Question

Gypsum is a widely occurring mineral. It is the sulphate of calcium with two molecules of water attached. On heating it loses three-quarters of its water and becomes:

• A. baking soda
• B. plaster of Paris
• C. a pearl
• D. an ultramarine

Answer 1

The correct option is B plaster of Paris

It is prepared by heating Gypsum to a temperature of 373K. When gypsum is heated to a temperature of 373K, it loses three-fourths of its water of crystallization and forms Plaster of Paris.

$\underset{\text{Gypsum}}{CaS{O}_4.2H_{2}O}\underset{373K}{\overset{\Delta }{\to }}\underset{\text{Plaster of Paris}}{CaS{O}_4.\frac{1}{2}{H}_{2}O}+\frac{3}{2}{H}_{2}O$