Question

Why Should Plaster of Paris be stored in air-tight containers?

Answer 1

Plaster of Paris:- Calcium sulfate hemihydrate(${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$) is commonly known as Plaster of Paris or POP.

The reason why POP must be kept in an airtight container is:-

The reason why POP must be kept in airtight containers is that when POP is exposed to the atmosphere it absorbs moisture and slowly converts to gypsum(Calcium sulfate dihydrate,${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}$) which is very hard and thus making POP unuseful.

Hence, this is why POP should be kept in airtight containers.