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To find out how current affects the rate of electrolysis

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Introduction

Electrolysis experiment. Aim: To find out how current affects the rate of electrolysis. Pre-test: Pre-test Apparatus: 1. Power Pack 2. Stop watch 3. 3 wires 4. Amp meter 5. A piece of Card 6. stop watch 7. Top pan balance Pre-test Method: 1. Check to see if all the apparatus work by forming a small circuit with a bulb 2. Collect apparatus and set them out like the diagram below. Ensure that the positive wire leads to the anode and the negative leads to the cathode. 3. Measure out 50 ml of copper sulphate 4. In to a small class beaker 5. Weigh cathode on top pan balance 6. Slide anode and cathode in to piece of card and place in electrolyte 7. Turn on the power pack 8. Time until two minutes 9. Weigh cathode make sure you do not scrape off any copper 10. Repeat three times 11. Repeat for each current Pre-test Findings: By doing this pre-test I have learnt that: * The analog amp meter is very unreliable it * To be very accurate I need to use a multi meter * To be careful not to scrape of copper when measuring weight * Make sure that the anode and the cathode do not touch during the experiment ...read more.

Middle

C + O2 =CO2.. [www.bbc.co.uk/physics/electrolysis/sos.12] I predict that the rate of electrolysis would be higher as the current increases. This is because electrolysis involves ions taking electrons from the cathode and depositing electrons at the cathode. If you increase the current you increases the flow of electricity, thus you increase the overall charge of the electrodes so ions can pick up more electrons each second. I also predict that the results will be directly proportional because if you double the current you double the charge so you double the amount of copper deposited. Faraday's law: Q (the amount of charge in Coulombs) = I (the current in Amps) x t (time in seconds). 1 mole of electrons is called a Faraday and is equal to 96500 coulombs. As copper is in a pair ( Cu2+) the formula would be: 96500 x 2 =193000, 2 Faradays One Faraday will deposit 1/2 a mole of copper metal So 1 mole of copper metal would be deposited Q= I x T 0.2 x 120 = 24 0.4 x 120 = 48 0.6 x 120= 72 0.8 x 120 =96 1 x 120=120 Atomic weight =64g Charge = 193000 Current x time= 0.2 x 300 = 60 60 x atomic weight of cathode = 60 x 64 ...read more.

Conclusion

However my results do not match the results that I had predicted. Predicted Actual 0.02 0.03 0.04 0.08 0.06 0.09 0.08 0.1 0.1 0.2 However they do show the pattern that I predicted. I had also predicted that the results would turn out to be directly proportional however they aren't. Conclusion: My results are consistent but not very accurate. The percentage accuracy for 0.2 amps is 66%, 0.4 amps 53%, 0.6amps 63%, 0.8 amps 60% and 1 amps 52%.They outline my theory that "the higher the current the more copper is deposited on the cathode". I predicted that the results would turn out to be directly proportional however they aren't. However I do not have any anomile results. I think that the reason for this error is that the current kept on fluctuating. Even when you are using the variable resistor the current would not stay the same you had to keep on adjusting it during the experiment making the test unfair. Another error was that the two electrodes may have touched. This was because there was no effective way of keeping them is place. If I was to redo this experiment I would use a clamp stand to hold the electrodes in place. ?? ?? ?? ?? Priya Patel Candidate no.:1269 Centre no:13228 ...read more.

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Response to the question

The student has answered the question and drawn the correct conclusions from their data. The essay is very thorough and covers all variables which could affect the experiment. Some of the content included is above GCSE level and shows ...

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Response to the question

The student has answered the question and drawn the correct conclusions from their data. The essay is very thorough and covers all variables which could affect the experiment. Some of the content included is above GCSE level and shows extended research around the subject to get as accurate results as the student can, although some sections included are irrelevant to the essay.

Level of analysis

The student shows evidence of trying to control as many variables as possible to increase the validity and reliability of the experiment which included repetition of trails. Although there is no evidence of the student calculating averages from their results. The pre-test section was impressive as it showed that the student was considering all aspects of the experiment and modified their method, which was fairly well written. The student also includes a safety list which is very in depth. In the conclusion the whole essay is nicely summarised and does include the calculation of percentage accuracy to show the reliability of their results and allows them to be critical of them. However these calculations, although brilliant to include, should be placed elsewhere in the essay as the conclusion shouldn’t include any new evidence.
The research section is very impressive as the student has tried to control all the variables in the experiment, even those not covered at GCSE. However the paragraph about how concentration affects the rate of electrolysis seems confused and is contradicting itself. An increase in the concentration of the solution should increase the rate of electrolysis as there are more ions available to accept electrons. Also the student fails to realise that the charge carriers are the ions in the solution and there is no flow of electrons between the electrodes. Furthermore, the resistivity of water is irrelevant as water does not conduct electricity without the presence of aqueous ions. In the paragraph below this the student makes another mistake by assuming that the rate is fixed when all the variables are constant. This is untrue as the more copper which precipitates out of the solution, the less ions available and the less surface available on the electrode. There are a few issues with the student’s knowledge of the behaviour and charge of ions, as the student states that the Cu2+ ion needs to lose electrons at the negative cathode where in fact it would gain them. This shows that the student doesn’t really understand the fundamentals behind the electrolysis process which is further emphasised with the final paragraph where they explain their prediction. Throughout the essay there is also an incorrect use of half equations. The section where the student tries to calculate something using faraday’s law is incorrect and completely irrelevant to the question.

Quality of writing

Although some concepts are misunderstood, the technical terms are used correctly most of the time. There are very few spelling and grammatical errors.


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Reviewed by zonexi 08/02/2012

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