The Question is from neet-chemistry chemical-bonding h-bond-dipole-moment, and it was created by the author Mr. S M HUSSAIN

Question

Which of the following explains the abnormally high boiling point of HF compared to other hydrogen halides?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Intermolecular forces and boiling point
 **Related Topics**: Hydrogen bonding, van der Waals forces, molar mass
 **Prerequisites**: Understanding of intermolecular forces and their effect on boiling points.
## SOLUTION PATHWAY
**Given Information**:
  The question asks why HF has an abnormally high boiling point compared to other hydrogen halides (HCl, HBr, HI).
  We need to compare the intermolecular forces present in these molecules.
**Method & Steps**:
 1. Compare the types of intermolecular forces present in HF and other hydrogen halides.
  Reasoning: Hydrogen halides exhibit various intermolecular forces, including van der Waals forces (London dispersion forces) and dipole-dipole interactions.  However, HF uniquely exhibits strong hydrogen bonding.
  Formula/Rule: None explicitly needed, but understanding the relative strengths of intermolecular forces is crucial (hydrogen bonding > dipole-dipole > London dispersion forces).
 2. Analyze the strength of hydrogen bonding in HF.
  Working:  Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (like F, O, or N) and is attracted to another electronegative atom in a nearby molecule.  Fluorine is the most electronegative element, leading to exceptionally strong hydrogen bonds in HF.
  Key Point: The strength of hydrogen bonds significantly impacts boiling point. Stronger intermolecular forces require more energy to overcome, resulting in higher boiling points.
 3. Compare the boiling points based on the identified intermolecular forces.
  Result: The strong hydrogen bonding in HF is responsible for its significantly higher boiling point compared to other hydrogen halides, where weaker van der Waals forces dominate.
  Verification:  Experimental boiling point data confirms that HF has a much higher boiling point than other hydrogen halides.
 ## OPTION ANALYSIS
A ✓: Strong intermolecular hydrogen bonding in HF. This is the correct explanation. Hydrogen bonding is a uniquely strong intermolecular force that significantly raises the boiling point.
B :x: Higher molar mass of HF. While molar mass does influence boiling point (larger molecules generally have higher boiling points due to increased London dispersion forces), it is not the primary reason for HF's exceptionally high boiling point compared to other hydrogen halides.  The molar mass difference is not significant enough to account for the observed difference in boiling points.
C :x: Greater van der Waals forces in HF. Van der Waals forces are present in all hydrogen halides, but they are significantly weaker than hydrogen bonding.  While van der Waals forces increase with molar mass, this effect is overshadowed by the strong hydrogen bonding in HF.
D :x: HF's ability to form ionic bonds. HF primarily forms hydrogen bonds, not ionic bonds.  Ionic bonds are much stronger than hydrogen bonds, but HF does not form ionic bonds in its liquid phase.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing hydrogen bonding with other intermolecular forces: Students may incorrectly attribute the high boiling point to other weaker intermolecular forces.
   How to avoid: Focus on the electronegativity difference and the presence of hydrogen bonded to a highly electronegative atom.
  2.Overemphasizing molar mass: Students might wrongly assume that molar mass is the sole determinant of boiling point.
   How to avoid: Remember that the type of intermolecular force is more significant than molar mass in determining boiling point, especially when comparing molecules with vastly different intermolecular forces.
 **Quick Tips**:
  1.Look for hydrogen bonding when comparing the boiling points of molecules containing H, O, N, or F.
  2.Hydrogen bonding is an exceptionally strong intermolecular force compared to dipole-dipole or van der Waals forces.

Mr. S M HUSSAIN · Answer

The correct Option is "Strong intermolecular hydrogen bonding in HF."

Mr. S M HUSSAIN · Answer

Higher molar mass of HF.

Mr. S M HUSSAIN · Answer

Greater van der Waals forces in HF.

Mr. S M HUSSAIN · Answer

HF's ability to form ionic bonds.

NEET Chemistry Chemical Bonding and Molecular Structure H-Bond, Dipole Moment MCQs

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