Question

Assuming complete ionization, same moles of which of the following compounds will require the least amount of acidified ${KMnO4}$ for complete oxidation ?

• A. ${ FeC2O4}$
• B. ${ Fe(NO2)2 }$
• C. ${FeSO4 }$
• D. ${FeSO3 }$

Answer 1

The Correct Option is C

To determine which compound requires the least amount of acidified ${KMnO_4}$ for complete oxidation, we need to consider the oxidation states of iron in these compounds and the change in oxidation state during the reaction.

1. Understanding Oxidation State Changes:
   • The oxidation state of iron in ${FeC_2O_4}$ is +2.
   • The oxidation state of iron in ${Fe(NO_2)_2}$ is also +2.
   • The oxidation state of iron in ${FeSO_4}$ is +2.
   • The oxidation state of iron in ${FeSO_3}$ is +2, assuming that sulfur is in the +4 state.

   All compounds initially have iron in the +2 oxidation state.

2. Oxidation Reaction with ${KMnO_4}$:
   • In acidic conditions, ${KMnO_4}$ oxidizes ${Fe^{2+}}$ to ${Fe^{3+}}$.
   • The relevant half-reaction is: ${Fe^{2+} \rightarrow Fe^{3+} + e^-}$
   • This means each mole of ${Fe^{2+}}$ requires one electron to be transferred to become ${Fe^{3+}}$.
3. Calculation of KMnO₄ Requirement:
   • The molecule of ${KMnO_4}$ in acidic solution gets reduced per the reaction: ${MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O}$.
   • This implies that 5 moles of electrons are required for the reduction of 1 mole of ${KMnO_4}$.
   • Thus, 1 mole of ${KMnO_4}$ can oxidize 5 moles of ${Fe^{2+}}$ to ${Fe^{3+}}$.
4. Conclusion:

   Since all the compounds contain iron in the +2 oxidation state initially, each not requiring any more or less of ${KMnO_4}$ compared to the others based on the moles of iron present in them, what distinguishes them is the presence of other oxidizable ions. Here, ${FeSO_4}$ does not have additional oxidizable components (like in ${FeC_2O_4}$ or ${FeSO_3}$), making it the one requiring the least amount of ${KMnO_4}$.

Therefore, the compound ${FeSO_4}$ requires the least amount of acidified ${KMnO_4}$ for complete oxidation.