Physical properties of carboxylic acids

  • Physical state: The first three members (upto 3 carbon atoms) are colourless, pungent smelling liquids. The next six members are oily liquids having unpleasant smell. The higher members are colourless waxy solids.
  • Solubility: The acids are polar. The lower members of the aliphatic carboxylic acid family (upto C-4) are highly soluble in water. The solubility decreases with the increase in the size of the alkyl group. All carboxylic acids are soluble in alcohol, ether and benzene etc. Benzoic acid (the simplest aromatic carboxylic acid) is sparingly soluble in cold water, and the solubility increases with increases in temperature. Benzoic acid is soluble in alcohol, ether etc.
  • Boiling Point: The boiling points of the carboxylic acids increases with molar mass, i.e. an acid containing larger number of C atoms has higher boiling point.

Carboxylic acids have higher boiling point than alcohols of comparable molecular mass.