Fall 2011 Chem 110 Exam III Monday, November 7, 6:30 pm – 7:45 pm
Data sheet and periodic table will be provided.
Conflicts: For legitimate PSU conflicts, sign up for a conflict exam during your lecture. Work, sports, extracurriculars, etc. do not qualify for the conflict exam.
Location: My Section: My TA: My Room: My PSU student ID number:
Bring: #2 pencils; PSU photo ID, Non-text programmable calculator.
Do NOT bring: Cell phones, PDA's, or any other electronic devices
Material Covered: Lectures 22 – 33, ALEKS Objectives 8 – 11
Format: 28 Multiple choice questions. Some calculations, some concept questions. A 100% Score earns 34 points out of 200 course points (17% of final grade).
Advice: Follow suggestions about how to prepare for exam (posted on Angel -> Lessons -> Learning tools). Do the sample practice exams on Angel; select handouts Do the online practice exams on Angel Do all homework problems –especially the blue packet! Go to the review sessions and office hours!
Jensen Chem 110 Chap 13 Page: 2
Week 11: Lectures 31 – 33
Lecture 31: W 11/2 Lecture 32: F 11/4 Lecture 33: M 11/7 (Exam Review) Reading:
BLB Ch 13.5 – 13.6 Homework:
BLB 13: 9, 58, 61, 69, 75; Supp 13: 13 - 18
Reminder:
Angel Quiz 10 due on Thur 11/3
ALEKS Objective 11 due on Sat 11/5
Angel Quiz 11 due on Sun 11/6
Jensen Office Hour: 501 Chemistry Building Tuesdays & Thursdays, 10:30 – 11:30 am
Exam 3: Mon, Nov. 7, 6:30 – 7:45 pm
Jensen Chem 110 Chap 13 Page: 3
Colligative Properties: Properties that depend only on the total number (concentration) of the
solute particles, but not on their identity
! 0.2 M aqueous solution of Pb(NO3)2 Is it an electrolyte? What ions or molecules (solute particles) are present in this solution? total concentration of solute particles =
! 0.2 M aqueous solution of HF Is it an electrolyte? What ions or molecules (solute particles) are present in this solution? total concentration of solute particles =
! 0.2 M solution of C6H12O6 (glucose)
Is it an electrolyte? What ions or molecules (solute particles) are present in this solution? total concentration of solute particles =
Jensen Chem 110 Chap 13 Page: 4
Examples of Colligative Properties
• vapor pressure lowering Raoult!s law: PA = XAPA°
PA ! vapor pressure of solution
XA ! mole fraction of solvent
PA° ! vapor pressure of pure solvent
• boiling point elevation "Tb = Kb m
Kb ! molal boiling point elevation constant
m ! total molality of all solute particles • freezing point depression
"Tf = Kf m
Kf ! molal freezing point depression constant
m ! total molality of all solute particles
• osmotic pressure
M ! total molarity of all solute particles
Jensen Chem 110 Chap 13 Page: 5
Vapor Pressure Lowing
Addition of a nonvolatile solute lowers the vapor pressure
pure solvent solvent + solute
Vapor pressure lowering is a colligative property that depends on total concentration of all solute
particles, but not on their identity
Raoult!s Law: PA = XAPA°
PA ! vapor pressure of solution PA° ! vapor pressure of pure solvent XA ! mole fraction of solvent
Jensen Chem 110 Chap 13 Page: 6
Example: Calculate the vapor pressure at
25 °C of a 40.0% by mass solution of
ordinary cane sugar (C12H22O11, a nonvolatile
non-electrolyte with MW = 342g/mol) in
water. The vapor pressure of pure water at
25 °C is 23.8 torr.
Jensen Chem 110 Chap 13 Page: 7
Phase Diagrams for a pure solvent and for a
solution of a nonvolatile solute
How is melting point affected by the solute particles?
How is boiling point affected by the solute particles?
Jensen Chem 110 Chap 13 Page: 8
Boiling Point Elevation &
Freezing Point Depression
Boiling point increase: "Tb = Kb m
Boiling point of solution = Tb,solvent + "Tb
Kb : molal boiling point elevation constant
Freezing point decrease: "Tf = Kf m
Freezing point of solution = Tb,solvent - "Tf
Kf : molal freezing point depression constant
! m ! total molality of all solute “particles” in the solution
! Kb and Kf are tabulated for different solvents
Eg. water Kb = 0.51°C/m; Kf = 1.86°C/m;
benzene Kb = 2.53°C/m Kf = 5.12°C/m
Jensen Chem 110 Chap 13 Page: 9
Daniel Fahrenheit Fahrenheit prepared a saturated ammonium chloride solution called a “Frigorific Mixture” (a solution that stabilizes at a fixed temperature). The mixture was 20.4% NH4Cl by weight. What was the freezing point of the mixture? The freezing point depression constant for H2O is 1.86 °C/m.
Jensen Chem 110 Chap 13 Page: 10
Practice Example: Ethanol normally boils at
78.4°C. The boiling point elevation constant
for ethanol is 1.22 °C/m. What is the boiling
point of a 1.00 m solution of CaCl2 in
ethanol?
A. 77.2°C
B. 79.6°C
C. 80.8°C
D. 82.1°C
E. 83.3°C
Jensen Chem 110 Chap 13 Page: 11
Practice Example: A solution contains 10.0 g
of an unknown liquid and 90.0 g water, and
has a freezing point of –3.33 °C. Assuming
that the solute is a non-electrolyte, what is
the molar mass of the unknown liquid? The
freezing point depression constant for water
is 1.86 °C/m.
A. 69.0 g/mol
B. 333 g/mol
C. 619 g/mol
D. 161 g/mol
E. 62.1 g/mol
Jensen Chem 110 Chap 13 Page: 12
Osmosis: Flow of molecules through a
semipermeable membrane NET movement of solvent is toward solution with higher solute concentration; movement continues until osmotic pressure builds up to stop it.
Osmotic pressure (#): pressure needed to stop osmotic flow of a molecule through a membrane
• # is osmotic pressure (units of atm) • R is gas constant in (L atm)/(mol K) • T is temperature in K • M is concentration in molarity (mol/L)
Jensen Chem 110 Chap 13 Page: 13
Example: What is the osmotic pressure of a
0.100 M solution of a non-electrolyte at
20 °C?
A. 1.00 atm
B. 2.41 atm
C. 0.164 atm
D. 4.82 atm
E. 1.64 atm
Jensen Chem 110 Chap 13 Page: 14
Practice Example: Calculate the molecular
weight of a small protein (a non-electrolyte)
if a 200 mg sample dissolved in 100 mL of
water has an osmotic pressure of 9.8 mmHg
at 25 °C.
A. 3.5 x 103 g/mol
B. 3.8 x 103 g/mol
C. 4.0 x 104 g/mol
D. 4.5 x 104 g/mol
E. 5.5 x 103 g/mol
Jensen Chem 110 Chap 13 Page: 15
Colligative properties Review:
Arrange the aqueous solutions according to
increasing boiling point.
i. 0.10 m Na2SO4
ii. 0.15 m AlCl3
iii. 0.20 m KNO3
A. i < ii < iii
B. i < iii < ii
C. ii < iii < i
D. iii < ii < i
E. iii < i < ii
According to increasing freezing point?
According to increasing vapor pressure?
Jensen Chem 110 Chap 13 Page: 16
Colloids
particle size
Small Large
true solution
colloidal dispersion
heterogeneous
mixture
uniform
molecules uniform
20–2000 Å particles
non-uniform
sedimentary particles
NaCl in H2O
milk (fat particles) fog (water droplets)
silt in river
Jensen Chem 110 Chap 13 Page: 17
Light Scattering
Tyndall effect: light is scattered when $ of light % particle size
For molecules (~5 Å), $ in x-ray region: • visible light passes through solutions
without scattering
For colloids (~200 nm), $ in visible region: • visible light passes through colloidal
suspensions with scattering (milk, fog)
• dust in atmosphere scatters smaller $ light, explains why the sky is blue
Jensen Chem 110 Chap 13 Page: 18
Hydrophilic vs. hydrophobic colloids
• hydrophilic: water-loving
• hydrophobic: water-fearing
• (water-soluble) proteins: hydrophobic core with hydrophilic surface
• detergents: hydrophobic tail with hydrophilic head