Question

Hydrogen peroxide is now generally prepared on industrial scale by the

• A. action of $H_{2}S{O}_4$ on barium peroxide
• B. action of $H_{2}S{O}_4$ on sodium peroxide
• C. electrolysis of $50\%$ $H_{2}S{O}_4$
• D. burning hydrogen in excess of oxygen

Answer 1

Answer: (C)

Industrial preparation of $H_2{O}_2$:
(A) By the electrolysis of $50\%$ $H_{2}S{O}_4:50\%H_{2}S{O}_4$ solution is electrolysed at $0^{\circ }$C between $Pt$ electrodes. The per disulphuric acid is formed.
$H_{2}S{O}_4\rightleftharpoons H^{+}+HS{O}_4^{-}$
At Anode : $2HS{O}_4^{-}\to H_2{S}_2{O}_8+2e$
At Cathode : $2H^{+}+2e\to H_2$
The obtained per disulphuric acid gives $H_2{O}_2$ on hydrolysis.
$H_2{S}_2{O}_8+2H_{2}O\rightleftharpoons H_2{O}_2+2H_{2}S{O}_4$
This $H_2{O}_2$ is separated by distillation at reduced pressure and thus, $30\%$ solution of $H_2{O}_2$ is obtained.
(B) By the auto-oxidation of $2$-ethyl-anthraquinol (Modem method): Anthraquinol, in a mixture of benzene and $n$-heptanol on treatment with air gives $H_2{O}_2$ and $2$-ethyl-anthraquinone. This $2$-ethyl-anthraquinone on hydrogenation gives $2$ anthraquinol in presence of $Pd$ catalyst.

It is a cyclic process and it only $H_2$ is consumed, $2$-ethyl-anthraquinone is reobtained during reaction.