Sodium thiosulfate

Sodium thiosulfate used in fixers, plating,, reductant, dechlorinating agent, sulfur dyeing agent, as a blush preventive

Item	Photographic grade	Industrial grade	Anhydrous grade
Appearance	colorless transparent crystal	colorless transparent crystal	white powder
Assay	≥99.00%	≥98.5%	≥97.0%
Water Insoluble matter	≤0.01%	≤0.03%	≤0.03%
Sulfide	≤0.001%	≤0.003%	≤0.001%
Fe	≤0.001%	≤0.003%	≤0.005%
PH	6.5~9.5	6.5~9.5	6.5~9.5
Water solution reaction	in accordance with the test	in accordance with the test	----
Granularity(g/g)	12~16	---	----

Sodium thiosulfate (Na2S2O3), also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”

The thiosulfate anion is tetrahedral in shape and  is notionally derived by replacing one of the oxygen atoms by a sulfur atom in a sulfate anion. The S-S distance indicates a single bond, implying that the sulfur bears significant negative charge and the S-O interactions have more double bond character. The first protonation of thiosulfate occurs at sulfur.