Question

Standard electrode potentials of $F{e}^{2+}+2e\to Fe$ and $F{e}^{3+}+3e\to Fe$ are $-0.440$V and $-0.036$V respectively. The standard electrode potential $\left(E^0\right)$ for $F{e}^{3+}+e\to F{e}^{2+}$ is:

• A. $-0.476$ V
• B. $-0.404$ V
• C. $+0.404$ V
• D. $+0.772$ V

Answer 1

Answer: (C)

$+0.404$ V

$F{e}^{2+}+2e^{-}\to Fe$ $E^o=-0.440V$....(i)

$F{e}^{3+}+3e^{-}\to Fe$ $E^o=-0.036V$....(ii)

To calculate, $F{e}^{3+}+e^{-}\to F{e}^{2+}$ $E^o=?$

Reversing equation (i)

$Fe\to F{e}^{2+}+2e^{-}$....(iii) $E^o=0.440V$

Adding equation (iii) and (ii)

$Fe\to F{e}^{2+}+2e^{-}$ $E^o=0.440V$

$F{e}^{3+}+3e^{-}\to Fe$ $E^o=-0.036V$

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$F{e}^{3+}+e^{-}\to F{e}^{2+}$

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$E^o=0.440-0.036=+0.404V$