Question

How is plaster of paris obtained ? What reaction is involved in the setting of a paste of plaster of paris? What is it used for? [3 MARKS]

Answer 1

Explanation: 3 Marks

1. Plaster of Paris is obtained by heating gypsum at 373 K. It loses water molecules and becomes ${\text{CaSO}}_4.\left(\frac{1}{2}\right){\text{H}}_2\text{O}$. The reaction involved is:

${\text{CaSO}}_4.2{\text{H}}_2\text{O}\to {\text{CaSO}}_4.\left(\frac{1}{2}\right){\text{H}}_2\text{O}+\frac{3}{2}{\text{H}}_2\text{O}$

Gypsum Plaster or Paris

2. When Plaster of Paris is mixed with water, it gets converted into gypsum.

${\text{CaSO}}_4.\left(\frac{1}{2}\right){\text{H}}_2\text{O}+\left(\frac{3}{2}\right){\text{H}}_2\text{O}\to {\text{CaSO}}_4.2{\text{H}}_2\text{O}$

Plaster of Paris Gypsum

3. Plaster of Paris is used for making statues and for setting of fractured bones by making cast around the fractured limbs.