Discuss the relative stability in aqueous solutions of +2 oxidation state among the elements: Cr, Mn, Fe and Co. How would you justify this situation?
(At. Nos. Cr = 24, Mn = 25, Fe = 26, Co = 27)
AnswerOn the basis of electrochemical series, the standard electrode potential shows the following order:
$E^\circ Mn^{2+}/Mn < E^\circ Cr^{2+}/Cr < E^\circ Fe^{2+}/Fe < E^\circ CO^{2+}/CO$
Therefore, $Co^{2+}$ gets easily reduced to metallic cobalt while it is difficult to reduce $Mn^{2+}$. Hence, $Mn^{2+}$ will be the most stable and the increasing stability order will be
$Co^{2+} < Fe^{2+} < Cr^{2+} < Mn^{2+}$