Question

(a) What is plaster of Paris ? Write the chemical formula of plaster of Paris.
(b) How is plaster of Paris prepared ? Write chemical equation of the reaction involved.
(c) Explain why plaster of Paris should be stored in a moisture-proof container.
(d) State two important uses of plaster of Paris.

Lakhmir Singh Chemistry Class 10

Answer 1

plaster of Paris is a white colour substance that becomes hard when come in the contact of water. it is prepared from the gypsum by heating it .
POP=Caso4.1/2H2O.
Calcium sulphate hemi hydrate.
it is prepared by heating the gypsum at 369 k of temperature.
this is stored in moisture proof container because it becomes hard when comes in the contact of water or moisture.
it is used for making statues and buildings.
it is also used to support fracture.

Answer 2

1. The name plaster of Paris came from the fact that it was first of all made by heating gypsum which was mainly found in Paris. The compound plaster of Paris is prepared by heating gypsum at $120^{o}C$.  

$CaSO_{4} .2H_2O$  → $CaSO_4.1/2H_2O + 3/2H_2O$  

The chemical formula for the plaster of Paris is ($CaSO_4$) $H_2O$ and is better known as calcium sulfate hemihydrate.

2. Plaster of Paris is prepared by heating gypsum at 373 K. On heating, it loses water molecules and becomes calcium sulphate hemihydrate ($CaSO_4.1/2 H_2O$) which is called Plaster of Paris.  

Plaster of Paris is used in hospitals for setting fractured bones in the right position to ensure correct healing.

3. Plaster of Paris (POP) should be stored in a moisture-proof container because Plaster of Paris, a powdery mass, absorbs water (moisture) to form a hard solid known as gypsum.  

$\frac{C}{(POP)}aSO_4.\frac{1}{2}H_2O+1\frac{1}{2}H_2O$ → $\frac{C}{gypsum(Hard solid)}aSO_4.2H_2O$

4. Some uses of plaster of Paris are -

• Plaster of Paris is used to make sculptures and metal castings used as decorative in buildings.

• It is also used in buildings to avoid fire hazards as Plaster of Paris is fire resistant.
• It is used as a coating on wood and metal structures to avoid any fire accidents.

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