[firefly08642]

I'm stuck on the question below, please give me a hint.
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The copper center in the blue protein azurin has the following stoichiometry: Cu2+ + ne- -> Cu+

When the ratio of Cu2+ to Cu + is measured at different potentials the following results were obtained at 25 degrees Celsius:

Potential/V                        Cu2+/Cu+
0.43                                       2421
0.36                                         158
0.29                                          10.4
0.23                                            1
0.18                                            0.14
0                                                1.3x10^-4
-0.11                                          1.8x10^-6

Calculate the standard redox potential of the copper center and the value of n.

This is what I think so far. I plot the graph of the ratio of Cu2+/Cu+ against the potential. I find the value of the potential when the ratio of Cu2+/Cu is zero, that is the standard potential?

[FeLiXe]

If I get this right, it works with the Nernst equation. Insert the values and calculate the standard potential.

[firefly08642]

I thought that at first too. But when I tried it for the first two data:
Potential/V                        Cu2+/Cu+
0.43                                      2421
0.36                                        158
The standard potential, E(standard) do not match. This is shown as below:

The Nerst equation is E(standard)=E+(RT/nF)lnQ
-RT/nF is a constant where n = 1, RT/nF=0.02692733..
-Q is the ratio is Cu2+/Cu+
-E is potential/V

Therefore, for the first data:

E(standard)=0.43+0.02682733xln2421=0.639

For the second data:

E(standard)=0.36+0.02682733xln158=0.495 <- do not match the E(standard) above.

[firefly08642]

Got the answer.

Plot the graph from the given data, which will give a straight line with a negative gradient. Compare with y=mx+c where c is the standard electrode potential and n could be found from the gradient.