Question

Plaster of Paris is hardened by

• A. liberating $C{O}_2$
• B. hydration
• C. dehydration
• D. changing into $CaC{O}_3$

Answer 1

Answer: (B)

When water is added to plaster of Paris, a substance, called gypsum that becomes hard; is formed. Thus, plaster of Paris is hardened by hydration.
$CaS{O}_4\cdot \underset{\text{Plaster of Paris}}{\frac{1}{2}{H}_{2}O}+1\frac{1}{2}{H}_{2}O⟶\underset{\text{gypsum (hard)}}{CaS{O}_4\cdot 2H_{2}O}$