Question

When a salt is heated with dil. $H_{2}S{O}_4$ and $KMn{O}_4$ solution, the pink colour of $KMn{O}_4$ is discharged, the mixture may contain?

• A. Sulphite
• B. Carbonate
• C. Nitrate
• D. Bicarbonate

Answer 1

Answer: (A)

Sulphite

${KMnO}_4$ is an oxidising agent, Hence salt must contain anion that can be oxidise to higher oxidation state. Hence salt must contain sulphide $\left({SO}_3^{2-}\right)$ which on oxidation with ${KMnO}_4$ give $\left({SO}_4^2\right)$ sulphate and ${KMnO}_4$ himself reduces to ${MnO}_2$ i.e. pink colour of ${KMnO}_4$ discharge.

${2H}^{+}+2{MnO}_4^{-}+3{SO}_3^{2-}\to 2{MnO}_2+H_{2}O+3{SO}_4^{2-}$

(pink)