Independent variable: concentration of the copper(II) sulfate solution.
Dependent variable: volume of the electrolyte solution, time, distance between the electrodes and the current.
Method:
1. Using the scourer, we cleaned the copper strips. Measured and recorded their mass.
2. We adjusted the current value using the variable resistor.
Placed both copper electrodes into the cell, making sure they were not in contact.
Filled the cell with the copper(II) sulfate solution, and connected the anode to the positive terminal and the cathode to the negative terminal.
5. The power supply was turned on and the ammeter passed a current of 1.0A through the cell for 10 minutes.
6. Removed the electrodes from the cell. Dipped them into a beaker with water and then into a solution of acetone.
7. Allowed the acetone to dry for a few seconds and then measured the mass of the electrodes and recorded their results.
9. Modifies the procedure by changing the concentration of the copper sulfate solution.
10. Repeated the process with a lower concentration and recorded the results.
Results:
1M 0.5M 0.01M
CathodeAnodeCathodeAnodeCathodeAnodeInitial mass(g)6.396.396.706.106.816.02Final mass(g)6.756.116.856.016.825.99Difference (g)+0.36-0.28+0.15-0.10+0.01-0.02
Observation: Anode is being corroded, therefore decrease in mass. Cathode had a shiny coating and had increased in mass.
Discussion: There were errors in this practical, which is shown by the results not being identical. During the electrolysis, the current is controlled and maintained at a constant. However an error could have occurred here. The same spacing between electrodes had to be constant, however an error could have occurred as the electrodes weren’t secured properly against the cell. Other error could have been caused by the fact that not all the ions had attached to the anode, and therefore ended up at the bottom of the solution. Other errors could have been caused by the use of the scales, which only show the mass to 2 decimal places.
The factor that was modified in this practical was the change in concentration, which had effected the mass of the electrodes. The mass change was graphed against the change in concentration of the electrolyte. There are two straight lines of best fit through the points on the graph, which represent, the mass gained at the cathode and the mass lost at the anode. The points on the graph are closely related but are not identical. This shows that an error could have occurred because the mass lost at the anode didn’t equal the mass gained at the cathode.
Conclusion: When the anode and cathode are absorbed in the electrolyte and an electric current is passed, the anode corrodes and dissolved in the electrolyte and a pure copper metal coating is built up on the cathode.