`H_(2)S` gas when passed through a solution of cations containing `HCl` precipitates the cations of second group in qualitative analysis but not those belonging to the fourth group. It is because

Options

A. presence of HCI decreases the sulphide ion sulphide ion concentration
B. sulphides of group IV are unstable in HCI
C. solubility product of group II sulphides is more than that of group IV sulphides
D. pressence of HCI increases the sulphide ion concentration

Answer

A

Explanation

`H_(2)S(aq.)hArr 2H^(+)(aq.)+S^(2-)(aq.)`
`H_(2)S` is a weak acid. The presence of HCI suppresses the ionization of `H_(2)O` due to common ion effect. As a result, the concentration of sulphide ions decreases. Since `K_(sp)` values of group II sulphides are lower than those of group IV sulphides, only the cations of group II precipitate.