Ammonium iron(II) sulfate

Ammonium iron(II) sulfate is a pale green crystalline double salt of iron(II) sulfate and ammonium sulfate. Its common hexahydrate, Mohr’s salt, is more stable in air than iron(II) sulfate alone.

Connect

Mohr’s salt: The hexahydrate of ammonium iron(II) sulfate, with formula (NH₄)₂Fe(SO₄)₂·6H₂O. This is the specific hydrated form most commonly meant by the compound’s name.
Redox titration: A volumetric analytical method that determines concentration through an oxidation–reduction reaction. Mohr’s salt is weighed to prepare iron(II) solutions for titrations.
Iron(II): The +2 oxidation state of iron, commonly present in aqueous solution as Fe²⁺. The compound releases iron(II) ions that act as reducing agents.
Iron(II) sulfate heptahydrate: A hydrated form of iron(II) sulfate with formula FeSO₄·7H₂O, commonly called green vitriol. It is a more air-sensitive iron(II) sulfate source than Mohr’s salt.
Karl Friedrich Mohr: A German chemist known for contributions to analytical chemistry and laboratory methods. The common name Mohr’s salt is associated with this chemist.
Double salt: A crystalline compound containing two different salts in a fixed stoichiometric ratio that dissociates into their constituent ions in solution. Ammonium iron(II) sulfate is classified as a double salt rather than a complex salt.
Permanganate titration: A redox titration in which permanganate ions oxidize an analyte and often serve as their own indicator. Iron(II) from this salt is commonly titrated with acidified permanganate.
Oxidation: A chemical process in which a species loses electrons or increases its oxidation state. Iron(II) is oxidized to iron(III) in the salt’s common analytical reactions.
Iron(III) ammonium sulfate: A double sulfate containing ammonium and iron(III), commonly crystallized as a dodecahydrate. Its iron is in the +3 state, unlike the iron(II) in this compound.
Volumetric analysis: Quantitative chemical analysis based on measuring the volume of a solution required for a reaction. Mohr’s salt became familiar through its role in classical volumetric analysis.