Question

State the number of water molecules present in crystals of washing soda and plaster of Paris. What are these molecules called?

Answer 1

The chemical formula of washing soda is $N{a}_{2}C{O}_3\cdot 10H_{2}O$

The chemical formula of plaster of Paris is $CaS{O}_4.\frac{1}{2}{H}_{2}O$

Hence,

No. of water molecules in washing soda$=10$

No. of water molecules in plaster of Paris$=\frac{1}{2}$

$\therefore$ These molecules are named as water of crystallization.