Chapter Learning Objectives
a. The chemical properties of acids and bases.
b. Acids and bases react with each other in a reaction
known as neutralization.
c. Acids are proton (H+) donors; bases are proton
acceptors that produce OH- in solution.
d. Learn some common acids and bases and their
properties, such as their strengths.
e. The pH measures the acidity of a solution: pH < 7.0
is acidic; pH > 7.0 is basic; pH = 7.0 is neutral.
f. Buffers are important for maintaining our health.
1
a. Acids
Arrhenius acids
• produce H+ ions in water.
H2O
HCl(g)
H+(aq) + Cl- (aq)
•
•
•
•
are electrolytes.
have a sour taste.
turn litmus red.
neutralize bases.
Hydronium ion – a hydrated proton, H3O+ = H+
2
Names of Acids
• Acids with H and a nonmetal are named with the prefix
hydro and end with ic acid.
HCl hydrochloric acid
• Acids with H and a polyatomic ion are named by
changing the end of the name of the polyatomic ion
from ate to ic acid or ite to ous acid.
ClO3− chlorate
HClO3 chloric acid
ClO2− chlorite
HClO2 chlorous acid
3
Names of Some Common Acids
4
Learning Check
Select the correct name for each of the following acids.
A. HBr
1. bromic acid
2. bromous acid
3. hydrobromic acid
B. H2CO3
1. carbonic acid
2. hydrocarbonic acid
3. carbonous acid
C. HBrO2
1. bromic acid
2. hydrobromous acid
3. bromous acid
5
Solution
A. HBr
3. hydrobromic acid
The name of an acid with H and one nonmetal uses
the prefix hydro and ends with ic acid.
B. H2CO3
1. carbonic acid
An acid with H and a polyatomic ion is named by
changing the end of an ate ion to ic acid.
C. HBrO2
3. bromous acid
This acid of bromite (BrO2-) is bromous acid.
6
a. Bases
Arrhenius bases
• produce OH− ions in
water.
• taste bitter or chalky.
• are electrolytes.
• feel soapy and slippery.
• neutralize acids.
7
Some Common Bases
Bases with OH- ions are named as the
hydroxide of the metal in the formula.
NaOH
sodium hydroxide
KOH
potassium hydroxide
Ba(OH)2
barium hydroxide
Al(OH)3
aluminum hydroxide
Fe(OH)3
iron(III) hydroxide
8
Learning Check
Match the formulas with the names.
A. ___HNO2
1) iodic acid
B. ___Ca(OH)2
2) sulfuric acid
C. ___H2SO4
3) sodium hydroxide
D. ___HIO3
4) nitrous acid
E. ___NaOH
5) calcium hydroxide
9
Solution
Match the formulas with the names.
A. 4 HNO2
B. 5 Ca(OH)2
nitrous acid
calcium hydroxide
C. 2 H2SO4
sulfuric acid
D. 1 HIO3
iodic acid
E. 3 NaOH
sodium hydroxide
10
Comparing Acids and Bases
11
Learning Check
Identify each as a characteristic of an
A) acid
or
B) base.
____1.
____2.
____3.
____4.
____5.
has a sour taste
produces OH- in aqueous solutions
has a chalky taste
is an electrolyte
produces H+ in aqueous solutions
12
Solution
Identify each as a characteristic of an
A) acid
or
B) base.
A
B
B
A, B
A
1.
2.
3.
4.
5.
has a sour taste
produces OH- in aqueous solutions
has a chalky taste
is an electrolyte
produces H+ in aqueous solutions
13
Definitions




Acidic Solutions – A solution that contains a higher
concentration of H3O+ ions than OH- ions.
Basic Solutions (Alkaline solution) – A solution that
contains a higher concentration of OH- ions than H3O+
ions
Salt – Ionic compounds composed of the cation from a
base and the anion from an acid.
Neutralization Reaction – Reaction of equivalent
quantities of an acid and a base
14
b. Neutralization Reactions
In a neutralization reaction
• an acid such as HCl reacts with a base such as NaOH.
HCl + H2O
H3O+ + Cl−
NaOH
Na+ + OH−
• the H3O+ from the acid and the OH− from the base form
water.
H3O+ + OH−
2 H2O
15
Neutralization Equations
In the equation for neutralization, an acid and a base
produce a salt and water.
acid
base
salt
water
HCl + NaOH
NaCl
+ H 2O
2HCl + Ca(OH)2
CaCl2
+ 2H2O
16
Neutralization of H2O
H3O+ (aq) + OH- (aq)  H2O(l) + H2O(l)
HCl(aq) + KOH(aq)  H2O(aq) + KCl(aq)
acid
base
water
salt
H2SO4(aq) + 2NaOH(aq)  2H2O(l) +
acid
base
water
Na2SO4(aq)
salt
17
Ionization of Water
In water,
• H+ is transferred from one H2O molecule to another.
• one water molecule acts as an acid, while another
acts as a base.
H2O + H2O
..
..
:O: H + H:O:
..
..
H
H
water water
H3O+
+ OH−
..
..
H:O:H + + :O:H−
..
..
H
hydronium hydroxide
ion (+)
ion (-)
Run the following web
9.3: The Autoionization of Water
animations/movies.
18
Pure Water is Neutral
In pure water,
• the ionization of water
molecules produces small,
but equal quantities of H3O+
and OH− ions.
• molar concentrations are
indicated in brackets as
[H3O+] and [OH−].
[H3O+]
[OH−]
= 1.0 x 10−7 M
= 1.0 x 10−7 M
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
19
Acidic Solutions
Adding an acid to pure water
• increases the [H3O+].
• cause the [H3O+] to exceed
1.0 x 10-7 M.
• decreases the [OH−].
20
Basic Solutions
Adding a base to pure water
• increases the [OH−].
• causes the [OH−] to exceed
1.0 x 10− 7M.
• decreases the [H3O+].
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
21
Comparison of [H3O+] and [OH−]
22
Ion Product of Water, Kw
The ion product constant, Kw, for water
• is the product of the concentrations of the hydronium
and hydroxide ions.
Kw
=
[ H3O+] [ OH− ]
• can be obtained from the concentrations in pure water.
Kw
=
[ H3O+] [ OH− ]
Kw
=
[1.0 x 10− 7 M] x [ 1.0 x 10− 7 M]
=
1.0 x 10− 14
23
[H3O+] and [OH−] in Solutions
In neutral, acidic, or basic solutions,
the Kw is always 1.0 x 10−14.
24
Guide to Calculating [H3O+]
25
Calculating [H3O+]
What is the [H3O+] of a solution if [OH−] is 5.0 x 10-8 M?
STEP 1: Write the Kw for water.
Kw =
[H3O+ ][OH− ] = 1.0 x 10−14
STEP 2: Rearrange the Kw expression.
[H3O+] =
1.0 x 10-14
[OH−]
STEP 3: Substitute [OH−].
[H3O+] = 1.0 x 10-14 = 2.0 x 10-7 M
5.0 x 10- 8
26
Learning Check
If lemon juice has [H3O+] of 2 x 10−3 M, what is
the [OH−] of the solution?
1) 2 x 10−11 M
2) 5 x 10−11 M
3) 5 x 10−12 M
27
Solution
3) 5 x 10−12 M
Rearrange the Kw to solve for [OH- ]
Kw = [H3O+ ][OH− ] = 1.0 x 10−14
[OH− ]
= 1.0 x 10 -14
2 x 10 - 3
=
5 x 10−12 M
28
Learning Check
The [OH−] of an ammonia solution is 4.0 x 10−2 M.
What is the [H3O+ ] of the solution?
1) 2.5 x 10− 11 M
2) 2.5 x 10−12 M
3) 2.5 x 10−13 M
29
Solution
3) 2.5 x 10−13 M
[ H3O+] =
1.0 x 10−14 = 2.5 x 10−13 M
4.0 x 10−2
30
c. BrØnsted-Lowry Acids and Bases
According to the BrØnsted-Lowry theory,
• acids donate a proton (H+).
• bases accept a proton (H+).
Run the following web 9.1: Proton Transfer with an Acid & a Base
animations/movies.
9.2: Reacting with Water
31
NH3, a BrØnsted-Lowry Base
In the reaction of ammonia and water,
• NH3 is the base that accept H+.
• H2O is the acid that donates H+.
32
d. Strengths of Acids
• A strong acid completely ionizes (100%) in aqueous
solutions.
HCl(g) + H2O(l)
H3O+ (aq) + Cl− (aq)
• A weak acid dissociates only slightly in water to form
a few ions in aqueous solutions.
H2CO3(aq) + H2O(l)
H3O+(aq) + HCO3− (aq)
33
Strong Acids
In water, the dissolved
molecules of a strong
acid
• dissociate into ions.
• give large
concentrations of H3O+
and the anion (A-).
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34
Weak Acids
In weak acids,
• only a few molecules
dissociate.
• most of the weak acid remains
as the undissociated
(molecular) form of the acid.
• the concentrations of the H3O+
and the anion (A-) are small.
HA(aq) + H2O(l)
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
H3O(aq) + A−(aq)
35
Strong and Weak Acids
• In an HCl solution, the
strong acid HCl
dissociates 100%.
• A solution of the weak
acid CH3COOH
contains mostly
molecules and a few
ions.
36
Strong Acids
Strong acids
• make up six of all the acids.
• have weak conjugate bases.
37
Weak Acids
Weak acids
• make up most of the acids.
• have strong conjugate bases.
38
Comparing Strong and Weak Acids
39
Strong Bases
Strong bases
• are formed from metals of
Groups 1A (1) and 2A (2).
• include LiOH, NaOH, KOH,
and Ca(OH)2.
• dissociate completely in water.
KOH(s)
K+(aq) + OH−(aq)
40
Weak Bases
Weak bases
• are most other bases.
• dissociate only slightly in water.
• form only a few ions in water.
NH3(g) + H2O(l)
NH4+(aq) + OH−(aq)
41
Learning Check
Identify each of the following as a strong or weak
acid or base.
A. HBr
B. HNO2
C. NaOH
D. H2SO4
E. Cu(OH)2
42
Solution
Identify each of the following as a strong or weak
acid or base.
A. HBr
strong acid
B. HNO2
weak acid
C. NaOH
strong base
D. H2SO4
strong acid
E. Cu(OH)2
weak base
43
Learning Check
Identify the stronger acid in each pair.
1. HNO2 or H2S
2. HCO3− or HBr
3. H3PO4 or H3O+
44
Solution
Identify the stronger acid in each pair.
1. HNO2
2. HBr
3. H3O+
45
Molarity (M)
Molarity (M) is
• a concentration term for solutions.
• gives the moles of solute in 1 L solution.
• moles of solute
liter of solution
46
Calculation of Molarity
What is the molarity of 0.500 L NaOH solution if it
contains 6.00 g NaOH?
STEP 1 Given 6.00 g NaOH in 0.500 L solution
Need molarity (mole/L)
STEP 2 Plan g NaOH
mole NaOH
molarity
47
Calculation of Molarity (cont.)
STEP 3 Conversion factors 1 mole NaOH = 40.0 g
1 mole NaOH
and 40.0 g NaOH
40.0 g NaOH
1 mole NaOH
STEP 4 Calculate molarity.
6.00 g NaOH x 1 mole NaOH = 0.150 mole
40.0 g NaOH
0.150 mole = 0.300 mole = 0.300 M NaOH
0.500 L
1L
48
Learning Check
What is the molarity of 325 mL of a solution containing
46.8 g of NaHCO3?
1)
0.557 M
2)
1.44 M
3)
1.71 M
49
Solution
3) 1.71 M
46.8 g NaHCO3 x 1 mole NaHCO3 = 0.557 mole NaHCO3
84.0 g NaHCO3
0.557 mole NaHCO3 = 1.71 M NaHCO3
0.325 L
50
e. pH Scale
The pH of a solution
A pH Meter
• is used to indicate the acidity of a solution.
• has values that usually range from 0 to 14.
• is acidic when the values are less than 7.
• is neutral with a pH of 7.
• is basic when the values are greater than 7.
51
pH of Everyday Substances
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52
Learning Check
Identify each solution as
1) acidic
2) basic
3) neutral
A. ___ HCl with a pH = 1.5
B. ___ pancreatic fluid [H3O+] = 1 x 10−8 M
C. ___ Sprite® soft drink pH = 3.0
D. ___ pH = 7.0
E. ___ [OH−] = 3 x 10−10 M
F. ___ [H3O+ ] = 5 x 10−12
53
Solution
A. 1
HCl with a pH = 1.5
B. 2
Pancreatic fluid [H3O+] = 1 x 10−8 M
C. 1
Sprite® soft drink pH = 3.0
D. 3
pH = 7.0
E. 1
[OH-] = 3 x 10−10 M
F. 2
[H3O+] = 5 x 10−12
54
Testing the pH of Solutions
The pH of solutions can be determined using
• a) pH meter
• b) pH paper
• c) indicators that have specific colors at different pH values.
Run the following web 9.4a: Detecting Acid-Base Rxns Using a pH Meter
animations/movies.
9.4b: pH Changes using HCl to Water
55
Calculating pH
pH is the negative log of the hydronium ion concentration.
pH = - log [H3O+]
Example: For a solution with [H3O+] = 1 x 10−4
pH = −log [1 x 10−4 ]
pH = - [-4.0]
pH = 4.0
Note: The number of decimal places in the pH equals
the significant figures in the coefficient of [H3O+].
4.0
1 SF in 1 x 10-4
56
Guide to pH Calculations
57
Significant Figures in pH
When expressing log values, the number of decimal
places in the pH is equal to the number of significant
figures in the coefficient of [H3O+].
[H3O+] = 1 x 10-4
pH = 4.0
[H3O+] = 8.0 x 10-6
pH = 5.10
[H3O+] = 2.4 x 10-8
pH = 7.62
58
Calculating pH
Find the pH of a solution with a [H3O+] of 1.0 x 10−3:
STEP 1 Enter [H3O+]
Enter 1 x 10-3 by pressing 1 (EE) 3
The EE key gives an exponent of 10 and
change sign (+/- key or – key)
STEP 2 Press log key and change sign
- log (1 x 10−3) = -[-3]
STEP 3 Adjust figures after decimal point to equal the
significant figures in the coefficient.
3
3.00 Two significant figures in 1.0 x 10−3
59
Learning Check
What is the pH of coffee if the [H3O+] is 1 x 10−5 M?
1) pH = 9.0
2) pH = 7.0
3) pH = 5.0
60
Solution
What is the pH of coffee if the [H3O+] is 1 x 10−5M?
3) pH = 5.0
pH = -log [1 x 10−5] = -(-5.0) = 5.0
61
Learning Check
A. The [H3O+] of tomato juice is 2 x 10−4 M.
What is the pH of the solution?
1) 4.0
2)
3.7
3)
10.3
B. The [OH−] of a solution is 1.0 x 10−3 M.
What is the pH of the solution?
1)
3.00
2) 11.00
3) -11.00
62
Solution
A. 2) 3.7
pH = - log [ 2 x 10-4] = 3.7
2 (EE) 4 (+/-) log (+/-)
B. 2) 11.00
Use the Kw to obtain [H3O+] = 1.0 x 10 −11
pH = - log [1.0 x 10 −11]
1.0 (EE) 11 (+/-) log (+/-)
63
[H3O+], [OH-], and pH Values
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
64
Calculating [H3O+] from pH
The [H3O+] can be expressed by using the pH as the
negative power of 10.
[H3O+] = 1 x 10 -pH
For pH = 3.0, the [H3O+] = 1 x 10 -3
On a calculator
1. Enter the pH value
3.0
2. Change sign
-3.0
3. Use the inverse log key (or 10x) to obtain
the [H30+].
= 1 x 10 -3 M
65
Learning Check
A. What is the [H3O+] of a solution with a pH of
10.0?
1) 1 x 10−4 M
2) 1 x 1010 M
3) 1 x 10−10 M
B. What is the [OH−] of a solution with a pH of
2.00?
1) 1.0 x 10− 2 M
2) 1.0 x 10−12 M
3) 2.0 M
66
Solution
A. What is the [H3O+] of a solution with a pH of 10.0?
3) 1 x 10-10 M
1 x 10-pH
B. What is the [OH−] of a solution with a pH of 2.00?
2) 1.0 x 10−12 M
[H3O+] = 1.0 x 10−2 M 1 x 10-pH
[OH−] = 1.0 x 10−14
= 1.0 x 10−12 M
1.0 x 10−2 M
67
f. Buffers
When an acid or
base is added
• to water, the pH
changes
drastically.
• to a buffer
solution, the pH is
maintained; pH
does not change.
68
Buffers
Buffers
• resist changes in pH from the addition of acid or base.
• in the body, absorb H3O+ or OH- from foods and cellular
processes to maintain pH.
• are important in the proper functioning of cells.
• in blood maintain a pH close to 7.4. A change in the pH
of the blood affects the uptake of oxygen and therefore
cellular processes.
69
Components of a Buffer
A buffered solution
• contains a combination of acid-base conjugate
pairs.
• may contain a weak acid and a salt of its conjugate
base.
• typically has equal concentrations of a weak acid
and its salt.
• may also contain a weak base and a salt of the
conjugate acid.
70
Buffer Action
In the acetic acid/acetate buffer with acetic acid
(CH3COOH) and sodium acetate (CH3COONa)
• The salt produces acetate ions and sodium ions.
CH3COONa(aq)
CH3COO-(aq) + Na+ (aq)
• The salt is added to provide a higher concentration of the
conjugate base CH3COO- than the weak acid alone.
CH3COOH(aq) + H2O(l)
CH3COO-(aq) + H3O+(aq)
Large amount
Large amount
71
Key Words

Acid
 Base
 Indicator
 Hydronium ion (H3O+)
 Polyprotic acid
 Strong acid
 Weak acid
 Alkali
 Hydroxide ion (OH-)

pH meter
 Strong base
 Weak base
 Amphoteric
 pH
 Neutral solution
 Conjugate acid-base
pair
 Buffer
 Neutralization
72