1. Chapter 9 Acids and Bases
Ionization of Water
The pH Scale
LecturePLUS Timberlake

2. LecturePLUS Timberlake
Ionization of Water
Occasionally, in water, a H+ is transferred between H2O molecules
H:O: :O:H H:O:H :O:H-
H H H
water molecules hydronium hydroxide ion (+) ion (-)
LecturePLUS Timberlake

3. LecturePLUS Timberlake
Pure Water is Neutral
Pure water contains small, but equal amounts of ions: H3O+ and OH-
H2O + H2O H3O OH-
hydronium hydroxide ion ion
1 x 10-7 M 1 x 10-7 M
H3O+
OH-
LecturePLUS Timberlake

4. LecturePLUS Timberlake
Ion Product of Water Kw
[ ] = Molar concentration
Kw = [ H3O+ ] [ OH- ]
= [ 1 x ][ 1 x 10-7 ]
= x 10-14
LecturePLUS Timberlake

5. LecturePLUS Timberlake
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+
OH-
LecturePLUS Timberlake

6. LecturePLUS Timberlake
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+]
OH-
H3O+
LecturePLUS Timberlake

7. LecturePLUS Timberlake
Using Kw
The [OH- ] of a solution is 1.0 x M. What is the [H3O+]?
Kw = [H3O+ ] [OH- ] = x 10-14
[H3O+] = 1.0 x 10-14
[OH-]
[H3O+] = x = 1.0 x M
1.0 x 10- 3
LecturePLUS Timberlake

8. LecturePLUS Timberlake
Learning Check pH1
The [H3O+] of lemon juice is 1.0 x 10-3 M. What is the [OH-] of the solution?
1) 1.0 x 103 M
2) 1.0 x M
3) 1.0 x 1011 M
LecturePLUS Timberlake

9. LecturePLUS Timberlake
Solution pH1
The [H3O+] of lemon juice is 1.0 x M. What is the [OH-]?
[OH- ] = x = 1.0 x M
1.0 x
LecturePLUS Timberlake

10. LecturePLUS Timberlake
Using the Calculator
1.0 x
4.0 x 10-5
Enter 1.0 EE +/  EE +/- 5
= 2.5 x
LecturePLUS Timberlake

11. LecturePLUS Timberlake
Learning Check pH2
The [OH-] of a solution is 5 x M. What is the [H3O+ ] of the solution?
1) 2 x M
2) 1 x 1010 M
3) 2 x M
LecturePLUS Timberlake

12. LecturePLUS Timberlake
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
5 x 10- 5
On some calculators:
1.0 EE +/  5 EE +/- 5 = 2 x M
LecturePLUS Timberlake

13. LecturePLUS Timberlake
Learning Check pH3
A.The [OH-] when [H3O+ ] of 1 x M
1) 1 x 10-6 M
2) 1 x 10-8 M
3) 1 x M
B.The [H3O+] when [OH- ] of 5 x M
1) 1 x M
2) 2 x M
3) 2 x 10-7 M
LecturePLUS Timberlake

14. LecturePLUS Timberlake
Solution pH3
Kw = [H3O+ ][OH-] = 1.0 x 10 14
A. (3) [OH- ] = x = 1.0 x
1.0 x 10- 4
B. (2) [H3O+] = x = 2 x
5 x 10- 9
LecturePLUS Timberlake

15. LecturePLUS TimberlakepH
Indicates the acidity [H3O+] of the solution
pH = - log [H3O+]
From the French pouvoir hydrogene
(“hydrogen power” or power of
hydrogen)
LecturePLUS Timberlake

16. pH A strong acid A strong base
SOURCE: pH
10-2
10-3
10-5
10-4
10-8
10-7
10-6
[H+] M
10-10
10-9
10-11
10-12
10-13
10-14
10-1
100
A strong acid
A strong base
Most living cells have a very narrow range of tolerance for pH, i.e. [H+].
The [H+] concentration will be important (either explicitly or implicitly) for many other topics in biology.
[H+] is controlled in all biological organisms, and in virtually all biochemical experiments.
Each pH unit represents a factor of 10 difference in [H+].
The pH scale goes from 0 to 14—because [H+][OH-] = 10-14

17. LecturePLUS TimberlakepH
In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M
LecturePLUS Timberlake

18. LecturePLUS Timberlake
pH Range
Neutral
[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Acidic
Basic
LecturePLUS Timberlake

19. LecturePLUS Timberlake
Some [H3O+] and pH
[H3O+] pH
1 x 10-5 M
1 x 10-9 M
1 x M
LecturePLUS Timberlake

20. LecturePLUS Timberlake
pH of Some Common Acids
gastric juice 1.0
lemon juice 2.3
vinegar
orange juice 3.5
coffee
milk
LecturePLUS Timberlake

21. LecturePLUS Timberlake
pH of Some Common Bases
blood
tears
seawater
milk of magnesia 10.6
household ammonia 11.0
LecturePLUS Timberlake

22. LecturePLUS Timberlake
Learning Check pH4
A. The [H3O+] of tomato juice is 1 x 10-4 M.
What is the pH of the solution?
1) ) 4 3) 8
B. The [OH-] of an ammonia solution is
1 x 10-3 M. What is the pH of the solution?
1) ) 11 3) -11
LecturePLUS Timberlake

23. LecturePLUS Timberlake
Solution pH4
A. pH = - log [ 1 x 10-4] = -(- 4) = 4
B. [H3O+] = 1 x 10-11
pH = - log [ 1 x ] = -(- 11) = 11
LecturePLUS Timberlake

24. LecturePLUS Timberlake
Learning Check pH5
The pH of a soap is 10. What is the [H3O+] of the soap solution?
1) 1 x M
2) 1 x 1010 M
3) 1 x M
LecturePLUS Timberlake

25. LecturePLUS Timberlake
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 M
LecturePLUS Timberlake

26. LecturePLUS Timberlake
pH on the Calculator
[H3O+] is 4.5 x 10-6 M
pH = x EXP(or EE) 6+/- LOG +/-
= 5.35
LecturePLUS Timberlake

27. LecturePLUS Timberlake
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
LecturePLUS Timberlake

28. LecturePLUS Timberlake
Solution pH6
A soap solution has a [H3O+] = 2.0 x 10-8 M. What is the pH of the solution?
B) EE /- LOG +/- = 7.7
LecturePLUS Timberlake

29. LecturePLUS Timberlake
Learning Check pH7
Identify each solution as
1. acidic basic 3. neutral
A. _____ HCl with a pH = 1.5
B. _____ Pancreatic fluid [H+] = 1 x 10-8 M
C. _____ Sprite soft drink pH = 3.0
D. _____ pH = 7.0
E. _____ [OH- ] = 3 x M
F. _____ [H+ ] = 5 x 10-12
LecturePLUS Timberlake

30. LecturePLUS Timberlake
Solution pH7
Identify each solution as
1. acidic basic 3. neutral
A. _1__ HCl with a pH = 1.5
B. _2__ Pancreatic fluid [H+] = 1 x 10-8 M
C. _1__ Sprite soft drink pH = 3.0
D. _3__ pH = 7.0
E. _1__ [OH-] = 3 x M
F. _2__ [H+] = 5 x 10-12
LecturePLUS Timberlake

31. LecturePLUS Timberlake
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
Adds to H+ of rain
H2CO H+ (aq) + HCO3-(aq)
Formation of acid rain:
1. Emission of sulfur and nitrogen oxides from the burning of fuels expecially coal with high S content, power stations, oil refineries, vehicles as well as bacterial decomposition, and lighting hitting N2
SO million tons in 1980
NO and NO2 22 million tons in 1980
Mt. St Helens (1980) 400,000 tons SO2
2. Reactions in the atmosphere form SO3
2SO2 + O2  2 SO3
3. Reactions with atmosphere water form acids
SO3 + H2O  H2SO4 sulfuric acid
NO + H2O  HNO2 nitrous acid
HNO2 + H2O  HNO3 nitric acid
4. Effects of Acid Rain
Decline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rain
Extensive fish kills in spring from runoff due to accumulation of large amounts of acid on the snow
Dissolves minerals Mg, Ca, and K from the soil and waxy coatings that protect leaves from bacteria
Corrodes metals, textiles, paper and leather
LecturePLUS Timberlake

32. LecturePLUS Timberlake
Sources of Acid Rain
Power stations
Oil refineries
Coal with high S content
Car and truck emissions
Bacterial decomposition, and lighting hitting N2
LecturePLUS Timberlake

33. LecturePLUS Timberlake
SO million tons in 1980
NO and NO 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 H2SO4 sulfuric acid
NO + H2O HNO2 nitrous acid
HNO2 + H2O HNO3 nitric acid
LecturePLUS Timberlake

34. LecturePLUS Timberlake
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
LecturePLUS Timberlake