Question

Distinguish between following:
Benzaldehyde and benzoic acid

Answer 1

Benzaldehyde and benzoic acid both are aromatic compounds, the difference is the group attached to the benzene ring. The functional group for aldehyde is –CHO and the functional group of carboxylic acid is –COOH.

Complete answer:
Benzaldehyde: Benzaldehyde is the simplest aromatic aldehyde which consists of a benzene ring joined with a single formyl group. The other name for benzoic acid is benzenedicarboxaldehyde. By the suffix itself it can be recognized that it is an aldehydic compound.
The structure of benzaldehyde is shown below.

Benzoic acid: Benzoic acid is the simplest aromatic carboxylic acid which consists of a benzene ring joined with a single carboxylic group. The other name for benzoic acid is carboxybenzene. By the suffix –oic itself it can be recognized that it is a carboxylic compound.
The structure of benzoic acid is shown below.

The benzaldehyde can be distinguished from benzoic acid by a sodium bicarbonate test. Benzoic acid is an acid, therefore on reacting with a base sodium bicarbonate it forms a sodium salt of benzoic acid by releasing carbon dioxide gas.
The reaction is shown below.

On the other hand, benzaldehyde does not give any reaction with sodium bicarbonate.

Note:
The other test used to distinguish benzaldehyde and benzoic acid is reacting with Tollen’s reagent also known as silver mirror test. Benzaldehyde reacts with ammoniacal solution of silver nitrate to generate silver mirror.