Question

Write the chemical names and formulae of plaster of Paris and gypsum.

Answer 1

Hint:The chemical formula of gypsum and plaster of Paris are almost the same and differ only in the amount of water of crystallization present in the molecules. If you recall their chemical formulae we can easily write their chemical name.

Complete answer:
Plaster of Paris:
The chemical formula of Plaster of Paris is given as $ CaS{O_4}.1/2{H_2}O $ .
Its chemical name can be written from the formula as Calcium Sulphate hemihydrate. It is named so because half a molecule of water is attached to the calcium sulphate salt.
Gypsum:
Gypsum is a hydrated crystalline salt of calcium sulphate. It is white in color, sparingly soluble in water and is not hard. The chemical formula of gypsum is given as $ CaS{O_4}.2{H_2}O $
Its chemical name can be written from the formula as Calcium sulphate dihydrate.
In a mixture of gypsum and water, the gypsum begins to harden as the water evaporates. For making artworks, casts of objects or sculptures and moulds, we use gypsum in the partly dehydrated form as plaster of Paris, i.e., $ 2CaS{O_4}.{H_2}O $
In other words, gypsum is the hydrated form of plaster of Paris. Plaster of Paris is obtained on the calcination of gypsum, i.e., heating gypsum at $ {120^{\text{o}}}C $ . When the white, dry powder of Plaster of Paris is mixed with water, it reforms into gypsum and sets into a hard mass which has a variety of applications.

Note:
Plaster of Paris is used to make fine artwork for the beautification and decoration of buildings and monuments. It is used to remake damaged tissue, plasters for repairing bones and also as casts in medical fields. Many fireproofing materials and fire protection systems also use Plaster of Paris.