Lab_12 - Topic 12 Experiment Batteries Electrochemical...

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Topic 12 Experiment Batteries, Electrochemical Cells, and Fuel Cells Introduction This experiment involves making several electrochemical cells (batteries) and measuring their potentials (voltages) as discussed in the case study. The response of electrochemical cells to changes in chemical concentration is an important application of electrochemistry. Electrochemistry can be used to measure the concentrations of chemical species. For example, in Topic 10 you used a pH meter to measure pH. pH meters use the principles of electrochemistry to quickly and reliably measure the [H + ] concentration of a solution. pH will be measured in this experiment using the reversible oxidation-reduction of hydroquinone to quinone, which is described in Chemical Foundations: pH Measurements . The reduction half-reaction for this system can be written as: C 6 H 4 O 2 (quinone) + 2H + + 2e - C 6 H 4 (OH) 2 (hydroquinone) Experimental Procedure Part A: Properties of electrochemical cells Use the following instructions to construct the four voltaic cells below in a well plate: a) Zn(s) | ZnSO 4 (0.1 M) || CuSO 4 (0.1 M) | Cu(s) b) Mg(s) | Mg(NO 3 ) 2 (0.1 M) || CuSO 4 (0.1 M) | Cu(s) c) Fe(s) | FeSO 4 (0.1 M) || CuSO 4 (0.1 M) | Cu(s) d) Cu(s) | CuSO 4 (0.1 M) || FeSO 4 (0.05M), FeCl 3 (0.05M) | C(s, graphite) Fill one well near the middle of the well plate with 0.1 M KNO 3 to use as the salt bridge solution. Fill one nearby well with the solution common to all cells (e.g., CuSO 4 (0.1M)) and place a copper electrode in the well. You should sand the surface of the metal electrodes (not the graphite) before using. Place the remaining solutions in other nearby wells and place the proper electrode in each. You may choose to use the template supplied in lab to organize your well plate. Twist a strip of paper towel and place one end of the paper towel into the salt solution and one into the copper half cell. Repeat for the other half cell of interest. To start the software, go to My Computer Shared drive 412 Voltaic Cells . Logger Pro should open and in a few seconds, the program should automatically detect the voltmeter with a potential reading. Attach the alligator clips to each other. Then under the Experiment section of the toolbar, select Zero to zero the instrument. Safety and Performance Alert : Do not allow the clips to dip into the solutions. To insure clean electrical contacts, sand all the electrodes except the graphite electrodes , if necessary. Handle all chemicals carefully.
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Attach the alligator clips to the electrodes of the electrochemical cell. When measuring cell potential, the positive terminal (red) must be connected to the cathode as indicated in the cell notation shown above. (See Chemical Foundations: Representation of an Electrochemical Cell ) Record the cell potential. Measure each cell at least twice (disconnect and reconnect the wires). If your results are not consistent, determine why and make the necessary corrections.
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This note was uploaded on 12/07/2011 for the course CHEM 004 taught by Professor Maalouf during the Spring '11 term at University of Iowa.

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Lab_12 - Topic 12 Experiment Batteries Electrochemical...

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