Question

A salt on heating with $dil.H_{2}S{O}_4$ and subsequently treatment with a few drops of dilute $K_{2}C{r}_2{O}_7$ turns into green solution. The salt may be a :

• A. Sulphate
• B. Nitrate
• C. Sulphite
• D. Chromate

Answer 1

The correct option is C Sulphite

Dilute HCl or $H_{2}S{O}_4$ decomposes sulphites with the evolution of sulphur dioxide.

$S{O}_3^{2-}+2H^{+}\to S{O}_2\uparrow +H_{2}O$

The gas can be identified

By green colour formation, when passed through acidified $K_{2}C{r}_2{O}_7$ solution.

$3S{O}_2\uparrow +\underset{orange}{C{r}_2{O}_7^{2-}}+2H^{+}\to 3S{O}_4^{2-}\underset{Greencolour}{+2C{r}^{3+}+H_{2}O}$

Option C is correct.