Question

Calcium Sulphate Hemihydrate is also known as ________.

Answer 1

Calcium Sulphate Hemihydrate:

1. CaSO₄.½ H₂O is a neutral salt formed by heating the gypsum $\mathrm{CaSO}.2{\mathrm{H}}_2\mathrm{O}$at 373K.
2. The heating is required to remove the water of crystallization from the gypsum.
3. It has the property to absorb 3/2 of water of crystallization when exposed to air and again form gypsum.

$$\begin{gathered} \mathrm{CaSO}.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\stackrel{373\mathrm{K}}{\to }{\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+\frac{3}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Gypsum}\mathrm{Plaster}\mathrm{of}\mathrm{paris} \end{gathered}$$

4. Calcium Sulphate Hemihydrate CaSO₄.½ H₂O is also known as plaster of Paris.

5. The name is derived, because of the large deposition of gypsum on Montmartre hill in Paris..

Hence, Calcium Sulphate Hemihydrate is also known as the Plaster of Paris (${\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$)