Ammonium ferrous sulphate is a pale green, crystalline double salt containing iron(II) in a highly stable form. The presence of ammonium ions and its well-defined hexahydrate structure protect the ferrous state from rapid oxidation, making it particularly valuable in analytical chemistry.

It is widely used as a primary standard in redox titrations, a reducing agent in various laboratory procedures, and a precursor in the preparation of other iron compounds. Outside the laboratory, it finds applications in electroplating, dyeing, and certain water treatment processes where controlled Fe(II) content is required.
Product grade and impurity levels should be aligned with the intended application, especially when analytical accuracy or stable ferrous ion concentration is critical.