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TGV12:
String wicks and glass wicks
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LINKS |
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Notes
on the video of string being heated.
The similarities between the decomposition of string and wood
are striking. Pause the video to allow students to answer
the questions. They should be able to suggest that
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the string darkens because it
decomposes as it gets hot |
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the tube fills with ‘smoke’
because a mixture of new substances is being formed
and some of them are condensing |
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we can see a flame
at the mouth of the tube because some of the new substances
react with oxygen the black material left at the end
is charcoal or ‘mostly carbon’. |
Although it is not prominent in the video, a small amount
of ash is left behind.
Notes on the video of two candles
This sequence is important as it can help students
to understand the role of the wick as something which carries
fuel to the reaction site: the faster the supply of fuel,
the higher the flame and the faster the candle is used up.
The answers to the questions are:
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The candle on the
left has the glass wick. |
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The string wick
glows where it sticks out of the flame is due to very
hot carbon (from the hot string decomposing) reacting
with the oxygen in the air. Inside the flame it decomposes
but it does not combust – its immediate surroundings
are wax in the gas state. |
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This is because
of the combustion at the end of the string wick. |
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The glass wick candle. The exposed
wick lengthens as the wax is used and more wax can boil
off at the same time, giving a larger flame (and using
the wax up at a faster rate as a result). |
The glass wick candle flame goes out even though there is
wax left because the fibres of the wick have become so hot
they have fused together, so there is no longer a flow of
wax to the reaction site.
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Science Enhancement Programme CD-ROM 2005 |
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user
guide |
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