Question

What happens when plaster of paris is mixed with water ?

Answer 1

1. When Plaster of Paris is mixed with water, crystallisation reaction occurs.
2. The product formed is orthorhombic Calcium sulphate dihydrate and some heat is also released.
3. In this reaction, the Plaster of Paris which is in powder form changes into plaster and is readily converted to solid which is also known as gypsum.
   $$\begin{gathered} {\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+1\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right) \\ \mathrm{Calcium}\mathrm{sulphate}\mathrm{Calcium}\mathrm{sulphate} \\ \mathrm{hemihydrate}\mathrm{dihydrate} \\ \mathrm{Plaster}\mathrm{of}\mathrm{paris}\mathrm{Gypsum} \end{gathered}$$