 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. ==preparation== sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide: : 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 Ã and the "thionate" and "thionite" s-o distances are 1.46 and 1.50 Ã, respectively.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.  ==uses== ===food additi
Disinfectants Food_additives Homebrewing Metabisulfites Sodium_compounds