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?