Sodium thiosulfate

Sodium thiosulfate is an inorganic sodium salt of thiosulfuric acid, used in photographic fixing, water treatment, and treatment of cyanide poisoning.

Thiosulfate ion: The S₂O₃²⁻ polyatomic ion, consisting of a central sulfur atom bonded to three oxygen atoms and one sulfur atom. This ion gives sodium thiosulfate its characteristic redox and complex-forming chemistry.
Photographic fixer: A processing solution that removes unexposed light-sensitive silver halides from photographic material. Sodium thiosulfate is the active fixing agent in many traditional photographic processes.
Thiosulfuric acid: An unstable sulfur oxyacid with formula H₂S₂O₃, whose salts are called thiosulfates. Sodium thiosulfate is the sodium salt derived from this acid.
Sodium metabisulfite: A sodium salt, Na₂S₂O₅, used as an antioxidant, preservative, and reducing agent. It can also remove chlorine, but its chemistry and applications differ from thiosulfate.
Silver halide: A light-sensitive compound of silver and a halogen, used in traditional photographic materials. Thiosulfate dissolves unexposed silver halide during photographic fixing.
Dechlorination: The removal or neutralization of chlorine compounds from water or other materials. Thiosulfate consumes residual chlorine in treated water and laboratory samples.
Sodium salts: Ionic compounds in which sodium cations balance negatively charged ions. The sodium ions balance the charge of thiosulfate in the crystalline salt.
Potassium ferricyanide: A water-soluble coordination compound used as a mild oxidizing agent in photographic processing. It can bleach metallic silver in photographic operations, opposite to thiosulfate's role in dissolving silver salts.
Silver thiosulfate complex: A soluble coordination complex formed when silver ions bind thiosulfate ligands. Complex formation carries silver halide away from photographic film during fixing.
Cyanide poisoning: A life-threatening condition in which cyanide disrupts cellular use of oxygen. Intravenous sodium thiosulfate is used with other medicines in some cyanide poisoning protocols.

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