The fixed no of water molecules present in a salt is called as water of crystallisation. Washing Soda (Na2Co3 . 10H2O) has 10 water molecules as water of crystallisation. It is obtained by heating baking soda.

Water of Crystallisation:

Water of crystallisation refers to the water molecules that are bound within the crystal lattice of a compound. These water molecules are an integral part of the crystal structure and are not chemically bonded to the compound. The water molecules are typically present as hydrated ions or as water molecules coordinated to metal ions.

Common Name and Chemical Formula:

One commercially important compound that has ten water molecules as water of crystallisation is copper sulfate pentahydrate. The common name of this compound is blue vitriol, and its chemical formula is CuSO4 · 5H2O.

Obtaining Copper Sulfate Pentahydrate:

Copper sulfate pentahydrate can be obtained by the reaction of copper oxide or copper carbonate with sulfuric acid. The chemical equation for this reaction is as follows:

CuO + H2SO4 → CuSO4 + H2O

Alternatively,

CuCO3 + H2SO4 → CuSO4 + CO2 + H2O

Once copper sulfate is formed, it can be crystallized by evaporating the water solvent. As the water evaporates, the copper sulfate molecules come together to form crystals with the water molecules trapped within their structure. These crystals are blue in color and have a pentahydrate structure.

Explanation:

When copper oxide (CuO) or copper carbonate (CuCO3) reacts with sulfuric acid (H2SO4), copper sulfate (CuSO4) is formed. This reaction can be represented by the chemical equation CuO + H2SO4 → CuSO4 + H2O or CuCO3 + H2SO4 → CuSO4 + CO2 + H2O.

Once copper sulfate is obtained, it can be crystallized by evaporating the water solvent. When water molecules evaporate from the solution, the copper sulfate molecules come closer together and form a crystal lattice structure. The water molecules that were previously coordinated with the copper sulfate ions become trapped within the crystal lattice, forming the water of crystallisation.

In the case of copper sulfate pentahydrate, five water molecules are bound to each copper sulfate molecule. These water molecules are weakly bonded to the copper sulfate ions through hydrogen bonding. The presence of these water molecules gives copper sulfate pentahydrate its characteristic blue color.

Copper sulfate pentahydrate is commercially important for various applications, including its use as a fungicide, algaecide, and in the preparation of Bordeaux mixture (a mixture used to control plant diseases).