Question

What is the oxidation number of $\mathrm{S}$ in ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$?

Answer 1

Oxidation number: Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to a more electronegative element.

Structure of ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$

Calculating the oxidation number of $\mathrm{S}$ in ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$

In ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$, two oxygen are involved in peroxide linkage as shown in the above structure. So, the oxidation number of two oxygen atoms are $-1$.

The oxidation state of Hydrogen(H) = +1

The oxidation state of Oxygen(O) = -2

Consider the oxidation state of Sulphur(S) = x

Now,

$$\begin{gathered} \left(+1\times 2\right)+\left(x\times 2\right)+\left(-2\times 6\right)+\left(-1\times 2\right)=0 \\ 2+2x-12-2=0 \\ 2x=14-2 \\ x=+6 \end{gathered}$$

Hence, the oxidation number of $\mathrm{S}$ in ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$ is $+6$.