Question

Explain the variation in E⁰ M²⁺/M³⁺ 3d series.

Answer 1

1. In transition series, as we move down from Ti to Zn, the standard reduction potential E⁰ _M²⁺/M³ value is approaching towards less negative value and copper has a positive reduction potential, i.e. elemental copper is more stable than Cu²⁺ . 

2. E⁰ _M²⁺/M​ value for manganese and zinc are more negative than regular trend. It is due to extra stability arises due to the half filled d⁵ configuration in Mn²⁺ and completely filled d¹⁰ configuration in Zn²⁺ . 

3. The standard electrode potential for the M³⁺ / M²⁺ half cell gives the relative stability between M³⁺and M²⁺. 

4. The high reduction potential of M³⁺/ M²⁺ indicates M²⁺ is more stable than M³⁺ . 

5. For Fe³⁺ / Fe²⁺ the reduction potential is 0.77 V, and this low value indicates that both Fe³⁺ and Fe²⁺can exist under normal condition. 

6. Mn³⁺ has a 3d² 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 [E° = +1.51 V]