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| Names | |
|---|---|
| IUPAC name disulfite | |
| Other names
metabisulfite ion pyrosulfite | |
| Identifiers | |
| PubChem CID | |
| CompTox Dashboard (EPA) | |
| Properties | |
| Chemical formula | S2O5 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa).
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Infobox references
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A disulfite, commonly known as metabisulfite, is a chemical compound containing the disulfite ion (metabisulfite ion) .
Chemistry
Production of the disulfite ion
The disulfite ion is a dimer of the bisulfite ion (HSO3). It can arise from:
In aqueous solution, the disulfite ion is formed in minor amounts by dehydration of bisulfite in an equilibrium:
- 2 HSO3 (aq)
S2O5 (aq) + H2O (l)
Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.
In fact, disulfite is the ion of disulfurous acid (pyrosulfurous acid), which originates from sulfurous acid in accordance with the dehydration reaction above:
- 2 H2SO3 → 2 HSO3 + 2 H → H2S2O5 + H2O
addition
The disulfite ion also arises from the addition of sulfur dioxide to the sulfite ion:
HSO3  SO3 + HSO3 + SO2 S2O5 |
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Other reactions
In aqueous solution, disulfite salts decompose with acids:
S2O5 + H → HSO3 + SO2
Examples of disulfites
- sodium metabisulfite (E223) and potassium metabisulfite (E224) are used as a preservative and antioxidant in food.
References
- International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 130. Electronic version.
- Bassam Z. Shakhashiri: Chemical demonstrations: a handbook for teachers of chemistry The University of Wisconsin Press @Google Books, 1992, p.9