Which of the following statements about Plaster of Paris (POP) is CORRECT?

Correct Option: POP is CaSO₄·½H₂O and hardens by reacting with water

Explanation:

Plaster of Paris (POP) is chemically known as Calcium Sulphate Hemihydrate. Its chemical formula is represented as:

${\mathrm{CaSO}}_4·\frac{1}{2}{H}_{2}O$

It is obtained by heating gypsum (${\mathrm{CaSO}}_4·2H_{2}O$) at approximately 373 K (100°C). During heating, gypsum loses three-fourths of its water of crystallization to form Plaster of Paris:

${\mathrm{CaSO}}_4·2H_{2}O\stackrel{\text{Heat at 373 K}}{\to }{\mathrm{CaSO}}_4·\frac{1}{2}{H}_{2}O+1\frac{1}{2}{H}_{2}O$

When Plaster of Paris is mixed with water, it rehydrates and hardens into a solid mass of gypsum. This setting process happens as a result of its reaction with water:

${\mathrm{CaSO}}_4·\frac{1}{2}{H}_{2}O+1\frac{1}{2}{H}_{2}O\to {\mathrm{CaSO}}_4·2H_{2}O$

Therefore, the statement "POP is CaSO₄·½H₂O and hardens by reacting with water" is correct.