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How is plaster of Paris chemically different from Gypsum ? How can they be inter -converted ? Write two uses of plaster of paris.

Answer»

Solution :Plaster of paris chemically is `CaSO_(4) ½H_(2)O`
Gypsum is `CaSO_(4).2H_(2)O`
On heating gypsum at 373 K, it loses water molecule and BECOMES calcium sulphate hemihydrate. `CaSO_(4) ½H_(2)O`.
Again on treating with water plaster of paris becomes gypsum. `underset("Plaster of paris")(CaSO_(4). ½H_(2)O) + 1½ H_(2)O rarr underset("Gypsum")(CaSO_(4).2H_(2)O)`
`underset("Gypsum")(CaSO_(4).2H_(2)O) underset(373 K)OVERSET("HEAT")rarr underset("Plaster of paris")(CaSO_(4). ½H_(2)O) + H_(2)O`


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