Aqua regia
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| Names | |
|---|---|
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IUPAC name
nitric acid hydrochloride
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| Other names
aqua regis, nitrohydrochloric acid
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| Identifiers | |
| 8007-56-5 | |
| 3D model (Jmol) | Interactive image |
| PubChem | 62687 |
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| Properties | |
| HNO3+3 HCl | |
| Appearance | red, yellow or gold fuming liquid |
| Density | 1.01–1.21 g/cm3 |
| Melting point | −42 °C (−44 °F; 231 K) |
| Boiling point | 108 °C (226 °F; 381 K) |
| miscible in water | |
| Vapor pressure | 21 mbar |
| Hazards | |
| NFPA 704 | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Aqua regia (Latin, lit. "royal water" or "king's water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange fuming liquid. Aqua regia was so named by alchemists because it can dissolve the noble metals gold and platinum. However, aqua regia does not dissolve or corrode all metals.
Aqua regia is primarily used to produce chloroauric acid, the electrolyte in the Wohlwill process. This process is used for refining the highest quality (99.999%) gold.
Aqua regia is also used in etching and in specific analytic procedures. It is also used in some laboratories to clean glassware of organic compounds and metal particles. This method is preferred over the "traditional" chromic acid bath for cleaning NMR tubes, because no traces of paramagnetic chromium can remain to spoil spectra. 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.
Due to the reaction between its components 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 local regulations may vary, aqua regia may be disposed of by careful neutralization, before being poured down the sink. If there is contamination by dissolved metals, the neutralized solution should be collected for disposal.
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Wikipedia