Disulfite
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| Names | |
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| IUPAC name
disulfite [1]
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| Other names
metabisulfite ion
pyrosulfite |
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| Identifiers | |
| PubChem | 159940 |
| Properties | |
| S2O5 | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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A disulfite, commonly known as metabisulfite, is a chemical compound containing the disulfite ion (metabisulfite ion) [S2O5]2−.
Contents
Reactions
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)
S2O52− (aq) + H2O (l)
Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.[2]
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−  SO32− + H+SO32− + SO2 S2O52− |
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Other reactions
In aqueous solution, disulfite salts decompose with acids:
- S2O52− + 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
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