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TGC4:
Boiling point
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LINKS |
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‘Think for Yourself’ question
‘Why does the thermometer reading stay at 100°
C when the water is boiling?’
A sample of water in the liquid state
changes to the gas state when the temperature is just above
100ºC.
This means that water cannot be above 100ºC and still
be in the liquid state. The temperature of the liquid water
stays at 100ºC when it is boiling. Note: There is a more
detailed consideration of what happens at boiling point in
the Advanced topic O2, 'A
Closer look at Boiling Point'.
Notes on the ‘Boiling wax’ video
Invite students to put a hand up to tell you when they think
the wax is boiling: you can pause the video and ask them to
vote and to explain why the decision is correct/ incorrect.
The students should tell you to stop once there are bubbles
throughout the liquid. The mist is wax (not droplets of water
in the liquid state). Wax boils at 383°C. Where the tube
is not being heated it will cool quite quickly because it
is much hotter than the surrounding air, so the wax will cool,
too. There is a small zone above the liquid but below the
mist where the wax will be in the gas
state.
‘Think for Yourself’ question
‘The boiling point of propanone is 56ºC:
this is lower than the boiling point of water. What does this
tell you about the particles of propanone?’
The particles of propanone have a
weaker ability to hold on to each other compared to particles
of water.
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Science Enhancement Programme CD-ROM 2005 |
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user
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