Question

$H_{2}S$ is passed through the solution in an acidic medium to precipitate the sulphides of group II cations but in an alkaline medium to precipitate the sulphides of group IV cations because:

• A. the sulphides of group II cations are more soluble than those of group IV cations
• B. the sulphides of group II cations have lower solubility products than those of group IV cations
• C. the sulphides of group II cations are soluble in an acidic medium, but those of group IV cations are not
• D. the sulphides of group IV cations are soluble in an alkaline medium but those of group II cations are not

Answer 1

The correct option is B the sulphides of group II cations have lower solubility products than those of group IV cations

Group $II$: sparingly soluble sulphides derived from $H{g}^{2+},P{b}^{2+},C{u}^{2+},C{d}^{2+}$ and $B{i}^{3+}$ ions (and in addition the sparingly soluble covalent sulphides $A{s}_2{S}_3,S{b}_2{S}_3$ and $SnS$) are precipitates by the passage by thr passage of hydrogen sulphide $\left(H_{2}S\right)$ through an scidic solution whose consectration of hydrogen ion is small

Sulphidic $K_{sp}$ at ${25}^{o}C$

$HgS$ $3\times {10}^{-52}$

$PbS$ $8\times {10}^{-28}$

$CuS$ $8\times {10}^{-36}$

$CdS$ $1\times {10}^{-27}$

$B{i}_2{S}_3$ $1\times {10}^{-96}$

The Ksp value of group II sulphide is quite low in comparison to Ksp values of group IV sulphides, hence they do not get precipitated in acidic medium, where $S^{2-}$ ion concentration is quite low.