Question

The mixture of concentrated ${\text{HCl}}$ and ${\text{HN}}{{\text{O}}_{\text{3}}}$ made in ${\text{3:1}}$ ratio contains:
A. ${\text{COC}}{{\text{l}}_{\text{2}}}$
B. ${\text{NOCl}}$
C. ${\text{NC}}{{\text{l}}_3}$
D. ${{\text{N}}_2}{{\text{O}}_4}$

Answer 1

Hint: We know that the mixture of concentrated ${\text{HCl}}$ and ${\text{HN}}{{\text{O}}_{\text{3}}}$ in ${\text{3:1}}$ ratio is known as aqua regia. The aqua regia is capable of dissolving noble metals. Aqua regia is used in refining gold with high purity.

Complete step by step solution:
The mixture of three parts of concentrated ${\text{HCl}}$ and one part of concentrated ${\text{HN}}{{\text{O}}_{\text{3}}}$ is known as aqua regia. Both these acids are strong acids. When two strong acids are combined together they react and form a highly acidic solution. The aqua regia is stronger than nitric acid or hydrochloric acid alone.
When three parts of concentrated hydrochloric acid $\left( {{\text{HCl}}} \right)$ and one part of concentrated nitric acid $\left( {{\text{HN}}{{\text{O}}_{\text{3}}}} \right)$ are mixed together the following reaction occurs.
${\text{3HCl}}\left( {{\text{aq}}} \right) + {\text{HN}}{{\text{O}}_{\text{3}}}\left( {{\text{aq}}} \right) \to {\text{NOCl}}\left( {\text{g}} \right) + {\text{C}}{{\text{l}}_{\text{2}}}\left( {\text{g}} \right) + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}}$
The aqua regia is a fuming liquid having dark yellow or dark orange colour. The fumes produced are due to the production of nitrosyl chloride gas $\left( {{\text{NOCl}}} \right)$ and chlorine gas $\left( {{\text{C}}{{\text{l}}_{\text{2}}}} \right)$.
Thus, the mixture of concentrated ${\text{HCl}}$ and ${\text{HN}}{{\text{O}}_{\text{3}}}$ made in ${\text{3:1}}$ ratio contains ${\text{NOCl}}$.

Thus, the correct option is (B) ${\text{NOCl}}$.

Additional Information:
Nitrosyl chloride $\left( {{\text{NOCl}}} \right)$ gas formed from aqua regia decomposes to form nitric oxide and chlorine. The reaction is as follows:
${\text{2NOCl}}\left( {\text{g}} \right) \to 2{\text{NO}}\left( {\text{g}} \right) + {\text{C}}{{\text{l}}_{\text{2}}}\left( {\text{g}} \right)$
Thus, aqua regia cannot be stored for a longer time duration because it decomposes.

Note:
Aqua regia is capable of dissolving noble metals like platinum, gold, silver, mercury, etc. Thus, aqua regia is also known as king’s water or royal water. Aqua regia is used in refining gold with high purity. The process of refining gold using aqua regia is known as Wohlwill process. In the Wohlwill process aqua regia acts as an electrolyte.