What is plaster of Paris? Write the chemical formula for plaster of Paris. (b) How is plaster of Paris prepared? Write chemical equation of the reaction involved. (c) Explain why plaster of Paris should be stored in a moisture-proof container. Write two important uses of plaster of Paris.

• Plaster of Paris is called calcium sulphate hemihydrate which is a hard substance made by the addition of water and gypsum. CaSO1/2H2O is the formula
• It is prepared by heating gypsum to a temperature at 373K and it loses 3/4th of its water of crystallisation and forms Plaster of Paris

CaSO4.2H2O → CaSO4.1/2H2O + 1 1/2H2O

• The presence of moisture can cause the slow setting of plaster of Paris by bringing about its hydration
• Used for healing the fracture of bones Used as fire proofing material.