Question

How is Gypsum different from Plaster of Paris?

Answer 1

Hint: Plaster of Paris is a white powder which is mostly used for beautification of ceilings of houses and buildings and for making statues, toys, blackboard chalk whereas gypsum is used for the manufacture of cement, wallboard, plaster of Paris, soil conditioning, a hardening retarder in Portland cement etc.

Complete answer:
Plaster of Paris or POP is the general name of calcium sulphate hemihydrate. Its chemical formula is \[CaS{O_4}.1/2{H_2}O\]. The chemical formula of gypsum is \[CaS{O_4}.2{H_2}O\] and its chemical name is calcium sulphate dihydrate. Therefore, it can be said that gypsum has two moles of crystallisation water whereas only half a mole of crystallisation water is available as Plaster of Paris.
Gypsum is a naturally occurring mineral while Plaster of Paris is obtained by heating gypsum at a temperature of \[373K\]. Hence, Plaster of Paris is a derivative of gypsum. Heating gypsum gives POP and adding water to POP gives gypsum as shown in the reaction below:
\[CaS{O_4}.1/2{H_2}O + 3/2{H_2}O \to CaS{O_4}.2{H_2}O\]
Gypsum cannot be moulded into different shapes while Plaster of Paris can be moulded into different shapes when moistened.

Note:
There are three types of gypsum selenite, alabaster and satin spar. Selenite is crystalline in nature and appears transparent or translucent. Alabaster grows into massive mineral beds. It has a light colour or lightly tinted colour (due to impurities). On the other hand, the satin spar is fibrous or silky in nature. Plaster of Paris got its name because earlier people living in areas near Paris used this material widely, to make plaster and cement.