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Question #44522

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The Question

An equimolar gaseous mixture of four halomethanes, \ce{CH3F}, \ce{CH3Cl}, \ce{CH3Br}, and \ce{CH3I}, is equilibrated with a minimum-boiling azeotropic mixture of ethanol and water at $320\text{ K}$ and $1\text{ atm}$ . Let $K_{H(F)}$ , $K_{H(Cl)}$ , $K_{H(Br)}$ , and $K_{H(I)}$ be their respective Henry's Law constants in this solvent system. Given that the dipole moments ( $\mu$ ) of the halomethanes follow the order \ce{CH3Cl} > \ce{CH3F} > \ce{CH3Br} > \ce{CH3I}, which of the following correctly identifies the order of their Henry's Law constants and the dominant physical factor dictating this trend?

Options

A.
$K_{H(F)} > K_{H(Cl)} > K_{H(Br)} > K_{H(I)}$ ; Solute polarizability and dispersion forces
B.
$K_{H(I)} > K_{H(Br)} > K_{H(F)} > K_{H(Cl)}$ ; Solute dipole moment and dipole-dipole interactions
C.
$K_{H(Cl)} < K_{H(F)} < K_{H(Br)} < K_{H(I)}$ ; Solute dipole moment and hydrogen bonding
D.
$K_{H(F)} > K_{H(Cl)} > K_{H(Br)} > K_{H(I)}$ ; Electronegativity of the halogen atom

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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

Azeotrope Boiling Point Logic|Henry’s Law Constant (Kh) Trends|C-X Bond Polarization and Polarizability

Why This Question Is Tricky

Common Mistakes

This question tests a 'Chemical Exception' where students incorrectly assume that in polar solvents, the solute's dipole moment is the primary driver of solubility (which would incorrectly predict CH3Cl as the most soluble and thus having the lowest Kh).

It forces the realization that for halogens, the massive increase in atomic size and polarizability down the group makes London dispersion forces the dominant factor in solvation thermodynamics, thereby inversely affecting the Henry's Law constant.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Solutions - Class 12
Concept	Azeotrope Boiling Point Logic
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free