Question

Dead burnt plaster is ______.

पर्याय

• CaSO₄

• \[\ce{CaSO4 . 1/2 H2O}\]

• CaSO₄.H₂O

• CaSO₄.2H₂O

Answer 1

Dead burnt plaster is CaSO₄.

Explanation:

Plaster of Paris is prepared by heating gypsum at 120^°C

\[\ce{\underset{Gypsum}{2CaSO4 . 2H2O} -> (\underset{Plaster of Paris}{CaSO4)2 . H2}O + 3H2O}\]

On heating plaster of Paris at 200°C, it forms anhydrous calcium sulphate, i.e., dead plaster which has no setting property as it absorbs water very slowly.

\[\ce{CaSO4 . 1/2 H2O ->[200°C] \underset{Anhydride}{CaSO4} ->[1100°C] CaO + SO3}\]