Magnesium Sulphate

Inorganic Compound of Class 12

It occurs in nature as minerals kiesserite (MgSO4.H2O), Epsom salt (MgSO4.7H2O) and kainite (KCl.MgSO4.3H2O).


It is formed by reacting magnesite (MgCO3) or dolomite with dilute sulphuric acid.

MgCO3 + H2SO4 →  MgSO4 + H2O + CO2

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

Dolomite (Insoluble)

It is commercially prepared by boiling kieserite mineral in water. The crystals are obtained when the solution is cooled.

MgSO4.H2O + 6H2O → MgSO4.7H2O


It is a colourless crystalline compound, soluble in water. The crystals are efflorescent and bitter in taste. It is isomorphous with ZnSO4.7H2O. It forms double sulphates with alkali metal sulphates, K2SO4.MgSO4.6H2O (Schonite).

Heating effect: When heated to 150°C, it changes to monohydrate. On further heating, it becomes anhydrous at 200°C. On strong heating, it decomposes into MgO.

MgSO4.7H2O Magnesium SulphateMgSO4.H2O Magnesium SulphateMgSO4Magnesium SulphateMgO + SO2 + ½O2

Magnesium sulphate is reduced by lampblack at 800°C.

2MgSO4 + C → 2MgO + 2SO2 + CO2


(i) as a purgative in medicine.

(ii) as a filler for paper.

(iii) as a mordant in dyeing and tanning industry.

(iv) in the manufacture of paints and soaps and in fire−proofing fabrics.

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