>>>
Kerry Whalley
Carol Neville
Geoff Phillips
Faye Jeffery
Janette Ellis
Peter Roberson
Greg Rickard
Pearson Education Australia
A division of Pearson Australia Group Pty Ltd Level 9, 5 Queens Road
Melbourne 3004 Australia www.pearsoned.com.au/schools
Offices in Sydney, Brisbane and Perth, and associated companies throughout the world.
Copyright © Pearson Education Australia
(a division of Pearson Australia Group Pty Ltd) 2005 First published 2005
All rights reserved. Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner.
Designed by Polar Design Edited by Kay Waters
Illustrated by Wendy Gorton, Bruce Rankin, Vasja Koman and John Ward Prepress work by The Type Factory
Set in Melior 10 pt
Produced by Pearson Education Australia Printed in Hong Kong
National Library of Australia Cataloguing–in–Publication data:
Science focus 4. Includes index.
For secondary school students. ISBN 0 1236 0447 8.
1. Science - Textbooks. I. Whalley, Kerry. II. Title. 500
UNIT
UNIT
UNIT
UNIT
UNIT
5Motion
1355.1
Describing motion 1365.2
Acceleration 1475.3
Newton’s first law 1535.4
Newton’s second law 1595.5
Newton’s third law 1645.6
Gravity 1695.7
Work and energy 176Chapter review 183
6
Health and disease
1856.1
Health 1866.2
Disease 1926.3
Infectious diseases 1966.4
Transmission and control of infectiousdiseases 203
6.5
Non-infectious diseases 211Chapter review 221
7
Evolution
2227.1
The evolution of a theory 2237.2
Evolution unravelled 2327.3
Evidence for evolution 2397.4
Human evolution 249Scence focus:Putting flesh on old bones:
archaeology and Australia today 255
Chapter review 260
8
Global issues
2628.1
Global warming 2638.2
The ozone layer 2728.3
Nuclear radiation: good or evil? 2768.4
Energy crisis 285Chapter review 293
9
Individual research
project
2949.1
Being an individual 295Science focus: Science can be funny 299
9.2
My investigation 302 Chapter review 308 Periodic table 310 Index 311 Acknowledgements iv Introduction vSyllabus correlation grid viii
Verbs 1
1
Chemical reactions
21.1
Writing chemical equations 31.2
More and faster! Rate and yieldconsiderations 10
1.3
100% organic 151.4
Maths in chemistry (on CD)Chapter review 22
2
Materials
232.1
Pure metals and alloys 242.2
Mining and minerals 292.3
Corrosion of metals 382.4
Plastics and fibres 43Science focus: Nanotechnology 54
2.5
Soaps (on CD) Chapter review 58 3Electricity and
communications
technology
593.1
Electricity 603.2
Electromagnetism 683.3
Waves in communication 763.4
The communications network 84Scence focus:Microwaves cook from
the inside 91
3.5
Electronics (on CD) Chapter review 93 4Genetics
954.1
Inheritance 964.2
Human inheritance 1064.3
The molecule of life 1144.4
Controlling inheritance 120Science focus: Biotechnology and
DNA fingerprinting 128 Chapter review 133
UNIT
UNIT
UNIT
UNIT
We would like to thank the following for permission to reproduce photographs and text. The following abbreviations are used in this list: t = top, b = bottom, l = left, r = right.
The Age: figure 2.1.5.
Andrea Simonato: figure SF 9.1. Auscape: figures 7.2.1, 7.2.8(l), 7.3.7. Australian Associated Press: figure 1.2.1. Australian Nuclear Science and Technology Organisation: figure 8.4.6.
Australian Picture Library: figures 4.2.3, 5.2.9; Joel W. Rogers, figure 2.1.3; Sandro Vannini, figure 2.1.4; William Taufic, figure 2.2.9; Penny Tweedie, figures 2.4.4, 2.4.9, 6.1.5, 6.4.5, 7.1.5; Rob Lewine, figure 4.2.1; Nick Rains, figure 6.1.6; Lester V. Bergman, figure 6.3.8; Jonathan Blair, figure 7.3.11; Larry Williams, figure 7.4.9; Pam Gardner, figure SF 7.5; Les Stone, figure 8.1.9; Ric Ergenbright, figure 9.1.3; Jim Sugar, figure 9.2.3.
Australian Radiation Protection and Nuclear Safety Agency: figure 8.4.9.
Blackmagic Design: figure 3.5.13 Bureau of Meteorology: figure 8.1.7.
CSIRO: figures 4.4.11, 8.1.5; ©CSIRO Human Nutrition. Reproduced from 12345+ Food and
Nutrition Plan (K. Baghurst et al., 1990) by permission of CSIRO Australia, figure 6.1.3.
David Heffernan: figures 3.5.1, 3.5.2, 3.5.5, 3.5.7, 3.5.9.
Dorling Kindersley: p. 2, figures 2.2.2, 3.1.8, 3.4.2, 7.3.5.
The DW Stock Picture Library: figure 7.1.1. Fairfax Images: figures 5.1.9, 5.7.2.
Getty Images: p. 135, figures 5.7.3, 6.1.7, 6.2.2, 6.4.10, p. 222, figures 7.1.3, 7.4.2, 8.3.9.
Greg Rickard: figure 2.1.2.
Jim Bowler: figures SF 7.2, SF 7.3(b), SF 7.4, SF 7.6.
Jim DeLillo: photo by Jim DeLillo, figure 3.4.10. Dr Karl Kruszelnicki: reproduced with kind
permission from the author of Great Mythconceptions, HarperCollins, 2004. Article can be found on his website <www.abc.net.au/science/k2/moments>: p. 91.
NASA: figures 5.5.2, 8.1.1(l), 8.1.1(r), 8.2.6.
Newspix: Anthony Weate, p. 23; Susan Turner, figure 2.2.4; James Knowler, figure 4.4.7; David Crosling, figure SF 7.7; News Limited, figure 8.4.8.
Pearson Education Australia: Ben Killingsworth, figures 1.3.3, 4.4.4; Tricia Confoy, figure 2.3.1; Elizabeth Anglin, figures 2.4.1, 2.5.2, SF 3.1, 4.4.2, SF 4.3, 6.3.2, 6.5.13, 9.1.4, 9.1.5, SF 9.3; Anna Small, figures 3.4.11, 4.2.11, SF 9.2; Peter Saffin, figures 4.2.4, SF 9.4. Photolibrary.com: figures 1.1.5, 1.2.2, 1.3.12, 1.4.5, 2.2.6, 2.4.12, 2.4.13, 2.5.4, SF 2.2, SF 2.4, SF 2.5, SF 2.6, SF 2.7, p. 59, 3.1.2, 3.2.3, 3.2.12, 3.3.6, 3.3.8, 3.3.10, 3.3.11, 3.4.3, 3.5.14, SF 3.2, p. 95, 4.1.1, 4.1.4, 4.1.6, 4.2.5, 4.3.6, 4.3.7, 4.4.1, 4.4.3, 4.4.9, SF 4.1, SF 4.2, SF 4.7, 5.1.2, 5.1.3, 5.2.1, 5.2.2, 5.3.1, 5.3.2, 5.3.3, 5.3.5, 5.6.3, 5.6.4, p. 185, 6.3.5, 6.3.6, 6.3.7, 6.3.9, 6.3.11, 6.4.1, 6.4.2, 6.4.4, 6.4.7, 6.4.8, 6.4.9, 6.5.1, 6.5.2, 6.5.4, 6.5.7, 6.5.8, 6.5.9, 6.5.10, 6.5.12, 6.5.14, 7.1.2, 7.1.4, 7.1.7, 7.1.9, 7.1.12, 7.1.13, 7.2.2, 7.2.11(b), 7.2.11(t), 7.4.4, 7.4.6, 7.4.7, 7.4.8, 8.3.2, 8.3.8, 8.3.11, 8.4.2, 8.4.7, 8.4.12, p. 294, 9.2.1, 9.2.2. The Picture Source: figure 2.4.10.
South Australian Museum: figure 7.3.3.
Willandra World Heritage Area Three Traditional Tribal Groups: published with the consent of the indigenous owners, figure SF 7.3(t).
Every effort has been made to trace and acknowledge copyright. However, if any infringement has occurred, the publishers tender their apologies and invite copyright owners to contact them.
Coursebook
The coursebook consists of nine chapters with the following features.
Chapter opening pages include: • the key
prescribed focus area for the chapter • outcomes presented in a way that students can easily understand • pre quiz questions to stimulate interest and test prior knowledge.
Chapter units open with a ‘context’ to encourage students to make meaning of science in terms of their everyday experiences. The units also reinforce contextual learning by presenting theory, photos, illustrations and ‘science focus’ segments in a format that is easy to read and follow.
Each PFA has one Science Focus special feature which uses a contextual approach to focus specifically on the outcomes of that PFA. Student activities on these pages allow further investigation and exploration of the material covered.
The Science Focus series has been written for the NSW Science syllabus, stages 4 and 5. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives. By learning from the Science Focus series students will become confident, creative, responsible and scientifically literate members of society.
Each unit ends with a set of questions. These begin with straightforward ‘checkpoint’ questions that build confidence, leading to ‘think’, ‘analyse’ and ‘skills’ questions that require further thought and application. Questions incorporate the syllabus ‘verbs’ so that students can begin to practise answering questions as required in examinations in later years.
The extension questions can be set for further exploration and assignment work and include a variety of structured tasks including research, creative writing and internet activities suitable for all students. Extension questions cater for a range of learning styles using the multiple intelligences approach, and may be used for extending more able students.
Online review questions
Auto-correcting chapter review questions can be used as a diagnostic tool or for revision at school or home, and include:
• multiple choice • matching
• labelling • fill in the blanks.
Companion Website
The Companion Website contains a wealth of support material forstudents and teachers, which has been written to enhance the content covered in the coursebook.
Destinations
A list of reviewed websites is available— these relate directly to chapter content for students to access.
Interactive activities
These are activities that apply and review concepts covered in the chapters. They are designed for students to work independently, and include:
• interactive animations to develop key skills and knowledge in a stimulating, visual and engaging way
• drag-and-drop activities to improve basic understandings in a fun and engaging way • QuickTime videos to enhance the learning of
content in a visual way. Key numeracy and literacy tasks are
indicated with icons.
Practical activities
follow the questions. These are placed at the end of the unit to allow teachers to choose when and how to best incorporate the practical work. Cross references to practical activities within the units signal suggested points
for practical work. Some
practical activities are ‘design-your-own’ (DYO) tasks.
Chapter review questions follow
the last unit in each chapter. These cover all chapter outcomes in a variety of question styles to provide opportunities for all students to consolidate new knowledge and skills.
The use of the Aboriginal flag in the coursebook denotes material that is included to cover Aboriginal perspectives in science.
DYO
Prac 1 Unit 1.2
Homework Book
The Homework Book provides a structured program to complement the coursebook. These homework activities:
• cover various skills required in the syllabus • offer consolidation of key
content and interesting extension activities • provide revision activities
for each chapter,
including the construction of a glossary
• cater for a multiple intelligences approach through varied activities
• have ‘Worksheet’ icons in the coursebook to denote when a homework activity is available.
Teacher resource centre
A wealth of teacher support material is provided and is password protected and includes:
• a chapter test for each chapter, in MS Word to allow editing by the teacher
• Coursebook answers • Homework Book answers • Teaching programs.
Teacher resource pack
Material in the teacher resource pack consists of a printout and electronic copy on CD. It includes: • curriculum correlation grids mapped in detail to
the NSW syllabus
• chapter-based teaching programs • contextual teaching programs • Coursebook answers
• chapter tests in MS Word • Homework Book answers. Worksheet 2.4 Metal experiments
A fully mapped and detailed correlation of the stage 5 curriculum outcomes is
available in the Science Focus 4 Teacher Resource Pack.
Note: ▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.
Science Focus 4
Stage 5 Syllabus Correlation
chapter
outcomes
5.1 ▲ 5.2 ▲ ▲ 5.3 ▲ ▲ 5.4 ▲ ▲ ▲ 5.5 ▲ 5.6•
•
•
5.7 5.8•
•
•
5.9 5.10•
5.11•
5.12•
•
•
•
5.13•
•
•
•
•
•
•
•
5.14•
•
•
•
•
•
•
•
5.15•
•
•
•
•
•
•
•
•
5.16•
•
•
•
•
•
•
•
•
5.17•
•
•
•
•
•
•
•
•
5.18•
•
•
•
•
•
•
•
•
5.19•
•
•
•
•
•
•
•
•
5.20•
•
•
•
•
•
•
5.21•
•
•
•
•
•
•
•
5.22•
•
•
•
•
•
•
5.23• • •
•
5.24•
•
5.25• • • • •
5.26• •
• • • • • •
5.27•
•
2
Materials
4
5
6
7
8
9
1
Chemical
reactions
3
Electricity
and
communi-cations
technology
Genetics
Motion
Health and
disease
Evolution
Global
issues
Individual
research
project
Explain relate cause and effect; make the relationships between things evident; provide the ‘why’
and/or ‘how’
Extrapolate infer from what is known
Gather collect items from different sources
Identify recognise and name
Interpret draw meaning from
Investigate plan, inquire into and draw conclusions
Justify support an argument or conclusion
List write down phrases only, without further explanation
Modify change in form or amount in some way
Outline sketch in general terms; indicate the main features of
Predict suggest what may happen based on available information
Present provide information for consideration
Propose put forward (e.g. a point of view, idea, argument, suggestion) for consideration or action
Recall present remembered ideas, facts or experiences
Recommend provide reasons in favour of
Record store information and observations for later
Recount retell a series of events
Research investigate through literature or practical investigation
State provide information without further explanation
Summarise express concisely the relevant details
Verbs
Science Focus 4 uses the following verbs in the student activities.
Account account for: state reasons for; report on give an account of: narrate a series of events
or transactions
Analyse identify components and the relationships among them; draw out and relate implications
Apply use, utilise, employ in a particular situation
Appreciate make a judgement about the value of
Assess make a judgement of value, quality, outcomes, results or size
Calculate determine from given facts, figures or information
Clarify make clear or plain
Classify arrange or include in classes/categories
Compare show how things are similar or different
Construct make; build; put together items or arguments
Contrast show how things are different or opposite
Critically add a degree or level of accuracy, depth,
(analyse/evaluate) knowledge and understanding, logic,
questioning, reflection or quality to (analysis/evaluation)
Deduce draw conclusions
Define state meaning and identify essential qualities
Demonstrate show by example
Describe provide characteristics and features
Discuss identify issues and provide points for and/or against
Distinguish recognise or note/indicate as being distinct or different from; note differences between
Evaluate make a judgement based on criteria; determine the value of
>
>
>
By the end of this chapter you should be able to:
write the formulas for some common chemicals
construct word equations for simple chemical reactions explain why the equations for
chemical reactions need to be balanced
construct balanced formula equations for chemical reactions
identify some compounds that use covalent bonding and others that use ionic bonding
identify the characteristics of some families of organic compounds.
1 List two states that you are in right now.
2 Write chemical formulas for water, carbon dioxide and hydrochloric acid.
3 What is dephlogisticated air?
4 Can matter be created or destroyed? If so, how?
5 How can you get two flames from a Bunsen burner?
6 Can ethanol be dangerous to your health?
Outcomes
5.2, 5.7.3Pre quiz
1
1
Chemical
Chemical
Key focus area:
The nature and practice of science
>
>
>
Equations and formulas
Chemical equations take the form:
reactants
→
productsThe substances present at the start of a reaction are called the reactants, and the new substances formed are called the products.
Chemical equations can be written as either word equations or balanced formula equations. For example, the reaction between magnesium and hydrochloric acid may be represented as the word equation:
magnesium + hydrochloric
→
magnesium + hydrogen acid chlorideor as a balanced formula equation:
Mg + 2HCl
→
MgCl2 + H2Whichever way we write it, the reaction probably looks something like that shown in Figure 1.1.1.
By now you should be able to write the symbols for many elements and the chemical formulas of many common compounds. If you are not yet sure how to do this, refer to Science Focus 3, Chapters 1 and 2, before
going any further. It is essential that you can write correct chemical formulas, or none of your equations will be correct.
Here are a few facts you may have forgotten: General:
• An element consists of only one type of atom, e.g. Fe, O2 and S6.
• A compound consists of two or more different atoms, chemically bonded together, e.g. H2O,
H2SO4 and CO2.
• Ions are charged particles. Positive ions are formed when metal atoms lose electrons, e.g. Na+, Mg2+
and Al3+. Negative ions are formed when non-metal atoms gain electrons, e.g. Cl–, S2– and N3–.
• A polyatomic ion or radical is a charged particle made up of more than one type of atom, e.g. NH4+,
SO42– and CO32–.
Pure metals:
• The bonding within metals (e.g. iron (Fe), gold (Au) and calcium (Ca)) is called metallic bonding. • All metals are solid at 25°C, except mercury (Hg),
which is liquid. Covalent bonding:
• Covalent bonding is the sharing of electrons and occurs only between metals and other non-metals, like carbon (C) and oxygen (O), sulfur (S) and hydrogen (H), nitrogen (N) and fluorine (F). • A molecule is composed of non-metals and is
the smallest number of atoms that exist bonded together in a stable form. Atoms of the noble gases (Group VIII) exist by themselves and are called monatomic. For carbon dioxide (CO2), a molecule
consists of one carbon atom and two oxygen atoms covalently bonded together. This molecular formula represents the number and type of atoms in the compound.
UNIT
UNIT
3.1
3.1
UNIT
UNIT
1.1
1.1
Chemical reactions occur around us all the time. A colour change or release of heat are signs that a chemical change is probably taking place. Chemical reactions can be very simple or highly complex. It is easy to record
context
Mg Mg2+ Cl Cl -Cl -Cl H H H H + + Fig 1.1.1The reaction between magnesium and hydrochloric acid
our observations of chemical reactions, but we also need to be able to represent what is going on at a chemical level. The easiest way to represent reactions is to use chemical equations.
>
>
>
Writing chemical equations
Writing chemical equations
• A diatomic molecule consists of two non-metal atoms covalently bonded together. Elements that exist as diatomic molecules are the gases hydrogen (H2),
oxygen (O2), nitrogen (N2),
fluorine (F2) and chlorine
(Cl2), the liquid bromine
(Br2), and solid iodine (I2).
Ionic bonding:
• Ionic bonding almost always involves metals combined with non-metals. Ionic compounds are crystalline solids, unless dissolved in water as an aqueous solution.
• The formula of an ionic
compound is not a molecular formula, since ionic compounds form large crystal lattices, not molecules. Instead the formula shows the ratio of ions in the crystal. For example, the ionic compound magnesium oxide has the formula MgO. This doesn’t mean that one atom of magnesium and one atom of oxygen move around together; it just means that in any sample of magnesium oxide, the ratio of magnesium ions Mg2+ to oxide ions
O2– is 1:1. A small crystal may contain a thousand magnesium ions and a thousand oxide ions, while a larger crystal may contain a million magnesium ions and a million oxide ions. Either way, the formula is simply MgO.
Two different ways of representing the structure of the ionic crystal caesium chloride
Cs+ ion Cs+ ion Cl–ion Cl–ion Fig 1.1.2 The bends When we breathe,
oxygen (O2) in the air is
absorbed and dissolved into our blood and used for respiration. Nitrogen
(N2) is also absorbed and
dissolved, but is not used. If a diver who is breathing compressed air rises from the deep too fast, the nitrogen forms bubbles in the diver’s blood. Crippling
pain and paralysis (the ‘bends’) often result. Divers often use a mix of
compressed oxygen (O2)
and helium (He), to remove much of the problem of nitrogen bubbles. It allows
a diver to come to the surface twenty times faster
than with compressed air.
Worksheet 1.1 Writing formulas
Sometimes more than one of a polyatomic ion is needed in a formula. This is when brackets are used, for example Fe2(SO4)3, Ca(OH)2, (NH4)2CO3.
Balancing chemical equations
Let’s take another look at the reaction between magnesium and hydrochloric acid.
Mg + 2HCl
→
MgCl2 + H2In this equation there are a lot of twos! But does each 2 mean the same thing?
The small numbers (like the ‘2’ in H2) are called
subscript numbers. These show how many of that type of atom or ion are in the formula. If there is no subscript number after an atom or ion, it means there is only one of that atom or ion in the formula. Brackets with more subscript numbers simply multiply everything inside. Take these examples: • H2O has 2 hydrogen (H) atoms and 1 oxygen (O)
atom.
• MgCl2 has 1 magnesium ion (Mg2+) and 2 chloride
ions (Cl–).
• Ca(OH)2 has 1 calcium ion (Ca2+) and 2 hydroxide
ions (OH–). The brackets indicate that overall there are 2 hydrogen (H) atoms and 2 oxygen (O) atoms. • Fe2(SO4)3 has 2 iron (Fe3+) ions and 3 sulfate ions
(SO42–). The brackets indicate overall that there are
3 sulfur (S) atoms and 12 oxygen (O) atoms. You cannot fiddle with or change subscript numbers. These numbers are determined by the place of each element in the periodic table. If you change subscript numbers then you are actually inventing new chemicals! Water (H2O), for example, is the safe
liquid we drink and wash in. H2O2 is also
a clear and colourless liquid but is a very strong corrosive bleach called hydrogen peroxide. See what happens if you fiddle with subscript numbers?
The larger numbers in front of formulas indicate how much of each chemical is being used and how much is being produced in the reaction. These are the numbers we can fiddle with to balance an equation. The Law of Conservation of Matter states that ‘matter can be neither created nor destroyed; it can only be changed from one form to another’. This means that there must be the same number of each type of atom on each side of the equation. The atoms
Prac 1 p. 9
UNIT
UNIT
1.1
1.1
The easiest way to balance equations is to
follow steps. To show this we will use another
example.
Sodium carbonate is added to nitric acid, producing sodium nitrate, water and carbon dioxide. • Step 1: Write the word equation for this reaction.
sodium + nitric
→
sodium + water + carbon carbonate acid nitrate dioxide• Step 2: Find the formula for each substance in the word equation.
Sodium carbonate is Na2CO3 and nitric acid is
HNO3.
Sodium nitrate is NaNO3, water is H2O and carbon
dioxide is CO2.
• Step 3: Use these formulas to write an unbalanced formula equation.
Na2CO3 + HNO3
→
NaNO3 + H2O + CO2• Step 4: Balance each element, one by one, until there are the same numbers of each type of atom on both sides.
Sodium (Na): Two on the left, but only one on the right. Put a big ‘2’ in front of the formula for sodium nitrate (NaNO3):
Na2CO3 + HNO3
→
2NaNO3 + H2O + CO2Carbon (C): One on each side. No balancing required.
Oxygen (O): Six on the left, but nine on the right. Placing a big ‘2’ in front of the formula for nitric acid (HNO3) solves the problem:
Na2CO3 + 2HNO3
→
2NaNO3 + H2O + CO2The other way to balance for oxygen would have been to put a ‘2’ in front of the formula for sodium carbonate. This would have solved the oxygen problem, but it would have unbalanced the numbers of sodium and carbon.
Hydrogen (H): There are now two on each side, so no more balancing is required.
• Step 5: Double check the numbers of atoms on each side to make sure your final equation is correct.
Na2CO3 + 2HNO3
→
2NaNO3 + H2O + CO2are simply being rearranged by the reaction. The unbalanced equation for the above reaction is:
Mg + HCl
→
MgCl2 + H2There is one magnesium on each side of the equation, so they are already balanced.
However, while there is only one hydrogen atom on the left, there are two on the right. These can be balanced by doubling the amount of HCl we use. A large ‘2’ is added in front of the HCl, giving us two hydrogen atoms on both sides.
Mg + 2HCl
→
MgCl2 + H2This also balances the chlorines. When an equation is balanced, the mass of the products is equal to the mass of the reactants. Nothing has been destroyed and nothing new has been created. All the atoms
have just been rearranged. This is known as the Law of Conservation of Mass, and is another way of stating the Law of Conservation of Matter. Cl H H H Cl H Putting a ‘2’ in front of a formula means two of that species e.g. 2HCl means
The smaller subscript numbers are different. They show how many of each type of atom are present.
H2O represents CH4 represents O H H H H C
Fig 1.1.3 What do the numbers in chemical
equations mean? Prac 2 p. 9 H H H H O O H H O H H O + + 2H2 O2 2H2O Fig 1.1.4
A balanced equation has the same number and types of atoms on each side of the equation.
Fuel cells
The hydrogen–oxygen fuel cells used in the Apollo space missions produced pure water as a by-product. The astronauts then used this for drinking. The equation for this reaction is:
>
>
>
Writing chemical equations
Reactant side: 2 Na, 1 C, 9 O, 2 H, 2 N Product side: 2 Na, 1 C, 9 O, 2 H, 2 N
Problem solved! Sometimes a bit of trial and error is required before you successfully balance an equation.
Following the steps above, you should find that
Al2O3 + C
→
CO + Albecomes the balanced equation
Al2O3 + 3C
→
3CO + 2AlWhich state are we in?
The reaction between calcium and oxygen, forming calcium oxide, may be represented as:
2Ca + O2
→
2CaOBut what form is each chemical in? Are they solid or liquid, a gas or dissolved in water? In order to complete the picture of the reaction, we use more subscripts to indicate the physical states of the reactants and products. These were briefly introduced in Chapter 2 of Science Focus 3. The subscripts used are:
• (s) for a solid substance • (g) for a gas
• (l) for a pure liquid
Lights, action!
Calcium oxide (quicklime) produces an intense white light when it is burnt and so was used as an early spotlight in theatres. The performers on stage were ‘in the limelight’, a term
that is still used for a person who is the centre
of attention.
• (aq) to show that a substance is in aqueous solution (i.e. dissolved in water).
Including states, the above reaction would look like this:
2Ca(s) + O2(g)
→
2CaO(s)All the details of the reaction are now clear. Two atoms of solid calcium react with one molecule of gaseous oxygen, producing two
solid calcium oxide ion clusters. This gives a lot more information than before. From this point on, try to write all your chemical equations including state subscripts.
Unless told otherwise, you should always write the states of reactants and products as they occur at Standard Laboratory Conditions (25°C and ‘normal’ 1 atmosphere pressure).
For example, at Standard Laboratory Conditions, mercury (Hg) is a liquid and sulfur (S) a yellow solid. They react to form mercury sulfide (HgS), the reaction being:
Hg(l) + S(s)
→
HgS(s)The fall of Rome
Lead poisoning probably played a significant part in the fall of the Roman Empire. Infertility was caused by drinking wine from leaden vessels. Lead
was also used as a cure for diarrhoea. Cosmetics used by ancient peoples included white lead on the face, mercury sulfide
as lipstick, and arsenic sulfide as eyeshadow; the
ultimate self-poisoner’s make-up kit!
Worksheet 1.2 Writing and balancing chemical equations
Worksheet 1.3 Revising chemical equations +
+ liquid mercury
solid sulfur solid mercury (II) sulfide
Hg(l) S(s) HgS(s)
Fig 1.1.6 Compounds have very different
physical properties from the elements that made them.
Writing chemical equations
Normally we think of nitrogen as a gas but it can also be cooled down to make it into a liquid.
UNIT
UNIT
1.1
1.1
1.1
UNIT
[
Questions
]
Checkpoint
Equations and formulas
1 Chemical equations have three main parts. State the
name of each part.
2 State what ‘+’ and ‘
→
’ mean in chemical equations.3 List the three main types of chemical bonding.
Balancing chemical equations
4 State the Law of Conservation of Matter.
5 Explain how the Law of Conservation of Matter applies
to chemical equations. Which state are we in?
6 State the symbols and name used to show the state of
matter of chemicals in chemical equations.
7 State the Standard Laboratory Conditions of
temperature and pressure.
Think
8 Compare the Law of Conservation of Mass with the
Law of Conservation of Matter.
9 Compare the use of subscript numbers in chemical
equations with the use of larger-sized numbers.
10 Contrast NaCl(s) with NaCl(aq).
11 Identify the molecules in the list below. a CO2 b H2O c NaCl d Li2CO3 e N2 f CaO g Ar
12 Calcium forms the ion Ca2+ and chlorine forms the chloride ion, Cl–. Identify the correct ionic formula for calcium chloride.
A CaCl B Ca2Cl
C CaCl2
D Ca2Cl
13 Explain why Na2SO4 is not a molecular formula, but
H2O is.
14 Identify the equation that is correctly balanced. A HNO3 + MgO
→
Mg(NO3)2 + H2OB 2HNO3 + MgO
→
Mg(NO3)2 + H2OC 2HNO3 + 2MgO
→
2Mg(NO3)2 + H2OD 2HNO3 + 3MgO
→
Mg(NO3)2 + H2O15 Identify the equation that is not balanced. A C5H12 + 8O2
→
CO2 + 6H2OB Mg + 2HCl
→
MgCl2 + H2C 2Zn + O2
→
2ZnOD 4Al + 3O2
→
2Al2O3Skills
16 At Standard Laboratory Conditions (SLC), oxygen
exists as O2(g). Construct the formula for each of these
substances at SLC, including the appropriate state: (aq), (l), (s), (g).
a water
b carbon dioxide c dilute sulfuric acid d calcium chloride e neon
f hydrogen
g magnesium carbonate crystals h dilute nitric acid
17 For each of the following substances, state: i the chemical formula
ii the type of bonding as metallic, ionic or covalent a magnesium b strontium sulfate c oxygen gas d carbon monoxide e calcium chloride f sulfur dioxide g sodium h argon
18 Modify the following equations so that they are
balanced.
a P4 + O2
→
P2O5b KClO3
→
KCl + O2c BaO + HNO3
→
Ba(NO3)2 + H2Od Pb3O4
→
PbO + O2e Pb(NO3)2
→
PbO + NO2 + O219 Modify these equations so that they are balanced.
Include any missing states.
a H2(g) + O2(g)
→
H2Ob Na + Cl2
→
NaCl(s)c CaCO3(s)
→
CaO(s) + O2d CH4 + O2
→
CO2 + H2O(g)e HNO3 + Ca(s)
→
Ca (NO3)2(aq) + H220 Jessica heated some bright blue copper(II) nitrate
>
>
>
Writing chemical equations
Writing chemical equations
[
Extension
]
Complete the following activities by
connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1 and clicking on the destinations button.
1 Investigate green chemistry.
a Describe what is meant by ‘green chemistry’. b Outline some examples of what is being done in
the study of green chemistry.
c Present your information as a poster to convince
the general public that green chemistry is important for society and the environment.
dioxide gas being produced. A glowing splint held at the top of the test tube re-lit, proving that oxygen gas was also produced. A fine black solid, copper(II) oxide, was left in the test tube.
a In this reaction state the reactants and the
products.
b Construct the word equation for this reaction. c Construct the balanced chemical equation,
including states.
21 For each of the following reactions, construct: i the word equation
ii the balanced formula equation, including states a Dilute hydrochloric acid reacts with grains of
sodium hydroxide. Water and sodium chloride are the products.
b Ammonia (NH3) gas is produced when
nitrogen gas is added to hydrogen gas.
c Carbon monoxide gas combines with
oxygen to form carbon dioxide gas.
d Solid iron combines with chlorine gas
to produce solid iron(III) chloride.
e Dilute sodium hydroxide solution is added
to dilute sulfuric acid. Sodium sulfate and water are produced.
f Ammonium nitrate dissolves in water to produce
ammonium and nitrate ions.
g Hydrochloric acid reacts with calcium metal. A
solution of calcium chloride is produced, through which rise bubbles of hydrogen.
Mass of sodium Mass of oxygen Mass of sodium oxide
reacting (grams) reacting (grams) produced (grams)
2.00 0.70 2.70
3.00 1.04 4.04
4.00 1.39 5.39
Analyse
22 David added some dilute hydrochloric acid to some
solid limestone (calcium carbonate) in a beaker. When he weighed the products after the bubbling had stopped, he noticed that there had been a reduction in mass.
Explain why his results did not seem to agree with the
Law of Conservation of Mass.
23 Solid sodium reacts with oxygen to produce solid
sodium oxide. The following experimental data were obtained for the reaction between sodium and oxygen, producing sodium oxide:
a Construct a word equation for this reaction. b Construct an unbalanced chemical equation for the
reaction, then balance it.
c Modify the equation to include the states of the
reactants and products.
d Explain how the above results prove the Law of
Conservation of Mass.
2 Connect to the CSIRO double helix website
and locate the ‘Cool Experiments’ page.
a Identify an experiment that involves a
chemical reaction and can safely be done at home.
b Perform the experiment and present a scientific
report on your findings.
3 Complete the tutorial on balancing chemical equations.
This may mean spending some time each day over about two weeks working through the tutorial. Record your self-assessment in a log during this time.
UNIT
UNIT
1.1
1.1
[
Practical activities
]
1.1
UNIT
Studying a reaction
Aim To make quantitative observations of the reaction of magnesium metal and an acid
Equipment
Magnesium strips, 1 M sulfuric acid, large beaker, small filter funnel, 100 mL measuring cylinder, cling wrap, gloves, lab coat, safety glasses
large beaker water filter funnel magnesium inverted measuring cylinder of acid cling wrap Fig 1.1.7 Method
1 Cut a 4 cm long strip of magnesium. Place it under the
filter funnel in the beaker.
2 Fill the beaker with water until it covers the filter funnel. 3 Fill the measuring cylinder with acid and cover it in cling
wrap.
4 Carefully invert the measuring cylinder on top of the filter
funnel. Let the neck of the filter funnel pierce the cling wrap.
5 After the bubbling seems to have stopped, measure the
volume of gas collected in the measuring cylinder.
Questions
1 Construct a word equation and the balanced formula
equation for this reaction. The products are hydrogen H2
and magnesium chloride MgCl2.
2 Calculate the volume of hydrogen gas that you would
expect to have been produced if you had used instead:
a an 8 cm strip of magnesium b a 1 cm strip of magnesium
Prac 1 Unit 1.1
Conservation of mass
Aim To investigate conservation of mass in a chemical reaction
Equipment
Solid calcium carbonate, 0.5 M hydrochloric acid, 200 mL conical flask, balloon, spatula, 100 mL measuring cylinder, lab coat, safety glasses, access to an electronic balance
Prac 2 Unit 1.1 calcium carbonate 30 mL acid conical flask balloon Fig 1.1.8 Method
1 Measure out approximately 0.2 g of calcium carbonate
in the conical flask.
2 Measure out 30 mL of hydrochloric acid into the
measuring cylinder.
3 Place the conical flask, measuring cylinder and balloon
on the balance and record their total weight.
4 Pour the acid into the conical flask and quickly place the
balloon on top.
5 When the reaction is complete, re-weigh the flask (with
balloon attached) and empty measuring cylinder.
Questions
1 Construct a word equation and balanced formula
equation for this reaction.
2 Assess whether your results agree with the Law of
Conservation of Mass.
3 If your results do not agree with the Law, propose
10
1.2
1.2
Some reactions are slow. Others are fast. When we take an antacid, we hope its reaction with the acids in our stomach will be a quick one, since it will relieve our indigestion. Some reactions are so fast, however, that they explode!
When solid potassium is added to water, large volumes of explosive hydrogen gas are rapidly
produced, the energy released by the reaction setting the hydrogen alight. Other reactions like the rusting of iron, or milk turning sour, are very slow. How quickly a reaction happens can make the difference between it being safe or dangerous. The speed of a reaction is also important in industry. When producing chemicals a slow reaction may be unprofitable. Speeding up industrial reactions is a very important area of chemistry. An especially important Australian example of this is the production of sulfuric acid.
co
nt
ex
t
UNIT
UNIT
>
>
>
Industrial reactions
For a reaction to be carried out profitably in industry it must occur fairly quickly, and it must give a good yield. The yield is the amount of product obtained, and can be expressed as the percentage of the
expected product that is obtained. For example, if 6 g of aluminium reacts according to the equation:
4Al(s) + 3O2(g)
→
2Al2O3(s)we could expect to obtain 11.3 g of Al2O3.
Fig 1.2.1
For a long time, hydrogen was blamed for the Hindenburg disaster.
If, for various reasons, only 5 g was obtained then the yield was 5/11.3 × 100 =
44%.
So how are a fast reaction rate and a good yield achieved?
The Hindenburg disaster
On 6 May 1937, the hydrogen-filled Hindenburg airship burst into flame while landing in New Jersey, USA. The
hydrogen was viewed as the culprit for many years. Extensive recent research has, however, discovered that hydrogen did not cause the initial
fire. The actual cause was the high flammability of the fabric cover. It was
made of a cotton substrate with an aluminised cellulose acetate butyrate
covering. The observations at the scene were consistent with a huge aluminium fire. The fabric was ignited by electrical activity in the atmosphere.
The hydrogen only exploded once the fire had burnt through the covering.
The electrolytic refinement of copper
1.2
1.2
UNIT
UNIT
Methods commonly used to improve yield include: • carrying out the reaction at a reasonably high
temperature. The higher the temperature, the greater the energy of the reactants, making the reaction more likely to occur.
• using a catalyst. Catalyst are substances that are not consumed in a reaction, but help the reaction to proceed more quickly.
• removing the products as they are formed. • constantly adding reactants to replace
those used up.
Specific reactions may have particular conditions associated with them.
Sulfuric acid, H
2
SO
4
As an example of an industrial process, we will look at the production of sulfuric acid, a chemical very important to our everyday lives. Sulfuric acid production dates back to the early alchemists. At one stage, concentrated sulfuric acid was called ‘oil of vitriol’ because it was prepared by distilling hydrated ferrous sulfate, FeSO4.7H2O, otherwise known as iron
vitriol.
Sulfuric acid is the cheapest bulk acid, and is sometimes referred to as the ‘king of chemicals’ because it is produced in such huge quantities worldwide. A country’s sulfuric acid production is considered an excellent indicator of its industrial well-being.
Uses of sulfuric acid
In the nineteenth century, the German chemist Baron Justus von Liebig discovered that when sulfuric acid was added to soil, it increased the amount of phosphorus in the soil for plants to use. The current largest single use of sulfuric acid is in making fertilisers, both superphosphate and ammonium sulfate. It is also used to make many organic
compounds, including ether, nitroglycerine and dyes. It is important in refining petroleum, making
paints and pigments, processing metals and making rayon. It is found in car batteries and used in the superconductor industry for cleaning.
Some properties of sulfuric acid
• Strong acid • Corrosive • Colourless liquid • Density 1.85 g/cm3 • Melting point 10.4°C Prac 1 p. 13 DYO
Some products made using sulfuric acid
rayon dyes car battery superconductors nitroglycerine Fig 1.2.3 Prac 3 p. 14 • Boiling point 340°C • Very soluble in water
• Dissolving the concentrated acid in water releases a lot of heat (highly exothermic).
• Is a dessicant (absorbs water from surroundings) • Can cause severe ‘burns’ to skin
• Can cause blindness if it gets in eyes.
Production of sulfuric acid
The contact process is the most commonly used method for producing sulfuric acid.
Drying tower Heat exchanger Converter Storage tanks SO2 SO2 + air SO3 SO3 SO2 + air air Water molten sulfur Diluter Absorption tower Conc. H2SO4
Sulfur burner Deduster
Fig 1.2.4
The contact process for the production of sulfuric acid
Step 1
Molten sulfur is burned in air to produce sulfur dioxide gas.
S(l) + O2(g)
→
SO2(g)Prac 2 p. 14
>
>
>
The O2 comes from air which has been dried with
96% H2SO4 and then had dust particles removed.
The yield is increased by making sure that plenty of oxygen is available.
Step 2
In the converter, the reaction rate is increased by heating the sulfur dioxide in oxygen. The catalyst vanadium oxide turns it into sulfur trioxide. This is a reversible reaction—it can occur in both directions.
2SO2(g) + O2(g)
→
2SO3(g)The converter used for sulfuric acid production
10% SO2 11% O2 feed gas heat exchangers to oleum or intermediate absorber from intermediate absorber to final absorber 420°C 600°C 63% conversion 84% conversion 93% conversion 99.5% conversion 450°C 510°C 450°C 475°C 420°C 535°C reaction bed 1 reaction bed 2 reaction bed 3 reaction bed 4 Fig 1.2.5
The gases are passed over several catalyst beds, rather than just one, to give them more chance of reacting, thus increasing the yield further.
Step 3
In the absorber, oleum (H2S2O7) is produced. Like the
other reactions involved in sulfuric acid manufacture, this is exothermic. The energy released can be used to make electricity, which helps maintain the cheap price of sulfuric acid.
SO3(g) + H2SO4(l)
→
H2S2O7(l)Step 4
Oleum is hydrated to form sulfuric acid.
H2S2O7(l) + H2O(l)
→
2H2SO4(l)You can see that to make this series of reactions occur faster and with high yield, they are maintained at a reasonably high temperature and a catalyst is used. Products are removed as they are formed, and fresh reactants are injected. This combination gives the industrial process for sulfuric acid
production a 99% yield.
Who was the False Geber?
The man who discovered sulfuric acid around 1300
did not write under his real name. Instead, he borrowed the name of Geber from a long-dead Arabic alchemist. His real name was never revealed, so this great chemist has always been known as the
False Geber.
1.2
UNIT
[
Questions
]
Checkpoint
Industrial reactions1 State an example of: a a fast reaction b a slow reaction
2 Clarify what is meant by the ‘yield’ of a reaction. 3 Clarify what is meant by the ‘rate’ of a reaction. 4 State what the ‘ideal’ yield of a reaction would be. 5 A fast reaction rate and a good yield are particularly
desirable for industrial reactions. Explain why.
Worksheet 1.4 Rates of reaction
6 Describe two ways to obtain a faster reaction rate.
Sulfuric acid
7 Sulfuric acid is known as ‘the king of chemicals’. Explain why.
8 State three major uses of sulfuric acid.
9 State five properties of concentrated sulfuric acid. 10 Identify the catalyst used in the contact process. 11 State the formula for the following substances:
a sulfuric acid b sulfur dioxide c sulfur trioxide d oleum
Think
12 Several catalyst beds are used in the contact process. Explain why.
13 Propose a reason why it is called the contact
process.
More and faster! Rate and yield considerations
UNIT
UNIT
[
Practical activities
]
1.2
UNIT
Rates of reactions 1
Aim To investigate the variables that affect reaction rates
Equipment
Lab coat, safety glasses, gloves, magnesium strips, ice, 1 M HCl, hydrogen peroxide solution, solid manganese dioxide, stopwatch, spatula, 4 test tubes, test-tube rack, 10 mL measuring cylinder, 2 ×100 mL beakers
Prac 1 Unit 1.2
14 Explain what happens in the converter, including how
the rate and yield are maximised.
15 Construct balanced equations for each step in the
production of sulfuric acid by the contact process.
16 Draw a simplified flow chart to demonstrate the four
steps in the contact process.
17 Evaluate the importance of considering the rate and
yield in an industrial reaction.
[
Extension
]
Investigate
1 Research a chemical reaction of industrial importance.
This may include one of the following:
• the Haber process for producing ammonia • the Ostwald process for producing nitric acid • the production of margarine
• the catalytic converter in car engines and power plants • the Solvay process for producing sodium hydrogen
carbonate
• the production of superphosphate
a Construct a labelled diagram or flow chart outlining
the chemical process.
b Describe how the reaction conditions are controlled
to obtain:
i the maximum yield of product ii a fast reaction rate
c Outline three significant uses for the product
obtained in the industrial process researched.
d Present your information in a form that is suitable for
display at a science fair.
2 The airbag in a car works because of a very fast
chemical reaction.
a Investigate how an airbag works.
b Present your findings in a brochure that explains
this clearly to car owners.
3 Sulfuric acid and sulfur dioxide can cause problems
in the environment. Research what these problems may be and produce a web page or PowerPoint presentation that outlines your information.
Surf
4 Find out more about the Hindenburg disaster by
connecting to the Science Focus 4 Companion Website at
www.pearsoned.com.au/schools, selecting
chapter 1 and clicking on the destinations
button. Write a newspaper article to assess the true chemical nature of the Hindenburg disaster.
1 Time the reaction from
the moment the magnesium is dropped into the acid, until there is no magnesium left.
2 For the second experiment,
cool the acid before adding the magnesium.
acid + Mg ice water
acid Fig 1.2.6
1.2
1.2
>>
Skills
18 Identify the elements that make up sulfuric acid. 19 It was expected that 2 tonnes of aluminium was to be
obtained from 4 tonnes of ore, but only 1.65 tonnes was obtained. Calculate the percentage yield.
>
>
>
Method
1 Add a 2 cm strip of magnesium to a test tube. 2 Add 5 mL of acid and time how long it takes for the
reaction to finish. The reaction is Mg(s) + 2HCl(aq)
→
MgCl2(aq) + H2(g)3 Place 5 mL of acid in the second test tube and sit it in a
beaker of ice water.
4 Once again, add a 2 cm strip of magnesium and time
how long it takes for the reaction to finish.
5 Add 2 mL of acid and 3 mL of water to a third test
tube.
6 Add a 2 cm strip of magnesium and time how long it
takes for the reaction to finish.
Rates of reactions 2
Aim To investigate how the surface area affects reaction rate
Equipment
Lab coat, safety glasses, gloves, marble chips (large and small), powdered calcium carbonate, dilute hydrochloric acid, stopwatch, spatula, 4 test tubes, test-tube rack, 10 mL measuring cylinder, electronic balance
Prac 2 Unit 1.2
DYO
7 Add 5 mL of hydrogen peroxide solution to each of two
beakers. Hydrogen peroxide gradually breaks down according to the equation
2H2O2(aq)
→
2H2O(l) + O2(g)8 To one beaker, add a very small amount of manganese
dioxide.
9 Compare the two beakers and record your observations.
Questions
1 Identify factors that made the reactions proceed faster
or slower.
2 Predict the effect of heating the reactions. 3 Identify the role of the manganese dioxide in the
hydrogen peroxide reaction.
Method
1 Using the equipment listed, design and perform an
experiment to test the effect of surface area on the rate of reaction.
2 Construct a graph to display your results.
Questions
1 Use your results to deduce how surface area affects
the rate of reacton.
2 Propose how your experiment could be improved.
TEACHER DEMONSTRATION
Dehydrating action of sulfuric acid
Note: This experiment should be performed in a fume cupboard.
Prac 3 Unit 1.2
Aim To observe the dehydration action of concentrated sulfuric acid
Equipment
Lab coat, safety glasses, gloves, conc. H2SO4,
blue copper(II) sulfate crystals, glucose or sucrose, 2 × 100 mL beakers, 2 spatulas
Method
1 Add 2–3 spatulas of blue copper(II) sulfate crystals to a
beaker.
2 Carefully pour about 10 mL of conc. H2SO4 over the
crystals.
3 Leave for a few minutes.
4 Add 2–3 spatulas of glucose or sucrose to another
beaker.
5 Carefully add about 15 mL of conc. H2SO4.
6 Leave for several minutes.
Questions
1 Describe your observations for each experiment. 2 Construct an equation for each reaction.
It is common nowadays to see organically grown produce in shops, and see labels that say ‘100% organic’ or ‘made from organic ingredients’. This means the food
has been grown by natural methods, avoiding the use of
synthetic chemicals such as insecticides. In chemistry, the term ‘organic’ refers to the chemistry of substances in
which carbon is the main element. Organic substances also contain other elements such as hydrogen, oxygen and nitrogen, but carbon is always the ‘backbone’. Organic substances are the basis of
all living things, and of everything that was once living.
Organic chemistry
Organic chemistry is the chemistry of carbon compounds. Carbon has four outer-shell (or valence) electrons and can covalently
bond with up to four other atoms, usually other carbon atoms, hydrogen or oxygen. In this way, carbon is unique Organic water
One brand of mineral water is currently being marketed as ‘100% organic’. Does this mean
that the water was ‘grown’ by natural methods or does it mean
that it is full of both living and dead organisms? Marketing campaigns frequently misuse
terminology and should be treated with care—for example,
a brand of marshmallows is currently being labelled as ‘fat free’. Marshmallows have always
been fat free, but are full of sugars, which will be converted
to fat if you eat too many!
Fig 1.3.1 This person contains many organic
compounds, including proteins, lipids and carbohydrates.
in that it is able to form millions of different stable compounds. Compounds like carbon monoxide (CO) and carbon dioxide (CO2)
are inorganic compounds, as are methane (CH4) and vinegar (acetic
acid, CH3COOH).
Multiple bonds
Before we go any further, it is important that you understand the difference between single bonds, double bonds and triple bonds. Some information to help you understand the bonds:
• A single bond is one pair of electrons being shared between two atoms.
• A double bond is two pairs of electrons being shared between two atoms.
• A triple bond is—you guessed it—three pairs of electrons being shared between two atoms. Carbon has atomic number 6, which means it contains six protons and six electrons. It has two electrons in the first shell, and four electrons in its outer (valence) shell, giving it an electronic configuration of 2.4. Its four valence electrons place it in Group IV of the Periodic Table. To achieve a stable eight valence electrons, carbon needs to gain four more electrons. It does so by forming four covalent bonds.
These can be: • four single bonds, or • two double bonds, or • a single and a triple bond, or
• one double bond and two single bonds.
Deadly rhubarb
Rhubarb contains high levels of a deadly organic
compound, oxalic acid. Although the edible stalks contain a very low level of oxalic acid, the level in the leaves is high, so high that during World War I, people died from eating them as a vegetable. Beetroot and peanuts also contain significant amounts of oxalic
acid, but you would have to eat a lot to overdose. Oxalic acid kills by lowering our blood calcium below the
critical level.
My necklace was once my grandmother!
Humans are built from organic substances and are
therefore a good source of carbon. Diamonds are one of the forms pure carbon
takes. A company in the United States, LifeGem Memorials, is developing a process to exploit these two facts: they intend to convert cremated human remains into diamonds, which can then be worn as jewellery by grieving
relatives!
context
UNIT
UNIT
>
>
>
Hydrocarbons
The simplest organic compounds are hydrocarbons. These are compounds that consist only of carbon and hydrogen. Hydrocarbon compounds are important in our everyday lives. Cars run on hydrocarbon fuels and other hydrocarbons lubricate their engines. The many plastics we use are derived from hydrocarbons.
Multiple bonds C C C C C C C C H H H H H H C C H H H H C C H H O shared pair of electrons T o shared pairs of electrons Th shared pairs of electrons Ethane contains
only single bonds
Ethene contains one carbon-carbon double bond and four carbon-hydrogen single bonds
Ethyne contains one carbon-carbon triple bond and two carbon-hydrogen single bonds
Single bond Double bond
Triple bond
Fig 1.3.2
Fig 1.3.3 These items are all hydrocarbon-based.
where n is the number of carbon atoms. Put simply, the number of hydrogen atoms equals double the number of carbon atoms plus two.
For example, if the compound contains two carbon atoms,
n = 2
then the number of hydrogen atoms in the molecule is
2n + 2 = (2 × 2) + 2 = 6
The molecular formula is therefore C2H6.
The alkanes form a related series of molecules called a homologous series. Each molecule in the series is a little bigger than the previous one: each subsequent molecule has an additional –CH2 unit
added to it. The first two members in the homologous series of alkanes are methane, CH4, and ethane, C2H6.
Methane and ethane
CH4 C2H6 H H H H C H H H C H H H C C C H H H H H H C H H H H methane ethane Fig 1.3.4
The first part of the name indicates how many carbon atoms are in the compound. The prefixes used for naming are listed in the table.
The second part of the name indicates what type of compound it is.
For alkanes, the name ends in –ane. For example, the alkane containing four carbons is called butane. It has the formula C4H10. Prefix Number of carbon atoms Meth 1 Eth 2 Prop 3 But 4 Pent 5 Hex 6 Hept 7 Oct 8 Non 9 Dec 10
Alkanes
Alkanes are hydrocarbons that contain only single bonds. They have the general formula
CnH2n + 2
UNIT
UNIT
Crude oil is formed from the remains of plants and animals that lived millions of years ago, and is composed mostly of alkanes. The crude oil is refined (separated into its components) by fractional
Fig 1.3.5 Crude oil forms from the remains of dead
animal and plants under the Earth’s crust. Oil rigs are used to extract the oil.
cool (25°C) very hot (400°C) Name of fraction How many carbons in chain? What is it used for?
Fuel for cars Fuel for jets 16–20 Fuel for central
heating. Can also be cracked to make smaller molecules Lubricating
oil
20–30 Oil for machines like cars. Can be cracked Fuel oil 30–40 Fuel for ships and
power stations Paraffin wax 40–50 Waxy papers,
candles, polishing Gas 1–4 Fuel Petrol 4–10 Kero 10–16 Diesel oil Bitumen 50 and over Roads crude oil in
Fig 1.3.6 Fractional distillation of crude oil
distillation. This means that the crude oil is heated and passed into a column where the components are separated according to their boiling points into the different fractions.
Some of the fractions are used as is, while others are cracked to produce shorter-chain alkanes and some new chemicals, alkenes. Cracking involves heating the large molecules in the presence of a catalyst. An example of one of these cracking reactions is shown in Figure 1.3.7. A cracking reaction H H H H H H H H H H H H H H H C C C H H C C C H H H C H H H H H H H H H C C C C H H H C C C + heptane ethene pentane heat Fig 1.3.7
Alkenes
Alkenes contain a double bond and have the general formula
CnH2n
This means the number of hydrogen atoms in the molecule is exactly double the number of carbon atoms. The two smallest alkenes are ethene and propene. Alkenes are named in the same way as alkanes, except that their names end in –ene.
The major use for alkenes is in making plastics such as polyethene, the material used to make shopping bags. The double bond can break, and the molecules can join end-on-end to form long polymer chains. You will learn more about this in Chapter 2, Materials.
1.3
>
>
>
Plastic bags kill thousands of sea birds and marine
animals every year. Fig 1.3.10
Alkenes H H H H C C H H H H C C C C2H4 C3H6 H C H H C H H H H C C H H H C ethene propene H H Fig 1.3.8 H H H H H H C H H C H H C C C H H H H C C C2H4 heat catalyst
Part of a polyethene polymer looks like:
Fig 1.3.9 The formation of
polyethene Checking out
Twenty million Australians use nearly seven billion plastic check-out bags every year! Organic chemicals have
changed the way we live and the resources we use. But we must also think carefully
about how we use them. Many organic chemicals are not biodegradable. This
means they do not break down naturally, but instead stay in the environment for hundreds and sometimes thousands of years. Plastic bags in the ocean are a great
cause of concern as they are mistaken for jellyfish by
turtles, whales, sea birds and other animals that eat them. Once in the gut the bags slowly and painfully kill the animal. The bag is then released back into the ocean, to kill again when the
animal’s body decomposes. Do you use alternatives to plastic bags when shopping?
Alkynes H H H C2H2 C3H4 C C C H H H H C H C H ethyne propyne C C C H H H C C C Fig 1.3.11
The simplest alkyne is ethyne, commonly called acetylene. It is highly reactive due to the presence of a triple bond. If acetylene is burned in a stream of oxygen, very high temperatures (almost 3000°C) are reached. This is why the oxyacetylene torch is used in welding. Other alkynes are used in many manufacturing processes.
Fig 1.3.12
Welders use an oxyacetylene torch that reaches temperatures of up to 3000°C.
Alkynes
Alkynes contain triple bonds and have the general formula
C2H2n – 2
The number of hydrogen atoms in an alkyne molecule is equal to double the number of carbon atoms minus two. Two alkynes are shown in Figure 1.3.11.
100% organic
100% organic
Alcohols
Alcohols contain the hydroxy group, –OH. The hydroxy group is known as a functional group. A functional group is an atom, or group of atoms, that affects the properties of a compound.