Q. The $E_{M^{3 +}/M^{2 +}}^{{^\circ}}\$ values for Cr, Mn, Fe and Co are -0.41 V, +1.57 V, +0.77 V and +1.97 V 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
Explanation
(a)
$E_{{Cr}^{3 +}/{Cr}^{2 +}}^{{^\circ}}\ = \ - \ 0.41\ V$
$E_{{Mn}^{3 +}/{Mn}^{2 +}}^{{^\circ}}\ \ = \ + \ 1.57\ V$
$E_{{Fe}^{3 +}/{Fe}^{2 +}}^{{^\circ}}\ = \ + \ 0.77\ V$
$E_{{Co}^{3 +}/{Co}^{2 +}}^{{^\circ}}\ = \ + \ 1.97\ V$
More negative value of $E_{red}^{{^\circ}}$ indicates better reducing agent thus easily oxidized. Thus, oxidation of ${Cr}^{2 +}$ to ${Cr}^{3 +}$ is the easiest.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.