Aqua regia has strong oxidation ability and is called the king of acid.

Some metals insoluble in nitric acid, such as gold and platinum, can be dissolved with aqua regia (platinum must be heated to react slowly).

Principle of aqua regia dissolving gold

Although the two components of aqua regia cannot dissolve gold alone, they can dissolve gold together. The principle is as follows: nitric acid is a very strong oxidant, which can dissolve a very small amount of gold, while hydrochloric acid can react with gold ions in solution to generate gold chloride, which makes gold ions leave the solution, so that nitric acid can further dissolve gold;

Au + NO3- + 4H+ → Au3+ + NO↑ + 2H2O

Aqua regia, also known as aqua regia, is a highly corrosive liquid with yellow smoke. It is a mixture of nitric acid and hydrochloric acid, in which the mixing ratio is 1:3. It is one of the few substances that can dissolve gold and platinum. This is also the origin of its name. However, some very inert metals such as tantalum will not be corroded by aqua regia. Aqua regia is used in etching process and some analytical processes. Aqua regia decomposes quickly.