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Midterm

chem_3351_third_hour_exam_key_fall_2016Exam


Department
Chemistry & Biochemistry
Course Code
CHEM 3351
Professor
All
Study Guide
Midterm

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Easily Legible Printed Name:______________________________
Page 1 of 8
CHEM 3351 (100), Fall 2016
Professor Walba
Third Hour Exam
November 15, 2016
scores:
1) 20
2) 20
3) 20
4) 20
5) 20
100
PLEASE read the questions very carefully!
PLEASE legibly print your name on each page of the exam.
H
He
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Ne
Cl
Ar
Br
I
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
35
53
1A
2A
3A
4A
5A
6A
7A
8A
CU Honor Code Pledge: On my honor, as a University of
Colorado at Boulder Student, I have neither given nor received
unauthorized assistance.
Signature: ______________________________________
Recitation TA Name: _____________________________
Recitation day and time: ___________________________
This is a closed-book exam. The use of notes, calculators, scratch
paper, or cell phones will not be allowed during the exam. You
may use models brought in a clear Ziploc bag. Please put all your
answers on the test in the appropriate place. Use the backs of the
pages for scratch (there are two additional blank scratch sheets
after the last page of the exam). DO NOT PUT ANSWERS ON
THE SCRATCH SHEETS.
Key

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Page 2 of 8 Total points for this page:
1 (20 pts) a) For each of the following pairs of compounds, circle the one with the higher boiling point, and
give the major reason why. Hint: In each case, the major reason will be one of the following weak
intermolecular interactions: van der Waals attractions, dipole-dipole interactions, or hydrogen bonding.
b) Soap is mostly a mixture of long-chain acid salts such as myristic acid potassium salt (1). Often the structure
of a soap molecule is represented by a squiggle for the hydrocarbon chain, and a ball at the end representing the
“polar head group” (2). In the space below the structures, draw a picture using the squiggle model for the soap
molecules, showing what you expect would happen if you put many of these molecules into water.
dipole-dipole
hydrogen bonding
Van der Waals
Van der Waals
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Page 3 of 8 Total points for this page:
Q1 - continued
c) Grease is mostly hydrocarbon, and is very insoluble in water. This makes hard to wash your greasy hands in
pure water. However, as you know, if you add a little soap, the grease magically goes into the water. Well,
maybe it’s not magic. Draw a cartoon suggesting how the soap might make the grease water-soluble.
d) Soap bubbles are “fluidy” spherical objects that are almost all just air. There is air on the outside of the soap
bubble, and there’s air on the inside. There is a flexible spherical “wall” between the air on the outside and the
inside that’s made out of soap molecules and water.
Since the wall is much thinner than the circumference of the sphere, at the molecular level it looks flat. Draw a
cartoon of what the bubble’s wall looks like at the molecular level, using the lines below to represent a small
part of the wall of the bubble from the side.
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