Chlorous acid

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Chlorous acid
Names
IUPAC name
Chlorous acid
Other names
Hypochloric acid
Hydrogen dioxochlorate(III)
Properties
HClO2
Molar mass 68.46 g/mol
Appearance Colorless unstable liquid
Odor Acrid
Miscible
Solubility Reacts with amines and alkali, hydrogen peroxide
Acidity (pKa) 1.96
Thermochemistry
-319.4 J·K−1·mol−1
175.3 kJ/mol
Hazards
Safety data sheet None
Related compounds
Related compounds
Hydrochloric acid
Hypochlorous acid
Chloric acid
Perchloric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chlorous acid is an inorganic compound with the formula HClO2. It is a weak acid.

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

Properties

Chemical

The pure acid is unstable, disproportionating to hypochlorous acid and chloric acid:

2 HClO2 → HClO + HClO3

Both resulting acids are also unstable in concentrated form, and will too further decompose to hydrochloric acid, perchloric acid chlorine, chlorine dioxide and oxygen.

Physical

Chlorous acid is an unstable clear liquid, with an acrid odor.

Availability

The compound is not sold and has to be made in situ.

Preparation

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

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

Projects

Handling

Safety

Chlorous acid is an unstable but corrosive compound. Wear proper protection when handling it.

Storage

Cannot be stored, decomposes.

Disposal

Can be neutralized with a base containing a reducing agent, like thiosulfate, sulfite or metabisulfite.

References

Relevant Sciencemadness threads