Question

Setting of plaster of paris involves

• A. Oxidation by atmospheric oxygen
• B. Reaction with atmospheric carbon dioxide
• C. Dehydration
• D. Hydration to yield another hydrate.

Answer 1

Answer: (D)

Hydration to yield another hydrate.

Answer 2

$CaSO_{4}.\frac{1}{2}\overset{\quad 1.5H_{2}O\quad}{\rightarrow}CaSO_{4}.2H_{2}O$

When mixed with water, it forms a plastic mass, within about half an hour, sets to a hard solid mass consisting of interlaced crystals of gypsum.