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AQUA - 5 reference results
aqua regia [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 reduction), but the chemical equilibrium 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 ion, 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 fortis: see nitric acid.

Alcoholic beverage obtained by distillation from wine or other fermented fruit juice or from various cereal grains that have first been brewed. The essential ingredient is usually a natural sugar or a starchy substance that may be easily converted into a sugar. The distillation process is based on the different boiling points of water (212 °F [100 °C]) and alcohol (173 °F [78.5 °C]). The alcohol vapours that arise while the fermented liquid boils are trapped and recondensed to create a liquid of much greater alcoholic strength. The resultant distillate is matured, often for several years, before it is packaged and sold. Seealso aquavit; brandy; gin; liqueur; rum; vodka; and whiskey.

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Inorganic compound, colourless, fuming, highly corrosive liquid, chemical formula HNO3. A common laboratory reagent, it is important in the manufacture of fertilizers and explosives (including nitroglycerin), as well as in organic syntheses, metallurgy, ore flotation, and reprocessing of spent nuclear fuel. A strong acid, it is toxic and can cause severe burns. It attacks most metals and is used for etching steel and photoengraving.

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