Chemistry: Solubility and Intermolecular Forces

Solubility

• Definition: The ability of a substance to dissolve in a solvent to form a homogeneous mixture
• Factors affecting solubility:
  • Temperature: Increasing temperature generally increases solubility
  • Pressure: Increasing pressure generally increases solubility
  • Polarity: Polar solvents dissolve polar solutes, non-polar solvents dissolve non-polar solutes
  • Molecular size and shape: Smaller molecules are more soluble than larger ones
• Types of solubility:
  • Miscible: Two liquids that can mix in any proportion (e.g., water and ethanol)
  • Immiscible: Two liquids that cannot mix (e.g., oil and water)
  • Partially miscible: Two liquids that can mix in limited proportions (e.g., phenol and water)

Intermolecular Forces

• Definition: Weak forces between molecules that hold them together in a substance
• Types of intermolecular forces:
  • London dispersion forces: Weak forces between non-polar molecules (e.g., methane, CH₄)
  • Dipole-dipole forces: Forces between polar molecules with permanent dipoles (e.g., water, H₂O)
  • Hydrogen bonding: Strong forces between molecules with hydrogen bonded to a highly electronegative atom (e.g., water, ammonia)
  • Ion-dipole forces: Forces between ions and polar molecules (e.g., sodium chloride, NaCl)
• Strength of intermolecular forces:
  • London dispersion forces < dipole-dipole forces < hydrogen bonding < ion-dipole forces
• Effects of intermolecular forces:
  • Boiling point: Higher boiling point indicates stronger intermolecular forces
  • Melting point: Higher melting point indicates stronger intermolecular forces
  • Viscosity: Thicker, more viscous liquids have stronger intermolecular forces