Perchloric Acid

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perchloric acid

[pər′klȯr·ik ′as·əd]
(inorganic chemistry)
HClO4 Strongly oxidizing, corrosive, colorless, hygroscopic liquid, boiling at 16°C (8 mmHg, or 1067 pascals); soluble in water; unstable in pure form, but stable when diluted in water; used in medicine, electrolytic baths, electropolishing, explosives, and analytical chemistry, and as a chemical intermediate. Also known as Fraude's reagent.

Perchloric Acid


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.


Rosolovskii, 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.


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Before highlighting the mechanism of the oxidation reaction it is worthwhile at this stage to have an idea regarding the reacting species of NCSA in aqueous acetic acid medium in the presence of perchloric acid.
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Perchloric acid and radioisotope hoods and biological safety cabinets are generally segregated from general chemical exhaust due to incompatibility or special operating conditions.
Two methods were used to measure total P on finely ground soil: (i) perchloric acid digestion (Sommers and Nelson 1972) and (ii) modified Kjeldhal digestion with sulfuric acid/potassium sulfate (Heffernan 1985).
The standards used for electrochemical detection were made fresh daily in 1 N perchloric acid (PCA) and included L-dopa, dopamine, dihydroxyphenyl acetic acid (DOPAC), and 3,4-dihydroxybenzylamine (DHBA).
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One gram of dried and ground plant tissue was digested with 10 mL of acid mixture (nitric acid, 750 mL; sulphuric acid, 150 mL; perchloric acid 60 per cent, 300 mL).
The sample was weighed and a total of 2 mL of 60% perchloric acid (Merck Darmstadt Germany) was added to samples in fume hood.