Exam Study Notes

Solubility in Pentane

• The substance with the greatest solubility in pentane (CH3CH2CH2CH2CH3) would be nonpolar. Pentane is a nonpolar solvent, and "like dissolves like".
• CCl4 (Carbon Tetrachloride) is nonpolar due to its symmetrical tetrahedral structure, allowing it to dissolve best in pentane.

Ion Interaction with Water

• Ions interact with water through ion-dipole interactions.
• Smaller ions with higher charge densities interact more strongly with water.
• Li+ (Lithium ion) would interact the strongest with water because it is the smallest.
• Na+ interacts the weakest with water

Intermolecular Forces

• London Dispersion Forces: These are present in all molecules and arise from temporary fluctuations in electron distribution. Example: He---CH4 and CCl4---CCl4
• Dipole-Induced Dipole: Occurs between a polar molecule and a nonpolar molecule where the polar molecule induces a temporary dipole in the nonpolar molecule. Example: H2O---CH4
• Dipole-Dipole: Occurs between two polar molecules. Example: NH3---PCl3
• Hydrogen Bond: A particularly strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (N, O, F). Example: CH3OH---NH3 and H2O---H2O
• Ion-Dipole: Occurs between an ion and a polar molecule. Example: Na+---H2O

Polarity of Molecules

• Polar Molecules: Have an uneven distribution of electron density due to differences in electronegativity and molecular geometry, resulting in a net dipole moment.
• Nonpolar Molecules: Have an even distribution of electron density, either because the bonds are nonpolar or because the polar bonds are arranged symmetrically and cancel each other out.

Solubility in Water

• Molecules that are the least soluble in water are nonpolar. "Like dissolves like," thus nonpolar solutes do not dissolve well in a polar solvent like water.
• From the given options, CH3CH2CH2CH3 is the least soluble in water because it is nonpolar.
• Molecules that are most likely to have the greatest solubility in water are polar and capable of hydrogen bonding.
• NH3 is most likely to have the greatest solubility in water due to its polarity and ability to form hydrogen bonds.

Benzene and Water Interactions

• Benzene (C6H6) is sparingly soluble in water because it is a nonpolar molecule.
• The intermolecular forces of attraction between water and benzene are dipole-induced dipole and London dispersion interactions.
• Water, being polar, can induce a temporary dipole in benzene, leading to dipole-induced dipole interactions.
• London dispersion forces are present between all molecules, including water and benzene.