Unit IV (Acid/Base) Review
ANSWER KEY
1. An equation representing the reaction of a weak acid with water is
A.
HCl + H2O ⇄ H3O+ + Cl-
B.
NH3 + H2O ⇄ NH4+ + OH-
C.
HCO3- H2O ⇄ H2CO3 + OH-
D.
HCOOH + H2O ⇄ H3O+ + HCOO-
2. The equilibrium expression for the ion product constant of water is
A.
Kw = [H3O+][OH-]
[H2O]
B.
Kw = [H3O+]2[O2]
C.
Kw = [H3O+][OH-]
D.
Kw = [H3O+]2[O2-]
3. Consider the following graph for the titration of 0.1 M NH 3 with 1.0 M HCl.
pH
14
I
II
7
III
IV
0
Volume HCl added
A buffer solution is present at point
A.
B.
C.
D.
I
II
III
IV
4. Consider the following equilibrium system for an indicator: HInd + H 2O ⇄ H3O+ + IndWhich two species must be of two different colours in order to be used as an indicator?
A.
B.
C.
D.
HInd and H2O
HInd and IndH3O+ and IndHind and H3O+
5. Which of the following indicators is yellow at pH 10.0?
A.
B.
C.
D.
methyl red
phenol red
thymol blue
methyl violet
6. A sample containing 1.20 x 10-2 mole HCl is completely neutralized by 100.0 mL of Sr(OH) 2. What is the
[Sr(OH)2]?
A.
B.
C.
D.
6.00 x 10-3 M
6.00 x 10-2 M
1.20 x 10-1 M
2.4 x 10-1 M
7. Which of the following titrations will have the highest pH at the equivalence point?
A.
B.
C.
D.
HBr with NH3
HNO2 with KOH
HCl with Na2CO3
HNO3 with NaOH
8. An Arrhenius acid is defined as a chemical species that
A.
B.
C.
D.
is a proton donor.
is a proton acceptor.
produces hydrogen ions in solution.
produces hydroxide ions in solution.
9. Consider the following acid-base equilibrium system: HC2O4- + H2BO3- ⇄ H3BO3 + C2O42Identify the Bronsted-Lowry bases in this equilibrium.
A.
B.
C.
D.
H2BO3HC2O4HC2O4H2BO3-
and
and
and
and
H3BO3
H3BO3
C2O42C2O42-
10. The equation representing the predominant reaction between NaCH 3COO with water is
A.
CH3COO- + H2O ⇄ CH3COOH + OH-
B.
CH3COO- + H2O ⇄ H2O + CH2COO2-
C.
CH3COOH + H2O ⇄ H3O+ + CH3COO-
D.
CH3COOH + H2O ⇄ CH3COOH2+ + OH-
11. Which of the following solutions will have the lowest electrical conductivity?
A.
B.
C.
D.
0.10 M HF
0.10 M NaF
0.10 M H2SO3
0.10 M NaHSO3
12. Which of the following is the strongest Bronsted-Lowry base?
A.
B.
C.
D.
NH3
CO32HSO3H2BO3-
13. A 1.0 x 10-4 M solution has a pH of 10.00. The solute is a
A.
B.
C.
D.
weak acid
weak base
strong acid]
strong base
14. Addition of HCl to water causes
A.
B.
C.
D.
both [H3O+] and [OH-] to increase
both [H3O+] and [OH-] to decrease
[H3O+] to increase and [OH-] to decrease
[H3O+] to decrease and [OH-] to increase
15. Consider the following:
I.
II.
III.
H2SO4
HSO4SO42-
Which of the above is/are present in a reagent bottle labeled 1.0 M H 2SO4?
A.
B.
C.
D.
I only
I and II only
II and III only
I, II, and III
16. The pH of 0.10 M KOH solution is
A.
B.
C.
D.
0.10
1.00
13.00
14.10
17. An indicator changes colour in the pH range 9.0 to 11.0. What is the value of the Ka for the indicator?
A.
B.
C.
D.
1
1
1
1
x
x
x
x
10-13
10-10
10-7
10-1
18. Which of the following are amphiprotic in aqueous solution?
I.
II.
III.
IV.
HBr
H2O
HCO3H2C6H5O7-
A
B.
C.
D.
I and II only
II and IV only
II, III, and IV only
I, II, III, and IV
19. Which of the following always applies at the transition point for the indicator Hind?
A.
B.
C.
D.
[Ind-] = [OH-]
[HInd] = [Ind-]
[Ind-] = [H3O+]
[HInd] = [H3O+]
20. Both acidic and basic solutions
A.
taste sour
B.
feel slippery
C.
conduct electricity
D.
turn blue litmus red
21. The conjugate acid of HPO42- is
A.
B.
C.
D.
PO43H2PO4H2PO42H2PO43-
22. Consider the following equilibrium: 2H2O(l) ⇄ H3O+(aq) + OH-(aq)
A small amount of Fe(H2O)63+ is added to water and equilibrium is re-established. Which of the following
represents the changes in ion concentrations?
A.
B.
C.
D.
[H3O+]
[OH-]
increases
increases
decreases
decreases
increases
decreases
decreases
increases
23. Consider the following equilibrium for an indicator: HInd + H2O ⇄ H3O+ + IndIn a solution of pH of 6.8, the colour of bromthymol blue is
A.
B.
C.
D.
blue because [HInd] = [Ind-]
green because [HInd] = [Ind-]
green because [HInd] < [Ind-]
yellow because [HInd] > [Ind-]
24. The indicator with Ka = 4 x 10-8 is
A.
B.
C.
D.
neutral red
methyl red
indigo carmine
phenolphthalein
25. In a titration a 25.00 mL sample of Sr(OH) 2 is completely neutralized by 28.60 mL of 0.100 M HCl. The
concentration of the Sr(OH)2 is
A.
B.
C.
D.
1.43
2.86
5.72
1.14
x
x
x
x
10-3 M
10-3 M
10-2 M
10-1 M
26. A student mixes 15.0 mL of 0.100 M NaOH with 10.0 mL of 0.200 M HCl. The resulting solution is
A.
B.
C.
D.
basic
acidic
neutral
amphiprotic
27. Which of the following salts will dissolve in water to produce a base solution?
A.
B.
C.
D.
LiF
CrCl3
KNO3
NH4Cl
28. What is the value of the Kb for HC6H5O72-?
A.
B.
C.
D.
5.9
2.4
4.1
1.7
x
x
x
x
10-10
10-8
10-7
10-5
29. The pOH of 0.015 M HCl solution is
A.
B.
C.
D.
0.97
1.80
12.18
13.03
30. Which of the following salts will dissolve in water to produce an acid solution?
A.
B.
C.
D.
LiF
CrCl3
KNO3
NaCl
31. A student mixes 400 mL of 0.100 M NaOH with 100 mL of 0.200 M H2SO4. The resulting solution has a pH of
A.
14.000
B.
0.000
C.
13.800
D.
7.000
32. The strongest acid in water is
A.
B.
C.
D.
HClO4
HI
HF
H3O+
33. The formula that has the highest pH in water is
A.
B.
C.
D.
HF
H2CO3
H2C2O4
HCN
34. The formula that has the highest pH in water is
A.
B.
C.
D.
NaF
NaCl
H2C2O4
NaCN
35. Acid is added to a buffer solution. When equilibrium is reestablished the buffering effect has resulted in [H 3O+]
A
B
C
D
increasing slightly
decreasing slightly
increasing considerably
decreasing considerably
36. A buffer solution will form when 0.10 M NaF is mixed with an equal volume of
A
B
C
D
0.10 M HF
0.10 M HCl
0.10 M NaCl
0.10 M NaOH
37. In which of the following are the reactants favoured?
A
HNO2 + CN- ⇄ NO2- + HCN
B
H2S + HCO3- ⇄ HS- + H2CO3
C
H3PO4 + NH3 ⇄ H2PO4- + NH4+
D
CH3COOH + PO43-
⇄ CH3COO- + HPO42-
38. Consider the following equilibrium: 2H2O(l) + energy ⇄ H3O+(aq) + OH-(aq)
What will cause the pH to increase and the Kw to decrease?
A
B
C
D
adding a strong acid
adding a strong base
increasing the temperature
decreasing the temperature
39. Which of the following acids has the weakest conjugate base?
A
B
C
D
HIO3
HNO2
H3PO4
CH3COOH
40. Which of the following represents the predominant reaction between HCO 3- and water?
A
2HCO3- ⇄ H2O + 2CO2
B
HCO3- + H2O ⇄ H2CO3
C
HCO3- + H2O ⇄
D
2HCO3- + H2O ⇄ H3O+ + CO32-
+ OH-
H3O+ + CO32+
OH- + CO2
Written Section
1. A chemist prepares a solution by dissolving the salt NaCN in water.
a) Write the equation for the dissociation reaction that occurs.
NaCN →
Na+
+
CN-
b) Write the equation for the hydrolysis reaction that occurs.
CN-
+
H2O
⇄ HCN
OH-
+
c) Calculate the value of the equilibrium constant for the hydrolysis
Kb(CN-)
=
Kw
Ka(HCN)
=
1.0 x 10-14
4.9 x 10-10
=
2.0 x 10-5
2. A 3.50 x 10-3 M sample of unknown acid, HA has a pH of 2.90. Calculate the value of the Ka and identify this
acid.
[H+] = 10-pH
= 10-2.90
HA
⇄
=
0.00126 M
H+
+
A-
I
0.00350 M
0
0
C
0.00126 M
0.00126 M
0.00126 M
E
0.00224 M
0.00126 M
0.00126 M
Ka
=
(0.00126)2
0.00224
=
7.1 x 10-4
Citric acid
3. Calculate the mass of NaOH needed to prepare 2.0 L of a solution with a pH of 12.00.
pOH
=
14.00 - 12.00
[OH-] = 10-2.00
2.0 L
x
=
=
2.00
=
0.80 g NaOH
0.010 M
0.010 mol
L
x
40.0 g
mole
4. A 1.00 M OCl- solution has an [OH-] of 5.75 x 10-4 M. Calculate the Kb for OCl-.
OCl-
+
H2O
⇄
HOCl
+
OH-
I
1.00 M
0
0
C
0.000575 M
0.000575 M
0.000575 M
E
0.9994 M
0.000575 M
0.000575 M
Kb
=
(0.000575)2 =
0.9994
3.31 x 10-7
5. Determine the pH of a 0.10 M solution of hydrogen cyanide.
HCN
⇄
H+
+
CN-
I
0.10 M
0
0
C
x
x
x
E
0.10 - x
x
x
small Ka approximation x = 0
Ka
=
x2
0.10
x = 7.0 x 10-6
=
4.9 x 10-10
pH = 5.15
6. Determine the pH of 0.100 M NH3.
NH3
+
H2O
⇄
NH4+
+
OH-
I
1.00 M
0
0
C
x
x
x
E
1.00 - x
x
x
small Kb approximation x = 0
Kb(NH3)
Kb
=
=
Kw
Ka(NH4+)
x2
0.100
x = 0.001336
=
=
1.0 x 10-14
5.6 x 10-10
=
1.786 x 10-5
1.786 x 10-5
= [OH-]
pOH = -log [OH-]
pOH = 2.87
pH = 11.13
7. Determine the pH of a saturated solution of Mg(OH) 2.
Mg(OH)2
⇄
x
4x3
Mg2+
x
=
5.6
+
2OH2x
x 10-12
[OH-] = 2x = 2.24 x 10 -4
pOH = 3.65
pH = 10.35