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Kerry Whalley Carol Neville Peter Roberson Greg Rickard Geoff Phillips Faye Jeffery Janette Ellis
Sydney, Melbourne, Brisbane, Perth and associated companies around the world
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
3
considerations
1.3 100% organic 1.4 Maths in chemistry
2
Materials
UNIT
Chapter review
2.1 2.2 2.3 2.4
23
Pure metals and alloys Mining and minerals Corrosion of metals Plastics and fibres Science focus: Nanotechnology 2.5 Soaps Chapter review
24 29 38 43 54 (on CD) 58
Electricity and communications technology
59
3.1 3.2 3.3 3.4
60 68 76 84
Electricity Electromagnetism Waves in communication The communications network Scence focus: Microwaves cook from the inside 3.5 Electronics Chapter review
91 (on CD) 93
4
Genetics
95
UNIT
UNIT
3
10 15 (on CD) 22
4.1 4.2 4.3 4.4
96 106 114 120
Inheritance Human inheritance The molecule of life Controlling inheritance Science focus: Biotechnology and DNA fingerprinting Chapter review
128 133
UNIT
1.1 Writing chemical equations 1.2 More and faster! Rate and yield
5.1 5.2 5.3 5.4 5.5 5.6 5.7
Describing motion Acceleration Newton’s first law Newton’s second law Newton’s third law Gravity Work and energy Chapter review
136 147 153 159 164 169 176 183
6
Health and disease
185
UNIT
2
135
6.1 6.2 6.3 6.4
186 192 196
Health Disease Infectious diseases Transmission and control of infectious diseases 6.5 Non-infectious diseases Chapter review
7
Evolution
UNIT
Chemical reactions
Motion
7.1 7.2 7.3 7.4
The evolution of a theory Evolution unravelled Evidence for evolution Human evolution Scence focus: Putting flesh on old bones: archaeology and Australia today Chapter review
8
Global issues
203 211 221
222 223 232 239 249 255 260
262
UNIT
1
5
8.1 8.2 8.3 8.4
Global warming The ozone layer Nuclear radiation: good or evil? Energy crisis Chapter review
263 272 276 285 293
9
Individual research project
294
UNIT
iv v viii 1
UNIT
Acknowledgements Introduction Syllabus correlation grid Verbs
9.1 Being an individual Science focus: Science can be funny 9.2 My investigation Chapter review
Periodic table Index
295 299 302 308 310 311
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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.
Jim DeLillo: photo by Jim DeLillo, figure 3.4.10.
The Age: figure 2.1.5.
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.
Andrea Simonato: figure SF 9.1.
NASA: figures 5.5.2, 8.1.1(l), 8.1.1(r), 8.2.6.
Auscape: figures 7.2.1, 7.2.8(l), 7.3.7.
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.
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.
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).
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.
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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.
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.
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.
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.
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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 Prac 1 Unit 1.2 practical work. Cross references to practical activities within DYO 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.
Companion Website The Companion Website contains a wealth of support material for students and teachers, which has been written to enhance the content covered in the coursebook.
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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.
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.
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.
Worksheet 2.4 Metal experiments
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 4.3 Pedigree analysis
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Science Focus 4
Stage 5 Syllabus Correlation
A fully mapped and detailed correlation of the stage 5 curriculum outcomes is available in the Science Focus 4 Teacher Resource Pack.
chapter
1 23456789
outcomes
Chemical reactions 5.1
Materials
Electricity and communications technology
Genetics
Motion
Health and disease
Evolution
Global issues
Individual research project
▲
▲
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 Note:
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• • • • • • • • • • • •
• •
•
• • • • • • • • • •
• •
▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.
• • • • • • • • • • • • • •
• • • • • • • • • • • • •
• • • • • • • • • •
• • • • • • •
•
•
• • •
•
Verbs Science Focus 4 uses the following verbs in the student activities. Explain
identify components and the relationships among them; draw out and relate implications
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
Apply
use, utilise, employ in a particular situation
Identify
recognise and name
Appreciate
make a judgement about the value of
Interpret
draw meaning from
Assess
make a judgement of value, quality, outcomes, results or size
Investigate
plan, inquire into and draw conclusions
Justify
support an argument or conclusion
Calculate
determine from given facts, figures or information
List
write down phrases only, without further explanation
Clarify
make clear or plain
Modify
change in form or amount in some way
Classify
arrange or include in classes/categories
Outline
Compare
show how things are similar or different
sketch in general terms; indicate the main features of
Construct
make; build; put together items or arguments
Predict
Contrast
show how things are different or opposite
suggest what may happen based on available information
Critically add a degree or level of accuracy, depth, (analyse/evaluate) knowledge and understanding, logic, questioning, reflection or quality to (analysis/evaluation)
Present
provide information for consideration
Propose
put forward (e.g. a point of view, idea, argument, suggestion) for consideration or action
Deduce
draw conclusions
Recall
Define
state meaning and identify essential qualities
present remembered ideas, facts or experiences
Demonstrate
show by example
Recommend
provide reasons in favour of
Describe
provide characteristics and features
Record
Discuss
identify issues and provide points for and/or against
store information and observations for later
Recount
retell a series of events
Account
account for: state reasons for; report on give an account of: narrate a series of events or transactions
Analyse
Distinguish
recognise or note/indicate as being distinct or different from; note differences between
Research
investigate through literature or practical investigation
Evaluate
make a judgement based on criteria; determine the value of
State
provide information without further explanation
Examine
inquire into
Summarise
express concisely the relevant details
1
Chemical reactions Key focus area:
5.2, 5.7.3
Outcomes
>>> The nature and practice of science 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
Pre quiz
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?
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1
3.1 UNIT
UNIT
context
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
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:
Equations and formulas Chemical equations take the form: reactants
→ products
The 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 acid
→ magnesium + hydrogen chloride
or as a balanced formula equation: Mg + 2HCl
→ MgCl2 + H2
Whichever 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
H
Cl Cl-
Mg
H H +
+
Mg2+ Cl-
H
Cl
The 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.
Fig 1.1.1
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 nonmetal 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 non-metals and other nonmetals, 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.
3
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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).
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.
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. Fig 1.1.2
Two different ways of representing the structure of the ionic crystal caesium chloride
Cs+ ion Cs+ ion
4
Cl– ion
Cl– ion
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. Worksheet 1.1 Writing formulas
Balancing chemical equations Let’s take another look at the reaction between magnesium and hydrochloric acid. Mg + 2HCl
→ MgCl2 + H2
In 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 Prac 1 p. 9 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
UNIT
1.1 The easiest way to balance equations is to The hydrogen–oxygen fuel follow steps. To show space o Apoll cells used in the this we will use another missions produced pure water as a by-product. The astronauts example. then used this for drinking. The Sodium carbonate is: on reacti equation for this is added to nitric acid, 2H2 + O2 → 2H2O producing sodium nitrate, water and carbon dioxide. • Step 1: Write the word equation for this reaction. Fuel cells
Putting a ‘2’ in front of a formula means two of that species e.g. 2HCl means
Cl
H
Cl
H
The smaller subscript numbers are different. They show how many of each type of atom are present. H2O represents
O H
H H
CH4 represents
C
H
sodium + nitric carbonate acid
H
H
Fig 1.1.3
Sodium carbonate is Na2CO3 and nitric acid is HNO3.
are simply being rearranged by the reaction. The unbalanced equation for the above reaction is:
Sodium nitrate is NaNO3, water is H2O and carbon dioxide is CO2.
→ MgCl2 + H2
There 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
sodium + water + carbon nitrate dioxide
• Step 2: Find the formula for each substance in the word equation.
What do the numbers in chemical equations mean?
Mg + HCl
→
→ MgCl2 + H2
This 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 Prac 2 of Conservation of Matter. p. 9
• Step 3: Use these formulas to write an unbalanced formula equation. Na2CO3 + HNO3
• 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
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:
+
O
H
O O
H H
H
H
2H2
+
O2
A balanced equation has the same number and types of atoms on each side of the equation.
→ 2NaNO3 + H2O + CO2
The 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.
O H H
→ 2NaNO3 + H2O + CO2
Carbon (C): One on each side. No balancing required.
Na2CO3 + 2HNO3
H
→ NaNO3 + H2O + CO2
2H2O
Fig 1.1.4
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 + CO2 5
>>>
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 + Al
becomes the balanced equation Al2O3 + 3C
→ 3CO + 2Al
Which state are we in? The reaction between calcium and oxygen, forming calcium oxide, may be represented as: 2Ca + O2 → 2CaO
But 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 Fig 1.1.5
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 The fall of Rome including state subscripts. Lead poisoning probably played a significant part Unless told otherwise, you in the fall of the Roman should always write the states of Empire. Infertility was reactants and products as they caused by drinking wine from leaden vessels. Lead occur at Standard Laboratory was also used as a cure Conditions (25°C and ‘normal’ for diarrhoea. Cosmetics 1 atmosphere pressure). used by ancient peoples For example, at Standard included white lead on the face, mercury sulfide Laboratory Conditions, mercury as lipstick, and arsenic (Hg) is a liquid and sulfur (S) sulfide as eyeshadow; the a yellow solid. They react to ultimate self-poisoner’s make-up kit! form mercury sulfide (HgS), the reaction being: Hg(l) + S(s)
Normally we think of nitrogen as a gas but it can also be cooled down to make it into a liquid.
→ HgS(s)
+
liquid mercury
Hg(l)
Fig 1.1.6
+
solid sulfur
solid mercury (II) sulfide
S(s)
HgS(s)
Compounds have very different physical properties from the elements that made them.
Worksheet 1.2 Writing and balancing chemical equations Worksheet 1.3 Revising chemical equations
6
UNIT
1.1
UNIT
1.1 [ 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 + H2O B 2HNO3 + MgO → Mg(NO3)2 + H2O C 2HNO3 + 2MgO → 2Mg(NO3)2 + H2O D 2HNO3 + 3MgO → Mg(NO3)2 + H2O
15 Identify the equation that is not balanced. A C5H12 + 8O2 → CO2 + 6H2O B Mg + 2HCl → MgCl2 + H2 C 2Zn + O2 → 2ZnO D 4Al + 3O2 → 2Al2O3
Skills 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 → P2O5 b KClO3 → KCl + O2 c BaO + HNO3 → Ba(NO3)2 + H2O d Pb3O4 → PbO + O2 e Pb(NO3)2 → PbO + NO2 + O2 19 Modify these equations so that they are balanced. Include any missing states. a H2(g) + O2(g) → H2O b Na + Cl2 → NaCl(s) c CaCO3(s) → CaO(s) + O2 d CH4 + O2 → CO2 + H2O(g) e HNO3 + Ca(s) → Ca (NO3)2(aq) + H2 20 Jessica heated some bright blue copper(II) nitrate crystals in a test tube. She noticed brown nitrogen
7
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Writing chemical equations
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.
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:
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 Mass of sodium Mass of oxygen Mass of sodium oxide chloride are the products. reacting (grams) reacting (grams) produced (grams) b Ammonia (NH3) gas is produced when 2.00 0.70 2.70 nitrogen gas is added to hydrogen gas. 3.00 1.04 4.04 c Carbon monoxide gas combines with oxygen to form carbon dioxide gas. 4.00 1.39 5.39 d Solid iron combines with chlorine gas to produce solid iron(III) chloride. a Construct a word equation for this reaction. e Dilute sodium hydroxide solution is added b Construct an unbalanced chemical equation for the to dilute sulfuric acid. Sodium sulfate and reaction, then balance it. water are produced. c Modify the equation to include the states of the f Ammonium nitrate dissolves in water to produce reactants and products. ammonium and nitrate ions. d Explain how the above results prove the Law of g Hydrochloric acid reacts with calcium metal. A Conservation of Mass. solution of calcium chloride is produced, through which rise bubbles of hydrogen.
[ 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.
8
2 Connect to the CSIRO double helix website and locate the ‘Cool Experiments’ page. a Identify an experiment that involves a DYO 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
1.1 Prac 1 Unit 1.1
UNIT
1.1 [ Practical activities ] Studying a reaction
Conservation of mass
Aim To make quantitative observations of the reaction of magnesium metal and an acid
Aim To investigate conservation of mass in a
Equipment Magnesium strips, 1 M sulfuric acid, large beaker, small filter funnel, 100 mL measuring cylinder, cling wrap, gloves, lab coat, safety glasses
Prac 2 Unit 1.1
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 Fig 1.1.8
inverted measuring cylinder of acid balloon large beaker
water
cling wrap
conical flask
filter funnel
30 mL acid magnesium calcium carbonate
Fig 1.1.7
Method 1 Cut a 4 cm long strip of magnesium. Place it under the filter funnel in the beaker.
Method
2 Fill the beaker with water until it covers the filter funnel.
1 Measure out approximately 0.2 g of calcium carbonate in the conical flask.
3 Fill the measuring cylinder with acid and cover it in cling wrap.
2 Measure out 30 mL of hydrochloric acid into the measuring cylinder.
4 Carefully invert the measuring cylinder on top of the filter funnel. Let the neck of the filter funnel pierce the cling wrap.
3 Place the conical flask, measuring cylinder and balloon on the balance and record their total weight.
5 After the bubbling seems to have stopped, measure the volume of gas collected in the measuring cylinder.
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 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
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 reasons why.
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UNIT
1. 2
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context
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 The Hindenburg disaster produced, the energy released by On 6 May 1937, the hydrogen-filled the reaction setting the hydrogen Hindenburg airship burst into flame alight. Other reactions like the while landing in New Jersey, USA. The hydrogen was viewed as the culprit rusting of iron, or milk turning for many years. Extensive recent sour, are very slow. How quickly research has, however, discovered For a long time, hydrogen was Fig 1.2.1 a reaction happens can make the that hydrogen did not cause the initial blamed for the Hindenburg disaster. high fire. The actual cause was the difference between it being safe or flammability of the fabric cover. It was dangerous. The speed of a reaction If, for various reasons, only 5 g was made of a cotton substrate with an aluminised cellulose acetate butyrate obtained then the yield was 5/11.3 × 100 = is also important in industry. covering. The observations at the 44%. When producing chemicals a slow scene were consistent with a huge d ignite So how are a fast reaction rate and a good reaction may be unprofitable. aluminium fire. The fabric was e. spher atmo the in ty activi yield achieved? by electrical Speeding up industrial reactions is The hydrogen only exploded once the a very important area of chemistry. fire had burnt through the covering. The electrolytic refinement of copper An especially important Australian produces copper bars like these. Fig 1.2.2 example of this is the production of sulfuric acid.
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.
10
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 Prac 1 p. 13 those used up. Specific reactions may have particular conditions associated with them. Prac 2 DYO p. 14
Sulfuric acid, H2SO4 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 Prac 3 and used in the superconductor industry for p. 14 cleaning.
Some properties of sulfuric acid • • • • •
Strong acid Corrosive Colourless liquid Density 1.85 g/cm3 Melting point 10.4°C
Fig 1.2.3
UNIT
1.2 Some products made using sulfuric acid superconductors nitroglycerine
car battery dyes rayon
• 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.
air
Sulfur burner
SO2
Deduster
SO2 + air
molten sulfur Diluter
Converter
Drying tower SO2 + air
SO3 Water
Storage tanks
Heat exchanger Absorption tower Conc. H2SO4
The contact process for the production of sulfuric acid
SO3
Fig 1.2.4
Step 1 Molten sulfur is burned in air to produce sulfur dioxide gas. S(l) + O2(g)
→ SO2(g) 11
More and faster! Rate and yield considerations 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.
>>> 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.
2SO2(g) + O2(g) → 2SO3(g)
Fig 1.2.5
SO3(g) + H2SO4(l)
Step 4 Oleum is hydrated to form sulfuric acid.
The converter used for sulfuric acid production
feed gas
420°C reaction bed 1
H2S2O7(l) + H2O(l)
10% SO2 11% O2
heat exchangers
600°C 63% conversion 450°C reaction bed 2 510°C 84% conversion 450°C reaction bed 3 475°C 93% conversion 420°C reaction bed 4 535°C 99.5% conversion
UNIT
1.2
to oleum or intermediate absorber from intermediate absorber to final absorber
→ 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.
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.
[ Questions ]
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.
Checkpoint Industrial reactions 1 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.
12
→ H2S2O7(l)
11 State the formula for the following substances: a sulfuric acid b sulfur dioxide c sulfur trioxide d oleum
Think
4 State what the ‘ideal’ yield of a reaction would be.
12 Several catalyst beds are used in the contact process. Explain why.
5 A fast reaction rate and a good yield are particularly desirable for industrial reactions. Explain why.
13 Propose a reason why it is called the contact process.
UNIT
1.2 Skills
14 Explain what happens in the converter, including how the rate and yield are maximised.
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.
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 ]
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.
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.
UNIT
1.2
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
[ Practical activities ]
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.
acid + Mg
ice water
Rates of reactions 1 Prac 1 Unit 1.2
acid
Aim To investigate the variables that affect reaction rates 1 Time the reaction from the moment the magnesium is dropped into the acid, until there is no magnesium left.
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
>>
2 For the second experiment, cool the acid before adding the magnesium.
Fig 1.2.6
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More and faster! rate and yield considerations
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.
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.
4 Once again, add a 2 cm strip of magnesium and time how long it takes for the reaction to finish.
Questions
5 Add 2 mL of acid and 3 mL of water to a third test tube.
1 Identify factors that made the reactions proceed faster or slower.
6 Add a 2 cm strip of magnesium and time how long it takes for the reaction to finish.
2 Predict the effect of heating the reactions. 3 Identify the role of the manganese dioxide in the hydrogen peroxide reaction.
Rates of reactions 2 Prac 2 Unit 1.2
DYO
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
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 Prac 3 Unit 1.2
Note: This experiment should be performed in a fume cupboard.
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.
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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.
UNIT
context
. 13 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 Organic water chemistry of substances in 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!
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
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!
Fig 1.3.1
This person contains many organic compounds, including proteins, lipids and carbohydrates.
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. Deadly rhubarb
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
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.
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.
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100% organic Fig 1.3.2
Multiple bonds Single bond
Double bond
C C
C
C
O shared pair of electrons
T o shared pairs of electrons
H
H
H
H C
C
H
C
H
H
H
H
Ethane contains only single bonds
H
C
Th shared pairs of electrons
C
C
then the number of hydrogen atoms in the molecule is 2n + 2 = (2 × 2) + 2 = 6
Triple bond
H
n=2
C
Ethene contains one carbon-carbon double bond and four carbon-hydrogen single bonds
C
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,
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.
H
Ethyne contains one carbon-carbon triple bond and two carbon-hydrogen single bonds
Fig 1.3.4
Methane and ethane
H
Hydrocarbons
H
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.
Fig 1.3.3
These items are all hydrocarbon-based.
Alkanes Alkanes are hydrocarbons that contain only single bonds. They have the general formula CnH2n + 2
16
C
H
H
H H
H methane CH4
H
C
C
H
H
H
C H
H
H H
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.
H
H C
C
H
H H
ethane C2H6
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
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
UNIT
1. 3 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. Fig 1.3.7
A cracking reaction
H C
H H
C
H
H
H H C
C H
H
H H C
C H
H C
heat
H H
H heptane H
H
H C
+
C H
H
H H
C
H
H C
C H
H C
H H
H pentane
ethene
Fig 1.3.5
C
H
H
Crude oil forms from the remains of dead animal and plants under the Earth’s crust. Oil rigs are used to extract the oil.
Alkenes cool (25°C)
crude oil in
very hot (400°C)
Fig 1.3.6
Name of fraction
How many carbons in chain?
What is it used for?
Gas
1–4
Fuel
Petrol
4–10
Fuel for cars
Kero
10–16
Fuel for jets
Diesel oil
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
Bitumen
Roads
50 and over
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.
Fractional distillation of crude oil
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100% organic Fig 1.3.8
Alkenes
H
H C
C
H
H
H
H
H C
H
C
C
H C H
H H
H
C
H
H
H H
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.
C
H
ethene
propene
C2H4
C3H6
Fig 1.3.11
Alkynes C
H H
H H
C
C
H
CC
H
C
C
H
H
C2H4
Checking out
heat catalyst
H
H
H
C
C
ethyne
propyne
H
H
C2H2
C3H4
Twenty million Australians Part of a polyethene polymer looks like: use nearly seven billion plastic check-out bags every H H H year! Organic chemicals have H H changed the way we live and C C C the resources we use. But ly careful think C C also we must H H H about how we use them. als chemic organic Many H H are not biodegradable. This means they do not break The formation of Fig 1.3.9 down naturally, but instead polyethene for ment environ the stay in hundreds and sometimes thousands of years. Plastic bags in the ocean are a great Plastic bags kill thousands of sea birds and marine cause of concern as they animals every year. Fig 1.3.10 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?
H
C
C
H
H
C
C
C
H H
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.
Welders use an oxyacetylene torch that reaches temperatures of up to 3000°C.
Fig 1.3.12
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.
18
The biological molecule cholesterol is an alcohol and an important component of our bodies.
H O
H H
C
C
H
H
H
H
H C
H H H
C
H C
C
H
H H
O
C
H
O C
H
H H May be called 1-propanol or 1-hydroxypropane. The hydroxy group is attached to the first carbon.
May be called ethanol or hydroxyethane.
H
C
H
H H
May be called 2-butanol or 2-hydroxybutane. The hydroxy group is attached to the second carbon.
Combustion of hydrocarbons and alcohols When hydrocarbons or alcohols burn in lots of oxygen, carbon dioxide and water are produced. This is called complete combustion. These reactions also produce heat energy, which may be harnessed, for example in coal-fired power stations, to produce electricity. In complete combustion: ethane + oxygen
2C2H6(g) + 7O2(g)
H
Fig 1.3.13
How to name alcohols
Ethanol is the alcohol in beer, wine and spirits and is the best known of the alcohols. Ethanol has many other uses, however: it is an excellent solvent, is found in many glues, paints and inks, and is used as a reactant to make rubbers and flavourings. One way to produce ethanol is by fermentation of fruit or vegetable matter. This reaction may be represented as: glucose C6H12O6(aq)
→ ethanol + carbon dioxide → 2C2H5OH(aq) + 2CO2(g)
The catalyst for this reaction is yeast. Another widely used alcohol is 1,2ethanediol, better known as antifreeze. The addition of this molecule to radiator fluid lowers the melting point of the liquid so that it won’t freeze in cold weather. Methanol is the main component of methylated spirits. Propanol is used as rubbing alcohol. 1,2,3-propanetriol, known as glycerine or glycerol, is a component of many moisturisers.
UNIT
1. 3
→ carbon dioxide + water → 4CO2(g) + 6H2O(g)
Sometimes, if the supply of oxygen is limited, incomplete combustion may occur. This is usually characterised by a black, smoky flame. In incomplete combustion, two reactions tend to occur simultaneously: ethane + oxygen
2C2H6(g) + 5O2(g) ethane + oxygen
2C2H6(g) + 3O2(g)
→ carbon monoxide + water → 4CO(g) + 6H2O(g) → carbon + water → 4C(s) + 6H2O(g)
Incomplete combustion produces less heat energy than complete combustion and can also produce a deadly pollutant, carbon monoxide gas.
Zero limit for L and P platers Since May 2004 the legal blood alcohol content in New South Wales for all learner and provisional licence holders has been zero. The reason for this limit is that a little bit of ethanol has a huge effect on your body. Low doses affect the reticular system—the primitive part of the brain that maintains consciousness and responsible behaviour. The initial effect you feel depends on how much sensory input you are getting, as this determines which brain pathways are affected. In quiet settings, you may become drowsy. In a social setting, you are more likely to feel stimulated. This is the result of the alcohol affecting the pathways dealing with inhibition. Ethanol is not a stimulant—it is a central nervous system depressant. Even in very small amounts, it slows your reflexes and impairs your judgement.
Incomplete combustion in car engines produces carbon, carbon monoxide and other chemicals that contribute to photochemical smog and air pollution.
Worksheet 1.5 Organic chemistry
Fig 1.3.14
Prac 1 p. 21
19
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100% organic
UNIT
1. 3
[ Questions ]
Checkpoint Organic chemistry 1 Clarify what is meant by ‘organic chemistry’. 2 List the main elements in organic compounds. 3 Explain what is meant by a ‘hydrocarbon’.
15 Complete the table by identifying the molecule or its formula. Molecule name
Molecular formula
Pentane C4H8
Multiple bonds
C10H18
4 Contrast single, double and triple bonds.
Hydrocarbons 5 List two examples of hydrocarbons that have: a single bonds only b a double bond c a triple bond
Hexene Octane C3H8 Propyne
6 List five important hydrocarbon products. 7 Explain what is meant by a ‘homologous series’.
Alkanes, alkenes and alkynes
16 Fractional distillation separates the alkane fractions in crude oil. Outline how this is achieved.
8 Identify the three homologues series of hydrocarbons.
17 State the name of the alcohol we drink.
9 State the name and formula for the: a first three alkanes b fourth alkene c first alkyne d polymer made from ethene
18 State another name for: a antifreeze b acetylene c methylated spirits 19 Identify the products formed from:
10 State the purpose of: a fractional distillation b cracking alkanes
Alcohols 11 Identify the special functional group that alcohols contain.
Combustion of hydrocarbons and alcohols 12 Distinguish between complete and incomplete combustion.
Think 13 Identify one carbon-based compound that is not an organic compound. 14 It is not possible for the molecules methene and methyne to exist. Account for this fact.
a the complete combustion of methane b the incomplete combustion of methane 20 Compared with the blue flame of a Bunsen burner, the yellow flame is relatively cool and very dirty, leaving a layer of black carbon on anything heated in it. Propose reasons why two flames can be so different when they burn the same gas.
Analyse 21 a Identify the reactants and the products in the fermentation equation. b State two uses for fermentation. 22 Explain the meaning of the statement: ‘Fermentation is catalysed by yeast’. 23 Evaluate complete and incomplete combustion in terms of their efficiency in releasing the energy in fuel, and their effect on the environment. 24 Discuss the importance of organic chemistry for society.
20
UNIT
1. 3 [ Extension ] Investigate 1 Carbon compounds play an important role in our everyday life. Research information on ten useful carbon compounds. For each compound: a State the correct chemical name and common name. b Construct a model. c Describe one significant use.
UNIT
1. 3
ACTIVITY Making molecules Use a molecular model building kit to construct models of some alkanes, alkenes, alkynes and alcohols. Draw and name the models you make.
[ Practical activity ] Complete and incomplete combustion
Prac 1 Unit 1.3
Aim To examine the products of complete and incomplete combustion Equipment
Ethanol, Pasteur pipette, kerosene with wick, lab coat, safety glasses, heat mat, watch-glass, candle
Method 1 Light the candle and note things like the colour of the flame and any sign of soot. 2 Put a few drops of ethanol on a watch-glass and light it carefully. Observe the flame. 3 Light the kerosene burner and observe the flame.
Questions
ethanol
kerosene
1 Describe any evidence observed for: a complete combustion b incomplete combustion 2 The molecular formula of ethanol is C2H5OH. Kerosene is a mixture of hydrocarbons with an average formula of C12H26. Explain the difference in the way these compounds burned, in terms of their formulas.
Fig 1.3.15
3 Is the burning of petrol in cars an example of complete combustion or incomplete combustion? Justify your answer.
21
UNIT
>>>
context
1. 4 In any reaction billions of atoms, ions and molecules are colliding with each other and rearranging each other. A single drop of water, for example, contains billions of water molecules and a beaker of water has many, many more. When chemists run an experiment, they deal with very large numbers of atoms, ions and molecules and not just single atoms or small groups of them. The numbers involved are
The mole If you were asked how many eggs are in a dozen, you would of course say 12. We use a dozen instead of counting individual eggs, so three dozen is 36 eggs, 10 dozen is 120 eggs and so on. The mole also stands for a group of things, although a mole has many more things in it than a dozen. The mole in chemistry has nothing to do with small, furry, burrowing animals but instead stands for a huge number, called Avogadro’s number. This number is an incredibly large 6.02 × 1023, or 602 000 000 000 000 000 000 000 or 602 thousand billion billion! There would be 6.02 × 1023 eggs in a mole of eggs, and a mole of people means 6.02 × 1023 people. This is well over a thousand billion times the current world population! In chemistry, a mole of carbon atoms would contain 6.02 × 1023 carbon atoms and a mole of water would have 6.02 × 1023 water molecules in it. The mole is useful in chemistry because it gives us a number of atoms or molecules that we can actually see and measure out. A single atom or molecule is far too small to work with.
so huge that a new way of counting is needed. This is where the mole comes in. The maths involved in chemistry is tricky at first, but very useful once you get the hang of it!
mole of carbon atoms must be 12 grams. The mass of one mole of oxygen atoms is 16 grams. Likewise, if we weighed out 127.6 g of tellurium (Te) then we would have a mole of tellurium atoms.
Fig 1.4.1
Typical information from the periodic table. Some periodic tables may be arranged slightly differently.
atomic number
atomic mass (the mass in grams) of 1 mole of these atoms
element symbol element name
Weighing a mole The periodic table on page 310 of the Science Focus 4 coursebook includes all the details of each element. It also includes the atomic mass (sometimes called the atomic weight) of the element. The atomic mass is the mass in grams of a mole of those atoms. For example, the atomic mass of carbon C is 12, so the mass of one CD2
How big is a mole? A mole of cane toads would cover an area the size of Queensland with a layer of amphibians many kilometres thick! Maybe we should call it a ‘toad’ instead!
Fig 1.4.2
Masses in a reaction
mercury + sulfur
→ mercury sulfide
→ 1 mole HgS(s)
or, using the atomic masses from the periodic table on page 310 of the coursebook: 200.6g Hg(l) + 32g S(s)
→ 232.6g HgS(s)
In words, this means that 200.6 g of mercury will react with 32 g of sulfur to produce 232.6 g of mercury sulfide. Let’s look at another reaction, this time between gallium and oxygen. Its word equation is: gallium + oxygen
e.g. calculate the formula mass of C2H6O2 This is made up of: 2 carbons 6 hydrogens 2 oxygens
2 carbons
2 oxygens
6 hydrogens
The formula mass is then:
= (2 × 12 g/mol) + (6 × 1 g/mol) + (2 × 16 g/mol) = 62 g/mol
→ HgS(s)
This tells us that one atom of mercury reacts with one atom of sulfur to form one ion cluster of mercury sulfide. It also tells us that one mole of mercury atoms would react with one mole of sulfur atoms to produce one mole of mercury sulfide. So: 1 mole Hg(l) + 1 mole S(s)
CALCULATING FORMULA MASSES
(2 × atomic mass of carbon) + (6 × atomic mass of hydrogen) + (2 × atomic mass of oxygen)
This formula equation is already balanced: Hg(l) + S(s)
Fig 1.4.3
Calculating formula masses
The mole is useful because it allows us to use the periodic table and balanced chemical equations. We can calculate exactly what mass of a reactant is required for a reaction and how much product the reaction will produce. As an example, let’s look at the reaction of liquid mercury with sulfur powder to form mercury sulfide. The word equation is:
UNIT
1.4
→ gallium oxide
The mass of 1 mole of a compound is called the formula mass. To calculate formula mass, simply break the substance down into its elements. For example, ammonium carbonate has the formula: (NH4)2CO3. This is made from 2 nitrogen atoms, 8 hydrogen atoms, 1 carbon atom and 3 oxygen atoms. From the periodic table, the atomic masses of these elements are:
Did Lecoq crow? For a scientist to name a new discovery after himself is simply not done. The element gallium was discovered and named in 1874 by Frenchman Paul Emile Lecoq de Boisbaudran. The name ‘gallium’ came from Gallia, the Latin name for France. But gallus is rooster in Latin, while ‘le coq’ is French for rooster. A coincidence, or was this Frenchman cleverly putting his personal stamp on his find?
The balanced chemical equation is: 4Ga(s) + 3O2(g) → 2Ga2O3(s)
In other words, four gallium atoms react with three molecules of oxygen gas to produce two ion clusters of gallium oxide. It also tells us that: 4 moles Ga(s) + 3 moles O2(g)
→ 2 moles Ga2O3(s)
Unlike the example above, here we need to do some calculations for masses: 4Ga(s) (69.7 g × 4) 278.8 g
+
3O2(g) (16 g × 6) 96 g
→
2Ga2O3(s) (69.7 g × 4) + (16 g × 6) 374.8 g
This means that 278.8 g of gallium reacts with 96 g of oxygen to give 374.8 g of gallium oxide, or: 278.8g Ga(s) + 96g O2(g)
→ 374.8g Ga2O3(s)
Element
Symbol
Atomic mass (grams)
Nitrogen
N
14
Hydrogen
H
1
Carbon
C
12
Oxygen
O
16
Hence, the formula mass = (14 g × 2) + (1 g × 8) + (12 g × 1) + (16 g × 3) = 96 g This means that one mole of (NH4)2CO3 has a mass of 96 grams.
Taking it a step further … Let’s look at the combustion of methane. CH4(g) + 2O2(g)
Prac 1 p. CD7
→ CO2(g) + 2H2O(l)
Formula mass of methane (CH4) = (12 g × 1) + (1 g × 4) = 16 g CD3
>>>
Maths in chemistry!
Dephlogisticated air
Formula mass of oxygen (O2) = 16 g × 2 = 32 g Formula mass of carbon dioxide (CO2) = (12 g × 1) + (16 g × 2) = 44 g Formula mass of water (H2O) = (1 g × 2) + (16 g × 1) = 18 g Fig 1.4.4
The combustion of methane
O H
H O
H H
C H
H
O O
+
H
H O
+
O O
C
O
This equation shows that 1 mole of methane molecules (16 g) reacts with 2 moles of oxygen molecules (2 × 32 g = 64 g), producing 1 mole of carbon dioxide molecules (44 g) and 2 moles of water molecules (2 × 18 g = 36 g). Another way this could be written is: 16g CH4(g) + 64g O2(g)
→ 44g CO2(g) + 36g H2O(l)
The mass of reactants is 80 g and so is the mass of products: the Law of Conservation of Mass is obeyed. Let’s say that we only have 8 grams of methane, and not 16 g as assumed in the equation above. The formula mass of methane is 16 g so this is equal to 8/16 or half of a mole. Half a mole of methane will only need half the oxygen and will obviously only produce half the amount of carbon dioxide and water, i.e.: Mass of oxygen used = 1/2 × 64 g = 32 g Mass of carbon dioxide produced = 1/2 × 44 g = 22 g Mass of water produced = 1/2 × 36 g = 18 g Getting the hang of it? Let’s try another example to make sure. Hydrogen sulfide reacts with chlorine gas to give hydrogen chloride gas and solid sulfur. The balanced chemical equation for this reaction is: H2S(g) + Cl2(g)
CD4
→ 2HCl(g) + S(s)
Fig 1.4.5
A portrait of Joseph Priestley
Joseph Priestley first isolated oxygen in the eighteenth century, calling it ‘dephlogisticated air’. Priestley was an English clergyman and was dubbed ‘Dr Phlogiston’ by newspaper reporters of the day. He was delighted with the effects of breathing his pure oxygen, dephlogisticated air. He wrote that ‘my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it’. Unfortunately, the mice died soon after in Priestley’s experiments. As predicted by Priestley, breathing pure oxygen became fashionable for a short time in the early 2000s, particularly in California, USA. Patrons of ‘oxygen bars’ would be hooked up to breathe bottled oxygen.
Using the atomic masses from the periodic table, the formula masses are found to be: H2S = 34 g Cl2 = 71 g HCl = 36.5 g S = 32 g In terms of masses we have: H2S(g) 32 g
+
Cl2(g) 71 g
→
2HCl(g) + S(s) 2 × 36.5 g 32 g
Another way of writing this could be: 32g H2S(g) + 71g Cl2(g)
→ 73g HCl(g) + 32g S(s)
But what if we don’t want 32 g of sulfur, but only want to produce, say, 4.5 g? How much of each reactant will we need to mix? Mass of one mole of sulfur = 32 g We don’t need one mole of sulfur, but need only a fraction of a mole. The fraction of sulfur produced = 4.5/32 mole. So we only need this mass of hydrogen sulfide reacting: = 4.5/32 × 34 g = 4.8 g The mass of chlorine reacting needs to be: = 4.5/32 × 71 g = 10 g
Breaking down formulas If you take a look at the formula for carbon dioxide, you can see that 12 g of its formula mass comes from
carbon, and the rest comes from oxygen. Calculated as a percentage of the total mass of 44 g we get: Percentage of carbon in carbon dioxide = 12/44 × 100 = 27% Percentage of oxygen in carbon dioxide = 32/44 × 100 = 73% Carbon dioxide can be formed in many ways. For example: C(s) + O2(g)
or
→ CO2(g)
2CO(g) + O2(g) → 2CO2(g)
Whichever way carbon dioxide is formed, it will always contain the same proportions of carbon and oxygen. This is called the Law of Constant
UNIT
1. 4 Proportions: this simply states that a compound will always have the same proportions of each element, regardless of how it was made.
10 Iron reacts with sulfur, producing iron(II) sulfide. a Given that iron(II) is Fe2+ and sulfide is S2–, construct the formula for the compound iron(II) sulfide. b Construct a balanced chemical equation for this reaction. c 55.9 g of iron completely reacts with sulfur. Calculate the mass of sulfur needed and the mass of iron(II) sulfide that will be produced.
Skills 11 Using the following equation:
UNIT
1. 4
2H2(g) + O2(g) → 2H2O(l)
[ Questions ]
Checkpoint The mole 1 Clarify what is meant by the term ‘mole’ in chemistry. 2 Outline why the ‘mole’ is used instead of individual atoms in chemistry.
Masses in a reaction 3 The large numbers that appear in front of compounds are the only ones we can alter to balance a chemical equation. Explain how these numbers relate to the number of moles of each chemical taking part in the reaction. 4 The formula mass of water is 18 g. Explain how this was calculated.
Taking it a step further 5 Explain how the mole ratios of reactants and products can be used practically in chemistry. 6 The Law of Conservation of Mass is obeyed in chemical reactions. State how the mole can be used to show this.
calculate a the number of moles of each reactant required b the number of moles of water produced c the masses of each reactant required and the expected mass of the product 12 Use the information from the periodic table on page 310 of the coursebook to calculate the formula mass of: a glucose, C6H12O6 b calcium nitrate, Ca(NO3)2 c hydrogen peroxide, H2O2 d sodium phosphate, Na3PO4 13 Given that the formula of lead oxide is PbO2 calculate the masses missing in the table below. Mass of lead reacting (g)
Mass of oxygen reacting (g)
Mass of lead oxide produced (g)
2.00 4.00 6.00 8.00
Breaking down formulas 7 Outline how the percentage of carbon in carbon dioxide can be calculated. 8 Clarify what is meant by the ‘Law of Constant Proportions’.
Think 9 Calculate the number of each in the following examples: a socks in a pair of socks b eggs in a dozen eggs c gold atoms in a mole of gold d H2O molecules in a mole of water e dozens of eggs in a mole of eggs f pairs of socks in a mole of socks
14 Calculate the percentage by mass of each element in potassium hydrogen carbonate, KHCO3.
Analyse 15 Consider these two reactions: Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) In a flask, 2.5 g of calcium reacted with sufficient hydrochloric acid. In another flask, 2.5 g of magnesium reacted with sufficient hydrochloric acid. a Identify the common product from both reactions.
CD5
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Maths in chemistry!
b Which flask would produce more gas? Justify your answer. (Hint: Think about how many moles of each metal there are at the start.) 16 Copper(II) carbonate (CuCO3) decomposes when heated, producing copper(II) oxide (CuO) and carbon dioxide (CO2). a Construct a formula equation for this reaction and balance it. b If 6 g of copper(II) oxide is produced, calculate the mass of copper(II) carbonate that must have reacted. 17 When methane gas (CH4) burns in oxygen (O2), carbon dioxide and water vapour are formed. a Construct a balanced formula equation for this reaction. b Calculate the minimum mass of oxygen needed for 4 g of methane to completely burn.
18 Nitrogen forms many different compounds with oxygen. One of these was found to contain 28 g of nitrogen for every 64 g of oxygen. a Calculate how many moles of nitrogen and of oxygen this is equivalent to. b Identify the probable formula of this compound. 19 Is it cheaper to buy sodium carbonate (washing soda) as the anhydrous (waterless) salt Na2CO3 at $2.00 per kilogram, or as the decahydrate salt, Na2CO3·10H2O, at $1.00 per kilogram? Justify your answer. 20 A student produced a compound that he believed was Al2O3. He found that his compound was 45% aluminium and 55% oxygen. Is it Al2O3? Justify your answer. 21 Sarah conducted an experiment where she burned 0.3 g of magnesium in oxygen. From her results she calculated that 0.7 g of magnesium oxide was produced. Her prac partner, Stephen, said that was impossible. Decide which of them is correct, and justify your answer.
[ Extension ] Investigate 1 Research information to discover how scientists have contributed to the understanding of maths in chemistry. a Describe how Amadeo Avogadro came to have a very important number named after him.
b Antoine Lavoisier deduced the Law of Constant Proportions. Explain how he did this. c Outline the contribution of one other chemist in this area. 2 Estimate how many people are alive in the world today. Is this equal to, more than, or less than a mole of people?
ACTIVITY Reacting ratios The following table shows the results of an experiment in which various masses of the fictional metallic element mysterium, symbol M, were reacted with sulfur, producing mysterium sulfide: xM(s) + yS(s) → MxSy(s) 1 List the reacting masses of sulfur in the table. 2 Construct a line graph of the mass of mysterium reacting (vertical axis) against the mass of sulfur reacting (horizontal axis). 3 Justify whether this graph proves the Law of Constant Proportions. 4 Explain why logically the graph should pass through the origin. 5 Use rise/run to calculate the slope or gradient of the graph. 6 Construct an equation for the straight line in the graph.
CD6
Mass of mysterium reacted (g)
Mass of sulfur reacted (g)
1.00
1.41
2.00
2.82
3.00
4.23
4.00
5.64
5.00
7.05
6.00
8.46
7.00
9.87
Mass of mysterium sulfide produced (g)
UNIT
1. 4 Prac 1 Unit 1.4
UNIT
1. 4 [ Practical activity ] Method
TEACHER DEMONSTRATION Reacting amounts
1 Clean the magnesium strip with the sandpaper. 2 Curl the magnesium strip and place in the crucible. Place the lid on, and weigh it.
Aim To calculate the mass of the product that should be obtained from reacting magnesium in air and compare with experimental data Equipment 5 cm magnesium strip, crucible with lid, tripod, Bunsen burner, pipe clay triangle, electronic balance, heat-proof mat, tongs, sandpaper, gloves, safety glasses, lab coat
3 Place the crucible on the pipe clay triangle over the Bunsen burner. DO NOT LOOK AT THE BURNING MAGNESIUM DIRECTLY OR ALLOW STUDENTS TO VIEW DIRECTLY. 4 Heat it until combustion starts. If necessary, lift the lid slightly from time to time to keep the combustion going. 5 When the combustion is complete, let the crucible cool, then reweigh it.
crucible, with lid, containing magnesium
Bunsen burner
Questions
pipe-clay triangle tripod
1 Constuct a balanced equation for the reaction of magnesium with oxygen, O2, producing magnesium oxide, MgO. 2 Record the mass of magnesium that reacted, and the mass of magnesium oxide produced. 3 Calculate the mass of magnesium oxide that you should have obtained from this amount of magnesium.
heat mat
4 Compare the theoretical mass with the actual mass. 5 Propose reasons why the theoretical and actual mass are probably close, but not exactly the same.
Fig 1.4.6
CD7
>>> Chapter review [ Summary questions ] 1 Clarify what the Law of Conservation of Mass means with regard to reactants and products. 2 Explain the purpose of using a chemical equation. 3 List the possible states in which chemicals may exist and list the symbols used for them in an equation. 4 Write a chemical equation demonstrating the following features: reactants and products, states of each substance, correctly written formulas, and numbers balancing the equation. 5 Define the term ‘SLC’. 6 State one thing that could make a reaction go faster, besides using a catalyst. 7 State the percentage yield obtained in the manufacture of sulfuric acid. 8 Summarise the four steps in the production of sulfuric acid. 9 Using equations, outline how the yield and rate are controlled in the contact process. 10 List three properties and uses of sulfuric acid. 11 Use an example to help define the term ‘homologous series’. 12 List five important uses for organic compounds.
[ Thinking questions ] 13 Assess whether a fast reaction rate guarantees a good yield. 14 Evaluate the need to consider rate and yield in industrial reactions. 15 Which of the following two formulas is a molecular formula? SO2 or Na2SO4 Justify your answer. 16 Modify the following chemical equations so that they are balanced. a Al(OH)3 + HNO3 → H2O + Al(NO3)3 b H2O + K → H2 + KOH 17 Describe organic chemistry.
22
18 Draw diagrams to demonstrate the molecular structure of ethane, ethene and ethyne. 19 An organic molecule has five carbon atoms. State its name if it is an alkane, alkene or alkyne. 20 Describe how a polymer is made from ethene.
[ Interpreting questions ] 21 Extrapolate in order to complete this word equation: magnesium + hydrochloric acid → 22 Describe in words what these equations are showing: a 2Na + 2H2O → H2 + 2NaOH b CuO + 2HNO3 → Cu(NO3)2 + H2O 23 Solid lithium carbonate reacts with dilute hydrochloric acid to produce a salt, water and carbon dioxide. a Identify the likely salt produced. b Construct a word equation for the reaction. c Construct a balanced formula equation for it, with subscripts indicating the states of each chemical. 24 For each of the reactions below, construct: i the word equation ii the balanced formula equation, including states a Dilute hydrochloric acid reacts with a lump of potassium hydroxide to produce water containing dissolved potassium chloride. b Sulfur dioxide is added to oxygen, producing sulfur trioxide gas. c Solid magnesium combines with chlorine gas to produce solid magnesium chloride. d Silver nitrate solution is added to sodium chloride solution, producing sodium nitrate solution and a precipitate of silver chloride. 25 Contrast complete and incomplete combustion. 26 Write the word and formula equations for the complete combustion of propane. 27 a Outline the process of fermentation. b Discuss the importance of fermentation as a chemical reaction. Worksheet 1.6 Chemical reactions crossword Worksheet 1.7 Sci-words
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2
Materials Key focus area
>>> The implications of science for society and the environment
relate the uses of substances to their properties explain how materials such as metals and plastics have changed our world construct word equations for the rusting of iron and the corrosion of aluminium
Outcomes
relate the properties of substances to their structures
5.4, 5.7.3, 5.11.1, 5.11.2, 5.12
By the end of this chapter you should be able to:
balance formula equations for the rusting of iron, the smelting of iron, and the electrolysis of sodium chloride explain how metals can be protected from corrosion discuss the impact of mining on Australian society and the environment explain why conservation and recycling of materials are important to our continued well-being.
nugget but sodium can’t?
2 What is slag and what has it got to do with iron?
3 Why do plastic objects often have a ‘bump’ or seam?
4 Why do we feel wet and clammy on hot days if we wear nylon but not if we wear cotton?
5 How does Thorpie’s Speedo swimsuit help him go faster?
Pre quiz
1 Why is it that gold can be found as a
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UNIT
context
2.1 The metals gold and silver have been much prized since primitive times. Copper, its alloy bronze, and later iron and its alloy steel, replaced the stone spearheads and axes of primitive humans, improving their chances when hunting and waging tribal fights. Each newly extracted metal allowed technology to change. And society changed with them.
Properties of metals Most metals are very dense, because metal atoms pack tightly together when they combine. Metal atoms also have low electronegativity, meaning that they have very little control over their outer-shell electrons. These electrons move freely throughout the metal without being bound to any one atom. This provides
free electrons, not bound to any single atom
Very few metals can be used as pure elements because they are generally too soft to be made into anything useful. Copper and aluminium are two of only a handful of metals that can be used in their pure form.
multidirectional bonding
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Electrons can carry current.
−
+
+
+
+
+
+
+
+
+
+ Electrons rapidly transfer heat.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
lattice (arrangement) of metal ions
24
Pure metals
Metal atoms lose control of their outer-shell electrons, which are free to wander.
Fig 2.1.1
bonding will not break even if layers shift
multidirectional bonding between the atoms and accounts for the following properties of metals: • They are malleable—the bonding allows them to stay together and not break apart when hammered or bent. • They are ductile—this is the ability to be drawn or stretched into wires. • They are electrical conductors—the free outer-shell electrons enable them to carry electrical currents. • They are heat conductors—these same electrons rapidly transfer heat, making metals excellent thermal conductors.
+
+
+
+
+
+
+
+
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+
Pure metal
Element symbol
Uses
Properties that make it particularly suited to its use
Aluminium
Al
Overhead electricity cables, saucepans and cans, Alfoil
Excellent conductor of heat and electricity, extremely light, non-toxic
Copper
Cu
Electrical wiring
Excellent electrical conductor Easily drawn into wires
Sodium
Na
Nuclear reactor coolant
Conducts heat well Melts at 98°C, allowing molten sodium to flow along pipes in the reactor
Zinc
Zn
Coating for iron (galvanised iron)
Protects iron from rusting
Tin
Sn
Coating for steel cans for food, liquid, etc.
Stops steel from rusting, non-toxic, unreactive
Mercury
Hg
Thermometers
Liquid at room temperature, expands rapidly when heated, leaves tubes clean once it retreats, leaving no traces
Lead
Pb
Flashing around windows and rooftops to stop water entry
Very soft and easily bent, resists corrosion
UNIT
2.1
Alloys An alloy consists of a metal combined with one or more other elements. An alloy has properties that are different from those of its components. These new properties are usually an improvement over those of the main or base metal in the alloy. For example, brass is more durable than its base metal, copper. Pure iron is extremely soft, but if small amounts of carbon are added, its strength increases dramatically. The alloy formed is steel. Mild steel has 0.5% carbon, while tool steel has about 1%. If the carbon content increases to between 2.4% and 4.5%, cast iron
Fig 2.1.2
Cast iron lace … very beautiful, very hard, but very brittle
is formed. This is strong but brittle and shatters easily if hit or dropped. Stainless steel has chromium (20%) and nickel (10%) added to stop rusting.
Jewellery used for body piercings is usually rust-resistant surgical-grade stainless steel but infection may still occur.
Fig 2.1.3
25
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Pure metals and alloys Pure gold jewellery would break if it was used for normal everyday wear. Instead, it is alloyed with silver or copper to increase its strength. The carat scale measures the amount of pure gold in jewellery, with pure gold rated as 24 carat. Jewellery is often 18 carat, meaning that it is 18/24 (threequarters or 75%) gold. Some alloys and their composition and uses are listed in the table.
UNIT
Gold cheaper than iron!
Damascus steel was used in the ancient world to manufacture swords of extreme strength. The exact technology was lost about 200 years ago but one recipe calls for ‘normal’ steel to be heated, then cooled in two stages. The final cooling was supposedly achieved by thrusting the sword into the body of a ‘muscular slave’. The strength of the slave apparently transferred on his death into the metal!
When the Egyptian Pharaoh Tutankhamen was buried 3400 years ago, two daggers were buried with him. One dagger had a blade of gold, the other iron. Because of its rarity at that time, the iron dagger was far more valuable than the gold one!
Fig 2.1.4
Tutankhamen’s dagger, with an iron blade and gold scabbard
Alloy
Composition
Uses
Advantages
Brass
70% Cu, 30% Zn
Household and nautical fittings, musical instruments
Appearance, limited corrosion, harder than pure copper
Bronze
95% Cu, 5% Sn
Statues, ornaments, bells
Appearance, little corrosion, harder than brass, sonorous (rings well when struck)
Duralumin
96% Al, 4% Cu, traces of Mg and Mn
Aircraft frames
Strong, light
Solder
60 to 70% Sn, 40 to 30% Pb
Joining metals together, electrical connections, low-friction bearings
Low melting point
Cupronickel
75% Cu, 25% Ni
‘Silver’ coins
Hard wearing, looks like silver, attractive
EPNS (electroplated nickel silver)
Cu, Ni, Ag
Plated onto cutlery, plates and bowls
Looks like silver, cheaper, resists corrosion
Alnico
Al, Ni, Co
Magnets
Aluminium is light, nickel and cobalt can be magnetised
Dental amalgam
Hg, Sn, Ag, Zn, Cu
Tooth fillings
Hardens slowly after being mixed
2.1
26
Wanted: muscular slave for short job!
[ Questions ]
Money, money, money! Australian ‘gold’ $1 and $2 coins contain 92% copper, 6% aluminium, 2% nickel and no gold. The ‘silver’ coins are 25% nickel, 75% copper and no silver. Metal was first used as money in about 2000 BC, but ‘coins’ were not invented until 600 BC in Lydia, Anatolia. They were crude beads of electrum, a naturally occurring alloy of silver and gold.
Worksheet 2.1 Toothache! Worksheet 2.2 Media analysis: Fry me to the moon
Checkpoint Properties of metals 1 State whether the following are true or false. a Metal atoms pack tightly together, giving metals high density. b Metal atoms have high electronegativity. c Free electrons in metals make the metals good conductors.
2 List the properties that all metals exhibit. 3 Explain whether metal atoms have high or low electronegativity.
Pure metals 4 Outline a factor that limits the use of pure metals. 5 List two metals that can be used in their pure form.
Prac 1 p. 28
UNIT
2.1 a State the breaking stress of: i a 50/50 alloy of copper/zinc ii an alloy of 20% Cu and 80% Zn iii an alloy containing 60% zinc iv pure copper v pure zinc b Identify the proportions of copper that make the alloy stronger than pure copper. c Identify the proportions of zinc that make it weaker than pure zinc. d Identify the strongest copper/zinc alloy. e Identify the composition of three alloys that all break at a strain of 25 x 106 N/m2.
Alloys 6 Define the term ‘alloy’. 7 Alloys have advantages over their parent metals. Clarify this statement using an example.
Think 8 Explain whether metals would be good or poor electrical conductors if they had a tight hold on their outer-shell electrons. 9 Are coins pure metals or alloys? Justify your answer. 10 List two properties of metals that make them ideal for electrical wiring. 11 Aluminium is used for overhead electrical cables, while copper is used for home wiring. Propose a reason why.
[ Extension ]
12 List three reasons why mercury is ideal for thermometers.
Investigate Analyse
1 Lead and mercury are described as cumulative poisons. a Explain what this means. b Describe how these metals get into the environment and into the bodies of animals. c Summarise the main effects of these metals on the human body. d Present your information as a newspaper article explaining the dangers of these metals to society and the environment.
13 State the base metal in a ferrous alloy. (Use element symbols to help you.) 14 List the different types of steel, in order from the lowest carbon content to the highest. 15 Use the table on page 26 to state which metal(s): a is most abundant in Australian ‘gold’ and ‘silver’ coins b is the only metal that is a liquid at normal room temperatures c is the main component of steel d is common to both the alloys brass and bronze e is added to iron to make stainless steel
2 Schools generally use red or green alcohol thermometers. a Investigate which metal was used in thermometers before alcohol. b Explain why this metal is no longer used. c Account for the use of alcohol thermometers.
16 Use the information on page 26 to state what fraction and percentage of pure gold is in: a a 12-carat gold ring b a 9-carat gold nose stud c a 22-carat gold chain
3 Some dentists are concerned about using dental amalgam as fillings in teeth. a Justify their concerns. b Outline some alternatives to using amalgam. 4 a Research the Bronze and Iron Ages. b Propose ways in which the discovery of copper/ bronze and iron/steel would have changed the way of life of people at that time. c Present your information as a poster or a creative story showing what life was like then.
Skills 17 The table below shows the stress that different alloys of copper and zinc can take before breaking. Construct a graph of stress (vertical axis) against the percentage of copper (horizontal axis). Analyse your graph to answer the following questions.
% Cu
0
10
20
30
40
50
60
70
80
90
100
Stress (N/m2 × 106 )
19
16
12
8
5
32
58
40
23
21
33
27
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Pure metals and alloys
UNIT
2.1
[ Practical activity ] How much is it worth? 3 Convert any prices per tonne into prices per gram by dividing by 1 000 000. For example, if aluminium is A$2781.40 per tonne, the price per gram is 2781.40 × 1 000 000 = A$0.00278 or 0.278 cents per gram.
Aim To calculate the value of metal in Australian Prac 1 Unit 2.1
coins
Equipment
$2, $1, 50 cent, 20 cent, 10 cent and 5 cent coins, the business section from a recent newspaper (not Monday), access to an electronic scale
4 Convert any prices per ounce into prices per gram by dividing by 28.35 5 Write a complete list of the prices in Australian dollars per gram.
Fig 2.1.5
6 Use an electronic balance to find the masses of a $1 and a $2 coin. 7 Copy and complete this calculation for each gold coin: Mass of coin = _____ g [put mass of coin here] Mass of copper in coin
= 92% of _____ = _____ g
Mass of aluminium in coin = 6% of Mass of nickel in coin
_____ = _____ g
= 2% of _____ = _____ g [put price per gram here]
[put mass of metals here] Cost of copper
= _____ × _____ = A$ _____
Cost of aluminium
= _____ × _____ = A$ _____
Cost of nickel
= _____ × _____ = A$ _____
8
Add the answers to find the total cost of the coin.
9
What percentage is this of its face value?
10 Use a similar method to calculate the value of the silver coins.
Questions
Method 1 Find the following values and copy them into your workbook: • the US to Australian dollar exchange rate • the prices of aluminium, copper and nickel 2 Convert any US dollar prices into Australian dollars by dividing by the exchange rate. For example, if A$1 = US$0.5064 and the price of aluminium was US$1408.50 per tonne, then its price in Australian dollars was 1408.50 × 0.5064 = A$2781.40 per tonne.
28
1
Deduce whether any of the coins are worth more than their face value.
2
Fifty-cent coins originally had silver in them, but now don’t. Explain why.
3
Use the prices of gold and silver to calculate the cost of each coin if they were really gold or silver.
UNIT
context
2.2 Metals have been used for thousands of years, the first to be used being the native metals such as gold. Unlike gold, most metals are not found as pure elements, but as compounds of oxygen. They need to be ‘released’ from their oxygen before they can be used. Over the centuries, metallurgists (scientists who specialise in metals) have developed a variety
Metals in the crust Metals make up only a quarter of the Earth’s crust. Oxygen and silicon make up the rest. The oxygen does not exist as a gas, but is chemically combined with metal atoms as solid oxides.
potassium 2.2% sodium 2.8%
of efficient and inexpensive ways of doing this. At first they used heat. The discovery of electricity, however, allowed for the extraction of many more metals, particularly aluminium. Imagine your life without metals! Gold, gold, gold!
as either a nugget or a vein of the metal trapped in another rock such as quartz. They just need a little cleaning or the surrounding rock removed. Native elements are so stable and unreactive that they have survived without reacting with the chemicals of the air, dirt or water. A vein of pure gold trapped in quartz
magnesium 2.2%
The earliest recorded discovery of gold in Australia was in 1823 at Bathurst, New South Wales by James McBrien, a Department of Lands surveyor. At the time McBrien was surveying a road along the Fish River, between Rydal and Bathurst. The first gold rush had begun!
Fig 2.2.2
all the other metals and non-metals 1.2%
calcium 3.6% iron 5% aluminium 8.1%
silicon 27.8%
Fig 2.2.1
oxygen 46.7%
The percentage abundance of elements in the Earth’s crust. Oxygen is by far the most abundant, being combined with metals as oxides or with silicon as silicon dioxide in sand or silicates.
Metals ready to go: native elements Native elements can be either non-metals, like carbon and sulphur, or metals, like silver, platinum, copper and gold. The metals can be found as pure elements,
29
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Mining and metals Metals that need work: minerals and ores All other metals are found combined with other elements as compounds. Minerals are rocks containing large amounts of a particular metal. If there is sufficient metal to make it worth mining, it is called an ore.
Is it worth mining?
Ore
Chemical composition
Metal extracted
Bauxite
Aluminium oxide, Al2O3
Aluminium, Al
Chalcopyrite
Copper iron sulfide, CuFeS2
Copper, Cu
Galena
Lead sulfide, PbS
Lead, Pb
Haematite
Iron oxide, Fe2O3
Iron, Fe
Pitchblende
Uranium oxide, U3O8
Uranium, U
Rutile
Titanium oxide, TiO2
Titanium, Ti
Sphalerite
Zinc sulfide, ZnS
Zinc, Zn
Mining produces valuable metals and creates jobs. Sometimes, however, mining is not worth its expense or the negative effects on society and the environment. Major ore deposits in Australia Legend Aluminium (bauxite) Copper (chalcopyrite) Gold Iron (haematite) Lead (galena) Uranium (pitchblende) Silver Titanium (rutile) Zinc (sphalerite)
Able Echo Island Darwin BaroteNabarlek Woodcutters Jabiluka Ranger Browns Koongarra Union Reefs Coronation Hill Mitchell Plateau Mt Todd Bulman Sorby HillsSandy Creek
Nabalco
Weipa Aurukun
Pera Head
Palmer River
McArthur River
Robe River-Deepdale Kintyre Mt Tom Price Rhodes Ridge Jimblebar Paraburdoo Channar Newman WESTERN AUSTRALIA Abra Marymia Fortnum Plutonic Peak Hill Bronzewing Reedys Weld Range Yeelirrie Cue Agnew-Lawlers Group Mt Magnet Mt Morgans Geraldton Youanmi Scuddles Mulga Rock Mt Gibson Koolyanobbing Kalgoorlie Group Copperhead Kambalda-St Ives Coolgardie Higginsville Jarrahdale Perth Norseman Bounty Pinjarra Del Park Wagerup Worsley Manyingee
Westmoreland Cairns Red Dome Constance Range NORTHERN TERRITORY Century Kidston Balcooma Tanami Gecko Lady Loretta Orlando Ben Lomond Gunpowder White Devil Woolgar Callie Charters Towers Area Peko Hilton Thalanga The Granites Mt Isa Wirralie Selwyn Bigrlyi Tick Hill Mt Coolon Plenty River Cannington Lucky Break Osborne Angela Arltunga Gladstone QUEENSLAND Cracow Mt Rawdon Dawson Valley Pandanus Creek
Admiral Bay
800
1200
1600
Gympie
SOUTH AUSTRALIA
Brisbane
Tarcoola
Olympic Dam
Beverly Beltana Honeymoon
Drake NEW SOUTH WALES
2000
Port Latta Rosebery Savage River
Kilometres
Bell Bay Beaconsfield TASMANIA
Henty
Hellyer
Hobart
Mt Lyell Risdon
30
Bingara
Elura Comet Valley Mt Gunson CSA Hillgrove Menninnie Dam Nillinghoo Radium Hill Mt Grainger Mineral Hill Whyalla Tomago Port Pirie Broken Hill Northparkes Lake Cowal Burra Kurri Kurri Newcastle West Wyalong Temora Adelaide Sydney VICTORIA Woodlawn Port Kembla Wedderburn Kangaroo Island Canberra Bendigo Stawell Benambra Ballarat Woods Point Portland Geelong Melbourne
N
400
Horn Island Wenlock River
Wollogorang (Redbank)
Blendevale Goongewa Cadjebut
Yarrie Bamboo Creek Marble Bar Nifty Telfer Nullagine
0
Fig 2.2.3
UNIT
2.2 The mining process Underground mines are used for the mining of deep ores but water penetration, possible collapse, venting of poisonous and explosive gases and the provision of fresh air for the miners are problems that must be managed. If the ore is close to the surface, open-cut mining is easier. An overburden of soil is removed and the ore is dredged out, creating benches, or steps that spiral into the hole. These are also used as access roads to haul the ore to the surface by truck. Open-cut mines cause problems including unsightliness, pollution of surrounding areas with dust, pooling of water, destruction of land above the ore, and the need to repair the land after mining ceases. Pollution and environmental degradation can be severe around mines and processing sites. This photo shows the effect of the Ok Tedi mine in Papua New Guinea.
Before mining begins, many important questions need to be asked: • How much ore is there and how concentrated is it? • How deep is the ore? What type of mine is needed? • Is the site close to existing ports and rail lines? • Is there a population centre nearby from which workers can be employed? • Who owns or controls the land? If they live there, will they be happy to shift? What compensation is appropriate? • What water and air pollution will it cause? • What damage will be done to the environment and how can it be minimised? • What will be the cost of building the mine and the processing plants, and repairing the environmental damage? • What is the current and expected future price of the metal? • What profit is expected?
Fig 2.2.4 Structure of an underground mine
Fig 2.2.5
mill and treatment plant
head frame
winder house ore conveyor
two-compartment shaft
cage or skip
ladder No. 1 level
drive (along the ore body)
pump line compressor
overhead stope
No. 2 level ORE BODY No. 3 level
underhand stope No. 4 level cross-cut
well
31
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Mining and metals Fig 2.2.6
An open-cut mine showing benches and environmental degradation
The activity series When metals react, they lose electrons to form positive ions. Some metals lose their electrons more easily than others. These metals are reactive and are harder to extract. Different extraction techniques are required, depending on the metal’s position in the activity series. As we move up the activity series: • the chance of metals reacting with chemicals becomes greater • the metals become less stable • there is less chance of finding the metals in their natural state • the compounds of the metals become more stable and more difficult to break down • the extraction process becomes more difficult and more expensive.
Concentration of the ore
Extraction by electrolysis
Impurities and waste called gangue are mined with the ore. The mined material is crushed by rollers or by large steel balls that fill a large rotating drum called a ball mill. Gravity and sieves separate some of the gangue, with the remainder then separated by froth-flotation. This is a technique pioneered in Broken Hill, New South Wales, in which the crushed ore floats away on a frothy emulsion of oil and water, leaving the gangue behind. The ore is now ready for extraction.
Electrolysis is such a powerful method that it could be used to extract any metal from its ore. It uses a huge amount of electricity, however, and is used only when there is no cheaper method available. A voltage is applied to a molten sample or solution of the ore and the positive metal ions move to the negative electrode. When it gets there, the ion is forced to take back its outer-shell electrons to form metal atoms that then plate the electrode.
Zn
Heating with C or CO
Fe Ni Sn Pb Cu
Roasting in air
Ag
Occurs naturally
Au
32
More expensive extraction
Al
Method of extraction needs to be more powerful
Mg
Ores more difficult to decompose
Ca
Compounds of the metal are more stable
Na
Metals become more reactive
Electrolysis
Electronegativity increases
K
Extraction method
Metals more likely to be found as native metals
Metal
Fig 2.2.7
UNIT
2.2 The extraction of sodium from molten rock salt by electrolysis
chlorine gas Cl2
CleNa+
Na+ ions take back electrons to form Na metal
iron ore limestone coke exhaust gas iron forms and trickles down (400°C)
ecarbon monoxide forms and rises (800°C) ee-
carbon dioxide forms and rises (1400°C)
hot air blast
Molten Na+Cl-
molten slag
molten iron
Sodium is made by electrolysis of sea water or, more commonly, rock salt. The salt is melted to break the salt crystals into its ions, then converted into pure elements by electrolysis. At the negative electrode: Na+ + e–
molten steel
→ Na
and at the positive electrode: 2Cl–
→ Cl2 +
2NaCl(l)
→ 2Na(l) + Cl2(g)
Prac 1 p. 37
Extraction by heat Heat is sometimes sufficient to extract the pure metal. Aluminium, more This is called smelting. The valuable than gold more reactive metals such is Aluminium cookware as lead, iron and zinc need d ate reported to have origin or per Em carbon or carbon monoxide nch when the Fre the ved ser III n leo po Na (CO) to help the conversion -day King of Siam (modern along. et qu Thailand) at a state ban and To extract iron, coke (a tes pla e in 1867. Th de ma re we d use y source of carbon), limestone ler cut s of aluminium, with les (CaCO3) and iron ore important guests eating (Fe2O3) are heated in a ld. go re pu of from plates d to har so s wa blast furnace. m niu mi Alu y, very extract that it was ver expensive at the time.
metal solidifies as it is drawn out by the rollers
2e –
Overall,
water-cooled mould
continuous sheet is cut into slabs water sprayed on hot metal
Smelting iron in a blast furnace and rolling it into shape
Fig 2.2.8
Smelting of iron occurs as a series of chemical reactions. First the coke reacts to form carbon dioxide: C(s) + O2(g)
→ CO2(g)
Limestone then decomposes, forming calcium oxide and more carbon dioxide: CaCO3(s)
→ CaO(s) + CO2(g) 33
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Mining and metals Carbon dioxide reacts with more coke, forming carbon monoxide: CO2(g) + C(s)
→ 2CO(g)
This reacts with the iron ore to form molten iron, which then runs to the bottom of the furnace: Fe2O3(s) + 3CO(g)
Luckily, iron is relatively common, since iron consumption is currently nine times that of all the other metals put together. Metals are non-renewable resources and all will eventually run out.
→ 2Fe(l) + 3CO2(g)
Waste calcium oxide reacts with sand in the iron ore, forming calcium silicate: CaO(s) + SiO2(s)
→ CaSiO3(l)
Calcium silicate is called slag and floats on the molten iron. Fig 2.2.9
Steel-making in action
Fig 2.2.10
More stable metals only need roasting in air. Most copper is extracted by roasting copper(I) sulfide, found in an ore called copper pyrites: Cu2S(s) + O2(g)
→ 2Cu(l) + SO2(g)
Recycling versus mining Metals that make up less than 0.1% of the Earth’s crust are considered to be scarce. Silver (abundance 0.000 01%) and gold (0.000 000 5%) are scarce and therefore expensive, but some of our most commonly used metals are considered scarce too: copper (0.007%), mercury (0.000 05%), zinc (0.013%), lead (0.0016%) and tin (0.004%).
34
More than 50% of all aluminium cans in Australia are collected and reprocessed.
Metal
Element symbol
Amount used per year (millions of tonnes)
Estimated year at which known reserves of the metal will run out
Iron
Fe
800
2110
Aluminium
Al
12
2350
Copper
Cu
8
2040
Zinc
Zn
4.5
2060
Lead
Pb
4
2020
Tin
Sn
0.25
2015
Eating gold In many cultures, it has been traditional to decorate food with pieces of gold leaf (fine layers of hammered gold). Many of Australia’s top restaurants are now using it too, on top of dishes such as risotto and even in cocktails. The gold leaf is eaten but has no taste, smell or texture. Injections of gold have been used for many years as relief from arthritis, so maybe this will help justify the cost of eating it!
Recycling of aluminium is common, because the production cost of new aluminium is twenty times more than the cost of recycling it. Recycling of many metals is often too expensive to make it worthwhile. The difficulty of separating the iron from tin in food cans makes it far too expensive to recycle iron at the moment, despite millions of cans being thrown out every year. Worksheet 2.3 Extraction of metals
UNIT
2.2
UNIT
2.2 [ Questions ]
Checkpoint Metals ready to go: native elements 1 Clarify what is meant by a ‘native element’. 2 List four examples of native elements. 3 State two forms in which native elements may be found.
Metals that need work: minerals and ores 4 Modify the following statements to make them correct. a Metals that are not native elements are found as alloys. b Rocks containing large amounts of ores are known as minerals. c A mineral contains sufficient metal to mine. 5 Use the table on page 30 to list three ores and the main metal they contain.
Is it worth mining? 6 A mining company decides not to mine a particular metal. State three factors that might have led to this decision. 7 State two features of a commercially successful mine.
The mining process 8 List the problems of an underground mine. 9 Construct a diagram showing the structure of an underground mine.
Concentration of the ore 10 From the following list of words, identify the correct terms to fill in the spaces below. extraction, froth flotation, ball mill, gangue, crushed Mined material is _________ by rollers or steel balls within a _________. Impurities known as _________ are separated by __________. The remaining ore is now ready for _________.
The activity series 11 Define the term ‘activity series’. 12 State the reason why some metals are more reactive than others. 13 Metals are extracted from their ores depending on their position in the activity series. List the extraction methods needed, in order from the least to the most active metals.
Extraction by electrolysis 14 List three metals that can only be extracted by electrolysis. 15 Use a diagram to explain how sodium is extracted from sodium chloride by electrolysis.
16 State a disadvantage of using electrolysis for extraction of metals.
Extraction by heat 17 List three metals that can be extracted by heat. 18 Construct a diagram of a blast furnace and label the important parts. 19 State the chemical formula for slag. 20 Construct the chemical equations for the smelting of iron ore.
Recycling versus mining 21 State whether the following statements are true or false. a Metals are known as renewable resources. b Iron is the most common metal in the Earth’s crust. c Metals that make up less than 0.1% of the Earth’s crust are scarce. 22 State one disadvantage and one advantage of recycling metals.
Think 23 Explain why a reactive metal atom like sodium (Na) has a very stable metal ion, Na+. 24 State which metal(s): a are extracted by electrolysis b are extracted in a blast furnace c are extracted by roasting in air d are native 25 Contrast the following: a slag and gangue b mineral and ore c overburden and ore d electrolysis and smelting e stable and reactive 26 Explain why metals higher up the activity series are more likely to be found as ores than as native elements. 27 Platinum is a native element. Explain where it should appear in the activity series. 28 Mining companies regularly take out mining leases on any land that may contain valuable mineral ores. This may even include the land on which you live. If the mining company holds the lease, it has the legal right to buy the land. Do you consider this acceptable? Justify your answer. 29 Contrast a shaft, a drive and a stope.
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35
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Mining and metals
Analyse 30 List three sites where each of the major ores listed in the table on page 30 are mined. 31 Use the words below to complete the flow chart in Figure 2.2.11 summarising the process of mining an ore and extracting the metal it contains. exploration, electrolysis, gangue, froth flotation, crushing, native-metal, roasting slag, blast furnace, open-cut, underground Fig 2.2.11
32 Use the activity series to predict whether these metal ions and metal atoms would swap electrons: a Na and Au+ b Na+ and Au c Mg and Cu2+ d Pb2+ and Al e Ca2+ and Cu
Skills 33 Construct a bar graph showing the elemental composition of the Earth’s crust. 34 The years for the first successful extraction of different metals are shown in the table.
overburden
Aluminium
1890 AD
Zinc
1500 AD
Iron
1400 BC
Lead
2000 BC
Copper
8000 BC
a Construct a time line showing these discoveries. b Use the activity series to explain why different metals were discovered at different times in history. extraction
b Use a map to summarise where it is processed and extracted. c Describe the transport facilities that probably had to be built to mine and shift the ore, giving consideration to whether it is near a large town. Al
Fe
Cu
Au
[ Extension ] Investigate 1 Research how car bodies can be recycled for their metals. Construct a poster aimed at convincing the public that recycling car bodies is a useful idea.
36
4 Underground miners used to carry canaries with them. Research why and use a cartoon to summarise your research. 5 The mobile phone revolution has brought with it a problem of recycling unwanted phones and batteries. Research what metals are used in making mobile phone batteries and the difficulties they produce if not recycled responsibly. Construct a brochure that could be used to inform the public.
Action
2 Research how to pan for gold and design an instruction sheet.
6 a Record the number of cans and types of cans your household throws out in a week. b Estimate how many cans are thrown out per year.
3 Locate a current mining town in Australia. a Describe the ore mined there.
7 a Construct a bar chart of current prices of metals listed in the commodity prices of the newspapers.
b Compare the current buy-back price of aluminium cans with the price for new aluminium from commodity prices in newspapers.
Creative writing Gold rush!
Surf 8 Complete the activity called ‘Start a Mine’ by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. Construct a poster showing how your mine progressed from start to finish.
UNIT
2.2 Prac 1 Unit 2.2
UNIT
2.2 A rich gold deposit has been discovered 100 metres under Richville, a very wealthy suburb in your area. A multinational mining company is deciding whether it should mine there. Prepare two letters to a newspaper, one supporting a mine and one against. Imagine that the gold had been discovered instead in a remote area of the outback inhabited by its traditional indigenous owners. What will you do now? Are your reasons for and against the same as before? Prepare another two new letters, one in favour of a mine and one against.
[ Practical activity ] Electrolysis of copper
2 Add a small spatula of black copper oxide.
Aim To extract solid copper from a solution
3 Carefully warm over a yellow Bunsen burner flame. Stir with the glass rod until all the copper oxide is dissolved and the solution is blue. Do not boil.
Equipment 1 M sulfuric acid, black copper oxide, spatula, 50 mL beaker, glass stirring rod, Bunsen burner, tripod, gauze mat, bench mat and matches, 12 V power pack, globe, electrodes and connecting leads, filter paper/paper towel
Method
4 Remove the beaker from the tripod and place on the bench mat. 5 Connect up the circuit as shown in Figure 2.2.12. Set the power pack on 6 V DC and allow it to run for a couple of minutes.
1 Pour approximately 20 mL of 1M sulfuric acid into the beaker.
6 Draw a diagram of the set-up. Mark the electrode being copper plated. What is happening at the other electrode and to the colour of the solution?
Fig 2.2.12
7 Turn off the power and remove the electrodes. Carefully remove any pure copper onto filter paper/paper towel.
Questions 1 Explain whether copper formed at the positive or negative electrode. 2 Explain what happened to the blue colour of the solution. 3 In this experiment, copper ions in the solution are taking back electrons to form copper atoms. Describe the evidence for this. 4 Construct a balanced chemical equation for what is happening to the copper ions. 5 Propose a reason why electrolysis is never used commercially to produce copper. 6 Aluminium can only be extracted by electrolysis. Propose a reason why copper and not aluminium was used in this experiment.
37
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UNIT
context
2. 3 The steel body of a car eventually bubbles and rusts away, but aluminium cans and gold jewellery stay ‘good’ forever. Why? They are all metals aren’t they? Some metals are more reactive than others. Reactive metals corrode when exposed to water, air or other chemicals, usually forming metallic oxides. Pure sodium and potassium react with just about
Corrosion of iron and steel Iron is common and cheap. Its alloy, steel, is extremely strong, making it the most commonly used metal on Earth—car bodies, skyscraper frames, concrete reinforcing, pins and needles are all made from various grades of steel. Unfortunately, most steels rust—they react with air and water to form a red coating of iron(III) oxide, Fe2O3. Rust is flaky and easy to dislodge, allowing the rusting process to continue into the next layer. The iron or steel gets thinner, loses its strength and gradually returns to the compound that it was extracted from. Although an extremely complex reaction, it can be summarised as: 4Fe(s) + 3O2(g)
Fig 2.3.1
38
→ 2Fe2O3(s)
Rusted corrugated iron—a common sight around Australia
anything—their corrosion is very quick and often explosive! In contrast, iron corrodes very slowly, while gold is extremely stable and corrosion is rare.
Fig 2.3.2
Rust is flaky and allows the rest of the iron to rust away too.
Breaks between the rust flakes allow water and oxygen to enter into deeper layers. Rusting causes iron(III) oxide (rust) iron to thin.
For rusting of iron to take place, both oxygen and water must be present as either liquid or vapour. The rusting process can be accelerated by salts or heat.
Corrosion protection Stainless steel is an alloy that resists rusting and is used for surgical apparatus, body piercings and equipment in conditions of high heat and salt, such as in kitchens and on boats. Other types of steel can
A stainless steel toaster
Fig 2.3.3
Method of protection
Uses
Advantages
UNIT
2.3 Disadvantages
Painting
Car bodies, cast iron lace
Cheap, easy, attractive
Chips and scratches easily
Layer of grease or oil
Tools, machine parts
Cheap, easy, lubricates parts
Messy, needs to be reapplied regularly
Plastic coating
Dishracks, outdoor furniture
Cheap, attractive
Cracks allow water to enter, plastic deteriorates with age
Tin plating
Food cans
Does not react with food, non-toxic, less reactive than iron/steel
Needs electrolysis to plate steel, expensive, scratches will rust
Chromium plating
Car parts
Attractive
Needs electrolysis to plate steel, expensive, scratches will rust
be protected by coatings that stop air and water from reaching the surface. A scratch or crack in the coating, however, allows rusting to start again. Another method is to coat the surface or attach another more reactive metal. Galvanised iron is iron dipped in molten zinc. Zinc is more reactive than iron and will react instead of it. This is called sacrificial protection. Scratches and chips will not rust, as long as some zinc is close by. Nails and roofing materials are commonly made from galvanised iron. Reactive magnesium blocks are often bolted onto steel structures such as piers and deepwater gas rigs and oil rigs at sea. Prac 1 The magnesium sacrifices itself to protect p. 41 the structure.
protective treatment. Anodising is a technique where the layer of aluminium oxide is deliberately built up using electrolysis. Colours may be added as the layers are deposited. Saucepans and window frames are often made from anodised aluminium. Prac 2 p. 42
Worksheet 2.4 Metal experiments
oxygen
water aluminium oxide layer
Zinc sacrifices itself to protect the iron it plates.
Fig 2.3.4
Aluminium oxide tightly binds to the metal.
Water and oxygen corrode zinc instead of iron.
Fig 2.3.5
Fe
Zn Fe
Fe scratch
Aluminium: reactive but it doesn’t corrode! Aluminium is a very reactive metal and the surface reacts almost immediately with the air to form a fine layer of dull grey aluminium oxide, Al2O3. Unlike rust, this layer does not flake and acts like a tightly bound layer of paint. Aluminium needs no further
2.3 UNIT
Zn
Aluminium oxide does not flake.
Aluminium oxide acts like the perfect paint layer—hard to scratch and non-flaky.
[ Questions ]
Checkpoint Corrosion of iron and steel 1 List three substances required for iron to rust. 2 State two things that speed up the rate at which iron rusts. 3 Construct the equation for the conversion of iron into rust.
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39
Corrosion of metals
Corrosion protection 4 List three ways in which iron and steel can be protected from corrosion. 5 Describe what is meant by ‘sacrificial protection’.
Aluminium: reactive but it doesn’t corrode! 6 State the name of the corrosion-resistant coating formed on aluminium. 7 Clarify what is meant by the term ‘anodising’.
Think 8 Use the equation from Question 3 to help you construct a balanced equation for the corrosion of aluminium (Al) in oxygen (O2) to form aluminium oxide (Al2O3). 9 Use the activity series to predict which metals would show little or no corrosion. 10 Zinc doesn’t rust but it does corrode. Explain. 11 The paint around a scratch on a car door will eventually bubble. Use your knowledge of the flaky nature of rust to explain why. 12 a Explain why the insides of cans of food are coated in tin or a thin layer of plastic. b You should never buy cans of food that are dented or scratched. Explain why. 13 Use the activity series to identify metals that would provide sacrificial protection to iron. 14 Galvanising gives better protection than painting an iron surface. Explain why.
>>> 15 Explain why iron rusts and crumbles, but aluminium just dulls. 16 Describe how you can tell whether an aluminium window frame has been anodised. 17 The magnesium blocks attached to piers dissolve away over time. Outline what needs to happen when they dissolve.
Analyse 18 You need to protect a zinc structure from corrosion. Predict which metals you could bolt onto the zinc to protect it. 19 ‘Iron is the most valuable metal on Earth.’ Justify this statement. 20 Three sheets of iron are each coated in a different metal: copper, magnesium and tin. Predict what will happen to each sheet if the coating is scratched. 21 Steel window frames would be a silly choice near the sea. Explain why. 22 The jewellery used in body piercing is surgical-grade stainless steel, platinum or gold. Explain why these metals, and not cheaper ones, are used.
Project Which metal is that? Find which metals or alloys are used for these purposes:
[ Extension ] Investigate 1
Research the following information and write a report, using illustrations where appropriate. a Explain why roof decking is corrugated or ‘ribbed’. b Outline what is meant by ‘Colorbond roofing’. c Outline the advantages and disadvantages of various metal roofing materials.
Action 2
40
Rust is red-orange. Red-orange rocks often have high iron content. Find photos of rocks or landscapes that are ‘rusty’. Construct a collage showing the pictures collected.
1 The filament in light bulbs 2 Hot and cold water pipes 3 Turns black when exposed to light and is used as film coating 4 Used in fireworks and single-use flash bulbs to give brilliant light 5 Part of haemoglobin, the part of our blood that carries oxygen 6 Added to ‘super’ petrol to avoid ‘knocking’ 7 Makes up the metal plates of a car battery 8 Is in the catalytic converters of car exhaust systems to remove pollutants 9 Used in smoke alarms as a radioactive source 10 A radioactive element used in atomic bombs 11 The metal that is used in many street lamps, giving an orange colouring
UNIT
2.3
UNIT
2.3 [ Practical activities ] Corrosion of iron Prac 1 Unit 2.3
Aim To investigate factors affecting the corrosion of iron Equipment 5 iron nails (not galvanised), copper wire, magnesium ribbon, distilled water, salt (sodium chloride) solution, fine sandpaper or steel wool, 4 test tubes, test-tube rack, Bunsen burner, bench mat and matches, 250 mL beaker, peg or tongs, marking pen
5 Put both into test tubes containing salt water. 6 Put another two nails in the other two test tubes, marking which contains fresh water. 7 Leave for three or four days. 8 Draw each nail, showing the location of any reddish rust and any white corrosion on the magnesium or blue/green corrosion on the copper.
Questions 1 Deduce which factors encourage rusting.
Method 1 Polish each nail with sandpaper or steel wool.
2 Describe the effect of heat on the rate of rusting.
2 Fill the 250 mL beaker with cold water.
3 List all the metals used, in order from most to least reactive.
3 Heat a nail in a blue Bunsen flame until red hot. Use the peg to drop it into the water. Record what happens. 4 Tightly wind the magnesium ribbon around a nail, and the copper wire around another nail.
4 Which test demonstrated sacrificial protection? Justify your answer. 5 Explain why one metal sacrificed itself and not the other. Fig 2.3.6
copper
peg 1
2
3
magnesium 4
red-hot nail
250 ml beaker
cold water water
salt solution
41
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Corrosion of metals
Anodised aluminium Aim To anodise a piece of aluminium Prac 2 Unit 2.3
Equipment Piece of aluminium, aluminium foil, 2 M sulfuric acid, detergent, fabric dye solution, safety glasses, 2 x 250 mL beakers, tongs, tissues, 12 V power pack with wires and alligator clips, retort stand, bosshead and clamp, Bunsen burner, tripod, gauze mat, bench mat and matches or hot plate
Method
4 Set on the lowest voltage, then gradually increase until it reaches 12 V. Leave for 15 minutes, then wash the piece of aluminium in water. 5 In the other beaker, heat the prepared solution of fabric dye, then place the aluminium piece in it. Leave for 10 minutes. 6 Rinse in fresh water and cool. 7 To seal the anodised surface, boil the piece in fresh water for a further 10 minutes.
1 Line one beaker with aluminium foil, then three-quarters fill it with sulfuric acid.
Questions
2 Scrub the piece of aluminium in warm water and detergent and dry well. Do not touch the aluminium with bare hands—use tongs.
1 Explain why the aluminium piece must be handled only with tongs after cleaning.
3 Place as shown in the diagram and connect to the power pack.
2 Aluminium is highly reactive but doesn’t seem to corrode as badly as iron. Explain why. 3 Describe what anodising produced. 4 Explain why anodising would not work with iron.
power pack
aluminium dilute sulfuric acid
Fig 2.3.7
42
aluminium foil
UNIT
context
2.4 Nowadays we take plastics for granted, but before 1950 plastics were almost unheard of. Think of all the things that you wouldn’t have if plastics had not been invented. Like metals before them, plastics changed technology and the way we build and use our world.
H H H
Carbon is a Group IV element and each carbon atom can bond with up to four other atoms. This gives carbon the ability to form continuous lattices (e.g. diamond and graphite) and an amazing variety of molecules. Most molecules found in living organisms, fossil fuels, drugs, plastics and fibres contain atoms of carbon. This puts them into the same category—they are all organic compounds.
Plastics are everywhere. Most packaging and many fibres are plastic.
Fig 2.4.1
methane H
Elephants on the billiard table! By 1868 elephants had been slaughtered in such huge numbers that the supply of ivory could not meet demand. The Phelan and Collender Company offered a US$10 000 award to anyone who could find a replacement for the ivory used in their production of billiard balls. In response, brothers John and Isaiah Hyatt developed a natural polymer, celluloid nitrate or celluloid. Although used for billiard balls, it found more use as photographic film. It was also used for dolls and false teeth, a worrying fact since celluloid is highly flammable!
H
H
H
Plastic: carbon-based compounds
C
H
H
H
C
C
H
H
H
H
H
O
C
C
C
C
H
H
O
ethanol (the alcohol H in beer, wine, spirits, etc.)
H
H
C C
C
C
C C
H
H benzene
H
H O
C
H
methyl butanoate (artificial rum flavouring)
H
Fig 2.4.2
Some organic molecules made of carbon
The properties of plastics make them extremely useful for a wide variety of applications. Plastics: • are good thermal and electrical insulators, having no free electrons to conduct electricity or heat • are strong and light and can be moulded into different shapes • do not react with water or oxygen, making them weather- and rot-resistant. This is both a good and a bad property—outdoor furniture will not rot, but plastic packaging won’t decompose when thrown out; plastics are not biodegradable. • become brittle over time if exposed to sunlight. Chemicals can be added, however, to make them more resistant. • can have other chemicals added to colour and reinforce them (e.g. glass fibres are added to a plastic resin to make fibreglass) • sometimes react with or dissolve in other organic substances (e.g. turpentine, methylated spirits, petrol) • can sometimes burn very easily, producing noxious fumes when they do—PVC produces hydrochloric acid fumes when it burns!
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Plastics and fibres
Plastic
Other names
Polythene
Polyethene
Uses Milk crates, rubbish bins, buckets, plastic bags, cling wrap, soft squeeze bottles
Acrylic PVC
Safety glasses, plastic screens Polyvinyl chloride, polychloroethene
Waterproof clothing, guttering, pipes
Nylon
Brush bristles, fabrics, rope, carpets
Polystyrene
Without bubbles (unexpanded): yoghurt and margarine containers; with bubbles (expanded): insulation, Eskies, cups, packaging
Melamine
Unbreakable dishes
Urea formaldehyde
Electric switches and plugs
Phenol formaldehyde
Door handles, saucepan handles
Monomers and polymers
Thermoplastic and thermosetting plastic
Plastics start with small molecules derived from the oil industry. A process called polymerisation combines them into larger molecules that make up plastic. The small molecules are called monomers and the big ones polymers. Poly is a Greek word that means ‘many’. Polyurethane is made from many urethane molecules, and polyethene is ‘many ethenes’. Imagine a monomer as a single ‘paperclip’. Noxious aircraft! The polymer Plastics and synthetic ‘polypaperclip’ fibres are used in the e becaus would be a string of interiors of aircraft they are light and can be connected paperclips. Prac 1 moulded into the shapes required. The toxic fumes and smoke they produce on burning have been the primary cause of death in otherwise survivable accidents. A fire started in a luggage compartment of a Saudi Arabian Airlines Lockheed Tristar soon after take-off from Riyadh in 1980, filling the cabin with toxic smoke. The plane returned to the airport and landed safely. Instead of evacuating as quickly as possible, the captain taxied and then ran the engines for a total of 6 minutes. All 301 people on board died, including the captain.
When lightly heated, many plastics soften and can be remoulded into new shapes. When cool, they reset. These materials are called thermoplastic, examples being PVC, polythene and acrylic. These polymers arrange themselves into long parallel chains, which slide over each other, allowing flexibility and stretch. If heated they It’s only natural! Many natural polymers retain their basic structure but can exist, too. Wood is made slip over each other to fill whatever from the organic polymers moulds they are poured into. cellulose, lignin and resin. Natural rubber, amber, Thermoplastics are manufactured gum, asphalt and pitch as powder, pellets or granules for are all natural organic shipping to other factories to be polymers. Asbestos is an heated and moulded. example of an inorganic
p. 51
(no carbon) polymer.
Worksheet 2.5 Shape-shifter of modern medical science
H
H
H
H
H
H
H
H
H
C
C
C
C
C
polymerisation C
C
H
C H
C
H
H
H
ethene monomers
Cl
H C
H
Cl
C
H C
H
polymerisation
C
H
H
chloroethene monomers
H H H H polyethene polymer
Cl
H
Cl
H
Cl
C
C
C
C
C
H H H H H polychloroethene (PVC) polymer
Many identical monomers join to make a polymer.
44
Fig 2.4.3
Fig 2.4.4
UNIT
2. 4 Resin has been added to the hooked end of this spear thrower and is being heated to make it sticky.
The first use of thermoplastics? Australian Aborigines have been using resins for thousands of years. Resins from certain plants become soft when heated and very hard when cooled—that is, they are thermoplastic. Resins are obtained from both Porcupine Grass (Triodia species) and Grass Trees (Xanthorrhea species). If a fire goes through an area of grass trees, the resin oozes out and forms bubbles in the sand around the base of the tree. The resin is collected and crushed to a powder. The end of a spear is dabbed in the crushed resin, and heated until the resin becomes sticky. This is repeated many times until there is enough resin to adhere a spearhead. The soft resin is also used to attach stone blades to the wooden handles of tools or weapons using a process called ‘hafting’.
Thermoplastics are recyclable as they can be heated, individual strands cannot move— re-melted and re-moulded many times. Recycling is an thermosetting plastics will char (burn at the important way of managing plastics as it keeps them edges) but will not soften. They therefore out of the environment. Plastics are not biodegradable need to be manufactured and moulded at Prac 2 p. 52 so they stay in tips and the environment for hundreds, the same time. Bakelite is an example of a even thousands, of years. Plastic bags are a major thermosetting plastic. concern for birds, animals and sea life since these creatures can become Thermosetting and thermoplastic Fig 2.4.5 tangled in them or try to feed on them, with the bag subsequently blocking Thermoplastic the animal’s digestive add heat tract. Because plastic bags do not decay, they are released once more into the environment when the long polymer chains animal’s carcass decays. Chains slip over each other and Thermosetting plastics the plastic melts. Thermosetting cannot be remoulded. The polymers have strong cross-linking bonds locking them into a giant molecular structure. Individual add heat strands cannot be shifted without breaking part of the structure. This makes thermosetting plastics hard (scratch resistant), Bonds break and the plastic brittle (will shatter if decomposes (chars). dropped) and rigid (not able to be bent). When
45
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Plastics and fibres Working with plastic Thermoplastics can be moulded into new shapes in a number of different ways.
Extrusion moulding Extrusion moulding is used to make many common items such as pipes, hoses, plastic straws, curtain tracks, rods and fibres.
Blow moulding Bottles are commonly made by blow moulding. A sign of blow moulding is the seam where the two halves of the mould met. Fig 2.4.6
This is the most common method of production. A knob of plastic where the plastic injection took place is left behind. Toys, bottle caps and outdoor furniture are commonly made by injection moulding.
heaters
screw
Ring-shaped die produces a continuous pipe.
mould in open position
plastic pipe
molten plastic
softened thermoplastic
nozzle Slit die produces a continuous strip.
Mould is closed.
46
Plastic expands to fill mould, leaving seam.
metal tube compressed air
Fig 2.4.7
Shellac is a common natural furniture varnish and wax, and is made from the excretions of tiny Tachardia lacca bugs. In 1907, Belgian chemist Leo Baekeland was working in the United States to make an artificial substitute for it. His equipment became clogged when he mixed phenol and formaldehyde. The new material could not be dissolved and was a superb thermal and electrical insulator. The plastic, bakelite, had been invented and found immediate and widespread use as electrical fittings and saucepan handles.
The nozzle creates the shape in extrusion moulding.
pellets of solid thermoplastic
motor
Bugs inspire the first synthetic plastic!
Injection moulding
metal tube
Molten plastic is expanded by compressed air to fill the mould in blow moulding.
Mould opens.
UNIT
2. 4 pellets of solid thermoplastic mould (two parts)
Injection site is left as a ‘bump’.
Are you stringing me along? ram
heating cylinder
molten plastic
Molten plastic is squeezed into a two-part mould to fill it.
Fig 2.4.8
Fibres were not just used as serious tools in Aboriginal life, they were used for fun! String games are common in indigenous cultures both in Australia and around the world. In these games, string figure designs were made that resembled objects used in everyday life, such as dilly bags and baskets. Designs also showed animals and people, or ideas such as the forces of nature. String games were used for learning and to help tell stories.
Natural and synthetic fibres A fibre is any substance that can be woven or knitted into a fabric. There are two main types—natural and synthetic.
Natural fibres Wool, mohair, silk, cotton, linen (flax), hair, fur and coir (the hairy covering of a coconut) are all natural fibres. They have had many uses for thousands of years. In many Aboriginal societies, making objects from plant fibres was an important activity. Items needed for hunting as well as for carrying and collecting food were made along with ritual objects for use in religious ceremonies. The parts of many plants provide fibre to make string, bags, rope, baskets, fishing nets or baskets, clothing and mats. Fibres come from the following plant parts: • underground stems (rhizomes) of plants such as the bulrush • leaves and stems of grass-like plants such as the mat-rush • bark of trees and shrubs such as some species of Acacia and native hibiscus. After the plant parts have been collected, the fibrous material is extracted and separated. Some materials are soaked in water until the nonfibrous tissue rots away. Chewing or scraping with a sharp rock or shell then flattens and softens the remaining fibres.
Fig 2.4.9
An Aboriginal woman using natural fibre to make a basket
On some trees, such as the paperbark, little preparation is needed. The bark is simply peeled from the trees and used to make water containers, mats and liners for babies’ baskets.
Synthetic fibres Synthetic fibres are made entirely from chemicals and are usually stronger than natural fibres. Nylon, Terylene, Lycra, Kevlar, Spandex, Elastane, polyesters and acrylics are all synthetic fibres. Synthetic fibres are produced by the extrusion of a polymer though a multi-holed head called a spinneret. Some use natural fibres as their building block. Wood and paper (a wood product) contain the natural
47
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Plastics and fibres
New, improved Concorde
Softened thermoplastic is squeezed out of a multi-holed nozzle called a spinneret. A synthetic fibre is formed.
Fig 2.4.10
polymer cellulose. If wood pulp is soaked in solutions of caustic soda (sodium hydroxide, NaOH), a sticky cellulose gum forms. When extruded, the gum forms a new fibre—viscose, acetate, tri-acetate and rayon all come from wood pulp.
Length and strength
Prac 3 p. 53
The molecules in a synthetic fibre are aligned along the thread, making them stronger than the plastics they came from. The fibre will be particularly strong if its molecules are long—the longer the molecule,
Fig 2.4.11
Longer molecules produce stronger fibres than shorter ones. The strongest are monofilaments. a pair of molecules
As molecules get longer the force of attraction between them increases.
the greater its attraction to In 2000 an Air France others that lie next to it, and the Concorde took off from Charles De Gaulle Airport stronger it will be. The fibre can in Paris. A tyre burst, still tear, though, since the end of sending fragments into each molecule represents a weak the wing, puncturing the fuel tanks. The spilled fuel spot. ignited and spelt the end Monofilaments are made for the plane. Concordes from molecules that are the same once again took to the sky in 2001, this time length as the fibre. There are no fuel tanks lined with with ends and therefore no weak spots. Kevlar. However, they never Fishing lines are monofilaments regained the patronage of of nylon. Monofilament materials before the catastrophe and were finally removed from are extremely strong and flexible, service in 2003. making them ideal for uses where a tear or puncture would be catastrophic: Kevlar is a monofilament that is five times stronger than steel, but half the density of fibreglass. It is used in bulletproof vests, the sails of ocean-going yachts and the fuel tanks (actually fuel-bags) of Formula 1 racing cars. Ropes, fibre-optic cables, automotive hoses, belts and gaskets are often made of Kevlar. Goalie masks in hockey use a fibreglass/Kevlar mix.
Other properties
The rough surfaces of natural fibres give them a large surface area that can absorb and hold water and dirt. In contrast, the surfaces of synthetic fibres are smooth, making them stain-resistant, water-repellent and ideal for clothing. Drip-dry or wash-and-wear fabrics are synthetic. Synthetics are uncomfortable in hot weather, however, as they do not absorb sweat. Instead, it stays on our skin, making us wet and clammy. Natural fibres absorb sweat and keep our skin dry. Synthetic fibres a monofilament are thermoplastic and will melt if heated: ironing must be done with care and tumbledrying is usually not Each recommended. Molecules separate at their ends.
Force
Prac 4 p. 53
molecule is the same length as the monofilament.
Length DYO
48
Prac 5 p. 53
Other fibres If synthetic fibres are heated strongly with no air present, they do not burn but char until all that is left is a fibre of pure carbon. Carbon fibre is extremely strong and when mixed with resins can be used for making lightweight and flexible structures ideal for bike frames and tennis racquets. Glass fibre is produced by running molten glass into a perforated steel bowl (like the barrel of a washing machine). When spun fast, glass threads fly out and then cool in the air. When mixed with resins, fibreglass is produced.
UNIT
2. 4 Swimming in shoes! Australians have always loved the beach but ht. until 1900 it was illegal to bathe in daylig ugh altho ed, allow was ng bathi 1902 From men and women had to swim separately and fully clothed—men wore neck-to-knee woollen bathers and women wore huge ! bathing dresses, caps, stockings and shoes g makin , heavy very Wool holds water and gets the In easy. ning drow and ult diffic ming swim 1930s Jantzen’s ‘Topper’ swimwear allowed es, men to zip off their top at secluded beach ss tople go to ed allow and in 1938 men were on the beaches of Perth. The bikini was launched in 1952, but the newly developed ers ‘lastex’ fabric needed bone or metal stiffen is wear swim rn Mode to prevent it slipping off! Lycra or ne Elasta , nylon from made only comm blends. Swimmers once again are wearing neck-to-knee bathers, to protect children from UV radiation and to allow competitive a swimmers to reduce drag. Adidas makes from made suit swim competitive full body suits Teflon-coated Lycra, while Speedo makes lled mode e textur a has from ‘Fastskin’, which on shark skin.
Shark skin has scales or ‘dermal teeth’ that reduce drag as the shark swims.
Fig 2.4.12
Speedo’s Fastskin material directs water flow in a similar way to that over a shark’s skin.
Fig 2.4.13
Worksheet 2.6 Recycling
UNIT
2. 4
[ Questions ]
Checkpoint Plastic: carbon-based compounds 1 State what is meant by an ‘organic compound’. 2 List three examples of organic compounds. 3 List these facts about carbon (C): a its group number b its period c the number of electrons in its outer shell d the maximum number of bonds it can form e two continuous lattices that it forms
Monomers and polymers 4 Identify the correct terms in the following list to fill in the spaces below. polymer, polymerisation, monomer, plastics A small molecule capable of joining together in a long chain is called a ________. When small molecules join together they form a ________. Small molecules join together in a process known as _______ and result in the production of ________.
Thermoplastic and thermosetting plastic 5 Define the term ‘thermoplastic’.
6 List three forms in which thermoplastics are manufactured. 7 Define the term ‘thermosetting’. 8 List three properties of plastics made by thermosetting.
Working with plastic 9 Use a diagram to demonstrate how extrusion moulding is achieved. 10 State the type of moulding used to make bottles. 11 List three plastic items made by injection moulding.
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49
Plastics and fibres
Natural and synthetic fibres 12 State whether the following are true or false: a A fibre is any substance that can be woven or knitted into a fabric. b Nylon, cotton and linen are all examples of natural fibres. c Natural fibres are produced using a spinneret. 13 a State the name of the method used to produce fibres. b State the name of the ‘nozzle’ used to produce fibres.
>>> 24 Explain how the length of a molecule affects the strength of a fibre. 25 Where do fibres tend to break? 26 Explain why care must be taken when drying and pressing synthetic fibres. 27 Explain how cross-links stop thermosetting plastics from melting. 28 Use Figure 2.4.3 to construct a general equation for the polymerisation reaction. 29 Evaluate the use of plastics in terms of their effect on society and the environment.
Length and strength 14 Use Figure 2.4.11 to outline what is meant by a monofilament. 15 Use an example to demonstrate the usefulness of a monofilament.
Other properties
Investigate
16 Outline three desirable and three undesirable properties of plastics.
1 Materials such as polystyrene are called foams. Research how plastic foams are made. In your answer, include the chemical equations involved.
17 Explain why natural fibres are able to absorb and hold water.
Other fibres 18 List three examples each of natural fibres, synthetic fibres made from plastics and synthetic fibres made from wood products.
Think 19 Contrast: a the surface of a natural fibre with that of a synthetic fibre b a monomer with a polymer c thermoplastic with thermosetting plastics d injection moulding with blow moulding 20 List examples of: a five synthetic polymers b three natural polymers c one inorganic polymer d three thermoplastic polymers e one thermosetting polymer f one monofilament 21 A train could be considered a polymer. State what the monomer would be. 22 Explain how thermoplastics can melt and then reset on cooling.
Analyse 23 Would the production of thermosetting plastic powder be a good idea? Justify your answer.
50
[ Extension ]
Action 2 Use a paperclip to represent a monomer. Link them together to construct models of a polymer, a thermoplastic and a thermosetting plastic. 3 Inspect ten plastic items around your home for seams or ‘bumps’. List the items as made by extrusion, blow or injection moulding. Present your findings in a table. 4 Inspect the washing/drying/ironing instructions on six different pieces of clothing. Present the information in a table showing the fibre composition of each. List any recommended washing instructions, noting whether ‘no heat’ is stated. 5 Gather information by counting how many plastic bags are collected in one week in your home from shopping. Discuss your results and include comments on whether alternatives could have been used.
Surf 6 Find out more about how plastics are recycled by connecting to the Science Focus 4 Companion Website at www.pearsoned.com. au/schools, selecting chapter 4 and clicking on the destinations button. a Construct a graph showing the amount of plastic used in Australia in each State. b Produce a report which outlines how plastics are recycled. c Justify the need to recycle plastics.
UNIT
2. 4
[ Practical activities ] Identifying plastics
2 Describe the appearance—is it transparent, translucent or opaque?
Aim To identify properties of some common Prac 1 Unit 2.4
UNIT
2. 4
plastics
3 Describe its flexibility—does it bend or is it stiff?
Equipment
4 Does it feel ‘waxy’?
Labelled pieces (each about 2 x 1 cm) of polythene, polystyrene, PVC, perspex, nylon, ‘mystery’ plastics, dissection board/bench mat, scissors, turpentine, nail polish remover, dilute hydrochloric acid (HCl), detergent, 250 mL beaker, tongs, access to meths burner set-up in fume hood Fig 2.4.14
turpentine
6 How hard is it to cut with scissors? 7 Are the cut edges smooth or jagged? Does the cut show bubbles or cells? 8 Add two drops of detergent to a 250 mL beaker of cold water. Add a plastic—does it float or sink? 9 Place a drop each of turpentine, HCl and nail polish remover onto three small squares of each plastic. Leave for five minutes and record whether each piece dissolved, went soft or remained hard. 10 Break each plastic into smaller pieces and use tongs to hold a piece in a meths burner flame.
HCl
2 drops of detergent
5 Does your fingernail or the scissors scratch it?
WARNING: The meths burner must be in a fume hood. If no fume hood is available, do not do any burning tests. Do not smell any fumes or smoke.
nail polish remover
11 Did the burning produce smoke? If so, what colour was the smoke? What colour was the flame? Did molten plastic drop from it? Did the drops burn as they fell?
This must be in a fume hood 250 mL beaker
12 Run tests to determine what each of the mystery plastics is.
meths burner
Questions 1 Identify each plastic as either thermoplastic or thermosetting. 2 Identify the mystery plastics.
Method 1 Copy the table below into your workbook. Your teacher may split you into groups to run all tests on one plastic only or to run one test on all the plastics. Polythene Appearance Flexibility Feel Ease of scratching Ease of cutting Description of cut Does it float? Effect of flame What dissolves it?
Polystyrene foam
PVC
3 Explain why the burning must be done in the fume hood and not in the lab.
Perspex
Nylon
4 Explain what is produced from PVC when it is burnt. 5 Deduce whether any plastics sink in, or react with, water. 6 A sample of plastic kept burning once it was lit. Its flame was blue with a yellow tip. Identify the plastic.
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Plastics and fibres
Making casein plastic Prac 2 Unit 2.4
Aim To make a polymer called casein from milk. Casein was an early plastic that is still used for buttons and some wood glues. It is hardened industrially with formalin.
8 After a couple of days, remove the mould and polish with the sandpaper. 9 Use tongs to hold a small amount of the dry casein in a Bunsen flame. Does it melt, burn or char?
Equipment
Extension
Full cream milk, vinegar, Bunsen burner, bench mat, tripod, gauze mat and matches, 100 mL measuring cylinder, 2 x 250 mL beakers, thermometer, glass stirring rod, elastic band, coarse cloth for straining, paper towel/filter paper, assorted moulds (bottle caps, moulded chocolate trays etc.), fine sandpaper, tongs
10 Chip off a piece of casein and find its mass. 11 For every 50 g of casein you chip off, measure out 20 g of borax and 40 mL of water. 12 Add the borax and water to a conical flask and swirl until dissolved. 13 Crumble the casein into the borax solution and shake until creamy glue is formed.
Method 1 Set up the Bunsen burner and tripod.
14 Use it to glue two chips of wood together. Use the clamp or elastic bands to hold the pieces together. Leave it overnight to ‘cure’, then try to separate the pieces of wood.
2 Place 100 mL of milk in one of the 250 mL beakers. Warm gently until it reaches 50°C. Do not overheat. 3 Add 10 mL vinegar and stir with the stirring rod. 4 The milk should curdle to form white lumps of curds (casein) and yellowish liquid called whey.
Questions 1 Deduce whether the casein plastic produced was thermosetting or thermoplastic.
5 Use the elastic band to secure the piece of cloth tightly over the other 250 mL beaker. Strain through the curds and whey.
2 State the purpose of the final test.
6 Carefully remove the cloth and squeeze to remove as much liquid as you can.
3 Identify a use of the casein.
7 Empty onto the paper towel/filter paper. Pat dry, then firmly press into moulds. Leave the casein to dry in the sun.
5 Little Miss Muffet ate her curds and whey. Explain whether you would.
4 Outline how casein is hardened industrially.
Fig 2.4.15
100
110
thermometer 90
10 mL vinegar
curds
50°C
elastic band
30
40
50
60
70
80
250 mL beaker
0
10
20
100 mL milk
curds
cloth whey
curds mould
filter paper
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UNIT
2. 4 TEACHER DEMONSTRATION Making nylon Prac 3 Unit 2.4
This demonstration must be done in a fume hood.
4
Aim To make a sample of nylon Equipment
Use tweezers to lift part of the layer of nylon formed between the solutions. Drape it over the glass stirring rod and wind the fibre out.
Questions
Fume hood, 1,6-diaminohexane, anhydrous sodium carbonate, sebacoyl chloride or adipoyl chloride, cyclohexane, 2 x 250 mL beakers, tweezers, glass stirring rod
1
Construct a three-frame cartoon or diagram to show how the nylon was made.
Method
2
Predict what would have formed if the two solutions had been allowed to mix.
3
The nylon fibre formed is not very useful. Explain why.
1
Dissolve 2.2 g of 1,6-diaminohexane and 5 g of anhydrous sodium carbonate in 50 mL of water.
2
In another beaker, mix 2 mL of sebacoyl chloride or adipoyl chloride in 50 mL of cyclohexane.
3
Gently pour the 1,6-diaminohexane solution down the side of the beaker and onto the top of the cyclohexane solution. The two solutions must not mix but must form layers.
Identifying fibres Aim To compare and contrast natural and Prac 4 Unit 2.4
synthetic fibres
Equipment
Labelled samples of fabrics (wool, cotton, linen, rayon, nylon, polyester), microscope, microscope slide and coverslip, pins or tweezers, metal tongs, matches, bench mat
Method 1 Remove an individual thread, about 2 cm long, from each fabric sample.
3 Explain why synthetic fibres have smoother surfaces than natural ones.
wool
4 List the fabrics in order from the safest near a flame to the most dangerous.
silk
cotton
5 Clothing fires are more common among children than adults and more common among girls than boys. Propose reasons why. 6 Recommend which fibres should be used for clothing for babies and young children.
linen
nylon
Fig 2.4.16
Fibres under the microscope
2 Place it on the microscope slide and use the tweezers or pins to tease the fibres apart.
Natural versus synthetic
3 Place a coverslip on top and inspect the fibres under the microscope. 4 In your workbook, sketch and label each fibre, taking note of its surface.
Prac 5 Unit 2.4
Plan and run an experiment to determine the amount of water different fabrics can hold.
5 Cut/tear a strip about 2 × 1 cm from each fabric. 6 Use tongs to hold a strip over the bench mat. Hold a lit match under the strip. Record your observations for each fabric. Did it catch fire, melt or char? What colour were the flame and smoke? What was left?
Questions 1 Match your samples with the diagrams in Figure 2.4.16.
Questions DYO
1 Construct a flow chart showing how you conducted your experiment. 2 List the fibres tested in order from those that held the least water to those that held the most. 3 Identify which of the fibres were synthetic.
2 Deduce which fibres were natural and which were synthetic.
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Science focus: Nanotechnology Prescribed focus area: The implications of science for society and the environment Michael Crichton’s novel Prey tells the story of research going horribly wrong. In this future world, self-replicating nanoscale robots take on their own existence and start to cooperate with each other. They prey on living creatures, including the research scientists who created them, to gain the building blocks they require to reproduce themselves. This book caused a very strong response in some people who saw nanotechnology as being far too dangerous and thought that the book predicted the future. At present, however, nanotechnology is still evolving and there is little risk. There is also very strong support within the scientific and medical communities for the development of nanotechnologies because of the huge benefits that might be gained. In the future it is unlikely that nanoscale robots could gain such independence, but they will certainly be developed and become highly useful to society for many reasons.
How small is a nanometre? Nanotechnology involves making and manipulating incredibly tiny objects. The size of the objects dealt with in nanotechnology is in the order of 10’s to 100’s of nanometres. One nanometre is equal to just one thousand millionth (one billionth) of a metre. A single atom has a diameter of about 0.10 to 0.3 nanometres, which gives you an idea of just how tiny the nanometre is.
A different approach Multidisciplined Working with incredibly small objects requires cooperation between scientists from various disciplines. Nanotechnology draws on chemistry, physics, electrical engineering, molecular biology, quantum physics and materials science. It offers a
How small is a nanometre? As you move from left to right across the diagram, each step is ten times smaller. Domain of nanotechnology Limit of human vision
Fig SF 2.1 The future?
Limit of light microscope Rhinovirus (common cold) ~30 nm
Note: There are 1000 millimetres (mm) in 1.0 metre (m). There are 1000 micrometres (µm) in 1.0 millimetre (mm). There are 1000 nanometres (nm) in 1.0 micrometre (µm).
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10 –
10 nm m =
Diameter of atoms ~0.10 to 0.30 nm
10
Carbon nanotubes ~1 nm
0.
Width of DNA molecule ~2 nm
10 – 9 1. 00 m nm =
.0
10 –
8 m nm =
Nanowire chemical detector wires are ~10 nm
10
Mitochondrion from human cell ~500 to 700 nm 10 – 7 0. 1 = 0 m 10 µ = 0 m nm
00
10 – 5 = = 0.0 m 10 1 µm0 m m
4 m = m m
10 –
10
0.
10 – 3 1. 00 m m = m
0.10 mm = 50 to 100 µm
10 – 6 m µm =
Human red blood cell ~6.0 µm
Human hair
~0.05 to
1.
Small fly 5.0 mm
huge range of possibilities, with applications already being explored in medicine, computing, electronics, engineering and lithography.
Top down Until recently the manufacture of the smallest of objects was a ‘top down’ approach. This means the substance would be engineered to reduce it down to the desired size, like sculpting a small statue from a large block of stone. This approach is suitable for micro-sized objects such as silicon chips and micro machines, which often use an etching process to make small components out of a larger piece of substance.
Fig SF 2.2
brick by brick. With STEM it is possible to manipulate single atoms on the surface of a material and to lay down incredibly thin surface layers on a substrate. Figure SF2.3 shows how a STEM operates. The STEM and sample are contained in a region which has had the air evacuated using a vacuum pump. The STEM piezotube probe is then moved over the surface of the sample, maintaining a fixed distance by ensuring the tunnelling current between the probe and sample does not change. Through computer analysis of the data collected, an image of the surface features of the sample can be produced. Using a STEM, individual atoms can be identified. With a secondary voltage applied between the tip of the probe and the surface, the chemical bonds holding a surface atom in position can be broken and the single surface atom moved. This ability to manipulate individual atoms has made bottom-up engineering of nanoscale objects a reality—it is now becoming possible to assemble something by moving individual atoms into position. Figure SF2.4 shows a STEM image of a surface that uses single atoms to represent data. The individual atoms hold data just like pits on a CD. Such data can be written and read using a STEM. Data storage at this scale means that 300 copies of a 300-page book could be stored on the cross section of a human hair.
These micromechanics components were created using a top-down approach to etch them out of silicon. For scale, a fly’s leg can be seen.
Bottom up The development of the scanning tunnelling electron microscope (STM or STEM) finally made it possible to produce images of an atom. It was quickly realised that with some modifications the STEM would be the perfect tool to directly manipulate the surface of a material on the atomic scale. This provided the opportunity to try and create structures from the bottom up. This means assembling a structure atom by atom, like building a house
The basic features of a scanning tunnelling electron microscope (STEM)
Distance control for piezotube to sample and scanning unit
Applied control voltage for piezotube containing electrodes
Fig SF 2.3
Piezotube generates a flow of electrons that is focused at the sample
Sample being studied Tunnelling current amplifier Data processing and display of images
Tunnelling electron current
Tunnelling voltage
55
Red gold
Fig SF 2.4
Individual silicon atoms (yellow) sit on this surface and represent data, like pits on a CD.
With the nanoscale so incredibly small, objects do not behave in the way expected at larger scales. ‘Quantum’ effects begin to act at the atomic level and this produces some very interesting results. For example, the metal gold is gold in colour when we look at a sample large enough to see with the human eye. But when gold atoms are arranged to produce tiny crystals of gold on the nanoscale, the gold appears red. These curious results show that we have a lot to learn about how substances behave at the nanoscale.
The future of nanotechnology A large amount of investment is going into nanotechnology research and development to produce innovative new products for the future. The possibilities are endless. Below are described some of the most promising areas where nanotechnology will be applied in the future.
Surfaces The ability to lay down incredibly thin layers of a substance onto the surface of other material can improve the properties of a substance and offers many advantages in chemistry and engineering. For example, laying down an incredibly thin protective coat on solar cells could improve transmission of light into the cells, and thereby improve their efficiency. Also, surfaces could be made self-cleaning by applying a coating that repels dirt. Manipulating the surface of materials can also make it possible to store vast amounts of information in very small spaces. A scanning beam interference lithography machine can be used to create gratings or grids with structures on the scale of a few nanometres. The structures created are used in astronomical devices such as space telescopes and satellites. A laser is used to create the pattern on the target surface. In the future this machine could be used to produce nanotechnology components for computers and machines.
56
A scanning beam interference lithography machine creates nanoscale grids and grates for space technology.
Fig SF 2.5
Medical An application of nanotechnology being explored is the creation of nanobots (nanoscale robots) to be placed in humans. Nanobots could monitor the internal conditions of the body, such as blood sugar levels, temperature, nervous activity or production of hormones by endocrine glands. Nanobots could be designed to seek out and destroy viruses and bacteria in the bloodstream. They could also be engineered
Fig SF 2.6
This nanobot is injecting a drug to kill cancerous cells in a human body. Could this be how we treat disease in the future?
to target certain cells in the body, identifying the cell and delivering a product to it. For example, a nanobot could be designed to detect cancerous cells. Drugs could be packaged inside the nanobots to be injected directly into the cancer cells with no damage to the normal cells of the patient.
This image of carbon nanotubes was created using a STEM. Carbon nanotubes have the potential to be used in electrical devices and have unusual properties. Much research is being done with carbon nanotubes, and their applications are likely to be diverse.
Fig SF 2.7
Computing Nanotechnology offers the potential to manufacture new, smaller, faster and more efficient integrated circuits for computing. It has made quantum computing possible, with incredible processing speeds far beyond the ability of present silicon-based microprocessors. Quantum computers would store and process information at an atomic level. A solid-state quantum computer element can be made by positioning phosphorus atoms 20 nanometres apart in very pure silicon. The phosphorus atoms behave as an incredibly tiny and extremely fast microprocessor. Promising research into quantum computing is being conducted at the University of New South Wales.
[ Student activities ] 1 Development of a quantum computer is being pursued energetically in a number of countries. The University of New South Wales (UNSW) has purchased a very expensive STEM to assist in its research. a Research the work being done on quantum computers at UNSW. b Summarise the work being done and any progress made to this point. c Compare this research with that being done in another location. 2 As a molecular biologist and nanoengineer, you have been given the task of designing a nanobot to help solve an important medical problem. a Identify a medical problem you would like to solve using nanobots, e.g. diabetes, cancer, HIV, haemophilia or another of your choice. b Construct a poster or model of a nanobot that could help solve this medical problem. Include labels or a key to show the features of your nanobot, and an explanation of how the nanobot will tackle the medical problem. 3 Tests on carbon nanotubes show that they have extraordinary, unexpected properties.
a Research carbon nanotubes to find out: i what they are ii what special properties they have iii their possible applications and uses iv why it would be important to conduct further research into carbon nanotubes b You are a research scientist and you want to work with carbon nanotubes but you need funding for your project. There is $1 000 000 in funding for nanotechnology available, but you have to appear to be at the forefront of research to get this. Using the information you have about carbon nanotubes, construct an application that will get the funding you need for your research. Include the possible outcomes and products you will create, and how they will benefit society. 4 Produce a poster, display or other presentation to teach the general public about nanotechnology, and what it may offer society in the future. You will need to conduct research to include information about: a examples of current and future research and products b public safety and any social issues c the importance of continuing to invest in this area of research
57
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UNIT
context
2.5 We always seem to be getting dirty or getting covered in oils and grease. Dirt, oils and grease are made from organic compounds that normally dissolve only in other organic substances. Although there are obvious problems in washing ourselves in turpentine,
methylated spirits or nail-polish remover, dry-cleaners use similar organic solvents to dissolve and remove grease from clothes. At home you need to use soap and water to get clean, but how does this work?
Making grease soluble Surfactants are molecules that assist water in dissolving dirt and grease.
Water Australians are too clean!
At home, water is our main washing liquid. It is a polar molecule, having small electrical charges on each of its atoms. Water will dissolve other polar molecules, like sugar, and ionic substances such as salt or sodium chloride (Na+Cl–), which have positive and negative ions. Water by itself will not dissolve grease.
Fig 2.5.1
Detergents, shampoos and soaps are surfactants.
Fig 2.5.2
Many babies suffer from eczema, or skin hypersensitivity. It seems that we are all using too much soap, bubble bath and shampoo, since all remove essential oils from the skin. This causes dryness and makes us susceptible to eczema. Dermatologists recommend using soap-free cleansers instead. For babies all that is generally needed is some bath oil or moisturiser.
Water is a polar molecule and can use its slight charges to dissolve ionic substances.
δ+ δ– H O
–
δ+ H
a water molecule
H H
δ+ δ+
+
–
– +
–
+
–
Water weakens the forces holding salt chemicals together.
H
δ+
O O
O
H
H H
δ–
δ–
δ–
δ+
δ+
δ+
H H
δ+ δ+
means slight negative charge
O
δ–
+
–
means slight positive charge
H H
δ+ δ+
O
δ–
CD8
Once separated, they are unlikely to rejoin.
Soap, shampoos and detergents are surfactants and have both organic and ionic parts. Surfactant molecules are similar to those of plastics in that they are long and have an organic carbon backbone. This will dissolve grease nicely. Unlike most molecules, however, they have a charged or ionic end. This is then joined to a metal ion (usually the sodium ion, Na+). This end will dissolve in water nicely. We now have the perfect molecule for dissolving grease—one end dissolves the grease, while the other end dissolves in water. Once the grease is dislodged, surfactant molecules surround it and keep it from re-depositing back onto the surface. These tiny dissolved liquid
What gorgeous hair! The molecules of most hair conditioners tend to have positively charged ends that are attracted to the weak negative charge of the hair. They stay there even when the hair dries. (Fabric softeners work in the same way.) Shampoos and conditioners are normally sold in separate bottles because their opposite charges interfere with each other if they are mixed. In combined shampoo-conditioners, the conditioner molecules are trapped in crystalline shells. When lathering hair, the shampoo works, but there is insufficient water to break down the conditioner crystals. These only break down on rinsing, when more water is present.
grease patches and the water form a mixture called an emulsion. The water can now wash away the grease. Hot water and agitation (vigorous movement) also help loosen the grease from the surface and keep it from re-depositing on it. Lather (bubbles) will also assist in keeping grease from dropping back and is particularly useful in situations where little water is used (e.g. shaving, washing cars, hair shampoo). Many fibres (including hair) take on a weak negative charge when wet. Once dissolved and carrying their load of grease, the soap or shampoo molecules also carry a negative charge and are thus less likely to re-deposit the grease back onto the fibre. Prac 1 Prac 2 p. CD11
and magnesium precipitates. These are left behind as a dirty grey substance called scum, which deposits as a dirty ring around basins and baths, or as scale in pipes and kettles. Soft water has less dissolved salts and soap produces less scum. Soap lathers better, feels smoother and more slippery in soft water, and less of it is required to get clean. Prac 3 p. CD12
UNIT
2.5 Scum-free and bubbles galore! Many New South Wales cities have excellent soft water: it lathers well and leaves very little scum. In other areas, ‘water softener’ systems are attached to each home’s water supply. Beads of zeolite replace the offending calcium and magnesium ions with sodium. Soap doesn’t react with sodium.
p. CD11
water
hydrophilic head (ionic end dissolves in water)
hydrophobic tail (organic end dissolves in grease) surfactant molecule
grease
Surfactant (soap, detergent) molecules have a hydrophobic end that hates water but loves grease. The other end is hydrophilic—it loves water.
Fig 2.5.4
Fig 2.5.3
Hard and soft water Tap water contains many impurities. If it has a lot of calcium and magnesium salts dissolved in it, then it is hard. Soap reacts with these salts to produce calcium
Lather (bubbles) keeps the dirt and grease from re-depositing on the hair.
Soap is made when natural fatty acids found in materials like vegetable oils and animal fats react with an alkaline (basic) solution such as sodium hydroxide. The process is called saponification and is summarised by the reaction: fat + alkaline solution
→ soap + glycerol
Skin soap
soda Bases such as caustic and ) ide rox (sodium hyd s are their alkaline solution they if s ou extremely danger The n. ski h wit t tac con in come its as y per slip skin becomes ation ific on sap go der un fats and form soap!
CD9
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Soaps
Whale soap?
Detergents are produced from chemicals in crude oil. The big advantage of detergents is that they don’t produce scum.
UNIT
2 .5
In the past, whale blubber was commonly the fat from which soap was made. Whales are now prote cted, however, and the fat used in soap manufactur e comes mostly from cows slaughtered for their meat. Just about any fat or oil can be used and many soaps are now made with vegetable or plant oils. Palmolive soap is named because it is made with palm oil and olive oil.
[ Questions ]
Checkpoint Water 1 Modify the following statements to make them correct: a Water is a non-polar molecule. b Sodium chloride is a polar molecule. c Water is able to dissolve grease. 2 State the types of substances that normally dissolve in water.
Making grease soluble 3 Identify the type of compound that grease is made of. 4 Some liquids are able to dissolve grease. List three such liquids. 5 List three ways in which grease is prevented from re-depositing on a surface. 6 State the reactants in saponification.
Hard and soft water
Think 10 Explain how soap is able to dissolve both in water and in grease. 11 Identify as many factors as you can that will affect the cleaning of a piece of fabric. 12 If lather doesn’t help to dissolve grease, explain how it helps to remove grease from a fabric. 13 If shaving cream did not lather, state where the cut whiskers would end up. 14 Identify three vegetable oils that could be used for the production of soap. 15 If animal fat is needed to produce soap, propose some sources of the fat.
Skills 16 Contrast detergent with soap. 17 Compare soap molecules with: a plastics b ionic compounds
7 Lathering results in ‘scum’ forming when water is hard. List the chemicals that cause water to be hard.
18 Construct a word equation for the production of soap.
8 Clarify what is meant by ‘soft water’.
19 Construct a diagram showing how soap helps grease to dissolve in water.
9 State the advantages of soft water.
Create
[ Extension ] Investigate 1 a Use a dictionary to define the term ‘phobia’ and include some examples. b One end of a surfactant molecule is hydrophobic and the other end is hydrophilic. Clarify the meaning of these terms and identify which end is which. 2 Conduct research on the Internet to answer the following questions: a List what is in a soap-free cleanser like Dove. b Scotch, 3M and ENJO all make cloths that clean without the use of chemicals. Describe how they do this.
CD10
20 Construct a three- to four-frame cartoon/diagram showing how shampoo-conditioners work.
c Research the dry-cleaning process. Describe how it cleans clothes, making reference to the chemistry involved. If necessary, use diagrams to assist your explanation. d Explain why soap films are often coloured. e Describe the machine that can make three-storeyhigh soap bubbles.
Action 3 Design a survey of soaps. Record your results in a table showing the first six ingredients of at least three different brands of soap, hair shampoos and shower gels. Identify and discuss any trends you find.
UNIT
2 .5
UNIT
2.5 [ Practical activities ] Fig 2.5.5
Make soap! Prac 1 Unit 2.5
WARNING: The soap made here uses and contains very corrosive sodium hydroxide. Do not get any sodium hydroxide on your skin or in your eyes. Do not use the soap produced.
250 mL beaker
5 mL oil water
Aim To produce a sample of soap Equipment Olive oil or coconut oil, 1 M sodium hydroxide solution, saturated solution of sodium chloride, kerosene, 3 test tubes, rubber stopper, 400 mL beaker, 100 mL beaker, 250 mL beaker, hot plate (preferably) or a Bunsen burner, bench mat, tripod, gauze mat, matches, filter paper or paper towel
Method 1 Pour about 5 mL of oil into a test tube.
test tube
yellow flame
10 mL sodium hydroxide solution
bench mat
2 Carefully add 10 mL of sodium hydroxide solution. 3 Place the test tube in a boiling water bath for 30 minutes. Shake the tube every few minutes to mix the contents. 4 Place 50 mL of the sodium chloride solution in the 100 mL beaker, then pour the hot oil mix in. The soap formed should float to the top.
9 Fill a fresh test tube with water, then add 3 or 4 drops of kerosene. This will be our ‘grease’. Stopper and shake. 10 Add some soap, then shake again. Compare with what you saw before.
5 Scoop up the soap and place it in the 250 mL beaker. Rinse a few times with a little water.
Questions
6 Let the soap dry on filter paper/paper towel.
1 Draw a cartoon explaining how soap was made here.
7 Two-thirds fill the other test tube with water and add a little soap.
2 Describe what happens to the kerosene in water alone.
8 Stopper and shake. Does it lather?
4 Construct a word equation for the reaction.
3 Describe the effect that the soap had on it.
How good is it? Prac 2 Unit 2.5
Aim To design and run an experiment that compares liquid and powder laundry detergents Equipment Powder and liquid laundry detergents
Method DYO
1 Identify all the variables or factors that would influence the effectiveness of laundry detergent in removing grease.
2 Choose one factor that you think would have a big effect.
3 Design and run an experiment that would test it. 4 Write a report on the effect of the variable you chose and why you think you obtained the result you did.
Questions 1 Draw a conclusion about the variable you tested. 2 Gather conclusions from other groups who tested different variables. Assess which variables had an effect and which didn’t.
CD11
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Soaps
How hard is it? Aim To test water hardness Prac 2 Unit 5.2
Equipment Distilled water, dilute magnesium sulfate solution, solution of calcium hydrogen carbonate, suspension of calcium carbonate in water, small chips of bath soap, shampoo, detergent, 5 test tubes, rubber stoppers to fit test tubes
6 Repeat the experiment but use a few drops of shampoo. 7 Repeat again with a few drops of detergent.
Questions 1 Describe what soap does in hard water.
Method 1 Put about 2 cm of distilled water and 2 cm of tap water into two separate test tubes.
2 Identify the solution that was the hardest. Justify your answer.
2 Put about 2 cm of each solution into the other test tubes.
3 Deduce whether the water showed any hardness when it contained shampoo or detergent.
3 Add a small chip of soap to all five tubes and stopper lightly.
4 Outline the advantage of detergent over soap.
4 Shake the tubes vigorously and watch for any lather that forms.
stopper Look for lather.
solution of different salts
Hold stopper and shake.
small chip of soap
Fig 2.5.6
CD12
5 Record your results in order from the solution that produced the most lather (the softest) to the one that produced the least lather (the hardest).
Is the water hard or soft?
5 Design a test to see if temperature has an effect on water hardness.
>>> Chapter review [ Summary questions ] 1 State an example of an alloy and its base metal. 2 State whether the additives in alloys are usually metals or non-metals. 3 List the carbon content of: a cast iron b tool steel
c mild steel
4 State how many carats are in pure gold. 5 If gold is 18-carat, state the percentage of gold present. 6 State a use for each of these materials: a aluminium d Duralumin b zinc e bronze c cast iron f haematite 7 State one example each of: a an alloy of copper b an alloy of iron c an impurity commonly added to iron d a commonly used pure metal e a non-metal abundant in the Earth’s crust f a scarce metal g a metal that is cheaper to recycle than to produce
g bauxite h celluloid i Kevlar
h i j k
an ore a native metal a natural fibre a synthetic fibre made from wood products l a monofilament fibre m a surfactant n an organic solvent
8 Identify a metal that is extracted by: a electrolysis b smelting
c roasting
9 List the ingredients for a blast furnace. 10 State the special name given to the corrosion of iron. 11 Outline what is meant by ‘anodised aluminium’. 12 List four properties of a thermosetting plastic.
[ Thinking questions ] 13 Rose-gold is a pink-gold colour. Propose a metal that could be added to the base metal to create this colour. 14 It is thought that iron simply oozed out of the rocks used to surround the cooking pits of ancient hunters. Compare these conditions with those of a blast furnace.
58
17 Explain why stainless steel is ideal for use as replacement bone (hips, tooth implants, knees). 18 Corrugated iron (steel) is galvanised and is commonly used for roofing. a Explain what will happen after all the zinc coating has corroded away. b Explain whether the zinc can be replaced. 19 If car bodies are galvanised, propose reasons why they are also painted. 20 Identify problems associated with using plastic shopping bags. 21 An optic fibre is transparent fibre that carries light unbroken from one end to the other. Explain whether an optic fibre needs to be a monofilament. 22 Explain why natural fibres cannot drip-dry.
[ Interpreting questions ] 23 Use a diagram to describe the bonding in metals that allows: a conduction of electricity b conduction of heat 24 Use the data in the table on page 34 to construct the following graphs: a a pie chart showing the amount of metals used each year b a bar graph showing when each metal is estimated to run out 25 Construct a diagram showing what happens in the electrolysis of copper chloride. Label the diagram and use chemical equations to show the chemical reactions at each electrode. 26 Aluminium metal is high on the activity series, yet is a commonly used metal. Use Figure 2.3.5 to explain why it does not rust. 27 Phenylethene is an ethene molecule with one hydrogen replaced by benzene, C6H6. a Construct a diagram of a phenylethene molecule. b Polystyrene foam uses phenylethene as its monomer. Construct a diagram showing ten phenylethene monomers joined to form the polymer polystyrene.
15 Primitive prospectors found gold and silver before any other metal. Explain why.
Worksheet 2.7 Materials crossword
16 Salt is often used in Europe and North America to help melt ice on roads. Their cars also rust more quickly than ours. Explain why.
Worksheet 2.8 Sci-words
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3
Electricity and communications technology Key focus area:
>>> The applications and uses of science
compare series and parallel circuits and describe everyday applications of each describe the relationship between voltage, resistance and current, and use Ohm’s law to calculate values of each
Outcomes
use an analogy to describe voltage, current and resistance
5.3, 5.6.1, 5.6.3, 5.12
By the end of this chapter you should be able to:
contrast AC with DC electricity describe how some electromagnetic devices operate describe the main components needed for efficient transmission of electricity explain how waves transmit energy list and describe the different forms of electromagnetic radiation contrast analogue with digital signals and their use in communication explain how communication signals can be transmitted
electricity that comes from our power points?
3 How do mobile phones find each other? 4 Describe an appliance that uses electromagnetism.
5 Who invented the telephone? 6 What is a digital message made up of?
Pre quiz
1 What do AM and FM on the radio dial stand for? 2 What are the voltage and frequency of the AC
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UNIT
context
3.1 We live in an ‘electrical’ society. Every day you use a wide variety of appliances that need electrical energy to run. Discmans, iPods, toasters, televisions, microwave ovens, computers and even the family car all need electricity. You might not appreciate how much you rely on electricity until you have A major blackout to go without.
A simple circuit A circuit is a path from one side of a power source (e.g. a cell, battery or power pack) to the other. The four basic parts of a simple circuit are: • an energy source, such as a cell or battery. A cell or battery can be thought of as a charge pump. • a conducting path (wires) for the electricity to flow through Fig 3.1.1
On 14 August 2003 an electrical failure suddenly hit the United States and Canada. About 50 million people in cities from New York to Toronto had no power. People were trapped in subway trains and elevators for hours. The loss related to the blackout was estimated at $6 billion. One month later, Italy’s 57 million people also were affected by a blackout. Luckily it occurred on a weekend so its initial impact was less dramatic and caused less economic damage. Some developing countries have regular ‘brownouts’ because their need for electricity exceeds their ability to generate it. Electricity supply must be ‘rationed’, and so suburbs and towns have times each day when no electricity is available.
Fig 3.1.2
Imagine this scene without electricity. What problems would it cause?
• an energy user or load, such as a globe, motor, buzzer, heating element or resistor • a switch to turn the current on and off.
A simple circuit and its equivalent circuit diagram circuit
circuit diagram
cell 1.5 V
1.5 V cell
+ –
switch
connecting wire
60
globe
Fig 3.1.4
The water pump and electrical circuits Conductor/lead
Cell
Unit
3.1 current (I) switch Globe
Battery
resistance
high voltage +
A
Closed switch
Fixed resistor
Open switch
Variable resistor
Ammeter
Leads connected
battery
low voltage – ground
valve V
Voltmeter
Common components in simple circuits
high pressure
Leads crossing
Fig 3.1.3
Inside a circuit There are three very important values in circuits that we can measure and calculate. • Whenever charge moves, we have a current. In most circuits the moving charges are electrons and current is defined as the rate of flow of those electrons. Current is measured in amperes (A) or amps for short. Sometimes in a circuit there will be more than one path that the current can take. More current will flow down the easier path and less down the harder one. In mathematical formulas, current is given the symbol I. • Depending on what part of the circuit we are talking about, voltage is a measure of how much energy: – is available from the battery or power pack to push current through the circuit. It may be thought of as the size of the ‘push’. – is used when current passes through a load. Voltage is measured in volts (V) and is sometimes referred to as potential difference. Voltage is given the symbol V in mathematical formulas. • Resistance is a measure of how much a load (e.g. globe, motor, resistor) restricts and reduces the flow of current. Resistance is measured in ohms, or Ω for short. In mathematical formulas, resistance is given the symbol R. To help you understand these terms we will use the analogy of a water pump circuit. In a water circuit, the pressure supplied by the pump (P) drives the water around the closed loop of a pipe at a certain flow rate (F). The waterwheel (W)
water wheel
pump low pressure water reservoir
restricts the flow, slowing down the water, using up its energy. The valve turns the flow of water on and off. In an electrical circuit, the energy or voltage (V) supplied by the battery drives the electrons around the circuit, causing an electric current (I). The resistance (R) slows the electrons, using up their energy. A switch turns the flow of electricity on and off.
Water in pipe
Units
Electricity in wire
Units
Pressure (P)
Pascals
Voltage (V)
Volts
Flow rate (F)
Litres/second
Current (I)
Amps
Resistance to flow (W)
Newtons
Resistance (R)
Ohms
Voltage A battery or power pack is the ‘pump’ of an electrical circuit. A water pump takes in water at low pressure, supplies energy to it and ejects it at high pressure. A battery or power pack takes in charge at low voltage, adds energy to it and ejects it at a higher voltage.
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Electricity
Resistance high voltage + low voltage
high pressure
–
low pressure
valve
A switch has voltage behind it, but no current if not switched on.
Fig 3.1.5
If closed, pressure is behind valve but no flow of water.
A waterwheel restricts the flow of water, slowing the water down and taking away its energy. Light globes, buzzers, motors, heating elements and resistors are loads that restrict the flow of current and remove energy from the electrons. These loads change the electrical energy into other forms such as sound, light, heat and kinetic (moving) energy. The filament of a light globe is a very thin wire. As the current tries to squeeze through, it encounters resistance and uses up some of its energy. In a thick wire, electrons move more freely and with little resistance. Little energy is lost. Increasing the resistance of the circuit will cause a decrease in the current, and results in more energy being used up by the load. Resistance in a circuit can be compared to a water wheel.
Fig 3.1.7
Voltage can be compared to the pressure of water in a pipe.
Current When current flows through a wire it moves freely, losing almost no Fatal currents energy. This is just like water in a A current as small as 0.1 to pipe where there is little resistance 0.2 amps can kill! Most deaths to slow the water down. A higher associated with electric shock icity electr the current means more electrons flow happen because interrupts the heartbeat, which past a point in a circuit every is controlled by small electrical second. currents in your body. High erous A current of 1 ampere means dang voltages are more than low ones because they can that 1 coulomb of charge passes drive a higher current through by a point in the circuit each your body. The 240 volts in our second. A coulomb is an amazing easily is lies home power supp 6 250 000 000 000 000 000 electronenough to drive a deadly current through your body. sized charges! Current can be compared to the rate of flow of water through a pipe.
Thick wire offers little resistance to flow of electrons.
A resistor acts as a load, converting electrical energy to heat and light.
A water wheel is like a load in the circuit. It converts kinetic energy of water to movement of the wheel.
Fig 3.1.6
A large pipe offers little resistance to flow of water.
Heat energy being released in a glowing resistor of an electric bar heater
62
Fig 3.1.8
Types of circuits
Ohm’s law
There are two basic types of circuits—series and parallel.
Ohm’s law describes the relationship between the current, voltage and resistance in a circuit. Typical results from this experiment may be:
Series circuits If you arrange two globes one after the other in a line with the battery, the globes are said to be in series. The voltage supplied is split between the two globes, but the current passing through each is the same. The two globes glow more dimly than a circuit with only one globe. If a globe in this circuit is removed or ‘blows’, the circuit is broken, so the other globe will not work either.
6V
6V
no current
bulb goes out 1A 3V
1A 3V
Current, I (amps)
A
0
0
B
3
1
C
6
2
D
9
3
E
12
4
V Resistor
bulb removed
E D C B A
A
Ohm’s law can be found using a circuit where the resistance is changed.
Fig 3.1.9
A series circuit with two globes
1A
Voltage, V (volts)
UNIT
3 .1
Variable resistor to alter current
Fig 3.1.11
Graphing these results shows that the electric current is directly proportional to the voltage (V α I). This means if the voltage is doubled, so is the current. A graph of Ohm’s law is therefore a straight line passing through the origin. The slope or gradient of the graph gives us the resistance. It can also be calculated by dividing the voltage by the current, R = V/I.
Parallel circuits R =
Ohm’s law
Slope =
V = slope I vertical rise horizontal run
= 62 = 3 12
∴R
=
3Ω
10 6
8 Voltage (V)
If you arrange the globes next to each other but on separate branches you have built a parallel circuit. The voltage used by each globe is the same, but the current is split between each branch. Each globe glows with equal brightness. If a globe in this circuit is removed or blows, the other globe will remain lit as there is still a circuit through which current Prac 1 Prac 2 p. 66 p. 66 may flow.
6 2 4
4A
6V
2A
2A
6V
2A
6V
current divides
4A
2A
2
6V 6V
no current
2A
1
2 3 Current (A)
Ohm’s law is shown by this graph.
4
5
Fig 3.1.12
Ohm’s law is stated as: Fig 3.1.10
A parallel circuit with two globes
Voltage = Current × Resistance V =IR
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Electricity
Fig 3.1.13
Using Ohm’s law
2ESISTANCE #URRENT
6
2
! )
)
2
!MMETER
4O USE THE TRIANGLE SIMPLY USE A FINGER TO COVER WHAT YOU WISH TO FIND 4HERE ARE ONLY THREE COMBINATIONS &IND