Aqua regia

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Aqua regia[a]
Names
IUPAC name
Nitric acid trihydrochloride
Other names
  • Aqua regis
  • Nitrohydrochloric acid
  • Royal water
Identifiers
3D model (JSmol)
UNII
  • [N+](=O)(O)[O-].Cl.Cl.Cl
Properties
HNO3 + 3 HCl
Appearance Fuming liquid. Freshly prepared aqua regia is colourless, but it turns yellow, orange or red within seconds.
Density 1.01–1.21 g/cm3
Melting point −42 °C (−44 °F; 231 K)
Boiling point 108 °C (226 °F; 381 K)
Miscible
Vapor pressure 21 mbar
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
0
OX
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Freshly prepared aqua regia to remove metal salt deposits
Freshly prepared aqua regia is colorless, but it turns orange within seconds. Here, fresh aqua regia has been added to these NMR tubes to remove all traces of organic material.

Aqua regia (/ˈreɪɡiə, ˈriːdʒiə/; from Latin, "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3.[b] 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. It was so named by alchemists because it can dissolve noble metals like gold and platinum, though not all metals.
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