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Potassium metabisulfite

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Potassium metabisulfite
Potassium metabisulfite
Names
Other names
  • Potassium pyrosulfite
  • Dipotassium disulfite
  • Potassium metabisulphite
  • Dipotassium disulphite
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.037.072 Edit this at Wikidata
E number E224 (preservatives)
PubChem CID
RTECS number
  • TT4920000
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2Key: RWPGFSMJFRPDDP-UHFFFAOYSA-L
  • InChI=1/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2Key: RWPGFSMJFRPDDP-NUQVWONBAF
SMILES
  • ..S(=O)S()(=O)=O
Properties
Chemical formula K2O5S2
Molar mass 222.31 g·mol
Appearance White crystalline powder
Odor Pungent (sulfur dioxide)
Density 2.34 g/cm (solid)
Melting point 190 °C (374 °F; 463 K) decomposes
Solubility in water 450 g/L (20 °C)
Solubility Insoluble in ethanol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards Irritant, asthma risk
GHS labelling:
Pictograms GHS05: CorrosiveGHS07: Exclamation mark
Signal word Danger
Hazard statements H315, H318, H335
Precautionary statements P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P310, P312, P321, P332+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1 0 0
Safety data sheet (SDS) ICSC 1175
Related compounds
Other anions Potassium bisulfite
Potassium sulfite
Other cations Sodium metabisulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkY verify (what is  ?) Infobox references
Chemical compound

Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour. It is mainly used as an antioxidant or chemical sterilant. As a disulfite, it is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite has a monoclinic crystal structure.

Preparation and reactions

Main article: bisulfite § Reactions

Potassium metabisulfite can be prepared by treating a solution of potassium hydroxide with sulfur dioxide.

2 SO2 + 2 KOH → K2S2O5 + H2O

It decomposes at 190 °C, yielding potassium sulfite and sulfur dioxide:

K2S2O5 → K2SO3 + SO2

Uses

It is used as a food additive, also known as E224. It is restricted in use and may cause allergic reactions in some sensitive persons.

Wine

Potassium metabisulfite is a common wine or must additive, in which it forms sulfur dioxide (SO2). Sulfur dioxide is a disinfectant. It also acts as a potent antioxidant, protecting both the color and delicate flavors of wine.

A high dose would be 3 grams of potassium metabisulfite per six-gallon bucket of must or around 132 milligrams per liter (yielding roughly 75 ppm of SO2) prior to fermentation; then 6 grams per six-gallon bucket (150 ppm of SO2) at bottling. Some countries regulate the SO2 content of wines.

Winemaking equipment is sanitized by spraying with a 1% SO2 (2 tsp potassium metabisulfite per L) solution.

Beer

Potassium metabisulfite is sometimes used in the brewing industry to inhibit the growth of wild bacteria and fungi. This step is called 'stabilizing'. It is also used to neutralize monochloramine from tap water. It is used both by homebrewers and commercial brewers alike. It is not used as much for brewing beer, because the wort is almost always boiled, which kills most microorganisms.

Other uses

  • Potassium metabisulfite is sometimes added to lemon juice as a preservative.
  • Potassium metabisulfite is used in the textile industry for dyeing and cotton printing.
  • Potassium metabisulfite is sometimes used to precipitate gold from solution in aqua regia (as an alternative to sodium sulfite).
  • It is a component of certain photographic developers and solutions used in photographic processing, keeping active developing species from contact with oxygen.
  • It is used as a bleaching agent in the production of coconut cream.
  • It is used in some pickles as a preservative.
  • It is used in tint etching iron-based metal samples for microstructural analysis.
  • It is used in aam papad as a preservative.

See also

References

  1. Barberá, José Jiménez; Metzger, Adolf; Wolf, Manfred (2000). "Sulfites, Thiosulfates, and Dithionitesl Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a25_477. ISBN 3527306730.
  2. Johnstone, H. F. (1946). "Sulfites and Pyrosulfites of the Alkali Metals". Inorganic Syntheses. Vol. 2. pp. 162–167. doi:10.1002/9780470132333.ch49. ISBN 9780470132333.
  3. List of E-number food additives
  4. Metcalfe, Dean D.; Simon, Ronald A. (2003). Food allergy: adverse reactions to food and food additives. Malden, MA: Wiley-Blackwell. pp. 324–339. ISBN 978-0-632-04601-0.
  5. Gorman-McAdams, Mary (July 9, 2020). "The Truth About Sulfites in Wine & the Myths of Red Wine Headaches". The Kitchn. Retrieved February 10, 2024.
  6. "Potassium Metabisulfite".
  7. "Color Metallography". 2011-05-04.
Potassium compounds
H, (pseudo)halogens
chalcogens
pnictogens
B, C group
transition metals
organic
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