The materials required for this science fair project:
- 1 beaker
- Tap water
- 200 milligrams of salt
- 1 stirrer
- 4 x 1.5V batteries and battery holders
- 2 jumper wires with crocodile clips at both ends
- 2 test tubes
- 2 PVC (polyvinyl chloride) insulated copper wires (5mm2), each measuring 150 millimeters in length
- 1 digital weighing scale
- 1 stopwatch
- 1 pair of pliers
- 1 black permanent marker
1. For this science fair project, the independent variables are the DC voltage and the concentration of salt in the electrolyte. The dependent variable is the time taken to collect the released hydrogen gas, and will be measured with the stopwatch. The constants (control variables) are the amount of oxygen collected in the test tube and the surface area of copper wire exposed to the electrolyte solution.
2. Using the pliers, strip both copper wires of approximately 30 millimeters of insulation on both ends. Bend the wire into ‘S’ shapes and place them inside the beaker, as shown below in Figure 1.
3. Fill the beaker with 300 milliliters of water and add 20 milligrams of salt. Stir to dissolve the salt in the water.
4. Draw a line using the permanent marker around the middle of each test tube, along its circumference. Fill the 2 test tubes with water and place them upside down inside the beaker, as shown in Figure 1. The exposed copper wire should be positioned inside the mouth of the test tube.
5. The test is started using one 1.5V battery. Using the jumper wires, connect the battery terminals to the copper wire hanging outside the beaker. Start the stopwatch immediately and record the time taken for the gas collected to reach the black line.
6. Repeat steps 3 to 5 by adding 40 mg, 60 mg and 80 mg of salt into 300 ml of water each time. Record the time taken for the hydrogen gas collected to reach the black line, for the different concentrations of salt.
7. Again, repeat steps 3 to 5, this time, using 2 batteries (3V), 3 batteries (4.5V) and 4 batteries (6V). The concentration of salt in the electrolyte should be kept constant, at 20 mg of salt to 300 ml of water. Record all measurements in a table, as shown below.
Use only batteries. Do not connect the wires to a mains supply.