1. Solution Properties 11.1 Solution Composition
11.2 The Energies of Solution Formation
11.3 Factors Affecting Solubility
11.4 The Vapor Pressures of Solutions
11.5 Boiling-Point Elevation and Freezing-Point Depression
11.6 Osmotic Pressure
11.7 Colligative Properties of Electrolyte Solutions
11.8 Colloids

2. Various Types of Solutions
Example
State of Solution
State of Solute
State of Solvent
Air, natural gas
Gas
Vodka, antifreeze
Liquid
Brass
Solid
Carbonated water (soda)
Seawater, sugar solution
Hydrogen in platinum

3. Solution Composition

4. Exercise #1
You have 1.00 mol of sugar in mL of solution. Calculate the concentration in units of molarity.
8.00 M

5. Exercise #2
You have a 10.0 M sugar solution. What volume of this solution do you need to have 2.00 mol of sugar?
0.200 L

6. Exercise #3
Consider separate solutions of NaOH and KCl made by dissolving g of each solute in mL of solution. Calculate the concentration of each solution in units of molarity.
10.0 M NaOH
5.37 M KCl

7. Exercise #4
What is the percent-by-mass concentration of glucose in a solution made my dissolving 5.5 g of glucose in 78.2 g of water?
6.6%

8. Exercise #5
A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in mL of water. Calculate the mole fraction of H3PO4. (Assume water has a density of 1.00 g/mL.)
0.0145

9. Exercise #6
A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in mL of water. Calculate the molality of the solution. (Assume water has a density of 1.00 g/mL.)
0.816 m

10. Formation of a Liquid Solution
Separating the solute into its individual components (expanding the solute).
Overcoming intermolecular forces in the solvent to make room for the solute (expanding the solvent).
Allowing the solute and solvent to interact to form the solution.

11. Steps in the Dissolving Process

12. Steps in the Dissolving Process
Steps 1 and 2 require energy, since forces must be overcome to expand the solute and solvent.
Step 3 usually releases energy.
Steps 1 and 2 are endothermic, and step 3 is often exothermic.

13. Enthalpy (Heat) of Solution
Enthalpy change associated with the formation of the solution is the sum of the ΔH values for the steps:
ΔHsoln = ΔH1 + ΔH2 + ΔH3
ΔHsoln may have a positive sign (energy absorbed) or a negative sign (energy released).

14. Enthalpy (Heat) of Solution

15. Concept Check
Explain why water and oil (a long chain hydrocarbon) do not mix. In your explanation, be sure to address how ΔH plays a role.

16. The Energy Terms for Various Types of Solutes and Solvents
Hsoln
Outcome
Polar solute, polar solvent
Large
Large, negative
Small
Solution forms
Nonpolar solute, polar solvent
Large, positive
No solution forms
Nonpolar solute, nonpolar solvent
Polar solute, nonpolar solvent

17. In General
One factor that favors a process is an increase in probability of the state when the solute and solvent are mixed.
Processes that require large amounts of energy tend not to occur.
Overall, remember that “like dissolves like”.

18. Factors Affecting Solubility
Structural Effects:
Polarity – “like dissolves like”
Pressure Effects:
Henry’s law – for solubility of gases
Temperature Effects:
Affecting aqueous solutions

19. Pressure Effects Henry’s law: c = kP
c = concentration of dissolved gas
k = constant
P = partial pressure of gas solute above the solution
Amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

20. A Gaseous Solute

21. Temperature Effects (for Aqueous Solutions)
Although the solubility of most solids in water increases with temperature, the solubilities of some substances decrease with increasing temperature.
Predicting temperature dependence of solubility is very difficult.
Solubility of a gas in solvent typically decreases with increasing temperature.

22. The Solubilities of Several Solids as a Function of Temperature

23. The Solubilities of Several Gases in Water

24. Ideal Solution: One that obeys Raoult’s Law

25. Vapor Pressures of Solutions of Nonvolatile Solutes
Nonvolatile solute lowers the vapor pressure of solvent.
Raoult’s Law:
Psoln = vapor pressure of solution
solv = mole fraction of solvent
= vapor pressure of pure solvent

26. Ideal Solutions Consisting of Two Volatile Liquids
Two volatile Liquids form ideal solution if:
they are structurally very similar, and
molecular interactions between nonidentical molecules were relatively similar to identical molecules.
The vapor of each liquid obeys Raoult’s Law:
PA = XAPoA; PB = XBPoB
PT = PA + PB = XAPoA + XBPoB
(X : mole fraction; Po : vapor pressure of pure liquid)

27. Summary of the Behavior of Various Types of Solutions of Two Volatile Liquids
Interactive Forces Between Solute (A) and Solvent (B) Particles
Hsoln
T for Solution Formation
Deviation from Raoult’s Law
Example
A  A, B  B  A  B
Zero
None (ideal solution)
Benzene-toluene
A  A, B  B < A  B
Negative (exothermic)
Positive
Negative
Acetone-water
A  A, B  B > A  B
Positive (endothermic)
Ethanol-hexane

28. Vapor Pressure for a Solution of Two Volatile Liquids

29. Laboratory Fractional Distillation Apparatus

30. Fractional Distillation Towers in Oil Refinaries

31. Refined Crude Oil Mixtures

32. Concept Check
For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation?
Hexane (C6H14) and chloroform (CHCl3)
Ethyl alcohol (C2H5OH) and water
Hexane (C6H14) and octane (C8H18)

33. Continue Next time…

34. Exercise #7 (a) The mole fractions of benzene and toluene;
A solution of benzene (C6H6) and toluene (C7H8) contains 50.0% benzene by mass. The vapor pressures of benzene and pure toluene at 25oC are 94.2 torr and 28.4 torr, respectively. Assuming ideal behavior, calculate the following:
(a) The mole fractions of benzene and toluene;
(b) The vapor pressure of each component in the mixture, and the total vapor pressure above the solution.
(c) The composition of the vapor in mole percent.

35. Exercise #8
A solution composed of 24.3 g acetone (CH3COCH3) and 39.5 g of carbon disilfide (CS2) has a measured vapor pressure of 645 torr at 35oC.
(a) Is the solution ideal or nonideal?
(b) If not, does it deviate positively or negatively from Raoult’s law?
(c) What can you say about the relative strength of carbon disulfide-acetone interactions compared to the acetone-acetone and carbon disulfide-carbon disulfide interaction?
(Vapor pressures at 35oC of pure acetone and pure carbon disulfide are 332 torr and 515 torr, respectively.)