Question

Why plaster of paris is wrriten as caso4.1/2h2o. Wjo is it posdible to have half a water molecule attached to cuso4

Answer 1

When hydrated calcium sulphate (CaSO4.2H2O) or gypsum is heated at 373K, it loses its water molecules and forms calcium sulphate hemihydrate . This hemihydrated form of calcium sulphate is known as Plaster of Paris. It is in the form of a white powder.

When the powder of Plaster of Paris is mixed with water, it becomes hard and solid gypsum. Plaster of Paris is generally used to support fractured bones in their correct positions.

Here, only half a water molecule is shown as the water of crystallization because two molecules of CaSO4 share one molecule of water.