Question

(a) Write the products formed when $C{H}_{3}CHO$ reacts with the following reagents :

(i) HCN

(ii) $H_{2}N-OH$

(iii) $C{H}_{3}CHO$ in the presence of dilute NaOH

(b) Give simple chemical tests to distinguish between the following pain of compounds :

(i) Benzoic acid and Phenol

(ii) Propanal and Propanone

Answer 1

(b) $NaHC{O}_3$ test: Benzoic acid decomposes $NaHC{O}_3$ to evolve $C{O}_2$ but phenol does not.

$\underset{\text{Benzoic acid}}{C_6{H}_5-COOH}+NaHC{O}_3\to C_6{H}_{5}COONa+C{O}_2\uparrow +H_{2}O$

$\underset{\text{Phenol}}{C_6{H}_{5}OH}\stackrel{NaHC{O}_3}{\to }$ No evolution of $C{O}_2$

(ii) Tollens' reagent test : Propanal reduces Tollen's reagent to shining silver mirror but propanone does not.

$\underset{C{H}_{3}C{H}_{2}CHO}{\text{Propanal}}+2\left[Ag\right(N{H}_3{)}_2]+3O{H}^{-}$

$\to C{H}_{3}C{H}_{2}CO{O}^{-}+\underset{\text{Silver mirror}}{2Ag}\downarrow +4N{H}_3+2H_{2}0$

$\stackrel{C{H}_{3}COC{H}_3}{\text{Propanone}}\stackrel{\text{Tollens's reagent}}{\to }$ No silver mirror