Ion–dipole forces Transitional Reasoning Download PDF

Questions

1. 1.

   A student investigates the factors influencing the strength of ion–dipole attractions by analyzing the hydration enthalpies of various metal cations dissolved in water. The experimental data shows that water dipoles interact significantly more strongly with $\text{Mg}^{2+}$ than with $\text{Na}^{+}$, and that $\text{Mg}^{2+}$ also forms stronger interactions than $\text{Ca}^{2+}$. Based on the electrostatic principles governing ion–dipole forces, which deduction best accounts for these observed trends?

   • A) Ion–dipole attraction strength depends solely on the dipole moment of the solvent, so changing cation charge or size has negligible influence on the attraction.
   • B) A larger ionic radius enhances ion–dipole attraction because it provides more surface area for multiple water molecules to coordinate simultaneously.
   • C) The strength of ion–dipole attractions increases with a higher ionic charge and a smaller ionic radius due to the resulting higher charge density.
   • D) Cations with lower positive charges attract the partially positive hydrogen atoms of water molecules with less electrostatic repulsion.