Question

Chemistry involved in the preparation of the Mohr’s Salt (FeSO₄•(NH₄)₂SO₄•6H₂O).

Answer 1

It is a double salt of FeSO₄ and (NH₄)₂SO₄

FeSO₄•7H₂O + (NH₄)₂SO₄ → FeSO₄•(NH₄)₂SO₄•6H₂O + H₂O

• In solution, double salts loose their identity. 

• Double salt exist only in solid or crystalline state but breaks down into their constituent ions when they are dissolved in water or any other solvent.

• It is prepared from ferrous sulphate and ammonium sulphate in the presence of dilute H₂SO₄. 

• Dilute H₂SO₄ is used to prevent the conversion of ferrous sulphate to ferric sulphate and also to prevent its hydrolysis.