Experiment 23 Voltaic and Electrolytic Cells Chemistry 1220 136 November 5st 2013 Raffeal Bennett Purpose The purpose of this experiment was to learn about voltaic cells and electrolytic cells and describe the similarities and differences The purpose was also to describe the key components and flow of electrons in electrochemical reactions and understand what the Ecell of a reaction indicates and how this relates to the equilibrium expression and thermodynamics Procedure Refer to pages 106 109 of General Chemistry 1220 Laboratory Manual by The Ohio State University Department of Chemistry Hayden McNeil Publishing 2013 2014 Sample Calculations See attached sheet Report Sheet A B Discussion By measuring the voltage drop between electrodes in their corresponding sulfate solution the cell potential can be calculated because the Ered of copper is known to be 0 34V Using the Ered of copper and the voltage drop the Ecell can be determined In the experiment the cell potential s of the half reactions were relatively accurate compared to the theoretical data For the copper reaction the change in voltage should have been very close to zero due to the fact both solutions and electrodes were the same The experimental Ecell value for copper was 332 V which when compared to the theoretical value of 340V it shows the voltage drop was nearly zero When comparing cell potentials to the theoretical iron had 728 V lead had 0 15 V Zinc had 1 4 V magnesium had 2 033 V and tin had 0 266 V For a number of these the difference between the experimental and theoretical was not very high even though the percent error may have been somewhat high Because the voltages are so small the slightest change in voltage could cause a significant change in the data The fact that the copper voltage drop was almost zero and all the others had relatively close values with the correct sign means the experimental data was fairly accurate To calculate the atomic weight element through the half reaction first the moles of electron and the change in mass have to be determined The change in mass is simply the mass at the beginning subtracted by the final mass of the electrode The number of moles is determined by multiplying the current by the duration of time the current was applied by one over Faraday s constant Once the mass and moles are established the atomic weight can be calculated by dividing the mass by the product of the moles of electrons and the mole ratio of electrons to copper In the experiment the atomic mass for the anode was calculated to be 288 3 amu and from the cathode was 226 5 amu There are a number of factors that could play a role in such the high percent error First the uncertainties of the measuring instruments could have played a small role in the relatively high percent error For example the uncertainty of the multimeter was 001V and 1mA Additionally the balance used had an uncertainty of 0001g Due to the fact the values of the data were so relatively small these uncertainties could have played a slight role in the cause of error Another potential source of error could be the electrodes not being completely dry or cleaned causing the changing in mass to increase which increases the atomic mass So if there was a small amount of water of acetone on the electrode the mass data would be higher than it should be A potential cause of the discrepancies in part A could be also from uncertainties but most likely from impurities in the solution creating a greater of smaller voltage drop Conclusion In the experiment the difference between voltaic cells and electrolytic cells was discovered Also the flow of electrons in electrochemical reactions was understood Lastly the cell potentials of six different elements were successfully determined and the atomic mass of copper was calculated by using information from a half reaction of copper This atomic weight was calculated by determining the moles of electron and the change in mass and was then compared the theoretical atomic weight