CHEM 171
EXAMINATION 1
October 9, 2008
Dr. Kimberly M. Broekemeier
NAME:_____________________Key______________________________
IA
II A
III B
IV B
VB
VI B
VII B
VIII
IB
II B
III A
IV A
VA
VI A
VII A
1
inert
gase
s
2
H
He
1.008
4.003
3
4
5
6
7
8
9
10
Li
Be
B
C
N
O
F
Ne
6.941 9.012
10.81 12.01 14.01 16.00 19.00 20.17
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
22.98 24.31
26.98 28.09 30.97 32.06 35.45 39.95
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
39.10 40.08 44.96 47.90 50.94 52.00 54.94 55.85 58.93 58.71 63.55 65.37 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
85.46 87.62 88.91 91.22 92.91 95.94 98.91 101.0 102.9 106.4 107.8 112.4 114.8 118.6 121.8 127.6 126.9 131.3
55
56
Cs
Ba
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
*
132.9 137.3 138.9 178.4 180.9
87
88
89
104
105
Fr
Ra
*
Ac
Rf
(223) 226.0 (227) (261)
Db
(262)
183.8
106
Sg
186.2 190.2 192.2 195.0 196.9 200.5 204.3 207.2 208.9 (210)
107
108
109
110
111
112
113
114
Bh
Hs
(210) (222)
Mt
(263) (262) (265) (266) (269) (272)
(277)
?
(289)
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 (147) 150.4 151.9 157.3 158.9 162.5 164.9 167.3 168.9 173.0 174.9
90
91
92
93
94
95
96
97
98
99
100
101
102
103
Th
Pa
U
Np
Pu
232.0 (231) 238.0 (237) (242)
I. Short Answer (46 points total)
Am
Cm
Bk
(243)
(247)
(247)
Cf
Es
Fm
Md
No
Lw
(251) (254) (253) (256) (254) (257)
1)
Give the missing name, symbol or formula for each of the following:
ammonium sulfide _(NH4)2S______
hydrogen carbonate ion
2)
AsF3 ___arsenic trifluoride______
diiodine heptoxide ___I2O7___
Rh2O3 ____rhodium (III) oxide_________
cobalt(III) nitrate __Co(NO3)3____
HIO3(aq) ___iodic acid_____
Balance the following reaction scheme with whole number coefficients:
__4__ NH3(g)
3)
Ca(ClO4)2 __calcium perchlorate____
_HCO3 ____
+
_5__ O2(g)
→
__4__ NO(g)
+
_6__ H2O(l)
Write the corresponding value (to 3 sig figs) for each of the following unit conversions.
3
6.24 g/cm = ______6.24_______ mg/mm
3
6
1.03 μm = _____1.03 x 10 _________ pm
g
103mg
100 cm 3
m
6.24
x
x(
) x(
)3 = 6.24
3
cm
g
m
1000 mm
1.03  m x
m
106  m
65
x
1012 pm
= 1.03 x 106
m
2+
4)
The species
5)
What is the average mass of an oxygen atom in amu?
___16.00 amu_______
What is the mass of a mole of naturally occurring oxygen atoms in g?
____16.00 g______
6)
Cu
has ___29_______ protons, ____36____ neutrons, and __27______ electrons.
Consider the elements of the third period. Identify, by symbol, ONE element which has the listed
characteristic. If none of the elements in the period has this property, answer NONE.
is a non-metal _Si, P, S, Cl, Ar__
is an alkali metal __Na___
is a halogen ___Cl_____
forms only 2+ ions __Mg_____
forms an anion with a 2- charge ___S____
exists as diatomic molecules in its elemental state __Cl_______
7)
Identify each of the following as a chemical process (C) or a physical process (P).
loss of electrons __C____
8)
dissolving NaCl into water ___P_____
Identify the following as an intensive (I) or extensive (E) property.
mass __E_____
density ___I______
9)
What is the molar mass (with units) for Cu3(PO4)2? _____380.59 g/mol____________________
10)
What is the charge on the copper ion in the compound given in question 9? ___+2_____
II. Multiple Choice (36 points total)
Circle the letter corresponding to the single BEST answer for each question.
1)
2)
3)
4)
In SI, the prefix used to indicate 10
6)
7)
has which symbol and name?
a. n and nano
c. p and pico
e. m and milli
b. f and femto
d. c and centi
f. μ and micro
Which of the following is not a basic or fundamental SI unit?
a. liter
c. Kelvin
e. kilogram
b. meter
d. Ampere
f. mole
Which one of the following species has the greatest mass?
a. a mol of hydrogen molecules
c. a hydrogen molecule
e. a neutron
b. a mol of hydrogen atoms
d. a hydrogen atom
f. a proton
Which one of the following represents the compounds which are ionic?
i. As4S6
5)
-12
ii. NaCl
iii. PCl3
iv. BaSO4
v. NH4NO3
a. i , vi
c. i , iii , vi
e. ii , iii , iv , v
b. ii , iv , v
d. iii , v
f. all are ionic
vi. Cl2O3
Which one of the following has the greatest mass percent sodium?
a. NaCl
c. Na3(PO4)
e. Na2O
b. Na2S
d. NaBr
f. Na3(AsO4)
What is the mass, in g, of 0.125 mol of calcium fluoride?
a. 4.90 g
c. 9.76 g
e. 2.38 g
b. 5.01 g
d. 1.25 g
f. 7.39 g
Which of the following, in water, would be strong electrolytes?
i) HNO3
ii) NaOH
iii) HCH3COO
iv) H2SO4
a. i, iv
c. ii, vi
e. vi
b. i, iii, iv, v
d. i, ii, iv
f. ii, iv
v) H3PO4
vi) NH3
8)
9)
10)
A compound containing only nitrogen and oxygen is known to be 25.9 % N by mass. What is the
empirical formula of this compound?
a. N2O5
c. NO
b. NO2
d. NO5
12)
f. N2O
How many mol of sodium are in 225 g of Na2CO3? (molar mass = 106.0 g/mol)
a. 4.25 mol
c. 0.471 mol
e. 2.12 mol
b. 0.942 mol
d. 12.7 mol
f. 6.37 mol
The equation below describes the reaction between elemental sodium and elemental chlorine. If 1.00
mol Na(s) is reacted with 2.00 mol Cl2(g), and the reaction goes to completion, which is the limiting
reactant, and how many moles of product are formed?
2 Na(s)
11)
e. N2O4
+
Cl2(g) →
2 NaCl(s)
a. sodium and 1.00 mol NaCl
b. chlorine and 1.00 mol NaCl
c. stoichiometric amounts and 1.00 mol NaCl
d. sodium and 2.00 mol NaCl
e. chlorine and 2.00 mol NaCl
f. stoichiometric amounts and 2.00 mol NaCl
Last week in lab, the masses and volumes of solutions were measured in order to determine the
density (mass/vol) of a solution of unknown density. In one part, the acccumulated mass of a beaker and
its contents was plotted versus the volume of the solution added to the beaker from a buret. One set of
data yielded the curve fit equation: y = 1.059 x + 126.8. What was the mass of the breaker and contents
after addition of 25.00 mL of the unknown solution to the beaker?
a. 100.3
b. 144.7
c. 101.8
d. 153.3
e. 151.8
f. 127.9
From your observations in the lab (Identification of Unknown Solutions), which one of the following
solutions forms an odor when treated with sulfuric acid?
a. Ba(OH)2(aq)
c. K2SO4(aq)
e. NH3(aq)
b. NH4Cl(aq)
d. HCl(aq)
f. NaC2H3O2(aq)
III. Problems (18 points total)
For each of the problems on the following page, show all setup, logic and work. Place units on all
quantities, use three significant figures, and place final result in the space provided (include units!!)
1)
A particular organic compound contains only carbon, hydrogen and sulfur. A 2.57 g sample of the
compound is processed in a combustion analyzer, which resulted in the production of 2.35 g CO2,
1.93 g H2O, and 3.42 g SO2. What is the empirical formula for this compound?
Molar mass: H2O (18.016 g/mol)
CO2 (44.01 g/mol)
SO2 (64.07 g/mol)
Compound + O2 → CO2 + H2O + SO2
2.35 g CO 2 x
1.93 g H 2 O x
3.42 g SO 2 x
mol CO 2
44 g
mol H 2 O
18.016 g
mol SO 2
64.06 g
x
1C
mol H 2 O
1 mol S
x
= 0.534 mol C
mol CO 2
2 mol H
x
mol SO 2
Emp. Form. = ____CH4S______
= 0.2143 mol H
= 0.0534
Divide by smallest number of moles (0.534) to get a ratio of 1C:4H:1S
2)
A hypothetical element (E) has an average atomic mass of 65.285 u. In nature, it exists as two isotopes:
65
67
E (exact mass = 64.789 u) and E (exact mass = 66.785 u). Determine the percent abundance of
each isotope.
65
% E _________75.15 %____________
%
67
E _________24.85 %_____________
65.285 = (x)(64.789) + (1-x)(66.785)
Solve for x:
65.285 = 64.789x + 66.785 – 66.785x
-1.500 = -1.996 x
x = 0.7515
3)
The following reaction describes the production of elemental iodine in small quantities from readily
available potassium iodide. When 4.50 g of KI(s) is treated with 2.69 g elemental chlorine, 3.25 g of
elemental iodine is recovered:
Cl2(g) + 2 KI(s) →
2 KCl(s) + I2(s)
a. Which reactant is the limiting reagent? (Prove by calculation) _____KI_______________
4.5 g KI x
mol KI
166.0 g
2.69 g Cl 2 x
x
mol Cl 2
70.90 g
1 mol I 2
2 mol KI
x
= 0.0136 mol I 2
1 mol I 2
1 mol Cl2
= 0.0379 mol I 2
The limiting reagent is KI, since less I2 can be formed. The same type of calculation could have been
done with determing the amount of KCl formed.
Convert moles to mass: 0.0136 mol I2 x 253.8 g/mol = 3.45 g theoretical yield.
Actual yield/theoretical yield x 100 = percentage yield
3.25/3.45 x 100 = 94.2
b. What is the percentage yield of elemental iodine?
_______94.2%____________