Science at key stage 3 (Year 7)
Unit 7H: Solutions
Section 2: How much salt can we get from rock salt?
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Objectives |
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- to use knowledge about separating mixtures to obtain a sample of salt from rock salt
- to evaluate methods used in terms of the mass of salt obtained
- that salt comes from a variety of sources and has many uses
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Activities |
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Outcomes |
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Children: |
- Present pupils with a sample of rock salt and say that pure salt can be obtained from this. Ask them to plan a way of obtaining a sample of pure salt. Extend this for some pupils by asking them how they could find out how much of their rock salt is pure salt and to compare their results with those of others. Ask pupils to produce an account of what they did, describing and explaining each stage. Emphasise that, although the salt dissolves, it doesn't disappear.
- Show a video about the occurrence, extraction and uses of salt. Relate this to the processes pupils have used in extracting their sample.
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- plan a method for obtaining a sample of salt from rock salt
- obtain a sample of salt
- explain why the mass of the salt sample was less than the mass of rock salt
- explain in terms of the original sample or in terms of techniques why results of different groups differ
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Points to note |
- The activity could be set in the context of comparing the salt content of different rock salts used on icy roads in winter, or of comparing the efficiency of different pupils' methods of obtaining a sample of salt.
- Extension: pupils could be asked to use secondary sources to find out more about salt,
eg its importance in diet and possible hazards, sources and history of use.
Safety
- teachers will need to check pupils' plans for health and safety before practical work begins
- pupils should not taste the salt after it has been purified
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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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