(a) Considering the energetics of solute-solute, solventsolvent, and solute- solvent interactions, explain why \(\mathrm{NaCl}\) dissolves in water but not in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right) .\) (b) What factors cause a cation to be strongly hydrated?

To explain the solubility of NaCl in water and benzene, we need to discuss three types of interactions: solute-solute interactions, solvent-solvent interactions, and solute-solvent interactions. * Solute-solute interactions: NaCl is an ionic compound, which means it consists of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). These ions are held together by strong ionic bonds. * Solvent-solvent interactions: In both water and benzene, the molecules are attracted to each other by intermolecular forces. Water has strong hydrogen bonding, while benzene has weaker dispersion forces. * Solute-solvent interactions: These interactions occur between the solute (NaCl) and the solvent (water or benzene).

When NaCl is added to water, the positive and negative ends of the water molecules are attracted to the respective oppositely charged ions of NaCl. These interactions are strong enough to break the ionic bonds in NaCl, causing it to dissolve. Moreover, the energy released during the process of solvation (formation of solute-solvent interactions) compensates for the energy required to break solute-solute and solvent-solvent interactions. Therefore, NaCl dissolves in water.

When NaCl is added to benzene, the much weaker dispersion forces between benzene molecules are unable to break the ionic bonds in NaCl. Additionally, the energy released during the solvation process in benzene is not sufficient to compensate for the energy required to break solute-solute and solvent-solvent interactions. Therefore, NaCl does not dissolve in benzene.

There are several factors that cause a cation to be strongly hydrated: * Charge: Cations with a higher charge have a stronger electrostatic attraction to the negative ends of water molecules, resulting in stronger hydration. * Size: Smaller cations have a greater charge density, which means the charge is concentrated over a smaller area. This increases the electrostatic attraction between the cation and water molecules, leading to stronger hydration. * Polarizability: Cations with a higher polarizability can induce dipoles in nearby water molecules, further increasing the strength of solute-solvent interactions and resulting in stronger hydration. In conclusion, NaCl dissolves in water due to strong solute-solvent interactions, while it does not dissolve in benzene because of weak solute-solvent interactions. Factors that cause a cation to be strongly hydrated include higher charge, smaller size, and greater polarizability.