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Question #44768

Difficulty: 8/10 | 🟢 Free

The Question

During the discharge cycle of a secondary battery, a localized pH gradient alters the redox behavior of the electrolyte. To investigate this thermodynamic shift, a technician constructs the following concentration-dependent electrochemical cell at 298 K298 \text{ K}:

Pt∣M2+(0.1 M),M3+(0.01 M)∣∣MnO4−(0.01 M),Mn2+(0.1 M),H+(pH=x)∣PtPt | M^{2+} (0.1 \text{ M}), M^{3+} (0.01 \text{ M}) || MnO_4^- (0.01 \text{ M}), Mn^{2+} (0.1 \text{ M}), H^+ (pH = x) | Pt

The technician observes that the cell potential is exactly 0 V0 \text{ V}, indicating that the KMnO4KMnO_4 indicator fails to spontaneously oxidize M2+M^{2+} under these specific conditions.

Given: EM3+/M2+∘=1.27 VE^\circ_{M^{3+}/M^{2+}} = 1.27 \text{ V} EMnO4−/Mn2+∘=1.51 VE^\circ_{MnO_4^-/Mn^{2+}} = 1.51 \text{ V} 2.303RTF=0.06 V\frac{2.303 RT}{F} = 0.06 \text{ V}

Calculate the value of xx (the pH of the cathodic compartment).

Options

  • A.

    2.5

  • B.

    3.0

  • C.

    2.0

  • D.

    1.0

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Secondary Battery Discharge Cycles|KMnO₄ Redox pH Dependency|E° (M³⁺/M²⁺) Redox Potential

Why This Question Is Tricky

Common Mistakes

This problem tests the Nernstian dependence of the MnO4−/Mn2+MnO_4^-/Mn^{2+} redox couple on pH and concentration gradients.

The 'Hidden Variable' is the formal potential shift caused by non-standard states.

Students frequently fall into the trap of ignoring the reaction quotient QQ and equating the standard potentials directly, which incorrectly yields pH=2.5pH = 2.5.

Furthermore, it evaluates the correct application of stoichiometric coefficients as exponents in the Nernst equation, specifically the 8th power for H+H^+ and the 5-electron transfer, which are common points of failure.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterElectrochemistry - Class 12
ConceptSecondary Battery Discharge Cycles
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree