The purpose of the experiment that I carried out was to monitor the quantity of Copper (Cu) metal deposited during the electrolysis of Copper Sulphate solution (CuSo4) using Copper electrodes, when certain variables were changed. These are the factors that could affect the amount of Copper metal deposited on the cathode:
1. Time
2. Current
3. Concentration of Solution
4. Quantity of Solution
5. Size of Electrodes
6. Distance between the electrodes
7. The surface of the electrodes
8. Amount of electrode exposed
The current was chosen as a variable because it is an easy quantity to measure and record, whilst at the same time maintaining the other variables at a constant level. The other variables must be kept constant to keep it a fair test. The other factors could be observed in later experiments, if I have time. It is possible to predict that the relationship of the amount of current and the amount of copper deposited on the Cathode (negative electrode) will be directly proportional to each other. The current will be accurate to the nearest 0.05 A and I will use a rheostat/variable resistor to measure the current. The time will be measured to the nearest second using a stop clock. I will make sure that my results are reliable by checking that most of them fit a pattern, and I will repeat the experiment. This method is a good way to test my hypothesis as the current is the only variable being changed and it is fairly accurate.
Method
The apparatus was set up as in the diagram below:
Copper Sulphate solution (50cm3) was poured into a small beaker. The two copper electrodes were thoroughly cleaned using water, to scratch off the layers of copper from previous experiments. The electrodes were weighed, their masses recorded and placed into the beaker containing Copper Sulphate solution. The electrodes were connected to a D.C power supply, variable resistor and ammeter. A varying current flowed (0.1, 0.15, 0.2, 0.25, 0.3 Amps) and the experiment was left for 3 minutes. After 3 minutes the DC power supply was switched off and both electrodes were removed from the solution. They were then washed by dipping in distilled water, and dried by dipping into propanone (a volatile liquid which evaporates quickly) and placed near a hairdryer to dry of any excess liquid. Once clean and dry both electrodes were both carefully weighed and their new masses recorded. The experiment was repeated until I had done the experiment with all 5 amounts of current. I did this three times.
The apparatus used for this experiment were:
1. D.C. power supply - for providing the power for the experiment.
2. Ammeter - for measuring the amount of current flowing though the circuit.
3. Electrodes [Anode (+) and Cathode (-)]
4. Variable Resistor - for changing the amount of current uses.
5. Circuit wires - for connecting up the apparatus to the power supply.
6. Beaker - for holding copper sulphate solution.
7. Copper sulphate solution - for doing the electrolysis experiment.
8. Water, propanone, hairdryer - for cleaning and drying the electrodes using them in descending order.
9. Stop clock – to measure the amount of time taken
Results
1st Experiment
Weight of cathode at start: 1.173 g
Weight of anode at start: 0.847 g
2nd Experiment
Weight of cathode at start: 1.146 g
Weight of anode at start: 0.880 g
The graphs for the results obtained are shown below:
Conclusion
The results obtained support the prediction that the more current is input, the more Copper metal is deposited on the cathode. It is now true to say that if the time is doubled the charge is doubled, and therefore the amount of copper produced. Proof of this can be seen in the results obtained. The actual results produce an almost straight-line graph, showing that the weight of the electrodes increase/decrease steadily as the current is increased steadily. This shows that the two are directly proportional. The amounts that the weights have changed by are increasing steadily with more current input. My results do agree fairly well with my hypothesis and the investigation follows scientific theories.
Evaluation
Although this was a successful experiment, there were some factors of the experiment, which could have been improved to make it even more successful. One of these factors could have been the electrodes, which, even after being cleaned were still quite dirty and obviously still had irremovable substances from previous experiments still attached to them. If this experiment were to be repeated for a second time, in need of greater accuracy, it would be important to have a new pair of electrodes, which have never been used before.
Another factor which may have affected the overall outcome of the investigation may have been the fact that the practical work of the investigation was carried over from lesson to lesson, meaning that variables such as the concentration or the amount of the Copper Sulphate solution could have changed between lessons. To overcome this problem, a stock solution of Copper Sulphate should have been made so as the concentration remained the same at all times. The same electrodes and equipment should have been used throughout. However, as this experiment was conducted through two separate lessons, different equipment was used, therefore altering the results. Also, when weighing, the same electrical balance should have been used as there may have been slight differences between the two balances. This is what could explain the anomalous result in the graph. However the results were precise enough and enough figures were produced in order for me to get a reasonable set of results.
I found this investigation very interesting and to add to this experiment, I can investigate more of the variables in this experiment, which may or may not affect the mass of copper deposited onto the cathode, such as changing the time or solution concentration. I could also use different equipment for the experiment, such as an A.C power supply, different solutions etc
