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Question #44513

Difficulty: 8/10 | 🟢 Free

The Question

A redox half-cell is prepared at 298 K298\text{ K} by mixing 50 mL50\text{ mL} of 0.40 M \ceFe2(SO4)30.40\text{ M } \ce{Fe_2(SO_4)_3} and 50 mL50\text{ mL} of 0.10 M \ceFeSO40.10\text{ M } \ce{FeSO_4}. In this highly concentrated electrolyte medium, the solution exhibits significant non-ideal behavior. The single-ion activity coefficients are determined to be γ\ceFe3+=0.01\gamma_{\ce{Fe^{3+}}} = 0.01 and γ\ceFe2+=0.10\gamma_{\ce{Fe^{2+}}} = 0.10. Given the standard reduction potential E\ceFe3+/Fe2+∘=0.770 VE^\circ_{\ce{Fe^{3+}/Fe^{2+}}} = 0.770\text{ V} and 2.303RTF=0.059 V\frac{2.303 RT}{F} = 0.059\text{ V}, calculate the actual reduction potential of this half-cell. (Given: log⁡2=0.301\log 2 = 0.301, log⁡5=0.699\log 5 = 0.699)

Options

  • A.

    0.764 V0.764\text{ V}

  • B.

    0.823 V0.823\text{ V}

  • C.

    0.806 V0.806\text{ V}

  • D.

    0.747 V0.747\text{ V}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Concentration Units Dependency|Nernst Equation Concentration Dependence|E° (M³⁺/M²⁺) Redox Potential

Why This Question Is Tricky

Common Mistakes

This problem tests the fundamental thermodynamic definition of the Nernst equation, where the reaction quotient Q is strictly a ratio of activities, not concentrations.

Students commonly fall into the trap of assuming a≈ca \approx c (molarity), which is only valid for highly dilute ideal solutions.

By providing a highly concentrated medium, the activity coefficients (γ\gamma) deviate massively from 1.

A secondary trap is the stoichiometric conversion from the salt \ceFe2(SO4)3\ce{Fe_2(SO_4)_3} to the ion \ceFe3+\ce{Fe^{3+}}, where students often forget the factor of 2, leading to incorrect concentration and activity values.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterSolutions - Class 12
ConceptConcentration Units Dependency
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree