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

(i) Benzaldehyde and Benzoic acid

(ii) Propanal and Propanone 

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 silver 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 positive iodoform test, as it contains CH₃CO group, whereas propanal does not give iodoform test. The reaction is as follows: