Chapter 9. Properties of Solutions
9.1 The Nature of Solutions
9.2 Determinants of Solubility
9.3 Characteristics of Aqueous
Solutions
9.4 Colligative Properties
9.5 Between Solutions and
Mixtures
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.1 Nature of Solutions
Learning objective:
Work with and interconvert concentration units
(mass %, molarity, molality, mole fraction, ppm
and ppb)
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.1 Nature of Solutions
 Solution – a homogeneous mixture of two or
more substances, in which one is called the
solvent and the other is the solute
 Solvent –
main medium, what is there in the largest
quantity
 Solute – dissolved in the solvent
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Phases of Solutions
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Solution Concentration
Mass Percent
Mass Solution
Mass Percent =
 100%
Total Mass Solution
Molarity
Molarity =
Moles Solute
Total Volume of Solution
Mole Fraction
nA
XA =
ntotal
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c=
nsolute
Vsolution
Molality
 Useful for applications where the temperature
(thus volume) of a solution changes.
 Defined as the number of moles of solute divided
by the mass of the solvent in kg
nsolute
cm =
msolvent
 Units are mol/kg
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 1 Molality
Hydrogen peroxide disinfectant typically contains 3.0%
H2O2 by mass. Assuming that the rest of the contents is
water, what is the molality of this disinfectant?
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 2 Concentration Conversions
Concentrated aqueous ammonia is 14.8 M and has a
density of 0.898 g/mL. Determine the molality and
mole fraction of ammonia in this solution.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.2 Determinants of Solubility
Learning objective:
Predict the relative solubilities of a solute in various
solvents, and explain in terms of intermolecular
forces
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.2 Determinants of Solubility
 Solubilities vary tremendously
 Miscible: when two liquids mix in all proportions (e.g.
Acetone and Water)
 Immiscible: when two liquids do not mix at all (e.g. oil
and water)
 Insoluble: when a solid does not dissolve in a solvent
(NaCl in gasoline)
 Saturated: a solution with the maximum possible
solute concentration
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Like Dissolves Like
 Refers to the similarity of intermolecular forces
 Compounds with similar polarity will be soluble in each
other.
e.g. water and ethanol are miscible (H-bonds in both)
e.g. water and hexane (C6H14) are immiscible (H-bonds
versus dispersion forces)
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 3 Solubility Trends
Give a molecular explanation of the following trend in
alcohol solubilities in water:
n-Propanol
n-Butanol
n-Pentanol
n-Hexanol
CH3CH2CH2OH
CH3CH2CH2CH2OH
CH3CH2CH2CH2CH2OH
CH3CH2CH2CH2CH2CH2OH
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Miscible
1.1 M
0.30 M
0.056 M
Solubility of Solids
1.
2.
3.
4.
Network solids (diamond, graphite) cannot
dissolve without breaking covalent bonds.
Molecular solids – “like dissolves like”
Metals – do not dissolve in water (some will react,
but not dissolve)
Ionic Solids – soluble in polar solvents such as
water, with some exceptions.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 4 Solubilities of Vitamins
Vitamins are organic molecules
that are required for proper
function but are not
synthesized by the human
body. Thus, vitamins must be
present in the foods people
eat. Vitamins fall into two
categories: fat-soluble, which
dissolve in fatty hydrocarbonlike tissues and water-soluble.
The structures of several
vitamins follow. Assign each
one to the appropriate
category.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Alloys
 Alloy: a mixture of substances with metallic properties.
(a solid solution)
 Some are true homogeneous solutions (e.g. brass)
 Others are heterogeneous (e.g. solder)
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Alloys
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Solubility of Salts
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9.3 Characteristics of Aqueous Solutions
Learning objective:
Calculate and explain solubilities in water
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9.3 Characteristics of Aqueous Solutions
 Water
 Most important solvent
 Medium in which life begins and is sustained
 The only small molecule that is not a gas under terrestrial
conditions (due to highly polar bonds and bent geometry)
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Solubility Equilibrium
 When a solute concentration reaches
the solubility of that substance, no
further net changes occur.
 If more solute molecules are dissolved,
others are precipitated
 A saturated solution in contact with
excess solute is in a state of dynamic
equilibrium.
 A dynamic equilibrium is represented
by double arrows
Solute (pure state) Ý Solute (aq)
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Energetics of Salt Solubility
 Molar heat of solution (DHsoln): net energy flow
resulting from the dissolution of a solid in water.
 Dependent on
energy to separate ions
 energy to break hydrogen bonds in the solvent
 energy released when solvent molecules form ion-dipole
interactions with ions.

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Heat of Solution
for NaCl
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Effect of Temperature
Most solids are more soluble at higher temperature
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Gas-Solution Equilibria
 The equilibrium concentration of a dissolved gas
increases linearly with the partial pressure of the
gas according to Henry’s Law:
gas  aq   eq = KH pgas eq
where KH is Henry’s Law constant, different for each
gas and solvent combination. KH is a function of
temperature.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Henry’s Law Constants in Water (M/bar)
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 5 Solubilities of Atmospheric Gases
The Earth’s atmosphere contains 78% N2, 21% O2 and
minor amounts of other gases including CO2 (0.0385%).
Determine the concentrations of N2, O2, and CO2 in
water at equilibrium with the Earth’s atmosphere at
25°C.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.4 Colligative Properties
Learning objective:
Understand the reason for and calculate the magnitudes
of colligative properties
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.4 Colligative Properties
 The presence of a solute affects some physical
properties of the solvent.
 The physical properties are referred to as colligative
properties.
Vapour Pressure (reduced)
 Freezing Point (reduced)
 Boiling Point (increased)
 Osmotic Pressure (increased)

 The magnitude of the colligative property depends only
on the concentration of the solute, not its identity.
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Vapor Pressure Reduction
 A pure solvent in a closed
system will reach a dynamic
equilibrium between the
liquid and vapour phases.
 The addition of a solute will
decrease the vapour pressure
because the solute molecules
reduce the rate of escape of
solvent molecules.
 Raoult’s Law quantifies this:
p vap, solution = X A p vap, A
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 6 Raoult’s Law
Calculate the vapour pressure of a 5% by mass benzoic
acid (C7H6O2 (aq))in ethanol solution at 35 °C. The
vapour pressure of pure ethanol at this temperature is
13.40 kPa.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Vapour Pressure of a Solution
If both the solvent (A) and solute (B) are both volatile, the
vapour pressure of the solution is:
p vap, solution = X A p vap, A  XBp vap, B
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Vapour Pressure of a Solution
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Example 9 – 7 Vapour Pressure of a Solution
A closed bottle contains a solution of 5.0% by mass
acetone ((CH3)2CO) in water. Calculate the vapour
pressure of this solution at 25 °C. The vapour pressure
of pure water at 25 °C is 3.17 kPa and that of pure
acetone is 30.7 kPa.
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Distillation
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Azeotropes
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Boiling and Freezing Points
 Boiling-point elevation – the increase in boiling point of
a solvent by adding a solute.
 Freezing-point depression – the lowering of the
freezing-point of a solvent by adding solute.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
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Freezing Point Depression
DTf = iK f b
where b is the molality (moles of solute/kg of solvent)
Kf is the cryoscopic constant of the solvent
i is the van’t Hoff factor:
e.g. i = 3 for Na2SO4 because Na2SO4 → 2 Na+ + SO42Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Boiling Point Elevation
D Tb = iKbb
Kf is the ebullioscopic constant of the solvent.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 8 Freezing Point Depression
Ethylene glycol (1,2-ethanediol) is added to automobile
radiators to prevent cooling water from freezing.
Estimate the freezing point of coolant that contains
2.00 kg of ethylene glycol in 5.00 L of water. Is this a
high enough concentration to protect a radiator in
Montreal, where the temperature may be as low as
-40 oC?
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Osmosis and Osmotic Pressure
 Osmosis – the movement
of solvent molecules
through a semipermeable
membrane to a region of
higher solute
concentration.
 The membrane allows
solvent, but not solute, to
pass through.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Osmotic Pressure
Osmotic Pressure, P: the
amount of external
pressure necessary to
equalize the transfer rates
across the membrane.
P = M RT
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Hemolysis of Red-Blood Cells
Hypotonic
Solution
Isotonic
Solution
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Hypertonic
Solution
Example 9 – 9 Isotonic Solutions
Isotonic intravenous solutions contain 49 g/L of glucose
(C6H12O6). What is the osmotic pressure of the blood?
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Determination of Molar Mass
 The osmotic pressure equation can be rearranged to
solve for molar mass (M).
mRT
P = cRT so P =
V(M)
and thus
mRT
M=
PV
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 9 – 10 Determining Molar Mass
A 25.00 mL aqueous solution containing 0.420 g of
hemoglobin has an osmotic pressure of 0.613 kPa at
27°C. What is the molar mass of hemoglobin?
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.5 Between Solutions and Mixtures
Learning objective:
Understand some aspects of colloidal suspensions
and surfactant solutions
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
9.5 Between Solutions and Mixtures
 Colloids – particles with dimensions between 1 nm and 1 mm
 Colloidal suspension – a dispersion that has properties between
those of a solution and a heterogeneous mixture.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Surfactants
 Substances that don’t dissolve in water are
hydrophobic.
 Substances that are miscible in water are hydrophilic.
 Surfactants: large linear molecules that have a
hydrophobic tail and a hydrophilic head.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Sodium lauryl sulphate is a
typical surfactant. It has an
ionic, hydrophilic polar head
and a hydrophobic nonpolar
tail.
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Cross-sectional molecular views of the structures that can form when
surfactant molecules are placed in water. The molecules may form a
monolayer at the surface, spherical clusters called micelles, or bilayer
structures called vesicles.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Lecithin, a common phospholipid,
has a hydrophobic tail and a
hydrophilic head.
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Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 9 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 9 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 9 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 9 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 9 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.