ferrous ammonium sulphate

Ammonium iron(II) sulfate, or Mohrs Salt, is a double salt of iron sulfate and ammonium sulfate, with the formula (NH4)2(Fe)(SO4)2.6H2O. Mohrs salt is preferred over iron(II) sulfate for titration purposes as it is much less affected by oxygen in the air than iron(II) sulfate, solutions of which tend to oxidise to iron(III). The oxidation of solutions of iron(II) is very pH dependent, occurring much more readily at high pH. The ammonium ions make solutions of Mohrs salt slightly acidic, which prevents this oxidation from occurring. The relevant equation for this is: