Thiosulfate

Thiosulfate is the polyatomic ion S₂O₃²⁻, with two sulfur atoms and three oxygen atoms. It forms a family of salts and participates in redox reactions and sulfur chemistry.

Thiosulfate structure: The arrangement of one central sulfur atom bonded to three oxygen atoms and a terminal sulfur atom in S₂O₃²⁻. The inequivalent sulfur atoms give the ion distinct bonding and reaction sites.
Sodium thiosulfate: A water-soluble sodium salt of the thiosulfate ion, Na₂S₂O₃. This widely used salt supplies thiosulfate in laboratory and industrial solutions.
Sulfate: The polyatomic ion SO₄²⁻, containing one sulfur atom bonded to four oxygen atoms. Replacing one sulfate oxygen with sulfur gives the compositional relationship behind thiosulfate.
Sodium thiosulfate pentahydrate: The crystalline compound Na₂S₂O₃·5H₂O, a common commercial form of sodium thiosulfate. This hydrate is the usual solid reagent used to prepare thiosulfate solutions.
Thiosulfate disproportionation: A redox reaction in which thiosulfate forms sulfur and sulfur dioxide in acidic solution. Acid destabilizes thiosulfate and reveals its tendency to form elemental sulfur.
Photographic fixer: A processing solution that removes undeveloped silver halides from photographic film or paper. Thiosulfate dissolves silver halides by forming soluble silver complexes.
Sulfite: The polyatomic ion SO₃²⁻, containing one sulfur atom bonded to three oxygen atoms. Sulfite has the same oxygen count as thiosulfate but lacks its second sulfur atom.
Ammonium thiosulfate: The ammonium salt (NH₄)₂S₂O₃, used chiefly as a sulfur-containing fertilizer and in photographic processing. It is a distinct thiosulfate salt with agricultural as well as photographic uses.
Iodometric titration: A titration method that measures an oxidant by liberating iodine and titrating it with a reducing agent. Thiosulfate reduces iodine quantitatively to iodide in the method's endpoint reaction.
Dechlorination: The removal or chemical reduction of chlorine compounds from water or other materials. Thiosulfate can reduce residual chlorine in water samples and treatment streams.

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