Question

A white colored powder is used by doctors for supporting fractured bones.
$(A)$ Write chemical name and formula of the powder.
$(B)$ When this white powder is mixed with water a hard-solid mass is obtained. Write a balanced chemical equation for the change.

Answer 1

Hint : Plaster of Paris is a white colored powder. It is made up of gypsum. The plaster gets its name because its main ingredient gypsum is found abundantly in Paris. The white powder will form a paste when it is mixed with water and it will harden into solid structures when dried.

Complete Step By Step Answer:
$(A)$ The white powder used by doctors for the fractured bone is plaster of Paris, it is referred to as Gypsum plaster, also known by its chemical name calcium sulphate hemihydrate. Its chemical formula is $CaS{O_4}.\dfrac{1}{2}{H_2}O$
$(B)$ Plaster of Paris sets into a hard mass in addition to water. The hard-solid mass is the gypsum; its chemical name is calcium sulphate dihydrate. The balanced reaction of making gypsum is:
$CaS{O_4}.\dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}O \to CaS{O_4}.2{H_2}O$
Plaster of Paris is manufactured by heating gypsum at $423K$ . On heating gypsum it loses water molecules and becomes calcium sulphate hemihydrate.
$CaS{O_4}.2{H_2}O\xrightarrow{{heat}}CaS{O_4}.0.5{H_2}O + 1.5{H_2}O$
When water is mixed with plaster of Paris it re-structures into gypsum for the process of hardening and setting.

Note :
When plaster or gypsum is heated at temperatures higher than $266^\circ F$ , then we obtain hemihydrates. The strength of plaster of Paris is not as strong as other compounds and it often requires external support when a large amount is used.