The d-And-f-Block Elements

The d-And-f-Block Elements

Question

Account for the following :
E° value for the Mn3+/Mn2+ couple is highly positive (+1.57 V) as compared to Cr3+/Cr2+.

Answer

Mn2+ exists in 3d5 configuration which is a half-filled configuration which provides extra stability to the Metal Ion. While Mn3+ will exist in 3d4 configuration which is less stable than 3d5. Hence the conversion from 3+ to 2+ is very feasible. Hence E° value is more. while in
 Cr+3 exist in 3d3 half-filled d orbital (3 e; electrons in t2g ) extra stability is attained by Cr+3 than Cr+2. Hence Cr+3 →Cr+2 is less feasible. And hence it has less reduction potential as compare to Mn+3/Mn+2.

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