Lecture Notes: Factors Affecting Solubility (Section 4.2)

Overview

• Three main factors affecting solubility:
  1. Solute-solvent interaction
  2. Pressure
  3. Temperature

Solute-Solvent Interaction

• General Rule: Like dissolves like
• Polar Compounds: Dissolve in other polar compounds
  • Example: Methanol and water (both have hydrogen bonding)
• Nonpolar Compounds: Dissolve in other nonpolar compounds
  • Example: Hexane and benzene (both have London dispersion forces)
• Key Criterion: Attraction between molecules of solute and solvent must be strong enough to overcome the attraction between same type molecules

Examples

• Ethanol and Water
  • Both are polar; both have hydrogen bonding
  • Ethanol is soluble in water
• Octane and Hexane
  • Both are nonpolar; both have London dispersion forces
  • Octane is soluble in hexane
• Octane and Water
  • Octane is nonpolar; water is polar
  • Octane is insoluble in water

Effect of Pressure

• Significant for gases in liquid solvents
• Direct Relationship: Solubility of a gas increases with pressure
  • Higher pressure forces more gas molecules to dissolve

Effect of Temperature

• Gases in Liquids
  • Solubility decreases with increasing temperature
    • Higher temperature increases energy of gas molecules, making them escape from the liquid
• Solids in Liquids
  • Solubility increases with increasing temperature
    • Higher temperature increases energy of solvent molecules, enabling them to break solute intermolecular interactions more effectively