Question

How is plaster of Paris is prepared? What is its chemical formula and chemical name?

Answer 1

Preparation of plaster of paris:-

1. Plaster of paris is nothing but hydrated Calcium sulfate.
2. When gypsum $({\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O})$ is heated at around $120°\mathrm{C}$, it gets partially dehydrated and forms plaster of paris.
3. The complete reaction is :

$\underset{\mathrm{Gypsum}}{{\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}\stackrel{120°\mathrm{C}}{\to }\underset{\mathrm{Plaster}\mathrm{of}\mathrm{paris}}{{\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{\frac{3}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)}$

Plaster of paris:-

1. The chemical name of plaster of paris is Calcium sulphate hemihydrate
2. Its chemical formula is ${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$.
3. It has got 0.5 molecules of water of crystallization.