| IUPAC name
| Other names
|Molar mass||68.46 g/mol|
|Appearance||Colorless unstable liquid|
|Solubility||Reacts with amines and alkali, hydrogen peroxide|
Std enthalpy of
|Safety data sheet||None|
| Hydrochloric acid|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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.
- 2 HClO2 → HClO + HClO3
Chlorous acid is an unstable clear liquid, with an acrid odor.
The compound is not sold and has to be made in situ.
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
- Make perchloric acid
Chlorous acid is an unstable but corrosive compound. Wear proper protection when handling it.
Cannot be stored, decomposes.
Can be neutralized with a base containing a reducing agent, like thiosulfate, sulfite or metabisulfite.