Chlorous acid is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula HClO₂. It is a

weak acid Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a hydron (chemistry), proton, H+, and an anion, A-. The Dissociation (chemistry), dissociation of a strong acid in solution is effectively comple ...

. Chlorine has

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

+3 in this acid. The pure substance is unstable, disproportionating to

hypochlorous acid Hypochlorous acid (HClO, HOCl, or ClHO) is a weak acid that forms when chlorine dissolves in water, and itself partially dissociates, forming hypochlorite, ClO−. HClO and ClO− are oxidizers, and the primary disinfection agents of chlorine so ...

(Cl oxidation state +1) and

chloric acid Chloric acid, H Cl O3, is an oxoacid of chlorine, and the formal precursor of chlorate salts. It is a strong acid ( p''K''a ≈ −2.7 (''***note: pKa not in agreement with properties in chem box at right'')) and oxidizing agent. Properties Chlo ...

(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, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...

, derived from this acid is stable. One example of a salt of this anion is the well-known

sodium chlorite Sodium chlorite (NaClO2) is a chemical compound used in the manufacturing of paper and as a disinfectant. Use The main application of sodium chlorite is the generation of chlorine dioxide for bleaching and stripping of textiles, pulp, and pa ...

. This and related salts are sometimes used in the production of

chlorine dioxide Chlorine dioxide is a chemical compound with the formula ClO2 that exists as yellowish-green gas above 11 °C, a reddish-brown liquid between 11 °C and −59 °C, and as bright orange crystals below −59 °C. It is usually ...

Preparation

HClO₂ can be prepared through reaction of barium or lead chlorite and dilute

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

: :Ba(ClO₂)₂ + H₂SO₄ → BaSO₄ + 2 HClO₂ :Pb(ClO₂)₂ + H₂SO₄ → PbSO₄ + 2 HClO₂

Stability

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

halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...

to form an isolable acid of formula HXO₂.Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier Neither

bromous acid Bromous acid is the inorganic compound with the formula of HBrO2. It is an unstable compound, although salts of its conjugate base – bromites – have been isolated. In acidic solution, bromites decompose to bromine.Egon Wiberg, Arnold Frederick ...

nor

iodous acid The iodite ion, or iodine dioxide anion, is the halite with the chemical formula . Within the ion the Iodine exists in the oxidation state of +3. Iodite anion Iodites (including iodous acid) are highly unstable and have been observed but never ...

has ever been isolated. A few salts of

, bromites, are known, but no

iodite The iodite ion, or iodine dioxide anion, is the halite with the chemical formula . Within the ion the Iodine exists in the oxidation state of +3. Iodite anion Iodites (including iodous acid) are highly unstable and have been observed but never ...

References

Chlorites Halogen oxoacids Hydrogen compounds Oxidizing acids Oxidizing agents {{Inorganic-compound-stub