Science at key stage 3 (Year 7)
Unit 7F: Simple chemical reactions
Section 8: What is needed for things to burn?
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Objectives |
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- that part of the air is used up during burning
- to suggest and evaluate explanations
- to suggest how to test an idea
- to produce a line graph from results and to draw conclusions from these
- to collaborate with others to share information and ideas, and to solve problems
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Activities |
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Outcomes |
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Children: |
- Show pupils the effect of putting a large glass container over a lighted candle floating on a trough of water and ask questions to help them explain what happens,
eg
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What was in the large container?
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Why did the candle go out?
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Why didn't it go out immediately?
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Why did the water rise up the container?
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What is made when a wax candle burns?
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What happens to this?
- Ask pupils in groups to work out explanations. Help them to evaluate their explanations through questioning and establish that part of the air was used up and that the candle could not continue to burn. Link back to earlier work on comparing burning in air and oxygen.
- Extend by asking pupils to investigate the idea that the candle goes out when part of the air is used up. Help them to turn this into a question that can be tested and to devise a way of getting results from which a graph can be plotted.
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- explain that the candle goes out when oxygen is used up
- suggest and evaluate ideas about why the water rose up the container
- generalise that the less oxygen there is the sooner the candle would go out and suggest a way of testing this
- draw a line graph of results; describe what it shows, relating this to the oxygen available for burning
- contribute usefully to group work
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Points to note |
- This activity provides an opportunity for pupils to suggest their own ideas and to think critically about these and the ideas of others. Teachers may wish to go into detail with some pupils about factors such as expansion of air on heating and solubility of carbon dioxide, but it is not necessary to do so.
- Extension: pupils could be asked to find out about earlier work on burning and oxygen by scientists,
eg Lavoisier, Priestley.
Safety
- use candles that are short and difficult to knock over and ensure they are set in a firm base. Teachers should check pupils' plans for health and safety before practical work begins
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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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