isopropylthioxanthone (ITX), bisphenol A
• Processing/cooking equipment: copper or other metal chips, lubricants, cleaning and sanitizing agents
• Naturally occurring toxins: mycotoxins, phytohemagglutinin, pyrrolizidine alkaloids, grayanotoxin, scombrotoxin (histamine), ciguatera, shellfish toxins (see shellfish poisoning), tetrodotoxin, among many others
Foodborne illness (also foodborne disease and colloquially referred to as food poisoning) is any illness resulting from the spoilage of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as prions (the agents of "mad cow disease"), and toxins such as aflatoxins in peanuts, poisonous mushrooms, and various species of beans that have not been boiled for at least 10 minutes.
Symptoms vary depending on the cause. A few broad generalizations can be made. For contaminants requiring an incubation period, symptoms may not manifest for hours to days, depending on the cause and on quantity of consumption. Longer incubation periods tend to cause sufferers to not associate the symptoms with the item consumed, so they may misattribute the symptoms to gastroenteritis, for example.
Symptoms often include vomiting, fever, and aches, and may include diarrhea. Bouts of vomiting can be repeated with an extended delay in between, because even if infected food was eliminated from the stomach in the first bout, microbes, like bacteria (if applicable), can pass through the stomach into the intestine and begin to multiply. Some types of microbes stay in the intestine.
In the United States, using FoodNet data from 2000 to 2007, the CDC estimated there were 47.8 million foodborne illnesses per year (16,000 cases for 100,000 inhabitants) with 9.4 million of these caused by 31 known identified pathogens.
• 127,839 were hospitalized (43 per 100,000 inhabitants per year).
• 3,037 people died (1.0 per 100,000 inhabitants per year).
Web Link
Center for Disease Control and Prevention : List of Foodborne Diseases.
https://www.cdc.gov/foodsafety/diseases/index.html
Summary
• Substances inherent in foods or substances produced during cooking processes that use high heat (e.g. frying, broiling, or grilling meats) may increase cancer risk.
• Two major categories of chemical contaminants according to the source of contamination and the mechanism by which they enter the food product are agrochemicals and environmental contaminants.
• The top four germs that cause illnesses from food eaten in the United States are Norovirus, Salmonella, Clostridium perfringens, and Campylobacter.
• Many different disease-causing germs can contaminate foods, so there are many different foodborne infections.
Contributors
• Libretext: An Introduction to Nutrition (Byerley).
• American Institute for Cancer Research
• Center for Disease Control and Prevention (CDC)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/17%3A_Food/17.08%3A_Problems_with_our_Food.txt |
Thumbnail: Ritalin SR 20 mg, a brand-name sustained-release formulation of methylphenidate. (CC SA-BY 3.0; ).
18: Drugs
Learning Objectives
• Know the difference between anti-inflammatory, analgesic and antipyretic drugs.
• Describe how aspirin and other NSAIDs work.
• Know the side effects of taking prescription and non-prescription medications
• Know the risks of addiction, abuse, and overdose of prescription opioids.
A drug is any substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via inhalation, injection, smoking, ingestion, absorption via a patch on the skin, suppository, or dissolution under the tongue.
Anti-inflammatory, analgesic (pain reliever or pain killer), and antipyretic (fever reducer) drugs are a heterogeneous group of compounds, often chemically unrelated (although most of them are organic acids), which nevertheless share certain therapeutic actions and side effects. The prototype is aspirin; hence these compounds are often referred to as aspirin-like drugs. All aspirin-like drugs are antipyretic, analgesic, and anti-inflammatory, but there are important differences in their activities. For example, acetaminophen is antipyretic and analgesic but is only weakly anti-inflammatory. The reason for the differences are not clear; variations in the sensitivity of enzymes in the target tissues may be important.
When employed as analgesics, these drugs are usually effective only against pain of low-to-moderate intensity, particularly that associated with inflammation. Aspirin drugs do not change the perception of sensory modalities other than pain. The type of pain is important; chronic postoperative pain or pain arising from inflammation is particularly well controlled by aspirin-like drugs, whereas pain arising from the hollow viscera is usually not relieved.
Over-the-counter (OTC) medicines are good for many types of pain. There are two main types of OTC pain medicines: acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs). Aspirin, naproxen (Aleve), and ibuprofen (Advil, Motrin) are examples of OTC NSAIDs.
If OTC medicines don't relieve ones pain, the doctor may prescribe something stronger. Many NSAIDs are also available at higher prescription doses. The most powerful pain relievers are opioids. They are very effective, but they can sometimes have serious side effects. There is also a risk of addiction. Because of the risks, you must use them only under a doctor's supervision.
Aspirin and other NSAIDs
Nonsteroidal anti-inflammatory drugs (NSAIDs) are members of a drug class that reduces pain, decreases fever, prevents blood clots, and in higher doses, decreases inflammation. Side effects depend on the specific drug but largely include an increased risk of gastrointestinal ulcers and bleeds, heart attack, and kidney disease.
The term nonsteroidal distinguishes these drugs from steroids, which while having a similar eicosanoid-depressing, anti-inflammatory action, have a broad range of other effects. First used in 1960, the term served to distance these medications from steroids, which were particularly stigmatised at the time due to the connotations with anabolic steroid abuse.The most prominent NSAIDs are aspirin, ibuprofen, and naproxen, all available over the counter (OTC) in most countries.
In the U.S., about 10 to 20 thousand tons of aspirin are consumed each year; it is our most popular analgesic. Aspirin is one of the most effective analgesic, antipyretic, and anti-inflammatory agents.
Chemical structure
Figure \(1\) Aspirin
Aspirin is known to interfere with the action of the platelets. As a result, some people who take a lot of aspirin experience easy bruising of the skin. Therefore, people who have major bleeding problems should not take aspirin. Also, keep in mind that aspirin should not be taken for 10-14 days before surgery (including surgery in the mouth) to avoid excessive bleeding during or after the operation. These side effects probably depend on aspirin-like drugs' ability to block endogenous prostaglandin biosynthesis. Platelet function appears to be disturbed because aspirin-like drugs prevent the formation by the platelets of thrombozane A2 (TXA2), a potent aggregating agent. This accounts for the tendency of these drugs to increase the bleeding time.
Other Aspirin-Like Drugs
There are other non-selective NSAIDs on the market, including diclofenac, ibuprofen, ketoprofen, meloxicam, naproxen, and oxaprozin. Ibuprofen and naproxen are available in both prescription and over-the-counter (OTC) versions. The doses in OTC ibuprofen (Advil and Motrin) or naproxen (Aleve) are about half the doses of prescription versions.
How NSAIDs Work?
Non-selective NSAIDs like aspirin work (Figure \(3\)) by inhibiting two enzymes that are involved with pain and inflammation—cyclooxygenase-1 and cyclooxygenase-2 (COX-1 and COX-2). These enzymes are involved with the ring closure and addition of oxygen to arachidonic acid converting to prostaglandins. The acetyl group on aspirin is hydrolzed and then bonded to the alcohol group of serine as an ester (Figure \(2\)). This has the effect of blocking the channel in the enzyme and arachidonic acid can not enter the active site of the enzyme. By inhibiting or blocking this enzyme, the synthesis of prostaglandins is blocked, which in turn relieves some of the effects of pain and fever. Aspirin is also thought to inhibit the prostaglandin synthesis involved with unwanted blood clotting in coronary heart disease. At the same time an injury while taking aspirin may cause more extensive bleeding.
COX-2 selective inhibitors are a newer type of medicine that block the COX-2 enzyme more than the COX-1 enzyme. The only COX-2 selective inhibitor currently on the market in the United States is the prescription drug Celebrex (celecoxib), which is marketed by Pfizer. It was believed that COX-2 inhibitors may be less likely to cause the stomach problems associated with the older NSAIDs, but all NSAIDs carry the risk of stomach problems.
Key Points to Remember With NSAIDs
• Too much can cause stomach bleeding. This risk increases in people who are over 60 years of age, are taking prescription blood thinners, are taking steroids, have a history of stomach bleeding or ulcers, and/or have other bleeding problems.
• Use of NSAIDs can also cause kidney damage. This risk may increase in people who are over 60 years of age, are taking a diuretic (a drug that increases the excretion of urine), have high blood pressure, heart disease, or pre-existing kidney disease.
Acetaminophen
Acetaminophen is an effective alternative to aspirin as an analgesic and antipyretic agent. However, its anti-inflammatory effect is minor and not clinically useful. It is commonly felt that acetaminophen may have fewer side effects than aspirin, but it should be noted that an acute overdose may produce severe or even fatal liver damage. Acetaminophen does not inhibit platelet aggregation and therefore is not useful for preventing vascular clotting.
Side effects are usually fewer than those of aspirin; the drug produces less gastric distress and less ringing in the ears. However, as stated previously, overdose can lead to severe damage of the liver.
Acetaminophen has been proved to be a reasonable substitute for aspirin when analgesic or antipyretic effectiveness is desired, especially in patients who cannot tolerate aspirin. This might include patients with peptic ulcer disease of gastric distress or those in whom the anticoagulant action of aspirin might be undesirable.
Key Points to Remember With Acetaminophen
• Taking a higher dose than recommended will not provide more relief and can be dangerous.
• Too much can lead to liver damage and death. Risk for liver damage may be increased in people who drink three or more alcoholic beverages a day while using acetaminophen-containing medicines.
• Be cautious when giving acetaminophen to children. Infant drop medications can be significantly stronger than regular children's medications. Read and follow the directions on the label every time you use a medicine. Be sure that your infant is getting the infants' pain formula and your older child is getting the children's pain formula.
Prescription Medications
Typical prescription pain relief medicines include opioids and non-opioid medications. Types of prescription opioid medications (Figures \(6\) and \(7\)) include:
• morphine, which is often used before and after surgical procedures to alleviate severe pain
• oxycodone, which is also often prescribed for moderate to severe pain
• codeine, which comes in combination with acetaminophen or other non-opioid pain relief medications and is often prescribed for mild to moderate pain
• hydrocodone, which comes in combination with acetaminophen or other non-opioid pain relief medications and is prescribed for moderate to moderately severe pain
Derived from opium, opioid drugs are very powerful products. They act by attaching to a specific "receptor" in the brain, spinal cord, and gastrointestinal tract. Opioids can change the way a person experiences pain. The term opium refers to the crude resinous extract obtained from the opium poppy. Crude opium contains a wide variety of ingredients, including morphine and codeine, both of which are widely used in medicine. The bulk of the ingredients of opium, however, consists of such organic substances as resins, oils, sugars, and proteins that account for more than 75 % of the weight of the opium but exert little pharmacological activity. Morphine is the major pain relieving drug found in opium, being approximately 10% of the crude exudate. Codeine is structurally close to morphine (see Figure \(6\)), although it is much less potent and amounts to only 0.5% of the opium extract. Heroin does not occur naturally but is a semisynthetic derivative produced by a chemical modification of morphine that increases the potency. It takes only 3 mg. of heroin to produce the same analgesic effect as 10 mg of morphine. However, at these equally effective doses, it may be difficult to distinguish between the effects of the two compounds.
Oxycodone and hydrocodone are used to relieve moderate to severe pain. Oxycodone and hydrocodone extended-release tablets and extended-release capsules are used to relieve severe pain in people who are expected to need pain medication around the clock for a long time and who cannot be treated with other medications.
Addiction and Overdose
Anyone who takes prescription opioids can become addicted to them. In fact, as many as one in four patients receiving long-term opioid therapy in a primary care setting struggles with opioid addiction. Once addicted, it can be hard to stop. In 2016, more than 11.5 million Americans reported misusing prescription opioids in the past year. Taking too many prescription opioids can stop a person’s breathing—leading to death.
Prescription opioid overdose deaths also often involve benzodiazepines. Benzodiazepines are central nervous system depressants used to sedate, induce sleep, prevent seizures, and relieve anxiety. Examples include alprazolam (Xanax®), diazepam (Valium®), and lorazepam (Ativan®). Avoid taking benzodiazepines while taking prescription opioids whenever possible.
Side Effects of Prescription Opioids
In addition to the serious risks of addiction, abuse, and overdose, the use of prescription opioids can have a number of side effects, even when taken as directed:
• Tolerance—meaning you might need to take more of the medication for the same pain relief
• Physical dependence—meaning you have symptoms of withdrawal when the medication is stopped
• Increased sensitivity to pain
• Constipation
• Nausea, vomiting, and dry mouth
• Sleepiness and dizziness
• Confusion
• Depression
• Low levels of testosterone that can result in lower sex drive, energy, and strength
• Itching and sweating
Opiate Antagonists
Naloxone, when administered to normal individuals, produces no analgesia, euphoria, or respiratory depression. However, it rapidly precipitates withdrawal in narcotic-dependent individuals. Naloxone antagonizes the actions of morphine at all its receptors.
The uses of naloxone include the reversal of the respiratory depression that follows acute narcotic intoxication and the reversal of narcotic-induced respiratory depression in newborns of mothers who have received narcotics. The use of naloxone is limited by a short duration of action and the necessity of parenteral route of administration.
Naltrexone became clinically available in 1985 as a new narcotic antagonist. Its actions resemble those of naloxone, but naltrexone is well is well absorbed orally and is long acting, necessitating only a dose of 50 to 100 mg. Therefore, it is useful in narcotic treatment programs where it is desired to maintain an individual on chronic therapy with a narcotic antagonist. In individuals taking naltrexone, subsequent injection of an opiate will produce little or no effect. naltrexone appears to be particularly effective for the treatment of narcotic dependence in addicts who have more to gain by being drug-free rather than drug dependant.
Combination Pain Relievers
Aspirin is often combined with acetaminophen in a single tablet for relief of arthritis and other painful conditions. Sometimes other drugs such as caffeine, an antihistamine, nasal drying agents, and sedatives are also added. Although some of these preparations may have special uses for certain acute conditions such as a cold or a headache, they should not be taken for a chronic (long-term) form of arthritis. If a combination is required, each drug should be prescribed separately. The dose of each should be adjusted individually to achieve the greatest benefit with the fewest side effects.
Hydrocodone is available in combination with other ingredients, and different combination products are prescribed for different uses. Some hydrocodone combination products are used to relieve moderate-to-severe pain. Other hydrocodone combination products are used to relieve cough. Hydrocodone is in a class of medications called opiate (narcotic) analgesics and in a class of medications called antitussives. Hydrocodone relieves pain by changing the way the brain and nervous system respond to pain. Hydrocodone relieves cough by decreasing activity in the part of the brain that causes coughing.
Web Link
A list of different hydrocodone combination products can be found on the link below.
https://medlineplus.gov/druginfo/meds/a601006.html
Summary
• Different types of medicine address different ailments. Anti-inflammatory drugs mediate inflammation, analgesics relieve pain, and antipyretic drugs help lower body temperature associated with fever.
• Over the counter (OTC) pain relievers relieve the minor aches and pains associated with conditions such as headaches, fever, colds, flu, arthritis, toothaches, and menstrual cramps.
• There are basically two types of OTC pain relievers: acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs).
• Aspirin and other aspirin-like drugs work by blocking the (COX-1 and COX-2) enzymes involved in pain and inflammation.
• Typical prescription pain relief medicines include opioids and non-opioid medications.
• In addition to the serious risks of addiction, abuse, and overdose, the use of prescription opioids can have a number of side effects, | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.01%3A_Pain_Relievers-_From_Aspirin_to_Oxycodone.txt |
Learning Objective
• Know the cause of the common cold and allergies.
• Know the chemical name, common name, and uses of different cough, cold, and allergy medicines.
The common cold is a viral infectious disease of the upper respiratory tract which affects primarily the nose. The symptoms of the common cold are believed to be primarily related to the immune response to the virus. Symptoms include coughing, sore throat, runny nose, and fever which usually resolve in seven to ten days, with some symptoms lasting up to three weeks. Well over 200 viruses are implicated in the cause of the common cold. The most commonly implicated virus is a rhinovirus (30–80%).
No cure for the common cold exists, but the symptoms can be treated. Antibiotics have no effect against viral infections and thus have no effect against the viruses that cause the common cold. Due to their side effects they cause overall harm; however, they are still frequently prescribed. It is the most frequent infectious disease in humans with the average adult contracting two to three colds a year and the average child contracting between six and twelve. These infections have been with humanity since antiquity.
Allergies are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.
Early exposure to potential allergens may be protective. Treatments for allergies include the avoidance of known allergens and the use of medications such as steroids and antihistamines. Histamine is concentrated in mast cells, cells whose function is essentially to release histamine and immunoglobins when tissue damage occurs. They are especially numerous in parts of the body that are injured often, such as the fingers and toes, or which enjoy frequent contact with the environment, such as the mucosa of the lips, nose, etc.
Types of Cold and Allergy Medications
Cold medicines are medications used by people with the common cold, cough, or related conditions. While a wide variety of drugs are marketed as cough suppressants, research shows there is often little or no measurable benefit in reducing cough symptoms. While they have been used by 10% of American children in any given week, they are not recommended in Canada or the United States in children six years or younger because of lack of evidence showing effect and concerns of harm. One version with codeine, guaifenesin, and pseudoephedrine was the 213th most commonly prescribed medication in 2017, in the United States, with more than two million prescriptions.
There are a number of different cough and cold medications, which may be used for various coughing symptoms. The commercially available products may include various combinations of any one or more of the following types of substances listed in the table below.
Table \(1\) Different Cough & Cold Medications.
Medication Function Examples
Mucokinetics, or mucolytics a class of drugs which aid in the clearance of mucus from the airways, lungs, bronchi, and trachea carbocisteine, ambroxol, and bromhexine.
Expectorants substances claimed to make coughing easier while enhancing the production of mucus and phlegm. acetylcysteine and guaifenesin.
Antitussives, or cough suppressants substances which suppress the coughing itself substances which suppress the coughing itself codeine, pholcodine, dextromethorphan, noscapine, and butamirate.
Antihistamines for allergic rhinitis may produce mild sedation and reduce other associated symptoms, like a runny nose and watery eyes diphenhydramine, chlorpheniramine, brompheniramine, loratadine, and cetirizine.
Decongestants relieve nasal congestion and sinus infection ephedrine, phenylephrine, pseudoephedrine, and oxymetazoline.
Fever or pain medication (antipyretic or analgesic) fever reducer or pain reliever paracetamol (called "acetaminophen " in the US) and NSAIDs such as aspirin, ibuprofen or naproxen
Syrups various substances supposed to soften the coughing honey or supplement syrup
Effectiveness
The efficacy of cough medication is questionable, particularly in children. A 2014 Cochrane review concluded that "There is no good evidence for or against the effectiveness of OTC medicines in acute cough". Some cough medicines may be no more effective than placebos for acute coughs in adults, including coughs related to upper respiratory tract infections. The American College of Chest Physicians emphasizes that cough medicines are not designed to treat whooping cough, a cough that is caused by bacteria and can last for months. No over-the-counter cough medicines have been found to be effective in cases of pneumonia. They are not recommended in those who have COPD, chronic bronchitis, or the common cold. There is not enough evidence to make recommendations for those who have a cough and cancer.
Medications
• Dextromethorphan (DXM) may be modestly effective in decreasing cough in adults with viral upper respiratory infections. However, in children it has not been found to be effective.
• Codeine was once viewed as the "gold standard" in cough suppressants, but this position is now questioned. Some recent placebo-controlled trials have found that it may be no better than a placebo for some causes including acute cough in children. It is thus not recommended for children. Additionally, there is no evidence that hydrocodone is useful in children. Similarly, a 2012 Dutch guideline does not recommend its use to treat acute cough.
• A number of other commercially available cough treatments have not been shown to be effective in viral upper respiratory infections. These include for adults: antihistamines, antihistamine-decongestant combinations, benzonatate, anti asthmatic-expectorant-mucolytic combinations, expectorant-bronchodilator combinations, leukotriene inhibitors, ambroxol, and guaifenesin, sometimes with analgesics, antipyretics, anti inflammatories, and anticholinergics - and for children: antihistamines, decongestants for clearing the nose, or combinations of these and leukotriene inhibitors for allergy and asthma. However, antihistamines cannot be used as an empirical therapy in case of chronic, or non specific cough especially in very young children. Long term diphenhydramine use is associated with negative outcomes in older people.
Antihistamines are drugs which treat hay fever and other allergies. Typically, people take antihistamines as an inexpensive, not patented (generic), drug that can be bought without a prescription and relieves from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use.
Although people typically use the word “antihistamine” to describe drugs for treating allergies, doctors and scientists use the term to describe a class of drug that opposes the activity of histamine receptors in the body. In this sense of the word, antihistamines are subclassified according to the histamine receptor that they act upon. The two largest classes of antihistamines are H1-antihistamines and H2-antihistamines.
H1-antihistamines work by binding to histamine H1 receptors in mast cells, smooth muscle, and endothelium in the body as well as in the tuberomammillary nucleus in the brain. Antihistamines that target the histamine H1-receptor are used to treat allergic reactions in the nose (e.g., itching, runny nose, and sneezing). In addition, they may be used to treat insomnia, motion sickness, or vertigo caused by problems with the inner ear. H2-antihistamines bind to histamine H2 receptors in the upper gastrointestinal tract, primarily in the stomach. Antihistamines that target the histamine H2-receptor are used to treat gastric acid conditions (e.g., peptic ulcers and acid reflux). Two common examples of antihistamines are shown below.
Alternative Medicine
Honey may be a minimally effective cough treatment. A Cochrane review found the evidence to recommend for or against its use in children to be weak. In light of this they found it was better than no treatment, placebo, and diphenhydramine but not better than dextromethorphan for relieving cough symptoms. Honey's use as a cough treatment has been linked on several occasions to infantile botulism and accordingly should not be used in children less than one year old.
Many alternative treatments are used to treat the common cold. A 2007 review states that, "alternative therapies (i.e., Echinacea, vitamin C, and zinc) are not recommended for treating common cold symptoms; however, ... Vitamin C prophylaxis may modestly reduce the duration and severity of the common cold in the general population and may reduce the incidence of the illness in persons exposed to physical and environmental stresses." A 2014 review also found insufficient evidence for Echinacea.
A 2009 review found that the evidence supporting the effectiveness of zinc is mixed with respect to cough, and a 2011 Cochrane review concluded that zinc "administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people". A 2003 review concluded: "Clinical trial data support the value of zinc in reducing the duration and severity of symptoms of the common cold when administered within 24 hours of the onset of common cold symptoms." Zinc gel in the nose may lead to long-term or permanent loss of smell. The FDA therefore discourages its use.
Adverse effects
A number of accidental overdoses and well-documented adverse effects suggested caution in children. The FDA in 2015 warned that the use of codeine-containing cough medication in children may cause breathing problems. Cold syrup overdose has been linked to visual and auditory hallucinations, rapid involuntary jaw, tongue and eye movements in children.
Summary
• The common cold (also known as nasopharyngitis, rhinopharyngitis, acute coryza, or a cold) is a viral infectious disease of the upper respiratory tract which affects primarily the nose. The symptoms of the common cold are believed to be primarily related to the immune response to the virus.
• An allergy is an immune response (with the release of histamines), or reaction, to substances (allergens) that are usually not harmful.
• A number of different cough and cold medications can be used to alleviate various symptoms but not diminish the intensity of the response. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.02%3A_Cold_and_Allergy_Medicines.txt |
Learning Objectives
• Differentiate between antibiotics and antiviral agents.
• Know the different antibiotics and antiviral agents and their mode of action.
The World Health Organization’s (WHO) International Classification of Diseases (ICD) is used in clinical fields to classify diseases and monitor morbidity (the number of cases of a disease) and mortality (the number of deaths due to a disease). In this section, we will introduce terminology used by the ICD (and in health-care professions in general) to describe and categorize various types of disease.
An infectious disease is any disease caused by the direct effect of a pathogen. A pathogen may be cellular (bacteria, parasites, and fungi) or acellular (viruses, viroids, and prions). Some infectious diseases are also communicable, meaning they are capable of being spread from person to person through either direct or indirect mechanisms. Some infectious communicable diseases are also considered contagious diseases, meaning they are easily spread from person to person. Not all contagious diseases are equally so; the degree to which a disease is contagious usually depends on how the pathogen is transmitted. For example, measles is a highly contagious viral disease that can be transmitted when an infected person coughs or sneezes and an uninfected person breathes in droplets containing the virus. Gonorrhea is not as contagious as measles because transmission of the pathogen (Neisseria gonorrhoeae) requires close intimate contact (usually sexual) between an infected person and an uninfected person.
Antibiotics
The modern era of the chemotherapy of infection started with the clinical use of sulfanilamide in 1936. The "golden age" of antimicrobial therapy began with the production of penicillin in 1941, when this compound was mass-produced and first made available for limited clinical trial. More than 30% of all hospitalized patients now receive one or more courses of therapy with antibiotics, and millions of potentially fatal infections have been cured. However, at the same time, these pharmaceutical agents have become among the most misused of those available to the practicing physician. One result of widespread use of antimicrobial agents has been the emergence of antibiotic-resistant pathogens, which in turn has created an ever-increasing need for new drugs. Many of these agents have also contributed significantly to the rising costs of medical care.
An antibiotic is any substance produced by a microorganism that is excreted to harm or kill another microorganism. Technically, antibiotics are microbial or fungal products. But these substances can be synthesized and mass produced in the laboratory to use against harmful microorganisms in the environment. Thus, the synthetic chemist has added greatly to our therapeutic armamentarium. Synthetic drugs such as isonaizid and theambutol represent important contributions for the treatment of tuberculosis. While many such antimicrobial agents are not properly termed antibiotics, since they are not produced by living organisms, little distinction should now be made between compounds of natural and synthetic origin.
Synthetic Antibiotics - Sulfonamides
Sulfonamide is the basis of several groups of drugs. The original antibacterial sulfonamides (sometimes called sulfa drugs or sulpha drugs) are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame. The sulfonylureas and thiazide diuretics are newer drug groups based on the antibacterial sulfonamides.
Sulfa allergies are common, and medications containing sulfonamides are prescribed carefully. It is important to make a distinction between sulfa drugs and other sulfur-containing drugs and additives, such as sulfates and sulfites, which are chemically unrelated to the sulfonamide group and do not cause the same hypersensitivity reactions seen in the sulfonamides.
Sulfonamides are structural analogs and competitive antagonists of para-aminobenzoic acid (PABA), and thus prevent normal bacterial utilization of PABA for the synthesis of the vitamin folic acid (Figure \(1\)). More specifically, sulfonamides are competitive inhibitors of the bacterial enzyme sulfihydropteroate synthase, which is responsible for the conversion of PABA into dihydrofolic acid, the immediate precursor of folic acid. Sensitive microorganisms are those that must synthesis their own folic acid; bacteria that can utilize preformed folic acid are not affected.
Cell Wall Synthesis Inhibitors - Penicillin and Cepalosphorins
The penicillins were the first antibiotics discovered as natural products from the mold Penicillium and was effective against Gram-positive bacteria. All penicillin derivatives produce their bacteriocidal effects by inhibition of bacterial cell wall synthesis. Specifically, the cross linking of peptides on the mucosaccharide chains is prevented. If cell walls are improperly made cell walls allow water to flow into the cell causing it to burst. A number of natural penicillins have been discovered, but only two purified compounds are in clinical use: penicillin G (intravenous use) and penicillin V (given by mouth). Several semisynthetic penicillins are effective against a broader spectrum of bacteria: these include the antistaphylococcal penicillins, aminopenicillins and the antipseudomonal penicillins.
Like penicillin, cephalosporins are valuable because of their low toxicity and their broad spectrum of action against various diseases. In this way, cephalosporin is very similar to penicillin. Cephalosporins are one of the most widely used antibiotics, and economically speaking, has about 29% of the antibiotic market. The cephalosporins are possibly the single most important group of antibiotics today and are equal in importance to penicillin. The structure and mode of action of the cephalosporins are similar to that of penicillin. They affect bacterial growth by inhibiting cell wall synthesis, in Gram-positive and -negative bacteria.
Figure \(3\) Cephalosporins.
Protein Synthesis Inhibitors - Erythromycin, Tetracycline, Streptomycin, and Chloramphenicol
Erythromycin is an orally effective antibiotic discovered in 1952 in the metabolic products of a strain of Streptocyces erythreus, originally obtained from a soil sample collected in the Philippine Archipelago. Erythromycin may be either bacteriostatic or bactericidal, depending on the microorganism and the concentration of the drug.
Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used during pregnancy to prevent Group B streptococcal infection in the newborn, as well as to improve delayed stomach emptying. It can be given intravenously and by mouth. An eye ointment is routinely recommended after delivery to prevent eye infections in the newborn.
Erythromycin and other macrolide antibiotics inhibit protein synthesis by binding to 50 S ribosomal subunits of sensitive microorganisms. (Humans do not have 50 S ribosomal subunits, but have ribosomes composed of 40 S and 60 S subunits). Certain resistant microorganisms with mutational changes in components of this subunit of the ribosome fail to bind the drug.
Tetracyclines have the broadest spectrum of antimicrobial activity. These may include: Aureomycin, Terramycin, and Panmycin. Four fused 6-membered rings, as shown in the figure below, form the basic structure from which the various tetracyclines are made. The various derivatives are different at one or more of four sites on the rigid, planar ring structure. The classical tetracyclines were derived from Streptomyces spp., but the newer derivatives are semisynthetic as is generally true for newer members of other drug groups.
Tetracyclines inhibit bacterial protein synthesis by blocking the attachment of the transfer RNA-amino acid to the ribosome. More precisely they are inhibitors of the codon-anticodon interaction. Tetracyclines can also inhibit protein synthesis in the host, but are less likely to reach the concentration required because eukaryotic cells do not have a tetracycline uptake mechanism.
Streptomycin
Streptomycin is effective against gram-negative bacteria, although it is also used in the treatment of tuberculosis. Streptomycin binds to the 30S ribosome and changes its shape so that it and inhibits protein synthesis by causing a misreading of messenger RNA information.
Chloramphenicol
Chloromycetin is also a broad spectrum antibiotic that possesses activity similar to the tetracylines. At present, it is the only antibiotic prepared synthetically. It is reserved for treatment of serious infections because it is potentially highly toxic to bone marrow cells. It inhibits protein synthesis by attaching to the ribosome and interferes with the formation of peptide bonds between amino acids. It behaves as an antimetabolite for the essential amino acid phenylalanine at ribosomal binding sites.
Figure \(6\) Inhibition of protein synthesis by erythtomycin, teracycline, streptomycin, and chloramphenicol.
A summary of the key features of different antibiotics is given in Table \(1\).
Table \(1\) Some Clinically Important Antibiotics.
Antibiotic Producer organism Activity Site or mode of action
Penicillin Penicillium chrysogenum Gram-positive bacteria Wall synthesis
Cephalosporin Cephalosporium acremonium Broad spectrum Wall synthesis
Griseofulvin Penicillium griseofulvum Dermatophytic fungi Microtubules
Bacitracin Bacillus subtilis Gram-positive bacteria Wall synthesis
Polymyxin B Bacillus polymyxa Gram-negative bacteria Cell membrane
Amphotericin B Streptomyces nodosus Fungi Cell membrane
Erythromycin Streptomyces erythreus Gram-positive bacteria Protein synthesis
Neomycin Streptomyces fradiae Broad spectrum Protein synthesis
Streptomycin Streptomyces griseus Gram-negative bacteria Protein synthesis
Tetracycline Streptomyces rimosus Broad spectrum Protein synthesis
Vancomycin Streptomyces orientalis Gram-positive bacteria Protein synthesis
Gentamicin Micromonospora purpurea Broad spectrum Protein synthesis
Rifamycin Streptomyces mediterranei Tuberculosis Protein synthesis
History of Penicillin and General Information
Alexander Fleming loved to play, both in the laboratory and out. He always loved snooker and golf and had many whimsical variants on the rules. In the lab he made "germ paintings," in which he would draw with his culture loop using spores of highly pigmented bacteria, which were invisible when he made the painting, but when cultured developed into brightly colored scenes. He followed what Max Delbruck would later call the "principle of limited sloppiness." Fleming abhorred a tidy, meticulous lab; he left culture dishes lying around for weeks and would often discover interesting things in them. Though the story has been told in many sometimes conflicting ways, something like this resulted in the discovery of penicillin. He seems to have left a culture dish lying on the lab bench and then gone away on vacation. When he returned a few spores of an unusual mold had germinated on the plate. When he cultured the bacteria on the plate he found that they grew up to within a few centimeters of the mold, but there were killed. A crude extract of the mold was then shown to have antibacterial properties. Fleming made this discovery in 1928 and by 1929 had named it penicillin (he was told by a colleague that the mold was a type of Penicillium and "penicillozyme" must have seemed cumbersome).
Fleming continued to use penicillin in his lab but not with any great enthusiasm and certainly not to the exclusion of many other projects. He never developed it into a clinically useful compound, though in 1929 he suggested that it might have important clinical applications. Because he was a bacteriologist and not a chemist, Fleming did not attempt to purify penicillin. He seems to have run into a dead end with penicillin and so during the 1930s, though he kept it in his lab, he did not do much with it. In the late 1930s Australian Howard Florey came to London to work with Charles Sherrington. He worked on lysozyme for a while and then became interested in penicillin. It was Florey, with Chain and other of his group that developed penicillin into a clinical antibiotic. They did this during 1940-41. Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology for Medicine.
Fleming became world-famous for penicillin, and was rightly acknowledged as the father of modern antibiotics, but Florey was just as rightly miffed at being denied much of the credit for creating the powerful medical tool we now know. Evidence does not suggest that Fleming deliberately denied Florey his due credit, but Fleming's peculiar, dry sense of humor seems to have caused him not to deny even the wildest attributions to him.
Viruses and Antiviral Drugs
Viruses cause a variety of diseases in animals, including humans, ranging from the common cold to potentially fatal illnesses like meningitis (FIgure \(1\)). These diseases can be treated by antiviral drugs or by vaccines, but some viruses, such as HIV, are capable of both avoiding the immune response and mutating to become resistant to antiviral drugs.
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit its development.
Antiviral drugs are one class of antimicrobials, a larger group which also includes antibiotic (also termed antibacterial), antifungal and antiparasitic drugs, or antiviral drugs based on monoclonal antibodies. Most antivirals are considered relatively to the host, and therefore can be used to treat infections. They should be distinguished from viricides, which are not medication but deactivate or destroy virus particles, either inside or outside the body. Natural viricides are produced by some plants such as eucalyptus and Australian tea trees.
DNA Viruses and RNA Viruses
Viruses are visible only under an electron microscope. They come in a variety of shapes, ranging from spherical to rod shaped. The fact that they contain either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—but never both—allows them to be divided into two major classes: DNA viruses and RNA viruses (Figure \(1\)).
Most RNA viruses use their nucleic acids in much the same way as the DNA viruses, penetrating a host cell and inducing it to replicate the viral RNA and synthesize viral proteins. The new RNA strands and viral proteins are then assembled into new viruses. Some RNA viruses, however, called retroviruses (Figure \(2\)), synthesize DNA in the host cell, in a process that is the reverse of the DNA-to-RNA transcription that normally occurs in cells. The synthesis of DNA from an RNA template is catalyzed by the enzyme reverse transcriptase.
Anti-viral Drugs
Antiviral drugs often have limited success in curing viral disease, but in many cases, they have been used to control and reduce symptoms for a wide variety of viral diseases. For most viruses, these drugs can inhibit the virus by blocking the actions of one or more of its proteins. It is important that the targeted proteins be encoded by viral genes and that these molecules are not present in a healthy host cell. In this way, viral growth is inhibited without damaging the host. There are large numbers of antiviral drugs available to treat infections, some specific for a particular virus and others that can affect multiple viruses.
Antivirals have been developed to treat genital herpes (herpes simplex II) and influenza. For genital herpes, drugs such as acyclovir can reduce the number and duration of episodes of active viral disease, during which patients develop viral lesions in their skin cells. As the virus remains latent in nervous tissue of the body for life, this drug is not curative but can make the symptoms of the disease more manageable. For influenza, drugs like Tamiflu (oseltamivir) (Figure \(3\)) can reduce the duration of “flu” symptoms by 1 or 2 days, but the drug does not prevent symptoms entirely. Tamiflu works by inhibiting an enzyme (viral neuraminidase) that allows new virions to leave their infected cells. Thus, Tamiflu inhibits the spread of virus from infected to uninfected cells. Other antiviral drugs, such as Ribavirin, have been used to treat a variety of viral infections, although its mechanism of action against certain viruses remains unclear.
By far, the most successful use of antivirals has been in the treatment of the retrovirus HIV, which causes a disease that, if untreated, is usually fatal within 10–12 years after infection. Anti-HIV drugs have been able to control viral replication to the point that individuals receiving these drugs survive for a significantly longer time than the untreated.
Anti-HIV drugs inhibit viral replication at many different phases of the HIV replicative cycle (Figure \(4\)). Drugs have been developed that inhibit the fusion of the HIV viral envelope with the plasma membrane of the host cell (fusion inhibitors), the conversion of its RNA genome into double-stranded DNA (reverse transcriptase inhibitors), the integration of the viral DNA into the host genome (integrase inhibitors), and the processing of viral proteins (protease inhibitors).
In 1987, azidothymidine (AZT, also known as zidovudine or the brand name Retrovir) became the first drug approved for the treatment of AIDS. It works by binding to reverse transcriptase in place of deoxythymidine triphosphate, after which, because AZT does not have a 3′OH group, further replication is blocked. In the past 10 years, several other drugs have been approved that also act by inhibiting the viral reverse transcriptase.
Raltegravir (Isentress) is a newer anti-AIDS drug that was approved by the FDA in October 2007. This drug inhibits the integrase enzyme that is needed to integrate the HIV DNA into cellular DNA, an essential step in the production of more HIV particles.
A major problem in treating HIV infections is that the virus can become resistant to any of these drugs. One way to combat the problem has been to administer a “cocktail” of drugs, typically a combination of two reverse transcriptase inhibitors along with a protease inhibitor. These treatments can significantly reduce the amount of HIV in an infected person.
The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs in an attempt to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multiple drugs that act on different viral targets is known as highly active antiretroviral therapy (HAART). HAART decreases the patient's total burden of HIV, maintains function of the immune system, and prevents opportunistic infections that often lead to death. HAART also prevents the transmission of HIV between serodiscordant same sex and opposite sex partners so long as the HIV-positive partner maintains an undetectable viral load.
A more detailed list of antivirals other than HIV is given in Table \(1\).
Table \(1\) Antivirals Used for Viruses Other Than HIV
Antiviral Brand Name Use
amantadine Symmetrel used prophylactically against influenza A ) in high-risk individuals. It prevents influenza A viruses from the uncoating step necessary for viral replication.
rimantidine Flumadine used for treatment and prophylaxis of influenza A. It prevents influenza A viruses from the uncoating step necessary for viral replication.
zanamivir: Relenza used to limit the duration of influenza A and B infections. It is an inhibitor of the influenza virus surface enzyme called neuraminidase that is needed for release of newly formed influenza viruses from the infected cell.
oseltamivir Tamiflu used limit the duration of influenza infections. It is an inhibitor of the influenza virus surface enzyme called neuraminidase that is needed for release of newly formed influenza viruses from the infected cell.
acyclovir Zovirax used against herpes simplex viruses (HSV) to treat genital herpes, mucocutaneous herpes in the immunosuppressed, HSV encephalitis, neonatal herpes, and to reduce the rate of recurrences of genital herpes. It is also used against varicella zoster viruses (VZV) ) to treat shingles. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
trifluridine Viroptic used to treat eye infection (keratitis and conjunctivitis) caused by HSV. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
famciclovir Famvir used to treat HSV and VZV infections. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
valacyclovir Valtrex used to treat HSV and VZV infections. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
penciclovir Denavir used in treating HSV infections. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
gancyclovir Cytovene; Vitrasert used in treating severe cytomegalovirus (CMV) infections such as retinitis. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
valganciclovir Valcyte used in treating severe CMV infections such as retinitis). It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
foscarnet Foscavir used in treating severe CMV infections such as retinitis. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
cidofovir Vistide used in treating CMV retinitis. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
fomivirsen Vitravene used in treating CMV retinitis. Fomivirsen inhibits cytomegalovirus (CMV) replication through an antisense RNA (microRNA or miRNA mechanism. The nucleotide sequence of fomivirsen is complementary to a sequence in mRNA transcripts (Figure \(1\)) that encodes several proteins responsible for regulation of viral gene expression that are essential for production of infectious CMV. Binding of fomivirsen to the target mRNA results in inhibition of protein synthesis, subsequently inhibiting virus replication.
ribavirin Copegus; Rebetol; Virazole used in treating severe acute respiratory syndrome (SARS). In combination with other drugs it is used to treat hepatitis C virus (HCV). It chemically resembles a normal RNA nucleoside. Once inserted into the growing RNA chain it inhibits further viral RNA replication.
telaprevir Incivek for the treatment of chronic hepatitis C (hepatitis C virus or HCV genotype 1). It is a protease inhibitor that binds to the active site of an HCV-encoded protease and prevent it from cleaving the long polyprotein from polycistronic HCV genes into proteins essential to the structure and function of HCV.
boceprevir
Victrelis for the treatment of chronic hepatitis C (hepatitis C virus or HCV genotype 1) infection. It is used in combination with peginterferon alfa and ribavirin. Boceprevir is a protease inhibitor that binds to the active site of an HCV-encoded protease and prevent it from cleaving the long polyprotein from polycistronic HCV genes into proteins essential to the structure and function of HCV.
simeprevir Olysio use for the treatment of chronic hepatitis C (hepatitis C virus or HCV genotype 1) infection. Used in combination with peginterferon alfa and ribavirin. Simeprevir is a protease inhibitor that binds to the active site of an HCV-encoded protease and prevent it from cleaving the long polyprotein from polycistronic HCV genes into proteins essential to the structure and function of HCV.
sofosbuvir Sovaldi Use for the treatment of chronic hepatitis C infection. Used in combination with ribavirin for hepatitis C virus or HCV genotypes 2 and 4; used in combination with peginterferon alfa and ribavirin for HCV genotypes 1 and 4. The second indication is the first approval of an interferon-free regimen for the treatment of chronic HCV infection. Sofosbuvir is a nucleotide polymerase inhibitor that binds to the active site of an HCV-encoded RNA polymerase preventing the synthesis of the viral RNA genome.
lamivudine Epivir-HBV used in treating chronic hepatitis B. It chemically resembles a normal DNA nucleoside. Once inserted into the growing DNA chain it inhibits further viral DNA replication.
adefovir dipivoxil Hepsera used in treating hepatitis B.
Web Link
A list of FDA-approved Antiretroviral drugs (last updated on April 12, 2018) used in the treatment of HIV infection can be found on the website: www.fda.gov/patients/hiv-treatment/antiretroviral-drugs-used-treatment-hiv-infection
Basic Research and Drug Development
The general idea behind modern antiviral drug design is to identify viral proteins, or parts of proteins, that can be disabled. These "targets" should generally be as unlike any proteins or parts of proteins in humans as possible, to reduce the likelihood of side effects. The targets should also be common across many strains of a virus, or even among different species of virus in the same family, so a single drug will have broad effectiveness. For example, a researcher might target a critical enzyme synthesized by the virus, but not by the patient, that is common across strains, and see what can be done to interfere with its operation.
Once targets are identified, candidate drugs can be selected, either from drugs already known to have appropriate effects or by actually designing the candidate at the molecular level with a computer-aided design program.
The target proteins can be manufactured in the lab for testing with candidate treatments by inserting the gene that synthesizes the target protein into bacteria or other kinds of cells. The cells are then cultured for mass production of the protein, which can then be exposed to various treatment candidates and evaluated with "rapid screening" technologies.
Prevention of Viral Diseases with Vaccination
While we do have limited numbers of effective antiviral drugs, such as those used to treat HIV and influenza, the primary method of controlling viral disease is by vaccination, which is intended to prevent outbreaks by building immunity to a virus or virus family (Figure \(1\)). Vaccines may be prepared using live viruses, killed viruses, or molecular subunits of the virus. The killed viral vaccines and subunit viruses are both incapable of causing disease.
Live viral vaccines are designed in the laboratory to cause few symptoms in recipients while giving them protective immunity against future infections. Polio was one disease that represented a milestone in the use of vaccines. Mass immunization campaigns in the 1950s (killed vaccine) and 1960s (live vaccine) significantly reduced the incidence of the disease, which caused muscle paralysis in children and generated a great amount of fear in the general population when regional epidemics occurred. The success of the polio vaccine paved the way for the routine dispensation of childhood vaccines against measles, mumps, rubella, chickenpox, and other diseases.
The danger of using live vaccines, which are usually more effective than killed vaccines, is the low but significant danger that these viruses will revert to their disease-causing form by back mutations. Live vaccines are usually made by attenuating (weakening) the “wild-type” (disease-causing) virus by growing it in the laboratory in tissues or at temperatures different from what the virus is accustomed to in the host. Adaptations to these new cells or temperatures induce mutations in the genomes of the virus, allowing it to grow better in the laboratory while inhibiting its ability to cause disease when reintroduced into conditions found in the host. These attenuated viruses thus still cause infection, but they do not grow very well, allowing the immune response to develop in time to prevent major disease. Back mutations occur when the vaccine undergoes mutations in the host such that it readapts to the host and can again cause disease, which can then be spread to other humans in an epidemic. This type of scenario happened as recently as 2007 in Nigeria where mutations in a polio vaccine led to an epidemic of polio in that country.
Some vaccines are in continuous development because certain viruses, such as influenza and HIV, have a high mutation rate compared to other viruses and normal host cells. With influenza, mutations in the surface molecules of the virus help the organism evade the protective immunity that may have been obtained in a previous influenza season, making it necessary for individuals to get vaccinated every year. Other viruses, such as those that cause the childhood diseases measles, mumps, and rubella, mutate so infrequently that the same vaccine is used year after year.
Summary
• An infectious disease is any disease caused by the direct effect of a pathogen (bacteria, parasites, fungi, viruses, viroids, and prions).
• Diseases can either be noninfectious (due to genetics and environment) or infectious (due to pathogens). Some infectious diseases are communicable (transmissible between individuals) or contagious (easily transmissible between individuals); others are noncommunicable, but may be contracted via contact with environmental reservoirs or animal.
• An antibiotic is any substance produced by a microorganism that is excreted to harm or kill another microorganism. Technically, antibiotics are microbial or fungal products.
• Most antibiotics inhibit bacterial growth by inhibiting cell wall synthesis or protein synthesis.
• Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses.
• The management of HIV/AIDS normally includes the use of multiple in an attempt to control .
• The primary method of controlling viral disease is by vaccination, which is intended to prevent outbreaks by building immunity to a virus or virus family | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.03%3A_Drugs_and_Infectious_Diseases.txt |
Learning Objective
• List the different types of cancer drugs and their mechanism of action.
Chemotherapy is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents) as part of a standardized chemotherapy regimen. Chemotherapy may be given with a curative intent (which almost always involves combinations of drugs), or it may aim to prolong life or to reduce symptoms (palliative chemotherapy). Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.
When fighting cancer, the entire population of neoplastic cells must be eradicated in order to obtain desired results. The concept of "total cell-kill" applies to chemotherapy as it does to other means of treatment: total excision of the tumor is necessary for surgical care, and complete destruction of all cancer cells is required for a cure with radiation therapy.
The available anticancer drugs have distinct mechanisms of action which may vary in their effects on different types of normal and cancer cells. A single "cure" for cancer has proved elusive since there is not a single type of cancer but as many as 100 different types of cancer. In addition, there are very few demonstrable biochemical differences between cancerous cells and normal cells. For this reason the effectiveness of many anticancer drugs is limited by their toxicity to normal rapidly growing cells in the intestinal and bone marrow areas. A final problem is that cancerous cells which are initially suppressed by a specific drug may develop a resistance to that drug. For this reason cancer chemotherapy may consist of using several drugs in combination for varying lengths of time.
Introduction
Chemotherapy drugs, are sometimes feared because of a patient's concern about toxic effects. Their role is to slow and hopefully halt the growth and spread of a cancer. There are three goals associated with the use of the most commonly-used anticancer agents.
1. Damage the DNA of the affected cancer cells.
2. Inhibit the synthesis of new DNA strands to stop the cell from replicating, because the replication of the cell is what allows the tumor to grow.
3. Stop mitosis or the actual splitting of the original cell into two new cells. Stopping mitosis stops cell division (replication) of the cancer and may ultimately halt the progression of the cancer.
Unfortunately, the majority of drugs currently on the market are not specific, which leads to the many common side effects associated with cancer chemotherapy. Because the common approach of all chemotherapy is to decrease the growth rate (cell division) of the cancer cells, the side effects are seen in bodily systems that naturally have a rapid turnover of cells including skin, hair, gastrointestinal, and bone marrow. These healthy, normal cells, also end up damaged by the chemotherapy program.
Categories of Chemotherapy Drugs
In general, chemotherapy agents can be divided into three main categories based on their mechanism of action as shown in the table below.
Table \(1\) Chemotherapy Drugs and Their Mechanism of Action
Category Specific Mode of Action Examples
Stop the synthesis of pre DNA molecule building blocks
"Antimetabolites"
These agents work in a number of different ways. DNA building blocks are folic acid, heterocyclic bases, and nucleotides, which are made naturally within cells. All of these agents work to block some step in the formation of nucleotides or deoxyribonucleotides (necessary for making DNA). When these steps are blocked, the nucleotides, which arethe building blocks of DNA and RNA, can not be synthesized. Thus the cells can not replicate because they cannot make DNA without the nucleotides. 1) methotrexate (Abitrexate®),2) fluorouracil (Adrucil®), 3) hydroxyurea (Hydrea®), 4) mercaptopurine (Purinethol®) and 5) thioguanine.
Directly damage the DNA in the nucleus of the cell
"Alkylating agents, antibiotics, topoisomerase inhibitors and intercalating agents."
These agents chemically damage DNA and RNA. They disrupt replication of the DNA and either totally halt replication or cause the manufacture of nonsense DNA or RNA (i.e. the new DNA or RNA does not code for anything useful). 5) cisplatin (Platinol®) and 7) antibiotics - daunorubicin (Cerubidine®), doxorubicin (Adriamycin®), and etoposide (VePesid®).
Effect the synthesis or breakdown of the mitotic spindles
"Mitotic disrupters"
Mitotic spindles serve as molecular railroads with "North and South Poles" in the cell when a cell starts to divide itself into two new cells. These spindles are very important because they help to split the newly copied DNA such that a copy goes to each of the two new cells during cell division. These drugs disrupt the formation of these spindles and therefore interrupt cell division. 8) mitotic disrupters include: Vinblastine (Velban®), Vincristine (Oncovin®) and Pacitaxel (Taxol®).
Antimetabolites
Methotrexate
Methotrexate inhibits folic acid reductase which is responsible for the conversion of folic acid to tetrahydrofolic acid. At two stages in the biosynthesis of purines(adenine and guanine) and at one stage in the synthesis of pyrimidines (thymine, cytosine, and uracil), one-carbon transfer reactions occur which require specific coenzymes synthesized in the cell from tetrahydrofolic acid.
Tetrahydrofolic acid itself is synthesized in the cell from folic acid with the help of an enzyme, folic acid reductase. Methotrexate looks a lot like folic acid to the enzyme, so it binds to it thinking that it is folic acid. In fact, methotrexate looks so good to the enzyme that it binds to it quite strongly and inhibits the enzyme. Thus, DNA synthesis cannot proceed because the coenzymes needed for one-carbon transfer reactions are not produced from tetrahydrofolic acid because there is no tetrahydrofolic acid. Again, without DNA, no cell division.
5-Fluorouracil
5-Fluorouracil (5-FU; Adrucil®, Fluorouracil, Efudex®, Fluoroplex®) is an effective pyrimidine antimetabolite. Fluorouracil is synthesized into the nucleotide, 5-fluoro-2-deoxyuridine. This product acts as an antimetabolite by inhibiting the synthesis of 2-deoxythymidine because the carbon - fluorine bond is extremely stable and prevents the addition of a methyl group in the 5-position. The failure to synthesize the thymidine nucleotide results in little or no production of DNA. Two other similar drugs include: gemcitabine (Gemzar®) and arabinosylcytosine (araC). They all work through similar mechanisms.
Hydroxyurea
Hydroxyurea blocks an enzyme which converts the cytosine nucleotide into the deoxy derivative. In addition, DNA synthesis is further inhibited because hydroxyurea blocks the incorporation of the thymidine nucleotide into the DNA strand.
Mercaptopurine
Mercaptopurine, a chemical analog of the purine adenine, inhibits the biosynthesis of adenine nucleotides by acting as an antimetabolite. In the body, 6-MP is converted to the corresponding ribonucleotide. 6-MP ribonucleotide is a potent inhibitor of the conversion of a compound called inosinic acid to adenine Without adenine, DNA cannot be synthesized. 6-MP also works by being incorporated into nucleic acids as thioguanosine, rendering the resulting nucleic acids (DNA, RNA) unable to direct proper protein synthesis.
Thioguanine
Thioguanine is an antimetabolite in the synthesis of guanine nucleotides.
Alkylating Agents, Topoisomerase Inhibitors, Antibiotics, and Intercalating agents
Alkylating Agents
Alkylating agents involve reactions with guanine in DNA. These drugs add methyl or other alkyl groups onto molecules where they do not belong. This in turn inhibits their correct utilization by base pairing and causes a miscoding of DNA.
There are six groups of alkylating agents: nitrogen mustards; ethylenimes; alkylsulfonates; triazenes; piperazines; and nitrosureas. Cyclosporamide is a classical example of the role of the host metabolism in the activation of an alkylating agent and is one or the most widely used agents of this class. It was hoped that the cancer cells might posses enzymes capable of accomplishing the cleavage, thus resulting in the selective production of an ated nitrogen mustard in the malignant cells. Compare the top and bottom structures in the graphic on the left.
Topoisomerase Inhibitors
Topoisomerase inhibitors are drugs that affect the activity of two enzymes: topoisomerase I and topoisomerase II. Inhibition of topoisomerase I or II interferes with both replication and transcription.
Two topoisomerase I inhibitors, irinotecan and topotecan, are semi-synthetically derived from camptothecin, which is obtained from the Chinese ornamental tree Camptotheca acuminata. Drugs that target topoisomerase II can be divided into two groups. The topoisomerase II inhibitors include etoposide, doxorubicin, mitoxantrone , teniposide, novobiocin, merbarone, and aclarubicin.
Antibiotics
A number of antibiotics such as anthracyclines, dactinomycin, bleomycin, adriamycin, mithramycin, bind to DNA and inactivate it. Thus the synthesis of RNA is prevented. General properties of these drugs include: interaction with DNA in a variety of different ways including intercalation (squeezing between the base pairs), DNA strand breakage and inhibition with the enzyme topoisomerase II. Most of these compounds have been isolated from natural sources and antibiotics. However, they lack the specificity of the antimicrobial antibiotics and thus produce significant toxicity.
The anthracyclines are among the most important antitumor drugs available. Doxorubicin is widely used for the treatment of several solid tumors while daunorubicin and idarubicin are used exclusively for the treatment of leukemia. These agents have a number of important effects including: intercalating (squeezing between the base pairs) with DNA affecting many functions of the DNA including DNA and RNA synthesis. Breakage of the DNA strand can also occur by inhibition of the enzyme topoisomerase II.
Dactinomycin (Actinomycin D)
At low concentrations dactinomycin inhibits DNA directed RNA synthesis and at higher concentrations DNA synthesis is also inhibited. All types of RNA are affected, but ribosomal RNA is more sensitive. Dactinomycin binds to double stranded DNA , permitting RNA chain initiation but blocking chain elongation. Binding to the DNA depends on the presence of guanine.
Intercalating Agents
Intercalating agents wedge between bases along the DNA. The intercalated drug molecules affect the structure of the DNA, preventing polymerase and other DNA binding proteins from functioning properly. The result is prevention of DNA synthesis, inhibition of transcription and induction of mutations. Examples include: Carboplatin and Cisplatin.
Mitotic Disrupters
Mitotic Disrupters
Plant alkaloids like vincristine prevent cell division, or mitosis. There are several phases of mitosis, one of which is the metaphase. During metaphase, the cell pulls duplicated DNA chromosomes to either side of the parent cell in structures called "spindles". These spindles ensure that each new cell gets a full set of DNA. Spindles are microtubular fibers formed with the help of the protein "tubulin". Vincristine binds to tubulin, thus preventing the formation of spindles and cell division.
Taxol
Paclitaxel (taxol) was first isolated from the from the bark of the Pacific Yew (Taxus brevifolia). Docetaxel is a more potent analog that is produced semisynthetically. In contrast to other microtubule antagonists, taxol disrupts the equilibrium between free tubulin and mircrotubules by shifting it in the direction of assembly, rather than disassembly. As a result, taxol treatment causes both the stabilization of microtubules and the formation of abnormal bundles of microtubules. The net effect is still the disruption of mitosis.
Combination Chemotherapy
In 1965, a major breakthrough in cancer therapy occurred. James F. Holland, Emil Freireich, and Emil Frei hypothesized that cancer chemotherapy should follow the strategy of antibiotic therapy for tuberculosis with combinations of drugs, each with a different mechanism of action. Cancer cells could conceivably mutate to become resistant to a single agent, but by using different drugs concurrently it would be more difficult for the tumor to develop resistance to the combination. Holland, Freireich, and Frei simultaneously administered methotrexate (an antifolate), vincristine (a Vinca alkaloid), 6-mercaptopurine (6-MP) and prednisone — together referred to as the POMP regimen — and induced long-term remissions in children with acute lymphoblastic leukaemia (ALL). With incremental refinements of original regimens, using randomized clinical studies by St. Jude Children's Research Hospital, the Medical Research Council in the UK (UKALL protocols) and German Berlin-Frankfurt-Münster clinical trials group (ALL-BFM protocols), ALL in children has become a largely curable disease.
This approach was extended to the lymphomas in 1963 by Vincent T. DeVita and George Canellos at the NCI, who ultimately proved in the late 1960s that nitrogen mustard, vincristine, procarbazine and prednisone — known as the MOPP regimen — could cure patients with Hodgkin's and non-Hodgkin's lymphoma.
Currently, nearly all successful cancer chemotherapy regimens use this paradigm of multiple drugs given simultaneously, called combination chemotherapy or polychemotherapy.
Table \(2\) The Common Combination Chemotherapy Regimens
Cancer type Drugs Acronym
Breast cancer Cyclophosphamide, methotrexate, 5-fluorouracil, vinorelbine CMF
Doxorubicin, cyclophosphamide AC
Hodgkin's lymphoma Docetaxel, doxorubicin, cyclophosphamide TAC
Doxorubicin, bleomycin, vinblastine, dacarbazine ABVD
Mustine, vincristine, procarbazine, prednisolone MOPP
Non-Hodgkin's lymphoma Cyclophosphamide, doxorubicin, vincristine, prednisolone CHOP
Germ cell tumor Bleomycin, etoposide, cisplatin BEP
Stomach cancer Epirubicin, cisplatin, 5-fluorouracil ECF
Epirubicin, cisplatin, capecitabine ECX
Bladder cancer Methotrexate, vincristine, doxorubicin, cisplatin MVAC
Lung cancer Cyclophosphamide, doxorubicin, vincristine, vinorelbine CAV
Colorectal cancer 5-fluorouracil, folinic acid, oxaliplatin FOLFOX
Summary
• Chemotherapy is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents) as part of a standardized chemotherapy regimen.
• Chemo drugs can be classified into three main categories based on their mechanism of action namely:
• Stop the synthesis of pre-DNA molecule building blocks
• Directly damage the DNA in the nucleus of the cell
• Effect the synthesis or breakdown of the mitotic spindles.
• Currently, nearly all successful cancer chemotherapy regimens use this paradigm of multiple drugs given simultaneously, called combination chemotherapy or polychemotherapy. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.04%3A_Chemicals_Against_Cancer.txt |
Learning Objectives
• Identify the major classes of hormones on the basis of chemical structure.
• Know the function of the common hormones.
Glands of the Endocrine System
The endocrine system is a system of glands called endocrine glands that release chemical messenger molecules into the bloodstream. The messenger molecules of the endocrine system are called endocrine hormones. The major glands of the endocrine system are shown in Figure \(1\). The major hormones of the human body and their effects are listed in Table \(1\).
Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. Once the hormone binds to the receptor, a chain of events is initiated that leads to the target cell’s response. Hormones play a critical role in the regulation of physiological processes because of the target cell responses they regulate. These responses contribute to human reproduction, growth and development of body tissues, metabolism, fluid, and electrolyte balance, sleep, and many other body functions. The major hormones of the human body and their effects are identified in Table \(1\).
Table \(1\) The Endocrine Glands and Their Major Hormones.
Endocrine gland Associated hormones Chemical class Effect
Pituitary Growth hormone (GH) Protein Promotes growth of body tissues
Prolactin (PRL) Peptide Promotes milk production
Thyroid-stimulating hormone (TSH) Glycoprotein Stimulates thyroid hormone release
Adrenocorticotropic hormone (ACTH) Peptide Stimulates hormone release by adrenal cortex
Follicle-stimulating hormone (FSH) Glycoprotein Stimulates gamete production
Luteinizing hormone (LH) Glycoprotein Stimulates androgen production by gonads
Antidiuretic hormone (ADH) Peptide Stimulates water reabsorption by kidneys
Oxytocin Peptide Stimulates uterine contractions during childbirth
Thyroid Thyroxine (T4), triiodothyronine (T3) Amine Stimulate basal metabolic rate
Calcitonin Peptide Reduces blood Ca2+ levels
Parathyroid Parathyroid hormone (PTH) Peptide Increases blood Ca2+ levels
Adrenal (cortex) Aldosterone Steroid Increases blood Na+ levels
Cortisol, corticosterone, cortisone Steroid Increase blood glucose levels
Adrenal (medulla) Epinephrine, norepinephrine Amine Stimulate fight-or-flight response
Pineal Melatonin Amine Regulates sleep cycles
Pancreas Insulin Protein Reduces blood glucose levels
Glucagon Protein Increases blood glucose levels
Testes Testosterone Steroid Stimulates development of male secondary sex characteristics and sperm production
Ovaries Estrogens and progesterone Steroid Stimulate development of female secondary sex characteristics and prepare the body for childbirth
Types of Hormones
The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids (Figure \(1\)). These chemical groups affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its function.
Amine Hormones
Hormones derived from the modification of amino acids are referred to as amine hormones. Typically, the original structure of the amino acid is modified such that a –COOH, or carboxyl, group is removed, whereas the −NH3+−NH3+, or amine, group remains.
Amine hormones are synthesized from the amino acids tryptophan or tyrosine. An example of a hormone derived from tryptophan is melatonin, which is secreted by the pineal gland and helps regulate circadian rhythm. Tyrosine derivatives include the metabolism-regulating thyroid hormones, as well as the catecholamines, such as epinephrine, norepinephrine, and dopamine. Epinephrine and norepinephrine are secreted by the adrenal medulla and play a role in the fight-or-flight response, whereas dopamine is secreted by the hypothalamus and inhibits the release of certain anterior pituitary hormones.
Peptide and Protein Hormones
Whereas the amine hormones are derived from a single amino acid, peptide and protein hormones consist of multiple amino acids that link to form an amino acid chain. Peptide hormones consist of short chains of amino acids, whereas protein hormones are longer polypeptides. Both types are synthesized like other body proteins: DNA is transcribed into mRNA, which is translated into an amino acid chain.
Examples of peptide hormones include antidiuretic hormone (ADH), a pituitary hormone important in fluid balance, and atrial-natriuretic peptide, which is produced by the heart and helps to decrease blood pressure. Some examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH), which has an attached carbohydrate group and is thus classified as a glycoprotein. FSH helps stimulate the maturation of eggs in the ovaries and sperm in the testes.
Steroid Hormones
Hormones are chemical messengers that are released in one tissue and transported through the circulatory system to one or more other tissues. One group of hormones is known as steroid hormones because these hormones are synthesized from cholesterol, which is also a steroid. There are two main groups of steroid hormones: adrenocortical hormones and sex hormones.
Adrenocortical hormones
The adrenocortical hormones, such as aldosterone and cortisol (Table \(1\)), are produced by the adrenal gland, which is located adjacent to each kidney. Aldosterone acts on most cells in the body, but it is particularly effective at enhancing the rate of reabsorption of sodium ions in the kidney tubules and increasing the secretion of potassium ions and/or hydrogen ions by the tubules. Because the concentration of sodium ions is the major factor influencing water retention in tissues, aldosterone promotes water retention and reduces urine output. Cortisol regulates several key metabolic reactions (for example, increasing glucose production and mobilizing fatty acids and amino acids). It also inhibits the inflammatory response of tissue to injury or stress. Cortisol and its analogs are therefore used pharmacologically as immunosuppressants after transplant operations and in the treatment of severe skin allergies and autoimmune diseases, such as rheumatoid arthritis.
Table \(2\) Representative Steroid Hormones and Their Physiological Effects
Hormone Effect
regulates salt metabolism; stimulates kidneys to retain sodium and excrete potassium
stimulates the conversion of proteins to carbohydrates
regulates the menstrual cycle; maintains pregnancy
stimulates female sex characteristics; regulates changes during the menstrual cycle
stimulates and maintains male sex characteristics
Sex Hormones
The sex hormones are a class of steroid hormones secreted by the gonads (ovaries or testes), the placenta, and the adrenal glands. Testosterone and androstenedione are the primary male sex hormones, or androgens, controlling the primary sexual characteristics of males, or the development of the male genital organs and the continuous production of sperm. Androgens are also responsible for the development of secondary male characteristics, such as facial hair, deep voice, and muscle strength. Two kinds of sex hormones are of particular importance in females: progesterone, which prepares the uterus for pregnancy and prevents the further release of eggs from the ovaries during pregnancy, and the estrogens, which are mainly responsible for the development of female secondary sexual characteristics, such as breast development and increased deposition of fat tissue in the breasts, the buttocks, and the thighs. Both males and females produce androgens and estrogens, differing in the amounts of secreted hormones rather than in the presence or absence of one or the other.
Sex hormones, both natural and synthetic, are sometimes used therapeutically. For example, a woman who has had her ovaries removed may be given female hormones to compensate. Some of the earliest chemical compounds employed in cancer chemotherapy were sex hormones. For example, estrogens are one treatment option for prostate cancer because they block the release and activity of testosterone. Testosterone enhances prostate cancer growth. Sex hormones are also administered in preparation for sex-change operations, to promote the development of the proper secondary sexual characteristics. Oral contraceptives are synthetic derivatives of the female sex hormones; they work by preventing ovulation.
Chemistry and Social Revolution: The Pill
Hormonal contraception methods prevent pregnancy by interfering with ovulation, fertilization, and/or implantation of the fertilized egg.
Oral contraceptives—combined pill (“The pill”)
The pill contains the hormones estrogen and progestin. It is taken daily to keep the ovaries from releasing an egg. The pill also causes changes in the lining of the uterus and the cervical mucus to keep the sperm from joining the egg.
Some women prefer the “extended cycle” pills. These have 12 weeks of pills that contain hormones (active) and 1 week of pills that don’t contain hormones (inactive). While taking extended cycle pills, women only have their period three to four times a year.
Many types of oral contraceptives are available. Talk with your doctor about which is best for you.
Your doctor may advise you not to take the pill if you:
• Are older than 35 and smoke
• Have a history of blood clots
• Have a history of breast, liver, or endometrial cancer
Antibiotics may reduce how well the pill works in some women. Talk to your doctor about a backup method of birth control if you need to take antibiotics.
Women should wait three weeks after giving birth to begin using birth control that contains both estrogen and progestin. These methods increase the risk of dangerous blood clots that could form after giving birth. Women who delivered by cesarean section or have other risk factors for blood clots, such as obesity, history of blood clots, smoking, or preeclampsia, should wait six weeks.
The patch
Also called by its brand name, Ortho Evra, this skin patch is worn on the lower abdomen, buttocks, outer arm, or upper body. It releases the hormones progestin and estrogen into the bloodstream to stop the ovaries from releasing eggs in most women. It also thickens the cervical mucus, which keeps the sperm from joining with the egg. You put on a new patch once a week for 3 weeks. You don’t use a patch the fourth week in order to have a period.
Women should wait three weeks after giving birth to begin using birth control that contains both estrogen and progestin. These methods increase the risk of dangerous blood clots that could form after giving birth. Women who delivered by cesarean section or have other risk factors for blood clots, such as obesity, history of blood clots, smoking, or preeclampsia, should wait six weeks.
Shot/injection
The birth control shot often is called by its brand name Depo-Provera. With this method you get injections, or shots, of the hormone progestin in the buttocks or arm every 3 months. A new type is injected under the skin. The birth control shot stops the ovaries from releasing an egg in most women. It also causes changes in the cervix that keep the sperm from joining with the egg.
Vaginal ring
This is a thin, flexible ring that releases the hormones progestin and estrogen. It works by stopping the ovaries from releasing eggs. It also thickens the cervical mucus, which keeps the sperm from joining the egg.
It is commonly called NuvaRing, its brand name. You squeeze the ring between your thumb and index finger and insert it into your vagina. You wear the ring for 3 weeks, take it out for the week that you have your period, and then put in a new ring.
Women should wait three weeks after giving birth to begin using birth control that contains both estrogen and progestin. These methods increase the risk of dangerous blood clots that could form after giving birth. Women who delivered by cesarean section or have other risk factors for blood clots, such as obesity, history of blood clots, smoking, or preeclampsia, should wait six weeks.
Implantable devices
These devices are inserted into the body and left in place for a few years.
Implantable rod
This is a matchstick-size, flexible rod that is put under the skin of the upper arm. It is often called by its brand name, Implanon. The rod releases a progestin, which causes changes in the lining of the uterus and the cervical mucus to keep the sperm from joining an egg. Less often, it stops the ovaries from releasing eggs. It is effective for up to 3 years.
Intrauterine devices or IUDs
• Hormonal IUD The hormonal IUD goes by the brand name Mirena. It is sometimes called an intrauterine system, or IUS. It releases progestin into the uterus, which keeps the ovaries from releasing an egg and causes the cervical mucus to thicken so sperm can’t reach the egg. It also affects the ability of a fertilized egg to successfully implant in the uterus. A doctor needs to put in a hormonal IUD. It can stay in your uterus for up to 5 years.
Emergency Contraceptives
Emergency contraceptives are used if a woman’s primary method of birth control fails. It should not be used as a regular method of birth control. The emergency contraceptive, Plan B One-Step or Next Step is also called the “morning after pill.”
Emergency contraception keeps a woman from getting pregnant when she has had unprotected vaginal intercourse. “Unprotected” can mean that no method of birth control was used. It can also mean that a birth control method was used but it was used incorrectly, or did not work (like a condom breaking). Or, a woman may have forgotten to take her birth control pills. She also may have been abused or forced to have sex. These are just some of the reasons women may need emergency contraception.
Emergency contraception can be taken as a single pill treatment or in two doses. A single dose treatment works as well as two doses and does not have more side effects. It works by stopping the ovaries from releasing an egg or keeping the sperm from joining with the egg. For the best chances for it to work, take the pill as soon as possible after unprotected sex. It should be taken within 72 hours after having unprotected sex.
A single-pill dose or two-pill dose of emergency contraception is available over-the-counter (OTC) for women ages 17 and older.
Summary
• A hormone is any member of a class of signaling molecules, produced by glands in multicellular organisms to regulate physiology and behavior.
• The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids.
• The two main groups of steroid hormones: adrenocortical hormones and sex hormones.
• Hormonal contraception methods prevent pregnancy by interfering with ovulation, fertilization, and/or implantation of the fertilized egg.
• Emergency contraceptives are used if a woman’s primary method of birth control fails.
Contributors
• Libretext: Anatomy and Physiology (OpenStax)
• Libretext: Human Biology (Wakim and Grewal)
• Libretexts: Survey of Chemistry (Cannon)
• Libretexts: The Basics of GOB Chemistry (Ball et.al.)
• Libretexts: Contemporary Health Issues (Lumen)
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.05%3A_Hormones_-_The_Regulators.txt |
Learning Objectives
• Define cardiovascular disease
• Identify the types of cardiovascular disease
• Identify risk factors that predispose for heart disease and stroke
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, heart failure, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, abnormal heart rhythms, congenital heart disease, valvular heart disease, carditis, aortic aneurysms, peripheral artery disease, thromboembolic disease, and venous thrombosis.
The underlying mechanisms vary depending on the disease. Coronary artery disease, stroke, and peripheral artery disease involve atherosclerosis. This may be caused by high blood pressure, smoking, diabetes mellitus, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol consumption, among others. High blood pressure is estimated to account for approximately 13% of CVD deaths, while tobacco accounts for 9%, diabetes 6%, lack of exercise 6% and obesity 5%. Rheumatic heart disease may follow untreated strep throat.
Lowering Blood Pressure
Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure typically does not cause symptoms. Long-term high blood pressure, however, is a major risk factor for coronary artery disease, stroke, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia.
Several classes of medications, collectively referred to as antihypertensive medications, are available for treating hypertension. First-line medications for hypertension include thiazide-diuretics, calcium channel blockers, angiotensin converting enzyme inhibitors (ACE inhibitors), and angiotensin receptor blockers (ARBs). These medications may be used alone or in combination (ACE inhibitors and ARBs are not recommended for use in combination); the latter option may serve to minimize counter-regulatory mechanisms that act to restore blood pressure values to pre-treatment levels. Most people require more than one medication to control their hypertension. Medications for blood pressure control should be implemented by a stepped care approach when target levels are not reached.
Normalizing Heart Rhythm
Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the heartbeat is irregular, too fast, or too slow. The heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath or chest pain. While most types of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.
There are four main groups of arrhythmia: extra beats, supraventricular tachycardias, ventricular arrhythmias and bradyarrhythmias. Extra beats include premature atrial contractions, premature ventricular contractions and premature junctional contractions. Supraventricular tachycardias include atrial fibrillation, atrial flutter and paroxysmal supraventricular tachycardia. Ventricular arrhythmias include ventricular fibrillation and ventricular tachycardia. Arrhythmias are due to problems with the electrical conduction system of the heart. Arrhythmias may also occur in children; however, the normal range for the heart rate is different and depends on age. A number of tests can help with diagnosis, including an electrocardiogram (ECG) and Holter monitor.
Most arrhythmias can be effectively treated. Treatments may include medications, medical procedures such as inserting a pacemaker, and surgery. Medications for a fast heart rate may include beta blockers, or antiarrhythmic agents such as procainamide, which attempt to restore a normal heart rhythm. This latter group may have more significant side effects, especially if taken for a long period of time. Pacemakers are often used for slow heart rates. Those with an irregular heartbeat are often treated with blood thinners to reduce the risk of complications. Those who have severe symptoms from an arrhythmia may receive urgent treatment with a controlled electric shock in the form of cardioversion or defibrillation.
Treating Coronary Artery Disease
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of plaque (atherosclerosis) in the arteries of the heart (Figure \(1\)). It is the most common of the cardiovascular diseases. Types include stable angina, unstable angina, myocardial infarction, and sudden cardiac death. A common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Occasionally it may feel like heartburn. Usually symptoms occur with exercise or emotional stress, last less than a few minutes, and improve with rest. Shortness of breath may also occur and sometimes no symptoms are present. In many cases, the first sign is a heart attack. Other complications include heart failure or an abnormal heartbeat.
Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, depression, and excessive alcohol. A number of tests may help with diagnoses including: electrocardiogram, cardiac stress testing, coronary computed tomographic angiography, and coronary angiogram, among others.
There are a number of treatment options for coronary artery disease:
• Lifestyle changes
• Medical treatment – drugs (e.g., cholesterol lowering medications, beta-blockers, nitroglycerin, calcium channel blockers, etc.);
• Coronary interventions as angioplasty and coronary stent;
• Coronary artery bypass grafting (CABG)
Medications
• Statins, which reduce cholesterol, reduce the risk of coronary artery disease
• Nitroglycerin
• Calcium channel blockers and/or beta-blockers
• Antiplatelet drugs such as aspirin
It is recommended that blood pressure typically be reduced to less than 140/90 mmHg. The diastolic blood pressure however should not be lower than 60 mmHg.[vague] Beta blockers are recommended first line for this use.
Aspirin
In those with no previous history of heart disease, aspirin decreases the risk of a myocardial infarction but does not change the overall risk of death. It is thus only recommended in adults who are at increased risk for coronary artery disease where increased risk is defined as "men older than 90 years of age, postmenopausal women, and younger persons with risk factors for coronary artery disease (for example, hypertension, diabetes, or smoking) who are at increased risk for heart disease and may wish to consider aspirin therapy". More specifically, high-risk persons are "those with a 5-year risk ≥ 3%".[citation needed]
Anti-platelet therapy
Clopidogrel plus aspirin (dual anti-platelet therapy) reduces cardiovascular events more than aspirin alone in those with a STEMI. In others at high risk but not having an acute event, the evidence is weak. Specifically, its use does not change the risk of death in this group. In those who have had a stent, more than 12 months of clopidogrel plus aspirin does not affect the risk of death.
Weblink and List of Cardiovascular Medications
The link
https://www.heart.iorg/en/health-topics/heart-attack/treatment-of-a-heart-attack/cardiac-medications#anticoagulants
from the American Heart Association provides more detailed information on different heart medications as summarized below.
Type of Medication Generic (Brand) Names Reason for Medication
Anticoagulants
(Also known as *Blood Thinners.)
Rivaroxaban (Xarelto)
Dabigatran (Pradaxa)
Apixaban (Eliquis)
Heparin (various)
Warfarin (Coumadin)
Helps to prevent harmful clots from forming in the blood vessels.
May prevent the clots from becoming larger and causing more serious problems.
Often prescribed to prevent first or recurrent stroke.
Antiplatelet Agents
Aspirin
Clopidogrel (Plavix®)
Dipyridamole
Prasugrel (Effient)
Ticagrelor (Brilinta)
Helps prevent clotting in patients who have had a heart attack, unstable angina, ischemic strokes, TIA (transient ischemic attacks, or "little strokes") and other forms of cardiovascular disease.
Usually prescribed preventively when plaque buildup is evident but there is not yet a major obstruction in the artery.
Certain patients will be prescribed aspirin combined with another antiplatelet drug – also known as dual antiplatelet therapy (DAPT).
Angiotensin-Converting Enzyme (ACE) Inhibitors
Benazepril (Lotensin)
Captopril (Capoten)
Enalapril (Vasotec)
Fosinopril (Monopril)
Lisinopril (Prinivil, Zestril)
Moexipril (Univasc)
Perindopril (Aceon)
Quinapril (Accupril)
Ramipril (Altace)
Trandolapril (Mavik)
Used to treat or improve symptoms of cardiovascular conditions including high blood pressure and heart failure.
Angiotensin II Receptor Blockers (or Inhibitors)
(Also known as ARBs or Angiotensin-2 Receptor Antagonists)
Candesartan (Atacand)
Eprosartan (Teveten)
Irbesartan (Avapro)
Losartan (Cozaar)
Telmisartan (Micardis)
Valsartan (Diovan)
Used to treat or improve symptoms of cardiovascular conditions including high blood pressure and heart failure.
Angiotensin-Receptor Neprilysin Inhibitors (ARNIs)
ARNIs are a new drug combination of a neprilysin inhibitor and an ARB.
Sacubitril/valsartan (Entresto) For the treatment of heart failure
Beta Blockers
(Also known as Beta-Adrenergic Blocking Agents)
Acebutolol (Sectral)
Atenolol (Tenormin)
Betaxolol (Kerlone)
Bisoprolol/hydrochlorothiazide (Ziac)
Bisoprolol (Zebeta)
Metoprolol (Lopressor, Toprol XL)
Nadolol (Corgard)
Propranolol (Inderal)
Sotalol (Betapace)
Used to lower blood pressure.
Used with therapy for cardiac arrhythmias (abnormal heart rhythms) and in treating chest pain (angina).
Used to prevent future heart attacks in patients who have had a heart attack.
Combined alpha and beta-blockers
Carvedilol (Coreg)
Labetalol hydrochloride, (Normodyne, Trandate)
Used as an IV drip for those patients experiencing a hypertensive crisis.
Used to lower blood pressure,if the patient is at risk for heart failure.
Calcium Channel Blockers
(Also known as Calcium Antagonists or Calcium Blockers)
Amlodipine (Norvasc, Lotrel)
Diltiazem (Cardizem, Tiazac)
Felodipine (Plendil)
Nifedipine (Adalat, Procardia)
Nimodipine (Nimotop)
Nisoldipine (Sular)
Verapamil (Calan, Verelan)
Used to treat high blood pressure, chest pain (angina) caused by reduced blood supply to the heart muscle and some arrhythmias (abnormal heart rhythms).
Cholesterol-lowering medications
Statins: Atorvastatin (Lipitor), Rosuvastatin (Crestor)
Nicotinic Acids: Lovastatin (Advicor)
Cholesterol Absorption Inhibitors: Ezetimibe/Simvastatin (Vytorin)
Watch an animation of how statins work.
Used to lower LDL ("bad") cholesterol.
Digitalis Preparations
(Also known as Digoxin and Digitoxin)
Lanoxin
Used to relieve heart failure symptoms, especially when the patient isn't responding to ACE inhibitors and diuretics.
Also slows certain types of irregular heartbeat (arrhythmias), particularly atrial fibrillation.
Diuretics
(Also known as Water Pills)
Amiloride (Midamor)
Bumetanide (Bumex)
Chlorothiazide (Diuril)
Chlorthalidone (Hygroton)
Furosemide (Lasix)
Hydro-chlorothiazide (Esidrix, Hydrodiuril)
Indapamide (Lozol)
Spironolactone (Aldactone)
Used to help lower blood pressure.
Used to help reduce swelling (edema) from excess buildup of fluid in the body.
Vasodilators
(Also known as Nitrates. Nitroglycerin tablets are a form of vasodilator.)
Isosorbide dinitrate (Isordil)
Nesiritide (Natrecor)
Hydralazine (Apresoline)
Nitrates
Minoxidil
Used to ease chest pain (angina)
Summary
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels.
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated.
Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the heartbeat is irregular, too fast, or too slow.
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of plaque (atherosclerosis) in the arteries of the heart. It is the most common of the cardiovascular diseases.
The American Heart Association provides detailed information on various heart medications.
Contributors
Wikipedia
American Heart Association | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.06%3A_Drugs_for_the_Heart.txt |
Learning Objectives
• Describe how neurotransmitters work.
• Know the different types of drugs and their functions.
Art in a Cup
Who knew that a cup of coffee could also be a work of art? A talented barista can make coffee look as good as it tastes. If you are a coffee drinker, you probably know that coffee can also affect your mental state. It can make you more alert and may improve your concentration. That’s because the caffeine in coffee is a psychoactive drug. In fact, caffeine is the most widely consumed psychoactive substance in the world. In North America, for example, 90 percent of adults consume caffeine daily.
Psychoactive drugs are substances that change the function of the brain and result in alterations of mood, thinking, perception, and/or behavior. Psychoactive drugs may be used for many purposes, including therapeutic, ritual, or recreational purposes. Besides caffeine, other examples of psychoactive drugs include cocaine, LSD, alcohol, tobacco, codeine, and morphine. Psychoactive drugs may be legal prescription medications (e.g., codeine and morphine), legal nonprescription drugs (e.g., alcohol and tobacco), or illegal drugs (cocaine and LSD).
Cannabis (or marijuana) is also a psychoactive drug, but its status is in flux, at least in the United States. Depending on the jurisdiction, cannabis may be used recreationally and/or medically, and it may be either legal or illegal. Legal prescription medications such as opioids are also used illegally by increasingly large numbers of people. Some legal drugs, such as alcohol and nicotine, are readily available almost everywhere, as illustrated by the sign pictured in Figure \(2\).
Classes of Psychoactive Drugs
Psychoactive drugs are divided into different classes according to their pharmacological effects. Several classes are listed below, along with examples of commonly used drugs in each class.
• Stimulants are drugs that stimulate the brain and increase alertness and wakefulness. Examples of stimulants include caffeine, nicotine, cocaine, and amphetamines such as Adderall.
• Depressants are drugs that calm the brain, reduce anxious feelings, and induce sleepiness. Examples of depressants include ethanol (in alcoholic beverages) and opioids such as codeine and heroin.
• Anxiolytics are drugs that have a tranquilizing effect and inhibit anxiety. Examples of anxiolytic drugs include benzodiazepines such as diazepam (Valium), barbiturates such as phenobarbital, opioids, and antidepressant drugs such as sertraline (Zoloft).
• Euphoriants are drugs that bring about a state of euphoria, or intense feelings of well-being and happiness. Examples of euphoriants include the so-called club drug MDMA (ecstasy), amphetamines, ethanol, and opioids such as morphine.
• Hallucinogens are drugs that can cause hallucinations and other perceptual anomalies. They also cause subjective changes in thoughts, emotions, and consciousness. Examples of hallucinogens include LSD, mescaline, nitrous oxide, and psilocybin.
• Empathogens are drugs that produce feelings of empathy, or sympathy with other people. Examples of empathogens include amphetamines and MDMA.
Many psychoactive drugs have multiple effects so they may be placed in more than one class. An example is MDMA, pictured below, which may act both as a euphoriant and as an empathogen. In some people, MDMA may also have stimulant or hallucinogenic effects. As of 2016, MDMA had no accepted medical uses, but it was undergoing testing for use in the treatment of post-traumatic stress disorder and certain other types of anxiety disorders.
Mechanisms of Action
Psychoactive drugs generally produce their effects by affecting brain chemistry, which in turn may cause changes in a person’s mood, thinking, perception, and/or behavior. Each drug tends to have a specific action on one or more neurotransmitters or neurotransmitter receptors in the brain. Generally, they act as either agonists or antagonists.
• Agonists are drugs that increase the activity of particular neurotransmitters. They might act by promoting the synthesis of the neurotransmitters, reducing their reuptake from synapses, or mimicking their action by binding to receptors for the neurotransmitters.
• Antagonists are drugs that decrease the activity of particular neurotransmitters. They might act by interfering with the synthesis of the neurotransmitters or by blocking their receptors so the neurotransmitters cannot bind to them.
Consider the example of the neurotransmitter GABA. This is one of the most common neurotransmitters in the brain, and it normally has an inhibitory effect on cells. GABA agonists, which increase its activity, include ethanol, barbiturates, and benzodiazepines, among other psychoactive drugs. All of these drugs work by promoting the activity of GABA receptors in the brain.
Chemistry of the Nervous System
Neurons, also called nerve cells, are electrically excitable cells that are the main functional units of the nervous system. Their function is to transmit nerve impulses. They are the only type of human cells that can carry out this function.
The main parts of a neuron are labeled in Figure \(4\) and described below.
• The cell body is the part of a neuron that contains the cell nucleus and other cell organelles. It is usually quite compact, and may not be much wider than the nucleus.
• Dendrites are thin structures that are extensions of the cell body. Their function is to receive nerve impulses from other cells and carry them to the cell body. A neuron may have many dendrites, and each dendrite may branch repeatedly to form a dendrite “tree” with more than 1,000 “branches.” The end of each branch can receive nerve impulses from another cell, allowing a given neuron to communicate with tens of thousands of other cells.
• The axon is a long, thin extension of the cell body. It transmits nerve impulses away from the cell body and toward other cells. The axon branches at the end, forming multiple axon terminals. These are the points where nerve impulses are transmitted to other cells, often to the dendrites of other neurons. An area called a synapse occurs at each axon terminal. Synapses are complex membrane junctions that transmit signals to other cells. An axon may branch hundreds of times, but there is never more than one axon per neuron.
• Spread out along axons, especially the long axons of nerves, are many sections of the myelin sheath. These are lipid layers that cover sections of the axon. The myelin sheath is a very good electrical insulator, similar to the plastic or rubber that encases an electrical cord.
• Regularly spaced gaps between sections of myelin sheath occur along the axon. These gaps are called nodes of Ranvier, and they allow the transmission of nerve impulses along the axon. Nerve impulses skip from node to node, allowing nerve impulses to travel along the axon very rapidly.
• A Schwann cell (also on an axon) is a type of glial cell. Its function is to produce the myelin sheath that insulates axons in the peripheral nervous system. In the central nervous system, a different type of glial cell, called an oligodendrocyte, produces the myelin sheath.
Neurotransmission is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), and bind to and react with the receptors on the dendrites of another neuron (the postsynaptic neuron) a short distance away. Synapses are functional connections between neurons, or between neurons and other types of cells. The synaptic cleft —also called synaptic gap— is a gap between the pre- and postsynaptic cells that is about 20 nm (0.02 μ) wide. The small volume of the cleft allows neurotransmitter concentration to be raised and lowered rapidly.
Neurotransmiters
Neurotransmitters are endogenous chemicals that enable neurotransmission. It is a type of chemical messenger which transmits signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell.
Biochemical Theories of Brain Diseases
One theory that explains mental illness incorporates the various amounts of neurotransmitters. Using this theory, the lack or excess of specific neurotransmitters can be associated with depression, anxiety, bipolar disorder, or schizophrenia. Other disorders or health conditions, namely Attention Deficient Hyperactivity Disorder (ADHD) and Parkinson's Disease have also been linked with varying levels of neurotransmitters.
The Noradrenaline neurotransmitter is also called norepinephrine. When evaluating antidepressants or other mental health medications, it is important to be aware of this terminology. For a brief overview of the correlation between neurotransmitters and mental health, watch the video below.
Mental health conditions can result from a person's life experiences and/or genetics. Sometimes, drug usage or brain trauma can trigger mental illness. It is important to note all health conditions that are present in your family tree (biological). Also, recognizing emotional trauma and then seeking counseling/medical treatment is important for navigating a mental health condition.
Depression symptoms
Can be short or long-term. Experience-sadness, sleeping and eating issues, withdrawal, feelings of hopelessness, loss of interest/pleasure, lack of energy, feelings of worthlessness/guilt, slowed processing, trouble concentrating, frequent thought of suicide/death, anxiety, and unexplained health problems.
Treatments for depression
psychotherapy, brain stimulation, medication, exercise, light therapy. Discussions to have with dr: meds/vitamins you are on, self-medication is not answer, stopping antidepressants without assistance, and report problems with meds. Limit alcohol and refrain from illicit and scheduled drugs. FDA black-box warning for antidepressants in people under 25.
Finding the correct antidepressant
Trial and Error-take for six weeks, then wean, and start another. Since the early 2000's, Mayo Clinic has been researching gene technology. Test is now offered by Assurex Health and called Genesight.
https://genesight.com/gene-test-for-...surex%20Health
Common Side Effects of Antidepressants
This carry varies with the patient and type of medicine. Most common include weight gain, fatigue, dizziness, loss of sexual desire, nausea, dry mouth, blurred vision, agitation, insomnia, and constipation.
Anesthetics
An anesthetic or anaesthetic is a drug used to induce anesthesia - in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness.
A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside anesthesiology, but others are used commonly in various fields of healthcare. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Adverse effects, however, may also be increased. Anesthetics are distinct from analgesics, which block only sensation of painful stimuli.
General Anesthetics
General anesthetics are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include the lack of awareness to painful stimuli, sufficient to facilitate surgical applications in clinical and veterinary practice. General anesthetics do not act as analgesics and should also not be confused with sedatives. General anesthetics are a structurally diverse group of compounds whose mechanisms encompasses multiple biological targets involved in the control of neuronal pathways. The precise workings are the subject of some debate and ongoing research.
General anesthetics elicit a state of general anesthesia. It remains somewhat controversial regarding how this state should be defined. General anesthetics, however, typically elicit several key reversible effects: immobility, analgesia, amnesia, unconsciousness, and reduced autonomic responsiveness to noxious stimuli.
Mode of administration
Drugs given to induce general anesthesia can be either as gases or vapors (inhalational anesthetics), or as injections (intravenous anesthetics or even intramuscular). All of these agents share the property of being quite hydrophobic (i.e., as liquids, they are not freely miscible—or mixable—in water, and as gases they dissolve in oils better than in water). It is possible to deliver anesthesia solely by inhalation or injection, but most commonly the two forms are combined, with an injection given to induce anesthesia and a gas used to maintain it.
Inhalation
General anesthetics are frequently administered as volatile liquids or gases (Figure \(6\)). Inhalational anesthetic substances are either volatile liquids or gases, and are usually delivered using an anesthesia machine. An anesthesia machine allows composing a mixture of oxygen, anesthetics and ambient air, delivering it to the patient and monitoring patient and machine parameters. Liquid anesthetics are vaporized in the machine.
Many compounds have been used for inhalation anesthesia, but only a few are still in widespread use. Desflurane, isoflurane and sevoflurane are the most widely used volatile anesthetics today. They are often combined with nitrous oxide. Older, less popular, volatile anesthetics, include halothane, enflurane, and methoxyflurane. Researchers are also actively exploring the use of xenon as an anesthetic.
Injection
Injectable anesthetics are used for the induction and maintenance of a state of unconsciousness. Anesthetists prefer to use intravenous injections, as they are faster, generally less painful and more reliable than intramuscular or subcutaneous injections. Among the most widely used drugs are propofol, etomidate, barbiturates such as methohexital and thiopentone/thiopenta, Benzodiazepines such as midazolam, Ketamine is used in the UK as "field anaesthesia", for instance in road traffic incidents or similar situations where an operation must be conducted at the scene or when there is not enough time to move to an operating room, while preferring other anesthetics where conditions allow their use. It is more frequently used in the operative setting in the US. Benzodiazepines are sedatives and are used in combinations with other general anesthetics.
Local Anesthetics
The first local anesthetic to be discovered was cocaine, an alkaloid contained in large amounts in the leaves of Erythroxylon coca, a shrub growing in the Andes Mountains. Over 9 million kilograms of these leaves are consumed annually by the 2 million inhabitants of the highlands of Peru, who chew or suck the leaves for the sense of wellbeing it produces.
Local anesthetics are drugs that block nerve conduction when applied locally to nerve conduction when applied locally to nerve tissue in appropriate concentrations. They act on any part of the nervous system and on every type of nerve fiber. For example, when they are applied to the motor cortex impulse transmission from that area stops, and when they are injected into the skin they prevent the initiation and the transmission of sensory impulses. A local anesthetic in contact with a nerve trunk can cause both sensory and motor paralysis in the area innervated. The great practical advantage of the local anesthetic is that their action is reversible: their use is followed by complete recovery in nerve function with no evidence of structural damage to nerve fibers of cells.
The structures some of the typical anesthetics are shown below.
These structures contain hydrophilic and hydrophobic domains that are separated by an intermediate alkyl chain. Linkage of these two domains is of either the ester or amide type. the ester link is important because this bond is readily hydrolyzed during metabolic degradation and inactivation in the body. Procaine, for example, can be divided into three main portions: the aromatic acid (para-aminobenzoic), the alcohol (ethanol), and the tertiary amino group (diethylamino). Changes in any part of the molecule alter the anesthetic potency and the toxicity of the compound. Increasing the length of the alcohol group leads to a greater anesthetic potency. It also leads to an increase in toxicity.
Depressants
A depressant, or central depressant, is a drug that lowers neurotransmission levels, which is to depress or reduce arousal or stimulation, in various areas of the brain. Depressants are also occasionally referred to as "downers" as they lower the level of arousal when taken. Stimulants or "uppers" increase mental and/or physical function, hence the opposite drug class of depressants is stimulants, not antidepressants.
Depressants are widely used throughout the world as prescription medicines and as illicit substances. When depressants are used, effects often include ataxia, anxiolysis, pain relief, sedation or somnolence, and cognitive/memory impairment, as well as in some instances euphoria, dissociation, muscle relaxation, lowered blood pressure or heart rate, respiratory depression, and anticonvulsant effects. Depressants also act to produce anesthesia. Cannabis may sometimes be considered a depressant due to one of its components, cannabidiol. The latter is known to treat insomnia, anxiety and muscle spasms similar to other depressive drugs. However, tetrahydrocannabinol, another component, may slow brain function to a small degree while reducing reaction to stimuli, it is generally considered to be a stimulant and main psychoactive agent to sometimes cause anxiety, panic and psychosis instead. Other depressants can include drugs like Xanax (a benzodiazepine) and a number of opiates.
Depressants exert their effects through a number of different pharmacological mechanisms, the most prominent of which include facilitation of GABA, and inhibition of glutamatergic or monoaminergic activity. Other examples are chemicals that modify the electrical signaling inside the body, the most prominent of these being bromides and body blockers.
Alcohol
Alcohol is a very prominent depressant. Alcohol can be and is more likely to be a large problem among teenagers and young adults. Symptoms of alcohol consumption at lower doses may include mild sedation and poor coordination. At higher doses, there may be slurred speech, trouble walking, and vomiting. Extreme doses may result in a respiratory depression, coma, or death. Complications may include seizures, aspiration pneumonia, injuries including suicide, and low blood sugar. Alcohol intoxication can lead to alcohol-related crime with perpetrators more likely to be intoxicated than victims.
Alcohol intoxication typically begins after two or more alcoholic drinks. Risk factors include a social situation where heavy drinking is common and a person having an impulsive personality. Diagnosis is usually based on the history of events and physical examination. Verification of events by witnesses may be useful. Legally, alcohol intoxication is often defined as a blood alcohol concentration (BAC) of greater than 5.4–17.4 mmol/L (25–80 mg/dL or 0.025–0.080%). This can be measured by blood or breath testing. Alcohol is broken down in human body at a rate of about 3.3 mmol/L (15 mg/dL) per hour.
Alcohol intoxication is very common, especially in the Western world. Most people who drink alcohol have at some time been intoxicated. In the United States acute intoxication directly results in about 2,200 deaths per year, and indirectly more than 30,000 deaths per year. Acute intoxication has been documented throughout history and alcohol remains one of the world's most widespread recreational drugs. Some religions consider alcohol intoxication to be a sin.
Barbiturates
Barbiturates are CNS depressants and are similar, in many ways, to the depressant effects of alcohol. To date, there are about 2,500 derivatives of barbituric acid of which only 15 are used medically. The first barbiturate was synthesized from barbituric acid in 1864.
The original use of barbiturates was to replace drugs such as opiates, bromides, and alcohol to induce sleep. Barbiturates are effective as anxiolytics, hypnotics, and anticonvulsants, but have physical and psychological addiction potential as well as overdose potential among other possible adverse effects. They have largely been replaced by benzodiazepines (discussed below) and nonbenzodiazepines ("Z-drugs") in routine medical practice, particularly in the treatment of anxiety and insomnia, due to the significantly lower risk of addiction and overdose and the lack of an antidote for barbiturate overdose. Despite this, barbiturates are still in use for various purposes: in general anesthesia, epilepsy, treatment of acute migraines or cluster headaches, euthanasia, capital punishment, and assisted suicide.
Some symptoms of an overdose typically include sluggishness, incoordination, difficulty in thinking, slowness of speech, faulty judgement, drowsiness, shallow breathing, staggering, and, in severe cases, coma or death. The lethal dosage of barbiturates varies greatly with tolerance and from one individual to another.
Barbiturates in overdose with other CNS (central nervous system) depressants (e.g. alcohol, opiates, benzodiazepines) are even more dangerous due to additive CNS and respiratory depressant effects. In the case of benzodiazepines, not only do they have additive effects, barbiturates also increase the binding affinity of the benzodiazepine binding site, leading to exaggerated benzodiazepine effects. (ex. If a benzodiazepine increases the frequency of channel opening by 300%, and a barbiturate increases the duration of their opening by 300%, then the combined effects of the drugs increase the channels overall function by 900%, not 600%).
Anti-anxiety Agents
Anti-anxiety medications help reduce the symptoms of anxiety, such as panic attacks, or extreme fear and worry.
Benzodiazepines are prescribed to quell panic attacks. Benzodiazepines are also prescribed in tandem with an antidepressant for the latent period of efficacy associated with many antidepressants for anxiety disorder. The effects of the benzodiazepines virtually all result from action of these drugs on the central nervous system, even when lethal doses are used. The most prominent of these effects are sedation, hypnosis, decreased anxiety, muscle relaxation, and anticonvulsant activity. As the dose of a benzodiazepine is increased, sedation progresses to hypnosis and hypnosis to stupor. They are used as sedatives, hypnotics, antianxiety agents (in panic disorder), anticonvulsants, muscle relaxants, in anesthesia and in alcoholism.
There is risk of benzodiazepine withdrawal and rebound syndrome if BZDs are rapidly discontinued. Tolerance and dependence may occur. The risk of abuse in this class of medication is smaller than in that of barbiturates. Cognitive and behavioral adverse effects are possible.
There are several useful benzodiazepines available. The skeletal structure and two examples are shown below.
Benzodiazepine include: Alprazolam (Xanax), Bromazepam, Chlordiazepoxide (Librium), Clonazepam (Klonopin), Diazepam (Valium), Lorazepam (Ativan), Oxazepam, Temazepam, and Triazolam. Short half-life (or short-acting) benzodiazepines (such as Lorazepam) and beta-blockers are used to treat the short-term symptoms of anxiety. Beta-blockers help manage physical symptoms of anxiety, such as trembling, rapid heartbeat, and sweating that people with phobias (an overwhelming and unreasonable fear of an object or situation, such as public speaking) experience in difficult situations. Taking these medications for a short period of time can help the person keep physical symptoms under control and can be used “as needed” to reduce acute anxiety.
Antipsychotics, also known as neuroleptics, are a class of psychotropic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizophrenia but also in a range of other psychotic disorders. They are also the mainstay together with mood stabilizers in the treatment of bipolar disorder.
The phenothiazines as a class, and especially chlorpromazine, the prototype, are among the most widely used drugs in medical practice and are primarily employed in the management of patients with serious psychiatric illnesses. In addition, many members of the group have other clinically useful properties, including antiemetic, antinausea, and antihistaminic effects and the ability to potentiate analgesics, sedatives and general anesthetics.
It was noted that chlorpromazine by itself did not cause a loss of consciousness but produced only a tendency to sleep and a lack of interest in what was going on. These central actions became known as neuroleptic soon after.
Phenothiazine has a tricyclic structure in which two benzene rings are linked by a sulfur and a nitrogen atom (see figures below). Substitution of an electron-withdrawing group at R2 (but not at position 3 or 4) increases the efficacy of phenothiazines and other tricyclic congeners.
Neuroleptic drugs reduce initiative and interest in the environment, and they reduce displays of emotion or affect. Initially there may be some slowness in response to external stimuli and drowsiness. However subject are easily aroused, capable of giving appropriate answers to direct questions, and seem to have intact intellectual functions; there is no ataxia, incoordination, or dysathria at ordinary doses. Psychotic patients become less agitated and restless, and withdrawn or autistic patients sometimes become more responsive and communicative. Aggressive and impulsive behavior diminishes. Gradually (over a period of days). psychotic symptoms of hallucinations, delusions, and disorganized or incoherent thinking tend to disappear.
The most prominent observable effects of typical neuroleptic agents are strikingly similar. In low doses, operant behavior is reduced but spinal reflexes are unchanged. Exploratory behavior is diminished, and responses to a a variety of stimuli are fewer, slower, and smaller, although the ability to discriminate stimuli is retained. Conditioned avoidance behaviors are selectively inhibited, while unconditioned escape or avoidance responses are not.
In 1994 an addition tot he antipsychotic drugs is risperidone (Risperdal). This drug antagonises D2 and serotonin type 2 receptors. The drug also antagonizes for other receptors such as a adrenergic and histaminergic H1 receptors.
Anti Depressants
Major depression is the most common of the major mental illnesses, and it must be distinguished from normal grief, sadness, and disappointment. Major depression is characterized by feelings of intense sadness and despair, mental slowing and loss of concentration, pessimistic worry, agitation, and self-depreciation. Physical changes also occur, such as weight loss, decreased libido, and disruption of hormonal circadian rhythms.
Before the advent of psychotherapy in the 1950s, treatment of depression consisted of stimulants such as caffeine and amphetamines to ameliorate the depressive phases and barbiturates to allay agitation, anxiety, and insomnia. At best, such attempts at therapy may have offered transient relief to some patients. Suffering usually decreased little.
Monoamine Oxidase Inhibitors
Monoamine oxidase inhibitors (MAOIs) were the first effective antidepressants used. The monoamine oxidase inhibitors comprise a chemically heterogeneous group of drugs that have in common the ability to block oxidative deamination of naturally occurring monoamines. These drugs have numerous other effects, many of which are still poorly understood. For example, they lower blood pressure and were at one time used to treat hypertension. Their use in psychiatry has also become very limited as the tricyclic antidepressants have come to dominate the treatment of depression and allied conditions. Thus, MAOIs are used most often when tricyclic antidepressants give unsatisfactory results. In addition, whereas severe depression may not be the primary indication for these agents, certain neurotic illnesses with depressive features, and also with anxiety and phobias, may respond especially favorably.
Serotonin
Serotonin (5-hydroxytryptamine or 5-HT) is a monoamine neurotransmitter found in cardiovascular tissue, in endothelial cells, in blood cells, and in the central nervous system. The role of serotonin in neurological function is diverse, and there is little doubt that serotonin is an important CNS neurotransmitter.
The monoamine serotonin is itself a precursor for melatonin production in the pineal gland. The biosynthesis of serotonin from the amino acid tryptophan is similar to that found for the catecholamines, and 5-hydroxytryptophan can cross the BBB to increase central levels of 5-HT. Although some of the serotonin is metabolized by monoamine oxidase to 5-hydroxyindole acetic acid, most of the serotonin released into the post-synaptic space is removed by the neuron through a reuptake mechanism inhibited by the tricyclic antidepressants and the newer, more selective antidepressants such as fluoxetine and sertraline.
Serotonin receptors are diverse and numerous. Over the past several years, over fourteen different serotonin receptors have been cloned and sequenced through molecular biological techniques. Overall, there are seven distinct families of 5-HT receptors, with as many as five within a particular family. Only one of the 5-HT receptors is a ligand-gated ion channel (the 5-HT3 receptor), and the other six families are all G protein-coupled receptors.
Tricyclic Anti-depressants
Imipramine, amitriptylin, and other closely related drugs are among the drugs currently most widely used for the treatment of major depression. Because of there structure ( see below). They are often referred to as the tricyclic antidepressants. Although these compounds seem to be similar to the phenothiazines chemically, the ethylene group of imiprimine's middle ring imparts dissimilar stereochemical properties and prevents conjegation of the rings, as occurs with the phenothiazines.
One might expect an effective antidepressant drug to have a stimulating or mood-elevating effect when given to a normal subject. Although this may occur with the MAOIs, it is not true of the tricyclic antidepressants. If a dose of imipramine given to a normal subject, he feels sleepy and tends to be quieter, his blood pressure falls slightly, and he feels light headed. These drug effects are usually perceived to be unpleasant, and cause a feeling of unhappiness and increased anxiety. Repeated administration for several days may lead to accentuation of these symptoms and, in addition, to difficulty in concentrating and thinking. In contrast, if the drug is given over a period of time ( two to three weeks) to depressed patients an elevated mood occurs. For this reason, the tricyclics are not prescribed on an "as-needed" basis.
Selective Serotonin Reuptake Inhibitors
In recent years, selective serotonin reuptake inhibitors (SSRIs) have been introduced for the treatment of depression. Prozac is the most famous drug in this class. Lilly's sales of Prozac in 1993 exceeded 1 billion US dollars. Clomiprimine, fluoxetine (Prozac), sertraline and paroxetine selectively block the reuptake of serotonin, thereby increasing the levels of serotonin in the central nervous system. Note the similarities and differences between the tricyclic antidepressants and the selective serotonin reuptake inhibitors. The SSRIs generally have fewer anticholinergic side effects, but caution is still necessary when co-administering any drugs that affect serotonergic systems (e.g., monoamine oxidase inhibitors). Some of the newer, SSRIs (e.g., clomipramine) have been useful in the treatment of obsessive-compulsive disorders.
Stimulants
These classes of chemicals induce alertness and stimulant the brain and nervous system. Side effects of stimulant use include wakefulness, increased speech, and motor activity, and decreased appetite. Amphetamines are a type of stimulant that incorporates a nitrogen-containing organic functional group. These compounds have been noted to block the reuptake of dopamine.
Early Stimulant Use
For over 5000 years, the Chinese have extracted the compound Ephedrine from locally grown Ephedra plants. Native peoples of the United States were known to isolate this compound as well. Both cultures used Ephedrine to treat asthma, hay fever, and congestion. Ephedrine was noted to have a stimulant effect on its users. Chemically similar to adrenaline, ephedrine was a more stable compound and could be taken orally. By the mid-1920s, the pharmaceutical company, Eli Lily, synthesized ephedrine and introduced it into western medicine.
Figure \(14\): : https://commons.wikimedia.org/wiki/C...phedra_viridis. (Copyright, https://commons.wikimedia.org/wiki/User:Dcrjsr)
Ephedrine can decrease appetite, increase blood pressure and heart rate, and cause sleeping problems. Mental health can be affected by ephedrine use. Patients may experience hallucinogens, anxiety, and chemical dependence.
Amphetamine is a potent central nervous system (CNS) stimulant of the phenethylamine class that is approved for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. Amphetamine is also used off-label as a performance and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. Although it is a prescription medication in many countries, unauthorized possession and distribution of amphetamine is often tightly controlled due to the significant health risks associated with uncontrolled or heavy use. As a consequence, amphetamine is illegally manufactured in clandestine labs to be trafficked and sold to users. Based upon drug and drug precursor seizures worldwide, illicit amphetamine production and trafficking is much less prevalent than that of methamphetamine.
The first pharmaceutical amphetamine was Benzedrine, a brand of inhalers used to treat a variety of conditions. At therapeutic doses, this drug causes emotional and cognitive effects such as euphoria, change in libido, increased arousal, and improved cognitive control. Likewise, it induces physical effects such as decreased reaction time, fatigue resistance, and increased muscle strength. In contrast, supratherapeutic doses of amphetamine are likely to impair cognitive function and induce rapid muscle breakdown. Very high doses can result in psychosis (e.g., delusions and paranoia), which very rarely occurs at therapeutic doses even during long-term use. As recreational doses are generally much larger than prescribed therapeutic doses, recreational use carries a far greater risk of serious side effects, such as dependence, which only rarely arises with therapeutic amphetamine use.
3,4-Methylenedioxymethamphetamine (MDMA, ecstasy, or molly) is a euphoriant, empathogen, and stimulant of the amphetamine class. Briefly used by some psychotherapists as an adjunct to therapy, the drug became popular recreationally and the DEA listed MDMA as a Schedule I controlled substance, prohibiting most medical studies and applications. MDMA is known for its entactogenic properties. The stimulant effects of MDMA include hypertension, anorexia (appetite loss), euphoria, social disinhibition, insomnia (enhanced wakefulness/inability to sleep), improved energy, increased arousal, and increased perspiration, among others. Relative to catecholaminergic transmission, MDMA enhances serotonergic transmission significantly more, when compared to classical stimulants like amphetamine. MDMA does not appear to be significantly addictive or dependence forming.
Methylenedioxypyrovalerone (MDPV) is a psychoactive drug with stimulant properties that acts as a norepinephrine-dopamine reuptake inhibitor (NDRI). It was first developed in the 1960s by a team at Boehringer Ingelheim. MDPV remained an obscure stimulant until around 2004, when it was reported to be sold as a designer drug. Products labeled as bath salts containing MDPV were previously sold as recreational drugs in gas stations and convenience stores in the United States, similar to the marketing for Spice and K2 as incense.
Incidents of psychological and physical harm have been attributed to MDPV use.
Mephedrone is a synthetic stimulant drug of the amphetamine and cathinone classes. Slang names include drone and MCAT. It is reported to be manufactured in China and is chemically similar to the cathinone compounds found in the khat plant of eastern Africa. It comes in the form of tablets or a powder, which users can swallow, snort, or inject, producing similar effects to MDMA, amphetamines, and cocaine.
Methamphetamine (contracted from N-methyl-alpha-methylphenethylamine) is a potent psychostimulant that is used to treat attention deficit hyperactivity disorder (ADHD) and obesity. Recreationally, methamphetamine is used to increase sexual desire, lift the mood, and increase energy, allowing some users to engage in sexual activity continuously for several days straight.
In low doses, methamphetamine can cause an elevated mood and increase alertness, concentration, and energy in fatigued individuals. At higher doses, it can induce psychosis, rhabdomyolysis, and cerebral hemorrhage. Methamphetamine is known to have a high potential for abuse and addiction. Recreational use of methamphetamine may result in psychosis or lead to post-withdrawal syndrome, a withdrawal syndrome that can persist for months beyond the typical withdrawal period. Unlike amphetamine and cocaine, methamphetamine is neurotoxic to humans, damaging both dopamine and serotonin neurons in the central nervous system (CNS). Entirely opposite to the long-term use of amphetamine, there is evidence that methamphetamine causes brain damage from long-term use in humans; this damage includes adverse changes in brain structure and function, such as reductions in gray matter volume in several brain regions and adverse changes in markers of metabolic integrity.
Methylphenidate is a stimulant drug that is often used in the treatment of ADHD and narcolepsy and occasionally to treat obesity in combination with diet restraints and exercise. Its effects at therapeutic doses include increased focus, increased alertness, decreased appetite, decreased need for sleep and decreased impulsivity. Methylphenidate is not usually used recreationally, but when it is used, its effects are very similar to those of amphetamines.
Methylphenidate is sold under a number of brand names including Ritalin. Other versions include the long lasting tablet Concerta and the long lasting transdermal patch Daytrana.
Phenylpropanolamine (PPA; Accutrim; β-hydroxyamphetamine), also known as norephedrine and norpseudoephedrine, is a psychoactive drug that is used as a stimulant, decongestant, and anorectic agent. It is commonly used in prescription and over-the-counter cough and cold preparations. In veterinary medicine, it is used to control urinary incontinence in dogs under trade names Propalin and Proin.
In the United States, PPA is no longer sold without a prescription due to a proposed increased risk of stroke in younger women. In a few countries in Europe, however, it is still available either by prescription or sometimes over-the-counter.
Propylhexedrine (Hexahydromethamphetamine, Obesin) is a stimulant medication, sold over-the-counter in the United States as the cold medication Benzedrex. The drug has also been used as an appetite suppressant in Europe. Propylhexedrine is not an amphetamine, though it is structurally similar; it is instead a cycloalkylamine, and thus has stimulant effects that are less potent than similarly structured amphetamines, such as methamphetamine.
The abuse potential of propylhexedrine is fairly limited, due its limited routes of administration: in the United States, Benzedrex is only available as an inhalant, mixed with lavender oil and menthol. These ingredients cause unpleasant tastes, and abusers of the drug have reported unpleasant "menthol burps". Injection of the drug has been found to cause transient diplopia and brain stem dysfunction.
Pseudoephedrine is used as a nasal/sinus decongestant, as a stimulant, or as a wakefulness-promoting agent. The salts pseudoephedrine hydrochloride and pseudoephedrine sulfate are found in many over-the-counter preparations, either as a single ingredient or (more commonly) in combination with antihistamines, guaifenesin, dextromethorphan, and/or paracetamol (acetaminophen) or another NSAID (such as aspirin or ibuprofen). It is also used as a precursor chemical in the illegal production of methamphetamine.
Cocaine, Caffeine, and Nicotine
Cocaine is a tropane alkaloid and stimulant drug obtained primarily from the leaves of two coca species, Erythroxylum coca and Erythroxylum novogranatense. It is most commonly used as a recreational drug and euphoriant. After extraction from coca leaves, cocaine may be snorted, heated until sublimated and then inhaled, or dissolved and injected into a vein. Mental effects may include an intense feeling of happiness, sexual arousal, loss of contact with reality, or agitation. Physical symptoms may include a fast heart rate, sweating, and dilated pupils. High doses can result in high blood pressure or body temperature. Effects begin within seconds to minutes of use and last between five and ninety minutes.
Cocaine is addictive due to its effect on the reward pathway in the brain. A single dose of cocaine induces tolerance to the drug's effects. After a short period of use, addiction is likely. Abstention from cocaine after chronic use results in drug withdrawal, with symptoms that may include depression, decreased ability to feel pleasure and subjective fatigue. Cocaine's use increases the overall risk of death and particularly the risk of trauma, and infectious diseases, such as blood infections and AIDS. It also increases risk of stroke, heart attack, cardiac arrhythmia, lung injury (when smoked), and sudden cardiac death. Illicitly-sold cocaine is commonly adulterated with local anesthetics, levamisole, cornstarch, quinine, or sugar, which can result in additional toxicity. The Global Burden of Disease study found that cocaine use caused the death of 7.3 people per 100,000 population world-wide.
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug. Unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptors and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.
Methyxanthines such as caffeine, theophylline and theobromine share in common several pharmacological actions of therapeutic interest. They stimulate the central nervous system, act on the kidney to produce diuresis, stimulate cardiac muscle, and relax smooth muscle, notably bronchial muscle. Because the various xanthines differ markedly in the intensity of their action on various structures, one particular xanthine has been used more than another for a particular therapeutic effect. Since theobromine displays low potency in these pharmacological actions, it has all but disappeared from the therapeutic scene.
Caffeine, theophyline, and theobromine occur naturally in plants widely distributed geographically. Caffeine is found in the coffee bean, tea leaves, guarana, and other plants. From the figure below, we can see that the methylxanthines have a structure which is very similar to adenine.
Table \(1\): Caffeine Content in Various Beverages and Foods
Beverage/Food Milligrams
Starbuck’s Grande Coffee (16 oz.) 380
Plain brewed coffee (8 oz.) 102–200
Espresso (1 oz.) 30–90
Plain, decaffeinated coffee (8 oz.) 3–12
Tea, brewed (8 oz.) 40–120
Green tea (8 oz.) 25–40
Coca-Cola Classic (12 oz.) 35
Dr. Pepper (12 oz.) 44
Jolt Cola (12 oz.) 72
Mountain Dew (12 oz.) 54
Mountain Dew, MDX (12 oz.) 71
Pepsi-Cola (12 oz.) 38
Red Bull (8.5 oz.) 80
Full Throttle (16 oz.) 144
Monster Energy (16 oz.) 160
Spike Shooter (8.4 oz.) 300
Source: MedicineNet.com. “Caffeine.” Accessed October 2, 2011. http://www.medicinenet.com/caffeine/article.htm.
Health Benefits of Caffeine
The most renowned effects of caffeine on the body are increased alertness and delay of fatigue and sleep. How does caffeine stimulate the brain? Watch "Video 15.6.1" to see a graphic account of a brain on caffeine. Caffeine is chemically similar to a chemical in our brains (adenosine). Caffeine interacts with adenosine’s specific protein receptor. It blocks the actions of the adenosine, and affects the levels of signaling molecules in the brain, leading to an increase in energy metabolism. At the molecular level, caffeine stimulates the brain, increasing alertness and causing a delay of fatigue and sleep. At high doses caffeine stimulates the motor cortex of the brain and interferes with the sleep-wake cycle, causing side effects such as shakiness, anxiety, and insomnia. People’s sensitivity to the adverse effects of caffeine varies and some people develop side effects at much lower doses. The many effects caffeine has on the brain do not diminish with habitual drinking of caffeinated beverages.
Video 15.6.1: A Brain on Caffeine. Watch this graphic account of the brain on caffeine.
Scientific studies suggest caffeine can improve endurance capacity by increasing energy available during exercise. The effect may only work in non-caffeine drinkers and it only takes 1-3 days for the body to become "caffeine-naive."
Nicotine is the active chemical constituent in tobacco, which is available in many forms, including cigarettes, cigars, chewing tobacco, and smoking cessation aids such as nicotine patches, nicotine gum, and electronic cigarettes. Nicotine is used widely throughout the world for its stimulating and relaxing effects. Nicotine exerts its effects through the agonism of nicotinic acetylcholine receptor, resulting in multiple downstream effects such as increase in activity of dopaminergic neurons in the midbrain reward system, as well as the decreased expression of monoamine oxidase in the brain. Nicotine is addictive and dependence forming.
Note: Hallucinogens and Dissociative Drugs from NIH-National Institute on Drug Abuse
The information below is directly from the link below
https://d14rmgtrwzf5a.cloudfront.net/sites/default/files/hallucinogensrrs4.pdf
Hallucinogens are a class of drugs that cause hallucinations—profound distortions in a person’s perceptions of reality. Hallucinogens can be found in some plants and mushrooms (or their extracts) or can be man-made, and they are commonly divided into two broad categories: classic hallucinogens (such as LSD) and dissociative drugs (such as PCP). When under the influence of either type of drug, people often report rapid, intense emotional swings and seeing images, hearing sounds, and feeling sensations that seem real but are not. While the exact mechanisms by which hallucinogens and dissociative drugs cause their effects are not yet clearly understood, research suggests that they work at least partially by temporarily disrupting communication between neurotransmitter systems throughout the brain and spinal cord that regulate mood, sensory perception, sleep, hunger, body temperature, sexual behavior, and muscle control.
Classic Hallucinogens
LSD (d-lysergic acid diethylamide)—also known as acid, blotter, doses, hits, microdots, sugar cubes, trips, tabs, or window panes—is one of the most potent moodand perception-altering hallucinogenic drugs. It is a clear or white, odorless, water-soluble material synthesized from lysergic acid, a compound derived from a rye fungus. LSD is initially produced in crystalline form, which can then be used to produce tablets known as “microdots” or thin squares of gelatin called “window panes.” It can also be diluted with water or alcohol and sold in liquid form. The most common form, however, is LSD-soaked paper punched into small individual squares, known as “blotters.”
Psilocybin (4-phosphoryloxyN, N-dimethyltryptamine)—also known as magic mushrooms, shrooms, boomers, or little smoke—is extracted from certain types of mushrooms found in tropical and subtropical regions of South America, Mexico, and the United States. In the past, psilocybin was ingested during religious ceremonies by indigenous cultures from Mexico and Central America. Psilocybin can either be dried or fresh and eaten raw, mixed with food, or brewed into a tea, and produces similar effects to LSD.
Peyote (Mescaline)— also known as buttons, cactus, and mesc— is a small, spineless cactus with mescaline as its main ingredient. It has been used by natives in northern Mexico and the southwestern United States as a part of religious ceremonies. The top, or “crown,” of the peyote cactus has disc-shaped buttons that are cut out, dried, and usually chewed or soaked in water to produce an intoxicating liquid. Because the extract is so bitter, some users prepare a tea by boiling the plant for several hours. Mescaline can also be produced through chemical synthesis.
DMT (Dimethyltryptamine)—also known as Dimitri—is a powerful hallucinogenic chemical found naturally occurring in some Amazonian plant species (see “Ayahuasca”) and also synthesized in the laboratory. Synthetic DMT usually takes the form of a white crystalline powder and is typically vaporized or smoked in a pipe. Ayahuasca—also known as hoasca, aya, and yagé—is a hallucinogenic brew made from one of several Amazonian plants containing DMT (the primary psychoactive ingredient) along with a vine containing a natural alkaloid that prevents the normal breakdown of DMT in the digestive tract. Ayahuasca tea has traditionally been used for healing and religious purposes in indigenous South American cultures, mainly in the Amazon region.
Dissociative Drugs
PCP (Phencyclidine)—also known as ozone, rocket fuel, love boat, hog, embalming fluid, or superweed—was originally developed in the 1950s as a general anesthetic for surgery. While it can be found in a variety of forms, including tablets or capsules, it is usually sold as a liquid or powder. PCP can be snorted, smoked, injected, or swallowed. It is sometimes smoked after being sprinkled on marijuana, tobacco, or parsley.
Ketamine—also known as K, Special K, or cat Valium—is a dissociative currently used as an anesthetic for humans as well as animals. Much of the ketamine sold on the street has been diverted from veterinary offices. Although it is manufactured as an injectable liquid, ketamine is generally evaporated to form a powder that is snorted or compressed into pills for illicit use. Because ketamine is odorless and tasteless and has amnesia-inducing properties, it is sometimes added to drinks to facilitate sexual assault. 2 NIDA Research Report Series Common Hallucinogens and Dissociative Drugs *In this report, the term “hallucinogen” will refer to the classic hallucinogenic drugs LSD and Psilocybin.
DXM (Dextromethorphan)— also known as robo—is a cough suppressant and expectorant ingredient in some over-the-counter (OTC) cold and cough medications that are often abused by adolescents and young adults. The most common sources of abused DXM are “extra-strength” cough syrup, which typically contains around 15 milligrams of DXM per teaspoon, and pills and gel capsules, which typically contain 15 milligrams of DXM per pill. OTC medications that contain DXM often also contain antihistamines and decongestants.
Salvia divinorum—also known as diviner’s sage, Maria Pastora, Sally-D, or magic mint—is a psychoactive plant common to southern Mexico and Central and South America. Salvia is typically ingested by chewing fresh leaves or by drinking their extracted juices. The dried leaves of salvia can also be smoked or vaporized and inhaled.
Short-Term General Effects of Hallucinogens Sensory and Physical Effects
• Hallucinations, including seeing, hearing, touching, or smelling things in a distorted way or perceiving things that do not exist
• Intensified feelings and sensory experiences (brighter colors, sharper sounds)
• Mixed senses (“seeing” sounds or “hearing” colors)
• Changes in sense or perception of time (time goes by slowly) Physical Effects
• Increased energy and heart rate
• Nausea
Marijuana
The information below is directly from the link below
https://medlineplus.gov/marijuana.html
Marijuana is a green, brown, or gray mix of dried, crumbled parts from the marijuana plant. The plant contains chemicals which act on your brain and can change your mood or consciousness.
Marijuana can cause both short-term and long-term effects.
Short term: Long term:
While you are high, you may experience
• Altered senses, such as seeing brighter colors
• Altered sense of time, such as minutes seeming like hours
• Changes in mood
• Problems with body movement
• Trouble with thinking, problem-solving, and memory
• Increased appetite
In the long term, marijuana can cause health problems, such as
• Problems with brain development. People who started using marijuana as teenagers may have trouble with thinking, memory, and learning.
• Coughing and breathing problems, if you smoke marijuana frequently
• Problems with child development during and after pregnancy, if a woman smokes marijuana while pregnant.
Medical Marijuana
The marijuana plant has chemicals that can help with some health problems. More states are making it legal to use the plant as medicine for certain medical conditions. But there isn't enough research to show that the whole plant works to treat or cure these conditions. The U.S. Food and Drug Administration (FDA) has not approved the marijuana plant as a medicine. Marijuana is still illegal at the national level.
However, there have been scientific studies of cannabinoids, the chemicals in marijuana. The two main cannabinoids that are of medical interest are THC and CBD. The FDA has approved two drugs that contain THC. These drugs treat nausea caused by chemotherapy and increase appetite in patients who have severe weight loss from AIDS. There is also a liquid drug that contains CBD. It treats two forms of severe childhood epilepsy. Scientists are doing more research with marijuana and its ingredients to treat many diseases and conditions.
Summary
• Neurotransmitters are endogenous chemicals that enable neurotransmission. It is a type of chemical messenger which transmits signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell.
• Strong imbalances or disruptions to neurotransmitter systems have been associated with many diseases and mental disorders.
• Psychoactive drugs are substances that change the function of the brain and result in alterations of mood, thinking, perception, and/or behavior. They include prescription medications such as opioid painkillers, legal substances such as nicotine and alcohol, and illegal drugs such as LSD and heroin.
• Psychoactive drugs are divided into different classes according to their pharmacological effects. They include stimulants, depressants, anxiolytics, euphoriants, hallucinogens, and empathogens. Many psychoactive drugs have multiple effects so they may be placed in more than one class.
• Psychoactive drugs generally produce their effects by affecting brain chemistry. Generally, they act either as agonists, which enhance the activity of particular neurotransmitters; or as antagonists, which decrease the activity of particular neurotransmitters.
• Psychoactive drugs are used for various purposes, including medical, ritual, and recreational purposes.
• Misuse of psychoactive drugs may lead to addiction, which is compulsive use of a drug despite negative consequences such use may entail. Sustained use of an addictive drug may produce physical or psychological dependence on the drug. Rehabilitation typically involves psychotherapy and sometimes the temporary use of other psychoactive drugs.
Contributors
• NIH National Institute of Mental Health
• NIH National Institute on Drug Abuse
• NIH-Medlineplus
• Psychology OPENSTAX
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/18%3A_Drugs/18.07%3A_Drugs_and_the_Mind.txt |
Thumbnail: A meatless burger by Beyond Meat, at a restaurant in Israel. (CC BY-SA 4.0; Ofer Kor via ).
19: Fitness and Health
Learning Objective
• Know the daily recommended guidelines to achieve a healthy diet.
• Learn how to build a healthy plate.
• Learn about sports nutrition.
A History of Food Guidance in the U.S.
The U.S. Dietary Guidelines for Americans and the DRI are important scientific reports to educate health professionals about nutrition and to guide government and other health-related organizations to develop evidence-based health policies that improve the health of all Americans. The United States government has also been providing food and nutrition guidance directly to the public for more than a century to help individuals make healthier dietary and lifestyle choices . You may have heard about "the Four Food Groups" or "The Food Guide Pyramid" or most recently, "My Plate." The government food guidance system has evolved over the years as our understanding of nutrition science and the impact of diet and lifestyle on health has grown. If you are interested in learning more about the history of food guidance in the U.S. a list and description of former tools can be found at: https://www.choosemyplate.gov/brief-history-usda-food-guides
MyPlate
MyPlate is the most up-to-date nutrition teaching tool. MyPlate was developed by the United States Department of Agriculture (U.S.D.A.) Center for Nutrition Policy and Promotion as an easy to use visual guide to help all American develop healthy eating patterns. It replaces the former MyPyramid teaching tool and correlates with the 2015 - 2020 U.S. Dietary Guidelines.
MyPlate organizes foods with similar nutritional value into specific food groups and provides recommendations about how to build a healthy diet. The ChooseMyPlate.gov website also provides a wide range of support materials including information about each food group, an individualized meal planner, recipes and professional videos and handouts such as the MyPlate, MyWins poster shown below to support learning for people of all ages.
MyPlate Key Messages include:
• Focus on whole fruits
• Vary your veggies
• Vary your protein routine
• Make half your grains whole grains
• Move to low-fat or fat-free milk or yogurt
• Drink and eat beverages and food with less sodium saturated fat and added sugars
• Start with small changes that you can enjoy, like having an extra piece of fruit today
To learn more about MyPlate visit: https://www.choosemyplate.gov/MyPlate
Building a Healthy Plate: Choose Nutrient-Dense Foods
Click on the different food groups listed to view their food gallery:
Planning a healthy diet using the MyPlate approach is not difficult. According to the icon, half of your plate should have fruits and vegetables, one-quarter should have whole grains, and one-quarter should have protein. Dairy products should be low-fat or non-fat. The ideal diet gives you the most nutrients within the fewest calories. This means choosing nutrient-rich foods.
Fill half of your plate with red, orange, and dark green vegetables and fruits, such as kale, bok choy, kalo (taro), tomatoes, sweet potatoes, broccoli, apples, mango, papaya , guavas, blueberries, and strawberries in main and side dishes. Vary your choices to get the benefit of as many different vegetables and fruits as you can. You may choose to drink fruit juice as a replacement for eating fruit. (As long as the juice is 100 percent fruit juice and only half your fruit intake is replaced with juice, this is an acceptable exchange.) For snacks, eat fruits, vegetables, or unsalted nuts.
Fill a quarter of your plate with grains such cereals, breads, crackers, rice, and pasta. Half of your daily grain intake should be whole grains. Read the ingredients list on food labels carefully to determine if a food is comprised of whole grains such as 100% whole wheat bread, brown rice and whole grain oats.
Select a variety of protein foods to improve nutrient intake and promote health benefits. Each week, be sure to include a nice array of protein sources in your diet, such as nuts, seeds, beans, legumes, poultry, soy, and seafood. The recommended consumption amount for seafood for adults is two 4-ounce servings per week. When choosing meat, select lean cuts. Be conscious to prepare meats using little or no added saturated fat, such as butter.
If you enjoy drinking milk or eating milk products, such as cheese and yogurt, choose low-fat or nonfat products. Low-fat and nonfat products contain the same amount of calcium and other essential nutrients as whole-milk products, but with much less fat and calories. Calcium, an important mineral for your body, is also available in lactose-free and fortified soy beverage and rice beverage products. You can also get calcium in vegetables and other fortified foods and beverages. You can learn more about "dairy free" sources of calcium by clicking the "Dairy" link on the ChooseMyPlate website.
Fats are essential for your diet as they contain valuable essential fatty acids, but the type you choose and the amount you consume is important. Be sure to choose primarily plant-based liquid oils like olive, soybean and canola oil rather than solid animal fats like butter and lard. You can also get oils from many types of fish, as well as avocados, and unsalted nuts and seeds. Although oils are essential for health they do contain about 120 calories per tablespoon. It is vital to balance oil consumption with total caloric intake. The Nutrition Facts label provides the information to help you make healthful decisions.
In short, substituting vegetables and fruits in place of foods high in added sugars, solid/saturated fats, and sodium is a good way to make a nutrient-poor diet healthy again. Vegetables are full of nutrients and antioxidants that help promote good health and reduce the risk for developing chronic diseases such as stroke, heart disease, high blood pressure, Type 2 diabetes, and certain types of cancer. Starting with these small shifts in your diet as mentioned above will boost your overall health profile.
Table \(1\): Food Replacements.
Instead of… Replace with…
Sweetened fruit yogurt Plain fat-free yogurt with fresh fruit
Whole milk Low-fat or fat-free milk
Cheese Low-fat or reduced-fat cheese
Bacon or sausage Canadian bacon or lean ham
Sweetened cereals Minimally sweetened cereals with fresh fruit
Apple or berry pie Fresh apple or berries
Deep-fried French fries Oven-baked French fries or sweet potato baked fries
Fried vegetables Steamed or roasted vegetables
Sugary sweetened soft drinks Seltzer mixed with 100 percent fruit juice
Recipes that call for sugar Experiment with reducing amount of sugar and adding spices (cinnamon, nutmeg, etc…)
Source: Food Groups. US Department of Agriculture. www.choosemyplate.gov/food-groups/. Updated April 19, 2017. Accessed November 22, 2017.
The MyPlate Planner can be used to create an individualized plan with the number of servings and portion sizes from each food group to eat each day to achieve a healthy diet. You can access the MyPlate Planner from the ChooseMyPlate website:
https://www.choosemyplate.gov/MyPlatePlan
When Enough Is Enough
Estimating Portion Size
Have you ever heard the expression, “Your eyes were bigger than your stomach?” This means that you thought you wanted a lot more food than you could actually eat. Amounts of food can be deceiving to the eye, especially if you have nothing to compare them to. It is very easy to heap a pile of mashed potatoes on your plate, particularly if it is a big plate, and not realize that you have just helped yourself to three portions instead of one.
The food industry makes following the 2015 Dietary Guidelines a challenge. In many restaurants and eating establishments, portion sizes have increased, use of SoFAS has increased, and consequently the typical meal contains more calories than it used to. In addition, our sedentary lives make it difficult to expend enough calories during normal daily activities. In fact, more than one-third of adults are not physically active at all.
As food sizes and servings increase it is important to limit the portions of food consumed on a regular basis. Dietitians have come up with some good hints to help people tell how large a portion of food they really have. Some suggest using common items such as a deck of cards while others advocate using your hand as a measuring rule.
See Table below for some examples.
Source: American Cancer Society. “Controlling Portion Sizes.” Last revised January 12, 2012. http://www.cancer.org/Healthy/EatHealthyGetActive/TakeControlofYourWeight/controlling-portion-sizes.
Table \(2\): Determining Food Portions.
Food Product Amount Object Comparison Hand Comparison
Pasta, rice ½ c. Tennis ball Cupped hand
Fresh vegetables 1 c. Baseball
Cooked vegetables ½ c. Cupped hand
Meat, poultry, fish 3 oz. Deck of cards Palm of your hand
Milk or other beverages 1 c. Fist
Salad dressing 1 Tbsp. Thumb
Oil 1 tsp. Thumb tip
everyday connection
If you wait many hours between meals, there is a good chance you will overeat. To refrain from overeating try consuming small meals at frequent intervals throughout the day as opposed to two or three large meals. Eat until you are satisfied, not until you feel “stuffed.” Eating slowly and savoring your food allows you to both enjoy what you eat and have time to realize that you are full before you get overfull. Your stomach is about the size of your fist but it expands if you eat excessive amounts of food at one sitting. Eating smaller meals will diminish the size of your appetite over time so you will feel satisfied with smaller amounts of food.
Discretionary Calories
When following a balanced, healthful diet with many nutrient-dense foods, you may consume enough of your daily nutrients before you reach your daily calorie limit. The remaining calories are discretionary (to be used according to your best judgment). To find out your discretionary calorie allowance, add up all the calories you consumed to achieve the recommended nutrient intakes and then subtract this number from your recommended daily caloric allowance. For example, someone who has a recommended 2,000-calorie per day diet may eat enough nutrient-dense foods to meet requirements after consuming only 1,814 calories. The remaining 186 calories are discretionary. See Table \(1\). These calories may be obtained from eating an additional piece of fruit, adding another teaspoon of olive oil on a salad or butter on a piece of bread, adding sugar or honey to cereal, or consuming an alcoholic beverage[1].
The amount of discretionary calories increases with physical activity level and decreases with age. For most physically active adults, the discretionary calorie allowance is, at most, 15 percent of the recommended caloric intake. By consuming nutrient-dense foods, you afford yourself a discretionary calorie allowance.
Table \(3\): Sample Menu Plan Containing 2,000 Calories.
Meal Calories Total Meal/Snack Calories
Breakfast
1 scrambled egg 92
with sliced mushrooms and spinach 7
½ whole-wheat muffin 67
1 tsp. margarine-like spread 15
1 orange 65
8 oz. low-sodium tomato juice 53 299
Snack
6 oz. fat-free flavored yogurt 100
with ½ c. raspberries 32 132
Lunch
1 sandwich on pumpernickel bread 160
with smoked turkey deli meat, 30
4 slices tomato 14
2 lettuce leaves 3
1 tsp. mustard 3
1 oz. baked potato chips 110
½ c. blueberries, with 1 tsp. sugar 57
8 oz. fat-free milk 90 467
Snack
1 banana 105
7 reduced-fat high-fiber crackers 120 225
Dinner
1 c. Greek salad (tomatoes, cucumbers, feta) 150
with 5 Greek olives, 45
with 1.5 tsp. olive oil 60
3 oz. grilled chicken breast 150
½ c. steamed asparagus 20
with 1 tsp. olive oil, 40
with 1 tsp. sesame seeds 18
½ c. cooked wild rice 83
with ½ c. chopped kale 18
1 whole-wheat dinner roll 4
with 1 tsp. almond butter 33 691
(Total calories from all meals and snacks = 1,814)
Discretionary calorie allowance: 186
(Total calories from all meals and snacks = 1,814)
Discretionary calorie allowance: 186
Web Links and DRI
You can access the MyPlate Planner from the ChooseMyPlate website:
https://www.choosemyplate.gov/MyPlatePlan
Recommended amounts of food from each food group at different calorie levels can be found on the link: https://health.gov/dietaryguidelines/2015/guidelines/appendix-3/
Dietary Reference Intakes (DRIs) are more than numbers in the table, even though that is often how many people view them. DRIs and Dietary Guidelines provide different information for different audiences.
• Dietary Guidelines provide qualitative advice to the public about diet and chronic disease prevention and maintaining health.
• DRIs provide quantitative advice to professionals about amounts of nutrients or food components to be of benefit.
• DRIs are a collective term to refer to these components:
• Estimated Average Requirement (EAR)
• Recommended Dietary Allowance (RDA)
• Adequate Intake (AI)
• Tolerable Upper Intake Level (UL). A number of people refer to the UL as simply the “upper limit”, leaving off “tolerable”.
The RDA is the measure that professionals use to assess the quality of people's diets. It is the requirement estimated to meet the needs of 97.5% of the population. But the RDA is calculated using the EAR. Therefore, the EAR needs to be set before an RDA can be set. There must be applicable research in order to set an EAR. An EAR is the estimated requirement for 50% of the population (hence the average in its name).
Nutrition and the Athlete
Nutrition is essential to your performance during all types of exercise. The foods consumed in your diet are used to provide the body with enough energy to fuel an activity regardless of the intensity of activity. Athletes have different nutritional needs to support the vigorous level they compete and practice at.
Energy Needs
To determine an athletes nutritional needs, it is important to revisit the concept of energy metabolism. Energy intake is the foundation of an athlete’s diet because it supports optimal body functions, determines the amount of intake of macronutrients and micronutrients, and assists in the maintaining of body composition. Energy needs for athletes increase depending on their energy expenditure. The energy expended during physical activity are contingent on the intensity, duration, and frequency of the exercise. Competitive athletes may need 3,000 to over 5,000 calories daily compared to a typical inactive individual who needs about 2,000 calories per day. Energy needs are also affected by an individual’s gender, age, and weight. Weight-bearing exercises, such as running, burn more calories per hour than non-weight bearing exercises, such as swimming. Weight-bearing exercises requires your body to move against gravity which requires more energy. Men are also able to burn more calories than women for the same activity because they have more muscle mass which requires more energy to support and move around.[1]
Body weight and composition can have a tremendous impact on exercise performance. Body weight and composition are considered the focal points of physique for athletes because they are the able to be manipulated the most. Energy intake can play a role in manipulating the physiques for athletes. For individuals competing in sports such as football and weight lifting, having a large amount of muscle mass and increased body weight may be beneficial. This can be obtained through a combination of increased energy intake, and protein. Although certain physiques are more advantageous for specific sports, it is important to remember that a single and rigid “optimal” body composition is not recommended for any group of athletes.[2]
Macronutrient Needs
The composition of macronutrients in the diet is a key factor in maximizing performance for athletes. Carbohydrates are an important fuel source for the brain and muscle during exercise. Carbohydrate storage in the liver and muscle cells are relatively limited and therefore it is important for athletes to consume enough carbohydrates from their diet. Carbohydrate needs should increase about 3-10 g/kg/day depending on the type of training or competition.[3] See Table \(1\) for carbohydrate needs for athletes depending on the intensity of the exercise.
Table \(4\): Daily Needs for Carbohydrate Fuel.
Activity Level Example of Exercise Increase of Carbohydrate (g/kg of athlete’s body weight/day)
Light Low intensity or skill based activities 3-5
Moderate Moderate exercise program (about 1 hour per day) 5-7
High Endurance program (about 1-3 hours per day of moderate to high intensity exercise) 6-10
Very High Extreme commitment (4-5 hours per day of moderate to high intensity exercise) 8-12
Source: Nutrition and Athletic Performance. American College of Sports Medicine.Medicine & Science in Sports & Exercise. 2016; 48(3), 543- 568.
https://journals.lww.com/acsm-msse/Fulltext/2016/03000/Nutrition_and_Athletic_Performance.25.aspx. Accessed March 17, 2018.
Fat is a necessary component of a healthy diet to provide energy, essential fatty acids and to facilitate the absorption of fat-soluble vitamins. Athletes are recommended to consume the same amount of fat in the diet as the general population, 20-35% of their energy intake. Although these recommendations are in accordance with public health guidelines, athletes should individualize their needs based on their training level and body composition goals. Athletes who choose to excessively restrict their fat intake in an effort to lose body weight or improve body composition should ensure they are still getting the minimum recommended amount of fat. Fat intakes below 20% of energy intake will reduce the intake of fat-soluble vitamins and essential fatty acids, especially omega 3’s. [4]
Although protein accounts for only about 5% of energy expended, dietary protein is necessary to support metabolic reactions (that generate ATP), and to help muscles with maintenance, growth, and repair. During exercise, these metabolic reactions for generating ATP rely heavily on proteins such as enzymes and transport proteins. It is recommended that athletes consume 1.2 to 2.0 g/kg/day of proteins in order to support these functions. Higher intakes may also be needed for short periods of intense training or when reducing energy intake.[5] See Table \(2\) below for a better representation of protein needs depending on extent of training and dietary sources.
Table \(5\): The Recommended Protein Intakes for Individuals.
Group Protein Intake (g/kg body weight)
Most adults 0.8
Endurance athletes 1.2 to 1.4
Vegetarian endurance athletes 1.3 to 1.5
Strength athletes 1.6 to 1.7
Vegetarian strength athletes 1.7 to 1.8
Source: Dietary Reference Intakes, 2002 ACSM/ADA/Dietitians of Canada Position Statement: Nutrition & Athletic Performance, 2001. Accessed March 17, 2018.
It is important to consume adequate amounts of protein and to understand that the quality of the protein consumed affects the amount needed. High protein foods such as meats, dairy, and eggs contain all of the essential amino acids in relative amounts that most efficiently meet the body’s needs for growth, maintenance and repair of muscles. Vegetarian diets contain protein that has lower digestibility and amino acid patterns that do not match human needs as closely as most animal proteins. To compensate for this as well as the fact that plant food protein sources also contain higher amounts of fiber, higher protein intakes are recommended for vegetarian athletes. (See Table 16.2 “The Recommended Protein Intakes for Individuals” )
Micronutrient Needs
Vitamins and minerals are essential for energy metabolism, the delivery of oxygen, protection against oxidative damage, and the repair of body structures. When exercise increases, the amount of many vitamins and minerals needed are also increased due to the excess loss in nutrients. Currently, there is not special micronutrient recommendations made for athletes but most athletes will meet their needs by consuming a balanced diet that meets their energy needs. Because the energy needs of athletes increase, they often consume extra vitamins and minerals. The major micronutrients of concern for athletes include iron, calcium, vitamin D, and some antioxidants. [6]
Web Links
Estimated Calorie Needs per Day, by Age, Sex, and Physical Activity: https://health.gov/dietaryguidelines/2015/guidelines/appendix-2/
Nutrition and a Healthy Diet
There are five key factors that make up a healthful diet:
1. A diet must be adequate, by providing sufficient amounts of each essential nutrient, as well as fiber and adequate calories.
2. A balanced diet results when you do not consume one nutrient at the expense of another, but rather get appropriate amounts of all nutrients.
3. Calorie control is necessary so that the amount of energy you get from the nutrients you consume equals the amount of energy you expend during your day’s activities.
4. Moderation means not eating to the extremes, neither too much nor too little.
5. Variety refers to consuming different foods from within each of the food groups on a regular basis.
A healthy diet is one that favors whole foods. As an alternative to modern processed foods, a healthy diet focuses on “real” fresh whole foods that have been sustaining people for generations. Whole foods supply the needed vitamins, minerals, protein, carbohydrates, fats, and fiber that are essential to good health. Commercially prepared and fast foods are often lacking nutrients and often contain inordinate amounts of sugar, salt, saturated and trans fats, all of which are associated with the development of diseases such as atherosclerosis, heart disease, stroke, cancer, obesity, diabetes, and other illnesses. A balanced diet is a mix of food from the different food groups (vegetables, legumes, fruits, grains, protein foods, and dairy).
Adequacy
An adequate diet is one that favors nutrient-dense foods. Nutrient-dense foods are defined as foods that contain many essential nutrients per calorie. Nutrient-dense foods are the opposite of “empty-calorie” foods, such as sugary carbonated beverages, which are also called “nutrient-poor.” Nutrient-dense foods include fruits and vegetables, lean meats, poultry, fish, low-fat dairy products, and whole grains. Choosing more nutrient-dense foods will facilitate weight loss, while simultaneously providing all necessary nutrients.
Balance
Balance the foods in your diet. Achieving balance in your diet entails not consuming one nutrient at the expense of another. For example, calcium is essential for healthy teeth and bones, but too much calcium will interfere with iron absorption. Most foods that are good sources of iron are poor sources of calcium, so in order to get the necessary amounts of calcium and iron from your diet, a proper balance between food choices is critical. Another example is that while sodium is an essential nutrient, excessive intake may contribute to congestive heart failure and chronic kidney disease in some people. Remember, everything must be consumed in the proper amounts.
Moderation
Eat in moderation. Moderation is crucial for optimal health and survival. Eating nutrient-poor foods each night for dinner will lead to health complications. But as part of an otherwise healthful diet and consumed only on a weekly basis, this should not significantly impact overall health. It’s important to remember that eating is, in part, about enjoyment and indulging with a spirit of moderation. This fits within a healthy diet.
Monitor food portions. For optimum weight maintenance, it is important to ensure that energy consumed from foods meets the energy expenditures required for body functions and activity. If not, the excess energy contributes to gradual, steady accumulation of stored body fat and weight gain. In order to lose body fat, you need to ensure that more calories are burned than consumed. Likewise, in order to gain weight, calories must be eaten in excess of what is expended daily.
Variety
Variety involves eating different foods from all the food groups. Eating a varied diet helps to ensure that you consume and absorb adequate amounts of all essential nutrients required for health. One of the major drawbacks of a monotonous diet is the risk of consuming too much of some nutrients and not enough of others. Trying new foods can also be a source of pleasure—you never know what foods you might like until you try them.
Developing a healthful diet can be rewarding, but be mindful that all of the principles presented must be followed to derive maximal health benefits. For instance, introducing variety in your diet can still result in the consumption of too many high-calorie, nutrient poor foods and inadequate nutrient intake if you do not also employ moderation and calorie control. Using all of these principles together will promote lasting health benefits.
Summary
• MyPlate is the most up-to-date nutrition teaching tool developed by the United States Department of Agriculture (U.S.D.A.) Center for Nutrition Policy and Promotion as an easy to use visual guide to help all American develop healthy eating patterns.
• Planning a healthy diet using the MyPlate approach is not difficult. According to the icon, half of your plate should have fruits and vegetables, one-quarter should have whole grains, and one-quarter should have protein. Dairy products should be low-fat or non-fat.
• Energy needs for athletes increase depending on their energy expenditure. The energy expended during physical activity are contingent on the intensity, duration, and frequency of the exercise. Competitive athletes may need 3,000 to over 5,000 calories daily compared to a typical inactive individual who needs about 2,000 calories per day. Energy needs are also affected by an individual’s gender, age, and weight.
• There are five key factors that make up a healthful diet namely: a. adequacy, b. balance, c. calorie control, d. moderation, and e. variety.
• The total number of calories a person needs each day varies depending on a number of factors, including the person’s age, sex, height, weight, and level of physical activity. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.01%3A_Calories_-_Quantity_and_Quality.txt |
Learning Objective
List the dietary requirements for vitamins and minerals.
Learn about food supplements.
Learn about water balance.
The importance of vitamins and minerals (micronutrients) in metabolism has been discussed in detail in section 17.4. Micronutrient needs in adults differ slightly according to sex. Young men and women who are very athletic and perspire a great deal also require extra sodium, potassium, and magnesium. Males require more of vitamins C and K, along with thiamine, riboflavin, and niacin. Females require extra iron due to menstruation. Therefore, it can be beneficial for some young adults to follow a daily multivitamin regimen to help meet nutrient needs. But as always, it is important to remember “food first, supplements second.” Table \(1\) shows the micronutrient recommendations for adult men and women.
Table \(1\) Micronutrient Levels during Adulthood.
Nutrient Adult Males Adult Females
Vitamin A (mcg) 900.0 700.0
Vitamin B6 (mg) 1.3 1.3
Vitamin B12 (mcg) 2.4 2.4
Vitamin C (mg) 90.0 75.0
Vitamin D (mcg) 5.0 5.0
Vitamin E (mg) 15.0 15.0
Vitamin K (mcg) 120.0 90.0
Calcium (mg) 1,000.0 1,000.0
Folate (mcg) 400.0 400.0
Iron (mg) 8.0 18.0
Magnesium (mg) 400.0 310.0
Niacin (mg) 16.0 14.0
Phosphorus (mg) 700.0 700.0
Riboflavin (mg) 1.3 1.1
Selenium 55.0 55.0
Thiamin (mg) 1.2 1.1
Zinc (mg) 11.0 8.0
Source: Institute of Medicine. 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Washington, DC: The National Academies Press. https://doi.org/10.17226/11537. Accessed December 10, 2017.
Food Supplements and Food Replacements
Current trends also include the use of supplementation to promote health and wellness. Vitamins, minerals, herbal remedies, and supplements of all kinds constitute big business and many of their advertising claims suggest that optimal health and eternal youth are just a pill away. Dietary supplements can be macronutrient (amino acids, proteins, essential fatty acids), micronutrient (vitamins and minerals that promote healthy body functions), probiotic (beneficial bacteria such as the kind found in the intestines), and herbally ( often target a specific body part, such as bones) based.
Some public health officials recommend a daily multivitamin due to the poor diet of most North Americans. The US Preventive Task Force also recommends a level of folate intake which can be easier to achieve with a supplement. In addition, the following people may benefit from taking daily vitamin and mineral supplements:[1]
• Women who are pregnant or breastfeeding
• Premenopausal women who may need extra calcium and iron
• Older adults
• People with health issues that affect their ability to eat
• Vegetarians, vegans, and others avoiding certain food groups
However, before you begin using dietary supplementation, consider that the word supplement denotes something being added. Vitamins, minerals, and other assorted remedies should be considered as extras. They are add-ons—not replacements—for a healthy diet. As food naturally contains nutrients in its proper package, remember that food should always be your primary source of nutrients. When considering taking supplements, it is important to recognize possible drawbacks that are specific to each kind:[2]
• Micronutrient Supplements: Some vitamins and minerals are toxic at high doses. Therefore, it is vital to adhere to the Tolerable Upper Intake Levels (UL) so as not to consume too much of any vitamin. For example, too much vitamin A is toxic to the liver. Symptoms of vitamin A toxicity can include tinnitus (ringing in the ears), blurred vision, hair loss, and skin rash. Too much niacin can cause a peptic ulcer, hyperglycemia, dizziness, and gout.
• Herbal Supplements: Some herbs cause side effects, such as heart palpitations and high blood pressure, and must be taken very carefully. Also, some herbs have contraindications with certain medicines. For example, Valerian and St. John’s Wort negatively interact with certain prescription medications, most notably antidepressants. Additionally, there is a real risk of overdosing on herbs because they do not come with warning labels or package inserts.
• Amino Acid Supplements: Certain amino acid supplements, which are often taken by bodybuilders among others, can increase the risk of consuming too much protein. An occasional amino acid drink in the place of a meal is not a problem. However, problems may arise if you add the supplement to your existing diet. Most Americans receive two to three times the amount of protein required on a daily basis from their existing diets—taking amino acid supplements just adds to the excess. Also, certain amino acids share the same transport systems in the absorption process; therefore, a concentrated excess of one amino acid obtained from a supplement may increase the probability of decreased absorption of another amino acid that uses the same transport system. This could lead to deficiency in the competing amino acid.
Supplement Claims and Restrictions
The Food and Drug Administration (FDA) regulates supplements, but it treats them like food rather than pharmaceuticals. Dietary supplements must meet the FDA’s Good Manufacturing Standards, but are not required to meet the standards for drugs, although some companies do so voluntarily. Also, although supplement manufacturers are allowed to say a particular ingredient may reduce the risk of a disease or disorder, or that it might specifically target certain body systems, these claims are not approved by the FDA. This is why labels that make structural and functional claims are required to carry a disclaimer saying the product is not intended “to diagnose, treat, cure, or prevent any disease.” In addition, in the United States, supplements are taken off the market only after the FDA has proven that they are hazardous.[3] To revisit the topic of structural and functional claims refer back to Chapter 12 “Nutrition Applications”.
Before Taking Supplements
The phrase caveat emptor means “buyer beware,” and it is important to keep the term in mind when considering supplementation. Just because a product is “natural” does not mean it can’t be harmful or dangerous, particularly if used inappropriately. The following are helpful questions to explore before deciding to take a supplement:
• Does the scientific community understand how this supplement works and are all its effects well known?
• Is there proof that the supplement actually performs in the manner that it claims?
• Does this supplement interact with food or medication?
• Is taking this supplement necessary for my health?
• Is the supplement affordable?
• Is the supplement safe and free from contaminants?
Lastly, please remember that a supplement is only as good as the diet that accompanies it. We cannot overstate the importance of eating a healthy, well-balanced diet designed to provide all of the necessary nutrients. Food contains many more beneficial substances, such as phytochemicals and fiber, that promote good health and cannot be duplicated with a pill or a regimen of supplements. Therefore, vitamins and other dietary supplements should never be a substitute for food. Nutrients should always be derived from food first.
Food: The Best Medicine
Poor dietary choices and a sedentary lifestyle account for about 300–600 thousand deaths every year according to the US Department of Health and Human Services. That number is thirteen times higher than the deaths due to gun violence.[4] The typical North American diet is too high in saturated fat, sodium, and sugar, and too low in fiber in the form of whole fruits, vegetables, and whole grains to keep people healthy. With so many threats to optimal health it is vital to address those factors that are under your control, namely dietary and lifestyle choices. A diet that supplies your body with the needed energy and nutrients daily will result in efficient body functioning and in protection from disease. Making sound nutritional choices can also provide support for individuals undergoing treatment for short-term or chronic conditions. Finding a balance between nutritional needs with concerns about drug interactions can hasten recovery, improve quality of life, and minimize the side effects from treatment protocols.
Body Fluids and Electrolytes
Maintaining the right level of water in your body is crucial to survival, as either too little or too much water in your body will result in less-than-optimal functioning. One mechanism to help ensure the body maintains water balance is thirst. Thirst is the result of your body’s physiology telling your brain to initiate the thought to take a drink. Sensory proteins detect when your mouth is dry, your blood volume too low, or blood electrolyte concentrations too high and send signals to the brain stimulating the conscious feeling to drink.
The latest National Health and Nutrition Examination Survey, covering the period from 2005 to 2008, reports that about 50 percent of Americans consume sugary drinks daily.
Excess consumption of sugary soft drinks have been scientifically proven to increase the risk for dental caries, obesity, Type 2 diabetes, and cardiovascular disease. In addition to sugary soft drinks, beverages containing added sugars include fruit drinks, sports drinks, energy drinks and sweetened bottled waters.
Sports drinks are designed to rehydrate the body after excessive fluid depletion. Electrolytes in particular promote normal rehydration to prevent fatigue during physical exertion. Are they a good choice for achieving the recommended fluid intake? Are they performance and endurance enhancers like they claim? Who should drink them?
Typically, eight ounces of a sports drink provides between fifty and eighty calories and 14 to 17 grams of carbohydrate, mostly in the form of simple sugars. Sodium and potassium are the most commonly included electrolytes in sports drinks, with the levels of these in sports drinks being highly variable. The American College of Sports Medicine says a sports drink should contain 125 milligrams of sodium per 8 ounces as it is helpful in replenishing some of the sodium lost in sweat and promotes fluid uptake in the small intestine, improving hydration.
Gatorade
Gatorade was created in 1965, by a team of scientists at the University of Florida College of Medicine, including Robert Cade, Dana Shires, Harry James Free, and Alejandro de Quesada. Following a request from Florida Gators football head coach Ray Graves, Gatorade was created to help athletes by acting as a replacement for body fluids lost during physical exertion. The earliest version of the beverage consisted of a mixture of water,sodium, sugar, potassium, phosphate, and lemon juice.Ten players on the University of Florida football team tested the first version of Gatorade during practices and games in 1965, and the tests were deemed successful.
The University of Florida researchers initially considered naming their product "Gator-Aid". They settled on the name Gatorade, however, since the researchers wanted to create a commercial product, not a scientifically-validated one.
University of Florida football player Chip Hinton testing Gatorade in 1965, pictured next to the leader of its team of inventors, Robert Cade. Source: Wikipedia
Regulation of Daily Water Input
Total water output per day averages 2.5 liters (Figure \(1\)). This must be balanced with water input. Our tissues produce around 300 milliliters of water per day through metabolic processes. The remainder of water output must be balanced by drinking fluids and eating solid foods. The average fluid consumption per day is 1.5 liters, and water gained from solid foods approximates 700 milliliters.
The Food and Nutrition Board of the Institute of Medicine (IOM) has set the Adequate Intake (AI) for water for adult males at 3.7 liters (15.6 cups) and at 2.7 liters (11 cups) for adult females. These intakes are higher than the average intake of 2.2 liters. It is important to note that the AI for water includes water from all dietary sources; that is, water coming from food as well as beverages. People are not expected to consume 15.6 or 11 cups of pure water per day. In America, approximately 20 percent of dietary water comes from solid foods.
Consequences of Deficiency or Excess
As with all nutrients, having too much or too little water has health consequences. Excessive water intake can dilute the levels of critical electrolytes in the blood. Water intoxication is rare, however when it does happen, it can be deadly. On the other hand, having too little water in the body is common. In fact, diarrhea-induced dehydration is the number-one cause of early-childhood death worldwide. In this section we will discuss subtle changes in electrolytes that compromise health on a chronic basis.
High-Hydration Status: Water Intoxication/ Hyponatremia
Water intoxication mainly affects athletes who overhydrate. Water intoxication is extremely rare, primarily because healthy kidneys are capable of excreting up to one liter of excess water per hour. Overhydration was unfortunately demonstrated in 2007 by Jennifer Strange, who drank six liters of water in three hours while competing in a “Hold Your Wee for a Wii” radio contest. Afterward she complained of a headache, vomited, and died.
Low-Hydration Status: Dehydration
Dehydration refers to water loss from the body without adequate replacement. It can result from either water loss or electrolyte imbalance, or, most commonly, both. Dehydration can be caused by prolonged physical activity without adequate water intake, heat exposure, excessive weight loss, vomiting, diarrhea, blood loss, infectious diseases, malnutrition, electrolyte imbalances, and very high glucose levels. Physiologically, dehydration decreases blood volume. The water in cells moves into the blood to compensate for the low blood-volume, and cells shrink. Signs and symptoms of dehydration include thirst, dizziness, fainting, headaches, low blood-pressure, fatigue, low to no urine output, and, in extreme cases, loss of consciousness and death. Signs and symptoms are usually noticeable after about 2 percent of total body water is lost.
Chronic dehydration is linked to higher incidences of some diseases. There is strong evidence that low-hydration status increases the risk for kidney stones and exercise-induced asthma. There is also some scientific evidence that chronic dehydration increases the risk for kidney disease, heart disease, and the development of hyperglycemia in people with diabetes. Older people often suffer from chronic dehydration as their thirst mechanism is no longer as sensitive as it used to be.
Summary
• Micronutrient needs in adults differ slightly according to sex. Young men and women who are very athletic and perspire a great deal also require extra sodium, potassium, and magnesium. Males require more of vitamins C and K, along with thiamine, riboflavin, and niacin. Females require extra iron due to menstruation.
• Current trends also include the use of supplementation to promote health and wellness. Dietary supplements can be macronutrient (amino acids, proteins, essential fatty acids), micronutrient (vitamins and minerals that promote healthy body functions), probiotic (beneficial bacteria such as the kind found in the intestines), and herbally ( often target a specific body part, such as bones) based.
• The Food and Nutrition Board of the Institute of Medicine (IOM) has set the Adequate Intake (AI) for water for adult males at 3.7 liters (15.6 cups) and at 2.7 liters (11 cups) for adult females. It is important to note that the AI for water includes water from all dietary sources; that is, water coming from food as well as beverages.
• Total water output per day averages 2.5 liters which must be balanced with water input.
• Excessive water intake can dilute the levels of critical electrolytes in the blood. Water intoxication is rare, however when it does happen, it can be deadly. On the other hand, having too little water in the body is common. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.02%3A_Vitamins_Minerals_Fluids_and_Electrolytes.txt |
Learning Objective
• Learn about various recommendations for weight loss and weight management.
With over 70 percent of Americans currently overweight or obese, it isn’t surprising that many individuals report engaging in weight management efforts. 1 In fact, a 2019 report from a national survey on current trends in weight loss attempts and strategies found that 42 percent of adults in the United States had recently attempted to lose weight, primarily through reduced food consumption and exercise.
The National Weight Control Registry (NWCR) has tracked over ten thousand people who have been successful in losing at least 30 pounds and maintaining this weight loss for at least one year. Their research findings show that 98 percent of participants in the registry modified their food intake, and 94 percent increased their physical activity, mainly by walking.
Although there were a great variety of approaches taken by NWCR members to achieve successful weight loss, most have reported that their approach involved adhering to a low-calorie, low-fat diet and doing high levels of activity (about one hour of exercise per day). Moreover, most members eat breakfast every day, watch fewer than ten hours of television per week, and weigh themselves at least once per week. About half of them lost weight on their own, and the other half used some type of weight-loss program. 11 In most scientific studies, successful weight loss is accomplished only by changing the diet and increasing physical activity together. Doing one without the other limits the amount of weight lost and the length of time that weight loss is sustained.
Evidence-Based Dietary Recommendations
The 2015 Dietary Guidelines for Americans offers specific, evidence-based recommendations for dietary changes aimed at keeping calorie intake in balance with physical activity, which is key for weight management. These recommendations include:
Follow a healthy eating pattern that accounts for all foods and beverages within an appropriate calorie level that includes:
• A variety of vegetables from all of the subgroups—dark green, red and orange, legumes (beans and peas), starchy, and other
• Fruits, especially whole fruits
• Grains, at least half of which are whole grains
• Fat-free or low-fat dairy, including milk, yogurt, cheese, and/or fortified soy beverages
• A variety of protein foods, including seafood, lean meats and poultry, eggs, legumes (beans and peas), and nuts, seeds, and soy products
• Oils
A healthy eating pattern limits:
• Saturated fats and trans fats
• Added sugars
• Sodium
Key quantitative recommendations are provided for several components of the diet that should be limited. These components are of particular public health concern in the United States, and the specified limits can help individuals achieve healthy eating patterns within calorie limits[5]:
• Consume less than 10 percent of calories per day from added sugars
• Consume less than 10 percent of calories per day from saturated fats
• Consume less than 2,300 milligrams (mg) per day of sodium
If alcohol is consumed, it should be consumed in moderation—up to one drink per day for women and up to two drinks per day for men—and only by adults of legal drinking age.
Dietary Food Trends
In the past, health was regarded merely as the absence of illness. However, a growing understanding of the complexity and potential of the human condition has prompted a new way of thinking about health. Today, we focus on the idea of wellness, which involves a great deal more than just not being sick. Wellness is a state of optimal well-being that enables an individual to maximize their potential. This concept includes a host of dimensions—physical, mental, emotional, social, environmental, and spiritual—which affect one’s quality of life. Striving for wellness begins with an examination of dietary choices.
Hundreds of years ago, when food was less accessible and daily life required much more physical activity, people worried less about obesity and more about simply getting enough to eat. In today’s industrialized nations, conveniences have solved some problems and introduced new ones, including the hand-in-hand obesity and diabetes epidemics. Fad diets gained popularity as more North Americans struggled with excess pounds. However, new evidence-based approaches that emphasize more holistic measures are on the rise. These new dietary trends encourage those seeking to lose weight to eat healthy, whole foods first, while adopting a more active lifestyle. These sound practices put dietary choices in the context of wellness and a healthier approach to life.
Functional Foods
Many people seek out foods that provide the greatest health benefits. This trend is giving rise to the idea of functional foods, which not only help meet basic nutritional needs but also are reported to fight illness and aging. According to the Academy of Nutrition and Dietetics (AND), formerly known as the The American Dietetic Association, functional foods may reduce the risk of disease or promote optimal health. The AND recognizes four types of functional foods. They are: conventional foods, modified foods, medical foods, and special dietary use foods.
The first group, conventional foods, represents the simplest form of functional foods. They are whole foods that have not been modified. Examples include whole fruits and vegetables (which are abundant in phytochemicals and antioxidants), yogurt and kefir (which contain natural probiotic bacteria that can help maintain digestive system health), and moderate amounts of dark chocolate, made with 70% or more cacao (which contains antioxidants).
Modified foods have been fortified, enriched, or enhanced with additional nutrients or bioactive compounds. Foods are modified using biotechnology to improve their nutritional value and health attributes. Examples of modified foods include calcium-fortified orange juice, breads enriched with B vitamins, iodized salt, cereals fortified with vitamins and minerals, margarine enhanced with plant sterols, and energy drinks that have been enriched with herbs (ginseng or guarana) or amino acids (taurine). It is important to consider that the health claims of some modified foods may be debatable, or entirely fraudulent. Check with a health professional regarding the effects of modified foods on your health.
Medical foods are designed for enteric administration under the guidance of a medical professional. (During enteric administration, food is treated so that it goes through the stomach undigested. Instead, the food is broken down in the intestines only.) Medical foods are created to meet very specific nutritional requirements. Examples of medical foods include liquid formulas for people with kidney disease, liver disease, diabetes, or other health issues. Medical food is also given to comatose patients through a gastronomy tube because they cannot eat by mouth.
Special dietary use foods do not have to be administered under a doctor’s care and can be found in a variety of stores. Similar to medical foods, they address special dietary needs and meet the nutritional requirements of certain health conditions. For example, a bottled oral supplement administered under medical supervision is a medical food, but it becomes a special dietary use food when it is sold to retail customers. Examples of special dietary use foods include gluten-free foods, lactose-free dairy products, and formulas and shakes that promote weight loss.
Popular Diets
The concept of functional foods represents initiatives aimed at addressing health problems. Certain diet plans take this concept one step further, by striving to prevent or treat specific conditions. For example, it is widely understood that people with diabetes need to follow a particular diet. Although some of these diet plans may be nutritionally sound, use caution because some diets may be fads or be so extreme that they actually cause health problems.
Before experimenting with a diet, discuss your plans with your doctor or a registered dietitian. Table \(1\) lists the pros and cons of the more popular diets. Some fall under the category of fad diets, while others are backed by scientific evidence. Those that fall into the latter category provide a good foundation to build a solid regimen for optimal health.
Table \(1\) The Pros and Cons of Seven Popular Diets.
Diet Pros Cons
DASH Diet
Recommended by the National Heart, Lung, and Blood Institute, the American Heart Association, and many physicians
Helps to lower blood pressure and cholesterol
Reduces risk of heart disease and stroke
Reduces risk of certain cancers
Reduces diabetes risk
There are very few negative factors associated with the DASH diet
Risk for hyponatremia
Gluten-Free Diet
Reduces the symptoms of gluten intolerance, such as chronic diarrhea, cramping, constipation, and bloating
Promotes healing of the small intestines for people with celiac disease, preventing malnutrition
May be beneficial for other autoimmune diseases, such as Parkinson’s disease, rheumatoid arthritis, and multiple sclerosis
Risk of folate, iron, thiamin, riboflavin, niacin, and vitamin B6 deficiencies
Special gluten-free products can be hard to find and expensive
Requires constant vigilance and careful food label reading, since gluten is found in many products
Low-Carb Diet
Restricts refined carbohydrates, such as white flour and white sugar
May temporarily improve blood sugar or blood cholesterol levels
Not entirely evidence-based
Results in higher fat and protein consumption
Does not meet the RDA for carbohydrates to provide glucose to the brain
Macrobiotic Diet
Low in saturated fats and high in fiber
Emphasizes whole foods and de-emphasizes processed foods
Rich in phytoestrogens, which may reduce the risk of estrogen-related cancers
Not entirely evidence-based
Lacks certain vitamins and minerals; supplements are often required
Can result in a very low caloric intake
Lack of energy may result from inadequate protein
Mediterranean Diet
A reduced risk of cardiovascular disease and mortality
A lower risk of cancer
De-emphasizes processed foods and emphasizes whole foods and healthy fats
Lower sodium intake, due to fewer processed foods
Emphasis on monosaturated fats leads to lower cholesterol
Highlighting fruits and vegetables raises consumption of antioxidants
Does not specify daily serving amounts
Potential for high fat and high calorie intake as nuts and oils are calorie-dense foods
Drinking one to two glasses of wine per day may not be healthy for those with certain conditions
Raw Food Diet
Emphasizes whole foods
Focuses on nutritionally-rich foods
Not entirely evidence-based
Very restrictive and limits protein and healthy fat intake
Could encourage the development of foodborne illness
Extremely difficult to follow
High in fiber which can cause essential nutrient deficiencies
Vegetarianism and Veganism
May reduce some chronic diseases such as cancer, heart disease, and Type 2 diabetes
May help with weight reduction and weight maintenance
Guidelines regarding fat and nutrient consumption must be followed
Higher risk for nutrient deficiencies such as protein, iron, zinc, omega-3, vitamin B12
Consumption of a high fiber diet interferes with mineral and nutrient bioavailability
Vegetarian and vegan protein sources are lower quality with majority missing at least one essential amino acids
Evidence-Based Physical Activity Recommendations
The other part of the energy balance equation is physical activity. The Dietary Guidelines are complemented by the 2018 Physical Activity Guidelines for Americans, issued by the Department of Health and Human Services (HHS) in an effort to provide evidence-based guidelines for appropriate physical activity levels. These guidelines provide recommendations to Americans aged three and older about how to improve health and reduce chronic disease risk through physical activity. Increased physical activity has been found to lower the risk of heart disease, stroke, high blood pressure, Type 2 diabetes, colon, breast, and lung cancer, falls and fractures, depression, and early death. Increased physical activity not only reduces disease risk, but also improves overall health by increasing cardiovascular and muscular fitness, increasing bone density and strength, improving cognitive function, and assisting in weight loss and weight maintenance.
The key guidelines for adults include the following:
• Adults should move more and sit less throughout the day. Some physical activity is better than none. Adults who sit less and do any amount of moderate-to-vigorous physical activity gain some health benefits.
• For substantial health benefits, adults should do at least 150 minutes (2 hours and 30 minutes) to 300 minutes (5 hours) per week of moderate-intensity aerobic activity, or 75 minutes (1 hour and 15 minutes) to 150 minutes (2 hours and 30 minutes) per week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity .
• Preferably, aerobic activity should be spread throughout the week.
• Engaging in physical activity beyond the equivalent of 300 minutes (5 hours) of moderate-intensity physical activity per week can result in additional health benefits and may help with weight loss and weight loss maintenance.
• Adults should also do muscle-strengthening activities of at least moderate intensity that involve all major muscle groups on 2 or more days per week, as these activities provide additional health benefits . Exercises such as push-ups, sit-ups, squats, and lifting weights are all examples of muscle-strengthening activities.
The 2018 Physical Activity Guidelines broadly classify moderate physical activities as those when you “can talk, but not sing, during the activity” and vigorous activities as those when you “cannot say more than a few words without pausing for a breath.” 14 Despite the indisputable benefits of regular physical activity, a 2018 report from the American Heart Association estimates that 8 out of 10 Americans do not meet these guidelines. 2
Given the number of Americans that are falling short on both nutrition and physical activity recommendations, it is easy to see that these two areas of behavior are of primary interest in improving the health and weight of our nation.
Evidence-Based Behavioral Recommendations
Behavioral weight loss interventions have been described as approaches “used to help individuals develop a set of skills to achieve a healthier weight. It is more than helping people to decide what to change; it is helping them identify how to change.” Cornerstones for these interventions typically include self-monitoring through daily recording of food intake and exercise, nutrition education and dietary changes, physical activity goals, and behavior modification. Research shows that these types of interventions can result in weight loss and a lower risk for type 2 diabetes, and similar maintenance strategies lead to less weight regained later.
Behavioral interventions have been shown to help individuals achieve and maintain weight loss of at least 5 percent from baseline weight. The Food and Drug Administration (FDA) considers a 5 percent weight loss to be clinically significant, as this level of weight loss has been shown to improve cardiometabolic risk factors such as blood lipid levels and insulin sensitivity. 17,18 The behavioral intervention team often includes primary care clinicians, dietitians , psychologists, behavioral therapists, exercise physiologists, and lifestyle coaches. These programs may include a variety of delivery methods, often through group classes of 10-20 participants both in-person and online, and may use print-based or technology-based materials and resources. The interventions usually span one to two years with more frequent contact in the initial months (weekly to bi-monthly) followed by less frequent contact (monthly) in the latter months, or maintenance phase.17 A variety of behavioral topics are covered over the course of the program and range from nutrition education and goal-setting to problem-solving and assertiveness. Relapse prevention is included as participants move into the maintenance phase.
Summary
• The 2015 Dietary Guidelines for Americans offers specific, evidence-based recommendations for dietary changes aimed at keeping calorie intake in balance with physical activity, which is key for weight management.
• These new dietary trends encourage those seeking to lose weight to eat healthy, whole foods first, while adopting a more active lifestyle. These sound practices put dietary choices in the context of wellness and a healthier approach to life.
• Increased physical activity not only reduces disease risk, but also improves overall health by increasing cardiovascular and muscular fitness, increasing bone density and strength, improving cognitive function, and assisting in weight loss and weight maintenance.
• Behavioral interventions have been shown to help individuals achieve and maintain weight loss of at least 5 percent from baseline weight. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.03%3A_Weight_Loss_-_Diets_and_Exercise.txt |
Learning Objectives
• Be able to calculate body mass index (BMI) given a particular weight and height.
• Name the factors that affect body composition and distribution.
What should you weigh? This has been a difficult question to answer because humans come in so many different sizes and shapes. We do know that carrying too much fat is not good for one's health. Thus fat is a huge factor in determining fitness. Ideal body weight (IBW) has been used to determine one's desirable weight.
Ideal Body Weight
The “ideal” healthy body weight for a particular person is dependent on many things, such as frame size, sex, muscle mass, bone density, age, and height. The perception of the “ideal” body weight is additionally dependent on cultural factors and the mainstream societal advertisement of beauty.
To standardize the “ideal” body weight and relate it to health, scientists have devised mathematical formulas to better define a healthy weight. These mathematically derived measurements are used by health professionals to correlate disease risk with populations of people and at the individual level. A clinician will take two measurements, one of weight and one of fat mass, in order to diagnose obesity. Some measurements of weight and body fat that do not require using technical equipment can easily be calculated and help provide an individual with information on weight, fat mass, and distribution, and their relative risk of some chronic diseases.
Body Mass Index: How to Measure It and Its Limitations
Body mass index (BMI) is calculated using height and weight measurements and is more predictive of body fatness than weight alone. BMI measurements are used to indicate whether an individual may be underweight (with a BMI less than 18.5), overweight (with a BMI over 25), or obese (with a BMI over 30). High BMI measurements can be warning signs of health hazards ahead, such as cardiovascular disease, Type 2 diabetes, and other chronic diseases. BMI-associated health risks vary by race. Asians face greater health risks for the same BMI than Caucasians, and Caucasians face greater health risks for the same BMI than African Americans.
Very high AND very low BMI's appear to increase a person's risk of dying. If you look at a graph of BMI (Figure $1$ ) as it relates to your risk of dying, it has a "J-shaped Curve" or a "U-shaped Curve" because being too low and/or too high both raise your risk of mortality. Instead, you'd like to be in the middle range of the BMI which is what they use for "Normal weight".
Calculating BMI
To calculate your BMI, multiply your weight in pounds by 703 (conversion factor for converting to metric units) and then divide the product by your height in inches, squared.
$BMI = [weight (lb) \times 703] \div height (in)^2 \nonumber$
or
$BMI = [weight (kg)] \div height (m)^2 \nonumber$
BMI Calculators and BMI Categories
The National Heart, Lung, and Blood Institute and the CDC have automatic BMI calculators on their websites:
To see how your BMI indicates the weight category you are in, see Table $1$ or use a chart of weight and height to figure out your BMI.
Table $1$ BMI Categories
Categories BMI
Underweight < 18.5
Normal weight 18.5–24.9
Overweight 25–29.9
Obese 30.0-34.9
Severe 35-40
Source: National Heart, Lung, and Blood Institute. Accessed November 4, 2012. http://www.nhlbi.nih.gov.
BMI Limitations
A BMI is a fairly simple measurement and does not take into account fat mass or fat distribution in the body, both of which are additional predictors of disease risk. Body fat weighs less than muscle mass. Therefore, BMI can sometimes underestimate the amount of body fat in overweight or obese people and overestimate it in more muscular people. For instance, a muscular athlete will have more muscle mass (which is heavier than fat mass) than a couch potato of the same height. Based on their BMIs the muscular athlete would be less “ideal” and may be categorized as more overweight or obese than the couch potato; however, this is an infrequent problem with BMI calculation. Additionally, an older person with osteoporosis (decreased bone mass) will have a lower BMI than an older person of the same height without osteoporosis, even though the person with osteoporosis may have more fat mass. A BMI is a useful inexpensive tool to categorize people and is highly correlative with disease risk, but other measurements are needed to diagnose obesity and more accurately assess disease risk.
BMI is not a good measure for children and adolescents because they are growing. A new BMI for these ages was recently introduced in which the weight in kg is divided by the height in meters cubed. Its use is not well-established yet.
BMI does not consider where the fat is located. Individuals with abdominal fat or android shape have a greater risk of obesity associated diseases than individuals who carry their fat in the hips (gynoid or "pear shape"). Men tend to be "apple-shaped" while women tend to be "pear shaped." Gynoid shape tends to be associated with fewer health risks. For this reason, a ratio of body waist circumference to hip circumference may be measured and the ratio calculated. If you are male and your ratio is greater than 0.95, then you have excessive abdominal fat. If you are female and your ratio is greater than 0.86, then you have excessive abdominal fat.
Measuring Body Fat Content
Water, organs, bone tissue, fat, and muscle tissue make up a person’s weight. Having more fat mass may be indicative of disease risk, but fat mass also varies with sex, age, and physical activity level. Females have more fat mass, which is needed for reproduction and, in part, is a consequence of different levels of hormones. The optimal fat content of a female is between 20 and 30 percent of her total weight and for a male is between 12 and 20 percent. Fat mass can be measured in a variety of ways. The simplest and lowest-cost way is the skin-fold test. A health professional uses a caliper to measure the thickness of skin on the back, arm, and other parts of the body and compares it to standards to assess body fatness. It is a noninvasive and fairly accurate method of measuring fat mass, but similar to BMI, is compared to standards of mostly young to middle-aged adults.
Other methods of measuring fat mass are more expensive and more technically challenging. They include:
• Underwater weighing. This technique requires a chamber full of water big enough for the whole body to fit in. First, a person is weighed outside the chamber and then weighed again while immersed in water. Bone and muscle weigh more than water, but fat does not—therefore a person with a higher muscle and bone mass will weigh more when in water than a person with less bone and muscle mass.
• Bioelectric Impedance Analysis (BIA). This device is based on the fact that fat slows down the passage of electricity through the body. When a small amount of electricity is passed through the body, the rate at which it travels is used to determine body composition. These devices are also sold for home use and commonly called body composition scales.
Figure $3$: BIA Hand Device. Image by United States Marine Corps / U.S. Public Domain.
Dual-energy X-ray absorptiometry (DEXA). This can be used to measure bone density. It also can determine fat content via the same method, which directs two low-dose X-ray beams through the body and determines the amount of the energy absorbed from the beams. The amount of energy absorbed is dependent on the body’s content of bone, lean tissue mass, and fat mass. Using standard mathematical formulas, fat content can be accurately estimated.
Figure $4$: Dual-Energy X-ray Absorptiometry (DEXA). “A Dual-energy X-ray absorptiometry (DEXA) scan” by Nick Smith / CC BY-SA 3.0.
Measuring Fat Distribution
Total body-fat mass is one predictor of health; another is how the fat is distributed in the body. You may have heard that fat on the hips is better than fat in the belly—this is true. Fat can be found in different areas in the body and it does not all act the same, meaning it differs physiologically based on location. Fat deposited in the abdominal cavity is called visceral fat and it is a better predictor of disease risk than total fat mass. Visceral fat releases hormones and inflammatory factors that contribute to disease risk. The only tool required for measuring visceral fat is a measuring tape. The measurement (of waist circumference) is taken just above the belly button. Men with a waist circumference greater than 40 inches and women with a waist circumference greater than 35 inches are predicted to face greater health risks.
Figure $5$: Fat Distribution.
The waist-to-hip ratio is often considered a better measurement than waist circumference alone in predicting disease risk. To calculate your waist-to-hip ratio, use a measuring tape to measure your waist circumference and then measure your hip circumference at its widest part. Next, divide the waist circumference by the hip circumference to arrive at the waist-to-hip ratio. Observational studies have demonstrated that people with “apple-shaped” bodies, (who carry more weight around the waist) have greater risks for chronic disease than those with “pear-shaped” bodies, (who carry more weight around the hips). A study published in the November 2005 issue of Lancet with more than twenty-seven thousand participants from fifty-two countries concluded that the waist-to-hip ratio is highly correlated with heart attack risk worldwide and is a better predictor of heart attacks than BMI.[1]. Abdominal obesity is defined by the World Health Organization (WHO) as having a waist-to-hip ratio above 0.90 for males and above 0.85 for females.
Summary
Most people who are overweight also have excessive body fat and therefore body weight is an indicator of obesity in much of the population.
To standardize the “ideal” body weight and relate it to health, scientists have devised some computational measurements to better define a healthy ideal weight. Body weight in relation to height is called BMI and is correlated with disease risk.
Total body fat mass is another predictor of disease risk; another is where the fat is distributed. Fat deposits in different areas in the body and do not all act the same, meaning it differs physiologically based on location. Visceral fat contributes more to disease risk, for example. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.04%3A_Measuring_Fitness.txt |
Learning Objectives
• Describe how muscle contraction occurs.
• Explain the difference between aerobic and anaerobic exercise.
Muscle cells are specialized for contraction. Muscles allow for motions such as walking, and they also facilitate bodily processes such as respiration and digestion. The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle (Figure \(1\)).
Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure.
Muscle Contraction
Muscle contraction occurs when muscle fibers get shorter. Literally, the muscle fibers get smaller in size. To understand how this happens, you need to know more about the structure of muscle fibers.
Structure of Muscle Fibers
Each muscle fiber contains hundreds of organelles called myofibrils. Each myofibril is made up of two types of protein filaments: actin filaments, which are thinner, and myosin filaments, which are thicker. Actin filaments are anchored to structures called Z lines (Figure 13.13.2). The region between two Z lines is called a sarcomere. Within a sarcomere, myosin filaments overlap the actin filaments. The myosin filaments have tiny structures called cross bridges that can attach to actin filaments.
Sliding Filament Theory
The most widely accepted theory explaining how muscle fibers contract is called the sliding filament theory. According to this theory, myosin filaments use energy from ATP to “walk” along the actin filaments with their cross bridges. This pulls the actin filaments closer together. The movement of the actin filaments also pulls the Z lines closer together, thus shortening the sarcomere.
When all of the sarcomeres in a muscle fiber shorten, the fiber contracts. A muscle fiber either contracts fully or it doesn’t contract at all. The number of fibers that contract determines the strength of the muscular force. When more fibers contract at the same time, the force is greater.
Muscles and Nerves
Muscles cannot contract on their own. They need a stimulus from a nerve cell to “tell” them to contract. Let’s say you decide to raise your hand in class. Your brain sends electrical messages to nerve cells, called motor neurons, in your arm and shoulder. The motor neurons, in turn, stimulate muscle fibers in your arm and shoulder to contract, causing your arm to rise. Involuntary contractions of cardiac and smooth muscles are also controlled by nerves.
Energy for Muscle Contraction: ATP
The source of energy that is used to power the movement of contraction in working muscles is adenosine triphosphate (ATP) – the body’s biochemical way to store and transport energy. ATP provides the energy for cross-bridge formation and filament sliding. However, ATP is not stored to a great extent in cells.
All muscle cells have a little ATP within them that they can use immediately – but only enough to last for about 3 seconds!
So once muscle contraction starts, the making of more ATP must start quickly. Since ATP is so important, the muscle cells have several different ways to make it. These systems work together in phases. The three biochemical systems for producing ATP are, in order:
1. Creatine phosphate can supply the energy needs of a working muscle at a very high rate, but only for about 8–10 seconds.
2. Glycogen is then used to make ATP from glucose. But this takes about 12 chemical reactions so it supplies energy more slowly than from creatine phosphate. It’s still pretty rapid, though, and will produce enough energy to last about 90 seconds. Oxygen is not needed – this is great, because it takes the heart and lungs some time to get increased oxygen supply to the muscles. A by-product of making ATP without using oxygen is lactic acid. You know when your muscles are building up lactic acid because it causes tiredness and soreness – the stitch.
3. Within two minutes of exercise, the body starts to supply working muscles with oxygen. When oxygen is present, aerobic respiration can take place to break down the glucose for ATP. This glucose can come from several places:
• remaining glucose supply in the muscle cells
• glucose from food in the intestine
• glycogen in the liver
• fat reserves in the muscles
• in extreme cases (like starvation), the body’s protein.
Aerobic respiration takes even more chemical reactions to produce ATP than either of the above two systems. It is the slowest of all three systems – but it can supply ATP for several hours or longer, as long as the supply of fuel lasts.
Aerobic Exercise: Plenty of Oxygen
Aerobic exercise (also known as cardio) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "relating to, involving, or requiring free oxygen", and refers to the use of oxygen to adequately meet energy demands during exercise. Generally, light-to-moderate intensity activities that are sufficiently supported by aerobic metabolism can be performed for extended periods of time. When practiced in this way, examples of cardiovascular/aerobic exercise are medium to long distance running/jogging, swimming, cycling, and walking, according to the first extensive research on aerobic exercise, conducted in the 1960s on over 5,000 U.S. Air Force personnel by Dr. Kenneth H. Cooper.
Cardio
Kenneth Cooper was the first person to introduce the concept of aerobic exercise. In the 1960s, Cooper started research into preventive medicine. He became intrigued by the belief that exercise can preserve one's health. In 1970 he created his own institute (the Cooper Institute) for non-profit research and education devoted to preventive medicine. He sparked millions into becoming active and is now known as the "father of aerobics".
What is generally called aerobic exercise might be better termed "solely aerobic", because it is designed to be low-intensity enough not to generate lactate (or lactic acid), so that all carbohydrate is aerobically turned into energy.
Initially during increased exertion, muscle glycogen is broken down to produce glucose, which undergoes glycolysis producing pyruvate (Figure \(4\)) which then reacts with oxygen(Krebs cycle, Chemiosmosis) to produce carbon dioxide and water and releases energy. As glycogen levels in the muscle begin to fall, glucose is released into the bloodstream by the liver, and fat metabolism is increased so that it can fuel the aerobic pathways. Aerobic exercise may be fueled by glycogen reserves, fat reserves, or a combination of both, depending on the intensity.
Aerobic exercise comprises innumerable forms. In general, it is performed at a moderate level of intensity over a relatively long period of time. For example, running a long distance at a moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity, while golf or two person team tennis, with brief bursts of activity punctuated by more frequent breaks, may not be predominantly aerobic. Some sports are thus inherently "aerobic", while other aerobic exercises, such as fartlek training or aerobic dance classes, are designed specifically to improve aerobic capacity and fitness. It is most common for aerobic exercises to involve the leg muscles, primarily or exclusively. There are some exceptions. For example, rowing to distances of 2,000 m or more is an aerobic sport that exercises several major muscle groups, including those of the legs, abdominals, chest, and arms. Common kettlebell exercises combine aerobic and anaerobic aspects.
Anaerobic Exercise and Oxygen Debt
Anaerobic exercise is a type of exercise that breaks down glucose in the body without using oxygen; anaerobic means “without oxygen”. In practical terms, this means that anaerobic exercise is more intense, but shorter in duration than aerobic exercise.The biochemistry of anaerobic exercise involves a process called glycolysis, in which glucose is converted to adenosine triphosphate (ATP), which is the primary source of energy for cellular reactions.Lactic acid is produced at an increased rate during anaerobic exercise, causing it to build up quickly (Figure \(5\)).Anaerobic exercise may be used to help build endurance, muscle strength, and power.
The by-product of anaerobic glycolysis—lactate—has traditionally been thought to be detrimental to muscle function. However, this appears likely only when lactate levels are very high. Elevated lactate levels are only one of many changes that occur within and around muscle cells during intense exercise that can lead to fatigue. Fatigue, that is muscle failure, is a complex subject that depends on more than just changes to lactate concentration. Energy availability, oxygen delivery, perception to pain, and other psychological factors all contribute to muscular fatigue. Elevated muscle and blood lactate concentrations are a natural consequence of any physical exertion. The effectiveness of anaerobic activity can be improved through training.
Anaerobic exercise also increases an individual's basal metabolic rate (BMR). Some examples of anaerobic exercises include sprints, high-intensity interval training (HIIT), and strength training.
Lactic acid can be converted back to pyruvate in well-oxygenated muscle cells; however, during exercise the focus in on maintaining muscle activity. Lactic acid is transported to the liver where it can be stored prior to conversion to glucose in the presence of oxygen via the Cori Cycle. The amount of oxygen required to restore the lactic acid balance is often referred to as the oxygen debt.
Overview of Anaerobic and Aerobic Metabolism
Anaerobic metabolism occurs in the cytosol of the muscle cells. As seen in Figure \(6\), a small amount of ATP is produced in the cytosol without the presence of oxygen. Anaerobic metabolism uses glucose as its only source of fuel and produces pyruvate and lactic acid. Pyruvate can then be used as fuel for aerobic metabolism. Aerobic metabolism takes place in the mitochondria of the cell and is able to use carbohydrates, protein or fat as its fuel source. Aerobic metabolism is a much slower process than anaerobic metabolism but produces majority of the ATP.
Different forms of exercise use different systems to produce ATP
A sprinter is getting ATP in a very different way to a marathon runner.
• Using creatine phosphate – This would be the major system used for short bursts (weightlifters or short distance sprinters) because it is fast but lasts for only 8–10 seconds.
• Using glycogen (no oxygen) – This lasts for 1.3–1.6 minutes, so it would be the system used in events like the 100 meter swim or the 200 m or 400 m run.
• Using aerobic respiration – This lasts for an unlimited time, so it’s the system used in endurance events like marathon running, rowing, distance skating and so on.
Fuel Sources for Aerobic and Anaerobic Metabolism
The fuel sources for anaerobic and aerobic metabolism will change depending on the amount of nutrients available and the type of metabolism. Glucose may come from blood glucose (which is from dietary carbohydrates or liver glycogen and glucose synthesis) or muscle glycogen. Glucose is the primary energy source for both anaerobic and aerobic metabolism. Fatty acids are stored as triglycerides in muscles but about 90% of stored energy is found in adipose tissue. As low to moderate intensity exercise continues using aerobic metabolism, fatty acids become the predominant fuel source for the exercising muscles. Although protein is not considered a major energy source, small amounts of amino acids are used while resting or doing an activity. The amount of amino acids used for energy metabolism increase if the total energy intake from your diet does not meet the nutrient needs or if you are involved in long endurance exercises.
Physical Activity Intensity and Fuel Use
The exercise intensity determines the contribution of the type of fuel source used for ATP production(see Figure \(8\)). Both anaerobic and aerobic metabolism combine during exercise to ensure that the muscles are equipped with enough ATP to carry out the demands placed on them. The amount of contribution from each type of metabolism will depend on the intensity of an activity. When low-intensity activities are performed, aerobic metabolism is used to supply enough ATP to muscles. However, during high-intensity activities more ATP is needed so the muscles must rely on both anaerobic and aerobic metabolism to meet the body’s demands.
During low-intensity activities, the body will use aerobic metabolism over anaerobic metabolism because it is more efficient by producing larger amounts of ATP. Fatty acids are the primary energy source during low-intensity activity. With fat reserves in the body being almost unlimited, low-intensity activities are able to continue for a long time. Along with fatty acids, a small amount of glucose is used as well. Glucose differs from fatty acids where glycogen storages can be depleted. As glycogen stores are depleted, fatigue will eventually set in.
Figure \(8\): The Effect of Exercise Intensity on Fuel Sources.
Summary
• The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Skeleton muscle tissue is composed of sarcomeres, the functional units of muscle tissue.
• Muscle contraction occurs when sarcomeres shorten, as thick and thin filaments slide past each other, which is called the sliding filament model of muscle contraction.
• ATP provides the energy for cross-bridge formation and filament sliding.
• Aerobic exercise (also known as cardio) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process (aerobic metabolism). Aerobic refers to the use of oxygen to adequately meet energy demands during exercise.
• Anaerobic exercise is a physical exercise intense enough that there is lack of oxygen. If there is a shortage of oxygen (anaerobic exercise, explosive movements), carbohydrate is consumed more rapidly and the pyruvate converts into lactate via the anaerobic process.
• The exercise intensity determines the contribution of the type of fuel source used for ATP production
Contributors
• General Biology OpenSTAX
• Template:ContribUofHawaiiNutrition
• Libretexts: Chemistry for Allied Health (Soult)
• Libretexts: Introductory Biology (CK-12)
• Wikipedia
• Anatomy and Physiology (Boundless) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.05%3A_Some_Muscular_Chemistry.txt |
Learning Objectives
• Know the different supplements and drugs that are used to maintain or enhance athletic performance.
• List the use and abuse of anabolic steroids.
Fitness Supplements
In October 1994, the Dietary Supplement Health and Education Act (DSHEA) was signed into law in the USA. Under DSHEA, responsibility for determining the safety of the dietary supplements changed from government to the manufacturer and supplements no longer required approval from the U.S. Food and Drug Administration (FDA) before distributing product. Since that time manufacturers did not have to provide FDA with the evidence to substantiate safety or effectiveness unless a new dietary ingredient was added. It is widely believed that the 1994 DSHEA further consolidated the position of the supplement industry and lead to additional product sales.
Protein
Bodybuilders may supplement their diets with protein for reasons of convenience, lower cost (relative to meat and fish products) and to avoid the concurrent consumption of carbohydrates and fats. In addition, some argue that bodybuilders, by virtue of their unique training and goals, require higher-than-average quantities of protein to support maximal muscle growth; however there is no compelling evidence and no scientific consensus for bodybuilders to consume more protein than the recommended dietary allowance.
Protein supplements are sold in ready-to-drink shakes, bars, meal replacement products (see below), bites, oats, gels and powders. Protein powders are the most popular and may have flavoring added for palatability. The powder is usually mixed with water, milk or juice and is generally consumed immediately before and after exercising, or in place of a meal. The sources of protein are as follows, and differ in protein quality depending on their amino acid profile and digestibility:
• Whey protein contains high levels of all the essential amino acids and branched-chain amino acids. It also has the highest content of the amino acid cysteine, which aids in the biosynthesis of glutathione. For bodybuilders whey protein provides amino acids used to aid in muscle recovery. Whey protein is derived from the process of making cheese from milk. There are three types of whey protein: whey concentrate, whey isolate, and whey hydrolysate. Whey concentrate is 29–89% protein by weight whereas whey isolate is 90%+ protein by weight. Whey hydrolysate is enzymatically predigested and therefore has the highest rate of digestion of all protein types. Whey protein is usually taken immediately before and after a workout
• Casein protein (or milk protein) has glutamine, and casomorphin. Casein is usually taken before going to bed.
• Soy protein from soybeans contain isoflavones, a type of phytoestrogen.
• Egg-white protein is a lactose- and dairy-free protein.
• Hemp protein from hemp seed, contains highly-digestible protein, and hemp oil is high in essential fatty acids.
• Rice protein, when made from the whole grain, is a protein source that is highly digestible and allergen free. Since rice protein is low in the amino acid lysine, it is often combined with pea protein powder to achieve a superior amino acid profile.
• Pea protein is a hypoallergenic protein with a lighter texture than most other protein powders. Pea protein has an amino acid profile similar to that of soy, but pea protein does not elicit concerns about unknown effects of phytoestrogens. Pea protein is also less allergenic than soy. Pea protein has high fiber content and has no allergic ingredients and therefore is easy for digestion as compared to whey protein. Pea protein is a slow digesting protein and is able to keep you full longer.
Some nutritionists claim that osteoporosis may occur from excessive protein intake because protein can put pressure on the kidneys and lead to bone loss due to calcium leaching. However, some have suggested that higher calcium excretion may be due to a corresponding increase in protein-induced calcium absorption in the intestines. In addition to complete proteins, some supplements will contain protein fragments such as branched-chain amino acids or individual amino acids (such as glutamine). Amino acids are considered to be inferior to whole protein and have been used by some companies to artificially inflate and falsify protein values in their product (protein spiking). Many protein supplements explicitly indicate on the label that no protein spiking has occurred.
Branched-chain amino acids
Amino acids are the building blocks of protein; the body breaks consumed protein into amino acids in the stomach and intestines. Amino acids are classified as essential, conditionally essential and non-essential. There are three branched-chain amino acids (BCAAs): leucine, isoleucine, and valine. All three branched-chain amino acids are essential amino acids. Each has numerous benefits on various biological processes in the body. Unlike other amino acids, BCAAs are metabolized in the muscle and have an anabolic/anti-catabolic effect on it. There is some evidence that BCAA's may enhance muscle recovery after intense physical activity and no side effects have been reported at this time.
Glutamine
Glutamine is the most abundant amino acid found in human muscle and is commonly found in supplements or as a micronized, instantly soluble powder because supplement manufacturers claim the body's natural glutamine stores are depleted during anaerobic exercise. Some studies have shown there to be no significant effect of glutamine on bench press strength, knee-extension torque or lean muscle mass when compared to controls taking a placebo, though another study found that glutamine is beneficial in raising T-helper/suppressor cell ratio in long-distance runners.
Essential fatty acids
The essential fatty acids (alpha-linolenic acid and linoleic acid) may be important to supplement while bodybuilding; these cannot readily be made in the body, but are required for various functions within the body to take place. Fatty fish, such as fresh salmon and trout are rich in essential fatty acids and fish oils can also be taken in supplement form. Flaxseed oil, often sold as a supplement on its own, is an ideal source of alpha-Linolenic acid, which can also be found in walnuts and pumpkin seeds.
Prohormone
Prohormones are precursors to hormones and are most typically sold to bodybuilders as a precursor to the natural hormone testosterone. This conversion requires naturally occurring enzymes in the body. Side effects are not uncommon, as prohormones can also convert further into DHT and estrogen. To deal with this, many supplements also have aromatase inhibitors and DHT blockers such as chrysin and 4-androstene-3,6,17-trione. To date most prohormone products have not been thoroughly studied, and the health effects of prolonged use are unknown. Although initially available over the counter, their purchase was made illegal without a prescription in the US in 2004, and they hold similar status in many other countries. They remain legal, however, in the United Kingdom and the wider European Union. Their use is prohibited by most sporting bodies.
Creatine
Creatine is an organic acid naturally occurring in the body that supplies energy to muscle cells for short bursts of energy (as required in lifting weights) via creatine phosphate replenishment of ATP. A number of scientific studies have shown that creatine can improve strength, energy, muscle mass, and recovery times. In addition, recent studies have also shown that creatine improves brain function. and reduces mental fatigue.Unlike steroids or other performance-enhancing drugs, creatine can be found naturally in many common foods such as herring, tuna, salmon, and beef.
Creatine increases what is known as cell volumization by drawing water into muscle cells, making them larger. This intracellular retention should not be confused with the common myth that creatine causes bloating (or intercellular water retention). Creatine is sold in a variety of forms, including creatine monohydrate and creatine ethyl ester, amongst others. Though all types of creatine are sold for the same purposes, there are subtle differences between them, such as price and necessary dosage. Some studies have suggested that consumption of creatine with protein and carbohydrates can have a greater effect than creatine combined with either protein or carbohydrates alone.
β-Hydroxy β-methylbutyrate
When combined with an appropriate exercise program, dietary supplementation with β-hydroxy β-methylbutyrate (HMB) has been shown to dose-dependently augment gains in muscle hypertrophy (i.e., the size of a muscle), muscle strength, and lean body mass, reduce exercise-induced skeletal muscle damage, and expedite recovery from high-intensity exercise. HMB is believed to produce these effects by increasing muscle protein synthesis and decreasing muscle protein breakdown by various mechanisms, including activation of the mechanistic target of rapamycin (mTOR) and inhibition of the proteasome in skeletal muscles. The inhibition of exercise-induced skeletal muscle damage by HMB is affected by the time that it is used relative to exercise. The greatest reduction in skeletal muscle damage from a single bout of exercise appears to occur when calcium HMB is ingested 1–2 hours prior to exercise.
Thermogenic products
A thermogenic is a broad term for any supplement that the manufacturer claims will cause thermogenesis, resulting in increased body temperature, increased metabolic rate, and consequently an increased rate in the burning of body fat and weight loss. Until 2004 almost every product found in this supplement category comprised the "ECA stack": ephedrine, caffeine and aspirin. However, on February 6, 2004 the Food and Drug Administration (FDA) banned the sale of ephedra and its alkaloid, ephedrine, for use in weight loss formulas. Several manufacturers replaced the ephedra component of the "ECA" stack with bitter orange or citrus aurantium (containing synephrine) instead of the ephedrine.
Controversies of Fitness Supplements
Mislabeling: According to University of Helsinki food safety professor Marina Heinonen, more than 90% of dietary supplement health claims are incorrect. While many of the claims are based on scientifically based physiological or biochemical processes, their use in bodybuilding parlance is often heavily colored by bodybuilding lore and industry marketing and as such may deviate considerably from traditional scientific usages of the terms. In addition, ingredients listed have been found at times to be different from the contents. In 2015, Consumer Reports reported unsafe levels of arsenic, cadmium, lead and mercury in several of the protein powders that were tested. Other studies in 2013 showed that one-third of the supplements tested contained unlisted steroids. In 2015 a CBC investigative report found that protein spiking (the addition of amino acid filler to manipulate analysis) was not uncommon, however many of the companies involved challenged these claims.
Health problems: The US FDA reports 50,000 health problems a year due to dietary supplements and these often involve bodybuilding supplements. For example, the "natural" best-seller Craze, 2012's "New Supplement of the Year" by bodybuilding.com, sold in Walmart, Amazon etc., was found to contain undisclosed amphetamine-like compounds. Also other products by Matt Cahill have contained dangerous substances causing blindness or liver damages, and experts say that Cahill is emblematic for the whole industry.
Liver damage: The incidence of liver damage from dietary supplements has tripled in a decade, the majority of these involved bodybuilding supplements. This resulted in liver transplants and, in some cases, death to the patient. Some have argued that the liver damage is more often caused by prescription drugs rather than supplements.
Lack of effectiveness: In addition to being potentially harmful, some have argued that there is little evidence to indicate any benefit to using bodybuilding supplements. For example, according to the IOC, no consensus had been reached in determining whether an individual in exercise training benefits from protein and amino acid supplements. "In view of the lack of compelling evidence to the contrary, no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise".
Caffeine and Athletic Performance
Caffeine is a proven ergogenic aid in humans. Caffeine improves athletic performance in aerobic (especially endurance sports) and anaerobic conditions. Moderate doses of caffeine (around 5 mg/kg) can improve sprint performance, cycling and running time trial performance, endurance (i.e., it delays the onset of muscle fatigue and central fatigue), and cycling power output. Caffeine increases basal metabolic rate in adults. Caffeine ingestion prior to aerobic exercise increases fat oxidation, particularly in persons with low physical fitness.
Caffeine improves muscular strength and power, and may enhance muscular endurance. Caffeine also enhances performance on anaerobic tests. Caffeine consumption before constant load exercise is associated with reduced perceived exertion. While this effect is not present during exercise-to-exhaustion exercise, performance is significantly enhanced. This is congruent with caffeine reducing perceived exertion, because exercise-to-exhaustion should end at the same point of fatigue. Caffeine also improves power output and reduces time to completion in aerobic time trials, an effect positively (but not exclusively) associated with longer duration exercise.
Anabolic Steroids
Anabolic steroids are synthetic, or human-made, variations of the male sex hormone testosterone. The proper term for these compounds is anabolic-androgenic steroids. "Anabolic" refers to muscle building, and "androgenic" refers to increased male sex characteristics. Some common names for anabolic steroids are Gear, Juice, Roids, and Stackers. Health care providers can prescribe steroids to treat hormonal issues, such as delayed puberty. Steroids can also treat diseases that cause muscle loss, such as cancer and AIDS. But some athletes and bodybuilders misuse these drugs in an attempt to boost performance or improve their physical appearance.
The majority of people who misuse steroids are male weightlifters in their 20s or 30s. Anabolic steroid misuse is much less common in women. It is difficult to measure steroid misuse in the United States because many national surveys do not measure it. However, use among teens is generally minimal. The 2016 NIDA-funded Monitoring the Future study has shown that past-year misuse of steroids has declined among 8th and 10th graders in recent years, while holding steady for 12th graders.
People who misuse anabolic steroids usually take them orally, inject them into muscles, or apply them to the skin as a gel or cream. These doses may be 10 to 100 times higher than doses prescribed to treat medical conditions.
Commons patterns for misusing steroids include:
• cycling—taking multiple doses for a period of time, stopping for a time, and then restarting
• stacking—combining two or more different steroids and mixing oral and/or injectable types
• pyramiding—slowly increasing the dose or frequency of steroid misuse, reaching a peak amount, and then gradually tapering off to zero
• plateauing—alternating, overlapping, or substituting with another steroid to avoid developing a tolerance
There is no scientific evidence that any of these practices reduce the harmful medical consequences of these drugs.
How Anabolic Steroids Work
Anabolic steroids work differently from other drugs of abuse; they do not have the same short-term effects on the brain. The most important difference is that steroids do not directly activate the reward system to cause a “high”; they also do not trigger rapid increases in the brain chemical dopamine, which reinforces most other types of drug taking behavior. Misuse of anabolic steroids might lead to negative mental effects, such as: paranoid (extreme, unreasonable) jealousy, extreme irritability and aggression (“roid rage”), delusions—false beliefs or ideas, impaired judgment, and mania. Aside from mental effects, steroid use commonly causes severe acne. It also causes the body to swell, especially in the hands and feet.
Anabolic steroid misuse might lead to serious, even permanent, health problems such as kidney problems or failure, liver damage and tumors, enlarged heart, high blood pressure, and changes in blood cholesterol, all of which increase the risk of stroke and heart attack, even in young people, and increased risk of blood clots. Several other effects are gender- and age-specific:
• In men: shrinking testicles, decreased sperm count, baldness, development of breasts, increased risk for prostate cancer
• In women: growth of facial hair or excess body hair, decreased breast size, male-pattern baldness, changes in or stop in the menstrual cycle, enlarged clitoris, deepened voice
• In teens: stunted growth (when high hormone levels from steroids signal to the body to stop bone growth too early) and stunted height (if teens use steroids before their growth spurt)
Some of these physical changes, such as shrinking sex organs in men, can add to mental side effects such as mood disorders.
Anabolic Steroids Addiction
Even though anabolic steroids do not cause the same high as other drugs, they can lead to a substance use disorder. A substance use disorder occurs when a person continues to misuse steroids, even though there are serious consequences for doing so. The most severe form of a substance use disorder is addiction. People might continue to misuse steroids despite physical problems, high costs to buy the drugs, and negative effects on their relationships. These behaviors reflect steroids' addictive potential.
Research has further found that some steroid users turn to other drugs, such as opioids, to reduce sleep problems and irritability caused by steroids. People who misuse steroids might experience withdrawal symptoms when they stop use, including:fatigue, restlessness, loss of appetite, sleep problems, decreased sex drive and steroid cravings.
One of the more serious withdrawal symptoms is depression, which can sometimes lead to suicide attempts. Some people seeking treatment for anabolic steroid addiction have found a combination of behavioral therapy and medications to be helpful. In certain cases of addiction, patients have taken medicines to help treat symptoms of withdrawal. For example, health care providers have prescribed antidepressants to treat depression and pain medicines for headaches and muscle and joint pain. Other medicines have been used to help restore the patient's hormonal system.
Drugs, Athletic Performance, and Drug Screening
In competitive sports, doping is the use of banned athletic performance-enhancing drugs by athletic competitors. The term doping is widely used by organizations that regulate sporting competitions. The use of drugs to enhance performance is considered unethical, and therefore prohibited, by most international sports organizations, including the International Olympic Committee. Furthermore, athletes (or athletic programs) taking explicit measures to evade detection exacerbate the ethical violation with overt deception and cheating.
The origins of doping in sports go back to the very creation of sport itself. From ancient usage of substances in chariot racing to more recent controversies in baseball and cycling, popular views among athletes have varied widely from country to country over the years. The general trend among authorities and sporting organizations over the past several decades has been to strictly regulate the use of drugs in sport. The reasons for the ban are mainly the health risks of performance-enhancing drugs, the equality of opportunity for athletes, and the exemplary effect of drug-free sport for the public. Anti-doping authorities state that using performance-enhancing drugs goes against the "spirit of sport".
Many sports organizations have banned the use of performance-enhancing drugs and have very strict rules and penalties for people who are caught using them. The International Amateur Athletic Federation, now World Athletics, was the first international governing body of sport to take the situation seriously. In 1928 they banned participants from doping, but with little in the way of testing available they had to rely on the word of the athlete that they were clean. It was not until 1966 that FIFA and Union Cycliste Internationale (cycling) joined the IAAF in the fight against drugs, followed by the International Olympic Committee the following year. Progression in pharmacology has always outstripped the ability of sports federations to implement rigorous testing procedures but since the creation of the World Anti-Doping Agency in 1999, it has become more effective to catch athletes who use drugs. The first tests for athletes were at the 1966 European Championships and two years later the IOC implemented their first drug tests at both the Summer and Winter Olympics. Anabolic steroids became prevalent during the 1970s and after a method of detection was found they were added to the IOC's prohibited substances list in 1975, after which the 1976 Summer Olympics in Montreal were the first Olympic games which tested for them.
Exercise and the Brain
The neurobiological effects of physical exercise are numerous and involve a wide range of interrelated effects on brain structure, brain function, and cognition.[1][2][3][4]A large body of research in humans has demonstrated that consistent aerobic exercise (e.g., 30 minutes every day) induces persistent improvements in certain cognitive functions, healthy alterations in gene expression in the brain, and beneficial forms of neuroplasticity and behavioral plasticity; some of these long-term effects include: increased neuron growth, increased neurological activity (e.g., c-Fos and BDNF signaling), improved stress coping, enhanced cognitive control of behavior, improved declarative, spatial, and working memory, and structural and functional improvements in brain structures and pathways associated with cognitive control and memory.[1][2][3][4][5][6][7][8][9][10] The effects of exercise on cognition have important implications for improving academic performance in children and college students, improving adult productivity, preserving cognitive function in old age, preventing or treating certain neurological disorders, and improving overall quality of life.[1][11][12]
In healthy adults, aerobic exercise has been shown to induce transient effects on cognition after a single exercise session and persistent effects on cognition following regular exercise over the course of several months.[1][10][13] People who regularly perform aerobic exercise (e.g., running, jogging, brisk walking, swimming, and cycling) have greater scores on neuropsychological function and performance tests that measure certain cognitive functions, such as attentional control, inhibitory control, cognitive flexibility, working memory updating and capacity, declarative memory, spatial memory, and information processing speed.[1][5][7][9][10][13] The transient effects of exercise on cognition include improvements in most executive functions (e.g., attention, working memory, cognitive flexibility, inhibitory control, problem solving, and decision making) and information processing speed for a period of up to 2 hours after exercising.[13]
Aerobic exercise induces short- and long-term effects on mood and emotional states by promoting positive affect, inhibiting negative affect, and decreasing the biological response to acute psychological stress.[13] Over the short-term, aerobic exercise functions as both an antidepressant and euphoriant,[14][15][16][17] whereas consistent exercise produces general improvements in mood and self-esteem.
Regular aerobic exercise improves symptoms associated with a variety of central nervous system disorders and may be used as an adjunct therapy for these disorders. There is clear evidence of exercise treatment efficacy for major depressive disorder and attention deficit hyperactivity disorder.[11][16][20][21][22][23] The American Academy of Neurology's clinical practice guideline for mild cognitive impairment indicates that clinicians should recommend regular exercise (two times per week) to individuals who have been diagnosed with this condition.[24] Reviews of clinical evidence also support the use of exercise as an adjunct therapy for certain neurodegenerative disorders, particularly Alzheimer’s disease and Parkinson's disease. Regular exercise is also associated with a lower risk of developing neurodegenerative disorders.[28][31] A large body of preclinical evidence and emerging clinical evidence supports the use of exercise as an adjunct therapy for the treatment and prevention of drug addictions. Regular exercise has also been proposed as an adjunct therapy for brain cancers.[37]
Endorphins play a major role in the body's inhibitory response to pain. Endorphin production can be triggered by vigorous aerobic exercise. The release of β-endorphin has been postulated to contribute to the phenomenon known as a "runner's high." Endorphins may contribute to the positive effect of exercise on anxiety and depression. The same phenomenon may also play a role in exercise addiction. Regular intense exercise may cause the brain to downregulate the production of endorphins in periods of rest to maintain homeostasis, causing a person to exercise more intensely in order to receive the same feeling. However, several studies have supported the hypothesis that the runner's high is due to the release of endocannabinoids rather than that of endorphins.
Summary
• Anabolic steroids are synthetic variations of the male sex hormone testosterone. Health care providers can prescribe steroids to treat various medical conditions. But some athletes and bodybuilders misuse these drugs to boost performance or improve their physical appearance.
• People who abuse anabolic steroids usually take them orally, inject them into the muscles, or apply them to the skin with a cream or gel.
• People misuse steroids in a variety of doses and schedules. Misuse of anabolic steroids might lead to short-term effects, including paranoid jealousy, extreme irritability and aggression, delusions, impaired judgment, and mania. Continued steroid misuse can act on some of the same brain pathways and chemicals that are affected by other drugs, including dopamine, serotonin, and opioid systems.
• Caffeine improves athletic performance in aerobic (especially endurance sports) and anaerobic conditions.
• Anabolic steroid misuse might lead to serious long-term, even permanent, health problems. Several other effects are gender- and age-specific.
• Even though anabolic steroids do not cause the same high as other drugs, they can lead to addiction. Some people seeking treatment for anabolic steroid addiction have found behavioral therapy and medications to be helpful. Medicines can help treat symptoms of withdrawal in some cases.
• The use of drugs to enhance performance is considered unethical, and therefore prohibited, by most international sports organizations, including the International Olympic Committee.
• Endorphin production can be triggered by vigorous aerobic exercise.
Contributors and Attributions
• Wikipedia
• National Institute on Drug Abuse; National Institutes of Health; U.S. Department of Health and Human Services. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/19%3A_Fitness_and_Health/19.06%3A_Drugs_Athletic_Performance_and_the_Brain.txt |
Thumbnail: Herbicide. (Pixabay License; zefe wu via Pixabay).
20: Chemistry Down on the Farm
Learning Objectives
• Identify the three main macronutrients, the secondary macronutrients, and micronutrients that are essential for plant growth.
• Describe the different types of commercial fertilizers.
A fertilizer is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply one or more plant nutrients essential to the growth of plants. Many sources of fertilizer exist, both natural and industrially produced.[1]Commercial fertilizers, are applied to agricultural crops to increase crop yields, using equipment similar to what is shown in Figure \(1\). Before the 1950s, most farming occurred on small family farms with limited use of chemicals. The shift since then to larger corporate farms has coincided with the use of chemical fertilizers in modern agricultural practices. The three major types of commercial fertilizer used in the U.S. are nitrogen, phosphate, and potash.
Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration. This article, like many on fertilizers, emphasizes the nutritional aspect. Fertilizers typically provide, in varying proportions:[15]
• three main macronutrients:
• Nitrogen (N): leaf growth
• Phosphorus (P): Development of roots, flowers, seeds, fruit;
• Potassium (K): Strong stem growth, movement of water in plants, promotion of flowering and fruiting;
• three secondary macronutrients: calcium (Ca), magnesium (Mg), and sulfur (S);
• micronutrients: copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B). Of occasional significance are silicon (Si), cobalt (Co), and vanadium (V).
The nutrients required for healthy plant life are classified according to the elements, but the elements are not used as fertilizers. Instead compounds containing these elements are the basis of fertilizers. The macro-nutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to 6.0% on a dry matter (DM) (0% moisture) basis. Plants are made up of four main elements: hydrogen, oxygen, carbon, and nitrogen. Carbon, hydrogen and oxygen are widely available as water and carbon dioxide. Although nitrogen makes up most of the atmosphere, it is in a form that is unavailable to plants. Nitrogen is the most important fertilizer since nitrogen is present in proteins, DNA and other components (e.g., chlorophyll). To be nutritious to plants, nitrogen must be made available in a "fixed" form. Only some bacteria and their host plants (notably legumes) can fix atmospheric nitrogen (N2) by converting it to ammonia. Phosphate is required for the production of DNA and ATP, the main energy carrier in cells, as well as certain lipids. Table \(1\) lists features of various plant essential nutrients.
Plant Essential Nutrients - Texas A&M Agri-life Extension (Essential Nutrients for Plants)
https://agrilifeextension.tamu.edu/l...ts-for-plants/
Figure \(2\) A large, modern fertilizer spreader (right). Source: WIkipedia
Nitrogen Fertilizers
Nitrogen fertilizers are made from ammonia (NH3) produced by the Haber-Bosch process. In this energy-intensive process, natural gas (CH4) usually supplies the hydrogen, and the nitrogen (N2) is derived from the air. This ammonia is used as a feedstock for all other nitrogen fertilizers, such as anhydrous ammonium nitrate (NH4NO3) and urea (CO(NH2)2).
Deposits of sodium nitrate (NaNO3) (Chilean saltpeter) are also found in the Atacama desert in Chile and was one of the original (1830) nitrogen-rich fertilizers used. It is still mined for fertilizer. Nitrates are also produced from ammonia by the Ostwald process. Detailed information on different nitrogen fertilizers is given in (Table \(2\)).
Nitrogen Fertilizers - USDA
Table \(2\) USDA Nitrogen Fertilizer Guide.
https://www.nrcs.usda.gov/Internet/F...4p2_068185.pdf
Phosphorus Fertilizers
Phosphate fertilizers are obtained by extraction from phosphate rock, which contains two principal phosphorus-containing minerals, fluorapatite Ca5(PO4)3F (CFA) and hydroxyapatite Ca5(PO4)3OH. These minerals are converted into water-soluble phosphate salts by treatment with sulfuric (H2SO4) or phosphoric acids (H3PO4). The large production of sulfuric acid is primarily motivated by this application. In the nitrophosphate process or Odda process (invented in 1927), phosphate rock with up to a 20% phosphorus (P) content is dissolved with nitric acid (HNO3) to produce a mixture of phosphoric acid (H3PO4) and calcium nitrate (Ca(NO3)2). This mixture can be combined with a potassium fertilizer to produce a compound fertilizer with the three macronutrients N, P and K in easily dissolved form.
Potassium Fertilizers
Potash is a mixture of potassium minerals used to make potassium (K) fertilizers. Potash is soluble in water, so the main effort in producing this nutrient from the ore involves some purification steps; e.g., to remove sodium chloride (NaCl) (common salt). Sometimes potash is referred to as K2O, as a matter of convenience to those describing the potassium content. In fact, potash fertilizers are usually potassium chloride, potassium sulfate, potassium carbonate, or potassium nitrate.[29]
Other Essential Elements
Calcium, magnesium, and sulfur are essential to plant growth but are needed in lesser amounts than nitrogen, phosphorus, and potassium but in larger amounts than the micronutrients. Calcium, magnesium, and phosphorus alter pH when added to the soil. Calcium and magnesium results to an elevation of pH levels while sulfur does the opposite.
Calcium provides structural support in growing plants. Magnesium is the central atom found in the chlorophyll molecule and thus has an important role in photosynthesis. Sulfur is needed in chlorophyll development and protein synthesis.
Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of parts-per-million (ppm), ranging from 0.15 to 400 ppm or less than 0.04% dry matter.[16][17] These elements are often present at the active sites of enzymes that carry out the plant's metabolism. Because these elements enable catalysts (enzymes) their impact far exceeds their weight percentage. The main micronutrients are molybdenum, zinc, boron, and copper. These elements are provided as water-soluble salts. Iron presents special problems because it converts to insoluble (bio-unavailable) compounds at moderate soil pH and phosphate concentrations. For this reason, iron is often administered as a chelate complex, e.g., the EDTA derivative. The micronutrient needs depend on the plant and the environment. For example, sugar beets appear to require boron, and legumes require cobalt,[1] while environmental conditions such as heat or drought make boron less available for plants.[23]
Fertilizers a Mixed Bag
Multi nutrient fertilizers are common. They consist of two or more nutrient components.
Binary (NP, NK, PK) fertilizers. Major two-component fertilizers provide both nitrogen and phosphorus to the plants. These are called NP fertilizers. The main NP fertilizers are monoammonium phosphate (MAP) and diammonium phosphate (DAP). The active ingredient in MAP is NH4H2PO4. The active ingredient in DAP is (NH4)2HPO4. About 85% of MAP and DAP fertilizers are soluble in water.
NPK fertilizers are three-component fertilizers providing nitrogen, phosphorus, and potassium.
NPK rating is a rating system describing the amount of nitrogen, phosphorus, and potassium in a fertilizer. NPK ratings consist of three numbers separated by dashes (e.g., 10-10-10 or 16-4-8) describing the chemical content of fertilizers.[20][21] The first number represents the percentage of nitrogen in the product; the second number, P2O5; the third, K2O. Fertilizers do not actually contain P2O5 or K2O, but the system is a conventional shorthand for the amount of the phosphorus (P) or potassium (K) in a fertilizer. A 50-pound (23 kg) bag of fertilizer labeled 16-4-8 contains 8 lb (3.6 kg) of nitrogen (16% of the 50 pounds), an amount of phosphorus equivalent to that in 2 pounds of P2O5 (4% of 50 pounds), and 4 pounds of K2O (8% of 50 pounds). Most fertilizers are labeled according to this N-P-K convention, although Australian convention, following an N-P-K-S system, adds a fourth number for sulfur, and uses elemental values for all values including P and K.[22]
Organic Fertilizers
“Organic fertilizers” can be described as those fertilizers with an organic — biologic — origin—that is, fertilizers derived from living or formerly living materials. Organic fertilizers can also describe commercially available and frequently packaged products that strive to follow the expectations and restrictions adopted by “organic agriculture” and ”environmentally friendly" gardening — related systems of food and plant production that significantly limit or strictly avoid the use of synthetic fertilizers and pesticides. The “organic fertilizer” products typically contain both some organic materials as well as acceptable additives such as nutritive rock powders, ground sea shells (crab, oyster, etc.), other prepared products such as seed meal or kelp, and cultivated microorganisms and derivatives.
Fertilizers of an organic origin (the first definition) include animal wastes, plant wastes from agriculture, compost, and treated sewage sludge (biosolids). Beyond manures, animal sources can include products from the slaughter of animals — bloodmeal, bone meal, feather meal, hides, hoofs, and horns all are typical components.[15] Organically derived materials available to industry such as sewage sludge may not be acceptable components of organic farming and gardening, because of factors ranging from residual contaminants to public perception. On the other hand, marketed “organic fertilizers” may include, and promote, processed organics because the materials have consumer appeal. No matter the definition nor composition, most of these products contain less-concentrated nutrients, and the nutrients are not as easily quantified. They can offer soil-building advantages as well as be appealing to those who are trying to farm / garden more “naturally”.[30]
In terms of volume, peat is the most widely used packaged organic soil amendment. It is an immature form of coal and improves the soil by aeration and absorbing water but confers no nutritional value to the plants. It is therefore not a fertilizer as defined in the beginning of the article, but rather an amendment. Coir, (derived from coconut husks), bark, and sawdust when added to soil all act similarly (but not identically) to peat and are also considered organic soil amendments - or texturizers - because of their limited nutritive inputs. Some organic additives can have a reverse effect on nutrients — fresh sawdust can consume soil nutrients as it breaks down, and may lower soil pH — but these same organic texturizers (as well as compost, etc.) may increase the availability of nutrients through improved cation exchange, or through increased growth of microorganisms that in turn increase availability of certain plant nutrients. Organic fertilizers such as composts and manures may be distributed locally without going into industry production, making actual consumption more difficult to quantify.
Effects of Fertilizer Runoffs
Phosphorus and nitrogen fertilizers when commonly used have major environmental effects. This is due to high rainfalls causing the fertilizers to be washed into waterways. Agricultural run-off is a major contributor to the eutrophication of fresh water bodies. For example, in the US, about half of all the lakes are eutrophic. The main contributor to eutrophication is phosphate, which is normally a limiting nutrient; high concentrations promote the growth of cyanobacteria and algae, the demise of which consumes oxygen. Cyanobacteria blooms ('algal blooms') can also produce harmful toxins that can accumulate in the food chain, and can be harmful to humans.
The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in many parts of oceans, especially in coastal zones, lakes and rivers. The resulting lack of dissolved oxygen greatly reduces the ability of these areas to sustain oceanic fauna. The number of oceanic dead zones near inhabited coastlines are increasing. As of 2006, the application of nitrogen fertilizer is being increasingly controlled in northwestern Europe and the United States. If eutrophication can be reversed, it may take decades[citation needed] before the accumulated nitrates in groundwater can be broken down by natural processes.
Summary
• A fertilizer is any material (of natural or synthetic origin) that is applied to soil or to plant tissues that provides one or more plant nutrients essential to the growth of plants.
• Nitrogen, phosphorus, and potassium are the main macronutrients and calcium, magnesium, and sulfur are the secondary macronutrients in fertilizers.
• Copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B) are essential micronutrients that are needed by plants in relatively smaller quantities than the macronutrients.
• Phosphorus and nitrogen fertilizers when commonly used have major environmental effects. This is due to high rainfalls causing the fertilizers to be washed into waterways. Agricultural run-off is a major contributor to the eutrophication of fresh water bodies.
Contributors and Attributions
• Wikipedia
US Department of Agriculture (USDA)
“Secondary Plant Nutrients: Calcium, Magnesium, and Sulfur.” Mississippi State University Extension Service, extension.msstate.edu/publications/secondary-plant-nutrients-calcium-magnesium-and-sulfur.
“Essential Nutrients for Plants - How Do Nutrients Affect Plant Growth?” Texas A&M AgriLife Extension Service, 4 Mar. 2019, agrilifeextension.tamu.edu/library/gardening/essential-nutrients-for-plants/. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/20%3A_Chemistry_Down_on_the_Farm/20.01%3A_Farming_and_Chemicals-_Fertilizers.txt |
Learning Objective
• List the different types of pesticides and their uses.
Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, antimicrobial, and fungicide. The most common of these are herbicides which account for approximately 80% of all pesticide use. Most pesticides are intended to serve as plant protection products (also known as crop protection products), which in general, protect plants from weeds, fungi, or insects. As an example, the fungus Alternaria solani is used to combat the aquatic weed Salvinia.
In general, a pesticide is a chemical (such as carbamate) or biological agent (such as a virus, bacterium, or fungus) that deters, incapacitates, kills, or otherwise discourages pests. Target pests can include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, cause nuisance, or spread disease, or are disease vectors. Along with these benefits, pesticides also have drawbacks, such as potential toxicity to humans and other species.
Pesticides can be classified by target organism (e.g., herbicides, insecticides, fungicides, rodenticides, and pediculicides – see table), chemical structure (e.g., organic, inorganic, synthetic, or biological (biopesticide), although the distinction can sometimes blur), and physical state (e.g. gaseous (fumigant)). Biopesticides include microbial pesticides and biochemical pesticides. Plant-derived pesticides, or "botanicals", have been developing quickly. These include the pyrethroids, rotenoids, nicotinoids, and a fourth group that includes strychnine and scilliroside.:15
Since before 2000 BC, humans have utilized pesticides to protect their crops. The first known pesticide was elemental sulfur dusting used in ancient Sumer about 4,500 years ago in ancient Mesopotamia. The Rig Veda, which is about 4,000 years old, mentions the use of poisonous plants for pest control.[13] By the 15th century, toxic chemicals such as arsenic, mercury, and lead were being applied to crops to kill pests. In the 17th century, nicotine sulfate was extracted from tobacco leaves for use as an insecticide. The 19th century saw the introduction of two more natural pesticides, pyrethrum, which is derived from chrysanthemums, and rotenone, which is derived from the roots of tropical vegetables.[14] Until the 1950s, arsenic-based pesticides were dominant.[15] Paul Müller discovered that DDT was a very effective insecticide. Organochlorines such as DDT were dominant, but they were replaced in the U.S. by organophosphates and carbamates by 1975. Since then, pyrethrin compounds have become the dominant insecticide.[15] Herbicides became common in the 1960s, led by "triazine and other nitrogen-based compounds, carboxylic acids such as 2,4-dichlorophenoxyacetic acid, and glyphosate".
The discussion in this section will be focused mainly on insecticides and the next section on herbicides and defoliants. Many pesticides can be grouped into chemical families. Prominent insecticide families include organochlorines, organophosphates, and carbamates.
Table \(1\) below gives the LD50 values for some insecticides. In each case, the chemical was fed to laboratory rats. Note that the lower the LD50, the more toxic the chemical.
Table \(1\) LD50 Values for Various Insecticides.
Chemical Category Oral LD50 in Rats
(mg/kg)
Aldicarb ("Temik") Carbamate 1
Carbaryl ("Sevin") Carbamate 307
DDT Chlorinated hydrocarbon 87
Dieldrin Chlorinated hydrocarbon 40
Diflubenzuron ("Dimilin") Chitin inhibitor 10,000
Malathion Organophosphate 885
Methoprene JH mimic 34,600
Methoxychlor Chlorinated hydrocarbon 5,000
Parathion Organophosphate 3
Piperonyl butoxide Synergist 7,500
Pyrethrins Plant extract 200
Rotenone Plant extract 60
Note: LD50 (abbreviation for "lethal dose, 50%") of a toxin, radiation, or pathogen is the dose required to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity. A lower LD50 is indicative of increased toxicity.
Benefits of Using Pesticides
Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers get an estimated fourfold return on money they spend on pesticides. One study found that not using pesticides reduced crop yields by about 10%. Another study, conducted in 1999, found that a ban on pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world hunger.
There are two levels of benefits for pesticide use, primary and secondary. Primary benefits are direct gains from the use of pesticides and secondary benefits are effects that are more long-term.
Primary benefits
Controlling pests and plant disease vectors
• Improved crop yields
• Improved crop/livestock quality
• Invasive species controlled
Controlling human/livestock disease vectors and nuisance organisms
• Human lives saved and disease reduced. Diseases controlled include malaria, with millions of lives having been saved or enhanced with the use of DDT alone.
• Animal lives saved and disease reduced
Controlling organisms that harm other human activities and structures
• Drivers view unobstructed
• Tree/brush/leaf hazards prevented
• Wooden structures protected
Monetary
In one study, it was estimated that for every dollar (\$1) that is spent on pesticides for crops can yield up to four dollars (\$4) in crops saved. This means based that, on the amount of money spent per year on pesticides, \$10 billion, there is an additional \$40 billion savings in crop that would be lost due to damage by insects and weeds. In general, farmers benefit from having an increase in crop yield and from being able to grow a variety of crops throughout the year. Consumers of agricultural products also benefit from being able to afford the vast quantities of produce available year-round.
DDT: The Dream Insecticide - or Nightmare
DDT was the first of a long line of insecticides based on hydrocarbons with chlorine atoms replacing some of the hydrogen atoms. Its chemical name is dichloro, diphenyl, trichloroethane (see Figure \(\PageIndex{1a}\)).
a. b.
Figure \(1\) a. DDT and b. dieldrin
Some others:
• methoxychlor
• dieldrin (see Figure \(\PageIndex{1a}\)).
• dicofol (Kelthane®)
• endosulfan (Thiodan®, Phaser®)
DDT was introduced during World War II and, along with penicillin and the sulfa drugs, was responsible for the fact that this was the first war in history where trauma killed more people - combatants and noncombatants alike - than infectious disease.
DDT is effective against
• vectors of human diseases such as
• malaria and yellow fever (both transmitted by mosquitoes)
• plague (transmitted by fleas)
• many crop pests
Prior to the introduction of DDT, the number of cases of malaria in Ceylon (now Sri Lanka) was more than a million a year. By 1963 the disease had been practically eliminated from the island. However, growing concern about the hazards of DDT led to its abandonment there in the mid-1960s, and soon thereafter malaria became common once again.
DDT was especially effective against malarial mosquitoes because of its persistence and resistance to breakdown in the environment. One or two sprays a year on the walls of homes kept them free of mosquitoes. But DDT has several serious drawbacks.
Development of Insect Resistance
As early as 1946, Swedish workers discovered populations of houseflies resistant to DDT. This was quickly followed by many other reports of developing resistance. Other chlorinated hydrocarbons (like dieldrin and methoxychlor) were developed as substitutes, but in time insects developed resistance to these as well.
Biomagnification
Although no harmful effects from average exposures to DDT have been seen in humans, DDT and other chlorinated hydrocarbons have been shown to harm other species, such as fishes, earthworms, and robins. The hazard of DDT to nontarget animals is particularly acute for those species living at the top of food chains. Carnivores at the ends of long food chains (e.g., ospreys, pelicans, falcons, and eagles) once suffered serious declines in fecundity and hence in population size because of this. High levels of chlorinated hydrocarbons interfere with forming eggshells of normal thickness.
Organophosphates
The organophosphates, e.g., parathion (Figure \(2\) ), are related to the nerve gases developed during World War II. They react irreversibly with the enzyme acetylcholinesterase, which is responsible for inactivating acetylcholine (ACh) at neuromuscular junctions and at certain synapses in the central and peripheral nervous systems.
Some other examples:
• malathion
• diazinon
• phosmet (Imidan®)
• chlorpyrifos (Lorsban®)
Some of the organophosphates are very toxic. Parathion, for example, is 30 times more toxic than DDT. Each year organophosphates poison thousands of humans throughout the world, causing hundreds of deaths. Medical personnel caring for poisoning victims are also at risk. They may be seriously poisoned by the excretions of, and even the vapors emanating from, their patients.
Unlike chlorinated hydrocarbons,
• Organophosphates break down quickly in the environment, and thus residues on crops are less likely to be a problem.
• They are not stored in animal tissue, so biomagnification has not been a problem either.
For these reasons, their use has greatly reduced the hazard to non target species like ospreys and eagles (at the price of a much greater hazard to humans). Development of resistance is just as much a problem as it is with the chlorinated hydrocarbons. The carbamates were introduced in an attempt to keep ahead.
Carbamates
Carbamate insecticides are also inhibitors of acetylcholinesterase, but their action is reversible.
Some examples:
• carbaryl (Sevin®)
• aldicarb (Temik®)
• methomyl (Lannate®)
Features:
• These compounds are rapidly detoxified and excreted so their risk to warm-blooded animals is less than the other agents we have looked at.
• They are degraded rapidly in the environment so persistence is not a problem.
• They are, however, a danger to many useful insects, especially honeybees.
Growth Regulators
The members of this diverse group interfere in one way or another with insect development. Although most insect growth regulators do not affect adults, for many pests, it is the larval stages that are the most destructive.
Chitin Inhibitors
These substances, diflubenzuron (Dimilin®) is an example, interfere with the synthesis of chitin, the material that makes up the insect exoskeleton. It seems to have very low toxicity for vertebrates, but is harmful to crustaceans as well as insects. Its effect on fungi, which also synthesize chitin, needs to be studied.
Molting Disruptors
Insects must periodically shed their exoskeleton — called molting — in order to grow. Each molt is triggered by a steroid hormone called ecdysone.
A few synthetic ecdysone
• agonists, e.g.,
• tebufenozide (Confirm®)
• methoxyfenozide (Intrepid®)
• inhibitors, e.g., azadirachtin (Neemix®)
are now used as insecticides.
Organic Pesticides
Generally speaking, pesticides derived from natural materials or living organisms are allowed in organic production as long as they do not contain synthetic additives or are not specifically prohibited on the National List under § 205.602. By contrast, most synthetic pesticides are not allowed; those few that are can be found on the National List under § 205.601.
Allowed inputs typically include but are not limited to the following:
Botanical pesticides. Botanicals are derived from plants. They include pyrethrum, rotenone, sabadilla, neem, ryania, and garlic. Strychnine and nicotine are also botanicals, but are expressly prohibited in organic production. Since botanical pesticides are relatively nonselective, they can affect natural predators and other nontarget organisms. Rotenone, for example, is highly toxic to fish. For this reason, many organic growers use botanical pesticides only as a last resort.
Spray oils. Vegetable- or animal-derived oils are generally allowed as suffocating (stylet) oils, summer oils, dormant oils, and surfactants. Some petroleum-derived oils, referred to as “narrowrange oils,” are allowed for the same purposes. Spray oils are commonly used to control scale and mite pests. There are two organizations that review products and publish lists of products allowed for organic production: the Organic Materials Review Institute (OMRI) and the Washington State Department of Agriculture (WSDA) Organic Food Program.
Insecticidal soaps. Fatty acid insecticidal soaps are synthetic pesticides specifically allowed in organic production. Safer® Brand Insect Killing Soap Concentrate II is a product that is commonly used by organic farmers. Insecticidal soaps can be hard on beneficial predatory mites, so they should be used with caution.
Minerals. Mineral-based pesticides include sulfur, copper products, diatomaceous earth, and kaolin clay. These must be used with caution, even though they are allowed. Sulfur can reduce the populations of some beneficial insects and may burn plants if used during hot weather. Diatomaceous earth can cause respiratory problems and itching in the farmworkers who apply it. Copper can accumulate in soils, so it is allowed with restrictions. The organic regulations state that “copper-based materials must be used in a manner that minimizes accumulation in the soil…” Certifiers may require soil testing to verify that copper is not accumulating in the soil. Certain highly toxic minerals, including arsenic and lead, are specifically prohibited.
Pheromones. Pheromones are chemicals released from insects that cause other insects of the same species to change their behavior. Pheromones are not considered pesticides because they do not kill the insects. The pheromones used for pest control are often called mating disrupters because they alter mating behavior. Being totally natural, the pheromones themselves are allowed in organic production. However, some of the inert ingredients in mating disrupter products are prohibited.
Biological Pesticides
Biopesticides, a contraction of 'biological pesticides', include several types of pest management intervention: through predatory, parasitic, or chemical relationships. The term has been associated historically with biological pest control – and by implication, the manipulation of living organisms. Regulatory positions can be influenced by public perceptions, thus:
• in the EU, biopesticides have been defined as "a form of pesticide based on micro-organisms or natural products".
• the US EPA states that they "include naturally occurring substances that control pests (biochemical pesticides), microorganisms that control pests (microbial pesticides), and pesticidal substances produced by plants containing added genetic material (plant-incorporated protectants) or PIPs".
They are obtained from organisms including plants, bacteria and other microbes, fungi, nematodes, etc.[page needed] They are often important components of integrated pest management (IPM) programmes, and have received much practical attention as substitutes to synthetic chemical plant protection products (PPPs).
Biopesticides can be classified into these classes:
• Microbial pesticides which consist of bacteria, entomopathogenic fungi or viruses (and sometimes includes the metabolites that bacteria or fungi produce). Entomopathogenic nematodes are also often classed as microbial pesticides, even though they are multi-cellular.[page needed]
• Bio-derived chemicals. Four groups are in commercial use: pyrethrum, rotenone, neem oil, and various essential oils are naturally occurring substances that control (or monitor in the case of pheromones) pests and microbial diseases.
• Plant-incorporated protectants (PIPs) have genetic material from other species incorporated into their genetic material (i.e. GM crops). Their use is controversial, especially in many European countries.
• RNAi pesticides, some of which are topical and some of which are absorbed by the crop.
Biopesticides have usually no known function in photosynthesis, growth or other basic aspects of plant physiology. Instead, they are active against biological pests. Many chemical compounds have been identified that are produced by plants to protect them from pests so they are called antifeedants. These materials are biodegradable and renewable alternatives, which can be economical for practical use. Organic farming systems embraces this approach to pest control.
Examples
Bacillus thuringiensis, a bacterium capable of causing disease of Lepidoptera, Coleoptera and Diptera, is a well-known insecticide example. The toxin from B. thuringiensis (Bt toxin) has been incorporated directly into plants through the use of genetic engineering. The use of Bt Toxin is particularly controversial. Its manufacturers claim it has little effect on other organisms, and is more environmentally friendly than synthetic pesticides.
Other microbial control agents include products based on:
• entomopathogenic fungi (e.g. Beauveria bassiana, Isaria fumosorosea, Lecanicillium and Metarhizium spp.),
• plant disease control agents: include Trichoderma spp. and Ampelomyces quisqualis (a hyper-parasite of grape powdery mildew); Bacillus subtilis is also used to control plant pathogens.
• beneficial nematodes attacking insect (e.g. Steinernema feltiae) or slug (e.g. Phasmarhabditis hermaphrodita) pests
• entomopathogenic viruses (e.g.. Cydia pomonella granulovirus).
• weeds and rodents have also been controlled with microbial agents.
Various naturally occurring materials, including fungal and plant extracts, have been described as biopesticides. Products in this category include:
• Insect pheromones and other semiochemicals
• Fermentation products such as Spinosad (a macro-cyclic lactone)
• Chitosan: a plant in the presence of this product will naturally induce systemic resistance (ISR) to allow the plant to defend itself against disease, pathogens and pests.
• Biopesticides may include natural plant-derived products, which include alkaloids, terpenoids, phenolics and other secondary chemicals. Certain vegetable oils such as canola oil are known to have pesticidal properties[citation needed]. Products based on extracts of plants such as garlic have now been registered in the EU and elsewhere
Genetically Engineered Insect and Virus Resistance
Genetically modified crops (GM crops) are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. Plant genomes can be engineered by physical methods or by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors. In most cases, the aim is to introduce a new trait to the plant which does not occur naturally in the species. Examples in food crops include resistance to certain pests, diseases, environmental conditions, reduction of spoilage, resistance to chemical treatments (e.g. resistance to a herbicide), or improving the nutrient profile of the crop.
Insects
Tobacco, corn, rice and some other crops have been engineered to express genes encoding for insecticidal proteins from Bacillus thuringiensis (Bt). The introduction of Bt crops during the period between 1996 and 2005 has been estimated to have reduced the total volume of insecticide active ingredient use in the United States by over 100 thousand tons. This represents a 19.4% reduction in insecticide use.
In the late 1990s, a genetically modified potato that was resistant to the Colorado potato beetle was withdrawn because major buyers rejected it, fearing consumer opposition.
Viruses
Papaya, potatoes, and squash have been engineered to resist viral pathogens such as cucumber mosaic virus which, despite its name, infects a wide variety of plants. Virus resistant papaya were developed in response to a papaya ringspot virus (PRV) outbreak in Hawaii in the late 1990s. They incorporate PRV DNA. By 2010, 80% of Hawaiian papaya plants were genetically modified.
Potatoes were engineered for resistance to potato leaf roll virus and Potato virus Y in 1998. Poor sales led to their market withdrawal after three years.
Yellow squash that were resistant to at first two, then three viruses were developed, beginning in the 1990s. The viruses are watermelon, cucumber and zucchini/courgette yellow mosaic. Squash was the second GM crop to be approved by US regulators. The trait was later added to zucchini.
Many strains of corn have been developed in recent years to combat the spread of Maize dwarf mosaic virus, a costly virus that causes stunted growth which is carried in Johnson grass and spread by aphid insect vectors. These strands are commercially available although the resistance is not standard among GM corn variants.
Sterile Insect Technique
The sterile insect technique (SIT)[1][2] is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are preferably male, as this is more cost-effective and the females may in some situations cause damage by laying eggs in the crop, or, in the case of mosquitoes, taking blood from humans. The sterile males compete with wild males to mate with the females. Females that mate with a sterile male produce no offspring, thus reducing the next generation's population. Sterile insects are not self-replicating and, therefore, cannot become established in the environment. Repeated release of sterile males over low population densities can further reduce and in cases of isolation eliminate pest populations, although cost-effective control with dense target populations is subjected to population suppression prior to the release of the sterile males.
The technique has successfully been used to eradicate the screw-worm fly (Cochliomyia hominivorax) from North and Central America. Many successes have been achieved for control of fruit fly pests, most particularly the Mediterranean fruit fly (Ceratitis capitata) and the Mexican fruit fly (Anastrepha ludens). Active research is being conducted to determine this technique's effectiveness in combatting the Queensland Fruit Fly (Bactrocera tyroni).
Sterilization is induced through the effects of irradiation on the reproductive cells of the insects. SIT does not involve the release of insects modified through transgenic (genetic engineering) processes.[3] Moreover, SIT does not introduce non-native species into an ecosystem.
Pheromones: The Sex Trap
A pheromone trap is a type of insect trap that uses pheromones to lure insects. Sex pheromones and aggregating pheromones are the most common types used. A pheromone-impregnated lure, as the red rubber septa in the picture, is encased in a conventional trap such as a bottle trap, Delta trap, water-pan trap, or funnel trap. Pheromone traps are used both to count insect populations by sampling, and to trap pests such as clothes moths to destroy them.
Juvenile Hormone (JH)
In some insects, the final molt produces an adult that looks pretty much like the earlier larval stages. In others, like moths and butterflies, the final molt of the larva (caterpillar) produces a pupa. After a period of metamorphosis, the adult moth emerges.
Ecdysone (a steroidal hormone) triggers larva-to-larva molts as long as another hormone, called juvenile hormone (JH) see (Figure \(3\) ), is present. In its absence, ecdysone promotes the pupa-to-adult molt. Thus normal metamorphosis seems to occur when the output of JH diminishes spontaneously in the mature caterpillar.
When solutions of JH are sprayed on mature caterpillars, or on the foliage upon which they are feeding, their normal development is upset. This raises the possibility of using JH as an insecticide (one that might avoid the problem of developing resistance).
As it turns out, JH is too unstable to be practical, but some synthetic JH mimics, e.g.,
• methoprene (Altosid®)
• pyriproxyfen (Esteem®, Knack®, Distance®)
• diofenolan
are now being used.
Summary
• The term pesticide includes the substances used to control pests (which includes insects, mites, nematodes, plant pathogens, weeds, and vertebrates).
• Many pesticides can be grouped into chemical families which mainly include the insecticides organochlorines (e.g. DDT and dieldrin), organophosphates (e.g. parathion and malathion), and carbamates (e.g. carbaryl and aldicarb).
• Use of organic and biological pesticides are alternative means of pest control that is gaining popularity.
Contributor
• Wikipedia
• USDA
• Libretext: Biology (Kimball) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/20%3A_Chemistry_Down_on_the_Farm/20.02%3A_The_War_against_Pests.txt |
Learning Objective
• Describe the different kinds of widely used herbicides.
• List the different types of pesticide poisoning.
Herbicides, also commonly known as weedkillers, are substances used to control unwanted plants.[1] Selective herbicides control specific weed species, while leaving the desired crop relatively unharmed, while non-selective herbicides (sometimes called total weedkillers in commercial products) can be used to clear waste ground, industrial and construction sites, railways and railway embankments as they kill all plant material with which they come into contact. Apart from selective/non-selective, other important distinctions include persistence (also known as residual action: how long the product stays in place and remains active), means of uptake (whether it is absorbed by above-ground foliage only, through the roots, or by other means), and mechanism of action (how it works). Historically, products such as common salt and other metal salts were used as herbicides, however these have gradually fallen out of favor and in some countries a number of these are banned due to their persistence in soil, and toxicity and groundwater contamination concerns. Herbicides have also been used in warfare and conflict.
A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the development of other herbicides and pesticides, allowed for the Green Revolution, an increase in agricultural production in mid-20th century.
Modern herbicides are often synthetic mimics of natural plant hormones which interfere with growth of the target plants. The term organic herbicide has come to mean herbicides intended for organic farming. Some plants also produce their own natural herbicides, such as the genus Juglans (walnuts), or the tree of heaven; such action of natural herbicides, and other related chemical interactions, is called allelopathy. Due to herbicide resistance - a major concern in agriculture - a number of products combine herbicides with different means of action. Integrated pest management may use herbicides alongside other pest control methods.
Although research into herbicides began in the early 20th century, the first major breakthrough was the result of research conducted in both the UK and the US during the Second World War into the potential use of herbicides in war.[5] The first modern herbicide, 2,4-D, was first discovered and synthesized by W. G. Templeman at Imperial Chemical Industries.
In the US in 2007, about 83% of all herbicide usage, determined by weight applied, was in agriculture.[1]:12 In 2007, world pesticide expenditures totaled about \$39.4 billion; herbicides were about 40% of those sales and constituted the biggest portion, followed by insecticides, fungicides, and other types.[1]:4 Herbicide is also used in forestry,[2] where certain formulations have been found to suppress hardwood varieties in favour of conifers after a clearcut,[3] as well as pasture systems, and management of areas set aside as wildlife habitat.
2,4 D and 2,4,5 T
Two of the oldest chemical herbicides used as defoliants are 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T). 2,4-D and 2,4,5-T are absorbed by broad-leafed plants, killing them by causing excessive hormonal growth. These phenoxy herbicides were designed to selectively kill weeds and unwanted plants in croplands. They were first introduced at the beginning of World War II and became widespread in use in agriculture following the end of the War.
When 2,4-D was commercially released in 1946, it triggered a worldwide revolution in agricultural output and became the first successful selective herbicide. It allowed for greatly enhanced weed control in wheat, maize (corn), rice, and similar cereal grass crops, because it kills dicots (broadleaf plants), but not most monocots (grasses). The low cost of 2,4-D has led to continued usage today, and it remains one of the most commonly used herbicides in the world. Like other acid herbicides, current formulations use either an amine salt (often trimethylamine) or one of many esters of the parent compound. These are easier to handle than the acid.
WEB LINKS
The Technical Fact Sheet for 2,4-D is found on the link below.
http://npic.orst.edu/factsheets/archive/2,4-DTech.html
Gervais, J.; Luukinen, B.; Buhl, K.; Stone, D. 2008. 2,4-D Technical Fact Sheet; National Pesticide Information Center, Oregon State
Agent Orange is a herbicide and defoliant chemical, one of the "tactical use" Rainbow Herbicides. It is widely known for its use by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. It is a mixture of equal parts of two herbicides, 2,4,5-T and 2,4-D. In addition to its damaging environmental effects, traces of dioxin (mainly TCDD, the most toxic of its type) found in the mixture have caused major health problems for many individuals who were exposed.
Atrazine and Glyphosate
Atrazine is a herbicide that is used to stop pre- and post-emergence broadleaf and grassy weeds in crops such as sorghum, maize, sugarcane, lupins, pine, and eucalypt plantations, and triazine-tolerant canola.
In the United States as of 2014, atrazine was the second-most widely used herbicide after glyphosate, with 76 million pounds (34 thousand metric tons) of it applied each year. Atrazine continues to be one of the most widely used herbicides in Australian agriculture. Its effect on corn yields has been estimated from 1% to 8%, with 3–4% being the conclusion of one economics review. In another study looking at combined data from 236 university corn field trials from 1986 to 2005, atrazine treatments showed an average of 5.7 bushels more per acre (~400 kg per hectare) than alternative herbicide treatments. Effects on sorghum yields have been estimated to be as high as 20%, owing in part to the absence of alternative weed control products that can be used on sorghum.
As of 2001, atrazine was the most commonly detected pesticide contaminating drinking water in the U.S.:44 Studies suggest it is an endocrine disruptor, an agent that can alter the natural hormonal system. Since 2003, the U.S. Environmental Protection Monitoring Agency (EPA) regularly checks atrazine levels in streams and watersheds that are direct exposed to atrazine runoff as part of the Atrazine Ecological Exposure Monitoring Program.
Glyphosate (N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant, seeFigure \(3\). It is an organophosphorus compound, specifically a phosphonate. It targets a broad range of weeds and is important in the production of fruits, vegetables, nuts, and glyphosate-resistant field crops such as corn and soybean. It is effective at managing invasive and noxious weeds. In addition, glyphosate breaks down in the environment, can be used for no-till and low-till farming which can reduce soil erosion, and is useful for integrated pest management.
It was discovered to be an herbicide by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market in 1974 under the trade name Roundup® , and Monsanto's last commercially relevant United States patent expired in 2000. Products containing glyphosate are sold in various formulations, including as liquid concentrate, solid, and ready-to-use liquid. Glyphosate can be applied in agricultural, residential and commercial settings using a wide range of application methods, including aerial sprays, ground broadcast sprayers of various types, shielded and hooded sprayers, wiper applicators, sponge bars, injection systems, and controlled droplet applicators.
Glyphosate is effective in killing a wide variety of plants, including grasses and broadleaf and woody plants. By volume, it is one of the most widely used herbicides. In 2007, glyphosate was the most used herbicide in the United States agricultural sector, with 180 to 185 million pounds (82,000 to 84,000 tonnes) applied, the second-most used in home and garden with 5 to 8 million pounds (2,300 to 3,600 tonnes) and government applied[clarification needed] 13 to 15 million pounds (5,900 to 6,800 tonnes) in industry and commerce. It is commonly used for agriculture, horticulture, viticulture, and silviculture purposes, as well as garden maintenance (including home use). It has a relatively small effect on some clover species and morning glory.
Glyphosate and related herbicides are often used in invasive species eradication and habitat restoration, especially to enhance native plant establishment in prairie ecosystems. The controlled application is usually combined with a selective herbicide and traditional methods of weed eradication such as mulching to achieve an optimal effect.
In many cities, glyphosate is sprayed along the sidewalks and streets, as well as crevices in between pavement where weeds often grow. However, up to 24% of glyphosate applied to hard surfaces can be run off by water. Glyphosate contamination of surface water is attributed to urban and agricultural use. Glyphosate is used to clear railroad tracks and get rid of unwanted aquatic vegetation.
Paraquat- A Preemergent Herbicide -and More
Paraquat (or N,N′-dimethyl-4,4′-bipyridinium dichloride, also known as Methyl Viologen, is an organic compound manufactured by Chevron. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic to human beings and animals due to its redox activity, which produces superoxide anions. It has been linked to the development of Parkinson's disease and is banned in several countries.
Although first synthesized in 1882,[9] paraquat's herbicidal properties were not recognized until 1955 in the Imperial Chemical Industries (ICI) laboratories at Jealott's Hill.[10][11] Paraquat (Figure \(4\)) was first manufactured and sold by ICI in early 1962 under the trade name Gramoxone, and is today among the most commonly used herbicides.
Paraquat is classified as a non-selective contact herbicide. The key characteristics that distinguish it from other agents used in plant protection products are:
• It kills a wide range of annual grasses and broad-leaved weeds and the tips of established perennial weeds.
• It is very fast-acting.
• It is rain-fast within minutes of application.
• It is partially inactivated upon contact with soil.[12][13]
These properties led to paraquat being used in the development of no-till farming.
Paraquat has been banned in the European Union since 2007. There is an ongoing international campaign for a global ban, but the cheap and therefore popular paraquat continues to be unrestricted in most developing countries. In the United States, paraquat is available primarily as a solution in various strengths. It is classified as "restricted use", which means that it can be used by licensed applicators only.
WEB LINK
A more detailed list of herbicides, trade names, and target species provided by the USDA WEB can be found on the link below.
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd496996.pdf
Organic herbicides
Recently, the term "organic" has come to imply products used in organic farming. Under this definition, an organic herbicide is one that can be used in a farming enterprise that has been classified as organic. Depending on the application, they may be less effective than synthetic herbicides[59] and are generally used along with cultural and mechanical weed control practices.
Homemade organic herbicides include:
• Corn gluten meal (CGM) is a natural pre-emergence weed control used in turfgrass, which reduces germination of many broadleaf and grass weeds.[60]
• Vinegar[61] is effective for 5–20% solutions of acetic acid, with higher concentrations most effective, but it mainly destroys surface growth, so respraying to treat regrowth is needed. Resistant plants generally succumb when weakened by respraying.
• Steam has been applied commercially, but is now considered uneconomical and inadequate.It controls surface growth but not underground growth and so respraying to treat regrowth of perennials is needed.
• Flame is considered more effective than steam, but suffers from the same difficulties.[65]
• D-limonene (citrus oil) is a natural degreasing agent that strips the waxy skin or cuticle from weeds, causing dehydration and ultimately death.
• Saltwater or salt applied in appropriate strengths to the rootzone will kill most plants.
Human Risks
A pesticide poisoning occurs when chemicals intended to control a pest affect non-target organisms such as humans, wildlife, plant or bees.
There are three types of pesticide poisoning.
The first of the three is a single and short-term very high level of exposure which can be experienced by individuals who commit suicide, as well as pesticide formulators. Most cases of intentional pesticide poisoning appear to be impulsive acts undertaken during stressful events, and the availability of pesticides strongly influences the incidence of self poisoning.
The second type of poisoning is long-term high-level exposure, which can occur in pesticide formulators and manufacturers. Extensive use puts agricultural workers in particular at increased risk for pesticide illnesses. Exposure can occur through inhalation of pesticide fumes, and often occurs in settings including greenhouse spraying operations and other closed environments like tractor cabs or while operating rotary fan mist sprayers in facilities or locations with poor ventilation systems. Workers in other industries are at risk for exposure as well. For example, commercial availability of pesticides in stores puts retail workers at risk for exposure and illness when they handle pesticide products. The ubiquity of pesticides puts emergency responders such as fire-fighters and police officers at risk, because they are often the first responders to emergency events and may be unaware of the presence of a poisoning hazard. The process of aircraft disinsection, in which pesticides are used on inbound international flights for insect and disease control, can also make flight attendants sick.
Different job functions can lead to different levels of exposure. Most occupational exposures are caused by absorption through exposed skin such as the face, hands, forearms, neck, and chest. This exposure is sometimes enhanced by inhalation in settings including spraying operations in greenhouses and other closed environments, tractor cabs, and the operation of rotary fan mist sprayers.
The third type of poisoning is a long-term low-level exposure, which individuals are exposed to from sources such as pesticide residues in food as well as contact with pesticide residues in the air, water, soil, sediment, food materials, plants and animals.[1][2][3][4]
In developing countries, such as Sri Lanka, pesticide poisonings from short-term very high level of exposure (acute poisoning) is the most worrisome type of poisoning. However, in developed countries, such as Canada, it is the complete opposite: acute pesticide poisoning is controlled, thus making the main issue long-term low-level exposure of pesticides.
Summary
• Herbicides (also known as weedkillers), are substances used to control unwanted plants.
• More widely used herbicides include 2,4-D (2,4-dichlorophenoxyacetic acid), 2,4,5-T( 2,4,5-trichlorophenoxyacetic acid), atrazine, glyphosate, and paraquat.
• Organic pesticides used in organic farming include corn gluten meal, vinegar, D-limonene, and salt water.
• Intentional or unintentional ingestion and/or exposure to pesticides can cause a range of health effects ranging from skin rashes to death.
• Wikipedia
• US EPA
• USDA | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/20%3A_Chemistry_Down_on_the_Farm/20.03%3A_Herbicides_and_Defoliants.txt |
Learning Objectives
• Describe what sustainable agriculture is.
• Describe the features of organic farming.
Sustainable agriculture” was addressed by Congress in the 1990 “Farm Bill”. Under that law, “the term sustainable agriculture means an integrated system of plant and animal production practices having a site-specific application that will, over the long term:
• satisfy human food and fiber needs;
• enhance environmental quality and the natural resource base upon which the agricultural economy depends;
• make the most efficient use of nonrenewable resources and on-farm resources and integrate, where appropriate, natural biological cycles and controls;
• sustain the economic viability of farm operations; and
• enhance the quality of life for farmers and society as a whole.”
Organic Farming is Good for Farmers, Consumers and the Environment
Organic agriculture is an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. Organic food is produced by farmers who emphasize the use of renewable resources and the conservation of soil and water to enhance environmental quality for future generations. Organic meat, poultry, eggs, and dairy products come from animals that are given no antibiotics or growth hormones. Organic food is produced without using most conventional pesticides, fertilizers made with synthetic ingredients or sewage sludge, or GMOs.
Organic production, with the corresponding practices to maintain soil fertility and soil health is therefore a more benign alternative to conventional, high-value horticulture. The organic food movement has been endorsed by the UN’s Food and Agricultural Organization, which maintains in a 2007 report that organic farming fights hunger, tackles climate change, and is good for farmers, consumers, and the environment. The strongest benefits of organic agriculture are its use of resources that are independent of fossil fuels, are locally available, incur minimal environmental stresses, and are cost effective.
IPM is a Combination of Common-Sense Practices
Integrated Pest Management (IPM) refers to a mix of farmer-driven, ecologically-based pest control practices that seeks to reduce reliance on synthetic chemical pesticides. It involves (a) managing pests (keeping them below economically damaging levels) rather than seeking to eradicate them; (b) relying, to the extent possible, on non-chemical measures to keep pest populations low; and (c) selecting and applying pesticides, when they have to be used, in a way that minimizes adverse effects on beneficial organisms, humans, and the environment. It is commonly understood that applying an IPM approach does not necessarily mean eliminating pesticide use, although this is often the case because pesticides are often over-used for a variety of reasons.
The IPM approach regards pesticides as mainly short-term corrective measures when more ecologically based control measures are not working adequately (sometimes referred to as using pesticides as the “last resort”). In those cases when pesticides are used, they should be selected and applied in such a manner as to minimize the amount of disruption that they cause to the environment, such as using products that are non-persistent and applying them in the most targeted way possible).
Biological Control
Biological control (biocontrol) is the use of one biological species to reduce populations of a different species. There has been a substantial increase in commercialization of biocontrol products, such as beneficial insects, cultivated predators and natural or non-toxic pest control products. Biocontrol is being mainstreamed to major agricultural commodities, such as cotton, corn and most commonly vegetable crops. Biocontrol is also slowly emerging in vector control in public health and in areas that for a long time mainly focused on chemical vector control in mosquito/malaria—and black fly/onchocerciasis—control programs. Successful and commercialized examples of biocontrol include ladybugs to depress aphid populations, parasitic wasps to reduce moth populations, use of the bacterium Bacillus thuringenensis to kill mosquito and moth larvae, and introduction of fungi, such as Trichoderma, to suppress fungal-caused plant diseases, leaf beetle (Galerucella calmariensis) to suppress purple loosestrife, a noxious weed (Figure \(1\)). In all of these cases, the idea is not to completely destroy the pathogen or pest, but rather to reduce the damage below economically significant values.
Intercropping Promotes Plant Interactions
Intercropping means growing two or more crops in close proximity to each other during part or all of their life cycles to promote soil improvement, biodiversity, and pest management. Incorporating intercropping principles into an agricultural operation increases diversity and interaction between plants, arthropods, mammals, birds and microorganisms resulting in a more stable crop-ecosystem and a more efficient use of space, water, sunlight, and nutrients (Figure \(2\)).This collaborative type of crop management mimics nature and is subject to fewer pest outbreaks, improved nutrient cycling and crop nutrient uptake, and increased water infiltration and moisture retention. Soil quality, water quality and wildlife habitat all benefit.
Organic Farming Practices Reduce Unnecessary Input Use
In modern agricultural practices, heavy machinery is used to prepare the seedbed for planting, to control weeds, and to harvest the crop. The use of heavy equipment has many advantages in saving time and labor, but can cause compaction of soil and disruption of the natural soil organisms. The problem with soil compaction is that increased soil density limits root penetration depth and may inhibit proper plant growth.
Alternative practices generally encourage minimal tillage or no tillage methods. With proper planning, this can simultaneously limit compaction, protect soil organisms, reduce costs (if performed correctly), promote water infiltration, and help to prevent topsoil erosion (Figure \(3\)) .
Tillage of fields does help to break up clods that were previously compacted, so best practices may vary at sites with different soil textures and composition. Another aspect of soil tillage is that it may lead to more rapid decomposition of organic matter due to greater soil aeration. Over large areas of farmland, this has the unintended consequence of releasing more carbon and nitrous oxides (greenhouse gases) into the atmosphere, thereby contributing to global warming effects. In no-till farming, carbon can actually become sequestered into the soil. Thus, no-till farming may be advantageous to sustainability issues on the local scale and the global scale. No-till systems of conservation farming have proved a major success in Latin America and are being used in South Asia and Africa.
Crop Rotation
Crop rotations are planned sequences of crops over time on the same field. Rotating crops provides productivity benefits by improving soil nutrient levels and breaking crop pest cycles. Farmers may also choose to rotate crops in order to reduce their production risk through diversification or to manage scarce resources, such as labor, during planting and harvesting timing. This strategy reduces the pesticide costs by naturally breaking the cycle of weeds, insects and diseases. Also, grass and legumes in a rotation protect water quality by preventing excess nutrients or chemicals from entering water supplies.
AN ALTERNATIVE TO SPRAYING: BOLLWORM CONTROL IN SHANDONG
Farmers in Shandong (China) have been using innovative methods to control bollworm infestation in cotton when this insect became resistant to most pesticides. Among the control measures implemented were:
1. The use of pest resistant cultivars and interplanting of cotton with wheat or maize.
2. Use of lamps and poplar twigs to trap and kill adults to lessen the number of adults.
3. If pesticides were used, they were applied on parts of cotton plant’s stem rather than by spraying the whole field (to protect natural enemies of the bollworm).
These and some additional biological control tools have proved to be effective in controlling insect populations and insect resistance, protecting surroundings and lowering costs.
AN ALTERNATIVE TO SPRAYING: BOLLWORM CONTROL IN SHANDONG
Farmers in Shandong (China) have been using innovative methods to control bollworm infestation in cotton when this insect became resistant to most pesticides. Among the control measures implemented were:
1. The use of pest resistant cultivars and interplanting of cotton with wheat or maize.
2. Use of lamps and poplar twigs to trap and kill adults to lessen the number of adults.
3. If pesticides were used, they were applied on parts of cotton plant’s stem rather than by spraying the whole field (to protect natural enemies of the bollworm).
These and some additional biological control tools have proved to be effective in controlling insect populations and insect resistance, protecting surroundings and lowering costs.
The Future of the Sustainable Agriculture Concept
Many in the agricultural community have adopted the sense of urgency and direction pointed to by the sustainable agriculture concept. Sustainability has become an integral component of many government, commercial, and non-profit agriculture research efforts, and it is beginning to be woven into agricultural policy. Increasing numbers of farmers and ranchers have embarked on their own paths to sustainability, incorporating integrated and innovative approaches into their own enterprises.
Summary
• Sustainable agriculture is farming in various ways, wherein society's current and future food and textile needs are met.
• Organic agriculture is an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/20%3A_Chemistry_Down_on_the_Farm/20.04%3A_Sustainable_Agriculture.txt |
Household chemicals are non-food chemicals that are commonly found and used in and around the average household. They are a type of consumer goods, designed particularly to assist cleaning, pest control and general hygiene purposes. Together with non-compostable household waste, the chemicals found in private household commodities pose a serious ecological problem. In addition to having slightly adverse up to seriously toxic effects when swallowed, chemical agents around may contain flammable or corrosive substances.
Thumbnail: Clorox brand bleach. (CC BY-SA 2.0; Adina Firestone via ).
21: Household Chemicals
Learning Objectives
• Describe the mechanism by which soaps exert their cleansing action.
• List the benefits and problems with using soap.
Personal Cleanliness
Soap is a salt of a fatty acid[1] used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used as thickeners, components of some lubricants, and precursors to catalysts.
When used for cleaning, soap solubilizes particles and grime, which can then be separated from the article being cleaned. In hand washing, as a surfactant, when lathered with a little water, soap kills microorganisms by disorganizing their membrane lipid bilayer and denaturing their proteins. It also emulsifies oils, enabling them to be carried away by running water.[2]
Industrially manufactured bar soaps became available in the late 18th century, as advertising campaigns in Europe and America promoted popular awareness of the relationship between cleanliness and health.[35] In modern times, the use of soap has become commonplace in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms (Figure \(1\)).
Soap Making: Fat Plus Lye Forms a Soap Plus Glycerol
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon.[10] A formula for soap consisting of water, alkali, and cassia oil was written on a Babylonian clay tablet around 2200 BC.[11]
The Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention a similar substance was used in the preparation of wool for weaving.[12]In the reign of Nabonidus (556–539 BC), a recipe for soap consisted of uhulu [ashes], cypress [oil] and sesame [seed oil] "for washing the stones for the servant girls".[13]In ancient Israel, the ashes from barilla plants, such as species of Salsola, saltwort (Seidlitzia rosmarinus) and Anabasis, were used in soap production, known as potash
Until the Industrial Revolution, soapmaking was conducted on a small scale and the product was rough. In 1780, James Keir established a chemical works at Tipton, for the manufacture of alkali from the sulfates of potash and soda, to which he afterwards added a soap manufactory. William Gossage produced low-priced, good-quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. American manufacturer Benjamin T. Babbitt introduced marketing innovations that included sale of bar soap and distribution of product samples. William Hesketh Lever and his brother, James, bought a small soap works in Warrington in 1886 and founded what is still one of the largest soap businesses, formerly called Lever Brothers and now called Unilever. These soap businesses were among the first to employ large-scale advertising campaigns. A poster advertising is shown in Figure \(2\).
Liquid soap was not invented until the nineteenth century; in 1865, William Shepphard patented a liquid version of soap.[40] In 1898, B.J. Johnson developed a soap derived from palm and olive oils; his company, the B.J. Johnson Soap Company, introduced "Palmolive" brand soap that same year.[41] This new brand of soap became popular rapidly, and to such a degree that B.J. Johnson Soap Company changed its name to Palmolive.[42]
Fats and oils can participate in a variety of chemical reactions—for example, because triglycerides are esters, they can be hydrolyzed in the presence of an acid, a base, or specific enzymes known as lipases. The hydrolysis of fats and oils in the presence of a base is used to make soap and is called saponification. Today most soaps are prepared through the hydrolysis of triglycerides (often from tallow, coconut oil, or both) using water under high pressure and temperature [700 lb/in2 (∼50 atm or 5,000 kPa) and 200°C]. Sodium carbonate or sodium hydroxide is then used to convert the fatty acids to their sodium salts (soap molecules):
Figure \(3\) Saponification.
How Soap Works
The cleansing action of soap is determined by its polar and non-polar structures in conjunction with an application of solubility principles. The long hydrocarbon chain is of course non-polar and hydrophobic (repelled by water). The "salt" end of the soap molecule is ionic and hydrophilic (water soluble). Examples of soap and detergent molecules, are shown in Figure \(4\). The use of such compounds as cleaning agents is facilitated by their surfactant character, which lowers the surface tension of water, allowing it to penetrate and wet a variety of materials.
When soap is added to water, the ionic-salt end of the molecule is attracted to water and dissolved in it. The non-polar hydrocarbon end of the soap molecule is repelled by water. A drop or two of soap in water forms a monolayer (Figure \(5\)) on the water surface as shown in the graphics on the left. The soap molecules "stand up" on the surface as the polar carboxyl salt end is attracted to the polar water. The non-polar hydrocarbon tails are repelled by the water, which makes them appear to stand up.
Soap vs. oil vs. water
Water alone is not able to penetrate grease or oil because they are of opposite polarity. When grease or oil (non-polar hydrocarbons) are mixed with a soap- water solution, the soap molecules work as a "bridge" between polar water molecules and non-polar oil molecules. Soap molecules have both properties of non-polar and polar at opposite ends of the molecule.
The oil is a pure hydrocarbon so it is non-polar. The non-polar hydrocarbon tail of the soap dissolves into the oil. That leaves the polar carboxylate ion of the soap molecules are sticking out of the oil droplets, the surface of each oil droplet is negatively charged. As a result, the oil droplets repel each other and remain suspended in solution (this is called an emulsion) to be washed away by a stream of water. The outside of the droplet is also coated with a layer of water molecules.
The graphic on Figure \(6\) although not strictly a representation of the above description is a micelle that works in much the same fashion. The oil would be a the center of the micelle.
Disadvantages and Advantages of Soap
The importance of soap to human civilization is documented by history, but some problems associated with its use have been recognized. One of these is caused by the weak acidity (pKa ca. 4.9) of the fatty acids. Solutions of alkali metal soaps are slightly alkaline (pH 8 to 9) due to hydrolysis. If the pH of a soap solution is lowered by acidic contaminants, insoluble fatty acids precipitate and form a scum. A second problem is caused by the presence of calcium and magnesium salts in the water supply (hard water). These divalent cations cause aggregation of the micelles, which then deposit as a dirty scum.
In the reaction below, the sodium cation in soap is replaced by calcium to form calcium stearate. The white precipitate, also termed as soap scum could form deposits on surfaces and inside plumbing.
2 C17H35COONa+ + Ca2+ → (C17H35COO)2Ca + 2 Na+
Soap is still widely popular product as it is a low cost, readily available product used for personal hygiene and cleanliness. Use of soap doesn't lead to pollution. Soap is biodegradable as it can be broken down by microorganisms found in sewage.
Can Soap Really Kill the Coronavirus ?
Video \(1\) Soap and coronavirus.
Water Softeners
Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins (see Figure \(7\)) but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.
How to soften hard water
Some wish to soften hard water to control its irritating, and in many cases damaging, effects. The diminished ability of soap to lather is not only annoying, but can also be potentially harmful economically. Businesses that depend on the foaming of soap, such as car washes and pet groomers, may wish to soften hard water to avoid excessive use of soap due to a decreased ability to lather. Likewise, it is often necessary to soften water that comes into contact with pipes to avoid the destructive and compromising build-up of deposits. Also, many people may find the calcifying effects that hard water has on faucets and other items unfavorable and choose to soften the water to prevent such mineral deposits from forming. Still others may dislike the sticky, dry feeling left by the precipitation of soap scum onto the skin. Whatever the reasons, there are many processes available to soften hard water.
Ion Exchange
One way to soften water is through a process called ion exchange. During ion exchange, the unwanted ions are "exchanged" for more acceptable ions. In many cases, it is desirable to replace the hard water ions, such as Ca2+ and Mg2+, with more agreeable ions, like that of Na+. To do this, the hard water is conducted through a zeolite or resin-containing column, which binds the unwanted ions to its surface and releases the more tolerable ions. In this process, the hard water ions become "fixed" ions because of their attachment to the resin material. These fixed ions displace the desirable ions (Na+), now referred to as counterions, from the column, thus exchanging the ions in the water. This process is illustrated in Figure \(8\).
Unfortunately, this process has the disadvantage of increasing the sodium content of drinking water, which could be potentially hazardous to the health of people with sodium-restricted diets.
Lime Softening
Another process is called lime softening. In this process, the compound calcium hydroxide, Ca(OH)2, is added to the hard water. The calcium hydroxide, or "slaked lime," raises the pH of the water and causes the calcium and magnesium to precipitate into CaCO3 and Mg(OH)2. These precipitates can then be easily filtered out due to their insolubility in water, shown below by the small solubility constant of magnesium hydroxide (the solubility product constant for calcium carbonate is shown above). After precipitation and removal of the offending ions, acid is added to bring the pH of the water back to normal.
\[Mg(OH)_{2 \; (s)} \rightleftharpoons Mg^{2+}_{(aq)} + 2OH^-_{(aq)} \tag{4a} \]
Chelation
Chelating agents can also be used to soften hard water. Polydentate ligands, such as the popular hexadentate ligand EDTA, bind the undesirable ions in hard water. These ligands are especially helpful in binding the magnesium and calcium cations, which as already mentioned are highly prevalent in hard water solutions. The chelating agent forms a very stable ring complex with the metal cations, which prevents them from interacting with any other substances that may be introduced to the solution, such as soap. In this way, chelators are able to diminish the negative effects associated with hard water. A simplified equation representing the chelation of the metal calcium cation (Ca2+) with the hexadentate ligand EDTA is shown below. The large value of the formation constant (Kf) reflects the tendency of the reaction to proceed to completion in the forward direction.
\[Ca^{2+} + EDTA^{4-} \longrightarrow [Ca(EDTA)]^{2-} \tag{5a} \]
Reverse Osmosis
The final process, reverse osmosis, uses high pressures to force the water through a semipermeable membrane. This membrane is generally intended to be impermeable to anything other than water. The membrane serves to filter out the larger ions and molecules responsible for the water's hardness, resulting in softened water. During this process, the water is forced from an area with a high concentration of solute in the form of dissolved metal ions and similar compounds, to an area that is very low in the concentration of these substances. In other words, the water moves from a state of hardness to a softer composition as the ions causing the water's hardness are prevented passage through the membrane. Reverse Osmosis does have a disadvantage of wasting wastewater compared to other water treatment methods. This process is shown in Figure \(9\) below. Note that this figure describes the desalination of salt water. However, the process for softening hard water is the same.
Making Hard Water Soft
Video \(2\) How to soften hard water.
Summary
• Soap, as a cleaning agent, solubilizes particles and grime, which can then be easily removed from the article being cleaned.
• In hand washing, soap is an excellent surfactant, that destroys microorganisms by damaging their cellular membranes and denaturing their proteins.
• Soap is an inexpensive, readily available cleaning agent that is also's effectivenes is diminished biodegradable. However, it's effectiveness is diminished when used with hard water. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.01%3A_Cleaning_with_Soap.txt |
Learning Objectives
• Describe different types of detergents.
• List the key components of detergents and their functions.
A detergent is a surfactant or a mixture of surfactants with cleansing properties in dilute solutions ((Figure \(1\))) . These substances are usually alkylbenzene sulfonates, a family of compounds that are similar to soap but are more soluble in hard water, because the polar sulfonate (of detergents) is less likely than the polar carboxylate (of soap) to bind to calcium and other ions found in hard water.
In domestic contexts, the term detergent by itself refers specifically to laundry detergent or dish detergent, as opposed to hand soap or other types of cleaning agents. Detergents are commonly available as powders or concentrated solutions. Detergents, like soaps, work because they are amphiphilic: partly hydrophilic (polar) and partly hydrophobic (non-polar). Their dual nature facilitates the mixture of hydrophobic compounds (like oil and grease) with water. Because air is not hydrophilic, detergents are also foaming agents to varying degrees.
Detergents are classified into three broad groupings, depending on the electrical charge of the surfactants.
Anionic detergents
Typical anionic detergents are alkylbenzenesulfonates (ABS). The alkylbenzene portion of these anions is lipophilic and the sulfonate is hydrophilic. An estimated 6 billion kilograms of anionic detergents are produced annually for domestic markets. Two different varieties have been popularized, those with branched alkyl groups and those with linear alkyl groups (see Figure \(2\)).
Branched Alkylbenzenesulfonates: Nonbiodegradable
Branched alkylbenzene sulfonates (BAS) were first introduced in the early 1930s and saw significant growth from the late 1940s onwards,[3] in early literature these synthetic detergents are often abbreviated as syndets.
Compared to traditional soaps BAS offered superior tolerance to hard water and better foaming.[5] However, the highly branched tail made it difficult to biodegrade.[6] BAS was widely blamed for the formation of large expanses of stable foam in areas of wastewater discharge such as lakes, rivers and coastal areas (sea foams), as well as foaming problems encountered in sewage treatment[7] and contamination of drinking water.[8] As such BAS was phased out of most detergent products during the 1960s, being replaced with linear alkylbenzene sulfonates (LAS). It is still important in certain agrochemical and industrial applications, where rapid biodegradability is of reduced importance.
Linear Alkylbenzensulfonates: Biodegradable
Linear alkylbenzene sulfonates (LAS) are prepared industrially by the sulfonation of linear alkylbenzenes (LABs), which can themselves be prepared in several ways.[2] The term "linear" refers to the starting alkenes rather than the final product. The compound biodegrades far more quickly than BAS, making it the safer choice over time. It is biodegraded rapidly under aerobic conditions with a half-life of approximately 1–3 weeks. Under anaerobic conditions it degrades very slowly or not at all, causing it to exist in high concentrations in sewage sludge, but this is not thought to be a cause for concern as it will rapidly degrade once returned to an oxygenated environment.
Cationic detergents
Cationic detergents are similar to the anionic ones, with a hydrophilic component, but, instead of the anionic sulfonate group, the cationic surfactants have quaternary ammonium as the polar end. The ammonium sulfate center is positively charged.[3]
Non-ionic and zwitter ionic detergents
Non-ionic detergents are characterized by their uncharged, hydrophilic headgroups. Typical non-ionic detergents are based on polyoxyethylene or a glycoside. Common examples of the former include Tween, Triton, and the Brij series. These materials are also known as ethoxylates or PEGylates and their metabolites, nonylphenol. Glycosides have a sugar as their uncharged hydrophilic headgroup. Examples include octyl thioglucoside and maltosides. HEGA and MEGA series detergents are similar, possessing a sugar alcohol as headgroup.
Zwitterionic detergents possess a net zero charge arising from the presence of equal numbers of +1 and −1 charged chemical groups. Examples include CHAPS. CHAPS is an abbreviation for 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.
Laundry Detergent
Laundry detergent, or washing powder, is a type of detergent (cleaning agent) used for cleaning laundry. Laundry detergent is manufactured in powder and liquid form.
While powdered and liquid detergents hold roughly equal share of the worldwide laundry detergent market in terms of value, powdered detergents are sold twice as much compared to liquids in terms of volume.[1]
Components
Laundry detergents may contain builders (50% by weight, approximately), surfactants (15%), bleach (7%), enzymes (2%), soil antideposition agents, foam regulators, corrosion inhibitors, optical brighteners, dye transfer inhibitors, fragrances, dyes, fillers and formulation aids.[4]
Builders
Builders (also called chelating or sequestering agents) are water softeners. Hard water contains calcium, magnesium, and metallic cations (primarily, iron, copper, and manganese). These cations react with surfactant anions to form insoluble compounds (metallic or lime soaps) which precipitate onto fabrics and washing machines and which are difficult to remove. Builders remove the hard water ions through precipitation, chelation, or ion exchange. In addition, they help remove soil by dispersion. In most European regions, the water is hard. In North America, Brazil, and Japan, the water is comparatively soft.
The earliest builders were sodium carbonate (washing soda) and sodium silicate (waterglass). Since the 1930s, phosphates (sodium phosphates) and polyphosphates (sodium hexametaphosphate) were introduced, continuing with the introduction of phosphonates (HEDP, ATMP, EDTMP). These agents are now known to have serious environmental consequences leading to a drive towards more environmentally benign phosphorus-free agents, such as polycarboxylates (EDTA, NTA), citrates (trisodium citrate), silicates (sodium silicate), gluconic acid and polyacrylic acid; or ion exchange agents like zeolites.
Surfactants
Surfactants are responsible for most of the cleaning performance in laundry detergent. They provide this by absorption and emulsification of soil into the water and also by reducing the water's surface tension to improve wetting.
Laundry detergents contain mostly anionic and non-ionic surfactants. Cationic surfactants are normally incompatible with anionic detergents and have poor cleaning efficiency; they are employed only for certain special effects, as fabric softeners, antistatic agents, and biocides. Zwitterionic surfactants are rarely employed in laundry detergents mainly for cost reasons. Most detergents use a combination of various surfactants to balance their performance.
Bleaches
Despite the name, modern laundry bleaches do not include household bleach (sodium hypochlorite). Laundry bleaches are typically stable adducts of hydrogen peroxide, such as sodium perborate and sodium percarbonate, these are inactive as solids but will release hydrogen peroxide upon exposure to water. The main targets of bleaches are oxidisible organic stains, which are usually of vegetable origin (e.g. chlorophyll, anthocyanin dyes, tannins, humic acids, and carotenoid pigments). Hydrogen peroxide is insufficiently active as a bleach at temperature below 60°C, which traditionally made hot washes the norm. The development of bleach activators in the 1970s and 80s allowed for cooler washing temperatures to be effective. These compounds, such as tetraacetylethylenediamine (TAED), react with hydrogen peroxide to produce peracetic acid, which is an even more effective bleach, particularly at lower temperatures.
Enzymes
The use of enzymes for laundry was introduced in 1913 by Otto Rohm. The first preparation was a pancreatic extract obtained from slaughtered animals, which was unstable against alkali and bleach. Only in the latter part of the century with the availability of thermally robust bacterial enzymes did this technology become mainstream.
Enzymes are required to degrade stubborn stains composed of proteins (milk, cocoa, blood, egg yolk, grass), fats (chocolate, fats, oils), starch (flour and potato stains), and cellulose (damaged cotton fibrils, vegetable and fruit stains). Each type of stain requires a different type of enzyme: proteases (savinase) for proteins, lipases for greases, α-amylases for carbohydrates, and cellulases for cellulose.
Other ingredients
Many other ingredients are added depending on the expected circumstances of use. Such additives modify the foaming properties of the product by either stabilizing or counteracting foam. Other ingredients increase or decrease the viscosity of the solution, or solubilize other ingredients. Corrosion inhibitors counteract damage to washing equipment. "Dye transfer inhibitors" prevent dyes from one article from colouring other items. "Antiredeposition agents" such as carboxymethyl cellulose are used to prevent fine soil particles from reattaching to the product being cleaned.
A number of ingredients affect aesthetic properties of the item to be cleaned or the detergent itself before or during use. These agents include optical brighteners, fabric softeners, and colourants. A variety of perfumes are also components of modern detergents, provided that they are compatible with the other components and do not affect the colour of the cleaned item. The perfumes are typically a mixture of many compounds, common classes include terpene alcohols (citronellol, geraniol, linalool, nerol) and their esters (linalyl acetate), aromatic aldehydes (helional, hexyl cinnamaldehyde, lilial) and synthetic musks (galaxolide).
Dishwashing Detergents
Dishwashing liquid (or washing-up liquid in British English), also known as dishwashing soap, dish detergent, and dish soap is a detergent used to assist in dishwashing. It is usually a highly-foaming mixture of surfactants with low skin irritation, and is primarily used for hand washing of glasses, plates, cutlery, and cooking utensils in a sink or bowl. In addition to its primary use, dishwashing liquid also has various informal applications, such as for creating bubbles, clothes washing and cleaning oil-affected birds.
Hand dishwashing is generally performed in the absence of a dishwashing machine, when large "hard-to-clean" items are present, or through preference. Some dishwashing liquids can harm household silver, fine glassware, anything with gold leaf, disposable plastics, and any objects made of brass, bronze, cast iron, pewter, tin, or wood, especially when combined with hot water and the action of a dishwasher. When dishwashing liquid is used on such objects it is intended that they be washed by hand.
Hand dishwashing detergents utilize surfactants to play the primary role in cleaning. The reduced surface tension of dishwashing water, and increasing solubility of modern surfactant mixtures, allows the water to run off the dishes in a dish rack very quickly. However, most people also rinse the dishes with pure water to make sure to get rid of any soap residue that could affect the taste of the food.
Dishwashing liquid can be a skin irritant and cause hand eczema. Those with "sensitive skin" are advised amongst other things to persuade someone else to do the washing up.
Dishwasher detergent is a detergent made for washing dishes in a dishwasher. Dishwasher detergent is different from dishwashing liquid made to wash dishes by hand.
When using a dishwasher, the user must select a special detergent for its use. All detergents are designed for use after the user scrapes leftover food from the dishes before washing. To function, the user places dishes in the dishwasher in such fashion that the surface of all dishes is open to the flow of water.
Most dishwasher detergents are incompatible for use with silver, brass, cast iron, bronze, aluminum, pewter, and goldleaf. They can also harm disposable plastic, anything wood, knives with hollow handles, and fine glassware.
Dishwashing detergents for dishwashers are manufactured and marketed variously as cartridges, gel, liquids, pacs, powder, and tablets. Any dishwashing liquid may contain bleach, enzymes, or rinsing aids. Some dishwashing detergents may be homemade, using ingredients such as borax, essential oil, eucalyptus oil and grated bar soap, among others.
Dishwashing detergents can be formulated to work under different circumstances. In some cases suitably formulated they can be used with cold water or sea water, although they will not generally work as well as those intended for, and used with, hot water.
Different kinds of dishwashing detergent contain different combinations of ingredients. Common ingredients include:
• Phosphates: Bind calcium and magnesium ions to prevent 'hard-water' type limescale deposits. They can cause ecological damage, and have been partially banned or phased out.
• Oxygen-based bleaching agents (older-style powders and liquids contain chlorine-based bleaching agents): Break up and bleach organic deposits.
• Non-ionic surfactants: Lower the surface tension of the water, emulsifies oil, lipid and fat food deposits, prevents droplet spotting on drying.
• Alkaline salts: These are a primary component in older and original-style dishwasher detergent powders[citation needed]. Highly alkaline salts attack and dissolve grease, but are extremely corrosive (fatal) if swallowed. Salts used may include metasilicates, alkali metal hydroxides, sodium carbonate etc.
• Enzymes: Break up protein-based food deposits, and possibly oil, lipid and fat deposits. The enzymes used are similar to the ones used in laundry.
• Anti-corrosion agent(s): Often sodium silicate, this prevents corrosion of dishwasher components.[citation needed]
Dishwashing detergent may also contain:[citation needed]
• Anti-foaming agents:[citation needed] Foam interferes with the washing action. Foam may affect operation of the machine's water-level sensors and will leak past the door seals.
• Additives to slow down the removal of glaze & patterns from glazed ceramics
• Perfumes
• Anti-caking agents (in granular detergent)
• Starches (in tablet based detergents)
• Gelling agents (in liquid/gel based detergents)
• Sand (inexpensive powdered detergents)
Dishwasher detergents are generally strongly alkaline (basic).
Inexpensive powders may contain sand. Such detergents may harm the dishes and the dishwasher. Powdered detergents are more likely to cause fading on china patterns.
Besides older style detergents for dishwashers, biodegradable detergents also exist for dishwashers. These detergents may be more environmentally friendly than conventional detergents.
Informal Uses
Reader's Digest notes its use as an ant killer, weed killer, to help spread water-borne fertilizer, and to wash human hair. Good Housekeeping says it can be used mixed with vinegar to attract and drown fruit flies. Dishwashing detergent has been used to clean mirrors as well as windows.
• Pling, an open source general purpose cleaner for glazed, plastic, chrome and inox bathroom and kitchen surfaces, published by Twibright Labs, uses dishwashing liquid as one of active ingredients.
• Dishwashing liquid can be mixed with water and additional ingredients such as glycerin and sugar to produce a bubble-blowing solution.
• Dishwashing liquid may be used for cleaning delicate clothing fabrics such as hosiery and lingerie.
• Dishwashing liquid is frequently recommended in a dilute solution to make decals and vinyl graphics easier to position when applying.
• In industry, dishwashing liquid is also used to inspect pressurized equipment for leaks, such as propane fittings. It is used to inspect pneumatic tires for flats, as well as for quality assurance during the installation process, and as a mounting bead lubricant.
• Dishwashing liquid has uses as an ingredient in making homemade garden pest deterrents. Oregon State University's Cooperative Extension Service notes the use of dishwashing liquid to get rid of spidermites. Dish soap has also been used to deter aphids. In some instances, the dish soap may be toxic to plant leaves and cause them to "burn". Use of soap or dish detergent to help spread pesticide on plants is noted by University of Georgia extension service, but not recommended.
• A solution of dishwashing liquid and water may be used to remove coffee, tea, olive oil, soda and fruit juice stains from fabrics. One dishwashing liquid brand has been used to remove stains from white or lightly-colored cloth napkins.
• Dishwashing liquid has been used to treat birds affected by oil spills. After the Exxon Valdez oil spill in 1989, the International Bird Rescue Research Center received hundreds of cases of dishwashing liquid that were used for this purpose. More dishwashing liquid was donated during the Deepwater Horizon oil spill to the International Bird Rescue Research Center and the Marine Mammal Center.
Environmental concerns
Phosphates in detergent became an environmental concern in the 1950s and the subject of bans in later years.[8] Phosphates make laundry cleaner but also cause eutrophication, particularly with poor wastewater treatment.[9]
A recent academic study of fragranced laundry products found "more than 25 VOCs emitted from dryer vents, with the highest concentrations of acetaldehyde, acetone, and ethanol. Seven of these VOCs are classified as hazardous air pollutants (HAPs) and two as carcinogenic HAPs (acetaldehyde and benzene)".[10]
The EEC Directive 73/404/EEC stipulates an average biodegradability of at least 90% for all types of surfactants used in detergents. The phosphate content of detergents is regulated in many countries, e.g., Austria, Germany, Italy, The Netherlands, Norway, Sweden, Switzerland, United States, Canada, and Japan.
Summary
• Detergents are classified into anionic, cationic, and non-ionic detergents and zwitterionic detergents based on the electrical charge of the surfactants.
• Variations in detergent formulations are based on its end-use (i.e. laundry or for kitchenware).
• Phosphates make laundry cleaner but also cause eutrophication, particularly with poor wastewater treatment.[9]
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.02%3A_Synthetic_Detergents.txt |
Learning Objectives
• Describe a fabric softener and its use.
• Describe bleaches and their use.
A fabric softener (or conditioner) is a conditioner that is typically applied to laundry during the rinse cycle in a washing machine. In contrast to laundry detergents, fabric softeners may be regarded as a kind of after-treatment laundry aid.[1]
Machine washing puts great mechanical stress on textiles, particularly natural fibers such as cotton and wool. The fibers at the fabric surface are squashed and frayed, and this condition hardens while drying the laundry in air, giving the laundry a harsh feel. Adding a liquid fabric softener to the final rinse (rinse-cycle softener) results in laundry that feels softer.[2][1]
Fabric softeners coat the surface of a fabric with chemical compounds that are electrically charged, causing threads to "stand up" from the surface and thereby imparting a softer and fluffier texture. Cationic softeners, like those shown in Figure \(1\). bind by electrostatic attraction to the negatively charged groups on the surface of the fibers and neutralize their charge. The long aliphatic chains then line up towards the outside of the fiber, imparting lubricity.
Fabric softeners impart antistatic properties to fabrics, and thus prevent the build-up of electrostatic charges on synthetic fibers, which in turn eliminates fabric cling during handling and wearing, crackling noises, and dust attraction. Also, fabric softeners make fabrics easier to iron and help reduce wrinkles in garments. In addition, they reduce drying times so that energy is saved when softened laundry is tumble-dried. Last but not least, they can also impart a pleasant fragrance to the laundry.[1]
Risks
As with soaps and detergents, fabric softeners may cause irritant dermatitis.[5] Manufacturers produce some fabric softeners without dyes and perfumes to reduce the risk of skin irritation. Fabric softener overuse may make clothes more flammable, due to the fat-based nature of most softeners. Some deaths have been attributed to this phenomenon,[6] and fabric softener makers recommend not using them on clothes labeled as flame-resistant.[citation needed]
Laundry Bleaches: Whiter Whites
Bleach is the generic name for any chemical product which is used industrially and domestically to clean, and to remove stains. It often refers, specifically, to a dilute solution of sodium hypochlorite, also called "liquid bleach".
Many bleaches have broad spectrum bactericidal properties, making them useful for disinfecting and sterilizing and are used in swimming pool sanitation to control bacteria, viruses, and algae and in many places where sterile conditions are required. They are also used in many industrial processes, notably in the bleaching of wood pulp. Bleaches also have other minor uses like removing mildew, killing weeds, and increasing the longevity of cut flowers.[1]
Bleaches work by reacting with many colored organic compounds, such as natural pigments, and turning them into colorless ones. While most bleaches are oxidizing agents (chemicals that can remove electrons from other molecules), some are reducing agents (that donate electrons).
Chlorine, a powerful oxidizer, is the active agent in many household bleaches. Since pure chlorine is a toxic corrosive gas, these products usually contain hypochlorite which releases chlorine when needed. "Bleaching powder" usually means a formulation containing calcium hypochlorite.
Oxidizing bleaching agents that do not contain chlorine are usually based on peroxides such as hydrogen peroxide, sodium percarbonate, and sodium perborate. These bleaches are called 'non-chlorine bleach,' 'oxygen bleach' or 'color-safe bleach.'[2]
Reducing bleaches have niche uses, such as sulfur dioxide used to bleach wool, either as gas or from solutions of sodium dithionite;[3] and sodium borohydride.
Bleaches generally react with many other organic substances besides the intended colored pigments, so they can weaken or damage natural materials like fibers, cloth, and leather, and intentionally applied dyes such as the indigo of denim. For the same reason, ingestion of the products, breathing of the fumes, or contact with skin or eyes can cause health damage.
Summary
• A fabric softener is an after-treatment laundry aid that imparts a softer and fluffier texture.
• Bleach is the generic name for any chemical product that is used industrially and domestically for cleaning and stain removal.
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.03%3A_Laundry_Auxiliaries-_Softeners_and_Bleaches.txt |
Learning Objective
• List various cleaners and their modes of action.
Cleaning agents or hard-surface cleaners are substances (usually liquids, powders, sprays, or granules) used to remove dirt, including dust, stains, bad smells, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removing offensive odor, and avoiding the spread of dirt and contaminants to oneself and others. Some cleaning agents can kill bacteria (e.g. door handle bacteria, as well as bacteria on worktops and other metallic surfaces) and clean at the same time. Others, called degreasers, contain organic solvents to help dissolve oils and fats.
Acidic cleaning agents are mainly used for removal of inorganic deposits like scaling. The active ingredients are normally strong mineral acids and chelants. Often, surfactants and corrosion inhibitors are added to the acid.
Hydrochloric acid is a common mineral acid typically used for concrete. Vinegar can also be used to clean hard surfaces and remove calcium deposits that also helps to maintain our environment bacteria free. Sulphuric acid is used in acidic drain cleaners to unblock clogged pipes by dissolving greases, proteins, and even carbohydrate-containing substances such as toilet tissue.
Alkaline cleaning agents contain strong bases like sodium hydroxide or potassium hydroxide. Bleach (pH 12) and ammonia (pH 11) are common alkaline cleaning agents. Often, dispersants, to prevent redeposition of dissolved dirt, and chelants, to attack rust, are added to the alkaline agent.
Alkaline cleaners can dissolve fats (including grease), oils, and protein-based substances.
Neutral washing agents are pH-neutral and based on non-ionic surfactants that disperse different types.
Scouring agents are mixtures of the usual cleaning chemicals (surfactants, water softeners) as well as abrasive powders. The abrasive powder must be of a uniform particle size.
Particles are usually smaller than 0.05 mm. Pumice, calcium carbonate (limestone, chalk, dolomite), kaolinite, quartz, soapstone or talc are often used as abrasives, i.e. polishing agents.
Special bleaching powders contain compounds that release sodium hypochlorite, the classical household bleaching agent. These precursor agents include trichloroisocyanuric acid and mixtures of sodium hypochlorite (“chlorinated orthophosphate”).
Examples of notable products include: Ajax, Bar Keepers Friend, Bon Ami, Comet, Vim, Zud, and others.
All-Purpose Cleaners
All-purpose cleansers (Figure \(1\)) contain mixtures of anionic and nonionic surfactants, polymeric phosphates or other sequestering agents, solvents, hydrotropic substances, polymeric compounds, corrosion inhibitors, skin-protective agents, and sometimes perfumes and colorants.[7] Aversive agents, such as denatonium, are occasionally added to cleaning products to discourage animals and small children from consuming them.
Some cleaners contain water-soluble organic solvents like glycol ethers and fatty alcohols, which ease the removal of oil, fat and paint. Disinfectant additives include quaternary ammonium compounds, phenol derivatives, terpene alcohols (pine oil), aldehydes, and aldehyde-amine condensation products.
All-purpose cleaners are usually concentrated solutions of surfactants and water softeners, which enhance the behavior of surfactant in hard water. Typical surfactants are alkylbenzenesulfonates, an anionic detergent, and modified fatty alcohols. A typical water softener is sodium triphosphate.
All-purpose cleansers are effective with most common kinds of dirt. Their dilute solutions are neutral or weakly alkaline, and are safe for use on most surfaces.
Special Purpose Cleaners
Traditional oven cleaners contain sodium hydroxide (lye), solvents, and other ingredients,[3][4][5] and work best when used in a slightly-warm (not hot) oven. If used in a self-cleaning oven, the lye will cause permanent damage to the oven.
New-style oven cleaners are based on ingredients other than lye. These products must be used in a cold oven. Most new-style oven cleaners can be used in self-cleaning ovens.
Oven cleaners are some of the most toxic household cleaning products available on the market.[6] Correct use of an oven cleaner may be reasonably safe, but incorrect use can have harmful effects.
One popular oven cleaner brand in the US is "Easy-Off", sold by Reckitt Benckiser. Popular choices in the UK include "Zep Oven Brite" and "Mr Muscle Oven Cleaner".
Toilet bowl cleaning agents often are aimed at removal of calcium carbonate deposits, which are attacked by acids. Powdered cleaners contain acids that come in the form of solid salts, such as sodium hydrogen sulfate. Liquid toilet bowl cleaners contain other acids, typically dilute hydrochloric, phosphoric, or formic acids. These convert the calcium carbonate into salts that are soluble in water or are easily rinsed away.
Chemical drain cleaners can be in solid or liquid form that are readily available through hardware stores, though some (primarily acidic ones) are intended for use by licensed plumbers.[1]Alkaline drain cleaners are available in either solid or liquid state while the acidic ones are usually in liquid form.
Metal cleaners are used for cleaning stainless steel sinks, faucets, metal trim, silverware, etc. These products contain abrasives (e.g., siliceous chalk, diatomaceous earth, alumina) with a particle size < 20 μm. Fatty alcohol or alkylphenol polyglycol ethers with 7-12 ethylene oxide (EO) units are used as surfactants.[7]
For ferrous metals, the cleaners contain chelating agents, abrasives, and surfactants. These agents include citric and phosphoric acids, which are nonaggressive. Surfactants are usually modified fatty alcohols. Silver cleaning is a specialty since silver is noble but tends to tarnish via formation of black silver sulfide, which is removable via silver-specific complexants such as thiourea.
Stainless steel, nickel, and chromium cleaners contain lactic, citric, or phosphoric acid. A solvent (mineral spirits) may be added.
Nonferrous metal cleaners contain ammonia, ammonium soaps (ammonium oleate, stearate) and chelating agents (ammonium citrate, oxalate).
For special type of precious metals especially those used for luxury watches and high-end jewelry, special type of cleaning agents are usually used to clean and protect them from the elements.
Glass cleaners. Light duty hard surface cleaners are not intended to handle heavy dirt and grease. Because these products are expected to clean without rinsing and result in a streak-free shine, they contain no salts. Typical window cleaning items consist of alcohols, either ethanol or isopropanol, and surfactants for dissolving grease. Other components include small amounts of ammonia as well as dyes and perfumes.
These are composed of organic,water-miscible solvent such as isopropyl alcohol and an alkaline detergent. Some glass cleaners also contain a fine, mild abrasive. Most glass cleaners are available as sprays or liquid. They are sprayed directly onto windows, mirrors and other glass surfaces or applied on with a soft cloth and rubbed off using a soft ,lint-free duster. A glass cloth ideal for the purpose and soft water to which some methylated spirit or vinegar is added which is an inexpensive glass cleaner.
Silverware can be freed of silver sulfide tarnish with thiourea, and either hydrochloric or sulfuric acid.
Building facade cleaners. For acid-resistant building facades, such as brick, acids are typically used. These include mixtures of phosphoric and hydrofluoric acids as well as surfactants. For acid-sensitive facades such as concrete, strongly alkaline cleaners are used such as sodium hydroxide and thickeners. Both types of cleaners require a rinsing and often special care since the solutions are aggressive toward skin.
Drain Cleaners: Danger and Usage Considerations
Danger arises from chemical drain cleaners' potential to injure eyes, lungs, and skin; and damage to clothing and household materials such as wood, paint, aluminum, and fiberglass. Chemical drain cleaners should be used only according to the manufacturer's instructions, as other use may cause injury.[7] Strongly corrosive and acid drain cleaners are among the most hazardous household products available to the public. Chemical drain cleaners can cause strong reactions—sometimes explosively—with other chemicals that may have been used previously, which can result in serious injury to anyone in the vicinity.[8] In one such incident, a five-year-old boy was left scarred for life after an acidic drain cleaner leaked through his bedroom ceiling as he slept.[9]
Strong Alkali Drain cleaners are equally capable of causing rapid, severe burns, as seen in the cases of a woman doused with concentrated lye in an attack. A small girl was also permanently disfigured by a common lye drain opener.,[10][11] Moreover, because the acidic or basic drain cleaners themselves are washed down the drain, this contributes to pollution in the water supply. The heat generation can also soften plastic PVC pipes, and the pressure buildup by gas generation can cause older pipes to burst. Commercial chemical based solutions can cause corrosion and other damage to your pipes and sewer lines[12]
Oftentimes, individuals may unknowingly mix two different types of drain cleaners, which can even lead to deadly results. For example, consider the mixing of an acidic and basic drain cleaner:
Sulfuric Acid + Sodium Hydroxide → sodium sulfate (a salt) + water
H2SO4 + 2 NaOH → Na2SO4 + 2H2O
The neutralization reaction of the acid and base may seem harmless, but in reality this reaction is extremely exothermic and can cause pipes to violently explode. Consider another example of mixing, this time between an acid drain cleaner and bleach:
Hydrochloric acid + bleach → water + table salt + chlorine gas
2HCl + NaClO → H2O + NaCl + Cl2
This reaction generates chlorine gas, which is toxic to the lungs.
Green Cleaners
Green cleaning refers to using cleaning methods and products with environmentally friendly ingredients and procedures which are designed to preserve human health and environmental quality.[1] Green cleaning techniques and products avoid the use of products which contain toxic chemicals, some of which emit volatile organic compounds causing respiratory, dermatological and other conditions.[2] Green cleaning can also describe the way residential and industrial cleaning products are manufactured, packaged and distributed. If the manufacturing process is environmentally friendly and the products are biodegradable, then the term "green" or "eco-friendly" may apply.
Common household ingredients that are safe to use on its own or in combination for a variety of cleaning applications include baking soda, soap, alcohol, cornstarch, lemon juice, white vinegar, citrus solvent, washing soda (SAL soda or sodium carbonate), oxygen bleach, vegetable oil, and hydrogen peroxide.
WEB LINK
The links below provide information on safe ingredients for homemade substitutions and homemade cleaning products.
https://learn.eartheasy.com/guides/non-toxic-home-cleaning/#homecleaning
Summary
• All-purpose cleansers are effective with most common kinds of dirt and are formulated to contain mixtures of surfactants, sequestering agents, solvents, hydrotropic substances, polymeric compounds, corrosion inhibitors, skin-protective agents, and sometimes perfumes and colorants.
• Special purpose cleaners are formulated with specific chemicals to effectively remove dirt, grime or stain from a particular surface (e.g. glass cleaner, metal cleaner, etc.) or appliance (e.g. oven cleaner).
• Green cleaners are gaining popularity among environmentalists who are interested in using cleaners that are made of biodegradable and eco-friendly ingredients.
Contributors
• Wikipedia
• Cowan, Shannon. “Non-Toxic Home Cleaning.” Eartheasy Guides & Articles, learn.eartheasy.com/guides/non-toxic-home-cleaning/. | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.04%3A_All-Purpose_and_Special_Purpose_Cleaning_Products.txt |
Learning Objective
• List the properties and uses of solvents, paints, and, waxes.
Solvents
A solvent is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. The quantity of solute that can dissolve in a specific volume of solvent varies with temperature. Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as paint thinners (e.g. toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g. hexane, petrol ether), in detergents (citrus terpenes) and in perfumes (ethanol). Water is a solvent for polar molecules and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within a cell. Solvents find various applications in chemical, pharmaceutical, oil, and gas industries, including in chemical syntheses and purification processes.
Most organic solvents are flammable or highly flammable, depending on their volatility. Exceptions are some chlorinated solvents like dichloromethane and chloroform. Mixtures of solvent vapors and air can explode. Solvent vapors are heavier than air; they will sink to the bottom and can travel large distances nearly undiluted. Solvent vapors can also be found in supposedly empty drums and cans, posing a flash fire hazard; hence empty containers of volatile solvents should be stored open and upside down.
Paints
Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture to objects.
Paint was one of the earliest inventions of humanity. Some cave paintings drawn with red or yellow ochre, hematite, manganese oxide, and charcoal may have been made by early Homo sapiens as long as 40,000 years ago.[3] Paint may be even older. In 2003 and 2004, South African archeologists reported finds in Blombos Cave of a 100,000-year-old human-made ochre-based mixture that could have been used like paint.[4][5] Further excavation in the same cave resulted in the 2011 report of a complete toolkit for grinding pigments and making a primitive paint-like substance.[5][6]
By the proper onset of the Industrial Revolution, in the mid-18th century, paint was being ground in steam-powered mills, and an alternative to lead-based pigments had been found in a white derivative of zinc oxide. Interior house painting increasingly became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was also increasingly used as an inexpensive binder.
In 1866, Sherwin-Williams Figure \(1\) in the United States opened as a large paint-maker and invented a paint that could be used from the tin without preparation.
The binder is the film-forming component of paint.[10] It is the only component that is always present among all the various types of formulations. Many binders are too thick to be applied and must be thinned. The type of thinner, if present, varies with the binder. The binder imparts properties such as gloss, durability, flexibility, and toughness.[11] Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, silanes or siloxanes or oils.
The main purposes of the diluent are to dissolve the polymer and adjust the viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and in some cases can affect the stability of the paint while in liquid state. Its main function is as the carrier for the non volatile components. To spread heavier oils (for example, linseed) as in oil-based interior house paint, a thinner oil is required. These volatile substances impart their properties temporarily—once the solvent has evaporated, the remaining paint is fixed to the surface. Some paints have no diluent. Water is the main diluent for water-borne paints, even the co-solvent types.
Solvent-borne, also called oil-based, paints can have various combinations of organic solvents as the diluent, including aliphatics, aromatics, alcohols, ketones and white spirit. Specific examples are organic solvents such as petroleum distillate, esters, glycol ethers, and the like. Sometimes volatile low-molecular weight synthetic resins also serve as diluents.
Pigments are granular solids incorporated in the paint to contribute color. Dyes are colorants that dissolve in the paint. Fillers are granular solids incorporated to impart toughness, texture, give the paint special properties,[16] or to reduce the cost of the paint. During production, the size of such particles can be measured with a Hegman gauge. Rather than using only solid particles, some paints contain dyes instead of or in combination with pigments.
Pigments can be classified as either natural or synthetic. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas.
Some pigments are toxic, such as the lead pigments that are used in lead paint. Paint manufacturers began replacing white lead pigments with titanium white (titanium dioxide), before lead was banned in paint for residential use in 1978 by the US Consumer Product Safety Commission. The titanium dioxide used in most paints today is often coated with silica/alumina/zirconium for various reasons, such as better exterior durability, or better hiding performance (opacity) promoted by more optimal spacing within the paint film.[17]
Waxes
Waxes are organic compounds, hydrocarbons that characteristically consist of long aliphatic alkyl chains, although aromatic compounds may also be present. Natural waxes may contain unsaturated bonds and include various functional groups such as fatty acids, primary and secondary alcohols, ketones, aldehydes and fatty acid esters. Synthetic waxes (e.g. polyethylene and polypropylene waxes) often consist of homologous series of long-chain aliphatic hydrocarbons (alkanes or paraffins) that lack functional groups.[1]
The best known animal wax is beeswax used in constructing the honeycombs of honeybees, but other insects secrete waxes. A major component of the beeswax is myricyl palmitate which is an ester of triacontanol and palmitic acid. Its melting point is 62-65 °C. Spermaceti occurs in large amounts in the head oil of the sperm whale. One of its main constituents is cetyl palmitate, another ester of a fatty acid and a fatty alcohol. Lanolin is a wax obtained from wool, consisting of esters of sterols.[1]
Plants secrete waxes into and on the surface of their cuticles as a way to control evaporation, wettability and hydration.[3] The epicuticular waxes of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, alkyl esters, fatty acids, primary and secondary alcohols, diols, ketones and aldehydes.[2] From the commercial perspective, the most important plant wax is carnauba wax, a hard wax obtained from the Brazilian palm Copernicia prunifera. Containing the ester myricyl cerotate, it has many applications, such as confectionery and other food coatings, car and furniture polish, floss coating, and surfboard wax. Other more specialized vegetable waxes include jojoba oil, candelilla wax and ouricury wax.
Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal or shale oil that consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms.Waxes are mainly consumed industrially as components of complex formulations, often for coatings.The main use of polyethylene and polypropylene waxes is in the formulation of colourants for plastics. Waxes confer matting effects and wear resistance to paints. Polyethylene waxes are incorporated into inks in the form of dispersions to decrease friction. They are employed as release agents, find use as slip agents in furniture, and confer corrosion resistance.
Waxes such as paraffin wax or beeswax, and hard fats such as tallow are used to make candles (Figure \(2\)). used for lighting and decoration. Waxes are used as finishes and coatings for wood products.[10] Beeswax is frequently used as a lubricant on drawer slides where wood to wood contact occurs. Waxes are used to make wax paper, impregnating and coating paper and card to waterproof it or make it resistant to staining, or to modify its surface properties. Waxes are also used in shoe polishes, wood polishes, and automotive polishes, as mold release agents in mold making, as a coating for many cheeses, and to waterproof leather and fabric. Wax has been used since antiquity as a temporary, removable model in lost-wax casting of gold, silver and other materials.
Wax with colorful pigments added has been used as a medium in encaustic painting, and is used today in the manufacture of crayons, china markers and colored pencils. Carbon paper, used for making duplicate typewritten documents was coated with carbon black suspended in wax, typically montan wax, but has largely been superseded by photocopiers and computer printers. In another context, lipstick and mascara are blends of various fats and waxes colored with pigments, and both beeswax and lanolin are used in other cosmetics. Ski wax is used in skiing and snowboarding. Also, the sports of surfing and skateboarding often use wax to enhance the performance.
Some waxes are considered food-safe and are used to coat wooden cutting boards and other items that come into contact with food. Beeswax or coloured synthetic wax is used to decorate Easter eggs in Romania, Ukraine, Poland, Lithuania and the Czech Republic. Paraffin wax is used in making chocolate covered sweets.
Summary
• A solvent is a liquid, solid, a gas, or a supercritical fluid that dissolves a solute to form a solution. Solvents are found in various personal and household items, and also used in chemical, pharmaceutical, oil, and gas industries, including in chemical syntheses and purification processes.
• Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture to objects.
• Natural and synthetic waxes are used for lighting, for surface coating and polishing, for waterproofing leather and fabric. Waxes are also key ingredients in cosmetics and personal care products.
• Wikipedia | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.05%3A_Solvents_Paints_and_Waxes.txt |
Learning Objectives
• List the main ingredients in different personal care products and their functions.
• Describe the steps in formation of temporary and permanent waves.
In the United States, the Food and Drug Administration (FDA), which regulates cosmetics, defines cosmetics as products "intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or functions". This broad definition includes any material intended for use as an ingredient of a cosmetic product, with the FDA specifically excluding pure soap from this category.
Cosmetics (Figure \(1\)) have been in use for thousands of years. Egyptian men and women used makeup to enhance their appearance. They were very fond of eyeliner and eye-shadows in dark colors including blue, red, and black. Ancient Sumerian men and women were possibly the first to invent and wear lipstick, about 5,000 years ago. They crushed gemstones and used them to decorate their faces, mainly on the lips and around the eyes.
According to one source, early major developments include:
• Kohl used by ancient Egypt as a protectant of the eye (Figure \(2\)).
• Castor oil used by ancient Egypt as a protective balm.
• Skin creams made of beeswax, olive oil, and rose water, described by Romans.
• Vaseline and lanolin in the nineteenth century.
Although modern makeup has been traditionally used mainly by women, an increasing number of men are using cosmetics usually associated with women to enhance or cover their own facial features such as blemishes and dark circles, as well the use of eyeshadow, mascara and lipstick by some. Cosmetics brands have increasingly also targeted men in the sale of cosmetics, with some products targeted specifically at men.
The Skin
The cutaneous membrane is the technical term for our skin. The skin’s primary role is to help protect the rest of the body’s tissues and organs from physical damage such as abrasions, chemical damage such as detergents, and biological damage from microorganisms. For example, while the skin harbors many permanent and transient bacteria, these bacteria are unable to enter the body when healthy, intact skin is present.
Our skin is made of three general layers (Figure \(3\)). In order from most superficial to deepest they are the epidermis, dermis, and subcutaneous tissue (hypodermis).
There are several different types of cells in the epidermis. All of the cells are necessary for the important functions of the epidermis.
• The epidermis consists mainly of stacks of keratin-producing epithelial cells called keratinocytes. These cells make up at least 90 percent of the epidermis. Near the top of the epidermis, these cells are also called squamous cells.
• Another 8 percent of epidermal cells are melanocytes. These cells produce the pigment melanin that protects the dermis from UV light.
• About 1 percent of epidermal cells are Langerhans cells. These are immune system cells that detect and fight pathogens entering the skin.
• Less than 1 percent of epidermal cells are Merkel cells, which respond to light touch and connect to nerve endings in the dermis.
The epidermis has several crucial functions in the body. These functions include protection, water retention, and vitamin D synthesis. The epidermis provides protection to underlying tissues from physical damage, pathogens, and UV light.
Skin Creams and Lotions
A lotion is a low-viscosity topical preparation intended for application to the skin. By contrast, creams and gels have higher viscosity, typically due to lower water content. Lotions are applied to external skin with bare hands, a brush, a clean cloth, or cotton wool.
While a lotion may be used as a medicine delivery system, many lotions, especially hand lotions and body lotions are meant instead to simply smooth, moisturize, soften and perhaps perfume the skin.
Most cosmetic lotions are moisturizing lotions, although other forms, such as tanning lotion, also exist.
Cosmetic lotions may be marketed as anti-aging lotions, which can also be classified as a cosmetic in many cases, and may contain fragrances. The Food and Drug Administration voiced concern about lotions not classified as drugs that advertise anti-aging or anti-wrinkle properties.
Most lotions are oil-in-water emulsions using a substance such as cetearyl alcohol to keep the emulsion together, but water-in-oil lotions are also formulated.
A cream is a preparation usually for application to the skin. Creams for application to mucous membranes such as those of the rectum or vagina are also used. Creams may be considered pharmaceutical products as even cosmetic creams are based on techniques developed by pharmacy and unmedicated creams are highly used in a variety of skin conditions (dermatoses). The use of the finger tip unit concept may be helpful in guiding how much topical cream is required to cover different areas.
Creams are semi-solid emulsions of oil and water. They are divided into two types: oil-in-water (O/W) creams which are composed of small droplets of oil dispersed in a continuous water phase, and water-in-oil (W/O) creams which are composed of small droplets of water dispersed in a continuous oily phase. Oil-in-water creams are more comfortable and cosmetically acceptable as they are less greasy and more easily washed off using water. Water-in-oil creams are more difficult to handle but many drugs which are incorporated into creams are hydrophobic and will be released more readily from a water-in-oil cream than an oil-in-water cream. Water-in-oil creams are also more moisturizing as they provide an oily barrier which reduces water loss from the stratum corneum, the outermost layer of the skin.
Ointment is a semisolid dosage form it is used for topical application to the medication
Water, oil, emulsifier, and thickening agent are four main ingredients of cold creams and lotions.
Moisturizer or moisturiser is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin.
Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives and humectants
Occlusives form a coating on the surface of the skin, keeping moisture from escaping.
Humectants absorb water. They can absorb this water from the air and moisturize the skin when the humidity is greater than 70%, but more commonly they draw water from the dermis into the epidermis, making skin dryer. A study published in Skin Research and Technology in 2001 found no link between humectants and moisturizing effect. When used in practical applications, they are almost always combined with occlusives.
Moisturizers often contain water, which acts as a temporary hydration agent and as a way for the absorption of some components and evaporation of the moisturizer.
There are many different types of moisturizers. Petrolatum is one of the most effective moisturizers, although it can be unpopular due to its oily consistency. Other popular moisturizers are cetyl alcohol, cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, stearyl alcohol and castor oil, as well as other oils.
Moisturizers may also be available as lotions, creams, ointments, bath oils, or soap substitutes.
Mineral oils and waxes are insensitive to oxidation or rancidity. For this reason, they have essentially replaced vegetable oils in emollients and topical medication.
Moisturizer cosmetics may additionally contain antioxidants, ceramides, emulsifiers, fragrances, penetration enhancers, preservatives, and solvents. Some products are marketed as having anti-wrinkle and skin enhancement effects. Many plant and animal extracts have been claimed to impart skin benefits, with little scientific evidence.
Shaving Creams
Shaving cream or shave cream is a category of cosmetics used for shaving preparation. The purpose of shaving cream is to soften the hair by providing lubrication.
Different types of shaving creams include aerosol shaving cream (also known as shaving foam), latherless shaving cream (also called brushless shaving cream and non-aerosol shaving cream), and lather shaving cream or lathering shaving cream. The term shaving cream can also refer to the lather produced with a shaving brush from shaving soap or a lather shaving cream.
Shaving creams commonly consist of an emulsion of oils, soaps or surfactants (e.g. triethanolamine steatrate), and water. In addition to soap, lather shaving creams include a humectant for softer consistency and keeping the lather moisturised. Brushless shaving creams, on the other hand, don't contain soap and so don't produce lather. They are an oil-in-water mixture to which humectants, wetting agents, and other ingredients are added. Aerosol shaving creams are basically lather shaving cream in liquid form with propellants, vegetable waxes, and various oils added.
Does Shaving Cream Do Anything?
Video \(1\) What is shaving cream?
Sunscreen and Sunblock
UVB radiation in sunlight allows the skin to produce vitamin D. This vitamin prevents bone disorders like rickets and osteoporosis (brittle bone disease). The American Academy of Dermatology suggests vitamin D be obtained through foods or nutritional supplements. Excessive exposure to UV can be damaging and the pigment melanin, deposited in cells at the base of the epidermis, helps to protect the underlying layers of the skin from this damage. Melanin also colors the skin and variations in the amount of melanin produces colors from pale yellow to black. The darker the skin tone, the more melanin one has, and the less likely skin cancer will occur.
Excess exposure to the sun can cause sunburn. This is common in humans, but light skinned animals like cats and pigs can also be sunburned, especially on the ears. Skin cancer can also result from excessive exposure to the sun. As holes in the ozone layer increase exposure to the sun’s UV rays, so too does the rate of skin cancer in humans and animals.
Sunscreens and sunblocks are designed to protect skin from ultraviolet rays. Sunblocks contain inorganic ingredients like zinc oxide or titanium dioxide. These chemicals act as UV filters by reflecting the sun's UV rays. Sunblocks can have grainy textures due to the inorganic components. The thick nature of a sunblock can make it difficult to spread evenly on the skin. Sunscreens contain organic compounds like oxybenzone, avobenzone, homosalate, and octinoxate (Figure \(4\)). By absorbing ultraviolet rays, these compounds decompose and give off heat. Sunscreens apply smoother than sunblocks. Often, manufacturers will combine sunscreen and sunblock ingredients to make their products.
Sun protection factor (SPF) measures a product's protection from UVB rays. SPF does not quantify protection from UVA radiation. The American Academy of Dermatology recommends you select a sunscreen or sunblock with a minimum SPF factor of 30. This SPF value means a lotion can filter out 97% of UVB rays. Moving to a SPF of 50 will only filter out 1 more percentage of UVB rays. Increasing a SPF factor past 30 really does very little in shielding skin from UVB radiation.
Products that protect skin from UVA must be labeled as being a broad spectrum. Sunblocks provide UVA and UVB protection, but sunscreens can vary on what they can screen. Every two hours, sunscreens/sunblocks should be reapplied to the skin. Sweating and swimming can remove sunscreen/sunblock products. No sun products are waterproof, but some are labeled as being water-resistant. Consumers are encouraged to reapply these products every two hours as well.
Sunscreen Label
Figure \(5\) Sunscreen label. Source: Badger: Healthy Body Care
Is Sunscreen Safe?
Check the link below on FAQs regarding sunscreen.
https://www.aad.org/public/everyday-care/sun-protection/sunscreen/understand-sunscreen-labels
Lipsticks and Lip Balms
Lipstick, lip gloss, lip liner, lip plumper, lip balm, lip stain, lip conditioner, lip primer, lip boosters, and lip butters: Lipsticks are intended to add color and texture to the lips and often come in a wide range of colors, as well as finishes such as matte, satin, gloss and lustre.
Lipstick contains wax, oils, antioxidants, and emollients. Wax provides the structure to the solid lipstick. Lipsticks may be made from several waxes such as beeswax, ozokerite and candelilla wax. Because of its high melting point, carnauba wax is a key ingredient in terms of strengthening the lipstick. Various oils and fats are used in lipsticks, such as olive oil, mineral oil, cocoa butter, lanolin, and petrolatum.
Lipsticks get their colors from a variety of pigments and lake dyes including, but not limited to bromo acid, D&C Red No. 21, Calcium Lake such as D&C Red 7 and D&C Red 34, and D&C Orange No. 17. Pink lipsticks are made by mixing white titanium dioxide and red shades. Both organic and inorganic pigments are employed.
Lip stains have a water or gel base and may contain alcohol to help the product stay on leaving a matte look. They temporarily saturate the lips with a dye. Usually designed to be waterproof, the product may come with an applicator brush, directly through the applicator, rollerball, or could be applied with a finger. Lip glosses are intended to add shine to the lips and may add a tint of color, as well as being scented or flavored. Lip balms are most often used to moisturize, tint, and protect the lips. Some brands contain sunscreen. Using a priming lip product such as lip balm or chapstick can prevent chapped lips.
Eye Make-up
• Mascara is a cosmetic commonly used to enhance the eyelashes. It may darken, thicken, lengthen, and/or define the eyelashes. Normally in one of three forms—liquid, powder, or cream—the modern mascara product has various formulas; however, most contain the same basic components of pigments, oils, waxes, and preservatives. The most common form of mascara is a liquid in a tube.
• Eye shadow (or eyeshadow) is a cosmetic applied primarily to the eyelids to make the wearer's eyes stand out or look more attractive. Eye shadow can also be applied under eyes or to brow bones.
Eye shadow can add depth and dimension to one's eyes, complement one's eye color, make one's eyes appear larger, or simply draw attention to the eyes. Eye shadow comes in many different colors and textures. It is usually made from a powder but can also be found in liquid, pencil, cream or mousse form. Just like other trends, eyeshadow looks also have trends.
Eye shadows typically consist of four types of ingredients: base fillers, binders, slip and preservatives. In order to make eye shadow, there must be a balance between the fillers and binders.
Base fillers are usually minerals such as mica, talc or kaolin clay, which add bulk and texture to eye shadow. They make up about 30% of eye shadow powders and 25% of cream eye shadows. Mica absorbs moisture, gives the eye shadow shine and luster, and makes it opaque. Mica powders, iron oxides and clays can give color pigments to eye shadows.
Binders help eye shadow adhere and stay attached to skin. Eye shadows can have dry or liquid binders. Zinc and magnesium, which are both white powders, are commonly used as dry binders. Zinc also adds color and can be used to increase the thickness of the eyeshadow. Silicone, paraffin wax, mineral oil or vegetable oils may be used as liquid binders.
Slip allows eye shadow to glide across the skin smoothly. Products may use silica or nylon, which are fine, colorless powders. Other types of slip include dimethicone, boron nitride or bismuth oxychloride.
Preservatives help products stay bacteria free and extend their lifespan. Common preservatives in eye shadow are glycol and tocopherol.
Eye liner or eyeliner is a cosmetic used to define the eyes. It is applied around the contours of the eye(s) to create a variety of aesthetic effects. It can come in the form of a pencil, a gel, or a liquid and can be found in almost any color. Traditional wax-based eye liners are made from about 20 components. About 50% by weight are waxes (e.g., Japan wax, fats, or related soft materials that easily glide on to the skin. Stearyl heptanoate is found in most cosmetic eyeliner. Typical pigments include black iron oxides, as well as smaller amounts of titanium dioxide and Prussian blue.
Eyebrow shaders, and pencils are often used to define the eyebrow or make it appear fuller. These can create an outline for the brows or mimic hairs where there are sparse areas. Brow gels are also used in creating a thicker brow; they allow for the hairs to be more textured, which gives the appearance of thicker, fuller brows. Lastly, brow powders or even eye shadows are used for those who want a fuller and more natural look, by placing the brow powder or eye shadow (closest to the natural hair color) in areas where there is less hair.
Deodorants and Antiperspirants
A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration in the armpits, groin, and feet, and in some cases vaginal secretions. A subclass of deodorants, called antiperspirants, prevents sweating itself, typically by blocking sweat glands. Antiperspirants are used on a wider range of body parts, at any place where sweat would be inconvenient or unsafe, since unwanted sweating can interfere with comfort, vision, and grip (due to slipping). Other types of deodorant allow sweating but prevent bacterial action on sweat, since human sweat only has a noticeable smell when it is decomposed by bacteria.
In the United States, the Food and Drug Administration classifies and regulates most deodorants as cosmetics but classifies antiperspirants as over-the-counter drugs.
In the United States, deodorants are classified and regulated as cosmetics by the U.S. Food and Drug Administration (FDA) and are designed to eliminate odor. Deodorants are often alcohol based. Alcohol initially stimulates sweating but may also temporarily kill bacteria. Other active ingredients in deodorants include sodium stearate, sodium chloride, and stearyl alcohol. Deodorants can be formulated with other, more persistent antimicrobials such as triclosan that slow bacterial growth or with metal chelant compounds such as EDTA. Deodorants may contain perfume fragrances or natural essential oils intended to mask the odor of perspiration. In the past, deodorants included chemicals such as zinc oxide, acids, ammonium chloride, sodium bicarbonate, and formaldehyde, but some of these ingredients were messy, irritating to the skin, or even carcinogenic.
Over-the-counter products, often labeled as "natural deodorant crystal", contain the chemical rock crystals potassium alum or ammonium alum, which prevents bacterial action on sweat. These have gained popularity as an alternative health product, in spite of concerns about possible risks related to aluminum (see below – all alum salts contain aluminum in the form of aluminum sulphate salts) and contact dermatitis.
In the United States, deodorants combined with antiperspirant agents are classified as drugs by the FDA. Antiperspirants attempt to stop or significantly reduce perspiration and thus reduce the moist climate in which bacteria thrive. Aluminium chloride, aluminium chlorohydrate, and aluminium-zirconium compounds, most notably aluminium zirconium tetrachlorohydrex gly and aluminium zirconium trichlorohydrex gly, are frequently used in antiperspirants. Aluminium chlorohydrate and aluminium-zirconium tetrachlorohydrate gly are the most frequent active ingredients in commercial antiperspirants. Aluminium-based complexes react with the electrolytes in the sweat to form a gel plug in the duct of the sweat gland. The plugs prevent the gland from excreting liquid and are removed over time by the natural sloughing of the skin. The metal salts work in another way to prevent sweat from reaching the surface of the skin: the aluminium salts interact with the keratin fibrils in the sweat ducts and form a physical plug that prevents sweat from reaching the skin’s surface. Aluminium salts also have a slight astringent effect on the pores; causing them to contract, further preventing sweat from reaching the surface of the skin. The blockage of a large number of sweat glands reduces the amount of sweat produced in the underarms, though this may vary from person to person. Methenamine (Figure \(7\)) in the form of cream or spray is effective in the treatment of excessive sweating and attendant odor. Antiperspirants are usually best applied before bed.
Toothpaste: Soap with Grit and Flavor
Toothpaste (Figure \(8\)) is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, assists in suppressing halitosis, and delivers active ingredients (most commonly fluoride) to help prevent tooth decay (dental caries) and gum disease (gingivitis). Salt and sodium bicarbonate (baking soda) are among materials that can be substituted for commercial toothpaste. Large amounts of swallowed toothpaste can be toxic.
In addition to 20%–42% water, toothpastes are derived from a variety of components, the three main ones being abrasives, fluoride, and detergents.
Abrasives constitute at least 50% of a typical toothpaste. These insoluble particles are designed to help remove plaque from the teeth. The removal of plaque and calculus prevents the accumulation of tartar and is widely claimed to help minimize cavities and periodontal disease, although the clinical significance of this benefit is debated. Representative abrasives include particles of aluminum hydroxide (Al(OH)3), calcium carbonate (CaCO3), various calcium hydrogen phosphates, various silicas and zeolites, and hydroxyapatite (Ca5(PO4)3OH).
Abrasives, like the dental polishing agents used in dentists' offices, also cause a small amount of enamel erosion which is termed "polishing" action. Some brands contain powdered white mica, which acts as a mild abrasive, and also adds a cosmetically pleasing glittery shimmer to the paste. The polishing of teeth removes stains from tooth surfaces, but has not been shown to improve dental health over and above the effects of the removal of plaque and calculus.
The abrasive effect of toothpaste is indicated by its RDA value. Too high RDA values are deleterious. Some dentists recommend toothpaste with an RDA value no higher than 50 for daily use.
Fluoride in various forms is the most popular active ingredient in toothpaste to prevent cavities. Fluoride is present in small amounts in plants, animals, and some natural water sources. The additional fluoride in toothpaste has beneficial effects on the formation of dental enamel and bones. Sodium fluoride (NaF) is the most common source of fluoride, but stannous fluoride (SnF2), olaflur (an organic salt of fluoride), and sodium monofluorophosphate (Na2PO3F) are also used. Stannous fluoride has been shown to be more effective than sodium fluoride in reducing the incidence of dental caries and controlling gingivitis, but causes somewhat more surface stains.
Much of the toothpaste sold in the United States has 1,000 to 1,100 parts per million fluoride. In European countries, such as the UK or Greece, the fluoride content is often higher; a NaF content of 0.312% w/w (1,450 ppm fluoride) is common. All of these concentrations are likely to prevent tooth decay, according to a 2019 Cochrane review. Concentrations below 1,000 ppm are not likely to be preventive, and the preventive effect increases with concentration. Clinical trials support the use of high fluoride dentifrices, as it was found to reduce the amount of plaque accumulated, decrease the number of mutans streptococci and lactobacilli and possibly promote calcium fluoride deposits to a higher degree than after the use of traditional fluoride containing dentifrices. However, these effects must be balanced with the increased risk of harm at higher concentrations.
Many, although not all, toothpastes contain sodium lauryl sulfate (SLS) or related surfactants (detergents). SLS is found in many other personal care products as well, such as shampoo, and is mainly a foaming agent, which enables uniform distribution of toothpaste, improving its cleansing power.
Other Components in toothpaste formulations include:
• Antibacterial agents. Triclosan or zinc chloride prevent gingivitis and, according to the American Dental Association, helps reduce tartar and bad breath.
• Flavorants. Toothpaste comes in a variety of colors and flavors intended to encourage use of the product. The three most common flavorants are peppermint, spearmint, and wintergreen.
• Reminalizers. Hydroxyapatite nanocrystals and a variety of calcium phosphates are included in formulations for remineralization, i.e. the reformation of enamel.
Agents are added to suppress the tendency of toothpaste to dry into a powder. Included are various sugar alcohols, such as glycerol, sorbitol, or xylitol, or related derivatives, such as 1,2-propylene glycol and polyethyleneglycol
Strontium chloride or potassium nitrate is included in some toothpastes to reduce sensitivity. Two systemic meta-analysis reviews reported that arginine, and calcium sodium phosphosilicate - CSPS containing toothpastes are also effective in alleviating dentinal hypersensitivity respectively. Another randomized clinical trial found superior effects when both formulas were combined together.
Sodium polyphosphate is added to minimize the formation of tartar. Other example to components in toothpastes is the Biotene, which has proved its efficiency in relieving the symptoms of dry mouth in people who suffer from xerostomia according to the results of two randomized clinical trials.
Chlorohexidine mouthwash has been popular for its positive effect on controlling plaque and gingivitis, however, a systemic review studied the effects of chlorohexidine toothpastes and found insufficient evidence to support its use, tooth surface discoloration was observed as a side effect upon using it, which is considered a negative side effect that can affect patients' compliance.
Sodium hydroxide, also known as lye or caustic soda, is listed as an inactive ingredient in some toothpaste, for example Colgate Total.
Some studies have demonstrated that toothpastes with xylitol as an ingredient are more effective at preventing dental caries in permanent teeth of children than toothpastes containing fluoride alone.
Perfumes, Colognes, and Aftershaves
Perfume (Figure \(9\)) is a mixture of fragrant essential oils or aroma compounds, fixatives and solvents, used to give the human body, animals, food, objects, and living-spaces an agreeable scent. Perfume types reflect the concentration of aromatic compounds in a solvent, which in fine fragrance is typically ethanol or a mix of water and ethanol. Various sources differ considerably in the definitions of perfume types. The intensity and longevity of a perfume is based on the concentration, intensity, and longevity of the aromatic compounds, or perfume oils, used. Specific terms are used to describe a fragrance's approximate concentration by the percent of perfume oil in the volume of the final product. The most widespread terms are:
• parfum or extrait, in English known as perfume extract, pure perfume, or simply perfume: 15–40% aromatic compounds (IFRA: typically ~20%);
• esprit de parfum (ESdP): 15–30% aromatic compounds, a seldom used strength concentration in between EdP and perfume;
• eau de parfum (EdP) or parfum de toilette (PdT) (The strength usually sold as "perfume"): 10–20% aromatic compounds (typically ~15%); sometimes called "eau de perfume" or "millésime"; parfum de toilette is a less common term, most popular in the 1980s, that is generally analogous to eau de parfum;
• eau de toilette (EdT): 5–15% aromatic compounds (typically ~10%); This is the staple for most masculine perfumes.
• eau de Cologne (EdC): often simply called cologne: 3–8% aromatic compounds (typically ~5%);
• eau fraiche: products sold as "splashes", "mists", "veils" and other imprecise terms. Generally these products contain 3% or less aromatic compounds and are diluted with water rather than oil or alcohol.
Perfume is described in a musical metaphor as having three sets of notes, making the harmonious scent accord. The notes unfold over time, with the immediate impression of the top note leading to the deeper middle notes, and the base notes gradually appearing as the final stage. These notes are created carefully with knowledge of the evaporation process of the perfume.
• Top notes: Also called the head notes. The scents that are perceived immediately on application of a perfume. Top notes consist of small, light molecules that evaporate quickly. They form a person's initial impression of a perfume and thus are very important in the selling of a perfume. Examples of top notes include mint, lavender and coriander.
• Middle notes: Also referred to as heart notes. The scent of a perfume that emerges just prior to the dissipation of the top note. The middle note compounds form the "heart" or main body of a perfume and act to mask the often unpleasant initial impression of base notes, which become more pleasant with time. Examples of middle notes include seawater, sandalwood and jasmine.
• Base notes: The scent of a perfume that appears close to the departure of the middle notes. The base and middle notes together are the main theme of a perfume. Base notes bring depth and solidity to a perfume. Compounds of this class of scents are typically rich and "deep" and are usually not perceived until 30 minutes after application. Examples of base notes include tobacco, amber and musk.
The scents in the top and middle notes are influenced by the base notes; conversely, the scents of the base notes will be altered by the types of fragrance materials used as middle notes. Manufacturers who publish perfume notes typically do so with the fragrance components presented as a fragrance pyramid, using imaginative and abstract terms for the components listed.
Aftershave is a product applied to skin after shaving. Traditionally it is an alcohol based liquid (splash), but it can be a lotion, gel, or even a paste.
It often contains an antiseptic agent such as denatured alcohol, stearate citrate or witch hazel to prevent infection of cuts, as well as to act as an astringent to reduce skin irritation. Menthol is used in some varieties as well to numb irritated skin.
An alcohol-based aftershave usually causes an immediate stinging sensation after applying it post-shave, with effects sometimes lasting several minutes, but most commonly only for seconds. For this reason, a market consisting of highly differentiated products has been created—some using alcohols, some not.
Aftershave balms are frequently recommended for winter use as they tend to be alcohol free and lotion-like, moisturizing the skin.
Some aftershaves use fragrance or essential oil to enhance scent. Moisturizers—natural and artificial, are often touted as able to soften the skin.
Aftershave is sometimes mistakenly referred to as Eau de Cologne due to the very similar nature of the two products. Some aftershave manufacturers encourage using their fragranced aftershave as if it were cologne, in order to increase sales by encouraging consumers to use it in a more versatile manner, rather than just after a shaving session. Some aftershaves were inspired by a cologne.
Early aftershaves included witch-hazel and bay rum, and have been documented in shaving guides. Both still are sold as aftershaves.
Hairy Chemistry
Hair keratin consists of many protein alpha-helices (Figure \(10\)). Three alpha-helices are interwoven into a left-handed coil called a protofibril. Eleven protofibrils are bonded and coiled together to make a microfibril. Hundreds of these microfibrils are cemented into an irregular bundle called a macrofibril. These in turn are mixed with dead and living cells to make a complete strand of hair.
The alpha-helices are extensively cross-linked with disulfide bonds from cysteine. These bonds enable keratin to have a somewhat elastic nature. If the alpha -helices stretch unevenly past each other, the disulfide cross-links return them to the original position when the tension is released.
Shampoo
Shampoo (/ʃæmˈpuː/) is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in bar form, like a bar of soap. Shampoo is used by applying it to wet hair, massaging the product into the scalp, and then rinsing it out. Some users may follow a shampooing with the use of hair conditioner.
The typical reason of using shampoo is to remove the unwanted build-up of sebum in the hair without stripping out so much as to make hair unmanageable. Shampoo is generally made by combining a surfactant, most often sodium lauryl sulfate or sodium laureth sulfate, with a co-surfactant, most often cocamidopropyl betaine in water. The sulphate ingredient acts as a surfactant, essentially heavy duty soap that makes it easier to trap oil and grease.
Specialty shampoos are marketed to people with dandruff, color-treated hair, gluten or wheat allergies, an interest in using an organic product, and infants and young children ("baby shampoo" is less irritating). There are also shampoos intended for animals that may contain insecticides or other medications to treat skin conditions or parasite infestations such as fleas.
Shampoo is generally made by combining a surfactant, most often sodium lauryl sulfate or sodium laureth sulfate, with a co-surfactant, most often cocamidopropyl betaine in water to form a thick, viscous liquid. Other essential ingredients include salt (sodium chloride), which is used to adjust the viscosity, a preservative and fragrance. Other ingredients are generally included in shampoo formulations to maximize the following qualities:
• pleasing foam
• ease of rinsing
• minimal skin and eye irritation
• thick or creamy feeling
• pleasant fragrance
• low toxicity
• good biodegradability
• slight acidity (pH less than 7)
• no damage to hair
• repair of damage already done to hair
Many shampoos are pearlescent. This effect is achieved by the addition of tiny flakes of suitable materials, e.g. glycol distearate, chemically derived from stearic acid, which may have either animal or vegetable origins. Glycol distearate is a wax. Many shampoos also include silicone to provide conditioning benefits.
How Does Shampoo Work?
Video \(2\) Shampoo applied to wet hair.
Hair Coloring
Hair color is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more eumelanin is present, the color of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color on the same person. Particular hair colors are often associated with ethnic groups, while gray or white hair is associated with age.
Hair coloring, or hair dyeing, is the practice of changing the hair color. The main reasons for this are cosmetic: to cover gray or white hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching.
Hair coloring can be done professionally by a hairdresser or independently at home. Today, hair coloring is very popular, with 75% of women and 18% of men living in Copenhagen having reported using hair dye (according to a study by the University of Copenhagen). At-home coloring in the United States reached \$1.9 billion in 2011 and was expected to rise to \$2.2 billion by 2016.
Hair color can be changed by a chemical process. Hair coloring is classed as "permanent" or "semi-permanent".
Permanent hair color means that the hair's structure has been chemically altered until it is eventually cut away. This does not mean that the synthetic color will remain permanently. During the process, the natural color is removed, one or more shades, and synthetic color has been put in its place. All pigments wash out of the cuticle. Natural color stays in much longer and artificial will fade the fastest (depending on the color molecules and the form of the dye pigments).
Permanent hair coloring requires three components: (1) 1,4-diaminobenzene (historically) or 2,5-diaminotoluene (currently), (2) a coupling agent, and (3) an oxidant. The process is typically performed under basic conditions. The mechanism of oxidation dyes involves three steps: 1) Oxidation of 1,4-diaminobenzene derivative to the quinone state. 2) Reaction of this diimine with a coupler compound (more detail below). 3) Oxidation of the resulting compound to give the final dye.
Steps in Permanent Hair Coloring
The first step shows the oxidation of p-phenylenediamine to the quinonediimine (C6H4(NH)2):
The second step involves the attack of this quinonediimine on the coupler.
In the third and final step, the product from the quinonediimine-coupler reaction oxidizes to the final hair dye.
It was once believed that the dye forms in the above reaction bonds to hair permanently. It was later shown that the main reason that this reaction imparts a permanent color on hair by producing larger dye molecules, which is locked inside the hair.
Semi-permanent color washes out over a period of time—typically four to six weeks, so root regrowth is less noticeable. The final color of each strand is affected by its original color and porosity, so there will be subtle variations in color across the head—more natural and less harsh than a permanent dye. However, this means that gray and white hair will not dye to the same color as the rest of the head (in fact, some white hair will not absorb the color at all). A few gray and white hairs will blend in sufficiently not to be noticeable, but as they become more widespread, there will come a point where a semi-permanent alone will not be enough. The move to 100% permanent color can be delayed by using a semi-permanent as a base color, with permanent highlights.
Semi-permanent hair color cannot lighten hair. Hair can only be lightened using chemical lighteners, such as bleach. Bleaching is always permanent because it removes the natural pigment.
"Rinses" are a form of temporary hair color, usually applied to hair during a shampoo and washed out again the next time the hair is wash.
Plant based dyes include henna, indigo and anthocyanin pigments extracted form blackcurrant skin waste.
How Does Hair Dye Work?
Video \(3\) Applying hair dye.
Permanent and Temporary Waving
Temporary Wave. When the hair gets wet, water molecules intrude into the keratin strands. The sheer numbers of water molecules are able to disrupt some of the hydrogen bonds which also help to keep the alpha-helices aligned. The helices are able to slip past each other and will retain a new shape in the hair drying process as new hydrogen bonds are formed. The hair strands are able for a short time to maintain the new curl in the hair.
A permanent hairstyle, commonly called a perm or "permanent" (sometimes called a "perm" to distinguish it from a "straight perm"), is a hairstyle consisting of styles set into the hair. The hairstyle may last a number of months, hence the name.
Perms may be applied using thermal or chemical means. In the latter method, chemicals are applied to the hair, which is then wrapped around forms to produce hairstyles. The same process is used for chemical straightening or relaxing, with the hair being flattened instead of curled during the chemical reaction.
The formation of disulfide bonds has a direct application in producing curls in hair by the permanent wave process. Disulfide bonds Figure \(12\) are formed by oxidation of the sulfhydryl groups on cysteine. Different protein chains or loops within a single chain are held together by the strong covalent disulfide bonds. The alpha-helices in the hair strands are bonded by disulfide links.
In the permanent wave process, a basic reducing substance (usually ammonium thioglycolate) is first added to reduce and rupture some of the disulfide cross-links, see Figure \(13\) below.
The hair is put on rollers or curlers. Since the alpha-helices are no longer tightly cross-linked to each other, the alpha-helices can shift positions in relation to each other. An oxidizing agent, usually a dilute solution of hydrogen peroxide, (also called the neutralizer) is added to reform the disulfide bonds in their new positions (Figure \(14\)). The permanent will hold these new disulfide bond positions until the hair grows out, since new hair growth is of course not treated.
Hair spray
Hair spray is a common household aqueous solution which is used to stiffen hair into a certain style. It was first developed and manufactured in 1948 by Chase Products, based in Broadview, Illinois. Weaker than hair gel or hair wax, it is sprayed directly onto the hair to hold styles for long periods of time. It sprays evenly over the hair using a pump or aerosol spray nozzle. The product may leave hair feeling 'crunchy' unless brushed out.
The active ingredients in hair spray are called polymers, which keep the hair stiff and firm without snapping. Solvents, which make up most of the content of the hairspray, are responsible for carrying these polymers in a solution.
Originally, the solvent found in hair spray was a chlorofluorocarbon (CFC). CFCs are nontoxic, nonflammable, and make almost ideal aerosol propellants. However, when research concluded that CFCs cause destruction of stratospheric ozone, they were replaced with other solvents, such as alcohols and hydrocarbons.
Hair sprays consist of the following components: concentrate, plasticizers, luster agents, and fragrances, as well as propellants.
One of the polymers used in hair spray is polyvinylpyrrolidone (Figure \(15\)) , which is water-soluble. The non-water-soluble polymer polydimethylsiloxane is added to make the hold last a bit longer. Some less common polymers found in hair spray include copolymers with vinyl acetate and copolymers with maleic anhydride.
Some hair sprays use natural polymers and solvents like vegetable gums dissolved in alcohol. One popular ingredient in natural hair sprays is gum arabic, which is made from the sap of various species of the acacia tree. Gum tragacanth is another herbal gum that is used to stiffen calico and crepe, as well as hair.
Hair Removers
Depilation is the removal of the part of the hair above the surface of the skin. The most common form of depilation is shaving or trimming. Another option is the use of chemical depilatories, which work by breaking the disulfide bonds that link the protein chains that give hair its strength.
A chemical depilatory is a cosmetic preparation used to remove hair from the skin. Common active ingredients are salts of thioglycolic acid and thiolactic acids. These compounds break the disulfide bonds in keratin and also hydrolyze the hair so that it is easily removed. Formerly, sulfides such as strontium sulfide were used, but due to their unpleasant odor, they have been replaced by thiols.
The main chemical reaction effected by the thioglycolate is:
2 HSCH2CO2H (thioglycolic acid) + R-S-S-R (cystine) → HO2CCH2-S-S-CH2CO2H (dithiodiglycolic acid) + 2 RSH (cysteine)
Chemical depilatories contain 5–6% calcium thioglycolate in a cream base (to avoid runoff). Calcium hydroxide or strontium hydroxide maintain a pH of about 12. Hair destruction requires about 10 minutes. Depilation is followed by careful rinsing with water, and various conditioners are applied to restore the skin's pH to normal. Depilation does not destroy the dermal papilla, and the hair grows back.
Chemical depilatories are available in gel, cream, lotion, aerosol, roll-on, and powder forms. Common brands include Nair, Magic Shave and Veet.
Depilatory ointments, or plasters, were known to Greek and Roman authors as psilothrum. In Jewish lore, King Solomon is said to have discovered a chemical depilatory made from a mixture of lime and water and orpiment (arsenic trisulfide).
Hair Restorers
Treatments for the various forms of hair loss have only moderate success. Three medications have evidence to support their use in male pattern hair loss: finasteride, dutasteride and minoxidil. They typically work better to prevent further hair loss than to regrow lost hair.
They may be used together when hair loss is progressive or further regrowth is desired after 12 months. Other medications include ketoconazole, and in female androgenic alopecia spironolactone and flutamide. Combinations of finasteride, minoxidil and ketoconazole are more effective than individual use.
Minoxidil is applied topically, is widely used for the treatment of hair loss. It may be effective in helping promote hair growth in both men and women with androgenic alopecia. About 40% of men experience hair regrowth after 3–6 months. It is the only topical product that is FDA approved in America for androgenic hair loss. However, increased hair loss has been reported.
Finasteride is used to treat male pattern hair loss. Treatment provides about 30% improvement in hair loss after six months of treatment, and effectiveness only persists as long as the drug is taken. There is no good evidence for its use in women. It may cause gynecomastia, erectile dysfunction and depression.
Dutasteride is used off label for male pattern hair loss.
There is tentative support for spironolactopne in women. Due to its feminising side effects and risk of infertility it is not often used by men. It can also cause low blood pressure, high blood potassium, and abnormal heart rhythms. Also, women who are pregnant or trying to become pregnant generally cannot use the medication as it is a teratogen, and can cause ambiguous genitalia in newborn children.
There is tentative evidence for flutamide in women; however, it is associated with relatively high rates of liver problems. Like spironolactone, it is typically only used by women.
Ketoconazole shampoo in conjunction with an oral 5α-reductase inhibitor such as finasteride or dutasteride has been used off label to treat androgenic alopecia.
Summary
• Various personal care products contain ingredients to protect the skin, protect the hair, promote hygiene, for aesthetic purposes etc.
• Temporary and permanent waves are formed due to the disruption and reformation of disulfide bonds in hair strands.
Contributors
• US FDA
• Elizabeth R. Gordon (Furman University)
• American Academy of Dermatology Association
• Libretext: Anatomy and Physiology 1 (Lumen)
• Libretext: Human Biology (Wakim and Grewal)
• Libretext: Supplemental Module (Biological Chemistry)
• Charles Ophardt, Professor Emeritus, Elmhurst College; Virtual Chembook | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/21%3A_Household_Chemicals/21.06%3A_Cosmetics_-_Personal_Care_Chemicals.txt |
What is Toxicology?
Toxicology is traditionally defined as "the science of poisons." Over time, our understanding of how various agents can cause harm to humans and other organisms has increased, resulting in a more descriptive definition of toxicology as "the study of the adverse effects of chemical, physical, or biological agents on living organisms and the ecosystem, including the prevention and amelioration of such adverse effects."
These adverse effects can take many forms, ranging from immediate death to subtle changes not appreciated until months or years later. They may occur at various levels within the body, such as an organ, a type of cell, or a specific biochemical. Our understanding of how toxic agents damage the body has progressed along with medical knowledge. We now know that various observable changes in anatomic or bodily functions actually result from previously unrecognized changes in specific biochemicals in the body.
A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include
• Prescription or over-the-counter medicines taken in doses that are too high
• Overdoses of illegal drugs
• Carbon monoxide from gas appliances
• Household products, such as laundry powder or furniture polish
• Pesticides
• Indoor or outdoor plants
• Metals such as lead and mercury
The effects of poisoning range from short-term illness to brain damage, coma, and death. To prevent poisoning it is important to use and store products exactly as their labels say. Keep dangerous products where children can't get to them. Treatment for poisoning depends on the type of poison.
Sources
National Institute of Health (NIH) US National Library of Medicine
22: Poisons
Learning Objectives
• List different plant and animal poisons and their properties.
• List various causes of food poisoning.
In biology, poisons are substances that cause death, injury or harm to organs, usually by chemical reactions or other activity on the molecular scales, when an organism absorbs a sufficient quantity.[1][2]The fields of medicine (particularly veterinary) and zoology often distinguish a poison from a toxin, and from a venom. Toxins are poisons produced by organisms in nature, and venoms are toxins injected by a bite or sting (this is exclusive to animals). The difference between venom and other poisons is the delivery method.
The history of poison stretches from before 4500 BCE to the present day. Poisons have been used for many purposes across the span of human existence, most commonly as weapons, anti-venoms, and medicines. Poison has allowed much progress in branches, toxicology, and technology, among other sciences.
Over the centuries, the variety of harmful uses of poisons continued to increase. The means for curing these poisons also advanced in parallel. In the modern world, intentional poisoning is less common than the Middle Ages. Rather, the more common concern is the risk of accidental poisoning from everyday substances and products.
Constructive uses for poisons have increased considerably in the modern world. Poisons are now used as pesticides, disinfectants, cleaning solutions, and preservatives. Nonetheless, poison continues to be used as a hunting tool in remote parts of developing countries, including Africa, South America, and Asia.
Poisonous Plants
Poisonous plants are plants that produce toxins that deter herbivores from consuming them. Plants cannot move to escape their predators, so they must have other means of protecting themselves from herbivorous animals. Some plants have physical defenses such as thorns, spines and prickles, but by far the most common type of protection is chemical. Over millennia, through the process of natural selection, plants have evolved the means to produce a vast and complicated array of chemical compounds in order to deter herbivores. Tannin, for example, is a defensive compound that emerged relatively early in the evolutionary history of plants, while more complex molecules such as polyacetylenes are found in younger groups of plants such as the Asterales. Many of the known plant defense compounds primarily defend against consumption by insects, though other animals, including humans, that consume such plants may also experience negative effects, ranging from mild discomfort to death. Several poisonous plants, the specific toxins and the poisonous effects are listed below.
Poison ivy (Figure \(1\)) - The poison Urushiol is an oily mixture of organic compounds with allergic properties. Symptoms of a reaction include itching, redness, swelling, and blisters. It is important to note that the blisters are not contagious.
Western water hemlock (Figure \(2\)) - The toxin, cicutoxin and oenanthotoxin, are conjugated polyacetylenes. These unsaturated alcohols have a strong carrot-like odor and are noncompetitive antagonists for the gamma-aminocutyric acid (GABA) neural transmitter in the central nervous system. GABA role is to inhibit neuron excitability; essentially it has a relaxing function. Blocking this results in convulsing and grand mal seizures and eventually death can occur.
Autumn skullcap - The toxin amatoxin in the form of γ-amanitin, β-amanitin, and α-amanitin causes severe abdominal pain, vomiting, and diarrhea may last for six-nine hours. The toxins affect the liver, results in gastrointestinal bleeding, coma, kidney failure, or even death, within seven days of consumption
Henbane - The toxins in this plant are atropine and scopolamine, found in leaves. Apoatropine and cuscohygrine are the main alkaloids of the root. The main alkaloid in seeds is hyoscyamine, little hyoscine and little atropine. the plant is toxic to cattle, wild animals, fish, and birds. Pigs are immune. In humans, it could cause hallucinations, dilated pupils, restlessness, fast heart, seizure, vomiting, high blood pressure, and ataxia. Initial effects last for 3-4 hours, after effects last up to three days.
Oak - Tannic acid, binds and precipitates proteins. Cattle, sheep, horses and goats are most affected while pigs are immune. In humans, Tannic acid poisoning could cause anorexia, depression, constipation, diarrhea, blood in urine. Signs typically occur around 3-7 days after consumption, with
The links below are an extensive, if incomplete, list of plants containing one or more poisonous parts that pose a serious risk of illness, injury, or death to humans or domestic animals. There is significant overlap between plants considered poisonous and those with psychotropic properties, some of which are toxic enough to present serious health risks at recreational doses. There is a distinction between plants that are poisonous because they naturally produce dangerous phytochemicals, and those that may become dangerous for other reasons, including but not limited to infection by bacterial, viral, or fungal parasites; the uptake of toxic compounds through contaminated soil or groundwater; and/or the ordinary processes of decay after the plant has died; this list deals exclusively with plants that produce phytochemicals. Many plants, such as peanuts, produce compounds that are only dangerous to people who have developed an allergic reaction to them, and with a few exceptions, those plants are not included here (see list of allergens instead). Despite the wide variety of plants considered poisonous, human fatalities caused by poisonous plants – especially resulting from accidental ingestion – are rare in the developed world.
WEB LINK
A more extensive list of poisonous plants can be found on the link below.
https://en.Wikipedia.org/wiki/List_o...isonous_plants
Poisonous Animals
Several deadly poisons are from snakes and spiders. Several poisonous animals, the specific toxins and the poisonous effects are listed below.
Timber rattlesnake - There are 4 types of toxin. Type A : A neurotoxin known as canebrake. Type B : A hemorrhagic and proteolytic toxin. Type A + B: Intergrade between snakes with Type A and Type B. Type C : relatively weak. The toxins could cause myokymia, defibrination syndrome, numbness, lightheadedness, weakness, vomiting, blurred vision, sweating, salivating. It can be treated with CroFab Antivenom.
Eastern coral snake (Figure \(3\)).- Phospholipase A2 and three-finger toxins (abbreviated as 3FTx). 3FTx proteins are neurotoxins, attacking nerve tissue. Phospholipase A2 can cause inflammation and pain at the site of the bite, though this is uncommon. The toxins could also cause slurred speech, double vision, muscle paralysis, and can lead to cardiac arrest if left untreated.
Cotton mouth snake - Cotton mouth toxins mainly consist of three protein families: phospholipase A2 (PLA2), metalloproteases (SVMP), and serine proteases (SVSP). PLA2s are responsible for inflammation and pain, while SVMPs are responsible for hemorrhage and SVSPs affect the coagulation of blood. The poison could lead to low blood pressure, weakness, change in skin color at site of bite, trouble breathing, nausea, increase in heart rate.
Black widow spider (Figure \(4\)) - Latrotoxins are the main component of the venom, but other compounds such as polypeptides, adenosine, and guanosine are active as well. Only the bite of the female is dangerous to humans, as their venom glands are very large. The toxin can cause pain and sweating at the site of the bite, muscle cramps, headache, nausea, vomiting, weakness. Typically only localized pain is felt, but in some cases the pain can spread. Symptoms typically last from 3-7 days after the bite takes place.
Brown recluse spider - Brown recluse venom possesses potentially deadly hemotoxins and cytotoxins that affect the red blood cells and their ability to clot. It is a mixture of enzymes such as collagenase, protease, and phospholipase. Symptoms include redness, fever, weakness, pain and nausea. In around 10% of victims necrosis can occur at the site of the bite, and in even fewer cases hemolysis (bursting of red blood cells) can occur.
Other Poisonous Animals
The list below is a partial list of animals that are poisonous to humans (and other animals), or put another way, their flesh is toxic if consumed, or in some cases touched:
Birds: Pitohui, Blue-capped ifrit, Little shrikethrush, Spur-winged goose[1] (diet-dependent), and Common quail (diet-dependent)
Snakes: Rhabdophis keelback snakes and Garter snake (diet-dependent, when feeding on Pacific newts)[2]
Frogs and toads: American toad, Asiatic toad, Cane toad, Colorado River toad, Common toad, Corroboree frog, European green toad, Fowler's toad, Mantella, and poison dart frog (Figure \(5\) ).
Salamanders: Pacific newts
Fish: Tetraodontidae (Blowfish, Pufferfish), Greenland shark, and Barracuda (age and diet dependent)
Cephalophods: Blue-ringed octopus and Pfeffer's flamboyant cuttlefish
Insects: Blister beetle, Birdwings, Milkweed butterfly, Battus (butterfly), Diamphidia, and Monarch (butterfly)
Food Poisoning
Foodborne illness (also foodborne disease and colloquially referred to as food poisoning)[1] is any illness resulting from the spoilage of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food,[2] as well as toxins such as poisonous mushrooms and various species of beans that have not been boiled for at least 10 minutes.
Many different disease-causing germs (Figure \(6\) below) can contaminate foods, so there are many different foodborne infections. The US CDC estimates that each year 48 million people get sick from a foodborne illness, 128,000 are hospitalized, and 3,000 die. Researchers have identified more than 250 foodborne diseases. Most of them are infections, caused by a variety of bacteria, viruses, and parasites. Harmful toxins and chemicals also can contaminate foods and cause foodborne illness.
Although anyone can get a foodborne illness, some people are more likely to develop one. Those groups include Pregnant women, Young children, Older adults, People with immune systems weakened from medical conditions, such as diabetes, liver disease, kidney disease, organ transplants, HIV/AIDS, or from receiving chemotherapy or radiation treatment. Most people with a foodborne illness get better without medical treatment, but people with severe symptoms should see their doctor.
Food Poisoning Symptoms
Common symptoms of foodborne diseases are nausea, vomiting, stomach cramps, and diarrhea. However, symptoms may differ among the different types of foodborne diseases. Symptoms can sometimes be severe and some foodborne illnesses can even be life-threatening. Most people have only mild illnesses, lasting a few hours to several days. However, some people need to be hospitalized, and some illnesses result in long-term health problems or even death. Infections transmitted by food can result in chronic arthritis, brain and nerve damage, and hemolytic uremic syndrome (HUS), which causes kidney failure.
Food poisoning symptoms may range from mild to severe and may differ depending on the germ you swallowed (see Table \(1\) below). After you consume a contaminated food or drink, it may take hours or days before you develop symptoms. See your doctor or healthcare provider if you have symptoms that are severe, including:
• High fever (temperature over 101.5°F, measured orally)
• Blood in stools
• Frequent vomiting that prevents keeping liquids down (which can lead to dehydration)
• Signs of dehydration, including a marked decrease in urination, a very dry mouth and throat, or feeling dizzy when standing up.
• Diarrhea that lasts more than 3 days
The top five germs that cause illnesses from food eaten in the United States are Norovirus, Salmonella, Clostridium perfringens, Campylobacter, and Staphylococcus aureus (Staph).
Some other germs don’t cause as many illnesses, but when they do, the illnesses are more likely to lead to hospitalization. Those germs include Clostridium botulinum (botulism), Listeria, Escherichia coli (E. coli), and Vibrio.
Table \(1\) Symptoms and Sources of 10 Foodborne Germs
Germ and Typical Time for Symptoms to Appear Typical Signs and Symptoms Common Food Sources
Campylobacter
2 – 5 days
Diarrhea (often bloody), stomach cramps/pain, fever Raw or undercooked poultry, raw (unpasteurized) milk, and contaminated water
Clostridium botulinum
18 – 36 hours
Double or blurred vision, drooping eyelids, slurred speech. Difficulty swallowing, breathing and dry mouth. Muscle weakness and paralysis. Symptoms start in the head and move down as severity increases Improperly canned or fermented foods, usually homemade. Prison-made illicit alcohol.
Clostridium perfringens
6 – 24 hours
Diarrhea, stomach cramps. Vomiting and fever are uncommon. Usually begins suddenly and lasts for less than 24 hours Beef or poultry, especially large roasts; gravies; dried or precooked foods
Cyclospora
1 week
Watery diarrhea, loss of appetite and weight loss. Stomach cramps/pain, bloating, increased gas, nausea, and fatigue. Raw fruits or vegetables, and herbs
Escherichia coli
3 – 4 days
Severe stomach cramps, diarrhea (often bloody), and vomiting. Around 5-10% of people diagnosed with this infection develop a life-threatening complication. Raw or undercooked ground beef, raw (unpasteurized) milk and juice, raw vegetables (such as lettuce), and raw sprouts, contaminated water
Listeria
1 – 4 weeks
Pregnant women typically experience fever and other flu-like symptoms, such as fatigue and muscle aches. Infections during pregnancy can lead to serious illness or even death in newborns.
Other people (most often older adults): headache, stiff neck, confusion, loss of balance and convulsions in addition to fever and muscle aches.
Raw (unpasteurized) milk, soft cheeses made with raw milk, raw sprouts, melons, hot dogs, pâtés, lunch meats, and cold cuts, smoked seafood
Norovirus
12 – 48 hours
Diarrhea, nausea/stomach pain, vomiting Infected person, contaminated food like leafy greens, fresh fruits, shellfish (such as oysters), or water, or by touching contaminated surfaces
Salmonella
12 – 72 hours
Diarrhea, fever, stomach cramps, vomiting Eggs, raw or undercooked poultry or meat, unpasteurized milk or juice, cheese, raw fruits and vegetables
Staphylococcus aureus (Staph)
30 minutes – 6 hours
Diarrhea, nausea, stomach cramps, vomiting Foods that are handled by people and not cooked (sliced meat, puddings, pastries, and sandwiches). Raw (unpasteurized) milk and cheese made from it.
Vibrio
1 – 4 days
Watery diarrhea, nausea. stomach cramps, vomiting, fever, chills Raw or undercooked shellfish, particularly oysters
The Top 5 Strangest Posions That Can Kill You
Video \(1\) Strange poisons.
Summary
• Various plants produce toxins that could be lethal or cause allergic reactions in herbivores. A few examples of poisonous plants include poison ivy, western water hemlock, autumn skullcap, henbane, oak, etc.
• Several deadly poisons come from snakes and spiders. Various birds, fishes, frogs, insects, etc. are deadly when consumed or touched due to their toxic flesh.
• The top five germs that cause illnesses from food eaten in the United States are Norovirus, Salmonella, Clostridium perfringens, Campylobacter, and Staphylococcus aureus (Staph).
Contributors
• Wikipedia
• Scioly.org
• USDA Agricultural Service
• US Center for Disease Control
• Libretexts: Nutrition (Coppola) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.01%3A_Natural_Poisons_and_Food_Poisoning.txt |
Learning Objective
• Describe the modes of action and treatments for different poisons.
Corrosive Substances
A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction. Corrosives are different from poisons in that corrosives are immediately dangerous to the tissues they contact, whereas poisons may have systemic toxic effects that require time to become evident. Colloquially, corrosives may be called poisons but the concepts are technically distinct. However, there is nothing which precludes a corrosive from being a poison; there are substances that are both corrosives and poisons.
There are several household products that contain chemical substances which are considered highly reactive and thus are very dangerous upon ingestion or skin contact. Chemical poisoning with corrosive agents occurs by ingestion of: acids (hydrochloric, nitric, sulfuric, perchloric, chloric), alkalis (sodium and potassium, soaps, detergents), heavy metal salts (sublimate), strong oxidizing agents, formalin, iodine tincture and many other chemical substances. Strong acids or bases, readily decomposes proteins and lipids through amide and ester hydrolysis upon contact with living tissues, such as skin and flesh.
Oxidizing Agents as Poisons
Household cleaning products with strong oxidizing agents like sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2) are dangerous when ingested. Generally speaking, the ingestion of bleaches (Figure \(2\)) will cause damage to the esophagus and stomach, possibly leading to death. On contact with the skin or eyes, it causes irritation, drying, and potentially burns. Inhalation of bleach fumes can damage the lungs. Personal protective equipment should always be used when using bleach. Bleach should never be mixed with vinegar or other acids as this will create highly toxic chlorine gas and can cause severe burns internally and externally. Mixing bleach with ammonia similarly produces toxic chloramine gas, which can burn the lungs. Mixing bleach with hydrogen peroxide results in an exothermic chemical reaction that releases oxygen, and may cause the contents to splatter and cause skin and eye injury. Heating bleach and boiling it may produce chlorates, a strong oxidizer which may lead to a fire or explosion.
Ozone. For the last few decades, scientists studied the effects of acute and chronic ozone exposure on human health. Hundreds of studies suggest that ozone is harmful to people at levels currently found in urban areas. Ozone has been shown to affect the respiratory, cardiovascular and central nervous system. Early death and problems in reproductive health and development are also shown to be associated with ozone exposure.
Acute ozone exposure ranges from hours to a few days. Because ozone is gas, it directly affects the lungs and the entire respiratory system. Inhaled ozone causes inflammation and acute -but reversible- changes in lung function, as well as airway hyperresponsiveness. These changes lead to shortness of breath, wheezing, and coughing which may exacerbate lung diseases, like asthma or chronic obstructive pulmonary disease (COPD) resulting in the need to receive medical treatment. Acute and chronic exposure to ozone has been shown to cause an increased risk of respiratory infections, due to the following mechanism.
Multiple studies have been conducted to determine the mechanism behind ozone's harmful effects, particularly in the lungs. These studies have shown that exposure to ozone causes changes in the immune response within the lung tissue, resulting in disruption of both the innate and adaptive immune response, as well as altering the protective function of lung epithelial cells. It is thought that these changes in immune response and the related inflammatory response are factors that likely contribute to the increased risk of lung infections, and worsening or triggering of asthma and reactive airways after exposure to ground-level ozone pollution.
Inhaling ozone not only affects the immune system and lungs, but it may also affect the heart as well. Ozone causes short-term autonomic imbalance leading to changes in heart rate and reduction in heart rate variability; and high levels exposure for as little as one-hour results in a supraventricular arrhythmia in the elderly, both increase the risk of premature death and stroke. Ozone may also lead to vasoconstriction resulting in increased systemic arterial pressure contributing to increased risk of cardiac morbidity and mortality in patients with pre-existing cardiac diseases.
Metabolic Poisons
Carbon monoxide and cyanide are chemical substances that interfere with the normal bodily functions i.e. during the delivery of oxygen to bodily tissues and cellular respiration.
Carbon Monoxide Poisoning
Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms (Figure \(2\)) are often described as "flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large exposures can result in loss of consciousness, arrhythmias, seizures, or death. The classically described "cherry red skin" rarely occurs. Long-term complications may include chronic fatigue, trouble with memory, and movement problems.
CO is a colorless and odorless gas which is initially non-irritating. It is produced during incomplete burning of organic matter. This can occur from motor vehicles, heaters, or cooking equipment that run on carbon-based fuels. Carbon monoxide primarily causes adverse effects by combining with hemoglobin to form carboxyhemoglobin (HbCO) preventing the blood from carrying oxygen and expelling carbon dioxide as carbaminohemoglobin. Additionally, many other hemoproteins such as myoglobin, Cytochrome P450, and mitochondrial cytochrome oxidase are affected, along with other metallic and non-metallic cellular targets.
Initial treatment for carbon monoxide poisoning is to immediately remove the person from the exposure without endangering further people. Those who are unconscious may require CPR on site. Administering oxygen via non-rebreather mask shortens the half-life of carbon monoxide from 320 minutes, when breathing normal air, to only 80 minutes. Oxygen hastens the dissociation of carbon monoxide from carboxyhemoglobin, thus turning it back into hemoglobin. Due to the possible severe effects in the baby, pregnant women are treated with oxygen for longer periods of time than non-pregnant people.
Cyanide Poisoning
Cyanide poisoning is poisoning that results from exposure to a number of forms of cyanide. Early symptoms include headache, dizziness, fast heart rate, shortness of breath, and vomiting. This may then be followed by seizures, slow heart rate, low blood pressure, loss of consciousness, and cardiac arrest. Onset of symptoms is usually within a few minutes. If a person survives, there may be long-term neurological problems.
Toxic cyanide-containing compounds include hydrogen cyanide gas and a number of cyanide salts. Poisoning is relatively common following breathing in smoke from a house fire. Other potential routes of exposure include workplaces involved in metal polishing, certain insecticides, and the medication nitroprusside. Liquid forms of cyanide can be absorbed through the skin. Cyanide ions interfere with cellular respiration, resulting in the body's tissues being unable to use oxygen.
In addition to its uses as a pesticide and insecticide, cyanide is contained in tobacco smoke and smoke from building fires, and is present in many seeds or kernels such as those of almonds, apricots, apples, oranges, and in foods including cassava (also known as tapioca, yuca or manioc), and bamboo shoots. Vitamin B12, in the form of hydroxocobalamin (also spelled hydroxycobalamin), may reduce the negative effects of chronic exposure, and a deficiency can lead to negative health effects following exposure. Flaxseed also contains cyanogenic glycosides.
Cyanide is a potent cytochrome c oxidase (COX, a.k.a Complex IV) inhibitor. As such, cyanide poisoning is a form of histotoxic hypoxia, because it interferes with an essential step in aerobic metabolism called oxidative phosphorylation.
The United States standard cyanide antidote kit first uses a small inhaled dose of amyl nitrite, followed by intravenous sodium nitrite, followed by intravenous sodium thiosulfate. Hydroxocobalamin is newly approved in the US and is available in Cyanokit antidote kits. Sulfanegen TEA, which could be delivered to the body through an intra-muscular (IM) injection, detoxifies cyanide and converts the cyanide into thiocyanate, a less toxic substance. Alternative methods of treating cyanide intoxication are used in other countries.
Arsenic Poisoning
Arsenic poisoning is a medical condition that occurs due to elevated levels of arsenic in the body. If arsenic poisoning occurs over a brief period of time, symptoms may include vomiting, abdominal pain, encephalopathy, and watery diarrhea that contains blood. Long-term exposure can result in thickening of the skin, darker skin, abdominal pain, diarrhea, heart disease, numbness, and cancer.
The most common reason for long-term exposure is contaminated drinking water. Groundwater most often becomes contaminated naturally; however, contamination may also occur from mining or agriculture. It may also be found in the soil and air. Recommended levels in water are less than 10–50 µg/L (10–50 parts per billion). Other routes of exposure include toxic waste sites and traditional medicines. Most cases of poisoning are accidental. Arsenic acts by changing the functioning of around 200 enzymes. Diagnosis is by testing the urine, blood, or hair.
Prevention is by using water that does not contain high levels of arsenic. This may be achieved by the use of special filters or using rainwater. There is not good evidence to support specific treatments for long-term poisoning. For acute poisonings treating dehydration is important. Dimercaptosuccinic acid (DMSA) or dimercaptopropane sulfonate (DMPS) may be used while dimercaprol (BAL) is not recommended. Hemodialysis may also be used.
WEBLINK
More Information on arsenic can be found on the link below
Heavy Metal Poisoning
Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, and tingling in the hands and feet. It causes almost 10% of intellectual disability of otherwise unknown cause and can result in behavioral problems. Some of the effects are permanent. In severe cases, anemia, seizures, coma, or death may occur.
Exposure to lead can occur by contaminated air, water, dust, food, or consumer products. Children are at greater risk as they are more likely to put objects in their mouth such as those that contain lead paint and absorb a greater proportion of the lead that they eat. Exposure at work is a common cause of lead poisoning in adults with certain occupations at particular risk. Diagnosis is typically by measurement of the blood lead level. The Centers for Disease Control (US) has set the upper limit for blood lead for adults at 10 µg/dl (10 µg/100 g) and for children at 5 µg/dl. Elevated lead may also be detected by changes in red blood cells or dense lines in the bones of children as seen on X-ray.
Lead has no known physiologically relevant role in the body, and its harmful effects are myriad. Lead and other heavy metals create reactive radicals which damage cell structures including DNA and cell membranes. Lead also interferes with DNA transcription, enzymes that help in the synthesis of vitamin D, and enzymes that maintain the integrity of the cell membrane. Anemia may result when the cell membranes of red blood cells become more fragile as the result of damage to their membranes. Lead interferes with metabolism of bones and teeth and alters the permeability of blood vessels and collagen synthesis. Lead may also be harmful to the developing immune system, causing production of excessive inflammatory proteins; this mechanism may mean that lead exposure is a risk factor for asthma in children. Lead exposure has also been associated with a decrease in activity of immune cells such as polymorphonuclear leukocytes. Lead also interferes with the normal metabolism of calcium in cells and causes it to build up within them.
Lead poisoning is preventable. This includes individual efforts such as removing lead-containing items from the home, workplace efforts such as improved ventilation and monitoring, state laws that ban the use of and national policies such as laws that ban lead in products such as paint, gasoline, ammunition, wheel weights, and fishing weights reduce allowable levels in water or soil, and provide for cleanup of contaminated soil. Workers' education could be helpful as well. The major treatments are removal of the source of lead and the use of medications that bind lead so it can be eliminated from the body, known as chelation therapy. Chelation therapy in children is recommended when blood levels are greater than 40–45 µg/dl. Medications used include dimercaprol, edetate calcium disodium, and succimer.
WEBLINKS
Links to various lead and mercury related topics can be found below
https://medlineplus.gov/leadpoisoning.html
https://medlineplus.gov/mercury.html
Mercury poisoning is a type of metal poisoning due to exposure to mercury. Symptoms depend upon the type, dose, method, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble speaking, trouble hearing, or trouble seeing. High-level exposure to methylmercury is known as Minamata disease. Methylmercury exposure in children may result in acrodynia (pink disease) in which the skin becomes pink and peels. Long-term complications may include kidney problems and decreased intelligence. The effects of long-term low-dose exposure to methylmercury are unclear.
Forms of mercury exposure include metal, vapor, salt, and organic compound. Most exposure is from eating fish, amalgam based dental fillings, or exposure at work. In fish, those higher up in the food chain generally have higher levels of mercury. Less commonly, poisoning may occur as a method of attempted suicide. Human activities that release mercury into the environment include the burning of coal and mining of gold. Tests of the blood, urine, and hair for mercury are available but do not relate well to the amount in the body.
The primary mechanism of mercury toxicity involves its irreversible inhibition of selenoenzymes, such as thioredoxin reductase. High mercury exposures deplete the amount of cellular selenium available for the biosynthesis of thioredoxin reductase and other selenoenzymes that prevent and reverse oxidative damage, which, if the depletion is severe and long lasting, results in brain cell dysfunctions that can ultimately cause death.
Prevention includes eating a diet low in mercury, removing mercury from medical and other devices, proper disposal of mercury, and not mining further mercury. In those with acute poisoning from inorganic mercury salts, chelation with either dimercaptosuccinic acid (DMSA) or dimercaptopropane sulfonate (DMPS) appears to improve outcomes if given within a few hours of exposure. Chelation for those with long-term exposure is of unclear benefit.
Cadmium poisoning. Cadmium is a naturally occurring toxic metal with common exposure in industrial workplaces, plant soils, and from smoking. Due to its low permissible exposure in humans, overexposure may occur even in situations where trace quantities of cadmium are found. Cadmium is used extensively in electroplating, although the nature of the operation does not generally lead to overexposure. Cadmium is also found in some industrial paints and may represent a hazard when sprayed. Operations involving removal of cadmium paints by scraping or blasting may pose a significant hazard. The primary use of cadmium is in the manufacturing of NiCd rechargeable batteries. The primary source for cadmium is as a byproduct of refining zinc metal. Exposures to cadmium are addressed in specific standards for the general industry, shipyard employment, the construction industry, and the agricultural industry.
Acute exposure to cadmium fumes may cause flu-like symptoms including chills, fever, and muscle ache sometimes referred to as "the cadmium blues." Symptoms may resolve after a week if there is no respiratory damage. More severe exposures can cause tracheo-bronchitis, pneumonitis, and pulmonary edema. Symptoms of inflammation may start hours after the exposure and include cough, dryness and irritation of the nose and throat, headache, dizziness, weakness, fever, chills, and chest pain.
Inhaling cadmium-laden dust quickly leads to respiratory tract and kidney problems which can be fatal (often from kidney failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver, bones, and the kidneys. Compounds containing cadmium are also carcinogenic.
Summary
• Corrosive poisons are chemicals (that can be found in many household products) that are considered highly reactive and thus are very dangerous upon ingestion or skin contact.
• Metabolic poisons such as carbon monoxide and cyanide interfere with the bodily functions.
• Human exposure to lead, mercury, and cadmium have affected the nervous system, respiratory system, brain, and other various organs.
Contributors
• Wikipedia
• US NIH MedlinePlus
• Chibishev, Andon, et al. “Corrosive Poisonings in Adults.” Materia Socio Medica, vol. 24, no. 2, 2012, p. 125., doi:10.5455/msm.2012.24.125-130.
• Robert J. Lancashire (University of West Indies-Mona) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.02%3A_Poisons_and_How_They_Act.txt |
Learning Objectives
• Describe the overall mechanism of neurotransmission.
• Describe how various nerve agents interrupt the neurotransmission process.
Acetylcholine is an organic chemical that functions in the brain and body of many types of animals, including humans, as a neurotransmitter—a chemical released by nerve cells to send signals to other cells. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts in the body that use or are affected by acetylcholine are referred to as cholinergic. Substances that interfere with acetylcholine activity are called anticholinergics.
Acetylcholine is the neurotransmitter used at the neuromuscular junction—in other words, it is the chemical that motor neurons of the nervous system release in order to activate muscles. This property means that drugs that affect cholinergic systems can have very dangerous effects ranging from paralysis to convulsions. Acetylcholine is also used as a neurotransmitter in the autonomic nervous system, both as an internal transmitter for the sympathetic nervous system and as the final product released by the parasympathetic nervous system.
In the brain, acetylcholine functions as a neurotransmitter and as a neuromodulator. The brain contains a number of cholinergic areas, each with distinct functions. They play an important role in arousal, attention, memory and motivation.
Mechanism of Action
When a normally functioning motor nerve is stimulated, it releases the neurotransmitter acetylcholine, which transmits the impulse to a muscle or organ.
1. During neurotransmission (Figure \(1\)), ACh is released from the presynaptic neuron into the synaptic cleft and binds to ACh receptors on the post-synaptic membrane, relaying the signal from the nerve.
2. AChE, also located on the post-synaptic membrane, terminates the signal transmission by hydrolyzing ACh (Figure \(2\)). Source: Wikipedia.
3. The liberated choline is taken up again by the pre-synaptic neuron and ACh is synthesized by combining with acetyl-CoA through the action of choline acetyltransferase.[19][20]
Nerve Poisons and the Acetylcholine Cycle
Botulinum toxin (Botox) is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species.[1] It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction and thus causes flaccid paralysis.[2]The toxin causes the disease botulism. The toxin is also used commercially for medical and cosmetic purposes.
Foodborne botulism can be transmitted through food that has not been heated correctly prior to being canned, or food from a can that has not been cooked correctly. Most infant botulism cases cannot be prevented because the bacteria that cause this disease are in soil and dust. The bacteria can also be found inside homes on floors, carpet, and countertops, even after cleaning. Honey can contain the bacteria that cause infant botulism, so children less than 12 months old should not be fed honey.
Curare is a generic term for various South American arrow poisons. The main active ingredient in curare is d-tubocurarine (Figure \(4\)), which has the chemical structure shown below.
In brief, d-tubocurarine, blocks competitively the transmitter action of acetylcholine. When the drug is applied directly to the end-plate of a single isolated muscle fiber under microscopic control, the muscle cell becomes insensitive to motor-nerve impulses and to direct applied acetylcholine; however, the end -plate region and the remainder of the muscle fiber membrane retain their normal sensitivity to the application of potassium ions, and the muscle fiber still responds to direct electrical stimulation. Because acetylcholine release into the neuromuscular junction muscle is what initiates contraction, curare causes muscle relaxation and paralysis.
Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that catalyzes the breakdown of acetylcholine, a neurotransmitter. Nerve agents are acetylcholinesterase inhibitors used as poison.
Poisoning by a nerve agent leads to constriction of pupils, profuse salivation, convulsions, and involuntary urination and defecation, with the first symptoms appearing in seconds after exposure. Death by asphyxiation or cardiac arrest may follow in minutes due to the loss of the body's control over respiratory and other muscles. Some nerve agents are readily vaporized or aerosolized, and the primary portal of entry into the body is the respiratory system. Nerve agents can also be absorbed through the skin, requiring that those likely to be subjected to such agents wear a full body suit in addition to a respirator.
Nerve agents are generally colorless to amber-colored, tasteless liquids that may evaporate to a gas. Agents Sarin and VX are odorless; Tabun has a slightly fruity odor and Soman has a slight camphor odor.
Organophosphorous Compounds as Insecticides and Weapons of War
This first class of nerve agents, the G-series, was accidentally discovered in Germany on December 23, 1936, by a research team headed by Gerhard Schrader working for IG Farben. Since 1934, Schrader had been working in a laboratory in Leverkusen to develop new types of insecticides for IG Farben. While working toward his goal of improved insecticide, Schrader experimented with numerous compounds, eventually leading to the preparation of tabun (GA).
In experiments, tabun was extremely potent against insects: as little as 5 ppm of tabun killed all the leaf lice he used in his initial experiment. In January 1937, Schrader observed the effects of nerve agents on human beings first-hand when a drop of tabun spilled onto a lab bench. Within minutes he and his laboratory assistant began to experience miosis (constriction of the pupils of the eyes), dizziness and severe shortness of breath. It took them three weeks to recover fully. The G-series naming system was created by the United States when it uncovered the German activities, labeling (Figure \(5\).
In 1935 the Nazi government had passed a decree that required all inventions of possible military significance to be reported to the Ministry of War, so in May 1937 Schrader sent a sample of tabun to the chemical warfare (CW) section of the Army Weapons Office in Berlin-Spandau. Schrader was summoned to the Wehrmacht chemical lab in Berlin to give a demonstration, after which Schrader's patent application and all related research was classified as secret. Colonel Rüdiger, head of the CW section, ordered the construction of new laboratories for the further investigation of tabun and other organophosphate compounds and Schrader soon moved to a new laboratory at Wuppertal-Elberfeld in the Ruhr valley to continue his research in secret throughout World War II. The compound was initially codenamed Le-100 and later Trilon-83.
Sarin was discovered by Schrader and his team in 1938 and named in honor of its discoverers: Schrader, Ambros, Gerhard Ritter, and von der Linde.[26] It was codenamed T-144 or Trilon-46. It was found to be more than ten times as potent as tabun.
Soman was discovered by Richard Kuhn in 1944 as he worked with the existing compounds; the name is derived from either the Greek 'to sleep' or the Latin 'to bludgeon'. It was codenamed T-300.
Cyclosarin was also discovered during WWII but the details were lost and it was rediscovered in 1949.
Some insecticides, including carbamates and organophosphates such as dichlorvos, malathion and parathion, are nerve agents (Figure \(6\)). The metabolism of insects is sufficiently different from mammals that these compounds have little effect on humans and other mammals at proper doses, but there is considerable concern
about the long-term exposure to these chemicals by farm workers and animals alike. At high enough doses, acute toxicity and death can occur through the same mechanism as other nerve agents. Some insecticides such as demeton, dimefox and paraoxon are sufficiently toxic to humans that they have been withdrawn from agricultural use, and were at one stage investigated for potential military applications. Paraoxon was allegedly used as an assassination weapon by the apartheid South African government as part of Project Coast. Organophosphate pesticide poisoning is a major cause of disability in many developing countries and is often the preferred method of suicide.[24]
Treatment
Standard treatment for nerve agent poisoning is a combination of an anticholinergic to manage the symptoms, and an oxime as an antidote. Anticholinergics treat the symptoms by reducing the effects of acetylcholine, while oximes displaces phosphate molecules from the active site of the cholinesterase enzymes, allowing the breakdown of acetylcholine. Military personnel are issued the combination in an autoinjector (e.g. ATNAA), for ease of use in stressful conditions.
Atropine (Figure \(7\) is the standard anticholinergic drug used to manage the symptoms of nerve agent poisoning. It acts as an antagonist to muscarinic acetylcholine receptors, blocking the effects of excess acetylcholine. Some synthetic anticholinergics, such as biperiden, may counteract the central symptoms of nerve agent poisoning more effectively than atropine, since they pass the blood–brain barrier better than atropine. While these drugs will save the life of a person affected by nerve agents, that person may be incapacitated briefly or for an extended period, depending on the extent of exposure. The endpoint of atropine administration is the clearing of bronchial secretions.
Pralidoxime chloride (also known as 2-PAMCl) is the standard oxime used to treat nerve agent poisoning. Rather than counteracting the initial effects of the nerve agent on the nervous system as does atropine, pralidoxime chloride reactivates the poisoned enzyme (acetylcholinesterase) by scavenging the phosphoryl group attached on the functional hydroxyl group of the enzyme, counteracting the nerve agent itself. Revival of acetylcholinesterase with pralidoxime chloride works more effectively on nicotinic receptors while blocking acetylcholine receptors with atropine is more effective on muscarinic receptors.
Anticonvulsants, such as diazepam, may be administered to manage seizures, improving long term prognosis and reducing risk of brain damage. This is not usually self-administered as its use is for actively seizing patients.
Summary
• Upon stimulation, a normally functioning motor nerve releases the neurotransmitter acetylcholine, which transmits the impulse to a muscle or organ.
• Nerve poisons (i.e. carbamates and organophosphorus compounds) disrupt the nervous system by inhibiting the function of the enzyme acetylcholinesterase. Acetylcholine thus builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop.
• The botulin toxin and curare interfere with nerve impulses (by preventing the release of acetylcholine) and causes flaccid (sagging) paralysis of muscles.
• Atropine (Figure \(7\) is the standard anticholinergic drug used to manage the symptoms of nerve agent poisoning.
Contributors and Attributions
• Wikipedia
Libretext: Microbiology (Boundless)
Libretext (Supplemental Module): Biological Chemistry | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.03%3A_More_Chemistry_of_the_Nervous_System.txt |
Learning Objectives
• Describe the LD50 value and its limitations.
• Know the LD50 value of various substances.
The LD50 is a standardized measure for expressing and comparing the toxicity of chemicals. The LD50 is the dose that kills half (50%) of the animals tested (LD = "lethal dose"). The animals are usually rats or mice, although rabbits, guinea pigs, hamsters, and so on are sometimes used. In all these tests, the dose must be calculated relative to the size of the animal. The most common units are milligrams of chemical per kilogram of test animal (mg/kg or ppm). (Table \(1\)) provides examples of LD50 values for various substances.
As a measure of toxicity, lethal dose is somewhat unreliable and results may vary greatly between testing facilities due to factors such as the genetic characteristics of the sample population, animal species tested, environmental factors and mode of administration.
There can be wide variability between species as well; what is relatively safe for rats may very well be extremely toxic for humans (cf. paracetamol toxicity), and vice versa. For example, chocolate, comparatively harmless to humans, is known to be toxic to many animals. When used to test venom from venomous creatures, such as snakes, LD50 results may be misleading due to the physiological differences between mice, rats, and humans. Many venomous snakes are specialized predators of mice, and their venom may be adapted specifically to incapacitate mice; and mongooses may be exceptionally resistant. While most mammals have a very similar physiology, LD50 results may or may not have equal bearing upon every mammal species, including humans.
Table \(1\): LD50 Values of Various Substances. Source: Wikipedia
Substance Animal Route LD50 (mg/kg)
Water rat, oral 90,000
Sucrose (table sugar) rat, oral 29,700
Glucose (blood sugar) rat, oral 25,800
Monosodium glutamate (MSG) rat, oral 16,600
Cadmium sulfide rat, oral 7,080
Ethanol (grain alcohol) rat, oral 7,060
Methanol human, oral 810
Sodium chloride (table salt) rat, oral 3,000
Metallic arsenic rat, oral 763
Arsenic trisulfide rat, oral 185-6400
Sodium cyanide rat, oral 6.4
Hydrogen cyanide mouse, oral 3.7
Ibuprofen rat, oral 636
Aspirin rat, oral 200
Caffeine rat, oral 192
Cocaine mouse, oral 96
Nicotine rat, oral 50
Heroin (diamorphine) mouse, intravenous 21.8
Methamphetamine rat, intraperitoneal 57
Mercury(II) chloride rat, oral 1
Strychnine human, oral 1-2
Sarin mouse, subcutaneous injection 172 microgram/kg
Ricin (from castor oil plant) rat, oral 20-30
Botulinum toxin (Botox) human, oral injection, inhalation 1 ng/kg
(Table \(2\)) gives the LD50 values of some insecticides. In each case, the chemical was fed to laboratory rats. Note that the lower the LD50, the more toxic the chemical. Even adjusting for the test animal's weight, the LD50 for one species is often quite different from that for another. Thus any LD50 value gives only a rough estimate of the risk to humans. The way in which the chemical is administered also has a marked effect on LD50 values. The chemical may be fed, injected, applied to the animal's skin, etc., and each method usually generates a different LD50.
Table \(2\): LD50 Values of Pesticides.
Chemical Category Oral LD50 in Rats (mg/kg)
Aldicarb ("Temik") Carbamate 1
Carbaryl ("Sevin") Carbamate 307
DDT Chlorinated hydrocarbon 87
Dieldrin Chlorinated hydrocarbon 40
Diflubenzuron ("Dimilin") Chitin inhibitor 10,000
Malathion Organophosphate 885
Methoprene JH mimic 34,600
Methoxychlor Chlorinated hydrocarbon 5,000
Parathion Organophosphate 3
Piperonyl butoxide Synergist 7,500
Pyrethrin Plant extract 200
Rotenone Plant extract 60
Summary
• The LD50 is the dose that kills half (50%) of the animals tested (LD = "lethal dose"). It is a standardized measure for expressing and comparing the toxicity of chemicals.
• LD50 values are given for common drugs (e.g. ibuprofen and aspirin), common household ingredients including water, table sugar (sucrose), salt (sodium chloride), insecticides (e.g. DDT and pyrethrin), and harmful drugs (e.g. cocaine and heroin).
Contributors and Attributions
• Wikipedia
• Libretexts: Biology (Kimball) | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.04%3A_The_Lethal_Dose.txt |
Learning Objective
• Describe the different mechanisms of drug detoxification in the liver.
The human liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs. The liver breaks down or modifies toxic substance, such as alcohol and most medicial products, in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor.
Alcohol Metabolism
Giving the liver enough time to fully metabolize the ingested alcohol is the only effective way to avoid alcohol toxicity. Drinking coffee or taking a shower will not help. The legal limit for intoxication is a BAC of 0.08. Taking into account the rate at which the liver metabolizes alcohol after drinking stops, and the alcohol excretion rate, it takes at least five hours for a legally intoxicated person to achieve sobriety.
The liver metabolizes up to 85% – 98% of the circulatory ethanol. The liver uses two metabolic processes to get rid of this circulatory ethanol as quickly and safely as possible.
1. Alcohol dehydrogenase system
2. Microsomal ethanol oxidizing system (MEOS)
Alcohol Dehydrogenase System
About 80 to 90% of the total hepatic ethanol uptake is processed via the alcohol dehydrogenase system.The degradation of ethanol begins in the liver. The enzyme that catalyzes this reaction is called alcohol dehydrogenase. The products from this reaction are acetaldehyde, NADH (a reduced coenzyme that carries electrons from one reaction to another) and H+ ion. Acetaldehyde is very toxic to the liver and the body’s cells. The moment acetaldehyde is produced; it must be degraded to protect the liver cells. The enzyme that will carry this type of degradation reaction is acetaldehyde dehydrogenase (ALDH). Acetaldehyde dehydrogenase converts acetaldehyde into acetate, a non-toxic molecule.
Microsomal Ethanol Oxidizing System (MEOS)
In a moderate drinker, about 10 to 20% of the total liver ethanol uptake is processed via the microsomal ethanol oxidizing system (MEOS). During periods of heavy drinking, the MEOS system will metabolize most of the excess ethanol ingested. Heavy drinking stimulates the human body to include the MEOS system enzymes to clear ethanol faster from the body.
The MEOS system is also located in the liver. Similar to the Alcohol dehydrogenase system, acetaldehyde dehydrogenase will immediately convert acetaldehyde into acetate, a non-toxic molecule. Other products from this reaction are NADH and H+ ion.
Fate of Acetate
The acetate produced (from the alcohol dehydrogenase system and microsomal ethanol oxidizing system) is either released into circulation or retained inside the liver cells. In the liver cells, acetate is converted to acetyl CoA where it is used to produce other molecules like CO2 or used in the synthesis of fatty acids and cholesterol.
Nicotine and Ammonia
In humans, nicotine is extensively metabolized in the liver into various metabolites. About 70-80% of nicotine is broken down to cotinine, the predominant metabolite. Other primary metabolites include nicotine N'-oxide, nornicotine, nicotine isomethonium ion, 2-hydroxynicotine and nicotine glucuronide. Under some conditions, other substances may be formed such as myosmine.
The liver converts ammonia into urea as part of the ornithine cycle or the urea cycle, and the urea is excreted in the urine.
Summary
• The liver is involved in the breakdown or modification of various substances in a process called drug metabolism, but the metabolites are not directly removed from the body.
• Ethanol is broken down through a series of steps (involving various liver enzymes) to carbon dioxide and water.
• Ethanol therapy is the traditional treatment for methanol and ethylene glycol poisoning.
• Nicotine is extensively metabolized in the liver into a variety of breakdown products whereas toxic ammonia is converted to non toxic urea.
Contributors and Attributions
• Wikipedia
• Benowitz, N. L., Hujjanen, J., Peyton III, J. Nicotine Chemistry, Metabolism, Kinetics, and Biomarkers. Hand Exp Pharmacol. 2009. (192): 29-60.
• Template:ContribUofHawaiiNutrition | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.05%3A_The_Liver_as_a_Detox_Facility.txt |
Learning Objectives
• Explain the process of cancer development.
• List the factors that may increase and lower the risk of cancer.
• Define teratogens and describe the birth defects that result from them.
A carcinogen is any agent that directly increases the incidence of cancer. Most, but not all carcinogens are mutagens. Carcinogens that do not directly damage DNA include substances that accelerate cell division, thereby leaving less opportunity for cell to repair induced mutations, or errors in replication. Carcinogens that act as mutagens may be biological, physical, or chemical in nature, although the term is most often used in relation to chemical substances.
Defining Cancer
Cancer is actually a group of more than 100 diseases, all of which involve abnormal cell growth with the potential to invade or spread to other parts of the body. In general terms, cancer occurs when the cell cycle is no longer regulated due to DNA damage. The number of potential underlying causes of this DNA damage is great, so there are many different risk factors for cancer. Any cells that become cancerous divide more quickly than normal cells. They may form a mass of abnormal cells called a tumor. The rapidly dividing cells take up nutrients and space, damaging the normal cells around them. If the cancer cells spread to other parts of the body, they invade and damage other tissues and organs. They may eventually lead to death.
By far, the most common of the 100-plus types of human cancer is basal cell carcinoma, the type of skin cancer Bernie Sanders had removed in 2016. Basal cell carcinoma makes up 40 percent of all new cancers each year in the United States. Other common types of cancer include lung, colorectal, prostate (in males), and breast (in females) cancers. These cancers are not as common as skin cancer, but they cause the majority of cancer deaths.
How Cancer Develops
Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The transformation of a normal cell into a cancer cell is a multi-step process that involves initiation, promotion, progression and finally malignancy (see Figure \(2\)). This process takes years and starts with a single cell in which the right genes are mutated so the cell does not appropriately die and begins to proliferate abnormally. Then, additional mutations occur that select for more rapidly growing cells within this population leading to a tumor with rapid growth and malignancy. By the time the cells are cancerous, proto-oncogenes have been activated and tumor suppressor genes inactivated. Even within the same tumor type, like colon cancer, the specific genes mutated can vary from person to person making cancer a unique disease for each individual.
How Cancer Spreads
Once a normal cell transforms into a cancer cell and starts dividing out of control, cancer cells can spread from the original site (called the primary tumor) to other tissues. This can occur in three different ways. One way is local spread, in which aggressively dividing cancer cells directly invade nearby tissues. Another way involves the lymphatic system. Cancer cells can spread to regional lymph nodes through lymph vessels that pass by the primary tumor.
The third way cancer cells can spread is through the blood to distant sites. This is called metastasis, and the new cancers that form are called metastases. Although the blood can carry cancer cells to tissues everywhere in the body, cancer cells generally grow only in certain sites (Figure \(3\)). Different types of cancers tend to metastasize to particular organs. The most common places for metastases to occur are the brain, lungs, bones, and liver. Almost all cancers can metastasize, especially during the late stages of the disease. Cancer that has metastasized generally has the worst prognosis and is associated with most cancer deaths.
Chemical Carcinogens
Chemical carcinogens (Table \(1\)) can be either natural or synthetic compounds that, based on animal feeding trials or epidemiological (i.e. human population) studies, increase the incidence of cancer. The definition of a chemical as a carcinogen is problematic for several reasons. Some chemicals become carcinogenic only after they are metabolized into another compound in the body; not all species or individuals may metabolize chemicals in the same way. Also, the carcinogenic properties of a compound are usually dependent on its dose. It can be difficult to define a relevant dose for both lab animals and humans. Nevertheless, when a correlation between cancer incidence and chemical exposure is observed, it is usually possible to find ways to reduce exposure to that chemical.
Table \(1\): Some Classes of Chemical Carcinogens.
Class Examples and/or Sources
PAHs (polycyclic aromatic hydrocarbons) benzo[a]pyrene and several other components of the smoke of cigarettes, wood, and fossil fuels
Aromatic amines compounds formed in food when meat (including fish, poultry) are cooked at high temperature
Nitrosamines and nitrosamides found in tobacco and in some smoked meat and fish
Azo dyes various dyes and pigments used in textiles, leather, paints.
Carbamates ethyl carbamate (urethane) found in some distilled beverages and fermented foods
Halogenated compounds e.g. pentachlorophenol used in some wood preservatives and pesticides.
Inorganic compounds asbestos; may induce chronic inflammation and reactive oxygen species
Miscellaneous compounds e.g. alkylating agents, phenolics
WEB LINK
A detailed list of occupational carcinogens can be found on the link below
https://bio.libretexts.org/Bookshelves/Human_Biology/Book:_Human_Biology_(Wakim_and_Grewal)/21:_Disease/21.7:_Cancer
The carcinogens implicated as the main causative agents of the four most common cancers worldwide are given in the table below. These four cancers are lung, breast, colon, and stomach cancers. Together they account for about 41% of worldwide cancer incidence and 42% of cancer deaths.
Table \(2\): Major Carcinogens Implicated In The Four Most Common Cancers Worldwide.
Type of Cancer Carcinogen
Lung Cancer Tobacco smoke
Breast Cancer Estrogen
Colon Cancer Tobacco smoke and bile acids: deoxycholic acid (DCA) or lithocholic acid (LCA)
Stomach Cancer Heliobacter pylori
WEB LINK
Note: A more detailed description for each major carcinogen listed in Table \(2\) can be found on the link below
https://en.Wikipedia.org/wiki/Carcin...cers_worldwide
Anticarcinogens
Dietary fiber and calorie restriction are two anti-carcinogen or anti-promoters that decrease the risk of tumor formation. Dietary fiber is both and is inversely associated with cancer, particularly colon cancer. So the more fiber you eat, the less risk you have of developing colon cancer. One mechanism by which fiber acts is hastening bile acid excretion. Fiber also increases the rate of passage of materials through the colon resulting in decreased production and exposure of the colon to cancer-causing agents, ie dilutes the concentration of carcinogens.
Animal studies have shown that restricting caloric intake by 30% reduces tumor growth and increases life span. The mechanism is not known but may be due to less oxidation thus damage to DNA.
Antioxidants can help block the action of initiators or promoters if their mode of action is to damage DNA by oxidation. Vitamin A, C, E, beta-carotene, and selenium are antioxidant nutrients. Some work locally, like vitamin E in the colon, while other work more globally like selenium and vitamin C. Vitamin A appears to work by keeping cells differentiated which slows the growth rate.
Other compounds in food, particularly fruits and vegetables, have been shown to slow tumor formation. Cruciferous vegetables (eg broccoli, cauliflower, cabbage, and Brussel sprouts to name a few) are rich in nutrients, fiber, glucosinolates which are sulfur-containing chemicals, indoles, and isothiocyanates. Animal studies have found these substances inhibit the development of cancer in several organs in rats and mice (Hecht SS. Inhibition of carcinogenesis by isothiocyanates. Drug Metabolism Reviews 2000;32(3-4):395-411; Murillo G, Mehta RG. Cruciferous vegetables and cancer prevention. Nutrition and Cancer 2001;41(1-2):17-28). Indoles and isothiocyanates help protect cells from DNA damage; help inactivate carcinogens; have antiviral and antibacterial effects; have anti-inflammatory effects; induce cell death (apoptosis); and inhibit tumor blood vessel formation (angiogenesis) and tumor cell migration (needed for metastasis) (National Cancer Institute, Cruciferous Vegetables and Cancer Prevention, 2012, https://www.cancer.gov/about-cancer/...les-fact-sheet). Studies in humans, however, have shown mixed results.
Test for Carcinogens
In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer, such mutagens are therefore carcinogens, although not all necessarily are. Many different systems for detecting mutagen have been developed. Animal systems may more accurately reflect the metabolism of human, however, they are expensive and time-consuming (may take around three years to complete), they are therefore not used as a first screen for mutagenicity or carcinogenicity.
The Ames test is a widely employed method that uses bacteria to test whether a given chemical can cause mutations in the DNA of the test organism. More formally, it is a biological assay to assess the mutagenic potential of chemical compounds. A positive test indicates that the chemical is mutagenic and therefore may act as a carcinogen, because cancer is often linked to mutation. The test serves as a quick and convenient assay to estimate the carcinogenic potential of a compound because standard carcinogen assays on mice and rats are time-consuming (taking two to three years to complete) and expensive. However, false-positives and false-negatives are known. Other tests, similar to the Ames tests have also been developed using yeast and other bacteria.
Drosophila, plants, and cell cultures have been used in various test assays for mutagenecity of chemicals.
In animal test systems, rodents are usually used in animal test. The chemicals under test are usually administered in the food and in the drinking water, but sometimes by dermal application, by gavage, or by inhalation, and carried out over the major part of the life span for rodents. Transgenic mouse assay using a mouse strain infected with a viral shuttle vector is another method for testing mutagens. Animals are first treated with suspected mutagen, the mouse DNA is then isolated and the phage segment recovered and used to infect E. coli.
Did You Know?
Video \(1\) Risk factors for cancer.
WEB LINKS - American Cancer Society and NIH:MedlinePlus & National Cancer Institute
Risk factors for Cancer
https://www.cancer.gov/about-cancer/causes-prevention/patient-prevention-overview-pdq#_199
Common Cancer Myths and Misconceptions
https://www.cancer.gov/about-cancer/causes-prevention/risk/myths
List of Probable Carcinogens
https://www.cancer.org/cancer/cancer-causes/general-info/known-and-probable-human-carcinogens.html?sitearea=who
Cancer Prevention: Take Charge of Your Lifestyle
https://medlineplus.gov/ency/patientinstructions/000825.htm
Cruciferous Vegetables and Cancer Prevention
https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/cruciferous-vegetables-fact-sheet
Birth Defects:Teratogens
A teratogen is a compound that permanently deforms the function or structure of a developing embryo or fetus in utero. In general, the degree of teratogenicity depends on:
• The potency of the drug as a mutagen.
• The susceptibility of the fetus to teratogenesis.
• The dose of the teratogen.
• The duration of teratogen exposure.
• The time of exposure.
• The degree of transfer from maternal to fetal circulation.
The global average of all live births complicated by malformation is 6% (Environmental Health Perspectives, (NIH), October 2009). The majority of these complications are due to unknown factors. The vast majority of recognized etiologies are genetic, with only 10% being attributed to environmental etiologies such as maternal health, infection, and toxicants. In general, the central nervous and skeletal systems are the most affected.
Thalidomide (a sedative previously marketed in Europe to prevent morning sickness) see Figure \(4\)is a classic teratogen that caused limb defects in babies born to women who took this drug in the 1960s (see Figure \(5\)). Thalidomide was first marketed in 1957 in West Germany, where it was available over the counter.[5][6] When first released, thalidomide was promoted for anxiety, trouble sleeping, "tension", and morning sickness.[6][7] While initially deemed to be safe in pregnancy, concerns regarding birth defects were noted in 1961 and the medication was removed from the market in Europe that year.[6][5] The total number of people affected by use during pregnancy is estimated at 10,000, of which about 40% died around the time of birth.[6][3] Those who survived had limb, eye, urinary tract, and heart problems.[5]
Its initial entry into the US market was prevented by Frances Kelsey at the FDA.[7] The birth defects of thalidomide led to the development of greater drug regulation and monitoring in many countries. in 2006 the U.S. Food and Drug Administration granted accelerated approval for thalidomide in combination with dexamethasone for the treatment of newly diagnosed multiple myeloma patients.
Women may encounter a number of other teratogens. Smoking is most likely to cause growth retardation, but has also been implicated in the prelabor rupture of the membranes, preterm labor, abruption of the placenta, spontaneous abortion, perinatal morbidity and mortality, and sudden infant death syndrome. Smoking may exert its effects through competitive binding of carbon monoxide with hemoglobin and/or through the various other components found in cigarettes that cause adverse biological effects.
Alcohol use in pregnancy may result in fetal alcohol syndrome (FAS) see Figure \(6\), which occurs in approximately 1% of all births. Children with FAS present with a flattened and thin upper lip, small palpebral fissures, epicanthal folds, flattened nasal bridge, and a short nose. They may also exhibit microcephaly, mental retardation, and have learning disabilities. It is not clear if there is any safe amount of alcohol consumption in pregnancy.
Cocaine generally produces growth restriction, preterm delivery, microcephaly, spontaneous abortion, placental abruption, limb anomalies, and central nervous system abnormalities. Cocaine appear to exert a number of its effects through peripheral vasoconstriction that leads to fetal hypoxia.
Women with indications for warfarin therapy should either abstain from pregnancy or switch to low molecular weight heparins. Warfarin typically produces mental retardation, growth restriction, nasal hypoplasia, and opthalmic abnormalities.
Angiotensin converting enzyme (ACE) inhibitors will cause fetal renal failure and oligohydramnios that lead to pulmonary hypoplasia and limb contracture. Fetal cranial bone abnormalities are also common.
Isotretinoin (Accutane), used to treat acne, may cause cardiac, oral, otological, thymic, and central nervous system abnormalities. In one quarter of cases, it causes mental retardation.
Other teratogenic substance classes and conditions include
• Various prescription drugs and nutrient deficiencies (e.g., insufficient folic acid).
• Chemical compounds such as methyl iodide (used in pesticides) and bisphenol A (used in plastics) are suspected teratogens.
Summary
• A carcinogen is any agent that directly increases the incidence of cancer.
• Cancer is caused by changes to the DNA which could be inherited or acquired.
• Various tests have been developed to test for carcinogens.
• The American Cancer Society provides an extensive list of probable chemical carcinogens including those found in processed foods and beverages, various household products, pesticides etc.
• The effects of a teratogen on the fetus depend on several factors: the potency of the teratogen, the susceptibility of the fetus to the teratogen, the dose and duration of teratogen exposure, the degree of transfer from maternal to fetal circulation, and when during development the exposure occurs.
• Approximately 10% of congenital malformations are attributed to environmental factors, and 20% are due to genetic or hereditary factors. The rest have unknown causes or are due to a mix of different factors.
• Cigarette components, alcohol, cocaine, warfarin, ACE inhibitors, and Accutane are all teratogens that affect fetal development.
Contributors and Attributions
Libretexts: Online Open Genetics (Nickle,T. & Barrette-Ng,I.)
Libretexts: Human Biology (Wakim and Grewal)
Libretexts: An Introduction to Nutrition (Byerley)
Libretexts: Anatomy and Physiology (Boundless)
Template:ContribOOG
Wikipedia
American Cancer Society
NIH-MedlinePlus
NIH- National Cancer Institute | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.06%3A_Carcinogens_and_Teratogens.txt |
Learning Objectives
• List the different types of hazardous wastes based on their classification.
• Describe the handling of hazardous waste.
Hazardous waste is waste that has substantial or potential threats to public health or the environment. Hazardous wastes may be found in different physical states such as gaseous, liquids, or solids. A hazardous waste is a special type of waste because it cannot be disposed of by common means like other by-products of our everyday lives. Depending on the physical state of the waste, treatment and solidification processes might be required.
Statutory Definition of Hazardous Waste
A discussion of the definition of hazardous waste should begin with Congress' original statutory definition of the term. RCRA (Resource Recovery and Conservation Act) §1004(5) defines hazardous waste as: A solid waste, or combination of solid waste, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may (a) cause, or significantly contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or (b) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.
Listed, Characteristic, and Mixed Wastes
Listed hazardous wastes (see Table \(1\)) are materials specifically listed as hazardous wastes which are from non-specific sources, specific sources, or discarded chemical products. Title 40 of the Code of Federal Regulations (CFR) in section 261 provides four lists (the F, K, P and U lists) of hazardous materials.
Table \(1\) List Hazardous Wastes. Source US EPA.
List Type Section Description of Waste
F List 40 CFR section 261.31
Wastes from common manufacturing and industrial processes
• Spent solvent wastes,
• Electroplating and other metal finishing wastes,
• Dioxin-bearing wastes,
• Chlorinated aliphatic hydrocarbons production,
• Wood preserving wastes,
• Petroleum refinery wastewater treatment sludges, and
• Multisource leachate.
K List 40 CFR section 261.32
Source specific wastes from 13 various industries and manufacturers namely:
• Wood preservation,
• Organic chemicals manufacturing,
• Pesticides manufacturing,
• Petroleum refining,
• Veterinary pharmaceuticals manufacturing,
• Inorganic pigment manufacturing,
• Inorganic chemicals manufacturing,
• Explosives manufacturing,
• Iron and steel production,
• Primary aluminum production,
• Secondary lead processing,
• Ink formulation, and
• Coking (processing of coal to produce coke).
P List 40 CFR section 261.33
Acute hazardous wastes from discarded commercial chemical products.
• The chemical in the waste must be unused; and
• The chemical in the waste must be in the form of a commercial chemical product.
U List 40 CFR section 261.33
Hazardous wastes from discarded commercial chemical products
• The chemical in the waste must be unused; and
• The chemical in the waste must be in the form of a commercial chemical product.
• Characteristic hazardous wastes are materials that are dangerous because it is toxic, corrosive, flammable, or reactive. Detailed information provided by the US Environmental Agency (US EPA) is summarized in Table \(2\).
Table \(2\) Characteristic Hazardous Wastes. Source US EPA.
Waste Characteristic EPA Waste Code Section Description of Waste
Ignitability D001 40 CFR section 261.21 Liquids with flash points below 60 °C (e.g. used solvents and waste oils), non-liquids that cause fire through specific conditions, ignitable compressed gases and oxidizers
Corrosivity D002 40 CFR section 261.22 Aqueous wastes with a pH of less than or equal to 2 (acids), a pH greater than or equal to 12.5 (bases) or based on the liquids ability to corrode steel. Example: battery acid
Reactivity D003 40 CFR section 261.23 Wastes that are unstable under normal conditions, may react with water, may give off toxic gases and may be capable of detonation or explosion under normal conditions or when heated. Examples: lithium–sulfur batteries and explosives.
Toxicity D004 through D043 40 CFR section 261.24 Wastes that are harmful when ingested or absorbed. Toxic waste can be reactive, ignitable, and corrosive. Examples: old batteries, pesticides, paint, and car oil
Mixed wastes is the term for hazardous wastes that also contain radioactive material and is regulated under the EPAs Resource Conservation and Recovery Act (RCRA) and the Department of Energy's Atomic Energy Act.
EPA's Cradle-to-Grave Hazardous Waste Management Program
https://www.epa.gov/hw/learn-basics-...ous-waste#hwid
In the mid-twentieth century, solid waste management issues rose to new heights of public concern in many areas of the United States because of increasing solid waste generation, shrinking disposal capacity, rising disposal costs, and public opposition to the siting of new disposal facilities. These solid waste management challenges continue today, as many communities are struggling to develop cost-effective, environmentally protective solutions. The growing amount of waste generated has made it increasingly important for solid waste management officials to develop strategies to manage wastes safely and cost effectively.
RCRA set up a framework for the proper management of hazardous waste . From this authority, EPA established a comprehensive regulatory program to ensure that hazardous waste is managed safely from "cradle to grave" meaning from the time it is created, while it is transported, treated, and stored, and until it is disposed:
Hazardous Waste Generation
Under RCRA, hazardous waste generators are the first link in the hazardous waste management system. All generators must determine if their waste is hazardous and must oversee the ultimate fate of the waste. Furthermore, generators must ensure and fully document that the hazardous waste that they produce is properly identified, managed, and treated prior to recycling or disposal. The degree of regulation that applies to each generator depends on the amount of waste that a generator produces.
Hazardous Waste Transportation
After generators produce a hazardous waste, transporters may move the waste to a facility that can recycle, treat, store or dispose of the waste. Since such transporters are moving regulated wastes on public roads, highways, rails and waterways, United States Department of Transportation hazardous materials regulations, as well as EPA's hazardous waste regulations, apply.
Hazardous Waste Recycling, Treatment, Storage and Disposal
To the extent possible, EPA tried to develop hazardous waste regulations that balance the conservation of resources, while ensuring the protection of human health and environment. Many hazardous wastes can be recycled safely and effectively, while other wastes will be treated and disposed of in landfills or incinerators.
Recycling hazardous waste has a variety of benefits including reducing the consumption of raw materials and the volume of waste materials that must be treated and disposed. However, improper storage of those materials might cause spills, leaks, fires, and contamination of soil and drinking water. To encourage hazardous waste recycling while protecting health and the environment, EPA developed regulations to ensure recycling would be performed in a safe manner.
Treatment Storage and Disposal Facilities (TSDFs) provide temporary storage and final treatment or disposal for hazardous wastes. Since they manage large volumes of waste and conduct activities that may present a higher degree of risk, TSDFs are stringently regulated. The TSDF requirements establish generic facility management standards, specific provisions governing hazardous waste management units and additional precautions designed to protect soil, ground water and air resources.
Comprehensive information on the final steps in EPA’s hazardous waste management program is available online, including Web pages and resources related to:
Summary
• Hazardous waste is defined as solid waste, or combination of solid waste, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may (a) cause, or significantly contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or (b) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.
• Listed wastes are wastes from common manufacturing and industrial processes, specific industries and can be generated from discarded commercial products.
• Characteristic wastes are wastes that exhibit any one or more of the following characteristic properties: ignitability, corrosivity, reactivity or toxicity.
• A waste that has a hazardous component and a radioactive component is called a mixed waste and is regulated under both the Resource Conservation and Recovery Act (RCRA) and the Atomic Energy Act.
• The Environmental Protection Agency (EPA) has developed a hazardous waste management program to ensure proper handling of hazardous waste from recycling, treatment, storage, and disposal.
• Wikipedia
• US EPA | textbooks/chem/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/22%3A_Poisons/22.07%3A_Hazardous_Wastes.txt |
These are homework exercises to accompany the Ball et al. "Beginning Chemistry" textmap, which is an introductory chemistry text aimed for a single semester or quarter beginning experience to the field. The textmaps survey some of the basic topics of chemistry. This survey should give student enough knowledge to appreciate the impact of chemistry in everyday life and, if necessary, prepare student for additional instruction in chemistry.
• 1: What Is Chemistry?
These are exercises and select solutions to company Chapter 1 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 2: Measurements
These are exercises and select solutions to company Chapter 2 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 3: Atoms, Molecules, and Ions
These are exercises and select solutions to company Chapter 3 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 4: Chemical Reactions and Equations
These are exercises and select solutions to company Chapter 4 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 5: Stoichiometry and the Mole
These are exercises and select solutions to company Chapter 5 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 6: Gases
These are exercises and select solutions to company Chapter 6 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 7: Energy and Chemistry
These are exercises and select solutions to company Chapter 7 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 8.E: Electronic Structure (Exercises)
These are exercises and select solutions to company Chapter 8 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 9: Chemical Bonds
These are exercises and select solutions to company Chapter 9 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 10: Solids and Liquids
These are exercises and select solutions to company Chapter 10 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 11: Solutions
These are exercises and select solutions to company Chapter 11 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 12: Acids and Bases
These are exercises and select solutions to company Chapter 12 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 14: Oxidation and Reduction
These are exercises and select solutions to company Chapter 14 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
• 15: Nuclear Chemistry
These are exercises and select solutions to company Chapter 15 of the "Beginning Chemistry" Textmap formulated around the Ball et al. textbook.
Exercises: Ball et al. (Beginning Chemistry)
1.1: Basic Definitions
Q1.1.1
Identify each as either matter or not matter.
1. a book
2. hate
3. light
4. a car
5. a fried egg
Q1.1.2
Give an example of matter in each phase: solid, liquid, or gas.
1. Does each statement represent a physical property or a chemical property?
1. Sulfur is yellow.
2. Steel wool burns when ignited by a flame.
3. A gallon of milk weighs over eight pounds.
2. Does each statement represent a physical property or a chemical property?
1. A pile of leaves slowly rots in the backyard.
2. In the presence of oxygen, hydrogen can interact to make water.
3. Gold can be stretched into very thin wires.
3. Does each statement represent a physical change or a chemical change?
1. Water boils and becomes steam.
2. Food is converted into usable form by the digestive system.
3. The alcohol in many thermometers freezes at about −40 degrees Fahrenheit.
4. Does each statement represent a physical change or a chemical change?
1. Graphite, a form of elemental carbon, can be turned into diamond, another form of carbon, at very high temperatures and pressures.
2. The house across the street has been painted a new color.
3. The elements sodium and chlorine come together to make a new substance called sodium chloride.
5. Distinguish between an element and a compound. About how many of each are known?
6. What is the difference between a homogeneous mixture and a heterogeneous mixture?
7. Identify each as a heterogeneous mixture or a homogeneous mixture.
1. Salt is mixed with pepper.
2. Sugar is dissolved in water.
3. Pasta is cooked in boiling water.
8. Identify each as a heterogeneous mixture or a homogeneous mixture.
1. air
2. dirt
3. a television set
9. In Exercise 9, which choices are also solutions?
10. In Exercise 10, which choices are also solutions?
11. Why is iron considered a metal?
12. Why is oxygen considered a nonmetal?
13. Distinguish between a metal and a nonmetal.
14. What properties do semimetals have?
15. Elemental carbon is a black, dull-looking solid that conducts heat and electricity well. It is very brittle and cannot be made into thin sheets or long wires. Of these properties, how does carbon behave as a metal? How does carbon behave as a nonmetal?
16. Pure silicon is shiny and silvery but does not conduct electricity or heat well. Of these properties, how does silicon behave as a metal? How does silicon behave as a nonmetal?
Answers
1. matter
2. not matter
3. not matter
4. matter
5. matter
1. physical property
2. chemical property
3. physical property
1. physical change
2. chemical change
3. physical change
1. An element is a fundamental chemical part of a substance; there are about 115 known elements. A compound is a combination of elements that acts as a different substance; there are over 50 million known substances.
1. heterogeneous
2. homogeneous
3. heterogeneous
1. Choice b is a solution.
1. Iron is a metal because it is solid, is shiny, and conducts electricity and heat well.
1. Metals are typically shiny, conduct electricity and heat well, and are malleable and ductile; nonmetals are a variety of colors and phases, are brittle in the solid phase, and do not conduct heat or electricity well.
1. Carbon behaves as a metal because it conducts heat and electricity well. It is a nonmetal because it is black and brittle and cannot be made into sheets or wires.
1.2: Chemistry as a Science
1. Describe the scientific method.
2. What is the scientific definition of a hypothesis? Why is the phrase a hypothesis is just a guess an inadequate definition?
3. Why do scientists need to perform experiments?
4. What is the scientific definition of a theory? How is this word misused in general conversation?
5. What is the scientific definition of a law? How does it differ from the everyday definition of a law?
6. Name an example of a field that is not considered a science.
1. Which of the following fields are studies of the natural universe?
1. biophysics (a mix of biology and physics)
2. art
3. business
1. Which of the following fields are studies of the natural universe?
2. accounting
3. geochemistry (a mix of geology and chemistry)
4. astronomy (the study of stars and planets [but not the earth])
1. Which of these statements are qualitative descriptions?
2. The Titanic was the largest passenger ship build at that time.
3. The population of the United States is about 306,000,000 people.
4. The peak of Mount Everest is 29,035 feet above sea level.
1. Which of these statements are qualitative descriptions?
2. A regular movie ticket in Cleveland costs \$6.00.
3. The weather in the Democratic Republic of the Congo is the wettest in all of Africa.
4. The deepest part of the Pacific Ocean is the Mariana Trench.
1. Of the statements in Exercise 9, which are quantitative?
Of the statements in Exercise 10, which are quantitative?
Answers
1. Simply stated, the scientific method includes three steps: (1) stating a hypothesis, (2) testing the hypothesis, and (3) refining the hypothesis.
2.
3. Scientists perform experiments to test their hypotheses because sometimes the nature of natural universe is not obvious.
4.
5. A scientific law is a specific statement that is thought to be never violated by the entire natural universe. Everyday laws are arbitrary limits that society puts on its members.
6.
1.
1. yes
2. no
3. no
•
•
1. qualitative
2. not qualitative
3. not qualitative
•
1. Statements b and c are quantitative. | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/01%3A_Chemistry_Matter_and_Measurement.txt |
2.1: Expressing Numbers
2.1.1
Express these numbers in scientific notation.
1. 56.9
2. 563,100
3. 0.0804
4. 0.00000667
2.1.2
Express these numbers in scientific notation.
1. −890,000
2. 602,000,000,000
3. 0.0000004099
4. 0.000000000000011
2.1.3
Express these numbers in scientific notation.
1. 0.00656
2. 65,600
3. 4,567,000
4. 0.000005507
2.1.4
Express these numbers in scientific notation.
1. 65
2. −321.09
3. 0.000077099
4. 0.000000000218
2.1.5
Express these numbers in standard notation.
1. 1.381 × 105
2. 5.22 × 10−7
3. 9.998 × 104
2.1.6
Express these numbers in standard notation.
1. 7.11 × 10−2
2. 9.18 × 102
3. 3.09 × 10−10
2.1.7
Express these numbers in standard notation.
1. 8.09 × 100
2. 3.088 × 10−5
3. −4.239 × 102
2.1.8
Express these numbers in standard notation.
1. 2.87 × 10−8
2. 1.78 × 1011
3. 1.381 × 10−23
2.1.9
These numbers are not written in proper scientific notation. Rewrite them so that they are in proper scientific notation.
1. 72.44 × 103
2. 9,943 × 10−5
3. 588,399 × 102
2.1.10
These numbers are not written in proper scientific notation. Rewrite them so that they are in proper scientific notation.
1. 0.000077 × 10−7
2. 0.000111 × 108
3. 602,000 × 1018
2.1.11
These numbers are not written in proper scientific notation. Rewrite them so that they are in proper scientific notation.
1. 345.1 × 102
2. 0.234 × 10−3
3. 1,800 × 10−2
2.1.12
These numbers are not written in proper scientific notation. Rewrite them so that they are in proper scientific notation.
1. 8,099 × 10−8
2. 34.5 × 100
3. 0.000332 × 104
2.1.13
Write these numbers in scientific notation by counting the number of places the decimal point is moved.
1. 123,456.78
2. 98,490
3. 0.000000445
2.1.14
Write these numbers in scientific notation by counting the number of places the decimal point is moved.
1. 0.000552
2. 1,987
3. 0.00000000887
2.1.15
Use your calculator to evaluate these expressions. Express the final answer in proper scientific notation.
1. 456 × (7.4 × 108) = ?
2. (3.02 × 105) ÷ (9.04 × 1015) = ?
3. 0.0044 × 0.000833 = ?
2.1.16
Use your calculator to evaluate these expressions. Express the final answer in proper scientific notation.
1. 98,000 × 23,000 = ?
2. 98,000 ÷ 23,000 = ?
3. (4.6 × 10−5) × (2.09 × 103) = ?
2.1.17
Use your calculator to evaluate these expressions. Express the final answer in proper scientific notation.
1. 45 × 132 ÷ 882 = ?
2. [(6.37 × 104) × (8.44 × 10−4)] ÷ (3.2209 × 1015) = ?
2.1.18
Use your calculator to evaluate these expressions. Express the final answer in proper scientific notation.
1. (9.09 × 108) ÷ [(6.33 × 109) × (4.066 × 10−7)] = ?
2. 9,345 × 34.866 ÷ 0.00665 = ?
Answers
1. 5.69 × 101
2. 5.631 × 105
3. 8.04 × 10−2
4. 6.67 × 10−6
1. 6.56 × 10−3
2. 6.56 × 104
3. 4.567 × 106
4. 5.507 × 10−6
•
1. 138,100
2. 0.000000522
3. 99,980
•
1. 8.09
2. 0.00003088
3. −423.9
•
1. 7.244 × 104
2. 9.943 × 10−2
3. 5.88399 × 107
•
1. 3.451 × 104
2. 2.34 × 10−4
3. 1.8 × 101
•
1. 1.2345678 × 105
2. 9.849 × 104
3. 4.45 × 10−7
•
1. 3.3744 × 1011
2. 3.3407 × 10−11
3. 3.665 × 10−6
•
1. 6.7346 × 100
2. 1.6691 × 10−14
2.2: Expressing Units
2.2.1
Identify the unit in each quantity.
• 2 boxes of crayons
• 3.5 grams of gold
2.2.2
Identify the unit in each quantity.
• 32 oz of cheddar cheese
• 0.045 cm3 of water
2.2.3
Identify the unit in each quantity.
• 9.58 s (the current world record in the 100 m dash)
• 6.14 m (the current world record in the pole vault)
2.2.4
Identify the unit in each quantity.
• 2 dozen eggs
• 2.4 km/s (the escape velocity of the moon, which is the velocity you need at the surface to escape the moon’s gravity)
2.2.5
Indicate what multiplier each prefix represents.
• k
• m
• M
2.2.6
Indicate what multiplier each prefix represents.
• c
• G
• μ
2.2.7
Give the prefix that represents each multiplier.
• 1/1,000th ×
• 1,000 ×
• 1,000,000,000 ×
2.2.8
Give the prefix that represents each multiplier.
• 1/1,000,000,000th ×
• 1/100th ×
• 1,000,000 ×
2.2.9
Complete the following table with the missing information.
Unit Abbreviation
kilosecond
mL
Mg
centimeter
2.2.10
Complete the following table with the missing information.
Unit Abbreviation
kilometer per second
second
cm3
μL
nanosecond
2.2.11
Express each quantity in a more appropriate unit. There may be more than one acceptable answer.
• 3.44 × 10−6 s
• 3,500 L
• 0.045 m
2.2.12
Express each quantity in a more appropriate unit. There may be more than one acceptable answer.
• 0.000066 m/s (Hint: you need consider only the unit in the numerator.)
• 4.66 × 106 s
• 7,654 L
2.2.13
Express each quantity in a more appropriate unit. There may be more than one acceptable answer.
• 43,600 mL
• 0.0000044 m
• 1,438 ms
2.2.14
Express each quantity in a more appropriate unit. There may be more than one acceptable answer.
• 0.000000345 m3
• 47,000,000 mm3
• 0.00665 L
2.2.15
Multiplicative prefixes are used for other units as well, such as computer memory. The basic unit of computer memory is the byte (b). What is the unit for one million bytes?
2.2.16
You may have heard the terms microscale or nanoscale to represent the sizes of small objects. What units of length do you think are useful at these scales? What fractions of the fundamental unit of length are these units?Acceleration is defined as a change in velocity per time. Propose a unit for acceleration in terms of the fundamental SI units.
2.2.17
Density is defined as the mass of an object divided by its volume. Propose a unit of density in terms of the fundamental SI units.
Answers
1. boxes of crayons
2. grams of gold
•
1. seconds
2. meters
•
1. 1,000 ×
2. 1/1,000 ×
3. 1,000,000 ×
•
1. milli-
2. kilo-
3. giga-
•
1.
1. Unit
Abbreviation
1. kilosecond
1. ks
1. milliliter
1. mL
1. megagram
1. Mg
1. centimeter
1. cm
1.
1.
1. 3.44 μs
2. 3.5 kL
3. 4.5 cm
•
1. 43.6 L
2. 4.4 µm
3. 1.438 s
•
1. megabytes (Mb)
2.
3. meters/second2
2.3: Significant Figures
2.3.1
Express each measurement to the correct number of significant figures.
2.3.2
Express each measurement to the correct number of significant figures.
2.3.3
How many significant figures do these numbers have?
1. 23
2. 23.0
3. 0.00023
4. 0.0002302
2.3.4
How many significant figures do these numbers have?
1. 5.44 × 108
2. 1.008 × 10−5
3. 43.09
4. 0.000000138
2.3.5
How many significant figures do these numbers have?
• 765,890
• 765,890.0
• 1.2000 × 105
• 0.0005060
2.3.6
How many significant figures do these numbers have?
• 0.009
• 0.0000009
• 65,444
• 65,040
2.3.7
Compute and express each answer with the proper number of significant figures, rounding as necessary.
• 56.0 + 3.44 = ?
• 0.00665 + 1.004 = ?
• 45.99 − 32.8 = ?
• 45.99 − 32.8 + 75.02 = ?
2.3.8
Compute and express each answer with the proper number of significant figures, rounding as necessary.
• 1.005 + 17.88 = ?
• 56,700 − 324 = ?
• 405,007 − 123.3 = ?
• 55.5 + 66.66 − 77.777 = ?
2.3.9
Compute and express each answer with the proper number of significant figures, rounding as necessary.
• 56.7 × 66.99 = ?
• 1.000 ÷ 77 = ?
• 1.000 ÷ 77.0 = ?
• 6.022 × 1.89 = ?
2.3.10
Compute and express each answer with the proper number of significant figures, rounding as necessary.
• 0.000440 × 17.22 = ?
• 203,000 ÷ 0.044 = ?
• 67 × 85.0 × 0.0028 = ?
• 999,999 ÷ 3,310 = ?
2.3.11
Write the number 87,449 in scientific notation with four significant figures.
2.3.12
Write the number 0.000066600 in scientific notation with five significant figures.
2.3.13
Write the number 306,000,000 in scientific notation to the proper number of significant figures.
2.3.14
Write the number 0.0000558 in scientific notation with two significant figures.
2.3.15
Perform each calculation and limit each answer to three significant figures.
• 67,883 × 0.004321 = ?
• (9.67 × 103) × 0.0055087 = ?
2.3.16
Perform each calculation and limit each answer to four significant figures.
1. 18,900 × 76.33 ÷ 0.00336 = ?
2. 0.77604 ÷ 76,003 × 8.888 = ?
Answers
1. 375 psi
2. 1.30 cm
•
1. two
2. three
3. two
4. four
•
1. five
2. seven
3. five
4. four
•
1. 59.4
2. 1.011
3. 13.2
4. 88.2
•
1. 3.80 × 103
2. 0.013
3. 0.0130
4. 11.4
•
1. 8.745 × 104
2. 6.6600 × 10−5
•
1. 293
2. 53.3
2.4: Converting Units
2.4.1
Write the two conversion factors that exist between the two given units.
1. milliliters and liters
2. microseconds and seconds
3. kilometers and meters
2.4.2
Write the two conversion factors that exist between the two given units.
• kilograms and grams
• milliseconds and seconds
• centimeters and meters
2.4.3
Perform the following conversions.
• 5.4 km to meters
• 0.665 m to millimeters
• 0.665 m to kilometers
2.4.4
Perform the following conversions.
• 90.6 mL to liters
• 0.00066 ML to liters
• 750 L to kiloliters
2.4.5
Perform the following conversions.
• 17.8 μg to grams
• 7.22 × 102 kg to grams
• 0.00118 g to nanograms
2.4.6
Perform the following conversions.
• 833 ns to seconds
• 5.809 s to milliseconds
• 2.77 × 106 s to megaseconds
2.4.7
Perform the following conversions.
• 9.44 m2 to square centimeters
• 3.44 × 108 mm3 to cubic meters
2.4.8
Perform the following conversions.
• 0.00444 cm3 to cubic meters
• 8.11 × 102 m2 to square nanometers
2.4.9
Why would it be inappropriate to convert square centimeters to cubic meters?
2.4.10
Why would it be inappropriate to convert from cubic meters to cubic seconds?
2.4.11
Perform the following conversions.
1. 45.0 m/min to meters/second
2. 0.000444 m/s to micrometers/second
3. 60.0 km/h to kilometers/second
2.4.12
Perform the following conversions.
• 3.4 × 102 cm/s to centimeters/minute
• 26.6 mm/s to millimeters/hour
• 13.7 kg/L to kilograms/milliliters
2.4.13
Perform the following conversions.
• 0.674 kL to milliliters
• 2.81 × 1012 mm to kilometers
• 94.5 kg to milligrams
2.4.14
Perform the following conversions.
• 6.79 × 10−6 kg to micrograms
• 1.22 mL to kiloliters
• 9.508 × 10−9 ks to milliseconds
2.4.15
Perform the following conversions.
• 6.77 × 1014 ms to kiloseconds
• 34,550,000 cm to kilometers
2.4.16
Perform the following conversions.
• 4.701 × 1015 mL to kiloliters
• 8.022 × 10−11 ks to microseconds
2.4.17
Perform the following conversions. Note that you will have to convert units in both the numerator and the denominator.
• 88 ft/s to miles/hour (Hint: use 5,280 ft = 1 mi.)
• 0.00667 km/h to meters/second
2.4.18
Perform the following conversions. Note that you will have to convert units in both the numerator and the denominator.
• 3.88 × 102 mm/s to kilometers/hour
• 1.004 kg/L to grams/milliliter
2.4.19
What is the area in square millimeters of a rectangle whose sides are 2.44 cm × 6.077 cm? Express the answer to the proper number of significant figures.
2.4.20
What is the volume in cubic centimeters of a cube with sides of 0.774 m? Express the answer to the proper number of significant figures.
2.4.21
The formula for the area of a triangle is 1/2 × base × height. What is the area of a triangle in square centimeters if its base is 1.007 m and its height is 0.665 m? Express the answer to the proper number of significant figures.
2.4.22
The formula for the area of a triangle is 1/2 × base × height. What is the area of a triangle in square meters if its base is 166 mm and its height is 930.0 mm? Express the answer to the proper number of significant figures.
Answers
1. $\frac{1000mL}{1L} and \frac{1L}{1000mL}$
2. $\frac{1000000\mu s}{1s}and \frac{1s}{1000000\mu s}$
3. $\frac{1000m}{1km}and \frac{1km}{1000m}$
1. 5,400 m
2. 665 mm
3. 6.65 × 10−4 km
•
1. 1.78 × 10−5 g
2. 7.22 × 105 g
3. 1.18 × 106 ng
•
1. 94,400 cm2
2. 0.344 m3
•
1. One is a unit of area, and the other is a unit of volume.
2.
1.
1. 0.75 m/s
2. 444 µm/s
3. 1.666 × 10−2 km/s
•
1. 674,000 mL
2. 2.81 × 106 km
3. 9.45 × 107 mg
•
1. 6.77 × 108 ks
2. 345.5 km
•
1. 6.0 × 101 mi/h
2. 0.00185 m/s
•
1. 1.48 × 103 mm2
2.
3. 3.35 × 103 cm2
2.5: Other Units - Temperature and Density
2.5.1
Perform the following conversions.
1. 255°F to degrees Celsius
2. −255°F to degrees Celsius
3. 50.0°C to degrees Fahrenheit
4. −50.0°C to degrees Fahrenheit
2.5.2
Perform the following conversions.
• 1,065°C to degrees Fahrenheit
• −222°C to degrees Fahrenheit
• 400.0°F to degrees Celsius
• 200.0°F to degrees Celsius
2.5.3
Perform the following conversions.
• 100.0°C to kelvins
• −100.0°C to kelvins
• 100 K to degrees Celsius
• 300 K to degrees Celsius
2.5.4
Perform the following conversions.
• 1,000.0 K to degrees Celsius
• 50.0 K to degrees Celsius
• 37.0°C to kelvins
• −37.0°C to kelvins
2.5.5
Convert 0 K to degrees Celsius. What is the significance of the temperature in degrees Celsius?
2.5.6
Convert 0 K to degrees Fahrenheit. What is the significance of the temperature in degrees Fahrenheit?
2.5.7
The hottest temperature ever recorded on the surface of the earth was 136°F in Libya in 1922. What is the temperature in degrees Celsius and in kelvins?
2.5.8
The coldest temperature ever recorded on the surface of the earth was −128.6°F in Vostok, Antarctica, in 1983. What is the temperature in degrees Celsius and in kelvins?
2.5.9
Give at least three possible units for density.
2.5.10
What are the units when density is inverted? Give three examples.
2.5.11
A sample of iron has a volume of 48.2 cm3. What is its mass?
2.5.12
A sample of air has a volume of 1,015 mL. What is its mass?
2.5.13
The volume of hydrogen used by the Hindenburg, the German airship that exploded in New Jersey in 1937, was 2.000 × 108 L. If hydrogen gas has a density of 0.0899 g/L, what mass of hydrogen was used by the airship?
2.5.14
The volume of an Olympic-sized swimming pool is 2.50 × 109 cm3. If the pool is filled with alcohol (d = 0.789 g/cm3), what mass of alcohol is in the pool?
2.5.15
A typical engagement ring has 0.77 cm3 of gold. What mass of gold is present?
2.5.16
A typical mercury thermometer has 0.039 mL of mercury in it. What mass of mercury is in the thermometer?
2.5.17
What is the volume of 100.0 g of lead if lead has a density of 11.34 g/cm3?
2.5.18
What is the volume of 255.0 g of uranium if uranium has a density of 19.05 g/cm3?
2.5.19
What is the volume in liters of 222 g of neon if neon has a density of 0.900 g/L?
2.5.20
What is the volume in liters of 20.5 g of sulfur hexafluoride if sulfur hexafluoride has a density of 6.164 g/L?
2.5.21
Which has the greater volume, 100.0 g of iron (d = 7.87 g/cm3) or 75.0 g of gold (d = 19.3 g/cm3)?
2.5.22
Which has the greater volume, 100.0 g of hydrogen gas (d = 0.0000899 g/cm3) or 25.0 g of argon gas (d = 0.00178 g/cm3)?
Answers
1. 124°C
2. −159°C
3. 122°F
4. −58°F
•
1. 373 K
2. 173 K
3. −173°C
4. 27°C
•
1. −273°C. This is the lowest possible temperature in degrees Celsius.
2.
3. 57.8°C; 331 K
4.
5. g/mL, g/L, and kg/L (answers will vary)
6.
7. 379 g
8.
9. 1.80 × 107 g
10.
11. 15 g
12.
13. 8.818 cm3
14.
15. 247 L
16.
17. The 100.0 g of iron has the greater volume
2.6: Additional Exercises
2.6.1
Evaluate 0.00000000552 × 0.0000000006188 and express the answer in scientific notation. You may have to rewrite the original numbers in scientific notation first.
2.6.2
Evaluate 333,999,500,000 ÷ 0.00000000003396 and express the answer in scientific notation. You may need to rewrite the original numbers in scientific notation first.
2.6.3
Express the number 6.022 × 1023 in standard notation.
2.6.4
Express the number 6.626 × 10−34 in standard notation.
2.6.5
When powers of 10 are multiplied together, the powers are added together. For example, 102 × 103 = 102+3 = 105. With this in mind, can you evaluate (4.506 × 104) × (1.003 × 102) without entering scientific notation into your calculator?
2.6.6
When powers of 10 are divided into each other, the bottom exponent is subtracted from the top exponent. For example, 105/103 = 105−3 = 102. With this in mind, can you evaluate (8.552 × 106) ÷ (3.129 × 103) without entering scientific notation into your calculator?
2.6.7
Consider the quantity two dozen eggs. Is the number in this quantity “two” or “two dozen”? Justify your choice.
2.6.8
Consider the quantity two dozen eggs. Is the unit in this quantity “eggs” or “dozen eggs”? Justify your choice.
2.6.9
Fill in the blank: 1 km = ______________ μm.
2.6.10
Fill in the blank: 1 Ms = ______________ ns.
2.6.11
Fill in the blank: 1 cL = ______________ ML.
2.5.12
Fill in the blank: 1 mg = ______________ kg.
2.6.13
Express 67.3 km/h in meters/second.
2.6.14
Express 0.00444 m/s in kilometers/hour.
2.6.15
Using the idea that 1.602 km = 1.000 mi, convert a speed of 60.0 mi/h into kilometers/hour.
2.6.16
Using the idea that 1.602 km = 1.000 mi, convert a speed of 60.0 km/h into miles/hour.
2.6.17
Convert 52.09 km/h into meters/second.
2.6.18
Convert 2.155 m/s into kilometers/hour.
2.6.19
Use the formulas for converting degrees Fahrenheit into degrees Celsius to determine the relative size of the Fahrenheit degree over the Celsius degree.
2.6.20
Use the formulas for converting degrees Celsius into kelvins to determine the relative size of the Celsius degree over kelvins.
2.6.21
What is the mass of 12.67 L of mercury?
2.6.22
What is the mass of 0.663 m3 of air?
2.6.23
What is the volume of 2.884 kg of gold?
2.6.24
What is the volume of 40.99 kg of cork? Assume a density of 0.22 g/cm3.
Answers
1. 3.42 × 10−18
2.
3. 602,200,000,000,000,000,000,000
4.
5. 4.520 × 106
6.
7. The quantity is two; dozen is the unit.
8.
9. 1,000,000,000
10.
11. 1/100,000,000
12.
13. 18.7 m/s
14.
15. 96.1 km/h
16.
17. 14.47 m/s
18.
19. One Fahrenheit degree is nine-fifths the size of a Celsius degree.
20.
21. 1.72 × 105 g
22.
23. 149 mL | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/02%3A_Elements_Atoms_and_the_Periodic_Table.txt |
3.1: Atomic Theory
1. List the three statements that make up the modern atomic theory.
2. Explain how atoms are composed.
3. Which is larger, a proton or an electron?
4. Which is larger, a neutron or an electron?
5. What are the charges for each of the three subatomic particles?
6. Where is most of the mass of an atom located?
7. Sketch a diagram of a boron atom, which has five protons and six neutrons in its nucleus.
8. Sketch a diagram of a helium atom, which has two protons and two neutrons in its nucleus.
9. Define atomic number. What is the atomic number for a boron atom?
10. What is the atomic number of helium?
11. Define isotope and give an example.
12. What is the difference between deuterium and tritium?
13. Which pair represents isotopes?
1. \[_{2}^{4}\textrm{He} \, and\: \, _{2}^{3}\textrm{He}\]
2. \[_{26}^{56}\textrm{Fe} \, and\: \, _{25}^{56}\textrm{Mn}\]
3. \[_{14}^{28}\textrm{Si} \, and\: \, _{15}^{31}\textrm{P}\]
14. Which pair represents isotopes?
1. \[_{20}^{40}\textrm{Ca} \, and\: \, _{19}^{40}\textrm{K}\]
2. \[_{26}^{56}\textrm{Fe} \, and\: \, _{28}^{56}\textrm{Fe}\]
3. \[_{92}^{238}\textrm{U} \, and\: \, _{92}^{235}\textrm{U}\]
1. Give complete symbols of each atom, including the atomic number and the mass number.
a. an oxygen atom with 8 protons and 8 neutrons
b. a potassium atom with 19 protons and 20 neutrons
c. a lithium atom with 3 protons and 4 neutron
2. Give complete symbols of each atom, including the atomic number and the mass number.
a. a magnesium atom with 12 protons and 12 neutrons
b. a magnesium atom with 12 protons and 13 neutrons
c. a xenon atom with 54 protons and 77 neutron
3. Americium-241 is an isotope used in smoke detectors. What is the complete symbol for this isotope?
18. Carbon-14 is an isotope used to perform radioactive dating tests on previously living material. What is the complete symbol for this isotope?
• Give atomic symbols for each element.
a. sodium
b. argon
c. nitrogen
d. radon
• Give atomic symbols for each element.
a. silver
b. gold
c. mercury
d. iodine
• Give the name of the element.
a.Si
b. Mn
c. Fe
d. Cr
• Give the name of the element.
a. F
b. Cl
c. Br
d. I
Answers
1. All matter is composed of atoms; atoms of the same element are the same, and atoms of different elements are different; atoms combine in whole-number ratios to form compounds.
2.
3. A proton is larger than an electron.
4. proton: 1+; electron: 1−; neutron: 0
5. The atomic number is the number of protons in a nucleus. Boron has an atomic number of five.
6.
7. Isotopes are atoms of the same element but with different numbers of neutrons. \[_{1}^{1}\textrm{H} \, and\: \, _{1}^{2}\textrm{H}\]
1. isotopes
2. not isotopes
3. not isotopes
1.
8.
1. \[_{8}^{16}\textrm{O}\]
2. \[_{19}^{39}\textrm{K}\]
3. \[_{3}^{7}\textrm{Li}\]
9. \[_{95}^{241}\textrm{Am}\]
10.
1. Na
2. Ar
3. N
4. Rn
11.
1. silicon
2. manganese
3. iron
4. chromium
3.2: Molecules and Chemical Nomenclature
1. Which of these formulas represent molecules? State how many atoms are in each molecule.
1. Fe
2. PCl3
3. P4
4. Ar
2. Which of these formulas represent molecules? State how many atoms are in each molecule.
1. I2
2. He
3. H2O
4. Al
3. What is the difference between CO and Co?
4. What is the difference between H2O and H2O2 (hydrogen peroxide)?
5. Give the proper formula for each diatomic element.
6. In 1986, when Halley’s comet last passed the earth, astronomers detected the presence of S2 in their telescopes. Why is sulfur not considered a diatomic element?
7. What is the stem of fluorine used in molecule names? CF4 is one example.
1. What is the stem of selenium used in molecule names? SiSe2 is an example.
2. Give the proper name for each molecule.
1. PF3
2. TeCl2
3. N2O3
3. Give the proper name for each molecule.
1. NO
2. CS2
3. As2O3
4. Give the proper name for each molecule.
1. XeF2
2. O2F2
3. SF6
5. Give the proper name for each molecule.
1. P4O10
2. B2O3
3. P2S3
6. Give the proper name for each molecule.
1. N2O
2. N2O4
3. N2O5
7. Give the proper name for each molecule.
1. SeO2
2. Cl2O
3. XeF6
8. Give the proper formula for each name.
1. dinitrogen pentoxide
2. tetraboron tricarbide
3. phosphorus pentachloride
9. Give the proper formula for each name.
1. nitrogen triiodide
2. diarsenic trisulfide
3. iodine trichloride
10. Give the proper formula for each name.
1. dioxygen dichloride
2. dinitrogen trisulfide
3. xenon tetrafluoride
11. Give the proper formula for each name.
1. chlorine dioxide
2. selenium dibromide
3. dinitrogen trioxide
12. Give the proper formula for each name.
1. iodine trifluoride
2. xenon trioxide
3. disulfur decafluoride
13. Give the proper formula for each name.
1. germanium dioxide
2. carbon disulfide
3. diselenium dibromide
Answers
1. not a molecule
2. a molecule; four atoms total
3. a molecule; four atoms total
1.
2. CO is a compound of carbon and oxygen; Co is the element cobalt.
3.
4. H2, O2, N2, F2, Cl2, Br2, I2
5.
6. fluor-
7.
1. phosphorus trifluoride
2. tellurium dichloride
3. dinitrogen trioxide
8.
1. xenon difluoride
2. dioxygen difluoride
3. sulfur hexafluoride
9.
1. dinitrogen monoxide
2. dinitrogen tetroxide
3. dinitrogen pentoxide
10.
1. N2O5
2. B4C3
3. PCl5
11.
1. O2Cl2
2. N2S3
3. XeF4
12.
1. IF3
2. XeO3
3. S2F10
3.3: Masses of Atoms and Molecules
1. Define atomic mass unit. What is its abbreviation?
2. Define atomic mass. What is its unit?
3. Estimate the mass, in whole numbers, of each isotope.
1. hydrogen-1
2. hydrogen-3
3. iron-56
4. Estimate the mass, in whole numbers, of each isotope.
1. phosphorus-31
2. carbon-14
3. americium-241
5. Determine the atomic mass of each element, given the isotopic composition.
1. lithium, which is 92.4% lithium-7 (mass 7.016 u) and 7.60% lithium-6 (mass 6.015 u)
2. oxygen, which is 99.76% oxygen-16 (mass 15.995 u), 0.038% oxygen-17 (mass 16.999 u), and 0.205% oxygen-18 (mass 17.999 u)
6. Determine the atomic mass of each element, given the isotopic composition.
1. neon, which is 90.48% neon-20 (mass 19.992 u), 0.27% neon-21 (mass 20.994 u), and 9.25% neon-22 (mass 21.991 u)
2. uranium, which is 99.27% uranium-238 (mass 238.051 u) and 0.720% uranium-235 (mass 235.044 u)
7. How far off would your answer be from Exercise 5a if you used whole-number masses for individual isotopes of lithium?
8. How far off would your answer be from Exercise 6b if you used whole-number masses for individual isotopes of uranium?
1. What is the atomic mass of an oxygen atom?
2. What is the molecular mass of oxygen in its elemental form?
1. What is the atomic mass of bromine?
2. What is the molecular mass of bromine in its elemental form?
9. Determine the mass of each substance.
1. F2
2. CO
3. CO2
10. Determine the mass of each substance.
1. Kr
2. KrF4
3. PF5
11. Determine the mass of each substance.
1. Na
2. B2O3
3. S2Cl2
12. Determine the mass of each substance.
1. IBr3
2. N2O5
3. CCl4
13. Determine the mass of each substance.
1. GeO2
2. IF3
3. XeF6
14. Determine the mass of each substance.
1. NO
2. N2O4
3. Ca
Answers
1. The atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its abbreviation is u.
2.
1. 1
2. 3
3. 56
3.
1. 6.940 u
2. 16.000 u
4.
5. We would get 6.924 u.
6.
1. 15.999 u
2. 31.998 u
7.
1. 37.996 u
2. 28.010 u
3. 44.009 u
8.
1. 22.990 u
2. 69.619 u
3. 135.036 u
9.
1. 104.64 u
2. 183.898 u
3. 245.281 u
3.4: Ions and Ionic Compounds
1. Explain how cations form.
2. Explain how anions form.
3. Give the charge each atom takes when it forms an ion. If more than one charge is possible, list both.
1. K
2. O
3. Co
4. Give the charge each atom takes when it forms an ion. If more than one charge is possible, list both.
1. Ca
2. I
3. Fe
5. Give the charge each atom takes when it forms an ion. If more than one charge is possible, list both.
1. Ag
2. Au
3. Br
6. Give the charge each atom takes when it forms an ion. If more than one charge is possible, list both.
1. S
2. Na
3. H
7. Name the ions from Exercise 3.
8. Name the ions from Exercise 4.
9. Name the ions from Exercise 5.
10. Name the ions from Exercise 6.
11. Give the formula and name for each ionic compound formed between the two listed ions.
1. Mg2+ and Cl
2. Fe2+ and O2−
3. Fe3+ and O2−
12. Give the formula and name for each ionic compound formed between the two listed ions.
1. K+ and S2−
2. Ag+ and Br
3. Sr2+ and N3−
13. Give the formula and name for each ionic compound formed between the two listed ions.
1. Cu2+ and F
2. Ca2+ and O2−
3. K+ and P3−
14. Give the formula and name for each ionic compound formed between the two listed ions.
1. Na+ and N3−
2. Co2+ and I
3. Au3+ and S2−
15. Give the formula and name for each ionic compound formed between the two listed ions.
1. K+ and SO42
2. NH4+ and S2−
3. NH4+ and PO43
16. Give the formula and name for each ionic compound formed between the two listed ions.
1. Ca2+ and NO3
2. Ca2+ and NO2
3. Sc3+ and C2H3O2
17. Give the formula and name for each ionic compound formed between the two listed ions.
1. Pb4+ and SO42
2. Na+ and I3
3. Li+ and Cr2O72
18. Give the formula and name for each ionic compound formed between the two listed ions.
1. NH4+ and N3−
2. Mg2+ and CO32
3. Al3+ and OH
19. Give the formula and name for each ionic compound formed between the two listed ions.
1. Ag+ and SO32
2. Na+ and HCO3
3. Fe3+ and ClO3
20. Give the formula and name for each ionic compound formed between the two listed ions.
1. Rb+ and O22
2. Au3+ and HSO4
3. Sr2+ and NO2
21. What is the difference between SO3 and SO32?
22. What is the difference between NO2 and NO2?
Answers
1. Cations form by losing electrons.
2.
1. 1+
2. 2−
3. 2+, 3+
3.
1. 1+
2. 1+, 3+
3. 1−
4.
1. the potassium ion
2. the oxide ion
3. the cobalt(II) and cobalt(III) ions, respectively
5.
1. the silver ion
2. the gold(I) and gold(III) ions, respectively
3. the bromide ion
6.
1. magnesium chloride, MgCl2
2. iron(II) oxide, FeO
3. iron(III) oxide, Fe2O3
7.
1. copper(II) fluoride, CuF2
2. calcium oxide, CaO
3. potassium phosphide, K3P
8.
1. potassium sulfate, K2SO4
2. ammonium sulfide, (NH4)2S
3. ammonium phosphate, (NH4)3PO4
9.
1. lead(IV) sulfate, Pb(SO4)2
2. sodium triiodide, NaI3
3. lithium dichromate, Li2Cr2O7
10.
1. silver sulfite, Ag2SO3
2. sodium hydrogen carbonate, NaHCO3
3. iron(III) chlorate, Fe(ClO3)3
11.
12. SO3 is sulfur trioxide, while SO32 is the sulfite ion.
3.5: Acids
1. Give the formula for each acid.
1. perchloric acid
2. hydriodic acid
2. Give the formula for each acid.
1. hydrosulfuric acid
2. phosphorous acid
3. Name each acid.
1. HF(aq)
2. HNO3(aq)
3. H2C2O4(aq)
4. Name each acid.
1. H2SO4(aq)
2. H3PO4(aq)
3. HCl(aq)
5. Name an acid found in food.
6. Name some properties that acids have in common.
Answers
1. HClO4(aq)
2. HI(aq)
1.
1. hydrofluoric acid
2. nitric acid
3. oxalic acid
2.
3. oxalic acid (answers will vary)
Additional Exercises
1. How many electrons does it take to make the mass of one proton?
2. How many protons does it take to make the mass of a neutron?
3. Dalton’s initial version of the modern atomic theory says that all atoms of the same element are the same. Is this actually correct? Why or why not?
4. How are atoms of the same element the same? How are atoms of the same element different?
5. Give complete atomic symbols for the three known isotopes of hydrogen.
6. A rare isotope of helium has a single neutron in its nucleus. Write the complete atomic symbol of this isotope.
7. Use its place on the periodic table to determine if indium, In, atomic number 49, is a metal or a nonmetal.
8. Only a few atoms of astatine, At, atomic number 85, have been detected. On the basis of its position on the periodic table, would you expect it to be a metal or a nonmetal?
9. Americium-241 is a crucial part of many smoke detectors. How many neutrons are present in its nucleus?
1. Potassium-40 is a radioactive isotope of potassium that is present in the human body. How many neutrons are present in its nucleus?
2. Determine the atomic mass of ruthenium from the given abundance and mass data.
Ruthenium-96 5.54% 95.907 u
Ruthenium-98 1.87% 97.905 u
Ruthenium-99 12.76% 98.906 u
Ruthenium-100 12.60% 99.904 u
Ruthenium-101 17.06% 100.906 u
Ruthenium-102 31.55% 101.904 u
Ruthenium-104 18.62% 103.905 u
1. Determine the atomic mass of tellurium from the given abundance and mass data.
Tellurium-120 0.09% 119.904 u
Tellurium-122 2.55% 121.903 u
Tellurium-123 0.89% 122.904 u
Tellurium-124 4.74% 123.903 u
Tellurium-125 7.07% 124.904 u
Tellurium-126 18.84% 125.903 u
Tellurium-128 31.74% 127.904 u
Tellurium-130 34.08% 129.906 u
1. One atomic mass unit has a mass of 1.6605 × 10−24 g. What is the mass of one atom of sodium?
2. One atomic mass unit has a mass of 1.6605 × 10−24 g. What is the mass of one atom of uranium?
• One atomic mass unit has a mass of 1.6605 × 10−24 g. What is the mass of one molecule of H2O?
• One atomic mass unit has a mass of 1.6605 × 10−24 g. What is the mass of one molecule of PF5?
• From their positions on the periodic table, will Cu and I form a molecular compound or an ionic compound?
1. From their positions on the periodic table, will N and S form a molecular compound or an ionic compound?
2. Mercury is an unusual element in that when it takes a 1+ charge as a cation, it always exists as the diatomic ion.
1. Propose a formula for the mercury(I) ion.
2. What is the formula of mercury(I) chloride?
3. Propose a formula for hydrogen peroxide, a substance used as a bleaching agent. (Curiously, this compound does not behave as an acid, despite its formula. It behaves more like a classic nonmetal-nonmetal, molecular compound.)
4. The uranyl cation has the formula UO22+. Propose formulas and names for the ionic compounds between the uranyl cation and F, SO42, and PO43.
5. The permanganate anion has the formula MnO4. Propose formulas and names for the ionic compounds between the permanganate ion and K+, Ca2+, and Fe3+.
Answers
1. about 1,800 electrons
2.
3. It is not strictly correct because of the existence of isotopes.
4.
5. \[_{1}^{1}\textrm{H},\; _{1}^{2}\textrm{H},\, and\; _{1}^{3}\textrm{H}\]
6.
7. It is a metal.
8.
9. 146 neutrons
10.
11. 101.065 u
12.
13. 3.817 × 10−23 g
14.
15. 2.991 × 10−23 g
16.
17. ionic
18.
19.
1. Hg22+
2. Hg2Cl2
20.
21. uranyl fluoride, UO2F2; uranyl sulfate, UO2SO4; uranyl phosphate, (UO2)3(PO4)2 | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/03%3A_Ionic_Bonding_and_Simple_Ionic_Compounds.txt |
4.2: The Chemical Equation
1. From the statement “nitrogen and hydrogen react to produce ammonia,” identify the reactants and the products.
2. From the statement “sodium metal reacts with water to produce sodium hydroxide and hydrogen,” identify the reactants and the products.
3. From the statement “magnesium hydroxide reacts with nitric acid to produce magnesium nitrate and water,” identify the reactants and the products.
4. From the statement “propane reacts with oxygen to produce carbon dioxide and water,” identify the reactants and the products.
5. Write and balance the chemical equation described by Exercise 1.
6. Write and balance the chemical equation described by Exercise 2.
7. Write and balance the chemical equation described by Exercise 3.
8. Write and balance the chemical equation described by Exercise 4. The formula for propane is C3H8.
9. Balance: ___NaClO3 → ___NaCl + ___O2
10. Balance: ___N2 + ___H2 → ___N2H4
11. Balance: ___Al + ___O2 → ___Al2O3
12. Balance: ___C2H4 + ___O2 → ___CO2 + ___H2O
13. How would you write the balanced chemical equation in Exercise 10 if all substances were gases?
1. How would you write the balanced chemical equation in Exercise 12 if all the substances except water were gases and water itself were a liquid?
Answers
1. reactants: nitrogen and hydrogen; product: ammonia
2.
3. reactants: magnesium hydroxide and nitric acid; products: magnesium nitrate and water
4.
5. N2 + 3H2 → 2NH3
6.
7. Mg(OH)2 + 2HNO3 → Mg(NO3)2 + 2H2O
8.
9. 2NaClO3 → 2NaCl + 3O2
10.
11. 4Al + 3O2 → 2Al2O3
12.
13. N2(g) + 3H2(g) → 2NH3(g)
4.3: Types of Chemical Reactions - Single and Double Displacement Reactions
1. What are the general characteristics that help you recognize single-replacement reactions?
2. What are the general characteristics that help you recognize double-replacement reactions?
3. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Zn + Fe(NO3)2 → ?
2. F2 + FeI3 → ?
4. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Li + MgSO4 → ?
2. NaBr + Cl2 → ?
5. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Sn + H2SO4 → ?
2. Al + NiBr2 → ?
6. Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Mg + HCl → ?
2. HI + Br2 → ?
7. Use the periodic table or the activity series to predict if each single-replacement reaction will occur and, if so, write a balanced chemical equation.
1. FeCl2 + Br2 → ?
2. Fe(NO3)3 + Al → ?
8. Use the periodic table or the activity series to predict if each single-replacement reaction will occur and, if so, write a balanced chemical equation.
1. Zn + Fe3(PO4)2 → ?
2. Ag + HNO3 → ?
9. Use the periodic table or the activity series to predict if each single-replacement reaction will occur and, if so, write a balanced chemical equation.
1. NaI + Cl2 → ?
2. AgCl + Au → ?
10. Use the periodic table or the activity series to predict if each single-replacement reaction will occur and, if so, write a balanced chemical equation.
1. Pt + H3PO4 → ?
2. Li + H2O → ? (Hint: treat H2O as if it were composed of H+ and OH ions.)
11. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Zn(NO3)2 + NaOH → ?
2. HCl + Na2S → ?
12. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Ca(C2H3O2)2 + HNO3 → ?
2. Na2CO3 + Sr(NO2)2 → ?
13. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Pb(NO3)2 + KBr → ?
2. K2O + MgCO3 → ?
14. Assuming that each double-replacement reaction occurs, predict the products and write each balanced chemical equation.
1. Sn(OH)2 + FeBr3 → ?
2. CsNO3 + KCl → ?
15. Use the solubility rules to predict if each double-replacement reaction will occur and, if so, write a balanced chemical equation.
1. Pb(NO3)2 + KBr → ?
2. K2O + Na2CO3 → ?
16. Use the solubility rules to predict if each double-replacement reaction will occur and, if so, write a balanced chemical equation.
1. Na2CO3 + Sr(NO2)2 → ?
2. (NH4)2SO4 + Ba(NO3)2 → ?
17. Use the solubility rules to predict if each double-replacement reaction will occur and, if so, write a balanced chemical equation.
1. K3PO4 + SrCl2 → ?
2. NaOH + MgCl2 → ?
18. Use the solubility rules to predict if each double-replacement reaction will occur and, if so, write a balanced chemical equation.
1. KC2H3O2 + Li2CO3 → ?
2. KOH + AgNO3 → ?
Answers
1. One element replaces another element in a compound.
2.
1. Zn + Fe(NO3)2 → Zn(NO3)2 + Fe
2. 3F2 + 2FeI3 → 3I2 + 2FeF3
3.
1. Sn + H2SO4 → SnSO4 + H2
2. 2Al + 3NiBr2 → 2AlBr3 + 3Ni
4.
1. No reaction occurs.
2. Fe(NO3)3 + Al → Al(NO3)3 + Fe
5.
1. 2NaI + Cl2 → 2NaCl + I2
2. No reaction occurs.
6.
1. Zn(NO3)2 + 2NaOH → Zn(OH)2 + 2NaNO3
2. 2HCl + Na2S → 2NaCl + H2S
7.
1. Pb(NO3)2 + 2KBr → PbBr2 + 2KNO3
2. K2O + MgCO3 → K2CO3 + MgO
8.
1. Pb(NO3)2 + 2KBr → PbBr2(s) + 2KNO3
2. No reaction occurs.
9.
1. 2K3PO4 + 3SrCl2 → Sr3(PO4)2(s) + 6KCl
2. 2NaOH + MgCl2 → 2NaCl + Mg(OH)2(s)
4.4: Ionic Equations - A Closer Look
1. Write a chemical equation that represents NaBr(s) dissociating in water.
2. Write a chemical equation that represents SrCl2(s) dissociating in water.
3. Write a chemical equation that represents (NH4)3PO4(s) dissociating in water.
4. Write a chemical equation that represents Fe(C2H3O2)3(s) dissociating in water.
5. Write the complete ionic equation for the reaction of FeCl2(aq) and AgNO3(aq). You may have to consult the solubility rules.
6. Write the complete ionic equation for the reaction of BaCl2(aq) and Na2SO4(aq). You may have to consult the solubility rules.
7. Write the complete ionic equation for the reaction of KCl(aq) and NaC2H3O2(aq). You may have to consult the solubility rules.
8. Write the complete ionic equation for the reaction of Fe2(SO4)3(aq) and Sr(NO3)2(aq). You may have to consult the solubility rules.
9. Write the net ionic equation for the reaction of FeCl2(aq) and AgNO3(aq). You may have to consult the solubility rules.
10. Write the net ionic equation for the reaction of BaCl2(aq) and Na2SO4(aq). You may have to consult the solubility rules.
11. Write the net ionic equation for the reaction of KCl(aq) and NaC2H3O2(aq). You may have to consult the solubility rules.
12. Write the net ionic equation for the reaction of Fe2(SO4)3(aq) and Sr(NO3)2(aq). You may have to consult the solubility rules.
13. Identify the spectator ions in Exercises 9 and 10.
1. Identify the spectator ions in Exercises 11 and 12.
Answers
1. NaBr(s) Na+(aq) + Br(aq)
2.
3. (NH4)3PO4(s) 3NH4+(aq) + PO43(aq)
4.
5. Fe2+(aq) + 2Cl(aq) + 2Ag+(aq) + 2NO3(aq) → Fe2+(aq) + 2NO3(aq) + 2AgCl(s)
6.
7. K+(aq) + Cl(aq) + Na+(aq) + C2H3O2(aq) → Na+(aq) + Cl(aq) + K+(aq) + C2H3O2(aq)
8.
9. 2Cl(aq) + 2Ag+(aq) → 2AgCl(s)
10.
11. There is no overall reaction.
12.
13. In Exercise 9, Fe2+(aq) and NO3(aq) are spectator ions; in Exercise 10, Na+(aq) and Cl(aq) are spectator ions.
4.5: Composition, Decomposition, and Combustion Reactions
1. Which is a composition reaction and which is not?
1. NaCl + AgNO3 → AgCl + NaNO3
2. CaO + CO2 → CaCO3
2. Which is a composition reaction and which is not?
1. H2 + Cl2 → 2HCl
2. 2HBr + Cl2 → 2HCl + Br2
3. Which is a composition reaction and which is not?
1. 2SO2 + O2 → 2SO3
2. 6C + 3H2 → C6H6
4. Which is a composition reaction and which is not?
1. 4Na + 2C + 3O2 → 2Na2CO3
2. Na2CO3 → Na2O + CO2
5. Which is a decomposition reaction and which is not?
1. HCl + NaOH → NaCl + H2O
2. CaCO3 → CaO + CO2
6. Which is a decomposition reaction and which is not?
1. 3O2 → 2O3
2. 2KClO3 → 2KCl + 3O2
7. Which is a decomposition reaction and which is not?
1. Na2O + CO2 → Na2CO3
2. H2SO3 → H2O + SO2
8. Which is a decomposition reaction and which is not?
1. 2C7H5N3O6 → 3N2 + 5H2O + 7CO + 7C
2. C6H12O6 + 6O2 → 6CO2 + 6H2O
9. Which is a combustion reaction and which is not?
1. C6H12O6 + 6O2 → 6CO2 + 6H2O
2. 2Fe2S3 + 9O2 → 2Fe2O3 + 6SO2
10. Which is a combustion reaction and which is not?
1. CH4 + 2F2 → CF4 + 2H2
2. 2H2 + O2 → 2H2O
11. Which is a combustion reaction and which is not?
1. P4 + 5O2 → 2P2O5
2. 2Al2S3 + 9O2 → 2Al2O3 + 6SO2
12. Which is a combustion reaction and which is not?
1. C2H4 + O2 → C2H4O2
2. C2H4 + Cl2 → C2H4Cl2
13. Is it possible for a composition reaction to also be a combustion reaction? Give an example to support your case.
14. Is it possible for a decomposition reaction to also be a combustion reaction? Give an example to support your case.
15. Complete and balance each combustion equation.
1. C4H9OH + O2 → ?
2. CH3NO2 + O2 → ?
16. Complete and balance each combustion equation.
1. B2H6 + O2 → ? (The oxide of boron formed is B2O3.)
2. Al2S3 + O2 → ? (The oxide of sulfur formed is SO2.)
3. Al2S3 + O2 → ? (The oxide of sulfur formed is SO3.)
Answers
1. not composition
2. composition
1.
1. composition
2. composition
2.
1. not decomposition
2. decomposition
3.
1. not decomposition
2. decomposition
4.
1. combustion
2. combustion
5.
1. combustion
2. combustion
6.
7. Yes; 2H2 + O2 → 2H2O (answers will vary)
8.
1. C4H9OH + 6O2 → 4CO2 + 5H2O
2. 4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2
4.6: Neutralization Reactions
1. What is the Arrhenius definition of an acid?
2. What is the Arrhenius definition of a base?
3. Predict the products of each acid-base combination listed. Assume that a neutralization reaction occurs.
1. HCl and KOH
2. H2SO4 and KOH
3. H3PO4 and Ni(OH)2
4. Predict the products of each acid-base combination listed. Assume that a neutralization reaction occurs.
1. HBr and Fe(OH)3
2. HNO2 and Al(OH)3
3. HClO3 and Mg(OH)2
5. Write a balanced chemical equation for each neutralization reaction in Exercise 3.
6. Write a balanced chemical equation for each neutralization reaction in Exercise 4.
7. Write a balanced chemical equation for the neutralization reaction between each given acid and base. Include the proper phase labels.
1. HI(aq) + KOH(aq) → ?
2. H2SO4(aq) + Ba(OH)2(aq) → ?
8. Write a balanced chemical equation for the neutralization reaction between each given acid and base. Include the proper phase labels.
1. HNO3(aq) + Fe(OH)3(s) → ?
2. H3PO4(aq) + CsOH(aq) → ?
9. Write the net ionic equation for each neutralization reaction in Exercise 7.
10. Write the net ionic equation for each neutralization reaction in Exercise 8.
11. Write the complete and net ionic equations for the neutralization reaction between HClO3(aq) and Zn(OH)2(s). Assume the salt is soluble.
12. Write the complete and net ionic equations for the neutralization reaction between H2C2O4(s) and Sr(OH)2(aq). Assume the salt is insoluble.
13. Explain why the net ionic equation for the neutralization reaction between HCl(aq) and KOH(aq) is the same as the net ionic equation for the neutralization reaction between HNO3(aq) and RbOH.
14. Explain why the net ionic equation for the neutralization reaction between HCl(aq) and KOH(aq) is different from the net ionic equation for the neutralization reaction between HCl(aq) and AgOH.
15. Write the complete and net ionic equations for the neutralization reaction between HCl(aq) and KOH(aq) using the hydronium ion in place of H+. What difference does it make when using the hydronium ion?
16. Write the complete and net ionic equations for the neutralization reaction between HClO3(aq) and Zn(OH)2(s) using the hydronium ion in place of H+. Assume the salt is soluble. What difference does it make when using the hydronium ion?
Answers
1. An Arrhenius acid increases the amount of H+ ions in an aqueous solution.
2.
1. KCl and H2O
2. K2SO4 and H2O
3. Ni3(PO4)2 and H2O
3.
1. HCl + KOH → KCl + H2O
2. H2SO4 + 2KOH → K2SO4 + 2H2O
3. 2H3PO4 + 3Ni(OH)2 → Ni3(PO4)2 + 6H2O
4.
1. HI(aq) + KOH(aq) → KI(aq) + H2O(ℓ)
2. H2SO4(aq) + Ba(OH)2(aq) → BaSO4(s) + 2H2O(ℓ)
5.
1. H+(aq) + OH(aq) → H2O(ℓ)
2. 2H+(aq) + SO42(aq) + Ba2+(aq) + 2OH(aq) → BaSO4(s) + 2H2O(ℓ)
6.
7. Complete ionic equation: 2H+(aq) + 2ClO3(aq) + Zn2+(aq) + 2OH(aq) → Zn2+(aq) + 2ClO3(aq) + 2H2O(ℓ)
Net ionic equation: 2H+(aq) + 2OH(aq) → 2H2O(ℓ)
1.
2. Because the salts are soluble in both cases, the net ionic reaction is just H+(aq) + OH(aq) → H2O(ℓ).
3.
4. Complete ionic equation: H3O+(aq) + Cl(aq) + K+(aq) + OH(aq) → 2H2O(ℓ) + K+(aq) + Cl(aq)
Net ionic equation: H3O+(aq) + OH(aq) → 2H2O(ℓ)
The difference is simply the presence of an extra water molecule as a product.
4.7: Oxidation-Reduction Reactions
1. Is the reaction
2K(s) + Br2(ℓ) → 2KBr(s)
an oxidation-reduction reaction? Explain your answer.
1. Is the reaction
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
an oxidation-reduction reaction? Explain your answer.
2. In the reaction
2Ca(s) + O2(g) → 2CaO
indicate what has lost electrons and what has gained electrons.
3. In the reaction
16Fe(s) + 3S8(s) → 8Fe2S3(s)
indicate what has lost electrons and what has gained electrons.
4. In the reaction
2Li(s) + O2(g) → Li2O2(s)
indicate what has been oxidized and what has been reduced.
5. In the reaction
2Ni(s) + 3I2(s) → 2NiI3(s)
indicate what has been oxidized and what has been reduced.
6. What are two different definitions of oxidation?
1. What are two different definitions of reduction?
2. Assign oxidation numbers to each atom in each substance.
1. P4
2. SO2
3. SO22−
4. Ca(NO3)2
3. Assign oxidation numbers to each atom in each substance.
1. PF5
2. (NH4)2S
3. Hg
4. Li2O2 (lithium peroxide)
4. Assign oxidation numbers to each atom in each substance.
1. CO
2. CO2
3. NiCl2
4. NiCl3
5. Assign oxidation numbers to each atom in each substance.
1. NaH (sodium hydride)
2. NO2
3. NO2
4. AgNO3
6. Assign oxidation numbers to each atom in each substance.
1. CH2O
2. NH3
3. Rb2SO4
4. Zn(C2H3O2)2
7. Assign oxidation numbers to each atom in each substance.
1. C6H6
2. B(OH)3
3. Li2S
4. Au
8. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
2NO + Cl2 → 2NOCl
1. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
Fe + SO3 → FeSO3
1. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
2KrF2 + 2H2O → 2Kr + 4HF + O2
2. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
SO3 + SCl2 → SOCl2 + SO2
3. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
2K + MgCl2 → 2KCl + Mg
1. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.
C7H16 + 11O2 → 7CO2 + 8H2O
Answers
1. Yes; both K and Br are changing oxidation numbers.
2.
3. Ca has lost electrons, and O has gained electrons.
4.
5. Li has been oxidized, and O has been reduced.
6.
7. loss of electrons; increase in oxidation number
8.
1. P: 0
2. S: +4; O: −2
3. S: +2; O: −2
4. Ca: 2+; N: +5; O: −2
9.
1. C: +2; O: −2
2. C: +4; O: −2
3. Ni: +2; Cl: −1
4. Ni: +3; Cl: −1
10.
1. C: 0; H: +1; O: −2
2. N: −3; H: +1
3. Rb: +1; S: +6; O: −2
4. Zn: +2; C: 0; H: +1; O: −2
11.
12. N is being oxidized, and Cl is being reduced.
13.
14. O is being oxidized, and Kr is being reduced.
15.
16. K is being oxidized, and Mg is being reduced.
Additional Exercises
1. Chemical equations can also be used to represent physical processes. Write a chemical reaction for the boiling of water, including the proper phase labels.
2. Chemical equations can also be used to represent physical processes. Write a chemical reaction for the freezing of water, including the proper phase labels.
3. Explain why
4Na(s) + 2Cl2(g) → 4NaCl(s)
should not be considered a proper chemical equation.
4. Explain why
H2(g) + 1/2O2(g) → H2O(ℓ)
should not be considered a proper chemical equation.
5. Does the chemical reaction represented by
3Zn(s) + 2Al(NO3)3(aq) → 3Zn(NO3)2(aq) + 2Al(s)
proceed as written? Why or why not?
6. Does the chemical reaction represented by
2Au(s) + 2HNO3(aq) → 2AuNO3(aq) + H2(g)
proceed as written? Gold is a relatively useful metal for certain applications, such as jewelry and electronics. Does your answer suggest why this is so?
7. Explain what is wrong with this double-replacement reaction.
NaCl(aq) + KBr(aq) → NaK(aq) + ClBr(aq)
8. Predict the products of and balance this double-replacement reaction.
Ag2SO4(aq) + SrCl2(aq) → ?
9. Write the complete and net ionic equations for this double-replacement reaction.
BaCl2(aq) + Ag2SO4(aq) → ?
10. Write the complete and net ionic equations for this double-replacement reaction.
Ag2SO4(aq) + SrCl2(aq) → ?
11. Identify the spectator ions in this reaction. What is the net ionic equation?
NaCl(aq) + KBr(aq) → NaBr(aq) + KCl(aq)
12. Complete this reaction and identify the spectator ions. What is the net ionic equation?
3H2SO4(aq) + 2Al(OH)3(s) → ?
13. Can a reaction be a composition reaction and a redox reaction at the same time? Give an example to support your answer.
14. Can a reaction be a combustion reaction and a redox reaction at the same time? Give an example to support your answer.
15. Can a reaction be a decomposition reaction and a redox reaction at the same time? Give an example to support your answer.
16. Can a reaction be a combustion reaction and a double-replacement reaction at the same time? Give an example to support your answer.
17. Why is CH4 not normally considered an acid?
1. Methyl alcohol has the formula CH3OH. Why would methyl alcohol not normally be considered a base?
2. What are the oxidation numbers of the nitrogen atoms in these substances?
1. N2
2. NH3
3. NO
4. N2O
5. NO2
6. N2O4
7. N2O5
8. NaNO3
3. What are the oxidation numbers of the sulfur atoms in these substances?
1. SF6
2. Na2SO4
3. K2SO3
4. SO3
5. SO2
6. S8
7. Na2S
4. Disproportion is a type of redox reaction in which the same substance is both oxidized and reduced. Identify the element that is disproportionating and indicate the initial and final oxidation numbers of that element.
2CuCl(aq) → CuCl2(aq) + Cu(s)
1. Disproportion is a type of redox reaction in which the same substance is both oxidized and reduced. Identify the element that is disproportionating and indicate the initial and final oxidation numbers of that element.
3Cl2(g) + 6OH(aq) → 5Cl(aq) + ClO3(aq) + 3H2O(ℓ)
Answers
1. H2O(ℓ) → H2O(g)
2.
3. The coefficients are not in their lowest whole-number ratio.
4.
5. No; zinc is lower in the activity series than aluminum.
6.
7. In the products, the cation is pairing with the cation, and the anion is pairing with the anion.
8.
9. Complete ionic equation: Ba2+(aq) + 2Cl(aq) + 2Ag+(aq) + SO42(aq) → BaSO4(s) + 2AgCl(s)
Net ionic equation: The net ionic equation is the same as the complete ionic equation.
10.
11. Each ion is a spectator ion; there is no overall net ionic equation.
12.
13. Yes; H2 + Cl2 → 2HCl (answers will vary)
14.
15. Yes; 2HCl → H2 + Cl2 (answers will vary)
16.
17. It does not increase the H+ ion concentration; it is not a compound of H+.
18.
19.
1. 0
2. −3
3. +2
4. +1
5. +4
6. +4
7. +5
8. +5
20.
21. Copper is disproportionating. Initially, its oxidation number is +1; in the products, its oxidation numbers are +2 and 0, respectively. | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/04%3A_Covalent_Bonding_and_Simple_Molecular_Compounds.txt |
5.1: Stoichiometry
1. Think back to the pound cake recipe. What possible conversion factors can you construct relating the components of the recipe?
2. Think back to the pancake recipe. What possible conversion factors can you construct relating the components of the recipe?
3. What are all the conversion factors that can be constructed from the balanced chemical reaction: $\ce{2H2(g) + O2(g) → 2H2O(ℓ)}?$
4. What are all the conversion factors that can be constructed from the balanced chemical reaction N2(g) + 3H2(g) → 2NH3(g)?
5. Given the chemical equation : Na(s) + H2O(ℓ) → NaOH(aq) + H2(g)
1. Balance the equation.
2. How many molecules of H2 are produced when 332 atoms of Na react?
6. Given the chemical equation: S(s) + O2(g) → SO3(g)
1. Balance the equation.
2. How many molecules of O2 are needed when 38 atoms of S react?
7. For the balanced chemical equation:
6H+(aq) + 2MnO4(aq) + 5H2O2(ℓ) → 2Mn2+(aq) + 5O2(g) + 8H2O(ℓ)
how many molecules of H2O are produced when 75 molecules of H2O2 react?
1. For the balanced chemical reaction
2C6H6(ℓ) + 15O2(g) → 12CO2(g) + 6H2O(ℓ)
how many molecules of CO2 are produced when 56 molecules of C6H6 react?
2. Given the balanced chemical equation
Fe2O3(s) + 3SO3(g) → Fe2(SO4)3
how many molecules of Fe2(SO4)3 are produced if 321 atoms of S are reacted?
3. For the balanced chemical equation
CuO(s) + H2S(g) → CuS + H2O(ℓ)
how many molecules of CuS are formed if 9,044 atoms of H react?
4. For the balanced chemical equation
Fe2O3(s) + 3SO3(g) → Fe2(SO4)3
suppose we need to make 145,000 molecules of Fe2(SO4)3. How many molecules of SO3 do we need?
1. One way to make sulfur hexafluoride is to react thioformaldehyde, CH2S, with elemental fluorine:
CH2S + 6F2 → CF4 + 2HF + SF6
If 45,750 molecules of SF6 are needed, how many molecules of F2 are required?
1. Construct the three independent conversion factors possible for these two reactions:
1. 2H2 + O2 → 2H2O
2. H2 + O2 → H2O2
Why are the ratios between H2 and O2 different?
The conversion factors are different because the stoichiometries of the balanced chemical reactions are different.
1. Construct the three independent conversion factors possible for these two reactions:
1. 2Na + Cl2 → 2NaCl
2. 4Na + 2Cl2 → 4NaCl
What similarities, if any, exist in the conversion factors from these two reactions?
Answers
1. $\frac{1\, pound\, butter}{1\, pound\, flour}$ or $\frac{1\, pound\, sugar}{1\, pound\, eggs}$ are two conversion factors that can be constructed from the pound cake recipe. Other conversion factors are also possible.1 pound butter1 pound flour
2.
3. $\frac{2\, molecules\, H_{2}}{1\, molecule\, O_{2}}$ , $\frac{1\, molecule\, O_{2}}{2\, molecules\, H_{2}O}$ , $\frac{2\, molecules\, H_{2}}{2\, molecules\, H_{2}O}$ and their reciprocals are the conversion factors that can be constructed.
4.
5.
1. 2Na(s) + 2H2O(ℓ) → 2NaOH(aq) + H2(g)
2. 166 molecules
6.
7. 120 molecules
8.
9. 107 molecules
10.
11. 435,000 molecules
12.
13.
1. $\frac{2\, molecules\, H_{2}}{1\, molecule\, O_{2}}\ , \frac{1\, molecule\, O_{2}}{2\, molecules\, H_{2}O}\ , \frac{2\, molecules\, H_{2}}{2\, molecules\, H_{2}O}$
2. $\frac{1\, molecules\, H_{2}}{1\, molecule\, O_{2}}\ , \frac{1\, molecule\, O_{2}}{2\, molecules\, H_{2}O_{2}}\ , \frac{1\, molecule\, H_{2}}{1\, molecule\, H_{2}O_{2}}$
5.2: The Mole
1. How many atoms are present in 4.55 mol of Fe?
2. How many atoms are present in 0.0665 mol of K?
3. How many molecules are present in 2.509 mol of H2S?
4. How many molecules are present in 0.336 mol of acetylene (C2H2)?
5. How many moles are present in 3.55 × 1024 Pb atoms?
6. How many moles are present in 2.09 × 1022 Ti atoms?
7. How many moles are present in 1.00 × 1023 PF3 molecules?
8. How many moles are present in 5.52 × 1025 penicillin molecules?
9. Determine the molar mass of each substance.
1. Si
2. SiH4
3. K2O
10. Determine the molar mass of each substance.
1. Cl2
2. SeCl2
3. Ca(C2H3O2)2
11. Determine the molar mass of each substance.
1. Al
2. Al2O3
3. CoCl3
12. Determine the molar mass of each substance.
1. O3
2. NaI
3. C12H22O11
13. What is the mass of 4.44 mol of Rb?
14. What is the mass of 0.311 mol of Xe?
15. What is the mass of 12.34 mol of Al2(SO4)3?
16. What is the mass of 0.0656 mol of PbCl2?
17. How many moles are present in 45.6 g of CO?
18. How many moles are present in 0.00339 g of LiF?
19. How many moles are present in 1.223 g of SF6?
20. How many moles are present in 48.8 g of BaCO3?
21. How many moles are present in 54.8 mL of mercury if the density of mercury is 13.6 g/mL?
22. How many moles are present in 56.83 mL of O2 if the density of O2 is 0.00133 g/mL?
Answers
1. 2.74 × 1024 atoms
2.
3. 1.511 × 1024 molecules
4.
5. 5.90 mol
6.
7. 0.166 mol
8.
9.
1. 28.086 g
2. 32.118 g
3. 94.195 g
10.
11.
1. 26.981 g
2. 101.959 g
3. 165.292 g
12.
13. 379 g
14.
15. 4,222 g
16.
17. 1.63 mol
18.
19. 0.008374 mol
20.
21. 3.72 mol
5.3: The Mole in Chemical Reactions
1. Express in mole terms what this chemical equation means: CH4 + 2O2 → CO2 + 2H2O
2. Express in mole terms what this chemical equation means.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
3. How many molecules of each substance are involved in the equation in Exercise 1 if it is interpreted in terms of moles?
4. How many molecules of each substance are involved in the equation in Exercise 2 if it is interpreted in terms of moles?
5. For the chemical equation
2C2H6 + 7O2 → 4CO2 + 6H2O
what equivalents can you write in terms of moles? Use the ⇔ sign.
6. For the chemical equation
2Al + 3Cl2 → 2AlCl3
what equivalents can you write in terms of moles? Use the ⇔ sign.
7. Write the balanced chemical reaction for the combustion of C5H12 (the products are CO2 and H2O) and determine how many moles of H2O are formed when 5.8 mol of O2 are reacted.
8. Write the balanced chemical reaction for the formation of Fe2(SO4)3 from Fe2O3 and SO3 and determine how many moles of Fe2(SO4)3 are formed when 12.7 mol of SO3 are reacted.
9. For the balanced chemical equation
3Cu(s) + 2NO3(aq) + 8H+(aq) → 3Cu2+(aq) + 4H2O(ℓ) + 2NO(g)
how many moles of Cu2+ are formed when 55.7 mol of H+ are reacted?
10. For the balanced chemical equation
Al(s) + 3Ag+(aq) → Al3+(aq) + 3Ag(s)
how many moles of Ag are produced when 0.661 mol of Al are reacted?
11. For the balanced chemical reaction
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(ℓ)
how many moles of H2O are produced when 0.669 mol of NH3 react?
12. For the balanced chemical reaction
4NaOH(aq) + 2S(s) + 3O2(g) → 2Na2SO4(aq) + 2H2O(ℓ)
how many moles of Na2SO4 are formed when 1.22 mol of O2 react?
13. For the balanced chemical reaction
4KO2(s) + 2CO2(g) → 2K2CO3(s) + 3O2(g)
determine the number of moles of both products formed when 6.88 mol of KO2 react.
1. For the balanced chemical reaction
2AlCl3 + 3H2O(ℓ) → Al2O3 + 6HCl(g)
determine the number of moles of both products formed when 0.0552 mol of AlCl3 react.
Answers
1. One mole of CH4 reacts with 2 mol of O2 to make 1 mol of CO2 and 2 mol of H2O.
2.
3. 6.022 × 1023 molecules of CH4, 1.2044 × 1024 molecules of O2, 6.022 × 1023 molecules of CO2, and 1.2044 × 1024 molecules of H2O
4.
5. 2 mol of C2H6 ⇔ 7 mol of O2 ⇔ 4 mol of CO2 ⇔ 6 mol of H2O
6.
7. C5H12 + 8O2 → 5CO2 + 6H2O; 4.4 mol
8.
9. 20.9 mol
10.
11. 1.00 mol
12.
13. 3.44 mol of K2CO3; 5.16 mol of O2
5.4: Mole-Mass and Mass-Mass Calculations
1. What mass of CO2 is produced by the combustion of 1.00 mol of CH4?CH4(g) + 2O2(g) → CO2(g) + 2H2O(ℓ)
2. What mass of H2O is produced by the combustion of 1.00 mol of CH4?
CH4(g) + 2O2(g) → CO2(g) + 2H2O(ℓ)
3. What mass of HgO is required to produce 0.692 mol of O2?
2HgO(s) → 2Hg(ℓ) + O2(g)
4. What mass of NaHCO3 is needed to produce 2.659 mol of CO2?
2NaHCO3(s) → Na2CO3(s) + H2O(ℓ) + CO2(g)
5. How many moles of Al can be produced from 10.87 g of Ag?
Al(NO3) 3(s) + 3Ag → Al + 3AgNO3
6. How many moles of HCl can be produced from 0.226 g of SOCl2?
SOCl2(ℓ) + H2O(ℓ) → SO2(g) + 2HCl(g)
7. How many moles of O2 are needed to prepare 1.00 g of Ca(NO3)2?
Ca(s) + N2(g) + 3O2(g) → Ca(NO3) 2(s)
8. How many moles of C2H5OH are needed to generate 106.7 g of H2O?
C2H5OH(ℓ) + 3O2(g) → 2CO2(g) + 3H2O(ℓ)
9. What mass of O2 can be generated by the decomposition of 100.0 g of NaClO3?
2NaClO3 → 2NaCl(s) + 3O2(g)
10. What mass of Li2O is needed to react with 1,060 g of CO2?
Li2O(aq) + CO2(g) → Li2CO3(aq)
11. What mass of Fe2O3 must be reacted to generate 324 g of Al2O3?
Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s)
12. What mass of Fe is generated when 100.0 g of Al are reacted?
Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s)
13. What mass of MnO2 is produced when 445 g of H2O are reacted?
H2O(ℓ) + 2MnO4(aq) + Br(aq) → BrO3(aq) + 2MnO2(s) + 2OH(aq)
14. What mass of PbSO4 is produced when 29.6 g of H2SO4 are reacted?
Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(ℓ)
15. If 83.9 g of ZnO are formed, what mass of Mn2O3 is formed with it?
Zn(s) + 2MnO2(s) → ZnO(s) + Mn2O3(s)
16. If 14.7 g of NO2 are reacted, what mass of H2O is reacted with it?
3NO2(g) + H2O(ℓ) → 2HNO3(aq) + NO(g)
17. If 88.4 g of CH2S are reacted, what mass of HF is produced?
CH2S + 6F2 → CF4 + 2HF + SF6
1. If 100.0 g of Cl2 are needed, what mass of NaOCl must be reacted?
NaOCl + HCl → NaOH + Cl2
Answers
1. 44.0 g
2.
3. 3.00 × 102 g
4.
5. 0.0336 mol
6.
7. 0.0183 mol
8.
9. 45.1 g
10.
11. 507 g
12.
13. 4.30 × 103 g
14.
15. 163 g
16.
17. 76.7 g
5.5: Yields
1. What is the difference between the theoretical yield and the actual yield?
2. What is the difference between the actual yield and the percent yield?
3. A worker isolates 2.675 g of SiF4 after reacting 2.339 g of SiO2 with HF. What are the theoretical yield and the actual yield?
SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(ℓ)
4. A worker synthesizes aspirin, C9H8O4, according to this chemical equation. If 12.66 g of C7H6O3 are reacted and 12.03 g of aspirin are isolated, what are the theoretical yield and the actual yield?
C7H6O3 + C4H6O3 → C9H8O4 + HC2H3O2
5. A chemist decomposes 1.006 g of NaHCO3 and obtains 0.0334 g of Na2CO3. What are the theoretical yield and the actual yield?
2NaHCO3(s) → Na2CO3(s) + H2O(ℓ) + CO2(g)
6. A chemist combusts a 3.009 g sample of C5H12 and obtains 3.774 g of H2O. What are the theoretical yield and the actual yield?
C5H12(ℓ) + 8O2(g) → 5CO2 + 6H2O(ℓ)
7. What is the percent yield in Exercise 3?
8. What is the percent yield in Exercise 4?
9. What is the percent yield in Exercise 5?
1. What is the percent yield in Exercise 6?
Answers
1. Theoretical yield is what you expect stoichiometrically from a chemical reaction; actual yield is what you actually get from a chemical reaction.
2.
3. theoretical yield = 4.052 g; actual yield = 2.675 g
4.
5. theoretical yield = 0.635 g; actual yield = 0.0334 g
6.
7. 66.02%
8.
9. 5.26%
5.6: Limiting Reagents
1. The box below shows a group of nitrogen and hydrogen molecules that will react to produce ammonia, NH3. What is the limiting reagent?
1. The box below shows a group of hydrogen and oxygen molecules that will react to produce water, H2O. What is the limiting reagent?
1. Given the statement “20.0 g of methane is burned in excess oxygen,” is it obvious which reactant is the limiting reagent?
2. Given the statement “the metal is heated in the presence of excess hydrogen,” is it obvious which substance is the limiting reagent despite not specifying any quantity of reactant?
3. Acetylene (C2H2) is formed by reacting 7.08 g of C and 4.92 g of H2.
2C(s) + H2(g) → C2H2(g)
What is the limiting reagent? How much of the other reactant is in excess?
4. Ethane (C2H6) is formed by reacting 7.08 g of C and 4.92 g of H2.
2C(s) + 3H2(g) → C2H6(g)
What is the limiting reagent? How much of the other reactant is in excess?
1. Given the initial amounts listed, what is the limiting reagent, and how much of the other reactant is in excess?
$\underset{35.6\, g}{P_{4}O_{6}(s)}+6\underset{4.77\, g}{H_{2}O(l)}\rightarrow 4H_{3}PO_{4}$
1. Given the initial amounts listed, what is the limiting reagent, and how much of the other reactant is in excess?
$\underset{377\, g}{3NO_{2}(g)}+\underset{244\, g}{H_{2}O(l)}\rightarrow 2HNO_{3}(aq)+NO(g)$
1. To form the precipitate PbCl2, 2.88 g of NaCl and 7.21 g of Pb(NO3)2 are mixed in solution. How much precipitate is formed? How much of which reactant is in excess?
1. In a neutralization reaction, 18.06 g of KOH are reacted with 13.43 g of HNO3. What mass of H2O is produced, and what mass of which reactant is in excess?
Answers
1. Nitrogen is the limiting reagent.
2.
3. Yes; methane is the limiting reagent.
4.
5. C is the limiting reagent; 4.33 g of H2 are left over.
6.
7. H2O is the limiting reagent; 25.9 g of P4O6 are left over.
8.
9. 6.06 g of PbCl2 are formed; 0.33 g of NaCl is left over.
5.7: Additional Exercises
1. How many molecules of O2 will react with 6.022 × 1023 molecules of H2 to make water? The reaction is 2H2(g) + O2(g) → 2H2O(ℓ).
2. How many molecules of H2 will react with 6.022 × 1023 molecules of N2 to make ammonia? The reaction is N2(g) + 3H2(g) → 2NH3(g).
3. How many moles are present in 6.411 kg of CO2? How many molecules is this?
4. How many moles are present in 2.998 mg of SCl4? How many molecules is this?
5. What is the mass in milligrams of 7.22 × 1020 molecules of CO2?
6. What is the mass in kilograms of 3.408 × 1025 molecules of SiS2?
7. What is the mass in grams of 1 molecule of H2O?
8. What is the mass in grams of 1 atom of Al?
9. What is the volume of 3.44 mol of Ga if the density of Ga is 6.08 g/mL?
10. What is the volume of 0.662 mol of He if the density of He is 0.1785 g/L?
11. For the chemical reaction
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(ℓ)
assume that 13.4 g of C4H10 reacts completely to products. The density of CO2 is 1.96 g/L. What volume in liters of CO2 is produced?
12. For the chemical reaction
2GaCl3(s) + 3H2(g) → 2Ga(ℓ) + 6HCl(g)
if 223 g of GaCl3 reacts completely to products and the density of Ga is 6.08 g/mL, what volume in milliliters of Ga is produced?
13. Calculate the mass of each product when 100.0 g of CuCl react according to the reaction
2CuCl(aq) → CuCl2(aq) + Cu(s)
What do you notice about the sum of the masses of the products? What concept is being illustrated here?
14. Calculate the mass of each product when 500.0 g of SnCl2 react according to the reaction
2SnCl2(aq) → SnCl4(aq) + Sn(s)
What do you notice about the sum of the masses of the products? What concept is being illustrated here?
15. What mass of CO2 is produced from the combustion of 1 gal of gasoline? The chemical formula of gasoline can be approximated as C8H18. Assume that there are 2,801 g of gasoline per gallon.
16. What mass of H2O is produced from the combustion of 1 gal of gasoline? The chemical formula of gasoline can be approximated as C8H18. Assume that there are 2,801 g of gasoline per gallon.
17. A chemical reaction has a theoretical yield of 19.98 g and a percent yield of 88.40%. What is the actual yield?
18. A chemical reaction has an actual yield of 19.98 g and a percent yield of 88.40%. What is the theoretical yield?
1. Given the initial amounts listed, what is the limiting reagent, and how much of the other reactants are in excess?
$\underset{35.0\, g}{P_{4}}+\underset{12.7\, g}{3NaOH}+\underset{9.33\, g}{3H_{2}O}\rightarrow 2Na_{2}HPO_{4}+PH_{3}$
1. Given the initial amounts listed, what is the limiting reagent, and how much of the other reactants are in excess?
$\underset{46.3\, g}{2NaCrO_{2}}+\underset{88.2\, g}{3NaBrO_{4}}+\underset{32.5\, g}{2NaOH}\rightarrow 3NaBrO_{3}+2Na_{2}CrO_{4}+H_{2}O$
1. Verify that it does not matter which product you use to predict the limiting reagent by using both products in this combustion reaction to determine the limiting reagent and the amount of the reactant in excess. Initial amounts of each reactant are given.
$\underset{26.3\, g}{C_{3}H_{8}}+\underset{21.8\, g}{5O_{2}}\rightarrow 3CO_{2}(g)+4H_{2}O(l)$
1. Just in case you suspect Exercise 21 is rigged, do it for another chemical reaction and verify that it does not matter which product you use to predict the limiting reagent by using both products in this combustion reaction to determine the limiting reagent and the amount of the reactant in excess. Initial amounts of each reactant are given.
$\underset{35.0\, g}{2P_{4}}+\underset{12.7\, g}{6NaOH}+\underset{9.33\, g}{6H_{2}O}\rightarrow 3Na_{2}HPO_{4}+5PH_{3}$
Answers
1. 1.2044 × 1024 molecules
2.
3. 145.7 mol; 8.77 × 1025 molecules
4.
5. 52.8 mg
6.
7. 2.99 × 10−23 g
8.
9. 39.4 mL
10.
11. 20.7 L
12.
13. 67.91 g of CuCl2; 32.09 g of Cu. The two masses add to 100.0 g, the initial amount of starting material, demonstrating the law of conservation of matter.
14.
15. 8,632 g
16.
17. 17.66 g
18.
19. The limiting reagent is NaOH; 21.9 g of P4 and 3.61 g of H2O are left over.
20.
21. Both products predict that O2 is the limiting reagent; 20.3 g of C3H8 are left over. | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/05%3A_Stoichiometry_and_the_Mole.txt |
6.1: Kinetic Theory of Gases
1. State the ideas behind the kinetic theory of gases.
2. The average speed of gas particles depends on what single variable?
3. Define ideal gas. Does an ideal gas exist?
1. What is a gas called that is not an ideal gas? Do such gases exist?
Answers
1. Gases consist of tiny particles of matter that are in constant motion. Gas particles are constantly colliding with each other and the walls of a container. These collisions are elastic; that is, there is no net loss of energy from the collisions. Gas particles are separated by large distances, with the size of a gas particle tiny compared to the distances that separate them. There are no interactive forces (i.e., attraction or repulsion) between the particles of a gas. The average speed of gas particles is dependent on the temperature of the gas.
2.
3. An ideal gas is a gas that exactly follows the statements of the kinetic theory of gases. Ideal gases do not exist, but the kinetic theory allows us to model them.
6.2: Pressure
1. Define pressure. What causes it?
2. Define and relate three units of pressure.
3. If a force of 16.7 N is pressed against an area of 2.44 m2, what is the pressure in pascals?
4. If a force of 2,546 N is pressed against an area of 0.0332 m2, what is the pressure in pascals?
5. Explain why the original definition of atmosphere did not work well.
6. What units of pressure are equal to each other?
7. How many atmospheres are in 889 mmHg?
8. How many atmospheres are in 223 torr?
9. How many torr are in 2.443 atm?
10. How many millimeters of mercury are in 0.334 atm?
11. How many millimeters of mercury are in 334 torr?
12. How many torr are in 0.777 mmHg?
13. How many pascals are there in 1 torr?
1. A pressure of 0.887 atm equals how many pascals?
Answers
1. Pressure is force per unit area. It is caused by gas particles hitting the walls of its container.
2.
3. 6.84 Pa
4.
5. Because the atmospheric pressure at sea level is variable, it is not a consistent unit of pressure.
6.
7. 1.17 atm
8.
9. 1,857 torr
10.
11. 334 mmHg
12.
13. 133 Pa
6.3: Gas Laws
1. Define gas law. What restrictions are there on the units that can be used for the physical properties?
2. What unit of temperature must be used for gas laws?
3. Boyle’s law relates the _____________ of a gas inversely with the ___________ of that gas.
4. Charles’s law relates the _____________ of a gas directly with the ___________ of that gas.
5. What properties must be held constant when applying Boyle’s law?
6. What properties must be held constant when applying Charles’s law?
7. A gas has an initial pressure of 1.445 atm and an initial volume of 1.009 L. What is its new pressure if volume is changed to 0.556 L? Assume temperature and amount are held constant.
8. A gas has an initial pressure of 633 torr and an initial volume of 87.3 mL. What is its new pressure if volume is changed to 45.0 mL? Assume temperature and amount are held constant.
9. A gas has an initial pressure of 4.33 atm and an initial volume of 5.88 L. What is its new volume if pressure is changed to 0.506 atm? Assume temperature and amount are held constant.
10. A gas has an initial pressure of 87.0 torr and an initial volume of 28.5 mL. What is its new volume if pressure is changed to 206 torr? Assume temperature and amount are held constant.
11. A gas has an initial volume of 638 mL and an initial pressure of 779 torr. What is its final volume in liters if its pressure is changed to 0.335 atm? Assume temperature and amount are held constant.
12. A gas has an initial volume of 0.966 L and an initial pressure of 3.07 atm. What is its final pressure in torr if its volume is changed to 3,450 mL? Assume temperature and amount are held constant.
13. A gas has an initial volume of 67.5 mL and an initial temperature of 315 K. What is its new volume if temperature is changed to 244 K? Assume pressure and amount are held constant.
14. A gas has an initial volume of 2.033 L and an initial temperature of 89.3 K. What is its volume if temperature is changed to 184 K? Assume pressure and amount are held constant.
15. A gas has an initial volume of 655 mL and an initial temperature of 295 K. What is its new temperature if volume is changed to 577 mL? Assume pressure and amount are held constant.
16. A gas has an initial volume of 14.98 L and an initial temperature of 238 K. What is its new temperature if volume is changed to 12.33 L? Assume pressure and amount are held constant.
17. A gas has an initial volume of 685 mL and an initial temperature of 29°C. What is its new temperature if volume is changed to 1.006 L? Assume pressure and amount are held constant.
1. A gas has an initial volume of 3.08 L and an initial temperature of −73°C. What is its new volume if temperature is changed to 104°C? Assume pressure and amount are held constant.
Answers
1. A gas law is a simple mathematical formula that allows one to predict the physical properties of a gas. The units of changing properties (volume, pressure, etc.) must be the same.
2.
3. pressure; volume
4.
5. amount of gas and temperature
6.
7. 2.62 atm
8.
9. 50.3 L
10.
11. 1.95 L
12.
13. 52.3 mL
14.
15. 260 K
16.
17. 444 K, or 171°C
6.4: Other Gas Laws
1. State Gay-Lussac’s law.
2. State Avogadro’s law.
3. Use Gay-Lussac’s law to determine the final pressure of a gas whose initial pressure is 602 torr, initial temperature is 356 K, and final temperature is 277 K. Assume volume and amount are held constant.
4. Use Gay-Lussac’s law to determine the final temperature of a gas whose initial pressure is 1.88 atm, initial temperature is 76.3 K, and final pressure is 6.29 atm. Assume volume and amount are held constant.
5. If 3.45 × 1022 atoms of Ar have a volume of 1.55 L at a certain temperature and pressure, what volume do 6.00 × 1023 atoms of Ar have at the same temperature and pressure?
6. If 5.55 × 1022 atoms of He occupy a volume of 2.06 L at 0°C at 1.00 atm pressure, what volume do 2.08 × 1023 atoms of He occupy under the same conditions?
7. Use Avogadro’s law to determine the final volume of a gas whose initial volume is 6.72 L, initial amount is 3.88 mol, and final amount is 6.10 mol. Assume pressure and temperature are held constant.
8. Use Avogadro’s law to determine the final amount of a gas whose initial volume is 885 mL, initial amount is 0.552 mol, and final volume is 1,477 mL. Assume pressure and temperature are held constant.
1. Use the combined gas law to complete this table. Assume that the amount remains constant in all cases.
V1 = P1 = T1 = V2 = P2 = T2 =
56.9 mL 334 torr 266 K 722 torr 334 K
0.976 L 2.33 atm 443 K 1.223 L 355 K
3.66 L 889 torr 23°C 2.19 L 739 torr
1. Use the combined gas law to complete this table. Assume that the amount remains constant in all cases.
V1 = P1 = T1 = V2 = P2 = T2 =
56.7 mL 1.07 atm −34°C 998 torr 375 K
3.49 L 338 torr 45°C 1,236 mL 392 K
2.09 mL 776 torr 45°C 0.461 mL 0.668 atm
1. A gas starts at the conditions 78.9 mL, 3.008 atm, and 56°C. Its conditions change to 35.6 mL and 2.55 atm. What is its final temperature?
2. The initial conditions of a sample of gas are 319 K, 3.087 L, and 591 torr. What is its final pressure if volume is changed to 2.222 L and temperature is changed to 299 K?
3. A gas starts with initial pressure of 7.11 atm, initial temperature of 66°C, and initial volume of 90.7 mL. If its conditions change to 33°C and 14.33 atm, what is its final volume?
4. A sample of gas doubles its pressure and doubles its absolute temperature. By what amount does the volume change?
Answers
1. The pressure of a gas is proportional to its absolute temperature.
2.
3. 468 torr
4.
5. 27.0 L
6.
1. 10.6 L
2.
3. V1 = P1 = T1 = V2 = P2 = T2 =
56.9 mL 334 torr 266 K 33.1 mL 722 torr 334 K
0.976 L 2.33 atm 443 K 1.223 L 1.49 atm 355 K
3.66 L 889 torr 23°C 2.19 L 739 torr 147 K, or −126°C
1. 126 K, or −147°C
2.
3. 40.6 mL
6.5: The Ideal Gas Law and Some Applications
1. What is the ideal gas law? What is the significance of R?
2. Why does R have different numerical values (see Table 6.6.1 "Values of the Ideal Gas Law Constant ")?
3. A sample of gas has a volume of 3.91 L, a temperature of 305 K, and a pressure of 2.09 atm. How many moles of gas are present?
4. A 3.88 mol sample of gas has a temperature of 28°C and a pressure of 885 torr. What is its volume?
5. A 0.0555 mol sample of Kr has a temperature of 188°C and a volume of 0.577 L. What pressure does it have?
6. If 1.000 mol of gas has a volume of 5.00 L and a pressure of 5.00 atm, what is its temperature?
7. A sample of 7.55 g of He has a volume of 5,520 mL and a temperature of 123°C. What is its pressure in torr?
8. A sample of 87.4 g of Cl2 has a temperature of −22°C and a pressure of 993 torr. What is its volume in milliliters?
9. A sample of Ne has a pressure of 0.772 atm and a volume of 18.95 L. If its temperature is 295 K, what mass is present in the sample?
10. A mercury lamp contains 0.0055 g of Hg vapor in a volume of 15.0 mL. If the operating temperature is 2,800 K, what is the pressure of the mercury vapor?
11. Oxygen is a product of the decomposition of mercury(II) oxide:
2HgO(s) → 2Hg(ℓ) + O2(g)
What volume of O2 is formed from the decomposition of 3.009 g of HgO if the gas has a pressure of 744 torr and a temperature of 122°C?
12. Lithium oxide is used to absorb carbon dioxide:
Li2O(s) + CO2(g) → Li2CO3(s)
What volume of CO2 can 6.77 g of Li2O absorb if the CO2 pressure is 3.5 × 10−4 atm and the temperature is 295 K?
13. What is the volume of 17.88 mol of Ar at STP?
14. How many moles are present in 334 L of H2 at STP?
15. How many liters, at STP, of CO2 are produced from 100.0 g of C8H18, the approximate formula of gasoline?
2C8H18(ℓ) + 25O2(g) → 16CO2(g) + 18H2O(ℓ)
1. How many liters, at STP, of O2 are required to burn 3.77 g of butane from a disposable lighter?
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(ℓ)
1. What is the density of each gas at STP?
1. He
2. Ne
3. Ar
4. Kr
2. What is the density of each gas at STP?
1. H2
2. O2
3. N2
3. What is the density of SF6 at 335 K and 788 torr?
4. What is the density of He at −200°C and 33.9 torr?
Answers
1. The ideal gas law is PV = nRT. R is the ideal gas law constant, which relates the other four variables.
2.
3. 0.327 mol
4.
5. 3.64 atm
6.
7. 8,440 torr
8.
9. 12.2 g
10.
11. 0.230 L
12.
13. 401 L
14.
15. 157 L
16.
1. 0.179 g/L
2. 0.901 g/L
3. 1.78 g/L
4. 3.74 g/L
17.
18. 5.51 g/L
6.6: Gas Mixtures
1. What is the total pressure of a gas mixture containing these partial pressures:
$P _{N_{2}}=0.78\, atm;\; P _{H_{2}}=0.33\, atm;\; P _{O_{2}}=1.59\, atm?$
1. What is the total pressure of a gas mixture containing these partial pressures: PNe = 312 torr, PHe = 799 torr, and PAr = 831 torr?
2. In a gas mixture of He and Ne, the total pressure is 335 torr and the partial pressure of He is 0.228 atm. What is the partial pressure of Ne?
3. In a gas mixture of O2 and N2, the total pressure is 2.66 atm and the partial pressure of O2 is 888 torr. What is the partial pressure of N2?
4. A 3.55 L container has a mixture of 56.7 g of Ar and 33.9 g of He at 33°C. What are the partial pressures of the gases and the total pressure inside the container?
5. A 772 mL container has a mixture of 2.99 g of H2 and 44.2 g of Xe at 388 K. What are the partial pressures of the gases and the total pressure inside the container?
6. A sample of O2 is collected over water in a 5.00 L container at 20°C. If the total pressure is 688 torr, how many moles of O2 are collected?
7. A sample of H2 is collected over water in a 3.55 L container at 50°C. If the total pressure is 445 torr, how many moles of H2 are collected?
8. A sample of CO is collected over water in a 25.00 L container at 5°C. If the total pressure is 0.112 atm, how many moles of CO are collected?
9. A sample of NO2 is collected over water in a 775 mL container at 25°C. If the total pressure is 0.990 atm, how many moles of NO2 are collected?
10. A sample of NO is collected over water in a 75.0 mL container at 25°C. If the total pressure is 0.495 atm, how many grams of NO are collected?
11. A sample of ClO2 is collected over water in a 0.800 L container at 15°C. If the total pressure is 1.002 atm, how many grams of ClO2 are collected?
12. Determine the mole fractions of each component when 44.5 g of He is mixed with 8.83 g of H2.
13. Determine the mole fractions of each component when 9.33 g of SO2 is mixed with 13.29 g of SO3.
14. In a container, 4.56 atm of F2 is combined with 2.66 atm of Cl2. What are the mole fractions of each component?
1. In a container, 77.3 atm of SiF4 are mixed with 33.9 atm of O2. What are the mole fractions of each component?
Answers
1. 2.70 atm
2.
3. 162 torr, or 0.213 atm
4.
5. PAr = 10.0 atm; PHe = 59.9 atm; Ptot = 69.9 atm
6.
7. 0.183 mol
8.
9. 0.113 mol
10.
1. 0.0440 g
2.
3. $\chi _{He}=0.718;\; \chi _{H_{2}}=0.282$
4.
5. $\chi _{F_{2}}=0.632;\; \chi _{Cl_{2}}=0.368$ | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/06%3A_Gases.txt |
8.1: Light
Q8.1.1
Describe the characteristics of a light wave.
Q8.1.1
Light has a wavelength and a frequency.
Q8.1.2
What is a characteristic of a particle of light?
Q8.1.3
What is the frequency of light if its wavelength is 7.33 × 10−5 m?
4.09 × 1012 s−1
Q8.1.4
What is the frequency of light if its wavelength is 1.226 m?
Q8.1.5
What is the frequency of light if its wavelength is 733 nm?
4.09 × 1014 s−1
Q8.1.6
What is the frequency of light if its wavelength is 8.528 cm?
Q8.1.7
What is the wavelength of light if its frequency is 8.19 × 1014 s−1?
3.66 × 10−7 m
Q8.1.8
What is the wavelength of light if its frequency is 3.66 × 106 s−1?
Q8.1.9
What is the wavelength of light if its frequency is 1.009 × 106 Hz?
297 m
Q8.1.10
What is the wavelength of light if its frequency is 3.79 × 10−3 Hz?
Q8.1.11
What is the energy of a photon if its frequency is 5.55 × 1013 s−1?
3.68 × 10−20 J
Q8.1.12
What is the energy of a photon if its frequency is 2.06 × 1018 s−1?
Q8.1.13
What is the energy of a photon if its wavelength is 5.88 × 10−4 m?
Q8.1.14
What is the energy of a photon if its wavelength is 1.888 × 102 m?
1.053 × 10−27 J
8.2: Quantum Numbers for Electrons
Q8.2.1
Differentiate between a continuous spectrum and a line spectrum.
Q8.2.1
A continuous spectrum is a range of light frequencies or wavelengths; a line spectrum shows only certain frequencies or wavelengths.
Q8.2.2
Under what circumstances is a continuous spectrum formed? Under what circumstances is a line spectrum formed?
Q8.2.3
What is the wavelength of light from the hydrogen atom spectrum when n = 3?
Q8.2.3
6.56 × 10−7 m, or 656 nm
Q8.2.4
What is the wavelength of light from the hydrogen atom spectrum when n = 5?
Q8.2.5
What are the restrictions on the principal quantum number?
Q8.2.5
The principal quantum number is restricted to being a positive whole number.
Q8.2.6
What are the restrictions on the angular momentum quantum number?
Q8.2.7
What are the restrictions on the magnetic quantum number?
Q8.2.7
The absolute value of m must be less than or equal to ℓ: |m| ≤ ℓ.
Q8.2.8
What are the restrictions on the spin quantum number?
Q8.2.9
What are the possible values for ℓ when n = 5?
Q8.2.9
ℓ can be 0, 1, 2, 3, or 4.
Q8.2.10
What are the possible values for ℓ when n = 1?
Q8.2.11
What are the possible values for m when ℓ = 3?
Q8.2.11
m can be −3, −2, −1, 0, 1, 2, or 3.
Q8.2.12
What are the possible values for m when ℓ = 6?
Q8.2.13
Describe the shape of an s orbital.
Q8.2.13
An s orbital is spherical in shape.
Q8.2.14
Describe the shape of a p orbital.
Q8.2.15
Which of these sets of quantum numbers is allowed? If it is not, explain why.
1. {5, 2, −1, −1/2}
2. {3, −1, −1, −1/2}
Q8.2.15
1. Because |m| must be less than ℓ, this set of quantum numbers is not allowed.
2. allowed
Q8.2.16
Which of these sets of quantum numbers is allowed? If it is not, explain why.
1. {4, 1, −2, +1/2}
2. {2, 0, 0, −1/2}
8.3: Organization of Electrons in Atoms
Q8.3.1
Give two possible sets of four quantum numbers for the electron in an H atom.
Q8.3.1
{1, 0, 0, 1/2} and [1, 0, 0, −1/2}
Q8.3.2
Give the possible sets of four quantum numbers for the electrons in a Li atom.
Q8.3.3
How many subshells are completely filled with electrons for Na? How many subshells are unfilled?
Q8.3.3
Three subshells (1s, 2s, 2p) are completely filled, and one shell (3s) is partially filled.
Q8.3.4
How many subshells are completely filled with electrons for Mg? How many subshells are unfilled?
Q8.3.5
What is the maximum number of electrons in the entire n = 2 shell?
8 electrons
Q8.3.6
What is the maximum number of electrons in the entire n = 4 shell?
Q8.3.7
Write the complete electron configuration for each atom.
1. Si, 14 electrons
2. Sc, 21 electrons
Q8.3.7
1. 1s22s22p63s23p2
2. 1s22s22p63s23p64s23d1
Q8.3.8
Write the complete electron configuration for each atom.
1. Br, 35 electrons
2. Be, 4 electrons
Q8.3.9
Write the complete electron configuration for each atom.
1. Cd, 48 electrons
2. Mg, 12 electrons
Q8.3.9
1. 1s22s22p63s23p64s23d104p65s24d10
2. 1s22s22p63s2
Q8.3.10
Write the complete electron configuration for each atom.
1. Cs, 55 electrons
2. Ar, 18 electrons
Q8.3.11
Write the abbreviated electron configuration for each atom in Exercise 7.
1. [Ne]3s23p2
2. [Ar]4s23d1
Q8.3.12
Write the abbreviated electron configuration for each atom in Exercise 8.
Q8.3.13
Write the abbreviated electron configuration for each atom in Exercise 9.
1. [Kr]5s24d10
2. [Ne]3s2
Q8.3.14
Write the abbreviated electron configuration for each atom in Exercise 10.
8.4: Electronic Structure and the Periodic Table
Q8.4.1
Where on the periodic table are s subshells being occupied by electrons?
Q8.4.1
the first two columns
Q8.4.2
Where on the periodic table are d subshells being occupied by electrons?
Q8.4.3
In what block is Ra found?
the s block
Q8.4.4
In what block is Br found?
Q8.4.5
What are the valence shell electron configurations of the elements in the second column of the periodic table?
ns2
Q8.4.6
What are the valence shell electron configurations of the elements in the next-to-last column of the periodic table?
Q8.4.7
What are the valence shell electron configurations of the elements in the first column of the p block?
ns2np1
Q8.4.8
What are the valence shell electron configurations of the elements in the last column of the p block?
Q8.4.9
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. Sr
2. S
Q8.4.9
1. 1s22s22p63s23p64s23d104p65s2
2. 1s22s22p63s23p4
Q8.4.10
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. Fe
2. Ba
Q8.4.11
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. V
2. Ar
Q8.4.11
1. 1s22s22p63s23p64s23d3
2. 1s22s22p63s23p6
Q8.4.12
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. Cl
2. K
Q8.4.13
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. Ge
2. C
Q8.4.13
1. 1s22s22p63s23p64s23d104p2
2. 1s22s22p2
Q8.4.14
From the element’s position on the periodic table, predict the electron configuration of each atom.
1. Mg
2. I
8.5: Periodic Trends
Q8.5.1
Write a chemical equation with an IE energy change.
Q8.5.1
Na(g) → Na+(g) + e ΔH = IE (answers will vary)
Q8.5.2
Write a chemical equation with an EA energy change.
Q8.5.3
State the trends in atomic radii as you go across and down the periodic table.
Q8.5.3
As you go across, atomic radii decrease; as you go down, atomic radii increase.
Q8.5.4
State the trends in IE as you go across and down the periodic table.
Q8.5.5
Which atom of each pair is larger?
1. Na or Cs
2. N or Bi
1. Cs
2. Bi
Q8.5.6
Which atom of each pair is larger?
1. C or Ge
2. Be or Ba
Q8.5.7
Which atom of each pair is larger?
1. K or Cl
2. Ba or Bi
1. K
2. Ba
Q8.5.8
Which atom of each pair is larger?
1. Si or S
2. H or He
Q8.5.9
Which atom has the higher IE?
1. Na or S
2. Ge or Br
1. S
2. Br
Q8.5.10
Which atom has the higher IE?
1. C or Ne
2. Rb or I
Q8.5.11
Which atom has the higher IE?
1. Li or Cs
2. Se or O
1. Li
2. O
Q8.5.12
Which atom has the higher IE?
1. Al or Ga
2. F or I
Q8.5.13
A third-row element has the following successive IEs: 738; 1,450; 7,734; and 10,550 kJ/mol. Identify the element.
Mg
Q8.5.14
A third-row element has the following successive IEs: 1,012; 1,903; 2,912; 4,940; 6,270; and 21,300 kJ/mol. Identify the element.
Q8.5.15
For which successive IE is there a large jump in IE for Ca?
Q8.5.15
The third IE shows a large jump in Ca.
Q8.5.16
For which successive IE is there a large jump in IE for Al?
Q8.5.17
Which atom has the greater magnitude of EA?
1. C or F
2. Al or Cl
1. F
2. Cl
Q8.5.18
Which atom has the greater magnitude of EA?
1. K or Br
2. Mg or S
QExtra.1
What is the frequency of light if its wavelength is 1.00 m?
3.00 × 108 s−1
QExtra.2
What is the wavelength of light if its frequency is 1.00 s−1?
QExtra.3
What is the energy of a photon if its wavelength is 1.00 meter?
1.99 × 10−22 J
QExtra.4
What is the energy of a photon if its frequency is 1.00 s−1?
QExtra.5
If visible light is defined by the wavelength limits of 400 nm and 700 nm, what is the energy range for visible light photons?
SExtra.5
4.97 × 10−19 J to 2.84 × 10−19 J
QExtra.6
Domestic microwave ovens use microwaves that have a wavelength of 122 mm. What is the energy of one photon of this microwave?
QExtra.7
Use the equation for the wavelengths of the lines of light in the H atom spectrum to calculate the wavelength of light emitted when n is 7 and 8.
SExtra.7
3.97 × 10−7 m and 3.89 × 10−7 m, respectively
QExtra.8
Use the equation for the wavelengths of the lines of light in the H atom spectrum to calculate the wavelengths of light emitted when n is 5 and 6.
QExtra.9
Make a table of all the possible values of the four quantum numbers when the principal quantum number n = 5.
SExtra.9
n m ms
5 0 0 1/2 or −1/2
5 1 −1, 0, 1 1/2 or −1/2
5 2 −2, −1, 0, 1, 2 1/2 or −1/2
5 3 −3, −2, −1, 0, 1, 2, 3 1/2 or −1/2
5 4 −4, −3, −2, −1, 0, 1, 2, 3, 4 1/2 or −1/2
QExtra.10
Make a table of all the possible values of m and ms when ℓ = 4. What is the lowest value of the principal quantum number for this to occur?
1. Predict the electron configurations of Sc through Zn.
2. From a source of actual electron configurations, determine how many exceptions there are from your predictions in part a.
SExtra.10
1. The electron configurations are predicted to end in 3d1, 3d2, 3d3, 3d4, 3d5, 3d6, 3d7, 3d8, 3d9, and 3d10.
2. Cr and Cu are exceptions.
QExtra.11
1. Predict the electron configurations of Ga through Kr.
2. From a source of actual electron configurations, determine how many exceptions there are from your predictions in part a.
QExtra.12
Recently, Russian chemists reported experimental evidence of element 117. Use the periodic table to predict its valence shell electron configuration.
SExtra.12
Element 117’s valence shell electron configuration should be 7s27p5.
QExtra.13
Bi (atomic number 83) is used in some stomach discomfort relievers. Using its place on the periodic table, predict its valence shell electron configuration.
QExtra.14
Which atom has a higher ionization energy (IE), O or P?
O
QExtra.15
Which atom has a higher IE, F or As?
QExtra.16
Which atom has a smaller radius, As or Cl?
Cl
QExtra.17
Which atom has a smaller radius, K or F?
QExtra.18
How many IEs does an H atom have? Write the chemical reactions for the successive ionizations.
SExtra.18
H has only one IE: H → H+ + e
QExtra.19
How many IEs does a Be atom have? Write the chemical reactions for the successive ionizations.
QExtra.20
Based on what you know of electrical charges, do you expect Na+ to be larger or smaller than Na?
smaller
QExtra.21
Based on what you know of electrical charges, do you expect Cl to be larger or smaller than Cl? | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/08%3A_Electronic_Structure.txt |
9.2: Lewis Electron Dot Diagrams
1. Explain why the first two dots in a Lewis electron dot diagram are drawn on the same side of the atomic symbol.
2. Is it necessary for the first dot around an atomic symbol to go on a particular side of the atomic symbol?
3. What column of the periodic table has Lewis electron dot diagrams with two electrons?
4. What column of the periodic table has Lewis electron dot diagrams that have six electrons in them?
5. Draw the Lewis electron dot diagram for each element.
1. strontium
2. silicon
6. Draw the Lewis electron dot diagram for each element.
1. krypton
2. sulfur
7. Draw the Lewis electron dot diagram for each element.
1. titanium
2. phosphorus
8. Draw the Lewis electron dot diagram for each element.
1. bromine
2. gallium
9. Draw the Lewis electron dot diagram for each ion.
1. Mg2+
2. S2−
10. Draw the Lewis electron dot diagram for each ion.
1. In+
2. Br
11. Draw the Lewis electron dot diagram for each ion.
1. Fe2+
2. N3−
12. Draw the Lewis electron dot diagram for each ion.
1. H+
2. H
Answers
1. The first two electrons in a valence shell are s electrons, which are paired.
2. the second column of the periodic table
1. Mg2+
1. Fe2+
9.3: Electron Transfer - Ionic Bonds
1. Comment on the possible formation of the K2+ ion. Why is its formation unlikely?
2. Comment on the possible formation of the Cl2− ion. Why is its formation unlikely?
3. How many electrons does a Ba atom have to lose to have a complete octet in its valence shell?
4. How many electrons does a Pb atom have to lose to have a complete octet in its valence shell?
5. How many electrons does an Se atom have to gain to have a complete octet in its valence shell?
6. How many electrons does an N atom have to gain to have a complete octet in its valence shell?
7. With arrows, illustrate the transfer of electrons to form potassium chloride from K atoms and Cl atoms.
8. With arrows, illustrate the transfer of electrons to form magnesium sulfide from Mg atoms and S atoms.
9. With arrows, illustrate the transfer of electrons to form scandium fluoride from Sc atoms and F atoms.
10. With arrows, illustrate the transfer of electrons to form rubidium phosphide from Rb atoms and P atoms.
11. Which ionic compound has the higher lattice energy—KI or MgO? Why?
12. Which ionic compound has the higher lattice energy—KI or LiF? Why?
1. Which ionic compound has the higher lattice energy—BaS or MgO? Why?
Answers
1. The K2+ ion is unlikely to form because the K+ ion already satisfies the octet rule and is rather stable.
2. two
3. two
4. MgO because the ions have a higher magnitude charge
5. MgO because the ions are smaller
9.4: Covalent Bonds
1. How many electrons will be in the valence shell of H atoms when it makes a covalent bond?
2. How many electrons will be in the valence shell of non-H atoms when they make covalent bonds?
3. What is the Lewis electron dot diagram of I2? Circle the electrons around each atom to verify that each valence shell is filled.
4. What is the Lewis electron dot diagram of H2S? Circle the electrons around each atom to verify that each valence shell is filled.
5. What is the Lewis electron dot diagram of NCl3? Circle the electrons around each atom to verify that each valence shell is filled.
6. What is the Lewis electron dot diagram of SiF4? Circle the electrons around each atom to verify that each valence shell is filled.
7. Draw the Lewis electron dot diagram for each substance.
1. SF2
2. BH4
8. Draw the Lewis electron dot diagram for each substance.
1. PI3
2. OH
9. Draw the Lewis electron dot diagram for each substance.
1. GeH4
2. ClF
10. Draw the Lewis electron dot diagram for each substance.
1. AsF3
2. NH4+
11. Draw the Lewis electron dot diagram for each substance. Double or triple bonds may be needed.
1. SiO2
2. C2H4 (assume two central atoms)
12. Draw the Lewis electron dot diagram for each substance. Double or triple bonds may be needed.
1. CN
2. C2Cl2 (assume two central atoms)
13. Draw the Lewis electron dot diagram for each substance. Double or triple bonds may be needed.
1. CS2
2. NH2CONH2 (assume that the N and C atoms are the central atoms)
14. Draw the Lewis electron dot diagram for each substance. Double or triple bonds may be needed.
1. POCl
2. HCOOH (assume that the C atom and one O atom are the central atoms)
Answers
1. two
9.5: Other Aspects of Covalent Bonds
1. Give an example of a nonpolar covalent bond. How do you know it is nonpolar?
2. Give an example of a polar covalent bond. How do you know it is polar?
3. How do you know which side of a polar bond has the partial negative charge? Identify the negatively charged side of each polar bond.
1. H–Cl
2. H–S
4. How do you know which side of a polar bond has the partial positive charge? Identify the positively charged side of each polar bond.
1. H–Cl
2. N-F
5. Label the bond between the given atoms as nonpolar covalent, slightly polar covalent, definitely polar covalent, or likely ionic.
1. H and C
2. C and F
3. K and F
6. Label the bond between the given atoms as nonpolar covalent, slightly polar covalent, definitely polar covalent, or likely ionic.
1. S and Cl
2. P and O
3. Cs and O
7. Which covalent bond is stronger—a C–C bond or a C–H bond?
8. Which covalent bond is stronger—an O–O double bond or an N–N double bond?
9. Estimate the enthalpy change for this reaction: N2 + 3H2 → 2NH3 .Start by drawing the Lewis electron dot diagrams for each substance.
10. Estimate the enthalpy change for this reaction. Start by drawing the Lewis electron dot diagrams for each substance: HN=NH + 2H2 → 2NH3
11. Estimate the enthalpy change for this reaction. Start by drawing the Lewis electron dot diagrams for each substance: CH4 + 2O2 → CO2 + 2H2O
12. Estimate the enthalpy change for this reaction. Start by drawing the Lewis electron dot diagrams for each substance: 4NH3 + 3O2 → 2N2 + 6H2O
Answers
1. H–H; it is nonpolar because the two atoms have the same electronegativities (answers will vary).
1. Cl side
2. S side
1. slightly polar covalent
2. definitely polar covalent
3. likely ionic
2. C–H bond
3. −80 kJ
4. −798 kJ
9.6: Violations of the Octet Rule
1. Why can an odd-electron molecule not satisfy the octet rule?
2. Why can an atom in the second row of the periodic table not form expanded valence shell molecules?
3. Draw an acceptable Lewis electron dot diagram for these molecules that violate the octet rule.
1. NO2
2. XeF4
4. Draw an acceptable Lewis electron dot diagram for these molecules that violate the octet rule.
1. BCl3
2. ClO2
5. Draw an acceptable Lewis electron dot diagram for these molecules that violate the octet rule.
1. POF3
2. ClF3
6. Draw an acceptable Lewis electron dot diagram for these molecules that violate the octet rule.
1. SF4
2. BeH2
Answers
1. There is no way all electrons can be paired if there are an odd number of them.
9.7: Molecular Shapes
1. What is the basic premise behind VSEPR?
2. What is the difference between the electron group geometry and the molecular geometry?
3. Identify the electron group geometry and the molecular geometry of each molecule.
1. H2S
2. POCl3
4. Identify the electron group geometry and the molecular geometry of each molecule.
1. CS2
2. H2S
5. Identify the electron group geometry and the molecular geometry of each molecule.
1. HCN
2. CCl4
6. Identify the electron group geometry and the molecular geometry of each molecule.
1. BI3
2. PH3
7. What is the geometry of each species?
1. CN
2. PO43−
8. What is the geometry of each species?
1. PO33−
2. NO3
9. What is the geometry of each species?
1. COF2
2. C2Cl2 (both C atoms are central atoms and are bonded to each other)
10. What is the geometry of each species?
1. CO32−
2. N2H4 (both N atoms are central atoms and are bonded to each other)
Answers
1. Electron pairs repel each other.
1. electron group geometry: tetrahedral; molecular geometry: bent
2. electron group geometry: tetrahedral; molecular geometry: tetrahedral
1. electron group geometry: linear; molecular geometry: linear
2. electron group geometry: tetrahedral; molecular geometry: tetrahedral
1. linear
2. tetrahedral
1. trigonal planar
2. linear and linear about each central atom
9.8 Additional Exercises
1. Explain why iron and copper have the same Lewis electron dot diagram when they have different numbers of electrons.
2. Name two ions with the same Lewis electron dot diagram as the Cl ion.
3. Based on the known trends, what ionic compound from the first column of the periodic table and the next-to-last column of the periodic table should have the highest lattice energy?
4. Based on the known trends, what ionic compound from the first column of the periodic table and the next-to-last column of the periodic table should have the lowest lattice energy?
5. P2 is not a stable form of phosphorus, but if it were, what would be its likely Lewis electron dot diagram?
6. Se2 is not a stable form of selenium, but if it were, what would be its likely Lewis electron dot diagram?
7. What are the Lewis electron dot diagrams of SO2, SO3, and SO42−?
8. What are the Lewis electron dot diagrams of PO33− and PO43−?
9. Which bond do you expect to be more polar—an O–H bond or an N–H bond?
10. Which bond do you expect to be more polar—an O–F bond or an S–O bond?
11. Use bond energies to estimate the energy change of this reaction.
C3H8 + 5O2 → 3CO2 + 4H2O
12. Use bond energies to estimate the energy change of this reaction.
N2H4 + O2 → N2 + 2H2O
13. Ethylene (C2H4) has two central atoms. Determine the geometry around each central atom and the shape of the overall molecule.
14. Hydrogen peroxide (H2O2) has two central atoms. Determine the geometry around each central atom and the shape of the overall molecule.
Answers
1. Iron has d electrons that typically are not shown on Lewis electron dot diagrams.
2. LiF
3. It would be like N2:
4. an O–H bond
5. −2,000 kJ
6. trigonal planar about both central C atoms | textbooks/chem/Introductory_Chemistry/Exercises%3A_General_Organic_and_Biological_Chemistry/Exercises%3A_Ball_et_al._(Beginning_Chemistry)/09%3A_Chemical_Bonds.txt |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.