Q20 of 30 Page 34

Why is plaster of Paris written as CaSO4 . 1/2 H2O? How is it possible to have half a water molecule attached to CuSO4?

On heating gypsum at 373K, it loses water molecules and become calcium sulphate hemihydrate (CaSO4.1/2H2O). This is called Plaster of Paris.

Plaster of Paris is written in this form (CaSO4.1/2H2O) because two formula units of CaSO4, share one molecule of water.


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