Question

Write the chemical equation of its preparation.

Hint:

Heating gypsum produces Plaster of Paris.

Answer 1

Chemical Equation for the Preparation of Plaster of Paris:

Plaster of Paris is prepared by heating Gypsum (Calcium sulphate dihydrate) at a temperature of about 100°C to 120°C. During heating, gypsum loses three-fourths of its water of crystallization and forms Plaster of Paris (Calcium sulphate hemihydrate).

Chemical Equation:
CaSO₄ · 2H₂O (s) → CaSO₄ · 1/2 H₂O (s) + 3/2 H₂O (g)

Explanation:
– Gypsum contains two molecules of water of crystallization.
– On controlled heating, it partially loses water.
– The product formed is Plaster of Paris.
– If heated above 120°C, it may lose all water and form anhydrous calcium sulphate.

Conclusion:
Thus, Plaster of Paris is prepared by heating gypsum, and the balanced chemical equation is:

CaSO₄ · 2H₂O → CaSO₄ · 1/2 H₂O + 3/2 H₂O