The Values
For the time allowance I am going to use 10 min. I think that is enough time for electrons be turning copper ions from the anode into copper atoms and letting them cling onto copper at the cathode. This would lead to enough copper deposition on the cathode so that an accurate measurement could be taken down.
I am going to try and use 5 different current values, 0.25, 0.50, 0.75, 1.00, 1.25 amps. I am going to be using these current values because I think these are the most suitable because. First of all, I have the a small current to start of with and so I can use the results of this value and compare it with the larger value(1 amp) and see what the kind of affect a small current has on the mass changes of the electrodes. Also I can investigate what other affect a small current has on the copper sulphate solution e.g. the increase in temperature. Secondly I have a constant amount of current increasing which makes it easier to calculate the changes of between each different experiment and so when I draw the graph I can see how the mass changes. An advantage of using these values is that the highest value is 1 amp and this really should really give off that much energy into heat which would warm the copper sulphate solution. So this would help a lot in keeping the same temperature in the experiments. The disadvantage of this is that the bigger the current the bigger the mass changes on the electrodes therefore this would lead to more accurate results
The Other Factors
The factors I am going to keep constant are going to be Time, Temp, depth of solution, separation of the electrodes and the Concentration of the copper sulphate solution.
First of all you need to keep the time constant because if no time is recorded the charge in the experiment can’t be calculated so keeping time constant in this experiment is vital.
Another point is that we are going to keep the separation of electrodes the same distance apart. We are going to do this because different separations of the electrodes create different resistances because the electrons have different distances to travel through the electrolyte. Therefore I am going to keep the distances between them the same in all of the experiments.
I am going to also keep the concentration of the solution the same also which is 2M. I am going to do this because this would mean that there is going to be the same number of copper ions in the solution, and I would like to keep this constant because this would lead to more accurate results.
Furthermore, we are going to keep the depth of the solution the same because I want the same amount of copper ions in the solution and this also links in with the emersion of the electrodes in the copper sulphate solution so also the same depth is going to keep the emersion of the electrodes at the same height, the height is going to be 8 cm. This is important because this depends on how much of the area of the electrodes are actually in the electrolyte being part of the electrolysis (being in the reaction).
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Method
First of all I am going to set up the apparatus (which is on a separate sheet) then I am going to get the two electrodes and first of all polish them with emery paper so I get rid of any copper impurities of the surface and so I get fresh copper. Then I am going to put them in water to get rid off any copper sulphate crystals from the last experiment and then I am going to put it in ethanol and then acetone simply to get rid off the water, the ethanol and acetone is going to evaporate quickly and therefore the water, ethanol and propane will be gone. This would lead to accurate measurements of the electrodes. After that I am going to make sure the electrodes are dry and then weigh them and take the readings down. Then I am going to name one of them cathode and the other anode. Furthermore, I am going to connect the anode to the plus and the cathode to the minus of the power box. After that I am going to make sure the electrodes are the same distance apart (2.5cm) in every experiment. When they are put into the solution I will also note down the emersion of electrodes in the electrolyte and make sure it’s the same and the temperature of the solution before the experiment and after. Then I will start running the current, the clock timer and move the variable resistor so the resistance lowers down the current to 0.25 amps.
I will let the experiment go on for 10 minutes I will be timing it with a stop clock I will try and turn off the experiment at exactly 10.0 min so I get best possible results. Also I expect the current to change while the experiment is going on so will keep a very close eye upon the readings of the ammeter and change the resistance is the current changes. Then while the experiment is going on for 10 min I will carefully watch the current and if it changes it will adjust it back with the variable resistor to what is should be. When the stop clock reaches 10.00 minutes I will switch off the power box straight away and stop the experiment.
Then straight away I will put in the thermometer and measure the temperature again and then pull out the electrodes. Moreover, I will dip the electrodes into water again, ethanol and then propane. After that I will make sure the electrodes are dry and weigh them again and record the readings. I will do the same for each of the different experiments where the currents are going to be from 0.25, 0.50, 0.75, 1.00 amps. Also I will be using the same electrodes and the same apparatus for each of the experiments.
Another point is that I am going repeat the experiment twice and make sure that my results are accurate and I will make sure that everything is kept constant as in the repeat as in the last experiment. Also I can plot a graph of my first experiment and then my second experiment so I can compare how accurate they are and make decisions of which results are anomalies.
Analysis
I am going to present my results on two graphs. One of the graphs I am going to plot the average, the first experiment and the repeat of the experiment results on it. From this I can compare what the differences are and suggest any anomalies.
On the other graph I am going to plot the results of the preliminary experiment , and the average and the prediction It is going to be mass gained at the cathode on the y axis and the current used at the x axis. I am then going to plot all the results and draw a best fit line through the origin. If I get a straight line going through the origin then the current used will be proportional to the mass gained at the cathode.
The prediction graph shows that the results that I should have obtained in the experiment. By looking at this graph I can compare my actual results and against what they should be. It shows that mass is directly proportional to current since the graph is obtained from the calculated results.
My actual results found by the experiment are generally a fraction smaller than what they should be, some of then quite inaccurate. This is probably due to the copper falling off the electrodes during the time between removing the plates from the Copper Sulphate and weighing them. In theory
This would solve my whole point of the experiment because this would tell me that the current used is proportional to the mass gained at the cathode.
I pretty much got a straight line in my results only a few of results were a little inaccurate. This suggests that the current used is proportional to the mass gained at the cathode.
From my results I can analyse that the current used is nearly proportional to the current used. My results do not equally match my predictions. Some results are inaccurate some are nearly perfect from what I calculated in the prediction.
When the current is varied for example, when it is big the mass deposited at the cathode should be bigger than with a small current. This is because the bigger the current the higher the flow of electrons. This means that more electrons flowing would speed up the ionic reaction Cu2+ + 2e- = Cu, Cu = Cu2+ + 2e-. For some reason when I used the current 0.50 amps the results were quite different to the rest in the experiment maybe this is were the temperature
Overall the results were just good enough to prove that there is a relationship between the mass deposited and the current used which answered my hypothesis.
Evaluation
The experiment itself worked pretty much perfectly apart from the resistance which kept on changing, this altered my current therefore I had to change the variable resistor to change this back to the set current of the experiment. I found that it sometimes was quite hard to adjust the current to the perfect number. This was also because I was using an old variable resistor which was quite stiff therefore was hard to adjust. The current suddenly just changed and you had to watch the current carefully so that you could change the current back in the least possible time. Most if the time the current was 0.01 of an amp bigger than it should be. So from this I can evaluate that the results may not be very accurate because of the slight change in the current. I believe these changes in the resistance occurred because the current warmed the solution up which would increase the energy in all particles therefore the process would have speeded up a little bit.
If I carried out this experiment again I would choose a better resistor which would be easier to alter. This would lead to extremely short periods of time between the time of change in the current and the alteration. From this I could get more accurate results. Also next time I would use higher current values because this would lead to bigger mass changes over the period of time and therefore even more accurate results could be obtained.
The most obvious consideration which could be improved was that copper deposits may have fallen off the electrode at various times, as it was being removed from the electrolyte, as it was being rinsed in distilled water, ethanol, as it was being dried in acetone or just when being moved. I was extremely careful in trying to limit this but it was almost always impossible. A better method would have been to simply allow the copper to dry in air because none would be lost in the acetone. This wasn't possible because it would have taken a long time and the experiment was carried out over a limited period.
Another point is that I was using 2M copper sulphate solution which was the mininimum we could use. This was because if had used more dilute solution there would have been too much water in the solution, therefore it would have reduced its conductivity. This would also have caused oxygen to be made at the cathode which is not at all what I want. So in the next experiment I would have rather used a higher concentration of copper sulphate, one so the solution would be more conductive which would mean that the resistance of the solution is much lower. If this resistance is lower, then this would also lead to more accurate results because I believe that the temperature would not change so much in the solution. This means that because there is less resistance there will be less heat given off too. From this I can tell that the collision of ions would be kept more or less the same. This means that when the temperature is higher the rate of collisions between copper ions in the solution is higher than when the solution is colder, this is because there is more energy in the solution. Klsadjfsahgfsajkfsal dfsl Therefore this would more accurate results throughout all of the experiments.
Also I think I should have chosen to take more results because in my graph I don’t really have enough points which are accurate enough so that I can draw a confident straight line. I suppose I was limited on the amount of time give to me therefore doing the experiment with further current values was not possible.
I did a repeat of my experiment so that I could get an average and hopefully obtain more accurate results. The results from my first experiment weren’t too close to the results of the second experiment. Some of them were nearly the same but the rest were different from the first experiment by at least 0.05g. This shows that a possible amount of error could have taken place more in the second experiment rather than in the first one. They could be any of which I mentioned in the analysis.
Also to extend my investigation even further I could for example use other salts such as copper chloride which should lead me to similar results. I could use any copper salt really because copper is the main part of the compound anyway. I would still get copper at cathode. I believe that this would have a different effect on the deposition of copper because copper chloride ions are different sizes and therefore would take longer or quicker to travel in the solution. This would also lead to changes in the resistance. Therefore the two solutions would have different resistances and I expect probably different conductivity depending of the concentration. Also if the solution was less resistant then I believe I would get more accurate results and bigger depositions because this would lead to more current passing through rather than part energy being changed into heat. If the solution had better conductivity then it would have to less resistance therefore less energy would be lost into heat which would warm the solution up and increase the activation energy and alter the resistance again leading to less accurate results because the current would change also.
Also what I could do is alter the concentration of the current which I already mentioned. This I believe would lead to greater depositions at the cathode because increasing the concentration would increase the number of ions in the solution therefore the conductivity of the solution would change. This means that more current will pass through than usually and so this should speed up the ionic reaction.
