Electrochemistry: In the first row for values in Table 2, the red probe was on t

Question

Electrochemistry:

In the first row for values in Table 2, the red probe was on the copper electrode, so you assume that reduction occurs at copper. From a table of standard reduction potentials you can find the standard reduction potential for Cu2+ being reduced to Cu, and its value is 0.340 V.

Use the equation (1) Eocell = Eoreduction half-cell - Eooxidation half-cell, but value is for reduction to find the standard reduction potential for the other five metals.

The equation above rearranges to () E ooxidation half-cell, but value is for reduction = 0.340 V - Eocell Record the calculated standard reduction potentials.

Rank the metals in an order that reflects your results and compare it to a table of standard reduction potentials.

Take the calculated value for the standard reduction potential for Pb and use it to replace the 0.340 value in equation (2).

Use the second row for values in Table 2 to calculate the standard reduction potentials for Zn, Al, Fe, and Ni.

How do they compare to the values that you calculated using copper as the cathode?

Explanation / Answer

General formula,

Eo = Ecathode - Eanode [both reduction potentials]

or,

Eo = Ecathode[red]-Eanode[oxd]

So here with Cu being the cathode,

Eo[Al] = 0.340 + 0.595 = 0.935 V

Eo[Fe] = 0.340 + 0.554 = 0.894 V

Eo[Ni] = 0.340 + 0.117 = 0.457 V

Eo[Pb] = 0.340 + 0.485 = 0.825 V

So the cell spontaneity order for Cu as cathode and the metals as anode can be aranged as, Al > Fe > Pb > Ni with Al as anode being the most spontaneous and Ni as anode as the least spontaneous.

Standard reduction of Pb = -0.126 V as cathode,

Eo[Al] = -0.126 + 0.595 = 0.469 V

Eo[Fe] = -0.126 + 0.554 = 0.428 V

Eo[Ni] = -0.126 + 0.117 = 0.009 V

Eo[Cu] = -0.126 - 0.340 = -0.466 V

In the case when Pb is used as cathode instead of Cu, we have the following order for sponteity of cell, Al > Fe > Ni > Cu, with Cu as non-spontaneous cell.

the first two metals Al and Fe shows no change in order when Pb replaces Cu as cathode, however, Ni shows a change.

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