Question

The number of water of crystallization molecules present in one molecule of plaster of Paris is:

• A. 4
• B. 0.5
• C. 0.2
• D. 1

Answer 1

The correct option is B 0.5

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. Chemical formula of plaster of Paris is ${\text{CaSO}}_4.\frac{1}{2}{\text{H}}_2\text{O}$.

Therefore, water of crystallization in one molecule of plaster of Paris is 0.5. Hence, it is also called calcium sulphate hemihydrate.