Question

Peroxy disulphuric acid $\left(H_2{S}_2{O}_8\right)$ can be prepared by electrolytic oxidation of $H_{2}S{O}_4$ as:
$2H_{2}S{O}_4\to H_2{S}_2{O}_8+2H^{+}+2e^{-}$
Oxygen and hydrogen are by products. In such an electrolysis $9.72litre$ of $H_2$ and $2.35$ litre of $O_2$ were generated at NTP. What is the mass of peroxy disulphuric acid formed?

Answer 1

Anodic reaction: $2H_{2}S{O}_4\to H_2{S}_2{O}_8+2H^{+}+2e^{-}$
$2H_{2}O\to 4H^{+}+O_2+2e^{-}$
Cathodic reaction : $2H_{2}O+2e^{-}\to 2O{H}^{-}+H_2$$

Total equivalent of $H_2{S}_2{O}_8+$ equivalent of oxygen $=$ Equivalent of $H_2$

$9.72litre{H}_2=\frac{9.72}{11.2}=0.868equivalent$

$2.35litre{O}_2=\frac{2.35}{5.6}=0.42equivalent$

Equivalent of $H_2{S}_2{O}_8=(0.868-0.420)$

$=0.448$

Mass of $H_2{S}_2{O}_8=0.448\times \frac{194}{2}=43.456g$.