As the air is pumped out of the test tube and the pressure decreases, the water starts to boil.


WATCH VIDEO 

Teachable Topics:

  • Ideal Gas Law
  • Phase Diagrams

Theory:

As air is pumped out of the test tube, the pressure inside the tube goes down. With less pressure, the water molecules can move about more freely and thus gain kinetic energy. As this happens, the heat energy required to break the intermolecular forces becomes less (the boiling point decreases). Once the boiling point is lowered to room temperature, the water boils and turns to water vapour.


Apparatus:

  • rotary vacuum pump
  • hose
  • acrylic sheet
  • silicon bathroom sealer
  • test tube
  • water

Procedure:

1. Hook your vacuum pump up to the test tube once it has been sealed air-tight.

2. Turn the vacuum pump on and remove the air from the beaker until it boils.

3. Observe.


How to make your vacuum chamber out of a test tube: 

  1. Pour a little water into your test tube.
  2. Using a square of acrylic plastic, make a lid for your test tube. To do this, first you must drill a hole in the centre of the plastic. The hole should be just big enough to thread your air hose through.
  3. Once you have threaded your hose through the plastic, squeeze silicon bathroom sealer where your hose comes through the plastic on one side. This is to make sure no air can leak out of your vacuum chamber.
  4. Let the silicon dry, this should take 30 minutes to 1 hour.
  5. Next, on the side that does not have silicon, attach the mouth of your test tube to the plastic base around where your hose comes through. To do this squeeze silicon sealer around the mouth of your test tube and press it to the plastic to create an air-tight seal. *** Make sure you still have water in the bottom of your test tube!
  6. Let the silicon dry.
  7. Your vacuum pump is now ready. Connect it to your vacuum pump with the hose and give it a try!