The materials required for this science fair project:
- 2 hydrilla plants (of approximately equal size)
- 2 beakers
- 2 test tubes
- 2 funnels
- 1 liter of water
- 1 ruler (measuring 150mm long)
- 10ml of engine oil
1. For this science fair project, the independent variable is whether or not there is a layer of oil on the surface of the water. The dependent variable is the amount of oxygen collected in the test tube. This is determined by measuring the length of the air trapped in the test tube with the ruler. The constants (control variables) are the size of the hydrilla plant, the size of the beaker, the amount of water and the size of the test tube used for air collection.
2. Fill each of the 2 beakers with 300ml of water and place one hydrilla plant inside each beaker. Next, invert the funnels and place them over the hydrilla plants in the beakers. The plant should be positioned inside the inverted funnel as shown in Figure 1 below.
3. Fill 2 test tubes with water and place them over the outlet of the funnels, as shown in Figure 1. There should not be any air inside the inverted test tubes before the start of the experiment.
4. Pour 10ml of engine oil into one of the beakers. The oil will spread evenly to form a thin layer.
5. Observe the amount of air collected in the test tubes to determine the level of oxygen produced by the hydrilla plants. Using a ruler, measure the height of the oxygen in the test tubes. Record your observations every hour for the next 5 hours.