Science at key stage 3 (Year 9)
Unit 9H: Using chemistry
Section 9: c. What happens to atoms and molecules when new materials are made?
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Objectives |
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- that the oxide weighs more than the element from which it was made
- to plot a graph and use it to obtain quantitative data
- that predictable masses of the oxide can be formed from given masses of magnesium
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Activities |
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Outcomes |
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Children: |
- Remind pupils of work they did earlier about making compounds from elements. Either demonstrate or ask pupils to find the increase in mass when magnesium burns in air. Compile a set of results from the class or provide pupils with a set of results and help them plot a graph of mass of magnesium oxide against mass of magnesium. Ask pupils a series of questions to elicit their ideas about what has happened,
eg
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Why does the magnesium oxide weigh more than the magnesium?
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How much magnesium oxide is formed from 1g/1.5g of magnesium?
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How much magnesium oxide do you think would be formed from 10g/15g of magnesium?
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Do these results conflict with the idea of conservation of mass?
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- state that the mass of magnesium oxide is greater than the magnesium, and explain this in terms of combination with oxygen
- recognise the relationship shown in the graph, and use this to predict how much magnesium oxide will be made from other starting masses of magnesium
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Points to note |
- Pupils will need a considerable amount of help if they are to get reasonable results from this activity. A prepared set of results will enable pupils to identify the linear relationships. These could be presented on a spreadsheet. It is more interesting to use class results and discuss why they may not show the linear relationship.
- Some pupils will be ready to appreciate that the mass of oxide formed can be predicted because magnesium oxide contains magnesium and oxygen atoms in the ratio 1:1. Others will simply appreciate why magnesium increases in mass.
Safety
- eye protection should be used. Crucibles remain hot for some time and should be left to cool on tripods
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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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