Question
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 \[dil.HN{{O}_{3}},\] it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.
A.
deep blue precipitate of $$Cu{\left( {OH} \right)_2}$$
B.
deep blue solution of $${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$$
C.
deep blue solution of $$Cu{\left( {N{O_3}} \right)_2}$$
D.
deep blue solution of $$Cu{\left( {OH} \right)_2} \cdot Cu{\left( {N{O_3}} \right)_2}$$
Answer :
deep blue solution of $${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$$
Solution :
\[CuS{{O}_{4}}+{{H}_{2}}S\xrightarrow{dil.\,HCl}\] \[\underset{\text{Black ppt}\text{.}}{\mathop{CuS\downarrow }}\,+{{H}_{2}}S{{O}_{4}}\]
\[CuS+2HN{{O}_{3\left( dil. \right)}}\xrightarrow{\Delta }\] \[\underset{\text{Blue solution}}{\mathop{Cu{{\left( N{{O}_{3}} \right)}_{2}}}}\,+{{H}_{2}}S\]
\[Cu{{\left( N{{O}_{3}} \right)}_{2}}+4N{{H}_{3}}\to \] \[\underset{\text{Deep blue solution}}{\mathop{{{\left[ Cu{{\left( N{{H}_{3}} \right)}_{4}} \right]}^{2+}}}}\,+2NO_{3}^{-}\]