Download Exam III Fall 1998 Answers

CHEM 1215
Exam III
John III. Gelder
November 11, 1998
Name KEY
TA's Name ________________________
Lab Section _______
INSTRUCTIONS:
1. This examination consists of a total of 7 different pages.
The last page includes a periodic table and a solubility
table. All work should be done in this booklet.
2. PRINT your name, TA's name and your lab section
number now in the space at the top of this sheet. DO
NOT SEPARATE THESE PAGES.
3. Answer all questions that you can and whenever called
for show your work clearly. Your method of solving
problems should pattern the approach used in lecture.
You do not have to show your work for the multiple
choice (if any) or short answer questions.
4. No credit will be awarded if your work is not shown in
problems 3 - 5 and 8 - 10.
5. Point values are shown next to the problem number.
6. Budget your time for each of the questions. Some
problems may have a low point value yet be very
challenging. If you do not recognize the solution to a
question quickly, skip it, and return to the question after
completing the easier problems.
7. Look through the exam before beginning; plan your
work; then begin.
8. R e l a x and do well.
SCORES
Page 2
Page 3
Page 4
Page 5
Page 6
TOTAL
_____
(30)
_____
(16)
_____
(30)
_____
(12)
_____
(12)
______
(100)
CHEM 1215 EXAM III
PAGE 2
(12) 1. Write the chemical formula(s) of the product(s) and balance the following reactions. Identify all
products phases as either (g)as, (l)iquid, (s)olid or (aq)ueous.
(8)
a)
2H 3PO 4(aq) + 3Ca(OH)2(aq) → Ca 3(PO4)2(s) + 6H2O (l)
b)
2Ba (s)
c)
K2 CO 3 (aq) +
+
2H 2O (l)
→ 2Ba(OH) 2(aq) + H2(g)
2HCl (aq) → CO 2 (g) + H2 O (l) + 2KCl(aq)
2. Write the balanced ionic and balanced net ionic chemical equations for any two of the reactions in
Problem 1. (Remember to include the correct charges on all ions and the phase of each species.)
1a, 1b or 1c)
Ionic equation:
3Ca 2+ (aq) + 6OH– (aq) + 6H+ (aq) + 2PO4 3– (aq) → Ca3 (PO 4 ) 2 (s) +
6H2 O (l)
Net Ionic equation:
Same as ionic equation
1a, 1b or 1c)
Ionic equation:
2Ba (s)
+
2H2 O (l)
→
2Ba 2+ (aq) + 2OH– (aq)
+ H2 (g)
Net Ionic equation:
Same as ionic equation
1a, 1b or 1c)
Ionic equation:
2K + (aq) + CO3 2– (aq) + 2H+ (aq) + 2Cl– (aq) →
C O 2 (g) +
H2 O (l) +
2K+ (aq) + 2Cl– (aq)
1a, 1b or 1c)
Ionic equation:
C O 3 2– (aq) + 2H+ (aq) → C O 2 (g) +
H2 O (l)
(10) 3. Dopamine, C8H11O2N, is a neurotransmitter. Determine the percent (by mass) composition of each of
the elements in dopamine.
96 g C
14 g N
C : 153 g C
· 100 = 62.7 % C
N : 153 g C H O N · 100 = 9.15 % N
H
O
N
8 11 2
8 11 2
32 g O
11 g H
O : 153 g C H O N · 100 = 20.9 % O
H : 153 g C H O N · 100 = 7.19 % H
8 11 2
8 11 2
CHEM 1215 EXAM III
PAGE 3
(10) 4. Find the empirical formula of a compound that is 48.38% carbon, 8.12% hydrogen, and 53.5% oxygen
by mass.
1 mol C
48.38 g C  1 2 . 0 g C = 4.03 mol C


1 mol H
8.12 g H  1 . 0 1 g H = 8.04 mol H


1
m
o
l
O
53.5 g O  1 6 . 0 0 g  = 3.34 mol O


 4 . 0 3 m o l C :  8 . 0 4 m o l H :  3 . 0 8 m o l O
3.34
3.34
3.34

 
 

1.21 C : 2.41 H : 1 O
1.21 x 5 C : 2.41 x 5 H : 1 x 5 O
= 6 C : 12 H : 5 O
C 6 H 12 O 5
(6) 5. The formula of the sulfate of an unknown metal, X, is X2(SO4)3. The compound also is 41.7% X,
19.4% S and 38.9% O. Determine the atomic mass and the symbol of the element X.
1 mol S
19.4 g S  3 2 . 0 g S = 0.606 mol S are in the compound.


According to the formula there are 2 moles X for every 3 moles S. Since we know
howmany moles of sulfur are in the compound we can determine how many moles of
X are present,
2 mol X
0.606 mol S  3 m o l S  = 0.404 mol X are in the compound.


Since o.404 moles of X weigh 41.7 grams the molar mass of X must be,
 4 1 . 7 g X  = 103 g · mol– 1
 0 . 4 0 4 m o l X
The unknown element is Rhodium, Rh.
CHEM 1215 EXAM III
PAGE 4
(20) 6. Complete the following table
M, Molar
g
Mass  mol


m, Mass of
n, Moles of
N, Number of atoms,
sample (g)
sample (mol)
molecules, or formula units
KClO3
123
29.5
0.241
1.45 x 1022 formula units
SO2
64
399
6.23
3.75 x 1024 molecules
unknown
78.2
4.91
6.28 x 10–2
3.78 x 1022 formula units
Mg3Al2(SiO4)3
403
9.99
2.48 x 10–2
1.49 x 1022 formula units
Formula
(10) 7. The thermite reaction
8Al(s) + 3Fe3O4(s) → 9Fe(s) + 4Al2O3(s)
Calculate how many grams of iron can be produced when 14.0 g of Al are combined with excess Fe3O4.
1 m o l A l 9 m o l F e  5 5 . 6 g F e
14.0 g Al  2 7 . 0 g A l 
= 10.8 g Cl2

 8 m o l A l  1 m o l F e 
CHEM 1215 EXAM III
PAGE 5
(12) 8. Acrylonitrile, C3H3N, is an important component for synthetic fibers and plastics. The compound is
synthesized from propene (C3H6), ammonia and oxygen according to the equation,
2C3H 3N (l) + 6H 2O (g)
2C3H 6(g) + 2NH 3(g) + 3O 2(g) →
89.5 g of propene are added to an amount of ammonia and oxygen. After the reaction occurs 1.65 moles
of C3H3N are produced. Answer each of the following,
a) the mass of C3H3N produced?
53.0 g

1.65 mol C3 H 3 N 
1
m
o l C 3 H 3 N  = 87.5 g C3 H 3 N

b) the mass of NH3 reacting?
2 mol NH3   17.0 g 
1.65 mol C3 H 3 N 
= 28.0 g NH3
2
 m o l C 3 H 3 N  1 m o l N H 3 
c) Is propene the limiting reagent in this reaction? Explain. (You may use a calculation to support your
answer.)
Need to determine how many grams of propene are required to form 1.65 mol of
acrylonitrile.
2 mol C H
39.0 g
1.65 mol C3 H 3 N  2 m o l C 3H 3N   1 m o l C H  = 64.4 g C3 H 3
3 3 
3 3

So 64.4 g C3 H 3 reacted. We began with 89.5 g of C 3 H 3 , therefore C3 H 3 is in excess.
CHEM 1215 EXAM III
PAGE 6
(12) 9. The reaction which occurs when an Alka-Seltzer™ tablet is added to water,
3NaHCO3(aq) + H3C6H5O7(aq) → 3CO2(g) + 3H2O(g) + Na3C6H5O7(aq)
One Alka-Seltzer tablet contains 1.92 g of sodium bicarbonate and 1.00 g of citric acid. What mass of
carbon dioxide gas will fizz out when one tablet is plopped into water?
1 mol
1.92 g NaHCO3  8 4 . 0 g = 0.229 mol NaHCO3


1 mol
1.00 g H3 C 6 H 5 O 7  1 9 2 . 0 g = 0.00521 mol H3 C 6 H 5 O 7


(moles NaHCO 3 ) o
0.229 mol
(moles
H 3 C 6 H 5 O 7 )required
0.0733 mol
(moles
H 3C 6H 5O 7)o
0.00521 mol
Conclusion
H 3 C 6 H 5 O 7 limiting,
NaHCO 3 excess
1 mol H 3 C 6 H 5 O 7 
0.229 mol NaHCO 3  3 mol NaHCO
= 0.0733 mol H3 C 6 H 5 O 7

3 
3 mol CO
44.0 g
0.00521 mol H3 C 6 H 5 O 7  1 mol H C H2 O   1 m o l C O  = 0 . 6 8 8 g C O 2

3 6 5 7 
2
CHEM 1215 EXAM III
Periodic Table of the Elements
IA
1
VIIIA
1
2
H
He
IIA
1.008
3
2
PAGE 7
IIIA IVA VA VIA VIIA 4.00
4
Li Be
6.94 9.01
11
12
3
Na Mg
22.99 24.30
19
20
4
5
6
7
5
6
7
8
9
10
B
C
N
O
F
Ne
10.81 12.01 14.01 16.00 19.00 20.18
13
14
15
16
17
18
IIIB IVB VB VIB VIIB
21
22
K Ca Sc Ti
23
24
25
VIII
26
27
IB
28
Al
Si
P
S
Cl Ar
31
32
33
34
35
IIB 26.98 28.09 30.97 32.06 35.45 39.95
29
30
36
V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
39.10 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
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb Sr
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
I
Xe
85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs Ba La Hf Ta W Re Os Ir
Pt Au Hg Tl Pb Bi Po At Rn
132.9 137.3 138.9 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)
87
88
89 104 105 106 107 108 109
Fr Ra Ac Rf Db Sg Bh Hs Mt
(223) 226.0 227.0 (261) (262) (263) (262) (265) (266)
58
Lanthanides
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
93
94
95
96
97
98
99 100 101 102 103
Actinides
Th Pa
U
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)
Ion
Solubility
–
NO3
ClO4
Cl
–
–
SO4
2–
2–
CO3
3–
PO4
2–
CrO4
-OH
S
2–
Na
+
NH4
+
K
+
Solubility Table
Exceptions
soluble
none
soluble
none
soluble
except Ag , Hg2 , *Pb
soluble
except Ca , Ba , Sr , Hg , Pb , Ag
insoluble
except Group IA and NH4
insoluble
except Group IA and NH4
insoluble
except Group IA, IIA and NH4
insoluble
except Group IA, *Ca , Ba , Sr
insoluble
except Group IA, IIA and NH4
soluble
none
soluble
none
soluble
none
+
2+
2+
2+
2+
2+
2+
2+
+
+
+
+
2+
2+
2+
+
*slightly soluble
CHEM 1215 EXAM III
PAGE 8