Products Description of Ammonium Thiosulfate CAS#7783-18-8
Ammonium thiosulfate has the chemical formula (NH₄)₂S₂O₃ and a molecular weight of 148.20. It appears as colorless monoclinic crystals, with a melting point of 150°C (decomposition) and a relative density of 1.679.
Ammonium thiosulfate is readily soluble in water, insoluble in ethanol, and slightly soluble in acetone. Its aqueous solution may precipitate sulfur when left standing for an extended period. Above 50°C, a concentrated aqueous solution gradually decomposes into sulfur and sulfate. In the presence of ammonia and hydrocyanic acid, it can form ammonium thiocyanate and ammonium sulfite.
The aqueous solution of ammonium thiosulfate can dissolve silver halides. Its solubility for silver chloride and silver bromide is greater than that of sodium thiosulfate, making it suitable for fast fixing applications. However, it also has a dissolving effect on the metallic silver that forms the image.
Ammonium thiosulfate can be prepared by adding excess ammonium carbonate to an aqueous solution of calcium thiosulfate. It can also be produced by reacting aqueous solutions of ammonium bisulfide and ammonium bisulfite at an accurate molar ratio of 1:2. Another preparation method involves removing sulfur through the double decomposition reaction of ammonium sulfite and ammonium polysulfide, followed by freezing and crystallization.
Key Physical & Chemical Properties
| Property | Specification |
|---|---|
| Chemical Formula | (NH₄)₂S₂O₃ |
| Appearance | White crystals / clear solution (60%) |
| Solubility | Highly soluble in water |
| N–S Content | Provides nitrogen and sulfur |
| Grades | Fertilizer / photographic / industrial |
Main Applications
Fertilizer: Sulfur–nitrogen fertilizer and raw material for liquid blends.
Photography: Fixing agent in photographic processing.
Dechlorination: Removes residual chlorine in water treatment.
Soil Amendment: Sulfur source for alkaline soils.
