|Jmol-3D images||Image 1|
|Molecular formula||Na2S2O5, Na-O-(S=O)-O-(S=O)-O-Na|
|Molar mass||190.107 g/mol|
|Appearance||white to yellow powder|
>170 °C (begins at 150 °C)
|Solubility in water||54 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|
|Other anions||Sodium sulfite
|Other cations||Potassium metabisulfite|
|Related compounds||Sodium dithionite
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.
Chemical structure 
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.
Food additive 
The acceptable daily intake is up to 0.7 mg per kg of body weight. Sodium metabisulfite has no side effects; it is oxidised in the liver to harmless sulfate and excreted in urine.[clarification needed]
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.
Other uses 
- Added to local anaesthetic(lidocaine etc.) solutions to prevent oxidation of vasoconstrictor adrenaline and thus improve the shelflife 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 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
Chemical properties 
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
See also 
- International Chemical Safety Card 1461
- The surprisingly elusive crystal structure of sodium metabisulfite
- 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