Question

What happens when gold is dissolved in aqua regia?

Answer 1

Hint :In order to answer this question, you must know about Aqua Regia. It is also known as royal water and it is used for the dissolution of gold. It is a mixture of hydrochloric acid and nitric acid present in the ratio of 3:1.

Complete Step By Step Answer:
Although gold is typically an inert metal, the unique action of nitric and hydrochloric acid causes it to dissolve in aqua regia. Nitric acid is a strong oxidising agent that can convert trace amounts of gold to its ionic form, $ A{u^{3 + }} $ . Once this ionic form is present in the solution, hydrochloric acid acts as a source of chlorine anions, which react with the gold cations to form tetrachloroaurate(lll) anions.
Since the reaction with hydrochloric acid is an equilibrium reaction that favours the formation of chloroaurate anions $ AuC{l_4}^ - $ , the gold ions are removed from the solution, allowing more oxidation to take place. Because the solution is so acidic, the chloroaurate anions protonate quickly to form chloroauric acid.
Hence, when gold is dissolved in aqua regia, chloroauric acid is formed. $ $ $ Au + HN{O_3} + 4HCl \to HAuC{l_4} + NO + 2{H_2}O $
Formation of $ AuC{l_4}^ - $ anion helps in the removal of the gold ion from the given solution.

Note :
There are various reasons for dissolving gold in aqua regia:
1) for refining gold, i.e., to make it more and more pure.
2) cleaning inert surfaces, like glass, from metallic or organic impurities.
3) making chlorine gas.
4) cleaning gold, platinum, etc.