1 Chapter 8: Acids and Bases Acids & Bases Ionization of Water pH Acid-Base Reactions.
10.5-10.6 Ionization of Water and the pH Scale. Ionization of Water 10.5.
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Transcript of 10.5-10.6 Ionization of Water and the pH Scale. Ionization of Water 10.5.
10.5-10.6Ionization of Water and the pH Scale
Ionization of Water
10.5
3
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 H3O+ + OH− .. .. .. .. :O: H + H:O: H:O:H + + :O:H−
.. .. .. .. H H H water water hydronium hydroxide
ion (+) ion (-)
Ionization of Water
4
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+] = 1.0 x 10−7 M
[OH−] = 1.0 x 10−7 MCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
5
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−].
6
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
7
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
Ion Product of Water, Kw
8
[H3O+] and [OH−] in Solutions
In neutral, acidic, or basic solutions, the Kw is always 1.0 x 10−14.
9
Guide to Calculating [H3O+]
10
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
The pH Scale
10.6
LecturePLUS Timberlake 12
pH
Indicates the acidity [H3O+] of the solution
pH = - log [H3O+]
From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen)
LecturePLUS Timberlake 13
In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M
pH
LecturePLUS Timberlake 14
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
LecturePLUS Timberlake 15
Some [H3O+] and pH
[H3O+] pH
1 x 10-5 M 5
1 x 10-9 M 9
1 x 10-11 M 11
LecturePLUS Timberlake 16
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
LecturePLUS Timberlake 17
pH of Some Common Bases
blood 7.4
tears 7.4
seawater 8.4
milk of magnesia 10.6
household ammonia 11.0
LecturePLUS Timberlake 18
pH on the Calculator
[H3O+] is 4.5 x 10-6 M
pH = 4.5 x EXP(or EE) 6+/- LOG +/-
= 5.35
LecturePLUS Timberlake 19
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
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 acidsSO3 + H2O H2SO4 sulfuric acid
NO + H2O HNO2 nitrous acid
HNO2 + H2O HNO3 nitric acid
4. Effects of Acid RainDecline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rainExtensive 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 bacteriaCorrodes metals, textiles, paper and leather
LecturePLUS Timberlake 20
Sources of Acid Rain
Power stationsOil refineries
Coal with high S content
Car and truck emissions
Bacterial decomposition, and lighting hitting N2
LecturePLUS Timberlake 21
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 sulfuric acid
NO + H2O HNO2 nitrous acid
HNO2 + H2O HNO3 nitric acid
LecturePLUS Timberlake 22
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