|Molar mass||190.107 g/mol|
|Appearance||white to yellow powder|
|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
|EU classification||Harmful (Xn)
|R-phrases||R22 R31 R41|
|S-phrases||(S2) S26 S39 S46|
|US health exposure limits (NIOSH):|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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.
- 2 HSO3− ⇌ H2O + S2O52−
which leaves solid Na2S2O5 behind.
The anion 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.
Sanitization and cleaning agent
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.
- Added to local anaesthetic (lidocaine etc.) solutions to prevent oxidation of vasoconstrictor adrenaline and thus improve the shelf life of the solution
- It is used in photography.
- Concentrated sodium metabisulfite can be used to remove tree stumps. Some brands contain 98% sodium metabisulfite, and cause degradation of lignin in the stumps, facilitating removal.
- It is also used as an excipient in some tablets, such as paracetamol. Approximately 0.5 mg is used in epinephrine autoinjectors such as the EpiPen.
- A very important health related aspect of this substance is that it can be added to a blood smear in a test for sickle cell anaemia (and other similar forms of haemoglobin mutation). The substances causes defunct cells to sickle (through a complex polymerisation) hence confirming disease.
- It is used as the source of SO2 in wine. An important anti-oxidant and bactericide
- It is also used to precipitate gold from auric acid (gold dissolved in aqua regia).
- It is used in waste treatment to chemically reduce hexavalent chromium to trivalent chromium which can then be precipitated and removed from an aqueous waste stream.
- It is used as a bleaching agent in the production of Coconut cream
- It is used as a SO2 source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes.
When mixed with water, sodium metabisulfite releases sulfur dioxide (SO2), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people. For this reason, sodium metabisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent.
Sodium metabisulfite releases sulfur dioxide in contact with strong acids:
- Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2
- Na2S2O5 → Na2SO3 + SO2
- "NIOSH Pocket Guide to Chemical Hazards". National Institute for Occupational Safety and Health (NIOSH). id=0566.
- Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.
- K. L. Carter, T. A. Siddiquee, K. L. Murphy, D. W. Bennett "The surprisingly elusive crystal structure of sodium metabisulfite" Acta Cryst. (2004). B60, 155-162. doi:10.1107/S0108768104003325
- Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, pp 324-339
- Milne, George W. A. (2005). Gardner's commercially important chemicals: synonyms, trade names, and properties. New York: Wiley-Interscience. p. 568. ISBN 0-471-73518-3.
- Food-Info.net : E-numbers : E223: Sodium disulphite
- Sodium sulfite. http://www.chemicalbook.com/ChemicalProductProperty_EN_cb4111698.htm
- International Chemical Safety Card 1461
- The surprisingly elusive crystal structure of sodium metabisulfite
- CDC - NIOSH Pocket Guide to Chemical Hazards