Question

The chemical formula of plaster of Paris is

• A. ${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}$
• B. ${\mathrm{CaSO}}_4.\mathrm{H}2\mathrm{O}$
• C. ${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$
• D. $2{\mathrm{CaSO}}_4.{\mathrm{H}}_2\mathrm{O}$

Answer 1

The correct option is C

${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$

The explanation for the correct answer:

Option (C): ${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$

• The plaster of paris is obtained by heating Gypsum$({\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O})$ at $120°-180°$.
• Plaster of Paris is also known as Calcium sulphate hemihydrate.
• The formula for Plater of Paris is ${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$
• It is commonly used in sculpting material and bandages.

The explanation for the incorrect answer:

Option (A): ${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}$

It is the formula of Gypsum.

Option (B): ${\mathrm{CaSO}}_4.{\mathrm{H}}_2\mathrm{O}$

It is a Calcium sulphate hydrate, salt of Calcium but not Plaster of Paris.

Option (D): $2{\mathrm{CaSO}}_4.{\mathrm{H}}_2\mathrm{O}$

It is a salt of Calcium, but not plaster of Paris

So, Option (C) is correct. The chemical formula for plaster of Paris is ${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$