Question

What is meant by water of crystallisation of a substance? Describe an activity to show that. [4 marks]

Answer 1

Water of crystallization is the fixed number of molecules which are present in one formula unit of salt. [ 1 mark]

Activity:

Aim: To show the water of crystallization

Materials required: Copper sulphate, bunsen burner, china dish.

Procedure: Put some copper sulphate crystals on china dish and heat it with bunsen burner. [1 mark]

Observation: The blue colour crystals of copper sulphate changes to white powder on removal of 5 molecules of water of crystallization. [1 mark]

Equation: ${\text{CuSO}}_4.5{\text{H}}_2\text{O}$ $\underrightarrow{\text{Heat}}{\text{CuSO}}_4+{\text{H}}_2\text{O}$

Conclusion: Colour change shows water of crystallization. [1 mark]