from loss of from acetic acid. The name "acetate" can also refer to a salt containing this anion, or an ester of acetic acid. Properties Acidity The hydrogen centre in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can separate from the molecule by ionization: Because of this release of the proton (), acetic acid has acidic character. Acetic acid is a weak monoprotic acid. In aqueous solution, it has a pKa value of 4.76. Its conjugate base is acetate (). A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated. However, in very dilute (< 10−6 M) solution acetic acid is >90% dissociated. Structure In solid acetic acid, the molecules form chains, individual molecules being interconnected by hydrogen bonds. In the vapour at , dimers can be detected. Dimers also occur in the liquid phase in dilute solutions in non-hydrogen-bonding solvents, and a certain extent in pure acetic acid, but are disrupted by hydrogen-bonding solvents. The dissociation enthalpy of the dimer is estimated at 65.0–66.0 kJ/mol, and the dissociation entropy at 154–157 J mol−1 K−1. Other carboxylic acids engage in similar intermolecular hydrogen bonding interactions. Solvent properties Liquid acetic acid is a hydrophilic (polar) protic solvent, similar to ethanol and water. With a relative static permittivity (dielectric constant) of 6.2, it dissolves not only polar compounds such as inorganic salts and sugars, but also non-polar compounds such as oils as well as polar solutes. It is miscible with polar and non-polar solvents such as water, chloroform, and hexane. With higher alkanes (starting with octane), acetic acid is not miscible at all compositions, and solubility of acetic acid in alkanes declines with longer n-alkanes. The solvent and miscibility properties of acetic acid make it a useful industrial chemical, for example, as a solvent in the production of dimethyl terephthalate. Biochemistry At physiological pHs, acetic acid is usually fully ionised to acetate. The acetyl group, formally derived from acetic acid, is fundamental to all forms of life. When bound to coenzyme A, it is central to the metabolism of carbohydrates and fats. Unlike longer-chain carboxylic acids (the fatty acids), acetic acid does not occur in natural triglycerides. However, the artificial triglyceride triacetin (glycerine triacetate) is a common food additive and is found in cosmetics and topical medicines. Acetic acid is produced and