Sodium Thiosulfate

About This Product

Sodium thiosulfate is supplied chiefly as the pentahydrate, Na2S2O3.5H2O, with CAS number 7772-98-7 for the anhydrous salt, as colourless crystals or white granules, very soluble in water and neutral in solution. Its chemistry turns on the unusual sulphur atom in the thiosulfate ion, which is in a low oxidation state and readily donates. That donation explains three quite different applications. In photography it converts insoluble silver halides to soluble silver thiosulfate complexes, dissolving away the unexposed silver and fixing the image, the role for which it was known as hypo for more than a century. In water treatment it reduces free chlorine and chloramine to chloride rapidly and without the sulphur dioxide odour of the sulfites, which makes it the usual choice for aquarium and fish-farm dechlorination and for neutralising chlorinated water before discharge. In toxicology it supplies sulphur to the enzyme rhodanese, which converts cyanide to thiocyanate, and it is a component of standard cyanide poisoning antidote kits. It is also used in gold leaching as a less hazardous alternative to cyanide and in analytical iodometric titration. It is used in dechlorination and aquaculture, photographic fixing, gold leaching, cyanide treatment, textile bleach neutralisation and analytical chemistry. Bio Green Chem supplies sodium thiosulfate to specification on assay, sulfite and sulfide content, insolubles, pH, iron and heavy metals.