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TGK1: Filtering
Notes on videos
Students should notice that the powdered chalk stays in the fine filter paper and the filtrate – the liquid that drips through - is clear. Using a coarse filter paper, the filtrate is cloudy: the filter paper has not trapped all the chalk.
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Notes on filter papers
Make sure that all the students understand what they are looking at: they should be able to tell which parts of each image are ‘fibre’ and which are ‘holes’. If you are using an interactive whiteboard it should be very easy to get a student to trace over some of the fibres using a pen or highlighter tool (If you are using a projector or a monitor, just trace the outlines with a finger).
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‘Think for yourself’ questions
How does filtering separate chalk from water?
The water particles can move and slip through the gaps between the fibres, but the ‘bits’ of chalk are too big to get through the gaps. This is because the ‘bits’ of chalk are billions of chalk particles stuck together, so they are much bigger than individual water particles.

Why doesn’t coarse filter paper separate this mixture?
The gaps are not small enough to catch the ‘bits’.

Why can’t filtering separate salt from a salt solution?
Individual salt particles are mixed in with the water particles. Salt particles can slip through the gaps with the water particles.
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tgk1: notes
tgk2: videos
tgk3: sample
tgk4: water cycle

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