What is Plaster of Paris? Write its uses.

Explanation

Gypsum on heating to a temp. of `120^(@)-130^(@)` C gives a semihydrate . It is known as plaster of Paris .
`underset("Gypsum")(CaSO_(4))2H_(2)O to underset("Plaster of Paris")(CaSO_(4).(1)/(2)H_(2)O)`
When a water paste of plaster of Paris is allowed to stand for sometime it sets to hard mass . This is called setting of Plaster of paris . This is an exothermic process and involves two stages . In the first stage, Plaster of Paris is converted into orthorhombic dihydrate . In the second stage, the orthorhombic dihydrate is converted into monoclinic dihydrate .
`underset("Plaster of Paris")(CaSO_(4)(1)/(2))H_(2)O to underset("dihydrate")underset("Orthorhombic")(CaSO_(4)).2H_(2)O to underset(("Gypsum"))underset("dihydrate")underset("Monoclinic")(CaSO_(4))2H_(2)O`
It is used (1) in making casts for statues, toys etc : (2) in surgical bandages for bone fracture (3) in making white chalks .