Perchloric acid

Perchloric acid is a mineral acid with the formula HClO4 . Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid and nitric acid . It is a powerful oxidizer when heated , but aqueous solutions of up to about 70% by weight at room temperature are generally safe, showing only strong acid characteristics and no oxidizing properties. Perchloric acid perchlorate salts , especially ammonium perchlorate , an important rocket fueluseful for preparingConstituent. Perchloric acids is dangerously corrosive and readily forms potentially explosive mixtures.


Perchloric acid is produced industrially in two ways. The conventional method exploits the high aqueous solubility of sodium perchlorate (209 g/100 mL water at room temperature). Treatment of such a solution with hydrochloric acid gives perchloric acids, precipitating solid sodium chloride:NaClO 4 + HCl → NaCl + HClO 4

The concentrated acid can be purified by distillation. The alternative route, which is more straightforward and avoids salts, requires the anodic oxidation of aqueous chlorine at the platinum electrode. [5] [6]

laboratory preparation

Treatment of barium perchlorate with sulfuric acid precipitates barium sulfate, leaving perchloric acid. It can also be made by boiling nitric acid with ammonium perchlorate and then adding hydrochloric acid. The reaction gives nitrous oxide and perchloric acids due to a concurrent reaction involving the ammonium ion and can be significantly concentrated and purified by boiling off the remaining nitric and hydrochloric acids.


Anhydrous perchloric acid is a volatile oily liquid at room temperature. It forms at least five hydrates, many of which have been characterized crystallographically. These solids contain perchlorate ions attached to H 2 O and H 3 O + centers via hydrogen bonds [7] perchloric acid forms an azeotrope with water, which contains about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are hygroscopic. Thus, if left open to air, concentrated perchloric acids dilutes itself by absorbing water from the air.

Dehydration of perchloric acid gives the anhydride dichlorine heptoxide: [8]2 HClO 4 + P 4 O 10 → Cl 2 O 7 + “H 2 P 4 O 11 “


Perchloric acid is mainly produced as a precursor to ammonium perchlorate, which is used in rocket fuel. The increase in rocketry has increased the production of perchloric acids. Several million kilograms are produced annually. [5] Perchloric acids is one of the most proven materials for etching liquid crystal displays and important electronics applications as well as ore extraction and has unique properties in analytical chemistry. [9] Additionally it is a useful component in etching chrome [10]

as an acid

Perchloric acid, a superacid, is one of the strongest Brnsted-Lowry acids. Its reason that p K has a lower than -9 is evidenced by the fact that its monohydrate contains discrete hydronium ions and can be isolated as a stable, crystalline solid, prepared as [H 3 ] O + ] [ chlorine monoxide
4[11] The most recent estimate of its aqueous pK is-15.2 ± 2.0 . [ 3 ] It provides strong acidity with minimal interference because perchlorate is weakly nucleophilic ( explain the high acidity of HClO4). Other acids of non-coordinating anions, such as fluoroboric acid and hexafluorophosphoric acid, are susceptible to hydrolysis, whereas perchloric acid is not. The acid is often preferred in some syntheses, despite the dangers associated with the explosiveness of its salts. [12] For similar reasons it is a useful eluent in ion exchange chromatography.

It is also used for electropolishing or etching of aluminum, molybdenum and other metals.


Given its strong oxidizing properties, perchloric acid is subject to extensive regulations. [13] It is highly reactive with metals (eg, aluminum) and organic materials (wood, plastics). Work done with perchloric acid with wash-down capability should be conducted in a fume hood to prevent accumulation of oxidizer in the ductwork.

On February 20, 1947, 17 people were killed and 150 injured in Los Angeles, California when a bath, consisting of 75% perchloric acid and 25% acetic anhydride by volume, exploded. The O’Connor electro-plating plant, 25 other buildings, and 40 automobiles were destroyed, and 250 nearby homes were damaged. The bath was being used to electro-polish aluminum furniture. Furthermore, when an iron rack was replaced with one coated with cellulose acetobutyrate (Tenit-2 Plastics), organic compounds were added to the superheating bath. A few minutes later the bath exploded.

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