Question

When Gypsum is heated to 393K, it forms:

• A. ${\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}$
• B. Dead burnt plaster
• C. ${\mathrm{CaSO}}_4.5{\mathrm{H}}_2\mathrm{O}$
• D. Anhydrous ${\mathrm{CaSO}}_4$

Answer 1

The correct option is A

${\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}$

• When Gypsum (Calcium sulfate dihydrate) is heated to 393 K, it forms Plaster of Paris (Calcium sulfate hemihydrate).
• The reaction can be given as follows: $$\begin{gathered} {\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\underset{∆}{\overset{393\mathrm{K}}{\to }}{\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+3/2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \left(\mathrm{Gypsum}\right)(\mathrm{Plaster}\mathrm{of}\mathrm{paris})(\mathrm{Water}) \end{gathered}$$.
• From the above reaction, it is clear that the product formed is ${\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}$(Plaster of Paris).

Hence, among the given options, option (a) ${\mathrm{CaSO}}_4.1/2{\mathrm{H}}_2\mathrm{O}$ is correct and all the other options are incorrect.