Question

Plaster of Paris is prepared by heating one of the following to a temperature of 100°C. This is:
(a) CaSO₃.2H₂O
(b) CaCl₂.2H₂O
(c) CaCO₃.2H₂O
(d) CaSO₄.2H₂O

Answer 1

CaSO₄.2H₂O
When CaSO₄.2H₂O (gypsum) is heated to a temperature of 100⁰C (373K), it loses three-fourths of its water of crystallisation and forms plaster of Paris (CaSO₄.1/2H₂O).