Question

WHY IS CALCIUM SULPHATE HEMIHYDRATED CALLED PLASTER OF PARIS ????????

Answer 1

Plaster of Paris (POP) is obtained by heating calcium sulphate hemi hydrate, also referred as gypsum for about 140-180 degree Celsius. It is found in large depositions in the Montmartre hill in Paris so called as plaster of paris.
2CaSO4.H2O is its chemical formula.

Answer 2

Plaster of Paris is obtained by heating gypsum or calcium sulphate dihydrate to about 140-180 degree Celsius. When heated to such a temperature, gypsum forms Plaster of Paris. The name is derived from the large deposits of gypsum in the Montmartre hill in Paris.