Chem 1011 – Intersession 2011
Class #14
23-May-11
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Class 14:Types of Solutions / Solution
Concentration
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Sec 12.2 – Types of Solution and Solubility
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Nature’s Tendency toward Mixing: Entropy
The Effect of Intermolecular Forces
Sec 12.5 – Expressing Solution Concentration
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Molarity
Molality
Parts by Mass and Parts by Volume
Mole Fraction and Mole Percent
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Terminology
• Solution
▫ homogeneous mixture made up of a solvent and a solute
▫ Solutions may be one of three phases: solid, liquid or gas
• Solvent
▫ solution component in which one or more solutes is
dissolved.
▫ Usually the solvent is present in greater amounts than the
solutes and determines the state of matter in which the
solution exists.
• Solute
▫ the solution component that is dissolved in the solvent.
▫ A solution may have several solutes, with the solutes
generally present in lesser amounts than the solvent.
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Solution Components
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
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Solution Types
Solution Phase
Solute
Phase
Solvent
Phase
Example
Gaseous Solutions
Gas
Gas
Air (mixture of many gases;
mainly N2(g) and O2(g))
Liquid Solutions
1) Gas
2) Liquid
3) Solid
All Liquid
1) Soft Drinks (CO2(g) in H2O(l))
2) Vodka (C2H5OH(l) in H2O(l))
3) Seawater (NaCl(s) in H2O(l))
Solid Solutions
Solid
Solid
Brass (Zn in Cu)
• Solutions that contain Hg and some other metal are called
amalgams.
• Solutions that contain metal solutes and a metal solvent are
called alloys.
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Spontaneous Mixing – Entropy
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Spontaneous Mixing – Entropy
• Most processes occur because the end result
has less potential energy.
• However, formation of a solution does not
necessarily lower the potential energy of the
system.
• When two ideal gases are put into the same
container, they spontaneously mix.
– the difference in attractive forces is
negligible
• The gases mix because the energy of the
system is lowered through the release of
entropy.
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
7
Entropy
• Entropy is the measure of energy
dispersal throughout the system.
• Energy has a spontaneous drive to
spread out over as large a volume as it is
allowed.
• By each gas expanding to fill the
container, it spreads its energy out and
lowers its entropy.
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Effect of Intermolecular Forces
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Solvent-solute interactions
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interaction between a solvent particle and a solute
particle.
Solvent-solvent interactions
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interaction between a solvent particle and another
solvent particle.
Solute-solute interactions
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interactions between a solute particle and another
solute particle.
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Effect of Intermolecular Forces
• Energy changes in the formation of most solutions also
involve differences in attractive forces between the
particles.
• In order for the solvent and solute to mix, you must
overcome
1. all of the solute–solute attractive forces.
2. some of the solvent–solvent attractive forces.
• Both processes are endothermic.
• At least some of the energy to do this comes from making
new solute–solvent attractions.

which is exothermic
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
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Effect of Intermolecular Forces
(a)Pure solvent → separated solvent molecules ∆Ha > 0 (endo)
(b)Pure solute → separated solute molecules
∆Hb > 0 (endo)
(c)Separated solvent and solute molecules → solution ∆Hc < 0
(exo)
• Overall: Pure solvent + pure solute → solution
∆Hsoln = ∆Ha + ∆Hb + ∆Hc
(endo or exothermic)
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Effect of Intermolecular Forces
DHb
DHc
DHa
A solution process may be endothermic, exothermic or have ∆Hsoln = 0,
depending on the magnitude of the enthalpy change in the mixing step.
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Effect of Intermolecular Forces
The relative strengths of these interactions will determine if a
solution will form.
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
13
Effect of Intermolecular Forces
“Like dissolves like” ie. polar solutes dissolve in polar
solvents; non-polar solutes dissolve in non-polar solvents
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Intermolecular Forces
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Effect of Intermolecular Forces
Solutes and solvents of opposite polarity generally do not
form solutions!
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
16
Problems
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Predict whether or not a solution will form in the
following mixtures:
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Hexane and octane (CH3(CH2)4CH3 vs. CH3(CH2)6CH3)
Octane and water (CH3(CH2)4CH3 vs. H2O)
In which solvent is solid iodine more likely to be
soluble, water (H2O) or carbon tetrachloride (CCl4)?
Why?
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Solution Formation and Equilibrium
(a) When solute is first
placed in the solvent
only dissolving occurs.
(b) After a time the
rate of crystallization
becomes significant.
(c) The solution
becomes saturated when
the rates of dissolving
and crystallization
become equal.
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Solution Types
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Saturated Solution
solution that contains the maximum quantity of solute that is
normally possible at a given temperature.
Undersaturated Solution
solution that contains less than the maximum quantity of
solute that the solvent is able to dissolve at a particular set of
conditions.
Supersaturated Solution
contains more solute than normally expected for a saturated
solution.
Supersaturated solutions are normally prepared by starting
with a saturated solution, heating it to a temperature where
more solute can be dissolved, and then slowly letting it cool to
the original temperature.
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
19
Solution Formation and Equilibrium
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For example, a solution of NaCl (the solute) in water (the
solvent) has been prepared, but we are unsure if it is
unsaturated, saturated, or supersaturated. We can
distinguish between these three types of solutions by
addition of a seed crystal (a single crystal of the solute,
NaCl)
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If the seed crystal dissolves, the solution is unsaturated.
If the seed crystal does not dissolve the solution is
saturated.
If the seed crystal does not dissolve, and the excess solute
recrystallizes (comes out of solution) the solution is
supersaturated.
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Solution Concentration
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There are a variety of ways to express solution
concentration
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Molarity
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Moles of Solute per Volume of Solvent (mol/L)
Molality
Moles of Solute per Mass of Solvent (mol/kg)
Parts by Mass and Parts by Volume
Mole Fraction and Mole Percent
We will focus mainly on molarity and mole
fraction / percent
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Molarity
• moles of solute per 1 liter of solution
• used because it describes how many molecules of
solute in each liter of solution
Types of Solutions / Solution Concentration
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Chem 1011 – Intersession 2011
Class #14
23-May-11
22
Mole Fraction / Mole Percent
• Mole Fraction
▫ the fraction of the moles of one component in the total moles of
all the components of the solution.
• total of all the mole fractions in a solution = 1
▫ unitless – moles / moles will cancel
• Convert to a percentage by multiplying by 100%
mole fraction of A 
where
moles of solute A
100%
total moles in solution
XA 
nA
100%
n total
n total  n A  n B  n C  ...  n solvent
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Problem
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A solution prepared by mixing 17.2 g of
ethylene glycol (molar mass C2H6O2 = 62.07
g/mol) with 0.500 kg of H2O to make 515 mL
of solution. Calculate its
a) molarity
b) mol fraction
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There are many more problems in your
textbook and in the tutorial practice sheet!
Please try them!
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Wednesday
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Sec 12.6 – Colligative Properties
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Osmotic Pressure
And Thursday!
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Midterm Review, 10:00am – 10:50am
C-3033
Types of Solutions / Solution Concentration
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