Question

A black coloured compound (A) on reaction with dilute \[{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}\] gives a gas (B) which on passing in a solution of an acid (C) gives a white turbidity (D). Gas (B) when passed in an acidified solution of a compound (E) gives a precipitate (F) soluble in dil. \[{\text{HN}}{{\text{O}}_{\text{3}}}\] . After boiling this solution when an excess of \[{\text{N}}{{\text{H}}_{\text{4}}}{\text{OH}}\] is added, a blue coloured compound (G) is formed. To this solution on addition of acetic acid and aqueous \[{{\text{K}}_{\text{4}}}{\text{ }}\left[ {{\text{Fe}}{{\left( {{\text{C N}}} \right)}_{\text{6}}}} \right]\] a chocolate precipitate (H) is obtained. On addition of an aqueous solution of \[{\text{BaC}}{{\text{1}}_{\text{2}}}\] to an aqueous solution of (E), a white precipitate insoluble in \[{\text{HN}}{{\text{O}}_{\text{3}}}\] is obtained. Identify (G) and (H).
(A) \[\left( {\text{G}} \right){\text{ -- }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}{{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)}_{\text{2}}}{\text{ }}\left( {\text{H}} \right){\text{ -- C}}{{\text{u}}_{\text{2}}}} \right[{\text{Fe}}{\left( {{\text{CN}}} \right)_{\text{6}}}{\text{]}}\]
(B) \[\left( {\text{G}} \right){\text{ -- }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{3}}}{{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)}_{\text{2}}}{\text{ }}\left( {\text{H}} \right){\text{ -- C}}{{\text{u}}_{\text{2}}}} \right[{\text{Fe}}{\left( {{\text{CN}}} \right)_{\text{6}}}{\text{]}}\]
(C) \[\left( {\text{G}} \right){\text{ -- }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}{{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)}_{\text{2}}}{\text{ }}\left( {\text{H}} \right){\text{ -- Cu}}} \right[{\text{Fe}}{\left( {{\text{CN}}} \right)_{\text{6}}}{\text{]}}\]
(D) \[\left( {\text{G}} \right){\text{ -- }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right){\text{ }}\left( {\text{H}} \right){\text{ -- C}}{{\text{u}}_2}} \right[{\text{Fe}}{\left( {{\text{CN}}} \right)_{\text{6}}}{\text{]}}\]

Answer 1

Hint: Cupric ions form complexes with ammonium hydroxide. Here ammonia is a ligand.
Iron also forms complex compounds with ligands such as cyanide ions.

Complete step by step answer:
The black coloured compound (A) is ferrous sulfide \[{\text{FeS}}\] . \[{\text{FeS}}\] on reaction with dilute \[{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}\] gives hydrogen sulphide gas (B)
\[{\text{FeS + }}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ }} \to {\text{ F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}{\text{ + }}{{\text{H}}_2}{\text{S}}\]
Hydrogen sulphide on passing in a solution of nitric acid (C) gives a white turbidity of sulphur (D).
\[{{\text{H}}_2}{\text{S + HN}}{{\text{O}}_3}{\text{ }} \to {\text{ }}{{\text{H}}_2}{\text{O + }}{{\text{N}}_2}{\text{ + S}}\]
 Hydrogen sulphide gas (B) when passed in an acidified solution of copper sulphate (E) gives a precipitate of copper(II) sulphide (F) soluble in dil. \[{\text{HN}}{{\text{O}}_{\text{3}}}\] .
\[{{\text{H}}_2}{\text{S + CuS}}{{\text{O}}_4}{\text{ }} \to {\text{ CuS + }}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}\]
After boiling this solution when an excess of \[{\text{N}}{{\text{H}}_{\text{4}}}{\text{OH}}\] is added, a blue coloured compound \[\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)} \right]\] (G) is formed.
\[{\text{CuS + N}}{{\text{H}}_4}{\text{OH}} \to \left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)} \right]\]
To this solution on addition of acetic acid and aqueous \[{{\text{K}}_{\text{4}}}{\text{ }}\left[ {{\text{Fe}}{{\left( {{\text{C N}}} \right)}_{\text{6}}}} \right]\] a chocolate precipitate \[{\text{C}}{{\text{u}}_2}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]\] (H) is obtained.
\[\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)} \right] + {\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}} + {{\text{K}}_{\text{4}}}{\text{ }}\left[ {{\text{Fe}}{{\left( {{\text{C N}}} \right)}_{\text{6}}}} \right] \to {\text{C}}{{\text{u}}_2}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]\]
On addition of an aqueous solution of \[{\text{BaC}}{{\text{1}}_{\text{2}}}\] to an aqueous solution of copper sulphate (E), a white precipitate insoluble in \[{\text{HN}}{{\text{O}}_{\text{3}}}\] is obtained.
\[{\text{CuS}}{{\text{O}}_4}{\text{ + BaC}}{{\text{l}}_2}{\text{ }} \to {\text{ BaS}}{{\text{O}}_4}{\text{ + CuC}}{{\text{l}}_2}\]

Hence, the correct option is the option (A) \[\left( {\text{G}} \right){\text{ -- }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{4}}}{{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)}_{\text{2}}}{\text{ }}\left( {\text{H}} \right){\text{ -- C}}{{\text{u}}_{\text{2}}}} \right[{\text{Fe}}{\left( {{\text{CN}}} \right)_{\text{6}}}{\text{]}}\]

Note: To detect the presence of particular ions in the compound, you react the compound with the suitable reagent. Then you observe the characteristic colour of the precipitate formed.