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
| Interaction | Intermolecular Force |
|---|---|
| He---CH4 | London Dispersion |
| Na+---H2O | Ion-Dipole |
| CCl4---CCl4 | London Dispersion |
| NH3---PCl3 | Dipole-Dipole |
| H2O---CH4 | Dipole-Induced Dipole |
| CH3OH---NH3 | Hydrogen Bond |
| H2O---H2O | Hydrogen Bond |
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.
| Molecule | Polarity |
|---|---|
| NH3 | Polar |
| H2O | Polar |
| CH4 | Nonpolar |
| CCl4 | Nonpolar |
| CH3OH | Polar |
| CH3CH2NH2 | Polar |
| CH3CH2CH2CH3 | Nonpolar |
| CO2 | Nonpolar |
| CH3OCH3 | Polar |
| CH3COOH | Polar |
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.