Perchloric acid (and inorganic perchlorates)

CAS 7601-90-3



HClO4 (maximum concentration commercially available is an aqueous solution containing about 72% HClO4 by weight)


Physical Properties

Colorless liquid

72% HClO4: bp 203 °C, mp -18 °C

Miscible with water





Vapor Pressure

6.8 mmHg at 25 °C


Toxicity Data

LD50 oral (rat)

1100 mg/kg


LD50 oral (dog)

400 mg/kg

Major Hazards

Highly corrosive to all tissues; reacts violently with many oxidizable substances; anhydrous form and certain salts are highly explosive.


Perchloric acid is a highly corrosive substance that causes severe burns on contact with the eyes, skin, and mucous membranes. The acute toxicity of perchloric acid is moderate. This substance is a severe irritant to the eyes, mucous membranes, and upper respiratory tract. Perchlorates are irritants to the body wherever they contact it.

Perchloric acid has not been shown to be carcinogenic or to show reproductive or developmental toxicity in humans


Flammability and Explosibility

Perchloric acid is noncombustible. The anhydrous (dehydrated) acid presents a serious explosion hazard. It is unstable and can decompose explosively at ordinary temperatures or in contact with many organic compounds.

Many heavy metal perchlorates and organic perchlorate salts are extremely sensitive explosives; the ammonium, alkali metal, and alkali earth perchlorates are somewhat less hazardous. Mixtures of perchlorates with many oxidizable substances are explosive.


Reactivity and Incompatibility

Cold 70% perchloric acid is a strong acid but is not considered to be a strong oxidizing agent; however, more concentrated solutions are good oxidizers. Temperature increases the oxidizing power of perchloric acid, and hot concentrated solutions are very dangerous. Evaporation of a spill of the 70% solution may lead to the formation of more dangerous concentrations. Reaction of 70% perchloric acid with cellulose materials such as wood,


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