Question

The E° values in respect of the electrodes of chromium (z = 24), manganese (z = 25) and iron (z = 26) are: Cr⁺³/Cr⁺² = – 0.4V, Mn⁺³/Mn⁺² = 1.5V; Fe⁺³/Fe⁺² – 0.80V. On the basis of the above information compare the feasibilities of further oxidation of their +2 oxidation states.

Answer 1

Cr⁺³ + e -> Cr⁺²: E° value is -0.4V. The negative value means Cr⁺³ is more stable or Cr⁺² is less stable. Mn⁺³ + e → Mn⁺²: E° value is 1.5V. Fe⁺³ + e → Fe⁺²: E° value is 0.80V.

Greater positive value for Mn⁺³/Mn⁺² than that for Fe⁺³/Fe⁺² shows that Mn⁺² is more stable than Fe⁺².

Hence, the stability of +2 oxidation state is in the order Cr⁺² < Fe⁺² < Mn⁺² or oxidation of their +2 state is in the order Cr⁺² > Fe⁺² > Mn⁺².