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Faraday's Constant

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Introduction

Determining Faraday's Constant by Electrolysis of Copper (II) Sulphate Aim: To find the value of the Faraday constant - the electric charge carried by one mole of electrons - from the electrolysis of aqueous copper(II) sulfate solution, using weighed copper electrodes. Faraday's Law: The amount of substance consumed or produced at one of the electrodes in an electrolytic cell is directly proportional to the amount of electricity that passes through the cell. By definition, one coulomb (C) of charge is transferred when a one-ampere (amp) current flows for one second (s): Introduction: 1) Excess aqueous 1.0M copper (II) sulphate solution will be electrolysed with copper electrodes. 2) Oxidation will occur at the anode, and reduction cathode: Faraday's Constant can be determined through electrolysis by using the increase in mass of the cathode and the charge in the circuit to calculate the total number of electrons that contributed towards the reduction of the copper ions. One mole of these electrons carries one Faraday of charge. The following formula can be used to work out Faraday's constant: F = Faraday's Constant I = current (amps) t = time (seconds) M = molar mass of copper (63.55) ...read more.

Middle

Time Change in Mass of Cathode seconds grams �1.00 s �0.002g 0 0.000 300 0.050 600 0.087 900 0.117 1200 0.158 1500 0.190 1800 0.230 2100 0.270 2400 0.290 2700 0.326 Uncertainties: Instrument Error of Instrument Error Calculation Error (%) Electronic Balance �0.001 grams (0.002/0.191) x 100 1.05 Voltmeter �0.01 Volts (0.05/0.6) x 100 8.33 Stop clock (human error) �2.0 seconds (2.0/300) x 100 0.67 Ammeter �0.01 Amps (0.01/0.35) x 100 2.86 Total Uncertainties affecting Results = 4.58% (the voltmeter error does not affect result, as it is not a component in the equation being used) Gradient: The gradient can be calculated from the graph. I am using the points at 0 and 1500 seconds because they are the easiest to identify the time for. Gradient = (change in mass of cathode) / time = 0.190 - 0 / 1500 - 0 = 0.190 / 1500 = 1.27 x 10-4 Faraday's Constant: I am using, again, the results obtained for 1500 seconds. Faraday's constant = (I . t . M) / (n . w) = (0.35 . 1500 . 63.55) / (2 . 0.190) = 87,799.34 C mol-1 � 4.58% Conclusion: From my data and calculations, I determined Faraday's Constant to be 87,799.34 C mol-1 � 4.58%. ...read more.

Conclusion

* Clean the electrodes with ethanol and tissue paper to get rid of grease prints. Inaccuracy when measuring the mass of the cathode after electrolysis The process of washing the cathode with distilled water to dispose of the copper sulphate solution that remained may also have involved the disposal of copper that was not fully attached to the cathode (caused by impurities). This would decrease the value for the increase in mass of the cathode greatly. * More care should be taken when handling the electrodes. * Tweezers could be used instead of fingers to minimise contact. * When washing the cathode, the distilled water could be squirted above the newly-formed layer of copper, and allowed to drip down into a beaker. This would be a gentler approach that would minimise loss of mass. When drying the cathode with tissue paper after washing, it was not fully dry, falsely increasing its mass when it was measured. * A hair-dryer could be used to dry the cathode. This would ensure that it is fully dry and it would also reduce the mass of copper lost due to rough handling. Problem/Error Source Prevention Method Impure CuSO4 used Filter solution before initiating investigation Irregular masses recorded Experiment should be repeated several times & an average taken 1 http://en.wikipedia.org/wiki/Faraday_constant - 9.24pm, 06/03/09 ?? ?? ?? ?? IB Chemistry Standard Brionna Wilson 12/11/2009 ...read more.

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