1. Colligative Properties of Solutions
Section 2 Colligative Properties of Solutions
Chapter 13
Colligative Properties of Solutions
Colligative properties - properties that depend on the concentration of solute particles but not on their identity
Vapor-Pressure Lowering
Freezing-Point Depression
Boiling-Point Elevation
Osmotic Pressure

2. Vapor-Pressure Lowering
Section 2 Colligative Properties of Solutions
Chapter 13
Vapor-Pressure Lowering
Nonvolatile substance - has little tendency to become a gas under existing conditions.
The boiling point and freezing point of a solution differ from those of the pure solvent.
A nonvolatile solute raises the boiling point and lowers the freezing point.

3. Comparing Volatile and Nonvolatile Liquids
Visual Concepts
Chapter 13
Comparing Volatile and Nonvolatile Liquids
Click below to watch the Visual Concept.
Visual Concept

4. Section 2 Colligative Properties of Solutions
Chapter 13

5. Vapor Pressures of Pure Water and a Water Solution
Section 2 Colligative Properties of Solutions
Chapter 13
Vapor Pressures of Pure Water and a Water Solution

6. Freezing-Point Depression
Section 2 Colligative Properties of Solutions
Chapter 13
Freezing-Point Depression
Freezing-point depression, ∆tf - difference between the freezing points of the pure solvent and a solution of a nonelectrolyte in that solvent.
Molal freezing-point constant (Kf ) - freezing-point depression of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute.
∆tf = Kfm

7. Molal Freezing-Point and Boiling-Point Constants
Section 2 Colligative Properties of Solutions
Chapter 13
Molal Freezing-Point and Boiling-Point Constants

8. Freezing-Point Depression
Visual Concepts
Chapter 13
Freezing-Point Depression
Click below to watch the Visual Concept.
Visual Concept

9. Freezing-Point Depression
Section 2 Colligative Properties of Solutions
Chapter 13
Freezing-Point Depression
Sample Problem C
What is the freezing-point depression of water in a solution of 17.1 g of sucrose, C12H22O11, in 200. g of water? What is the actual freezing point of the solution?

10. Boiling-Point Elevation
Section 2 Colligative Properties of Solutions
Chapter 13
Boiling-Point Elevation
Boiling-point elevation, ∆tb - difference between the boiling points of the pure solvent and a nonelectrolyte solution of that solvent.
Molal boiling-point constant (Kb) - boiling-point elevation of the solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute.
∆tb = Kbm

11. Boiling-Point Elevation and the Presence of Solutes
Visual Concepts
Chapter 13
Boiling-Point Elevation and the Presence of Solutes
Click below to watch the Visual Concept.
Visual Concept

12. Boiling-Point Elevation
Section 2 Colligative Properties of Solutions
Chapter 13
Boiling-Point Elevation
Sample Problem E
What is the boiling-point elevation of a solution made from 20.1 g of a nonelectrolyte solute and g of water? The molar mass of the solute is 62.0 g.

13. Chapter 13 Osmotic Pressure
Section 2 Colligative Properties of Solutions
Chapter 13
Osmotic Pressure
Semipermeable membrane - allows the passage of some particles while blocking the passage of others.
Osmosis - movement of solvent through a semipermeable membrane from the side of lower solute concentration to the side of higher solute concentration
Osmotic pressure - external pressure that must be applied to stop osmosis.

14. Chapter 13 Osmotic Pressure
Section 2 Colligative Properties of Solutions
Chapter 13
Osmotic Pressure

15. Electrolytes and Colligative Properties
Section 2 Colligative Properties of Solutions
Chapter 13
Electrolytes and Colligative Properties
Electrolytes depress the freezing point and elevate the boiling point of a solvent more than expected.
Electrolytes produce more than 1 mol of solute particles for each mole of compound dissolved.
mol of solute particles 1 2 3

16. Chapter 13 Calculated Values for Electrolyte Solutions
Section 2 Colligative Properties of Solutions
Chapter 13
Calculated Values for Electrolyte Solutions
Colligative properties depend on the total concentration of solute particles.
The changes in colligative properties caused by electrolytes will be proportional to the total molality of all dissolved particles, not to formula units.
For the same molal concentrations of sucrose and sodium chloride, you would expect the effect on colligative properties to be twice as large for sodium chloride as for sucrose.

17. Electrolytes and Colligative Properties
Section 2 Colligative Properties of Solutions
Chapter 13
Electrolytes and Colligative Properties
Sample Problem F
What is the expected change in the freezing point of water in a solution of 62.5 g of barium nitrate, Ba(NO3)2, in 1.00 kg of water?

18. Electrolytes and Colligative Properties
Section 2 Colligative Properties of Solutions
Chapter 13
Electrolytes and Colligative Properties
Sample Problem F Solution
Given: solute mass and formula = 62.5 g Ba(NO3)2
solvent mass and identity = 1.00 kg water
∆tf = Kfm
Unknown: expected freezing-point depression
Solution:

19. Electrolytes and Colligative Properties
Section 2 Colligative Properties of Solutions
Chapter 13
Electrolytes and Colligative Properties
Sample Problem F Solution
Solution:

20. Electrolytes and Colligative Properties
Section 2 Colligative Properties of Solutions
Chapter 13
Electrolytes and Colligative Properties
Sample Problem F Solution
Solution:
Each formula unit of barium nitrate yields three ions in solution.

21. Chapter 13 Actual Values for Electrolyte Solutions
Section 2 Colligative Properties of Solutions
Chapter 13
Actual Values for Electrolyte Solutions
The actual values of the colligative properties for all strong electrolytes are almost what would be expected based on the number of particles they produce in solution.

22. Chapter 13 Actual Values for Electrolyte Solutions
Section 2 Colligative Properties of Solutions
Chapter 13
Actual Values for Electrolyte Solutions
The differences between the expected and calculated values are caused by the attractive forces that exist between dissociated ions in aqueous solution.
According to Debye and Hückel a cluster of hydrated ions can act as a single unit rather than as individual ions, causing the effective total concentration to be less than expected.
Ions of higher charge have lower effective concentrations than ions with smaller charge.