Question

59 g of an amide obtained from a carboxylic acid, RCOOH, upon heating with alkali liberated 17 g of ammonia. Atomic masses of C, H, N and O are 12, 1, 14 and 16 respectively. The acid is 

(a) Formic acid 

(b) Acetic acid 

(c) Propionic acid 

(d) Benzoic acid

Answer 1

(b) Acetic acid 

\(RCOOH \longrightarrow \underset {59\,g}{RCONH_2}\xrightarrow {OH^-} \underset {17\,g}{NH_3}\)

Since 17 g of NH₃ is liberated from 59 of acid amide; the amide has molecular mass of 59, i.e. RCONH₂ = 59 

R + 12 + 16 + 14 + 2 = 59; 

R + 44 = 59 

∴ R = 15

Hence R is CH₃ group and thus acid is CH₃COOH (acetic acid).