Physical Properties of Solutions
Chapter 12
with bits of Chapter 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Review:
What is a solution?
homogenous mixture of 2 or more substances
What is a solute?
What is a solvent?
L IQUID S OLUTIONS

Miscibility

Limit on the amount of one liquid that
can dissolve in another

Ethanol and water are miscible in all
proportions

Oil and water are immiscible. They
cannot mix in any proportions.
Three types of interactions in the solution process:
• solvent-solvent interaction
• solute-solute interaction
• solvent-solute interaction
DHsoln = DH1 + DH2 + DH3
“ 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


polar molecules are soluble in polar solvents


CCl4 in C6H6
C2H5OH in H2O
ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)
C OLLOID
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
T YNDALL E FFECT

Scattering of light beam caused by the
reflection from suspended particles
C OLLOID – T YNDALL E FFECT
S USPENSION – T YNDALL E FFECT
S OLUTION – T YNDALL E FFECT
S OLUTION S ATURATION
saturated solution:
contains the maximum amount of a solute that will dissolve in
a given solvent at a specific temperature
unsaturated solution:
contains less solute than the solvent has the capacity to
dissolve at a specific temperature
supersaturated solution:
contains more solute than is present in a saturated solution at
a specific temperature
W HAT IS A
SUPERSATURATED SOLUTION ?

Observe the heat pack:


What is inside the container?
Click the disc on the inside:

What happens?

Why does this occur?
S UPERSATURATION
Sodium acetate crystals rapidly form when a
seed crystal is added to a supersaturated
solution of sodium acetate.
Seed Crystal Video
FACTORS A FFECTING THE
R ATE OF D ISSOLUTION
To increase the rate of dissolution:
What would  Increase surface area of solute
you do to
 Stirring or shaking to increase contact
make
between the solvent and solute surface
lemonade
mix faster?

Increase temperature, more collisions
between solute and solvent
C RYSTALLIZATION VS
P RECIPITATION

Crystallization:
process in which dissolved solute comes out
of solution and forms crystals

Precipitation:
when an insoluble solid forms from the
reaction of two solutions
E LECTROLYTES
Electrolyte:
substance that, when dissolved in water, results in a
solution that can conduct electricity
• can be strong or weak
Nonelectrolyte:
substance that, when dissolved, results in a solution
that does not conduct electricity
E LECTROLYTES
____________
____________
____________
E LECTROLYTES D EMO

Water

Sodium Chloride Solution

Sugar Solution

Pure Acetic Acid

Acetic Acid Solution

Gatorade

Rubbing Alcohol
W HAT CAUSES A STRONG
ELECTROLYTE ?
Strong Electrolyte – 100% dissociation
Cations (+) and Anions (-)
NaCl (s)
H2O
Na+ (aq) + Cl- (aq)
Weak Electrolyte – not completely dissociated
CH3COOH
CH3COO- (aq) + H+ (aq)
W HAT CAUSES A
NONELECTROLYTE ?
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6 (s)
H2O
C6H12O6 (aq)
Strong Electrolyte Weak Electrolyte
Nonelectrolyte
HCl
CH3COOH
(NH2)2CO
HNO3
HF
CH3OH
HClO4
HNO2
C2H5OH
NaOH
H2O
C12H22O11
Ionic Compounds
H OW DOES A SOLUTION FORM ?
Hydration:
process in which an ion is surrounded by water
dRemember the polarity of water:
d+
H2O
How will the water molecule arrange around a specific ion?
H YDRATION ON THE
PARTICLE L EVEL
the molecules are arranged in a specific manner
Solvation Process Simulation
P RECIPITATION R EACTIONS
Precipitate: insoluble solid that separates from solution
precipitate
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I-
PbI2 (s) + 2Na+ + 2NO3-
ionic equation
Pb2+ + 2IPbI2
PbI2 (s)
net ionic equation
Na+ and NO3- are spectator ions
W RITING N ET I ONIC
E QUATIONS
1. Write the balanced molecular equation.
2. Determine precipitate from solubility rules
3. Write the ionic equation showing the strong electrolytes
4. Cancel the spectator ions on both sides of the ionic equation
DON’T FORGET YOUR
SOLUBILITY RULES!!!
N ET I ONIC E QUATION
P RACTICE
Write the net ionic equation for the reaction of
silver nitrate with sodium chloride.
AgNO3 (aq) + NaCl (aq)
AgCl (s) + NaNO3 (aq)
Ag+ + NO3- + Na+ + Cl-
AgCl (s) + Na+ + NO3-
Ag+ + Cl-
AgCl (s)
C ONCENTRATION
Concentration: amount of solute present in
a given quantity of solvent or solution
C ONCENTRATION
C ALCULATIONS
Percent by Mass
mass of solute
x 100%
% by mass =
mass of solute + mass of solvent
mass of solute x 100%
=
mass of solution
Mole Fraction (X)
moles of A
XA =
sum of moles of all components
H OW TO C ALCULATE
C ONCENTRATION
Molarity (M)
M =
moles of solute
liters of solution
Molality (m)
m =
moles of solute
kilograms of solvent
Why is molarity not a
preferred unit under
certain conditions?
Volume of a solution
changes with temperature
C ALCULATIONS

Molarity:


How many grams of NaOH are needed to
make 250 mL of a 5.00 M NaOH
solution?
Molality:

What is the molality of a solution of 10.0
g of NaOH dissolved in 0.100 kg of
water?
I MPORTANT R ELATIONSHIPS
moles of solute
M =
liters of solution
moles of solute
m =
mass of solvent (kg)
Total mass of solution = mass of solute + mass of solvent
W HAT
5.86 M
IS THE MOLALITY OF A
(C 2 H 5 OH) SOLUTION
DENSITY IS 0.927 G / M L?
ETHANOL
WHOSE
1. Assume 1 L of solution
5.86 moles ethanol (solute)
2. Find grams of solute
= 270 g eth
3. Find grams of solution
(1000 mL x 0.927 g/mL) = 927 g solution
4. Find kg of solvent
g of solvent = g of soln – g of solute
= 657 g = .657 kg
5. Calculate molality
= 8.92 m
W HAT IS THE MOLALITY OF A 62.5%
SODIUM CHLORIDE SOLUTION ?
1.
Assume 100 grams of solution
2.
Find moles of solute
3.
Find kg of solvent
4.
Calculate molality
A DDITIVE C ONCENTRATION
If 25.0 mL of 3.75 M NaCl solution is added to
50.00 mL of 1.35 M NaCl solution. What is
the molarity of the resulting solution?
S OLUTION S TOICHIOMETRY
50.0 mL of a 2.0 M solution of AgNO3 is reacted
with a 50.0 mL of a 1.5 M solution of
Na3PO4. How many grams of Ag3PO4 are
produced?
G RAVIMETRIC A NALYSIS
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
G RAVIMETRIC A NALYSIS CONT.
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to
determine information about unknown reactants
D ILUTION
procedure for preparing a less concentrated solution from a more
concentrated solution
Dilution
Add Solvent
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
How would you prepare 60.0 mL of 0.2 M
HNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00
Vi =
Mf = 0.200
MfVf
Mi
Vf = 0.06 L
Vi = ? L
0.200 x 0.06
=
= 0.003 L = 3 mL
4.00
3 mL of acid + 57 mL of water = 60 mL of solution
H OW TO P REPARE A S OLUTION
T EMPERATURE AND
S OLUBILITY
Solid solubility and temperature
solubility increases with
increasing temperature
solubility decreases with
increasing temperature
T EMPERATURE AND
S OLUBILITY
Gas solubility and temperature
solubility usually
decreases with
increasing temperature
H ENRY ’ S L AW IS USED TO
M EASURE VAPOR P RESSURE

Some gases react with water and cause a
greater solubility than expected

Exceptions to Henry’s Law

Carbon Dioxide
CO2 + H2O

H2CO3
Ammonia
NH3 + H2O
NH4+OH-
S OLUBILITY C URVES

Identify the solubility at a
specific temperature.

Identify the temperature at
which something can dissolve.

Identify whether something is
saturated, unsaturated, or
supersaturated.

Identify which one is a gas.

Identify solubility in different
amounts of water.

Identify how much will
crystallize with a temperature
change.
C OLLIGATIVE P ROPERTIES OF
N ONELECTROLYTES

Colligative properties: properties that
depend only on the number of solute
particles in solution and not on the nature
of the solute particles

Vapor Pressure Lowering

Boiling Point Elevation

Freezing Point Depression

Osmotic Pressure
VAPOR P RESSURE L OWERING
Calculating Partial Vapor Pressure for Solvent
P1 = X1 P 1
0
P 10 = vapor pressure of pure solvent
X1 = mole fraction of the solvent
Finding the change in partial pressure with one solute:
(Xsolute + Xsolvent = 1)
X2 = 1 – X1
DP = X2 P 01
X2 = mole fraction of the solute
B OILING -P OINT E LEVATION
DTb = Tb – T b0
T b0 = boiling point of the pure solvent
T b = boiling point of the solution
DTb = Kb m
m = molality of the solution
Kb = molal boiling-point
elevation constant (0C/m)
F REEZING -P OINT D EPRESSION
DTf = T 0f – Tf
T
0
f
= freezing point of the pure solvent
T f = freezing point of the solution
DTf = Kf m
m = molality of the solution
Kf = molal freezing-point
depression constant (0C/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 62.01 g.
DTf = Kf m
Kf water = 1.86 0C/m
moles of solute
m =
mass of solvent (kg)
478 g x
1 mol
62.01 g
=
= 2.41 m
3.202 kg solvent
DTf = Kf m = 1.86 0C/m x 2.41 m = 4.48 0C
DTf = T 0f – Tf
Tf = T 0f – DTf = 0.00 0C – 4.48 0C = -4.48 0C
O SMOTIC P RESSURE ( P )
Osmosis: selective passage of solvent molecules through a porous
membrane from a dilute solution to a more concentrated one.
semipermeable membrane allows the passage of solvent molecules but
blocks the passage of solute molecules.
Osmotic pressure (p) : pressure required to stop osmosis
dilute
more
concentrated
O SMOTIC P RESSURE ( P )
High
P
Low
P
p = MRT
M = molarity of the solution
R = gas constant (0.0821 L·atm/mol·K)
T = temperature (in K)
O SMOTIC P RESSURE C ALCULATION

The average osmotic pressure of seawater is
about 30.0 atm at 25oC. Calculate the molar
concentration of an aqueous solution of
urea that is isotonic with seawater.

Solution:
M=
π
RT
=
30.0 atm
(0.0821 Latm/molK)(298 K)
= 1.23 M
E QUATION S UMMARY
Vapor-Pressure Lowering
P1 = X1 P 10
Boiling-Point Elevation
DTb = Kb m
Freezing-Point Depression
DTf = Kf m
Osmotic Pressure (p)
p = MRT
C OLLIGATIVE P ROPERTIES OF
E LECTROLYTE S OLUTIONS
0.1 m Na+ ions & 0.1 m Cl- ions
0.1 m NaCl solution
0.1 m NaCl solution
van’t Hoff factor (i) =
0.2 m ions in solution
actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
i should be
nonelectrolytes
NaCl
CaCl2
1
2
3
E LECTROLYTE S OLUTION
E QUATIONS
Boiling-Point Elevation
DTb = i Kb m
Freezing-Point Depression
DTf = i Kf m
Osmotic Pressure (p)
p = iMRT
VAN ’ T
H OFF FACTOR