It is also important to keep the temperature of the electrodes the same each time because when the electrode is hot, they will expand, once again increasing surface area and making my results bias. To make sure that this will have no affect when I conduct the experiment I will always do the experiment at room temperature away from the window. This means that the outdoor weather will not affect it either.
Time is also an input variable. If I varied the time it would also vary the amount of current that will pass through both electrodes, and current is directly proportional to the loss in mass at the anode. This is because with a greater charge, the copper at the anode has to decompose more to give more electrons. To make sure that the time has no affect on the loss of mass at the anode, I will time each experiment for five minutes only. This way it will remain the same in each test and will not affect my results.
I have considered what affect the solution’s coverage of the anode has, and I think it is also important to keep this controlled, as this will also affect the loss of mass at the anode because the solution is the circuit’s connection between both electrodes. If it only covers half of the anode, only half of the anode will be able to transfer its copper ions and therefore the loss in mass will be far less. Therefore, to eliminate chances of this bias I will use the same length electrodes each time and clip them at the top of the same sized beaker. As the volume of the electrolyte will always be the same as well, it should mean that coverage should remain the same.
I believe it is also important to keep the circuit in DC (direct current) throughout the investigation because with AC (alternating current) the current will keep changing direction. This will affect which electrode is the anode and which is the cathode. If the initial anode starts losing mass due to the lack of electrons, it will gain them back again when the current changes direction because this electrode will now be concentrated with electrons. Therefore, the mass of the anode will keep changing and the anode will keep changing electrode. Therefore, to avoid this confusion, I will simply use DC.
****It is important to keep the molarity of the copper sulphate solution the same. This is because the greater the molarity of the solution the more copper ions there are available to take the electrons from the cathode. The faster that the electrons are taken from the cathode, the faster the copper at the anode decomposes to give the same number of electrons. This therefore means that the molarity of the copper sulphate solution affects the loss in mass at the anode. To avoid this bias I will keep the molarity of the solution at one each time.
Finally, my experiment set up ensures that the electrodes will not touch at any point on the experiment. This will bias the results because there will be no contact with the solution and therefore the electrodes will not gain or lose mass because they will not come into contact with the copper ions in the solution. They will always be clipped at opposite parts of the beaker and if they do come into contact, I will re-do the result.
It is also important to maintain an accurate test because this will enable me to see a clearer trend. To ensure that I get accurate results I will measure time to the nearest millisecond. Liquid will always be measured in the smallest cylinders possible, to enable me to get it closer to the mark required. I will always use 200 ml of copper sulphate solution. It will also be measured to the nearest millilitre, which is a more accurate unit. I will repeat each result three times so that I can get a better idea of the correct results and exclude odd results. The weights recorded for the anode will be measured by an electronic scale, which is more accurate, and to the nearest milligram.
I will ensure a safe test by keeping the glass beakers away from the edge. My hands will be dry at all times when coming into contact with the electricity, and all wires shall be insulated while all plugs shall be earthed. The wires will be kept off the floor to avoid tripping up, and I will keep a clean area to work with which will minimize accidents and breakages as well.
I predict that the greater the current the greater the loss in mass at the anode. To explain how I have come to this conclusion, I will first explain what is happening in the circuit:
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 you increase the current, there will be more electrons available at the cathode to make copper atoms.
The current is a measure of how many electrons flow through the circuit in a given time, so if the time is kept constant, the current only affects the number of electrons passing. Therefore, the current would only affect the number of copper atoms decomposed, and their combined mass. In fact, if the mass of copper required is doubled, the current must be doubled to allow double the number of electrons to pass through the circuit in the same amount of time,
EQUIPMENTS
The equipment I used to make my measurements was an ammeter and weighing scales to weigh the anode each time. I also used measuring cylinders to measure the volume of copper sulphate solution. The apparatus I used for accuracy was small measuring cylinders. An electronic scale ensured that there was no human error involved in weighing, and it measure to two decimal places, which is quite accurate. The stopwatch measured in milliseconds and the current was measured in milliamps to ensure accuracy.
These are the results that I obtained when following the procedure detailed in my plan. I did each result three times to give accuracy and make it easier to spot a general trend and the anomalous results.
New
Discussion
From the results obtained and the graphs, it is indicated that the mass of copper deposited at the cathode is directly proportional to the current. It is also indicated that the mass of copper is directly proportional to time. However, during the experiment it was realised that it was extremely difficult to measure the gain of copper on the cathode, since by cleaning the electrode with lab coat, and washing it under the tap, some of the copper deposited was knocked off. Nevertheless, this washing process was vital because the need the eliminate the copper sulphate crystals that may grow on the electrodes from time to time. The results would have been better if the experiment was left on for longer, say, 5 minutes, to compensate for the error. Also, it would have been more sensible if I had not left the electrodes in the Copper Sulphate solution over half-term. It was found that the mass of copper lost at the anode should be exactly the same as the mass of copper gained at the anode, since the concentration of Cu2+ ions in the electrolyte does not change. Every copper ion reduced at the cathode, one copper atom must be oxidized at the anode to keep the electrical charge balanced. This made it possible for the loss of copper at the anode to be used as a part of the results. The loss at anode can be more accurately measured since one cannot alter the mass of the anode significantly if it had been dried properly (since the copper does not drop off).
The concentration of electrolyte did not have a significant effect on the gain of copper at the cathode. However, when the concentration dropped to less than 0.1 M the conductivity of the solution was changed by such a huge amount that the PSU in use was no longer able to pump through the desired current. This alters the current, thus declaring the results invalid since current was expected to affect, and did affect the mass of copper deposited at cathode. The drop in the mass deposited in very low concentrations was due to the drop in current rather than the concentration itself. If a more powerful PSU was available (say, 100V max), and a more sensitive variable resistor was used, even at low concentrations, it should not have had an effect on the mass of copper deposited at the cathode.
