Using Cabomba or Elodea plants, more commonly known as pondweed, within a boiling water tube can help with this experiment.
These aquatic plants are easy to grow and commonly available from aquarium shops.
Method
1. Fill the boiling tube with sodium hydrogen carbonate solution and place it into the rack.
2. Cut an 8 cm long piece of pondweed, then place it into the tube using the tweezers before immersing it gently with the glass rod.
3. Position the light source five centimetres from the tube, turn it on and leave it for five minutes.
4. Start the stopwatch and count the bubbles produced for one minute.
5. Repeat steps 3 and 4 five times, recording the results each time in a table.
6. Calculate the average number of bubbles produced in one minute at a 5 cm distance.
7. Repeat steps 3 to 6 at different distances from the light source, ensuring that you adjust the length in consistent increments, such as 5 cm from the tube, 10 cm, 15 cm, and so on.
8. Plot a graph of oxygen produced (number of bubbles) against the distance from the tube, remembering that the independent variable goes on the x-axis.