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Sodium

Sodium is the 7th most abundant element by weight found in earth’s crust.

Atomic Number: 11

Atomic Weight: 23

Electronic Configuration: 1s2 2s2 sp6 3s1

Valency : 1

Minerals of sodium

Chile salt petre

NaNO3

Glauber’s salt

Na2SO4.10H2O

Borax or sodium borate

Na2B4O7.10H2O

Rock salt

NaCl

Albite or soda feldspar

Na2O.Al2O3.6SiO2 or NaAlSi3O8

Extraction of sodium

Sodium is extracted by Down’s process through electrolysis of fused sodium chloride.

In this method, sodium is obtained by the electrolysis of mixture of sodium chloride (40%) and calcium chloride (60%) in fused state. The function of calcium chloride is to lower the operating temperature from 1080 K (m.pt. of NaCl) to about 850 K. The main reason for lowering the temperature are:

The melting point of sodium chloride is very high it is very difficult to maintain it in the molten state during electrolysis.

Sodium is considerably volatile at the temperature needed for the electrolysis and therefore, a part of the metal produced is vapourised.

Molten sodium gets dispersed in molten chloride to form a metallic fog (colloidal solution) at high temperature.

Both sodium and chlorine, the two products of the electrolysis, have a corrosive action on the material of the vessel employed for the electrolysis at such a high temperature.

The cell consists of a steel tank lined with fire bricks. A circular graphite anode is placed in the centre of the cell which is surrounded by a cylindrical iron cathode. The anode and cathode are separated by a steel gauge cylinder through which molten sodium chloride can pass but molten sodium cannot. The purpose of using steel gauge is to keep sodium separate from chlorine which would otherwise react with chlorine. The anode is covered by a dome – shaped steel hood which provides the out – let for the escape of chlorine gas. The molten metal liberated at the cathode moves up and flow into the receiver containing kerosene oil. The following reactions take place:

NaCl → Na++Cl- (Ionization)

At Cathode: Na+ + e- → Na

At ande: Cl- + Cl- → Cl2

Properties of Sodium

Sodium is a soft white metal with silver – like lustre, and can also be obtained in tetragonal crystalline form. It dissolves in liquid ammonia, giving intense blue solution. The colloidal sodium in ether medium can be obtained by Svedbergls method by suspending the metal in ether and passing an oscillatory discharge from Letden jar arrangement. The colour of colloid is violet. The metal burnes in air to form Na2O and Na2O2. When heated with mercury, it forms an amulgam of varying compositions, NaHg, NaHg4 etc. In the organic qualititative work, the fusion with sodium metal is a common process. It is soluble in alcohol, forming C2H5ONa and is very much used as such. When sodium is heated with ammonia gas, sodamide is formed

2NH3 + 2Na 2NaNH2 +H2

It combines with a number of non-metals on heating

2Na + Cl2 →  2NaCl

2Na + S →  2Na2S

2Na + H2 →  2NaH

With water, a violent action takes place and hydrogen gas is evolved.

2Na + 2H2O→  2NaOH + H2

It displaces hydrogen from acids

2HCl + 2Na → 2NaCl + H2

It acts as a reducing agents because of its ease with which it can lose its valence electron.

Al2O3 + 6Na → 2Al + 3Na2O

SiO2 + 4Na → Si + 2Na2O

CO2 + 4Na → 2Na2CO3 + C

Uses of Sodium:

Following are some of the many uses of sodium metal

In the manufacturing of sodium peroxide, sodium cyanide and sodium methoxide

As a reducing agent in the extraction of boron and silicon in the form of sodium amalgam.

As a reagent in organic analysis.

Because of its high thermal conductivity, it is employed for filling valves of aircraft engines.

In the production of rich yellow light by sealing it in electric bulb containing argon or mercury vapour.

In organic reactions such as condensation, polymerization, isomerization and preparation of metal alkyls and aryls.

Sodium Hydroxide/ Caustic Soda (NaOH)

Caustic soda is an article of great commercial importance and, therefore, is prepared on a large scale.

Electreolystic Process for perparation of NaOH:

This involves the electrolysis  of a solution of sodium chloride. The solution contains sodium, chloride, hydrogen and hydroxide ions. In passing the current sodium and hydrogen ions move toward the cathode but hydrogen ions are able to accept the electrons more easily than sodium ions, with the result that hydrogen gas is liberated with the decomposition of more water molecules while sodium ions remain in the solution. At anode chloride ions give up electrons in preference to hydroxide ions and thus chlorine gas is liberated there.

At Anode

At cathode

Overall reaction

2H2O + 2e → H2 + OH-

2Cl- → Cl2 + 2e

2Na++Cl-+H2O → 2Na++OH- +H2 +Cl2

The solution on electrolysis , therefore , becomes richer in sodium hydroxide

When calcium hydroxide is added to sodium carbonate solution, calcium carbonate is precipitated, leaving sodium hydroxide in solution

Na2CO3 + Ca(OH)2 → CaCO3 ¯ + 2NaOH

Properties:

NaOH is stable towards heat but is reduced to metal when heated with carbon

2NaOH + 2C →  2Na +2CO + H2

FeCl3 + 3NaOH →  Fe(OH)3 + 3NaCl

NH4Cl + NaOH → NaCl + NH3 (pungent smell) + H2O

HgCl2 + 2NaOH → HgO (yellow powder) + 2NaCl + H2O

Zn(OH)2 ¯ + 2NaOH → Na2ZnO2 + 2H2O

Al2O3 ¯ + 2NaOH → 2NaAlO2 + H2O

SiO2 + 2NaOH→ Na2SiO3 + H2O

3P + 3 NaOH +3H2O→ PH3 + 3NaH2PO2

2Al + 2 NaOH + 2H2O → 3H2 + 2NaAlO2

Question 1: Valency of Sodium metal is

a. 1

b. 2

c. 3

d. 4

Question 2: Which of the following compounds is not an ore of sodium metal?

a. Glauber’s salt

b. Rock salt

c. Albite

d. Lignite

Question 3: Which gas is produced at anode during electrolysis of sodium chloride?

a. Hydrogen

b. Chlorine

c. Oxygen

d. Hydrogen chloride

Question 4: Zn(OH)2¯ + 2NaOH → Na2ZnO2 + ?

a. H2

b. H2O

c. Na2O

d. NaOH

Q.1

Q.2

Q.3

Q.4

a

d

a

b

Related Resources

Look here for past year papers of IIT JEE  to get an idea about the type of questions asked in exam

You should also refer to ther syllabus of chemistry for IIT JEE which would help you to plan your study
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