Question

A solution containing As3+, Cd2+, Ni2+ and Zn2+ is made alkaline with dilute NH4OH and treated with H2S. The precipitate obtained will consist of

(a) As2 S3 and CdS

(b) CdS, NiS and ZnS

(c) NiS and ZnS

(d) Sulphide of all ions

Answer 1

Correct option (d) Sulphide of all ions

Explanation:

As3+ and Cd2+ are the **** of group II, whereas Ni2+ & Zn2+ are the **** of group IV. The solubility product of group IV **** is higher as compared to group II. NH4OH increases the ionisation of H2S by removing H+ of H2S as unionisable water.

Thus excess of sulphide ions are present which leads to the precipitation of all the four ions.

Note : HCl decreases ionisation of H2S whereas NH4OH increases the ionisation of H2S.