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To determine the value of Faraday constant (quantity of electricity per mole) by using electrolysis of Copper.

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Introduction

1) Title: QN1 A Quantitative study of electrolysis 2) Aim/Objective: To determine the value of Faraday constant (quantity of electricity per mole) by using electrolysis of Copper. 3) Results: Before electrolysis: Weight of cathode = 2.164 g Weight of anode = 2.502 g After electrolysis: Weight of cathode = 2.237 g Weight of anode = 2.435 g Time of electrolysis = 20 minutes = 1200 seconds Ammeter reading = 0.19A 4) Calculation/interpretation: The equation of the electrolysis reaction at the cathode: Cu2+(aq.) + 2e- Cu(s.) Gain in weight of cathode = 2.237g - 2.164g = 0.073 g Loss in weight of anode = 2.520 - 2.435g = 0.085 g No. of moles of loss in cupper anode = 0.085 / 63.5 = 0.00134 mol Quantity of electricity required = 0.00134 mol * 2 = 0.00268 mol Quantity of electricity supplied = 1200 * 0.19 = 228C Faraday Constant = quantity of electricity / no.

Middle

ions might not be very soluble at that moment. After that, the copper electrodes were rinsed with propanone and heated under a Bunsen flame. Since propanone can remove grease or oil, this treatment could leash off the sebum which we have left on the electrodes when transferring them. Of course, when rinsing them by propanone, a pairs of forceps was used. After rinsing, the copper electrodes were warmed high on a Bunsen flame to evaporate propanone more quickly. However, they should be placed high above the Bunsen flame because propanone is flammable and a Bunsen flame can oxidize the copper plate, forming copper (II) oxide on their surface, which will finally lead to a heavier weight and smaller Faraday Constant. The value of the Faraday Constant was calculated to be smaller than the literature one (96500 Cmol-1) due to a number of errors. For instance, it was inevitable that the electricity supply was not exactly 0.19A in the time interval 20 minutes.

Conclusion

This can explain why the gain in weight of the cathode and the loss in weight in the anode were not the same. So if the gain in weight of the cathode was taken into consideration, the calculated value of the Faraday Constant would be larger. After finding out the value of the Faraday Constant, the thickness of the metal plating can also be calculated. According to the formulae Density = Mass / Volume and Volume = Thickness * Surface Area, since the density of copper (8920kgm3), the surface area, the mass of copper formed are all known, the thickness of the plating can be known. It is actually calculated by: Mass / Density / Surface area. Such electrolysis process performed in this experiment is useful in electro-plating. It can plate a certain object by placing it on the cathode, and the metal to be plated onto the object will be put on the anode. 6) Conclusion: The Faraday constant was calculated to be 161000 C mol-1. ?? ?? ?? ?? Yu Wing Yee 6A(30) - 1 -

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