Epsom salt Its Preparation & Use

Magensium sulphate occurs as kieserite MgSO₄.H₂O in Stassfurt (Germany) deposit or as Epsom salt in the mineral water of the Epsom springs in England.

Method of Preparation of Epsom salt MgSO₄.7H₂O

(i) From dolomite

The dolomite ore is boiled with dil. H₂SO₄.

CaCO₃.MgCO₃ + 2H₂SO₄ → CaSO₄ ↓ + MgSO₄ + 2H₂O + 2CO₂

The ppt of calcium sulphate are filtered off and the solution on concentration and cooling gives crystals of MgSO₄.7H₂O.

(ii) From Magnesite

The magensite ore is powdered and dissolved in dilute H₂SO₄. The resulting solution is concentrated and cooled when crystals of MgSO₄.7H₂O separate out.

MgCO₃ + H₂SO₄ → MgSO₄ + H₂O + CO₂

(iii) From Kieserite

The mineral Kieserite (MgSO₄.H₂O) is powdered and dissolved in water. The resulting solution upon concentration and cooling gives crystals of MgSO₄.7H₂O.

(iv) Laboratory Preparation

In the laboratory MgSO₄ is prepared by dissolving Mg metal or MgO or MgCO₃ with dilute H₂SO₄.

The resulting solution upon concentration and cooling gives crystals of MgSO₄.7H₂O.

Also Check: Baking Soda

Properties of Epsom salt MgSO₄.7H₂O

It is deliquescent and readily dissolves in water. Hydrates with 12, 6 and 1 molecule of water of crystallisation are also known. All these hydrates are converted into the anhydrous salt, when heated to 200°C and on further heating they decompose to form the oxide. Magnesium sulphate gives rise to double salt with the alkali sulphate.

(i) Magnesium sulphate is a colourless efflorescent crystalline solid highly soluble in water.

(ii) Isomorphism

MgSO₄.7H₂O is isomorphous with ZnSO₄.7H₂O & FeSO₄.7H₂O compounds having same crystal structure are called isomorphous and the phenomenon is called Isomorphism.

(iii) Action of Heat

When heated it losses 6 molecules of water to give Magnesium sulphate monohydrate which becomes anhydrous when heated to 503 K and finally decomposes to MgO & SO₃ gas on strong heating.

Uses of Epsom salt MgSO₄.7H₂O

(i) MgSO₄ is used as purgative medicine.

(ii) It is used as mordant for cotton in dyeing industry.

(iii) It is used in preparation of fire proof textile and wood.

(iv) Anhydrous MgSO₄ is used as a drying agent in organic chemistry.

(v) It is used in preparation of platinised asbestors which is used as a catalyst in the contact process for the manufacture of H₂SO₄.