Question

The dihydrate of calcium sulphate is commercially known as ______.

Answer 1

Gypsum:

• Gypsum is a hydrated Calcium sulfate, and its chemical formula is ${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}.$
• It is a naturally occurring mineral that is soft, white or grey in colour.
• On heating Gypsum $\left({\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\right)$ at $373\mathrm{K}$, Plaster of Paris/Calcium sulphate hemihydrate (${\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}$) is obtained.

$\underset{(\mathrm{Calcium}\mathrm{sulphate}\mathrm{dihydrate})}{{\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}\stackrel{373\mathrm{K}}{\to }\underset{(\mathrm{Calcium}\mathrm{sulphate}\mathrm{hemihydrate})}{{\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}$.

Therefore, the dihydrate of calcium sulfate is commercially known as Gypsum.