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perchloric acid[pər′klȯr·ik ′as·əd]
HClO4 a monobasic acid in which the chlorine has an oxidation number of + 7. Anhydrous perchloric acid is a colorless mobile liquid, which fumes in the air; it has a density of 1.761 g/cm3 at 20°C, a melting point of – 102°C, and a boiling point of 110°C. Perchloric acid is one of the strongest inorganic acids; its corresponding salts are the perchlorates (seePERCHLORATE). Anhydrous perchloric acid is very reactive and unstable. With water it forms a series of hydrates HClO4 · nH2O, where n = 0.25 to 4. Aqueous solutions of perchloric acid are stable and have a low oxidizing capability. With water, perchloric acid forms an azeotropic mixture, which boils at 203°C and contains 72 percent HClO4.
Aqueous solutions of perchloric acid are produced by the electrochemical oxidation of hydrochloric acid or chlorine dissolved in strong perchloric acid or by the exchange decomposition of sodium perchlorate or potassium perchlorate by strong inorganic acids. Concentrated aqueous solutions of perchloric acid are widely used in analytical chemistry, as well as in the production of perchlorates.
Anhydrous perchloric acid is produced by the interaction of sodium perchlorate or potassium perchlorate with strong sulfuric acid or by the interaction of aqueous solutions of perchloric acid with oleum (fuming sulfuric acid). It cannot be stored for long periods or transported long distances, since it decomposes slowly under ordinary conditions, becomes colored by the chlorine oxides formed during its decomposition, and may explode spontaneously.
Perchloric acid is used in the separation of complex ores and the analysis of minerals; it is also used as a catalyst.
REFERENCESRosolovskii, V. la. Khimiia bezvodnoi khlornoi kisloty. Moscow, 1966.
Iakimenko, L. M. Proizvodstvo khlora, kausticheskoi sody i neorganicheskikh khlorproduktov. Moscow, 1974.
Iakimenko, L. M., and M. I. Pasmanik. Spravochnik po proizvodstvu khlora, kausticheskoi sody i osnovnykh khlorproduktov, 2nd ed. Moscow, 1976.
L. M. IAKIMENKO