Question

Setting of Plaster of paris involves:
A.Oxidation with atmospheric oxygen
B.Combination with atmospheric $C{O_2}$
C.Dehydration
D.Hydration to yield another hydrate

Answer 1

Hint: We can define plaster of paris as a white powdery slightly hydrated calcium sulfate made by calcination of gypsum and used chiefly for casts and molds in the form of a quick-setting paste with water.

Complete step by step answer:
A quick-setting gypsum plaster containing fine white powder that is calcium sulfate hemihydrate that hardens when moistened and permitted to dry. Since it is prepared from the abundant gypsum found near Paris, it is commonly known as plaster of paris.
So we can prepare plaster of paris by heating gypsum at a temperature of ${150^ \circ }C$. We can write the preparation reaction of plaster of plastic as,
$\begin{gathered}
  CaS{O_4}.2{H_2}O\xrightarrow{\vartriangle }CaS{O_4}.\dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}{O_{\left( g \right)}} \\
  \;\;\;\;\;Gypsum\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;{\text{Plaster of paris}} \\
\end{gathered} $
Let us know that the setting of Plaster of Paris involves hydration to yield another hydrate. Setting is an example of an exothermic process.
We can obtain gypsum by the hydration of plaster of Paris. We can write the chemical equation as,
$\begin{gathered}
  CaS{O_4}.\dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}O \to CaS{O_4}.2{H_2}O \\
  Plaster\;of\;{\text{paris Gypsum}} \\
\end{gathered} $
We have to know that plaster of Paris is calcium sulphate hemihydrate and gypsum is calcium sulphate dihydrate.

So, the correct answer is Option D .

Note:
We can also use plaster of Paris in,
In orthopedics to put casts around fractured bones.
Used in making replicas as it would not shrink even if it’s sunk in water.
Used to make sculptures and metal castings.
Plaster of Paris fire resistant, hence used in building to avoid fire hazards.
Used on wood coating and metal structures to avoid accidents based on fire.
Used as protective coating on walls and ceilings.
Used as mould and casting agents for decorative elements.
Used to give aesthetic touches to the building.
Used in the making of historical monuments and structures.
Used in fresco painting.