Mass At The Electrodes Essay, Research Paper
To find out how varying the current affects the loss in mass of the anode and the gain in mass in the cathode Introduction- Purifying Metals It has been found that when a copper solution is electrolysed using copper electrodes, the anode looses mass and the cathode gains mass. This is an investigation into howvarying the current affects the change in mass of the electrodes during electrolysis. PREVIOUS KNOWLEDGE. From previous knowledge and preliminary experiments, I already know that- – The anode loses mass and the cathode gains mass. This is because : copper atoms at the anode lose electrons and turn into copper ions which are dissolved into the solution. Copper ions in the solution gain electrons ath the cathode and are turned into atoms which stay at the cathode and the cathode gains mass. Since the current thought the electrodes are absolutely equal, the change in mass of each electrode should be absolutely identical (in theory). – Factors affecting this change are- – The surface area of the electrodes (because more of the electrode is in contact). – The concentration and volume of the electrolyte. – The temperature of the whole apparatus. – The distance between the electrodes (because this can affect the current through the whole apparatus). I will keep all of these constant for all the experiments to make the test fair. – I have knowledge from the textbook- “GCSE Chemistry” by Ingram and Gallhager. It gives explanations of what happens during the experiment and the equations for the reactions- At the anode-Cu + Cu2+ 2e- At the cathodeCu2+ + 2e-Cu. METHOD To make the test fair, I will only vary one variable at a time. I will perform 5 experiments, each lasting eight minutes. I will perform them from 1 to 5 amps, (in 1 amp intervals). I will repeat each experiment twice (more if necessary) – to have confidence in the results and to show up any anomalous results. I will measure- – The mass of the electrodes before and after each electrolysis. – And therefore the change in mass of the electrodes. Before starting the series of experiments, prepare the electrodes by sanding them down with sandpaper to clean them then wash them as described below. 1. Set up appartaus and circuit as shown in circuit diagram below. 2. Turn on the power pack and start the stoopwatch simultaneously. 3. Immediately adjust the rheostat until the ampmeter reads the desired current. 4. Turn off the power pack after eight minutes. 5. Wash the electrodes as described below. 6. Weigh the electrodes ( to 2 d.p.) Record the change in mass. I will use Copper (II) sulphate as an electrolyte. Before and after each electrolysis (and before weighing the electrodes), I will clean the electrodes, first using water, then using etanol and finally with propanol. To vary the current, I will use an rheostat. I will wear safety glasses whilst carring out the experiment. I will weigh the electrodes using a top pan balance. I will time the test using a stopwatch PREDICTION. I predict that the increased ammount of coulombs per second (amps) passing along the wire and through the electrolyte will be directly proportionate to the change in mass of the electrodes. This is because more ions are turning into atoms (more e- ’s are in put in to the equation.). Analysis I have drawn a line graph of my results using a ‘best fit line’. I used the averages of my results to draw this. I immediately observed from the graph that the relationship between the current and the loss of mass of the anode was directly proportional. The loss in mass increases with the amps. The results follow this trend because the increased amps means that more electrons are passing around the circuit and therefore more ions are changing into atoms and v.v. It is directly proportional because the mathematical relationship between the axes follows the formula- (amps x 480) / 96500 x 63.5 = change in mass in grams. 2 My results thrill support my prediction and the two match very well. All my results came within 0.3g of my predicted results. This is very good and is probably the result of the variables being kept more or less constant. I identified one anomalous result of the whole set I obtained. It is the very first result I got and I have omitted it while drawing the graph. Evaluation I think that my experiments worked well overall. In my opinion, my results were very reliable and sufficient enough to validate my analysis. I think I had enough values of the current for a sufficient range. My results were very good because the averages of my results were all within 0.3 of a gram of the theoretical results that I worked out for my planning. This also applies to how well my experiments supported my prediction, and I am pleased to say they did this very well. I also think that the way I carried out my experiments was a very efficient was one of the best ways possible (excluding extreme measures for accuracy not suitable for an SC-1). If I were to perform these experiments again, I could improve the results by repeating the tests more and by keeping all variables religiously constant (except the current of course). This would include the temperature of the apparatus and the distance between the electrodes. A huge improvement of the results could be made by using a better (newer) rheostat. During the experiments, I identified a wide fluctuation in the current while the electrolysis was being carried out. Although the temperature was roughly constant at the start of each electrolysis, when a current is passed through the apparatus, heat is generated and this may affect the rate of the changing of the mass of the electrodes because the ions have more energy. If I was to further the investigation, I could go into 0.5 amp intervals instead of 1amp and I could investigate into higher voltages (and see if there is a maximum current where there is a limit to the rate of mass change). I could also investigate how the concentration of the electrolyte changes the change in mass of the electrodes. The only glitch in my results was the very first electrolysis I performed- I got 0.40 g of change in mass in the anode when the theoretical result was 0.16. This was quickly ironed out when I repeated that particular experiment twice more so it was obvious that it was a one off and I omitted it when I drew my graph. This anomalous result was probably the cause of a lapse of concentration on my part, in which a slip in the electrodes which resulted in the current increasing and therefore more ions changing into electrons and v.v.