Question

why should plaster of paris stored in the moisture proof container?

Answer 1

because it changes into hard mass gypsum when come with the contact of moisture

Answer 2

● Player of Paris (Calcium Sulphate hemihydrate ) is stored in moisture proof container because when it comes in contact with water or moisture present in the air, it reacts with the water and forms gypsum, which is a hard substance.
Once, gypsum is formed, it cannot be used. It needs to heated to 370 K to convert it back to plaster of paris. That is why, plaster of paris is stored in moisture proof container.