Science at key stage 3 (Year 7)
Unit 7H: Solutions
Section 5: a. How can chromatography separate and identify substances in mixtures?
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Objectives |
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- that a mixture of two or more solutes which are soluble in a particular solvent can be separated by chromatography
- to separate and identify materials using chromatography
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Activities |
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Outcomes |
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Children: |
- Remind pupils of work they did earlier on showing whether a liquid was pure or not. Explain that they are going to explore some other techniques for this.
- Demonstrate how to separate the different coloured compounds in an ink mixture on blotting or filter paper, using a wick of the paper dipped into the solvent (water). Discuss and establish with pupils why different coloured ink solids travel different distances, perhaps using the analogy of the solvent particles giving the solute particles 'piggyback rides', so those which attach more firmly to the solvent particles can be carried further than those which do not, in a given amount of time.
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- use chromatography to separate and identify different solutes
- use particle ideas to explain how chromatography works
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Points to note |
- Extension: pupils could be asked to find out at home whether food colourings, inks in felt-tip pens or markers are single dyes or mixtures of dye.
Safety
- if solvents other than water are used, pupils should be taught to handle them safely
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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