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Question #44314
The Question
Consider the standard reduction potentials at for Group 14 elements \ce{Sn} and \ce{Pb}:
Two thermodynamic equilibrium constants are defined as follows: : Equilibrium constant for the oxidation of \ce{Sn^{2+}(aq)} by \ce{Pb^{4+}(aq)}K_2\frac{[\ce{Sn^{2+}}]}{[\ce{Pb^{2+}}]}$ established when excess finely divided \ce{Sn(s)} and \ce{Pb(s)} metals are added to an aqueous solution containing \ce{Pb^{2+}(aq)} and \ce{Sn^{2+}(aq)} ions.
Assuming , calculate the values of and respectively.
Options
- A.
and
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and
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and
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
Inert Pair Effect|Metal Activity Series Logic|E° (M²⁺/M) Anomalies
Why This Question Is Tricky
Common Mistakes
This problem tests the 'Metal Activity Series Logic' trap combined with the 'Inert Pair Effect'.
Students typically assume that metallic character and reactivity increase monotonically down a group, which would imply Pb displaces Sn (leading to a negative E° and K_2 = 10^{-1/3}).
However, the relativistic contraction of the 6s orbital in Pb significantly increases its ionization enthalpy (IE_1 + IE_2) compared to Sn.
This hidden variable makes Pb less reactive than Sn, resulting in a less negative reduction potential for Pb2+/Pb.
The problem forces students to trust the thermodynamic data over naive periodic trends and correctly apply the Nernst equation with n=2 for both the +4/+2 and +2/0 couples.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Classification of Elements and Periodicity in Properties - Class 11 Part 1 |
| Concept | Inert Pair Effect |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |