Question

Account for the following:

E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺.

Answer 1

In case of Mn '+2' oxidation state is more stable than '+3' oxidation state and in case of Cr '+3' oxidation state is more stable than '+2' oxidation state.

Answer 2

The E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for the Cr³⁺/Cr²⁺ couple. This is because the Mn²⁺ ion is particularly stable due to the extra stability of its half-filled valence electronic configuration (3d⁵). Thus Mn³⁺ ion has a very high tendency to gain an electron and form the much more stable Mn²⁺ ion.