Physical Properties of carboxylic acids

Physical Properties of carboxylic acids.

i) Aliphatic carboxylic acid upto nine carbon atoms are colour less liquids with pungent odour. The higher members are odourless wax like solids.

ii) Carboxylic acids have higher boiling point than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more association of carboxylic acid molecules through intermolecular hydrogen bonding.

Inter molecular hydrogen bonding

In fact, most of the carboxylic acids exist as dimer in its vapour phase.

iii) Lower aliphatic carboxylic acids (up to four carbon) are miscible with water due to the formation of hydrogen bonds with water. Higher carboxylic acid are insoluble in water due to increased hydrophobic interaction of hydrocarbon part. The simplest aromatic carboxylic acid, benzoic acid is insoluble in water.

iv) Vinegar is 6 to 8% solution of acetic acid in water. Pure acetic acid is called glacial acetic acid. Because it forms ice like crystal when cooled. When aqueous acetic acid is cooled at 289.5 K, acetic acid solidifies and forms ice like crystals, where as water remains in liquid state and removed by filtration. This process is repeated to obtain glacial acetic acid.