Chlorous acid

Chlorous acid
IUPAC name
Chlorous acid
13898-47-0 N
3D model (Jmol) Interactive image
ChEBI CHEBI:29219 YesY
ChemSpider 22861 YesY
KEGG C01486 YesY
PubChem 24453
Molar mass 68.46 g/mol
Acidity (pKa) 1.96
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chlorous acid is an inorganic compound with the formula HClO2. It is a weak acid. Chlorine has oxidation state +3 in this acid. The pure substance is unstable, disproportionating to hypochlorous acid (Cl oxidation state +1) and chloric acid (Cl oxidation state +5):

2 HClO2 → HClO + HClO3

Although the acid is difficult to obtain in pure substance, the conjugate base, chlorite, derived from this acid is stable. One example of a salt of this anion is the well-known sodium chlorite. This and related salts are sometimes used in the production of chlorine dioxide.


HClO2 can be prepared through reaction of barium chlorite and dilute sulfuric acid:

Ba(ClO2)2 + H2SO4 → BaSO4 + 2HClO2


Chlorous acid is a powerful oxidizing agent, although its tendency to disproportionation counteracts its oxidizing potential.

Chlorine is the only halogen to form an isolable acid of formula HXO2.[1] Neither bromous acid nor iodous acid has ever been isolated. A few salts of bromous acid, bromites, are known, but no iodites.[1]


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  1. 1 2 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5

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