Colligative Colligative PropertiesProperties
Learning Target:What are the four colligative properties of solutions?Determine the boiling point elevation and freezing point depression of a solution.
Main IdeaMain Idea• Colligative properties depend on the
number of solute particles in a solution.
Colligative PropertyColligative Property• Colligative properties are 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 colligative properties:– Vapor Pressure Reduction– Boiling Point Elevation– Freezing point depression– Osmotic Pressure
Vapor Pressure ReductionVapor 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.
Boiling Point Elevation (Boiling Point Elevation (ΔΔTTbb))
• 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.
Boiling Point ElevationBoiling Point Elevation
Boiling Point Elevation (Boiling Point Elevation (ΔΔTTbb))
• ΔTb = Kbm
• Kb = boiling point elevation constant
• m= molality
Freezing Point Depression Freezing Point Depression ((ΔΔTTff))
• 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
Osmotic PressureOsmotic Pressure• Osmosis: The movement
of water molecules from high water concentration to low water concentration.
• Osmotic pressure is the amount of additional pressure caused by water molecules that moved into the concentrated solution.
Osmotic Pressure & types of Osmotic Pressure & types of solutionssolutions
• 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
ExamplesExamples• 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
Example 2Example 2• What is the freezing point depression
when 153g of bromine is added to 1000. g of benzene?