When the voltage of an electrochemical cell is

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Including drawings in your notebook may help. When the voltage of an electrochemical cell is positive, then the positive pole of the voltmeter is connected to the positive electrode of the voltaic cell, i.e., the cathode. When the voltage of an electrochemical cell is negative, then the positive pole of the voltmeter is connected to the negative electrode of the galvanic cell, i.e., the anode. e) Change the electrode in the red alligator clip and record the voltage of another half- cell, keeping the Ag/Ag + half-cell as the reference. Continue for each half-cell. f) Measure the cell potential for a Cu / Cu 2+ || Zn / Zn 2+ cell by changing the black alligator clip to the copper electrode and the red alligator clip to the zinc electrode. Record the voltage for this combination. Repeat this measurement of the cell potential for a Cu/Cu 2+ ||Fe 3+ ,Fe 2+ /Pt cell. Data analysis of Cell Potentials During the lab session you will be recording (in your lab notebook) voltages associated with five combinations of half-cells. In your lab report you will construct a table of data similar to Table 1 shown below. The cell voltages you measure will go into the second column. Table 1: Cell Potentials Electrodes in Cell E cell (V) (observed during lab) E 0 cell (V) Negative Electrode Oxidation Reaction E 0 Oxidation (V) Reduction Reaction E 0 Reduction (V) Ag / Ag + Cu / Cu 2+ Ag / Ag + Pt/Fe 3+ / Fe +2 Ag / Ag + Zn / Zn 2+ Cu / Cu 2+ Zn / Zn 2+ Cu / Cu 2+ Pt/Fe 3+ / Fe +2
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Chemistry 132 Lab Manual Page 47 a) Oxidation occurs at the negative pole in a cell; write the oxidation reaction for each of the cells. The companion electrode system must undergo reduction. Write the reduction reaction occurring in each cell. b) Use the silver cell as a standard potential, that is assume E Ag + /Ag = 0 . 0 V (whether in reduction or oxidation). Enter that value in the table, for all Ag electrode systems used in cell measurements. Since E cell = E oxidation + E reduction , one can calculate E values for all the electrode systems, in which the Ag + /Ag system was involved. Enter the corresponding values into the table. c) Use the values and relationships in b) and the fact that for any given electrode system E reduction = – E oxidation to complete the table of E values. The best way to do this is to use one of the E values found in b) in another cell with that electrode system. That potential, along with E cell will enable you to find the potential for the other electrode. Continue this process with other cells until all electrode potentials have been determined. In your lab report you should organize a second table similar to Table 2 for electrode (half-cell) potentials derived from the above measurements. Table 2: Half-cell reduction potentials E 0 reduction (V) using E 0 (Ag + /Ag)=0.00 V Electrode reaction in reduction E 0 reduction (V) after assigning E 0 (Ag + /Ag)=0.80 V and E 0 (H + /H 2 ) = 0.00 Volts The cell-potential data in Table 1 are based on a standard Ag + / Ag electrode.
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