The apparatus will be set up as shown below:
Before connecting the copper electrodes to the circuit, I will weigh them both with the electronic weighing machine in order to enable me to compare the weights of the electrodes after electrolysis with the weights before electrolysis. By comparing these weights, I will be able to work out the change in weight and thus find out how much copper has been deposited at the cathode and how much has been taken from the anode. This will in turn tell me if my predictions were correct. After each separate test, I will disconnect the copper electrodes and clean them by first dipping them into water in order to remove any copper sulphate solution, and then in propanone and then I will dry them with a hairdryer. The reason for putting the electrodes propanone after water is because propanone is an alcohol so it naturally evaporates very quickly. This means that the electrodes will dry quickly once in front of the hairdryer, leaving pure copper without any copper sulphate, water or propanone.
I will be using the rheostat to adjust the electric current and the ammeter will read how much current is passing through. At first, I will adjust the rheostat so that it reads 0.2A on the ammeter. Then, after each test and after having cleaned, weighed and reconnected the electrodes, I will increase the electric current by readjusting the rheostat. Each time, I will increase the current by 0.2 A so that at first the current will be 0.2A, then 0.4A, then 0.6A, then 0.8A and then finally 1.0A. Thus, the final current (1.0A) will be 5 times the original (0.2A). I will repeat the experiment four times in order to enable me to calculate an average and to make sure that my results are accurate and correct. This means that I will be making a total of 20 readings which will help me draw up valid conclusions. Each time, I will leave my experiment going for 2mins.
Safety is a very important issue in every experiment. Taking this into consideration, I have taken all possible precautions to ensure the safety of myself and of others around me. There are several things in the experiment that could harm people if not handled properly. For example, copper sulphate solution is very harmful and poisonous so I must ensure it does not come near my eyes or mouth. Because of this, it is important that I wear safety glasses and make sure that the beaker containing the copper sulphate solution is not left carelessly on the edge of the worktop so it cannot be knocked over. Electricity is another danger in my experiment. I will therefore take great care when connecting the experiment and make sure I do not expose myself or anybody else to any danger. Propanone is also extremely flammable so I must make sure that no potential fire comes near it. As well as ensuring that my experiment is safe, I must also be cautious about other experiments going on around me and advise others if they are not taking necessary safety precautions.
In order to guarantee that my results are precise and accurate, I will ensure that my experiment is a fair test by keeping the following factors the same:
- the electric current passed through the copper sulphate solution during each individual test. This will be kept constant in order to ensure that electrical current levels do not increase, decrease or fluctuate from the intended current. If this is not kept constant, then more or fewer electrons will be supplied to the cathode which will mean more or less copper will be deposited. This will make my results inaccurate and unreliable, preventing me from drawing a valid conclusion.
- the size of the electrodes throughout the experiment. This will be kept constant because if they had larger or smaller surface areas, it would affect the space available for either copper to discharge and be deposited in the case of the cathode, or for copper to be released into the electrolyte in the case of the anode. As well as using the same electrodes, this also means that they must be submerged into the copper sulphate solution equally at each individual test.
- the copper sulphate solution. This must be kept the same because if it was changed, the copper sulphate concentration in the solution may differ which would produce unreliable and inaccurate results as there may be more/less copper available for the cathode to discharge.
- the distance between the electrodes. This should be kept constant because copper ions being released from the anode will have a longer or shorter way to travel to get to the cathode. This would affect the amount of copper deposited at the cathode in the given time.
- the time each test is left for. This must be kept constant because, if the time is altered, the copper will have more/less time to decompose and discharge at the cathode and this will produce unreliable and inaccurate results.
My measurements will be significantly accurate and precise as I am using accurate apparatus to conduct my experiments. The weights of the copper electrodes will be weighed to 0.01g and the current will be measured to 0.01A. The weight will be measured by an accurate electrical weighing machine but the current will be measured using a mechanical and fairly old ammeter but it is, nevertheless, accurate. I will time the experiment using a very accurate stopwatch which times to 0.01sec. These apparatus will allow me to obtain reliable and essential results will in turn help me to draw up valid conclusions.
My plan is a good way to carry out the investigation for a number of reasons. Firstly, almost everything can be controlled in the intended way which means that my results will be very accurate. Secondly, my measurements will be precise because of the most accurate measuring instruments available to me that I have chosen to use (e.g. ammeter, accurate electronic weighing machine, accurate stopwatch). Thirdly, I will be repeating the experiment four times and so I will be able to calculate the average measurements and make sure that my results are reliable. I have ensured that my experiment is a fair test by controlling the electric current passing through the electrolytic cell, the surface area of the copper electrodes immersed in the copper sulphate solution, the concentration of copper sulphate in solution, the distance between the electrodes and the time each test is left for. My experiment is also a good way of carrying out the investigation because it will allow me to gain enough accurate and reliable results over a good range to allow me to test my hypothesis and draw valid conclusions.
Before conducting my final experiment I arranged to conduct a trial experiment. This trial experiment was intended to familiarise me with the experiment before I did the final one and also to help me improve the method I was working on and to guide me on the best way to conduct the actual experiment. In the trial experiment I tested my method and ameliorated it, correcting any mistakes and building on any faulty points. It caused me to think about the surface area of the electrodes immersed in the electrolyte and how it was important to control in order to ensure that my experiment was a fair test. It also helped me to decide on the time I would leave the experiment as I found that 2mins is sufficient time for electrolysis to occur and for enough to happen so that I could draw valid conclusions. Apart from improving my method, the trial experiment also gave me confidence in my hypothesis and in what I was doing. It also helped me to set-up and conduct the final experiment as quickly as possible, thus making it possible for me to repeat the experiment 4 times.
Results: Here are the results for my experiment along with the changes in mass after electrolysis has taken place:
(the minus sign indicates a decrease in mass)
Here are the averages of my experiment:
(the minus sign indicates a decrease in mass)
Below is a line graph showing the average change in mass of the cathode:
As can be seen, the line of best fit in the graph above goes through all the points plotted. This shows that my results are very accurate and that my predictions are right. I predicted that, as the current increases, the amount of copper deposited at the cathode will also increase. My results not only prove my prediction, but they also prove Faraday’s first law of electrolysis which states that that the mass of a given element liberated during electrolysis is directly proportional to the quantity of electrical current consumed during electrolysis. As can be seen from the graph, as the current doubles, the mass of the copper being discharged at the cathode also doubles. This proves that the mass of the element liberated during electrolysis (copper) is directly proportional to the electric current.
Below is a line graph showing the average change in mass of the anode:
As can be seen, the line of best fit in the graph above does not go through all the points. As a matter of fact it goes through all the points except for the first one which shows that my results are very accurate and reliable indeed. I have drawn this graph in order to prove the prediction that I made in which I stated that copper ions from the anode will be released into the copper sulphate solution and so the anode would get lighter. I also stated that as the electric current increases, the amount of copper being released from the copper anode would also increase because more electrons are being drawn from the anode and taken to the cathode so positive copper ions are attracted to the negative cathode and therefore leave the anode and go to the cathode.
Conclusion: From my experiment I have found out that increasing the amount of electric currents flowing through the copper sulphate solution electrolyte will increase the amount of copper deposited at the cathode and increase the amount of copper released from the anode. Similarly, decreasing the amount of electric current will decrease the amount of copper deposited at the cathode and decrease the amount of copper released from the anode.
The scientific explanation for my results is that when an electric supply is connected to the electrolytic cell, electrons flow from the anode to the battery and from the battery to the cathode. This is why the anode is positive as electrons have been drawn from it, and why the cathode is negative as electrons are given to it. As the electrolyte is of course an ionic compound, it contains positive and negative ions. As I have stated above, the copper ions are positive and are therefore attracted to the cathode. When the copper ions reach the cathode, they are discharged by the plentiful electrodes being put into the cathode. Thus they become copper atoms. This is shown by the equation:
Cu²+ + 2e- → Cu
This shows that two electrons are needed to discharge each copper ion.
In addition to the copper in the copper sulphate solution being decomposed, positive copper ions from the positive anode are also being attracted to the negative cathode. Therefore, positive copper ions are released from the anode into the copper sulphate solution. In effect, the copper anode is constantly supplying the electrolyte with copper which is then in turn discharged and deposited at the cathode. This means that electrolysis will not cease until the copper anode immersed in the electrolyte is completely decomposed in which case the electric current stops flowing as the anode is no longer connecting the rest of the circuit to the electrolyte. Thus the electrolyte will never go clear and lose all its copper and sulphur and oxygen.
Moreover, if the electric current is greater, more electrons are being supplied to the cathode and more taken from the anode which means that copper ions can be discharged at a quicker rate at the cathode as there are more electrons, and that more copper ions can be supplied to the electrolyte by the anode as more electrons are being taken away from it. Similarly, if the electric current is smaller, fewer electrons are being supplied to the cathode and fewer taken from the anode.
Michael Faraday was one of the first scientists to study electrolysis. His first law of electrolysis states that the mass of a given element liberated during electrolysis is directly proportional to the quantity of electrical current consumed during electrolysis. This supports my results entirely.
The results of my experiment agree perfectly with my predictions. I predicted that as the electric current increases, the copper being deposited at the cathode will increase as will the amount of copper being released from the anode. That is exactly what happened in my experiment and exactly what my results show. My results also show that the amount of copper deposited at the cathode is directly proportional to the amount of electric current passing through the electrolytic cell. This is precisely what Faraday’s first law of electrolysis states.
Evaluation: My experiment was a very good way of carrying out the investigation because it gave me enough measurements as well as observations to draw a valid and well-founded conclusion. I repeated the experiment four times which made my results more reliable and allowed me to calculate averages. The experiment was also a fair test and I considered all the factors that could affect my experiment and I set out to control them as best I could. I made sure that I kept the constants strictly under control which I did successfully with the help of the accurate measuring instruments that I utilised. The trial experiment that I conducted helped in a number of ways to improve my method and thus made my final experiment an even better way to have carried out the investigation.
My measurements were accurate and precise enough for me to draw a valid and sound conclusion. They were precise and accurately taken. The measuring instruments helped me greatly with their accuracy and easily controlled functions. The environment around the experiment could be controlled easily and the experiment itself could be conducted with ease, precision and accuracy. The range of my measurements was wide enough for me to prove my hypothesis and the scientific theory and to draw up a valid conclusion. As well as this, my measurements agreed very well with each other in each of the four repetitions and there were no anomalous results at all. This shows that, as well as the experiment being a good way of carrying out the investigation, that my measurements and results were sufficient and very reliable. In addition, I can tell that my results were adequate and satisfactory by the smooth line of best fit on my graph. The line went through all the points in the case of the graph showing the change in mass of the cathode and all the points but one in the case of the graph showing the change in mass of the anode.
However, I do think that there are some improvements that I could make to my experiment in order to produce more reliable results. Part of my plan to make my experiment a fair test was to ensure that the same surface area of the electrodes was immersed inside the copper sulphate solution. Even though I tried my hardest to stick to this concept, I do not think it was done accurately enough. The change was extremely minute so I do not think it affected my results much but it is a point on which I could make improvements. In the future, I could draw a line marking how far the electrodes should be immersed. However, this would not solve the problem entirely as copper is constantly moving from the anode to the cathode and so the amount of copper at each cathode would always be changing. This means that the surface area of the cathode would continuously be increasing while the surface area of the anode would continuously be decreasing. Again, this change would be so minute, it could not be detected. Another problem is that I had to use three different cathodes and three different anodes because I did not finish my experiment in one lesson. Instead my experiment took me three lessons to complete. This change of electrodes would have affected their surface areas which would in turn affect the rate of electrolysis. This problem could have been overcome if I had continued to conduct my experiment or if I had taken or reserved the electrodes that I had been using for my experiment. Another problem with my experiment was that I had to adjust the current with the rheostat while electrolysis was taking place. This meant that at first the current was lower than it should be and then it was adjusted. This could have produced some inaccuracies in my results. It would be more accurate to prepare the rheostat beforehand and thus have it ready on the precise current. Another inaccuracy was the water and propanone I used to clean the copper electrodes with. Because of the many experiments taking place and because many people had cleaned their electrodes so many times, the distilled water and propanone had become contaminated with copper sulphate solution which could be seen as both the distilled water and propanone had a blue tinge to them. This meant that some copper sulphate solution was still on my copper electrodes when I was drying them. This could have caused some inaccuracies in the weight of the copper electrodes but the difference would have been so minute, it could not have been detected on the weighing machine. I could solve this problem by changing the water and propanone each time. However, this would be extremely wasteful and quite unnecessary.
There are some further methods that I could carry out in order to provide more evidence for my conclusions. I could, for example, use a different metal and a different electrolyte to see whether the same thing happens with any metal. I could, for example, have used silver electrodes and silver nitrate solution as my electrolyte. This would have further proven my hypothesis and provided me with more evidence with which I could draw general conclusions for all metals.