To demonstrate the effects of reduced vapour pressure on water. This
demonstration consists of a beaker of water placed inside a bell jar,
using a vacuum pump to remove all the air.
- Bell Jar
- Vacuum pump
- Water (fill beaker less than half full)
- Fill beaker with warm water. The temperature of the water should
be hot but not too hot to touch.
- Record the temperature of the water.
- Add a few boiling chips to ensure that the water boils without
- Place in bell jar.
- Turn on vacuum pump.
- Watch the water boil
- After it has been boiling for a while turn off vacuum pump and
return air to the chamber.
- Record the temperature of the water again.
To demonstrate the effect of heat transfer. Thermal energy is removed
from a flower to show conduction. Then oxygen is
condensed on the side of a metal container filled with liquid nitrogen.
The liquid oxygen is collected and a glowing splint test is used to
confirm the presence of increased concentrations of oxygen.
- Liquid nitrogen
- Metal container
- Tall narrow container (clear is better)
- Test tube
- Pour some nitrogen in to the tall narrow container.
- Hold the container in the air, asking the students to notice how
much it's boiling.
- Place the container a surface and ask students to notice how much
it is boiling then.
- Place flower in the nitrogen. The flower will be very brittle,
however the purpose for this demonstration is to notice the increased
boiling and the transfer of energy to the nitrogen to the flower.
- Pour the nitrogen into the metal container.
- Hold the container above off the table asking a student what they
notice about the bottom of the container (liquid dripping off).
- Talk about what the liquid could be.
- Catch some in a test tube (the liquid is about -187 degrees C).
- Use a glowing splint to show oxygen.
To demonstrate the effects of increased vapour pressure on liquid
nitrogen. This demonstration is done inside a pop bottle so the end
result is that the pop bottle will explode. The explosion is loud and MUST be done outside.
pop bottle attachment
- Section of threaded pipe
- Metal Washer (inner diameter slightly smaller than outer
diameter of pipe)
- Pressure Gage
- Digital thermocouple thermometer
- Pop bottles
- liquid nitrogen
- Pour some nitrogen into the pop bottle.
- Place a balloon over the top and talk about what is blowing up
- Let the balloon pop or remove it (letting it fly around the room
is good too). To make this faster hold the balloon on the table
(conduction) or in the air (convection) again this can illustrate the
differences in heat transfer.
- GO OUTSIDE.
- Secure pop bottle attachment to a stand or fence post behind a
sheet of Plexiglas.
- Add more nitrogen to the bottle (if you add more the pressure
will increase faster however the bottle pressure tolerance will
increase, try before you demo to find the right balance). About .5L
seems to work well.
- Screw bottle on to attachment and stand back.
- Collect data while pressure is building.
- Data can be plotted by hand or using simple free software such as
- goggles for all working near the liquid nitrogen
- gloves for all touching containers of liquid nitrogen
- Plexiglas to place between demonstrations and the audience.