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

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.