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Question #44759

Difficulty: 8/10 | 🟢 Free

The Question

A student sets up the following concentration cell at TT K to model localized electrochemical corrosion:

\ceCu(s)∣Cu+(aq,0.002M)∣∣Cu+(aq,0.2M)∣Cu(s)\ce{Cu(s) | Cu+ (aq, 0.002 M) || Cu+ (aq, 0.2 M) | Cu(s)}

The student assumes that \ceCu+\ce{Cu+} is perfectly stable in aqueous solution and calculates the theoretical electromotive force of the cell as EidealE_{ideal}. However, \ceCu+\ce{Cu+} undergoes spontaneous disproportionation. The system is allowed to reach chemical equilibrium in both half-cells before any current is drawn. The actual measured electromotive force of the cell is ErealE_{real}.

Given standard reduction potentials at TT K: E\ceCu+/Cu∘=0.52 VE^\circ_{\ce{Cu+/Cu}} = 0.52 \text{ V} and E\ceCu2+/Cu∘=0.34 VE^\circ_{\ce{Cu^{2+}/Cu}} = 0.34 \text{ V}.

Assume activity coefficients are unity and 2.303RTF=0.06 V\frac{2.303 RT}{F} = 0.06 \text{ V}. Identify the correct set of values for (Eideal,Ereal,log⁡10Keq)(E_{ideal}, E_{real}, \log_{10} K_{eq}), where KeqK_{eq} is the equilibrium constant for the disproportionation of \ceCu+\ce{Cu+}.

Options

  • A.

    0.12 V,0.06 V,60.12 \text{ V}, 0.06 \text{ V}, 6

  • B.

    0.12 V,0.12 V,60.12 \text{ V}, 0.12 \text{ V}, 6

  • C.

    0.06 V,0.03 V,30.06 \text{ V}, 0.03 \text{ V}, 3

  • D.

    0.12 V,0.00 V,120.12 \text{ V}, 0.00 \text{ V}, 12

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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

Concentration Cells|Corrosion as Electrochemical Process|E° (M²⁺/M) Anomalies|Variable Oxidation State Stability

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of electrochemistry and inorganic stability.

Students often blindly apply the Nernst equation to nominal concentrations, ignoring the thermodynamic instability of the \ceCu+\ce{Cu+} ion in aqueous media.

The 'hidden variable' is the spontaneous disproportionation of \ceCu+\ce{Cu+} into \ceCu2+\ce{Cu^{2+}} and \ceCu(s)\ce{Cu(s)}.

A secondary trap is failing to recognize that after disproportionation, the cell potential is governed by the \ceCu2+/Cu\ce{Cu^{2+}/Cu} couple.

Because n=2n=2 for this couple, the pre-logarithmic factor is halved, resulting in an actual cell potential exactly half of the naively calculated ideal potential.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterElectrochemistry - Class 12
ConceptConcentration Cells
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree