(a) Write the products of the following reactions:
(ii) 2C6H5CHO + Conc.NaOH →
(iii) CH3COOH + Cl2/P →
(b) Give simple chemical tests to distinguish between the following pairs of compounds:
(i) Benzaldehyde and benzoic acid
(ii) Propanal and propanone

(a) :
(i) Ref. image
(ii) 2C6H5CHO + conc.NaOH → C6H5CH2OH + C6H5COONa
(iii) CH3COOH + Cl2/P → ClCH2COOH
(b) :
(i) Benzaldehyde and Benzoic acid
Test -1: Through sodium bicarbonate
Benzaldehyde does not react with sodium bicarbonate. However, benzoic acid will produce brisk effervescence on reaction with sodium bicarbonate as shown in the given reaction:
C6H5COOH + NaHCO3 → C6H5COONa + H2O + CO2
Test -2: Through Tollen's reagent
Benzaldehyde reacts with an ammoniacal solution of sliver nitrate to form a silver mirror.
C6H5CHO + 2[Ag(NH3)2] + 3OH⁻ → C6H5COO⁻ + 2Ag + 2H2O + 4NH3
However, no such reaction is given by benzoic acid
(ii) Test - 1: Iodoform Test
Propanone gives a positive iodoform test, as it contains CH3CO group, whereas propanal does not give an iodoform test. The reaction is as follows:
CH3COCH3 (propanone) + 3I2 + 4NaOH → CHI3 (iodoform (yellow)) + 3NaI + CH3COONa + 3H2O
CH3CH2CHO (Propanal) + 3I2 + 4NaOH → No reaction