The Electrolysis Of Copper Sulphate Solution Using — страница 2

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external circuit, one copper ion should be formed at the anode and one copper ion discharged at the cathode. One would expect the mass loss of the anode to equal the mass gain at the cathode, as explained earlier, for every two electrons, at the cathode one copper ion is discharged, whilst at the anode, one copper ion is formed This can be explained with the ionic theory, which basically states that the electrons flow away from the cathode, to the anode where the Cu2+ ions take 2 electrons from the negative electrode and become Cu atoms, thus mass loss at cathode = mass gain at the anode. This does support the prediction, as the two lines are at most only 0.018 grams apart, or 10% inaccurate, using the formula difference ¸ theoretical X 100. The other pattern is that the mass

change µ current, This is shown by the construction lines on the graph, which show that when the current is 0.2A, the mass lost at the anode is 0.035g, and the mass gained at the cathode is 0.04g, and when the current doubles to 0.4A, the mass change also doubles as the mass lost at the anode is 0.07g, and the mass gained at the cathode is 0.078g. This is because, as explained in the planning section, 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 As t is a constant at 10min, then q µ i. My results support this as the

greatest error was only 0.01g, or 12.5%. Evaluation There were several sources of error in this experiment as none of the results were 100% accurate. These error could have been caused by the fact that not all the ions “stick” to the anode, and so end up at the bottom of the solution. This happens most at higher levels of current, and causes the mass lost at the cathode to be greater than the mass gained at the anode. Also the temperature of the solution raised at higher currents by 5º 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). Which show the highest value and the lowest, with the average in the middle. This shows that for the 0.20A reading, the anode difference is 0.01A, and the cathode difference is 0.02A, both very small variations. For the 0.40A reading, the anode difference is 0.07A, a much greater difference, and the cathode variation was smaller, at 0.02A. The 0.60A anode difference was only 0.01A, and the cathode was the same. The 0.80A anode and cathode variation were also 0.01A. The final reading, 1.00A anode difference was 0.03, and the cathode variation was 0A. This nearly fits the pattern of the greatest variation being at the top,

except for the 1.00A cathode variation of 0A. This increasing variation is caused primarily by two things, firstly the temperature of the solution increases more at higher current values, so the ions travel faster, and so do not stay on to the anode as well, and secondly the increased current itself has the effect of making less ions sticking to the cathode. The anomalous result for in the 0.40A value for the anode was probably caused by one or both of the crocodile clips touching the solution, so less electrons flow through the copper, and so less are transferred to the cathode. The range of my results were from 0.20A to 1.00A, with an average discrepancy of 0.02A from the average reading, which although there was one large anomalous result is quite small, is quite a small