Question

what is plaster of paris ? how is it obtained from gypsum ?

Answer 1

Plaster of Paris is created by heating gypsum crystals, a soft mineral made of calcium sulphate dihydrate, to turn them into a dry powder.
When it is mixed with water it reforms into a gypsum paste which is used as a building material for wall surfacing and fireproofing, or for creating sculptures and other art works.
A chemical reaction occurs when the water is added to the dry plaster, in some cases reaching temperatures of up to up to 302F (150C), capable of causing serious injury.One of the most common uses is to help broken bones to mend – thin layers of bandage dipped with wet plaster are wrapped around the limb but not in direct contact with the skin.
Plaster of paris does not generally shrink or crack when dry, making it an excellent medium for casting molds

Plaster of paris is prepared by heating gypsum (CaSO₄.2H₂O) at 120°C in rotary kilns, where it gets partially dehydrated.The temperature should be kept below 140°C otherwise further dehydration will take place and the setting property of the plaster will be partially reduced.