Chloroauric acid

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Chloroauric acid
Chloroauric acid by Tdep.png
Chloroauric acid in solution above unreacted gold
Other names
Auric acid
Aurochloric acid
Brown gold chloride
Chlorauric acid
Hydrogen aurichloride
Hydrogen tetrachloroaurate
Molar mass 339.785 g/mol (anhydrous)
393.833 g/mol (trihydrate)
411.85 g/mol (tetrahydrate)
Appearance Orange-yellow solid
Density 3.9 g/cm3 (anhydrous)
2.89 g/cm3 (tetrahydrate)
Melting point 254 °C (489 °F; 527 K) (decomposes)
Boiling point Decomposes
350 g/100 ml
Solubility Soluble in alcohols, esters, ethers, ketones
Safety data sheet Sigma-Aldrich (hydrated)
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chloroauric acid  (HAuCl4) is an orange solid commonly encountered in gold refinement, extraction and chemistry.



Many reducing agents reduce chloroauric acid to metallic gold, which falls out of solution as a yellow powder. Oxalic acid and sodium metabisulfite are often used in this way to produce the pure metal from dissolved scrap gold.

Like other Au(III) compounds, reaction with gaseous or solutions of ammonia will precipitate the dangerously explosive 'fulminating gold', with explosive properties similar to silver acetylide.


While hygroscopic, solutions and the solid are stable at standard conditions. 


As expected, chloroauric acid is expensive and often only marketed for high end chemistry applications. Because of this, it is generally only available from suppliers at a very high purity, driving up the price further. 


Chloroauric acid is prepared by dissolving gold in aqua regia, a mix of concentrated hydrochloric and nitric acids. This results in an orange-yellow solution that can be dried in a desiccator. The solid is very hygroscopic, so calculating accurate yields based on weight is difficult. 


  • Refining gold from scrap



The usual precautions when dealing with strong acids should be in place, as not only is chloroauric acid a strong acid, but unless dried, solutions may contain traces of either of the two corrosive mineral acids used to make it. 


Shouldn't be stored for long periods of time.


Due the price of gold, all efforts should obviously be taken to avoid any wastage. Solutions of Au(III) are not overly toxic, but due to the ease at which it can be reduced, solutions of Au(III) should be reduced to the metal before disposal.


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