Demonstrations



Demonstration 1:

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.

Materials:

Instructions:

  1. Fill beaker with warm water. The temperature of the water should be hot but not too hot to touch.
  2. Record the temperature of the water.
  3. Add a few boiling chips to ensure that the water boils without super heating.
  4. Place in bell jar.
  5. Turn on vacuum pump.
  6. Watch the water boil
  7. After it has been boiling for a while turn off vacuum pump and return air to the chamber.
  8. Record the temperature of the water again.

Demonstration 2:

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.

Materials:

Instructions:

  1. Pour some nitrogen in to the tall narrow container.
  2. Hold the container in the air, asking the students to notice how much it's boiling.
  3. Place the container a surface and ask students to notice how much it is boiling then.
  4. 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.
  5. Pour the nitrogen into the metal container.
  6. Hold the container above off the table asking a student what they notice about the bottom of the container (liquid dripping off).
  7. Talk about what the liquid could be.
  8. Catch some in a test tube (the liquid is about -187 degrees C).
  9. Use a glowing splint to show oxygen.

Demonstration 3:

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.

Materials:

Instructions:

  1. Pour some nitrogen into the pop bottle.
  2. Place a balloon over the top and talk about what is blowing up the balloon.
  3. 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.
  4. GO OUTSIDE.
  5. Secure pop bottle attachment to a stand or fence post behind a sheet of Plexiglas.
  6. 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.
  7. Screw bottle on to attachment and stand back.
  8. Collect data while pressure is building.
  9. Data can be plotted by hand or using simple free software such as gnuplot.

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