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 chemi ...
with the formula HClO
2. 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. ...
+3 in this acid. The pure substance is unstable,
disproportionating
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...
to
hypochlorous acid (Cl oxidation state +1) and
chloric acid (Cl oxidation state +5):
: 2 HClO
2 → HClO + HClO
3
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 chl ...
, 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 pap ...
. 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
HClO
2 can be prepared through reaction of barium or lead chlorite and dilute
sulfuric acid:
:Ba(ClO
2)
2 + H
2SO
4 → BaSO
4 + 2 HClO
2
:Pb(ClO
2)
2 + H
2SO
4 → PbSO
4 + 2 HClO
2
Stability
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 HXO
2.
[Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier ] Neither
bromous acid nor
iodous acid has ever been isolated. A few salts of
bromous acid, bromites, are known, but no
iodites.
References
Chlorites
Halogen oxoacids
Hydrogen compounds
Oxidizing acids
Oxidizing agents
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