Question

Aqua Regia is a mixture of:
A. 3:1 conc. $HCl$ and conc. $HN{{O}_{3}}$
B. 3:1 conc. $HN{{O}_{3}}$ and conc. ${{H}_{2}}S{{O}_{4}}$
C. 3:1 conc. $HN{{O}_{3}}$ and conc. $HCl$
D. 1:3 conc. $HCl$ and conc. $HN{{O}_{3}}$

Answer 1

Hint: Also known as “Royal Water”, by the alchemists. It was so called because of its ability to dissolve gold and other noble metals. A complete study of the structure can help us to find the ratio of the components by which aqua regia is formed.

Complete Solution :
Aqua Regia is a yellowish orange fuming liquid which can dissolve any noble metal. It is a mixture of three parts of concentrated hydrochloric acid and one part of concentrated nitric acid. This is the molar ratio of aqua regia.
Therefore, we can say that aqua regia is a mixture of conc. $HCl$ and conc. $HN{{O}_{3}}$ in a ratio of 3:1.
Hence, the correct answer is 3:1 conc. $HCl$ and conc. $HN{{O}_{3}}$.
Therefore, Option A is the correct option.
The following is the structure of aqua regia, it will help us to have a closer look at the diagram:

Aqua Regia is chemically inert and it will not oxidize in air at any temperature.
So, the correct answer is “Option B”.

Note: Let us give a glance at the fields which requires the use of Aqua Regia:
- Firstly, aqua regia is used in the glassware industries. It is used to clean the glasses.
- Secondly, Aqua Regia is used in the gold refining industries. Here is the reaction of aqua regia with gold. Gold reacts with nitrate ions and protons to form oxidized gold, nitrogen dioxide and water. The oxidized gold further combines with chlorine ions to form tetrachloroaurate.
\[\begin{align}
  & A{{u}_{(s)}}+3N{{O}_{3}}{{^{-}}_{(aq)}}+6{{H}^{+}}_{(aq)}\xrightarrow{{}}A{{u}^{3+}}_{(aq)}+3N{{O}_{2}}_{(g)}+3{{H}_{2}}{{O}_{(l)}} \\
 & A{{u}^{3+}}_{(aq)}+4C{{l}^{-}}_{(aq)}\xrightarrow{{}}AuC{{l}_{4}}{{^{-}}_{(aq)}} \\
\end{align}\]

- The reason why aqua regia can dissolve gold, which is usually inert, is because of the fact that each of its component acids (that is hydrochloric acid and nitric acid) performs a different function.