Ammonium iron(II) sulfate, or Mohr’s salt, is the inorganic compound with the formula (NH4)2Fe(SO4)2·6H2O. Containing two different cations, Fe2+ and NH4+, it is classified as a double salt of ferrous sulfate and ammonium sulfate. It is a common laboratory reagent. Like the other ferrous sulfate salts, ferrous ammonium sulfate dissolves in water to give the aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry. Ferrous ammonium sulfate hexahydrate is a hydrate that is the hexahydrate form of ferrous ammonium sulfate. Acts as an iron ion donor for building Fe-S clusters in vitro. It is a hydrate and an iron molecular entity. Formula FeH20N2O14S2 Molar mass 392.125 g/mol CAS Number 7783-85-9 Density 1.86 g/cm3 Purity/Grade 99% (ACS Reagent) Appearance Solid Melting point/freezing point 100°C (212°F) – dec.