Question

Why only ${As}^{+3}$ gets precipitated as ${As}_2{S}_3$ and not ${Zn}^{+2}$ as $ZnS$ when $H_{2}S$ is passed through an acidic solution containing ${As}^{+3}$ and ${Zn}^{+2}$?

• A. Solubility product of ${As}_2{S}_3$ is less than that of $ZnS$
• B. Enough ${As}^{+3}$ are present in acidic medium
• C. Zinc salt does not ionise in acidic medium
• D. Solubility product changes in presence of an acid

Answer 1

The correct option is A Solubility product of ${As}_2{S}_3$ is less than that of $ZnS$

The species having minimum value of $K_{sp}$ will get precipitated first of all because ionic product will exceed the solubility product of such species.

$K_{sp}$ of ${As}_2{S}_3$ is less than $ZnS$. In acid medium ionisation of $H_{2}S$ is suppressed (common ion effect) and $K_{sp}$ of $ZnS$ does not exceed.