Table 1A
1
1
Periodic of the Elements
2A
2
8A
18
1.0079
H
3A
13
4A
14
5A
15
6A
16
7A
17
2
4.0026
He
3
6.941
Li
4
9.0122
Be
5
10.811
B
6
12.011
C
7
14.0067
N P
8
15.9994
O S
9
18.9984
F
10
20.1797
Ne Ar
11
22.9898
Na K
12
24.3050
Mg Ca Sr
3B
3
4B
4
5B
5
6B
6
7B
7
8
8B
9
10
1B
11
2B
12
13
26.9815
Al
14
28.0855
Si
15
16
17
30.9738
32.066
35.4527
Cl
18
39.948
19
20
21
39.0983
40.078
44.9559
Sc Y
22
47.88
Ti
23
50.9415
V
24
51.9961
Cr
25
54.9380
Mn Tc
26
55.847
Fe
27
58.9332
Co
28
58.69
Ni
29
63.546
Cu Ag
30
Zn
31
65.39
69.723
Ga In Tl
32
Ge Sn
33
72.61
74.9216
As
34
Se Te
35
78.96
79.904
Br I
36
83.80
Kr
37
85.4678
Rb Cs Fr
38
39
40
87.62
88.9059
91.224
Zr
41
92.9064
Nb Ta
42
Mo W
43
44
95.94
(98)
101.07
Ru
45
102.9055
Rh Ir
46
106.42
Pd Pt
47
48
107.8682
112.411
Cd
49
50
51
114.82
118.710
121.75
Sb Bi
52
53
54
127.60
126.9045
131.39
Xe
55
56
132.9054
137.327
Ba
57
138.9055
La
72
178.49
Hf
73
74
75
180.9479
183.85
186.207
Re Bh
76
Os Hs
77
78
79
190.2
192.22
195.08
196.9665
Au
80
200.59
Hg
81
82
204.3833
Pb
83
84
207.2
208.9804
Po
85
(209)
(210)
At
86
Rn
(222)
87
88
(223)
Ra
89
(226)
Ac
104
(227)
(261)
Rf
105
Db
106
(262)
Sg
107
108
109
(263)
(262)
(265)
Mt
(266)
58
140.115
Ce Th
59
140.9076
Pr
60
144.24
Nd U
61
(145)
Pm
62
150.36
Sm Pu
63
151.965
Eu
64
157.25
Gd
65
158.9253
Tb
66
162.50
Dy Cf
67
164.9303
Ho Es
68
167.26
Er
69
168.9342
Tm Md
(258)
70
173.04
Yb
71
174.967
Lu Lr
90
91
232.0381 231.0359 238.0289
Pa
92
93
(237)
Np
94
95
(244)
Am
(243)
96
Cm
(247)
97
(247)
Bk
98
99
100
(251)
(252)
Fm
(257)
101
102
(259)
No
103
(260)
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. R=8.314 J/(K-mol)=0.082 L-atm/(molK) For carbonic acid (H2CO3): pK1=6.4; pK2=10.2 If you need any other constants, ask the TA proctoring the exam. 001 (part 1 of 1) 10 points The ionization constants for an imaginary weak acid H3 A are K1 = 1.0 10-3 , K2 = 1.0 10-7 , and K3 = 1.0 10-11 . Would a water solution of NaH2 A be acidic, basic, or neutral? Hint: Write the chemical equation and the equilibrium constant for the two possible reactions. 1. acidic because of further ionization of H2 A- correct 2. acidic because of the hydrolysis of H2 A- 3. basic because of the further ionization of H2 A- 4. neutral 5. basic because of the hydrolysis of H2 A- Explanation: H2 A- H+ + HA2- K2 = 10-7 H2 A- + H 2 O Kb3 = H3 A + OH- Kw 10-14 = 10-11 = Ka1 10-2 4. HClO3 5. HCl
2
Explanation: The weakest acid will have the strongest conjugate base. Remember that the more oxyzen atoms that surround an acid, the stronger it becomes. This means that HClO is the weakest acid listed above, so it will have the strongest conjugate base. 003 (part 1 of 1) 10 points Calculate the standard free energy of the reaction 2 I(g) , K = 6.8 at 1200 K . I2 (g) 1. -19 kJ/mol correct 2. 68 kJ/mol 3. -20.0 kJ/mol 4. 2.0 kJ/mol 5. 2.98 kJ/mol 6. 75.5 kJ/mol 7. -23.2 kJ/mol Explanation: G = - R T ln K r J K mol = -19124.8 J/mol = - 8.314 (1200 K) ln(6.8)
002 (part 1 of 1) 10 points Which acid has the strongest conjugate base? 1. HClO4 2. HClO correct 3. HClO2
004 (part 1 of 1) 10 points For an endothermic reaction, what would happen to the numerical value of Kc if we increase the temperature at constant pressure? 1. Kc would increase. correct 2. Kc would either increase or decrease, depending on the number of moles of gas involved.
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe 3. Kc would decrease. 4. Kc would not change. 5. Kc would either increase or decrease, depending on the concentrations. Explanation: An endothermic reaction absorbs heat in forming products, so at a higher temperature the forward reaction is favored, increasing Kc which reflects the ratio of products to reactants. 005 (part 1 of 1) 10 points At 25 C, Kc = 4.1 108 for the reaction N2 (g) + 3 H2 (g) 2 NH3 (g) . Calculate K at 25 C for this reaction. 1. 1.7 10
9
3
K = 1080 at a certain temperature. Initially, all reactants and products have concentrations equal to 12 M. What is the approximate concentration of oxygen at equilibrium? 1. 18 M 2. 6 M 3. 3 M correct 4. 0 M 5. 12 M
Explanation: 008 (part 1 of 1) 10 points Calculate the [H+ ] in a solution which shows a pH of 11.70. 1. 11.7 M
2. 6.9 105 correct 3. 2.5 10
11
2. 2.0 10-12 M correct 3. None of these
8
4. 9.7 107 5. 4.1 10 4. 5.0 10-3 M 5. 2.3 M
Explanation: 006 (part 1 of 1) 10 points Which of the following is an acid? 1. NH3 2. NaOH 3. CH4 4. HNO3 correct 5. NaCl Explanation: 007 (part 1 of 1) 10 points For the reaction 4 NH3 (g) + 3 O2 (g) 2 N2 (g) + 6 H2 O(g) ,
Explanation: 009 (part 1 of 1) 10 points Write the equilibrium constant for 2 NaBr(aq) + Pb(ClO4 )2 (aq) PbBr2 (s) + 2 NaClO4 (aq) . 1. K = [Pb2+ ][Br- ]2 2. K = 3. K = 1 [Pb2+ ][Br- ]2
1 [Pb(ClO4 )2 ][NaBr]2 [PbBr2 ] 4. K = [Pb2+ ][Br- ]2
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe [NaClO4 ]2 correct [NaBr]2 [Pb(ClO4 )2 ]
4
5. K =
Explanation: 010 (part 1 of 1) 10 points In the reversible reaction SO3 2- + H3 O+ , HSO- + H2 O 3 what two substances act as acids in the Bronsted-Lowry sense? 1. HSO- and H2 O 3 2. SO2- and H3 O+ 3 3. some other pair 4. HSO- and H3 O+ correct 3 5. H3 O+ and H2 O Explanation: 011 (part 1 of 1) 10 points A water solution of sodium acetate is basic because 1. the statement is false; a water solution of sodium acetate is acidic. 2. the acetate ion acts as a Bronsted-Lowrey acid in a reaction with water. 3. the acetate ion acts as a Bronsted-Lowrey base in a reaction with water. correct 4. the conjugate base of the acetate ion is a strong base. 5. sodium acetate is only weakly ionized. Explanation: In water, sodium acetate dissociates into sodium ions (spectator ions) acetate and ions which hydrolyze to produce hydroxide ions. CH3 COO- + H2 O CH3 COOH + OH- The acetate ion accepts a proton from a water molecule.
012 (part 1 of 1) 10 points The ionization constant Kw of water at 60 C is 1.0 10-13 . What is the pH of pure water at this temperature? 1. 6.5 correct 2. 5.5 3. 13.0 4. 7.0 5. 7.5 Explanation: Kw = 1.0 10-13 2 H2 O H3 O- + OH-
Kw = [H3 O+ ][OH- ] = 1.0 10-13 In pure water [H3 O+ ] = [OH- ] = 1 10-13 M = 3.16228 10-7 M pH = - log 3.16228 10-7 = 6.5 013 (part 1 of 1) 10 points A solution of 0.2 M boric acid is prepared as an eye wash. What is the approximate pH of this solution? For boric acid Ka = 7.2 10-10 . 1. pH = 5 correct 2. pH = 3 3. pH = 7 4. pH = 6 5. pH = 4 Explanation: 014 (part 1 of 1) 10 points Which of the acids
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe I. HBrO3 II. GaCl3 III. HSO- 4 IV. AlF3 are classified as Lewis acids but are not Bronsted-Lowry acids? 1. II and IV correct 2. II and III 3. I and II 4. I and IV 5. None of these Explanation: Lewis acids accept a share in an electron pair. A Bronsted-Lowry acid is a proton donor. I and III would be Bronsted acids. Therefore, only II and IV can be the correct answer. 015 (part 1 of 1) 10 points Consider the reaction 4 NH3 (g) + 7 O2 (g) 2 N2 O4 (g) + 6 H2 O(g) Initially, [NH3 (g)] = [O2 (g)] = 3.60 M; at equilibrium [N2 O4 (g)] = 0.60 M. Calculate the equilibrium concentration for NH3 . 1. 1.80 M 2. 3.20 M 3. 2.40 M correct 4. 2.80 M 5. 3.60 M Explanation: Explanation: 016 (part 1 of 1) 10 points Suppose the exothermic reaction 2 SO2 (g) + O2 (g) 2 SO3 (g) comes to equilibrium. Then we increase the temperature and decrease the total pressure simultaneously.
5
What will be the effect on the net amount of SO3 (g)? 1. It may either increase, decrease, or remain the same, depending on the numerical value of the equilibrium constant. 2. It may either increase, decrease, or remain the same, depending on the sizes of the temperature and pressure changes. 3. It decreases. correct 4. It does not change. 5. It increases. Explanation: Increasing the temperature adds heat to this exothermic reaction and shifts equilibrium to the left. Decreasing total pressure shifts equilibrium in the direction where more moles of gas are formed. 017 (part 1 of 1) 10 points The conjugate base of H2 SO4 is: 1. H2 O 2. H3 O+ 3. H3 SO+ 4 4. HSO- correct 4 5. SO2- 4 6. H2 SO3 7. OH-
018 (part 1 of 1) 10 points The reaction 2 A B + C has a Kc of 0.2. The reaction is commenced with initial concentrations [A] = 0.2 M, [B] = 0.2 M and [C] = 0.2 M. In what direction does the reaction occur?
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe 1. The reaction shifts to the left to reach equilibrium. correct 2. Cannot be determined without knowing the temperature. 3. The reaction is already at equilibrium. 4. The reaction shifts to the right to reach equilibrium. Explanation: Keq = 0.2 [A] = [B] = [C] = 0.2 M [B][C] (0.2 M)(0.2 M) Q= = 2 [A] (0.2 M)2 = 1.0 > Keq = 0.2 Therefore equilibrium will shift to the left. 019 (part 1 of 1) 10 points The ratio of NaA to HA (a weak acid with Ka = 3.6 10-6 ) in an aqueous solution is 3 to 4. What is the concentration of H+ (same as [H3 O+ ] )? 1. 3.8 10-3 M 2. 3.6 10-6 M 3. 2.7 10-6 M 4. 1.8 10-6 M 5. 4.8 10-6 M correct Explanation: 020 (part 1 of 1) 10 points Suppose that a sample of pure water is saturated with gaseous CO2 to form a solution of carbonic acid. Which response has the following species arranged in the order of decreasing concentrations at equilibrium (from highest concentration to lowest concentration)? 1. H+ , H2 CO3 , HCO- , CO2- 3 3 2. H2 CO3 , H ,
+
6
3. H2 CO3 , HCO- , H+ , CO2- 3 3 4. CO2- , H+ , HCO- , H2 CO3 3 3 5. HCO- , H2 CO3 , CO2- , H+ 3 3 Explanation: Since carbonic acid is a weak acid, it is only partially dissociated, so in a solution of carbonic acid, the dominant species would be H2 CO3 . To the extent it does dissociate, it dissociates into H+ and HCO- . HCO- , 3 3 in turn, can dissociate into H+ and CO2- , 3 but again this only happens to a very small extent. Thus more H+ will be present than HCO- , and very little CO2- will be present. 3 3 021 (part 1 of 1) 10 points Kc = 4.9 105 for the reaction A(g) 2 B(g) .
What is Kc for the reaction 2 B(g) 1. 1.59 10-6 2. 2.45 10-6 3. 3.40 10-6 4. 2.04 10-6 correct 5. 9.81 10-6 Explanation: 022 (part 1 of 1) 10 points Which solution is acidic? 1. MH+ = 5.79 10-10 M 2. MH+ = 1.27 10-9 M 3. MOH- = 1.77 10-10 M correct 4. MOH- = 0.0065 M A(g) ?
HCO- , 3
CO2- 3
correct
Explanation:
Elbel, Brittany Exam 2 Due: Mar 7 2006, noon Inst: J A Holcombe An acidic solution has an MH+ greater than 1 10-7 M, and a MOH- less than 1 10-7 M. 023 (part 1 of 1) 10 points HClO reacts with water to form ClO1- and a hydronium ion. Which statement is true for this reaction? 1. The hydronium ion is the conjugate base of HClO. 2. ClO1- is the conjugate base of HClO. correct 3. The hydronium ion is the conjugate acid of HClO. 4. H2 O is the conjugate base of HClO. 5. ClO1- is the conjugate acid of HClO. 6. H2 O is the conjugate acid of HClO. Explanation: 024 (part 1 of 1) 10 points What is the pH of a solution obtained by mixing 3.15 g HNO3 and 2.6 g NaBr in water to create 755 L of solution? The molar mass of HNO3 is 63.1 g/mol and the molar mass of NaBr is 102.9 g/mol. 1. 5.23 4. Z4, Z2, Z3, Z1 correct 2. 6.15 3. 4.48 4. 4.18 correct 5. 1.12 6. 4.00 7. 3.54 8. 2.38 9. 3.88 Explanation:
7
025 (part 1 of 1) 10 points If G = 27.1 kJ at 25 C for the reaction CH3 COOH(aq) + H2 O( ) CH3 COO- (aq) + H3 O+ (aq) , calculate Ka for this reaction at 298 K.
1. 1.01 2. 5.63 104 3. 1.15 10-11 4. 9.89 10-1 5. 1.78 10-5 correct Explanation: 026 (part 1 of 1) 10 points Place the following in order of increasing pOH: Z1) lemon juice Z2) blood Z3) pure water Z4) household ammonia 1. Z2, Z3, Z4, Z1 2. Z2, Z3, Z1, Z4 3. Z1, Z3, Z2, Z4
Explanation: Of the solutions listed, only lemon juice is acidic. It contains the weak acid, citric acid. 027 (part 1 of 1) 10 points For any reaction at equilibrium, G < 0. 1. False correct 2. True Explanation: