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

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

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.

Preparation

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

Stability

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

Chlorine is the only halogen

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

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.