Question

what is crystallisation? where is it used? why is this better them evaporation?​

Answer 1

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Crystallization or crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. 

Purification by crystallization is a better technique as compared to evaporation by dryness. Some solids like sugar decompose or get charred in evaporation to dryness. Also impurities are not removed in this method. However, all these drawbacks are overcome in crystallization.