Worksheet: Solvation

In this worksheet, we will practice describing the solvation mechanisms of molecules and ionic solids and the enthalpic and entropic changes involved.

Q1:

Why are Na+ and Cl ions strongly solvated in water but not in hexane?

  • AIon-dipole forces between the ions and water are stronger than the hexane-ion forces because hexane is nonpolar and thus interacts with ions far more weakly.
  • BChloride ions deprotonate water molecules, and the resulting ion-ion interactions are stronger in total than the ionic bonds of sodium chloride. Hexane cannot be deprotonated and thus interacts with ions far more weakly.
  • CHexane molecules are much larger than water molecules, so they cannot pack around the small sodium and chloride ions as easily as water can.
  • DDissolution of ions in hexane is entropically costly, as interactions with ions force the hexane molecules into less flexible folded conformations.
  • EWater molecules are bent, so ions can occupy the space between OH bonds. Hexane molecules are straight and thus cannot interact with ions in this way.

Q2:

Fill in the blanks: Typically, as the temperature of the solvent increases, solids become soluble, and gases become soluble.

  • Amore, more
  • Bless, less
  • Cmore, less
  • Dless, more

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