Question

7. (10 pts) List the intermolecular forces between the compounds in the previous problem and water. ict will have the highest solubility in water, and which the lowest? Explain

Answer 1

Types of Intermolecular Forces

1. Ion-Dipole Forces (these may not be true IMF, but we will call them IMFs)
   • Solutions
2. Dipole-Dipole Forces (between two polar molecules)
   • Pure substance or solutions
3. Hydrogen Bonding (special type of dipole-dipole)
   • Pure substance or solutions
4. Dipole-Induced Dipole (between polar and nonpolar molecules)
   • Solutions
5. Instantaneous Dipole-Induced Diploe (between two nonpolar molecules, often called London Dispersion Forces)
   1. Solutions or Pure Substances

Intermolecular Forces: Effect on Solubility Main Idea: “Like dissolves like.” The stronger the intermolecular forces between solute molecule and solvent molecule, the greater the solubility of the solute in the solvent.

• Polar molecules are soluble in polar solvents (Predominant intermolecular force is dipole-dipole attraction between polar solute molecule and polar solvent molecule).

• Nonpolar molecules are soluble in nonpolar solvents (Predominant intermolecular force is London dispersion attraction between nonpolar solute molecule and nonpolar solvent molecule).

• Polar molecules and nonpolar molecules do not mix.

Trends

1. Between two polar molecules, the molecule with the smaller hydrocarbon portion (or the larger polar portion) is more soluble in water.

CH₃CH₂OH Soluble in water

CH₃CH₃CH₃CH₃CH₃CH₂OH Insoluble in water CH₂(OH)CH(OH)CH(OH)CH(OH)CH(OH)CH₂OH Soluble in water. Large but many OHs that can hydrogen bond with water.

2. If completely nonpolar, insoluble in water (and soluble in nonpolar solvents).

CH₃CH₃CH₃CH₃CH₃CH₃ Insoluble in water