Separating Mixtures
Chemistry: AQA GCSE Higher, topic 1.1.6
Separation Techniques
We can normally separate mixtures and compounds into the elements or compounds found in them. We use physical processes to separate them - these don't create new chemical substances. Separation processes include:
Filtration
- Filtration separates mixtures that contain insoluble (can't dissolve) solids and liquids (which are soluble).
- Filtration is performed by pouring the mixture through filter paper:
- The insoluble solid is trapped by the filter paper.
- The liquid runs through the filter paper and is collected below.
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Crystallisation
- Crystallisation separates solutions into their different parts: dissolved solids (solutes) and liquids (solvents).
- Crystallisation is performed by heating 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.
Chromatography
- 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)?
Chromatography
What is Chromatography used to separate?
A student filters sand out of salty water and is left with a clear salt solution. What technique should the student use next to obtain solid salt crystals?
A student pours a mixture of chalk powder and water through filter paper. What is collected below the paper?