Question

Aqua regia is a mixture of _______and_______ in _______ ratio.
(A) Nitric acid, hydrochloric acid, 3:1
(B) Nitric acid, hydrochloric acid, 1:3
(C) Hydrochloric acid, sulphuric acid, 1:3
(D) Sulphuric acid, hydrochloric acid, 3:1

Answer 1

Hint: Aqua regia is a Latin phrase which means “king of water”. It is a yellow-orange fuming liquid. It can dissolve the noble metals, gold and platinum, though not all metals.

Complete step by step answer:
Aqua regia may also be called as royal water or nitro-muriatic acid (the name given to it in 1789 by Antoine Lavoiser). It is a highly corrosive mixture of hydrochloric acid and nitric acid of ratio 3:1. It is called royal water, referring to the acid’s ability to dissolve the noble metals like gold, platinum and palladium. It does not dissolve all the noble metals.

Let us see how to make aqua regia-
* As we know, the preferred molar ratio for aqua regia is 3 moles hydrochloric acid to 1 mole of nitric acid. However, concentrated HCl is typically 35%, while concentrated nitric acid is 65%.
* Generally, only small volumes of aqua regia are prepared at a time.
* Pour the nitric acid into the hydrochloric acid; do not pour concentrated hydrochloric acid into nitric acid, to reduce the risk of splattering hot acid.
* Initially, the mixture will be colorless. It will deepen in color to form a fuming golden or orange-red liquid that will smell strongly of chlorine.
Therefore, aqua regia is a mixture of hydrochloric acid and nitric acid in the ratio of 3:1. Hence, option A is the required answer.

Note: As we have already seen aqua regia is really very scary. Mixing two strong acids produces heat and releases toxic vapors. Once mixed, the acids continue to react. Even after decomposition occurs, the liquid remains a strong, corrosive acid.