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The Electrolysis Of Copper (ii) Sulphate Solution Using Copper Electrodes

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20l COURSEWORK2000/2001 SAM MOED CHEMISTRY: THE ELECTROLYSIS OF COPPER (II) SULPHATE SOLUTION USING COPPER ELECTRODES 1.PLANNING: A. POSSIBLE FACTORS WHICH COULD AFFECT THE MASS OF COPPER DEPOSITED OR LOST: There are in fact many factors that could affect the mass of Copper lost or deposited on the electrodes: * The current intensity or strength * Time (for how long the current is passed) * Concentration of the CuSO4 solution * Size and surface area of the plates * Depth of immersion of plates * Temperature of solution * Distance between plates * Voltage The factor that is to be investigated in this experiment is one of these: current intensity and so all the others will have to be kept constant to be sure that any correlation between the increase in current and the increase in mass is due to the former only. B. Electrolysis in general Electrolysis is the chemical decomposition of an ionic compound by the passing through it of an electric current. The ionic compound must either be in the molten state or in aqueous solution; this is because the ions need to be mobile since it is the movement of ions that constitutes the conductivity. Electrodes are rods or in this case plates of a conducting material by which current enters or leaves the ionic compound called the electrolyte. The negative electrode is called the cathode by which the current enters the electrolyte and the positive electrode is called the anode by which the current leaves the electrolyte. The ions become attracted to their oppositely charged electrodes; so the anions go the anode and the Cations to the Cathode. When these ions reach the electrodes lose their charge by the processes of oxidation at the anode and reduction at the cathode, the term for this is discharging. When the anode is made of an unreactive metal, such as in this experiment Copper, no anion actually discharges at it. ...read more.


Although this amount was very small it seems as if it has affect the results significantly. At the anode Copper is lost so little can "fall off" during the cleaning and drying processes (only that which was half removed from the anode at removal of it from the Copper(II) Sulphate) but the reason that the mass of Copper lost is higher than that gained at the cathode is because there may have been some water left on the anode when massing it. But then one could say the same to be true for the cathode and it most likely was true that water increased the mass but at the cathode Copper is deposited, sometimes very loosely. This means that during the processes of cleaning by distilled water and drying in acetone some is likely to simply fall off reducing or over compensating for this effect of excess water which hasn't evaporated from the electrode when massed. So the mass deposited at the cathode is increased by excess water but decreased by loss of Copper. When examining the graph of the mean values extremely closely I saw that none of the mean results were on the best line of fit. The results at higher currents seemed to be above the best line of fit and the results at the lower currents below it. This means that the increase in mass is greater at higher currents in proportion to what would be expected. It is also true that the temperature increase was greater in the higher currents. Could there be any correlation between the two? This correlation can be explained by collision theory. Larger currents cause the temperature of the electrolyte to rise more. So at higher currents the temperature increases more as shown by the recorded temperatures. Increasing the temperature of the electrolyte increases the proportion of activated ions attaining Ea (activation energy). This means that there will be an increase in the frequency of collisions of the activated ions with the electrodes and so the mass of product would be expected to increase. ...read more.


Sulphate. But is the same true in other electrolyses. Further work could be carried out to investigate this. The electrolysis using different electrolytes to prove that the relationship found in this experiment when using reactive electrodes is true generally for all electrolyses. ELECTROLYSIS OF Cu(NO3)2 solution using Copper electrodes: The ionic equations would be the same for this as for those in the main experiment: At the anode no ions would discharge since it is easier for Copper electrodes to lose electrons which become Copper ions which pass into the solution: Cu(s) - 2electrons --> Cu2+ (aq) AtthecathodeCu2+ discharges in preference to H+ since it is lower in the reactivity series: Cu2+ + 2electrons --> Cu This electrolysis should also have the overall effect of transferring Copper from the anode to the cathode because for every Copper ion produced in the solution from the anode one Copper ion is discharged at the cathode; so mass lost at anode should equal mass gained at cathode without changing the concentration of the Cu(NO3)2. This experiment could be carried out and should give exactly the same results. ELECTROPLATING A METAL WITH SILVER: The anode would be made of silver and the cathode would be the metal that we wanted to be plated. The electrolyte would have to be a solution of a soluble salt of silver such as Silver Nitrate (AgNO3). Since the anode is made of silver which is an unreactive metal no ions actually discharge at it since it is easier for the anode to lose electrons which become Silver ions in the solution: Ag(s) - electron --> Ag+ At the cathode the Silver ions discharge in preference since they are lower than H+ ions: Ag+ (aq) + electron --> Ag(s) It would be expected that the mass of Silver lost at the anode equals that gained at the cathode since one ion is passed into the solution at the anode and one is discharged at the cathode so gain in mass at the cathode should equal loss in mass from the anode without changing the concentration of the electrolyte solution. ...read more.

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