Answer to Question #161776 in Inorganic Chemistry for Satyajay Mandal

Question

I have heard that aqua regia is a mixture of two monovalent acids (HNO₃ & HCl) in the ratio 1:3, what happens if it is neutralized by a mixture of two monovalent alkalis in the ratio of 1:3, which are both preferably metal hydroxides?

Answer 1

Aqua regia is often used to dissolve gold. Neither nitric acid or hydrochloric acid can do this alone. Nitric acid will act as the oxidizer and is used to form gold ions (Au3+). The hydrochloric acid is then used to react with the gold ions to form tetrachloroaurate(III) anions.

Since, it is a mixture of concentrated acids, its pH value is almost near to zero. This means that it is highly acidic.

Pour excess and waste aqua regia into a large quantity of ice (500 grams of ice per 100 mL of aqua regia). Neutralize the mixture with an aqueous basic solution, such as 1M or 10% sodium hydroxide (NaOH) or saturated sodium bicarbonate (NaHCO3) in water until pH is neutral.