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Colligative Properties

Colligative Properties . Learning Target: What are the four colligative properties of solutions? Determine the boiling point elevation and freezing point depression of a solution. Main Idea. Colligative properties depend on the number of solute particles in a solution.

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Colligative Properties

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  1. Colligative Properties Learning Target: What are the four colligative properties of solutions? Determine the boiling point elevation and freezing point depression of a solution.

  2. Main Idea • Colligative properties depend on the number of solute particles in a solution.

  3. Colligative Property • Colligative propertiesare physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles. • Ionic compounds are electrolytes because they dissociate in water to form a solution that conducts electricity. • Some molecular compounds are also electrolytes.

  4. 4 colligative properties: • Vapor Pressure Reduction • Boiling Point Elevation • Freezing point depression • Osmotic Pressure

  5. Vapor Pressure Reduction • Molecules of nonvolite solute take up space, thus preventing some solvent molecules to vaporize. • Condensation continues at the same rate, but vaporization slows down. • Since condensation > vaporization, vapor pressure is reduced.

  6. Boiling Point Elevation (ΔTb) • Adding a nonvolite solute, reduces vapor pressure, more energy is needed to make the solutions boil, raising the boiling point. • Boiling point elevation = BP of the solution - BP of the solvent. • Directly proportional to the number of solute molecules.

  7. Boiling Point Elevation

  8. Boiling Point Elevation (ΔTb) • ΔTb = Kbm • Kb = boiling point elevation constant • m= molality

  9. Freezing Point Depression (ΔTf) • The ability of a solute to lower freezing point of the solution. • Directly proportional to the molality of the solute. • ΔTf = Kfm • Kf = freezing point depression constant • m= molality

  10. Osmotic Pressure • Osmosis: The movement of water molecules from high water concentration to low water concentration. • Osmotic pressureis the amount of additional pressure caused by water molecules that moved into the concentrated solution.

  11. Osmotic Pressure & types of solutions • Isotonic concentration: solute concentration is the same on both sides of the membrane. • Hypertonic: higher solute concentration than the solution • Hypotonic: lower solute concentration than the solution

  12. Examples • 1. How much will the boiling point of water be elevated if 100. g of sucrose (C12H22O11) is added to 500.g of water? Kb for water is 0.52 °C/m. • ΔTb = kbx m

  13. Example 2 • What is the freezing point depression when 153g of bromine is added to 1000. g of benzene?

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