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Question #44679

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following three unbalanced redox reactions involving mixed-valence oxides in an acidic medium:

I. \ceFe3O4(s)+MnO4−(aq)+H+(aq)−>Fe3+(aq)+Mn2+(aq)+H2O(l)\ce{Fe3O4(s) + MnO4^{-}(aq) + H+(aq) -> Fe^{3+}(aq) + Mn^{2+}(aq) + H2O(l)} II. \cePb3O4(s)+H2O2(aq)+H+(aq)−>Pb2+(aq)+O2(g)+H2O(l)\ce{Pb3O4(s) + H2O2(aq) + H+(aq) -> Pb^{2+}(aq) + O2(g) + H2O(l)} III. \ceMn3O4(s)+C2O42−(aq)+H+(aq)−>Mn2+(aq)+CO2(g)+H2O(l)\ce{Mn3O4(s) + C2O4^{2-}(aq) + H+(aq) -> Mn^{2+}(aq) + CO2(g) + H2O(l)}

Let n1,n2,n_1, n_2, and n3n_3 be the nn-factors (valency factors) of \ceFe3O4\ce{Fe3O4}, \cePb3O4\ce{Pb3O4}, and \ceMn3O4\ce{Mn3O4} respectively in the above reactions. Let f1,f2,f_1, f_2, and f3f_3 be the exact fraction of metal atoms in each respective oxide formula unit that undergo a change in their oxidation state during the reactions.

Calculate the value of the expression: Ω=n1f1+n2f2+n3f3\Omega = \frac{n_1}{f_1} + \frac{n_2}{f_2} + \frac{n_3}{f_3}

Options

  • A.

    1212

  • B.

    55

  • C.

    1515

  • D.

    99

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Law of Multiple Proportions|Average vs. Actual Oxidation State|Disproportionation Constraints

Why This Question Is Tricky

Common Mistakes

The core trap tests the distinction between 'average' and 'actual' oxidation states in mixed-valence oxides.

Students often rely on the mathematical average (+8/3) to balance redox reactions.

While this works for calculating overall electron transfer (nn-factor), it completely fails when determining the physical reality of the reaction-specifically, how many atoms actually participate in the electron exchange.

By asking for the fraction of atoms reacting (ff), the question forces students to recall the exact lattice composition of these spinels and mixed oxides.

Furthermore, it tests periodic trends: \ceFe3O4\ce{Fe3O4} and \ceMn3O4\ce{Mn3O4} contain +2 and +3 states, whereas \cePb3O4\ce{Pb3O4} contains +2 and +4 states due to the inert pair effect (relativistic s-orbital contraction), making f2f_2 and f3f_3 different despite similar empirical formulas.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterSome Basic Concepts of Chemistry - Class 11 Part 1
ConceptLaw of Multiple Proportions
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree