Question

Setting of plaster of paris is.

• A. Oxidation with atmospheric oxygen
• B. Combination with atmospheric $CO_{2}$
• C. Dehydration
• D. Hydration to yield another hydrate

Answer 1

Answer: (D)

Hydration to yield another hydrate

Answer 2

Setting of plaster of paris is exothermic process

$CaSO_{4}.\frac{1}{2}H_{2}O\overset{\quad H_{2}O\quad}{\rightarrow}\underset{\text{Orthorhombic }}{CaSO_{4}.2H_{2}O}$

& \text{Mono orthorhombic } \\ & \text{Gypsum} \end{aligned}}{CaSO_{4}.2H_{2}O}$$ The setting is due to formation of another hydrate.