Preparation of Ferrous ammonium sulphate (Mohr’s salt)

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.