aqua regia


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aqua regia

(äk`wə rē`jēə) [Lat.,=royal water], corrosive, fuming yellow liquid prepared by mixing one volume of concentrated nitric acid with three to four volumes of concentrated hydrochloric acid. It was so named by the alchemists because it dissolves gold and platinum, the "royal" metals, which do not dissolve in nitric or hydrochloric acid alone. Its fumes and yellow color are caused by reaction of nitric acid, HNO3, with hydrogen chloride, HCl, to form nitrosyl chloride, NOCl, chlorine, Cl2, and water; both chlorine and nitrosyl chloride are yellow-colored and volatile. The nitrosyl chloride further decomposes to nitric oxide, NO, and chlorine. Nitric acid is a powerful oxidizing agent (see oxidation and reductionoxidation and reduction,
complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation
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), but the chemical equilibriumchemical equilibrium,
state of balance in which two opposing reversible chemical reactions proceed at constant equal rates with no net change in the system. For example, when hydrogen gas, H2, and iodine gas, I2
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 for its reaction with gold, Au, only permits formation of a tiny amount of Au+3 ion, so the amount of gold dissolved in pure nitric acid is undetectable. The presence of chloride ion, Cl, allows formation of the stable chloraurate complex ioncomplex ion,
charged molecular aggregate (see ion), consisting of a metallic atom or ion to which is attached one or more electron-donating molecules. In some complex ions, such as sulfate, SO4−2
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, AuCl4. Because of the high concentration of chloride ion in aqua regia, the Au+3 is reacted almost as soon as it is formed, keeping its concentration low; this allows oxidation of more Au to Au+3, and the gold is dissolved. The gold may also react directly with the free chlorine in aqua regia, since chlorine is a powerful oxidizing agent.

Aqua Regia

 

a mixture of concentrated hydrochloric and nitric acids, usually one part nitric acid and three parts hydrochloric acid. Aqua regia is a yellow liquid with the odor of nitrogen oxides and chlorine. It has strong oxidizing properties owing to the liberation of chlorine in the reactions

3HCl + HNO3 = Cl2 + NOCl + 2H2O

2NOCl = 2NO + Cl2

Aqua regia dissolves all metals with the exception of silver, rhodium, and iridium. It even dissolves gold—hence the name “aqua regia,” given by alchemists who considered gold the king of metals. Aqua regia is used as a laboratory reagent in such processes as the refining of gold and platinum and the production of metal chlorides.

aqua regia

[¦äk·wə ′rē·jə]
(inorganic chemistry)
A fuming, highly corrosive, volatile liquid with a suffocating odor made by mixing 1 part concentrated nitric acid and 3 parts concentrated hydrochloric acid; reacts with all metals, including silver and gold.

aqua regia

a yellow fuming corrosive mixture of one part nitric acid and three to four parts hydrochloric acid, used in metallurgy for dissolving metals, including gold
References in periodicals archive ?
The findings in this report are subject to some limitations, which include the wide range of results obtained from the use of the aqua regia method known to be susceptible to acid interference.
The samples were air freighted to the ALS Chemex Lab in Brisbane, Australia for geochemical analysis by ICP-MS following aqua regia digestion (detection limit 1 ppb).
Gold content in the soil was determined by analyzing 10 gram samples of minus 200 mesh, adding 10 ml 1:1 aqua regia, absorbing with active carbon, reducing to ashes, dissolving in another 5 ml 1:1 aqua regia with gold detection by spectrophotometer.
The gold content of each sample was determined by analyzing 20-gram sample of the minus 200-mesh material through an aqua regia acid digestion and then analyzed for gold using atomic absorption.
Separately, Mascot's Board also approved the acquisition of Aqua Regia for a value of approximately $0.
Mascot's combination with eJiva's solutions business and Toronto Development Center will become effective January 1, 2003 while its combination with Aqua Regia will become effective April 1, 2003.
All samples have been shipped to ALS Chemex Laboratories in Vancouver where the analytical procedure consists of pulverizing split samples followed by aqua regia digestion and atomic absorption finish.
In a significant strategic move to enhance Mascot's business, the Company today announced the proposal to acquire eJiva and Aqua Regia.
As an extended part of the acquisition Mascot will also acquire the Hyderabad-based Aqua Regia, a technology services and consulting company, which provides offshore services exclusively to eJiva.
Analyses were completed at ALS Chemex Laboratories in Vancouver using pulverized split samples with aqua regia digestion and atomic absorption finish.