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# Setting of Plaster of Paris involves:A. Oxidisation with atmospheric oxygen.B. Combination with atmospheric $\text{C}{{\text{O}}_{\text{2}}}$.C. Dehydration.D. Hydration to yield another hydrate.

Last updated date: 09th Apr 2024
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Hint: Plaster of Paris can be represented as $\text{2CaS}{{\text{O}}_{\text{4}}}\text{.2}{{\text{H}}_{\text{2}}}\text{O}$. Setting means adding hydrogen and the process of setting plaster of Paris is exothermic.

- The setting of plaster of Paris takes place by hydration due to the formation of a solid crystalline hydrate.
- Hardening of plaster of Paris is a hydration reaction, which is the reverse of the dehydration of gypsum.
- Plaster of Paris quickly sets to a hard mass when made into a thin paste with water.
- A slight expansion takes place in the process and heat is evolved.
$\text{2CaS}{{\text{O}}_{\text{4}}}\text{.}{{\text{H}}_{\text{2}}}\text{O}\underset{{{\text{H}}_{\text{2}}}\text{O}}{\overset{\text{setting}}{\mathop{\to }}}\,\text{CaS}{{\text{O}}_{\text{4}}}\text{.2}{{\text{H}}_{\text{2}}}\text{O}$.
Therefore option(D). Hydration to yield another hydrate is the correct answer.

The formula of plaster of Paris is $\text{2CaS}{{\text{O}}_{\text{4}}}\text{.2}{{\text{H}}_{\text{2}}}\text{O}$