The EM3+∣M2+∘ values forCr Mn, Fe and Coare -0.41, + 1.57, 0.77 and +1.97 V respectively. For which one of these metals the change in oxidation state from +2 to +3 easiest?

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

Solution:

We are given that ${Cr}^{3 +} + e^{-} ⇌ {Cr}^{2 +} E^{\circ} = - 0.41 V {Fe}^{3 +} + e^{-} ⇌ {Fe}^{2 +} E^{\circ} = 0.77 V$ ${Mn}^{3 +} + e^{-} ⇌ {Mn}^{2 +} E^{\circ} = 1.57 V {Co}^{3 +} + e^{-} ⇌ {Co}^{2 +} E^{\circ} = 1.97 V$ ${Cr}^{3 +}$ will show least tendency to convert to ${Cr}^{2 +}$ . On the other hand ${Cr}^{2 +}$ will show maximum tendency to convert to ${Cr}^{3 -}$ .

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

Solution:

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