Question

Out of ${H_2}{S_2}{O_3},\,{H_2}{S_4}{O_6},\,{H_2}S{O_5}\, and \,{H_2}{S_2}{O_8}$ peroxy acids are
A) ${H_2}{S_2}{O_3},\,{H_2}{S_4}{O_6}$
B) ${H_2}{S_4}{O_6},\,{H_2}S{O_5}$
C) ${H_2}S{O_5},\,{H_2}{S_2}{O_8}$
D) ${H_2}{S_2}{O_3}\,and\,{H_2}{S_2}{O_8}$

Answer 1

The compounds which have an -O-O-H atomic group in place of an -O-H group are peroxy acids. They are also known as peracids.

Complete Solution :
Peroxy acids are the class of chemical compounds in which the -OH group is replaced by the atomic group -OOH. Peroxy acids usually are prepared by reaction of the oxy acid with hydrogen peroxide; small amounts of sulfuric or other strong acids often are used to accelerate the reaction of weak oxy acids. The peroxy acids are used primarily as oxidizing agents; they readily add oxygen to alkenes to give epoxides and are used to convert ketones to esters and amines to nitro compounds, amine oxides, or nitroso compounds.
The general formula of a peroxy acid is R-O-O-R’.
Carboxylic acids are better acids than peroxy acids because the carboxylate ion is stabilised by resonance between the two oxygens which is not the case in the conjugate base of peroxy acids.
Now, these oxyacids have special structures.
The structure of ${H_2}{S_2}{O_3}$ is:

The structure of ${H_2}{S_4}{O_6}$ is:

The structure of ${H_2}S{O_5}$ is:

The structure of ${H_2}{S_2}{O_8}$ is:

It can be clearly seen that ${H_2}S{O_5}$ and ${H_2}{S_2}{O_8}$ have peroxy linkages in them.
So, ${H_2}S{O_5}$ and ${H_2}{S_2}{O_8}$ are peroxy acids.
So, the correct answer is “Option C”.

Note: Note that peroxy acids are also called in short as peracids and these have the acidic –OOH group and these acids particularly peroxy carboxylic acids are 1000 times weaker when compared to that of parent carboxylic acid because of the absence of resonance stabilization of anion.