Cambridge IGCSE Chemistry · Syllabus 0620 · Experimental Techniques and Chemical Analysis
Crystallisation
What is Crystallisation?
A purification method that obtains a dissolved solid as crystals. The solution is heated to evaporate some of the solvent until it reaches the point of crystallisation, then allowed to cool. As the temperature falls the maximum concentration that can stay dissolved falls, so the excess solute separates as crystals. These are filtered off, washed with a little cold solvent and dried. Soluble impurities stay behind in the remaining solution.
This definition is part of the Experimental Techniques and Chemical Analysis chapter in Cambridge IGCSE Chemistry.
Common mistakes with Crystallisation
- 27. “Use a separating funnel to separate the mixture.” Why it fails A separating funnel is not one of the five methods named in statement 12.4.1, so it is not the expected answer — and it only works at all for liquids that do not mix. Correct Choose from a suitable solvent, filtration, crystallisation, simple distillation and fractional distillation, and justify the choice from the property data. Check Ethanol and water are miscible, so no layers form; fractional distillation is the method.