Chlorous acid
Chlorous acid is an inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula HClO2. It is a weak acid
Weak acid
A weak acid is an acid that dissociates incompletely. It does not release all of its hydrogens in a solution, donating only a partial amount of its protons to the solution...

. Chlorine has oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

 +3 in this acid. The pure substance is unstable, disproportionating
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....

 to hypochlorous acid
Hypochlorous acid
Hypochlorous acid is a weak acid with the chemical formula HClO. It forms when chlorine dissolves in water. It cannot be isolated in pure form due to rapid equilibration with its precursor...

 (Cl oxidation state +1) and chloric acid
Chloric acid
Chloric acid, HClO3, is an oxoacid of chlorine, and the formal precursor of chlorate salts. It is a strong acid and oxidizing agent....

 (Cl oxidation state +5):
2 HClO2 → HClO + HClO3

Although the acid is difficult to obtain in pure substance, the conjugate base, chlorite
The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...

, derived from this acid are stable. One example is the salt is well known sodium chlorite
Sodium chlorite
Sodium chlorite is a chemical compound used in the manufacture of paper.-Use:The main application of sodium chlorite is the generation of chlorine dioxide for bleaching and stripping of textiles, pulp, and paper. It is also used for disinfection of a few municipal water treatment plants after...

. 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
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

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
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

 to form an isolable acid of formula HXO2. Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

 resists oxidation above the 1+ level. Neither bromous acid nor iodous acid have been isolated. A few salts of bromous acid
Bromous acid
Bromous acid with the formula HBrO2 has bromine in the +3 oxidation state. The salts of bromous acid are called bromites. The acid is not stable and only occurs as an intermediate, for example in the oxidation of hypobromites.- Chemistry :...

, bromites, are known, but no iodites.
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