Chemistry 102(01) Spring 2012
CTH 328 9:30-10:45 am
Instructor: Dr. Upali Siriwardane
e-mail: upali@latech.edu
Office: CTH 311 Phone 257-4941
Office Hours: M,W 8:00-9:00 & 11:00-12:00 am;
Tu,Th,F 8:00 - 10:00 am..
Exams: 9:30-10:45 am, CTH 328.
March 26 , 2012 (Test 1): Chapter 13
April 18 , 2012 (Test 2): Chapter 14 &15
May 14 , 2012 (Test 3): Chapter 16 &18
Optional Comprehensive Final Exam: May 17, 2012 :
Chapters 13, 14, 15, 16, 17, and 18
CHEM 102, Spring 2012 LA TECH
15-1
Chapter 15. The Chemistry of Solutes and
Solutions
15.1
15.2
15.3
15.4
15.5
Solubility and Intermolecular Forces
Enthalpy, Entropy, and Dissolving Solids
Solubility and Equilibrium
Temperature and Solubility
Pressure and Dissolving Gases in Liquids: Henry's
Law
15.6 Solution Concentration: Keeping Track of Units
15.7 Vapor Pressures, Boiling Points, and Freezing Points
of Solutions
15.8 Osmotic Pressure of Solutions
15.9 Colloids
15.10 Surfactants
15.11 Water: Natural, Clean, and Otherwise
CHEM 102, Spring 2012 LA TECH
15-2
Solution Concentration Units
a) Molarity (M)
b) Molality (m)
c) Mole fraction (Ca)
d) Mass percent (% weight)
e) Volume percent (% volume)
f) "Proof"
g) ppm and ppb
CHEM 102, Spring 2012 LA TECH
15-3
1) Define following solution concentration units:
a) Molarity (M)
b) Molality (m)
c) Mole fraction (Ca)
d) Mass percent (% weight)
e) Volume percent (% volume)
f) "Proof"
CHEM 102, Spring 2012 LA TECH
g) ppm and ppb
15-4
Molarity
The number of moles of solute per liter of
solution.
molarity  M
moles of solute
M=
liter of solution
units  molar = moles/liter = M
CHEM 102, Spring 2012 LA TECH
15-5
Molarity Calculation
An aqueous solution 58.5 g of NaCl and 2206g
water has a density of 1.108 g/cm3. Calculate the
Molarity of the solution.
58.5 g  1 mole
Solution volume  58.5 g + 2206 g in L
2264.5 g solution
1 cm3 solution
1 L solution
1.108 g solution
1000 cm3 solution
= 2.044 L solution
1.00 mole NaCl
Molarity of NaCl solution = ------------------------- = 0.489
M
2.044 L solution
CHEM 102, Spring 2012 LA TECH
15-6
Molality
number of moles of solute particles (ions or
molecules) per kilogram of solvent
#moles solute
m=
#kilograms of solvent
Calculate the molality of C2H5OH in water
solution which is prepared by mixing 75.0 mL
of C2H5OH and 125 g of H2O at 20oC. The
density of C2H5OH is 0.789 g/mL.
CHEM 102, Spring 2012 LA TECH
15-7
Molarity Calculation
75.0 mL C2H5OH
0.789 g C2H5OH
1 mole C2H5OH
1 mL
46.08 g C2H5OH
= 1.284 C2H5OH
125 g of H2O = 0.125 kg H2O
1.284 mole C2H5OH
Molality(m) = ------------------------ = 10.27 m
0.125 kg H2O
CHEM 102, Spring 2012 LA TECH
15-8
Mole Fraction
Xi =
#moles of component i
total number of moles
Calculate the mole fraction of benzene in a
benzene(C6H6)-chloroform(CHCl3) solution
which contains 60 g of benzene and 30 g of
chloroform.
M.W. = 78.12 (C6H6)
M.W. = 119.37 (CHCl3)
CHEM 102, Spring 2012 LA TECH
15-9
Mole Fraction Calculation
moles of a
na
Mola Fraction(ca) = ------------------- = -------------moles of na + moles nb na + nb
a = C6H6
b = CHCl3
nC6H6
Mola Fraction(ca) = -----------------nC6H6 + nCHCl3
m.w (C6H6) = 78.12 g/mole m.w (CHCl3) = 119.37 g/mole
60/78.12 = 0.768 mole C6H6
30/119.37 = 0.251 mole CHCl3
ca(C6H6) = 0.768/ 0.786+ 0.251
=0.754
Ca(CHCl3) = 0.0.251/ 0.786+ 0.251 = 0.246
1.000
CHEM 102, Spring 2012 LA TECH
15-10
Weight Percent
wt % =
#g of solute
#g of solution
 102
Volume Percent
Vol % =
#L of solute
#L of solution
 102
Proof
proof = Vol % x 2
CHEM 102, Spring 2012 LA TECH
15-11
Problem
What is the mole fraction of ethanol,
C2H5OH, in ethanol solution that is
40.%(w/w) ethanol, C2H5OH, by mass?
a. 0.40 b. 0.46 c. 0.21 d. 0.54
CHEM 102, Spring 2012 LA TECH
15-12
Parts per Million
#g of solute
#mg of solute
 106 =
ppm =
#g of solution
#kg of solution
#mL solute
ppm =
#L of solution
Parts per Billion
#g of solute
ppb =
#g of solution
CHEM 102, Spring 2012 LA TECH
 109 =
#micro-g of solute
#kg of solution
15-13
ppm and ppb conversions
1 ppm = (1g/ 1x 106g) 1x 106
= (1/1000 g) x 1x 106
1x 106 / 1000g
= mg/ 1x 103 g
= mg/ L
1 ppb = (1g/ 1x 109g) 1x 109
= (1/1000000 g)
1x 109/1000000g
= mg/ 1x 103 g
= mg/ L
CHEM 102, Spring 2012 LA TECH
15-14
Problem
A solution of hydrogen peroxide is 30.0%
H2O2 by mass and has a density of 1.11
g/cm3. The MOLARITY of the solution is:
a) 7.94 M b) 8.82 M
e) none of these
c) 9.79 M d) 0.980
M.W. = 34.02 (H2O2)
CHEM 102, Spring 2012 LA TECH
15-15
Comparison of Concentration
Terms
CHEM 102, Spring 2012 LA TECH
15-16
Effect of Solutes on Solution
Colligative Properties
Colligative Properties: Depend on the number of
particles not on the identity of the particles
Solution Colligative Properties
a) Vapor Pressure Lowering
b) Freezing Point Depression
c) Boiling Point Elevation
d) Osmotic Pressure
Two types of solutes affect colligative properties
differently
a) Volatile solutes (covalent)
b) nonvolatile solutes (ionic)
CHEM 102, Spring 2012 LA TECH
15-17
Vapor Pressure of
Pure Water vs. Sea Water
CHEM 102, Spring 2012 LA TECH
15-18
Vapor Pressure Lowering
Raoult’s Law
P1 = X1P1o
Psol = csolvent Psolvent
Psol = (1-csolute) Psolvent
The vapor pressure above a glucose-water
solution at 25oC is 23.8 torr. What is the mole
fraction of glucose (non-dissociating solute)
in the solution. The vapor pressure of water
at 25oC is 30.5 torr.
CHEM 102, Spring 2012 LA TECH
15-19
Vapor Pressure Lowering
CHEM 102, Spring 2012 LA TECH
15-20
Effect on Boling and Freezing point
CHEM 102, Spring 2012 LA TECH
15-21
Boiling Point Elevation
CHEM 102, Spring 2012 LA TECH
15-22
Boiling Point Elevation
DTb = Tfinal - Tinitial
(DTb = bpsolution - bppure solvent)
DTb = kb x m
where kb => boiling point elevation constant
m => molality of all solutes in solution
Freezing Point Depression
(DTf
= fppure solvent - fpsolution)
DTf = kf x m
where kf => freezing point depression constant
m => molality of all solutes in solution
For electrolytes multiply
i => number of particles per formula unit
CHEM 102, Spring 2012 LA TECH
15-23
Boiling Point Elevation & Freezing
point Depression Constants
CHEM 102, Spring 2012 LA TECH
15-24
Freezing Point Depression Problem
What is the freezing point of a 0.500
m aqueous solution of glucose? (Kf
for H2O is 1.86 oC/m)
(DTf = fppure solvent - fpsolution)
DTf = kf x m
CHEM 102, Spring 2012 LA TECH
15-25
Calculation of Molecular Weight
A 2.25g sample of a compound is dissolved
in 125 g of benzene. The freezing point of
the solution is 1.02oC. What is the
molecular weight of the compound? Kf for
benzene = 5.12 oC/m, freezing point =
5.5oC.
DTf = kf x m
m = moles/ kg of solvent
MW = g/moles
CHEM 102, Spring 2012 LA TECH
15-26
Solvent Freezing
CHEM 102, Spring 2012 LA TECH
15-27
Colligative Properties of
Electrolytes
Number of solute particles in the solution depends
on dissociation into ions expressed as Van’t Hoff
facotor(i)
Van’t Hoff facotor (i)
moles of particles in solution
moles of
solutes dissolved
CHEM 102, Spring 2012 LA TECH
15-28
Colligative Properties of Electrolytes
Ionic vs. covalent substances
vpwater > vp1M sucrose > vp1M NaCl > vp 1M CaCl2
1 mole sucrose = 1 mole molecules (i = 1)
1 mole NaCl = 2 mole of ions (i = 2)
1 mole CaCl2 = 3 moles ions (i = 3)
i => number of particles per formula
unit
Psol = (1- i csolute) Psolvent
DTf = i kf x m
DTb = i kb x m
P = i MRT
CHEM 102, Spring 2012 LA TECH
15-29
Osmosis
CHEM 102, Spring 2012 LA TECH
15-30
Measuring Osmotic Pressure
CHEM 102, Spring 2012 LA TECH
15-31
Osmosis and the Cell
CHEM 102, Spring 2012 LA TECH
15-32
Osmotic Pressure
P = MRTi
where P => osmotic pressure
M => concentration
R => gas constant
T => absolute Kelvin temperature
i => number of particles per formula
unit
CHEM 102, Spring 2012 LA TECH
15-33
Calculation
Calculate the osmotic pressure in
atm at 20oC of an aqueous solution
containing 5.0 g of sucrose
(C12H22O11), in 100.0 mL solution.
M.W.(C12H22O11)= 342.34
P = MRT
R = 0.0821 L-atm/mol K
= 62.4 L-torr/mol K
CHEM 102, Spring 2012 LA TECH
15-34
Calculation
Calculate the osmotic pressure in torr
of a 0.500 M solution of NaCl in water at
25oC. Assume a 100%
dissociation of NaCl.
CHEM 102, Spring 2012 LA TECH
15-35
Which one has higher Osmotic
Pressure
Define the Van't Hoff factor (i).
Which of the following solutions
will show the highest osmotic
pressure:
a) 0.2 M Na3PO4
b) 0.2 M C6H12O6 (glucose)
c) 0.3 M Al2(SO4)3
d) 0.3 M CaCl2
e) 0.3 M NaCl
15-36
CHEM 102, Spring 2012 LA TECH
Normal vs. Reverse Osmosis
CHEM 102, Spring 2012 LA TECH
15-37
Deviations from Raoult’s Law
Vapor Pressure
Intermolecular forces between components in a
dissolved solution cause deviations from the
adjustment to vapor pressure.
Pvap A
Pvap B
cA
CHEM 102, Spring 2012 LA TECH
15-38
Ideal, Negative, Positive Behavior of Vapor
Pressure of Two Volatile Liquids
CHEM 102, Spring 2012 LA TECH
15-39
Ideal, Negative, Positive Behavior
of Vapor Pressure
Predict the type of behavior (ideal,
negative, positive) based on vapor
pressure of the following pairs of
volatile liquids and explain it in terms
of intermolecular attractions:
a) Acetone/water(CH3)2CO/H2O
b) Ethanol(C2H5OH)/hexane(C6H14)
c) Benzene (C6H6)/toluene CH3C6H5.
CHEM 102, Spring 2012 LA TECH
15-40
Acetone/water(CH3)2CO/H2O
CHEM 102, Spring 2012 LA TECH
15-41
Ethanol(C2H5OH)/hexane(C6H14)
CHEM 102, Spring 2012 LA TECH
15-42
Benzene (C6H6)/toluene CH3C6H5
CHEM 102, Spring 2012 LA TECH
15-43
Types of Solutions
a) True solutions
b) Colloids (Tyndall effect)
c) Suspensions.
CHEM 102, Spring 2012 LA TECH
15-44
CHEM 102, Spring 2012 LA TECH
15-45
Solution vs. Dispersion vs. Suspension
Smaller particles => Larger particles
Colloidal
True solution dispersion
Suspension
Particles
particles
Particle size
Properties
Example
Ions & molecules
Colloids
Large-sized
0.2-2.0 nm
2-2000 nm
>2000 nm
* Don’t settle out
* Don’t settle out * Settle out on
on standing
on standing
on standing
* Not filterable
* Not filterable * Filterable
Sea water
Fog
River silt
CHEM 102, Spring 2012 LA TECH
15-46
Tyndall Effect
CHEM 102, Spring 2012 LA TECH
15-47
Surfactants
CHEM 102, Spring 2012 LA TECH
15-48
Soaps and Detergents
O
H
C
O-Na+
H 2CH2C
H 2C
H 2C
H 2CH2C
H 2C
H 2C
H 2CH2C
H 2C
H 2C
H 2CH2C
H 2C
H 2C
3C
Hydrophobic end
Hydrophilic end
sodium stearate
H
C
H 2CH2C
H 2C
H 2C
H 2CH2C
H 2C
H 2C
H 2CH2C
H 2O
S
3C
O-3N
a
+
sodium lauryl sulfate
CHEM 102, Spring 2012 LA TECH
15-49
Cleaning Action
CHEM 102, Spring 2012 LA TECH
15-50
Earth’s Water Supply
CHEM 102, Spring 2012 LA TECH
15-51
Treatment of Drinking Water
CHEM 102, Spring 2012 LA TECH
15-52
Hard Water
natural water containing relatively high
concentrations of Ca+2, Mg+2, Fe+3, or Mn+2
cations and CO3-2 and HCO3-1 anions
CHEM 102, Spring 2012 LA TECH
15-53
Common
Hazardous
Household
Chemicals
CHEM 102, Spring 2012 LA TECH
15-54