Question

Gold dissolve in aqua-regia forming:
a.) Auric chloride
b.) Aurous chloride
c.) Chloroauric acid
d.) Aurous nitrate

Answer 1

Hint: Gold is dissolved in a mixture also known as royal water. This mixture is also used to dissolve metal like palladium, gallium and other noble metals.

Complete Solution :
- Gold is a metal which is soft and mostly unreactive, this is the main reason why gold is used to make jewelleries because it does not react when exposed to water, air etc. let’s talk about reaction of gold in detail.
- Gold metal is usually stable in air but it does dissolve in solution of aqueous cyanide in the presence of air. It does not react with water.
Gold reacts with halogens and generally forms trihalides gold with chlorine and bromine however it forms monohalide gold when it reacts with iodine.
- Aqua regia also known as royal water is used for the dissolution of gold. It is a mixture of hydrochloric acid and nitric acid present in the ratio of 3:1 or we can say that aqua regia is formed by mixing three parts of nitric acid and one part of hydrochloric acid. The name aqua regia was coined because this solution can dissolve gold which is known as the king of metals. When gold dissolves in aqua regia, chloroauric acid is formed.
- The reaction involved is mentioned below:
$$Au+HN{O}_3+4HCl\to HAuC{l}_4+NO+2H_{2}O$$
So, the correct answer is “Option B”.

Note: Formation of $AuC{l_4}^{-}$ anion helps in the removal of the gold ion from the given solution and after that the further oxidation of gold ions takes place. Chloroauric acid is produced by dissolution of gold.