Chapter 9 Acids and Bases
Ionization of Water The pH Scale
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Ionization of Water
Occasionally, in water, a H+ is transferred between H2O molecules
..
H:O: +
..
..
H:O:H +
..
+
..
H
:O:H
..
H
..
:O:H..
H
water molecules
hydronium ion (+)
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hydroxide ion (-)
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Pure Water is Neutral
Pure water contains small, but equal amounts of ions: H3O+ and OH-
H2O + H2O
H3O+
+
OH-
H3O+
OH-
hydronium hydroxide ion ion
1 x 10-7 M 1 x 10-7 M
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Ion Product of Water Kw
[ Kw ] = Molar concentration = =
=
[ H3O+ ] [ OH- ] [ 1 x 10-7 ][ 1 x 10-7 ]
1 x 10-14
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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-]
H3O+
OH5
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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+]
H3O+
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OH6
Using Kw
The [OH- ] of a solution is 1.0 x 10- 3 M. What is the [H3O+]?
Kw = [H3O+ ] [OH- ] = 1.0 x 10-14
[H3O+] = [H3O+] =
1.0 x 10-14 [OH-] 1.0 x 10-14 1.0 x 10- 3
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= 1.0 x 10-11 M
Learning Check pH1
The [H3O+] of lemon juice is 1.0 x 10-3 M. What is the [OH-] of the solution?
1) 2) 1.0 x 103 M 1.0 x 10-11 M
3)
1.0 x 1011 M
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Solution pH1
The [H3O+] of lemon juice is 1.0 x 10- 3 M.
What is the [OH-]?
[OH- ] = 1.0 x 10 -14 1.0 x 10 - 3 = 1.0 x 10-11 M
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Using the Calculator
1.0 x 10 -14 4.0 x 10-5 Enter 1.0 EE +/- 14 4.0 EE +/- 5
= 2.5 x 10 -10
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Learning Check pH2
The [OH-] of a solution is 5 x 10 -5 M. What is the [H3O+ ] of the solution? 1) 2) 3) 2 x 10- 5 M 1 x 1010 M 2 x 10-10 M
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Solution pH2
The [OH-] of a water solution is 5 x 10-5 M. What is the [H3O+] in the solution? [ H3O+] = 1.0 x 10 -14 5 x 10- 5
On some calculators:
1.0 EE +/- 14 5 EE +/- 5 = 2 x 10 -10 M
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Learning Check pH3
A.The [OH-] when [H3O+ ] of 1 x 10- 4 M 1) 1 x 10-6 M 2) 1 x 10-8 M 3) 1 x 10-10 M B.The [H3O+] when [OH- ] of 5 x 10-9 M 1) 1 x 10- 6 M 2) 2 x 10- 6 M 3) 2 x 10-7 M
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Solution pH3
Kw = [H3O+ ][OH-] = 1.0 x 10 14 A. (3) [OH- ] = 1.0 x 10 -14 = 1.0 x 10 -10 1.0 x 10- 4
B. (2) [H3O+] = 1.0 x 10 -14 = 2 x 10 - 6
5 x 10- 9
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pH
Indicates the acidity [H3O+] of the solution
pH = - log [H3O+]
From the French pouvoir hydrogene
(“hydrogen power” or power of hydrogen)
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pH
In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M
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pH Range
0 1 2 3 4 5
Acidic
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7 8 9 10 11 12 13 14
Basic
Neutral
[H+]>[OH-]
[H+] = [OH-]
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[OH-]>[H+]
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Some [H3O+] and pH [H3O+] 1 x 10-5 M 1 x 10-9 M
1 x 10-11 M
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pH 5 9
11
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pH of Some Common Acids
gastric juice lemon juice vinegar orange juice
coffee milk
1.0 2.3 2.8 3.5
5.0 6.6
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pH of Some Common Bases
blood tears seawater milk of magnesia household ammonia 7.4 7.4 8.4 10.6 11.0
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Learning Check pH4
A. The [H3O+] of tomato juice is 1 x 10-4 M. What is the pH of the solution? 1) - 4 2) 4 3) 8 B. The [OH-] of an ammonia solution is 1 x 10-3 M. What is the pH of the solution? 1) 3 2) 11
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3)
-11
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Solution pH4
A. pH = - log [ 1 x 10-4] = -(- 4) = 4 B. [H3O+] = 1 x 10-11 pH = - log [ 1 x 10- 11] = -(- 11) = 11
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Learning Check pH5
The pH of a soap is 10. What is the [H3O+] of the soap solution? 1) 1 x 10 - 4 M 2) 1 x 1010 M 3) 1 x 10 - 10 M
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Solution pH5
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
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pH on the Calculator
[H3O+] is 4.5 x 10-6 M pH = 4.5 x EXP(or EE) 6+/- LOG +/= 5.35
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Learning Check pH6
A soap solution has a [H3O+] = 2 x 10-8 M. What is the pH of the solution?
1) 8 2) 7.7 3) 6
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Solution pH6
A soap solution has a [H3O+] = 2.0 x 10-8 M. What is the pH of the solution? B) 2.0 EE 8 +/LOG +/- = 7.7
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Learning Check pH7
Identify each solution as 1. acidic 2. basic A. _____ B. _____ C. _____ D. _____ HCl with a pH = 1.5 Pancreatic fluid [H+] = 1 x 10-8 M Sprite soft drink pH = 3.0 pH = 7.0
3. neutral
E. _____ F. _____
[OH- ] = 3 x 10-10 M [H+ ] = 5 x 10-12
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Solution pH7
Identify each solution as 1. acidic 2. basic
A. _1__ B. _2__ C. _1__ HCl with a pH = 1.5 Pancreatic fluid [H+] = 1 x 10-8 M Sprite soft drink pH = 3.0
3. neutral
D. _3__ E. _1__ F. _2__
pH = 7.0 [OH-] = 3 x 10-10 M [H+] = 5 x 10-12
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Acid Rain
Unpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is “acid rain“ CO2 in the air forms carbonic acid
CO2 + H2O H2CO3 H+ (aq) + HCO3-(aq)
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Adds to H+ of rain
H2CO3
Sources of Acid Rain
Power stations Oil refineries Coal with high S content Car and truck emissions Bacterial decomposition, and lighting
hitting N2
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SO2 NO and NO2
26 million tons in 1980 22 million tons in 1980
Mt. St Helens (1980)
400,000 tons SO2
Reactions with oxygen in air form SO3
2SO2 + O2 2 SO3
Reactions with water in air form acids
SO3 + H2O NO + H2O
HNO2 + H2O
H2SO4 sulfuric acid HNO2 nitrous acid
HNO3 nitric acid
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Effects of Acid Rain
Leaches Al from soil, which kills fish Fish kills in spring from runoff due to
accumulation of large amounts of acid in
snow
Dissolves waxy coatings that protect leaves
from bacteria
Corrodes metals, textiles, paper and leather
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