Ammoniumtiosulfat

Ammoniumtiosulfat, or ammonium thiosulfate, is the inorganic compound with the formula (NH4)2S2O3. It is the ammonium salt of thiosulfuric acid and appears as a white crystalline or powdery solid that is highly soluble in water. In aqueous solution it provides the thiosulfate anion S2O3^2- and can act as a reducing agent in certain reactions.

Preparation can occur by neutralization of thiosulfuric acid with an ammonium salt, or by reaction of sulfurous/thiosulfuric acid species with ammonium compounds. It may also be generated in situ in analytical procedures where thiosulfate is required.

Properties include high water solubility and hygroscopicity. It is relatively stable under neutral conditions but can decompose upon heating or in the presence of strong acids, yielding sulfite and elemental sulfur. Acidification of ammonium thiosulfate can produce sulfur dioxide and sulfur according to the general thiosulfate behavior: S2O3^2- + 2 H+ → SO2 + S + H2O.

Uses are largely historical and specialized. It served as a fixing agent in early photographic processes and acts as a source of thiosulfate in certain analytical chemistry procedures, where it helps dissolve or react with specific substrates.

Safety and handling: Ammonium thiosulfate is irritating to skin and eyes. Use appropriate personal protective equipment, work in a well-ventilated area, and avoid contact with acids or oxidizers. Stored in a tightly closed container in a cool, dry place away from incompatible materials.

See also: Thiosulfate, ammonium salts, sulfurous compounds.