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What is thiosulfate used for?

Addtime:2016/8/22 hits:

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) rightarrow AgS2O3- + Br-
    S2O32- + AgS2O3- doublearrow 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.
  • Paper manufacture and dechlorination of water. Thiosulfate ion is used to remove chlorine (hypochlorite) from water or from solutions used to bleach paper pulp:

    HOCl + 2 S2O32-  Cl- + S4O62- + OH-

  • Dissolved oxygen testing and chemical analysis of oxidantsThiosulfate is a reducing titrant used for determining many oxidizing agents. For example, hypochlorite concentrations in bleach can be determined using the reaction above. 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.

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