CHEM 108 (Spring-2006)
Exam. 2 – (Section 001) (104 pts)
Name: --------------------------------------------------------------------------, CLID # -------------------------------LAST NAME, First
(Circle the alphabet segment of your LAST NAME): A, B
C-G
H-M
N-P
Q-Z
Please answer the following questions:
Part I: Multiple Choices (44 pts: 11 @ 4 pts each). Circle the ONE best answer:
1. Consider the following equilibrium:
2 SO2 (g) + O2 (g)
2 SO3 (g)
∆Hº = -198 kJ
Which of these changes would cause an increase in the SO3/SO2 mole ratio?
a) adding a catalyst
b) remove O2 (g)
c) decreasing the temperature
d) decreasing the pressure
2. Given the following Ka values:
HC2H3O2 (Ka = 1.8 x 10-5),
HOCl (Ka = 2.9 x 10-8),
Which of the following is the weakest base?
HClO3 (Ka = 5.0 x 102),
HCN (Ka = 6.2 x 10-10)
a) C2H3O2-
b) OCl-
c) ClO3-
d) CN-
3. What is the pH of 0.005 M Ca(OH)2?
a) 2.0
b) 1.0 x 10-12
c) 11.7
d) 12.0
4. The conjugate acid of HPO42- is
a) PO43-
b) H3PO4
c) H2PO42-
d) H2PO4-
5. Consider the equilibrium of water with gaseous hydrogen and oxygen:
2 H2O (g)
2 H2 (g) + O2 (g)
Kp = 7.8 x 10-16 at 930 o C
What is the value of Kp for the reaction, if it is written as:
H2 (g) + ½ O2 (g)
H2O (g)
a) 3.6 x 107
b) 1.3 x 1015
c) 6.4 x 1014
d) -7.8 x 10-16
6. Which of the following mixtures would be a buffer?
a) 5 mL I M NaOH + 50 mL 1 M HC2H3O2 (acetic acid)
b)
25 mL 1 M NaOH + 50 mL 1 M NH3 (aq)
c)
50 mL 1 M NaOH + 50 mL 1 M HCl
d)
50 mL 1 M HCl + 50 mL 1 M NH3 (aq)
1
7. At a certain temperature, Kp = 25 for the following reaction:
NH4Cl (s)
NH3 (g) + HCl (g)
What is the total pressure, in atm, of the gases at equilibrium?
a) 25
b) 10
c) 5
d) more information is required
8. Consider 0.10 M solution of the following substances. Which would be the highest pH?
a) NaCl
b) NaF
c) NH4NO3
d) NH3 (aq)
9. A mixture was prepared with [CO] = 0.035, [Cl2] = 0.015, and [COCl2] = 0.95. It is known that Kc
for the equilibrium: CO (g) + Cl2 (g)
COCl2 (g) is 1.2 x 103 at 400 o C. Predict what will
happen
a) The reaction occurs at the reverse direction.
b) The reaction occurs at the forward direction.
c) The reaction is at equilibrium.
d) it is impossible to predict without more information
10. If 380.0 mL of 0.308 M KOH is added to 200.0 mL of 0.680 M HCl, will the mixture be
a) acidic
b) amphoteric
c) basic
d) neutral
11. Determine the pH of 0.35 M HOCl. The Ka of HOCl is 2.9 x 10-8?
a) 4.00
b) 7.53
c) 1.0 x 10-4
d) no answer was given
____________________________________________________________________________________
Part II. (20 pts)
1. (8 pts) Use the graph shown below to answer the following questions:
a) sketch the titration curve for the titration of 25 mL of 0.1 M KOH by 0.1 M HCl
b) label the two axes
c) Which of the following indicators that can be used to detect the equivalence point for this titration
(circle it)?
Indicator
color change
pH range
Thymol blue
red – yellow
1.2 – 2.8
Bromophenol blue
yellow – blue
3.0 – 4.6
Methyl red
red – yellow
4.2 – 6.3
Bromothymol blue
yellow – blue
6.0 – 7.6
Cresol blue
yellow – red
7.2 – 8.8
Phenopththalein
colorless – pink
8.3 – 10.0
2
2. (12 pts: 4 @ 3 pts) Fill the blanks in each of the following sentences:
a) The equilibrium constant expression for the reaction:
CaCO3 (s) + 2 HF (aq)
2 CaF2 (s) + H2O (l) + CO2 (g)
is evaluated by the expression K = ---------------------------b) According to Brønsted-Lowry, the base is defined as a ----------------------------c) The acid base indicator changes its color when its pKa = ------------------- of the solution.
d) A species that can either accept or donate a proton is called ---------------------------.
______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Part III (40 pts: 4 @ 10 pts each) Calculations: Show all work for full credit. Please express all
answers with proper units and correct number of significant figures.
1. (10 pts) For the equilibrium: PCl5 (g)
PCl3 (g) + Cl2 (g)
5.0 moles of PCl5 are placed in a 10.0 L flask at 200 ˚C and allowed to come to equilibrium. Analysis
shows that 1.0 mole of Cl2 is present in the equilibrium mixture.
a) Determine the value of Kp at 200 ˚C.
Kp =
b) Determine the direction of equilibrium (product favored, reactant favored or out of favor)
2. A solution of hydrazine, N2H4, has a concentration of 0.25 M. What is the pH of the solution, and
what is the percentage ionization of hydrazine (hydrazine has Kb = 1.7 x 10-6)?
pH = 10.81
% ionization = 0.26%
3
3. What is the pH of a solution obtained by adding 1.15 mg of aniline hydrochloride, C6H5NH3+Cl(Ka = 1.4 x 10-5) to 3.18 L of 0.105 M aniline, C6H5NH2?
pH =
4. In the titration of 20.0 mL of 0.150 M hypochlorous acid, HClO (Ka = 2.9 x 10-8) with 0.100 M NaOH
solution:
a) What is the volume of NaOH required for neutralization?
b) What is the pH of the solution at the equivalence point?
a) Volume of NaOH = 30 mL
b) pH =
4
PREFERENCE SHEET FOR CHEM 108
Exam 2 – Spring 2006
You will have 55 minutes to complete this exam. The exam has 4 pages plus a reference page.
When you are told to do so, tear off the Periodic cover sheet and use as required during exam.
Constants & Useful Equation :
Gas Constant: R = 8.3145 J/K.mol = 8.3145 x 10-3 kJ/K.mol = 0.0821 L atm/mol.K
K = 273 + °C
1 atm = 760 torr = 760 mmHg
d (density) = mass (m)/volume (V)
Cg = k.Pg
ni = Pi/Pt
χ1.P1o
π = [C]RT
∆T = i. Km.
P1 =
Rate = k[A]
ln [A]o = kt
[A]
ln[A] = - kt + ln[A]o
Rate = k[A]2
1/[A] - 1/[A]o = kt
t1/2 = 1/k[A]o
Rate = k
[A] = - kt + [A]o
t1/2 = [A]o/2k
-Ea/RT
k = Ae
∆P1 =
PV = nRT
χ2.P1o
t1/2 = ln 2/k = 0.693/k
ln k = (-Ea/R)(1/T) + ln A
1
1
2
H
Periodic Table of the Elements
He
1.01
3
2
3
5
6
7
8
Li Be
B
C
N
O F
6.94 9.01
10.81 12.01 14.01 16.00 19.00 20.18
11
13
4
12
14
15
9
10
Ne
16
17
S
Cl Ar
18
Na Mg
Al Si P
22.99 24.30
26.98 28.08 30.97 32.06 35.45 39.95
19
4
4.00
20
21
22
23
K Ca Sc Ti V
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
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
5
6
38
39
Rb Sr Y
40
41
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
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
132.9 137.3 138.9 178.5 181.0 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)
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)
87
7
88
89
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)
5
6
7