Question

Noble metals get dissolved in aqua regia the composition of aqua regia is:
(A) $3HCl+HN{{O}_{3}}$
(B) $3HN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}$
(C) $HCl+3HN{{O}_{3}}$
(D) $HN{{O}_{3}}+3{{H}_{2}}S{{O}_{4}}$

Answer 1

Hint: Write the reaction of a noble metal with aqua regia. Now identify the products formed. From this you will get an idea of the composition of the aqua regia. Now balance the chemical reaction. With this you can calculate the stoichiometric coefficient of each component of aqua regia.

Complete step by step solution:
Aqua regia also called king's water or royal water is a yellow-orange fuming liquid used to dissolve precious metals as well as inert or noble metals.
Aqua regia is primarily used in the production of chloroauric acid, the electrolyte used in the Wohlwill process. This process is used for refining of gold and produces gold with a purity of about 99.999%.
Along with this aqua regia is used in etching and in analytic procedures in specific. Due to inter reaction between the components of aqua regia, it loses its effectiveness very quickly due to lack of original components.
Aqua regia is a mixture of the compounds, nitric acid and hydrochloric acid. The ratio of composition is 1:3 respectively. This means that 3 moles of hydrochloric acid are present for every 1 mole of nitric acid in a standard solution of aqua regia.

Therefore, the composition in terms of molecular formula is $3HCl+HN{{O}_{3}}$. The correct answer is option (A).

Note: It is important to know that although aqua regia is a very useful chemical, it is highly hazardous to the human skin. Aqua regia causes corrosion when it comes in contact with moisture thus having long lasting effects on the skin. Always use safety apparatus while handling such a corrosive chemical.