Slide 1 ___________________________________
___________________________________ ___________________________________ Chapter 16
___________________________________ Acids and Bases
___________________________________ ___________________________________ ___________________________________ Slide Chapter 16
2 Table of Contents
16.1
16.2
16.3
16.4
16.5
16.6
___________________________________
___________________________________ Acids and Bases
Acid Strength
Water as an Acid and a Base
The pH Scale
Calculating the pH of Strong Acid Solutions
Buffered Solutions
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Slide Section 16.1
3 Acids and Bases
2
___________________________________
___________________________________ Models of Acids and Bases
___________________________________ • Arrhenius: Acids produce H+ ions in solution,
bases produce OH– ions.
• Brønsted–Lowry: Acids are proton (H+) donors,
bases are proton acceptors.
HCl + H2O → Cl– + H3O+
acid base
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___________________________________
Slide Section 16.1
4 Acids and Bases
___________________________________ Acid in Water
HA(aq) +
acid
•
•
H2O(l)
base
___________________________________ H3O+(aq) + A–(aq)
conjugate
conjugate
acid
base
___________________________________ ___________________________________ Conjugate base is everything that remains of the acid
molecule after a proton is lost.
Conjugate acid is formed when the proton is transferred
to the base.
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Slide Section 16.1
5 Acids and Bases
4
___________________________________
___________________________________ ___________________________________ ___________________________________ ___________________________________ •
Water acts as a base accepting a proton from the acid.
•
Forms hydronium ion (H3O+).
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Slide Section 16.1
6 Acids and Bases
5
___________________________________
___________________________________ Concept Check
___________________________________ Which of the following represent conjugate
acid–base pairs?
a)
b)
c)
d)
___________________________________ ___________________________________ HCl, HNO3
H3O+, OH–
H2SO4, SO42–
HCN, CN–
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Slide Section 16.2
7 Acid Strength
___________________________________
___________________________________ Strong Acid
___________________________________ • Completely ionized or completely dissociated
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Slide Section 16.2
8 Acid Strength
7
___________________________________
___________________________________ Weak Acid
___________________________________ • Most of the acid molecules remain intact.
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Slide Section 16.2
9 Acid Strength
8
___________________________________
___________________________________ Behavior of Acids of Different Strengths in Aqueous Solution
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Slide Section 16.2
10 Acid Strength
•
___________________________________
___________________________________ ___________________________________ A strong acid contains a
relatively weak
conjugate base.
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Slide Section 16.2
11 Acid Strength
10
___________________________________
___________________________________ Ways to Describe Acid Strength
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Slide Section 16.2
12 Acid Strength
11
___________________________________
___________________________________ Common Strong Acids
•
•
•
•
___________________________________ Sulfuric acid, H2SO4
Hydrochloric acid, HCl
Nitric acid, HNO3
Perchloric acid, HClO4
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Slide Section 16.2
13 Acid Strength
•
•
___________________________________
___________________________________ Oxyacid – acidic proton is attached to an oxygen atom
Organic acid – have a carbon atom backbone and
commonly contain the carboxyl group:
___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ƒ
Typically a weak acid
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Slide Section 16.2
14 Acid Strength
13
___________________________________
___________________________________ Concept Check
___________________________________ Consider a 1.0 M solution of HCl.
___________________________________ Order the following from strongest to weakest
base and explain:
H2O(l)
A–(aq) (from weak acid HA)
Cl–(aq)
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Slide Section 16.2
15 Acid Strength
14
___________________________________
___________________________________ Let’s Think About It…
___________________________________ • How good is Cl–(aq) as a base?
• Is A–(aq) a good base?
___________________________________ ___________________________________ The bases from strongest to weakest are:
___________________________________ A–, H2O, Cl–
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___________________________________
Slide Section 16.2
16 Acid Strength
___________________________________ Concept Check
___________________________________ Acetic acid (HC2H3O2) and HCN are both weak
acids. Acetic acid is a stronger acid than HCN.
___________________________________ ___________________________________ Arrange these bases from weakest to strongest
and explain your answer:
___________________________________ H2O
Cl–
CN–
C2H3O2–
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___________________________________
Slide Section 16.2
17 Acid Strength
___________________________________ Let’s Think About It…
___________________________________ • H2O(l) + H2O(l)
acid
base
H3O+(aq) + OH–(aq)
conjugate conjugate
acid
base
–14
• At 25°C, Kw = 1.0 x 10
___________________________________ ___________________________________ The bases from weakest to strongest are:
___________________________________ Cl–, H2O, C2H3O2–, CN–
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Slide Section 16.3
18 Water as an Acid and a Base
17
___________________________________
___________________________________ Water as an Acid and a Base
___________________________________ • Water is amphoteric:
ƒ Behaves either as an acid or as a base.
• At 25°C:
Kw = [H+][OH–] = 1.0 × 10–14
• No matter what the solution contains, the
product of [H+] and [OH–] must always equal
1.0 × 10–14 at 25°C.
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Slide Section 16.3
19 Water as an Acid and a Base
___________________________________
___________________________________ Three Possible Situations
___________________________________ • [H+] = [OH–]; neutral solution
• [H+] > [OH–]; acidic solution
• [H+] < [OH–]; basic solution
___________________________________ ___________________________________ In each case, however,
Kw = [H+][OH–] = 1.0 × 10–14.
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Slide Section 16.3
20 Water as an Acid and a Base
19
___________________________________
___________________________________ Concept Check
___________________________________ In an acidic aqueous solution, which statement
below is correct?
___________________________________ [H+] < 1.0 × 10–7 M
[H+] > 1.0 × 10–7 M
[OH–] > 1.0 × 10–7 M
[H+] < [OH–]
a)
b)
c)
d)
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Slide Section 16.3
21 Water as an Acid and a Base
20
___________________________________
___________________________________ Exercise
___________________________________ [OH–]
= 2.0 x
M, the
In an aqueous solution in which
[H+] = ________ M, and the solution is ________.
a)
b)
c)
d)
10–10
___________________________________ 2.0 × 10–10 M ; basic
1.0 × 10–14 M ; acidic
5.0 × 10–5 M ; acidic
5.0 × 10–5 M ; basic
___________________________________ ___________________________________ [H+] = Kw/[OH–] = 1.0 × 10–14/2.0 × 10–10 = 5.0 × 10–5 M.
Since [H+] is greater than [OH–], the solution is acidic.
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Slide Section 16.4
22 The pH Scale
•
•
•
•
___________________________________
___________________________________ ___________________________________ pH = –log[H+]
A compact way to represent solution acidity.
pH decreases as [H+] increases.
Significant figures:
ƒ The number of decimal places in the log is
equal to the number of significant figures in
the original number.
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Slide Section 16.4
23 The pH Scale
22
___________________________________
___________________________________ pH Range
___________________________________ • pH = 7; neutral
• pH > 7; basic
ƒ Higher the pH, more basic.
• pH < 7; acidic
ƒ Lower the pH, more acidic.
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Slide Section 16.4
24 The pH Scale
23
___________________________________
___________________________________ The pH Scale and
pH Values of Some
Common
Substances
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Slide Section 16.4
25 The pH Scale
___________________________________
___________________________________ Exercise
___________________________________ Calculate the pH for each of the following
solutions.
___________________________________ a) 1.0 × 10–4 M H+
___________________________________ pH = –log[H+] = –log(1.0 × 10–4 M) = 4.00
___________________________________ b) 0.040 M OH–
Kw = [H+][OH–] = 1.00 × 10–14 = [H+](0.040 M) = 2.5 × 10–13 M H+
pH = –log[H+] = –log(2.5 × 10–13 M) = 12.60
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Slide Section 16.4
26 The pH Scale
25
___________________________________
___________________________________ Exercise
___________________________________ The pH of a solution is 5.85. What is the
for this solution?
[H+]
___________________________________ [H+] = 1.4 × 10–6 M
___________________________________ [H+] = 10^–5.85 = 1.4 × 10–6 M
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Slide Section 16.4
27 The pH Scale
26
___________________________________
___________________________________ pH and pOH
___________________________________ • Recall:
Kw = [H+][OH–]
___________________________________ –log Kw = –log[H+] – log[OH–]
___________________________________ pKw = pH + pOH
___________________________________ 14.00 = pH + pOH
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Slide Section 16.4
28 The pH Scale
___________________________________
___________________________________ Exercise
___________________________________ Calculate the pOH for each of the following
solutions.
___________________________________ a) 1.0 × 10–4 M H+
___________________________________ pH = –log[H+] = –log(1.0 × 10–4 M) = 4.00;
___________________________________ So, 14.00 = 4.00 + pOH; pOH = 10.00
b) 0.040 M OH–
___________________________________ pOH = –log[OH–] = –log(0.040 M) = 1.40
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Slide Section 16.4
29 The pH Scale
28
___________________________________
___________________________________ Exercise
___________________________________ The pH of a solution is 5.85. What is the
[OH–] for this solution?
___________________________________ [OH–] = 7.1 × 10–9 M
___________________________________ 14.00 = 5.85 + pOH; pOH = 8.15
[OH–] = 10^–8.15 = 7.1 × 10–9 M
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Slide Section 16.5
30 Calculating the pH of Strong Acid Solutions
29
___________________________________
___________________________________ ___________________________________ • Determine the [H+].
2.0 M HCl → 2.0 M H+ and 2.0 M Cl–
• pH = −log[H+]
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___________________________________
Slide Section 16.5
31 Calculating the pH of Strong Acid Solutions
___________________________________ Concept Check
___________________________________ Consider an aqueous solution of 2.0 ×
HCl. What is the pH?
10–3
M
___________________________________ ___________________________________ pH = 2.70
___________________________________ 2.0 × 10–3 M HCl → 2.0 × 10–3 M H+ and 2.0 × 10–3 M Cl–
pH = –log[H+]
pH = –log(2.0 × 10–3 M)
pH = 2.70
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___________________________________
Slide Section 16.5
32 Calculating the pH of Strong Acid Solutions
___________________________________ Concept Check
___________________________________ Calculate the pH of a 1.5 ×
HCl.
10–11
M solution of
___________________________________ ___________________________________ pH = 7.00
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___________________________________
Slide Section 16.5
33 Calculating the pH of Strong Acid Solutions
___________________________________ Concept Check
___________________________________ Calculate the pH of a 1.5 ×
HNO3.
10–2
M solution of
___________________________________ ___________________________________ pH = 1.82
___________________________________ pH = –log[H+]
pH = –log(1.5 × 10–2 M)
pH = 1.82
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Slide Section 16.6
34 Buffered Solutions
___________________________________
___________________________________ ___________________________________ • Buffered solution – resists a change in its pH
when either an acid or a base has been added.
ƒ Presence of a weak acid and its conjugate
base buffers the solution.
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Slide Section 16.6
35 Buffered Solutions
34
___________________________________
___________________________________ The Characteristics of a Buffer
___________________________________ 1. The solution contains a weak acid HA and its
conjugate base A–.
2. The buffer resists changes in pH by reacting
with any added H+ or OH– so that these ions do
not accumulate.
3. Any added H+ reacts with the base A–.
H+(aq) + A–(aq) → HA(aq)
4. Any added OH– reacts with the weak acid HA.
OH–(aq) + HA(aq) → H2O(l) + A–(aq)
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Slide Section 16.6
36 Buffered Solutions
35
___________________________________
___________________________________ Concept Check
___________________________________ If a solution is buffered with NH3 to which has been
added NH4Cl, what reaction will occur if a strong base
such as NaOH is added?
a)
b)
c)
d)
___________________________________ ___________________________________ NaOH + NH3 → NaNH4O
NaOH + NH4+ → Na+ + NH3 + H2O
NaOH + Cl– → NaCl + OH–
NaOH + H2O → NaH3O2
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