1. Physical Properties of Solutions
Chapter 12

2. Solution Formation
A solution is a homogeneous mixture of two or more substances, consisting of ions or molecules.
A colloid, although it also appears to be homogeneous, consists of comparatively large particles of a substance dispersed throughout another substance.
In this chapter, we will examine the properties of each of these systems. 2

3. A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount

4. Types of Solutions Solutions may exist as gases, liquids, or solids.
The solute is the dissolved substance. In the case of a solution of a gas or solid in a liquid, it is the gas or solid. Otherwise, it is the component of lesser amount.
The solvent is the dissolving medium. Generally it is the component of greater amount. 2

5. Gaseous Solutions
Nonreactive gases can mix in all proportions to give a gaseous solution.
Fluids that dissolve in each other in all proportions are said to be miscible fluids.
If two fluids do not mix, they are said to be immiscible.
For example, air is a solution of oxygen, nitrogen, and smaller amounts of other gases. 2

6. Liquid Solutions
Liquid solutions are the most common types of solutions found in the chemistry lab.
Many inorganic compounds are soluble in water or other suitable solvents.
Rates of chemical reactions increase when the likelihood of molecular collisions increases.
This increase in molecular collisions is enhanced when molecules move freely in solution. 2

7. Solid Solutions Solid solutions of metals are referred to as alloys.
Brass is an alloy composed of copper and zinc.
Bronze is an alloy of copper and tin.
Pewter is an alloy of zinc and tin. 2

8. Solubility and the Solution Process
The amount of a substance that will dissolve in a solvent is referred to as its solubility.
Many factors affect solubility, such as temperature and, in some cases, pressure.
There is a limit as to how much of a given solute will dissolve at a given temperature.
A saturated solution is one holding as much solute as is allowed at a stated temperature. 2

9. A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.

10. Three types of interactions in the solution process:
solvent-solvent interaction
solute-solute interaction
solvent-solute interaction
DHsoln = DH1 + DH2 + DH3

11. “like dissolves like”
Two substances with similar intermolecular forces are likely to be soluble in each other.
non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
polar molecules are soluble in polar solvents
C2H5OH in H2O
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)

12. Molecular Solutions H O
Polar molecules interact well with polar solvents such as water.
The dipole-dipole interactions of water with a polar solvent can be easily explained as electrostatic attraction. d+ d-
polar
solute H O 2

13. Molecular Solutions
Nonpolar solutes interact with nonpolar solvents primarily due to London forces.
Heptane, C7H16, and octane, C8H18, are both nonpolar components of gasoline and are completely miscible liquids.
However, for water to mix with gasoline, hydrogen bonds must be broken and replaced with weaker London forces between water and the gasoline.
Therefore gasoline and water are nearly immiscible. 2

14. Ionic Solutions
Polar solvents, such as water, also interact well with ionic solutes.
Since ionic compounds are the extreme in polarity, we can illustrate the electrostatic attractions of water for cations and anions. + - H O d- d+ 2

15. Effects of Temperature and Pressure on Solubility
The solubility of solutes is very temperature dependent.
For gases dissolved in liquids, as temperature increases, solubility decreases.
On the other hand, for most solids dissolved in liquids, solubility increases as temperature increases. 2

16. Temperature Change
Heat can be evolved or absorbed when an ionic compound dissolves in water.
This heat of solution can be quite noticeable.
When NaOH dissolves in water, it gets very warm (the solution process is exothermic).
On the other hand, when ammonium nitrate dissolves in water, it becomes very cold (the solution process is endothermic). 2

17. Pressure Change
Henry’s Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas in direct contact with the liquid.
Expressed mathematically, the law is
where S is the solubility of the gas, kH is the Henry’s law constant characteristic of the solution, and P is the partial pressure of the gas. 2

18. Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature

19. Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubilities.
Suppose you have 90 g KNO3 contaminated with 10 g NaCl.
Fractional crystallization:
Dissolve sample in 100 mL of water at 600C
Cool solution to 00C
All NaCl will stay in solution (s = 34.2g/100g)
78 g of PURE KNO3 will precipitate (s = 12 g/100g). 90 g – 12 g = 78 g

20. Temperature and Solubility
O2 gas solubility and temperature
solubility usually decreases with increasing temperature

21. Pressure and Solubility of Gases
The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).
c is the concentration (M) of the dissolved gas
c = kP
P is the pressure of the gas over the solution
k is a constant for each gas (mol/L•atm) that depends only on temperature
low P
high P
low c
high c

22. Chemistry In Action: The Killer Lake
8/21/86
CO2 Cloud Released
1700 Casualties
Trigger?
earthquake
landslide
strong Winds
Lake Nyos, West Africa

23. Ways of Expressing Concentration
Concentration expressions are a ratio of the amount of solute to the amount of solvent or solution.
The quantity of solute, solvent, or solution can be expressed in volumes or in molar or mass amounts.
Thus, there are several ways to express the concentration of a solution. 2

24. Molarity
The molarity of a solution is the moles of solute in a liter of solution.
For example, 0.20 mol of ethylene glycol dissolved in enough water to give 2.0 L of solution has a molarity of 2

25. Mass Percentage of Solute
The mass percentage of solute is defined as:
For example, a 3.5% sodium chloride solution contains 3.5 grams NaCl in grams of solution. 2

26. Molality
The molality of a solution is the moles of solute per kilogram of solvent.
For example, 0.20 mol of ethylene glycol dissolved in 2.0 x 103 g (= 2.0 kg) of water has a molality of 2

27. A Problem to Consider
What is the molality of a solution containing 5.67 g of glucose, C6H12O6, dissolved in 25.2 g of water?
First, convert the mass of glucose to moles.
Then, divide it by the kilograms of solvent (water). 2

28. Mole Fraction
The mole fraction of a component “A” (A) in a solution is defined as the moles of the component substance divided by the total moles of solution (that is, moles of solute and solvent).
For example, 1 mol ethylene glycol in 9 mol water gives a mole fraction for the ethylene glycol of 1/10 = 0.10. 2

29. A Problem to Consider
An aqueous solution is m glucose. What are the mole fractions of each of the components?
A m solution contains mol of glucose in 1.00 kg of water. After converting the 1.00 kg H2O into moles, we can calculate the mole fractions. 2

30. A Problem to Consider
An aqueous solution is m glucose. What are the mole fractions of each of the components? 2

31. Colligative Properties of Solutions
The colligative properties of solutions are those properties that depend on solute concentration.
These properties include:
vapor pressure reduction
freezing point depression
boiling point elevation
osmosis
First, we must look into ways of expressing the concentration of a solution. 2

32. Colligative Properties of Nonelectrolyte Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
P1 = X1 P 1
P 1
= vapor pressure of pure solvent
X1 = mole fraction of the solvent
Raoult’s law
If the solution contains only one solute:
X1 = 1 – X2
P 1
- P1 = DP = X2
X2 = mole fraction of the solute

33. PA = XA P A
Ideal Solution
PB = XB P B
PT = PA + PB
PT = XA P A
+ XB P B

34. < & > & PT is greater than predicted by Raoults’s law
PT is less than
predicted by Raoults’s law
Force
A-B
A-A
B-B
<
&
Force
A-B
A-A
B-B
>
&

35. Vapor Pressure of a Solution
If a solution contains a volatile solute, then each component contributes to the vapor pressure of the solution.
In other words, the vapor pressure of the solution is the sum of the partial vapor pressures of the solvent and the solute.
Volatile compounds can be separated using fractional distillation. 2

36. Fractional Distillation Apparatus

37. Boiling Point Elevation
The normal boiling point of a liquid is the temperature at which its vapor pressure equals 1 atm.
Because vapor pressure is reduced in the presence of a nonvolatile solute, a greater temperature must be reached to achieve boiling.
The boiling point elevation, DTb is a colligative property equal to the boiling point of the solution minus the boiling point of the pure solvent. 2

38. Boiling-Point Elevation
DTb = Tb – T b
T b is the boiling point of
the pure solvent
T b is the boiling point of
the solution
Tb > T b
DTb > 0
DTb = Kb m
m is the molality of the solution
Kb is the molal boiling-point
elevation constant (0C/m)
for a given solvent

39. Freezing-Point Depression
DTf = T f – Tf
T f is the freezing point of
the pure solvent
T f is the freezing point of
the solution
T f > Tf
DTf > 0
DTf = Kf m
m is the molality of the solution
Kf is the molal freezing-point
depression constant (0C/m)
for a given solvent

41. A Problem to Consider
An aqueous solution is m in glucose. What are the boiling point and freezing point for this solution?
Kb and Kf for water as oC/m and 1.86 oC/m, respectively. Therefore,
The boiling point of the solution is oC and the freezing point is –0.041oC. 2

42. DTf = Kf m Kf water = 1.86 0C/m DTf = Kf m
What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is g.
DTf = Kf m
Kf water = C/m =
3.202 kg solvent
478 g x
1 mol
62.01 g
m =
moles of solute
mass of solvent (kg)
= 2.41 m
DTf = Kf m
= C/m x 2.41 m = C
DTf = T f – Tf
Tf = T f – DTf
= C – C = C

43. Osmotic Pressure (p)
Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.
A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.
Osmotic pressure (p) is the pressure required to stop osmosis.
more
concentrated
dilute

44. Osmotic pressure is a colligative property of a solution equal to the pressure that, when applied to the solution, just stops osmosis. 2

45. Osmotic Pressure (p) p = MRT High P Low P
M is the molarity of the solution
R is the gas constant
T is the temperature (in K)

46. A cell in an:
isotonic
solution
hypotonic
hypertonic

47. Colligative Properties of Nonelectrolyte Solutions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
Vapor-Pressure Lowering
P1 = X1 P 1
Boiling-Point Elevation
DTb = Kb m
Freezing-Point Depression
DTf = Kf m
Osmotic Pressure (p)
p = MRT

48. Colligative Properties of Ionic Solutions
The colligative properties of solutions depend on the total concentration of solute particles.
Consequently, ionic solutes that dissociate in solution provide higher effective solute concentration than nonelectrolytes.
For example, when NaCl dissolves, each formula unit provides two solute particles. 2

49. Colligative Properties of Electrolyte Solutions
0.1 m NaCl solution
0.1 m Na+ ions & 0.1 m Cl- ions
Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
0.1 m NaCl solution
0.2 m ions in solution
van’t Hoff factor (i) =
actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
i should be
nonelectrolytes 1
NaCl 2
CaCl2 3

50. Colligative Properties of Electrolyte Solutions
Boiling-Point Elevation
DTb = i Kb m
Freezing-Point Depression
DTf = i Kf m
Osmotic Pressure (p)
p = iMRT

51. A Problem to Consider
Estimate the freezing point of a m aqueous solution of aluminum sulfate, Al2(SO4)3. Assume the value of i is based on the formula.
When aluminum sulfate dissolves in water, it dissociates into five ions.
Therefore, you assume i = 5. 2

52. A Problem to Consider
Estimate the freezing point of a m aqueous solution of aluminum sulfate, Al2(SO4)3. Assume the value of i is based on the formula.
The freezing point depression is
The estimated freezing point is –0.093oC. 2

53. Chemistry In Action:
Desalination

54. A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus solution
collodial particles are much larger than solute molecules
collodial suspension is not as homogeneous as a solution

55. Colloids
A colloid is a dispersion of particles of one substance (the dispersed phase) throughout another substance or solution (the continuous phase).
A colloid differs from a true solution in that the dispersed particles are larger than normal molecules.
The particles range from 1 x 103 pm to about 2 x 105 pm. 2

56. The Tyndall Effect
The scattering of light by colloidal-size particles is known as the Tyndall effect.
For example, a ray of sunshine passing against a dark background shows up many fine dust particles by light scattering. 2

57. Types of Colloids
Colloids are characterized according to the state of the dispersed phase and the state of the continuous phase.
A sol consists of solid particles dispersed throughout a liquid.
An aerosol consists of liquid droplets or solid particles dispersed throughout a gas.
An emulsion consists of liquid droplets dispersed throughout another liquid. 2

58. Hydrophilic and Hydrophobic Colloids
Colloids in which the continuous phase is water are divided into two major classes.
A hydrophilic colloid is a colloid in which there is a strong attraction between the dispersed phase and the continuous phase (water).
A hydrophobic colloid is a colloid in which there is a lack of attraction of the dispersed phase for the continuous phase (water). 2

59. Coagulation
Coagulation is the process by which the dispersed phase of a colloid is made to aggregate and thereby separate from the continuous phase.
Soil suspended in river water coagulates when it meets the concentrated ionic solution of the ocean. The Mississippi Delta was formed this way. 2

60. Association Colloids
A micelle is a colloidal-sized particle formed by the association of molecules, each of which has a hydrophobic end and a hydrophilic end.
A colloid in which the dispersed phase consists of micelles is called an association colloid.
Ordinary soap in water provides an example of an association colloid. 2

61. The Cleansing Action of Soap

62. WORKED EXAMPLES

64. Worked Example 12.2

66. Worked Example 12.4

69. Worked Example 12.7

70. Worked Example 12.8

71. Worked Example 12.9

72. Worked Example 12.10

73. Worked Example 12.11