Transition and Inner Transition Elements — Chemistry STD 12 — Question
Tamilnadu BoardEnglish MediumSTD 12ChemistryTransition and Inner Transition Elements3 Marks
Question
Compare the reduction potentials of $Mn ^{3+} / Mn ^{2+}$ and $Fe ^{3+} / Fe ^{2+}$.
✓
Answer
$\text { 1. } Mn ^{3+}+ e ^{-} \rightarrow Mn ^{2+}$
$E ^{\circ}=+1.51 V$
$Fe ^{3+}+ e ^{-} \rightarrow Fe ^{2+}$
$E ^{\circ}=+0.77 V $
2. The high reduction potential of $Mn ^{3+} / Mn ^{2+}$ indicates $Mn ^{2+}$ is more stable than $Mn ^{3+}$. For $Fe ^{3+} / Fe ^{2+}$ the reduction potential is 0.77 V , this low value indicates that both $Fe ^{3+}$ and $Fe ^{2+}$ can exist under normal conditions.
3. The drop from Mn to Fe is due to the electronic structure of the ions concerned. $Mn ^{3+}$ has $3 d^4$ configuration while that of $Mn ^{2+}$ is $3 d^5$. The extra stability associated with a half filled d sub-shell makes the reduction of $Mn ^{3+}$ very feasible.
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