The Free High School Science Texts: Textbooks for High School Students Chemistry

The Free High School Science Texts: Textbooks for High School Students Chemistry
FHSST Authors
The Free High School Science Texts:
Textbooks for High School Students
Studying the Sciences
Chemistry
Grades 10 - 12
Version 0
November 9, 2008
ii
Copyright 2007 “Free High School Science Texts”
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FHSST Core Team
Mark Horner ; Samuel Halliday ; Sarah Blyth ; Rory Adams ; Spencer Wheaton
FHSST Editors
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Whitfield
FHSST Contributors
Rory Adams ; Prashant Arora ; Richard Baxter ; Dr. Sarah Blyth ; Sebastian Bodenstein ;
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Daniels ; Sean Dobbs ; Fernando Durrell ; Dr. Dan Dwyer ; Frans van Eeden ; Giovanni
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Andrew Kubik ; Dr. Marco van Leeuwen ; Dr. Anton Machacek ; Dr. Komal Maheshwari ;
Kosma von Maltitz ; Nicole Masureik ; John Mathew ; JoEllen McBride ; Nikolai Meures ;
Riana Meyer ; Jenny Miller ; Abdul Mirza ; Asogan Moodaly ; Jothi Moodley ; Nolene Naidu ;
Tyrone Negus ; Thomas O’Donnell ; Dr. Markus Oldenburg ; Dr. Jaynie Padayachee ;
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iii
iv
Contents
I
II
Introduction
1
Matter and Materials
3
1 Classification of Matter - Grade 10
1.1
1.2
5
Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.1.1
Heterogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
1.1.2
Homogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
1.1.3
Separating mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
Pure Substances: Elements and Compounds . . . . . . . . . . . . . . . . . . . .
9
1.2.1
Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
1.2.2
Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
1.3
Giving names and formulae to substances . . . . . . . . . . . . . . . . . . . . . 10
1.4
Metals, Semi-metals and Non-metals . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.1
Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.2
Non-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.3
Semi-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5
Electrical conductors, semi-conductors and insulators . . . . . . . . . . . . . . . 14
1.6
Thermal Conductors and Insulators . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.7
Magnetic and Non-magnetic Materials . . . . . . . . . . . . . . . . . . . . . . . 17
1.8
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2 What are the objects around us made of? - Grade 10
21
2.1
Introduction: The atom as the building block of matter . . . . . . . . . . . . . . 21
2.2
Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1
Representing molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3
Intramolecular and intermolecular forces . . . . . . . . . . . . . . . . . . . . . . 25
2.4
The Kinetic Theory of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5
The Properties of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3 The Atom - Grade 10
3.1
35
Models of the Atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.1
The Plum Pudding Model . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.2
Rutherford’s model of the atom
v
. . . . . . . . . . . . . . . . . . . . . . 36
CONTENTS
3.1.3
3.2
3.3
CONTENTS
The Bohr Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.1
How heavy is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.2
How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Atomic structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.3.1
The Electron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3.2
The Nucleus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4
Atomic number and atomic mass number . . . . . . . . . . . . . . . . . . . . . 40
3.5
Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.6
3.7
3.8
3.9
3.5.1
What is an isotope? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.5.2
Relative atomic mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Energy quantisation and electron configuration . . . . . . . . . . . . . . . . . . 46
3.6.1
The energy of electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.6.2
Energy quantisation and line emission spectra . . . . . . . . . . . . . . . 47
3.6.3
Electron configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.6.4
Core and valence electrons . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.6.5
The importance of understanding electron configuration . . . . . . . . . 51
Ionisation Energy and the Periodic Table . . . . . . . . . . . . . . . . . . . . . . 53
3.7.1
Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.7.2
Ionisation Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
The Arrangement of Atoms in the Periodic Table . . . . . . . . . . . . . . . . . 56
3.8.1
Groups in the periodic table
. . . . . . . . . . . . . . . . . . . . . . . . 56
3.8.2
Periods in the periodic table . . . . . . . . . . . . . . . . . . . . . . . . 58
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4 Atomic Combinations - Grade 11
63
4.1
Why do atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2
Energy and bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3
What happens when atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.4
Covalent Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.4.1
The nature of the covalent bond . . . . . . . . . . . . . . . . . . . . . . 65
4.5
Lewis notation and molecular structure . . . . . . . . . . . . . . . . . . . . . . . 69
4.6
Electronegativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7
4.8
4.6.1
Non-polar and polar covalent bonds . . . . . . . . . . . . . . . . . . . . 73
4.6.2
Polar molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Ionic Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.7.1
The nature of the ionic bond . . . . . . . . . . . . . . . . . . . . . . . . 74
4.7.2
The crystal lattice structure of ionic compounds . . . . . . . . . . . . . . 76
4.7.3
Properties of Ionic Compounds . . . . . . . . . . . . . . . . . . . . . . . 76
Metallic bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.8.1
The nature of the metallic bond . . . . . . . . . . . . . . . . . . . . . . 76
4.8.2
The properties of metals . . . . . . . . . . . . . . . . . . . . . . . . . . 77
vi
CONTENTS
4.9
CONTENTS
Writing chemical formulae
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.9.1
The formulae of covalent compounds . . . . . . . . . . . . . . . . . . . . 78
4.9.2
The formulae of ionic compounds . . . . . . . . . . . . . . . . . . . . . 80
4.10 The Shape of Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.10.1 Valence Shell Electron Pair Repulsion (VSEPR) theory . . . . . . . . . . 82
4.10.2 Determining the shape of a molecule . . . . . . . . . . . . . . . . . . . . 82
4.11 Oxidation numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5 Intermolecular Forces - Grade 11
91
5.1
Types of Intermolecular Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.2
Understanding intermolecular forces . . . . . . . . . . . . . . . . . . . . . . . . 94
5.3
Intermolecular forces in liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.4
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6 Solutions and solubility - Grade 11
101
6.1
Types of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.2
Forces and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.3
Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
6.4
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7 Atomic Nuclei - Grade 11
107
7.1
Nuclear structure and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.2
The Discovery of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.3
Radioactivity and Types of Radiation . . . . . . . . . . . . . . . . . . . . . . . . 108
7.4
7.3.1
Alpha (α) particles and alpha decay . . . . . . . . . . . . . . . . . . . . 109
7.3.2
Beta (β) particles and beta decay . . . . . . . . . . . . . . . . . . . . . 109
7.3.3
Gamma (γ) rays and gamma decay . . . . . . . . . . . . . . . . . . . . . 110
Sources of radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
7.4.1
Natural background radiation . . . . . . . . . . . . . . . . . . . . . . . . 112
7.4.2
Man-made sources of radiation . . . . . . . . . . . . . . . . . . . . . . . 113
7.5
The ’half-life’ of an element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7.6
The Dangers of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
7.7
The Uses of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7.8
Nuclear Fission
7.9
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
7.8.1
The Atomic bomb - an abuse of nuclear fission . . . . . . . . . . . . . . 119
7.8.2
Nuclear power - harnessing energy . . . . . . . . . . . . . . . . . . . . . 120
Nuclear Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.10 Nucleosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.10.1 Age of Nucleosynthesis (225 s - 103 s) . . . . . . . . . . . . . . . . . . . 121
7.10.2 Age of Ions (103 s - 1013 s) . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.10.3 Age of Atoms (1013 s - 1015 s) . . . . . . . . . . . . . . . . . . . . . . . 122
7.10.4 Age of Stars and Galaxies (the universe today) . . . . . . . . . . . . . . 122
7.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
vii
CONTENTS
CONTENTS
8 Thermal Properties and Ideal Gases - Grade 11
125
8.1
A review of the kinetic theory of matter . . . . . . . . . . . . . . . . . . . . . . 125
8.2
Boyle’s Law: Pressure and volume of an enclosed gas . . . . . . . . . . . . . . . 126
8.3
Charles’s Law: Volume and Temperature of an enclosed gas . . . . . . . . . . . 132
8.4
The relationship between temperature and pressure . . . . . . . . . . . . . . . . 136
8.5
The general gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8.6
The ideal gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
8.7
Molar volume of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
8.8
Ideal gases and non-ideal gas behaviour . . . . . . . . . . . . . . . . . . . . . . 146
8.9
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
9 Organic Molecules - Grade 12
151
9.1
What is organic chemistry? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
9.2
Sources of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
9.3
Unique properties of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4
Representing organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4.1
Molecular formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4.2
Structural formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
9.4.3
Condensed structural formula . . . . . . . . . . . . . . . . . . . . . . . . 153
9.5
Isomerism in organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 154
9.6
Functional groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
9.7
The Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
9.7.1
The Alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
9.7.2
Naming the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
9.7.3
Properties of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.7.4
Reactions of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.7.5
The alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
9.7.6
Naming the alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
9.7.7
The properties of the alkenes . . . . . . . . . . . . . . . . . . . . . . . . 169
9.7.8
Reactions of the alkenes
9.7.9
The Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
. . . . . . . . . . . . . . . . . . . . . . . . . . 169
9.7.10 Naming the alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
9.8
9.9
The Alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
9.8.1
Naming the alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
9.8.2
Physical and chemical properties of the alcohols . . . . . . . . . . . . . . 175
Carboxylic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
9.9.1
Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
9.9.2
Derivatives of carboxylic acids: The esters . . . . . . . . . . . . . . . . . 178
9.10 The Amino Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
9.11 The Carbonyl Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
9.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
viii
CONTENTS
CONTENTS
10 Organic Macromolecules - Grade 12
185
10.1 Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
10.2 How do polymers form? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.2.1 Addition polymerisation . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.2.2 Condensation polymerisation . . . . . . . . . . . . . . . . . . . . . . . . 188
10.3 The chemical properties of polymers . . . . . . . . . . . . . . . . . . . . . . . . 190
10.4 Types of polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5.1 The uses of plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
10.5.2 Thermoplastics and thermosetting plastics . . . . . . . . . . . . . . . . . 194
10.5.3 Plastics and the environment . . . . . . . . . . . . . . . . . . . . . . . . 195
10.6 Biological Macromolecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
10.6.1 Carbohydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
10.6.2 Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
10.6.3 Nucleic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
10.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
III
Chemical Change
209
11 Physical and Chemical Change - Grade 10
211
11.1 Physical changes in matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
11.2 Chemical Changes in Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
11.2.1 Decomposition reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 213
11.2.2 Synthesis reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
11.3 Energy changes in chemical reactions . . . . . . . . . . . . . . . . . . . . . . . . 217
11.4 Conservation of atoms and mass in reactions . . . . . . . . . . . . . . . . . . . . 217
11.5 Law of constant composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.6 Volume relationships in gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
12 Representing Chemical Change - Grade 10
223
12.1 Chemical symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
12.2 Writing chemical formulae
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.3 Balancing chemical equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.3.1 The law of conservation of mass . . . . . . . . . . . . . . . . . . . . . . 224
12.3.2 Steps to balance a chemical equation
. . . . . . . . . . . . . . . . . . . 226
12.4 State symbols and other information . . . . . . . . . . . . . . . . . . . . . . . . 230
12.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
13 Quantitative Aspects of Chemical Change - Grade 11
233
13.1 The Mole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
13.2 Molar Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
13.3 An equation to calculate moles and mass in chemical reactions . . . . . . . . . . 237
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13.4 Molecules and compounds
CONTENTS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
13.5 The Composition of Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
13.6 Molar Volumes of Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
13.7 Molar concentrations in liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
13.8 Stoichiometric calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
13.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
14 Energy Changes In Chemical Reactions - Grade 11
255
14.1 What causes the energy changes in chemical reactions? . . . . . . . . . . . . . . 255
14.2 Exothermic and endothermic reactions . . . . . . . . . . . . . . . . . . . . . . . 255
14.3 The heat of reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
14.4 Examples of endothermic and exothermic reactions . . . . . . . . . . . . . . . . 259
14.5 Spontaneous and non-spontaneous reactions . . . . . . . . . . . . . . . . . . . . 260
14.6 Activation energy and the activated complex . . . . . . . . . . . . . . . . . . . . 261
14.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
15 Types of Reactions - Grade 11
267
15.1 Acid-base reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.1 What are acids and bases? . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.2 Defining acids and bases . . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.3 Conjugate acid-base pairs . . . . . . . . . . . . . . . . . . . . . . . . . . 269
15.1.4 Acid-base reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
15.1.5 Acid-carbonate reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 274
15.2 Redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
15.2.1 Oxidation and reduction
. . . . . . . . . . . . . . . . . . . . . . . . . . 277
15.2.2 Redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
15.3 Addition, substitution and elimination reactions . . . . . . . . . . . . . . . . . . 280
15.3.1 Addition reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
15.3.2 Elimination reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
15.3.3 Substitution reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
15.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
16 Reaction Rates - Grade 12
287
16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
16.2 Factors affecting reaction rates . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
16.3 Reaction rates and collision theory . . . . . . . . . . . . . . . . . . . . . . . . . 293
16.4 Measuring Rates of Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
16.5 Mechanism of reaction and catalysis . . . . . . . . . . . . . . . . . . . . . . . . 297
16.6 Chemical equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
16.6.1 Open and closed systems . . . . . . . . . . . . . . . . . . . . . . . . . . 302
16.6.2 Reversible reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
16.6.3 Chemical equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
16.7 The equilibrium constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
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CONTENTS
16.7.1 Calculating the equilibrium constant . . . . . . . . . . . . . . . . . . . . 305
16.7.2 The meaning of kc values . . . . . . . . . . . . . . . . . . . . . . . . . . 306
16.8 Le Chatelier’s principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
16.8.1 The effect of concentration on equilibrium . . . . . . . . . . . . . . . . . 310
16.8.2 The effect of temperature on equilibrium . . . . . . . . . . . . . . . . . . 310
16.8.3 The effect of pressure on equilibrium . . . . . . . . . . . . . . . . . . . . 312
16.9 Industrial applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
16.10Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
17 Electrochemical Reactions - Grade 12
319
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
17.2 The Galvanic Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
17.2.1 Half-cell reactions in the Zn-Cu cell . . . . . . . . . . . . . . . . . . . . 321
17.2.2 Components of the Zn-Cu cell . . . . . . . . . . . . . . . . . . . . . . . 322
17.2.3 The Galvanic cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
17.2.4 Uses and applications of the galvanic cell . . . . . . . . . . . . . . . . . 324
17.3 The Electrolytic cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
17.3.1 The electrolysis of copper sulphate . . . . . . . . . . . . . . . . . . . . . 326
17.3.2 The electrolysis of water . . . . . . . . . . . . . . . . . . . . . . . . . . 327
17.3.3 A comparison of galvanic and electrolytic cells . . . . . . . . . . . . . . . 328
17.4 Standard Electrode Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
17.4.1 The different reactivities of metals . . . . . . . . . . . . . . . . . . . . . 329
17.4.2 Equilibrium reactions in half cells . . . . . . . . . . . . . . . . . . . . . . 329
17.4.3 Measuring electrode potential . . . . . . . . . . . . . . . . . . . . . . . . 330
17.4.4 The standard hydrogen electrode . . . . . . . . . . . . . . . . . . . . . . 330
17.4.5 Standard electrode potentials . . . . . . . . . . . . . . . . . . . . . . . . 333
17.4.6 Combining half cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
17.4.7 Uses of standard electrode potential . . . . . . . . . . . . . . . . . . . . 338
17.5 Balancing redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
17.6 Applications of electrochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.6.1 Electroplating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.6.2 The production of chlorine . . . . . . . . . . . . . . . . . . . . . . . . . 348
17.6.3 Extraction of aluminium
. . . . . . . . . . . . . . . . . . . . . . . . . . 349
17.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
IV
Chemical Systems
353
18 The Water Cycle - Grade 10
355
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
18.2 The importance of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
18.3 The movement of water through the water cycle . . . . . . . . . . . . . . . . . . 356
18.4 The microscopic structure of water . . . . . . . . . . . . . . . . . . . . . . . . . 359
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18.4.1 The polar nature of water . . . . . . . . . . . . . . . . . . . . . . . . . . 359
18.4.2 Hydrogen bonding in water molecules . . . . . . . . . . . . . . . . . . . 359
18.5 The unique properties of water . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
18.6 Water conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
18.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
19 Global Cycles: The Nitrogen Cycle - Grade 10
369
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
19.2 Nitrogen fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
19.3 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
19.4 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
19.5 Human Influences on the Nitrogen Cycle . . . . . . . . . . . . . . . . . . . . . . 372
19.6 The industrial fixation of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . 373
19.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
20 The Hydrosphere - Grade 10
377
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
20.2 Interactions of the hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
20.3 Exploring the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
20.4 The Importance of the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . 379
20.5 Ions in aqueous solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
20.5.1 Dissociation in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
20.5.2 Ions and water hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
20.5.3 The pH scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
20.5.4 Acid rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
20.6 Electrolytes, ionisation and conductivity . . . . . . . . . . . . . . . . . . . . . . 386
20.6.1 Electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
20.6.2 Non-electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
20.6.3 Factors that affect the conductivity of water . . . . . . . . . . . . . . . . 387
20.7 Precipitation reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
20.8 Testing for common anions in solution . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.1 Test for a chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.2 Test for a sulphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.3 Test for a carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
20.8.4 Test for bromides and iodides . . . . . . . . . . . . . . . . . . . . . . . . 392
20.9 Threats to the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
20.10Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
21 The Lithosphere - Grade 11
397
21.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
21.2 The chemistry of the earth’s crust . . . . . . . . . . . . . . . . . . . . . . . . . 398
21.3 A brief history of mineral use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
21.4 Energy resources and their uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
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21.5 Mining and Mineral Processing: Gold . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.2 Mining the Gold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.3 Processing the gold ore . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.4 Characteristics and uses of gold . . . . . . . . . . . . . . . . . . . . . . . 402
21.5.5 Environmental impacts of gold mining . . . . . . . . . . . . . . . . . . . 404
21.6 Mining and mineral processing: Iron . . . . . . . . . . . . . . . . . . . . . . . . 406
21.6.1 Iron mining and iron ore processing . . . . . . . . . . . . . . . . . . . . . 406
21.6.2 Types of iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
21.6.3 Iron in South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
21.7 Mining and mineral processing: Phosphates . . . . . . . . . . . . . . . . . . . . 409
21.7.1 Mining phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
21.7.2 Uses of phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
21.8 Energy resources and their uses: Coal . . . . . . . . . . . . . . . . . . . . . . . 411
21.8.1 The formation of coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
21.8.2 How coal is removed from the ground . . . . . . . . . . . . . . . . . . . 411
21.8.3 The uses of coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
21.8.4 Coal and the South African economy . . . . . . . . . . . . . . . . . . . . 412
21.8.5 The environmental impacts of coal mining . . . . . . . . . . . . . . . . . 413
21.9 Energy resources and their uses: Oil . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.1 How oil is formed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.2 Extracting oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.3 Other oil products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
21.9.4 The environmental impacts of oil extraction and use . . . . . . . . . . . 415
21.10Alternative energy resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
21.11Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
22 The Atmosphere - Grade 11
421
22.1 The composition of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . . 421
22.2 The structure of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.1 The troposphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.2 The stratosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.3 The mesosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.2.4 The thermosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.3 Greenhouse gases and global warming . . . . . . . . . . . . . . . . . . . . . . . 426
22.3.1 The heating of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . 426
22.3.2 The greenhouse gases and global warming . . . . . . . . . . . . . . . . . 426
22.3.3 The consequences of global warming . . . . . . . . . . . . . . . . . . . . 429
22.3.4 Taking action to combat global warming . . . . . . . . . . . . . . . . . . 430
22.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
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23 The Chemical Industry - Grade 12
435
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2 Sasol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2.1 Sasol today: Technology and production . . . . . . . . . . . . . . . . . . 436
23.2.2 Sasol and the environment . . . . . . . . . . . . . . . . . . . . . . . . . 440
23.3 The Chloralkali Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
23.3.1 The Industrial Production of Chlorine and Sodium Hydroxide . . . . . . . 442
23.3.2 Soaps and Detergents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
23.4 The Fertiliser Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.1 The value of nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.2 The Role of fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.3 The Industrial Production of Fertilisers . . . . . . . . . . . . . . . . . . . 451
23.4.4 Fertilisers and the Environment: Eutrophication . . . . . . . . . . . . . . 454
23.5 Electrochemistry and batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.1 How batteries work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.2 Battery capacity and energy . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.3 Lead-acid batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.4 The zinc-carbon dry cell . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
23.5.5 Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . 460
23.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
A GNU Free Documentation License
467
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Chapter 18
The Water Cycle - Grade 10
18.1
Introduction
You may have heard the word ’cycle’ many times before. Think for example of the word ’bicycle’
or the regular ’cycle tests’ that you may have at school. A cycle is a series of events that repeats
itself. In the case of a bicycle, the wheel turns through a full circle before beginning the motion
again, while cycle tests happen regularly, normally every week or every two weeks. Because a
cycle repeats itself, it doesn’t have a beginning or an end.
Our Earth is a closed system. This means that it can exchange energy with its surroundings
(i.e. the rest of the solar system), but no new matter is brought into the system. For this reason,
it is important that all the elements and molecules on Earth are recycled so that they are never
completely used up. In the next two sections, we are going to take a closer look at two cycles
that are very important for life on Earth. They are the water cycle and the nitrogen cycle.
18.2
The importance of water
For many people, it is so easy to take water for granted, and yet life on Earth would not exist
were it not for this extraordinary compound. Not only is it believed that the first forms of life
actually started in water, but most of the cells in living organisms contain between 70% and
95% water. Here in the cells, water acts as a solvent and helps to transport vital materials such
as food and oxygen to where they are needed, and also removes waste products such as carbon
dioxide and ammonia from the body. For many animals and plants, water is their home. Think
for example of fish and amphibians that live either all or part of the time in rivers, dams and the
oceans. In other words, if water did not exist, no life would be possible.
Apart from allowing life to exist, water also has a number of other functions. Water shapes the
landscape around us by wearing away at rocks and also transports and deposits sediments on
floodplains and along coastal regions. Water also plays a very important role in helping to regulate Earth’s climate. We will discuss this again later in the chapter. As humans we use water in
our homes, in industry, in mining, irrigation and even as a source of electricitiy in hydro-electric
schemes. In fact, if we were able to view Earth from space, we would see that almost three
quarters of our planet’s surface is covered in water. It is because of this that Earth is sometimes
called the ’Blue Planet’. Most of this water is stored in the oceans, with the rest found in ice
(e.g. glaciers), groundwater (e.g. boreholes), surface water (e.g. rivers, lakes, estuaries, dams)
and in the atmosphere as clouds and water vapour.
teresting In the search for life on other planets, one of the first things that scientists look
Interesting
Fact
Fact
for is water. However, most planets are either too close to the sun (and therefore
355
18.3
CHAPTER 18. THE WATER CYCLE - GRADE 10
too hot) for water to exist in liquid form, or they are too far away and therefore
too cold. So, even if water were to be found, the conditions are unlikely to allow
it to exist in a form that can support the diversity of life that we see on Earth.
18.3
The movement of water through the water cycle
The water cycle is the continuous movement of water over, above, and beneath the Earth’s
surface. As water moves, it changes phase between liquid (water), solid (ice) and gas (water
vapour). It is powered by solar energy and, because it is a cycle, it has no beginning or end.
Definition: The Water Cycle
The water cycle is the continuous circulation of water across the Earth. The water cycle is
driven by solar radiation and it includes the atmosphere, land, surface water and groundwater. As water moves through the cycle, it changes state between liquid, solid, and gas
phases. The actual movement of water from one part of the cycle to another (e.g. from
river to ocean) is the result of processes such as evaporation, precipitation, infiltration and
runoff.
The movement of water through the water cycle is shown in figure 18.1. In the figure, each
process within this cycle is numbered. Each process will be described below.
1. The source of energy
The water cycle is driven by the sun, which provides the heat energy that is needed for
many of the other processes to take place.
2. Evaporation
When water on the earth’s surface is heated by the sun, the average energy of the water
molecules increases and some of the molecules are able to leave the liquid phase and
become water vapour. This is called evaporation. Evaporation is the change of water from
a liquid to a gas as it moves from the ground, or from bodies of water like the ocean,
rivers and dams, into the atmosphere.
3. Transpiration
Transpiration is the evaporation of water from the aerial parts of plants, especially the
leaves but also from the stems, flowers and fruits. This is another way that liquid water
can enter the atmosphere as a gas.
4. Condensation
When evaporation takes place, water vapour rises in the atmosphere and cools as the
altitude (height above the ground) increases. As the temperature drops, the energy of the
water vapour molecules also decreases, until the molecules don’t have enough energy to
stay in the gas phase. At this point, condensation occurs. Condensation is the change of
water from water vapour (gas) into liquid water droplets in the air. Clouds, fog and mist
are all examples of condensation. A cloud is actually a collection of lots and lots of tiny
water droplets. This mostly takes place in the upper atmosphere but can also take place
close to the ground if there is a significant temperature change.
teresting Have you ever tried breathing out on a very cold day? It looks as though
Interesting
Fact
Fact
you are breathing out smoke! The moist air that you breathe out is much
warmer than the air outside your body. As this warm, moist air comes into
356
CHAPTER 18. THE WATER CYCLE - GRADE 10
18.3
1
SUN
Condensation forms
clouds
4
Rain falls onto the
soil, flows into the
rivers or seeps into
the soil
5
Rain falls
directly into
rivers, dams
or the
oceans
7
2
Surface water
Evaporation
3
Some rain seeps into
the soil and becomes
part of the ground water
supply
6
Ground water may feed into
rivers or will eventually lead
into the sea
Figure 18.1: The water cycle
contact with the colder air outside, its temperature drops very quickly and
the water vapour in the air you breathe out condenses. The ’smoke’ that
you see is actually formed in much the same way as clouds form in the upper
atmosphere.
5. Precipitation
Precipitation occurs when water falls back to the earth’s surface in the form of rain or
snow. Rain will fall as soon as a cloud becomes too saturated with water droplets. Snow is
similar to rain, except that it is frozen. Snow only falls if temperatures in the atmosphere
are around freezing. The freeing point of water is 00 C).
6. Infiltration
If precipitation occurs, some of this water will filter into the soil and collect underground.
This is called infiltration. This water may evaporate again from the soil at a later stage,
or the underground water may seep into another water body.
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18.3
CHAPTER 18. THE WATER CYCLE - GRADE 10
7. Surface runoff
This refers to the many ways that water moves across the land. This includes surface runoff
such as when water flows along a road and into a drain, or when water flows straight across
the sand. It also includes channel runoff when water flows in rivers and streams. As it
flows, the water may infiltrate into the ground, evaporate into the air, become stored in
lakes or reservoirs, or be extracted for agricultural or other human uses.
Important: It is important to realise that the water cycle is all about energy exchanges.
The sun is the original energy source. Energy from the sun heats the water and causes
evaporation. This energy is stored in water vapour as latent heat. When the water vapour
condenses again, the latent heat is released, and helps to drive circulation in the atmosphere.
The liquid water falls to earth, and will evaporate again at a later stage. The atmospheric
circulation patterns that occur because of these exchanges of heat are very important in
influencing climate patterns.
Activity :: Experiment : The Water Cycle
Materials:
Tile or piece of plastic (e.g. lid of ice-cream container) to make a hill slope; glass
fish tank with a lid; beaker with ice cubes; lamp; water
Set up a model of the water cycle as follows:
lamp
ice cubes
glass tank
slope
water
1. Lean the plastic against one side so that it creates a ’hill slope’ as shown in the
diagram.
2. Pour water into the bottom of the tank until about a quarter of the hill slope
is covered.
3. Close the fish tank lid.
4. Place the beaker with ice on the lid directly above the hill slope.
5. Turn the lamp on and position it so that it shines over the water.
6. Leave the model like this for 20-30 minutes and then observe what happens.
Make sure that you don’t touch the lamp as it will be very hot!
Observation questions:
1. Which parts of the water cycle can you see taking place in the model?
2. Which parts of the water cycle are not represented in the model?
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18.4
3. Can you think of how those parts that are not shown could be represented?
4. What is the energy source in the model? What would the energy source be in
reality?
5. What do you think the function of the ice is in the beaker?
18.4
The microscopic structure of water
In many ways, water behaves very differently from other liquids. These properties are directly
related to the microscopic structure of water, and more specifically to the shape of the molecule
and its polar nature, and to the bonds that hold water molecules together.
18.4.1
The polar nature of water
Every water molecule is made up of one oxygen atom that is bonded to two hydrogen atoms.
When atoms bond, the nucleus of each atom has an attractive force on the electrons of the other
atoms. This ’pull’ is stronger in some atoms than in others and is called the electronegativity of
the atom. In a water molecule, the oxygen atom has a higher electronegativty than the hydrogen
atoms and therefore attracts the electrons more strongly. The result is that the oxygen atom
has a slightly negative charge and the two hydrogen atoms each have a slightly positive charge.
The water molecule is said to be polar because the electrical charge is not evenly distributed
in the molecule. One part of the molecule has a different charge to other parts. You will learn
more about this in chapter 4.
Oxygen
(slightly negative charge)
Hydrogen
O
(slightly positive charge)
H
H
Hydrogen
(slightly positive charge)
Figure 18.2: Diagrams showing the structure of a water molecule. Each molecule is made up of
two hydrogen atoms that are attached to one oxygen atom.
18.4.2
Hydrogen bonding in water molecules
In every water molecule, the forces that hold the individual atoms together are called intramolecular forces. But there are also forces between different water molecules. These are
called intermolecular forces (figure 18.3). You will learn more about these at a later stage, but
for now it is enough to know that in water, molecules are held together by hydrogen bonds.
Hydrogen bonds are a much stronger type of intermolecular force than those found in many
other substances, and this affects the properties of water.
Important: Intramolecular and intermolecular forces
359
18.5
CHAPTER 18. THE WATER CYCLE - GRADE 10
If you find these terms confusing, remember that ’intra’ means within (i.e. the forces within
a molecule). An introvert is someone who doesn’t express emotions and feelings outwardly.
They tend to be quieter and keep to themselves. ’Inter’ means between (i.e. the forces between
molecules). An international cricket match is a match between two different countries.
intermolecular forces
H
intramolecular forces
O
O
H
O
O
H
O
O
Figure 18.3: Intermolecular and intramolecular forces in water. Note that the diagram on the
left only shows intermolecular forces. The intramolecular forces are between the atoms of each
water molecule.
18.5
The unique properties of water
Because of its polar nature and the strong hydrogen bonds between its molecules, water has
some special properties that are quite different to those of other substances.
1. Absorption of infra-red radiation
The polar nature of the water molecule means that it is able to absorb infra-red radiation
(heat) from the sun. As a result of this, the oceans and other water bodies act as heat
reservoirs, and are able to help moderate the Earth’s climate.
2. Specific heat
Definition: Specific heat
Specific heat is the amount of heat energy that is needed to increase the temperature of a
substance by one degree.
Water has a high specific heat, meaning that a lot of energy must be absorbed by water
before its temperature changes.
Activity :: Demonstration : The high specific heat of water
(a) Pour about 100 ml of water into a glass beaker.
(b) Place the beaker on a stand and heat it over a bunsen burner for about 2
minutes.
(c) After this time, carefully touch the side of the beaker (Make sure you touch
the glass very lightly because it will be very hot and may burn you!). Then
use the end of a finger to test the temperature of the water.
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CHAPTER 18. THE WATER CYCLE - GRADE 10
18.5
What do you notice? Which of the two (glass or water) is the hottest?
You have probably observed this phenomenon if you have boiled water in a pot on the
stove. The metal of the pot heats up very quickly, and can burn your fingers if you touch
it, while the water may take several minutes before its temperature increases even slightly.
How can we explain this in terms of hydrogen bonding? Remember that increasing the
temperature of a substance means that its particles will move more quickly. However,
before they can move faster, the bonds between them must be broken. In the case of
water, these bonds are strong hydrogen bonds, and so a lot of energy is needed just to
break these, before the particles can start moving faster.
It is the high specific heat of water and its ability to absorb infra-red radiation that allows
it to regulate climate. Have you noticed how places that are closer to the sea have less
extreme daily temperatures than those that are inland? During the day, the oceans heat
up slowly, and so the air moving from the oceans across land is cool. Land temperatures
are cooler than they would be if they were further from the sea. At night, the oceans lose
the heat that they have absorbed very slowly, and so sea breezes blowing across the land
are relatively warm. This means that at night, coastal regions are generally slightly warmer
than areas that are further from the sea.
By contrast, places further from the sea experience higher maximum temperatures, and
lower minimum temperatures. In other words, their temperature range is higher than that
for coastal regions. The same principle also applies on a global scale. The large amount of
water across Earth’s surface helps to regulate temperatures by storing infra-red radiation
(heat) from the sun, and then releasing it very slowly so that it never becomes too hot or
too cold, and life is able to exist comfortably. In a similar way, water also helps to keep
the temperature of the internal environment of living organisms relatively constant. This
is very important. In humans, for example, a change in body temperature of only a few
degrees can be deadly.
3. Melting point and boiling point
The melting point of water is 00 C and its boiling point is 1000C. This large difference
between the melting and boiling point is very important because it means that water can
exist as a liquid over a large range of temperatures. The three phases of water are shown
in figure 18.4.
4. High heat of vaporisation
Definition: Heat of vaporisation
Heat of vaporisation is the energy that is needed to change a given quantity of a substance
into a gas.
The strength of the hydrogen bonds between water molecules also means that it has a
high heat of vaporisation. ’Heat of vaporisation’ is the heat energy that is needed to
change water from the liquid to the gas phase. Because the bonds between molecules are
strong, water has to be heated to 1000 C before it changes phase. At this temperature,
the molecules have enough energy to break the bonds that hold the molecules together.
The heat of vaporisation for water is 40.65 kJ/mol. It is very lucky for life on earth that
water does have a high heat of vaporisation. Can you imagine what a problem it would
be if water’s heat of vaporisation was much lower? All the water that makes up the cells
in our bodies would evaporate and most of the water on earth would no longer be able to
exist as a liquid!
5. Less dense solid phase
Another unusual property of water is that its solid phase (ice) is less dense than its liquid
phase. You can observe this if you put ice into a glass of water. The ice doesn’t sink to
361
18.5
CHAPTER 18. THE WATER CYCLE - GRADE 10
Gas (water vapour)
co n
eva dens
p o a ti o
rat n
io n
on
a ti
lim o n
s u b a ti
re- blim
su
Liquid
Solid (ice)
freezing
melting
Figure 18.4: Changes in phase of water
the bottom of the glass, but floats on top of the liquid. This phenomenon is also related to
the hydrogen bonds between water molecules. While other materials contract when they
solidify, water expands. The ability of ice to float as it solidifies is a very important factor
in the environment. If ice sank, then eventually all ponds, lakes, and even the oceans would
freeze solid as soon as temperatures dropped below freezing, making life as we know it
impossible on Earth. During summer, only the upper few inches of the ocean would thaw.
Instead, when a deep body of water cools, the floating ice insulates the liquid water below,
preventing it from freezing and allowing life to exist under the frozen surface.
Figure 18.5: Ice cubes floating in water
teresting Antarctica, the ’frozen continent’, has one of the world’s largest and deepest
Interesting
Fact
Fact
freshwater lakes. And this lake is hidden beneath 4 kilometres of ice! Lake
Vostok is 200 km long and 50 km wide. The thick, glacial blanket of ice acts
as an insulator, preventing the water from freezing.
6. Water as a solvent
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CHAPTER 18. THE WATER CYCLE - GRADE 10
18.6
Water is also a very good solvent, meaning that it is easy for other substances to dissolve
in it. It is very seldom, in fact, that we find pure water. Most of the time, the water that
we drink and use has all kinds of substances dissolved in it. It is these that make water
taste different in different areas. So why, then, is it important that water is such a good
solvent? We will look at just a few examples.
• Firstly, think about the animals and plants that live in aquatic environments such
as rivers, dams or in the sea. All of these living organisms either need oxygen for
respiration or carbon dioxide for photosynthesis, or both. How do they get these
gases from the water in which they live? Oxygen and carbon dioxide are just two
of the substances that dissolve easily in water, and this is how plants and animals
obtain the gases that they need to survive. Instead of being available as gases in the
atmosphere, they are present in solution in the surrounding water.
• Secondly, consider the fact that all plants need nitrogen to grow, and that they absorb
this nitrogen from compounds such as nitrates and nitrates that are present in the
soil. The question remains, however, as to how these nitrates and nitrites are able to
be present in the soil at all, when most of the Earth’s nitrogen is in a gaseous form
in the atmosphere. Part of the answer lies in the fact that nitrogen oxides, which
are formed during flashes of lightning, can be dissolved in rainwater and transported
into the soil in this way, to be absorbed by plants. The other part of the answer lies
in the activities of nitrogen-fixing bacteria in the soil, but this is a topic that we will
return to in a later section.
It should be clear now, that water is an amazing compound, and that without its unique properties, life on Earth would definitely not be possible.
Exercise: The properties of water
1. A learner returns home from school on a hot afternoon. In order to get cold
water to drink, she adds ice cubes to a glass of water. She makes the following
observations:
• The ice cubes float in the water.
• After a while the water becomes cold and the ice cubes melt.
(a) What property of ice cubes allows them to float in the water?
(b) Briefly explain why the water gets cold when the ice cubes melt.
(c) Briefly describe how the property you mentioned earlier affects the survival
of aquatic life during winter.
2. Which properties of water allow it to remain in its liquid phase over a large
temperature range? Explain why this is important for life on earth.
18.6
Water conservation
Water is a very precious substance and yet far too often, earth’s water resources are abused and
taken for granted. How many times have you walked past polluted rivers and streams, or seen
the flow of water in a river reduced to almost nothing because of its extraction for industrial and
other uses? And if you were able to test the quality of the water you see, you would probably
be shocked. Often our water resources are contaminated with chemicals such as pesticides and
fertilisers. If water is to continue playing all the important functions that were discussed earlier,
it is vital that we reduce the impact of humans on these resources.
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18.6
CHAPTER 18. THE WATER CYCLE - GRADE 10
Activity :: Group work : Human impacts on the water cycle
Read the following extract from an article, entitled ’The Effects of Urbanisation
on the Water Cycle’ by Susan Donaldson, and then answer the questions that follow.
As our communities grow, we notice many visible changes including housing developments, road networks, expansion of services and more. These
changes have an impact on our precious water resources, with pollution
of water being one of many such impacts. To understand these impacts
you will need to have a good knowledge of the water cycle!
It is interesting to note that the oceans contain most of earth’s water
(about 97%). Of the freshwater supplies on earth, 78% is tied up in polar
ice caps and snow, leaving only a very small fraction available for use by
humans. Of the available fresh water, 98% is present as groundwater,
while the remaining 2% is in the form of surface water. Because our
usable water supply is so limited, it is vitally important to protect water
quality. Within the water cycle, there is no ’new’ water ever produced on
the earth. The water we use today has been in existence for billions of
years. The water cycle continually renews and refreshes this finite water
supply.
So how exactly does urbanisation affect the water cycle? The increase
in hard surfaces (e.g. roads, roofs, parking lots) decreases the amount
of water that can soak into the ground. This increases the amount of
surface runoff. The runoff water will collect many of the pollutants that
have accumulated on these surfaces (e.g. oil from cars) and carry them
into other water bodies such as rivers or the ocean. Because there is less
infiltration, peak flows of stormwater runoff are larger and arrive earlier,
increasing the size of urban floods. If groundwater supplies are reduced
enough, this may affect stream flows during dry weather periods because
it is the groundwater that seeps to the surface at these times.
Atmospheric pollution can also have an impact because condensing water
vapour will pick up these pollutants (e.g. SO2 , CO2 and NO2 ) and return
them to earth into other water bodies. However, while the effects of
urbanisation on water quality can be major, these impacts can be reduced
if wise decisions are made during the process of development.
Questions
1. In groups, try to explain...
(a) what is meant by ’urbanisation’
(b) how urbanisation can affect water quality
2. Explain why it is so important to preserve the quality of our water supplies.
3. The article gives some examples of human impacts on water quality. In what
other ways do human activities affect water quality?
4. What do you think some of the consequences of these impacts might be for
humans and other forms of life?
5. Imagine that you are the city manager in your own city or the city closest to
you. What changes would you introduce to try to protect the quality of water
resources in your urban area?
6. What measures could be introduced in rural areas to protect water quality?
Apart from the pollution of water resources, the overuse of water is also a problem. In looking
at the water cycle, it is easy sometimes to think that water is a never-ending resource. In a sense
this is true because water cannot be destroyed. However, the availability of water may vary from
place to place. In South Africa for example, many regions are extremely dry and receive very
little rainfall. The same is true for many other parts of the world, where the scarcity of water
364
CHAPTER 18. THE WATER CYCLE - GRADE 10
18.6
is a life and death issue. The present threat of global warming is also likely to affect water
resources. Some climate models suggest that rising temperatures could increase the variability
of climate and decrease rainfall in South Africa. With this in mind, and remembering that South
Africa is already a dry country, it is vitally important that we manage our water use carefully. In
addition to this, the less water there is available, the more likely it is that water quality will also
decrease. A decrease in water quality limits how water can be used and developed.
At present, the demands being placed on South Africa’s water resources are large. Table 18.1
shows the water requirements that were predicted for the year 2000. The figures in the table
were taken from South Africa’s National Water Resource Strategy, produced by the Department
of Water Affairs and Forestry in 2004. In the table, ’rural’ means water for domestic use and
stock watering in rural areas, while ’urban’ means water for domestic, industrial and commercial
use in the urban area. ’Afforestation’ is included because many plantations reduce stream flow
because of the large amounts of water they need to survive.
Table 18.1: The predicted water requirements for various water management areas in South
Africa for 2000 (million m3 /annum)
Water management
area
Irrigation
Urban
Rural
Limpopo
Thukela
Upper Vaal
Upper Orange
Breede
Country total
238
204
114
780
577
7920
34
52
635
126
39
2897
28
31
43
60
11
574
Mining
and bulk
industrial
14
46
173
2
0
755
Power
generation
7
1
80
0
0
297
Afforestation Total
1
0
0
0
6
428
Activity :: Case Study : South Africa’s water requirements
Refer to table 18.1 and then answer the following questions:
1. Which water management area in South Africa has the highest need for water...
(a)
(b)
(c)
(d)
in the mining and industry sector?
for power generation?
in the irrigation sector?
Suggest reasons for each of your answers above.
2. For South Africa as a whole...
(a) Which activity uses the most water?
(b) Which activity uses the least water?
3. Complete the following table, by calculating the percentage (%) that each
activity contributes to the total water requirements in South Africa for the year
2000.
Water use activity
Irrigation
Urban
Rural
Mining and bulk industry
Power generation
Afforestation
% of SA’s total water requirements
365
322
334
1045
968
633
12871
18.7
CHAPTER 18. THE WATER CYCLE - GRADE 10
Table 18.2: The available water yield in South Africa in 2000 for various water management
areas (million m3 /annum)
Water management Surface
Ground Irrigation Urban
Mining Total loarea
water
and
cal yield
bulk
industrial
Limpopo
160
98
8
15
0
281
Thukela
666
15
23
24
9
737
Upper Vaal
598
32
11
343
146
1130
Upper Orange
4311
65
34
37
0
4447
Breede
687
109
54
16
0
866
Country total
10240
1088
675
970
254
13227
Now look at table 18.2, which shows the amount of water available in South Africa during 2000.
In the table, ’usable return flow’ means the amount of water that can be reused after it has been
used for irrigation, urban or mining.
Activity :: Case Study : Water conservation
Refer to table 18.2 and then answer the following questions:
1. Explain what is meant by...
(a) surface water
(b) ground water
2. Which water management area has the...
(a)
(b)
(c)
(d)
lowest surface water yield?
highest surface water yield?
lowest total yield?
highest total yield?
3. Look at the country’s total water requirements for 2000 and the total available
yield.
(a) Calculate what percentage of the country’s water yield is already being
used up.
(b) Do you think that the country’s total water requirements will increase or
decrease in the coming years? Give a reason for your answer.
4. South Africa is already placing a huge strain on existing water resources. In
groups of 3-4, discuss ways that the country’s demand for water could be
reduced. Present your ideas to the rest of the class for discussion.
18.7
Summary
• Water is critical for the survival of life on Earth. It is an important part of the cells of
living organisms and is used by humans in homes, industry, mining and agriculture.
• Water moves between the land and sky in the water cycle. The water cycle describes
the changes in phase that take place in water as it circulates across the Earth. The water
cycle is driven by solar radiation.
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CHAPTER 18. THE WATER CYCLE - GRADE 10
18.7
• Some of the important processes that form part of the water cycle are evaporation, transpiration, condensation, precipitation, infiltration and surface runoff. Together these processes
ensure that water is cycled between the land and sky.
• It is the microscopic structure of water that determines its unique properties.
• Water molecules are polar and are held together by hydrogen bonds. These characteristics
affect the properties of water.
• Some of the unique properties of water include its ability to absorb infra-red radiation, its
high specific heat, high heat of vaporisation and the fact that the solid phase of water is
less dense that its liquid phase.
• These properties of water help it to sustain life on Earth by moderating climate, regulating
the internal environment of living organisms and allowing liquid water to exist below ice,
even if temperatures are below zero.
• Water is also a good solvent. This property means that it is a good transport medium
in the cells of living organisms, and that it can dissolve gases and other compounds that
may be needed by aquatic plants and animals.
• Human activities threaten the quality of water resources through pollution and altered
runoff patterns.
• As human populations grow, there is a greater demand for water. In many areas, this
demand exceeds the amount of water available for use. Managing water wisely is important
in ensuring that there will always be water available both for human use, and to maintain
natural ecosystems.
Exercise: Summary Exercise
1. Give a word or term for each of the following phrases:
(a)
(b)
(c)
(d)
The
The
The
The
continuous circulation of water across the earth.
change in phase of water from gas to liquid.
movement of water across a land surface.
temperature at which water changes from liquid to gas.
2. In each of the following multiple choice questions, choose the one correct answer
from the list provided.
(a) Many of the unique properties of water (e.g. its high specific heat and
high boiling point) are due to:
i. strong covalent bonds between the hydrogen and oxygen atoms in each
water molecule
ii. the equal distribution of charge in a water molecule
iii. strong hydrogen bonds between water molecules
iv. the linear arrangement of atoms in a water molecule
(b) Which of the following statements is false?
i. Most of the water on earth is in the oceans.
ii. The hardening of surfaces in urban areas results in increased surface
runoff.
iii. Water conservation is important because water cannot be recycled.
iv. Irrigation is one of the largest water users in South Africa.
3. The sketch below shows a process that leads to rainfall in town X. The town
has been relying only on rainfall for its water supply because it has no access
to rivers or tap water. A group of people told the community that they will
never run out of rainwater because it will never stop raining.
367
18.7
CHAPTER 18. THE WATER CYCLE - GRADE 10
Cloud
P2
P1
Town X
Sea
(a) List the processes labelled P1 and P2 that lead to rainfall in town X.
(b) Is this group of people correct in saying that town X will never run out of
rainwater? Justify your answer using the sketch.
Recently, the amount of rainwater has decreased significantly. Various
reasons have been given to explain the drought. Some of the community
members are blaming this group who told them that it will never stop
raining.
(c) What scientific arguments can you use to convince the community members that this group of people should not be blamed for the drought?
(d) What possible strategies can the community leaders adopt to ensure that
they have a regular supply of water.
368
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the Document, free of added material. If you use the latter option, you must take reasonably
prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this
Transparent copy will remain thus accessible at the stated location until at least one year after
the last time you distribute an Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the Document well before
redistributing any large number of copies, to give them a chance to provide you with an updated
version of the Document.
MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of
sections A and A above, provided that you release the Modified Version under precisely this
License, with the Modified Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy of it. In addition, you
must do these things in the Modified Version:
1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document,
and from those of previous versions (which should, if there were any, be listed in the History
section of the Document). You may use the same title as a previous version if the original
publisher of that version gives permission.
2. List on the Title Page, as authors, one or more persons or entities responsible for authorship
of the modifications in the Modified Version, together with at least five of the principal
authors of the Document (all of its principal authors, if it has fewer than five), unless they
release you from this requirement.
3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
4. Preserve all the copyright notices of the Document.
5. Add an appropriate copyright notice for your modifications adjacent to the other copyright
notices.
6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the
Addendum below.
7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts
given in the Document’s license notice.
8. Include an unaltered copy of this License.
9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating
at least the title, year, new authors, and publisher of the Modified Version as given on the
Title Page. If there is no section Entitled “History” in the Document, create one stating
the title, year, authors, and publisher of the Document as given on its Title Page, then
add an item describing the Modified Version as stated in the previous sentence.
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APPENDIX A. GNU FREE DOCUMENTATION LICENSE
10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document
for previous versions it was based on. These may be placed in the “History” section. You
may omit a network location for a work that was published at least four years before the
Document itself, or if the original publisher of the version it refers to gives permission.
11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the
section, and preserve in the section all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their
titles. Section numbers or the equivalent are not considered part of the section titles.
13. Delete any section Entitled “Endorsements”. Such a section may not be included in the
Modified Version.
14. Do not re-title any existing section to be Entitled “Endorsements” or to conflict in title
with any Invariant Section.
15. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary
Sections and contain no material copied from the Document, you may at your option designate
some or all of these sections as invariant. To do this, add their titles to the list of Invariant
Sections in the Modified Version’s license notice. These titles must be distinct from any other
section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements
of your Modified Version by various parties–for example, statements of peer review or that the
text has been approved by an organisation as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25
words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only
one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through
arrangements made by) any one entity. If the Document already includes a cover text for the
same cover, previously added by you or by arrangement made by the same entity you are acting
on behalf of, you may not add another; but you may replace the old one, on explicit permission
from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use
their names for publicity for or to assert or imply endorsement of any Modified Version.
COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the
terms defined in section A above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them
all as Invariant Sections of your combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant
Sections may be replaced with a single copy. If there are multiple Invariant Sections with the
same name but different contents, make the title of each such section unique by adding at the
end of it, in parentheses, the name of the original author or publisher of that section if known,
or else a unique number. Make the same adjustment to the section titles in the list of Invariant
Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original
documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled
“Endorsements”.
470
APPENDIX A. GNU FREE DOCUMENTATION LICENSE
COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under
this License, and replace the individual copies of this License in the various documents with a
single copy that is included in the collection, provided that you follow the rules of this License
for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under
this License, provided you insert a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of that document.
AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents
or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the
copyright resulting from the compilation is not used to limit the legal rights of the compilation’s
users beyond what the individual works permit. When the Document is included an aggregate,
this License does not apply to the other works in the aggregate which are not themselves derivative
works of the Document.
If the Cover Text requirement of section A is applicable to these copies of the Document, then if
the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be
placed on covers that bracket the Document within the aggregate, or the electronic equivalent
of covers if the Document is in electronic form. Otherwise they must appear on printed covers
that bracket the whole aggregate.
TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section A. Replacing Invariant Sections with translations requires
special permission from their copyright holders, but you may include translations of some or
all Invariant Sections in addition to the original versions of these Invariant Sections. You may
include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and
the original versions of those notices and disclaimers. In case of a disagreement between the
translation and the original version of this License or a notice or disclaimer, the original version
will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the
requirement (section A) to Preserve its Title (section A) will typically require changing the actual
title.
TERMINATION
You may not copy, modify, sub-license, or distribute the Document except as expressly provided
for under this License. Any other attempt to copy, modify, sub-license or distribute the Document
is void, and will automatically terminate your rights under this License. However, parties who
have received copies, or rights, from you under this License will not have their licenses terminated
so long as such parties remain in full compliance.
FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation
License from time to time. Such new versions will be similar in spirit to the present version, but
may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
471
APPENDIX A. GNU FREE DOCUMENTATION LICENSE
Each version of the License is given a distinguishing version number. If the Document specifies
that a particular numbered version of this License “or any later version” applies to it, you have the
option of following the terms and conditions either of that specified version or of any later version
that has been published (not as a draft) by the Free Software Foundation. If the Document does
not specify a version number of this License, you may choose any version ever published (not as
a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document
and put the following copyright and license notices just after the title page:
c YEAR YOUR NAME. Permission is granted to copy, distribute and/or
Copyright modify this document under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the
license is included in the section entitled “GNU Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.”
line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST,
and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three,
merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these
examples in parallel under your choice of free software license, such as the GNU General Public
License, to permit their use in free software.
472
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