Pure gold precipitate produced by the aqua regia chemical refining processĪqua regia dissolves gold, although neither constituent acid will do so alone. If there is contamination by dissolved metals, the neutralized solution should be collected for disposal. While local regulations may vary, aqua regia may be disposed of by careful neutralization, before being poured down the sink. īecause its components react quickly, resulting in its decomposition, aqua regia quickly loses its effectiveness (yet remains a strong acid), so its components are usually only mixed immediately before use. While chromic acid baths are discouraged because of the high toxicity of chromium and the potential for explosions, aqua regia is itself very corrosive and has been implicated in several explosions due to mishandling. This method is preferred among most over the more traditional chromic acid bath for cleaning NMR tubes, because no traces of paramagnetic chromium can remain to spoil spectra. It is also used in some laboratories to clean glassware of organic compounds and metal particles. Because nitric oxide readily reacts with atmospheric oxygen, the gases produced also contain nitrogen dioxide, NO 2 (red fume):Ģ NO + O 2 → 2 NO 2 Applications Īqua regia is primarily used to produce chloroauric acid, the electrolyte in the Wohlwill process for refining the highest purity (99.999%) gold.Īqua regia is also used in etching and in specific analytic procedures. Therefore, in addition to nitrosyl chloride and chlorine, the fumes over aqua regia also contain nitric oxide (NO). This dissociation is equilibrium-limited. Nitrosyl chloride (NOCl) can further decompose into nitric oxide (NO) and elemental chlorine ( Cl 2): As the volatile products escape from solution, aqua regia loses its potency. These reactions result in the volatile products nitrosyl chloride and chlorine gas:Īs evidenced by the fuming nature and characteristic yellow color of aqua regia. Upon mixing of concentrated hydrochloric acid and concentrated nitric acid, chemical reactions occur.
It was named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.
Freshly prepared aqua regia is colorless, but it turns yellow, orange or red within seconds from the formation of nitrosyl chloride and nitrogen dioxide. Here, fresh aqua regia has been added to these NMR tubes to remove all traces of organic material.Īqua regia ( / ˈ r eɪ ɡ i ə, ˈ r iː dʒ i ə/ from Latin, literally "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Freshly prepared aqua regia is colorless, but it turns orange within seconds.
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