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Quantitative electrolysis concerns the amount of product obtained in an electrolysis, and the various calculations to find the mass of a product using the different variables.

Extracts from this document...

Introduction

PLANNING: Factors that effect electrolysis: Quantitative electrolysis: Quantitative electrolysis concerns the amount of product obtained in an electrolysis, and the various calculations to find the mass of a product using the different variables. Factors that affect the mass of product gained during electrolysis. 1. Current intensity 2. The time during which the current was passed through 3. Concentration of the solution 4. Potential difference (V) 5. Temperature of solution 6. Depth of immersion 7. Size of electrodes 8. Distance between the electrodes. Investigation During the course of my experiment I shall be investigating current. This means that all the other variables must be kept constant to ensure that the test is fair. So different currents will be passed: a) For the same amount of time. b) With the same Copper (II) Sulphate solution. c) With the same voltage throughout. d) The depth of immersion will be kept constant e) The distance between the electrodes and f) The volume of the CuSO4 shall be kept constant. g) So will the size of the electrodes. h) In theory the temperature should also be kept constant, but this is not possible because the solution will be heated up as the current is passed through; so it shall be monitored instead. Background information What is electrolysis? "It is a chemical decomposition produced by passing a current through a conducting liquid" Oxford Concise English, Tenth Edition. During electrolysis, Therefore if a current, which is the number of electrons flowing in a given time is increased, the number of ions discharged must also increase. Therefore doubling the number of electrons flowing in a given time, will double the number of ions discharged and so the number of ions discharged will be directly proportional to the current. The same applies for time. When ions discharge, products are obtained. Increasing the number of ions discharged will increase the mass of product formed. ...read more.

Middle

(N.B. It is important to keep looking at the ammeter during the course of the test because the ampage changes on its own.) Then once the weights of the electrodes have been recorded the test shall be done twice for each of the following ampages: - 0.7A - 1.0A - 1.3A - 1.6A - 1.9A I have chosen these values because I think they will give me good results for the following reasons: 1. I have already conducted this experiment and when the current is below 2.0A, it causes less heat. 2. Obviously if the current is 0.0A I shall not get a reading at all, so I have spaced out the different currents between 0.4 and 2.0A. 3. I have chosen to take six readings testing each one twice to get a good average and a good spread of results. 4. The time was spread over five minutes because as I have already carried out this experiment. I found that if the current was not passed through for long enough, the change in mass at the electrodes was barely noticeable. Diagram NB: It doesn't matter which way around the circuit is set up providing all the components are installed. It is important though to keep track of which electrode is the anode and which is the cathode. Safety Precautions ` As a safety precaution, the acitone was placed in a fume cupboard as it is highly flammable. Rubber gloves were available to any who wished to use them. Coats were hung up on the coat hangers and stool were placed under benches. The bags were left at the front of the classroom. Hypothesis and Predictions My hypothesises are: 1. Mass ? Current x Time 2. Mass lost at the anode = mass gained at the cathode 3. The higher the current, the higher the temperature rise. OBTAINING EVIDENCE: During the experiment Current intensity: Independent Variable How long the current was passed for: 5.0 minutes... ...read more.

Conclusion

I think that the graph is not what it should have been. There are several possible alternatives: a) From first looking at the graph it would seem obvious that all the points concerning the anode are correct except for A5 which is a little out of place. But I don't think so: b) After looking more carefully at the graph while keeping in mind the fact that "Mass lost at the anode = mass gained at the cathode" we can start to see which points are correct. It becomes apparent the A1, A2, A3 and A4, and so are C1, C2, C3, and C4 because they are exactly lined up. (C1 is a bit out of place it should be a bit lower, (i.e. 0.4, -0.030). I think that A3, A5, C3 and C5 Should be move closer to the x axis. The reason for them being to low shall be investigated later. During the experiment my attention was not always glued to the ammeter as it should have been because I was busy taking the readings for temperatures every 30 seconds. A few times I found that it had shot up and because it is hard (impossible) to tell for how long it had done so I was unable to compensate. I simply brought the reading back to what it was supposed to be. Potential sources of error The fact that the ammeter reading had to be adjusted at the start of each test meant that it was running at the wrong ampage for a few seconds. The electrodes may not have been perfectly sanded down and they wouldn't have gripped the copper so well. The electrodes shrunk making the experiment more inaccurate. Energy loss through heat which I couldn't do anything about. Suggested Amendments Find a better way of preparing the electrodes. Start with new electrodes when the old ones start to wear down. ( N.B. this would not make the experiment entirely accurate any way because their size would be changing although it might do some good. Keep constant control of the rheostat. 2 1 2 ...read more.

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