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
xiv
Chapter 1
Classification of Matter - Grade 10
All the objects that we see in the world around us, are made of matter. Matter makes up the
air we breathe, the ground we walk on, the food we eat and the animals and plants that live
around us. Even our own human bodies are made of matter!
Different objects can be made of different types of matter, or materials. For example, a cupboard (an object) is made of wood, nails and hinges (the materials). The properties of the
materials will affect the properties of the object. In the example of the cupboard, the strength
of the wood and metals make the cupboard strong and durable. In the same way, the raincoats
that you wear during bad weather, are made of a material that is waterproof. The electrical wires
in your home are made of metal because metals are a type of material that is able to conduct
electricity. It is very important to understand the properties of materials, so that we can use
them in our homes, in industry and in other applications. In this chapter, we will be looking at
different types of materials and their properties.
The diagram below shows one way in which matter can be classified (grouped) according to
its different properties. As you read further in this chapter, you will see that there are also
other ways of classifying materials, for example according to whether they are good electrical
conductors.
MATTER
MIXTURES
Homogeneous
PURE SUBSTANCES
Heterogeneous
Elements
Metals
Magnetic
Compounds
Non-metals
Non-magnetic
Figure 1.1: The classification of matter
1.1
Mixtures
We see mixtures all the time in our everyday lives. A stew, for example, is a mixture of different
foods such as meat and vegetables; sea water is a mixture of water, salt and other substances,
and air is a mixture of gases such as carbon dioxide, oxygen and nitrogen.
5
1.1
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
Definition: Mixture
A mixture is a combination of more than one substance, where these substances are not
bonded to each other.
In a mixture, the substances that make up the mixture:
• are not in a fixed ratio
Imagine, for example, that you have a 250 ml beaker of water. It doesn’t matter whether
you add 20 g, 40 g, 100 g or any other mass of sand to the water; it will still be called a
mixture of sand and water.
• keep their physical properties
In the example we used of the sand and water, neither of these substances has changed in
any way when they are mixed together. Even though the sand is in water, it still has the
same properties as when it was out of the water.
• can be separated by mechanical means
To separate something by ’mechanical means’, means that there is no chemical process
involved. In our sand and water example, it is possible to separate the mixture by simply
pouring the water through a filter. Something physical is done to the mixture, rather than
something chemical.
Some other examples of mixtures include blood (a mixture of blood cells, platelets and plasma),
steel (a mixture of iron and other materials) and the gold that is used to make jewellery. The
gold in jewellery is not pure gold but is a mixture of metals. The carat of the gold gives an idea
of how much gold is in the item.
We can group mixtures further by dividing them into those that are heterogeneous and those
that are homogeneous.
1.1.1
Heterogeneous mixtures
A heterogeneous mixture does not have a definite composition. Think of a pizza, that is a
mixture of cheese, tomato, mushrooms and peppers. Each slice will probably be slightly different
from the next because the toppings like the mushrooms and peppers are not evenly distributed.
Another example would be granite, a type of rock. Granite is made up of lots of different mineral
substances including quartz and feldspar. But these minerals are not spread evenly through the
rock and so some parts of the rock may have more quartz than others. Another example is
a mixture of oil and water. Although you may add one substance to the other, they will stay
separate in the mixture. We say that these heterogeneous mixtures are non-uniform, in other
words they are not exactly the same throughout.
Definition: Heterogeneous mixture
A heterogeneous mixture is one that is non-uniform, and where the different components
of the mixture can be seen.
1.1.2
Homogeneous mixtures
A homogeneous mixture has a definite composition, and specific properties. In a homogeneous
mixture, the different parts cannot be seen. A solution of salt dissolved in water is an example
of a homogeneous mixture. When the salt dissolves, it will spread evenly through the water so
that all parts of the solution are the same, and you can no longer see the salt as being separate
from the water. Think also of a powdered drink that you mix with water. Provided you give the
container a good shake after you have added the powder to the water, the drink will have the
same sweet taste for anyone who drinks it, it won’t matter whether they take a sip from the top
6
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.1
or from the bottom. The air we breathe is another example of a homogeneous mixture since it is
made up of different gases which are in a constant ratio, and which can’t be distinguished from
each other.
Definition: Homogeneous mixture
A homogeneous mixture is one that is uniform, and where the different components of the
mixture cannot be seen.
An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal,
where the resulting material has metallic properties. Alloys are usually made to improve on the
properties of the elements that make them up. Steel for example, is much stronger than iron,
which is its main component.
1.1.3
Separating mixtures
Sometimes it is important to be able to separate a mixture. There are lots of different ways to
do this. These are some examples:
• Filtration
A piece of filter paper in a funnel can be used to separate a mixture of sand and water.
• Heating / evaporation
Sometimes, heating a solution causes the water to evaporate, leaving the other part of the
mixture behind. You can try this using a salt solution.
• Centrifugation
This is a laboratory process which uses the centrifugal force of spinning objects to separate
out the heavier substances from a mixture. This process is used to separate the cells and
plasma in blood. When the test tubes that hold the blood are spun round in the machine,
the heavier cells sink to the bottom of the test tube. Can you think of a reason why it
might be important to have a way of separating blood in this way?
• Dialysis
This is an interesting way of separating a mixture because it can be used in some important
applications. Dialysis works using a process called diffusion. Diffusion takes place when
one substance in a mixture moves from an area where it has a high concentration to an
area where its concentration is lower. This movement takes place across a semi-permeable
membrane. A semi-permeable membrane is a barrier that lets some things move across it,
but not others. This process is very important for people whose kidneys are not functioning
properly, an illness called renal failure.
teresting Normally, healthy kidneys remove waste products from the blood. When a person
Interesting
Fact
Fact
has renal failure, their kidneys cannot do this any more, and this can be lifethreatening. Using dialysis, the blood of the patient flows on one side of a
semi-permeable membrane. On the other side there will be a fluid that has no
waste products but lots of other important substances such as potassium ions
(K + ) that the person will need. Waste products from the blood diffuse from
where their concentration is high (i.e. in the person’s blood) into the ’clean’
fluid on the other side of the membrane. The potassium ions will move in the
opposite direction from the fluid into the blood. Through this process, waste
products are taken out of the blood so that the person stays healthy.
7
1.1
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
Activity :: Investigation : The separation of a salt solution
Aim:
To demonstrate that a homogeneous salt solution can be separated using physical
methods.
Apparatus:
glass beaker, salt, water, retort stand, bunsen burner.
Method:
1. Pour a small amount of water (about 20 ml) into a beaker.
2. Measure a teaspoon of salt and pour this into the water.
3. Stir until the salt dissolves completely. This is now called a salt solution. This
salt solution is a homogeneous mixture.
4. Place the beaker on a retort stand over a bunsen burner and heat gently. You
should increase the heat until the water almost boils.
5. Watch the beaker until all the water has evaporated. What do you see in the
beaker?
H2 O
salt
solution
water evaporates
when the solution
is heated
salt crystals
remain at the
bottom of the beaker
stand
bunsen
burner
Results:
The water evaporates from the beaker and tiny grains of salt remain at the
bottom.
Conclusion:
The sodium chloride solution, which was a homogeneous mixture of salt and
water, has been separated using heating and evaporation.
Activity :: Discussion : Separating mixtures
Work in groups of 3-4
Imagine that you have been given a container which holds a mixture of sand,
iron filings (small pieces of iron metal), salt and small stones of different sizes. Is
this a homogeneous or a heterogeneous mixture? In your group, discuss how you
would go about separating this mixture into the four materials that it contains.
8
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.2
Exercise: Mixtures
1. Which of the following subtances are mixtures?
(a)
(b)
(c)
(d)
(e)
(f)
tap water
brass (an alloy of copper and zinc)
concrete
aluminium
Coca cola
distilled water
2. In each of the examples above, say whether the mixture is homogeneous or
heterogeneous
1.2
Pure Substances: Elements and Compounds
Any material that is not a mixture, is called a pure substance. Pure substances include elements
and compounds. It is much more difficult to break down pure substances into their parts, and
complex chemical methods are needed to do this.
1.2.1
Elements
An element is a chemical substance that can’t be divided or changed into other chemical
substances by any ordinary chemical means. The smallest unit of an element is the atom.
Definition: Element
An element is a substance that cannot be broken down into other substances through
chemical means.
There are 109 known elements. Most of these are natural, but some are man-made. The
elements we know are represented in the Periodic Table of the Elements, where each element
is abbreviated to a chemical symbol. Examples of elements are magnesium (Mg), hydrogen (H),
oxygen (O) and carbon (C). On the Periodic Table you will notice that some of the abbreviations
do not seem to match the elements they represent. The element iron, for example, has the
chemical formula Fe. This is because the elements were originally given Latin names. Iron has
the abbreviation Fe because its Latin name is ’ferrum’. In the same way, sodium’s Latin name
is ’natrium’ (Na) and gold’s is ’aurum’ (Au).
1.2.2
Compounds
A compound is a chemical substance that forms when two or more elements combine in a fixed
ratio. Water (H2 O), for example, is a compound that is made up of two hydrogen atoms for
every one oxygen atom. Sodium chloride (NaCl) is a compound made up of one sodium atom
for every chlorine atom. An important characteristic of a compound is that it has a chemical
formula, which describes the ratio in which the atoms of each element in the compound occur.
Definition: Compound
A substance made up of two or more elements that are joined together in a fixed ratio.
Diagram 1.2 might help you to understand the difference between the terms element, mixture
and compound. Iron (Fe) and sulfur (S) are two elements. When they are added together, they
9
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
Fe
A mixture of iron and sulfur
S
Fe S
S
An atom
of the element iron
(Fe)
S
S
S
Fe
Fe
Fe
Fe
Fe
Fe
S
S
Fe
S
S
Fe
Fe
S
An atom
of the element sulfur (S)
Fe S
1.3
The compound iron sulfide
(FeS)
Figure 1.2: Understanding the difference between a mixture and a compound
form a mixture or iron and sulfur. The iron and sulfur are not joined together. However, if
the mixture is heated, a new compound is formed, which is called iron sulfide (FeS). In this
compound, the iron and sulfur are joined to each other in a ratio of 1:1. In other words, one
atom of iron is joined to one atom of sulfur in the compound iron sulfide.
Exercise: Elements, mixtures and compounds
1. In the following table, tick whether each of the substances listed is a mixture
or a pure substance. If it is a mixture, also say whether it is a homogeneous or
heterogeneous mixture.
Substance
Mixture or pure
Homogeneous
heterogeneous
mixture
or
fizzy colddrink
steel
oxygen
iron filings
smoke
limestone (CaCO3 )
2. In each of the following cases, say whether the substance is an element, a
mixture or a compound.
(a)
(b)
(c)
(d)
(e)
1.3
Cu
iron and sulfur
Al
H2 SO4
SO3
Giving names and formulae to substances
It is easy to describe elements and mixtures. But how are compounds named? In the example
of iron sulfide that was used earlier, which element is named first, and which ’ending’ is given
to the compound name (in this case, the ending is -ide)?
The following are some guidelines for naming compounds:
10
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.3
1. The compound name will always include the names of the elements that are part of it.
• A compound of iron (Fe) and sulfur (S) is iron sulf ide (FeS)
• A compound of potassium (K) and bromine (S) is potassium bromide (KBr)
• A compound of sodium (Na) and chlorine (Cl) is sodium chlor ide (NaCl)
2. In a compound, the element that is to the left and lower down on the Periodic Table,
is used first when naming the compound. In the example of NaCl, sodium is a group 1
element on the left hand side of the table, while chlorine is in group 7 on the right of the
table. Sodium therefore comes first in the compound name. The same is true for FeS and
KBr.
3. The symbols of the elements can be used to represent compounds e.g. FeS, NaCl and
KBr. These are called chemical formulae. In these three examples, the ratio of the
elements in each compound is 1:1. So, for FeS, there is one atom of iron for every atom
of sulfur in the compound.
4. A compound may contain compound ions. Some of the more common compound ions
and their names are shown below.
Name of compound ion
Carbonate
sulphate
Hydroxide
Ammonium
Nitrate
Hydrogen carbonate
Phosphate
Chlorate
Cyanide
Chromate
Permanganate
formula
CO3 2−
SO4 2−
OH−
NH4 +
NO3 −
HCO3 −
PO4 3−
ClO3 −
CN−
CrO4 2−
MnO4 −
5. When there are only two elements in the compound, the compound is often given a suffix
(ending) of -ide. You would have seen this in some of the examples we have used so far.
When a non-metal is combined with oxygen to form a negative ion (anion) which then
combines with a positive ion (cation) from hydrogen or a metal, then the suffix of the
name will be ...ate or ...ite. NO−
3 for example, is a negative ion, which may combine with
a cation such as hydrogen (HNO3 ) or a metal like potassium (KNO3 ). The NO−
3 anion
has the name nitrate. SO3 in a formula is sulphite, e.g. sodium sulphite (Na2 SO3 ). SO4
is sulphate and PO4 is phosphate.
6. Prefixes can be used to describe the ratio of the elements that are in the compound. You
should know the following prefixes: ’mono’ (one), ’di’ (two) and ’tri’ (three).
• CO (carbon monoxide) - There is one atom of oxygen for every one atom of carbon
• N O2 (nitrogen dioxide) - There are two atoms of oxygen for every one atom of
nitrogen
• SO3 (sulfur trioxide) - There are three atoms of oxygen for every one atom of sulfur
Important:
When numbers are written as ’subscripts’ in compounds (i.e. they are written below the
element symbol), this tells us how many atoms of that element there are in relation to other
elements in the compound. For example in nitrogen dioxide (NO2 ) there are two oxygen
atoms for every one atom of nitrogen. In sulfur trioxide (SO3 ), there are three oxygen atoms
for every one atom of sulfur in the compound. Later, when we start looking at chemical
equations, you will notice that sometimes there are numbers before the compound name.
For example, 2H2 O means that there are two molecules of water, and that in each molecule
there are two hydrogen atoms for every one oxygen atom.
11
1.3
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
Exercise: Naming compounds
1. The formula for calcium carbonate is CaCO3 .
(a) Is calcium carbonate a mixture or a compound? Give a reason for your
answer.
(b) What is the ratio of Ca:C:O atoms in the formula?
2. Give the name of each of the following substances.
(a)
(b)
(c)
(d)
(e)
(f)
KBr
HCl
KMnO4
NO2
NH4 OH
Na2 SO4
3. Give the chemical formula for each of the following compounds.
(a)
(b)
(c)
(d)
(e)
potassium nitrate
sodium iodide
barium sulphate
nitrogen dioxide
sodium monosulphate
4. Refer to the diagram below, showing sodium chloride and water, and then
answer the questions that follow.
(a)
(b)
(c)
(d)
What is the chemical formula for water?
What is the chemical formula for sodium chloride?
Label the water and sodium chloride in the diagram.
Which of the following statements most accurately describes the picture?
i. The picture shows a mixture of an element and a compound
ii. The picture shows a mixture of two compounds
iii. The picture shows two compounds that have been chemically bonded
to each other
5. What is the formula of this molecule?
H
H
H
A
B
C
D
C
C
H
H
C6 H2 O
C2 H6 O
2C6HO
2 CH6 O
12
O
H
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.4
1.4
Metals, Semi-metals and Non-metals
The elements in the Periodic Table can also be divided according to whether they are metals,
semi-metals or non-metals. On the right hand side of the Periodic Table is a dark ’zigzag’ line.
This line separates all the elements that are metals from those that are non-metals. Metals are
found on the left of the line, and non-metals are those on the right. Metals, semi-metals and
non-metals all have their own specific properties.
1.4.1
Metals
Examples of metals include copper (Cu), zinc (Zn), gold (Au) and silver (Ag). On the Periodic
Table, the metals are on the left of the zig-zag line. There are a large number of elements that
are metals. The following are some of the properties of metals:
• Thermal conductors
Metals are good conductors of heat and are therefore used in cooking utensils such as pots
and pans.
• Electrical conductors
Metals are good conductors of electricity, and are therefore used in electrical conducting
wires.
• Shiny metallic lustre
Metals have a characteristic shiny appearance and are often used to make jewellery.
• Malleable
This means that they can be bent into shape without breaking.
• Ductile
Metals can stretched into thin wires such as copper, which can then be used to conduct
electricity.
• Melting point
Metals usually have a high melting point and can therefore be used to make cooking pots
and other equipment that needs to become very hot, without being damaged.
You can see how the properties of metals make them very useful in certain applications.
Activity :: Group Work : Looking at metals
1. Collect a number of metal items from your home or school. Some examples
are listed below:
•
•
•
•
•
•
hammer
electrical wiring
cooking pots
jewellery
burglar bars
coins
2. In groups of 3-4, combine your collection of metal objects.
3. What is the function of each of these objects?
4. Discuss why you think metal was used to make each object. You should consider
the properties of metals when you answer this question.
13
1.5
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.4.2
Non-metals
In contrast to metals, non-metals are poor thermal conductors, good electrical insulators (meaning that they do not conduct electrical charge) and are neither malleable nor ductile. The
non-metals are found on the right hand side of the Periodic Table, and include elements such as
sulfur (S), phosphorus (P), nitrogen (N) and oxygen (O).
1.4.3
Semi-metals
Semi-metals have mostly non-metallic properties. One of their distinguishing characteristics is
that their conductivity increases as their temperature increases. This is the opposite of what
happens in metals. The semi-metals include elements such as silicon (Si) and germanium (Ge).
Notice where these elements are positioned in the Periodic Table.
1.5
Electrical conductors, semi-conductors and insulators
An electrical conductor is a substance that allows an electrical current to pass through it.
Many electrical conductors are metals, but non-metals can also be good conductors. Copper is
one of the best electrical conductors, and this is why it is used to make conducting wire. In
reality, silver actually has an even higher electrical conductivity than copper, but because silver
is so expensive, it is not practical to use it for electrical wiring because such large amounts are
needed. In the overhead power lines that we see above us, aluminium is used. The aluminium
usually surrounds a steel core which adds tensile strength to the metal so that it doesn’t break
when it is stretched across distances. Occasionally gold is used to make wire, not because it is
a particularly good conductor, but because it is very resistant to surface corrosion. Corrosion is
when a material starts to deteriorate at the surface because of its reactions with the surroundings, for example oxygen and water in the air.
An insulator is a non-conducting material that does not carry any charge. Examples of insulators
would be plastic and wood. Do you understand now why electrical wires are normally covered
with plastic insulation? Semi-conductors behave like insulators when they are cold, and like
conductors when they are hot. The elements silicon and germanium are examples of semiconductors.
Definition: Conductors and insulators
A conductor allows the easy movement or flow of something such as heat or electrical charge
through it. Insulators are the opposite to conductors because they inhibit or reduce the flow
of heat, electrical charge, sound etc through them.
Activity :: Experiment : Electrical conductivity
Aim:
To investigate the electrical conductivity of a number of substances
Apparatus:
• two or three cells
• light bulb
• crocodile clips
• wire leads
• a selection of test substances (e.g. a piece of plastic, aluminium can, metal
pencil sharpener, metal magnet, wood, chalk).
14
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.6
light bulb
battery
test substance
X
crocodile clip
Method:
1. Set up the circuit as shown above, so that the test substance is held between
the two crocodile clips. The wire leads should be connected to the cells and
the light bulb should also be connected into the circuit.
2. Place the test substances one by one between the crocodile clips and see what
happens to the light bulb.
Results:
Record your results in the table below:
Test substance
Metal/non-metal
Does
glow?
bulb
Conductor or
insulator
Conclusions:
In the substances that were tested, the metals were able to conduct electricity
and the non-metals were not. Metals are good electrical conductors and non-metals
are not.
1.6
Thermal Conductors and Insulators
A thermal conductor is a material that allows energy in the form of heat, to be transferred
within the material, without any movement of the material itself. An easy way to understand
this concept is through a simple demonstration.
Activity :: Demonstration : Thermal conductivity
Aim:
To demonstrate the ability of different substances to conduct heat.
Apparatus:
15
1.6
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
You will need two cups (made from the same material e.g. plastic); a metal
spoon and a plastic spoon.
Method:
• Pour boiling water into the two cups so that they are about half full.
• At the same time, place a metal spoon into one cup and a plastic spoon in the
other.
• Note which spoon heats up more quickly
Results:
The metal spoon heats up more quickly than the plastic spoon. In other words,
the metal conducts heat well, but the plastic does not.
Conclusion:
Metal is a good thermal conductor, while plastic is a poor thermal conductor.
This explains why cooking pots are metal, but their handles are often plastic or
wooden. The pot itself must be metal so that heat from the cooking surface can
heat up the pot to cook the food inside it, but the handle is made from a poor
thermal conductor so that the heat does not burn the hand of the person who is
cooking.
An insulator is a material that does not allow a transfer of electricity or energy. Materials that
are poor thermal conductors can also be described as being good insulators.
teresting Water is a better thermal conductor than air and conducts heat away from the
Interesting
Fact
Fact
body about 20 times more efficiently than air. A person who is not wearing
a wetsuit, will lose heat very quickly to the water around them and can be
vulnerable to hypothermia. Wetsuits help to preserve body heat by trapping a
layer of water against the skin. This water is then warmed by body heat and acts
as an insulator. Wetsuits are made out of closed-cell, foam neoprene. Neoprene
is a synthetic rubber that contains small bubbles of nitrogen gas when made for
use as wetsuit material. Nitrogen gas has very low thermal conductivity, so it
does not allow heat from the body (or the water trapped between the body and
the wetsuit) to be lost to the water outside of the wetsuit. In this way a person
in a wetsuit is able to keep their body temperature much higher than they would
otherwise.
Activity :: Investigation : A closer look at thermal conductivity
Look at the table below, which shows the thermal conductivity of a number
of different materials, and then answer the questions that follow. The higher the
number in the second column, the better the material is at conducting heat (i.e. it is
a good thermal conductor). Remember that a material that conducts heat efficiently,
will also lose heat more quickly than an insulating material.
16
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
Material
Silver
Stainless steel
Standard glass
Concrete
Red brick
Water
Snow
Wood
Polystyrene
Air
1.7
Thermal Conductivity (W/m/K)
429
16
1.05
0.9 - 2
0.69
0.58
0.5 - 0.25
0.04 - 0.12
0.03
0.024
Use this information to answer the following questions:
1. Name two materials that are good thermal conductors.
2. Name two materials that are good insulators.
3. Explain why:
(a) cooler boxes are often made of polystyrene
(b) homes that are made from wood need less internal heating during the
winter months.
(c) igloos (homes made from snow) are so good at maintaining warm temperatures, even in freezing conditions.
teresting It is a known fact that well-insulated buildings need less energy for heating than
Interesting
Fact
Fact
do buildings that have no insulation. Two building materials that are being used
more and more worldwide, are mineral wool and polystyrene. Mineral wool
is a good insulator because it holds air still in the matrix of the wool so that
heat is not lost. Since air is a poor conductor and a good insulator, this helps
to keep energy within the building. Polystyrene is also a good insulator and is
able to keep cool things cool and hot things hot! It has the added advantage of
being resistant to moisture, mould and mildew.
Remember that concepts such as conductivity and insulation are not only relevant in the building,
industrial and home environments. Think for example of the layer of blubber or fat that we find
in animals. In very cold environments, fat and blubber not only provide protection, but also act
as an insulator to help the animal to keep its body temperature at the right level. This is known
as thermoregulation.
1.7
Magnetic and Non-magnetic Materials
We have now looked at a number of ways in which matter can be grouped, such as into metals,
semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and
insulators. One way in which we can further group metals, is to divide them into those that are
magnetic and those that are non-magnetic.
Definition: Magnetism
Magnetism is one of the phenomena by which materials exert attractive or repulsive forces
on other materials.
17
1.8
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
A metal is said to be ferromagnetic if it can be magnetised (i.e. made into a magnet). If you
hold a magnet very close to a metal object, it may happen that its own electrical field will be
induced and the object becomes magnetic. Some metals keep their magnetism for longer than
others. Look at iron and steel for example. Iron loses its magnetism quite quickly if it is taken
away from the magnet. Steel on the other hand will stay magnetic for a longer time. Steel is
often used to make permanent magnets that can be used for a variety of purposes.
Magnets are used to sort the metals in a scrap yard, in compasses to find direction, in the magnetic strips of video tapes and ATM cards where information must be stored, in computers and
TV’s, as well as in generators and electric motors.
Activity :: Investigation : Magnetism
You can test whether an object is magnetic or not by holding another magnet
close to it. If the object is attracted to the magnet, then it too is magnetic.
Find some objects in your classroom or your home and test whether they are
magnetic or not. Then complete the table below:
Object
Magnetic
magnetic
or
non-
Activity :: Group Discussion : Properties of materials
In groups of 4-5, discuss how our knowledge of the properties of materials has
allowed society to:
• develop advanced computer technology
• provide homes with electricity
• find ways to conserve energy
1.8
Summary
• All the objects and substances that we see in the world are made of matter.
• This matter can be classified according to whether it is a mixture or a pure substance.
• A mixture is a combination of one or more substances that are not chemically bonded
to each other. Examples of mixtures are air (a mixture of different gases) and blood (a
mixture of cells, platelets and plasma).
• The main characteristics of mixtures are that the substances that make them up are not
in a fixed ratio, they keep their individual properties and they can be separated from each
other using mechanical means.
18
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
1.8
• A heterogeneous mixture is non-uniform and the different parts of the mixture can be
seen. An example would be a mixture of sand and salt.
• A homogeneous mixture is uniform, and the different components of the mixture can’t
be seen. An example would be a salt solution. A salt solution is a mixture of salt and
water. The salt dissolves in the water, meaning that you can’t see the individual salt
particles. They are interspersed between the water molecules. Another example is a metal
alloy such as steel.
• Mixtures can be separated using a number of methods such as filtration, heating, evaporation, centrifugation and dialysis.
• Pure substances can be further divided into elements and compounds.
• An element is a substance that can’t be broken down into simpler substances through
chemical means.
• All the elements are recorded in the Periodic Table of the Elements. Each element has
its own chemical symbol. Examples are iron (Fe), sulfur (S), calcium (Ca), magnesium
(Mg) and fluorine (F).
• A compound is a substance that is made up of two or more elements that are chemically
bonded to each other in a fixed ratio. Examples of compounds are sodium chloride (NaCl),
iron sulfide (FeS), calcium carbonate (CaCO3 ) and water (H2 O).
• When naming compounds and writing their chemical formula, it is important to know
the elements that are in the compound, how many atoms of each of these elements will
combine in the compound and where the elements are in the Periodic Table. A number of
rules can then be followed to name the compound.
• Another way of classifying matter is into metals (e.g. iron, gold, copper), semi-metals
(e.g. silicon and germanium) and non-metals (e.g. sulfur, phosphorus and nitrogen).
• Metals are good electrical and thermal conductors, they have a shiny lustre, they are
malleable and ductile, and they have a high melting point. These properties make metals
very useful in electrical wires, cooking utensils, jewellery and many other applications.
• A further way of classifying matter is into electrical conductors, semi-conductors and
insulators.
• An electrical conductor allows an electrical current to pass through it. Most metals are
good electrical conductors.
• An electrical insulator is not able to carry an electrical current. Examples are plastic,
wood, cotton material and ceramic.
• Materials may also be classified as thermal conductors or thermal insulators depending
on whether or not they are able to conduct heat.
• Materials may also be either magnetic or non-magnetic.
Exercise: Summary
1. For each of the following multiple choice questions, choose one correct answer
from the list provided.
A Which of the following can be classified as a mixture:
i. sugar
ii. table salt
iii. air
iv. Iron
B An element can be defined as:
19
1.8
CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10
i. A substance that cannot be separated into two or more substances by
ordinary chemical (or physical) means
ii. A substance with constant composition
iii. A substance that contains two or more substances, in definite proportion by weight
iv. A uniform substance
2. Classify each of the following substances as an element, a compound, a solution(homogeneous mixture), or a heterogeneous mixture: salt, pure water, soil,
salt water, pure air, carbon dioxide, gold and bronze
3. Look at the table below. In the first column (A) is a list of substances. In the
second column (B) is a description of the group that each of these substances
belongs in. Match up the substance in Column A with the description in
Column B.
Column A
iron
H2 S
sugar solution
sand and stones
steel
Column B
a compound containing 2 elements
a heterogeneous mixture
a metal alloy
an element
a homogeneous mixture
4. You are given a test tube that contains a mixture of iron filings and sulfur. You
are asked to weigh the amount of iron in the sample.
a Suggest one method that you could use to separate the iron filings from
the sulfur.
b What property of metals allows you to do this?
5. Given the following descriptions, write the chemical formula for each of the
following substances:
a silver metal
b a compound that contains only potassium and bromine
c a gas that contains the elements carbon and oxygen in a ratio of 1:2
6. Give the names of each of the following compounds:
a NaBr
b BaSO4
c SO2
7. For each of the following materials, say what properties of the material make
it important in carrying out its particular function.
a
b
c
d
e
f
tar on roads
iron burglar bars
plastic furniture
metal jewellery
clay for building
cotton clothing
20
APPENDIX A. GNU FREE DOCUMENTATION LICENSE
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APPENDIX A. GNU FREE DOCUMENTATION LICENSE
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