AIM: To prepare crystals of Mohr’s salt.
Mohr’s salt i.e. ferrous ammonium sulphate [FeSO4.(NH4)2SO4.6H2O] is a double salt. It can be prepared by making an equimolar solution of hydrated ferrous sulphate and ammonium sulphate in a minimum amount of water. A few ml of diluted H2SO4 is added to prevent the hydrolysis of FeSO4.7H2O. Cooling of the hot saturated solution yields lights green crystals of Mohr’s salt.
FeSO4.7H2O + (NH4)2 SO4 → FeSO4.(NH4)2SO4.6H2O + H2O
Colour of the crystals: Light green
Shape of the crystals: Monoclinic.