It is important to keep the temperature of electrodes the same, as when they are heated they expand and therefore the surface area increases. To make sure that this will have no effect on my experiment, I will always conduct my experiment at room temperature away from the windows. Charge is the main factor the deposition of copper depends upon. This is evident as with the increase of charge, the speed and rate of copper production is also increased. Charge consists of ‘time’ and ‘current’; therefore they are critical in copper production and must be kept constant if they are not being experimented.
CHARGE (Q) = CURRENT (I) * TIME (S)
The molarity of copper chloride also needs to be kept the same. This is because the greater the molarity of the copper chloride solution, the more ions there are available to take electrons from the cathode. Hence this means that the molarity of copper chloride solution affects the copper production. To avoid this bias the molarity will be kept at 0.25 for each test.
Apart from what constitutes the electrolytic cell (including the power supply), the main equipments that will be used are stated as follows. A beaker is required to work with the copper sulphate solution. To measure and control the time a stopwatch will be used, and finally a weighing scale is needed to weigh the electrodes before and after the discharge of electricity. The electrodes will be weighed in units of grams, to two decimal places.
Five values of time will be used to provide a generally large range, and they will be spaced out at 5 minutes intervals, starting from five minutes 5,10,15,20,25 (minutes). Finally the experiment will be set up in such a way as to ensure that the electrodes do not touch each other at any point of the experiment. They will be clipped at opposite ends of the beaker, and if they do come into contact, the experiment will be repeated again. I found out that this was a problem when I did my preliminary experiments. I established that the two electrodes touching each other during the experiment interfered with the result, and therefore they must be kept apart throughout the experiment.
It is important to maintain an accurate test because this will enable me to work with a clearer trend. To ensure accurate results I will measure time to the nearest millisecond. 75ml of copper chloride solution will be always used, measured to the nearest millilitre. I will repeat each test three times so that more accurate results are acquired, also clearly excluding the anomaly. Additionally, the electrodes will be weighed using digital scales, which are more accurate than analogue scales.
Some safety precautions need to be taken. Copper chloride solution is poisonous, so it must not be inhaled, and surely not taken internally. Great caution also needs to be taken that the solution does not come in contact with the eyes. The experiment must also be conducted in a well-ventilated area, caution against the poisonous product, chlorine. We will do our experiment in the laboratory fume cupboard. This will stray the poisonous chlorine away from our contact.
PREDICTIONS
The amount of copper deposited on the cathode depends on the number of electrons passing through the current, i.e. upon the charge passed through the cell. The charge passed, Q in coulombs, is related to the current and time, by Faraday’s law: Q= I*T
I = current measured in amps T = time in seconds Q = charge in units of coulombs
It is therefore possible to predict that the relationship will be directly proportional between the time the current flows and the mass of Copper deposited on the Cathode (negative electrode). I can therefore predict that if I double the time of the experiment, I will therefore be doubling the charge. 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.”
CHANGE IN PLAN
Due to lack of time we were given the results to the experiment using the input variable concentration and copper chloride used as the electrolyte. This obviously is not the same variable as initially planned, but this would not be of great inconvenience. In this instance the time was kept constant, and the concentration was varied from 0.25 molar to 2.0 molar. 0.25M, 0.5M, 1.0M, 1.5M, 2.0M
Concerning the prediction for the concentration variable, I predict that the outcome will be just the same. The relationship between the concentration of copper chloride solution and the amount of copper deposited will be directly proportional. I will explain the reason for my prediction. Electrons flow from the power pack to the cathode. The copper cations are attracted to the negatively charged cathode by an electrostatic force. Therefore if the concentration of copper chloride solution is increased then there will be more copper ions available to take from the cathode. In simple terms there will be more molecules to split up to form copper atoms. I can therefore predict that the amount of copper deposited is directly proportional to the concentration of the electrolyte.
METHOD
The apparatus was set up as in the diagram below:
Copper ions preferentially discharge over hydrogen Cu²+ + 2eֿ Cu
Copper chloride solution (75cm3) was poured into a small beaker. The carbon cathode was brand new and unused, important to maintain a fair test. The electrode was weighed, its mass recorded and placed into the beaker containing Copper chloride solution. The electrodes were connected to crocodile clips, and the clips to the power pack. Extra care was taken to keep the electrodes away from each other, so that it does not intercept with the reaction. A steady voltage flowed and the experiments ran for a period of 5 minutes. At that time the current was switched off and the cathode was removed from the solution. It was then washed with water, and dried by a hair-drying machine.
Once clean and dry the cathode was carefully weighed and its subsequent mass recorded. The five concentration values (0.25, 0.5, 1.0, 1.5, 2.0) were each repeated three times to improve the accuracy of the results.
RESULTS
The graphical representation of the results of electrolysis of copper chloride
CONCLUSION/ ANALYSIS
The results obtained support the prediction that the greater concentration, the more copper metal is deposited on the cathode. It is now true to say that if the concentration is doubled, the amount of copper produced is also doubled. Proof of this can be seen in the obtained results:
At 0.25 molar 0.11 grams of Copper is produced.
At 0.5 molar 0.23 grams of Copper is produced.
0.23 grams is nearly the exact double of 0.11 grams. This proves the prediction that the higher the concentration, the higher the amount of Copper produced.
The actual results produce a graph with positive correlation, though there was seemingly one problem in the graph. The graph contained an anomaly and that was at the point of 2.0 molar concentrations. That specific point was too above the usual stage and the possibilities for its cause will be discussed later in the evaluation. The general result of the graph shows that:
As the concentration increases, the mass of copper deposited also increases.
The reason for the increase of copper concurrently with the concentration is due to the following principle. Increasing the concentration means increasing number of the molecules to be split and therefore more atoms (of copper) are produced.
This is because the greater the molarity of the copper chloride solution the more copper ions there are available to take the electrons from the cathode.
EVALUATION
This experiment was quite a success in terms accuracy and reliability. Care was taken to ensure a fair test and each value of concentration was investigated thrice.
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 a good clean 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 imperative to have a very good electrode-cleaning agent.
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 could have altered between lessons. One big problem that was encountered throughout the experiment was that the same cathode could not be always used, due to availability and breakage. The same electrodes and equipment should have been used throughout. This is what could explain the anomaly (“freak” result) in the graph, at 2.0 molar concentrations. The results might have been more reliable if the experiment was left on for longer, something like 10 minutes, to compensate for the errors.
Though the experiment was conducted away from windows, for wind and temperature not to impede on my results, I still believe the temperature could have been another source from which we draw the anomaly.
Overall I found my results, compared to my prediction, very compelling. Although there were problems associated with the experiment, I believe the results produced are reliable and convincing. Relative to the best-fit line, the points are very near, apart from the anomaly, which, as mentioned, was probably caused by the problems encountered with the cathode.
Extending the duration of time for which the current was discharged can further enhance this specific investigation. Increasing the range of concentration variables is also another possibility to advance this experiment.
I found this investigation very interesting and increasing the range of variables that were used could further enhance it. I am looking forward to investigating 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 Quantity or Temperature variable.
