Chemistry
FIFTH EDITION
by Steven S. Zumdahl
University of Illinois
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Mifflin Company. All rights reserved.
1
Chemistry
FIFTH EDITION
Chapter 14
Acids and Bases
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2
Percent Dissociation (Ionization)
amount dissociated( M )
% dissociation 
 100%
initial concentration( M )
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Let’s Do
Problem 63
Note:
For solutions of any weak acid HA,
[H+] decreases as [HA]0 decreases;
BUT
The Percent Dissociation increases
as [HA]0 decreases.
For a given weak acid, the percent dissociation
Increases as the acid becomes more dilute.
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Figure 14.10
The Effect of
Dilution on the
Percent
Dissociation and
(H+) of a Weak
Acid Solution
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Calculating Ka from
Percent Dissociation of a Weak Acid
See Sample Exercise 14.11
page 643
Let’s Do Problem #65
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6
Section 14.6
Bases
• Arrhenius Base:
Substance that produces OH- ions in
aqueous solution.
•Bronsted-Lowry Base:
A proton acceptor
•Basic Solution: pH > 7
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Section 14.6
Bases
•“Strong” and “weak” are used in the same
sense for bases as for acids.
•strong = complete dissociation (hydroxide
ion supplied to solution)
•NaOH(s)  Na+(aq) + OH(aq)
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Strong Bases
Group 1A Hydroxides
NaOH
KOH
LiOH
RbOH
CsOH
Group 2A Hydroxides
Ca(OH)2
Ba(OH)2
Sr(OH)2
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Strong Bases
Group 1A Hydroxides
NaOH
KOH
LiOH
 very expensive
RbOH
 very expensive
CsOH
 very expensive
Group 2A Hydroxides
Ca(OH)2
Ba(OH)2
Sr(OH)2
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Important & Interesting Information
about Bases
READ Section 14.6!
Calculating the pH of Strong Base Solutions
Assume 100 % Dissociation
pH dominated by OH- from the dissociation.
Let’s do #77, together!!!
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A base does not have to contain hydroxide ion.
Many are proton acceptors &
They increase the hydroxide ion concentration
because of their reaction with water.
NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)
base
acid
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•These bases typically have
at least one unshared pair of electrons
that is capable of forming a bond with a
proton.
•Examples given on page 646.
•Bases have a lone pair of electrons located
on a nitrogen atom.
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13
Substituted Ammonia Molecules
• Amines
General Formula
RxN(H)3-x
• Read Chemical Impact on page
648.
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14
Bases
(continued)
•weak = very little dissociation (or reaction with
water)
•H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq)
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Base Dissociation Constant (Kb)
• B (aq) + H2O(l)  BH+ (aq) + OH-(aq)
Kb = [BH+]_[OH-]
[B]
These types of Bases are Weak Bases.
Kb tend to be small.
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Table of Kb found in Table 14.3
on page 647 and in Appendix.
Calculate the pH of solutions of Weak Bases
Let’s do # 83, 85a, 89b & 91 together!!!
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17
Section 14.7
Polyprotic Acids
•
. . . can furnish more than one proton (H+) to
the solution.
H 2CO3  H   HCO3
( Ka1 )
HCO3  H   CO32 
( Ka 2 )
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• All polyprotic acids dissociate in a stepwise
Manner -= i.e., one proton at a time.
• Each step has its own equilibrium constant.
• For a typical weak polyprotic acid
Ka1 > Ka2 > Ka3
i.e., each step of dissociation is
successively weaker.
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As protons are lost from polyprotic acids,
a negative charge on the acid increases.
It becomes more difficult to remove
a positively charged proton from a
negatively charged species.
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Let’s look at Examples on page 650
• H2CO3
· H3PO4
• See Table 14.4 on page 651 for
Stepwise Dissociation Constants
for Common Polyprotic Acids.
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For a typical Polyprotic acid in water,
ONLY the 1st dissociation step is
Important in determining the pH.
Therefore, the pH calculation of a weak
polyprotic acid is identical to a weak
monoprotic acid.
Let’s do Problem # 95.
Homework: Extra Problem -Do #96
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WHAT ABOUT SULFURIC ACID?
Sulfuric acid is unique:
(1) It is a strong acid in its 1st dissociation step.
H2SO4  H+ (aq) + HSO4- (aq) Ka1 = 
(2) It is a weak acid in its second step.
HSO4- (aq)  H+ (aq) + SO42- (aq)
Ka2 = 1.2 x 10-2
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WHAT ABOUT SULFURIC ACID?
For conc. of 1.0 M or higher,
only the 1st step makes an important
contribution.
For dilute concs. (< 1.0 M) ,the 2nd
dissociation step makes a contribution.
Let’s Do # 97
Read Exer. 14.16 & 14.17 p653
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Section 14.8
Acid-Base Properties of Salts
Salts = Ionic compounds
Salts can behave as ACIDS or BASES.
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1. Salts that produce neutral solutions.
Composed of cations from strong bases
and anions from strong acids.
Example: NaCl. NaNO3, KCl
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2. Salts that produce basic solutions.
Composed of cations with neutral properties
and anions which are the conjugate
base of a weak acid.
Example: NaCH3COO
Major species:
Na+ is neutral
CH3COO- is conjugate base of weak acid
H2O is weakly amphoteric
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CH3COO1- + H2O  CH3COOH + OH1-
CH3COO1- in water produces OH1- ions
 Basic solution
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CH3COO1- + H2O  CH3COOH + OH1KB = [CH3COOH] [OH1-]
[CH3COO1-]
CH3COOH + H2O  CH3COO1- + H1+
KA = [CH3COO1-] [ H1+]
[CH3COOH]
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KA x K B
= [CH3COO1-] [ H1+] x [CH3COOH] [OH1-]
[CH3COOH]
[CH3COO1-]
=
[H1+] [OH1-]
=
Kw
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For any weak acid and its conjugate base:
Ka x Kb = Kw
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3. Salts that produce acidic solutions.
Composed of cations which are the
conjugate acid of a weak base and
anions with neutral properties.
Example: NH4Cl
Major species: Cl-, H2O, & NH4+
NH41+ (aq)  NH3 (aq) + H1+ (aq)
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• Let’s Do
Problems # 99,
101, 103, 105a,
107
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Another type of salt gives acidic solutions
those with
Hydrated ions of highly charged metal
Dissolve AlCl3 in water.
Al(H2O)63+ is formed.
It is a weak acid.
Al(H2O)63+ (aq)  Al(OH)(H2O)52+ (aq) + H+ (aq)
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Figure 14.12
The Al(H2O)63+ Ion
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A high charge on the metal ion (Al3+)
polarizes the O—H bonds & makes
these water molecules more acidic
than the O—H bonds ordinarily are
in water.
Let’s Do Problem # 109
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Salts with 2 ions that can affect the pH
Too complicated to deal with quantitatively.
One can predict if Acidic, Basic or Neutral
Compare Ka & Kb
1. If Ka > Kb, then Acidic
2. If Ka < Kb, then Basic
3. If Ka = Kb, then Neutral
Let’s Do Problem 111
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Acid-Base Properties of Salts
See Table 14.6 on page 660
Cation
neutral
neutral
Acidic
or Basic
neutral
basic
Anion
neutral
conj base of
weak acid
conj acid of
neutral
acidic
weak base
conj acid of conj base of depends on
weak base weak acid
Ka & Kb
values
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Example
NaCl
NaF
NH4Cl
Al2(SO4)3
38
Section 14.9
Structure and Acid-Base Properties
Read pages 661 - 662
• Two factors for acidity in binary
compounds:
 Bond
Polarity (high is good)
 Bond
Strength (low is good)
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39
Oxyacids
H—O—X
Acid Strength Increases with an increase
in the number of oxygen atoms.
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Figure 14.11
The Effect of the
Number of Attached
Oxygens on the O-H
Bond in a Series of of
Chlorine Oxyacids
Electronegative oxygen
atoms pull electrons away
from the Cl atoms & the
O—H bond.
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HClO4
Strongest
Acid
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Hydrated metal ions
Example: Al(H2O)63+
Greater the charge on a metal ion the
greater the acidity of the attached water molecules.
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Section 14.10
Acid Base Properties of Oxides
A compound containing the H—O—X group
Will produce
1. an acidic sol’n in water if the O—X bond
is strong and covalent.
Example:
H2SO4; O—S bonds are strong &
covalent. Therefore, O—H bonds break
to produce protons.
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2. a basic sol’n in water if the O—X bond
is ionic.
Example:
Na—O—H
O—Na bonds are ionic and therefore
Break in water to give Na+ & OH-
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Oxides
• Acidic Oxides (Acid Anhydrides):
 OX
bond is strong and covalent.
 Dissolve
in water & form acidic sol’ns.
 Non-metal
oxides form acid sol’ns in water.
• SO2, NO2, CrO3
EXAMPLES:
SO3 + H2O (l)  H2SO4 (aq)
SO2 + H2O (l)  H2SO3 (aq)
CO2 + H2O (l)  H2CO3 (aq)
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Oxides
• Basic Oxides (Basic Anhydrides):
 OX
bond is ionic.
 Dissolve
 Metal
in water & form basic sol’ns.
oxides form basic sol’ns in water.
• K2O, CaO
EXAMPLES
CaO (s) + H2O (l)  Ca(OH)2 (aq)
K2O (s) + H2O (l)  2 KOH (aq)
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Section 14.11
Lewis Acids and Bases
• Lewis Acid: electron pair acceptor
• Lewis Base: electron pair donor
Al3+ + 6 O
Acid
H
3+
H
Al
H
Base
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O
H
6
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Figure 14.12
The Al(H2O)63+ Ion
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Lewis Acid-Base Model –
Most general model for acid-base
behavior.
Lewis Model encompasses the BronstedLowry model, but the reverse is not
true.
Lewis Acids can be a species without H+.
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Let’s Do Problems # 119, 121, 123, 124.
Section 14.12
Strategy for Solving Acid-Base
Problems: A Summary
READ!!!!!!!!!!!!!!!!!!!
ALSO!! Good “Review” p. 668-672
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