1. Concentrations and Colligative Properties
SOLUTIONS II
Concentrations and Colligative Properties

2. Solution Concentrations
Always:
concentration = amount of solute_____
amount of solvent or solution
Expressed as relative amounts:
dilute or concentrated
unsaturated or saturated
Most often expressed with specific amounts of each component
CHM PGCC Barbara A. Gage

3. Percent Solution By volume: By mass: By mass/volume:
(volume must have the
same units)
By mass:
(mass must have the
By mass/volume:
(generally grams
and mL)
CHM PGCC Barbara A. Gage

4. Percent Solution
What is the % m/v of a solution containing 35 g of sodium sulfate in 500 mL of water solution?
What would the % be if the solute was potassium acetate?
2. Since the nature of the substance does not play a part in the calculation the % value does not change.
CHM PGCC Barbara A. Gage

5. Percent Solution
How many grams of copper (II) chloride are required to make 345 mL of a 25% solution (m/v)?
CHM PGCC Barbara A. Gage

6. Molarity (again)
Because many reactions happen between substances in solution, it is important to have a concentration based on moles.
CHM PGCC Barbara A. Gage

7. Molarity
How many grams of sodium phosphate are required to make 250 mL of a M solution?
CHM PGCC Barbara A. Gage

8. Reactions with Solutions
How many mL of 0.30 M NaCl are needed to react with 20.0 mL of 0.12 M Pb(NO3)2?
2 NaCl (aq) + Pb(NO3)2 (aq)  PbCl2 (s) + 2 NaNO3 (aq)
CHM PGCC Barbara A. Gage

9. Converting a concentrated solution to a dilute solution.
Figure 3.11
Converting a concentrated solution to a dilute solution.
CHM PGCC Barbara A. Gage

10. Dilution Calculations
For dilutions use the formula:
Ci x Vi = Cf x Vf
Where Ci = initial concentration
Vi = initial volume
Cf = final concentration
Vf = final volume
You can use any type of concentration or volume unit as long as they are the same.
CHM PGCC Barbara A. Gage

11. Dilution Calculations
How many mL of 0.50 M KCl are required to make 1.5 L of 0.20 M KCl?
CHM PGCC Barbara A. Gage

12. Colligative Properties
Properties that change depending on the number of particles dispersed in a solvent
Vapor pressure lowering
CHM PGCC Barbara A. Gage

13. The effect of a solute on the vapor pressure of a solution.
Figure 13.11
The effect of a solute on the vapor pressure of a solution.
CHM PGCC Barbara A. Gage

14. Colligative Properties
Properties that change depending on the number of particles dispersed in a solvent
Vapor pressure lowering
Boiling point elevation
Freezing point depression
CHM PGCC Barbara A. Gage

15. Phase diagrams of solvent and solution.
Figure 13.12
Phase diagrams of solvent and solution.
CHM PGCC Barbara A. Gage

16. Boiling and Freezing Point Changes
ΔTb = Kb x m where m= moles solute
kg solvent
Kb = boiling pt constant
ΔTf = Kf x m
Kf = freezing point constant
Applications…
CHM PGCC Barbara A. Gage

17. Table 13.5 Molal Boiling Point Elevation and Freezing Point
Depression Constants of Several Solvents
Boiling
Point (0C)*
Melting
Point (0C)
Solvent
Kb (0C/m)
Kf (0C/m)
Acetic acid
117.9
3.07
16.6
3.90
Benzene
80.1
2.53
5.5
4.90
Carbon disulfide
46.2
2.34
-111.5
3.83
Carbon tetrachloride
76.5
5.03
-23
30.
Chloroform
61.7
3.63
-63.5
4.70
Diethyl ether
34.5
2.02
-116.2
1.79
Ethanol
78.5
1.22
-117.3
1.99
Water
100.0
0.512
0.0
1.86
*at 1 atm.
CHM PGCC Barbara A. Gage

18. Colligative Properties
Properties that change depending on the number of particles dispersed in a solvent
Vapor pressure lowering
Boiling point elevation
Freezing point depression
Osmotic pressure – movement of solvent particles across a semipermeable membrane
CHM PGCC Barbara A. Gage

19. The development of osmotic pressure.
Figure 13.13
The development of osmotic pressure.
Applied pressure needed to prevent volume increase
osmotic pressure
pure solvent
solution
semipermeable membrane
net movement of solvent
CHM PGCC Barbara A. Gage

20. Osmotic Pressure Remember PV = nRT? P V = n R T P = n R T V Π = M RT
Where Π = osmotic pressure
M = molarity
CHM PGCC Barbara A. Gage

21. Osmosis and cells
When a cell is placed in a solution with a hypertonic (higher solute concentration but less water) water flows out of the cell and the cell shrinks (crenation).
When a cell is placed in a hypotonic solution (less solute but more water), water flows into the cell and the cell swells and may burst (hemolysis).
CHM PGCC Barbara A. Gage

22. i = Colligative Properties of Electrolyte Solutions
For electrolyte solutions, the compound formula
tells us how many particles are in the solution.
The van’t Hoft factor, i, tells us what the “effective” number of ions are in the solution.
van’t Hoff factor (i)
i =
measured value for electrolyte solution
expected value for nonelectrolyte solution
For vapor pressure lowering: P = i(solutex P0solvent)
For boiling point elevation: Tb = i(bm)
For freezing point depression: Tf = i(fm)
For osmotic pressure :  = i(MRT)
CHM PGCC Barbara A. Gage