What is crystallisation? Why is crystallisation used?
Crystallisation is a process used to purify solid substances. It involves dissolving an impure solid in a suitable solvent, heating it, and then allowing it to cool slowly so that pure crystals of the substance form, leaving impurities behind in the solution.
It is a physical change and more effective than simple evaporation.
Why is Crystallisation Used?
- To obtain pure solids from their impure forms.
- To remove soluble impurities that cannot be separated by filtration.
- To produce crystals of definite shape and size.
- To avoid decomposition: Some solids decompose or lose their chemical properties when heated strongly (which happens in evaporation), but crystallisation is gentler.
Example:
Crystallisation is used to purify salt obtained from sea water. The salt is dissolved in water, filtered, and then crystallised to remove impurities like sand or insoluble materials.
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