Everything about Thiosulfate totally explained
Thiosulfate (S
2O
32−) is an
oxyanion of
sulfur produced by the reaction of
sulfite ions with elemental sulfur in boiling water. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes. It instantly dechlorinates water, and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is also useful in smelting silver ore, in producing leather goods, and to set dyes in textiles.
Sodium thiosulfate was widely used to fix black and white photography negatives after the developing stage.
Thiosulfates are stable only in neutral or
alkaline solutions, but not in acidic solutions, due to decomposition to
sulfite and
sulfur, the sulfite being dehydrated to
sulfur dioxide:
» S
2O
32−(aq) + 2H
+(aq) → SO
2(g) + S(s) + H
2O
This reaction may be used to generate a temporary aqueous
suspension of particles and demonstrate the
Rayleigh scattering of
light in
physics. If white light is shone from below, blue light is seen from above and orange from sideways, due to the same mechanisms that color the sky at mid-day and dusk.
Thiosulfates react with halogens differently, which can be attributed the decrease of oxidizing power down the halogen group:
» 2S
2O
32−(aq) + I
2(aq) → S
4O
62−(aq) + 2I
−(aq)
» S
2O
32−(aq) + 4Br
2(aq) + 5H
2O(l) → 2SO
42−(aq) + 8Br
−(aq) + 10H
+(aq)
» S
2O
32−(aq) + 4Cl
2(aq) + 5H
2O(l) → 2SO
42−(aq) + 8Cl
−(aq) + 10H
+(aq)
Uses of thiosulfates include the dissolving of
silver salts from
photographic film. In this context,
sodium thiosulfate is often referred to as
hypo.
Thiosulfate is also a very aggressive species for the metal
corrosion. Steel and stainless steel are particularly sensitive to
pitting corrosion induced by thiosulfate. Addition of
molybdenum to stainless steel is needed to improve its resistance to pitting (AISI 316L hMo). Thiosulfates are also often produced by incomplete oxidation of
sulfides (pyrite oxidation) or partial reduction of sulfate (
Kraft paper).
Source
Thiosulfate ion General Chemistry Online, Frostburg State University 
Further Information
Get more info on 'Thiosulfate'.
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