Ferrous ammonium sulphate (Mohr’s salt)
It is a double salt. A double salt is a substance obtained by the combination of two different salts which crystallize together as a single substance but ionize as two distinct salts when dissolved in water.
Mohr’s salt is prepared by dissolving an equimolar mixture of hydrated ferrous sulphate and ammonium sulphate in water containing a little of sulphuric acid and the crystallization from the solution.
On crystallization light green crystals of ferrous ammonium sulphate separate out.
Ferrous sulphate FeSO4.7H2O
Ammonium sulphate (NH4)2SO4
Mohr’s salt FeSO4.(NH4)2SO4.6H2O
Apparatus and materials required
Two beakers, china-dish, funnel, funnel-stand, glass rod, wash bottle, tripod stand, wire-gauze,
Ferrous sulphate crystals, ammonium sulphate crystals, dilute sulphuric acid, and ethyl alcohol.