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Investigating one of the factors that affects the mass of copper deposited when copper sulphate solution is electrolysed using copper electrodes

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Introduction

Amanda Gaulter October 2001 Investigating one of the factors that affects the mass of copper deposited when copper sulphate solution is electrolysed using copper electrodes Factors: current time temperature molarity/concentration of solution volume of solution size of electrodes I have decided to investigate how current affects the mass of copper deposited as it is an easy quantity to measure and record, whilst at the same time keeping the other variables constant. Variables: Independent: current Dependant: mass of copper deposited on electrodes Constant: time that each solution is electrolysed for temperature volume of copper sulphate size of beaker size of electrodes molarity of solution To make it a fair test: � keep the temperature the same throughout the experiment as this may alter the final results � keep the concentration of copper sulphate the same throughout. Too low a concentration wouldn't affect the electrolysis as the current wouldn't flow properly so that not much would happen, and too high a concentration would be dangerous. I am going to use a concentration of 0.5M. � keep the volume of CuSO4 the same as a bigger volume would mean more copper ions which would therefore affect the results. � keep the size of the beaker the same as this would vary the amount of the electrode to be covered in the solution which would affect the results. � keep the size of the electrodes as similar as possible as if one electrode was bigger than the other there would be the same mass of copper deposited only there would be a difference in the thickness of the layers of copper; a thicker layer would flake off more easily. Pilot Study Results: current (A) time (mins) Mass at anode (g) before after change mass at cathode (g) before after change 0.1 0.2 5 10 1.11 1.10 -0.01 1.14 0.96 -0.18 1.17 1.18 0.01 1.03 1.17 0.14 These results show that the anode loses mass whilst electrolysing the solution and the cathode gains mass. ...read more.

Middle

It is a good idea to swap the anode and cathode round each time as this will mean that there is not a huge build up of copper on one of the electrodes. Safety Copper sulphate is not harmful unless swallowed, however at 0.5M it can be irritant to the eyes and skin so be sure to wear safety glasses and an apron and wash any spillages immediately. Propanone is also highly flammable so do not let it get near to any hot objects such as the hair drier. Prediction Using my background knowledge I can determine that there will be an increase of mass at the cathode due to the copper being deposited, and there will be a decrease in mass at the anode because it is losing its copper atoms to the cathode. This agrees with the results from my pilot study also. I also predict that the current will be directly proportional to copper deposited because in my pilot study when the current increased the change in mass also increased. Both of Faraday's laws support this prediction. It is also possible to predict that there will be the same mass lost at the anode as the mass gained at the cathode. This is because, using my background knowledge I found that all the copper which is released from the anode floats into the solution and over to the cathode, which it is attracted to. The half equations at both electrodes also support the prediction that the mass lost is the same as the mass gained because the product at the anode is the same as the ingredients at the cathode. For example the anode produces Cu and 2e from Cu and the cathode uses Cu and 2e to make Cu. Using Faraday's laws we can also predict the mass of copper which will be deposited at the cathode for the different currents. ...read more.

Conclusion

The reason for the cathode being less precise than the anode is that whilst washing the cathode after it had been in the solution some of the copper may have fallen off which would have altered the mass. As for the anode there is nothing to be washed away by only the water. This is a very hard factor to overcome as it is essential to wash the electrodes in order to remove the copper sulphate, a lot more care could be taken though, perhaps running the water over the electrode much more mildly. Despite the anomalous ones the results did follow the basic pattern that I had predicted. However, on very few of the currents did the mass gained at the cathode prove to be equal to the mass lost at the anode. This may have been because the solution was not left to electrolyse for long enough. If the experiment were to be repeated the solutions should be left for longer, perhaps 20 minutes, however, it was impossible to leave them for this long this time because our lessons were not long enough. Although my results do support my predictions made they are not accurate enough to support a firm conclusion. The experiment would have to be done using more technical equipment, perhaps in a proper laboratory where the temperature is always constant, in order to produce reliable findings. It would also have been nice to do some more repeats in order to make the results more reliable, however, this was once again impossible due to the time factor. I found this investigation very interesting yet I would have liked to taken it to further levels of investigation. Perhaps investigating how different factors affect the experiment or maybe seeing how electrolysing copper sulphate with copper electrodes could be used in business such as the copper plating industry and what current would have to be used there, and so on. ...read more.

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