Sodium sulfite

Sodium sulphite
Sodium sulfite
anhydrous
hydrate
Names
IUPAC name
Sodium sulfite
Other names
  • Hypo clear (photography)
  • E221
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.929 Edit this at Wikidata
EC Number
  • 231-821-4
E number E221 (preservatives)
RTECS number
  • WE2150000
UNII
  • InChI=1S/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 checkY
    Key: GEHJYWRUCIMESM-UHFFFAOYSA-L checkY
  • 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
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)
1.565
Structure
Hexagonal (anhydrous)
Monoclinic (heptahydrate)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 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
2
0
0
Flash point Non-flammable
Safety data sheet (SDS) ICSC 1200
Related 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).
☒N verify (what is checkY☒N ?)

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.[1] A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.[2]

  1. ^ "High Yield Pulp Production by Modified Sulfite Process" (PDF). Retrieved 2023-10-19.
  2. ^ Cite error: The named reference IS was invoked but never defined (see the help page).