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

Options

A. deep blue precipitate of `Cu(OH)_(2)`
B. deep blue solution of `[Cu(NH_(3))_(4)]^(2+)`
C. deep blue solution of `Cu(NO_(3))_(2)`
D. deep blue solution of `Cu(OH)_(2).Cu(NO_(3))_(2)`

Answer

B

Explanation

`underset(CuSO_(4)+H_(2)Soverset(Dil.HCl)tounderset("Blck ppt.")(CuS+H_(2)SO_(4)),Cus+2HNO_(3)tounderset("Blue solution")(Cu(NO_(3))_(2))+H_(2)S`
`Cu(N_(3))_(2)+4NH_(3)tounderset(("Deep blue solution"))[[Cu(NH_(3))_(4)]^(2+)+2NO_(3)^(-)`