Chapter 12
Solutions and Their Behavior
Solutions
The Solution Process
Why do things dissolve?
1) The driving force towards a more random state
(entropy)
2) The attractive forces between solute and solvent
(enthalpy)
Intermolecular Forces!!!
Solutions
A solution is a homogeneous mixture, but

A solution
a particular
homogeneous
mixture
A
of mixture.
that's
not the is
full
definition.type
Homogeneous
where
all
particles
exist
as
individual
Mixtures
in chemistry
are
means
that the
mixture is
thecombinations
same
all the
molecules
or
ions.
This
is
the
definition
of
different
substances
where
each
way through. You could take two same-sized
of a solution.
substance
its chemical
properties.
samples:
oneretains
from the
bottom and
one from
mixtures
separated by
theGenerally,
top and they
wouldcan
be be
identical.
non-chemicalmixtures
means such
as filtration,
Homogeneous
do not
settle out if
heating,
or centrifugation.
left
to sit undisturbed,
whereas a
heterogeneous mixture would. Blood is a
good example of a heterogeneous mixture.
Solutions





A solution has two components: the solute and the
solvent.
The solvent is the substance in greater amount.
It is usually a liquid, but could be a gas or even a
solid. Water is defined as the universal solvent .
The solute is the substance in lesser amount.
The solute is usually a solid, but could be a liquid
or gas.
Dissolving Process- the Solvent rips the solute apart molecule by
molecule or ion by ion. If a solute is soluble that means that a
solvent is able to rip it apart.
LIKE
DISSOLVE
LIKE
Polar solvents can only dissolve
polar solutes and Non-Polar solvents can only
dissolve non-polar solutes.
Like Dissolves Like
Polar to Polar
Non-polar to Non-polar
Polar dissolves Polar Non-polar dissolves Non-Polar
Intermolecular Forces in Solutions
(ionic and polar substances tend to be water-soluble)
Solubility
Solubility is the amount of a substance
that will dissolve in a given amount
of solvent

Recall dissociation equations
NaCl(s) ⇆ NaCl(aq) = Na+(aq) + Cl–(aq)
molecular form
ionic form
solute(undissolved) ⇆ solute(dissolved)
Factors Affecting Solubility
Most solids are more soluble at higher temp, most
gases are less soluble at higher temp
At Higher pressures there is no significant effect for
solid or liquid solutes, but there is a major effect
with gaseous solutes dissolved in liquid solvents
Henry’s Law: gases are more soluble at higher
pressure (e.g. Pepsi/Coke/Root Beer …)
Sg ∝ Pg or Sg = kHPg
or S1/P1 = S2/P2
where S = solubility, P = pressure, kH = Henry’s law constant (depends on gas)
What happens when there is to much
Solute to be dissolved?

The Solute falls to the bottom unaffected.
What if the solute is already dissolved?
There are three types of solutions
that pertain to this question.
1) Saturated
2) Unsaturated
3) Supersaturated.
Maximum vs Minimum Solubility
A solution that contains the maximum amount of dissolved
solute in a given amount of solvent is considered
SATURATED.
UNSATURATED means the solution can add more solvent
at the existing conditions.
SUPERSATURATED Solution – a solution that contains
more than maximum solute at the given conditions a very
unstable solution.
A Supersaturated Solution Videos
Fun
with Sodium Acetate
Solubility
Solubility The concentration of solute in
solution when the solution is saturated.
(Expressed as g/100 mL H2O)
Solubility is measured and recorded with a solubility
graph.
Solubility Graph
Solubility Curves of Pure Substances
•The curve shows the # of grams of
solute in a saturated solution
containing 100 mL or 100 g of water at
a certain temperature.
150
140
KI
130
120
110
NaNO3
•Any amount of solute below the line
indicates the solution is unsaturated at
a certain temperature
grams solute per 100 grams H2O
100
90
KNO3
80
70
NH4Cl
NH3
60
50
•Any amount of solute above the line in
which all of the solute has dissolved
shows the solution is supersaturated.
KCl
40
NaCl
30
20
KClO3
10
Ce2(SO4)3
0
0
10
20
30
40
50
60
Temperature/Celsuis
70
80
90
100
Solution Concentration




The word concentration refers to how much solute
is dissolved.
Dilute means that only a little solute is dissolved
and concentrated means a lot is dissolved.
These are NOT numerical type numbers, but they
are words you should be familiar with.
There are three concentration words that are
numerical in nature: % by mass, molarity and
molality.
Percentage by mass
The % by mass is calculated by dividing the
mass of solute dissolved by the mass of the
total solution.
mass solute (g)
% mass 
x100
mass of solution (g)
Percentage by mass
Example problem:
What is the percentage by mass of a 500.0 g
salt solution that has 25.0 g of CaCl2 in
475.0 g of water?
25.0 g
% mass 
x100  5.00%CaCl 2
500.0 g
Molarity

The molarity of a solution is calculated by taking
the moles of solute and dividing by the liters of
solution.
moles solute (mol)
Molarity (M) 
liters solution (L)
Molarity (M)




Example #1 - Suppose we had 1.00 mole of sucrose (it's
about 342.3 grams) and proceeded to mix it into some
water. It would dissolve and make sugar water. We keep
adding water, dissolving and stirring until all the solid was
gone. We then made sure that when everything was wellmixed, there was exactly 1.00 liter of solution.
What would be the molarity of this solution?
The answer is 1.00 mol/L. Notice that both the units of mol
and L remain. Neither cancels.
A replacement for mol/L is often used. It is a capital M. So
if you write 1.00 M for the answer, then that is correct.
Molarity

Example #2 - Suppose you had 2.00 moles of
solute dissolved into 1.00 L of solution. What's
the molarity?

The answer is 2.00 M.
Notice that no mention of a specific substance is
mentioned at all. The molarity would be the same.
It doesn't matter if it is sucrose, sodium chloride
or any other substance. One mole of anything
contains 6.02 x 1023 units.

Molarity


Now, let's change from using moles to grams.
Example #4 - Suppose you had 100.0 grams of
NaCl and you dissolved it in exactly 2.00 L of
solution. What would be the molarity of the
solution?
100.0 g NaCl
1

1 mol NaCl
58.5 g NaCl
1
2.00 L
The answer is .855 mol/L (or 0.855 M). Sometimes,
a book will write out the word "molar," as in 0.855molar.
Molarity
Try these examples problems :

5) Calculate the molarity of 25.0 grams of KBr
dissolved in 750.0 mL.

6) 80.0 grams of glucose (C6H12O6, mol. wt =
180. g/mol) is dissolved in enough water to
make 1.00 L of solution. What is its molarity?
Molality
The molality of a solution is calculated by taking the moles
of solute and dividing by the kilograms of solvent.
This is a second method of calculating concentration one
that becomes more useful for colligative properties.
moles solute (mol)
Molality (m) 
kilograms of solvent
Molality
Example #1 - Suppose we had 1.00 mole of
sucrose (it's about 342.3 grams) and proceeded to
mix it into exactly 1.00 liter water. It would
dissolve and make sugar water. We keep adding
water, dissolving and stirring until all the solid
was gone. We then made sure everything was
well-mixed.
 What would be the molality of this solution?
Notice that my one liter of water weighs 1000
grams (density of water = 1.00 g / mL and 1000
mL of water in a liter). 1000 g is 1.00 kg, so:

Molality

The answer is 1.00 mol/kg. Notice that both the units
of mol and kg remain. Neither cancels.

A replacement for mol/kg is often used. It is a lowercase m and is often in italics, m. Some textbooks also
put in a dash, like this: 1.00-m.
Molality

Example #2 - Suppose you had 2.00 moles of solute
dissolved into 1.00 L of solvent. What's the molality?

The answer is 2.00 m.
Notice that no mention of a specific substance is mentioned
at all. The molarity would be the same. It doesn't matter if it
is sucrose, sodium chloride or any other substance. One mole
of anything contains 6.022 x 1023 units.

Molality



Now, let's change from using moles to grams.
Example #4 - Suppose you had 100 grams of NaCl and
you dissolved it in exactly 2.00 kg of pure water (the
solvent). What would be the molality of the solution?
100.0 g NaCl
1 mol NaCl
1
1
58.5 g NaCl
2.00 kg
The Answer is 0.855 mol/kg (or 0.855 m). Sometimes,
a book will write out the word "molal," as in 0.855molal.
Molality
Try these examples problems:

5) Calculate the molality of 25.0 grams of KBr
dissolved in 750.0 mL pure water.

6) 80.0 grams of glucose (C6H12O6 mol. wt =
180. g/mol) is dissolved in1.00 kg of water.
Calculate the molality.
Changing the Concentration
Dilution

To dilute a solution means to add more solvent
without the addition of more solute. The
resulting solution is thoroughly mixed and all
parts of the solution are evenly distributed.

The total number of solute particles stays
constant, from this you can determine the
Concentration.

moles before dilution = moles after dilution
Dilution


From the definition of molarity, we know that the
moles of solute equals the molarity times the volume.
So we can substitute MV (molarity times volume) into
the above equation, like this:
M1V1= M2V2

The "sub one" refers to the situation before dilution and
the "sub two" refers to after dilution.
Dilution

Example #1 - 53.4 mL of a 1.50 M solution of NaCl is
on hand, but you need some 0.800 M solution. How
many mL of 0.800 M can you make?
Using the dilution equation, we write:
M1V1= M2V2
(1.50 mol/L) (53.4 mL) = (0.800 mol/L) (x)
Solving the equation for x gives an answer of 100. mL.

Notice that the volumes need not be converted to liters.
Any old volume measurement is fine, just so long as the
same one is used on each side.
Dilutions
Example #2 - 100.0 mL of 2.500 M KBr solution
is on hand. You need 0.5500 M. What is the final
volume of solution which results? How do you
make this solution?
M1V1= M2V2
(2.500 mol/L) (100.0 mL) = (0.5500 mol/L) (x)


x = 454.5 mL Sometimes the problem might ask
how much more water must be added. In this last
case, the answer is 454.5 - 100.0 = 354.5 mL.