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nitric acid, chemical compound, HNO3, colorless, highly corrosive, poisonous liquid that gives off choking fumes in moist air. It is miscible with water in all proportions. It forms an azeotrope (constant-boiling mixture) that has the composition 68% nitric acid and 32% water and that boils at 120.5°C. The nitric acid of commerce is typically a solution of 52% to 68% nitric acid in water. More concentrated solutions are available. Solutions containing over 86% nitric acid are commonly called fuming nitric acid; they often have a reddish-brown color from dissolved nitrogen oxides. Nitric acid is a strong oxidizing agent. It ionizes readily in solution, forming a good conductor of electricity. It reacts with metals, oxides, and hydroxides, forming nitrate salts. Chief uses of nitric acid are in the preparation of fertilizers, e.g., ammonium nitrate, and explosives. It is also used in the manufacture of chemicals, e.g., in making dyes. It is produced chiefly by oxidation of ammonia (the Ostwald process). Small amounts are produced by the treatment of sodium nitrate with sulfuric acid. Nitric acid was known to the alchemists as aqua fortis; the name is used in commerce for impure grades of it. Aqua regia is a mixture of nitric and hydrochloric acids.
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