Both Cus and ZnS are precipitated if `H_(2)S` gas is passed through an alkaline solution of `Cu^(2+) and Zn^(2+)`. Explain.

Explanation

In aqueous solution, `H_(2)S` ionises to establish the following equilibrium,
`H_(2)S(aq)+2H_(2)O(l) hArr 2H_(3)O^(+)(aq)+S^(2-)(aq)`
The degree of ionisation of `H_(2)S` increases in alkaline solution because `OH^(-)` ions present in the solution react with `H_(3)O^(+)` ions to form unionised water molecules. this shifts the equilibrium to right, thereby increasing the concentration of `S^(2-)` ions. in presence of a high concentration of `S^(2-)` ions. `[Cu^(2+)][S^(2-)] gt K_(sp)(CuS) and [Zn^(2+)][S^(2-)] gt K_(sp)(ZnS)`. as a resut, both CuS and ZnS are precipitated.