AP Chemistry Unit 3.10 Solubility

Solutions and Solubility

  • “Like dissolves Like” (don’t say it in exam) → Water dissolves polar molecules (have dipole moment) and does not dissolve nonpolar molecules
    • polar–polar and nonpolar–nonpolar → are more attracted to each other than themselves → the heat of solution is expected to be small → solution forms because the process is energetically favorable
    • Nonpolar-Nonpolar: the larger and more polarizable the electron cloud = stronger LDF = the more interactions will occur with the solvent → increases solubility
  • Solutions form when the solute and solvent attract to each other more than themselves
  • Polar–nonpolar and nonpolar–polar → are more attracted to themselves than each other → heat of solution is expected to be large and positive → large amount of energy required prevents solution formation

Solution Particle Diagrams

  • In questions, will have to show charges on ions, multiple water molecules oriented correctly, correct sizes (anion bigger than cation) and number of particles

 Factors Affecting Solubility

Structure Effects

  • Substances with similar intermolecular forces tend to be soluble (solid solute) in one another
    • Molecular structure determines polarity → structure and solubility are connected
  • Hydrocarbons: Long chains of covalently bonded carbon and hydrogen
    • Nonpolar (Hydrophobic)
      • Only polar if has electronegative charge (O2, Su, F, N → electronegative atoms)

 Pressure Effects

  • Pressure does not affect the solubilities of solids or liquids but does increase the solubility of a gas
  • Pressure increases → compresses gas molecules, creating room for additional gas molecules and forcing more of them into the solution

Temperature Effects (For Aqueous Solutions)

  • Most solids are more soluble at higher temps (there are some important exceptions), but the amount of solid that can be dissolved may increase or decrease with increasing temperature
  • Solubility of gasses in liquids decreases with increasing temperature
    • Increasing temp → increases KE of gas particles → causes more motion and they break interMF more easily → solute and solvent can’t interact to form a solution as efficiently

Intermolecular Forces

  • Stronger InterMF → increases attraction between the solute molecules and solvent → increases solubility
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