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The Free High School Science Texts: Textbooks for High School Students Studying the Sciences Chemistry Grades 10 - 12

Version 0 November 9, 2008

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FHSST Core Team
Mark Horner ; Samuel Halliday ; Sarah Blyth ; Rory Adams ; Spencer Wheaton

FHSST Editors
Jaynie Padayachee ; Joanne Boulle ; Diana Mulcahy ; Annette Nell ; Ren? Toerien ; Donovan e Whit?eld

FHSST Contributors
Rory Adams ; Prashant Arora ; Richard Baxter ; Dr. Sarah Blyth ; Sebastian Bodenstein ; Graeme Broster ; Richard Case ; Brett Cocks ; Tim Crombie ; Dr. Anne Dabrowski ; Laura Daniels ; Sean Dobbs ; Fernando Durrell ; Dr. Dan Dwyer ; Frans van Eeden ; Giovanni Franzoni ; Ingrid von Glehn ; Tamara von Glehn ; Lindsay Glesener ; Dr. Vanessa Godfrey ; Dr. Johan Gonzalez ; Hemant Gopal ; Umeshree Govender ; Heather Gray ; Lynn Gree? ; Dr. Tom Gutierrez ; Brooke Haag ; Kate Hadley ; Dr. Sam Halliday ; Asheena Hanuman ; Neil Hart ; Nicholas Hatcher ; Dr. Mark Horner ; Robert Hovden ; Mfandaidza Hove ; Jennifer Hsieh ; Clare Johnson ; Luke Jordan ; Tana Joseph ; Dr. Jennifer Klay ; Lara Kruger ; Sihle Kubheka ; 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 ; Nicolette Pekeur ; Sirika Pillay ; Jacques Plaut ; Andrea Prinsloo ; Joseph Raimondo ; Sanya Rajani ; Prof. Sergey Rakityansky ; Alastair Ramlakan ; Razvan Remsing ; Max Richter ; Sean Riddle ; Evan Robinson ; Dr. Andrew Rose ; Bianca Ruddy ; Katie Russell ; Duncan Scott ; Helen Seals ; Ian Sherratt ; Roger Sielo? ; Bradley Smith ; Greg Solomon ; Mike Stringer ; Shen Tian ; Robert Torregrosa ; Jimmy Tseng ; Helen Waugh ; Dr. Dawn Webber ; Michelle Wen ; Dr. Alexander Wetzler ; Dr. Spencer Wheaton ; Vivian White ; Dr. Gerald Wigger ; Harry Wiggins ; Wendy Williams ; Julie Wilson ; Andrew Wood ; Emma Wormauld ; Sahal Yacoob ; Jean Youssef Contributors and editors have made a sincere e?ort to produce an accurate and useful resource. Should you have suggestions, ?nd mistakes or be prepared to donate material for inclusion, please don’t hesitate to contact us. We intend to work with all who are willing to help make this a continuously evolving resource!

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iii

iv

Contents
I II Introduction Matter and Materials 1 3
5 5 6 6 7 9 9 9

1 Classi?cation of Matter - Grade 10 1.1 Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 1.1.2 1.1.3 1.2 Heterogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . Homogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . Separating mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Pure Substances: Elements and Compounds . . . . . . . . . . . . . . . . . . . . 1.2.1 1.2.2 Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.3 1.4

Giving names and formulae to substances . . . . . . . . . . . . . . . . . . . . . 10 Metals, Semi-metals and Non-metals . . . . . . . . . . . . . . . . . . . . . . . . 13 1.4.1 1.4.2 1.4.3 Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Non-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Semi-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.5 1.6 1.7 1.8

Electrical conductors, semi-conductors and insulators . . . . . . . . . . . . . . . 14 Thermal Conductors and Insulators . . . . . . . . . . . . . . . . . . . . . . . . . 15 Magnetic and Non-magnetic Materials . . . . . . . . . . . . . . . . . . . . . . . 17 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 21

2 What are the objects around us made of? - Grade 10 2.1 2.2

Introduction: The atom as the building block of matter . . . . . . . . . . . . . . 21 Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.1 Representing molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3 2.4 2.5 2.6

Intramolecular and intermolecular forces . . . . . . . . . . . . . . . . . . . . . . 25 The Kinetic Theory of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 The Properties of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 35

3 The Atom - Grade 10 3.1

Models of the Atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1.1 3.1.2 The Plum Pudding Model . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Rutherford’s model of the atom v . . . . . . . . . . . . . . . . . . . . . . 36

CONTENTS 3.1.3 3.2

CONTENTS The Bohr Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2.1 3.2.2 How heavy is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.3

Atomic structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.3.1 3.3.2 The Electron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 The Nucleus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.4 3.5

Atomic number and atomic mass number . . . . . . . . . . . . . . . . . . . . . 40 Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.5.1 3.5.2 What is an isotope? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Relative atomic mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.6

Energy quantisation and electron con?guration . . . . . . . . . . . . . . . . . . 46 3.6.1 3.6.2 3.6.3 3.6.4 3.6.5 The energy of electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Energy quantisation and line emission spectra . . . . . . . . . . . . . . . 47 Electron con?guration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Core and valence electrons . . . . . . . . . . . . . . . . . . . . . . . . . 51 The importance of understanding electron con?guration . . . . . . . . . 51

3.7

Ionisation Energy and the Periodic Table . . . . . . . . . . . . . . . . . . . . . . 53 3.7.1 3.7.2 Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Ionisation Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

3.8

The Arrangement of Atoms in the Periodic Table . . . . . . . . . . . . . . . . . 56 3.8.1 3.8.2 Groups in the periodic table . . . . . . . . . . . . . . . . . . . . . . . . 56

Periods in the periodic table . . . . . . . . . . . . . . . . . . . . . . . . 58

3.9

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 63

4 Atomic Combinations - Grade 11 4.1 4.2 4.3 4.4

Why do atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Energy and bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 What happens when atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . 65 Covalent Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.4.1 The nature of the covalent bond . . . . . . . . . . . . . . . . . . . . . . 65

4.5 4.6

Lewis notation and molecular structure . . . . . . . . . . . . . . . . . . . . . . . 69 Electronegativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.6.1 4.6.2 Non-polar and polar covalent bonds . . . . . . . . . . . . . . . . . . . . 73 Polar molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

4.7

Ionic Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.7.1 4.7.2 4.7.3 The nature of the ionic bond . . . . . . . . . . . . . . . . . . . . . . . . 74 The crystal lattice structure of ionic compounds . . . . . . . . . . . . . . 76 Properties of Ionic Compounds . . . . . . . . . . . . . . . . . . . . . . . 76

4.8

Metallic bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.8.1 4.8.2 The nature of the metallic bond . . . . . . . . . . . . . . . . . . . . . . 76 The properties of metals . . . . . . . . . . . . . . . . . . . . . . . . . . 77 vi

CONTENTS 4.9 Writing chemical formulae 4.9.1 4.9.2

CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

The formulae of covalent compounds . . . . . . . . . . . . . . . . . . . . 78 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 5.1 5.2 5.3 5.4 91

Types of Intermolecular Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Understanding intermolecular forces . . . . . . . . . . . . . . . . . . . . . . . . 94 Intermolecular forces in liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 101

6 Solutions and solubility - Grade 11 6.1 6.2 6.3 6.4

Types of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Forces and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 107

7 Atomic Nuclei - Grade 11 7.1 7.2 7.3

Nuclear structure and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 The Discovery of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Radioactivity and Types of Radiation . . . . . . . . . . . . . . . . . . . . . . . . 108 7.3.1 7.3.2 7.3.3 Alpha (α) particles and alpha decay . . . . . . . . . . . . . . . . . . . . 109 Beta (β) particles and beta decay . . . . . . . . . . . . . . . . . . . . . 109 Gamma (γ) rays and gamma decay . . . . . . . . . . . . . . . . . . . . . 110 Natural background radiation . . . . . . . . . . . . . . . . . . . . . . . . 112 Man-made sources of radiation . . . . . . . . . . . . . . . . . . . . . . . 113

7.4

Sources of radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 7.4.1 7.4.2

7.5 7.6 7.7 7.8

The ’half-life’ of an element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 The Dangers of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 The Uses of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Nuclear Fission 7.8.1 7.8.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 The Atomic bomb - an abuse of nuclear ?ssion . . . . . . . . . . . . . . 119 Nuclear power - harnessing energy . . . . . . . . . . . . . . . . . . . . . 120

7.9

Nuclear Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 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

7.10 Nucleosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

7.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 vii

CONTENTS 8 Thermal Properties and Ideal Gases - Grade 11 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9

CONTENTS 125

A review of the kinetic theory of matter . . . . . . . . . . . . . . . . . . . . . . 125 Boyle’s Law: Pressure and volume of an enclosed gas . . . . . . . . . . . . . . . 126 Charles’s Law: Volume and Temperature of an enclosed gas . . . . . . . . . . . 132 The relationship between temperature and pressure . . . . . . . . . . . . . . . . 136 The general gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 The ideal gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Molar volume of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Ideal gases and non-ideal gas behaviour . . . . . . . . . . . . . . . . . . . . . . 146 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 151

9 Organic Molecules - Grade 12 9.1 9.2 9.3 9.4

What is organic chemistry? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Sources of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Unique properties of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Representing organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 152 9.4.1 9.4.2 9.4.3 Molecular formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Structural formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Condensed structural formula . . . . . . . . . . . . . . . . . . . . . . . . 153

9.5 9.6 9.7

Isomerism in organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Functional groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 The Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 9.7.1 9.7.2 9.7.3 9.7.4 9.7.5 9.7.6 9.7.7 9.7.8 9.7.9 The Alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Naming the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Properties of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Reactions of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163 The alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Naming the alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 The properties of the alkenes . . . . . . . . . . . . . . . . . . . . . . . . 169 Reactions of the alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . 169

The Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

9.7.10 Naming the alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 9.8 The Alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 9.8.1 9.8.2 9.9 Naming the alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Physical and chemical properties of the alcohols . . . . . . . . . . . . . . 175

Carboxylic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 9.9.1 9.9.2 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 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 10 Organic Macromolecules - Grade 12

CONTENTS 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
211

11 Physical and Chemical Change - Grade 10

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 ix

CONTENTS 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 De?ning 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 a?ecting 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 x

CONTENTS

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 e?ect of concentration on equilibrium . . . . . . . . . . . . . . . . . 310 16.8.2 The e?ect of temperature on equilibrium . . . . . . . . . . . . . . . . . . 310 16.8.3 The e?ect 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 di?erent 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
355

18 The Water Cycle - Grade 10

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 xi

CONTENTS

CONTENTS

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 ?xation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 19.3 Nitri?cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 19.4 Denitri?cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 19.5 Human In?uences on the Nitrogen Cycle . . . . . . . . . . . . . . . . . . . . . . 372 19.6 The industrial ?xation 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 a?ect 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 xii

CONTENTS

CONTENTS

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 xiii

CONTENTS 23 The Chemical Industry - Grade 12

CONTENTS 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

xiv

Chapter 22

The Atmosphere - Grade 11
Our earth is truly an amazing planet! Not only is it exactly the right distance from the sun to have temperatures that will support life, but it is also one of the only planets to have liquid water on its surface. In addition, our earth has an atmosphere that has just the right composition to allow life to exist. The atmosphere is the layer of gases that surrounds the earth. We may not always be aware of them, but without these gases, life on earth would de?nitely not be possible. The atmosphere provides the gases that animals and plants need for respiration (breathing) and photosynthesis (the production of food), it helps to keep temperatures on earth constant and also protects us from the sun’s harmful radiation. In this chapter, we are going to take a closer look at the chemistry of the earth’s atmosphere and at some of the human activities that threaten the delicate balance that exists in this part of our planet.

22.1

The composition of the atmosphere

Earth’s atmosphere is a mixture of gases. Two important gases are nitrogen and oxygen, which make up about 78.1% and 20.9% of the atmosphere respectively. A third gas, Argon, contributes about 0.9%, and a number of other gases such as carbon dioxide, methane, water vapour, helium and ozone make up the remaining 0.1%. In an earlier chapter, we discussed the importance of nitrogen as a component of proteins, the building blocks of life. Similarly, oxygen is essential for life because it is the gas we need for respiration. We will discuss the importance of some of the other gases later in this chapter.

teresting Interesting Fact Fact
The earth’s early atmosphere was very di?erent from what it is today. When the earth formed around 4.5 billion years ago, there was probably no atmosphere. Some scientists believe that the earliest atmosphere contained gases such as water vapour, carbon dioxide, nitrogen and sulfur which were released from inside the planet as a result of volcanic activity. Many scientists also believe that the ?rst stage in the evolution of life, around 4 billion years ago, needed an oxygen-free environment. At a later stage, these primitive forms of plant life began to release small amounts of oxygen into the atmosphere as a product of photosynthesis. During photosynthesis, plants use carbon dioxide, water and sunlight to produce simple sugars. Oxygen is also released in the process. 6CO2 + 6H2 O + sunlight → C6 H12 O6 + 6O2 This build-up of oxygen in the atmosphere eventually led to the formation of the ozone layer, which helped to ?lter the sun’s harmful UV radiation so that plants were able to ?ourish 421

22.2

CHAPTER 22. THE ATMOSPHERE - GRADE 11

in di?erent environments. As plants became more widespread and photosythesis increased, so did the production of oxygen. The increase in the amount of oxygen in the atmosphere would have allowed more forms of life to exist.

If you have ever had to climb to a very high altitude (altitude means the ’height’ in the atmosphere), you will have noticed that it becomes very di?cult to breathe, and many climbers su?er from ’altitude sickness’ before they reach their destination. This is because the density of gases becomes less as you move higher in the atmosphere. It is gravity that holds the atmosphere close to the earth. As you move higher, this force weakens slightly and so the gas particles become more spread out. In e?ect, when you are at a high altitude, the gases in the atmosphere haven’t changed, but there are fewer oxygen molecules in the same amount of air that you are able to breathe.

De?nition: Earth’s atmosphere The Earth’s atmosphere is a layer of gases that surround the planet, and which are held there by the Earth’s gravity. The atmosphere contains roughly 78.1% nitrogen, 20.9% oxygen, 0.9% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount of water vapour. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

22.2

The structure of the atmosphere

The earth’s atmosphere is divided into di?erent layers, each with its own particular characteristics (?gure 22.1).

22.2.1

The troposphere

The troposphere is the lowest level in the atmosphere, and it is the part in which we live. The troposphere varies in thickness, and extends from the ground to a height of about 7km at the poles and about 18km at the equator. An important characteristic of the troposphere is that its temperature decreases with an increase in altitude. In other words, as you climb higher, it will get colder. You will have noticed this if you have climbed a mountain, or if you have moved from a city at a high altitude to one which is lower; the average temperature is often lower where the altitude is higher. This is because the troposphere is heated from the ’bottom up’. In other words, places that are closer to the Earth’s surface will be warmer than those at higher altitudes. The heating of the atmosphere will be discussed in more detail later in this chapter. The word troposphere comes from the Greek tropos, meaning turning or mixing. The troposphere is the most turbulent part of the atmosphere and is the part where our weather takes place. Weather is the state of the air at a particular place and time e.g. if it is warm or cold, wet or dry, and how cloudy or windy it is. Generally, jet aircraft ?y just above the troposphere to avoid all this turbulence.

22.2.2

The stratosphere

Above the troposphere is another layer called the stratosphere, where most long distance aircraft ?y. The stratosphere extends from altitudes of 10 to 50km. If you have ever been in an aeroplane and have looked out the window once you are well into the ?ight, you will have noticed 422

CHAPTER 22. THE ATMOSPHERE - GRADE 11

22.2

120 110 100 90 80 70 Mesosphere Height (km) 60 50 40 Stratosphere 30 20 10 0 -100 Troposphere Thermosphere

-90

-80

-70

-60

-50 -40 -30 -20 Temperature (? C)

-10

0

10

20

Figure 22.1: A generalised diagram showing the structure of the atmosphere to a height of 110 km that you are actually ?ying above the level of the clouds. As we have already mentioned, clouds and weather occur in the troposphere, whereas the stratosphere has very stable atmospheric conditions and very little turbulence. It is easy to understand why aircraft choose to ?y here! The stratosphere is di?erent from the troposphere because its temperature increases as altitude increases. This is because the stratosphere absorbs solar radiation directly, meaning that the upper layers closer to the sun will be warmer. The upper layers of the stratosphere are also warmer because of the presence of the ozone layer. Ozone (O3 ) is formed when solar radiation splits an oxygen molecule (O2 ) into two atoms of oxygen. Each individual atom is then able to combine with an oxygen molecule to form ozone. The two reactions are shown below: O2 → O + O

O + O2 → O3 The change from one type of molecule to another produces energy, and this contributes to higher temperatures in the upper part of the stratosphere. An important function of the ozone layer is to absorb UV radiation and reduce the amount of harmful radiation that reaches the Earth’s surface.

Extension: CFCs and the ozone layer 423

22.2

CHAPTER 22. THE ATMOSPHERE - GRADE 11 You may have heard people talking about ’the hole in the ozone layer’. What do they mean by this and do we need to be worried about it? Most of the earth’s ozone is found in the stratosphere and this limits the amount of UV radiation that reaches the earth. However, human activities have once again disrupted the chemistry of the atmosphere. Chloro?uorocarbons (CFC’s) are compounds found in aerosol cans, fridges and airconditioners. In aerosol cans, it is the CFC’s that cause the substance to be sprayed outwards. The bad side of CFC’s is that, when they are released into the atmosphere, they break down ozone molecules so that the ozone is no longer able to protect us as much from UV rays. The ’ozone hole’ is actually a thinning of the ozone layer approximately above Antarctica. Let’s take a closer look at the chemical reactions that are involved in breaking down ozone: 1. When CFC’s react with UV radiation, a carbon-chlorine bond in the chloro?uorocarbon breaks and a new compound is formed, with a chlorine atom. CF Cl3 + U V → CF Cl2 + Cl 2. The single chlorine atom reacts with ozone to form a molecule of chlorine monoxide and oxygen gas. In the process, ozone is destroyed. Cl + O3 → ClO + O2

3. The chlorine monoxide then reacts with a free oxygen atom (UV radiation breaks O2 down into single oxygen atoms) to form oxygen gas and a single chlorine atom. ClO + O → Cl + O2 4. The chlorine atom is then free to attack more ozone molecules, and the process continues. A single CFC molecule can destroy 100 000 ozone molecules. One possible consequence of ozone depletion is an increase in the incidence of skin cancer because there is more UV radiation reaching earth’s surface. CFC replacements are now being used to reduce emissions, and scientists are trying to ?nd ways to restore ozone levels in the atmosphere.

22.2.3

The mesosphere

The mesosphere is located about 50-80/85km above Earth’s surface. Within this layer, temperature decreases with increasing altitude. Temperatures in the upper mesosphere can fall as low as -100?C in some areas. Millions of meteors burn up daily in the mesosphere because of collisions with the gas particles that are present in this layer. This leads to a high concentration of iron and other metal atoms.

22.2.4

The thermosphere

The thermosphere exists at altitudes above 80 km. In this part of the atmosphere, ultraviolet (UV) and shorter X-Ray radiation from the sun cause neutral gas atoms to be ionised. At these radiation frequencies, photons from the solar radiation are able to dislodge electrons from neutral atoms and molecules during a collision. A plasma is formed, which consists of negative free electrons and positive ions. This part of the atmosphere is called the ionosphere. At the same time that ionisation takes place however, an opposing process called recombination also begins. Some of the free electrons are drawn to the positive ions, and combine again with them if they are in close enough contact. Since the gas density increases at lower altitudes, the recombination process occurs more often here because the gas molecules and ions are closer together. The 424

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22.2

ionisation process produces energy which means that the upper parts of the thermosphere, which are dominated by ionisation, have a higher temperature than the lower layers where recombination takes place. Overall, temperature in the thermosphere increases with an increase in altitude.

Extension: The ionosphere and radio waves The ionosphere is of practical importance because it allows radio waves to be transmitted. A radio wave is a type of electromagnetic radiation that humans use to transmit information without wires. When using high-frequency bands, the ionosphere is used to re?ect the transmitted radio beam. When a radio wave reaches the ionosphere, the electric ?eld in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio wave energy is given up to this mechanical oscillation. The oscillating electron will then either recombine with a positive ion, or will re-radiate the original wave energy back downward again. The beam returns to the Earth’s surface, and may then be re?ected back into the ionosphere for a second bounce.

teresting Interesting Fact Fact
The ionosphere is also home to the auroras. Auroras are caused by the collision of charged particles (e.g. electrons) with atoms in the earth’s upper atmosphere. Charged particles are energised and so, when they collide with atoms, the atoms also become energised. Shortly afterwards, the atoms emit the energy they have gained, as light. Often these emissions are from oxygen atoms, resulting in a greenish glow (wavelength 557.7 nm) and, at lower energy levels or higher altitudes, a dark red glow (wavelength 630 nm). Many other colours can also be observed. For example, emissions from atomic nitrogen are blue, and emissions from molecular nitrogen are purple. Auroras emit visible light (as described above), and also infra-red, ultraviolet and x-rays, which can be observed from space.

Exercise: The composition of the atmosphere 1. Complete the following summary table by providing the missing information for each layer in the atmosphere. Atmospheric Height (km) Gas composition General characlayer teristics Troposphere 0-18 Turbulent; part of atmosphere where weather occurs Ozone reduces harmful radiation reaching Earth Mesosphere High concentration of metal atoms more than 80 km 2. Use your knowledge of the atmosphere to explain the following statements: 425

22.3

CHAPTER 22. THE ATMOSPHERE - GRADE 11 (a) Athletes who live in coastal areas need to acclimatise if they are competing at high altitudes. (b) Higher incidences of skin cancer have been recorded in areas where the ozone layer in the atmosphere is thin. (c) During a ?ight, turbulence generally decreases above a certain altitude.

22.3
22.3.1

Greenhouse gases and global warming
The heating of the atmosphere

As we mentioned earlier, the distance of the earth from the sun is not the only reason that temperatures on earth are within a range that is suitable to support life. The composition of the atmosphere is also critically important. The earth receives electromagnetic energy from the sun in the visible spectrum. There are also small amounts of infrared and ultraviolet radiation in this incoming solar energy. Most of the radiation is shortwave radiation, and it passes easily through the atmosphere towards the earth’s surface, with some being re?ected before reaching the surface. At the surface, some of the energy is absorbed, and this heats up the earth’s surface. But the situation is a little more complex than this. A large amount of the sun’s energy is re-radiated from the surface back into the atmosphere as infrared radiation, which is invisible. As this radiation passes through the atmosphere, some of it is absorbed by greenhouse gases such as carbon dioxide, water vapour and methane. These gases are very important because they re-emit the energy back towards the surface. By doing this, they help to warm the lower layers of the atmosphere even further. It is this ’re-emission’ of heat by greenhouse gases, combined with surface heating and other processes (e.g. conduction and advection) that maintain temperatures at exactly the right level to support life. Without the presence of greenhouse gases, most of the sun’s energy would be lost and the Earth would be a lot colder than it is! A simpli?ed diagram of the heating of the atmosphere is shown in ?gure 22.2.

22.3.2

The greenhouse gases and global warming

Many of the greenhouse gases occur naturally in small quantities in the atmosphere. However, human activities have greatly increased their concentration, and this has led to a lot of concern about the impact that this could have in increasing global temperatures. This phenomenon is known as global warming. Because the natural concentrations of these gases are low, even a small increase in their concentration as a result of human emissions, could have a big e?ect on temperature. But before we go on, let’s look at where some of these human gas emissions come from. ? Carbon dioxide (CO2 ) Carbon dioxide enters the atmosphere through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of other chemical reactions (e.g. the manufacture of cement). Carbon dioxide can also be removed from the atmosphere when it is absorbed by plants during photosynthesis. ? Methane (CH4 ) Methane is emitted when coal, natural gas and oil are produced and transported. Methane emissions can also come from livestock and other agricultural practices and from the decay of organic waste. 426

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sun

Outgoing long-wave infrared radiation Incoming short-wave solar radiation atmosphere

infrared radiation is absorbed and re-emitted by greenhouse gases in the atmosphere

earth’s surface

Figure 22.2: The heating of the Earth’s atmosphere

? Nitrous oxide (N2 O) Nitrous oxide is emitted by agriculture and industry, and when fossil fuels and solid waste are burned. ? Fluorinated gases (e.g. hydro?uorocarbons, per?uorocarbons, and sulfur hexa?uoride) These gases are all synthetic, in other words they are man-made. They are emitted from a variety of industrial processes. Fluorinated gases are sometimes used in the place of other ozone-depleting substances (e.g. CFC’s). These are very powerful greenhouse gases, and are sometimes referred to as High Global Warming Potential gases (’High GWP gases’). Overpopulation is a major problem in reducing greenhouse gas emissions, and in slowing down global warming. As populations grow, their demands on resources (e.g. energy) increase, and so does their production of greenhouse gases.

Extension: Ice core drilling - Taking a look at earth’s past climate Global warming is a very controversial issue. While many people are convinced that the increase in average global temperatures is directly related to the increase in atmospheric concentrations of carbon dioxide, others argue that the climatic changes we are seeing are part of a natural pattern. One way in which scientists are able to understand what is happening at present, is to understand the earth’s past atmosphere, and the factors that a?ected its temperature. So how, you may be asking, do we know what the earth’s past climate was like? One method that is used is ice core drilling. Antarctica is the coldest continent on earth, and because of this there is very little melting that takes place. Over thousands of years, ice has accumulated in layers and has become more and more compacted as new ice is added. This is partly why Antarctica is also on average one of the highest continents! On average, the ice sheet that covers Antarctica is 2500 m thick, and at its deepest location, is 4700 m thick. 427

22.3

CHAPTER 22. THE ATMOSPHERE - GRADE 11 As the snow is deposited on top of the ice sheet each year, it traps di?erent chemicals and impurities which are dissolved in the ice. The ice and impurities hold information about the Earth’s environment and climate at the time that the ice was deposited. Drilling an ice core from the surface down, is like taking a journey back in time. The deeper into the ice you venture, the older the layer of ice. By analysing the gases and oxygen isotopes that are present (along with many other techniques) in the ice at various points in the earth’s history, scientists can start to piece together a picture of what the earth’s climate must have been like.

Top layers are the most recently deposited Increasing age

Bottom layers are the oldest

One of the most well known ice cores was the one drilled at a Russian station called Vostok in central Antarctica. So far, data has been gathered for dates as far back as 160 000 years!

Activity :: Case Study : Looking at past climatic trends Make sure that you have read the ’Information box’ on ice core drilling before you try this activity. The values in the table below were extrapolated from data obtained by scientists studying the Vostok ice core. ’Local temperature change’ means by how much the temperature at that time was di?erent from what it is today. For example, if the local temperature change 160 000 years ago was -9? C, this means that atmospheric temperatures at that time were 9? C lower than what they are today. ’ppm’ means ’parts per million’ and is a unit of measurement for gas concentrations. 428

CHAPTER 22. THE ATMOSPHERE - GRADE 11 Years before present (x 1000) 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 (1850) Present Questions 1. On the same set of axes, draw graphs to show how temperature and carbon dioxide concentrations have changed over the last 160 000 years. Hint: ’Years before present’ will go on the x-axis, and should be given negative values. 2. Compare the graphs that you have drawn. What do you notice? 3. Is there a relationship between temperature and the atmospheric concentration of carbon dioxide? 4. Do these graphs prove that temperature changes are determined by the concentration of gases such as carbon dioxide in the atmosphere? Explain your answer. 5. What other factors might you need to consider when analysing climatic trends? Local temperature change (? C) -9 -10 -10 -3 +1 -4 -8 -5 -6 -8 -9 -7 -8 -7 -9 -2 -0.5 Carbon dioxide (ppm) 190 205 240 280 278 240 225 230 220 250 190 220 180 225 200 260 280 371

22.3

22.3.3

The consequences of global warming

Activity :: Group Discussion : The impacts of global warming In groups of 3-4, read the following extracts and then answer the questions that follow. By 2050 Warming to Doom Million Species, Study Says By 2050, rising temperatures exacerbated by human-induced belches of carbon dioxide and other greenhouse gases could send more than a million of Earth’s land-dwelling plants and animals down the road to extinction, according to a recent study. ”Climate change now represents at least as great a threat to the number of species surviving on Earth as habitatdestruction and modi?cation,” said Chris Thomas, a conservation biologist at the University of Leeds in the United Kingdom. The researchers worked independently in six biodiversity-rich regions around the world, from Australia to South Africa, plugging ?eld data on species distribution and regional climate into computer models that simulated the 429

22.3

CHAPTER 22. THE ATMOSPHERE - GRADE 11 ways species’ ranges are expected to move in response to temperature and climate changes. According to the researchers’ collective results, the predicted range of climate change by 2050 will place 15 to 35 percent of the 1 103 species studied at risk of extinction. National Geographic News, 12 July 2004 Global Warming May Dry Up Africa’s Rivers, Study Suggests Many climate scientists already predict that less rain will fall annually in parts of Africa within 50 years due to global warming. Now new research suggests that even a small decrease in rainfall on the continent could cause a drastic reduction in river water, the lifeblood for rural populations in Africa. A decrease in water availability could occur across about 25 percent of the continent, according to the new study. Hardest hit would be areas in northwestern and southern Africa, with some of the most serious e?ects striking large areas of Botswana and South Africa. To predict future rainfall, the scientists compared 21 of what they consider to be the best climate change models developed by research teams around the world. On average, the models forecast a 10 to 20% drop in rainfall in northwestern and southern Africa by 2070. With a 20% decrease, Cape Town would be left with just 42% of its river water, and ”Botswana would completely dry up,” de Wit said. In parts of northern Africa, river water levels would drop below 50%. Less river water would have serious implications not just for people but for the many animal species whose habitats rely on regular water supplies. National Geographic News, 3 March 2006 Discussion questions 1. What is meant by ’biodiversity’ ? 2. Explain why global warming is likely to cause a loss of biodiversity. 3. Why do you think a loss of biodiversity is of such concern to conservationists? 4. Suggest some plant or animal species in South Africa that you think might be particularly vulnerable to extinction if temperatures were to rise signi?cantly. Explain why you chose these species. 5. In what way do people, animals and plants rely on river water? 6. What e?ect do you think a 50% drop in river water level in some parts of Africa would have on the people living in these countries? 7. Discuss some of the other likely impacts of global warming that we can expect (e.g. sea level rise, melting of polar ice caps, changes in ocean currents).

22.3.4

Taking action to combat global warming

Global warming is a major concern at present. A number of organisations, panels and research bodies have been working to gather accurate and relevant information so that a true picture of our current situation can be painted. One important orgaisation that you may have heard of is the Intergovernmental Panel on Climate Change (IPCC). The IPCC was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), to evaluate the risk of climate change brought on by humans. You may also have heard of the Kyoto Protocol, which will be discussed a little later.

430

CHAPTER 22. THE ATMOSPHERE - GRADE 11 Activity :: Group Discussion : World carbon dioxide emissions The data in the table below shows carbon dioxide emissions from the consumption of fossil fuels (in million metric tons of carbon dioxide). Region or Country United States Brazil France UK Saudi Arabia Botswana South Africa India World Total Questions 1. Using a coloured pen, highlight those countries that are ’developed’ and those that are ’developing’. 2. Explain why CO2 emissions are so much higher in developed countries than in developing countries. 3. How does South Africa compare to the other developing countries, and also to the developed countries? Carbon dioxide emissions are a major problem worldwide. The Kyoto Protocol was signed in Kyoto, Japan in December 1997. Its main objective was to reduce global greenhouse gas emissions by encouraging countries to become signatories to the guidelines that had been laid out in the protocol. These guidelines set targets for the world’s major producers to reduce their emissions within a certain time. However, some of the worst contributors to greenhouse gas emissions (e.g. USA) were not prepared to sign the protocol, partly because of the potential e?ect this would have on the country’s economy, which relies on industry and other ’high emission’ activities. Panel discussion Form groups with 5 people in each. Each person in the group must adopt one of the following roles during the discussion: ? the owner of a large industry ? an environmental scientist ? an economist ? a politician ? a chairperson for the discussion In your group, you are going to discuss some of the economic and environmental implications for a country that decides to sign the Kyoto Protocol. Each person will have the opportunity to express the view of the character they have adopted. You may ask questions of the other people, or challenge their ideas, provided that you ask permission from the chairperson ?rst. 1980 4754 186 487 608 175 1.26 234 299 18333 1985 4585 187 394 588 179 1.45 298 439 19412 1990 5013 222 368 598 207 2.68 295 588 21426 1995 5292 288 372 555 233 3.44 344 867 22033 2000 5815 345 399 551 288 4.16 378 1000 23851 2004 5912 336 405 579 365 3.83 429 1112 27043

22.4

22.4

Summary

? The atmosphere is the layer of gases that surrounds Earth. These gases are important in sustaining life, regulating temperature and protecting Earth from harmful radiation. ? The gases that make up the atmosphere are nitrogen, oxygen, carbon dioxide and others e.g. water vapour, methane. ? There are four layer in the atmosphere, each with their own characteristics. 431

22.4

CHAPTER 22. THE ATMOSPHERE - GRADE 11

? The troposphere is the lowest layer and here, temperature decreases with an increase in altitude. The troposphere is where weather occurs. ? The next layer is the stratosphere where temperature increases with an increase in altitude because of the presence of ozone in this layer, and the direct heating from the sun. ? The depletion of the ozone layer is largely because of CFC’s, which break down ozone through a series of chemical reactions. ? The mesosphere is characterised by very cold temperatures and meteor collisions. The mesosphere contains high concentrations of metal atoms. ? In the thermosphere, neutral atoms are ionised by UV and X-ray radiation from the sun. Temperature increases with an increase in altitude because of the energy that is released during this ionisation process, which occurs mostly in the upper thermosphere. ? The thermosphere is also known as the ionosphere, and is the part of the atmosphere where radio waves can be transmitted. ? The auroras are bright coloured skies that occur when charged particles collide with atoms in the upper atmosphere. Depending on the type of atom, energy is released as light at di?erent wavelengths. ? The Earth is heated by radiation from the sun. Incoming radiation has a short wavelength and some is absorbed directly by the Earth’s surface. However, a large amount of energy is re-radiated as longwave infrared radiation. ? Greenhouse gases such as carbon dioxide, water vapour and methane absorb infrared radiation and re-emit it back towards the Earth’s surface. In this way, the bottom layers of the atmsophere are kept much warmer than they would be if all the infrared radiation was lost. ? Human activities such as the burning of fossil fuels, increase the concentration of greenhouse gases in the atmosphere and may contribute towards global warming. ? Some of the impacts of global warming include changing climate patterns, rising sea levels and a loss of biodiversity, to name a few. Interventions are needed to reduce this phenomenon.

Exercise: Summary Exercise 1. The atmosphere is a relatively thin layer of gases which support life and provide protection to living organisms. The force of gravity holds the atmosphere against the earth. The diagram below shows the temperatures associated with the various layers that make up the atmosphere and the altitude (height) from the earth’s surface. 432

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22.4

120 110 100 90 80 70 Height (km) 60 50 40 30 20 10 0 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 Temperature (? C) 0 10 20

E

D

C

B

A

(a) Write down the names of the layers A, B and D of the atmosphere. (b) In which one of the layers of the atmosphere is ozone found? (c) Give an explanation for the decrease in temperature as altitude increases in layer A. (d) In layer B, there is a steady increase in temperature as the altitude increases. Write down an explanation for this trend. 2. Planet Earth in Danger It is now accepted that greenhouse gases are to blame for planet earth getting warmer. The increase in the number of sudden ?oods in Asia and droughts in Africa; the rising sea level and increasing average temperatures are global concerns. Without natural greenhouse gases,like carbon dioxide and water vapour,life on earth is not possible. However, the increase in levels of carbon dioxide in the atmosphere since the Industrial Revolution is of great concern. Greater disasters are to come, which will create millions of climate refugees. It is our duty to take action for the sake of future generations who will pay dearly for the wait-and-see attitude of the current generation. Urgent action to reduce waste is needed. Global warming is a global challenge and calls for a global response now, not later. (Adapted from a speech by the French President, Jacques Chirac) (a) How do greenhouse gases, such as carbon dioxide, heat up the earth’s surface? (b) Draw a Lewis structure for the carbon dioxide molecule (c) The chemical bonds within the carbon dioxide molecule are polar. Support this statement by performing a calculation using the table of electronegativities. (d) Classify the carbon dioxide molecule as polar or non-polar. Give a reason for your answer. (e) Suggest ONE way in which YOU can help to reduce the emissions of greenhouse gases. 3. Plants need carbon dioxide (CO2 ) to manufacture food. However, the engines of motor vehicles cause too much carbon dioxide to be released into the atmosphere. (a) State the possible consequence of having too much carbon dioxide in the atmosphere. 433

22.4

CHAPTER 22. THE ATMOSPHERE - GRADE 11 (b) Explain two possible e?ects on humans if the amount of carbon dioxide in the atmosphere becomes too low. (DoE Exemplar Paper Grade 11, 2007)

434

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