Phosphorous acid

Phosphorous acid is the compound described by the formula H₃PO₃. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds.

Nomenclature

The term phosphorous acid is the IUPAC name for the compound P(OH)₃. In the context of chemistry, the term is used more broadly to refer to the family of compounds H_nPO₃-n.

Properties

Phosphorous acid is a weak acid. It is diprotic, not triprotic as might be suggested by this formula. The compound is colorless and odorless, and is soluble in water.

Preparation

Phosphorous acid is prepared by hydrolysis of phosphorus trichloride with water or steam:

PCl₃ + 3 H₂O → H₃PO₃ + 3 HCl

Uses

Phosphorous acid is mainly used for preparing phosphite salts, such as potassium phosphite. These salts are used as reducing agents and in the preparation of other phosphorus compounds.

Safety

Phosphorous acid and its salts are toxic and should be handled with care.

See also

• Phosphoric acid
• Phosphorus pentoxide
• Phosphorus trichloride

References

Phosphorous acid Resources
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