Question

Compare the reduction potentials of Mn³⁺/Mn²⁺ and Fe³⁺ / Fe²⁺

Answer 1

1. Mn³⁺ + e^- → Mn²⁺

E° = + 1.51V 

Fe³⁺ + e^- → Fe²⁺

E° = + 0.77V

2. The high reduction potential of Mn³⁺ / Mn²⁺ indicates Mn²⁺ is more stable than Mn³⁺ . For Fe³⁺ / Fe²⁺ the reduction potential is 0.77V, this low value indicates that both Fe³⁺ and Fe²⁺ can exist under normal conditions. 

3. The drop from Mn to Fe is due to the electronic structure of the ions concerned. Mn³⁺ has 3d⁴ configuration while that of Mn²⁺ is 3d⁵ . The extra stability associated with a half filled d sub-shell makes the reduction of Mn³⁺ very feasible.