Thiosulfate

File:Thiosulfate-ion-2D-dimensions.png

The structure of the thiosulfate anion

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A ball-and-stick model of the thiosulfate anion

Thiosulfate (S₂O₃²⁻) 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:

S₂O₃²⁻(aq) + 2H⁺(aq) → SO₂(g) + S(s) + H₂O

This reaction is usually used to generate a temporary aqueous suspension to demonstrate the scattering of light in physics. If the light is shone from below, blue light is seen from above, and orange from sideways.

Thiosulfates react with halogens differently, which can be attributed the decrease of oxidizing power down the halogen group:

2S₂O₃²⁻(aq) + I₂(aq) → S₄O₆²⁻(aq) + 2I⁻(aq)

S₂O₃²⁻(aq) + 4Br₂(aq) + 5H₂O(l) → 2SO₄²⁻(aq) + 8Br⁻(aq) + 10H⁺(aq)

S₂O₃²⁻(aq) + 4Cl₂(aq) + 5H₂O(l) → 2SO₄²⁻(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.

See also

• Sodium thiosulfate

Source

Thiosulfate ion General Chemistry Online, Frostburg State University

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