Unit 9 Lecture Day 4-Colligative Properties
-
Upload
putri-nur-auliya -
Category
Documents
-
view
216 -
download
0
Transcript of Unit 9 Lecture Day 4-Colligative Properties
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
1/41
COLLIGATIVEPROPERTIES
Unit 9Chapter 12
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
2/41
Definition:
The properties of a solution that are dependant
only on the number of solute particles in
solution.
Vapor pressure lowering
Boiling point elevation
Freezing point depression
Osmotic pressure
COLLIGATIVE PROPERTIES
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
3/41
The equilibrium vapor pressure of a solvent with anonvolatile solute is shown in (a).
The equilibrium vapor pressure of a pure solvent is shownin (b).
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
4/41
Which equilibrium has a higher vapor
pressure?
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
5/41
The presence of solute particles results in
fewer solvent molecules sitting at the surface
to escape.
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
6/41
According to RaoultsLaw, the vapor pressure
of a solution with a non-volatile solute is equal
to the vapor pressure of the pure solvent at
that temperature multiplied by its mole fraction.
Psolv = Psolv Xsolv
VAPOR PRESSURELOWERING
The vapor pressure of the solvent is
proportional to the relative number of solventmolecules at the surface the mole fraction
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
7/41
When the solute-solvent attractions are stronger thanthe original solvent-solvent attractions, the solutionvapor pressure will be lower. This is typically the casewhen the solute is nonvolatile.
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
8/41
Definition:
When the vapor pressure of a solvent
containing a solute is compared to the vapor
pressure of the pure solvent, the solutions
vapor pressure is found to be lower.Psolv Psolv= P
VAPOR PRESSURELOWERING
Vapor pressure of
the pure solvent
Vapor pressure of
the solvent insolution
Amount by which
the solvents vaporpressure changed
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
9/41
Eugenol, C10H12O2, is the chief constituent of oil of clove. It is a
pale yellow liquid that dissolves in ethanol, C2H5OH; it has aboiling point of 255C (thus, it has a relatively low vapor
pressure at room temperature). What is the vapor pressure
lowering at 20.0C of ethanol containing 8.56 g of eugenol in
50.0 g of ethanol? The vapor pressure of ethanol at 20.0C is
44.6 mmHg.
VAPOR PRESSURELOWERING
Psolv = Psolv
Xsolv
Psolv Psolv= P
Solute
Solvent
P
Psolv = 44.6 mm Hg Psolv Psolv= P
Psolv Psolv Xsolv =
P
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
10/41
Eugenol, C10H12O2, is the chief constituent of oil of clove. It is a
pale yellow liquid that dissolves in ethanol, C2H5OH; it has aboiling point of 255C (thus, it has a relatively low vapor
pressure at room temperature). What is the vapor pressure
lowering at 20.0C of ethanol containing 8.56 g of eugenol in
50.0 g of ethanol? The vapor pressure of ethanol at 20.0C is
44.6 mmHg.
VAPOR PRESSURELOWERING
Psolv = Psolv
Xsolv
Psolv Psolv= P
Solute
Psolv = 44.6 mm Hg
Psolv Psolv Xsolv =
P(44.6)(44.6) Xsolv =
P
Solvent
8.56gEugenol 1mol
164.22g 0.0521mol
50.0gEthanol 1mol
46..07g 1.086mol
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
11/41
Eugenol, C10H12O2, is the chief constituent of oil of clove. It is a
pale yellow liquid that dissolves in ethanol, C2H5OH; it has aboiling point of 255C (thus, it has a relatively low vapor
pressure at room temperature). What is the vapor pressure
lowering at 20.0C of ethanol containing 8.56 g of eugenol in
50.0 g of ethanol? The vapor pressure of ethanol at 20.0C is
44.6 mmHg.
VAPOR PRESSURELOWERING
Psolv = Psolv
Xsolv
Psolv Psolv= P
Solute
Psolv = 44.6 mm Hg
Psolv Psolv Xsolv =
P(44.6)(44.6) Xsolv =
P
Solvent
solv 1.086mol
1.086mol 0.0521molsolv 0.954
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
12/41
Eugenol, C10H12O2, is the chief constituent of oil of clove. It is a
pale yellow liquid that dissolves in ethanol, C2H5OH; it has aboiling point of 255C (thus, it has a relatively low vapor
pressure at room temperature). What is the vapor pressure
lowering at 20.0C of ethanol containing 8.56 g of eugenol in
50.0 g of ethanol? The vapor pressure of ethanol at 20.0C is
44.6 mmHg.
VAPOR PRESSURELOWERING
Psolv = Psolv
Xsolv
Psolv Psolv= P
Solute
Psolv = 44.6 mm Hg
Psolv Psolv Xsolv =
P(44.6)(44.6)(0.954) = P
Solvent
2.05 mm Hg = P
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
13/41
Remember that for a gaseous solution
(homogeneous mixture), the total pressure of
the solution is the sum of the partial pressures.
(Whos law is that?)
Therefore
Ptotal = Psolvent + Psolute
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
14/41
This means that Raoults law can also beapplied to the vapor pressure of a solution witha volatile solute. The total vapor pressure ofthe mixture would be equal to the vaporpressure created by the solvent added to the
vapor pressure created by the volatile solute.
Ptotal = Psolv Xsolv + Psolute
Xsolute
VAPOR PRESSURELOWERING
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
15/41
PRESSURE LOWERING
AFFECT? In the diagram notice
that the vapor pressurelowers when a solventis mixed with anonvolatile solute.
The Psolv increasesas the temperatureincreases; similarly, thePsolv increases as thetemperature increases.
This means that thelowering of the vaporpressure leads to ahigher boiling point ofthe solution.
Vapor Pressure
(mm Hg)
Temperature (C)
Solvent + Solute
Solvent
P
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
16/41
Definition:
The boiling point of a solution is greater than
the boiling point of the pure solvent because
the solution (which has a lower vapor
pressure) will need to be heated to a highertemperature in order for the vapor pressure to
become equal to the external pressure (i.e.,
the boiling point).
BOILING POINT ELEVATION
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
17/41
The boiling point elevation, Tb, is the
difference between the higher boiling point of
the solution and the boiling point of the pure
solvent.
Tb = Tb Tb
BOILING POINT ELEVATION
Boiling point
elevation
Boiling point
of solution
Boiling point of
pure solvent
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
18/41
The boiling point elevation, Tb
, is directly
proportional to the molality of the solute.
Tb = kb msolute
BOILING POINT ELEVATION
Boiling point
elevation
molal boiling point
elevation constant
molality of
the solute
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
19/41
MOLAL BOILING POINT
ELEVATION CONSTANT
Each solvent has a
different boiling
point constant.
Solvent
Tb ofpure
solvent
(C)
kb
(C/m)
Water 100.00 +0.5121
Benzene 80.10 +2.53
Camphor 207.4 +5.611
Chloroform 61.70 +3.63
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
20/41
A solution was made up of eugenol, C10H12O2, in diethyl ether. If
the solution was 0.575 m eugenol in ether, what was the boilingpoint of the solution? The boiling point of pure ether is 34.6C
and the boiling-point-elevation constant is 2.02C/m.
BOILING POINT ELEVATION
Tb = kb msoluteTb = Tb Tb
Solute
Solve
ntTb
Tb = 34.6Ckb = 2.02C/m
m = 0.575 m
Tb = ??
kb msolute= Tb = TbTb(2.02C/m)(0.575 m) = Tb
(34.6C)35.8C = Tb
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
21/41
antifreeze, cocoa, gasoline and ethanol,
salted pasta water (just kidding)
BOILING POINT ELEVATION
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
22/41
Addition of a nonvolatile solute to the volatile
solvent increases the attractions (and lowers
the vapor pressure). This means that the
particles are closer together so a lower
temperature allows them to freeze.
FREEZING POINTDEPRESSION
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
23/41
The freezing point depression, Tf
, is the
difference between the higher freezing point of
the pure solvent and the freezing point of the
solution.
Tf= Tf Tf
FREEZING POINTDEPRESSION
Freezing point
depression
Freezing point
of pure solvent
Freezing point
of solution
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
24/41
The freezing point depression, Tf
, is directly
proportional to the molality of the solute.
Tf= kf msolute
FREEZING POINTDEPRESSION
Freezing point
depression
molal freezing
point depression
constant
molality of
the solute
MOLAL FREEZING POINT
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
25/41
MOLAL FREEZING POINT
DEPRESSION CONSTANT
Each solvent has a
different freezing
point constant.
Solvent
Tf ofpure
solvent
(C)
kb
(C/m)
Water 0.0 +1.86
Benzene 5.50 +5.12
Camphor 179.95 +39.7
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
26/41
A solution was made up of 0.575 m eugenol, C10H12O2, in diethyl
ether. What was the freezing point of the solution? The freezingpoint of pure ether is -116.3C and the freezing-point-depression
constant is
1.79C/m.
FREEZING POINTDEPRESSION
Tf= kf msoluteTf= Tf Tf
SoluteSolve
ntTf
Tf =116.3Ckf= 1.79C/m
m = 0.575 m
Tf= ??
kf msolute= Tf= TfTf(1.79C/m)(0.575 m) = (116.3C)
Tf117.3C = Tb
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
27/41
antifreeze (HEAT), salt on icy roads,
making ice cream, Crystal Lake freezes
before the pond in Veterans Acres
FREEZING POINTDEPRESSION
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
28/41
COLLIGATIVE PROPERTYANIMATION
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.htmlhttp://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.htmlhttp://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.htmlhttp://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html -
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
29/41
Osmosis is the diffusion of small molecules
through a semi-permeable membrane.
Usually, osmosis is seen in the net movement
of the solvent from the pure solvent (low solute
concentration) to solution (high soluteconcentration).
OSMOTIC PRESSURE
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
30/41
The membrane is
termed semi-
permeable because
small molecules such
as water or small ions(Na+ or K+) may pass
in either direction
through the
membrane.
OSMOTIC PRESSURE
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
31/41
The solute reduces the mole fraction of the
solvent in a solution. The lower the mole
fraction of solvent, the greater the net flow
of solvent molecules into the solution (and
greater osmotic pressure).
OSMOSIS
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
32/41
OSMOTIC PRESSURE
Osmotic pressure is the pressure necessary to just
stop osmosis. This is done by pressing on the
solution side to increase the movement of solvent
particles from the solution back into the puresolvent.
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
33/41
Osmotic pressure is proportional to the
molar concentration of the solute.
OSMOTIC PRESSURE
MRT PV nRTP
n
VRT
Notice how this equation is
based on the ideal gas
law:
Osmotic
pressure
Molarity of
the solute
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
34/41
Dextran, a polymer of glucose units, is produced by bacteria
growing in sucrose solutions. Solutions of dextran in water havebeen used as a blood plasma substitute. What is the osmotic
pressure (in mmHg) at 21C of a solution containing 1.50 g of
dextran dissolved in 100.0 mL of aqueous solution, if the average
molecular weight of the dextran is 4.0 x 104 amu?
OSMOTIC PRESSURE
SoluteSolvent =
H2O
MRT
MRT
1.50g 1mol
4.0x104 g 3.75x105 mol
M 3.75x10
5 mol
0.1000L 3.75x104 M
3.75x104 M 0.0821 atmLmolL 294K 0.00905atm 6.9mmHg
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
35/41
reverse osmosis, vinegar and eggs, water
transportation in plants, blood pressure
(normal osmotic pressure when compared
to pure water), dialysis of cell walls,
desalinating ocean water
OSMOTIC PRESSURE
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
36/41
When a nonelectrolyte solute dissolves in a
solvent, it dissolves without separating into
ions.
Like methanol dissolving in waterCH3OH(l) CH3OH(aq)
Nonelectrolyte Solutes
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
37/41
When an electrolyte solute dissolves in a
solvent, it does separate into ions.
Like sodium sulfate dissolving in water
Na2SO4(s) 2 Na+(aq) + 1 SO42(aq)
Electrolyte Solutes
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
38/41
Since colligative properties depend on the
number of solute particles, not the identity
of the solute, an electrolyte influences those
properties more than a nonelectrolyte.
A 1.0 M sodium sulfate solution creates how many
particles?
Na2SO4(s) 2 Na+(aq) + 1 SO4
2(aq)
Electrolyte Solutes
2 + 1 = 3 particles
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
39/41
A strong electrolyte, such as Na2SO4, will
dissolve 100 %, creating one particle for
each dissociated ion.
These particles are called the vant Hoff
factor, i.
What is i for potassium phosphate?
Electrolyte Solutes
K3PO4(s) 3 K+(aq) + 1 PO4
3(aq)
4
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
40/41
A weak electrolyte, such as Ag3PO4, will
NOT dissolve 100 %. This means that
fewer particles will be able to influence the
colligative properties.
What is i for silver phosphate?
Electrolyte Solutes
Ag3PO4(s) 3 Ag+(aq) + 1 PO4
3(aq)
-
8/22/2019 Unit 9 Lecture Day 4-Colligative Properties
41/41
How does this change the colligative
properties?
Electrolyte Solutes
Vapor Pressure
LoweringBoiling Point Elevation
Freezing Point
DepressionOsmotic Pressure
P1 1P1o
moleSolvent
moleSolvent (i)moleSolute
P1o
Tb kb m i Tb Tb
o
Tf kf m i Tf
o Tf
iMRT