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Question #44789
The Question
Consider the following electrochemical cell with transference operating at :
is an ideal dilute aqueous buffer containing and . Assume the activity coefficients for all species in are unity ().
is a concentrated aqueous buffer containing and . Due to the high concentration of the organic amine, the dielectric constant of the medium is significantly lowered, altering the solvation dynamics. The activity coefficients in are determined to be: , , and (due to the salting-out effect).
The thermodynamic acid dissociation constant of is . The transport numbers of the ions across the liquid junction are and .
Given: , , and .
Calculate the total electromotive force () of the cell.
Options
- A.
-0.015 V
- B.
-0.036 V
- C.
-0.006 V
- D.
+0.030 V
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
Liquid Junction Potential|Electrode Potential Dependencies|Basicity-Solvation Competition
Why This Question Is Tricky
Common Mistakes
This problem tests the 'Basicity-Solvation Competition' and the breakdown of the ideal Nernst equation.
Students typically assume that in a buffer where , the .
However, at high concentrations, especially with organic amines, the solvent's dielectric constant drops, drastically altering activity coefficients ().
The trap is twofold: (1) The Nernst equation strictly relies on thermodynamic activity, not concentration, shifting the electrode potential. (2) The Liquid Junction Potential (LJP) must also be calculated using mean ionic activities (), not molarities.
Failing to account for in either the buffer equilibrium (Option B) or the LJP equation (Option C) leads to incorrect potentials.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Electrochemistry - Class 12 |
| Concept | Liquid Junction Potential |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |