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| ==Chemistry== | ==Chemistry== | ||
| ===Production of the disulfite ion=== | |||
| balls tee hee | |||
| The disulfite ion is a ] of the ] ion (HSO<sub>3</sub><sup>−</sup>). It can arise from: | |||
| ''']''' | |||
| In aqueous solution, the disulfite ion is formed in minor amounts by dehydration of bisulfite in an equilibrium: | |||
| : 2 HSO<sub>3</sub><sup>−</sup> (aq) ] S<sub>2</sub>O<sub>5</sub><sup>2−</sup> (aq) + H<sub>2</sub>O (l) | |||
| Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.<ref name=Bassam>Bassam Z. Shakhashiri: The University of Wisconsin Press @Google Books, 1992, p.9</ref> | |||
| In fact, disulfite is the ion of ] (pyrosulfurous acid), which originates from ] in accordance with the dehydration reaction above:<br /> | |||
| :2 H<sub>2</sub>SO<sub>3</sub> → 2 HSO<sub>3</sub><sup>−</sup> + 2 H<sup>+</sup> → H<sub>2</sub>S<sub>2</sub>O<sub>5</sub> + H<sub>2</sub>O | |||
| '''addition''' | |||
| The disulfite ion also arises from the addition of ] to the ] ion:<br /> | |||
| {| class="wikitable" | |||
| |- | |||
| |HSO<sub>3</sub><sup>−</sup> ] SO<sub>3</sub><sup>2−</sup> + H<sup>+</sup><br /><br />SO<sub>3</sub><sup>2−</sup> + SO<sub>2</sub> ] S<sub>2</sub>O<sub>5</sub><sup>2−</sup> || || ] | |||
| |} | |||
| ===Other reactions=== | ===Other reactions=== | ||
Revision as of 01:09, 15 December 2011
Not to be confused with Bisulfite. | |
| 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 |
 |
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