Chapter 16
Acids and Bases
Ionization of Water
The pH Scale
7-4
Measuring pH
• Why measure pH?
–Everything from swimming pools,
soil conditions for plants, medical
diagnosis, soaps and shampoos,
etc.
• Sometimes we can use indicators,
other times we might need a pH
meter
pH of Some Common Acids
gastric juice
1.0
lemon juice
2.3
vinegar
2.8
orange juice
3.5
coffee
5.0
milk
6.6
pH of Some Common Bases
blood
7.4
tears
7.4
seawater
8.4
milk of magnesia
10.6
household ammonia
11.0
Calculating pH,
pOH
pH = -log10 [H3O+]
pOH = -log10 [OH-]
Relationship between pH and pOH
pH + pOH = 14
Finding [H3O+], [OH-] from pH, pOH
[H3O+] = 10-pH
[OH-] = 10-pOH
In pure water, [H3O+] = [OH-] = 1  10 –7
Kw = 1  10 –14
pH + pOH = 14
pH
pOH
pH = -log[H+]
pOH = -log[OH-]
[H+]
[OH-]
[H+][OH-] = 1.0  10-14
pH
+
pOH
=
14
Ionization of Water
Occasionally, in water, a H+ is transferred
between H2O molecules
..
..
H:O: +
:O:H
..
H
..
H
water molecules
..
H:O:H +
..
..
+
:O:H..
H
hydronium
ion (+)
hydroxide
ion (-)
Pure Water is Neutral
Pure water contains small, but equal
amounts of ions: H3O+ and OH-
H2O + H2O
H 3O +
OH-
H3O+
+
OH-
hydronium hydroxide
ion
ion
1 x 10-7 M 1 x 10-7 M
Ion Product of Water Kw
[
] = Molar concentration
Kw
=
[ H3O+ ] [ OH- ]
=
[ 1 x 10-7 ][ 1 x 10-7 ]
=
1 x 10-14
Acids
 Increase H+
 HCl (g) + H2O (l)
H3O+ (aq) + Cl- (aq)
 More [H3O+] than water > 1 x 10-7M
 As H3O+ increases, OH- decreases
[H3O+] > [OH-]
Bases
Increase the hydroxide ions (OH-)
H2O
NaOH (s)
Na+(aq) + OH- (aq)
More [OH-] than water, [OH-] > 1 x 10-7M
 When OH- increases, H3O+ decreases
[OH] > [H3O+]
Using Kw
The [OH- ] of a solution is 1.0 x 10- 3 M. What
is the [H3O+]?
Kw
=
[H3O+] =
[H3O+ ] [OH- ]
= 1.0 x 10-14
1.0 x 10-14
[OH-]
[H3O+] =
1.0 x 10-14
1.0 x 10- 3
= 1.0 x 10-11 M
Learning Check pH
The [H3O+] of lemon juice is 3.0 x 10-3 M. What
is the [OH-] of the solution?
Kw
=
[OH- ]
[H3O+ ] [OH- ]
=
= 1.0 x 10-14
1.0 x 10-14
[H3O+]
[OH- ] =
1.0 x 10-14
3.0 x 10- 3
= 3.3 x 10-12 M
pH
The [H3O+] of lemon juice is 9.0 x 10- 4 M.
What is the [OH-]?
[OH- ] = 1.0 x 10 -14
9.0 x 10 - 4
=
1.1 x 10-11 M
The [H3O+] is 4.0 x 10- 5 M. What is
the [OH-]?
1.0 x 10 -14
4.0 x 10-5
Enter 1.0 EE +/- 14  4.0 EE +/- 5
= 2.5 x 10 -10
Solution pH
B.The [H3O+] when [OH- ] of 5 x 10-9
M
Kw = [H3O+ ][OH-] = 1.0 x 10 14
[H3O+] =
1.0 x 10 -14 = 2 x 10 - 6
5 x 10- 9
pH
 Indicates the acidity [H3O+] of the solution
 pH = - log [H3O+]
 From the French pouvoir hydrogene
(“hydrogen power” or power of
hydrogen)
pH
In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M
pH Range
0
1
2
3 4 5
6
7 8 9 10 11 12 13 14
Basic
Acidic
Neutral
[H+]>[OH-]
[H+] = [OH-]
[OH-]>[H+]
pH
A. The [H3O+] of tomato juice is 1 x 10-4 M.
What is the pH of the solution?
answer: 4
pH = - log [ 1 x 10-4] = -(- 4) = 4
pH
B. The [OH-] of an ammonia solution is
1 x 10-3 M. What is the pH of the solution?
Answer: 11
[H3O+] = 1 x 10-11
pH = - log [ 1 x 10- 11] = -(- 11) = 11
Some [H3O+] and pH
[H3O+]
pH
1 x 10-5 M
5
1 x 10-9 M
9
1 x 10-11 M
11
Solution pH
The pH of a soap is 10. What is the
[H3O+] of the soap solution?
[H3O+]
= 1 x 10-pH M
= 1 x 10-10 M
pH on the Calculator
[H3O+] is 4.5 x 10-6 M. What is the pH.
pH = 4.5 x EXP(or EE) 6+/- LOG +/= 5.35
Learning Check pH
A soap solution has a [H3O+] = 2 x 10-8 M.
What is the pH of the solution?
pH
A soap solution has a [H3O+] = 2.0 x 10-8
M. What is the pH of the solution?
2.0
EE
8
+/-
LOG +/- = 7.7
Learning Check
Identify each solution as
1. acidic
2. basic
3. neutral
1
A. _____
HCl with a pH = 1.5
2
B. _____
Pancreatic fluid [H+] = 1 x 10-8 M
1
C. _____
Sprite soft drink pH = 3.0
3
D. _____
pH = 7.0
E. _____
1
[OH- ] = 3 x 10-10 M
F. _____
2
[H+ ] = 5 x 10-12
What is the [H3O+ ] or [OH- ] in each of
the following solutions, also state if the
solution is neutral, acidic, or basic.
a. 1  10 -5 M OHb. 1  10 -7 M OHa. 1.0 x 10 M
+
c. 10.0 M H
b. 1.0 x 10 M
-9
-7
c. 1.0 x 10-15 M