Separating Mixtures
Chemistry: Cambridge International GCSE Supplement, topic 12.1.4
Separation Techniques
We can normally separate mixtures and compounds into the elements or compounds that are found in them. We use physical processes to separate them. These processes don't create new chemical substances (there are no chemical reactions). Some separation processes are:
Filtration
- Separates mixtures of insoluble (can't dissolve) solids and liquids.
- Done by pouring the mixture through filter paper:
- The insoluble solid is trapped.
- The liquid runs through the paper and is collected below.
- 'Filtrate' is the name for a liquid or solution that has passed through a filter.
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Crystallisation
- Separates solutions into their constituent (different) parts: dissolved solids (solutes) and liquids (solvents).
- Heat the mixture so that the solvent evaporates.
- Eventually, crystals of the solute (dissolved solids) will form.
- We can collect the solvent (liquid) by condensing it as it evaporates.
- 'Residue' is the name for a substance that remains after evaporation, distillation, filtration or any similar process.
Chromatography
- Separates solutions with a number of different solutes (solids) in the solvent (liquid).
- Place a drop of the solution to be separated near the bottom of a piece of chromatography paper. Dip the very bottom of the paper into a suitable solvent. The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it.
- Different solutes (solids) move at different speeds, so they separate on the paper.
Test yourself on Separating Mixtures
Which of these techniques separates solutions with more than one type of dissolved solid (solute)?
Filtration
Chromatography
What is Chromatography used to separate?