Question

`H_(2)S` in the presence of HCl precipitates II group but not IV group because `:`
A. HCl activates `H_(2)S`
B. `HCl` increases concentration of `Cl^(-)`
C. `HCl` decreases concentration of `S^(2-)`
D. `HCl` lowers the solubility of `H_(2)S` in solution

Answer 1

Correct Answer - 3
`H_(2)ShArr 2H^(+)+S^(2-),HClhArrH_(2)^(+)+Cl^(-)`.
Due to common ion effect, the ionisation of `H_(2)S` is suppressed and thus low concentration of `S^(2-)` ions is obtained. This much of `S^(2-)` ions concentration is enough to precipitate only `II^(nd)` group cations `(` because of the low `K_(SP)` of `II^(nd)` group sulphides ).