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TGK1:
Filtering
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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.
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).
‘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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Science Enhancement Programme CD-ROM 2005 |
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