CHEM 132, Chapter 10

• Solution


  Homogeneous mixture of a solute dissolved in a solvent
• Molarity


  Moles of solute per liters of solution
• Mass by percent


  Common for dilute aqueous solutions
• Mole fraction


  Moles of one substance per total moles of a mixture, commonly used for gas mixtures
• Molality


  Doesn't change with temperature, unlike molarity
• Like dissolves like


  A polar solvent must be used to dissolve a polar or ionic solute
• Solute-solute


  Breaks bonds/IMF and is endothermic
• Solvent-solvent


  Breaks bonds/IMF and is endothermic
• Solute-solvent


  Breaks bonds/IMF and is exothermic
• Oil and water don't mix


  Oil has weak IMF and is non polar so the solute-solvent interactions are very weak, therefore they can't overcome solvent-solvent interactions of water
• Enthalpy change


  Associated with the dispersal of a solute in water
• Factors that affect solubility


  • Structure- size, shape, polarity
  • Pressure-especially for gases
  • Temperature
• Molecular structure


  Determines polarity
• If solute and solvent are similar


  Solubility is favored
• Pressure has little effect on solubility of solids or liquids


  But significantly increases solubility of a gas
• If pressure is increased

  Gas concentration increases
• Henry's law

  The amount of gas dissolved is directly proportional to the pressure of gas above solution
• Most solids increase solubility in water with increasing temperature


  (some are opposite)
• Temperature dependence of a solid's solubility can be determined only with experiment
• Liquid solutions


  Have different physical properties than pure solvents
• Colligative property


  The fact that identity of a solute is irrelevant, only how much is present matters
• Colligative properties


  • Vapor pressure lowering
  • Freezing point depression
  • Boiling point elevation
  • Osmotic pressure
• Vapor pressure lowering


  The presence of a nonvolatile solute lowers the vapor pressure of a solvent
• Raoult's law


  The solute lowers the vapor pressure of a solvent
• Ideal solution


  A liquid-liquid solution that obeys Raoult's law
• For ideal solutions, the identity of solute doesn't matter, only moles of particles matter
• Solute-solute, solvent-solvent, and solute-solvent interactions are similar and not extremely strong in ideal solutions
• When solvent and solute strongly attract


  Solvent molecules cannot turn to vapor as easily
• When solvent and solute very weakly attract


  Solvent molecules can turn to vapor more easily
• Colligative properties want to be as dilute as possible
• Boiling point elevation


  A nonvolatile solute lowers vapor pressure of solvent, increasing boiling point
• Freezing point depression


  Freezing point of solutions are lower than that of pure solvent
• Osmotic pressure


  Excess pressure on solution arises because of difference in liquid levels
• Osmosis


  The flow of solvent into a solution through semi-permeable membrane that separates them
• Small concentrations of solution produce relatively large osmotic pressures and can characterize solutions and determine molar mass
• Isotonic solutions


  Have ideal osmotic pressures
• Van't Hoff Factor (i)

  The number of particles a solute breaks into
• To determine I, count the number of ions in a salt's formula (expected value)