Question

The overall reaction 2Co3+(aq) + 2Cl-(aq) ? 2Co2+(aq) + Cl2(g) has the standard cell voltage Eocell= 0.46 V.

Given that Cl2(g) + 2e-? 2Cl-(aq), Eo = 1.36 V,

calculate the standard reduction potential for the following the half reaction at 25oC:

Co3+ + e-? Co2+

1.82 V
-0.90 V
0.90 V
-1.82 V

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

The given overall reaction will be as follows.

      $2Co^{3+}(aq) + 2Cl^{-}(aq) \rightarrow 2Co^{2+}(aq) + Cl_{2}(g)$

It is given that standard potential of the cell is 0.46 V.

Hence, the oxidation and reduction half reactions of the cell are as follows.

Reduction-half reaction: $Cl_{2}(g) + 2e^{-} \rightarrow 2Cl^{-}(aq)$,    $E^{o} = 1.36 V$

Oxidation-half reaction: $2Co^{3+}(aq) \rightarrow 2Co^{2+}(aq)$,  $E^{o} = ?$

Now, expression of $E^{o}_{cell}$ of this reaction is as follows.

        $E^{o}_{cell} = E^{o}_{Co^{3+}/Co^{2+}} - E^{o}_{Cl_{2}/Cl^{-}}$

Putting the given values into the above formula as follows.

     0.46 V =  $E^{o}_{Co^{3+}/Co^{2+}}$ - 1.36 V

  $E^{o}_{Co^{3+}/Co^{2+}}$ = 1.82 V

Thus, we can conclude that standard potential of the given half cell is 1.82 V.