`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. the presence of HCl decreases the sulphide ion concentration
B. the presence of HCl increase the sulphide ion concentration
C. the solubility product of group II suplphides is more than that of group IV sulphides
D. the sulphides of group IV cations are unstable in HCl

Answer

A

Explanation

In qualitative analysis of cations of second group, `H_(2)S` gas is passed in the presence of HCl. Therefore, due to common ion, effect lower concentration of sulphide ions is obtained which is sufficient for the precipitation of second group cations in the from of their sulphides due to lower value of their solubility products `(K_(sp))` . Here fourth group cations are not precipitated because they require more sulphide ions for exceeding their ionic product to their solubility products which is not obtained here due to common ion effect