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An Investigation of the Variation of Electrode Potential with Electrolyte Concentration.

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Introduction

William Murdoch A LEVEL PRACTICAL ASSESSMENT An Investigation of the Variation of Electrode Potential with Electrolyte Concentration Aim: The aim of the experiment is to investigate the variation in the potential of a silver electrode as the electrolyte concentration is varied. Apparatus: 1.0 molar CuSO4(aq) Copper metal Electrode 0.1 molar AgNO3(aq) Silver metal Electrode 100ml volumetric flask (x4) Labels Bungs (x4) Distilled water Funnel Dropper Pipette and filler 100ml Pyrex beakers (x10) Glass paper Filter paper Saturated KNO3(aq) High resistance voltmeter Crocodile clips Wire Safety goggles Method: 10cm� of 0.1 molar AgNO3(aq) was pipetted into a 100cm� volumetric flask. Distilled water was added to the flask to make it up to just below the 100cm� mark. With a bung in the top, the solution was shaken to make it homogenous. A few more drops of water were added to the flask so that the meniscus was level with the 100cm� mark. The flask was labelled as having a 0.01 molar concentration. From the 0.01 molar flask, 10cm� of the solution was pipetted into an empty volumetric flask. ...read more.

Middle

F = faraday constant R = gas constant T = temperature The Nurst equation is used because it is in the form of the equation: y = mx + c Where: Y (axis) = EAg M (gradient constant) = RT/ZF X (axis) = Ln [Ag+] C (intercept) = EAg When plotted on the graph, the results give a straight line according to this equation. The Ln[Ag+] is proportional to the electrode potential of the silver electrode. This is because in the Nurst equation, RT/ZF and EAg are constant. Therefore, EAg must be proportional to EAg standard. The intercept, (c) is the EAg according to the Nurst equation. It should therefore intercept at 0.8 volts. However, the intercept is at 0.845 volts. This is an inaccuracy of 5.625% (0.045/0.8 x 100). The inaccuracies responsible are discussed in the section following. It is worth noting here that the intercept is higher than expected because the EAg readings are too high. A possible explanation for this is that the concentration of the 0.1 molar AgNO3(aq) ...read more.

Conclusion

A possible improvement would be to use a standard hydrogen half-cell or a Calomel half-cell instead of the copper half-cell, (ensuring that the conditions are standard). This would avoid using the equation: Ecell = Erhs - Elhs Another advantage is that the platinum electrode is inert. It is far less likely to be chemically corrupted than the copper electrode. The inaccuracy caused by having solutions, which are too diluted, could be overcome simply by using increasing concentrations of AgNO3(aq), rather than decreasing amounts . For example, the concentration could start at 1.1M and increase from there. The graph could then be extrapolated back to intercept the y-axis. This was not possible in this experiment. However, a control could have been used to ensure that the conductivity of water had not been reached. To do this, a silver half-cell could be set up, but using pure water as the electrolyte. When connected to the copper half-cell, the Ecell reading of this could be compared to those of the lower concentrations of AgNO3(aq), to see if there was still a formidable difference. ...read more.

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