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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: + :O:H H:O:H + + :O:H-
. . . . . . . . H H H
water molecules hydroxonium hydroxide ion (+) 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-
hydroxonium hydroxide
ion ion
1 x 10-7 M 1 x 10-7 MH3O+ OH-
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Ion Product of Water Kw
[ ] = Molar concentration
Kw = [ 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+
OH-
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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+OH-
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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+] = 1.0 x 10-14
[OH-]
[H3O+] = 1.0 x 10-14 = 1.0 x 10-11 M
1.0 x 10- 3
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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 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 10-11 M 1.0 x 10 - 3
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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 x 10- 5 M
2) 1 x 1010 M
3) 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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In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M
pH
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pH Range
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutral
[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Acidic Basic
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Some [H3O+] and pH
[H3O+] pH
1 x 10-5 M 5
1 x 10-9 M 9
1 x 10-11 M 11
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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
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pH of Some Common Bases
blood 7.4
tears 7.4
seawater 8.4
milk of magnesia 10.6
household ammonia11.0
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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 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 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 10-10 M
F. _____ [H+ ] = 5 x 10-12
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Solution pH7
Identify each solution as
1. acidic 2. 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 10-10 M
F. _2__ [H+] = 5 x 10-12
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Acid RainUnpolluted 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
H2CO3 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
SO2 26 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
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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 26 million tons in 1980
NO and NO2 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 H2SO4 sulphuric acid
NO + H2O HNO2 nitrous acid
HNO2 + H2O 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