Effect of Heat on Hydrous Salts

When heated, hydrous crystals lose their water of crystallisation and turn into a powder. They may also lose their colour. They are then said to be anhydrous.

Experiment

Take hydrated copper (II) sulphate crystals in a test-tube and heat. On heating, the blue crystals in the test tube start turning white. Water vapours are released that condense on the cooler part of the test tube. Collect the water drops in a dish. The crystalline copper sulphate turns to amorphous form. Allow the white amorphous powder in the test tube to cool down and then add the water collected in the dish to it, white amorphous powder turns back to blue crystalline form (Fig.6.15).