Question

What is meant by water of crystallization of a substance? Describe an activity to show the water of crystallization.

Answer 1

Hint: Water of crystallization is also known as water of hydration. You can think about the water molecules that occur inside the crystals. Water is often integrated in the formation of crystals from aqueous solution.

Complete answer:
The water molecules correlated with a crystalline substance is known as ‘water of crystallisation’. In other words, the number of water molecules chemically merged together or combined in a definite molecular proportion with the salt in its crystalline state is called as water of crystallization. Any substance containing water of crystallization is called a hydrate or a hydrous substance. When this hydrated substance is heated, the water gets expelled out from it and then the substance becomes anhydrous.
Activity:
Aim: To show the water of crystallization of a substance
Materials required: Copper sulphate (\[CuS{O_4}.5{H_2}O\]), Bunsen Burner, China dish.
Procedure: Put 2g of copper sulphate crystals on a china dish and heat it using Bunsen burner.
Observations: The blue colour crystals of Copper sulphate changes its colour to white powder removing 5 molecules of water of crystallization. The chemical reaction can be understood from the following equation:
$CuSO_4.5H_2O\to CuSO_4$
Conclusion: Crystalline substances contain water of crystallisation that are lost on heating.

Note: Alternative example of water of crystallization is gypsum. Gypsum is a soft mass with the formula \[CaS{O_4}.2{H_2}O\]. When gypsum is heated, plaster of paris is formed by losing its water of crystallization. Plaster of paris is a hard mass having the formula \[CaS{O_4}.\dfrac{1}{2}{H_2}O\].