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Question #104019
The Question
An aqueous solution is prepared by dissolving of glycine (, ) in of pure water. The pH of the solution is carefully adjusted to using a negligible volume of reagent. Given that the acid dissociation constants for glycine are and , determine the freezing point of the resulting solution. (Assume ideal behavior).
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
Molecular Mass Abnormalities|Amino Acid Zwitterion pH Sensitivity|Inductive Effect Trends
Why This Question Is Tricky
Examiner Levers
Approximation Bait
Options are extremely close; tests precision vs. early rounding.
Difficulty Boost : +3Common Mistakes
This question tests the conceptual understanding of the van't Hoff factor (i) for amino acids at their isoelectric point (pI).
Students often fall into two traps: (1) Assuming that because the zwitterion has two charged centers, it behaves like a strong electrolyte and dissociates (i=2, leading to Option B). (2) Assuming that the carboxylic acid group causes dimerization via hydrogen bonding, similar to acetic acid in benzene (i=0.5, leading to Option C).
The hidden variable is recognizing that at the pI, the net charge is zero, and the molecule exists as a single, non-dissociating solvated entity in water, making i=1.
Additionally, the problem employs an 'Assumed Constant Trap' by requiring the student to recall the standard cryoscopic constant (Kf) for water.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Solutions - Class 12 |
| Concept | Molecular Mass Abnormalities |
| Difficulty | 5 |
| Cognitive Load | 6 |
| Target Solve Time | 150 sec |
| Access | Free |