The Electrolysis Of Copper Sulphate Solution Using — страница 3

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variation, therefore The evidence is strong enough to say that the mass lost at the cathode equals the mass gained at the anode, and that q µ i, as the greatest error was only 0.01g, or 12.5%. If This experiment was to be done more accurately, I would have to use more accurate apparatus, such as a newer ammeter, a balance with more digits, a more accurate way of controlling the current, maybe with a computer, and likewise with the temperature. I also could have kept the size and separation of the electrodes the same. I also could have made sure that the crocodile clips were completely out of the electrolyte. Also I could have taken a much wider range of readings, from 0.01A to 10A at smaller intervals, and I could have timed for different times, and I could have investigated the

other variables, such as the temperature of the electrolyte, the concentration of the electrolyte, the separation of he electrodes, and the size of the electrodes. The Electrolysis Of Copper Sulphate Solution Using Copper Electrodes Planning Electrolysis is the decomposition of a substance by the passage of an electrical current. I a typical set up, two electrodes (conducting rods immersed in an electrolyte). Voltage is applied to the electrodes with a power pack. The electrolyte must be an ionic compound that is molten or in aqueous solution, in order for it to conduct electricity. Electric current is caused by the movement of charged particles. In a normal circuit, theses charged particles are electrons, which are effectively pumped through the metal wire by the power pack. In

the electrolyte these charged particles are mobile ions. At the electrodes electrons are given to the cat ions cathode (-), and are released at the anode (+), so the current flows. Therefore species are gaining electrons at the cathode, and so being oxidised, whilst electrons are taken away at the cathode (reduction). At the cathode there is preferential discharge of ions according to the position of the element in the reactivity series. When aqueous copper salts are electrolysed, the cat ions present is he solution are hydrogen ions, which come from the water, and copper ions, so copper is formed at the cathode. Cu”(aq) + 2e- > Cu(s) At the anode the reaction occurring depends on the nature of the electrode. If the electrode is inert, then normally it is found that the ions

are discharged in the order halide then hydroxide before sulphate. However, this order may change depending on concentration. An example of this is platinum electrodes. Those made of carbon behave similarly, but a carbon anode will react with oxygen as it is released forming oxides of carbon, like in an aluminum smelter. Copper electrodes are not inert, instead of incoming anions being discharged, the copper goes into solution: Cu(s) > Cu” (aq) + 2e- The reaction occurring at the anode during the electrolysis of a copper salt is the reverse of the cathode reaction. So for every two electrons passing through the external circuit, one copper ion should be formed at the anode and one copper ion discharged at the cathode. So overall copper is being transferred from anode to

cathode, as is exploited in electroplating and in purifying copper. 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. 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