Question

why POP should be stored in moisture proof container

Answer 1

because POP is water sensitive and became very hard on gaining moisture and can't be used again. So POP should be stored in moisture proof container

Answer 2

Answer: Because it results in the formation of gypsum.

Explanation:

POP is the abbreviated form of Plaster of Paris having chemical formula of $CaSO_4.\frac{1}{2}H_2O$ and chemical name of calcium sulfate hemihydrate.

It is formed by the heating of gypsum at 400°C. It can be brought back again when POP absorbs moisture.

The equation for the formation of gypsum from Plaster of Paris follows:

$CaSO_4.\frac{1}{2}H_2O+\frac{3}{2}H_2O\rightarrow CaSO_4.2H_2O$

Chemical name of gypsum is calcium sulfate bihydrate.

Hence, POP must be kept in the moisture proof container.