Question

Plaster of Paris has a remarkable property of setting with water. On mixing with one-third its weight of water, it forms a plastic mass that sets into a hard mass of interlocking crystals of ____ within 5 to 15 min.
A. `CaSO_(4).2H_(2)O`
B. `CaSO_(4).H_(2)O`
C. `CaSO_(4).3H_(2)O`
D. `CaSO_(4).4H_(2)O`

Answer 1

Correct Answer - A
Due to this reaction, it is called plaster. The addtionof common salt accelerates the rate of setting,while a little borax or alum reduced it. The setting of POP is believed to be due to dehydration and its reconversioninto gypsum
`2CaSO_(4).(1)/(2)H_(2)O+3H_(2)Oto2CaSO_(4).2H_(2)O`
During the process of setting slight expansion (1%) in volume occurs. As a result it can take up the shape and impression of the mould in which it is put.