The chemical formula of Plaster of Paris is:

\({\mathrm{CaSO}}_{4}\cdot 2{\mathrm{H}}_{2}\mathrm{O}\)

\({\mathrm{Na}}_{2}{\mathrm{CO}}_{3}\cdot 10{\mathrm{H}}_{2}\mathrm{O}\)

\({\mathrm{CaSO}}_{4}\cdot \frac{1}{2}{\mathrm{H}}_{2}\mathrm{O}\)

\({\mathrm{Na}}_{2}{\mathrm{CO}}_{3}\cdot {\mathrm{H}}_{2}\mathrm{O}\)