Which intermolecular force is dominant in a mixture of NH_3 and KCl?

• A. London dispersion forces
• B. Ion-dipole interactions
• C. Hydrogen bonding
• D. Dipole-dipole interactions

Answer: (B)

Verified step by step guidance

1. Identify the types of species present in the mixture: NH_3 is a polar molecule capable of hydrogen bonding, and KCl is an ionic compound that dissociates into K^+ and Cl^- ions in solution.
2. Recall the main types of intermolecular forces: London dispersion forces (present in all molecules), dipole-dipole interactions (between polar molecules), hydrogen bonding (a special strong dipole-dipole interaction involving N, O, or F bonded to H), and ion-dipole interactions (between ions and polar molecules).
3. Consider that KCl dissociates into ions, so the interactions involving ions and polar molecules (ion-dipole interactions) are possible and often stronger than dipole-dipole or hydrogen bonding in mixtures containing ions.
4. Compare the strength of forces: ion-dipole interactions are generally stronger than hydrogen bonding and dipole-dipole interactions because they involve full charges interacting with dipoles, rather than partial charges.
5. Conclude that in a mixture of NH_3 and KCl, the dominant intermolecular force is ion-dipole interactions between the NH_3 molecules (dipoles) and the K^+ and Cl^- ions.