Question

The $E_{M^{3+}/M^{2+}}^{\circ }$ values for $Cr,Mn,Fe$ and $Co$ are $0.41,+1.57,+0.77$ and $+1.97V$, respectively. For which one of these metals the change in oxidation state from $+2$ to $+3$ is easiest?

• A. $Cr$
• B. $Mn$
• C. $Fe$
• D. $Co$

Answer 1

Answer: (A)

$E_{C{r}^{3+}/C{r}^{2+}}^{\circ }=-0.41V$

$E_{M{n}^{3+}/M{n}^{2+}}^{\circ }=+1.57V$

$E^{\circ }F{e}^{3+}/F{e}^{2+}=+0.77V$

$E_{C{o}^{3+}/C{0}^2+}^{\circ }=+1.9$

More negative value of $E_{\text{red }}^{\circ }$ indicates better reducing agent, thus easily oxidised. Thus, oxidation of $C{r}^{2+}$ to $C{r}^{3+}$ is the easiest.