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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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
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23 The Chemical Industry - Grade 12
435
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2 Sasol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2.1 Sasol today: Technology and production . . . . . . . . . . . . . . . . . . 436
23.2.2 Sasol and the environment . . . . . . . . . . . . . . . . . . . . . . . . . 440
23.3 The Chloralkali Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
23.3.1 The Industrial Production of Chlorine and Sodium Hydroxide . . . . . . . 442
23.3.2 Soaps and Detergents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
23.4 The Fertiliser Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.1 The value of nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.2 The Role of fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.3 The Industrial Production of Fertilisers . . . . . . . . . . . . . . . . . . . 451
23.4.4 Fertilisers and the Environment: Eutrophication . . . . . . . . . . . . . . 454
23.5 Electrochemistry and batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.1 How batteries work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.2 Battery capacity and energy . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.3 Lead-acid batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.4 The zinc-carbon dry cell . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
23.5.5 Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . 460
23.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
A GNU Free Documentation License
467
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Chapter 10
Organic Macromolecules - Grade
12
As its name suggests, a macromolecule is a large molecule that forms when lots of smaller
molecules are joined together. In this chapter, we will be taking a closer look at the structure
and properties of different macromolecules, and at how they form.
10.1
Polymers
Some macromolecules are made up of lots of repeating structural units called monomers. To
put it more simply, a monomer is like a building block. When lots of similar monomers are joined
together by covalent bonds, they form a polymer. In an organic polymer, the monomers would
be joined by the carbon atoms of the polymer ’backbone’. A polymer can also be inorganic, in
which case there may be atoms such as silicon in the place of carbon atoms. The key feature
that makes a polymer different from other macromolecules, is the repetition of identical or similar
monomers in the polymer chain. The examples shown below will help to make these concepts
clearer.
Definition: Polymer
Polymer is a term used to describe large molecules consisting of repeating structural units,
or monomers, connected by covalent chemical bonds.
1. Polyethene
Chapter 9 looked at the structure of a group of hydrocarbons called the alkenes. One
example is the molecule ethene. The structural formula of ethene is is shown in figure
10.1. When lots of ethene molecules bond together, a polymer called polyethene is
formed. Ethene is the monomer which, when joined to other ethene molecules, forms the
polymer polyethene. Polyethene is a cheap plastic that is used to make plastic bags and
bottles.
(a)
H
H
C
H
(b)
C
H
H
H
H
H
C
C
C
C
H
H
H
H
Figure 10.1: (a) Ethene monomer and (b) polyethene polymer
185
10.2
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
A polymer may be a chain of thousands of monomers, and so it is impossible to draw
the entire polymer. Rather, the structure of a polymer can be condensed and represented
as shown in figure 10.2. The monomer is enclosed in brackets and the ’n’ represents the
number of ethene molecules in the polymer, where ’n’ is any whole number. What this
shows is that the ethene monomer is repeated an indefinite number of times in a molecule
of polyethene.
n
H
H
C
C
H
H
Figure 10.2: A simplified representation of a polyethene molecule
2. Polypropene
Another example of a polymer is polypropene (fig 10.3). Polypropene is also a plastic, but
is stronger than polyethene and is used to make crates, fibres and ropes. In this polymer,
the monomer is the alkene called propene.
(a)
CH3
H
C
H
C
H
(b)
CH3
H
CH3
H
C
C
C
C
H
H
H
H
CH3
H
C
C
H
H
or n
Figure 10.3: (a) Propene monomer and (b) polypropene polymer
10.2
How do polymers form?
Polymers are formed through a process called polymerisation, where monomer molecules react together to form a polymer chain. Two types of polymerisation reactions are addition
polymerisation and condensation polymerisation.
Definition: Polymerisation
In chemistry, polymerisation is a process of bonding monomers, or single units together
through a variety of reaction mechanisms to form longer chains called polymers.
10.2.1
Addition polymerisation
In this type of reaction, monomer molecules are added to a growing polymer chain one at a time.
No small molecules are eliminated in the process. An example of this type of reaction is the
formation of polyethene from ethene (fig 10.1). When molecules of ethene are joined to each
other, the only thing that changes is that the double bond between the carbon atoms in each
ethene monomer is replaced by a single bond so that a new carbon-carbon bond can be formed
with the next monomer in the chain. In other words, the monomer is an unsaturated compound
which, after an addition reaction, becomes a saturated compound.
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Extension: Initiation, propagation and termination
There are three stages in the process of addition polymerisation. Initiation refers
to a chemical reaction that triggers off another reaction. In other words, initiation
is the starting point of the polymerisation reaction. Chain propagation is the part
where monomers are continually added to form a longer and longer polymer chain.
During chain propagation, it is the reactive end groups of the polymer chain that
react in each propagation step, to add a new monomer to the chain. Once a monomer
has been added, the reactive part of the polymer is now in this last monomer unit
so that propagation will continue. Termination refers to a chemical reaction that
destroys the reactive part of the polymer chain so that propagation stops.
Worked Example 48: Polymerisation reactions
Question: A polymerisation reaction takes place and the following polymer is
formed:
n
W
X
C
C
Y
Z
Note: W, X, Y and Z could represent a number of different atoms or combinations
of atoms e.g. H, F, Cl or CH3 .
1. Give the structural formula of the monomer of this polymer.
2. To what group of organic compounds does this monomer belong?
3. What type of polymerisation reaction has taken place to join these monomers
to form the polymer?
Answer
Step 1 : Look at the structure of the repeating unit in the polymer to
determine the monomer.
The monomer is:
W
X
C
C
Y
Z
Step 2 : Look at the atoms and bonds in the monomer to determine which
group of organic compounds it belongs to.
The monomer has a double bond between two carbon atoms. The monomer must
be an alkene.
Step 3 : Determine the type of polymerisation reaction.
In this example, unsaturated monomers combine to form a saturated polymer. No
atoms are lost or gained for the bonds between monomers to form. They are simply
added to each other. This is an addition reaction.
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10.2
10.2
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.2.2
Condensation polymerisation
In this type of reaction, two monomer molecules form a covalent bond and a small molecule such
as water is lost in the bonding process. Nearly all biological reactions are of this type. Polyester
and nylon are examples of polymers that form through condensation polymerisation.
1. Polyester
Polyesters are a group of polymers that contain the ester functional group in their main
chain. Although there are many forms of polyesters, the term polyester usually refers to
polyethylene terephthalate (PET). PET is made from ethylene glycol (an alcohol) and
terephthalic acid (an acid). In the reaction, a hydrogen atom is lost from the alcohol, and
a hydroxyl group is lost from the carboxylic acid. Together these form one water molecule
which is lost during condensation reactions. A new bond is formed between an oxygen
and a carbon atom. This bond is called an ester linkage. The reaction is shown in figure
10.4.
(a)
CH2 CH2
HO
+
OH
HO
ethylene glycol
O
O
C
C
terephthalic acid
H2 O molecule lost
(b)
HO
CH2 CH2
O
O
O
C
C
OH
ester linkage
Figure 10.4: An acid and an alcohol monomer react (a) to form a molecule of the polyester
’polyethylene terephthalate’ (b).
Polyesters have a number of characteristics which make them very useful. They are resistant to stretching and shrinking, they are easily washed and dry quickly, and they are
resistant to mildew. It is for these reasons that polyesters are being used more and more
in textiles. Polyesters are stretched out into fibres and can then be made into fabric and
articles of clothing. In the home, polyesters are used to make clothing, carpets, curtains,
sheets, pillows and upholstery.
teresting Polyester is not just a textile. Polyethylene terephthalate is in fact a plastic
Interesting
Fact
Fact
which can also be used to make plastic drink bottles. Many drink bottles
are recycled by being reheated and turned into polyester fibres. This type
of recycling helps to reduce disposal problems.
2. Nylon
Nylon was the first polymer to be commercially successful. Nylon replaced silk, and was
used to make parachutes during World War 2. Nylon is very strong and resistant, and is
used in fishing line, shoes, toothbrush bristles, guitar strings and machine parts to name
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.2
just a few. Nylon is formed from the reaction of an amine (1,6-diaminohexane) and an acid
monomer (adipic acid) (figure 10.5). The bond that forms between the two monomers is
called an amide linkage. An amide linkage forms between a nitrogen atom in the amine
monomer and the carbonyl group in the carboxylic acid.
(a)
H
H
N
H
(CH2 )4
N
O
+
H
HO
C
O
(CH2 )4
C
OH
H2 O molecule is lost
(b)
H
H
N
(CH2 )4
H
O
N
C
O
(CH2 )4
C
OH
amide linkage
Figure 10.5: An amine and an acid monomer (a) combine to form a section of a nylon polymer
(b).
teresting Nylon was first introduced around 1939 and was in high demand to make stockInteresting
Fact
Fact
ings. However, as World War 2 progressed, nylon was used more and more to
make parachutes, and so stockings became more difficult to buy. After the war,
when manufacturers were able to shift their focus from parachutes back to stockings, a number of riots took place as women queued to get stockings. In one of
the worst disturbances, 40 000 women queued up for 13 000 pairs of stockings,
which led to fights breaking out!
Exercise: Polymers
1. The following monomer is a reactant in a polymerisation reaction:
H
CH3
C
C
H
CH3
(a) What is the IUPAC name of this monomer?
(b) Give the structural formula of the polymer that is formed in this polymerisation reaction.
(c) Is the reaction an addition or condensation reaction?
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
2. The polymer below is the product of a polymerisation reaction.
(a)
(b)
(c)
(d)
H
Cl
H
Cl
H
Cl
C
C
C
C
C
C
H
H
H
H
H
H
Give the structural formula of the monomer in this polymer.
What is the name of the monomer?
Draw the abbreviated structural formula for the polymer.
Has this polymer been formed through an addition or condensation polymerisation reaction?
3. A condensation reaction takes place between methanol and methanoic acid.
(a) Give the structural formula for...
i. methanol
ii. methanoic acid
iii. the product of the reaction
(b) What is the name of the product? (Hint: The product is an ester)
10.3
The chemical properties of polymers
The attractive forces between polymer chains play a large part in determining a polymer’s properties. Because polymer chains are so long, these interchain forces are very important. It is usually
the side groups on the polymer that determine what types of intermolecular forces will exist.
The greater the strength of the intermolecular forces, the greater will be the tensile strength and
melting point of the polymer. Below are some examples:
• Hydrogen bonds between adjacent chains
Polymers that contain amide or carbonyl groups can form hydrogen bonds between adjacent chains. The positive hydrogen atoms in the N-H groups of one chain are strongly
attracted to the oxygen atoms in the C=O groups on another. Polymers that contain urea
linkages would fall into this category. The structural formula for urea is shown in figure
10.6. Polymers that contain urea linkages have high tensile strength and a high melting
point.
O
C
H2 N
NH2
Figure 10.6: The structural formula for urea
• Dipole-dipole bonds between adjacent chains
Polyesters have dipole-dipole bonding between their polymer chains. Dipole bonding is
not as strong as hydrogen bonding, so a polyester’s melting point and strength are lower
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10.4
than those of the polymers where there are hydrogen bonds between the chains. However,
the weaker bonds between the chains means that polyesters have greater flexibility. The
greater the flexibility of a polymer, the more likely it is to be moulded or stretched into
fibres.
• Weak van der Waal’s forces
Other molecules such as ethene do not have a permanent dipole and so the attractive forces
between polyethene chains arise from weak van der Waals forces. Polyethene therefore has
a lower melting point than many other polymers.
10.4
Types of polymers
There are many different types of polymers. Some are organic, while others are inorganic. Organic
polymers can be broadly grouped into either synthetic/semi-synthetic (artificial) or biological
(natural) polymers. We are going to take a look at two groups of organic polymers: plastics,
which are usually synthetic or semi-synthetic and biological macromolecules which are natural
polymers. Both of these groups of polymers play a very important role in our lives.
10.5
Plastics
In today’s world, we can hardly imagine life without plastic. From cellphones to food packaging,
fishing line to plumbing pipes, compact discs to electronic equipment, plastics have become a
very important part of our daily lives. ”Plastics” cover a range of synthetic and semi-synthetic
organic polymers. Their name comes from the fact that they are ’malleable’, in other words their
shape can be changed and moulded.
Definition: Plastic
Plastic covers a range of synthetic or semisynthetic organic polymers. Plastics may contain
other substances to improve their performance. Their name comes from the fact that many
of them are malleable, in other words they have the property of plasticity.
It was only in the nineteenth century that it was discovered that plastics could be made by
chemically changing natural polymers. For centuries before this, only natural organic polymers
had been used. Examples of natural organic polymers include waxes from plants, cellulose (a
plant polymer used in fibres and ropes) and natural rubber from rubber trees. But in many
cases, these natural organic polymers didn’t have the characteristics that were needed for them
to be used in specific ways. Natural rubber for example, is sensitive to temperature and becomes
sticky and smelly in hot weather and brittle in cold weather.
In 1834 two inventors, Friedrich Ludersdorf of Germany and Nathaniel Hayward of the US,
independently discovered that adding sulfur to raw rubber helped to stop the material from
becoming sticky. After this, Charles Goodyear discovered that heating this modified rubber
made it more resistant to abrasion, more elastic and much less sensitive to temperature. What
these inventors had done was to improve the properties of a natural polymer so that it could be
used in new ways. An important use of rubber now is in vehicle tyres, where these properties of
rubber are critically important.
teresting The first true plastic (i.e. one that was not based on any material found in
Interesting
Fact
Fact
nature) was Bakelite, a cheap, strong and durable plastic. Some of these plastics
are still used for example in electronic circuit boards, where their properties of
insulation and heat resistance are very important.
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.5.1
The uses of plastics
There is such a variety of different plastics available, each having their own specific properties
and uses. The following are just a few examples.
• Polystyrene
Polystyrene (figure 15.2) is a common plastic that is used in model kits, disposable eating
utensils and a variety of other products. In the polystyrene polymer, the monomer is
styrene, a liquid hydrocarbon that is manufactured from petroleum.
CH2
CH2
CH
CH2
CH
CH
CH2
CH
polymerisation
etc
Figure 10.7: The polymerisation of a styrene monomer to form a polystyrene polymer
• Polyvinylchloride (PVC)
Polyvinyl chloride (PVC) (figure 10.8) is used in plumbing, gutters, electronic equipment,
wires and food packaging. The side chains of PVC contain chlorine atoms, which give it
its particular characteristics.
H
n
Cl
C
H
C
H
Figure 10.8: Polyvinyl chloride
teresting
Interesting
Fact
Fact
Many vinyl products have other chemicals added to them to give them particular properties. Some of these chemicals, called additives, can leach out
of the vinyl products. In PVC, plasticizers are used to make PVC more
flexible. Because many baby toys are made from PVC, there is concern that
some of these products may leach into the mouths of the babies that are
chewing on them. In the USA, most companies have stopped making PVC
toys. There are also concerns that some of the plasticizers added to PVC
may cause a number of health conditions including cancer.
• Synthetic rubber
Another plastic that was critical to the World War 2 effort was synthetic rubber, which was
produced in a variety of forms. Not only were worldwide natural rubber supplies limited,
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10.5
but most rubber-producing areas were under Japanese control. Rubber was needed for
tyres and parts of war machinery. After the war, synthetic rubber also played an important
part in the space race and nuclear arms race.
• Polyethene/polyethylene (PE)
Polyethylene (figure 10.1) was discovered in 1933. It is a cheap, flexible and durable plastic
and is used to make films and packaging materials, containers and car fittings. One of
the most well known polyethylene products is ’Tupperware’, the sealable food containers
designed by Earl Tupper and promoted through a network of housewives!
• Polytetrafluoroethylene (PTFE)
Polytetrafluoroethylene (figure 10.9) is more commonly known as ’Teflon’ and is most well
known for its use in non-stick frying pans. Teflon is also used to make the breathable fabric
Gore-Tex.
F
F
C
C
F
F
n
F
F
C
C
F
F
Figure 10.9: A tetra fluoroethylene monomer and polytetrafluoroethylene polymer
Table 10.1 summarises the formulae, properties and uses of some of the most common plastics.
Table 10.1: A summary of the formulae, properties and uses of some common plastics
Name
Polyethene (low density)
Polyethene (high density)
Polypropene
Formula
-(CH2 -CH2 )n -
Monomer
CH2 =CH2
Properties
soft, waxy solid
-(CH2 -CH2 )n -
CH2 =CH2
rigid
-[CH2 -CH(CH3 )]n -
CH2 =CHCH3
different
grades:
some are soft and
others hard
strong, rigid
Polyvinylchloride
-(CH2 -CHCl)n (PVC)
Polystyrene
-[CH2 -CH(C6 H5 )]n
Polytetrafluoroethylene -(CF2 -CF2 )n -
CH2 =CHCl
CH2 =CHC6 H5 hard, rigid
CF2 =CF2
resistant, smooth,
solid
Uses
film wrap and plastic
bags
electrical insulation,
bottles and toys
carpets and upholstery
pipes, flooring
toys, packaging
non-stick surfaces,
electrical insulation
Exercise: Plastics
1. It is possible for macromolecules to be composed of more than one type of
repeating monomer. The resulting polymer is called a copolymer. Varying
the monomers that combine to form a polymer, is one way of controlling the
properties of the resulting material. Refer to the table below which shows a
number of different copolymers of rubber, and answer the questions that follow:
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10.5
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
Monomer A
H2 C=CHCl
Monomer B
H2 C=CCl2
Copolymer
Saran
H2 C=CHC6 H5
H2 C=C-CH=CH2
H2 C=CHCN
H2 C=C-CH=CH2
SBR (styrene
butadiene
rubber)
Nitrile rubber
H2 C=C(CH3 )2
F2 C=CF(CF3 )
H2 C=C-CH=CH2
H2 C=CHF
Butyl rubber
Viton
Uses
films and fibres
tyres
adhesives and
hoses
inner tubes
gaskets
(a) Give the structural formula for each of the monomers of nitrile rubber.
(b) Give the structural formula of the copolymer viton.
(c) In what ways would you expect the properties of SBR to be different from
nitrile rubber?
(d) Suggest a reason why the properties of these polymers are different.
2. In your home, find as many examples of different types of plastics that you
can. Bring them to school and show them to your group. Together, use your
examples to complete the following table:
Object
10.5.2
Type of plastic
Properties
Uses
Thermoplastics and thermosetting plastics
A thermoplastic is a plastic that can be melted to a liquid when it is heated and freezes to
a brittle, glassy state when it is cooled enough. These properties of thermoplastics are mostly
due to the fact that the forces between chains are weak. This also means that these plastics
can be easily stretched or moulded into any shape. Examples of thermoplastics include nylon,
polystyrene, polyethylene, polypropylene and PVC. Thermoplastics are more easily recyclable
than some other plastics.
Thermosetting plastics differ from thermoplastics because once they have been formed, they
cannot be remelted or remoulded. Examples include bakelite, vulcanised rubber, melanine (used
to make furniture), and many glues. Thermosetting plastics are generally stronger than thermoplastics and are better suited to being used in situations where there are high temperatures.
They are not able to be recycled. Thermosetting plastics have strong covalent bonds between
chains and this makes them very strong.
Activity :: Case Study : Biodegradable plastics
Read the article below and then answer the questions that follow.
Our whole world seems to be wrapped in plastic. Almost every product we
buy, most of the food we eat and many of the liquids we drink come encased in
plastic. Plastic packaging provides excellent protection for the product, it is cheap
to manufacture and seems to last forever. Lasting forever, however, is proving to
be a major environmental problem. Another problem is that traditional plastics are
manufactured from non-renewable resources - oil, coal and natural gas. In an effort
to overcome these problems, researchers and engineers have been trying to develop
biodegradable plastics that are made from renewable resources, such as plants.
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.5
The term biodegradable means that a substance can be broken down into simpler
substances by the activities of living organisms, and therefore is unlikely to remain
in the environment. The reason most plastics are not biodegradable is because their
long polymer molecules are too large and too tightly bonded together to be broken
apart and used by decomposer organisms. However, plastics based on natural plant
polymers that come from wheat or corn starch have molecules that can be more
easily broken down by microbes.
Starch is a natural polymer. It is a white, granular carbohydrate produced by
plants during photosynthesis and it serves as the plant’s energy store. Many plants
contain large amounts of starch. Starch can be processed directly into a bioplastic
but, because it is soluble in water, articles made from starch will swell and deform
when exposed to moisture, and this limits its use. This problem can be overcome
by changing starch into a different polymer. First, starch is harvested from corn,
wheat or potatoes, then microorganisms transform it into lactic acid, a monomer.
Finally, the lactic acid is chemically treated to cause the molecules of lactic acid to
link up into long chains or polymers, which bond together to form a plastic called
polylactide (PLA).
PLA can be used for products such as plant pots and disposable nappies. It has
been commercially available in some countries since 1990, and certain blends have
proved successful in medical implants, sutures and drug delivery systems because
they are able to dissolve away over time. However, because PLA is much more
expensive than normal plastics, it has not become as popular as one would have
hoped.
Questions
1. In your own words, explain what is meant by a ’biodegradable plastic’.
2. Using your knowledge of chemical bonding, explain why some polymers are
biodegradable and others are not.
3. Explain why lactic acid is a more useful monomer than starch, when making a
biodegradable plastic.
4. If you were a consumer (shopper), would you choose to buy a biodegradable
plastic rather than another? Explain your answer.
5. What do you think could be done to make biodegradable plastics more popular
with consumers?
10.5.3
Plastics and the environment
Although plastics have had a huge impact globally, there is also an environmental price that has
to be paid for their use. The following are just some of the ways in which plastics can cause
damage to the environment.
1. Waste disposal
Plastics are not easily broken down by micro-organisms and therefore most are not easily
biodegradeable. This leads to waste dispoal problems.
2. Air pollution
When plastics burn, they can produce toxic gases such as carbon monoxide, hydrogen
cyanide and hydrogen chloride (particularly from PVC and other plastics that contain
chlorine and nitrogen).
3. Recycling
It is very difficult to recycle plastics because each type of plastic has different properties
and so different recycling methods may be needed for each plastic. However, attempts
are being made to find ways of recycling plastics more effectively. Some plastics can
be remelted and re-used, while others can be ground up and used as a filler. However,
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10.6
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
one of the problems with recycling plastics is that they have to be sorted according to
plastic type. This process is difficult to do with machinery, and therefore needs a lot
of labour. Alternatively, plastics should be re-used. In many countries, including South
Africa, shoppers must now pay for plastic bags. This encourages people to collect and
re-use the bags they already have.
Activity :: Case Study : Plastic pollution in South Africa
Read the following extract, taken from ’Planet Ark’ (September 2003), and then
answer the questions that follow.
South Africa launches a programme this week to exterminate its ”national
flower” - the millions of used plastic bags that litter the landscape.
Beginning on Friday, plastic shopping bags used in the country must be
both thicker and more recyclable, a move officials hope will stop people from simply tossing them away. ”Government has targeted plastic
bags because they are the most visible kind of waste,” said Phindile Makwakwa, spokeswoman for the Department of Environmental Affairs and
Tourism. ”But this is mostly about changing people’s mindsets about the
environment.”
South Africa is awash in plastic pollution. Plastic bags are such a common
eyesore that they are dubbed ”roadside daisies” and referred to as the
national flower. Bill Naude of the Plastics Federation of South Africa said
the country used about eight billion plastic bags annually, a figure which
could drop by 50 percent if the new law works.
It is difficult sometimes to imagine exactly how much waste is produced in our
country every year. Where does all of this go to? You are going to do some simple
calculations to try to estimate the volume of plastic packets that is produced in
South Africa every year.
1. Take a plastic shopping packet and squash it into a tight ball.
(a) Measure the approximate length, breadth and depth of your squashed plastic bag.
(b) Calculate the approximate volume that is occupied by the packet.
(c) Now calculate the approximate volume of your classroom by measuring its
length, breadth and height.
(d) Calculate the number of squashed plastic packets that would fit into a
classroom of this volume.
(e) If South Africa produces an average of 8 billion plastic bags each year, how
many clasrooms would be filled if all of these bags were thrown away and
not re-used?
2. What has South Africa done to try to reduce the number of plastic bags that
are produced?
3. Do you think this has helped the situation?
4. What can you do to reduce the amount of plastic that you throw away?
10.6
Biological Macromolecules
A biological macromolecule is one that is found in living organisms. Biological macromolecules
include molecules such as carbohydrates, proteins and nucleic acids. Lipids are also biological
macromolecules. They are essential for all forms of life to survive.
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.6
Definition: Biological macromolecule
A biological macromolecule is a polymer that occurs naturally in living organisms. These
molecules are essential to the survival of life.
10.6.1
Carbohydrates
Carbohydrates include the sugars and their polymers. One key characteristic of the carbohydrates is that they contain only the elements carbon, hydrogen and oxygen. In the carbohydrate
monomers, every carbon except one has a hydroxyl group attached to it, and the remaining
carbon atom is double bonded to an oxygen atom to form a carbonyl group. One of the most
important monomers in the carbohydrates is glucose (figure 10.10). The glucose molecule can
exist in an open-chain (acyclic) and ring (cyclic) form.
(a)
O
C1
OH
H
OH
OH
OH
C2
C3
C4
C5
C6
H
OH
H
H
H
H
H
CH2 OH
(b)
C5
O
H
C4 OH
H
C3
C2
H
OH
H
OH
H
C1
OH
Figure 10.10: The open chain (a) and cyclic (b) structure of a glucose molecule
Glucose is produced during photosynthesis, which takes place in plants. During photosynthesis,
sunlight (solar energy), water and carbon dioxide are involved in a chemical reaction that produces
glucose and oxygen. This glucose is stored in various ways in the plant.
The photosynthesis reaction is as follows:
6CO2 + 6H2 O + sunlight → C6 H12 O6 + 6O2
Glucose is an important source of energy for both the plant itself, and also for the other animals
and organisms that may feed on it. Glucose plays a critical role in cellular respiration, which is
a chemical reaction that occurs in the cells of all living organisms. During this reaction, glucose
and oxygen react to produce carbon dioxide, water and ATP energy. ATP is a type of energy
that can be used by the body’s cells so that they can function normally. The purpose of eating
then, is to obtain glucose which the body can then convert into the ATP energy it needs to be
able to survive.
The reaction for cellular respiration is as follows:
6C6 H12 O6 + 602 → 6CO2 + 6H2 O + ATP (cell energy)
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We don’t often eat glucose in its simple form. More often, we eat complex carbohydrates that
our bodies have to break down into individual glucose molecules before they can be used in cellular respiration. These complex carbohydrates are polymers, which form through condensation
polymerisation reactions (figure 10.11). Starch and cellulose are two example of carbohydrates
that are polymers composed of glucose monomers.
CH2 OH
(a)
CH2 OH
C5
O
H
C4 OH
H
C3
C2
H
OH
H
OH
H
+
C
OH
C5
H
C4
OH
O
H
C4 OH
H
C3
C2
H
OH
OH
CH2 OH
(b)
C5
H
H
C
OH
CH2 OH
O
H
C5
O
H
C4 OH
H
C3
C2
H
OH
H
H
C
C3
C2
H
H
OH
O
H
C
+ H2 O
OH
Figure 10.11: Two glucose monomers (a) undergo a condensation reaction to produce a section
of a carbohydrate polymer (b). One molecule of water is produced for every two monomers that
react.
• Starch
Starch is used by plants to store excess glucose, and consists of long chains of glucose
monomers. Potatoes are made up almost entirely of starch. This is why potatoes are such
a good source of energy. Animals are also able to store glucose, but in this case it is stored
as a compound called glycogen, rather than as starch.
• Cellulose
Cellulose is also made up of chains of glucose molecules, but the bonding between the
polymers is slightly different from that in starch. Cellulose is found in the cell walls of
plants and is used by plants as a building material.
teresting It is very difficult for animals to digest the cellulose in plants that they
Interesting
Fact
Fact
may have been feeding on. However, fungi and some protozoa are able to
break down cellulose. Many animals, including termites and cows, use these
organisms to break cellulose down into glucose, which they can then use
more easily.
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10.6.2
10.6
Proteins
Proteins are an incredibly important part of any cell, and they carry out a number of functions
such as support, storage and transport within the body. The monomers of proteins are called
amino acids. An amino acid is an organic molecule that contains a carboxyl and an amino
group, as well as a carbon side chain. The carbon side chain varies from one amino acid to the
next, and is sometimes simply represented by the letter ’R’ in a molecule’s structural formula.
Figure 10.12 shows some examples of different amino acids.
Carboxyl group
H
H2 N
Amino group
C
H
O
H
H2 N
C
C
O
C
CH3
OH
OH
Side chain (’R’)
glycine
alanine
H
H2 N
C
O
C
CH2
OH
OH
serine
Figure 10.12: Three amino acids: glycine, alanine and serine
Although each of these amino acids has the same basic structure, their side chains (’R’ groups)
are different. In the amino acid glycine, the side chain consists only of a hydrogen atom, while
alanine has a methyl side chain. The ’R’ group in serine is CH2 - OH. Amongst other things,
the side chains affect whether the amino acid is hydrophilic (attracted to water) or hydrophobic
(repelled by water). If the side chain is polar, then the amino acid is hydrophilic, but if the side
chain is non-polar then the amino acid is hydrophobic. Glycine and alanine both have non-polar
side chains, while serine has a polar side chain.
Extension: Charged regions in an amino acid
In an amino acid, the amino group acts as a base because the nitrogen atom has a
pair of unpaired electrons which it can use to bond to a hydrogen ion. The amino
group therefore attracts the hydrogen ion from the carboxyl group, and ends up having a charge of +1. The carboxyl group from which the hydrogen ion has been taken
then has a charge of -1. The amino acid glycine can therefore also be represented
as shown in the figure below.
199
10.6
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
H
H3 N+
O
C
C
H
O−
glycine
When two amino acid monomers are close together, they may be joined to each other by peptide
bonds (figure 10.13) to form a polypeptide chain. . The reaction is a condensation reaction.
Polypeptides can vary in length from a few amino acids to a thousand or more. The polpeptide
chains are then joined to each other in different ways to form a protein. It is the sequence of
the amino acids in the polymer that gives a protein its particular properties.
The sequence of the amino acids in the chain is known as the protein’s primary structure. As
the chain grows in size, it begins to twist, curl and fold upon itself. The different parts of the
polypeptide are held together by hydrogen bonds, which form between hydrogen atoms in one
part of the chain and oxygen or nitrogen atoms in another part of the chain. This is known as
the secondary structure of the protein. Sometimes, in this coiled helical structure, bonds may
form between the side chains (R groups) of the amino acids. This results in even more irregular
contortions of the protein. This is called the tertiary structure of the protein.
(a)
H2 N
H
C
O
H
+
C
H
H2 N
C
CH3
OH
O
C
OH
Peptide bond
(b)
H2 N
H
O
C
C
H
H
N
C
H
CH3
O
C
+ H2 O
OH
Figure 10.13: Two amino acids (glycine and alanine) combine to form part of a polypeptide
chain. The amino acids are joined by a peptide bond between a carbon atom of one amino acid
and a nitrogen atom of the other amino acid.
teresting There are twenty different amino acids that exist. All cells, both plant and
Interesting
Fact
Fact
animal, build their proteins from only twenty amino acids. At first, this seems
like a very small number, especially considering the huge number of different
200
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.6
proteins that exist. However, if you consider that most proteins are made up of
polypeptide chains that contain at least 100 amino acids, you will start to realise
the endless possible combinations of amino acids that are available.
The functions of proteins
Proteins have a number of functions in living organisms.
• Structural proteins such as collagen in animal connective tissue and keratin in hair, horns
and feather quills, all provide support.
• Storage proteins such as albumin in egg white provide a source of energy. Plants store
proteins in their seeds to provide energy for the new growing plant.
• Transport proteins transport other substances in the body. Haemoglobin in the blood
for example, is a protein that contains iron. Haemoglobin has an affinity (attraction) for
oxygen and so this is how oxygen is transported around the body in the blood.
• Hormonal proteins coordinate the body’s activities. Insulin for example, is a hormonal
protein that controls the sugar levels in the blood.
• Enzymes are chemical catalysts and speed up chemical reactions. Digestive enzymes such
as salivary amylase in your saliva, help to break down polymers in food. Enzymes play an
important role in all cellular reactions such as respiration, photosynthesis and many others.
Activity :: Research Project : Macromolecules in our daily diet
1. In order to keep our bodies healthy, it is important that we eat a balanced
diet with the right amounts of carbohydrates, proteins and fats. Fats are an
important source of energy, they provide insulation for the body, and they also
provide a protective layer around many vital organs. Our bodies also need
certain essential vitamins and minerals. Most food packaging has a label that
provides this information.
Choose a number of different food items that you eat. Look at the food label
for each, and then complete the following table:
Food
Carbohydrates Proteins (%)
Fats (%)
(%)
(a) Which food type contains the largest proportion of protein?
(b) Which food type contains the largest proportion of carbohydrates?
(c) Which of the food types you have listed would you consider to be the
’healthiest’ ? Give a reason for your answer.
2. In an effort to lose weight, many people choose to diet. There are many diets
on offer, each of which is based on particular theories about how to lose weight
most effectively. Look at the list of diets below:
• Vegetarian diet
• Low fat diet
• Atkin’s diet
201
10.6
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
• Weight Watchers
For each of these diets, answer the following questions:
(a) What theory of weight loss does each type of diet propose?
(b) What are the benefits of the diet?
(c) What are the potential problems with the diet?
Exercise: Carbohydrates and proteins
1. Give the structural formula for each of the following:
(a) A polymer chain, consisting of three glucose molecules.
(b) A polypeptide chain, consisting of two molecules of alanine and one molecule
of serine.
2. Write balanced equations to show the polymerisation reactions that produce
the polymers described above.
3. The following polypeptide is the end product of a polymerisation reaction:
H2 N
H
O
C
C
CH3
H
O
N
C
C
H
CH2
H
N
C
H
H
O
C
OH
SH
(a) Give the structural formula of the monomers that make up the polypeptide.
(b) On the structural formula of the first monomer, label the amino group and
the carboxyl group.
(c) What is the chemical formula for the carbon side chain in the second
monomer?
(d) Name the bond that forms between the monomers of the polypeptide.
10.6.3
Nucleic Acids
You will remember that we mentioned earlier that each protein is different because of its unique
sequence of amino acids. But what controls how the amino acids arrange themselves to form
the specific proteins that are needed by an organism? This task is for the gene. A gene contains
DNA (deoxyribonucleic acid) which is a polymer that belongs to a class of compounds called the
nucleic acids. DNA is the genetic material that organisms inherit from their parents. It is DNA
that provides the genetic coding that is needed to form the specific proteins that an organism
needs. Another nucleic acid is RNA (ribonucleic acid).
The DNA polymer is made up of monomers called nucleotides. Each nucleotide has three
parts: a sugar, a phosphate and a nitrogenous base. The diagram in figure 10.14 may help you
to understand this better.
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CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
phosphate sugar
10.6
nitrogenous base
DNA polymer made up of
four nucleotides
nucleotide
Figure 10.14: Nucleotide monomers make up the DNA polymer
There are five different nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T)
and uracil (U). It is the sequence of the nitrogenous bases in a DNA polymer that will determine
the genetic code for that organism. Three consecutive nitrogenous bases provide the coding
for one amino acid. So, for example, if the nitrogenous bases on three nucleotides are uracil,
cytosine and uracil (in that order), one serine amino acid will become part of the polypeptide
chain. The polypeptide chain is built up in this way until it is long enough (and with the right
amino acid sequence) to be a protein. Since proteins control much of what happens in living
organisms, it is easy to see how important nucleic acids are as the starting point of this process.
teresting A single defect in even one nucleotide, can be devastating to an organism.
Interesting
Fact
Fact
One example of this is a disease called sickle cell anaemia. Because of one
wrong nucletide in the genetic code, the body produces a protein called sickle
haemoglobin. Haemoglobin is the protein in red blood cells that helps to
transport oxygen around the body. When sickle haemoglobin is produced, the
red blood cells change shape. This process damages the red blood cell membrane,
and can cause the cells to become stuck in blood vessels. This then means that
the red blood cells, whcih are carrying oxygen, can’t get to the tissues where
they are needed. This can cause serious organ damage. Individuals who have
sickle cell anaemia generally have a lower life expectancy.
Table 10.2 shows some other examples of genetic coding for different amino acids.
Exercise: Nucleic acids
203
10.7
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
Table 10.2: Nitrogenouse base sequences and the corresponding amino acid
Nitrogenous base sequence
Amino acid
UUU
Phenylalanine
CUU
Leucine
UCU
Serine
UAU
Tyrosine
UGU
Cysteine
GUU
Valine
GCU
Alanine
GGU
Glycine
1. For each of the following, say whether the statement is true or false. If the
statement is false, give a reason for your answer.
(a) Deoxyribonucleic acid (DNA) is an example of a polymer and a nucleotide
is an example of a monomer.
(b) Thymine and uracil are examples of nucleotides.
(c) A person’s DNA will determine what proteins their body will produce, and
therefore what characteristics they will have.
(d) An amino acid is a protein monomer.
(e) A polypeptide that consists of five amino acids, will also contain five nucleotides.
2. For each of the following sequences of nitrogenous bases, write down the amino
acid/s that will be part of the polypeptide chain.
(a) UUU
(b) UCUUUU
(c) GGUUAUGUUGGU
3. A polypeptide chain consists of three amino acids. The sequence of nitrogenous
bases in the nucleotides of the DNA is GCUGGUGCU. Give the structural
formula of the polypeptide.
10.7
Summary
• A polymer is a macromolecule that is made up of many repeating structural units called
monomers which are joined by covalent bonds.
• Polymers that contain carbon atoms in the main chain are called organic polymers.
• Organic polymers can be divided into natural organic polymers (e.g. natural rubber) or
synthetic organic polymers (e.g. polystyrene).
• The polymer polyethene for example, is made up of many ethene monomers that have
been joined into a polymer chain.
• Polymers form through a process called polymerisation.
• Two examples of polymerisation reactions are addition and condensation reactions.
• An addition reaction occurs when unsaturated monomers (e.g. alkenes) are added to
each other one by one. The breaking of a double bond between carbon atoms in the
monomer, means that a bond can form with the next monomer. The polymer polyethene
is formed through an addition reaction.
204
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
10.7
• In a condensation reaction, a molecule of water is released as a product of the reaction.
The water molecule is made up of atoms that have been lost from each of the monomers.
Polyesters and nylon are polymers that are produced through a condensation reaction.
• The chemical properties of polymers (e.g. tensile strength and melting point) are determined by the types of atoms in the polymer, and by the strength of the bonds between
adjacent polymer chains. The stronger the bonds, the greater the strength of the polymer,
and the higher its melting point.
• One group of synthetic organic polymers, are the plastics.
• Polystyrene is a plastic that is made up of styrene monomers. Polystyrene is used a lot
in packaging.
• Polyvinyl chloride (PVC) consists of vinyl chloride monomers. PVC is used to make pipes
and flooring.
• Polyethene, or polyethylene, is made from ethene monomers. Polyethene is used to
make film wrapping, plastic bags, electrical insulation and bottles.
• Polytetrafluoroethylene is used in non-stick frying pans and electrical insulation.
• A thermoplastic can be heated and melted to a liquid. It freezes to a brittle, glassy state
when cooled very quickly. Examples of thermoplastics are polyethene and PVC.
• A thermoset plastic cannot be melted or re-shaped once formed. Examples of thermoset
plastics are vulcanised rubber and melanine.
• It is not easy to recycle all plastics, and so they create environmental problems.
• Some of these environmental problems include issues of waste disposal, air pollution and
recycling.
• A biological macromolecule is a polymer that occurs naturally in living organisms.
• Examples of biological macromolecules include carbohydrates and proteins, both of which
are essential for life to survive.
• Carbohydrates include the sugars and their polymers, and are an important source of
energy in living organisms.
• Glucose is a carbohydrate monomer. Glucose is the molecule that is needed for photosynthesis in plants.
• The glucose monomer is also a building block for carbohydrate polymers such as starch,
glycogen and cellulose.
• Proteins have a number of important functions. These include their roles in structures,
transport, storage, hormonal proteins and enzymes.
• A protein consists of monomers called amino acids, which are joined by peptide bonds.
• A protein has a primary, secondary and tertiary structure.
• An amino acid is an organic molecule, made up of a carboxyl and an amino group, as
well as a carbon side chain of varying lengths.
• It is the sequence of amino acids that determines the nature of the protein.
• It is the DNA of an organism that determines the order in which amino acids combine to
make a protein.
• DNA is a nucleic acid. DNA is a polymer, and is made up of monomers called nucleotides.
• Each nucleotide consists of a sugar, a phosphate and a nitrogenous base. It is the
sequence of the nitrogenous bases that provides the ’code’ for the arrangement of the
amino acids in a protein.
205
10.7
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
Exercise: Summary exercise
1. Give one word for each of the following descriptions:
(a) A chain of monomers joined by covalent bonds.
(b) A polymerisation reaction that produces a molecule of water for every two
monomers that bond.
(c) The bond that forms between an alcohol and a carboxylic acid monomer
during a polymerisation reaction.
(d) The name given to a protein monomer.
(e) A six-carbon sugar monomer.
(f) The monomer of DNA, which determines the sequence of amino acids that
will make up a protein.
2. For each of the following questions, choose the one correct answer from the
list provided.
(a) A polymer is made up of monomers, each of which has the formula CH2 =CHCN.
The formula of the polymer is:
i. -(CH2 =CHCN)n ii. -(CH2 -CHCN)n iii. -(CH-CHCN)n iv. -(CH3 -CHCN)n (b) A polymer has the formula -[CO(CH2 )4 CO-NH(CH2 )6NH]n -. Which of
the following statements is true?
i. The polymer is the product of an addition reaction.
ii. The polymer is a polyester.
iii. The polymer contains an amide linkage.
iv. The polymer contains an ester linkage.
(c) Glucose...
i. is a monomer that is produced during cellular respiration
ii. is a sugar polymer
iii. is the monomer of starch
iv. is a polymer produced during photosynthesis
3. The following monomers are involved in a polymerisation reaction:
H2 N
H
O
C
C
OH
+
H
(a)
(b)
(c)
(d)
(e)
H2 N
H
O
C
C
OH
H
Give the structural formula of the polymer that is produced.
Is the reaction an addition or condensation reaction?
To what group of organic compounds do the two monomers belong?
What is the name of the monomers?
What type of bond forms between the monomers in the final polymer?
4. The table below shows the melting point for three plastics. Suggest a reason
why the melting point of PVC is higher than the melting point for polyethene,
but lower than that for polyester.
Plastic
Polyethene
PVC
Polyester
Melting point (0 C)
105 - 115
212
260
206
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
5. An amino acid has the formula H2 NCH(CH2 CH2 SCH3 )COOH.
(a) Give the structural formula of this amino acid.
(b) What is the chemical formula of the carbon side chain in this molecule?
(c) Are there any peptide bonds in this molecule? Give a reason for your
answer.
207
10.7
10.7
CHAPTER 10. ORGANIC MACROMOLECULES - GRADE 12
208
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