Question

Give simple chemical tests to distinguish between the following pair of compounds:

Benzaldehyde and Benzoic acid

Give simple chemical test to distinguish between Benzoic acid and Benzaldehyde.

Answer 1

Through sodium bicarbonate:

Benzaldehyde does not react with sodium bicarbonate. However, benzoic acid will produce brisk effervescence in reaction with sodium bicarbonate, as shown in the given reaction:

\[\ce{C6H5COOH + NaHCO3 -> C6H5COO^-Na+ + CO2 ↑ + H2O}\]

\[\ce{C6H5CHO ->[NaHCO3 solution] No effervescene}\]

Through Tollen's reagent:

Benzaldehyde reacts with an ammonia solution of silver nitrate to form a silver mirror.

\[\ce{C6H5CHO + 2[Ag(NH3)2]+ + 3OH^- -> C6H5COO^- + 2Ag + 2H2O + 4NH3}\]

However, no such reaction is given by benzoic acid.

Answer 2

Benzoic acid reacts with ethanol in the presence of dilute sulphuric acid to form sweet-smelling ester Ethyl benzoate. This reaction is not given by benzaldehyde.