Sodium bisulfite

Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO₃. Sodium bisulfite in fact is not a real compound,[2] but a mixture of salts that dissolve in water to give solutions composed of sodium and bisulfite ions. It is a white solid with an odour of sulfur dioxide. Regardless of its ill-defined nature, "sodium bisulfite" is a food additive with E number E222.

Sodium bisulfite

Names
IUPAC name Sodium hydrogen sulfite
Other names E222, sodium bisulphite
Identifiers
CAS Number	7631-90-5
3D model (JSmol)	Interactive image
ChEBI	CHEBI:26709
ChEMBL	ChEMBL1689285
ChemSpider	571016
ECHA InfoCard	100.028.680
E number	E222 (preservatives)
PubChem CID	23665763
RTECS number	VZ2000000
UNII	TZX5469Z6I
CompTox Dashboard (EPA)	DTXSID8034902
InChI InChI=1S/Na.H2O3S/c;1-4(2)3/h;(H2,1,2,3)/q+1;/p-1 Key: DWAQJAXMDSEUJJ-UHFFFAOYSA-M InChI=1/Na.H2O3S/c;1-4(2)3/h;(H2,1,2,3)/q+1;/p-1 Key: DWAQJAXMDSEUJJ-REWHXWOFAL
SMILES [Na+].[O-]S(=O)O
Properties
Chemical formula	NaHSO3
Molar mass	104.061 g/mol
Appearance	White solid
Odor	Slight sulfurous odor
Density	1.48 g/cm^3
Melting point	150 °C (302 °F; 423 K)
Boiling point	315 °C (599 °F; 588 K)
Solubility in water	42 g/100 mL
Refractive index (nD)	1.526
Hazards
EU classification (DSD) (outdated)	Harmful (Xn)
R-phrases (outdated)	R22 R31
S-phrases (outdated)	(S2), S25, S46
NFPA 704 (fire diamond)	0 2 1
Flash point	Non-flammable
NIOSH (US health exposure limits):
PEL (Permissible)	none[1]
REL (Recommended)	TWA 5 mg/m^3[1]
IDLH (Immediate danger)	N.D.[1]
Related compounds
Other anions	Sodium sulfite Sodium metabisulfite
Other cations	Potassium bisulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Sodium bisulfite solutions can be prepared by treating a solution of suitable base, such as sodium hydroxide or sodium bicarbonate with sulfur dioxide.

SO₂ + NaOH → NaHSO₃

SO₂ + NaHCO₃ → NaHSO₃ + CO₂

Attempts to crystallise the product yield sodium disulfite, Na₂S₂O₅.[3]

Reactivity and uses

A tank containing 25% sodium bisulfite at a water treatment plant in Sunnyvale, California.

Sodium bisulfite is a common industrial reducing agent, as it readily reacts with dissolved oxygen:

2 NaHSO₃ + O₂ → 2 NaHSO₄

It is usually added to large piping systems to prevent oxidative corrosion. In biochemical engineering applications, it is helpful to maintain anaerobic conditions within a reactor.

It is used for preserving food and beverages.

See also

• Sodium metabisulfite
• Calcium bisulfite
• Potassium bisulfite
• Croscarmellose sodium
• Sulfurous acid

References

1. NIOSH Pocket Guide to Chemical Hazards. "#0561". National Institute for Occupational Safety and Health (NIOSH).
2. Tudela, David; Jenkins, H. Donald B. (2003). "New Methods to Estimate Lattice Energies: Application to the Relative Stabilities of Bisulfite (HSO₃⁻) and Metabisulfite (S₂O₅^2-) Salts". Journal of Chemical Education. 80 (12): 1482. Bibcode:2003JChEd..80.1482T. doi:10.1021/ed080p1482.
3. 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.