CHEM 152 Lab 5 Report
CHEM 152 Lab 5 Report CHEM 152
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This 4 page Class Notes was uploaded by Angel Lee on Tuesday June 9, 2015. The Class Notes belongs to CHEM 152 at University of Washington taught by Kevin O'Malley in Spring 2015. Since its upload, it has received 1384 views. For similar materials see General Chemistry in Chemistry at University of Washington.
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Date Created: 06/09/15
Name Quiz Section ID Number Lab Partner Note Chem 152 Experiment 5 Electrochemistry All sections of this report except the structural formulas Total Points 60 5 notebook 55 template must be typed By signing below you certify that you have not falsified data that you have not plagiarized any part of this lab report and that all calculations and responses other than the reporting of raw data are your own independent work Failure to sign this declaration will result in 5 points beind deducted from your report score Signature Purpose and Method The first goal is to experimentally determine the standard reduction potentials of AgAg PbPb2 CuCu2 and ZnZn2 and write the spontaneous reaction for each pair of half cells that are connected How is this accomplished 4 pts The standard reduction potentials and spontaniety of the half cell reactions for AgAg PbPb2 CuCu2 and ZnZn2 are determined by connecting each half cell to the AgAgCl reference electrode and measuring the reduction potentials using a Fluke multimeter If the fluke multimeter shows a positive reading we can conclude that this reaction is spontaneous and the black lead is connected to the anode which undergoes oxidation while the red lead is connected to the cathode which undergoes reduction On the other hand if the fluke multimeter shows a negative reading we can conclude that the reaction is spontaneous in the reverse direction and the black lead is connected to the cathode while the red lead is connected to the anode The remaining goals are to construct a a battery with E 17 V and b a cell with Ecell 050V How are these accomplished 4 pts A battery is constructed by two electrochemical cells that are connected in a series The specific voltage of 17 V is attained by connecting the half cells in a specific combination that would in this case produce the maximum voltage In other words the half cells with the positive or greater reduction potentials are used as the cathodes while the half cells with the negative or lesser reduction potentials are used as the anodes In the following section of the experiment we can use data from the first part of the experiment to find the half cell reaction that would gives us a E0 closest to 05 V AftenNards we can use the Nernst equation to solve for Q E E0 00591 V log Q n lf Q is greater than 1 because the molarity of the anode cannot be increased due to the materials provided in the lab the molarity of the cathode will be decreased by dilution with DI water If the Q is less than 1 the molarity of the cathode will be decreased by dilution with water The molarity will be decreased by using Q to solve for the new wanted molarity of either the cathode or anode The new molarity will then be inserted into the following equation to solve for the required addition of DI water M1 V1 M2 V2 Data and Calculations Part I Standard Potentials Standard Potentials vs SilverSilver Chloride Reference Electrode Cell Number Potential V Cathode Anode vs AgAgCl Electrode Electrode spontaneous rxn 1 Ag 0561 V Ag Ag AgCI 2 Zn 0768 V Ag AgCI Zn 3 Pb 0365 V Ag AgCI Pb 4 Cu 0141 V Cu Ag AgCl 8 pts Spontaneous Reaction between each half cell and AgAgCl reference Cell 1 quot equot gt S 2 Zn S gt Znquot2 3 S gt Pbquot2 4 Cuquot2 S gt Cu S quot Page 1 of 4 Page 2 of 4 Using the data from Table 111 in the Zumdahl text type the calculation for the expected Eo value for the Cu2Cu AgAgCl cell 2 pts Cathode reduction Cu E0 034 V written as reduction potential anode oxidation AgAgCl E0 022 V written as reduction potential E cel E0 cathode E anode 034 V 022 V 012 V Based on your measured potential for this cell and the literature value for the standard reduction potential for the AgAgCl reference electrode what would you expect the overall potential to be for the spontaneous reaction between your Cu2Cu electrode and a standard hydrogen eletrode Type your calculation for the expected standard reduction potential vs the SHE as well as the o error between this value and the literature value 3 pts literature standard reduction potential Of Cu2Cu E0 034 V written as reduction potential Standard reduction potential of Cu2Cu with respect to SHE measured potential E AgAgCl reference 0141 V 022 V 0361 V percent error lactual theoreticall 100 O361 034 100 62 theoretical 034 Zinc 2 and Lead 3 ECGquot V Expected Ecell V based on YOUR E values Actual value of your measurement V 0403 0396 Oxidation Halfreaction Zns gt Znquot2aq 2equot Reduction Half reaction Pbquot2aq 2equot gt Pbs Type the calculation of of the expected potential based on YOUR measured E0 values this is one calc example E cell E0 cathode E anode Cathode reduction Zn E0 0768 V written as a reduction potential Anode oxidation Pb E0 0365 V written as a reduction potential 0768 V 0365 V 0403 V Pa lk Ba e es CellLine Notation for battery with voltage greater than 1 7V Pbs Pbquot2 aq 1 M H Cuquot2aq 1 M Cus Zns Znquot2aq 1 M H Agquotaq 1 M Ags I Measured Voltage 1819 Note For the battery you will have more than one cell so just write the notation for each cell separated by a semicolon Part III Concentration Effects Copper Concentration Cell half cells 4 and 5 Potential V Expected Potential V Write out the spontaneous reaction Measured Calculated not cellline notation 0041 0030 Cuquot2 aq 1 M Cu 3 gt Cuquot2aq 01 M Cu 3 Type the calculation for the expected cell potential E E0 E In Q E0 00591 V log Q applicable because reaction occurs at room temperature nF n E 0 V 00591 V log anode 00591 V log 01 M 0030 V 2 cathode 2 1 M Page 3 of 4 2 pts 6 pts 4 pts 5 pts CellLine notation for cell that should give exactly 050V I Pbs Pbquot2 aq Cuquot2 aq Cus I Type the calculations used to determine how to prepare the concentration cell Actual value of your measurement V 0497 E E0 00591 V log Q 05 V cathode reduction Cu E0 0141 V written as a reduction potential n anode oxidation Pb E0 0365 V written as a reduction potential E E0 00591 V log Q 2 05 V 0506 0006 V 00591 V log Q Q Pbquot2 1476 Since Q is greater than 1 Pbquot2 1 M 2 CuA2 Cu 2 1 M 1476 0677 M E0 E cathode E anode 0141 V 0365 V 0506 V M1 v1 M2 v2 14 mL 1 M 0677 M v2 V2 207 mL Dilute copper nitrate solution until the graduated cylinder reads this volume and then pour the solution back into the vial connecting it as the cathode Results and Discussion 1 Discuss how well your EO value for the Cu electrode compares with the literature value Reference your o error calculation on the second page of this report and discuss reasonable sources of error 4 pts My EO value of the Cu electrode yielded a percent error of 62 percent More specfically my EO value was slightly higher than the theoretical EO value A possible source of error for this section of the experiment is the presence of DI water inside the vials before the start of the experiment Before the start of the experiment the vials were not completly dry and had some unknown fluids inside These fluids could have reduced the concentration Cuquot2 therefore effecting Q to be less than one and increasing the E Another possible source of error could be the environment in which the experiment was performed It was quite stuffy inside the lab so it is possible that the temperature was not precisely at a room temperature of 25 degrees which could also affect Q 2 Explain why the concentration cell should initially have a nonzero voltage Which half cell will produce electrons 4 pts Although the standard reduction potential for a concentration cell is equal to zero the concentration cell should have a nonzero voltage because the system is not at equilibrium or Q is not equal to K As long as Q is not equal to K the differing concentrations of the two compartments will continue to drive the reaction Therefore as long as the system is not at equilibrium Ecell will not equal zero In addition because the system is being driven to reach equilibrium the concentration of the higher molarity 1 M will continue to decrease as the concentration of the lower molarity 01 M will increase In order for the concentration of the higher molarity to decrease the copper ions must be reduced into copper Therefore the half cell with the higher molarity will act as the cathode and gain electrons while the half cell with the lower molarity will act as the anode and produce and lose electrons 3 Ithhe potegitial of the cell you assembled in Part III Step 2 exactly 050V Give reasonable reasons why your cell voltage is NOT exactly 050 4 pts When we first connected the two cells the fluke multimeter read 050V However as time elapsed the value continued to decrease We predict the cell voltage for the battery is not exactly 050V for several reasons One of them being that because we are dealing with very small amounts it is possible that we could have not diluted the solution precisely It is possible that we could have added too much or too less DI water therefore affecting the final concentration In addition another reason why our cell voltage may not be exact could be due to human error as we measured the voltage using the multimeter Although it is unikely it is possible that the electrode could have at one point touched each other and affect the voltage The other source of error in our experiment could be the temperature of the lab The calculations for the needed change in the concentration was done using a form of the Nernst equation that specifies a room temperature of 25 degrees Celsius Because we could not find the thermometer in the lab we were not able to verify whether the temperature of the room was 25 degrees Therefore it is possible the assumptions used in our calculations could have affected our results Laboratory Waste Evaluation 1 pt Laboratory waste is considered anything generated during an experiment that is disposed of down the sewer drain thrown in the garbage collected in a container for disposal by the UW Environmental Health amp Safety department or released into the environment Based on the written lab procedure and your actions during the lab list the identity and approximate amount mass or volume of waste that you generated while performing this experiment 35 mL1 M AgNO3 35 mL 1 M ZnN032 35 mL 1 M PbN032 35 mL 1 M CuN032 35 mL 01 M CuN032 6 pieces of cellulose film Silver Zinc Lead and Copper wires sand paper electricity 3 paper towels 100 mL of DI water 10 mL of KNOB Page 4 of 4 4 pts
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