Aqua regia

• King acid
• Aqua regis
• Aqua regia

Yellow to reddish-brown liquid

Liquid

Completely miscible with water

Risk

Template: Infobox chemical / molecular formula search is not possible

Aqua regia, rarely also called King acid is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a 3:1 ratio.

Naming

The name of aqua regia (Latin aqua aqua regia or registered, royal water ') derives from the ability of this mixture to solve the " royal " precious metals gold and platinum. Gold thereby Tetrachloridogold ( III) acid, platinum, platinum ( IV) chloride from the resulting Hexachloridoplatinsäure formed.

Chemical effect on other materials

For the aggressiveness of aqua regia are not responsible acids per se, but the reaction product formed when both acids are mixed.

There arise nascent chlorine and nitrosyl chloride ( NOCl ) which gold and other precious metals such as platinum and palladium are able to oxidize. Silver is not dissolved because this is passivated by the formation of an insoluble silver chloride layer from further attack. The high concentration of chloride ions increase the solubility of the noble metals, they are dissolved in the form of anionic chlorido complexes; illustrated here using the example of the reaction of gold to Tetrachloridogoldsäure:

Zirconium, hafnium, niobium, tantalum, titanium, ruthenium, tungsten and resist attack by aqua regia at room temperature due to passivation.

Aqua regia decomposes by itself, with chlorine as a radical, nitrosyl chloride and nitrogen oxides are released. Therefore, it is usually prepared fresh immediately prior to use of the two acids.

Aqua regia, a mixture of nitric acid and hydrochloric acid has Gefahrgutrecht the UN number UN 1798. His promotion on European roads is prohibited under the European Convention on the carriage of dangerous goods by road.

Applications

• With the help of aqua regia and a precious metal preparations for porcelain and stained glass are made.
• In analytical chemistry aqua regia application is in the digestion of poorly soluble material samples. (see also aqua regia digestion)
• In different concentrations, it still serves today to the Karätigkeit to check ( an old term for fineness ) of gold. The solubility of an abrasion test in the various solutions is tested.

Previously aqua regia was applied externally ( in high dilution ):

" In the winter of 1857-58 I had a sick in my wards, which anesthesia zurückbehielt of frostbite of the feet, while I applied, among other locale bathrooms with aqua regia. "

Historical anecdote

As in World War II, German troops occupied in April 1940, the Danish capital, Copenhagen, in the laboratory working of Niels Bohr Hungarian chemist George de Hevesy dissolved the gold Nobel Prize medals of German physicists Max von Laue and James Franck in aqua regia, so as to access to be prevented by the Nazis. From Laue and Franck were in opposition to National Socialism in Germany and, therefore, had their medals Niels Bohr entrusted to prevent such a confiscation in Germany; the Hitler government forbade all Germans accepting or carrying the Nobel Prize, after the anti-Nazi Carl von Ossietzky had received the Nobel Peace Prize in 1935. After the war, de Hevesy extracted in aqua regia, the "hidden" gold and gave it to the Royal Swedish Academy of Sciences, which produced therefrom new medals and handed back to von Laue and Franck.