Question

Using the standard electrode potential, find out the pair between which redox reaction is not feasible.

$E^{o}$ values: $Fe^{3 +}/Fe^{2 +} = + 0.77;I_{2}/I^{-} = + 0.54;$

$Cu^{2 +}/Cu = + 0.34;Ag^{+}/Ag = + 0.80V$

• A. $Fe^{3 +}$and $I^{-}$
• B. $Ag^{+}$ and Cu
• C. $Fe^{3 +}$ and Cu
• D. Ag and $Fe^{3 +}$

Answer 1

Answer: (D)

Ag and $Fe^{3 +}$

Answer 2

: For the reaction,

$2Fe^{3 +} + 2I^{-} \rightarrow 2Fe^{2 +} + I_{2}$

$E_{cell}^{o} = E_{Fe^{3 +}/Fe^{2 +}}^{o} - E_{I_{2}/I^{-}}^{o}$

$= 0.77 - (0.54) = + 0.23V$

Here, $E_{cell}^{o}$ is + ve so, the reaction is feasible. For the reaction,

$Cu + 2Ag^{+} \rightarrow Cu^{2 +} + 2Ag$

$E_{cell}^{o} = E_{Ag^{+}/Ag}^{o} - E_{Cu^{2 +}/Cu}^{o}$

$= 0.80 - (0.34) = + 0.46V$

Here , $E_{cell}^{o}$is + ve so, the reaction is feasible. For the reaction,

$2Fe^{3 +} + Cu \rightarrow 2Fe^{2 +} + Cu^{2 +}$

$E_{cell}^{o} = E_{Fe^{3 +}/Fe^{2 +}}^{o} - E_{Cu^{2 +}/Cu}^{o}$

$= 0.77 - (0.80) = - 0.03V$

Here, $E_{cell}^{o}$ is negative so, the reaction is not feasible.