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Question #44552
The Question
An aqueous solution of is treated with excess 2,2'-bipyridine (bipy) at 298 K. At an initial pH of 7.0, the system reaches equilibrium to form a deeply colored octahedral complex . The pH of the solution is then lowered to 1.0 by the dropwise addition of concentrated , and the system is allowed to reach a new equilibrium, resulting in a pale green octahedral complex .
Assuming no oxidation of the metal center occurs, identify the spin-only magnetic moments () of complexes and , respectively, and the total number of chelate rings present in a single molecule of complex .
Options
- A.
0.00 BM, 4.90 BM, 3
- B.
4.90 BM, 0.00 BM, 3
- C.
0.00 BM, 4.90 BM, 6
- D.
4.90 BM, 4.90 BM, 0
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
Ligand Denticity Variations|Spin-Only Magnetic Moment|Magnetic Moment Quenching
Why This Question Is Tricky
Common Mistakes
This problem tests the 'Hidden Variable' of pH-dependent ligand quenching and its effect on Crystal Field Splitting Energy (CFSE).
Students often memorize that bipyridine forms strong-field, low-spin complexes with Fe(II) and assume the magnetic moment is an intrinsic constant.
The trap lies in failing to recognize that at low pH, the basic nitrogen atoms of the ligand protonate, reducing its denticity to zero.
This forces a ligand substitution with water, drastically lowering the CFSE and triggering a thermodynamic transition from a low-spin to a high-spin state.
Distractor C traps students who confuse the number of coordinating atoms (6) with the number of chelate rings (3).
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Coordination Compounds - Class 12 |
| Concept | Ligand Denticity Variations |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |