Our Objective

To show that crystals of copper sulphate contain water of crystallization.

   The Theory

Crystallization is a method of separating solids from liquids or, to put it another way, a purification step. The most common way for filtering saltwater is this. A few water molecules are a crucial component of the crystal structure of certain salts. The water molecules that build up a crystal's structure are referred to as the water of crystallization. Salts that include the water that induces crystallization are known as hydrated salts.

The water of crystallization

A set number of molecules in one formula of a unit of salt is referred to as crystallization water. Hydrates are crystal salts that include water throughout the crystallization process. Water crystallization is also known as crystallization water or hydration water. Heat has a strong effect on these crystals.

Examples of water of crystallization are Washing soda, Gypsum, Proteins with more than 50% water of crystallization and copper sulphate pentahydrate with five molecules of water of crystallization are examples of water of crystallization. Hydrated Copper sulphate is represented as CuSO₄.5H₂O It means 5 molecules of water is associated each other.

Blue crystals of copper sulphate contains water of crystallization. These crystals dehydrate on heating to lose water of crystallization at a particular temperature and also change their colour.

CuSO₄.5H₂O(Blue) →CuSO₄.H₂O(Bluish white) →CuSO₄ (White)

If the dehydrated copper sulphate solid material is allowed to cool in air, then it regains blue colour after gaining water molecules from the atmosphere.

CuSO₄ + 5H₂O → CuSO₄.5H₂O

Learning outcomes

• According to your studies, when a hydrated sample of copper sulphate is heated, it loses the water of crystallization and becomes dehydrated, resulting in a white colour.
• This copper sulphate that has been dehydrated regains water.
• As a result, the precise reason of colour change is hydration and dehydration.