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TGA4:
Notes on videos of lead and salt melting
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Notes
on the video of lead melting
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Many students may never have
seen lead or know anything about it: it would be helpful
to have a piece of lead for them to look at. |
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The key points to note are that
the lead only melts when it reaches its melting point
temperature, that lead is a liquid above this temperature
and so you can pour it, and that it becomes solid as
soon as the temperature falls below its melting point. |
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A sub-title describes the lead
as ‘freezing’. You can use this as an opportunity
to remind students that ‘freezing’ does
not necessarily imply that something is ‘cold’,
just that it is changing from a liquid to a solid. |
Notes on the video of salt melting
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It would be
helpful to have a large lump of salt to show students. |
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As the video starts,
you might want to pause it to ask students why there
are three flames heating up the test tube. (It is going
to need a lot more heat to reach its melting point than
either the wax or the lead seen previously. Each flame
is at the same temperature as the single flame, but
the hotter something is compared to its surroundings,
the faster it cools, so we need to supply heat energy
more quickly to balance this.) |
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You may also wish
to ask students, ‘What other evidence is there
that the liquid and solid we see in the test tube are
not ice and water?’ (The solid salt sinks in the
liquid salt, whereas ice floats in water). |
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Science Enhancement Programme CD-ROM 2005 |
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user
guide |
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