UCD CHE 008A - Experiment 12: Electrochemistry

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Experiment 12 Electrochemistry Discussion The goal of this experiment is to measure relative reduction potentials of metals while comprehending the relationship between reaction spontaneity and reduction potentials Additionally this lab included finding Faraday s constant and Avogadro s number through the use of electrolysis In part 1 a salt bridge was formed between different metal ions In part 2 aluminum was put inside of a specific solution to determine if the solution was exothermic or endothermic In part 3 copper was placed in AgNO3 solution and the reaction was observed Finally in part 4 electrolysis was performed The relative reduction potentials of metals were measured with the use of a voltmeter The black probe was connected to the copper metal and the red probe was connected to the silver metal The purpose of choosing two different metals as the reference to measure relative reduction potentials is to have a reference to compare the values to The general trend in the measured and actual reduction potentials when referenced to the Hydrogen Electrode were not significantly off from each other In this specific experiment the voltmeter had issues so the reading came out to be a little lower than the actual reduction potentials Other possible errors include the barometric pressure in the room affecting the solutions To observe the reaction of aluminum and CuCl2 aq CuCl2 was added to a test tube 1 70 V 0 34 V and a strip of aluminum was added to the test tube The half cell reactions and potentials observed Al3 aq 3e Al s Cu2 aq 2e Cu s The observations from this part of the experiment is that the aluminum strip got rusty and had build up around it This indicates that the reaction is exothermic The balanced cell reaction and the cell potential 2Al s 3Cu2 aq 2Al3 aq 3Cu s 2 04 V Since the value of cell potential for the cell reaction is positive the reaction is indicated to be spontaneous To observe the reaction of copper and AgNO3 aq AgNO3 was added to a test tube and a strip of copper metal was added to this test tube The half cell reactions and the half cell potentials observed Ag aq e Ag s Cu2 aq 2e Cu s 0 80 V 0 34 V The observations from part 3 of the experiment are that the copper strip turned gray as well as the top of the solution which also turned a bit cloudy The balanced cell reaction and the cell potential 2Ag aq Cu s 2Ag s Cu2 aq Since the value of cell potential for the cell reaction is positive the reaction is indicated to be spontaneous 0 46 V To find Faraday s Constant F and Avogadro s number NA the observations of the 0 34 0 V 0 34 V average readings of the voltmeter the times in seconds of the reaction and the mass of copper was used The half cell reaction that occurred at the anode and at the cathode and the half cell potentials are Cathode 2H aq 2e H2 g Anode Cu s Cu2 aq 2e The balanced cell reaction and cell potential Cu s 2H aq Cu2 aq H2 s The value of cell potential for the overall reaction is negative so this means that the reaction is nonspontaneous To provide the energy needed to drive a nonspontaneous reaction in this experiment a power supply was used To determine Faraday s Constant F and Avogadro s number NA the times in seconds of the reaction and the mass of copper was used The bubbling in the reaction showed that the half cell reactions occurred From the H2 gas produced at the cathode Faraday s Constant was calculated to be 77157 C mol of electrons and the percent error was 20 From the H2 gas produced at the cathode Avogadro s number was calculated to be 4 8 10 23 1 mol and the percent error was 20 From the moles of copper dissolved from the copper anode Faraday s Constant was calculated to be 1 04 10 5 C mol of electrons and the percent error was 7 79 From the moles of copper dissolved from the copper anode Avogadro s number was calculated to be 6 49 10 23 1 mol and the percent error was 7 79 One possible error from this experiment can be from the technical issues with the voltmeter indicating the high percent errors in calculations


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UCD CHE 008A - Experiment 12: Electrochemistry

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