Question

Setting of plaster of Peris involves

• 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 involves hydration to yield another hydrate. Setting is an exothermic process. On hydration of plaster of Paris, converts into gypsum. $\underset{ \text { Paster of Paris }}{ CaSO _{4} \cdot \frac{1}{2} H _{2} O} +\frac{3}{2} H _{2} O \rightarrow \underset{\text { Gypsum }}{ CaSO _{4} \cdot 2 H _{2} O}$ Plaster of Paris is calcium sulphate hemihydrate. Gypsum is calcium sulphate dihydrate.