Question

Given standard $E^{\ominus }$:

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

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

The $E^{\ominus }$ of $F{e}^{3+}+e^{-}\to F{e}^{2+}$ is:

• A. $0.604V$
• B. $0.476V$
• C. $0.404V$
• D. $0.772V$

Answer 1

Answer: (D)

$F{e}^{3+}+3e^{-}\to Fe\left(E_1\right)$ .... (i)

$F{e}^{2+}+2e^{-}\to Fe\left(E_2\right)$ .... (ii)

Net equation $F{e}^{3+}+e^{-}\to F{e}^{2+}\left(E_3\right)$ .... (iii)

[Obtained by equation (i) - (ii)]

$E_3=\frac{n_1{E}_1-n_2{E}_2}{n_3}=\frac{3(-0.036)-2(-0.440)}{1}$

$=0.772V$

Option D is correct.