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("Salt")(CuSO_(4))+H_(2)S overset("Dil.HCI")rarr underset(("Black ppt."))(CuS)+H_(2)SO_(4)" ,"" "CuS + 2HNO_(3) rarr underset(("Blue solution"))(Cu(NO_(3))_(2))+H_(2)S`
`Cu(NO_(3))_(2) + 4NH_(3) rarr underset(("Deep blue solution"))([Cu(NH_(3))_(4)]^(2+)) + 2NO_(3)^(-)`