Ncert Exercises & Solutions

1. Give a method for the manufacture of hydrogen peroxide and explain the reactions involved therein.

2. Illustrate oxidising, reducing and acidic properties of hydrogen peroxide with equations.

(i) $H_{2} O_{2}$ is industrially manufatured by the auto-oxidation of 2alkylanthraquinols

2 - ethylanthraquinol ⇌_{H_{2} / Pd}^{O_{2} / (air)} H_{2} O_{2} + Oxidised product

In this case, 1%

H_{2} O_{2}

is formed. It is extracted with water and concentrated to

~

30% (by mass) by distillation under reduced pressure. It can be further concentrated to

~

85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure

H_{2} O_{2}

(ii)

H_{2} O_{2}

acts as an oxidising as well as reducing agent in both acidic and alkaline media.

Following reactions are described below

(a) Oxidising action in acidic medium

2 {Fe}^{2 +} (aq) + 2 H^{+} (aq) + H_{2} O_{2} (aq) \to 2 {Fe}^{3 +} (aq) + 2 H_{2} O (l)

PbS (s) + 4 H_{2} O_{2} (aq) \to {PbSO}_{4} (s) + 4 H_{2} O (l)

(b) Reducing action in acidic medium

2 {MnO}_{4}^{-} + 6 H^{+} + 5 H_{2} O_{2} \to 2 {Mn}^{2 +} + 8 H_{2} O + 5 O_{2}

HOCl + H_{2} O_{2} \to H_{3} O^{+} + {Cl}^{-} + O_{2}

2 {Fe}^{2 +} + H_{2} O_{2} \to 2 {Fe}^{3 +} + 2 {OH}^{-}

{Mn}^{2 +} + H_{2} O_{2} \to {Mn}^{4 +} + 2 {OH}^{-}

(d) Reducing action in basic medium

I_{2} + H_{2} O_{2} + 2 {OH}^{-} \to 2 I^{-} + 2 H_{2} O + O_{2}

2 {MnO}_{4} + 3 H_{2} O_{2} \to 2 {MnO}_{2} + 3 O_{2} + 2 H_{2} O + 2 {OH}^{-}