Ammonium iron (III) sulfate 2.5% is an aqueous solution used in analytical chemistry as an oxidizing agent and in water treatment. In analytical chemistry it is known as a reagent for Volhard titration, in which it is used as an indicator for the determination of chloride ions in a sample. In this process, it reacts with the silver chloride formed by silver nitrate in the sample to produce a red ferric thiocyanate that signals the end point of the titration.

Ammonium ferric sulfate is particularly well suited to this method because it is stable, readily available and readily soluble in water. Its chemical mode of operation is based on the ability of ferric ions to act as oxidizing agents and on the formation of stable complexes with various anions.

In water treatment, ammonium iron (III) sulfate is used as a flocculant. It helps remove unwanted particles and impurities from water by converting them into larger flocs that are easier to settle or filter.

Compared to similar products, ammonium iron (III) sulfate offers the advantage of being stable in aqueous solutions and having low toxicity. This facilitates the handling and application of the reagent in various fields, both in analytical chemistry and water treatment.