Aqua regia

Mixture of nitric acid and hydrochloric acid in a 1:3 molar ratio

Aqua regia (from Latin, "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar mixing ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but it turns yellow, orange, or red within seconds from the formation of nitrosyl chloride and nitrogen dioxide.

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