Question

(i) Write the chemical name and formula of "Plaster of Paris".

(ii) How is it prepared?

(iii) Write chemical equations of the reaction.

Answer 1

Plaster of Paris: Plaster of Paris is a white powdery chemical compound commonly used in sculpting materials and gauze bandages. Following are the properties of Plaster of Paris:

1. It is found in a white-colored powder state.
2. When it is mixed with water, gypsum crystals are formed from which it attains a solid state.
3. Plaster of Paris forms Anhydrous Calcium Sulfate at 473K.

(i) The chemical name of Plaster of Paris: The chemical name of Plaster of Paris is Calcium sulfate hemihydrate$\left({\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\right)$.

(ii) Preparation of Plaster of Paris: The Plaster of Paris is prepared by heating Gypsum$\left({\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\right)$ at 373 K. On heating, Gypsum loses water molecules and becomes Calcium sulfate hemihydrate$\left({\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\right)$.

(iii) Chemical equation of the reaction:
$\underset{\mathrm{Gypsum}}{{\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}}\left(\mathrm{s}\right)\to \underset{\mathrm{Plaster}\mathrm{of}\mathrm{Paris}}{{\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}\mathrm{Crystal}}{\frac{3}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$