Question

Name a crystalline salt which does not contain water of crystallisation.

Answer 1

Hint: Before answering the question we should have an idea about the concept of water of crystallisation. So, water of crystallisation is defined as the water molecules that are present inside the crystals. Water is often incorporated in the formation of crystals from aqueous solutions.

Complete answer:
Among the various examples of crystalline salts which do not contain water of crystallisation, we have taken the example of potassium chloride.
The chemical formula of potassium chloride is $K-Cl$
Potassium chloride is odourless, and has a white or colourless vitreous crystal appearance.
When potassium chloride is dissolved in water, the ions get hydrated. The ion dipole forces attract the positive (hydrogen) end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative (oxygen) ends to the positive potassium ions. Thus, when water is added to potassium chloride, the salt just dissociates into ions and cannot form crystals that contain water as a structural component. Dissolution of potassium chloride is an endothermic process. In order to separate potassium chloride and water we can use the process of simple distillation.
The presence of water of crystallisation is compound dependent. Even if the compound is formed from aqueous solution, it is not necessary for the compound to have water of crystallisation. Water of crystallisation is present in the hydrated salts. It is responsible for providing geometry and shape to the structure.

Note: Some other salts that do not have the water of crystallization are barium sulphate, sodium nitrate, etc.
A well-known example of salts that have the water of crystallization is blue vitriol or hydrated copper sulphate with the formula $CuS{{O}_{4}}\cdot 5{{H}_{2}}O$ When we heat this crystalline salt, the water in it evaporates and it becomes amorphous and white in colour. This shows us that the water of hydration contributes to the structure and colour of the salt.