Variables
The factors that my effect the outcome of the experiment are:
1. Time
2. Current
3. Temperature
4. Molarity/Concentration of Solution
5. Quantity of Solution
6. Size of Electrodes
7. Distance between the electrodes
8. The surface of the electrodes
My controlled variable will be the Charge (amps). My independent variable will be the Time and the dependent variable will be the mass of the cathode (grams).
Prediction
It is possible to predict that the relationship will be directly proportional between the charge and the mass of Copper deposited on the Cathode (negative electrode). I can therefore predict that if I increase the charge, the mass of the Cathode will increase. This statement can be supported by both of Faraday's Laws.
Faraday's First Law of electrolysis states that:
"The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed"
Faraday's Second Law of electrolysis states that:
"The mass of an element deposited by one Faraday of electricity is equal to the atomic mass in grams of the element divided by the number of electrons required to discharge one ion of the element."
Another piece of scientific theory we can use to support our predictions is:
At the anode (+):
Cu ® Cu2+ + 2e-
At the cathode (-):
Cu2+ + 2e- ® Cu
The copper at the anode releases copper ions and electrons, which float in the solution towards the cathode, where the copper ions and electrons deposit copper onto the cathode.
Results
(Graph is attached to the Back of this booklet)
Analysis
The results obtained support the prediction that the longer the current is left to flow; the more Copper metal is deposited on the cathode. It is now true to say that if the charge is increased the mass of the cathode also increases. Proof of this can be seen in the obtained results.
At 300 Coulombs the mass of the cathode is 121.76 grams
At 600 Coulombs the mass of the cathode is 121.87 grams
The actual results produce an almost straight-line graph, showing that:
Therefore, it has now been proved, through this experiment, that both of Faraday's Laws Of Electrolysis are correct.
Faraday's First Law of electrolysis states that:
"The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed"
Faraday's Second Law of electrolysis states that:
"The mass of an element deposited by one Faraday of electricity is equal to the atomic mass in grams of the element divided by the number of electrons required to discharge one ion of the element."
It has also been discovered that the copper anode releases copper ions and electrons, which form copper at the cathode.
At the anode (+):
Cu –2e = Cu2+
At the Cathode (-):
Cu2+ + 2e = Cu
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 were 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 imperative to have a new pair of electrodes, which have never been used before.
Another improvement could have been in the drying technique itself. The solution I used to evaporate the excess Copper Sulphate solution may have remained on the electrode during the weighing which would increase the weight making the experiment less accurate. This could be improved by first cleaning the electrode with distilled water, dipping them in propanone then placing them next to an electric heater to evaporate the excess propanone.
To improve the accuracy of this experiment, it could be repeated many times to produce a more accurate average result.