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What is thiosulfate used for?

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Introduction

What is thiosulfate used for? Most of thiosulfate's usefulness stems from its ability to convert certain insoluble metal compounds into soluble complexes, and its ability to act as a mild reducing agent. * Photographic fixing agent. An emulsion of sodium thiosulfate (called hypo by photographers) is used to stop development of exposed film. Thiosulfate converts undeveloped silver bromide grains in the film into water-soluble silver thiosulfate complexes that can be removed when the film is washed. S2O32- + AgBr(s) AgS2O3- + Br- S2O32- + AgS2O3- Ag(S2O3)3- * Extracting silver from ores. Thiosulfate's ability to convert silver compounds into soluble silver complexes also makes it useful in ore processing. ...read more.

Middle

Thiosulfate is also used as a titrant in determining biochemical oxygen demand (the extent to which oxygen within a sample can support microbial life) [RPI]. * Whitening cotton fabrics, bone, straw, and ivory. Some materials are weakened or yellowed when bleached. Thiosulfate solutions can sometimes be used to whiten these materials. See Garments: Discoloration/Yellowing from Age [NCSU] Where does thiosulfate ion come from? Thiosulfate is produced industrially by several different reactions: * Reaction of sulfur with sodium sulfite in boiling aqueous solution, S8 + 8 SO32- 8 S2O32- * Reaction of SO2 gas with sulfide/carbonate liquor (a byproduct of paper manufacturing). ...read more.

Conclusion

Solutions of thiosulfate break down into sulfur, sulfites, and sulfates when exposed to acids, light, metal ions, and bacteria. Thiosulfate is a reducing agent. It is routinely used as a titrant to determine concentrations of oxidants such as hypochlorite in bleach and dissolved oxygen in water. It instantly dechlorinates water, and is used to stop bleaching action in the papermaking industry. Thiosulfate forms water-soluble complexes with many metals, making it useful in photo processing (where it dissolves excess silver bromide on the surface of exposed film, preventing excessive darkening). Thiosulfate is also useful in the extraction of silver from silver ore, in leather manufacture, and as a mordant in the textile industry. Formula Name Water Solubility Uses Resources Na2S2O3 Sodium thiosulfate (Hypo) High Fixative in photographic development; water dechlorination; paper manufacture; whitening agent ...read more.

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