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Colligative Properties

Colligative Properties. Boiling point Vapor pressure Freezing point Osmotic pressure. Colligative: particles are particles. Physical vs Chemical. Mixing is physical process; chemical properties don’t change Properties of solutions are similar to those of the pure substances

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Colligative Properties

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  1. Colligative Properties Boiling point Vapor pressure Freezing point Osmotic pressure

  2. Colligative: particles are particles

  3. Physical vs Chemical • Mixing is physical process; chemical properties don’t change • Properties of solutions are similar to those of the pure substances • Addition of a foreign substance to water alters the properties slightly

  4. Colligative properties for nonvolatile solutes: Temperature Heat added

  5. Counting particles • 1 mole of a molecular solid → 1 mole of particles • 1 mole of NaCl→ Na+ + Cl- 2 moles of particles • 1 mole of CaCl2 → Ca2++ 2 Cl- 3 moles of particles Van’t Hoff factor

  6. Electrolytes Electrolytes are simply dissolved ions like Na+ or K+ Non electrolytes are molecular compounds like sugar

  7. Colligative properties How it works

  8. Which would evaporate quickest ?

  9. Raoult's Law VP = VPsolv x mole of solvent Total moles of particles

  10. Elevation of boiling point

  11. BPttotal = BPtsolv + ΔTb where ΔTb = molality * Kb * i with Kb = ebullioscopic constant (0.52°C kg/mol for water) i = Van't Hoff factor

  12. Depression of freezing point

  13. FPttotal = FPtsolvent - ΔTf where ΔTf = molality * Kf * I Kf = cryoscopic constant (1.86°C kg/mol for water) i = Van't Hoff factor

  14. Depression of osmotic pressure

  15. CFU 1 • What does non volatile mean? • Which non volatile solute NaCl or Glucose Would have the have the most impact on vapor pressure? • Which would have the most impact on Boiling point?

  16. CFU 1 • If you add 1 mole of NaCl to 100g grams of water what is the Molality • What is the difference between molality and Molarity

  17. CFU 2 • What is a nonelectrolyte? • What is meant by aqueous? • What is the value of Kb for water? • What is the value of Kf for water?

  18. CFU 2 • What would be the boiling point and freezing point of a 0.625m aqueous solution of any nonvolatile, nonelectrolyte solute? • non electrolyte means VHF of 1 • ΔTf = VHF x m x Kf • = 1 x 0.625 x -1.86 • = -1.1625Freezing point = 0 -1.1625 • ΔTb = VHF x m x Kb • = 1 x 0.625 x +0.52 • = 0.325 Boiling point = 100 +0.325 = 100.325oC

  19. Liquid

  20. Temperature Heat added

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