Question

What is water of crystallisation? Write the common name and chemical formula of a commercially important compound which has ten water molecules. How is this compound obtained? Write the chemical equation involved .List any two uses of this compound.

Answer 1

The water of crystallization is caused by forming purified crystals from an aqueous solution. These crystals do not include contaminants. These crystals are easily affected by the heat.

Complete step by step solution:
The water of crystallization refers to water that is found in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation. The water of crystallization or the water of hydration is the water that occurs in the crystals. It is denoted as a hydrated compound $n{{H}_{2}}O$
Let's consider example gypsum is a soft mass having the formula $CaS{{O}_{4}}\cdot 2{{H}_{2}}O$ When we heat gypsum, plaster of Paris is formed by losing the water of crystallization. The Plaster of Paris is a hard mass with the formula ${{\left( CaS{{O}_{4}} \right)}_{2}}{{H}_{2}}O$
Blue copper sulfate crystals which seem to be dry contain water of crystallization. When we heat the crystals, this water is removed and the salt turns white. If you moisten the crystals again with water, you will find that the blue colour of the crystals reappears. The above-mentioned step completely describes that blue copper sulfate contains water of crystallization.

The water molecules which are part of the structure of a crystal of a salt are called Water of crystallization. The common name and chemical formula of a commercially important compound which has ten water molecules is Sodium Carbonate [washing soda] $N{{a}_{2}}C{{O}_{3}}\cdot 10{{H}_{2}}O$

Preparation:
A cold and Conc. Solution of Sodium chloride is reacted with Ammonia and Carbon dioxide to obtain Sodium Hydrogen Carbonate. $NaCl+N{{H}_{3}}+{{H}_{2}}O+C{{O}_{2}}\to NaHC{{O}_{3}}+N{{H}_{4}}Cl$
Sodium Hydrogenarbonate is separated by filtration, dried and heated. On heating, sodium hydrogen carbonate decomposes to form Sodium carbonate.
$2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O$
Anhydrous sodium carbonate is dissolved in water and to get 10 molecules of water of crystallisation. $N{{a}_{2}}C{{O}_{3}}+10{{H}_{2}}O\to N{{a}_{2}}C{{O}_{3}}\cdot 10{{H}_{2}}O~$

Note: The water of crystallization is the fixed number of water molecules present in one formula unit of salt. Five water molecules are present in one formula unit of blue copper sulfate. The chemical formula for hydrated blue copper sulfate is $CuS{{O}_{4}}\cdot 5{{H}_{2}}O$