Cambridge IGCSE Chemistry Fourth Edition PDF

The Cambridge IGCSE™ Chemistry series consists of a Student’s Book, Boost eBook, Workbooks and Teacher’s Guide with Boost Subscription. Cambridge Cambridge Cambridge Cambridge Cambridge IGCSE™ Chemistry IGCSE™ Chemistry IGCSE™ Chemistry IGCSE™ Chemistr...

The Cambridge IGCSE™ Chemistry series consists of a Student’s Book, Boost eBook, Workbooks and Teacher’s Guide with Boost Subscription. Cambridge Cambridge Cambridge Cambridge Cambridge IGCSE™ Chemistry IGCSE™ Chemistry IGCSE™ Chemistry IGCSE™ Chemistry IGCSE™ Chemistry Fourth Edition Fourth Edition Workbook Third Practical Skills Teacher’s Guide 9781398310506 Boost eBook Edition Workbook with Boost 9781398310780 9781398310537 9781398310513 Subscription 9781398310520 To explore the entire series, visit www.hoddereducation.com/cambridge-igcse-science Cambridge IGCSE™ Chemistry Teacher’s Guide with Boost Subscription Created with teachers and students in schools across the globe, Boost is the next generation in digital learning for schools and colleges, bringing quality content and new technology together in one interactive website. The Teacher’s Guide includes a print handbook and a subscription to Boost, where you will find a range of online resources to support your teaching. Confidently deliver the revised syllabus: guidance on how to approach the syllabus from experienced authors, practical support to help you work scientifically, as well as lesson plans based on the provided scheme of work. Develop key concepts and skills: let students see how their skills are developing with a range of worksheets, formative knowledge tests and detailed answers to all the questions in the accompanying Student’s Book, Workbook and Practical Skills Workbook. Enhance learning: videos and animations on key concepts, mathematical skills and practicals plus audio of technical terms to support vocabulary flashcards. To purchase Cambridge IGCSE™ Chemistry Teacher’s Guide with Boost Subscription, visit www.hoddereducation.com/cambridge-igcse-science 18/02/2021 09:22  Cambridge IGCSE™ Chemistry Fourth Edition Bryan Earl Doug Wilford 9781398310506.indb 1 24/02/21 10:02 PM  Cambridge International copyright material in this publication is reproduced under licence and remains the intellectual property of Cambridge Assessment International Education. Cambridge Assessment International Education bears no responsibility for the example answers to questions taken from its past question papers which are contained in this publication. Exam-style questions (and sample answers) have been written by the authors. In examinations, the way marks are awarded may be different. References to assessment and/or assessment preparation are the publisher’s interpretation of the syllabus requirements and may not fully reflect the approach of Cambridge Assessment International Education. 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However, the Publishers and the authors accept no legal responsibility on any issue arising from this check; whilst every effort has been made to carefully check the instructions for practical work described in this book, it is still the duty and legal obligation of schools to carry out their own risk assessments for each practical in accordance with local health and safety requirements. For further health and safety information (e.g. Hazcards) please refer to CLEAPSS at www.cleapss.org.uk. Hachette UK’s policy is to use papers that are natural, renewable and recyclable products and made from wood grown in well-managed forests and other controlled sources. The logging and manufacturing processes are expected to conform to the environmental regulations of the country of origin. Orders: please contact Hachette UK Distribution, Hely Hutchinson Centre, Milton Road, Didcot, Oxfordshire, OX11 7HH. Telephone: +44 (0)1235 827827. Email [email protected] Lines are open from 9 a.m. to 5 p.m., Monday to Friday. You can also order through our website: www.hoddereducation.co.uk ISBN: 978 1 3983 1050 6 © Bryan Earl and Doug Wilford 2021 First edition published in 2002, Second edition published in 2009, Third edition published in 2014, This edition published in 2021 by Hodder Education, An Hachette UK Company Carmelite House 50 Victoria Embankment London EC4Y 0DZ www.hoddereducation.com Impression number 10 9 8 7 6 5 4 3 2 1 Year 2025 2024 2023 2022 2021 All rights reserved. Apart from any use permitted under UK copyright law, no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, or held within any information storage and retrieval system, without permission in writing from the publisher or under licence from the Copyright Licensing Agency Limited. Further details of such licences (for reprographic reproduction) may be obtained from the Copyright Licensing Agency Limited, www.cla.co.uk Cover photo © Björn Wylezich - stock.adobe.com Illustrations by Integra Software Services Pvt. Ltd., Pondicherry, India. Typeset in ITC Officina Sans Std Book 11.5/13 by Integra Software Services Pvt. Ltd, Pondicherry, India Printed in Slovenia A catalogue record for this title is available from the British Library. 9781398310506.indb 2 24/02/21 10:02 PM  Contents Acknowledgementsvi How to use this book ix Scientific enquiry x 1 States of matter 1 1.1 Solids, liquids and gases 1 1.2 The kinetic particle theory of matter 2 1.3 Changes of state 4 1.4 The effects of temperature and pressure on the volume of a gas 6 1.5 Diffusion 7 2 Atoms, elements and compounds 10 2.1 Elements10 2.2 Compounds 14 2.3 Mixtures 18 2.4 Inside atoms 20 3 Bonding and structure 30 3.1 Ionic bonding 30 3.2 Covalent bonding 38 3.3 Metallic bonding 50 4 Stoichiometry – chemical calculations 54 4.1 Relative atomic mass 54 4.2 Calculating moles 55 4.3 Moles and compounds 57 4.4 Calculating formulae 60 4.5 Moles and chemical equations 62 5 Electrochemistry 69 5.1 Electricity and chemistry 69 5.2 Electrolysis of lead(II) bromide (Teacher demonstration) 70 5.3 Electrolysis of aluminium oxide 72 5.4 Electrolysis of aqueous solutions 75 5.5 Electrolysis of copper(II) sulfate aqueous solution 78 5.6 Fuel cells 81 5.7 Electroplating 82 6 Chemical energetics 87 6.1 Substances from petroleum 87 6.2 Fossil fuels 90 6.3 What is a fuel? 90 6.4 Alternative sources to fossil fuels 91 6.5 Exothermic and endothermic reactions 91 iii 9781398310506.indb 3 24/02/21 10:02 PM  7 Chemical reactions 100 7.1 Reactions 100 7.2 Factors that affect the rate of a reaction 101 7.3 Enzymes 107 7.4 Reversible reactions and equilibrium 108 7.5 Ammonia – an important nitrogen-containing chemical 109 7.6 Industrial manufacture of sulfuric acid – the Contact process 111 8 Acids, bases and salts 116 8.1 Acids and alkalis 116 8.2 Formation of salts 120 8.3 Methods of preparing soluble salts 121 8.4 Preparing insoluble salts 124 8.5 Testing for different salts 124 8.6 Water of crystallisation 126 9 The Periodic Table 134 9.1 Development of the Periodic Table 134 9.2 Electronic configuration and the Periodic Table 137 9.3 Group I – the alkali metals 137 9.4 Group VII – the halogens 141 9.5 Group VIII – the noble gases 145 9.6 Transition elements 145 9.7 The position of hydrogen 147 10Metals 150 10.1 Properties of metals 150 10.2 Metal reactions 151 10.3 Reactivity of metals and their uses 153 10.4 Identifying metal ions 156 10.5 Extraction of metals 157 10.6 Metal corrosion 161 10.7 Alloys 165 11 Chemistry of the environment 170 11.1 Water 170 11.2 Artificial fertilisers 175 11.3 The air 177 11.4 Atmospheric pollution 179 12Organic chemistry 1 188 12.1 Alkanes 188 12.2 The chemical behaviour of alkanes 191 12.3 Alkenes 194 12.4 The chemical behaviour of alkenes 196 12.5 Polymers 198 iv 9781398310506.indb 4 24/02/21 10:02 PM  13Organic chemistry 2 206 13.1 Functional groups 206 13.2 Alcohols (R–OH) 206 13.3 Carboxylic acids 211 13.4 Esters212 13.5 Condensation polymers 214 13.6 Natural polyamides 216 14Experimental techniques and chemical analysis 221 14.1 Apparatus used for measurement in chemistry 221 14.2 Separating mixtures 224 14.3 Qualitative analysis 233 Theory past paper questions 240 Alternative to Practical past paper questions 255 Glossary262 Index269 Periodic Table of Elements 275 v 9781398310506.indb 5 24/02/21 10:02 PM  Acknowledgements The authors would like to thank Irene, Katharine, Lambert Photography/Science Photo Library, b © Michael and Barbara for their patience, support and midosemsem – Fotolia; p.33 © Science Source/ encouragement throughout the production of this Science Photo Library; p.36 l © Martyn F. Chillmaid, textbook. We would also like to thank the editorial r © Martyn F. Chillmaid; p.37 (left column) l © and publishing teams at Hodder Education who have Martyn F. Chillmaid, r © Martyn F. Chillmaid, (right supported us on the journey over the past year. column) Courtesy of the University of Illinois at Urbana-Champaign Archives; p.38 © Andrew Source acknowledgements Lambert Photography/Science Photo Library; p.40 © pp. 13, 38, 40, 41, 42, 189, 195, 196, 198, 199, 200 Andrew Lambert Photography/Science Photo Library; and 213 p.41 l © Andrew Lambert Photography/Science The molecular models shown were made using Photo Library, r © Andrew Lambert Photography/ the Molymod® system available from Molymod® Science Photo Library; p.42 © Andrew Lambert Molecular Models, Spiring Enterprises Limited, Photography/Science Photo Library; p.44 © Billingshurst, West Sussex RH14 9NF England. 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Chillmaid/Science Photography/Science Photo Library, r © Leonid Photo Library. viii 9781398310506_FM.indd 8 25/02/21 5:28 PM  How to use this book To make your study of Chemistry for Cambridge As you read through the book, you will notice that IGCSE™ as rewarding and successful as possible, some text is shaded yellow. This indicates that the this textbook, endorsed by Cambridge Assessment highlighted material is Supplement content only. International Education, offers the following Text that is not shaded covers the Core syllabus. If important features: you are studying the Extended syllabus, you should look at both the Core and Supplement sections. FOCUS POINTS Each topic starts with a bullet point summary of what you will encounter within the topic. Practical skills These boxes identify the key practical skills This is followed by a short outline of the topic you need to understand as part of completing so that you know what to expect over the next the course. few pages. Key definitions Test yourself These provide explanations of the meanings of key words as required by the syllabus. These questions appear regularly throughout the chapter so you can check your understanding as you progress. Worked examples Revision checklist These boxes give step-by-step guidance on how to approach different sorts of calculations, with follow-up questions so At the end of each chapter, a revision checklist will you can practise these skills. allow you to recap what you have learned in each topic and double-check that you understand the key concepts before moving on. Going further Exam-style questions These boxes take your learning further than is required by the Cambridge syllabus so that you have the opportunity to stretch yourself. Each chapter is followed by exam-style questions to help familiarise learners with the style of Answers are provided online with the accompanying questions they may see in their examinations. Cambridge IGCSE Chemistry Teacher’s Guide. A Practical These will also prove useful in consolidating your Skills Workbook is also available to further support learning. Past paper questions are also provided you in developing your practical skills as part of at the end of the book. carrying out experiments. ix 9781398310506.indb 9 24/02/21 10:02 PM  Scientific enquiry Throughout your IGCSE Chemistry course, you will obtained. Most importantly, it is essential that need to carry out experiments and investigations you carry out a risk assessment before you do any aimed at developing some of the skills and abilities practical work. that scientists use to solve real-life problems. 3 Make and record observations – the data you Simple experiments may be designed to measure, need to answer the questions you have set for example, the temperature of a solution or the yourself can only be found if you have planned rate of a chemical reaction. Longer experiments, your investigation sensibly and carefully. For or investigations, may be designed to allow you to example, you might start to use a measuring actually see the relationship between two or more cylinder to collect a gas, but as you develop physical quantities such as how rate of reaction your ideas you may realise a burette might be varies with temperature and concentration. more appropriate and more accurate. Be careful Investigations are likely to come about from the not to dismantle the equipment/apparatus until topic you are currently studying in class, and your you have completed your analysis of the data, teacher may provide you with suggestions. For all and you are sure you do not need to repeat any investigations, both your teacher and you must of the measurements! If you have to reset your consider the safety aspects of the chemicals and equipment/apparatus, it may add further errors apparatus involved. You should never simply carry to the results you have obtained. out a chemistry investigation without consideration Ensure that all your data, numeric or of the hazards of the chemicals or getting the observational, is displayed in a clear format. This approval of your teacher. will often be in the form of headed tables with To carry out an investigation, you will need to: the correct units being shown to the appropriate degree of precision. 1 Select and safely use suitable techniques, 4 Interpret and evaluate observations – the apparatus and materials – your aim must be to results you obtain from any investigation must safely collect sufficient evidence using the most be displayed carefully and to the accuracy of appropriate apparatus for the technique you have the equipment you have chosen to use. Your chosen. Being able to draw and label diagrams choice of presentation will help you interpret correctly to show how the equipment will be used your evidence and make conclusions. Often is also important. Your techniques will need to be your presentation will be in the form of a graph explained clearly to do a proper risk assessment. or a table. For some graphs, you may need to For example, how to carry out a titration, how calculate gradients or use it to find values at a you are going to follow the rate of the reaction specific point during the investigation by drawing you are using, or how to test for ions and gases. intercepts. Good chemists keep looking at the 2 Plan your experiment – this is an important part data and alter the way in which it is obtained to of doing science and involves working out what get more accurate results. You should be able to you are going to do to try to find answers to evaluate whether your data is good or bad. If it is the questions you have set yourself. Predictions good, were there any anomalous results? Why did based on work you have been studying or you get them? are doing in class may help you develop the 5 Evaluate methods and suggest possible investigation in terms of the number and type improvements – at the end of your investigation, of observations or data needed. You will also you must be able to evaluate the equipment, need to be able to identify the independent methods and techniques that you have used. and dependent variables. For example, if you Think about any sources of errors that could have are trying to find out how temperature affects affected your results by the use of the wrong the rate of a reaction, the temperature will be equipment. Consider, if you were able to carry out the independent variable, but the dependent the investigation again, what you would change. variable might be the volume of gas collected. The more data you obtain, the easier it is to spot Other variables such as concentration need to be anomalous results. controlled so that they will not affect the data x 9781398310506.indb 10 24/02/21 10:02 PM  A written report of any chemical investigation label each axis of a graph with the name and unit would normally be made of these fixed components: of the quantity being plotted. Make sure that the scale you use allows the points to fill up as much » First, state the aim of the work at the very of the graph paper as possible. beginning to inform your teacher what you were Clearly explain the calculations involved in doing the investigation to find out. the interpretation of your data and give the » A list of all items of equipment/apparatus used significant figures appropriate to the equipment and a record of the smallest division of the scale used. of each measuring device you have used (see » Conclusions can be obtained from the graphs Chapter 14). For example, burettes can be read and calculations you carry out. Your conclusions to two decimal places, to the nearest 0.05 cm3, from the data obtained might be different from where the second decimal place is either a 0 those that you expected. Even so it is very if the bottom of the meniscus is on the scale important for any scientist to come to terms with division, or a 5 if it is between the divisions. the findings of their experimental result, good If the meniscus was between 24.10 cm3 and or bad! 24.20 cm3, the reading would be 24.15 cm3. » In the evaluation you should make a comparison » You must show that you have considered the between the conclusions of your investigation safety of yourself and others before you carry and your expectations: how close or how different out any practical work. Provide a list of all the were they? You should comment on the reliability chemicals you will use, as well as the ones you and accuracy of the observations and the data will produce, and do a risk assessment to check obtained. Could you have improved the method on all the hazards of the chemicals. The results to give better or more accurate results? Would a of your risk assessment might indicate that you pH probe have been better than using universal need to work in a well-ventilated room or in a indicator to find the point of neutralisation in a fume cupboard. In some cases you may need the titration? Were there any anomalous points on assistance of your teacher. If in doubt, always ask your graphs, or any unusual data or observations? your teacher for advice. Highlight these and try to give an explanation. » Clearly state the details of the methods used, starting with the wearing of eye protection. The methods should be shown as numbered steps and Suggestions for should be made as clear as possible. Ideas of the number of measurements that will be made and investigations their frequency should be stated. Observations Some suggested investigations are outlined in this should be clear and you should use changes book as follows: in colour and physical state as part of your 1 Find which vinegars contain the most acid. observations. (Chapter 8) » Presentation of results and calculations. If you 2 Find the molar volume of hydrogen by reacting made several measurements of a quantity, draw magnesium with hydrochloric acid. (Chapter 4) up a table in which to record your results. Use 3 Determination of the enthalpy of combustion the column headings, or start of rows, to name of ethanol. (Chapter 6) exactly what the measurement is and state the 4 The effect of changing the surface area of a units used; for example, in a rates of reaction reactant on the rate of reaction. (Chapter 7) experiment, ‘Mass of calcium carbonate/g’. 5 Use the anion and cation methods of Give numeric values to the number of identification to find the ions present in tap significant figures appropriate to the equipment water. (Chapter 14) being used, for example, a mass could be 6 Show that ammonia is a weak base by measuring recorded to 0.5 g or 0.05 g depending on the its pH and conductivity, and comparing your resolution of the top-pan balance you use. Take results with those from a solution of sodium averages and remember that anomalous or non- hydroxide with the same concentration. (Chapter 8) concordant results should not be used in their 7 Determine the melting point of stearic acid. calculation. If you decide to make a graph of your (Chapter 1) results, you will need at least six data points 8 How can sodium chloride be obtained from rock taken over as large a range as possible; be sure to salt? (Chapter 14) xi 9781398310506.indb 11 24/02/21 10:02 PM  9 What are the effects of acid rain on a variety of A further example involves the well-known building materials? (Chapter 11) Russian chemist Dimitri Mendeleev. He realised that 10 Which is the best temperature, between 34 and the physical and chemical properties of the known 40°C, for the fermentation of sugar to take place? elements were related to their atomic mass in a (Chapter 12) ‘periodic’ way, and arranged them so that groups of 11 What are the chemical properties of the weak elements with similar properties fell into vertical organic acid, ethanoic acid? (Chapter 13) columns in his table. However, in devising his 12 Do foodstuffs contain carbon? (Chapter 12) table, Mendeleev did not conform completely to the order of atomic mass, with some elements swapped Ideas and evidence in science around. It took time for his ideas to gain acceptance because the increase in atomic mass was not regular In some of the investigations you perform in the when moving from one element to another. We school laboratory, you may find that you do not now know, with the development of atomic theory interpret your data in the same way as your friends and a better understanding of chemical processes, do; perhaps you will argue with them as to the best that the elements in the Periodic Table are not all way to explain your results and try to convince in atomic mass order. It took until 1934, with an them that your interpretation is right. Scientific understanding of atomic number and post-Russian controversy frequently arises through people revolution, for the Periodic Table to be finally interpreting evidence differently. accepted in the form you see today. For example, our ideas about atoms have changed There are many different types of scientists over time. Scientists have developed new models with specialties in their own areas of work such of atoms over the centuries as they collected new as chemistry and physics, but they all work in the experimental evidence. If we go back to the Greeks same way. They come up with new theories and in the 5th century bc, they thought matter was ideas, they carry out work to find the evidence to composed of indivisible building blocks which they establish whether their ideas are correct and, if not, called atomos. However, the idea was essentially why. Scientists rely on other scientists checking forgotten for more than 2000 years. Then John their work, often improving the ideas of everyone Dalton published his ideas about atoms in 1800. He and moving science forward. The use of new ideas suggested that all matter was made of tiny particles is often beneficial to everyone in the world, for called atoms, which he imagined as tiny spheres example, the discovery of vaccines for Covid-19, or that could not be divided. It then took another the push to improve battery manufacture for use 100 years before Joseph Thomson, Ernest Rutherford in electric cars which would in turn help solve one and James Chadwick carried out experiments and of the biggest problems we have to face: global discovered that there was a structure within the warming. Scientists are working hard to stop global atom. This saw the continuous development of what warming but their ideas are not always embraced we know today as atomic theory. because of economic and political factors. xii 9781398310506.indb 12 24/02/21 10:02 PM  1 States of matter FOCUS POINTS ★ What is the structure of matter? ★ What are the three states of matter? ★ How does kinetic particle theory help us understand how matter behaves? In this first chapter, you will look at the three states of matter: solids, liquids and gases. The structure of these states of matter and how the structures can be changed from one to another is key to understanding the states of matter. You will use the kinetic particle theory to help explain how matter behaves, so you can understand the difference in the properties of the three states of matter and how the properties are linked to the strength of bonds between the particles they contain. Why, for example, can you compress gases but cannot compress a solid? By the end of this chapter, you should be able to answer this question and use the ideas involved to help you to understand many everyday observations, such as why car windows mist up on a cold morning or why dew forms on grass at night. 1.1 Solids, liquids and gases Chemistry is about what matter is like and how it behaves, and our explanations and predictions of its behaviour. What is matter? This word is used to cover all the substances and materials from which the physical universe is composed. There are many millions of different substances known, and all of them can be categorised as solids, liquids or gases (Figure 1.1). These are what we call the three states of matter. b Liquid a Solid c Gas ▲ Figure 1.1 Water in three different states 1 9781398310506.indb 1 24/02/21 10:03 PM  1 States of matter A solid, at a given temperature, has a definite The main points of the theory are: volume and shape which may be affected by changes » All matter is made up of tiny, moving particles, in temperature. Solids usually increase slightly in size invisible to your eye. Different substances have when heated, called expansion (Figure 1.2), different types of particles (atoms, molecules or and usually decrease in size if cooled, called ions) of varying sizes. contraction. » The particles move all the time. The higher the A liquid, at a given temperature, has a temperature, the faster they move on average. fixed volume and will take up the shape of any » Heavier particles move more slowly than lighter container into which it is poured. Like a solid, a ones at a given temperature. liquid’s volume is slightly affected by changes in temperature. The kinetic particle theory can be used as a A gas, at a given temperature, has neither a scientific model to explain how the arrangement definite shape nor a definite volume. It will take up of particles relates to the properties of the three the shape of any container into which it is placed states of matter. and will spread out evenly within it. Unlike solids and liquids, the volumes of gases are affected Explaining the states of matter greatly by changes in temperature. In a solid, the particles attract one another. There Liquids and gases, unlike solids, are compressible. are attractive forces between the particles which This means that their volume can be reduced by hold them close together. The particles have little the application of pressure. Gases are much more freedom of movement and can only vibrate about compressible than liquids. a fixed position. They are arranged in a regular manner, which explains why many solids form crystals. It is possible to model such crystals by using spheres to represent the particles. For example, Figure 1.3a shows spheres built up in a regular way to represent the structure of a chrome alum crystal. The shape is very similar to that of a part of an actual chrome alum crystal (Figure 1.3b). ▲ Figure 1.2 Without expansion gaps between the rails, the track would buckle in hot weather 1.2 The kinetic particle theory of matter The kinetic particle theory helps to explain the way that matter behaves. It is based on the idea that all matter is made up of tiny particles. This theory explains the physical properties of matter in terms of the movement of the particles from which it is made. a A model of a chrome alum crystal 2 9781398310506.indb 2 24/02/21 10:03 PM  1.2 The kinetic particle theory of matter ▲ Figure 1.5 Sodium chloride crystals In a liquid, the particles are still close together but they move around in a random way and often collide with one another. The forces of attraction between the particles in a liquid are weaker than those in a solid. Particles in the liquid form of a substance have more energy on average than the particles in the solid form of the same substance. b An actual chrome alum crystal In a gas, the particles are relatively far apart. ▲ Figure 1.3 They are free to move anywhere within the container in which they are held. They move randomly at very Studies using X-ray crystallography (Figure 1.4) have high velocities, much more rapidly than those in a confirmed how particles are arranged in crystal liquid. They collide with each other, but less often structures. When crystals of a pure substance than in a liquid, and they also collide with the walls form under a given set of conditions, the particles of the container. They exert virtually no forces of are always arranged (or packed) in the same way. attraction on each other because they are relatively However, the particles may be packed in different far apart. Such forces, however, are very significant. ways in crystals of different substances. For If they did not exist, we could not have solids or example, common salt (sodium chloride) has its liquids (see Changes of state, p. 4). particles arranged to give cubic crystals as shown in The arrangement of particles in solids, liquids Figure 1.5. and gases is shown in Figure 1.6. Solid Particles only vibrate about fixed positions. Regular structure. Liquid Particles have some freedom and can move around each other. Collide often. Gas Particles move freely and at random in all the space available. Collide less often than in liquid. ▲ Figure 1.4 A modern X-ray crystallography instrument ▲ Figure 1.6 The arrangement of particles in solids, liquids used for studying crystal structure and gases 3 9781398310506.indb 3 24/02/21 10:03 PM  1 States of matter of attraction between themselves and the other Test yourself particles in the liquid and they escape to form a gas. 1 When a metal (such as copper) is heated, it The liquid begins to evaporate as a gas is formed. expands. Explain what happens to the metal Eventually, a temperature is reached at which particles as the solid metal expands. the particles are trying to escape from the liquid so quickly that bubbles of gas actually start to form inside the liquid. This temperature is called the 1.3 Changes of state boiling point of the substance. At the boiling point, The kinetic particle theory model can be used to the pressure of the gas created above the liquid explain how a substance changes from one state to equals that of the air, which is atmospheric pressure. another. If a solid is heated, the particles vibrate Liquids with high boiling points have stronger faster as they gain energy. This makes them ‘push’ forces between their particles than liquids with low their neighbouring particles further away. This boiling points. causes an increase in the volume of the solid, When a gas is cooled, the average energy of the such that the solid expands, and we can say that particles decreases and the particles move closer expansion has taken place. together. The forces of attraction between the particles Eventually, the heat energy causes the forces of now become significant and cause the gas to condense attraction to weaken. The regular pattern of the into a liquid. When a liquid is cooled, it freezes to form structure breaks down, and the particles can now a solid. Energy is released in each of these changes. move around each other. The solid has melted. The Changes of state are examples of physical temperature at which this takes place is called the changes. Whenever a physical change of state melting point of the substance. The temperature occurs, the temperature remains constant during the of a melting pure solid will not rise until it has all change. During a physical change, no new substance melted. When the substance has become a liquid, is formed. there are still very significant forces of attraction between the particles, which is why the substance Heating and cooling curves is a liquid and not a gas. The graph shown in Figure 1.7 was drawn by Solids which have high melting points have plotting the temperature of water as it was stronger forces of attraction between their particles heated steadily from −15°C to 110°C. You can see than those which have low melting points. A list of from the curve that changes of state have taken some substances with their corresponding melting place. When the temperature was first measured, and boiling points is shown in Table 1.1. only ice was present. After a short time, the curve ▼ Table 1.1 Melting points and boiling points of substances flattens showing that even though heat energy is Substance Melting point/°C Boiling point/°C being put in, the temperature remains constant. Aluminium 661 2467 Ethanol −117 79 110 100 Magnesium oxide 827 3627 Liquid and All gas (liquid gas Mercury −30 357 Temperature/ºC water and Methane −182 −164 water vapour) Oxygen −218 −183 All Sodium chloride 801 1413 liquid Sulfur 113 445 0 (liquid All Solid and liquid water) Water 0 100 15 solid (ice and liquid (ice) water) If a liquid is heated, the average energy of the Time/minutes particles increases and the particles will move around ▲ Figure 1.7 Graph of temperature against time for the even faster. Some particles at the surface of the change from ice at −15°C to water to steam liquid have enough energy to overcome the forces 4 9781398310506.indb 4 24/02/21 10:03 PM  1.3 Changes of state Practical skills Changes of state For safe experiments/demonstrations which Clamp are related to this chapter, please refer to the Cambridge IGCSE Chemistry Practical Skills Thermometer Workbook, which is also part of this series. Safety Boiling tube l Eye protection must be worn. l Take care when handling and using hot water. Stearic acid The apparatus on the right was set up to obtain Beaker a cooling curve for stearic acid. The stearic acid Warm water was placed into a boiling tube which was then placed in a beaker of water that was heated to 80°C, which is above the melting point of 1 Why was it important to remove the boiling stearic acid. tube with the stearic acid from the water? 2 Why was the stearic acid stirred with the The boiling tube was then removed from the thermometer? beaker and the temperature of the stearic acid 3 Why were temperature readings taken every was recorded every minute for 12 minutes using minute for 12 minutes? the thermometer to stir the stearic acid while it was a liquid. The following data was obtained from the experiment: Time/mins 0 1 2 3 4 5 6 7 8 9 10 11 12 Temperature/°C 79 76 73 70 69 69 69 69 69 67 64 62 60 4 Draw and label axes for plotting this data. 6 a At what temperature did the stearic acid 5 Plot the points and draw a line of best fit. begin to change state? b How could you tell this from your graph? c Explain what is happening at this temperature. In ice, the particles of water are close together melting point. A sharp melting point therefore and are attracted to one another. For ice to melt, indicates that it is a pure sample. The addition or the particles must obtain sufficient energy to presence of impurities lowers the melting point. overcome the forces of attraction between the water particles, so that relative movement can You can find the melting point of a substance take place. The heat energy is being used to using the apparatus shown in Figure 1.8. The overcome these forces. addition or presence of impurities lowers the The temperature will begin to rise again melting point. A mixture of substances also has a only after all the ice has melted. Generally, the lower melting point than a pure substance, and the heating curve for a pure solid always stops rising melting point will be over a range of temperatures at its melting point and gives rise to a sharp and not sharp. 5 9781398310506.indb 5 24/02/21 10:03 PM  1 States of matter Thermometer What do you think has caused the difference between the balloons in Figure 1.9? The pressure inside a balloon is caused by the gas particles striking the inside surface of the balloon. At a higher temperature, there is an increased pressure Melting point tube inside the balloon (Figure 1.10). This is due to the Rubber band gas particles having more energy and therefore moving around faster, which results in the particles Oil striking the inside surface of the balloon more Solid frequently, which leads to an increase in pressure. Heat ▲ Figure 1.8 If a substance, such as the solid in the melting point tube, is heated slowly, this apparatus can be used to find the melting point of the substance In the same way, if you want to boil a liquid, such as water, you have to give it some extra energy. This can be seen on the graph in Figure 1.7, where the curve levels out at 100°C – the boiling point of water. Solids and liquids can be identified from their characteristic melting and boiling points. ▲ Figure 1.10 The gas particles striking the surface The reverse processes of condensing and freezing create the pressure occur when a substance is cooled. Energy is given out when the gas condenses to the liquid and the Since the balloon is made from an elastic material, liquid freezes to give the solid. the increased pressure causes the balloon to stretch and the volume increases. An increase in volume of a gas with increased temperature 1.4 The effects of is a property of all gases. French scientist J.A.C. temperature and pressure Charles made an observation like this in 1781 and concluded that when the temperature of a gas on the volume of a gas increased, the volume also increased at a fixed pressure. We can extend this idea to suggest that changing the pressure of a fixed volume of a gas must have an effect on the temperature of the gas. If you have ever used a bicycle pump to blow up a bicycle tyre then you may have felt the pump get hotter the more you used it. As you use the pump you increase pressure on the air in the pump. Such an increase in pressure causes the gas molecules to move closer together so the molecules to collide more frequently and more frictional forces come into play, which causes the temperature to rise. In addition, as the molecules are forced closer to one another, intermolecular bonds form, again increasing the temperature of the gas. As the temperature of the gas increases, ▲ Figure 1.9 Temperature changes the volume of the air in a this also causes the molecules to move faster, balloon. Higher temperatures increase the volume of the causing even more collisions. balloon and cold temperatures reduce its volume. 6 9781398310506.indb 6 24/02/21 10:03 PM  1.5 Diffusion Diffusion can be explained by the kinetic Test yourself particle theory. This theory states that all matter 2 Why do gases expand more than solids for the is made up of many small particles which are same increase in temperature? constantly moving. In a solid, as we have seen, 3 Ice on a car windscreen will disappear as you the particles simply vibrate about a fixed point. drive along, even without the heater on. Explain However, in a gas, the particles move randomly why this happens. 4 When salt is placed on ice, the ice melts. past one another, colliding with each other. Explain why this happens. 5 Draw and label a graph of water at 100°C being allowed to cool to −5°C. 1.5 Diffusion When you go through the door of a restaurant, you can often smell the food being cooked. For this to happen, gas particles must be leaving the pans the food is being cooked in and be spreading out through the air in the restaurant. This spreading out of a gas is called diffusion and it takes place in a haphazard and random way. All gases diffuse to fill the space available. ▲ Figure 1.12 Hydrochloric acid (left) and ammonia Figure 1.11 shows two gas jars on top of each other. (right) diffuse at different rates Liquid bromine has been placed in the bottom gas Gases diffuse at different rates. If one piece of jar (left photo) and then left for a day (right photo). cotton wool is soaked in concentrated ammonia The brown-red fumes are gaseous bromine that has solution and another is soaked in concentrated spread evenly throughout both the gas jars from the hydrochloric acid and these are put at opposite liquid present in the lower gas jar. ends of a dry glass tube, then after a few minutes a white cloud of ammonium chloride appears. Figure 1.12 shows the position at which the two gases meet and react. The white cloud forms in the position shown because the ammonia particles are lighter; they have a smaller relative molecular mass (Chapter 4, p. 54) than the hydrogen chloride particles (released from the hydrochloric acid) and so move faster, such that the gas diffuses more quickly. (See Chemistry Practical Skills Workbook for more detail of this experiment.) This experiment is a teacher demonstration only, which must be carried out in a fume cupboard. If considering carrying out this practical, teachers should refer to the Practical Skills Workbook for full guidance ▲ Figure 1.11 After 24 hours the bromine fumes have and safety notes. diffused throughout both gas jars 7 9781398310506.indb 7 24/02/21 10:03 PM  1 States of matter Diffusion also takes place in liquids (Figure 1.13) but it is a much slower process than in gases. This Revision checklist is because the particles of a liquid move much more After studying Chapter 1 you should be able to: slowly. ✔ State the three states of matter and describe the structure arrangement of the particles in each. ✔ Explain the properties of the three states of matter using ideas about the separation and movement of particles. ✔ Name the changes of state and describe what happens to the particles in a substance when they occur. ✔ Explain what is happening when a substance changes state. ✔ Describe what happens to a given amount ▲ Figure 1.13 Diffusion of green food colouring can take of gas when temperature and/or pressure days to reach the stage shown on the right decreases and increases. ✔ Use the kinetic particle theory to explain the When diffusion takes place between a liquid and effects of pressure and temperature on the a gas, it is known as intimate mixing. Kinetic volume of a gas. particle theory can be used to explain this process. ✔ Describe the process of diffusion and explain It states that collisions are taking place randomly why gases diffuse. between particles in a liquid or a gas and that there ✔ Describe and explain the rate of diffusion of a is sufficient space between the particles of one gas in terms of its relative molecular mass. substance for the particles of the other substance to move into. Test yourself 6 When a jar of coffee is opened, people can often smell it from anywhere in the room. Use the kinetic particle theory to explain how this happens. 7 Describe, with the aid of diagrams, the diffusion of a drop of green food colouring added to the bottom of a beaker. 8 Explain why diffusion is faster in gases than in liquids. 9 Explain why a gas with a low relative molecular mass can diffuse faster than a gas with a high relative molecular mass at the same temperature. 8 9781398310506.indb 8 24/02/21 10:03 PM  Exam-style questions Exam-style questions 1 a Sketch diagrams to show the arrangement of a Describe what you would observe after: particles in: i a few hours i solid oxygen ii several days. ii liquid oxygen iii oxygen gas. b Explain your answer to Question 5a using b Describe how the particles move in these your ideas of the kinetic particle theory. three states of matter. c State the physical process that takes place in c Explain, using the kinetic particle theory, this experiment. what happens to the particles in oxygen as it is cooled down. 6 The apparatus shown below was set up. Stopper White cloud Glass tube 2 Explain the meaning of each of the following terms. In your answer include an example to help with your explanation. a expansion b contraction c physical change Cotton wool soaked Cotton wool soaked d diffusion in concentrated in concentrated hydrochloric acid ammonia solution e random motion 3 a Explain why solids do not diffuse. When this apparatus is used, the following b Give two examples of diffusion of gases things are observed. Explain why each of these and liquids found in your house. is observed. 4 Explain the following, using the ideas you have a A white cloud is formed. learned about the kinetic particle theory: b It took a few minutes before the white a When you take a block of butter out of the cloud formed. fridge, it is quite hard. However, after 15 c The white cloud formed further from the minutes it is soft enough to spread. cotton wool soaked in ammonia than that b When you come home from school and open soaked in hydrochloric acid. the door, you can smell food being cooked. d Cooling the concentrated ammonia and c A football is blown up until it is hard on hydrochloric acid before carrying out the a hot summer’s day. In the evening the experiment increased the time taken for football feels softer. the white cloud to form. d When a person wearing perfume enters a room, it takes several minutes for the smell to reach the back of the room. 5 Some green food colouring was carefully added to the bottom of a beaker of water using a syringe. The beaker was then covered and left for several days. Beaker Water Green food colouring 9 9781398310506.indb 9 24/02/21 10:03 PM  2 Atoms, elements and compounds FOCUS POINTS ★ How are elements, molecules, ions, compounds and mixtures different from each other? ★ How do the properties of the particles in an atom lead to an atom’s structure? ★ What do oxidation and reduction mean? ★ What is an isotope? In Chapter 1, you saw that all matter is made up of particles. In this chapter you will look closely at these particles and see that they are made up of atoms. Atoms are the smallest part of elements. An element is made up of one type of atom and can be either a metal or a non-metal. Metals and non-metals have different properties. You will look at how atoms of different elements can combine to form substances called compounds, and how this combining occurs in a chemical reaction. By the end of the chapter you should be able to write a simple word or symbol equation to represent these reactions. You will see that although atoms are the smallest part of an element that shares the chemical properties of that element, they are made from even smaller particles. By learning about the properties and behaviour of these smaller particles (electrons, protons and neutrons), you will be able to see how they affect the chemical properties of elements and compounds. The universe is made up of a very large number of In 1803, John Dalton suggested that each element substances (Figure 2.1), and our own part of the was composed of its own kind of particles, which he universe is no exception. When we examine this vast called atoms. Atoms are much too small to be seen. array of substances more closely, it is found that they We now know that about 20 × 106 of them would are made up of some basic substances which were stretch over a length of only 1 cm. given the name elements in 1661 by Robert Boyle. 2.1 Elements As well as not being able to be broken down into a simpler substance, each element is made up of only one kind of atom. The word atom comes from the Greek word atomos meaning ‘unsplittable’. For example, aluminium is an element which is made up of only aluminium atoms. It is not possible to obtain a simpler substance chemically from the aluminium atoms. You can only combine it with other elements to make more complex substances, such as aluminium oxide, aluminium nitrate or aluminium sulfate. One hundred and eighteen elements have now been identified. Twenty of these do not occur in nature and have been made artificially by scientists. They include elements such as curium and flerovium. ▲ Figure 2.1 Structures in the universe, such as stars, Ninety-eight of the elements occur naturally and planets and meteorites, are made of millions of range from some very reactive gases, such as substances. These are made up mainly from just 91 fluorine and chlorine, to gold and platinum, which elements, all of which occur naturally on the Earth 10 9781398310506.indb 10 24/02/21 10:03 PM  2.1 Elements are unreactive elements. A physical property is any ▼ Table 2.1 Physical data for some metallic and characteristic of a substance that we can measure. non-metallic elements at room temperature and pressure The elements have different properties that we can measure, and we can then classify them according to Metal or Density/ Melting Boiling those properties. Element non-metal g cm−3