Use to table to answer question A and B Cell Measured Total Potential from Multi
ID: 570563 • Letter: U
Question
Use to table to answer question A and B
Cell
Measured Total Potential from Multimeter (V)1
(Cu) Electrode Standard Potential (V)2
Metal Electrode Experimental Potential (V)3
Metal Electrode Theoretical Potential (V)4
Metal Electrode Potential % Error
Cell Reactions5
G (kJ)6
Cu/Sn
.446
0.34 V
0.34-0.446 = -0.106
-0.14
Cathode:
Anode:
Net:
-2*96500*0.446/1000 = -86.078
Cu/Al
.751
0.34 V
0.34-0.751 = -0.411
-1.66
Cathode:
Anode:
Net:
-6*96500*0.751/1000 = -434.829
Cu/Fe
.526
0.34 V
0.34-0.526 = -0.186
-0.41
Cathode:
Anode:
Net:
-2*96500*0.526/1000 = -101.518
Cu/Zn
-.987
0.34 V
0.34-(-0.987) = 1.327
-0.76
Cathode:
Anode:
Net:
-2*96500*(-0.987)/1000 = 190.491
Metal Electrode Potential (% Error):
1. Cu/Sn: [{-0.14-(-0.106)}/-0.14]*100 = 24.3
2. Cu/Al = [{-1.66-(-0.411)}/-1.66]*100 = 75.2
3. Cu/Fe: [{-0.41-(-0.186)}/-0.41]*100 = 54.6
4. Cu/Zn: Non-spontaneous reaction
(a) Rank your electrochemical cells in this experiment in order of decreasing voltage (V) and decreasing Gibbs free energy (G). Is the ranking the same in both cases? If not, explain what that may be the case.
(b) How is knowing G in addition to V helpful when considering an electrochemical cell?
Cell
Measured Total Potential from Multimeter (V)1
(Cu) Electrode Standard Potential (V)2
Metal Electrode Experimental Potential (V)3
Metal Electrode Theoretical Potential (V)4
Metal Electrode Potential % Error
Cell Reactions5
G (kJ)6
Cu/Sn
.446
0.34 V
0.34-0.446 = -0.106
-0.14
Cathode:
Anode:
Net:
Cu2+ + 2e- Cu
Sn Sn2+ + 2e-
Cu2+ + Sn Cu + Sn2+
-2*96500*0.446/1000 = -86.078
Cu/Al
.751
0.34 V
0.34-0.751 = -0.411
-1.66
Cathode:
Anode:
Net:
Cu2+ + 2e- Cu
Al Al3++ 3e-
3Cu2+ + 2Al 3Cu + 2Al3+
-6*96500*0.751/1000 = -434.829
Cu/Fe
.526
0.34 V
0.34-0.526 = -0.186
-0.41
Cathode:
Anode:
Net:
Cu2+ + 2e- Cu
Fe Fe2++ 2e-
Cu2+ + Fe Cu + Fe2+
-2*96500*0.526/1000 = -101.518
Cu/Zn
-.987
0.34 V
0.34-(-0.987) = 1.327
-0.76
Cathode:
Anode:
Net:
Cu2+ + 2e- Cu
Zn Zn2+ + 2e-
Cu2+ + Zn Cu + Zn2+
-2*96500*(-0.987)/1000 = 190.491
Explanation / Answer
(a) The order of measured total potential will be
Cu/Al (0.756) > Cu/Fe (0.526) > Cu/Sn (0.446) > Cu/Zn(-0.987)
Order of Delta G value will be
Cu/Zn (190.491 kJ) > Cu/Sn (-86.078 kJ) > Cu/Fe (-101.518 kJ) > Cu/Al (-434.829)
The ranking will not be same in the both cases. Since, Delta G = -nFEcell, so due to the negative sign in fron the ranking of Delta G will be opposite to that of ranking of voltage
2)
Delta G is negative implies that the reaction is possible, since Ecell in that case will be positive. The sign of delta G can predict that the correct set of oxidants/reductants have been selected in setting up the cell at anode and cathode respectively
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