CHEM 107 (Fall-2007)
Final Exam (105 pts)
Name: ------------------------------------------------------------------------, Clid # ------------------------------LAST NAME, First
(Circle the alphabet segment of your LAST NAME): A-C
D-H
I-L
M-R
S-Z
Please answer the following questions:
Part I: Multiple Choices (54 pts: 18 @ 3 pts each). Circle the ONE best answer:
1. Which of the following molecules is classified as predominantly ionic?
a) SO3
b) OCl2
d) P2S5
d) NaN3
2. Which of the following species have linear molecular shape?
I) SO2
III) NO2+
II) OF2
IV) XeF2
a) III and IV
b) only IV
c) I and III
d) I and II
3. Which of the following ions is expected to be paramagnetic?
a) Zn2+
b) O2-
c) Cu+
d) Co2+
4. Calculate the wavelength, in meters, of microwave radiation that corresponds to an energy of 2.63
J/mol photons.
a) 2.63
b) 4.55 x 10-2
c) 1.14 x 108
d) none of the above
5. The ground state electron configuration of tantalum, Ta (Z = 73) is
a) [Xe] 5d3 6s2
b) [Xe] 4f14 5d3 6s2
c) [Xe] 4f14 6d3 6s2
d) [Xe] 4f14 5d5
6. Aluminum and oxygen react according to the following equation:
4 Al (s) + 3 O2 (g)
2 Al2O3 (s)
What mass of Al2O3, in grams, can be made by reacting 4.6 g of Al with excess oxygen?
a) 35
b) 17
c) 1.2
d) 8.7
7. If a gold ring has a mass of 5.50 g in temperature from 25.0 to 28.0 ºC, how much heat is
absorbed? (specific heat of gold is 0.129 J/g ºC)
a) 2.1 J
b) -2.1 J
c) 0.24 J
d) 130 J
1
8. Which name is incorrect?
a) Mg3P2: magnesium phosphide
b) Cr2(SO4)3: chromium(III) sulfate
c) S2F2: disulfur difluoride
d) TiO2: titanium dioxide
9. Calculate ∆H° for the following reaction using the given enthalpies of formation.
2 NO (g) + 5 O2 (g)
2 NO2 (g)
∆Hf° NO (g) = 90.25 kJ/mol & ∆Hf° NO2 (g) = 33.18 kJ/mol
a. +57.07 kJ
b) -57.02 kJ
c) -114.14
d) +114.14 kJ
10. Two aqueous solutions of AgNO3 and NaCl are mixed. Which of the following diagrams best
represents the mixture?
11. What is the best description of Einstein’s explanation of the photoelectric effect?
a) Electrons have a definite mass.
b) Light consists of particles with a definite energy.
c) Ejection of photons occurs when the intensity of light increases beyond a certain minimum.
d) Ejection of electrons occurs when the energy of the photon is greater than a certain minimum.
12. Which of the following molecules is expected to be polar?
a) BeF2
b) CO2
c) XeF4
d) NF3
13. Which of the following has the greatest first ionization energy?
a) Br
b) Sn
c) Se
d) Kr
14. The greatest deviation from the Ideal Gas Law is expected at:
a) high T, high P
b) high T, low P
c) low T, high P
d) low T, low P
15. To what speed, in meters per second, must neutrons be accelerated to have an associated
wavelength of 174 pm? (mass of neutron = 1.675 x 10-27 kg)
a) 2.27 x 103
a) 2.27 x 106
c) 2.2 x 109
d) 2.27
2
16. How many non-bonding electron pairs are there around the central atom in the Lewis structure of
SeF4?
a) 1
b) 2
c) 3
d) 4
17. If gallium, atomic number 31, combines with selenium, atomic number 34, what is the most likely
formula based on your knowledge of the periodic nature of the elements?
a) Ga2Se3
b) GaSe2
c) Ga2Se
d) GaSe
18. Which of the following species would have the largest radius?
a) P3-
b) S2-
c) K+
d) N3-
Part II. (9 pts) Bonding and molecular structure
1. For N2O molecule (laughing gas, NNO):
a) Draw the Lewis structure of the molecule as well as the resonance structures (draw all if there is
any)
b) number σ and π bonds
c) bond angle
d) the molecular shape of the molecule
a) Lewis Structure & resonance (if there is any)
b) # of σ bonds --------
# of π bonds ---------
c) Bond angle ---------------------
d) Molecular shape -------------------3
Part III. Calculations (42 pts: 6 @ 7 pts) Show all work for full credit. Please express all answers
with the proper units and correct number of significant figures.
1. When heated, lithium reacts with nitrogen to form lithium nitride:
6 Li (s) + N2 (s)
2 Li3N (s)
If 12.3 g of Li are heated with 33.6 g of N2:
a) Determine the limiting reactant then
b) What is the theoretical yield of the reaction?
c) If 5.89 g of Li3N is formed. What is the percent yield of the reaction?
a) Limiting reactant
b) Theoretical yield
c) Percent yield
20.6 g
28.6%
4
2. A piece of sodium metal undergoes complete reaction with water as follows:
2 Na (s) + 2 H2O (l)
2 NaOH (aq) + H2 (g)
The hydrogen gas generated was collected over water at 25.0 °C and 1.00 atm. The volume of the wet
gas is 246 mL. Calculate the number of grams of sodium used in the reaction. The vapor pressure of
H2O at 25°C is 23.79 mmHg.
Mass of Na =
3. Calculate the standard heat of formation of carbon disulfide, CS2 from its elements
{C (graphite) + 2 S (rhombic)
CS2 (l)}, given that:
C (graphite) + O2 (g)
CO2 (g)
∆H°rxn = -393.5 kJ
S (rhombic) + O2 (g)
SO2 (g)
∆H°rxn = -296.4 kJ
CS2 (l) + 3 O2 (g)
CO2 (g) + 2 SO2 (g)
∆H°rxn = -1073.6 kJ
∆H°f (CS2, l) =
5
4. Vitamin C is essential for prevention of scurvy (and large doses may be effective in preventing colds).
Combustion of a 0.2000-g sample of this carbon-hydrogen-oxygen compound yields 0.2998 g CO2
and 0.0819 g H2O. What is the empirical formula of vitamin C? In another experiment, the molar
mass of the vitamin was found to be about 178 g/mol. What is the molecular formula of vitamin C?
Empirical Formula
Molecular Formula
C3H4O3
(C3H4O3)2
5. Milk of magnesia is an aqueous suspension of magnesium hydroxide, Mg(OH)2 used to treat acid
indigestion. Calculate the volume of a 0.035 M HCl solution (a typical acid concentration in an upset
stomach) needed to react with two spoonfuls of milk of magnesia (approximately 10.0 mL, at 0.080 g
Mg(OH)2/mL). Hint: you may need to write the chemical equation for the neutralization reaction of
Mg(OH)2 with HCl.
Volume = 0.788 L
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6. An electron in the hydrogen atom makes a transition from an energy state of principal quantum
numbers ni to the n = 2 state. If the photon emitted has a wavelength of 434 nm. What is the value
of ni?
ni = 5
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PREFERENCE SHEET FOR
CHEM 107
Final Exam – Fall 2007
You will have 140 minutes to complete this exam. The exam has 7 pages plus the Periodic Table and
Reference page.
When you are told to do so, tear off the Periodic Table and reference cover sheets and use as required
during the exam.
Equations and Constants:
Density (d) = mass/volume
PV = nRT
K.E. = ½ mv2
root mean square velocity, urms = (3RT/M)1/2
(Rate of effusion of A/Rate of effusion of B) = (MB/MA)1/2
∆E = RH [(1/ni2) – (1/nf2)]
E=hν
c=λν
h = 6.626 x 10-34 J.s
c = 3.00 x 108 m/s
λ = h/mu
RH = 2.180 x 10-18 J
Avogadro’s Number = 6.022 x 1023
R = 0.0821 L.atm/mol.K = 8.314 J/K.mol
1 atm = 760 torr = 760 mmHg
At STP 1 mol of a gas = 22.414 L
1 pm = 10-12 m
q = C.∆T = ms ∆T
General Solubility Guidelines
All nitrates are soluble.
All salts of sodium, potassium and ammonium are soluble.
All chlorides, bromides and iodides are soluble except Ag+, Hg22+, and Pb2+.
All sulfates are soluble except Ba2+, Sr2+, Pb2+ and Hg22+.
All acetates, chlorates and perchlorates are soluble.
Everything else will be considered insoluble.
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1
1
2
H
Periodic Table of the Elements
He
1.01
3
2
3
4
5
6
4.00
4
5
6
7
8
9
10
Li Be
B
C
N
O
F
Ne
6.94
9.01
10.81 12.01 14.01 16.00 19.00 20.18
11
12
13
14
15
16
17
18
Na Mg
Al Si
P
S
Cl Ar
22.99 24.30
26.98 28.08 30.97 32.06 35.45 39.95
19
20
K
Ca Sc Ti V
39.1
40.08 44.96 47.88 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.38 69.72 72.59 74.92 78.96 79.90 83.80
37
38
21
39
Rb Sr Y
22
40
23
41
24
25
26
27
28
29
30
31
32
33
34
35
36
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
42
43
44
45
46
47
48
49
50
51
52
53
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I
54
Xe
85.47 87.62 88.91 91.22 92.91 95.94 (98)
101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.1
55
76
56
57
72
73
74
75
77
Cs Ba La Hf Ta W Re Os Ir
78
79
80
81
82
83
84
85
86
Pt Au Hg Tl Pb Bi Po At Rn
132.9 137.3 138.9 178.5 181.0 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)
87
7
88
89
104 105 106 107 108 109 110 111 112
Fr Ra Ac Rf Db Sg Bh Hs Mt Uun Uuu Uub
(223) 226.0 227.0 (261) (262) (263) (262) (265) (266) (269) (272) (277)
58
59
60
61
62
63
64
65
66
67
68
69
70
71
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
140.1 140.9 144.2 (145) 150.4 152.0 157.2 158.9 162.5 164.9 167.3 168.9 173.0 175.0
90
91
92
Th Pa U
93
94
95
96
97
98
99
100 101 102 103
Np Pu Am Cm Bk Cf Es Fm Md No Lr
232.0 231.0 238.0 237.0 (244) (243) (247) (247) (251) (252) (257) (258) (259) (260)
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