Chapter Fourteen:
ACIDS AND BASES
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Contents
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14-1 The Nature of Acids and Bases
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Arrheniuis postulates that acids produce
hydrogen ios in aqueous solution, while
bases produce hydroxide ions.
Danish chemist Johannes Bronsted and the
English chemist Thomas Lowry
In terms of the Bronsted-Lowry model, an acids is a
proton (H+) donor, and a base is a proton acceptor.
Arrhenius: Acids produce H+ in solution, bases produce
OHion.
Brønsted-Lowry:Acids are H+ donors, bases are proton
acceptors. HCl + H2O  Cl+ H3O+
HCl + H2O  Cl+ H3O+
acid base
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Models of Acids and Bases

Arrhenius: Acids produce H+ in solution, bases produce
OH-ion.

Brønsted-Lowry: Acids are H+ donors, bases are proton
acceptors.
HCl + H2O → Cl-+ H3O+
acid base
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Conjugate acid-base pair
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The equilibrium expression for Ka
HA(aq) + H2O
H3O+(aq) + A-(aq)
acid
onjugate
cid
base
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conjugate
base
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Brønsted-Lowry Reaction
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Ex 14.1 Acid Dissociation (lonization)
Reactions
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Write the simple dissociation (ionization) reaction (omitting
water) for each of the following acids.

a. Hydrochloric acid (HCl)

b. Acetic acid (HC2H3O2)

c. The ammonium ion (NH4+)

d. The anilinium ion (C6H5NH3+)

e. The hydrated aluminum(III) ion [Al(H2O)6]3+
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The Bronsted- Lowry model is
not limited to aqeous solutions
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In this reaction is donated by the hydrogen chloride to
the ammonia, as shown these Lewis structure.
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14-2 Acid Strength
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The strength of an acid is defined by the equilibrium
position of its dissociation (ionization) reaction.
Before
dissociation
After dissociation at
equilibrium
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Figure 14.5
The relationship of acid strength and conjugate
base strength for the ionization reaction.
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A strong acid is virtually 100 %
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dissociated in water.
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Acid Strength
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Figure 14.6
(a) A strong acid HA is completely ionized in
water. (b) A weak acid HB exists mostly as
undissociated HB molecules in water. Note that
the water molecules are not sown in this figure.
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Acid Ionization Equilibrium
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Self-Ionization of Water
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ct
a
e
R
HA(aq) + H2O
acid base
H3O+(aq) + A-(aq)
conjugate conjugate
acid
base
What is the equilibrium constant
expression for an acid acting in water?
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Think!

How good is Cl-(aq) as a base?

Is A-(aq) a good base?
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Think!


H2O(aq) + H2O
acid
base
H3O+(aq) + OH-(aq)
conjugate conjugate
acid
base
At 25
C, Kw = 1.0 x 10-14
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Values of Ka
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Appendix 5.1 contains a table of Ka values.
Organic acids:
carboxyl group
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Ex 14.2 Relative Base Strength
Using Table 14.2, arrange the following species
according to their strengths as bases: H2O, F-,
Cl-, NO2-, and CN-.
Solution
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Water as an Acid and a Base
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Kw
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There are three possible situations:
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Ex 14.3 Calculating [H+] and [OH-]

Calculate [H+] or [OH-] as required for each of the
following solutions at 25℃, and state whether the
solution is neutral, acid, or basic.

a. 1.0 × 10 -5 M OH-

b. 1.0 × 10-7 M OH-

c. 10.0 M H+
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Solution:
Ex 14.4 Autoionization of Water
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At 60 ℃, the value of Kw is 1 × 10-13.
a. Using Le Chatelier’
s principle, predict whether the
reaction is exothermic or endothermic.
2 H 2O(l )  H 3O (aq) OH (aq)
b. Calculate [H+] and [OH-] in a neutral solution at 60
℃.
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Solution:
14.3 The pH Scale
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The pH Scale
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Ex 14.5 Calculating pH and pOH
Calculate pH and pOH for each of the
following solutions at 25 ℃
a. 1.0 × 10 -3 M OHb. 1.0 M OH-
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Solution:
(a)
(b)
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The pH scale and pH
values of some
common substances
Figure 14.8
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Ex 14.6 Calculating pH
The pH of a sample of human blood was measured
to be 7.41 at 25℃. Calculate pOH, [H+], and [OH-]
for the sample.
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14-4 Calculating the pH of Strong
Acid Solutions
Ex 14.7 pH of Strong Acids
M HCl.
a. Calculate the pH of 0.10 M HNO3.
b. Calculate the pH of 1.0 × 10
Solution:
(a)
(b)
-10
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14-5 Calculating the pH of Weak Acid
Solutions
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Ex 14.17 Calculating Ka from Percent Dissociation
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Lactic acid is a waste product that accumulates in muscle tissue
during exertion, leading to pain and a feeling of fatigue. In a
0.100 M aqueous solution, lactic acid is 3.7% dissociated .
Calculate the value of Ka for this acid.
Solution:
14.6 Bases
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Ex 14.12 The pH of Strong Bases
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Calculate the pH of a 5.0 x 102- M NaOH.
Solution:
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The lone pair is located on a nitrogen atom
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Kb
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Ex 14.13 The pH of Weak Bases I
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Calculates the pH for a 15.0 M NH3(Kb = 1.8 x 10-5).
Solution:
14.7 Polyprotic Acids
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Polyprotic acids
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Ex14.15 The pH of a Polyprotic Acid
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Calculate the pH of a 5.0 M H3PO4 solution and the
equilibrium concentrations of the species H3PO4, H2PO4-,
HPO42-, and PO43-.
Solution: a.
e.
b.
c.
f.
d.
Acid-Base Properties of Salts
Cation
neutral
neutral
conjugate
acid of
weak base
conjugate
acid of
weak base
Anion
neutral
conjugate
base of
weak acid
neutral
conjugate
base of
weak acid
Acidic
or Basic
neutral
basic
Example
NaCl
NaF
acidic
NH4Cl
depends on
Ka & K b
values
Al2(SO4)3
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14-8 Acid-Base Properties of Salts
Salts That Produce Neutral Solutions
KCl, NaCl, NaNO3, and KNO3 are neutral.
Salts That produce Basic Solutions
The pH of the solution will be determined by the conjugate
anions of weak acids, such as CN-, acetate ion C2H3O2-.
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Ex 14.18 Salts as Weak Bases
Calculating the pH of a 0.30 M NaF
solution. The Ka value for HF is 7.2 x 10-4.
Solution:
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Base Strength in Aqueous Solutions
Relative base strength: OH- > CN- > H2O
Salts That Produce Acidic Solutions
Table 14.5 Qualitative Prediction of pH of Salt
Solutions of Salts for Which Both Cation and
Anion Have Acidic or basic properties
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Various Types of Salts
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14-9 The Effect of Structure on
Acid-Base Properties
Table 14.7 Bond Strengths and Acid
Strengths for Hydrogen Halides
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The structure effect

Two factors for acidity in binary compounds:

Bond Polarity (high is good)

Bond Strength (low is good)
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The Effect of Structure on Acid-Base Properties
The effect of number of
attracted oxygens on the
O-H bond in a series of
chlorine oxyacids.
Figure 14.11
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14-10 Acid-Base Properties of Oxides
Oxides

Acidic Oxides (Acid Anhydrides):
• O
X
bond is strong and covalent.
SO2, NO2, CrO3
 Basic Oxides (Basic Anhydrides):
• O
X
bond is ionic.
K2O, CaO
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14-11 The Lewis Acid-Base
Model
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Three Models for Acids and Bases
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Lewis model
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Lewis acid-Lewis base reaction
Hydration of a metal ion.
3+
Al3+ + 6 O
H
H
Al
H
O
H
Figure 14.12
Reaction of BF3 with NH3
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Al3+
ion accepts one electron
pair from each of six water
molecules to form Al(H2O)63+.
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14-12 Strategy for Solving Acid-Base
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Problems: A Summary