Ferrous ammonium sulfate, also known as ammonium iron(II) sulfate or Mohr's salt, is a chemical compound with the molecular structure (NH4)2Fe(SO4)2. It also exists as a hexahydrate. Its simplified molecular formula is (NH4)2Fe(SO4)2, and its molecular weight is 284.05 for the anhydrous form and 392.14 for the hexahydrate.
Ammonium iron(II) sulfate is obtained from iron, ammonia and sulfuric acid, while the hexahydrate is produced by a reaction between ammonium sulfate and ferrous sulfate. Commonly, a very pure form of Mohr's salt is used during the process of titration. It is also used in Fricke's dosemeter in order to measure large doses of gamma rays.