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Sodium sulfite

Sodium sulfite
Names IUPAC name
Sodium sulfite
Other names
  • Hypo clear (photography)
  • E221
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard100.028.929EC Number
  • 231-821-4
E numberE221 (preservatives)
RTECS number
  • WE2150000
UNII
  • InChI=1S/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
    Key: GEHJYWRUCIMESM-UHFFFAOYSA-L
  • InChI=1/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
    Key: GEHJYWRUCIMESM-NUQVWONBAK
  • [O-]S(=O)[O-].[Na+].[Na+]
Properties Na2SO3Molar mass126.043g/mol Appearance White solid OdorOdorless Density2.633g/cm (anhydrous)
1.561g/cm (heptahydrate) Melting point33.4 °C (92.1 °F; 306.5 K) (dehydration of heptahydrate)
500 °C (anhydrous) Boiling pointDecomposes 27.0g/100mL water (20°C) SolubilitySoluble in glycerol
Insoluble in ammonia, chlorinelog P−4 Acidity (pKa) ~9 (heptahydrate) 1.565 Structure Hexagonal (anhydrous)
Monoclinic (heptahydrate) Hazards NFPA 704 (fire diamond)
2
0
0
Flash pointNon-flammable Safety data sheet (SDS) ICSC 1200Related compounds
Other anions
Sodium selenite
Other cations
Potassium sulfite
Related compounds
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).
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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. It is also suitable for the softening of lignin in the pulping and refining processes of wood and lignocellulosic materials. A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.

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