Natriumtiosulfaatin

Natriumtiosulfaatti, often referred to as sodium thiosulfate, is a chemical compound with the formula Na₂S₂O₃. It is commonly found in its hydrated form, Na₂S₂O₃·5H₂O, which is the pentahydrate. This compound typically appears as colorless, crystalline solids. It is highly soluble in water and insoluble in ethanol.

In its most common application, sodium thiosulfate is used as a photographic fixer. In traditional film photography, it is used to dissolve unexposed silver halide crystals from the photographic emulsion after development, making the image permanent. This process is known as "hypo" fixing, a term derived from the historical name for sodium thiosulfate.

Beyond photography, sodium thiosulfate has several other industrial and medical uses. It is employed in the textile industry as a dechlorinating agent, neutralizing residual chlorine after bleaching. In water treatment, it can be used to remove chlorine from treated water. Medically, it is used as an antidote for cyanide poisoning, where it helps to convert cyanide into a less toxic thiocyanate compound that can be excreted by the body. It also finds use in some dermatological treatments and as a reagent in analytical chemistry.