Which compound has a higher boiling point, HF or HCl, and what is the main reason for this difference?

• A. HF, because it is a nonpolar molecule.
• B. HF, because it forms strong hydrogen bonds between its molecules.
• C. HCl, because it has a higher molar mass than HF.
• D. HCl, because it is more acidic than HF.

Answer: (B)

Verified step by step guidance

1. Identify the types of intermolecular forces present in HF and HCl molecules. HF molecules exhibit hydrogen bonding due to the highly electronegative fluorine atom bonded to hydrogen, while HCl molecules primarily exhibit dipole-dipole interactions and London dispersion forces.
2. Recall that hydrogen bonding is a particularly strong type of dipole-dipole interaction that significantly increases the boiling point of a substance compared to molecules that do not form hydrogen bonds.
3. Consider the molecular polarity: HF is a polar molecule with a strong dipole moment, and the presence of hydrogen bonding leads to stronger intermolecular attractions than in HCl, which is also polar but lacks hydrogen bonding.
4. Evaluate the effect of molar mass on boiling point: although HCl has a higher molar mass than HF, the difference in intermolecular forces (hydrogen bonding vs. dipole-dipole) has a greater impact on boiling point than molar mass alone.
5. Conclude that HF has a higher boiling point than HCl primarily because HF molecules form strong hydrogen bonds, which require more energy (higher temperature) to break during the phase change from liquid to gas.