Question

The product obtained from the electrolytic oxidation of acidified sulphate solutions, is :

• A. HO$_3$SOSO$_3$H
• B. HO$_2$SOSO$_2$H
• C. HO$_3$SOOSO$_3$H
• D. HSO$_4^-$

Hint:

Compounds with the prefix "peroxo-" or "peroxy-" contain an -O-O- linkage where oxygen has an oxidation state of -1. Peroxodisulphuric acid ($H_2S_2O_8$) and Caro's acid ($H_2SO_5$) are important examples in sulfur chemistry.

Answer 1

The Correct Option is C

The electrolytic oxidation of an acidified concentrated solution of a sulphate, such as ammonium sulphate or sulfuric acid, at high current density is a method for preparing peroxodisulphates.
At the anode, the bisulphate ion ($HSO_4^-$) or sulphate ion ($SO_4^{2-}$) is oxidized. The primary reaction is the coupling of two bisulphate radicals.
The overall anode reaction can be represented as:
$2HSO_4^- (aq) \rightarrow S_2O_8^{2-} (aq) + 2H^+ (aq) + 2e^-$
The product is the peroxodisulphate ion, $S_2O_8^{2-}$. The corresponding acid is peroxodisulphuric acid, $H_2S_2O_8$, also known as Marshall's acid.
Let's examine the structure of this acid. It contains a peroxide linkage (-O-O-) between the two sulfur atoms. The structure is:
\begin{center} O \hspace{0.5cm} O
\vspace{-0.2cm} $\parallel$ \hspace{0.5cm} $\parallel$
HO-S-O-O-S-OH
\vspace{-0.2cm} $\parallel$ \hspace{0.5cm} $\parallel$
\vspace{0.1cm} O \hspace{0.5cm} O \end{center} The condensed structural formula is $HO_3SOOSO_3H$. This matches option (C).
Option (A) $HO_3SOSO_3H$ represents pyrosulphuric acid ($H_2S_2O_7$), which does not have the peroxide link.