Question

A compound called gypsum has the property of hardening when mixed with proper quantity of water. Identify the compound. Write the chemical equation of its preparation. Mention one important use of the compound.

Answer 1

1. Plaster of Paris

Plaster of Paris $\left({\mathrm{CaSO}}_4.0.5{\mathrm{H}}_2\mathrm{O}\right)$ is the compound that can be used for the preparation of gypsum. The chemical name of gypsum is Calcium sulphate dihydrate. Gypsum is represented by the chemical formula ${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}$.

2. Preparation of plaster of Paris

Gypsum on heating releases water molecules and forms the plaster of Paris. The reaction is shown below.

$$\begin{gathered} {\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\stackrel{\mathrm{Heat}}{\to }{\mathrm{CaSO}}_4.0.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+1.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \left(\mathrm{Gypsum}\right)(\mathrm{Plaster}\mathrm{of}\mathrm{Paris})\left(\mathrm{Water}\right) \end{gathered}$$

3. Use of plaster of Paris

It is used in hospitals for the immobilization of the fractured bones of the body.