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Electrolysis using copper electrodes

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Chemistry Lab Report Electrolysis of copper (II) sulphate solution Introduction: Electrolysis is the electrolytic dissociation and decomposition of a chosen electrolyte carried out by the passage of electricity through its molten or aqueous form. It involves the presence of two electrodes with different charges that attract the cations and anions respectively from the electrolyte. It is a process used to extract metals such as aluminium or purify copper etc. In this experiment we shall observe the electrolysis of Copper (II) Sulphate solution. Ions present : Cu�+ , H+, OH- , SO4�- Equation of products at cathode: Cu�+ + 2e Cu (Reduction) Equation of products formed at anode: 4 OH- O2 + 2H2O + 4e (Oxidation) Net Equation = 2 Cu�+ + 4 OH- Cu + O2 + 2H2O Aim: To measure the change in mass of the electrodes, anode and cathode, during electrolysis and so attempt to work out what must have happened. Apparatus: ==> A Power Supply ==> Copper (II) sulphate solution ==> Two carbon (inert) electrodes ==> An ammeter ==> A Rheostat ==> Sand Paper, de-ionised water, ethanol, propane ==> Wires with alligator clips to make connections ==> A digital balance ==> Stopwatch Method: 1. ...read more.


0.0002331606218 ? 2(15.99) = 0.007456476684g ( the mass of oxygen that should be liberated at the anode) Because C + O2 CO2 Therefore: 0.0002331606218 moles of oxygen = 0.0002331606218 moles of carbon used from electrode ? 0.0002331606218 ? 12 = 0.002797927462g ( the mass of carbon that should be used up at the anode) * Total mass lost from the anode should be 0.002797927462g * Total mass gained at the cathode should be 0.0296113989g Thus, total change in mass of electrodes should be: + 0.0296113989 - 0.00279792746 = + 0.02681347144g RESULT for Experiment 1: Quite ironically, the electrodes actually lost 0.03g. Even though the electrodes should have gained about 0.027g, they lost 0.03g. It was then noticed that some of the carbon from the electrodes had settled at the bottom of the beaker containing aqueous copper sulphate. The reason identified was inevitable. This setting of particles of carbon at the bottom of the beaker cannot be prevented. Experiment 2: Theoretical calculations Current = 2.5 Amps Time = 60 ? 15 = 900 seconds Because: Cu�+ + 2e Cu Therefore: 2 ? 96500 = 1 (moles of copper) ? 96500 = 0.5 900 ? 2.5 = ? ...read more.


= 212% 0.268 Experiment 2 2250 (2.5 ? 900) 64.27 64.61 + 0.670 +0.34 0.67 - 0.34 = 49.3% 0.67 Conclusion: Overall, this experiment was not very successful. Some results were obtained; however, none of the reading showed exact similarity to the theoretical mass change and thus produced a high percentage of error. It has, however, been noticed that by increasing the current and getting higher theoretical masses to compare with; a better result can be obtained. Evaluation: Some of the factors like settling of carbon at the bottom of the beaker were not under our control, however, other factors such as cleaning the electrodes carefully, weighing accurately etc could have been done better to produce more accurate results: ==> A more accurate digital balance, giving weights up to 4d.p, should have been used to identify the slightest change in mass. ==> The mass of the aqueous copper sulphate before and after the experiment could have been measure to see how much the carbon particles from the electrodes add to the weight of the solution after the mass of oxygen and copper liberated/deposited is subtracted. ==> More variations in current could have been used. ==> The effect of varying time could have also been seen ?? ?? ?? ?? Ira Gupta X - B ...read more.

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