Download Chem25-FALL 2021-Exam3 GP answers

Exam #3
CHEM025 - Section 03 & 04
General Chemistry I --- Fall 2021
10/29/2021
Instructor: Prof. G. Pantouris
Questions
32 multiple choice
(100 pts)
Find the correct answer (3.125 pts/question).
1. Which of the following solutions will be the best buffer at a pH of 4.74? (Ka for HC2H3O2 is
1.8 × 10-5; Kb for NH3 is 1.8 × 10-5.)
A)
B)
C)
D)
E)
7.0 M NaOH and 7.0 M NaCl
10.0 M HC2H3O2 and 10.0 M NH4Cl
0.10 M NH3 and 0.10 M NH4Cl
5.0 M HC2H3O2 and 5.0 M NaC2H3O2
5.0 M HC2H3O2 and 5.0 M HCl
2. Which of the following species is not amphoteric?
a. H2PO4–
b. HPO42–
c. H2O
d. HCO3–
e. All of these are amphoteric
3. Which of the following are considered acid-base reactions per Brønsted-Lowry definition?
I. NH3 (g) + HCl (g) ⟺ NH4Cl (s)
II. NH3 (aq) + H2O (aq) ⟺ NH4+ (aq) + OH- (aq)
III. H2PO4- (aq) + H2O (aq) ⟺ HPO42- (aq) + H+ (aq)
a. I and II
b. II and III
c. III only
d. I only
e. All of them
4. Which of the following represents a conjugate acid-base pair?
a.
b.
c.
d.
e.
H2PO4– and PO43–
HNO3 and NO3–
HCl and IHSO4– and SO32–
H2CO3 and CO32-
2
5. Which of the following species is not amphoteric?
a.
b.
c.
d.
e.
H2PO4–
HPO42–
H2O
HSO4–
All of them are amphoteric.
6. Consider the following hypothetical reaction where HA is a weak acid.
A– + H+
⟺
HA
K= 10
The Ka value for this reaction is
a.
b.
c.
d.
e.
0.01
0.1
1
10
100
7. 50.00 mL of 0.0155 M HI (aq) is mixed with 75.00 mL of 0.0106 M Ba(OH)2 (aq). What is
the pH of the final solution?
a.
b.
c.
d.
e.
11.12
10.89
6.89
10.51
2.48
8. Arrange the following 0.5 M solutions from lowest to highest pH:
HI, HF, CH3COOH, Ba(OH)2, NaCN
Ka for HCN is 6.2 × 10–10;
Ka for HF is 7.2 × 10–4;
Ka for HC2H3O2 is 1.8 × 10–5;
a.
b.
c.
d.
e.
HI, CH3COOH, HF, NaCN, Ba(OH)2
HI, CH3COOH, NaCN, HF, Ba(OH)2
HI, HF, CH3COOH, NaCN, Ba(OH)2
CH3COOH, HI, Ba(OH)2, NaCN, HF
Ba(OH)2, HF, CH3COOH, NaCN, HI
3
9. In deciding which of two acids is the stronger, one must know
a.
b.
c.
d.
e.
the pH of each solution only
the concentration of each acid solution only
the pOH of each solution and Kw
the equilibrium constant of each acid only
All of the above
10. At a particular temperature, the ion-product constant of water, Kw, is 1.7 × 10–14. What is the
pH of pure water at this temperature?
a.
b.
c.
d.
e.
6.73
7.00
7.12
6.77
6.88
11. Consider a neutral solution at a given temperature. Which statement(s) is/are true?
a.
b.
c.
d.
e.
pH=7.00
[H+] = [OH–]
Kw=1x10-14
[H+]= 1x 10-7
all the above
12. You have 1.00 M methylamine. Calculate the pH (Kb = 4.38 x 10−4).
a.
b.
c.
d.
e.
12.32
10.89
11.98
13.87
6.58
13. Calculate the pH of a 0.01 M H2SO4 (Ka2 = 1.2×10–2)
a.
b.
c.
d.
e.
1.84
2.89
2.33
3.10
4.98
4
14. As pure water is heated, its pH decreases. This means that
a.
b.
c.
d.
e.
[OH–] > [H+]
[H+] > [OH–]
the water is no longer neutral
Two of these are correct
None of these is correct
15. Calculate the pH of a 0.040 M perchloric acid solution
a.
b.
c.
d.
e.
1.40
2.10
12.60
4.89
6.87
16. The pH of a 0.6 M solution of a weak acid is 4.0. What percent of the acid has ionized?
a.
b.
c.
d.
e.
7%
10%
0.00017%
1.2%
0.000005%
17. Which of the following indicates the most acidic solution?
a.
b.
c.
d.
pOH = 5.9
[H+] = 0.3 M
[H+] = 1.0 × 10–4 M
[OH–] = 0.5 M
5
18. A solution contains 0.50 HA (Ka = 2.0 × 10-8) and 0.22 M NaA. Calculate the pH after
0.05mol of NaOH is added to 1.00 L of this solution.
a.
b.
c.
d.
e.
7.48
7.70
7.34
7.95
7.19
19. The pH of a solution made of 0.100 mol of a weak monoprotic acid HA in 1.000 L of
solution is 1.47. Calculate Ka for this acid.
a.
b.
c.
d.
e.
0.90
0
0.100
0.0174
70
20. Consider a solution of 2.0 M HCN and 1.0 M NaCN (Ka for HCN = 6.2 × 10–10). Which of
the following statements is true?
a.
b.
c.
d.
e.
The solution is not a buffer
[OH–] > [H+]
[OH–] < [H+]
[OH–] = [H+]
None of these is true
21. How many moles of HCl(g) must be added to 1.0 L of 2.0 M NaOH to achieve a pH of 0.00?
(Neglect any volume change.)
a.
b.
c.
d.
e.
3.0 mol
10. mol
1.0 mol
2.0 mol
none of these
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22. The pH at the equivalence point of a titration of a weak acid with a strong base is
a.
More data are needed to answer this question.
b.
equal to 7.00.
c.
greater than 7.00.
d.
less than 7.00.
23. If 16 mL of 0.78 M HCl is added to 109 mL of 0.20 M NaOH, what is the final pH?
a.
0.76
b.
12.87
c.
13.24
d.
7.00
e.
1.13
24. The solubility, in moles per liter, of Ag2CrO4 is 1.3 × 10–4 M at 25°C. Calculate Ksp for this
compound.
a. 2.3 × 10–13
b. 6.1 × 10–9
c. 8.8 × 10–12
d. 4.7 × 10–13
e. 8.8 × 10–3
25. Solubility Products (Ksp)
BaSO4
CoS
PbSO4
AgBr
BaCO3
1.5 × 10–9
5.0 × 10–22
1.3 × 10–8
5.0 × 10–13
1.6 × 10–9
Which of the following compounds is the most soluble (in moles per liter)?
a. PbSO4
b. BaSO4
c. CoS
d. AgBr
e. BaCO3
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26. Consider a strong acid/strong base titration
Which of the following statement(s) is wrong?
a.
b.
c.
d.
e.
Point E shows the equivalence point of this titration
At point F, NaOH is in excess
At point D, pH= pKa
At point A, pH = - log [H+]
At point B, NaOH is the limiting reactant
27. Consider the following titration curve
At the equivalence point, the pH is
a.
b.
c.
d.
Acidic
Basic
Neutral
More information is needed
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28. A solution of hydrochloric acid of unknown concentration was titrated with 0.12 M NaOH. If
a 250-mL sample of the HCl solution required exactly 24 mL of the NaOH solution to reach
the equivalence point, what was the pH of the HCl solution?
a. 3.56
b. 2.99
c. 4.81
d. 2.27
e. 1.94
29. Consider the titration of 50 mL of 0.10 M acetic acid (HC2H3O2, Ka = 1.8 x 10-5) with 0.10 M
NaOH. What is the pH of the solution when 25.0 mL of 0.10 M NaOH has been added?
a. 3.99
b. 4.74
c. 5.21
d. 3.56
e. 0.89
30. Consider the titration of 50 mL of 0.200 M HClO4 with 0.100 M LiOH. What is the pH of the
solution when 150.0 ml LiOH has been added?
a. 10.78
b. 11.04
c. 12.40
d. 13.89
e. 13.97
31. & 32. Choose A
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