Lecture 16.3- Colligative Properties


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Section 16.3 lecture, on colligative properties of solutions, for honors and prep chemistry

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Lecture 16.3- Colligative Properties

  1. 1. Bellwork Write out a numbered list of steps that you could follow to prepare a 1M aqueous solution of KCl.
  2. 2. Colligative Properties of Solutions The wood frog is a remarkable creature because it can survive being frozen. Scientists believe that a substance in the cells of this frog acts as a natural antifreeze, which prevents the cells from freezing. You will discover how a solute can change the freezing point of a solution.
  3. 3. 16.3 Vapor-Pressure Lowering Colligative properties depend on the number of dissolved particles. It doesn’t matter what type of particle it is.
  4. 4. 16.3 Three important colligative properties of solutions are • vapor-pressure lowering • boiling-point elevation • freezing-point depression
  5. 5. 16.3 In a pure solvent, equilibrium is established between the liquid and the vapor.
  6. 6. 16.3 In a solution, solute particles reduce the number of free solvent particles able to escape the liquid. Equilibrium is established at a lower vapor pressure.
  7. 7. 16.3 The decrease in a solution’s vapor pressure is proportional to the number of particles the solute makes in solution.
  8. 8. 1 mol glucose = 1 mol particles 1 mol NaCl = 2 mol particles (1 mol Na+ and 1 mol Cl-) 1 mol CaCl2 = 3 mol particles (1 mol Ca2+ and 2 mol Cl-) 1 mole of CaCl2 has the most effect because it makes more particles
  9. 9. 16.3 The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent is the freezing-point depression.
  10. 10. 16.3 The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity.
  11. 11. 16.3 Adding salt to icy roads and sidewalks lowers the freezing point of water. Much or all of the ice will melt.
  12. 12. 16.3 Boiling-Point Elevation The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent is the boiling-point elevation. The same antifreeze added to automobile engines to prevent freeze-ups in winter, protects the engine from boiling over in summer.
  13. 13. 16.3 The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent. The boiling point of water increases by 0.512°C for every mole of particles that the solute forms when dissolved in 1000 g of water.
  14. 14. Colligative Properties depend on the amount of dissolved particles NOT THE TYPE. These are the same thing. Lower Vapor pressure is lowered vapor pressure = higher boiling point!! Boiling point is elevated The temperature range over which water is a liquid is Freezing point is depressed increased.