Cambridge O Level Chemistry Bryan Earl.pdf

 The Cambridge O Level Chemistry series consists of a Student’s Book and Boost eBook. Cambridge O Level Chemistry 9781398310599 Cambridge O Level Chemistry Boost eBook 9781398310988 310599 Cambridge O Level Chemistry CV.indd 6...

 The Cambridge O Level Chemistry series consists of a Student’s Book and Boost eBook. Cambridge O Level Chemistry 9781398310599 Cambridge O Level Chemistry Boost eBook 9781398310988 310599 Cambridge O Level Chemistry CV.indd 6 25/03/2021 14:43  Cambridge O Level Chemistry Bryan Earl Doug Wilford Book 1.indb 1 05/04/21 6:14 PM  The Publishers would like to thank the following for permission to reproduce copyright material. Acknowledgements 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. 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We have carried out a health and safety check of this text and have attempted to identify all recognised hazards and suggest appropriate cautions. 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: 9781398310599 © Bryan Earl and Doug Wilford 2021 First 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 Integra Software Services Pvt. Ltd., Pondicherry, India Printed in the UK A catalogue record for this title is available from the British Library. Book 1.indb 2 05/04/21 6:14 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 37 3.3 Metallic bonding 49 4 Stoichiometry – chemical calculations 52 4.1 Relative atomic mass 52 4.2 Calculating moles 53 4.3 Moles and compounds 55 4.4 Calculating formulae 58 4.5 Moles and chemical equations 60 5 Electrochemistry 66 5.1 Electricity and chemistry 66 5.2 Electrolysis of lead(II) bromide (teacher demonstration) 67 5.3 Electrolysis of aluminium oxide 69 5.4 Electrolysis of aqueous solutions 72 5.5 Electrolysis of copper(II) sulfate aqueous solution 75 5.6 Fuel cells 78 5.7 Electroplating 79 6 Chemical energetics 83 6.1 Substances from petroleum 83 6.2 Fossil fuels 86 6.3 What is a fuel? 86 6.4 Alternative sources to fossil fuels 87 6.5 Exothermic and endothermic reactions 87 iii Book 1.indb 3 05/04/21 6:14 PM  7 Chemical reactions 96 7.1 Reactions 96 7.2 Factors that affect the rate of a reaction 97 7.3 Enzymes 103 7.4 Reversible reactions and equilibrium 104 7.5 Ammonia – an important nitrogen-containing chemical 105 7.6 Industrial manufacture of sulfuric acid – the Contact process 108 8 Acids, bases and salts 112 8.1 Acids and alkalis 112 8.2 Formation of salts 116 8.3 Methods of preparing soluble salts 117 8.4 Preparing insoluble salts 120 8.5 Testing for different salts 120 8.6 Water of crystallisation 122 9 The Periodic Table 129 9.1 Development of the Periodic Table 129 9.2 Electronic configuration and the Periodic Table 132 9.3 Group I – the alkali metals 132 9.4 Group VII – the halogens 136 9.5 Group VIII – the noble gases 140 9.6 Transition elements 140 9.7 The position of hydrogen 142 10Metals 145 10.1 Properties of metals 145 10.2 Metal reactions 146 10.3 Reactivity of metals and their uses 148 10.4 Identifying metal ions 151 10.5 Extraction of metals 152 10.6 Metal corrosion 156 10.7 Alloys 159 11 Chemistry of the environment 164 11.1 Water 164 11.2 Artificial fertilisers 168 11.3 The air 171 11.4 Atmospheric pollution 172 12Organic chemistry 1 182 12.1 Alkanes 182 12.2 The chemical behaviour of alkanes 185 12.3 Alkenes 187 12.4 The chemical behaviour of alkenes 189 12.5 Polymers 191 iv Book 1.indb 4 05/04/21 6:14 PM  13Organic chemistry 2 199 13.1 Functional groups 199 13.2 Alcohols (R–OH) 199 13.3 Carboxylic acids 204 13.4 Esters205 13.5 Condensation polymers 207 13.6 Natural polyamides 209 14Experimental techniques and chemical analysis 212 14.1 Apparatus used for measurement in chemistry 212 14.2 Separating mixtures 215 14.3 Qualitative analysis 224 Theory past paper questions 231 Alternative to Practical past paper questions 240 Glossary246 Index253 Periodic Table of Elements 259 v Book 1.indb 5 05/04/21 6:14 PM  Acknowledgements The authors would like to thank Irene, Katharine, Martyn F. Chillmaid, r © Martyn F. Chillmaid; p.36 Michael and Barbara for their patience, support and (left column) l © Martyn F. Chillmaid, r © Martyn F. encouragement throughout the production of this Chillmaid, (right column) Courtesy of the University textbook. We would also like to thank the editorial of Illinois at Urbana-Champaign Archives; p.38 © and publishing teams at Hodder Education who have Andrew Lambert Photography/Science Photo Library; supported us on the journey over the past year. p.39 © Andrew Lambert Photography/Science Photo Library; p.40 l © Andrew Lambert Photography/ Source acknowledgements Science Photo Library, r © Andrew Lambert pp.13, 37, 39, 40, 41, 183, 188, 189, 192, 193 and 206. 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Thanks to Molymod.com for providing © Turtle Rock Scientific/Science Source/Science the models, b © Paul Cooper / Rex Features; p.208 l Photo Library r © Science Photo Library, (right © Andrew Lambert Photography/Science Photo column) r © Giphotostock/Science Photo Library; Library, r © Leonid Shcheglov – Fotolia; p.212 © p.227 l © Andrew Lambert Photography/Science burnel11 – Fotolia; p.213 tl © Martyn F Chillmaid, tr Photo Library, r © Martyn F. Chillmaid/Science Photo © Martyn F Chillmaid, br © Martyn F Chillmaid; Library. p.214 © Maurice Savage/Alamy Stock Photo; p.217 viii Book 1.indb 8 05/04/21 6:14 PM  How to use this book To make your study of Chemistry for Cambridge Key definitions O Level as rewarding and successful as possible, These provide explanations of the meanings of key words this textbook, endorsed by Cambridge Assessment as required by the syllabus. International Education, offers the following important features: Practical skills FOCUS POINTS Each topic starts with a bullet point summary of These boxes identify the key practical skills what you will encounter within the topic. you need to understand as part of completing the course. This is followed by a short outline of the topic so that you know what to expect over the next few pages. Worked examples These boxes give step-by-step guidance on how to approach different sorts of calculations, with follow-up questions so Test yourself you can practise these skills. These questions appear regularly throughout the chapter so you can check your understanding as you progress. Going further Revision checklist These boxes take your learning further than is required by the Cambridge syllabus so that you have At the end of each chapter, a revision checklist will the opportunity to stretch yourself. allow you to recap what you have learned in each topic and double-check that you understand the key Answers are provided online at concepts before moving on. www.hoddereducation.com/cambridgeextras Exam-style questions Each chapter is followed by exam-style questions to help familiarise learners with the style of questions they may see in their examinations. These will also prove useful in consolidating your learning. Past paper questions are also provided at the end of the book. ix Book 1.indb 9 05/04/21 6:14 PM  Scientific enquiry Throughout your O Level Chemistry course you will they will not affect the data obtained. Most need to carry out experiments and investigations importantly, it is essential that you carry out a aimed at developing some of the skills and abilities risk assessment before you do any 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 not to dismantle the equipment/apparatus until the topic you are currently studying in class, and you have completed your analysis of the data, your teacher may provide you with suggestions. For and you are sure you do not need to repeat any all 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 to apparatus involved. You should never simply carry 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 data and alter the way in which it is obtained part of doing science and involves working to get more accurate results. You should be able out what you are going to do to try to find to evaluate whether your data is good or bad. answers to the questions you have set yourself. If it is good, were there any anomalous results? Predictions based on work you have been Why did you get them? studying or are doing in class may help you 5 Evaluate methods and suggest possible develop the investigation in terms of the number improvements – at the end of your investigation and type of observations or data needed. you must be able to evaluate the equipment, You will also need to be able to identify the methods and techniques that you have used. independent and dependent variables. For Think about any sources of errors that could have example, if you are trying to find out how affected your results by the use of the wrong temperature affects the rate of a reaction, the equipment. Consider, if you were able to carry out temperature will be the independent variable, the investigation again, what you would change. but the dependent variable might be the The more data you obtain the easier it is to spot volume of gas collected. Other variables such anomalous results. as concentration need to be controlled so that x Book 1.indb 10 05/04/21 6:14 PM  A written report of any chemical investigation each axis of a graph with the name and unit of would normally be made of these fixed components: 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 Clearly explain the calculations involved were doing the investigation to find out. in the interpretation of your data and give » A list of all items of equipment/apparatus used the significant figures appropriate to the and a record of the smallest division of the scale equipment 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 out any practical work. Provide a list of all the different were they? You should comment on chemicals you will use, as well as the ones you the reliability and accuracy of the observations will produce, and do a risk assessment to check and the data obtained. Could you have improved on all the hazards of the chemicals. The results the method to give better or more accurate of your risk assessment might indicate that you results? Would a pH probe have been better need to work in a well-ventilated room or in a than using universal indicator to find the point fume cupboard. In some cases, you may need the of neutralisation in a titration? Were there any assistance of your teacher. If in doubt, always anomalous points on your graphs, or any unusual ask your teacher for advice. data or observations? Highlight these and try to » Clearly state the details of the methods used, give an explanation. starting with the wearing of eye protection. The methods should be shown as numbered steps and should be made as clear as possible. Suggestions for Ideas of the number of measurements that will be made and their frequency should be stated. investigations Observations should be clear and you should use Some suggested investigations are outlined in this changes in colour and physical state as part of book as follows: your observations. 1 Find which vinegars contain the most acid. » Presentation of results and calculations. If you (Chapter 8) made several measurements of a quantity, draw 2 Find the molar volume of hydrogen by reacting up a table in which to record your results. Use magnesium with hydrochloric acid. (Chapter 4) the column headings, or start of rows, to name 3 Determination of the enthalpy of combustion exactly what the measurement is and state the of ethanol. (Chapter 6) units used; for example in a rates of reaction 4 The effect of changing the surface area of a experiment, ‘Mass of calcium carbonate/g’. reactant on the rate of reaction. (Chapter 7) Give numeric values to the number of 5 Use the anion and cation methods of significant figures appropriate to the equipment identification to find the ions present in tap being used, for example a mass could be recorded water. (Chapter 14) to 0.5 g or 0.05 g depending on the resolution 6 Show that ammonia is a weak base by measuring of the top-pan balance you use. Take averages its pH and conductivity, and comparing your and remember that anomalous or non-concordant results with those from a solution of sodium results should not be used in their calculation. hydroxide with the same concentration. If you decide to make a graph of your results (Chapter 8) you will need at least six data points taken over 7 Determine the melting point of stearic acid. as large a range as possible; be sure to label (Chapter 1) xi Book 1.indb 11 05/04/21 6:14 PM  8 How can sodium chloride be obtained from rock A further example involves the well-known salt? (Chapter 14) Russian chemist Dimitri Mendeleev. He realised that 9 What are the effects of acid rain on a variety of the physical and chemical properties of the known building materials? (Chapter 11) elements were related to their atomic mass in a 10 Which is the best temperature, between 34 and ‘periodic’ way, and arranged them so that groups of 40°C, for the fermentation of sugar to take place? elements with similar properties fell into vertical (Chapter 12) columns in his table. However, in devising his 11 What are the chemical properties of the weak table, Mendeleev did not conform completely to the organic acid, ethanoic acid? (Chapter 13) order of atomic mass, with some elements swapped 12 Do foodstuffs contain carbon? (Chapter 12) around. It took time for his ideas to gain acceptance because the increase in atomic mass was not regular Ideas and evidence in science when moving from one element to another. We now know, with the development of atomic theory In some of the investigations you perform in the and a better understanding of chemical processes, school laboratory, you may find that you do not that the elements in the Periodic Table are not all interpret your data in the same way as your friends in atomic mass order. It took until 1934, with an do; perhaps you will argue with them as to the best understanding of atomic number and post-Russian way to explain your results and try to convince revolution, for the Periodic Table to be finally them that your interpretation is right. Scientific accepted in the form you see today. controversy frequently arises through people There are many different types of scientists interpreting evidence differently. with specialties in their own areas of work such For example, our ideas about atoms have changed as chemistry and physics, but they all work in the over time. Scientists have developed new models same way. They come up with new theories and of atoms over the centuries as they collected new ideas, they carry out work to find the evidence to experimental evidence. If we go back to the Greeks establish whether their ideas are correct and, if not, in the 5th century bc, they thought matter was why. Scientists rely on other scientists checking composed of indivisible building blocks which they their work, often improving the ideas of everyone called atomos. However, the idea was essentially and moving science forward. The use of new ideas forgotten for more than 2000 years. Then John is often beneficial to everyone in the world, for Dalton published his ideas about atoms in 1800. He example the discovery of vaccines for Covid-19, or suggested that all matter was made of tiny particles the push to improve battery manufacture for use called atoms, which he imagined as tiny spheres in electric cars which would in turn help solve one that could not be divided. It then took another of the biggest problems we have to face: global 100 years before Joseph Thomson, Ernest Rutherford warming. Scientists are working hard to stop global and James Chadwick carried out experiments and warming but their ideas are not always embraced discovered that there was a structure within the because of economic and political factors. atom. This saw the continuous development of what we know today as atomic theory. xii Book 1.indb 12 05/04/21 6:14 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 Book 1.indb 1 05/04/21 6:14 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 composed 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 fixed temperature, the faster they move on average. volume and will take the shape of any container » Heavier particles move more slowly than lighter into which it is poured. Like a solid, a liquid’s ones at a given temperature. 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 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 evenly within it. Unlike solids and liquids, the volumes of gases are affected greatly by Explaining the states of matter 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 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 bend when it expanded 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 composed 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 Book 1.indb 2 05/04/21 6:14 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 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 Book 1.indb 3 05/04/21 6:14 PM  1 States of matter liquid have enough energy to overcome the forces Test yourself of attraction between themselves and the other 1 When a metal (such as copper) is heated, it particles in the liquid and they escape to form a gas. expands. Explain what happens to the metal The liquid begins to evaporate as a gas is formed. particles as the solid metal expands. Eventually, a temperature is reached at which the particles are trying to escape from the liquid so quickly that bubbles of gas actually start to form 1.3 Changes of state inside the liquid. This temperature is called the 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 occurs, melting point of the substance. The temperature the temperature remains constant during the change. of a melting pure solid will not rise until it has all During a physical change, no new substance is melted. When the substance has become a liquid 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 heated stronger forces of attraction between their particles steadily from −15°C to 110°C. You can see from than those which have low melting points. A list of the curve that changes of state have taken place. some substances with their corresponding melting When the temperature was first measured, only ice and boiling points is shown in Table 1.1. was present. After a short time, the curve flattens ▼ Table 1.1 Melting points and boiling points of substances showing that even though heat energy is being put in, the temperature remains constant. Substance Melting point/°C Boiling point/°C Aluminium 661 2467 110 Ethanol −117 79 100 Liquid and All Magnesium oxide 827 3627 gas (liquid gas Mercury −30 357 Temperature/ºC water and water Methane −182 −164 vapour) Oxygen −218 −183 All Sodium chloride 801 1413 liquid 0 (liquid Sulfur 113 445 All Solid and liquid water) 15 solid (ice and liquid Water 0 100 (ice) water) If a liquid is heated, the average energy of the Time/minutes particles increases and the particles will move ▲ 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 4 Book 1.indb 4 05/04/21 6:14 PM  1.3 Changes of state Practical skills Changes of state Safety l Eye protection must be worn. 1 Why was it important to remove the boiling l Take care when handling and using hot water. tube with the stearic acid from the water? 2 Why was the stearic acid stirred with the The apparatus below was set up to obtain a thermometer? cooling curve for stearic acid. The stearic acid 3 Why were temperature readings taken every was placed into a boiling tube which was then minute for 12 minutes? placed in a beaker of water that was heated 4 Draw and label axes for plotting this data. to 80°C, which is above the melting point of 5 Plot the points and draw a line of best fit. stearic acid. 6 a At what temperature did the stearic acid The boiling tube was then removed from the begin to change state? beaker and the temperature of the stearic acid b How could you tell this from your graph? was recorded every minute for 12 minutes (see c Explain what is happening at this table below) using the thermometer to stir the temperature. stearic acid while it was a liquid. Clamp Thermometer Boiling tube Stearic acid Beaker Warm water 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 In ice, the particles of water are close together and A sharp melting point therefore indicates that it is a are attracted to one another. For ice to melt, the pure sample. The addition or presence of impurities particles must obtain sufficient energy to overcome lowers the melting point. the forces of attraction between the water particles, You can find the melting point of a substance so that relative movement can take place. The heat using the apparatus shown in Figure 1.8. The energy is being used to overcome these forces. addition or presence of impurities lowers the The temperature will begin to rise again only melting point. A mixture of substances also has a after all the ice has melted. Generally, the heating lower melting point than a pure substance, and the curve for a pure solid always stops rising at its melting point will be over a range of temperatures melting point and produce a sharp melting point. and not sharp. 5 Book 1.indb 5 05/04/21 6:14 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 (Figure 1.10). At a higher temperature there is an increased pressure inside the Melting point balloon. This is due to the gas particles having more Rubber band tube energy and therefore moving around faster, which results in the particles striking the inside surface Oil of the balloon more frequently, which leads to an Solid 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. The reverse processes of condensing and freezing occur when a substance is cooled. Energy is given out when the gas condenses to the liquid and the ▲ Figure 1.10 The gas particles striking the surface create liquid freezes to give the solid. the pressure Since the balloon is made from an elastic material, the 1.4 The effects of increased pressure causes the balloon to stretch and the volume increases. An increase in volume of a gas temperature and pressure with increased temperature is a property of all gases. on the volume of a gas French scientist J.A.C. Charles made an observation like this in 1781 and concluded that when the temperature 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 and the molecules to collide more frequently. As a result, more frictional forces come into play, and this causes the temperature to rise. In addition, as the molecules are forced closer to one another, intermolecular bonds form, again increasing ▲ Figure 1.9 Temperature changes the volume of the air in a the temperature of the gas. As the temperature of the balloon. Higher temperatures increase the volume of the gas increases, this also causes the molecules to move balloon and cold temperatures reduce its volume. faster, causing even more collisions. 6 Book 1.indb 6 05/04/21 6:14 PM  1.5 Diffusion many small particles which are constantly moving. Test yourself In a solid, as we have seen, the particles simply 2 Why do gases expand more than solids for the vibrate about a fixed point. However, in a gas, the same increase in temperature? particles move randomly past one another, colliding 3 Ice on a car windscreen will disappear as you with each other. drive, even without the heater on. Explain why this happens. 4 When salt is placed on ice, the ice melts. 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 through the air in the restaurant. This spreading of a gas is called diffusion and it occurs in a haphazard and random way. ▲ Figure 1.12 Hydrochloric acid (left) and ammonia (right) All gases diffuse to fill the space available. diffuse at different rates Figure 1.11 shows two gas jars on top of each other. 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. 52) than the hydrogen chloride particles (released from the hydrochloric acid) and so move faster, such that the gas diffuses more quickly. 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 and safety notes. Diffusion also takes place in liquids (Figure 1.13) ▲ Figure 1.11 After 24 hours the bromine fumes have but it is a much slower process than in gases. This diffused throughout both gas jars is because the particles of a liquid move much more Diffusion can be explained by the kinetic particle slowly. theory. This theory states that all matter is made of 7 Book 1.indb 7 05/04/21 6:14 PM  1 States of matter Revision checklist After studying Chapter 1 you should be able to: ✔ 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 (a) (b) happens to the particles in a substance when they occur. ▲ Figure 1.13 Diffusion of green food colouring can take days to reach the stage shown in (b) ✔ Explain what is happening when a substance changes state. Diffusion can also take place between a liquid and a ✔ Describe what happens to a given amount of gas gas. Kinetic particle theory can be used to explain when temperature and/or pressure decreases this process. It states that collisions are taking and increases. place randomly between particles in a liquid or a ✔ Describe the process of diffusion and explain why gas and that there is sufficient space between the gases diffuse. particles of one substance for the particles of the ✔ Explain why the rate of diffusion depends on the other substance to move into. molecular mass of the particles. 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 coloring 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 Book 1.indb 8 05/04/21 6:15 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 b Explain your answer to Question 5a using iii oxygen gas. your ideas of the kinetic particle theory. b Describe how the particles move in these c State the physical process that takes place in three states of matter. this experiment. c Explain, using the kinetic particle theory, 6 The apparatus shown below was set up. what happens to the particles in oxygen Stopper White cloud Glass tube as it is cooled down. 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 Cotton wool soaked Cotton wool soaked c physical change in concentrated in concentrated d diffusion hydrochloric acid ammonia solution e random motion When this apparatus is used, the following 3 a Explain why solids do not diffuse. things are observed. Explain why each of these b Give two examples of diffusion of gases is observed. and liquids found in your house. a A white cloud is formed. 4 Explain the following, using the ideas you have b It took a few minutes before the white cloud learned about the kinetic particle theory: formed. a When you take a block of butter out of the c The white cloud formed further from the fridge, it is quite hard. However, after 15 cotton wool soaked in ammonia than that minutes it is soft enough to spread. soaked in hydrochloric acid. b When you come home from school and open d Cooling the concentrated ammonia and the door, you can smell food being cooked. hydrochloric acid before carrying out the c A football is blown up until it is hard on experiment increased the time taken for a hot summer’s day. In the evening the the white cloud to form. football feels softer. 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 untouched for several days. Beaker Water green food colouring 9 Book 1.indb 9 05/04/21 6:15 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 consists 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, planets and meteorites, are made of millions of Ninety-eight of the elements occur naturally and substances. These are made up mainly from just 91 range from some very reactive gases, such as elements, all of which occur naturally on the Earth fluorine and chlorine, to gold and platinum, which 10 Book 1.indb 10 05/04/21 6:15 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 point/°C point/°C All elements can be classified according to their Aluminium Metal 2.70 660 2580 various properties. A simple way to do this is to Copper Metal 8.92 1083 2567 classify them as metals or non-metals (Figures 2.2 Gold Metal 19.29 1065 2807 and 2.3). Table 2.1 shows the physical property Iron Metal 7.87 1535 2750 data for some common metallic and non-metallic elements. You will notice from Table 2.1 that many Lead Metal 11.34 328 1740 metals have high densities, high melting points and Magnesium Metal 1.74 649 1107 high boiling points, and that most non-metals have Nickel Metal 8.90 1453 2732 low densities, low melting points and low boiling Silver Metal 10.50 962 2212 points. Table 2.2 summarises the different properties Zinc Metal 7.14 420 907 of metals and non-metals. Carbon Non-metal 2.25 Sublimes at 3642 Hydrogen Non-metal 0.07 a −259 −253 Nitrogen Non-metal 0.88 b −210 −196 Oxygen Non-metal 1.15 c −218 −183 Sulfur Non-metal 2.07 113 445 Source: Earl B., Wilford L.D.R. Chemistry data book. Nelson Blackie, 1991 a: at −254°C; b: at −197°C; c: at −184?