Question

Identify the correct statement
A. Gypsum contains a lower percentage of plaster of calcium than plaster of Paris
B. Gypsum is obtained by heating plaster of Paris
C. Plaster of Paris can be obtained by hydration of gypsum
D. Plaster of Paris is obtained by partial oxidation of gypsum

Answer 1

Hint: Gypsum has the chemical formula \[{\rm{CaS}}{{\rm{O}}_{\rm{4}}}{\rm{.2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\]. When heated at 393 K, it gives the compound calcium sulphate . When it is heated in air, water gets removed and converted initially to calcium sulphate hemihydrate or plaster and, if heated, more conversion to anhydrous calcium sulphate.

Complete Step by Step Answer:
Gypsum is widely excavated and also used as a fertiliser. It is the major unit in several structures of plaster, blackboard or sidewalk chalk, and drywall. The arrangement of gypsum has tiers of calcium and sulphate ions that are tightly bound together. These layers are linked by sheets of anion water molecules through weaker hydrogen bonding. This compound, when heated at 393 K, the water of crystallisation is lost and forms calcium sulphate 's calcium hemihydrate. Hemihydrate of calcium sulphate is also known as plaster of Paris.

The reaction occurs as follows: \[2(CaS{O_4}.2{H_2}O)\overset{393K}{\rightarrow}2(CaS{O_4}).{H_2}O\]\[ + 3{H_2}O\]

The temperature must not rise above 473K, leading to a loss of whole water. Anhydrous salt will be left called dead burnt plaster having no plaster of Paris properties. Plaster of Paris is a white powder.
The formula of plaster of paris is \[2\left( {{\rm{CaS}}{{\rm{O}}_{\rm{4}}}} \right){\rm{.}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\].
By analysing the formula of gypsum and plaster of Paris we see that gypsum contains a lower percentage of plaster calcium than plaster of Paris.
So, option A is correct.

Note: Plaster of Paris is utilised for generating moulds for pottery, ceramics, etc. It is employed for preparing statues, models, and other ornamental entities. It is utilised in surgical bandages for fixing torn and fractured bones in the body by immobilising the affected part of the body that has the fracture or sprain.