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Question #44759
The Question
A student sets up the following concentration cell at K to model localized electrochemical corrosion:
The student assumes that is perfectly stable in aqueous solution and calculates the theoretical electromotive force of the cell as . However, 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 .
Given standard reduction potentials at K: and .
Assume activity coefficients are unity and . Identify the correct set of values for , where is the equilibrium constant for the disproportionation of .
Options
- A.
- B.
- C.
- D.
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
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 ion in aqueous media.
The 'hidden variable' is the spontaneous disproportionation of into and .
A secondary trap is failing to recognize that after disproportionation, the cell potential is governed by the couple.
Because 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
| Subject | Chemistry |
| Chapter | Electrochemistry - Class 12 |
| Concept | Concentration Cells |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |