What is meant by ‘water of crystallisation’ of a substance?
Describe an activity to show that blue copper sulphate crystals contain water of crystallisation.
The water molecules associated with a crystalline substance is called ‘water of crystallisation’.
To show crystalline salts contain water of crystallisation.
Materials Required: CuSO4.5H2O (Blue vitriol), boiling tube, burner, cork, delivery tube, test tube, clamp stand.
Procedure:
1. Take 2g of CuSO4.5H2O in a boiling tube fitted in a clamp stand.
2. Observe its colour. Fit it with cork and delivery tube bent at two right angles which dips into a test tube.
3. Heat crystals in boiling tube. ‘
4. Observe vapours being condensed in test tube.
5. Cool the crystals and add few drops of water into it.
Observation: Water vapours get condensed in a test tube and colour of blue crystals changes into white. On adding water to anhydrous copper sulphate, it changes into blue again.
Chemical Reaction:
CuSO4.5H2O + heat → CuSO4 + 5H2O
Blue vitriol White
Conclusion: Crystalline substances have water of crystallisation which are lost on heating.