Sodium sulfite
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Names | |||
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IUPAC name
Sodium sulfite
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Other names
Hypo clear (photography)
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Identifiers | |||
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3D model (JSmol)
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard | 100.028.929 | ||
EC Number |
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E number | E221 (preservatives) | ||
PubChem CID
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RTECS number |
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UNII | |||
CompTox Dashboard (EPA)
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Properties | |||
Na2SO3 | |||
Molar mass | 126.043 g/mol | ||
Appearance | White solid | ||
Odor | Odorless | ||
Density | 2.633 g/cm3 (anhydrous) 1.561 g/cm3 (heptahydrate) | ||
Melting point | 33.4 °C (92.1 °F; 306.5 K) (dehydration of heptahydrate) 500 °C (anhydrous) | ||
Boiling point | Decomposes | ||
27.0 g/100 mL water (20 °C) | |||
Solubility | Soluble in glycerol Insoluble in ammonia, chlorine | ||
log P | −4 | ||
Acidity (pKa) | ~9 (heptahydrate) | ||
Refractive index (nD)
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1.565 | ||
Structure | |||
Hexagonal (anhydrous) Monoclinic (heptahydrate) | |||
Hazards | |||
Safety data sheet (SDS) | ICSC 1200 | ||
NFPA 704 (fire diamond) |
2
0
0 | ||
Flash point | Non-flammable | ||
Related compounds | |||
Other anions
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Sodium selenite | ||
Other cations
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Potassium sulfite | ||
Related compounds
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Sodium bisulfite Sodium metabisulfite Sodium sulfate | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
what is ?) | (|||
Infobox references | |||
Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.[1]
Preparation[]
Sodium sulfite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide. When conducted in warm water, Na2SO3 initially precipitates as a white solid. With more SO2, the solid dissolves to give the disulfite, which crystallizes upon cooling.[1]
- SO2 + 2 NaOH → Na2SO3 + H2O
Sodium sulfite is made industrially by treating sulfur dioxide with a solution of sodium carbonate.[2] The overall reaction is:
- SO2 + Na2CO3 → Na2SO3 + CO2
Applications[]
Sodium sulfite is primarily used in the pulp and paper industry.[3]
As an oxygen scavenger agent, it is used to treat water being fed to steam boilers to avoid corrosion problems,[4] in the photographic industry, it protects developer solutions from oxidation and (as hypo clear solution) to wash fixer (sodium thiosulfate) from film and photo-paper emulsions.
As a reducing agent it is used in the textile industry as a bleaching, desulfurizing, and dechlorinating agent (e.g. in swimming pools). Its reducing properties are exploited in its use as a preservative to prevent dried fruit from discoloring, and for preserving meats.
It is used as a reagent in sulfonation and sulfomethylation agent. It is used in the production of sodium thiosulfate.
Reactions[]
Heptahydrate[]
If sodium sulfite is allowed to crystallize from aqueous solution at room temperature or below, it does so as a heptahydrate.[1] The heptahydrate crystals effloresce in warm dry air. Heptahydrate crystals also oxidize in air to form the sulfate. The anhydrous form is much more stable against oxidation by air.[5]
References[]
- ^ a b c Johnstone, H. F. (1946). "Sulfites and Pyrosulfites of the Alkali Metals". Inorganic Syntheses. Inorganic Syntheses. 2. pp. 162–167. doi:10.1002/9780470132333.ch49. ISBN 9780470132333.
- ^ Weil, Edward D.; Sandler, Stanley R. (1999). "Sulfur Compounds". In Kroschwitz, Jacqueline I. (ed.). Kirk-Othmer Concise Encylclopedia of Chemical Technology (4th ed.). New York: John Wiley & Sons, Inc. p. 1937. ISBN 978-0471419617.
- ^ 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.
- ^ "Pre-boiler and Boiler Corrosion Control | GE Water".
- ^ Merck Index of Chemicals and Drugs, 9th ed. monograph 8451
- Photographic chemicals
- Sodium compounds
- Sulfites
- E-number additives