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Sodium metabisulfite

Sodium metabisulfite
Sodium metabisulfite
Structure of sodium metabisulfite
Names
Other names
Sodium pyrosulfite
Sodium disulfite
Identifiers
7681-57-4 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:114786 N
ChEMBL ChEMBL2016976 N
ECHA InfoCard 100.028.794
EC Number 231-673-0
E number E223 (preservatives)
PubChem 656671
RTECS number UX8225000
Properties
Na2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass 190.107 g/mol
Appearance white to yellow powder
Odor faint SO2
Density 1.48 g/cm3
Melting point 170 °C (338 °F; 443 K) decomposition begins at 150 °C
45.1 g/100 mL (0 °C)
65.3 g/100 mL (20 °C)
81.7 g/100 mL (100 °C)
Solubility very soluble in glycerol
soluble in ethanol
Hazards
Safety data sheet Mallinckrodt MSDS
Harmful (Xn)
Irritant (Xi)
R-phrases R22 R31 R41
S-phrases (S2) S26 S39 S46
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
PEL (Permissible)
none
REL (Recommended)
TWA 5 mg/m3
IDLH (Immediate danger)
N.D.
Related compounds
Other anions
Sodium sulfite
Sodium bisulfite
Other cations
Potassium metabisulfite
Related compounds
Sodium dithionite
Sodium thiosulfate
Sodium sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium (metabisulfite). It is used as a disinfectant, antioxidant and preservative agent.

Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide:

which leaves solid Na2S2O5 behind.

The anion metabisulfite is a hybrid of dithionite (S2O42−) and dithionate (S2O62−). The anion consists of an SO2 group linked to an SO3 group, with the negative charge more localized on the SO3 end. The S–S bond length is 2.22 Å, and the "thionate" and "thionite" S–O distances are 1.46 and 1.50 Å respectively.

It is used as a preservative and antioxidant in food and is also known as E223.

It may cause allergic reactions in those who are sensitive to sulfites, including respiratory reactions in asthmatics, anaphylaxis and other allergic reactions in sensitive individuals.

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.

The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight. Sodium metabisulfite oxidizes in the liver to sulfate which is excreted in the urine.

It is commonly used in homebrewing and winemaking to sanitize equipment. It is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems. It is also used to remove chloramine from drinking water after treatment.


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