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If $E^\circ_{Fe^{2+}/Fe} = -0.441$ V and $E^\circ_{Fe^{3+}/Fe^{2+}} = 0.771$ V, the standard EMF of the reaction $Fe + 2Fe^{3+} \rightarrow 3Fe^{2+}$ will be :
A
0.330 V
B
1.653 V
C
1.212 V
D
0.111 V
Detailed Solution
For the cell reaction $Fe + 2Fe^{3+} \rightarrow 3Fe^{2+}$:
Anode reaction (oxidation): $Fe \rightarrow Fe^{2+} + 2e^-$
Cathode reaction (reduction): $2Fe^{3+} + 2e^- \rightarrow 2Fe^{2+}$
$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$, where both $E^\circ$ values are reduction potentials.
$E^\circ_{cell} = 0.771 - (-0.441)$
$E^\circ_{cell} = 1.212$ V
EMF is an intensive property, so the potentials are not multiplied by the number of electrons.
Anode reaction (oxidation): $Fe \rightarrow Fe^{2+} + 2e^-$
Cathode reaction (reduction): $2Fe^{3+} + 2e^- \rightarrow 2Fe^{2+}$
$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$, where both $E^\circ$ values are reduction potentials.
$E^\circ_{cell} = 0.771 - (-0.441)$
$E^\circ_{cell} = 1.212$ V
EMF is an intensive property, so the potentials are not multiplied by the number of electrons.