Chemistry
Third Edition
Julia Burdge
Lecture PowerPoints
Chapter 16
Acids and Bases
Copyright © 2012, The McGraw-Hill Compaies, Inc. Permission required for reproduction or display.
CHAPTER
16.1
16.2
16.3
16.4
16.5
16.6
16.7
16.8
16.9
16
Acids and Bases
Brønsted Acids and Bases
The Acid-Base Properties of Water
The pH Scale
Strong Acids and Bases
Weak Acids and Acid Ionization Constants
Weak Bases and Base Ionization Constants
Conjugate Acid-Base Pairs
Diprotic and Polyprotic Acids
Molecular Structure and Acid Strength
2
CHAPTER
16
Acids and Bases
16.10 Acid-Base Properties of Salt Solutions
16.11 Acid-Base Properties of Oxides and Hydroxides
16.12 Lewis Acids and Bases
3
16.1
Brønsted Acids and Bases
Topics
Brønsted Acids and Bases
4
16.1
Brønsted Acids and Bases
Brønsted Acids and Bases
A Brønsted acid is a substance that can donate a proton and a
Brønsted base is a substance that can accept a proton.
5
16.1
Brønsted Acids and Bases
Brønsted Acids and Bases
6
16.1
Brønsted Acids and Bases
Brønsted Acids and Bases
7
16.1
Brønsted Acids and Bases
Brønsted Acids and Bases
8
16.1
Brønsted Acids and Bases
Brønsted Acids and Bases
9
SAMPLE PROBLEM
16.1
What is
(a) the conjugate base of HNO3,
(b) the conjugate acid of O2–,
(c) the conjugate base of HSO4– , and
(d) the conjugate acid of HCO3– ?
Strategy
To find the conjugate base of a species, remove a proton from
the formula.
To find the conjugate acid of a species, add a proton to the
formula.
10
SAMPLE PROBLEM
16.1
What is
(a) the conjugate base of HNO3,
(b) the conjugate acid of O2–,
(c) the conjugate base of HSO4– , and
(d) the conjugate acid of HCO3– ?
Solution
11
16.2
The Acid-Base Properties of Water
Topics
The Acid-Base Properties of Water
12
16.2
The Acid-Base Properties of Water
The Acid-Base Properties of Water
A species that can behave either as a Brønsted acid or a
Brønsted base is called amphoteric.
This reaction is known as the autoionization of water.
13
16.2
The Acid-Base Properties of Water
The Acid-Base Properties of Water
In pure water at 25°C:
14
16.2
The Acid-Base Properties of Water
The Acid-Base Properties of Water
The relative amounts of H3O+ and OH– determine whether a
solution is neutral, acidic, or basic.
• When [H3O+] = [OH–], the solution is neutral.
• When [H3O+] > [OH–], the solution is acidic.
• When [H3O+] < [OH–], the solution is basic.
15
SAMPLE PROBLEM
16.3
The concentration of hydronium ions in stomach acid is 0.10
M. Calculate the concentration of hydroxide ions in stomach
acid at 25°C.
Strategy
Use the value of Kw to determine [OH–] when [H3O+] = 0.10 M.
Setup
16
SAMPLE PROBLEM
16.3
Solution
17
16.3
The pH Scale
Topics
The pH Scale
18
16.3
The pH Scale
The pH Scale
Because [H3O+] = [OH–] = 1.0 × 10–7 M in pure water at 25°C,
the pH of pure water at 25°C is
–log (1.0 × 10–7) = 7.00
19
16.3
The pH Scale
The pH Scale
Remember, too, that a solution in which [H3O+] = [OH–] is
neutral.
At 25°C, therefore, a neutral solution has pH 7.00.
An acidic solution, one in which [H3O+] > [OH–], has pH < 7.00,
whereas a basic solution, in which [H3O+] < [OH–], has
pH > 7.00.
20
16.3
The pH Scale
21
16.3
The pH Scale
The pH Scale
22
16.3
The pH Scale
The pH Scale
A measured pH can be used to determine experimentally the
concentration of hydronium ion in solution.
23
SAMPLE PROBLEM
16.4
Determine the pH of a solution at 25°C in which the
hydronium ion concentration is
(a) 3.5 × 10–4 M,
(b) 1.7 × 10–7 M, and
(c) 8.8 × 10–11 M.
Setup
24
SAMPLE PROBLEM
16.4
Solution
25
SAMPLE PROBLEM
16.5
Calculate the hydronium ion concentration in a solution at
25°C in which the pH is (a) 4.76, (b) 11.95, and (c) 8.01.
Setup
Solution
26
16.3
The pH Scale
The pH Scale
A pOH scale analogous to the pH scale can be defined using
the negative base-10 logarithm of the hydroxide ion
concentration of a solution, [OH–].
27
16.3
The pH Scale
The pH Scale
28
16.3
The pH Scale
The pH Scale
29
SAMPLE PROBLEM
16.6
Determine the pOH of a solution at 25°C in which the
hydroxide ion concentration is
(a) 3.7 × 10–5 M,
(b) 4.1 × 10–7 M, and
(c) 8.3 × 10–2 M.
Setup
30
SAMPLE PROBLEM
16.6
Solution
31
SAMPLE PROBLEM
16.7
Calculate the hydroxide ion concentration in a solution at
25°C in which the pOH is
(a) 4.91,
(b) 9.03, and
(c) 10.55.
Setup
32
SAMPLE PROBLEM
16.7
Solution
33
16.4
Strong Acids and Bases
Topics
Strong Acids
Strong Bases
34
16.4
Strong Acids and Bases
Strong Acids
The ionization of strong acids and the dissociation of strong
bases generally are not treated as equilibria but rather as
processes that go to completion.
This makes the determination of pH for a solution of strong
acid or strong base relatively simple.
35
16.4
Strong Acids and Bases
Strong Acids
Remember that although sulfuric acid has two ionizable
protons, only the first ionization is complete.
It is a good idea to commit this short list of strong acids to
memory.
36
16.4
Strong Acids and Bases
Strong Acids
Because the ionization of a strong acid is complete, the
concentration of hydronium ion at equilibrium is equal to the
starting concentration of the strong acid.
37
SAMPLE PROBLEM
16.8
Calculate the pH of an aqueous solution at 25°C that is
(a) 0.035 M in HI,
(b) 1.2 × 10–4 M in HNO3, and
(c) 6.7 × 10–5 M in HClO4.
Strategy
HI, HNO3, and HClO4 are all strong acids, so the concentration
of hydronium ion in each solution is the same as the stated
concentration of the acid.
38
SAMPLE PROBLEM
16.8
Setup
Solution
39
SAMPLE PROBLEM
16.9
Calculate the concentration of HCl in a solution at 25°C that
has pH
(a) 4.95,
(b) 3.45, and
(c) 2.78.
Setup
40
SAMPLE PROBLEM
16.9
Solution
41
16.4
Strong Acids and Bases
Strong Bases
The list of strong bases is also fairly short. It consists of the
hydroxides of alkali metals (Group 1A) and the hydroxides of
the heaviest alkaline earth metals (Group 2A).
The dissociation of a strong base is, for practical purposes,
complete.
42
16.4
Strong Acids and Bases
Strong Bases
Group 1A Hydroxides
Group 2A Hydroxides
43
16.4
Strong Acids and Bases
Strong Bases
As with strong acids, because the reaction goes to
completion, the pH of a strong-base solution is relatively easy
to calculate.
44
SAMPLE PROBLEM
16.10
Calculate the pOH of the following aqueous solutions at 25°C:
(a) 0.013 M LiOH,
(b) 0.013 M Ba(OH)2,
(c) 9.2 × 10–5 M KOH.
Strategy
LiOH, Ba(OH)2, and KOH are all strong bases.
Use reaction stoichiometry to determine hydroxide ion
concentration and
to determine pOH.
45
SAMPLE PROBLEM
16.10
Setup
(a) The hydroxide ion concentration is simply equal to the
concentration of the base. Therefore, [OH–] = [LiOH] =
0.013 M.
(b) The hydroxide ion concentration is twice that of the base:
Therefore, [OH–] = 2 × [Ba(OH)2] = 2(0.013 M) = 0.026 M.
(c) The hydroxide ion concentration is equal to the
concentration of the base. Therefore,
[OH–] = [KOH] = 9.2 × 10–5 M.
46
SAMPLE PROBLEM
16.10
Solution
47
SAMPLE PROBLEM
16.11
An aqueous solution of a strong base has pH 8.15 at 25°C.
Calculate the original concentration of base in the solution
(a) if the base is NaOH and
(b) if the base is Ba(OH)2.
48
SAMPLE PROBLEM
16.11
Strategy
Use
to convert from pH to pOH and
to determine the hydroxide ion concentration.
Consider the stoichiometry of dissociation in each case to
determine the concentration of the base itself.
49
SAMPLE PROBLEM
16.11
Setup
(a) The dissociation of 1 mole of NaOH produces 1 mole of
OH–. Therefore, the concentration of the base is equal to
the concentration of hydroxide ion.
(b) The dissociation of 1 mole of Ba(OH)2 produces 2 moles of
OH–. Therefore, the concentration of the base is only onehalf the concentration of hydroxide ion.
50
SAMPLE PROBLEM
16.11
Solution
51
16.5
Weak Acids and Acid Ionization Constants
Topics
The Ionization Constant, Ka
Calculating pH from Ka
Percent Ionization
Using pH to Determine Ka
52
16.5
Weak Acids and Acid Ionization Constants
The Ionization Constant, Ka
Most acids are weak acids, which ionize only to a limited
extent in water.
At equilibrium, an aqueous solution of a weak acid contains a
mixture of aqueous acid molecules, hydronium ions, and the
corresponding conjugate base.
The degree to which a weak acid ionizes depends on the
concentration of the acid and the equilibrium constant for the
ionization.
53
16.5
Weak Acids and Acid Ionization Constants
The Ionization Constant, Ka
Ka is called the acid ionization constant.
Although all weak acids ionize less than 100 percent, they
vary in strength
54
16.5
Weak Acids and Acid Ionization Constants
The Ionization Constant, Ka
The magnitude of Ka indicates how strong a weak acid is.
A large Ka value indicates a stronger acid, whereas a small Ka
value indicates a weaker acid.
55
16.5
Weak Acids and Acid Ionization Constants
The Ionization Constant, Ka
56
16.5
Weak Acids and Acid Ionization Constants
Calculating pH from Ka
57
16.5
Weak Acids and Acid Ionization Constants
Calculating pH from Ka
58
16.5
Weak Acids and Acid Ionization Constants
Calculating pH from Ka
59
16.5
Weak Acids and Acid Ionization Constants
Calculating pH from Ka
This shortcut gives a good approximation as long as the
magnitude of x is significantly smaller than the initial acid
concentration.
As a rule, it is acceptable to use this shortcut if the calculated
value of x is less than 5 percent of the initial acid
concentration.
This is the formula for the percent ionization of the acid.
60
SAMPLE PROBLEM
16.12
The Ka of hypochlorous acid (HClO) is 3.5 × 10–8. Calculate the
pH of a solution at 25°C that is 0.0075 M in HClO.
Setup
61
SAMPLE PROBLEM
16.12
Setup
Solution
62
SAMPLE PROBLEM
16.12
Solution
63
16.5
Weak Acids and Acid Ionization Constants
Percent Ionization
64
SAMPLE PROBLEM
16.13
Determine pH and percent ionization for acetic acid solutions
at 25°C with concentrations (a) 0.15 M, (b) 0.015 M, and (c)
0.0015 M.
Setup
Ka for acetic acid is 1.8 × 10–5.
65
SAMPLE PROBLEM
16.13
Solution
66
SAMPLE PROBLEM
16.13
Solution
67
16.5
Weak Acids and Acid Ionization Constants
Using pH to Determine Ka
Suppose we want to determine the Ka of a weak acid (HA) and
we know that a 0.25 M solution of the acid has a pH of 3.47 at
25°C.
[H3O+] = 10–3.47 = 3.39 × 10–4 M
68
SAMPLE PROBLEM
16.14
Aspirin (acetylsalicylic acid, HC9H7O4) is a weak acid. It ionizes
in water according to the equation
A 0.10-M aqueous solution of aspirin
has a pH of 2.27 at 25°C. Determine
the Ka of aspirin.
69
SAMPLE PROBLEM
16.14
Setup
Solution
70
16.6
Weak Bases and Base Ionization Constants
Topics
The Ionization Constant, Kb
Calculating pH from Kb
Using pH to Determine Kb
71
16.6
Weak Bases and Base Ionization Constants
The Ionization Constant, Kb
Just as most acids are weak, most bases are also weak.
The ionization of a weak base is incomplete and is treated in
the same way as the ionization of a weak acid.
72
16.6
Weak Bases and Base Ionization Constants
The Ionization Constant, Kb
73
16.6
Weak Bases and Base Ionization Constants
The Ionization Constant, Kb
74
16.6
Weak Bases and Base Ionization Constants
Calculating pH from Kb
Solving problems involving weak bases requires the same
approach we used for weak acids.
It is important to remember, though, that solving for x in a
typical weak base problem gives us the hydroxide ion
concentration rather than the hydronium ion concentration.
75
SAMPLE PROBLEM
16.15
What is the pH of a 0.040 M ammonia solution at 25°C?
Setup
Solution
76
SAMPLE PROBLEM
16.15
Solution
77
SAMPLE PROBLEM
16.15
Solution
78
16.6
Weak Bases and Base Ionization Constants
Using pH to Determine Kb
Just as we can use pH to determine the Ka of a weak acid, we
can also use it to determine the Kb of a weak base.
79
SAMPLE PROBLEM
16.16
Caffeine, the stimulant in coffee and tea, is a weak base that
ionizes in water according to the equation
A 0.15-M solution of caffeine at 25°C
has a pH of 8.45. Determine the Kb
of caffeine.
80
SAMPLE PROBLEM
16.16
Setup
Solution
81
16.7
Conjugate Acid-Base Pairs
Topics
The Strength of a Conjugate Acid or Base
The Relationship Between Ka and Kb of a Conjugate AcidBase Pair
82
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
The chloride ion, which is the conjugate base of a strong acid,
is an example of a weak conjugate base.
83
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
The fluoride ion, which is the conjugate base of a weak acid, is
an example of a strong conjugate base.
Conversely, a strong base has a weak conjugate acid and a
weak base has a strong conjugate acid.
84
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
85
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
86
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
It is important to recognize that the words strong and weak
do not mean the same thing in the context of conjugate acids
and conjugate bases as they do in the context of acids and
bases in general.
A strong conjugate reacts with water—either accepting a
proton from it or donating a proton to it—to a small but
measurable extent.
87
16.7
Conjugate Acid-Base Pairs
The Strength of a Conjugate Acid or Base
A strong conjugate acid acts as a weak Brønsted acid in water;
and a strong conjugate base acts as a weak Brønsted base in
water.
A weak conjugate does not react with water to any
measurable extent.
88
16.7
Conjugate Acid-Base Pairs
The Relationship Between Ka and Kb of a Conjugate Acid-Base
Pair
89
16.7
Conjugate Acid-Base Pairs
The Relationship Between Ka and Kb of a Conjugate Acid-Base
Pair
90
16.7
Conjugate Acid-Base Pairs
The Relationship Between Ka and Kb of a Conjugate Acid-Base
Pair
91
SAMPLE PROBLEM
16.17
Determine
(a) Kb of the acetate ion (CH3COO–),
(b) Ka of the methylammonium ion (CH3NH3+ ),
(c) Kb of the fluoride ion (F–), and
(d) Ka of the ammonium ion (NH4+ ).
Setup
92
SAMPLE PROBLEM
16.17
Solution
93
16.8
Diprotic and Polyprotic Acids
Topics
Diprotic and Polyprotic Acids
94
16.8
Diprotic and Polyprotic Acids
Diprotic and Polyprotic Acids
95
16.8
Diprotic and Polyprotic Acids
Diprotic and Polyprotic Acids
96
16.8
Diprotic and Polyprotic Acids
Diprotic and Polyprotic Acids
97
SAMPLE PROBLEM
16.18
Oxalic acid (H2C2O4) is a poisonous substance used mainly as a
bleaching agent.
Calculate the concentrations of all species present at
equilibrium in a 0.10-M solution at 25°C.
Setup
98
SAMPLE PROBLEM
16.18
Setup
Solution
99
SAMPLE PROBLEM
16.18
Solution
100
SAMPLE PROBLEM
16.18
Solution
101
SAMPLE PROBLEM
16.18
Solution
102
SAMPLE PROBLEM
16.18
Solution
103
16.9
Molecular Structure and Acid Strength
Topics
Hydrohalic Acids
Oxoacids
Carboxylic Acids
104
16.9
Molecular Structure and Acid Strength
Hydrohalic Acids
The strength of an acid is measured by its tendency to ionize:
Two factors influence the extent to which the acid undergoes
ionization.
One is the strength of the H—X bond. The stronger the bond,
the more difficult it is for the HX molecule to break up and
hence the weaker the acid.
The other factor is the polarity of the H—X bond.
105
16.9
Molecular Structure and Acid Strength
Hydrohalic Acids
If the bond is highly polarized (i.e., if there is a large
accumulation of positive and negative charges on the H and X
atoms, respectively), HX will tend to break up into H+ and X–
ions.
A high degree of polarity, therefore, gives rise to a stronger
acid.
106
16.9
Molecular Structure and Acid Strength
Hydrohalic Acids
107
16.9
Molecular Structure and Acid Strength
Oxoacids
An oxoacid contains hydrogen, oxygen, and a central,
nonmetal atom.
108
16.9
Molecular Structure and Acid Strength
Oxoacids
To compare their strengths, it is convenient to divide the
oxoacids into two groups:
1. Oxoacids having different central atoms that are from the
same group of the periodic table and that have the same
oxidation number.
109
16.9
Molecular Structure and Acid Strength
Oxoacids
Within this group, acid strength increases with increasing
electronegativity of the central atom.
Cl is more electronegative than Br; the O—H bond is more
polar in chloric acid than in bromic acid .
110
16.9
Molecular Structure and Acid Strength
Oxoacids
2. Oxoacids having the same central atom but different
numbers of oxygen atoms.
Within this group, acid strength increases with increasing
oxidation number of the central atom.
111
16.9
Molecular Structure and Acid Strength
Oxoacids
The ability of chlorine to draw electrons away from the OH
group (thus making the O—H bond more polar) increases
with the number of electronegative O atoms attached to Cl.
112
SAMPLE PROBLEM
16.19
Predict the relative strengths of the oxoacids in each of the
following groups:
(a) HClO, HBrO, and HIO;
(b) HNO3 and HNO2.
Strategy
In each group, compare the electronegativities or oxidation
numbers of the central atoms to determine which O H bonds
are the most polar.
The more polar the O—H bond, the more readily it is broken
and the stronger the acid.
113
SAMPLE PROBLEM
16.19
Setup
(a) In a group with different central atoms, we must compare
electronegativities. The electronegativities of the central
atoms in this group decrease as follows: Cl > Br > I.
(b) These two acids have the same central atom but differ in
the number of attached oxygen atoms. In a group such as
this, the greater the number of attached oxygen atoms,
the higher the oxidation number of the central atom and
the stronger the acid.
114
SAMPLE PROBLEM
16.19
Solution
115
16.9
Molecular Structure and Acid Strength
Carboxylic Acids
The conjugate base of a carboxylic acid, called a carboxylate
anion, RCOO–, can be represented by more than one
resonance structure:
116
16.9
Molecular Structure and Acid Strength
Carboxylic Acids
The strength of carboxylic acids depends on the nature of the
R group.
The presence of the electronegative Cl atom in chloroacetic
acid shifts the electron density toward the R group, thereby
making the O—H bond more polar. Chloroacetic acid is the
stronger of the two acids.
117
16.10 Acid-Base Properties of Salt Solutions
Topics
Basic Salt Solutions
Acidic Salt Solutions
Neutral Salt Solutions
Salts in Which Both the Cation and the Anion Hydrolyze
118
16.10 Acid-Base Properties of Salt Solutions
Basic Salt Solutions
Consider a solution of the salt sodium fluoride (NaF).
This is a specific example of salt hydrolysis, in which ions
produced by the dissociation of a salt react with water to
produce either hydroxide ions or hydronium ions—thus
impacting pH.
119
16.10 Acid-Base Properties of Salt Solutions
Basic Salt Solutions
In general, an anion that is the conjugate base of a weak acid
reacts with water to produce hydroxide ion.
Other examples include the acetate ion (CH3COO–), the nitrite
ion (NO2–), the sulfite ion (SO32–), and the hydrogen carbonate
ion (HCO3–).
120
SAMPLE PROBLEM
16.20
Calculate the pH of a 0.10-M solution of sodium fluoride
(NaF) at 25°C.
Setup
121
SAMPLE PROBLEM
16.20
Solution
122
16.10 Acid-Base Properties of Salt Solutions
Acidic Salt Solutions
123
SAMPLE PROBLEM
16.21
Calculate the pH of a 0.10-M solution of ammonium chloride
(NH4Cl) at 25°C.
Setup
124
SAMPLE PROBLEM
16.21
Solution
125
16.10 Acid-Base Properties of Salt Solutions
Acidic Salt Solutions
The metal ion in a dissolved salt can also react with water to
produce an acidic solution.
The extent of hydrolysis is greatest for the small and highly
charged metal cations such as Al3+, Cr3+, Fe3+, Bi3+, and Be2+.
126
16.10 Acid-Base Properties of Salt Solutions
Acidic Salt Solutions
For example, when aluminum chloride dissolves in water,
each Al3+ ion becomes associated with six water molecules.
127
16.10 Acid-Base Properties of Salt Solutions
Acidic Salt Solutions
Al(OH)(H2O)52+ can undergo further ionization:
and so on.
It is generally sufficient, however, to take into account only
the first stage of hydrolysis when determining the pH of a
solution that contains metal ions.
128
16.10 Acid-Base Properties of Salt Solutions
Neutral Salt Solutions
The extent of hydrolysis is greatest for the smallest and most
highly charged metal ions because a compact, highly charged
ion is more effective in polarizing the O—H bond and
facilitating ionization.
This is why relatively large ions of low charge, including the
metal cations of Groups 1A and 2A (the cations of the strong
bases), do not undergo significant hydrolysis (Be2+ is an
exception).
Thus, most metal cations of Groups 1A and 2A do not impact
the pH of a solution.
129
16.10 Acid-Base Properties of Salt Solutions
Neutral Salt Solutions
Similarly, anions that are conjugate bases of strong acids do
not hydrolyze to any significant degree.
Consequently, a salt composed of the cation of a strong base
and the anion of a strong acid, such as NaCl, produces a
neutral solution.
130
16.10 Acid-Base Properties of Salt Solutions
Neutral Salt Solutions
131
SAMPLE PROBLEM
16.22
Predict whether a 0.10-M solution of each of the following
salts will be basic, acidic, or neutral:
(a) LiI,
(b) NH4NO3,
(c) Sr(NO3)2,
(d) KNO2,
(e) NaCN.
Strategy
Identify the ions present in each solution, and determine
which, if any, will impact the pH of the solution.
132
SAMPLE PROBLEM
16.22
(a) LiI, (b) NH4NO3, (c) Sr(NO3)2, (d) KNO2, (e) NaCN.
Setup
(a) Ions in solution: Li+ and I–. Li+ is a Group 1A cation; I– is the
conjugate base of the strong acid HI. Therefore, neither
ion hydrolyzes to any significant degree.
(b) Ions in solution: NH4+ and NO3– . NH4+ is the conjugate
acid of the weak base NH3; NO3– is the conjugate base of
the strong acid HNO3. In this case, the cation will
hydrolyze, making the pH acidic:
133
SAMPLE PROBLEM
16.22
(a) LiI, (b) NH4NO3, (c) Sr(NO3)2, (d) KNO2, (e) NaCN.
Setup
c. Ions in solution: Sr2+ and NO3– . Sr2+ is a heavy Group 2A
cation; NO3– is the conjugate base of the strong acid
HNO3. Neither ion hydrolyzes to any significant degree.
d. Ions in solution: K+ and NO2– . K+ is a Group 1A cation;
NO2– is the conjugate base of the weak acid HNO2. In this
case, the anion hydrolyzes, thus making the pH basic:
134
SAMPLE PROBLEM
16.22
(a) LiI, (b) NH4NO3, (c) Sr(NO3)2, (d) KNO2, (e) NaCN.
Setup
e. Ions in solution: Na+ and CN–. Na+ is a Group 1A cation;
CN– is the conjugate base of the weak acid HCN. In this
case, too, the anion hydrolyzes, thus making the pH basic:
135
SAMPLE PROBLEM
16.22
(a) LiI, (b) NH4NO3, (c) Sr(NO3)2, (d) KNO2, (e) NaCN.
Solution
136
16.10 Acid-Base Properties of Salt Solutions
Salts in Which Both the Cation and the Anion Hydrolyze
• When Kb > Ka, the solution is basic.
• When Kb < Ka, the solution is acidic.
• When Kb  Ka, the solution is neutral or nearly neutral.
137
16.11 Acid-Base Properties of Oxides and
Hydroxides
Topics
Oxides of Metals and Nonmetals
Basic and Amphoteric Hydroxides
138
16.11 Acid-Base Properties of Oxides and
Hydroxides
Oxides of Metals and Nonmetals
139
16.11 Acid-Base Properties of Oxides and
Hydroxides
Oxides of Metals and Nonmetals
140
16.11 Acid-Base Properties of Oxides and
Hydroxides
Oxides of Metals and Nonmetals
Aluminum oxide (Al2O3) is amphoteric.
141
16.11 Acid-Base Properties of Oxides and
Hydroxides
Oxides of Metals and Nonmetals
Some transition metal oxides in which the metal has a high
oxidation number act as acidic oxides.
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16.11 Acid-Base Properties of Oxides and
Hydroxides
Basic and Amphoteric Hydroxides
All the alkali and alkaline earth metal hydroxides, except
Be(OH)2, are basic.
Be(OH)2, Al(OH)3, Sn(OH)2, Pb(OH)2, Cr(OH)3, Cu(OH)2,
Zn(OH)2, and Cd(OH)2 are amphoteric.
All amphoteric hydroxides are insoluble, but beryllium
hydroxide reacts with both acids and bases as follows:
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16.11 Acid-Base Properties of Oxides and
Hydroxides
Basic and Amphoteric Hydroxides
Aluminum hydroxide reacts with both acids and bases in a
similar fashion:
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16.12 Lewis Acids and Bases
Topics
Lewis Acids and Bases
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16.12 Lewis Acids and Bases
Lewis Acids and Bases
A Lewis base is a substance that can donate a pair of
electrons.
A Lewis acid is a substance that can accept a pair of electrons.
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16.12 Lewis Acids and Bases
Lewis Acids and Bases
147
16.12 Lewis Acids and Bases
Lewis Acids and Bases
148
SAMPLE PROBLEM
16.23
Identify the Lewis acid and Lewis base in each of the following
reactions:
Setup
(a)
(b) Metal ions act as Lewis acids, accepting electron pairs
from anions or molecules with lone pairs.
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SAMPLE PROBLEM
16.23
Solution
(a)
(b) Hg2+ accepts four pairs of electrons from the CN– ions.
Therefore, Hg2+ is the Lewis acid and CN– is the Lewis
base.
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