Insert picture from
First page of chapter
Chapter 13
Physical Properties
of Solutions
1
13.1 Types of Solutions
Copyright McGraw-Hill 2009
2
13.1 Types of Solutions
Solution classifications based on amount of
solute dissolved relative to the maximum:
• Saturated – maximum amount at a given
temperature (This amount is termed the
solubility of the solute.)
• Unsaturated – less than the maximum
• Supersaturated – more than a saturated
solution but is an unstable condition
Copyright McGraw-Hill 2009
3
unsaturated
saturated
heat
supersaturated
Copyright McGraw-Hill 2009
4
Conversion of a Supersaturated Solution to a
Saturated Solution
Copyright McGraw-Hill 2009
5
13.2 A Molecular View of the
Solution Process
Factors that determine solubility
• Intermolecular forces present in the
formation of a solution
– Solute-solute interactions
– Solvent-solvent interactions
– Solute-solvent interactions
Copyright McGraw-Hill 2009
6
Hsoln  H1  H2  H3
Copyright McGraw-Hill 2009
7
exothermic
Hsoln  H1  H2  H3
endothermic
H1  H 2  H 3
H soln  0
H1  H 2  H3
H soln  0
Copyright McGraw-Hill 2009
8
Solubility can be predicted based on “like
dissolves like” in terms of intermolecular forces.
For example: water and methanol are both polar
and dissolve in each other
O
H
H
• Two liquids that are soluble in each other in all
proportions are term miscible.
• Ions readily dissolve in polar solvent due to
solvation by the solvent molecules.
Copyright McGraw-Hill 2009
9
Predict whether Vitamin B6 is water soluble
or fat soluble.
Copyright McGraw-Hill 2009
10
polar groups
Water soluble due to the presence of polar
groups.
Copyright McGraw-Hill 2009
11
• Energy and entropy
– Exothermic processes are generally more
favorable than endothermic processes
– Solutions do form when the overall process is
endothermic
– Entropy (randomness or disorder) contributes
to the solution process
• Entropy tends to increase for all
process
• A solution is more disordered than the
isolated solute and solvent
Copyright McGraw-Hill 2009
12
13.3 Concentration Units
• Molality (m) – number of moles of solute dissolved
in 1 kg (1000 g) of solvent
moles of solute
molality  m 
mass of solution (in kg)
• Percent by Mass – ratio of mass of solute to the
mass of the solution times 100
mass of solute
percent by mass 
x100
mass of solute  mass of solvent
Copyright McGraw-Hill 2009
13
Units analogous to percent by mass (part per
hundred) to express very small concentrations
• Parts per million (ppm)
mass * of solute
6
ppm 
x10
mass * of solution
• Parts per billion (ppb)
mass * of solute
9
ppb 
x10
mass * of solution
*masses must be expressed in the same units
Copyright McGraw-Hill 2009
14
Choice of units depends on the purpose of the
experiment
• Mole fraction – used for gases and vapor
pressures of solutions
• Molarity – commonly used since volumes of
solutions are easy to measure
• Molality – temperature independent
• Percent by Mass – temperature independent
and need not know molar masses
• Conversion between units requires the use of
density if any mass to volume or volume to mass
conversion in needed.
Copyright McGraw-Hill 2009
15
Determine the a) molality, b) percent by
mass and c) the ppm concentrations of a
solution prepared by dissolving 15.56 g of
glucose (C6H12O6) in 255 g of water.
Copyright McGraw-Hill 2009
16
a) molality
Molar mass of glucose = 180.2 g/mol
mol
mol glucose  15.56 g x
 0.086349 mol
180.2 g
3
1
10 g
m  0.086349 mol x
x
 0.339 m
255 g kg
Copyright McGraw-Hill 2009
17
b) percent by mass
15.56 g
x100  57.51% glucose
270.56 g
c) ppm
15.56 g
x10 6  5.751x10 4 ppm glucose
270.56 g
Copyright McGraw-Hill 2009
18
13.4 Factors that Affect Solubility
• Temperature
– The solubility of solids may increase,
decrease or remain relatively constant
with increasing temperature
– The solubility of gases decreases with
increasing temperature
• Thermal pollution – a consequence of
the relation between gas solubility and
temperature
Copyright McGraw-Hill 2009
19
Temperature Dependence of the Solubility
of Selected Solids
Copyright McGraw-Hill 2009
20
• Pressure – significantly affects only the
solubility of gases
– Henry’s law – the solubility of a gas, c, is
directly proportional to the pressure of the
gas, P, over the solution
c P
c  kP
where c, is in mol/L, k is Henry’s law
constant with units of mol/L. atm and P is
in atm.
Copyright McGraw-Hill 2009
21
Molecular View at Different Pressures
P1
P2
P1< P2
Copyright McGraw-Hill 2009
22
Calculate the pressure of O2 necessary to
generate an aqueous solution that is
3.4 x 102 M in O2 at 25°C. The Henry’s law
constant for O2 in water at 25°C is 1.3 x 103
mol/L . atm.
Copyright McGraw-Hill 2009
23
c  kP
2
c 3.4x10 mol
L  atm
P 
x
3
k
L
1.3x10 mol
P  26.2 atm
Copyright McGraw-Hill 2009
24
13.5 Colligative Properties
Colligative properties depend only on the
number of solute particles in solution and not the
nature of the solute
• Vapor-Pressure lowering
– Nonvolatile solute (no appreciable pressure)
• Vapor pressure of the solvent is decreased
– Volatile solute (exhibit appreciable pressure)
• Vapor pressure is the sum of the individual
pressures
Copyright McGraw-Hill 2009
25
– Raoult’s law – quantitative expression of the
solution vapor pressure
• Nonvolatile solute (P1 is the solution vapor
pressure, P0 is the vapor pressure of the
pure substance, and c is the mole fraction.)
P1  c1P10
• Volatile solute (PT is the solution vapor
0
0
P
P
pressure, A and B are vapor pressures
of pure solution components)
PT  c A P  c P
0
A
Copyright McGraw-Hill 2009
0
B B
26
Entropy and Vapor Pressure Lowering
Copyright McGraw-Hill 2009
27
Ideal Solution* of Benzene and Toluene
*Obeys Raoult’s law
Copyright McGraw-Hill 2009
28
Calculate the vapor pressure of a solution
made by dissolving 115 g of urea, a nonvolatile
solute, [(NH2)2CO; molar mass = 60.06 g/mol]
in 485 g of water at 25°C.
(At 25°C, PH2O  23.8 mmHg.)
Copyright McGraw-Hill 2009
29
PH2O  c
molH2O
mol urea
cH O
2
0
H2O H2O
P
mol
 485 gx
 26.91 mol
18.02 g
mol
 115 g x
 1.915 mol
60.06 g
26.91 mol

 0.9336
26.91 mol  1.915 mol
PH2O  0.9392 x 23.8 mmHg  22.2 mmHg
Copyright McGraw-Hill 2009
30
• Boiling-Point Elevation (Tb)
– The boiling point of a solution, Tb, of a
nonvolatile solute will be higher than that of the
0
pure solvent, Tb .
Tb  Tb  T
0
b
– Elevation is directly proportional to the molal
concentration.
Tb  Kbm
– Kb is the molal boiling-point elevation constant.
Copyright McGraw-Hill 2009
31
Effect of Vapor Pressure Lowering
Effect on Boiling Point
Copyright McGraw-Hill 2009
32
Copyright McGraw-Hill 2009
33
• Freezing-Point Depression (Tf)
– The freezing point of a solution, Tf, will be lower
0
than that of the pure solvent, Tf .
Tf  Tf0  Tf
– Depression is directly proportional to the molal
concentration.
Tf  K f m
– Kf is the molal freezing-point elevation constant.
Copyright McGraw-Hill 2009
34
Effect of Vapor Pressure Lowering
Effect on Freezing Point
Copyright McGraw-Hill 2009
35
Entropy and Freezing Point
Copyright McGraw-Hill 2009
36
Calculate a) the freezing point and b) the
boiling point of a solution containing 268 g of
ethylene glycol and 1015 g of water. (The
molar mass of ethylene glycol (C2H6O2) is
62.07 g/mol. Kb and Kf for water are 0.512°C/m
and 1.86°C/m, respectively.)
Copyright McGraw-Hill 2009
37
a) freezing point
mol
mol ethylene glycol  268 g x
 4.318 mol
62.07 g
3
1
10 g
m  4.318 mol x
x
 4.254 m
1015 g kg
1.86 o C
Tf 
x 4.254 m  7.91o C
m
7.91o C  0.00 o C  Tf
Tf  7.91 C
o
Copyright McGraw-Hill 2009
38
b) boiling point
0.512o C
Tb 
x 4.254 m  2.18 o C
m
2.18 C  Tb  100.00 C
o
o
Tb  102.18 C
o
Copyright McGraw-Hill 2009
39
Osmosis - Selective passage of solvent
molecules through a semipermeable
membrane
solvent
solution
solvent
Copyright McGraw-Hill 2009
solution
40
• Osmotic Pressure (p)
– Pressure required to stop osmosis
– Directly proportional to molar concentration, M
p = MRT
where R is 0.08206 L.atm/mol . K and T is in
kelvins
Copyright McGraw-Hill 2009
41
• Solutions of Electrolytes
– Dissociation of strong and weak electrolytes
affects the number of particles in a solution
– van’t Hoft factor (i) – accounts for the effect
of dissociation
actual number of particles in solution after dissociation
i
number of formula units initially dissolved in solution
Copyright McGraw-Hill 2009
42
Modified Equations for Colligative Properties
Tf  iKf m
Tb  iKbm
p  iRTM
Copyright McGraw-Hill 2009
43
Copyright McGraw-Hill 2009
44
Formation of ion pairs affects colligative properties
Copyright McGraw-Hill 2009
45
Copyright McGraw-Hill 2009
46
The freezing-point depression of a 0.100 m
MgSO4 solution is 0.225°C. Determine the
experimental van’t Hoff factor of MgSO4 at
this concentration.
Copyright McGraw-Hill 2009
47
One approach:
Tf  iKf m
o
1.86
C
o
0.225 C  i
x 0.100 m
m
i  1.21
Note, at this concentration the dissociation of MgSO4 is
not complete.
Copyright McGraw-Hill 2009
48
Another approach to the same problem:
Ideal freezing point depression
o
1.86 C
Tf 
x 0.100 m  0.186 o C
m
Compare ideal and real freezing point depression
0.225 o C
i
 1.21
o
0.186 C
Copyright McGraw-Hill 2009
49
A solution made by dissolving 25.0 mg of
insulin in 5.00 mL of water has an osmotic
pressure of 15.5 mmHg at 25°C. Calculate
the molar mass of insulin. (Assume that
there is no change in volume when the
insulin is added to the water and that insulin
is a nondissociating solute.)
Copyright McGraw-Hill 2009
50
Calculate the M of the solution
atm
p  15.5 mmHg x
 2.039x10 2 atm
760 mmHg
p
mol  K
1
M
 2.039x10 atm x
x
RT
0.08206 L  atm 298 K
2
4
8.338
x
10
mol
4
M  8.338 x 10 M 
L
Copyright McGraw-Hill 2009
51
Calculate the moles of insulin
8.340 x 104 mol
103 L
mol 
x 5.00 mL x
 4.169 x10 6 mol
L
mL
Molar mass is ratio of grams to moles
10 3 g
1
x
M 25.0 mg x
mg
4.169 x10 6 mol
6.00 x 103 g
M 
mol
Copyright McGraw-Hill 2009
52
13.7 Colloids
A colloid is a dispersion of particles of one
substance throughout another substance.
• Intermediate between a homogenous and
heterogeneous mixture
• Range of particle size: 103 – 106 pm
• Categories
– Aerosols
– Foams
– Emulsions
– Sols
Copyright McGraw-Hill 2009
53
– Gels
Copyright McGraw-Hill 2009
54
• Exhibit the Tyndall effect
colloid
solution
Copyright McGraw-Hill 2009
55
Fog – A Familiar Manifestation of the Tyndall Effect
Copyright McGraw-Hill 2009
56
• Many important colloids are aqueous and
can be further classified.
– Hydrophilic (water loving)
– Hydrophobic (water fearing)
Hydrophilic groups on the surface of a protein
stabilize the molecule in water
Copyright McGraw-Hill 2009
57
Stabilization of Hydrophobic Colloidal Particles by Ion
Adsorption
Copyright McGraw-Hill 2009
58
Removal of Grease by Soap (Sodium Stearate)
Copyright McGraw-Hill 2009
59
Emulsification –
• stabilization of an unstable colloid
• accomplished by the addition of an
emulsifier or emulsifying agent
Sodium glycoholate – a bile salt or biological
emulsifying agent for ingested fats
Copyright McGraw-Hill 2009
60