fall 2011 chem 110 exam iii week 11: lectures 31 – 33courses.chem.psu.edu/chem110fall/lecture...

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


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 =


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


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


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.


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?


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


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.


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


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


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)


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


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


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?


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


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


Hydrophilic vs. hydrophobic colloids

• hydrophilic: water-loving

• hydrophobic: water-fearing

• (water-soluble) proteins: hydrophobic core with hydrophilic surface

• detergents: hydrophobic tail with hydrophilic head

fall 2011 chem 110 exam iii week 11: lectures 31 – 33courses.chem.psu.edu/chem110fall/lecture...

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