PRACTICE EXAM 1-B
CHEMISTRY E-1ax
LAST NAME: ________________________________________
FIRST NAME: ________________________________________
You should give yourself 2 hours to complete this exam
NOTES:
1. This exam has 6 pages with 6 problems, plus the cover sheet, useful information,
periodic table, and scrap paper.
2. Note the point values of each exam question, and consider where you can best spend
your time.
3. Answer all questions on the exam sheets. Put your final answers in the boxes
provided. If you must use the back, then please indicate that clearly!
4. Do not use red pen!
5. For full credit, show all calculations; this also helps us award partial credit.
6. All numerical answers must include correct units for full credit.
1. ____________
2. ____________
3. ____________
4. ____________
5. ____________
6. ____________
TOTAL: ___________ / 100
1
1.
Osmium (Os, atomic number 76) is the densest stable element, with a density of 22.59 g/mL.
a)
The most common isotope of osmium is
neutrons in one atom of
192
76
192
76
Os . Determine the number of protons and
Os . (2 pts)
# of protons =
b)
# of neutrons =
Osmium can form an ion with a +3 charge. Determine the number of protons and electrons in
one ion of Os+3. (2 pts)
# of protons =
c)
# of electrons =
Determine the number of osmium atoms contained in 2.00 pounds of osmium. (6 pts)
# of Os atoms =
d)
Determine the mass in milligrams of 1.00 cubic inch of osmium. Express your answer in
scientific notation. (6 pts)
mass =
1
atoms
mg
( ______ / 16 pts)
2
2.
Solid magnesium metal will react with oxygen gas to form solid magnesium oxide.
a)
Write a complete, balanced equation for the reaction of magnesium with oxygen as
described above. (Please include state symbols such as (s), (aq), etc.) (2 pts)
b)
Is this an oxidation-reduction reaction? (2 pts) (circle)
c)
1.120 grams of finely powdered magnesium metal is heated in the presence of oxygen.
Calculate the mass of MgO that would be produced if all of the magnesium reacts. (4 pts)
yes
no
mass =
In actuality, this reaction does not proceed to completion. When 1.120 grams of
magnesium was heated, some of the magnesium reacted with oxygen, and the total mass
of both the unreacted magnesium and the magnesium oxide combined is 1.331 grams.
d)
Based on the increase in mass during this reaction, determine the mass of oxygen that
reacted with the magnesium in this reaction. (2 pts)
mass of O2 =
e)
Now that you know the mass of oxygen gas that reacted, calculate the actual mass of
magnesium oxide that was formed. (4 pts)
mass =
f)
Determine the percent yield for this reaction. (2 pts)
percent yield =
2
( ______ / 16 pts)
3
3.
Compound X contains only the elements C, H, and O.
a)
When 5.00 grams of Compound X are completely combusted in excess oxygen, 11.46 g of
CO2 and 1.88 g of H2O are collected. Determine the empirical formula of Compound X.
(12 pts)
empirical formula:
b)
Other experiments reveal that the molar mass of Compound X is approximately 288 g/mol.
Determine the molecular formula of Compound X. (4 pts)
molecular formula:
3
( ______ / 16 pts)
4
4.
a)
Write the chemical formula for each of the following species. (1 pt each)
Magnesium Permanganate
Sulfuric Acid
Silver Chromate
Iron (III) Oxide
Dinitrogen Pentoxide
Ammonia
b)
Write an acceptable chemical name for each of the following. (1 pt each)
CuSO4
NO2
NH4NO2
c)
Write the oxidation state of each atom in the box above the atom. (1 pt per box)
Na2S2O3
d)
C5H5
–
For parts (i) and (ii) below, consider the following balanced chemical reaction:
2 NO + O2 ! 2 NO2
i) Which of the following is a correct statement about the stoichiometry of this reaction?
(Circle the best answer below.) (2 pts)
a) 2 grams of NO will react with 1 gram of O2 to produce 2 grams of NO2.
b) 2 molecules of NO will react with 1 molecule of O2 to produce 2 molecules of NO2.
c) 2 moles of NO will react with 1 mole of O2 to produce 2 moles of NO2.
d) Both (b) and (c) are correct statements.
e) Statements (a), (b), and (c) are all correct statements.
ii) If 3 moles of NO are mixed with 2 moles of O2 and this reaction goes to completion,
how many moles of NO2 will be formed? (Circle the best answer below.) (2 pts)
a) 1 moles
4
b) 2 moles
c) 3 moles
d) 4 moles
e) 5 moles
( ______ / 18 pts)
5
5.
The following two solutions are mixed together:
200.0 mL of 0.200-molar lead (II) nitrate, Pb(NO3)2
300.0 mL of 0.400-molar potassium iodide, KI
A yellow precipitate of lead (II) iodide, PbI2, is formed in a double displacement reaction.
a)
Write a complete, balanced equation, and then a net ionic equation for this chemical
reaction. (Please include state symbols such as (s), (aq), etc.) (6 pts)
Complete:
Net Ionic:
b)
Calculate the mass of lead (II) iodide that would be formed, assuming the reaction goes to
completion, and determine the molar concentration of all ions in the resulting solution.
(Note: Assuming that the reaction goes to completion, some of the concentrations may be
effectively zero.) (12 pts)
mass of PbI2 formed =
[Pb2+] =
[K+] =
5
[NO3–] =
[I–] =
( ______ / 18 pts)
6
6.
You are given 10.00 grams of a mixture of potassium hydroxide, KOH, and barium
hydroxide, Ba(OH)2. You dissolve this mixture in 100. mL of water and titrate the
resulting solution with 0.500 M H2SO4. Complete neutralization of this solution requires
127 mL of H2SO4. Determine the mass of potassium hydroxide and barium hydroxide in
the original mixture. (16 pts)
mass of KOH =
mass of Ba(OH)2 =
6
( ______ / 16 pts)
Scrap Paper
Nothing on this page will be graded unless you clearly indicate
on a specific problem that additional work is located here.
Useful Information
This page will NOT be collected after the exam.
We will NOT grade anything written on this page.
Avogadro’s Number = 6.02 ! 1023
Density of water = 1.00 g/mL
Unit Conversions:
1 mile = 5280 feet
1 foot = 12 inches
1 inch = 2.54 cm
1 mL = 1 cm3
1 kg = 2.205 pounds
27
Co
28
Ni
29
Cu
30
Zn
Fr
Cs
227.03
Ac
138.91
89
La
Y
88.91
57
(261)
Rf
178.49
104
Hf
Zr
91.22
72
47.88
40
Actinide series
Lanthanide series
Ra
Ba
Sr
44.96
39
231.04
Pa
232.04
Th
140.91
91
140.12
90
59
Pr
58
Ce
(263)
183.85
[106]
W
Mo
95.94
74
52.00
42
(262)
Ha
180.95
105
Ta
Nb
92.91
73
50.94
41
238.03
U
144.24
92
60
Nd
(262)
186.21
[107]
Re
Tc
(98)
75
54.94
43
237.05
Np
(145)
93
61
Pm
(265)
190.20
[108]
Os
Ru
101.07
76
55.85
44
(244)
Pu
150.36
94
62
Sm
(266)
192.22
[109]
Ir
Rh
102.91
77
58.93
45
(243)
Am
151.96
95
63
Eu
195.08
Pt
Pd
106.42
78
58.69
46
(247)
Cm
157.25
96
64
Gd
196.97
Au
Ag
107.87
79
63.55
47
(247)
Bk
158.93
97
65
Tb
200.59
Hg
Cd
112.41
80
65.39
48
(251)
Cf
162.50
98
66
Dy
204.38
Tl
In
114.82
81
69.72
49
Ga
(252)
Es
164.93
99
67
Ho
207.20
Pb
Sn
118.71
82
72.61
50
Ge
(257)
Fm
167.26
100
68
Er
208.98
Bi
Sb
121.76
83
74.92
51
As
(258)
Md
168.93
101
69
Tm
(209)
Po
Te
127.60
84
78.96
52
Se
(259)
No
173.04
102
70
Yb
(210)
At
I
126.91
85
79.90
53
Br
35.45
35
Cl
226.03
26
Fe
S
32.07
34
19.00
17
(223)
25
Mn
P
30.97
33
16.00
16
137.33
88
24
Cr
Si
28.09
32
14.01
15
132.91
87
V
23
Al
26.98
31
12.01
14
87.62
56
Rb
Ca
Mg
10.81
13
(260)
Lr
174.97
103
71
Lu
(222)
Rn
Xe
131.29
86
83.80
54
Kr
Ar
39.95
36
20.18
18
Ne
85.47
55
Ti
22
F
40.08
38
21
Sc
O
39.10
37
K
Na
Li
24.31
20
N
9
22.99
19
C
8
9.012
12
B
7
6.941
11
Be
6
4.003
10
5
4
1.008
3
2
He
H
1
PERIODIC TABLE OF THE ELEMENTS