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What is Aqua Regia?

The ancient alchemists called gold the "king of metals". Gold does not have normal acid, so when it was opened acid, which can dissolve this noble metal, the alchemists called it the"Royal vodka" (Aqua regia is more correctly translated from Latin as "Royal water"). Aqua Regia can dissolve not only the gold, and platinum.

What is Aqua Regia? It is a mixture of two acids - hydrochloric and nitrogen in the ratio of 3:1 (three volume parts of hydrochloric acid to 1 volume part nitric acid). Aqua Regia - yellow liquid with the odor of chlorine and oxides of nitrogen.

First Imperial vodka received Italian alchemist Bonaventure in 1270 it is Curious that at the moment hydrochloric acid was not yet known to science. Tsarskaya vodka then prepared by distilling a mixture of nitrate, copper sulphate and alum with the addition of ammonia.

Oxidative properties of Aqua Regia when storing lost, because in the air it evaporates chlorine, and it is important in the oxidation reactions. Therefore suitable only freshly prepared reagent.

As Aqua Regia effect on precious metals?

First, nitric acid reacts with the salt. This created two strongest oxidant - nitrosylchloride and chlorine:

HNO3 + 3HCl = NOCl + Cl2 + 2H2O.

These two reagent paired able to oxidize gold even at room temperature:

Au + NOCl2 + Cl2 = AuCl3 + NO.

The resulting chloride of gold AuCl3 immediately attaches one molecule of hydrochloric acid HCl, forming tetrachlorosilane acid (known as "gold chloride"):

AuCl3 + HCl = H [AuCl4]].

Total oxidation of gold Imperial vodka looks like this:

Au + 4HCl + HNO3 = H [AuCl4] + NO ↑ + 2H2O.

Tetrachlorotoluene acid crystallizes with four molecules of water: H(AuCl4) · 4H2O. the Crystals of her pale yellow, aqueous solution also painted in yellow color.

Similar reaction takes place with platinum with the formation of hexachloroplatinic acid H2 [PtCl6]:

3Pt + 18 HCl + 4HNO3 = 3 H2 [PtCl6] + 4NO ↑ + 8H2O

To get from the hydrate by tetrachlorotoluene acid pure gold is very simple: it needs to be heated. When heated "gold chloride" decomposes with evolution of HCl and reddish-brown crystals of chloride of gold (III) AuCl3. If you handle the solution of chloride of gold (III) hydroxide lye NaOH, falls yellow-brown oxide of gold(III) AU(OH)3, which upon heating is converted into oxide gold AI2O3. And oxide gold at temperatures above 220° decomposes: AI2Of3 = 4Au + 3O2.

By the way...

Gold, in addition to Aqua Regia dissolves in hot concentrated selenium acid:

2Au + 6H2SeO4 = Au2 (SeO4)3 + 3H2 SeO3 + 3H2O.

This is interesting!

A unique property of Aqua Regia was used during the Second World war, the famous Danish physicist and Nobel laureate Niels Bohr. In 1943, fleeing from the Nazi invaders, he was forced to leave Copenhagen. But he held two gold Nobel medal to his fellow German physicists anti-fascists James Franck and max von Laue (medal of the Boron was removed from Denmark earlier). Not risking to take the medals with him, he dissolved them in Aqua Regia and put unremarkable bottle away on the shelf, where it remained many bottles of bubbles with different liquids. Returning after the war in his laboratory, Boron primarily found precious bottle. At his request, the staff was isolated from the solution of gold and re-made both medals.

(read more here)

 


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Your comments:

petrtaranenko@rambler.ru
2013-08-07 10:49:55
A wonderful invention!!But in your home to determine the presence of gold on the product?
Chemist
2012-03-30 04:21:22
Oxidant in Aqua Regia is nitrosylchloride, or more specifically nitrosyl-cation.
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