Reduction Potentials

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MCAT Physical › Reduction Potentials

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The standard reduction potentials for iron and nickel are as follows:

$Fe^{2+} + 2e^{-} \rightarrow Fe$ $E^{\circ} = -0.45$

$Ni^{2+} + 2e^{-} \rightarrow Ni$ $E^{\circ} = -0.26$

If a galvanic cell is made using these two metals, what is the standard voltage for the cell?

Explanation

A galvanic cell is spontaneous, meaning that there will be a positive cell voltage. In order for this to take place, the more negative reduction potential must be flipped so that the metal is oxidized.

$Ni^{2+} + 2e^{-} \rightarrow Ni$ $E^{\circ}_{red} = -0.26$

$Fe \rightarrow Fe^{2+} + 2e^{-}$ $E^{\circ}_{ox} = 0.45$

Adding these values together gives a standard cell voltage of .

Consider the half reaction below.

$\small Ni^{2+}(aq) +2e^{-}\rightarrow Ni(s)$

$E^o_{Ni}=-0.23V$

Which of the following statements is true about the oxidation of nickel?

The oxidation of nickel has a potential of 0.23V

It is not possible to oxidize nickel

The oxidation of nickel has a potential of 0V

The nickel will gain electrons when oxidized

None of these are true

Explanation

Reduction potentials are typically provided in table form. Since the oxidation potential of an element is the negative of the reduction potential, it can be determined by viewing a reduction table.

Since the reduction potential for nickel is given as –0.23V, we can conclude that the oxidation potential for nickel is 0.23V.

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