Question

The oxidation numbers of the sulphur atoms in peroxomonosulphuric acid $(H_{2}S{O}_5)$ and peroxodisulphuric acid $(H_2{S}_2{O}_8)$ are respectively

• A. $+8$ and $+7$
• B. $+3$ and $+3$
• C. $+6$ and $+6$
• D. $+4$ and $+6$

Answer 1

Answer: (C)

Both the peroxomonosulphuric acid $\left(H_{2}S{O}_5\right)$ and peroxodisulphuric acid $\left(H_2{S}_2{O}_8\right)$ have peroxide linkage and have the following structures.
Thus, the oxidation number of $S$ in $H_{2}S{O}_5$ is calculated as:
$\underset{(\text{ for }H)}{2\times (+1)}+\underset{(\text{ for }S)}{X}+\underset{\text{ for }O}{3\times (-2)}\times \underset{\text{ (for peroxide) }}{2\times (-1)}=0$
$2+x-6-2=0$
$\therefore x=+6$
Thus, oxidation number of $S$ in $H_2{S}_2{O}_8$ is calculated as
$\underset{(\text{ for }H}{2\times (+1)}+\underset{(\text{ for }S)}{2\times (x)}+\underset{(\text{ for }O)}{6\times (-2)}+\underset{\text{(for peroxide)}}{2\times (-1)}=0$
$2+2x-12+2=0$
$\therefore x=+6$