Ammonium iron(II) sulfate solution (Mohr's salt solution) is used as a primary standard in redox titrations, particularly for calibrating potassium permanganate and other oxidizing agents. This stabilized aqueous solution (100 g/L in H2O, with 1% aluminum chips to prevent oxidation) offers high purity and stability, enabling direct use or accurate dilution for standard solutions in analytical chemistry. It is commonly applied in educational laboratories for teaching titration techniques due to its reliable reactivity and well-defined stoichiometry. Additionally, it is utilized in environmental analysis, such as determining chemical oxygen demand (COD) in water and wastewater samples, and serves as a starting material in the synthesis of iron-containing compounds in research and industrial chemical processes where controlled release of ferrous ions (Fe²⁺) is required.