Ammonium iron(II) sulfate dodecahydrate (Mohr's salt) is primarily used as a stable primary standard in redox titrations. It provides a reliable source of Fe(II) ions for standardizing strong oxidizing agents, including potassium permanganate (KMnO₄), potassium dichromate (K₂Cr₂O₇), and cerium(IV) ammonium sulfate. Unlike anhydrous ferrous sulfate, Mohr's salt resists aerial oxidation, ensuring accuracy in preparations. The titration endpoints are detected by the color change of the titrant (e.g., persistent pink for excess KMnO₄) or external indicators like diphenylamine sulfonate for dichromate. Commonly applied in analytical chemistry for water quality testing, iron quantification in samples, and quality control in industrial labs. Also utilized in educational laboratories to illustrate redox principles and volumetric analysis techniques.