Name_____________________________________ ____
Student ID Number__________________________ __
TA Name_____________________ _____________
Lab Section_________________________________
Winter 2017 – Enderle
CHEMISTRY 2A
Exam II
Instructions:
CLOSED BOOK EXAM! No books, notes, or additional scrap paper
are permitted. All information required is contained on the exam. Place
all work in the space provided. If you require additional space, use the
back of the exam.
(1) Read each question carefully. Circle Part I answers on front page.
(2) There is no partial credit for the problems in Part I. You will lose
10 points if you do not circle your multiple choice answers on the
front page or if you do not write your TA’s name or section in the
space above.
(3) The last two pages contain a periodic table and some useful
information. You may remove these pages for easy access.
(4) Graded exams will be returned in lab sections next week.
(5) If you finish early, RECHECK YOUR ANSWERS!
U.C. Davis is an Honor Institution
Possible Points
1–16. 48 points
Points
17–19.
21 points
20–21. 10 points
22–23. 20 points
24. 07 points
Total Score (106)
Points
Multiple Choice
(circle one)
1.
A B C D E
2.
A B C D E
3.
A B C D E
4.
A B C D E
5.
A B C D E
6.
A B C D E
7.
A B C D E
8.
A B C D E
9.
A B C D E
10.
A B C D E
11.
A B C D E
12.
A B C D E
13.
A B C D E
14.
A B C D E
15.
A B C D E
Exam II
Page 2 of 10
Part I: Multiple Choice, Concepts & Short Calculations
Circle the correct answer and enter your response on the cover – No partial credit (3 pts each)
1. Simplify the units of the following units: (m3 )(Pa)
A. Pa
B. N
C. kg
D. J
E. unitless
2. Which of the following is most likely to act as a reducing agent?
A. H2S B. SO2 C. SO3 D. H2SO4 E. H2S2O8
3. The illustration to the right shows neon, a monoatomic gas, in a fixed volume
container. What do you suppose is between the circles, if the circles represent the
neon atoms?
A. air B. dust C. pollutants D. nothing E. oxygen
4. The neutralization of 25.0 mL of 0.24 M HCl requires 5.0 mL of NaOH. What is
the molarity of the NaOH solution?
A. 0.6 M B. 2.4 M C. 1.2 M D. 0.048 M E. 5.0 M
5. As the temperature of a gas in a sealed, rigid container is increased, what happens to the density
of the gas?
A. Increases
B. Decreases
C. Does not change
D. Cannot predict
E. Both increases & decreases
6. Each element has unique emission lines with its what?
A. Atomic line spectra
B. Blackbody radiation C. Photoelectric effect
D. Wave-particle duality E. Uncertainty principle
7. A sample of helium gas occupies a volume of 38 L at 780 torr and 25°C. What volume would the
gas occupy at 0°C and 1 atm?
A. 40 L B. 38 L C. 36 L D. 34 L E. 25 L
8. In the reaction:
2 Al(s) + 6 HCl(aq) → 2 AlCl3(aq) + 3 H2(g)
(Here STP designates 273 K & 1.00 atm)
A. 67.2 L of H2(g) at STP is collected for every mole of Al reacted
B. 33.6 L of H2(g) is collected for every mole of Al reacted, regardless of the temperature and
pressure
C. 1.24 cm3 H2(g) at STP is collected for every milligram of Al reacted
D. 6 L HCl(aq) is consumed for every 3 L H2(g) produced
E. 22.4 L of H2(g) is produced for every mole of Al reacted
9. A gaseous hydrocarbon weighing 0.290 g occupies a volume of 125 mL at 25°C and 760 mmHg.
What is the molar mass of this compound?
A. 113 g/mol B. 4.76 × 103 g/mol C. 56.7 g/mol D. 10.5 g/mol E. 43.1 g/mol
Exam II
Page 3 of 10
10. Which one of the following statements accurately describe an aspect of the breakdown of an
ideal gas into a real gas?
A. As the pressure increases, the gas becomes real because there are more interactions and
attractions.
B. As the temperature decreases, the molecules move more slowly such that the effects of
interparticle interactions are significant.
C. As the moles of a gas in the container increases, there is a higher change that molecules
could interact with each other.
D. The molecules in a container take up volume that is not negligible.
E. All of the above
11. How many spin up (+½) electrons can have the following set of quantum numbers:
n = 7 and ℓ = 0?
A. 1
B. 2
C. 3
D. 4
E. 7
12. How many unpaired electrons are in the ground state electron configuration of calcium?
A. 5 B. 2 C. 0 D. 1 E. 3
13. If 4.800 × 10-5 mol of uranium-238 will effuse through a hole in 125 seconds, how many mol of
uranium-235 will effuse through the same hole in the same amount of time?
A. 4.74 × 10-5 B. 4.77 × 10-5 C. 4.80 × 10-5 D. 4.83 × 10-5 E. 4.86 × 10-5
14. The root-mean-square velocity (m/s) of N2 gas at 35°C is…
A. 52.0 B. 177 C. 5.58 D. 524 E. 16.6
15. Calculate the following ratio for a gas at Kelvin temperatures T1 and T2 where T2 = 2T1.
Average kinetic energy at T1 : Average kinetic energy at T2
A. 2.0 B. 0.50 C. 0.71 D. 1.0 E. 1.4
16. A hydrogen atom has a radius of 0.05 nm. The position accuracy of the electron in the hydrogen
atom is 1% the length of the radius. What is the uncertainty in determining the velocity (m/s)?
A. 1 x 108
B. 1x 10-19 C. 1 x 10-16 D. 1 x 10-22
Exam II
Page 4 of 10
Part II: Short Answer
17. (6 points) Fill in the blanks with what is missing. Fill in either the correct ground state electron
configuration (noble gas configuration in spdf condensed form) or the correct neutral element.
W
1s22s22p63s23p63d104s24p64d105s25p64f145d46s2
Br
[Ar] 4s23d104p5
18. (6 points) Write all acceptable values for the missing quantum numbers (n, ℓ, mℓ, ms) in each row
of the table. Note that each row corresponds to a unique set of quantum numbers, and each box may
have more than one acceptable answer. You must determine all possible values for full credit.
n
ℓ
mℓ
ms
2
0,1
-1, 0, 1
+½
4
3
–3
–½
19. (9 points total) Consider an electron with the following quantum numbers to answer parts A
through D:
n = 2, ℓ = 1
A. (2 points) What orbital does this electron belong to? (i.e. 1s, 3d, etc.) 2p
B. (2 points) How many radial nodes does the orbital contain? 0
C. (2 points) How many angular nodes does the orbital contain? 1
D. (3 points) Draw all orbitals given by the quantum numbers above. Include labels for all axes
and nodes.
Shading not required
Exam II
Page 5 of 10
20. (6 points) Circle the correct answer.
Question:
Circle the correct answer.
Which element has the larger atomic radius?
Se
Cl
Which species has the larger radius?
S2-
S
Mg+
Mg2+
Which species has the smaller radius?
21. (4 points) Circle the first statement in the following line of reasoning where a conceptually
incorrect statement was made. All statements refer to the same system. There is only one answer to
this question.
1. You have two gases, A and B, in two separate containers of equal volume and at equal pressure
and temperature.
2. Therefore, you must have the same number of moles of each gas.
3. Because the two temperatures are equal, the average kinetic energies of the two samples are
equal.
4. Therefore, since the energy of such a system corresponds to translational motion…
…the root mean square velocities of the two are equal,
and thus the particles in each sample move, on average, with the same relative speed.
Since A and B are different gases, each must have a different molar mass.
If A has a higher molar mass than B, the particles of A must be hitting the sides of the container
with more force.
9. Thus the pressure in the container of gas A must be higher than that in the container with gas
B.
10. However, one of our initial assumptions was that the pressures were equal.
5.
6.
7.
8.
Exam II
Page 6 of 10
22. (8 points) Fill in the blank: in the column marked “Answer,” fill in the answer that best
describes the statement. Each answer is only two or four-words long.
Answer
Statement
1. The migration of gas particles through space.
Diffusion
Collision Frequency
2. This concept is directly proportional to velocity and
number of particles and indirectly proportional to volume.
Gas
3. This state of matter has relatively low density and can
readily expand or compress.
Endpoint
4. At this point in a titration, the indicator will change
colors.
23. (12 points total) Fill in the blanks in the table below using the given information regarding an
election. Report numerical answers in the units indicated in the table. Use the table at the bottom of
the page to identify the electromagnetic region in this question.
ni
nf
λ (nm)
ν (Hz)
E (J)
u (m/s)
Initial
Final
Wavelength
Frequency
Energy
De Broglie
Velocity
10
9
38860
7.714 x 1012
5.111 x 10-21
18.72
Electromagnetic
Region
Infrared
In this question, is energy released or absorbed? ____Released______________________
Exam II
Page 7 of 10
Part III: Long Answer
Please show all work – Partial credit
24. (7 points total) A sample of nitrogen gas was collected over water at 26°C when the barometric
pressure was 747 Torr. The gas had a volume of 6.523 L. The vapor pressure of water at 26°C is 25.21
Torr.
a) (3 points) What is the partial pressure of the nitrogen gas in Torr?
Ptot = PN2 + PH2O
747 = PN2 + 25.2
PN2 = 721 Torr
Answer:
b) (4 points) How many grams of nitrogen gas were collected? If you could not solve part A, use
700 Torr.
n = PV/RT = (721/760 atm)(6.523 L)/(0.08206)(26+273) = 0.252 mol N2
0.252 mol (28.02 g/mol) = 7.07 g N2
For 700 Torr:
n = PV/RT = (700/760 atm)(6.523 L)/(0.08206)(26+273) = 0.245 mol N2
0.245 mol (28.02 g/mol) = 6.86 g N2
Answer:
Exam II
Page 8 of 10
Solubility Rules:
Compounds that are soluble or mostly soluble
• Group 1, NH4+, chlorates, acetates, nitrates
• Halides (except Pb2+, Ag+, and Hg22+)
• Sulfates (except Ca2+, Sr2+, Ba2+, Pb2+, and Hg22+)
Compounds that are insoluble
• Hydroxides, sulfides (except above rule, and group 2 sulfides)
• Carbonates, phosphates, chromates (except above rules)
Conversions:
1 atm = 14.7 psi = 101,325 Pa = 760 mmHg = 1.01325 bar = 760 Torr; 1in = 2.54 cm; 12 in = 1 ft
Constants:
R = 8.3145 J / mol K = 0.08206 L atm / mol K
c = 2.9979 x 108 m / s
h = 6.626 x 10-34 J s
-31
m (electron) = 9.109 x 10 kg m (proton) = 1.673 x 10-27 kg
d (H2O) = 1.0 g / cm3
g = 9.81 m / s2
Avogadro’s number = 6.022 x 1023 / mol
RH = 2.179 x 10-18 J
m (neutron) = 1.675 x 10-27 kg
Equations and Various Tables:
 b  b 2  4ac
ax + bx + c = 0; x =
2a
2
1 
 1
  3.2881 10 s  2  2 
n 
2
15
1
En 
p = mu
 Z 2 RH
n2

h
mu
P=dgh E=hν
c=λν
Exam II
 x p 
Page 9 of 10
h
4
effusion  rateA
MB

effusion  rateB
MA
Ek 
n2h2
8mL2
1
1 
E  RH  2  2 
n n 
f 
 i
eK = ½mu2 = 3/2RT

n2a 
 P  2 V  nb  nRT
V 

 ( x) 
2  nx 
sin 
, n  1,2,3,...
L  L 
urms  u 2 
3RT
M
PV = nRT Ptotal = P1 + P2 + …
xA = nA / ntot = PA / Ptot = VA / Vtot
Exam II
Page 10 of 10