Question

The oxidation numbers of the sulphur atoms in peroxomonosulphuric acid $(H_{2}SO_{5})$ 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)

$+6$ and $+6$

Answer 2

Both the peroxomonosulphuric acid $\left( H _{2} SO _{5}\right)$ 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 $H _{2} SO _{5}$ 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
$\underset{(\text{ for } H}{2 \times (+1)} + \underset{(\text{ for } S)}{2\times (x)} +\underset{(\text{ for } O)}{6\times (-2)} +\underset{\text{(for peroxide)}}{2\times (-1)} = 0$
$2+2 x -12+2=0$
$\therefore x =+6$