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I have chosen to do electrolysis of Copper Sulphate with copper electrodes rather than the alternatives, sulphuric acid with graphite electrodes, because then I would have to collect gas (which is more difficult) rather than a solid.

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Introduction

Chemistry Coursework - Plan I have chosen to do electrolysis of Copper Sulphate with copper electrodes rather than the alternatives, sulphuric acid with graphite electrodes, because then I would have to collect gas (which is more difficult) rather than a solid. Initial Aim To find out how a change in current that passes through a copper sulphate solution changes the amount of product at the cathode. This is what I intially investigated in my preliminary experiment. I found out that this was was more problematic than verying time would be because when the current got higher the temperature within the circuit changed and as a result the current was not constant. I decided that time would be much easier to vary. New Aim To find out how the amount of time for which a current passes through a copper sulphate solution changes the amount of product at the cathode. Hypothesis I think that the increase in time for which current passes through the copper sulphate solution will be directly proportional to the amount of copper produced at the cathode and directly proportional to the amount of copper reduced from the anode. This follows exactly with Faraday's first law or electricity and chemistry: 'The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed'. I also predict that a small amount of sludge will be deposited at the bottom of the beaker. ...read more.

Middle

Therefore by changing the amount of time the current is applied for (and thus the number of coulombs of electricity passed), I should be able to vary the amount of copper deposited proportionately. Also, it means I am able to make accurate predictions before the experiment is actually carried out and use them to test how accurate my results are. Predictions The following formulae will be used to predict my results: Quantity of charge (coulombs) = current (amps) x time (seconds) Number of moles of electrons = charge/96500 Cu2+ + 2e(-) --> Cu (for one mole of copper, 2 moles of electrons are needed) Mass = moles x RFM (to convert to mass of solid) 0 MINS No solid will be formed 5MINS 0.54 x 300 = 162 162/96500 = 0.00167 0.00167/2 = 0.000835 0.000835 x 64 = 0.05344 0.053g 10 MINS 0.54 x 600 = 324 324/96500 = 0.00335 0.00335/2 = 0.00167 0.00167 x 64 = 0.10688 0.107g 15 MINS 0.54 x 900 = 486 486/96500 = 0.00503 0.00503/2 = 0.002515 0.002515 x 64 = 0.16096 0.161g 20 MINS 0.54 x 1200 = 648 648/96500 = 0.00671 0.00671/2 = 0.003355 0.003355 x 64 = 0.21472 0.215g 25 MINS 0.54 x 1500 = 810 810/96500 = 0.00839 0.00839/2 = 0.004195 0.004195 x 64 = 0.26848 0.267g Chemistry Coursework - Obtaining No alterations to the proposed method were needed because the obtaining aspect of the experiment was very successful. I think the the results obtained are very accurate when the equipment used is put into consideration. ...read more.

Conclusion

I could investigate the other variables, such as the temperature of the electrolyte, the concentration of the electrolight, the distance between the electrodes and the size of the electrodes. However investigating these would not allow me to make predictions or refer to Faraday's laws. I have used my method successfully to perform an accurate experiment and obtain accurate results form which I have proven my hypothesis correct and acquired only one abnormal result. This abnormality was almost certainly caused by one or more of the following: * Washing off some of the copper when cleaning the elctrode with propanone. * The copper not sticking to the electrode and fallen into the solution when removing the electrode. * Apparatus problems; there may have been something adding weight on the scales thus not giving the true weight of the electrode. * Human error; while leaving the experiment someone may have stopped the stop watch and then starting it again giving us a longer time for electrolysis or someone may have done something to the circuit by mistake,the probability of this is very small though. If I wanted to prove Faraday's 1st and 2nd laws and my hypothesis even further I would do the electrolysis of sulphuric acid using graphite electrodes. This woul produce hydrogen gas at the cathode and oxygen gas at the anode. Because they are gases I would have to measure the volume rather than the gas. I woiuld do this by collecting the gas in a measuring cylinder filled with water. Diagram ...read more.

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