Question

Write chemical tests to distinguish between the following pairs.
$a.$ Pent$-2-$one and pent$-3-$one
$b.$ Propanal and benzaldehyde
$c.$ Ethanol and ethanoic acid.

Answer 1

(i) Distinguish between pentane-z-one and pentane-z-one.

Penta-z-one and pentane-z-one can be distinguished by Iodoform test.

Pentan-z-one reacts to Indoform test as pentane-z-one is a methyl ketone.

Pentan-z-one does not react to Iodoform test

(ii) Distinguish between propanal and benzaldehyde propanal and benzaldehyde both being aldehydes reacts to toll ends test but gives different products.

Propanal reduces Tollen's reagent and becomes propanoate in and leaving silver mirror.

${CH}_3{CH}_2+2{\left[Ag{\left({NH}_3\right)}_2\right]}^{+}+{3OH}^{-}\to {CH}_3{CH}_2{COO}^{-}+Ag\downarrow +{4NH}_3+2H_{2}O$

Propanal Tollens reagent propanateion silver mirror ammonia water

Benzaldehyde reduces Tollen's reagent and becomes Benzoate ion by giving a red brown precipitate of ${Cu}_{2}O$.

$C_6{H}_{5}CHO+2{\left[Ag{\left({NH}_3\right)}_2\right]}^{+}+3{OH}^{-}⟶C_6{H}_5{COO}^{-}+Ag\downarrow +4{NH}_3+2H_{2}O$

Benzaldehyde Tollen's reagent Benzaateion Silver mirror amoonia water

(iii) Distinguish between ethanol and ethanoic acid. Ethnol do not reach with sodium bicarbonate where as ethanoic acid reacts with sodium bicarbonate to give ${CO}_2$.

$C_2{H}_{5}OH+NaH{CO}_3⟶$ No reaction

Ethanol Sodium bicarbonate

${CH}_{3}COOH+NaH{CO}_3⟶{CH}_{3}COONa+H_{2}O+{CO}_2$

Ethanic acid Sodium sodium water carbon

bicarbonate acetate dioxide