Question

A white powder is used by doctors to support fractured bones. (a)Write the name and chemical formula of the powder. (b)How is this powder prepared? (c)When this white powder is mixed with water, a hard solid mass is obtained. Write a balanced chemical equation for the change.

Answer 1

Plaster of Paris (Calcium Sulphate hemihydrate) is a white colour powder popularly used in fracture cases by the Orthopaedics. It helps in the healing process because it does not allow movement of bones. It is prepared from heating of gypsum at a high temperature. Gypsum is a naturally present mineral while plaster of Paris is manufactured artificially. It is a dry and extremely porous substance. It is non-toxic in nature. It is super dry in nature.

Complete answer:
(a)The name of the powder used is-Calcium sulphate hemihydrate commonly known as Plaster of Paris and the formula of the compound is- $CaS{O_4}.\dfrac{1}{2}{H_2}O$ .
(b)The powder is prepared by heating gypsum (Calcium sulphate dihydrate) at $120^\circ C$ the equation for which is given as follows- $CaS{O_4}.2{H_2}O \to CaS{O_4}.\dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}O$
(c) When this white powder of Calcium sulphate dihydrate or Plaster of Paris is mixed with water, a crystallization reaction will take place which results in the formation of solid Calcium sulphate dihydrate or gypsum with the release of heat which causes the water to evaporate.
The balanced equation for this change is given as follows- $CaS{O_4}.\dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}O \to CaS{O_4}.2{H_2}O$ .

Note:
Plaster of Paris got its name because it was first manufactured by gypsum in Paris. It is also commonly called P.O.P. Apart from repairing fractures it is used in Manufacturing purposes also. It can also be used for making cheap ornaments, toys, black boards, making surfaces smooth, sealing air gaps and many more.