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Electrolysis Investigation

Extracts from this document...

Introduction

Planning I did some preliminary work to see which current values, and for how long to time. The results of this are in the tables below: Electrode-1A Mass before (g) Mass after (g) Mass change (g) Anode 1.38 1.30 -0.08 Cathode 1.35 1.65 +0.30This was done for 10 minutes. The mass lost at the anode should equal the mass gained at the cathode, which this doesn't, it has a percentage inaccuracy of 0.22� .30x100= 73% which is very inaccurate, This may be due to the current being too high, so the copper does not all transfer properly, but lies on the bottom of the beaker, therefore a lower current must be used, as in the table below: Electrode-0.1A Mass before (g) Mass after (g) Mass change (g) Anode 1.42 1.35 -0.07 Cathode 1.16 1.21 +0.05This was also one for ten minutes, and shows much more accurate results, as the percentage inaccuracy is only 0.02� 0.07x100=29%, which is still inaccurate, but is a lot better . This could be due to the current value being to low, so I will take a range of 5 results from 0.1Amp to 1Amp at 0.2Amp intervals. Each electrolysis will last 10 minutes, and each will be repeated twice so that a more accurate average can be taken. Variables * Temperature of the electrolyte * The concentration of the electrolyte * The separation of he electrodes * The size of the ...read more.

Middle

Also the temperature of the solution raised at higher currents by 5� C This would cause less ions to turn to copper at the anode, and make the current more, as there is less resistance. The size of the electrodes was also never exactly the same, as they were reused, so the amount of electrolysis differed from experiment to experiment. The separation of the electrodes was a small source of error, as they were not always exactly the same distance apart. The current which was controlled with the rheostat was not always the same, as the amount of copper decreases, so does the resistance, and so the current increases. Other errors could have been caused by the apparatus, such as the ammeter, which is quite old, and may not be perfectly calibrated, and the scales, which only show the mass to 2 decimal places. The rest are cut of with out rounding. Therefore this experiment could have been made more accurate by using lower current values, with the same size and separation of electrodes, controlling the current so that the temperature is constant, and the current more accurately controlled, and using a more accurate ammeter and a balance which rounds the other decimal places. My results showed many inaccuracies, shown by the accuracy bars on the graph (green for anode, and red for cathode). ...read more.

Conclusion

Also the concentration should remain constant. The amount of copper deposited on the cathode and lost from the anode depends on the number of electrons passing through the circuit, i.e. upon the charge passed through the cell. Now the charge passed, q (in Coulombs), is related to the current. I )in amps) and time, t (in seconds), by Faraday's law: q=ixt therefore I will predict that the mass change of the copper electrodes is directly proportional to the current and the time. Factors which will effect the mass change of the electrodes are: * Temperature * Concentration * Distance between electrodes * Size of electrodes These factors may alter the resistance of the circuit, so they must be kept constant to keep the experiment a fair test. Safety * Copper sulphate solution is poisonous, so must not be taken internally, or come in contact with the eyes. * Propane is highly flammable, so must be kept away from flame. Damages eyes and skin, so safety glasses must be worn. Method Copper sulphate solution is electrolysed using clean copper electrodes which are weighed before and after use. To make sure that copper are dry and clean after use, they are rinsed in distilled water, and then propane. During the electrolysis, the current is controlled and maintained at a constant value by a rheostat in the circuit. Five current values in the range 0-1.25A are used, each for a period of 10 minutes, repeating each value three times to improve the accuracy of the results ...read more.

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