1. Colligative Properties
Section 15.3
Colligative Properties

2. Colligative Properties
Physical properties of solutions that depend on the number – not the identity – of solute particles dissolved
The greater the number of particles dissolved in solution, the greater the effect on colligative properties

3. Electrolytes
Ionic compounds dissociate in water when forming a solution
The solutions formed conduct electric currents
These compounds are called electrolytes
Some molecular compounds also ionize in aqueous solution and are called electrolytes

4. KCl(s) → K+(aq) + Cl-(aq)
Electrolytes
KCl(s) → K+(aq) + Cl-(aq)
One mole of KCl produces one mole of potassium ions (K+) and one mole of chloride ions (Cl-)
The number of particles in solution is greater than the number of particles in the solid KCl

5. Electrolytes
Strong electrolytes ionize completely and produce many ions in solution
Weak electrolytes only partially ionize

6. Nonelectrolytes
Many molecular compounds dissolve but do not form ions in solution
They form solutions that do not conduct electric currents
These substances are known as nonelectrolytes
One mole of a nonelectrolyte will form only one mole of particles in solution

7. Nonelectrolytes C12H22O11(s) → C12H22O11(aq)
One mole of sucrose produces one mole of sucrose particles in solution
The number of particles in solution is equal to the number of particles in the solid sucrose

8. Greatest Effect?
Which would have the greatest effect on colligative properties?
Mg(NO3)2
Three moles of particles in solution
C6H12O6(s)
One mole of particles in solution
AlBr3(s)
Four moles of particles in solution
HCl(s)
Two moles of particles in solution
AlBr3
→ Mg+2(aq) + 2NO3-(aq)
→ C6H12O6(aq)
→ Al+3(aq) + 3Br-(aq)
→ H+(aq) + Cl-(aq)

9. Colligative Properties
Vapor Pressure Lowering
Vapor pressure: pressure exerted by liquid particles that have escaped the liquid’s surface and entered gaseous state
When only water molecules occupy the surface, any water molecule with enough energy will evaporate

10. Colligative Properties
Vapor Pressure Lowering
In a solution, the surface area of the liquid is occupied by solute and solvent particles, decreasing area from which water can escape
Fewer water molecules leave solution, resulting in lower vapor pressure

11. Colligative Properties
Vapor Pressure Lowering
Vapor pressure is a colligative property because it changes due to the addition of solute particles
With more solute particles in solution, fewer water molecules at the surface escape into the gaseous state
Thus, the vapor pressure decreases

12. Colligative Properties
Boiling Point Elevation
Boiling point: the temperature at which vapor pressure of substance equals atmospheric pressure; substance can move to gaseous state
Boiling point of water is 100°C
Adding solute lowers the vapor pressure for solution
Solution particles must have more energy to vaporize or boil

13. Colligative Properties
Boiling Point Elevation
More kinetic energy is necessary
Heating to a higher temperature provides the energy necessary to raise the vapor pressure to atmospheric pressure
Boiling point elevation is the temperature difference between the boiling point of pure solvent and that of solution
Colligative property because the greater the number of particles in solution , the greater the boiling point elevation

14. Colligative Properties Quiz
Colligative properties depend on the __________ of solute particles, not the identity.
Which substance has the greatest effect on colligative properties?
KCl C12H22O11 CaCl2 NaCl
Vapor pressure is caused by particles in a closed container entering the __________ state. Adding a solute _______ the vapor pressure.
________ occurs when the vapor pressure equals the atmospheric pressure. Adding a solute will __________the boiling point.
number
gaseous
lowers
Boiling
elevate

15. Colligative Properties
Freezing Point Depression
Freezing point: the temperature at which particles do not have sufficient energy to overcome interparticle attraction and move into the organized structure of solid state
Adding solute interferes with attractive forces and prevents freezing
Temperature must be lowered even more to freeze

16. Colligative Properties
Freezing Point Depression
Freezing point depression: temperature difference between freezing point of pure solvent and of solution
Practical Applications of Freezing Point Depression
De-icing highways with calcium chloride or magnesium chloride during winter
Using rock salt (mineral form of sodium chloride) with ice to make ice cream

17. Colligative Properties
Osmotic Pressure
Osmosis: diffusion of solvent particles through a semipermeable membrane from an area of high solvent concentration to lower solvent concentration
A semipermeable membrane is a thin sheet of a substance with pores, which acts as a barrier allowing some particles, but not others, to cross

18. Colligative Properties
Osmotic Pressure
When a dilute solution (or pure solvent) is separated from a concentrated solution by a semipermeable membrane, water molecules (solvent) move from the dilute solution to the concentrated one but solute particles do not
Dilute Solution
low solute/high solvent
semipermeable membrane
Concentrated Solution
high solute/low solvent
H2O

19. Colligative Properties
Osmotic Pressure
Osmotic pressure is the additional pressure caused by water molecules moving across the semipermeable barrier
Colligative property because it depends upon the number of solute particles in a specified volume of solution

20. Colligative Properties Quiz
Adding a solute will _______________ the freezing point.
Practical applications of this colligative property include:
____________________
Diffusion of solvent particles across a semipermeable membrane is called __________. Particles move from a _______ solution to a _____________solution.
Pressure caused by water moving across the semipermeable membrane is known as _______________
depress/lower
De-icing highways
Making ice cream
osmosis
dilute
concentrated
osmotic pressure

21. Colligative Properties
Respond to three questions at bottom of page 12 in Solutions Notes.
Questions should be completed for Unit 8 Notebook Check

22. Your GO-GO-MO Table should have three completed entries.
Topic
My Info About Topic (GO)
A Friend’s Info (GO)
A Different Friend’s Info (MO)
Homogeneous mixtures
Solvation process
Factors affecting solvation
Your GO-GO-MO Table should have three completed entries.

23. Add the next five topics to your table as indicated above.
GO-GO-MO
Topic
My Info About Topic (GO)
A Friend’s Info (GO)
A Different Friend’s Info (MO)
Like dissolves like
Solution concentration
Molarity
Preparing molar solutions
Colligative properties
Add the next five topics to your table as indicated above.