In qualitative analysis when H 2 S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO 3 , it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.

Question

Philoid · Accepted Answer

when H₂S is passed through an aqueous solution of salt acidified with dilute HCl

Cu²⁺ + H₂S CuS + 2H⁺

Black precipitate of copper sulphide is formed. When copper sulphide is heated with dil. HNO₃ it gives blue colour of copper nitrate( on boiling), when aqueous solution of ammonia is added to it deep blue colour of tetraammine copper(II)sulphate [Cu(NH₃)₄]² is obtained.

CuS + dil.HNO₃ Cu(NO₃)₂

Cu(NO₃)₂ + 4NH₃ [Cu(NH₃)₄]²⁺

Hence the correct option is (ii)

In qualitative analysis when H2S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO3, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.