Question

Crystallisation is a better technique than simple evaporation. Give two reasons to justify the statement.

Answer 1

The crystallisation technique is better than evaporation because of the following reasons:

1. In evaporation, the solution is heated to dryness which may result in some solids decomposing, or charred, but there is no such problem in the crystallisation method.
2. In both the techniques, the solution of an impure solid is prepared in a solvent, which is then filtered to remove the insoluble impurities. However, some impurities may remain in the solution even after filtration and evaporation, these impurities may remain along with the solid. But in crystallisation, crystals of only pure solid will crystallise leaving behind the impurities in the solution.

The process of crystallisation is thus preferred for the purification of salt from seawater.