Question

What is dead plaster or burnt plaster and how it is made?

Answer 1

Dead plaster or burnt plaster:

• Anhydrous ${\mathrm{CaSO}}_4$(Calcium sulfate) is called dead plaster or burnt plaster because it does not set like Plaster Of Paris when moistened with water.
• When Plaster of Paris is heated above 393 K, its water of crystallization is lost and leftover anhydrous Calcium sulfate is called the dead burnt plaster.
• The balanced chemical reaction can be represented as:

$$\begin{gathered} {\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\underset{∆}{\overset{393\mathrm{K}}{\to }}{\mathrm{CaSO}}_4\left(\mathrm{s}\right)+\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ (\mathrm{Plaster}\mathrm{Of}\mathrm{Paris})(\mathrm{Anhydrous}\mathrm{Calcium}\mathrm{sulfate})\left(\mathrm{Water}\right) \end{gathered}$$