Question

aqua regia is a mixture of Hcl and conc. HNO3 in the ratio of 3:1. it can dissolve gold and platinum. aqua regia is a strong oxidising agent why​

Answer 1

Answer:

Nitric acid is a strong oxidising agent, but the chemical equilibrium for its reaction with gold, Au, only permits formation of a tiny amount of Au+3 ion, so the amount of gold dissolved in pure nitric acid is undetectable. The presence of chloride ion, Cl-, allows formation of the stable chloraurate complex ion, AuCl4-. Because of the high concentration of chloride ion in aqua regia, the Au+3 is reacted almost as soon as it is formed, keeping its concentration low; this allows oxidation of more Au to Au+3, and the gold is dissolved. The gold may also react directly with the free chlorine in aqua regia, since chlorine is a powerful oxidizing agent.