1B Wi15 Practice Exam 2

Chem 1B Practice Exam 2
Use the following table for questions 1-2:
Reaction
E° (volts)
–
–
+2.87
F2 + 2e  2F
–
–
+1.36
Cl2 + 2e  2Cl
+
–
+0.80
Ag + e  Ag
2+
–
+0.34
Cu + 2e  Cu
2+
–
–0.28
Co + 2e  Co
–0.44
Fe2+ + 2e–  Fe
3+
–
–1.66
Al + 3e  Al
–2.71
Na+ + e–  Na
1. Which of the following would be the best reducing agent?
A) Cl2
B) F2
C) Na
D) Na+
E) F–
2. Silver will spontaneously reduce which of the following?
A) Fe2+
B) Co2+
C) Na+
D) Al3+
E) none of these
3. Nickel is electroplated from a NiSO4 solution. A constant current of 5.00 A is applied by an
external power supply. How long will it take to deposit 100. g of Ni metal? The atomic mass of Ni
is 58.69 g/mol.
A) 18.3 hours
B) 1.20 hours
C) 63.1 minutes
D) 56.7 seconds
E) 9.1 hours
Consider the following galvanic cell for questions 4-6:
Cd2+ + 2 e– → Cd (s)
Eo = – 0.40 V
VO2+ + 2H+ + e– → VO2+ + H2O Eo = 1.00 V
4. What is the oxidizing agent for the spontaneous reaction that occurs when this is used as a galvanic
cell?
A) Cd2+
B) Cd (s)
C) VO2+
D) VO2+
E) H+
5. What is the value of the standard cell potential for the galvanic cell?
A) +0.60 V
B) +1.40 V
C) –1.40 V
D) –0.60 V
E) +2.40 V
6. If the concentration of Cd2+ is reduced from 1.0 M to 0.01 M, and all other concentrations remain at
their standard values, what happens to the potential of the cell?
A) The cell potential increases
B) The cell potential decreases
C) The cell potential remains the same
D) The cell potential will be negative
E) none of the above
7. A concentration cell is constructed using two Ni electrodes with Ni2+ concentrations of 1.64 M and
2.85 x 10–4 M in the two half-cells. Given the standard reduction potential:
Ni2+ + 2e– → Ni E° = –0.23 V
Calculate the cell potential, E, at 25°C.
A) +0.341 V
B) –0.222 V
C) –0.256 V
D) +0.111 V
E) –0.0078 V
8. Consider the galvanic cell shown below:
The standard reduction potentials are as follows:
E° = –0.73 V
Cr3+ + 3e–  Cr(s)
–
–
E° = +1.09 V
Br2(aq) + 2e  2Br
What is the value of E for this cell at 25°C?
A) 2.21 V
B) 1.76 V
C) 2.12 V
D) 1.88 V
E) 0.59 V
9. A galvanic cell is described as follows. Cu(s) | Cu2+ (1 M) || Fe3+ (1 M), Fe2+ (1 M) | Pt
Which of the following will increase the cell voltage the most?
A) halve [Cu2+ ]
B) halve [Fe2+ ]
C) double [Cu2+ ]
D) double [Fe2+ ]
E) cut the Cu electrode in half
Use the following for questions 10-11:
In a common car battery, six identical cells each carry out the following reaction:
Pb + PbO2 + 2HSO4– + 2H+  2PbSO4 + 2H2O
10. For such a cell, E° is 2.04 V. Calculate G° at 25°C.
A) -787 kJ
B) -98 kJ
C) -394 kJ
D) -197 kJ
E) -0.121 kJ
11. Suppose that to start a car on a cold morning, 136 amperes is drawn for 16.0 seconds from such a
cell. How many grams of Pb are consumed? (The atomic mass of Pb is 207.19 g/mol.)
A) 9.35 g
B) 2.34 g
C) 4.67 g
D) 0.00913 g
E) 0.428 g
12. The mechanism for a reaction consists of the following two steps.
NO2 + NO2  NO3 + NO
NO3 + CO  NO2 + CO2
For this mechanism, which of the following statements is true?
A) NO2 is an intermediate
B) NO2 is a catalyst
C) NO3 is an intermediate
D) NO3 is a catalyst
E) Both (b) and (c) are true
13. Consider the second-order reaction aA  products (which has a first half-life of 22 s). If the
concentration of A after 13.4 seconds is 0.46 M, determine the initial concentration of A.
A) 0.69 M
B) 0.18 M
C) 0.36 M
D) 0.26 M
E) 0.74 M
14. A first-order reaction is 43% complete at the end of 18 min. What is the value of the rate constant?
A) 3.1 x 10-2 min-1
B) 0.21 min-1
C) 0.031 min-1
D) 4.7 x 10-2 min-1
E) 1.4 x 10-2 min-1
15. For the reaction, A  B, the activation energy, Ea = 65 kJ/mol, and ΔE = 15 kJ/mol.
What is the activation energy for the reverse reaction, B  A?
A) 80 kJ /mol
B) 40 kJ /mol
C) 15 kJ /mol
D) 50 kJ /mol
E) 65 kJ /mol
16. The activation energy for the reaction H2(g) + I2(g)  2HI(g) is changed from 184 kJ/mol to
59.0 kJ/mol at 600. K by the introduction of a Pt catalyst. Calculate the value of the ratio
rate(catalyzed)/rate(uncatalyzed).
A) 1.00
B) 7.62 x 1010
C) 1.38
D) 0.321
E) 1.31 x 10–11
17. According to collision theory, which condition(s) must be met in order for molecules to react?
1. The reacting molecules must collide with sufficient energy to initiate the process of breaking
and forming bonds.
2. A catalyst must be in contact with the reacting molecules for a reaction to occur.
3. The reacting molecules must collide with an orientation that can lead to rearrangement of the
atoms.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1 and 3
18. Consider the following mechanism.
H2S = H+ + HS–
fast equilibrium
Cl2 + HS– → H+ + 2 Cl– + S
slow
+
–
Cl2 + H2S → 2 H + 2 Cl + S fast
In the rate law for the mechanism given above, what is the order with respect to H+?
A) –1
B) –2
C) 1
D) 2
E) ½
19. The reaction of (CH3)3CBr with hydroxide ion proceeds with the formation of (CH3)3COH.
(CH3)3CBr (aq) + OH– (aq)  (CH3)3COH (aq) + Br– (aq)
The following data were obtained at 55°C.
[(CH3)3CBr]0
[HO–]0 Initial Rate
Exp.
(mol/L)
(mol/L) (mol/L • s)
1
0.10
0.10
1.0  10–3
2
0.20
0.10
2.0  10–3
3
0.10
0.20
1.0  10–3
4
0.30
0.20
?
What will the initial rate (in mol/L • s) be in Experiment 4?
A)
B)
C)
D)
E)
3.0  10–3
6.0  10–3
9.0  10–3
18  10–3
none of these
20. The reaction A  B + C is known to be zero order in A with a rate constant of 3.8  10–2 mol/L • s
at 25° C. An experiment was run at 25°C where [A]0 = 1.8  10–3 M. What is the rate after 6.7
minutes?
A)
B)
C)
D)
E)
3.8  10–2 mol/L • s
1.5  10–11 mol/L • s
6.7  10–4 mol/L • s
1.8  10–3 mol/L • s
6.8  10–5 mol/L • s
21. Experimental data for the reaction A → 2 B + C have been plotted in the following three
different ways (with concentration units in mol/L).
If the initial concentration is [A]0 = 0.1 M, what is the concentration of A after 10.0 seconds?
A) 0.009 M
B) 0.09 M
C) 0.008 M
D) 0.006 M
E) None of the above
22. The reaction A  B + C is known to be zero order in A with a rate constant of 4.8  10–2 mol/L • s
at 25° C. An experiment was run at 25°C where [A]0 = 2.2 M. What is the concentration of B after
6.0 s?
A)
B)
C)
D)
E)
8.5  10–1 M
1.9 M
1.1  10–1 M
2.9  10–1 M
2.2 M
23. The reaction 3NO  N2O + NO2 is found to obey the rate law Rate = k[NO]2. If the first half-life
of the reaction is found to be 4.4 s, what is the length of the fourth half-life?
A) 8.3 s
B) 18 s
C) 70 s
D) 26 s
E) 35.2 s
24. For which of the following transitions would a hydrogen atom absorb a photon with the longest
wavelength?
A) n = 1 to n = 2
B) n = 2 to n = 4
C) n = 5 to n = 1
D) n = 7 to n = 6
E) n = 5 to n = 6
25. Which of the following frequencies corresponds to light with the longest wavelength?
A)
3.00  1013 s–1
B)
4.12  105 s–1
C)
8.50  1020 s–1
D)
9.12  1012 s–1
E)
3.20  109 s–1
26. Which type of experiment demonstrates that an electron has the properties of a wave?
A) nuclear fission
B) electron diffraction
C) light emission from atomic gases
D) mass spectroscopy
E) photoelectric effect
Answers:
1. C
2. E
3. A
4. C
5. B
6. A
7. D
8. D
9. B
10. C
11. B
12. C
13. E
14. A or C
15. D
16. B
17. E
18. A
19. A
20. A
21. A
22. D
23. E
24. E
25. B
26. B