Science at key stage 3 (Year 8)
Unit 8G: Rocks and weathering
Section 2: How does rain cause rocks to weather?
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Objectives |
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- that rocks at the Earth's surface disintegrate through exposure to water in the environment, which causes chemical reactions
- how to record results over a period of time
- to use knowledge and understanding of the composition of igneous rocks to explain results of changes over time
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Activities |
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Outcomes |
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Children: |
- Take pupils to observe rock materials out of doors,
eg in a cemetery or on a high street, or show them pictures, video clips of rocks/building materials in the locality of the school.
- Ask pupils to compare older surfaces with new or chipped surfaces to record evidence of discoloration and/or crumbling. Ask them to speculate about possible causes. Note the effects of weathering under trees or adjacent to soil and ask pupils to suggest reasons for this.
- Remind pupils about earlier work on acids and alkalis and show that samples of rainwater are slightly acidic.
- Ask pupils to compare fresh granite with weathered granite to observe any changes to minerals. Simulate wet, oxygen-rich, acidic conditions using dilute hydrochloric acid and hydrogen peroxide in a 50:50 mixture. Place a sample of granite in the solution and capture the changes daily for up to two weeks using a digital camera to create a time-lapse sequence. Ask pupils to examine, describe and explain the changes using a computer-generated slide show. Discuss with them why this is an effective way of recording results.
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- describe changes in rocks and building materials over time
- identify acidic rain as a cause of chemical weathering
- describe and evaluate the use of time-lapse photography to record gradual changes
- describe changes in granite exposed to acid and relate these to changes in particular grains that are dissolved by acids
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Points to note |
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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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