AQA GCSE (9–1)
Chemistry Student Book
Ann Daniels Series editor: Ed Walsh
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William Collins’ dream of knowledge for all began with the publication of his first book in 1819. A self-educated mill worker, he not only enriched millions of lives, but also founded a flourishing publishing house. Today, staying true to this spirit, Collins books are packed with inspiration, innovation and practical expertise. They place you at the centre of a world of possibility and give you exactly what you need to explore it. Collins. Freedom to teach
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A catalogue record for this book is available from the British Library Commissioned by Lucy Rowland and Lizzie Catford Edited by Hamish Baxter Project managed by Elektra Media Ltd Development edited by Tim Jackson and Lynette Woodward Copy edited by Dr Sarah Ryan and Lynette Woodward Proofread by Ali Craig and Laurice Seuss Typeset by Jouve India and Ken Vail Graphic Design Cover design by We are Laura Printed by CPI Group (UK) Ltd, Croydon, CR0 4YY Cover images © Shutterstock/watchara, Shutterstock/Everett Historical
Approval message from AQA This textbook has been approved by AQA for use with our qualification. This means that we have checked that it broadly covers the specification and we are satisfied with the overall quality. Full details of our approval process can be found on our website. We approve textbooks because we know how important it is for teachers and students to have the right resources to support their teaching and learning. However, the publisher is ultimately responsible for the editorial control and quality of this book. Please note that when teaching the GCSE Chemistry course, you must refer to AQA’s specification as your definitive source of information. While this book has been written to match the specification, it cannot provide complete coverage of every aspect of the course. A wide range of other useful resources can be found on the relevant subject pages of our website: aqa.org.uk
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ACKNOWLEDGEMENTS The publishers gratefully acknowledge the permissions granted to reproduce copyright material in this book. Every effort has been made to contact the holders of copyright material, but if any have been inadvertently overlooked, the Publisher will be pleased to make the necessary arrangements at the first opportunity. Chapter 1 p12 Smith1972/Shutterstock, grey color/Shutterstock, thieury/Shutterstock, pan_kung/Shutterstock; p13 Olga Popova/Shutterstock, Albert Russ/Shutterstock, HUANSHENG XU/Shutterstock; p14 Fablok/Shutterstock, motorolka/Shutterstock, ANDREW LAMBERT PHOTOGRAPHY/ SCIENCE PHOTO LIBRARY; p15; Smith1972/Shutterstock p16 Evgeny Karandaev/Shutterstock; p18 brumhildich/Shutterstock, Yenyu Shih/ Shutterstock; p20 Ufuk ZIVANA/Shutterstock; p21 PROF. PETER FOWLER/SCIENCE PHOTO LIBRARY; p22 GRAHAM J. HILLS/SCIENCE PHOTO LIBRARY; p24 SSSCCC/Shutterstock; p32 Boris15/Shutterstock; p33 ppl/Shutterstock; p34 demarcomedia/Shutterstock, Jeffrey B. Banke/ Shutterstock, Triff/Shutterstock, Gail Johnson/Shutterstock; p35 Anneka/Shutterstock, Mona Makela/Shutterstock, Asmus Koefoed/ Shutterstock, Popartic/Shutterstock; p40 DenisNata/Shutterstock; p41 tonyz20/Shutterstock; p42 ANDREW LAMBERT PHOTOGRAPHY/ SCIENCE PHOTO LIBRARY, tarog/Shutterstock, ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY; p44 SCIENCE PHOTO LIBRARY; p45 SCIENCE PHOTO LIBRARY; p49 HUANSHENG XU/Shutterstock, Andraž Cerar/Shutterstock; Chapter 2 p56 Chaiwuth Wichitdho/Shutterstock, Andraž Cerar/Shutterstock, bouybin/Shutterstock, Arsenis Spyros/Shutterstock; p57 yongyut rukkachatsuwa/Shutterstock, fivespots/Shutterstock, Shaiith/Shutterstock; p58 Shi Yali/Shutterstock, Lori Werhane/Shutterstock, izzzy71/ Shutterstock; p61 YuriyK/Shutterstock; p68 ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY; p75 Jens Ottoson/Shutterstock; p76 iceink/Shutterstock; p78 Tatiana Popova/Shutterstock, science photo/Shutterstock; p79 Timur Djafarov/Shutterstock, Flegere/ Shutterstock; p80 Yeko Photo Studio/Shutterstock; p81 Georgi Roshkov/Shutterstock; p82 Vladimir A Veljanovski/Shutterstock; p83 Aumm graphixphoto/Shutterstock; p86 Konstantin L/Shutterstock; p88 Syda Productions/Shutterstock Chapter 3 p96 llsshaya/Shutterstock, eldar nurkovic/Shutterstock, EM Karuna/Shutterstock, yurok/Shutterstock; p97 thodonal88/Shutterstock, The palms/Shutterstock; p102 SCIENCE PHOTO LIBRARY; p103 GIPhotoStock/SCIENCE PHOTO LIBRARY; p104 Gjermund/Shutterstock; p108 MingHsiang Chuang/Shutterstock; p110 li jianbing/Shutterstock; p114 Michal Kowalski; p115 Lindsey Moore/Shutterstock; p116 Ming-Hsiang Chuang/Shutterstock, motorolka/Shutterstock, Martin M303/Shutterstock; p117 Dong liu/Shutterstock; Chapter 4 p130 jordache/Shutterstock; p130 Sabine Kappel/Shutterstock; p165 GIPhotoStock/SCIENCE PHOTO LIBRARY; p169 NagyDodo/Shutterstock; p130 Dionisvera/Shutterstock, Ivaschenko Roman/Shutterstock, Slavoljub Pantelic/Shutterstock; p179 SCIENCE PHOTO LIBRARY; p190 gualtiero boffi/Shutterstock, Anna Shkolnaya/Shutterstock, iladm/Shutterstock, Chad Zuber/Shutterstock, Sisacorn/Shutterstock; p131 Albert Russ/Shutterstock, mikeledray/Shutterstock, CHARLES D. WINTERS/SCIENCE PHOTO LIBRARY; p132 Kaband/Shutterstock; P133 JERRY MASON/SCIENCE PHOTO LIBRARY; P134 SCIENCE PHOTO LIBRARY; P134 Filip Fuxa/Shutterstock; P136 Jiri Vaclavek/Shutterstock; P142 NagyDodo/Shutterstock; P148 Igor Stevanovic/Shutterstock; P158 CHOKCHAI POOMICHAIYA / Shutterstock; p192 Andrey_Popov/ Shutterstock; p196 Albert Russ/Shutterstock, Eugene Sergeev/Shutterstock; p200 Darren Brode/Shutterstock, petrmalinak/Shutterstock; p203 MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY; Chapter 5 p172 gualtiero boffi/Shutterstock , Dino Osmic/Shutterstock, Dziewul/Shutterstock, Anna Shkolnaya/Shutterstock, Darren Brode/ Shutterstock; p173 Albert Russ/Shutterstock; p174 Andrey_Popov/Shutterstock; p180 Albert Russ/Shutterstock, Eugene Sergeev/ Shutterstock; p184 Darren Brode/Shutterstock, petrmalinak/Shutterstock; Chapter 6 p192 Petrova Maria/Shutterstock, jmarkow/shutterstock, ggw1962/Shutterstock; p195 MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY; p198 iladm/Shutterstock, RUI FERREIRA/Shutterstock; p210 ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY, MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY; p214 Dennis Sabo/Shutterstock; Chapter 7 p226 PHOTO FUN/Shutterstock, stockphoto mania/Shutterstock, Tarzhanova/Shutterstock, www.BillionPhotos.com/Shutterstock; p227 Charles Knowles/Shutterstock, A. Aleksandravicius/Shutterstock, Toniflap/Shutterstock, nito/Shutterstock, nechaevkon/Shutterstock; p228 iurii/Shutterstock; p232 jmarkow/Shutterstock; p233 ggw1962/Shutterstock; p236 pixinoo/Shutterstock; p237 Olivier Le Queinec/ Shutterstock, ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY; p242 Anneka/Shutterstock; p243 Balakir Alla/Shutterstock; p244 Jiri Slama/Shutterstock; p246 Myimagine/Shutterstock, underverse/Shutterstock; p252 Elena Schweitzer/Shutterstock; p253 molekuul. be/Shutterstock; Chapter 8 p262 Swapan Photography/Shutterstock, ggw1962/shutterstock, YuriyK/Shutterstock, MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY anyaivanova/Shutterstock; p263 ggw1962/Shutterstock, Italianvideophotoagency/Shutterstock, piximage/Shutterstock; ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY p264 Lakeview Images/Shutterstock; p265 ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY; p266 STILLFX/Shutterstock; p274 Magdalena Kowalik/Shutterstock; p275 pryzmat/Shutterstock; p278 ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY; p279 MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY; p282 tanewpix/Shutterstock; p283 extender_01/Shutterstock; p284 SCIENCE PHOTO LIBRARY; Chapter 9 p292 Ammit Jack/Shutterstock, Gualberto Becerra/Shutterstock, Jan Martin Will/Shutterstock, Hung Chung Chih/Shutterstock, Alexey Stiop/ Shutterstock; p293 Khoroshunova Olga/Shutterstock, Unicus/Shutterstock, Filip Fuxa/Shutterstock; Looker_Studio/Shutterstock; p296 J. Helgason/Shutterstock, James Steidl/Shutterstock; p297 Khoroshunova Olga/Shutterstock; p298 Unicus/Shutterstock, attem/Shutterstock; p299 Ekaterina Pokrovsky/Shutterstock; p300 Lee Prince/Shutterstock, M Rutherford/Shutterstock, schankz/Shutterstock; p305 Dudarev Mikhail/Shutterstock, Huguette Roe/Shutterstock; p306 Sohel Parvez Haque/Shutterstock, Silken Photography/Shutterstock, Saikat Paul/ Shutterstock; p307 Matty Symons/Shutterstock; p308 Filip Fuxa/Shutterstock, martin33/Shutterstock, Tomasz Darul/Shutterstock; p312 donikz/Shutterstock; p313 Warren Price Photography/Shutterstock; p314 Alexander Raths/Shutterstock, MikeDotta/Shutterstock; p315 Petr Vopenka/Shutterstock, J. Helgason/Shutterstock, Laurence Gough/Shutterstock; Chapter 10 p322 sculpies/Shutterstock, Artisticco/Shutterstock, Matee Nuserm/Shutterstock, yurok/Shutterstock; p323 science photo/Shutterstock, JuliusKielaitis/Shutterstock, Alessandro Colle/Shutterstock, Fotokostic/Shutterstock, Dmitry Kalinovsky/Shutterstock; p324 freedom100m/ Shutterstock; p325 Olga Danylenko/Shutterstock, spwidoff/Shutterstock, p326 Designua/Shutterstock, ventdusud/Shutterstock, muratart/ Shutterstock; p327 goodcat/Shutterstock; p330 Reddogs/Shutterstock; p331 Vaclav Volrab/shutterstock; p332 Mark Schwettmann/ Shutterstock, Zoonar RF/ThinkStock; p333 MAXIMILIAN STOCK LTD/SCIENCE PHOTO LIBRARY, Jose Arcos Aguilar/Shutterstock; p335 wavebreakmedia/Shutterstock, xshot/Shutterstock; p 336 Pavel L Photo and Video/Shutterstock, freedomnaruk/Shutterstock; p337 Therina Groenewald/Shutterstock, Huguette Roe/Shutterstock; p338 sima/Shutterstock, the palms/Shutterstock; p339 dani3315/Shutterstock; p340 marekusz/Shutterstock, Africa Studio/Shutterstock; p341 Stoyan Yotov/Shutterstock, stockcreations/Shutterstock; p342 CREATISTA/ Shutterstock, pilipphoto/Shutterstock, Anatol Tyshkevich/Shutterstock; p343 Maxisport/Shutterstock, padu_foto/Shutterstock; p344 Stockr/ Shutterstock; p345 hacohob/Shutterstock; p346 Josef Hanus/Shutterstock;
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You can use this book if you are studying Combined Science: Trilogy
Contents
you will need to master all of the ideas and concepts on these pages you will need to master some of the ideas and concepts on these pages.
How to use this book
6
Chapter 1 Atomic structure and the periodic table 12
1.1
Elements and compounds Atoms, formulae and equations 1.3 Mixtures 1.4 Changing ideas about atoms 1.5 Modelling the atom 1.6 Relating charges and masses 1.7 Sub-atomic particles 1.8 Electronic structure 1.9 The periodic table 1.10 Developing the periodic table 1.11 Comparing metals and non-metals 1.12 Metals and non-metals 1.13 Key concept: The outer electrons 1.14 Exploring Group 0 1.15 Exploring Group 1 1.16 Exploring Group 7 1.17 Reaction trends and predicting reactions 1.18 Transition metals 1.19 Maths skills: Standard form and making estimates 1.2
14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Chapter 2 Structure, bonding and the properties of matter 56
2.1
Chemical bonds Ionic bonding 2.3 Ionic compounds 2.4 Covalent bonding 2.5 Metallic bonding 2.6 Three states of matter 2.7 Properties of ionic compounds 2.8 Properties of small molecules 2.9 Polymer structures 2.10 Giant covalent structures 2.11 Properties of metals and alloys 2.12 Diamond 2.13 Graphite 2.14 Graphene and fullerenes 2.15 Nanoparticles, their properties and uses 2.16 Key concept: Sizes of particles and orders of magnitude 2.17 Maths skills: Visualise and represent 2D and 3D shapes 2.2
58 60 62 64 66 68 70 72 74 76 78 80 82 84 86
90
Key concept: Conservation of mass and balanced equations 3.2 Relative formula mass 3.1
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98 100
102 104 106 108 110 112 114 116 118 120 122 124
Chapter 4 Chemical changes 130
88
Chapter 3 Chemical quantities and calculations 96
3.3 Mass changes when gases are in reactions 3.4 Chemical measurements and uncertainty 3.5 Moles 3.6 Amounts of substances in equations 3.7 Using moles to balance equations 3.8 Concentration of solutions 3.9 Key concept: Percentage yield 3.10 Atom economy 3.11 Using concentrations of solutions 3.12 Amounts of substance in volumes of gases 3.13 Key concept: Amounts in Chemistry 3.14 Maths skills: Change the subject of an equation Metal oxides Reactivity series 4.3 Extraction of metals 4.4 Oxidation and reduction in terms of electrons 4.5 Reaction of metals with acids 4.6 Neutralisation of acids and salt production 4.7 Soluble salts 4.8 Required practical: Preparing a pure, dry sample of a soluble salt from an insoluble oxide or carbonate 4.9 pH and neutralisation 4.10 Required practical: Finding the reacting volumes of solutions of acid and alkali by titration 4.11 Strong and weak acids 4.12 The process of electrolysis 4.13 Electrolysis of molten ionic compounds 4.14 Using electrolysis to extract metals 4.15 Electrolysis of aqueous solutions 4.16 Required practical: Investigating what happens when aqueous solutions are electrolysed using inert electrodes 4.17 Key concept: Electron transfer, oxidation and reduction 4.18 Maths skills: Make order of magnitude calculations 4.1
4.2
132 134 136 138 140 142 144
146 148
150 152 154 156 158 160
162 164 166
Chapter 5 Energy changes 172
Key concept: Endothermic and exothermic reactions 174 5.2 Required practical: Investigate the variables that affect temperature changes in reacting solutions such as, acid plus metals, acid plus carbonates, neutralisations, displacement of metals 176 5.1
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5.3 5.4 5.5 5.6 5.7
Reaction profiles Energy change of reactions Cells and batteries Fuel cells Maths skills: Recognise and use expressions in decimal form
178 180 182 184 186
Chapter 6 The rate and extent of chemical change 192
6.1 6.2 6.3 6.4 6.5
6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14
Measuring rates 194 Key concept: Limiting reactants and molar masses 196 Calculating rates 198 Factors affecting rates 200 Required practical: Investigate how changes in concentration affect the rates of reactions by a method involving the production of gas and a method involving a colour change 202 Factors increasing the rate 204 Collision theory 206 Catalysts 208 Reversible reactions and energy changes 210 Equilibrium 212 Changing concentration and equilibrium 214 Changing temperature and equilibrium 216 Changing pressure and equilibrium 218 Maths skills: Use the slope of a tangent as a measure of rate of change 220
Chapter 7 Hydrocarbons
226
228
7.1
Crude oil, hydrocarbons and alkanes Fractional distillation and petrochemicals 7.3 Properties of hydrocarbons 7.4 Combustion 7.5 Cracking and alkenes 7.6 Structure and formulae of alkenes 7.7 Reactions of alkenes 7.8 Alcohols 7.9 Carboxylic acids 7.10 Addition polymerisation 7.11 Condensation polymerisation 7.12 Amino acids 7.13 DNA and other naturally occurring polymers 7.14 Key concept: Intermolecular forces 7.15 Maths skills: Visualise and represent 3D models
252 254 256
Chapter 8 Chemical analysis
262
264 266 268
Key concept: Pure substances 8.2 Formulations 8.3 Chromatography 8.1
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270 272 274 276 278
280 282 284 286
Chapter 9 The atmosphere
292
294 296 298 300 302 304 306 308
7.2
230 232 234 236 238 240 242 244 246 248 250
Required practical: Investigate how paper chromatography can be used in forensic science to identify an ink mixture used in a forgery 8.5 Test for gases 8.6 Flame test 8.7 Metal hydroxides 8.8 Test for anions 8.9 Required practical: Use chemical tests to identify the ions in unknown single ionic compounds 8.10 Instrumental methods 8.11 Flame emission spectroscopy 8.12 Maths skills: Use an appropriate number of significant figures 8.4
9.1
Proportions of gases in the atmosphere The Earth’s early atmosphere 9.3 How oxygen increased 9.4 How carbon dioxide decreased 9.5 Key concept: Greenhouse gases 9.6 Human activities 9.7 Global climate change 9.8 Carbon footprint and its reduction 9.9 Limitations on carbon footprint reduction 9.10 Atmospheric pollutants from fuels 9.11 Properties and effects of atmospheric pollutants 9.12 Maths skills: Use ratios, fractions and percentages 9.2
310 312 314 316
Chapter 10 Sustainable development 322
Key concept: Using the Earth’s resources and sustainable development 324 10.2 Potable water 326 10.3 Required practical: Analysis and purification of water samples from different sources, including pH, dissolved solids and distillation 328 10.4 Waste water treatment 330 10.5 Alternative methods of metal extraction 332 10.6 Life cycle assessment and recycling 334 10.7 Ways of reducing the use of resources 336 10.8 Corrosion and its prevention 338 10.9 Alloys as useful materials 340 10.10 Ceramics, polymers and composites 342 10.11 Haber process 344 10.12 Production and use of NPK fertilisers 346 Maths skills: Translate information 10.13 between graphical and numerical form 348 10.1
Glossary 355 Index 361
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Chemistry
How to use this book Remember! to cover all the content of the AQA Chemistry Specification you should study the text and attempt the End of Chapter Questions.
Learning objectives which are Higher tier only appear in a purple background box. Chemistry
Extraction of metals
These tell you what you will be learning about in the lesson and are linked to the AQA specification.
KEY WORDS
Learning objectives: s¬ identify substances reduced by loss of oxygen s¬ explain how extraction methods depend on metal reactivity s¬ interpret or evaluate information on specific metal extraction processes.
iron(III) oxide reactivity reduction reduction with carbon
There has been a rapid rise in the need for iron to make steel due to urbanisation in the last decade. Which country is driving this need for more metal extraction?
This introduces the topic and puts the science into an interesting context.
China
Rest of world
Mt 1,600 1,200 800 400 0
1980
1985
1990
1995
2000
2005
2010
2014
Figure 4.15 Graph of increase in steel consumption. What has happened to consumption by China? Figure 4.16 Haematite, Fe2O3 , is the common ore of iron.
Reduction Metals such as gold are found in the Earth as the metal itself because it is unreactive. Most metals, however, are found as compounds because they react with other elements. Chemical reactions are needed to extract the metal. The reactions needed depend on the reactivity of the metal.
Each topic is divided into three sections. The level of challenge gets harder with each section.
Metals more reactive than carbon need to be extracted by electrolysis.
For example:
potassium sodium calcium magnesium aluminium
Metals less reactive than carbon can be extracted from their oxides by reduction with carbon.
For example:
zinc iron lead
Figure 4.17 Zinc blende, ZnS , is the common ore of zinc.
Reduction involves the loss of oxygen. In the reactions needed to extract zinc, two stages are needed. a to convert the ore zinc blende (ZnS) to zinc oxide b to convert the zinc oxide to zinc The second stage is the reduction of zinc using carbon. zinc oxide + carbon → zinc + carbon dioxide
136
6
AQA GCSE Chemistry: Student Book
AQA GCSE Chemistry: Student Book
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Important scientiďŹ c vocabulary is highlighted. You can check the meanings in the Glossary at the end of the book.
1
In the second stage of extracting, zinc oxide is changed to zinc as in the equation above. State which substance is oxidised and which is reduced.
Reduction using carbon
Each section has levelappropriate questions, so you can check and apply your knowledge.
4.3 REMEMBER!
4OÂŹEXTRACTÂŹIRONx You do not need to know the details of zinc extraction or details of the processes used in the extraction of iron. You need to know about oxidation and reduction.
)RONOREISREDUCED WHICHMEANSTAKINGAWAYOXYGEN  4HISISDONEWITHAREDUCINGAGENT  4HEREDUCINGAGENTUSEDISCARBONMONOXIDE  #ARBONMONOXIDEISMADEBYHEATINGCARBON  )NINDUSTRYTHEPROCESSHASMANYSTEPSBUTPUTSIMPLY CARBON OXYGEN → CARBONMONOXIDE
ÂŹ
IRONOXIDE CARBONMONOXIDE → IRON CARBONDIOXIDE
ÂŹ
# /  → #/
ÂŹ
I
&E2/   #/ → &E  #/2
ÂŹ
II
2
In equation (i) explain which substance has been oxidised.
3
In equation (ii) explain which substance has been oxidised and which substance has been reduced.
4
The ore cuprite contains copper (II) oxide (Cu2O) and can be smelted with carbon. The ore is mixed with coal and roasted in a furnace. Copper metal and carbon monoxide, CO, are produced.
&IGUREÂŹ ÂŹMolten iron extracted from iron ore.
a Write a balanced equation for the reaction. b State what is happening to the copper(II) oxide and carbon.
HIGHER TIER ONLY
Ionic equations
KEY INFORMATION
Each topic has some fascinating additional background information.
This is done by reacting the iron ore ‘haematite’, which is iron oxide, with carbon monoxide.
)NTHEEXTRACTIONOFZINC THEEQUATIONSARE  ZINCSULlDE OXYGEN→ ZINCOXIDE SULFURDIOXIDE
For Foundation tier, you do not need to understand the content in the Higher tier only boxes. For Higher tier you should aim to understand the other sections, as well as the content in the Higher tier only boxes.
DID YOU KNOW?
THEN :N/ #→ :N #/2 4HEHALFEQUATIONFORZINCIONSCONVERTINGTOZINCIS :N   E → :N )NTHEEXTRACTIONOFIRON THEHALFEQUATIONFORTHElNAL REACTION II IS 
Most iron extracted is turned into steel, by adding carbon and other elements. Steel, an alloy, is less easily corroded.
&E   E –→ &E 5
Write a full balanced symbol equation for the conversion of zinc sulďŹ de, ZnS, to zinc oxide, ZnO, and sulfur dioxide, SO2
6
The iron half equation is derived from reaction (ii) for the extraction of iron. Write this half equation.
Google search: 'mining iron ore or Bessemer process'
137
Look for the internet search terms at the bottom of the page.
How to use this book
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Chemistry The first page of a chapter has links to ideas you have met before, which you can now build on.
This page gives a summary of the exciting new ideas you will be learning about in the chapter.
Chemistry
ELEMENTS, MIXTURES AND COMPOUNDS
WHAT MODEL DO WE USE TO REPRESENT AN ATOM?
s¬ MIXTURES¬CAN¬BE¬SEPARATED¬EASILY¬BY¬l¬LTERING¬AND¬OTHER¬ WAYS s¬ %LEMENTS¬CANNOT¬BE¬BROKEN¬DOWN¬BY¬CHEMICAL¬MEANS s¬ #OMPOUNDS¬ARE¬MADE¬FROM¬ELEMENTS¬CHEMICALLY¬COMBINED
s¬ %LECTRONS¬l¬LL¬THE¬SHELLS¬AROUND¬THE¬NUCLEUS¬IN¬SET¬PATTERN¬ ORDERS ¬ s¬ 0ROTONS¬AND¬NEUTRONS¬MAKE¬UP¬THE¬NUCLEUS s¬ %LECTRONS¬CAN¬BE¬LOST¬FROM¬OR¬GAINED¬INTO¬THE¬OUTER¬SHELL
ATOMS AND THEIR STRUCTURE
HOW DID THE MODEL OF THE ATOM DEVELOP?
s¬ %LECTRONS¬HAVE¬A¬NEGATIVE¬CHARGE ¬ s¬ !TOMS¬HAVE¬A¬NUCLEUS¬WITH¬A¬POSITIVE¬CHARGE s¬ %LECTRONS¬ORBIT¬THE¬NUCLEUS¬IN¬SHELLS
s¬ !TOMS¬USED¬TO¬BE¬THOUGHT¬OF¬AS¬SMALL¬UNBREAKABLE¬SPHERES s¬ %XPERIMENTS¬LED¬TO¬IDEAS¬OF¬ATOMS¬WITH¬A¬NUCLEUS¬AND¬ ELECTRONS s¬ %LECTRONS¬IN¬SHELLS¬AND¬THE¬DISCOVERY¬OF¬THE¬NEUTRON¬CAME¬LATER
SOME ELEMENTS AND THEIR COMPOUNDS
WHY CAN WE USE CARBON DATING?
s¬ (ELIUM¬IS¬UNREACTIVE¬AND¬USED¬IN¬BALLOONS s¬ 3ODIUM¬CHLORIDE¬IS¬USED¬TO¬m¬AVOUR¬AND¬PRESERVE¬FOOD ¬ s¬ #HLORINE¬IS¬USED¬TO¬KILL¬BACTERIA¬IN¬SWIMMING¬POOLS
s¬ !TOMS¬OF¬AN¬ELEMENT¬ALWAYS¬HAVE¬THE¬SAME¬NUMBER¬OF¬ PROTONS s¬ 4HEY¬DO¬NOT¬ALWAYS¬HAVE¬THE¬SAME¬NUMBERS¬OF¬NEUTRONS s¬ %LEMENTS¬EXIST¬AS¬DIFFERENT¬ISOTOPES
METALS IN THE PERIODIC TABLE
WHY IS HELIUM SO UNREACTIVE AND SODIUM SO REACTIVE?
s¬ 'OLD ¬SILVER¬AND¬PLATINUM¬ARE¬PRECIOUS¬METALS ¬ s¬ -ERCURY¬IS¬A¬LIQUID¬METAL s¬ :INC ¬COPPER¬AND¬IRON¬ARE¬USED¬TO¬MAKE¬MANY¬USEFUL¬ OBJECTS
s¬ 4HE¬OUTER¬SHELL¬OF¬HELIUM¬CAN¬TAKE¬NO¬MORE¬ELECTRONS s¬ 4HE¬OUTER¬SHELL¬OF¬SODIUM¬HAS¬ ¬ELECTRON¬WHICH¬IT¬NEEDS¬TO¬ lose s¬ -ETALS¬NEED¬TO¬LOSE¬ELECTRONS ¬NON METALS¬DO¬NOT
METALS AND NON-METALS
WHAT DO TRANSITION METAL COMPOUND SOLUTIONS LOOK LIKE?
s¬ 'OLD ¬IRON ¬COPPER¬AND¬LEAD¬ARE¬METALS¬KNOWN¬FOR¬ CENTURIES s¬ /XYGEN¬AND¬NITROGEN¬ARE¬GASES¬OF¬THE¬AIR s¬ 3ULFUR¬IS¬A¬YELLOW¬NON METAL
C
s¬ 4RANSITION¬METALS¬ARE¬HARDER¬AND¬STRONGER¬THAN¬'ROUP¬ ¬METALS ¬ s¬ 4RANSITION¬METALS¬ARE¬OFTEN¬USED¬AS¬CATALYSTS s¬ 4RANSITION¬METAL¬COMPOUNDS¬OFTEN¬FORM¬COLOURED¬SOLUTIONS
CHAPTER OPENING 12
C
Spot the difference in these isotopes
Atomic structure and the periodic table
AQA GCSE Chemistry: Student Book
13
The Key Concept pages focus on a core ideas. Once you have understood the key concept in a chapter, it should develop your understanding of the whole topic.
Chemistry
KEY CONCEPT
KEY CONCEPT
1.13
The outer electrons Learning objectives: s¬ RECOGNISE¬WHEN¬ELECTRONS¬TRANSFER s¬ RECOGNISE¬WHEN¬ATOMS¬SHARE¬ELECTRONS s¬ PREDICT¬WHEN¬ELECTRONS¬ARE¬TRANSFERRED¬MOST¬EASILY
KEY WORDS
MAKE¬UP¬A¬STABLE¬OUTER¬SHELL ¬4HEY¬WILL¬TRANSFER¬IN¬FROM¬THE¬ OUTER¬SHELL¬OF¬ANOTHER¬ATOM
transfer share electrons outer shell
)F¬AN¬ATOM¬HAS¬AN¬UNSTABLE¬NUMBER¬OF¬ELECTRONS¬IN¬ITS¬OUTER¬ SHELL¬THIS¬ATOM¬WILL¬SHARE¬ITS¬ELECTRONS¬WITH¬ELECTRONS¬FROM¬ OTHER¬ATOMS ¬#OMMON¬EXAMPLES¬OF¬ATOMS¬THAT¬DO¬THIS¬ARE¬ CARBON¬AND¬HYDROGEN ¬4HEY¬ALSO¬SHARE¬ELECTRONS¬WITH¬EACH¬ OTHER¬AND¬WITH¬OXYGEN¬ATOMS
Stable atoms The noble gases are all very unreactive. Their atoms are very stable and do not react with other atoms. This is because their outer shells contain eight electrons, (except He which contains two electrons). This stable number of electrons in the outer electron shell means there is no tendency to transfer electrons.
Ar
He
#HEMICAL¬REACTIVITY¬AND¬CHEMICAL¬REACTIONS¬DEPEND¬ON¬THE¬ NUMBER¬OF¬ELECTRONS¬IN¬THE¬OUTER¬SHELL ¬ (OWEVER ¬NOTE¬THAT¬ THIS¬IS¬NOT¬ALWAYS¬TRUE¬IN¬REACTIONS¬OF¬TRANSITION¬METALS
2
Predict the number of ‘outer’ electrons lithium has.
Transferring or sharing?
Li
F
fluorine atom 2, 7
)F¬AN¬ATOM¬HAS¬SIX¬OR¬SEVEN¬ELECTRONS¬IN¬ITS¬OUTER¬SHELL ¬ ELECTRONS¬FROM¬OTHER¬ATOMS¬WILL¬ADD¬IN¬TO¬THE¬@SPACES ¬TO¬
38
KEY CONCEPT
8
AQA GCSE Chemistry: Student Book
C
H
H
K
0OTASSIUM¬REACTS¬MORE¬QUICKLY¬THAN¬LITHIUM
H
4HIS¬IS¬BECAUSE¬THE¬OUTER¬ELECTRON¬IS¬FURTHER¬AWAY¬FROM¬ITS¬ NUCLEUS¬IN¬A¬POTASSIUM¬ATOM¬THAN¬IN¬A¬LITHIUM¬ATOM 4HE¬@PULL ¬ON¬THE¬ELECTRON¬BY¬THE¬POTASSIUM¬NUCLEUS¬IS¬LESS¬ THAN¬THE¬@PULL ¬ON¬THE¬ELECTRON¬BY¬THE¬LITHIUM¬NUCLEUS ¬4HE¬ ELECTRON¬OF¬POTASSIUM¬IS¬MORE¬EASILY¬LOST¬ TRANSFERRED¬OUT
H
Li
3O¬POTASSIUM¬IS¬MORE¬REACTIVE &LUORINE¬AND¬BROMINE¬BOTH¬NEED¬TO¬GAIN¬ONE¬ELECTRON¬TO¬ BECOME¬STABLE¬ATOMS &LUORINE¬REACTS¬MORE¬VIGOROUSLY¬THAN¬BROMINE
F
4HIS¬IS¬BECAUSE¬THE¬OUTER¬ELECTRON¬SHELL¬IS¬NEARER¬TO¬ITS¬ NUCLEUS¬IN¬A¬m¬UORINE¬ATOM¬THAN¬IN¬A¬BROMINE¬ATOM
Mg
O
Na
F
)F¬AN¬ATOM¬HAS¬ONE¬OR¬TWO¬ELECTRONS¬IN¬ITS¬OUTER¬SHELL¬THESE¬ ELECTRONS¬WILL¬TRANSFER¬OUT ¬4HEY¬WILL¬TRANSFER¬TO¬THE¬OUTER¬ SHELL¬OF¬ANOTHER¬ATOM
Adding in other electrons
Predict how many electrons are shared by two fluorine atoms.
3OME¬ELEMENTS¬ARE¬MORE¬REACTIVE¬THAN¬OTHERS ¬4HIS¬CAN¬BE¬ BECAUSE¬THEIR¬OUTER¬ELECTRONS¬TRANSFER¬out¬MORE¬EASILY¬THAN¬ OTHERS¬OR¬TRANSFER¬in¬MORE¬EASILY¬THAN¬OTHERS
s¬ THEY¬CAN¬BE¬TRANSFERRED¬TO¬THE¬OUTER¬SHELL¬OF¬ANOTHER¬ATOM s¬ THEY¬CAN¬HAVE¬OTHER¬ELECTRONS¬ADDED¬TO¬THEIR¬OUTER¬SHELL¬ FROM¬ANOTHER¬ATOM s¬ THEY¬CAN¬BE¬SHARED¬WITH¬ANOTHER¬ATOM Name two noble gases that have eight electrons in their outer shell.
4
0OTASSIUM¬AND¬LITHIUM¬BOTH¬NEED¬TO¬LOSE¬ONE¬ELECTRON¬TO¬ BECOME¬STABLE¬ATOMS
lithium atom 2, 1
4HREE¬THINGS¬CAN¬HAPPEN¬TO¬THE¬ELECTRONS¬IN¬THE¬OUTER¬SHELL
1
Suggest how many ‘spaces’ in the outer shell an oxygen atom has.
Transferring electrons transfer of an electron
Less stable atoms !LL¬OTHER¬ATOMS¬ARE¬LESS¬STABLE ¬4HEIR¬ELECTRONS¬MOVE¬OR¬SHARE¬ WITH¬OTHER¬ELECTRONS¬TO¬TRY¬TO¬BECOME¬AS¬STABLE¬AS¬THE¬ATOMS¬ WITH¬ ¬ELECTRONS¬IN¬THEIR¬OUTER¬SHELL
H
H
3
4HE¬@PULL ¬ON¬THE¬ELECTRON¬COMING¬IN¬TO¬l¬LL¬THE¬@SPACE ¬IN¬THE¬ m¬UORINE¬OUTER¬RING¬BY¬THE¬m¬UORINE¬NUCLEUS¬IS¬MORE¬THAN¬THE¬ @PULL ¬ON¬THE¬ELECTRON¬BY¬THE¬BROMINE¬NUCLEUS ¬4HE¬ELECTRON¬ OF¬m¬UORINE¬IS¬MORE¬EASILY¬GAINED¬ TRANSFERRED¬IN ¬3O¬m¬UORINE¬ IS¬MORE¬REACTIVE 5
Explain, using ideas about ‘the pull of the nucleus’ why sodium is more reactive than lithium.
6
Explain the reactivity of chlorine within group 7 in terms of the ‘pull of the nucleus’.
Google search: ‘electron transfer’
39
AQA GCSE Chemistry: Student Book
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The tasks – which get a bit more difficult as you go through – challenge you to apply your science skills and knowledge to the new context.
There is a dedicated page for every Required Practical in the AQA specification. They help you to analyse the practical and to answer questions about it.
Chemistry
REQUIRED PRACTICAL
REQUIRED PRACTICAL
6
The solution is collected after the removal of the excess solid.
KEY WORDS
To obtain the product from the solution two more processes are needed:
insoluble oxide carbonate filter crystallisation
Learning objectives: t describe a practical procedure for producing a salt from a solid and an acid t explain the apparatus, materials and techniques used for making the salt t describe how to safely manipulate apparatus and accurately measure melting points.
t evaporation t crystallisation To make a better product a pure sample is needed. The crystals formed will need to be: t washed and dried t recrystallised Think about these further questions for making pure magnesium sulfate:
Being able to choose the correct techniques and carry out a specified procedure to produce a pure product is an important skill for scientists. You will probably know how to complete each of the necessary techniques separately but can you explain how to use them together to produce a product safely?
These pages are designed to help you think about aspects of the investigation rather than to guide you through it step by step.
The making of magnesium sulfate from magnesium carbonate can be done in several stages using different pieces of apparatus.
Sam
MP ° C
40.3
40.5
Alex
MP ° C
41.6
41.4
Explain the affect of impurities on the melting point.
11
Suggest why it might have been advisable for Sam and Alex to take another temperature measurement.
spatula warm acid
4
Describe the safety measures that need to be taken when adding substances.
5
After the two substances are mixed and stirred Figure 4.32 as in Figure 4.32b, explain why there is some solid left in the bottom of the solution.
146
unreacted solid
and funnel
powdered metal or base
State the units of measurement for each substance.
REMEMBER! It is helpful to imagine setting up the apparatus needed and draw each part of the procedure by stages.
10
c filter paper
State how the quantities are measured.
Explain how the purity of the final sample is tested.
Most salts have a very high melting point, so a special heater would be needed.
a
3
Explain how the purity of the salt can be improved.
9
DID YOU KNOW?
This diagram has some stages of an experimental plan depicted but not all stages.
2
Describe how the first sample of dry impure salt is obtained from the solution.
8
When a sample of product has been made, it needs to be tested for purity. Sam and Alex made samples of calcium nitrate crystals. They looked up the melting point for these crystals and found it was 42.7 °C. These are their results. Who made the purest sample?
Carrying out procedures
Identify the two substances needed to make magnesium sulfate.
7
Measuring accurately
A number of different skills are needed to carry out the production of a sample of a chemical. This section looks at the skills of selecting techniques, apparatus and materials and managing safety.
1
4.8
Using apparatus and techniques
Preparing a pure, dry sample of a soluble salt from an insoluble oxide or carbonate
In Figure 4.32a the quantities of two chemicals have been measured to make the salt:
The excess solid is removed as in Figure 4.32c. Name the process of removal of the solid.
12
Give the equation for the reaction between magnesium carbonate, MgCO3 and the acid?
13
Calculate the mass of the two substances needed to produce 6 g of MgSO4
14
Explain why the solid MgCO3 needs to be added in excess of the amount calculated.
b
salt solution
15
What may happen to the yield if the aim is to increase purity?
16 The uncertainty in reading the thermometer was plus or minus unreacted metal or base
0.2°C. Discuss whether the difference in melting point between the data book value and the measurements is significant. Explain which of the results are most accurate.
salt solution
Google search: ‘preparation of soluble salts’
REQUIRED PRACTICAL AQA GCSE Chemistry: Student Book
147
The Maths Skills pages focus on the maths requirements in the AQA specification, explaining concepts and providing opportunities to practise.
Chemistry MATHS SKILLS
MATHS SKILLS Make order of magnitude calculations
KEY WORDS
Learning objectives:
magnitude
• • •
use graphs and diagrams to apply the pH scale to acid rain distribution calculate the concentration of acids calculate the effect of hydrogen ion concentration on the numerical value of pH.
It is important to be able to calculate the concentrations of acid for using them in reactions and monitoring the acidity of rainfall. The concentration of an acid depends on the concentration of hydrogen ions [H+], so we use a logarithmic scale to describe acidity more easily called the pH scale. Can you remember what the numbers of the scale represents?
The concentration of acids is measured in g / dm3 or mol / dm3. The shorthand is to write a square bracket [HA] to mean concentration.
derived
(Ar: H is 1, N is 14, O is 16)
relative
< 4.3 4.3 – 4.4 4.4 – 4.5 4.5 – 4.7 > 4.7
Finding what happens to the pH as acid is diluted or neutralised: What does pH mean? It is a scale that is derived from the concentration of hydrogen ions in an acid solution. If the concentration of a strong acid is 0.1 mol / dm3, then the concentration of hydrogen ions, [H +], is also 0.1 mol / dm3. In standard form this is 10 –1 mol / dm3. The pH number is the ‘index’ number but positive. So the pH of this solution is pH 1. If the concentration decreases by a factor of 10, the standard form decreases by the index of –1 and the pH increases by positive 1. Concentration of acid in standard form in mol / dm3
pH
0.1
10 -1
1
0.01
10 -2
2
0.001
10 -3
3
6000
0.0001
10 -4
4
5000
0.00001
10 -5
5
0.000001
10 -6
6
0.0000001
10 -7
7
Thousand tonnes of sulfur dioxide equivalent 8000
4000 3000
Sulfur Dioxide (SO2)
Nitrogen Oxide (NOX)
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
1000
Ammonia (NH3)
So you can see from the table that as the concentration of the acid decreases by a factor of 10, the pH increases by one unit. 8
Determine the pH of a solution with [H+]= 0.000001.
9
Estimate the concentration of hydrogen ions for a solution that turned universal indicator green.
Source: Ricardo-AEA, Office for National Statistics
Figure 4.60 Acidity of Rainfall in Britain
166
AQA GCSE Chemistry: Student Book
5
What mass of sulfuric acid is needed to make a solution [H2SO4 ] = 0.05 mol / dm3?
6
9.13 g of hydrochloric acid was dissolved in 250 cm3 of water. Calculate the concentration of hydrochloric acid in mol/ dm3.
7
0.46 g of methanoic acid, HCOOH, was dissolved in 200 cm3 of water. Calculate the concentration of methanoic acid in mol/dm3.
DID YOU KNOW?
2000
0
MATHS SKILLS
What mass of sulfuric acid, H2SO4, is needed to make a solution [H2SO4 ] = 1 mol / dm3 ? (Ar: S is 32)
7000
2001
Calculate the approximate ratio of sulfur dioxide equivalents for 1990 and 2011.
Concentration of acid in mol / dm3
2000
3
Estimate the decrease in sulfur dioxide in thousand tonnes equivalent from 1990 to 2006 from the graph.
4
1000 cm3 solution that contains 6.3 g has decreased only the mass by a factor of 10 not the volume, so the concentration reduces by a factor of 10, so [HNO3] = 6.3 g / dm3 and [HNO3] = 0.1 mol / dm3
Figure 4.59 Acidity of Rainfall in Britain
1995
2
Which side of the UK experiences rainfall that is the most acidic? Explain how you can tell from the data.
Robert Angus Smith first showed a relationship between atmospheric pollution and acid rain in 1852 and used the term acid rain in 1872. It took us 100 years to take the issue seriously and do something about it!
100 cm3 solution that contains 6.3 g has decreased both volume and mass by a factor of 10, so the concentration remains the same, [HNO3] = 63 g / dm3 and also [HNO3] = 1 mol / dm3
Acidity of Rainfall/pH
1990
1
Mr: HNO3 = 1 + 14 + (3 × 16) = 63
If a solution of nitric acid contains 63 g of acid dissolved in 1 dm3 of water the [HNO3] = 63 g / dm3 The relative formula mass is also the mass of 1 mole or the molar mass, so the [HNO3] = 1 mol / dm3
Acidity of Rainfall in Britain.
Figure 4.59 shows a map where the rainfall has a pH of less than 5.6 and so is more acidic than usual. However, there is some better news about sulfur dioxide levels now that power stations have changed. They either burn gas instead or sulfur dioxide is removed from the emissions in power stations still burning coal. This means that the amount of sulfur dioxide being released has been reducing since 1990 as you can see in the bar chart, Figure 4.60.
DID YOU KNOW?
The relative formula mass (Mr) of nitric acid HNO3 is calculated from the relative atomic masses (Ar)
logarithmic scale
Acid rain Non-polluted rain water has a pH of 5.6. If water has a pH lower than that it is called ‘acid rain’. We have seen that the causes of acid rain are polluting gases, such as sulfur dioxide, dissolving in rainwater. Sulfur dioxide comes from burning fossil fuels, especially coal, for electricity generation, transport, heating and industrial processes.
4.18
HIGHER TIER ONLY
Concentrations of acid
The pH value is actually a value on a logarithm scale. The pH equals the negative log to the base 10 of the hydrogen ion concentration. This is more elegantly written as: pH = -log10[H+ aq].
Google search: ‘orders of magnitude’
167
How to use this book
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Chemistry
These lists at the end of a chapter act as a checklist of the key ideas of the chapter. In each row, the green box gives the ideas or skills that you should master ďŹ rst. Then you can aim to master the ideas and skills in the blue box. Once you have achieved those you can move on to those in the red box.
Chemistry
Check your progress
Worked example
You should be able to:
+IMÂŹANDÂŹ*OÂŹAREÂŹELECTROLYSINGÂŹDILUTEÂŹSULFURICÂŹACID 1
â&#x2013; identify that metals react
â&#x17E;&#x17E; â&#x2013; explain reduction and
â&#x17E;&#x17E; â&#x2013; identify metal oxides as bases
â&#x2013; describe the reactions, if any, of metals with water or dilute acids to place these metals in order of reactivity
â&#x17E;&#x17E;
â&#x17E;&#x17E; â&#x2013; deduce an order of reactivity of
2
â&#x17E;&#x17E; â&#x2013; interpret or evaluate
3
with oxygen to form metal oxides
oxidation by loss or gain of oxygen
â&#x2013; explain how the reactivity is related to the tendency of the metal to form its positive ion
â&#x2013; identify substances oxidised â&#x17E;&#x17E; â&#x2013; explain how extraction or reduced by gain or loss of oxygen
methods depend on metal reactivity
information on speciďŹ c metal extraction processes
â&#x17E;&#x17E; â&#x2013; write ionic equations for
â&#x2013; describe how to make salts from metals and acids
â&#x17E;&#x17E;
â&#x17E;&#x17E;
â&#x2013; write full balanced symbol equations for making salts
b hydrogen
c sulfur
Describe how they will test for hydrogen gas.
It pops with a lighted splint.
Construct the half equation for the discharge of hydrogen at the electrode.
The charge on the ion and the gain of an electron are correct. The molecule H2 is correct. The equation needs to be balanced, 2H+ + 2eâ&#x2C6;&#x2019; â&#x2020;&#x2019; H2
H+ + e - â&#x2020;&#x2019; H 2
displacement reactions
â&#x2013; use half equations to describe oxidation and reduction
The answer oxygen is correct.
d oxygen This test is correct.
metals based on experimental results
â&#x17E;&#x17E; â&#x2013; use the reactivity series
to predict displacement reactions
a nitrogen
or alkalis
â&#x2013; use experimental results of
displacement reactions to conďŹ rm the reactivity series
Identify the substance seen at the anode.
4
Next Kim and Jo want to electrolyse copper sulfate. Jo says that they cannot use solid copper sulfate. Explain why.
This answer is partly correct. The ions need be free to move to conduct electricity, so need to be molten or in solution.
The ions need to be free to move.
â&#x2013; describe how to make pure, â&#x17E;&#x17E; â&#x2013; explain how to name a salt
â&#x17E;&#x17E; â&#x2013; derive a formula for a salt from
â&#x2013; describe the use of universal â&#x17E;&#x17E; â&#x2013; use the pH scale to identify
â&#x17E;&#x17E; â&#x2013; investigate pH changes when a
dry samples of soluble salts
indicator to measure pH
acidic or alkaline solutions
â&#x17E;&#x17E; â&#x2013; describe neutralisation
â&#x17E;&#x17E; â&#x2013; explain the terms dilute and
â&#x2013; describe the use of an electrolyte, anode and cathode in an electrolysis
â&#x17E;&#x17E;
â&#x17E;&#x17E; â&#x2013; write half equations for the
â&#x2013; explain why electrolytes
â&#x17E;&#x17E; â&#x2013; describe the products of
â&#x17E;&#x17E; â&#x2013; predict the products of the
â&#x2013; explain why some metals
â&#x17E;&#x17E; â&#x2013; explain the process of the
â&#x17E;&#x17E; â&#x2013; explain which non-metals
need to be molten to conduct electricity
need to be extracted by electrolysis
through the effect on hydrogen ions and pH
â&#x2013; identify reactions at electrodes during electrolysis
molten binary electrolytes
electrolysis of aluminium oxide
â&#x2013; use apparatus to electrolyse â&#x17E;&#x17E; â&#x2013; explain which metals (or aqueous solutions in the laboratory
â&#x2013; explain the electrolysis of
copper sulfate using inert electrodes
hydrogen) are formed at the cathode in preference
â&#x17E;&#x17E; â&#x2013; predict the products of
the electrolysis of aqueous solutions
The answer is correct. 5
strong acid neutralises a strong alkali.
â&#x2013; explain weak and strong acids by the degree of ionisation
168
its ions
a Describe what will happen at the cathode.
It will get a coat of pink/brown copper.
concentrated as the amounts of substances dissolved
b Describe what they will see at the anode.
It will disintegrate. c What will they see happening to the copper sulfate solution?
electrode reactions and complete and balance half equations
electrolysis of binary ionic compounds in the molten state are formed at the anode in preference
â&#x17E;&#x17E; â&#x2013; predict the products of the
electrolysis of aqueous solutions containing a single ionic compound
â&#x17E;&#x17E; â&#x2013; represent reactions at
electrodes by half equations
AQA GCSE Chemistry: Student Book
They choose to use a solution. They pass a current through the solution of copper sulfate, using carbon electrodes.
It will stay blue.
6
Construct the half equation for the discharge of copper at an electrode and explain whether this reaction is oxidation or reduction. Explain why copper is deposited and hydrogen is not evolved.
Cu 2+ + 2e- â&#x2020;&#x2019; Cu This is reduction as electrons are gained (RIG). Copper is deposited because it is more reactive than hydrogen.
The student needs to be clear that this happens with copper electrodes, not carbon, and is used in the purification process. The answer should be that bubbles of oxygen will appear.
The answer is again confused with the purification process. The correct answer is that the blue colour disappears. This is due to the copper depositing from the solution on to the electrode.
The half equation is correct. Reduction is correct â&#x20AC;&#x201C; no need for the memory aid. Copper is less reactive than hydrogen, (which is why it is deposited).
Worked example
169
Use the comments to help you understand how to answer questions. Read each question and answer. Try to decide if, and how, the answer can be improved. Finally, read the comments and try to answer the questions yourself. END OF CHAPTER
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The End of Chapter Questions allow you and your teacher to check that you have understood the ideas in the chapter, can apply these to new situations, and can explain new science using the skills and knowledge you have gained. The questions start off easier and get harder. If you are taking Foundation tier try to answer all the questions in the Getting started and Going further sections. If you are taking Higher Tier try to answer all the questions in the Going further, More challenging and Most demanding sections.
Chemistry
End of chapter questions
More challenging 13 Explain oxidation in terms of electron transfer using sodium chloride, NaCl, as
Getting started 1
an example.
Which oxide is a base? a carbon dioxide
2
¬-ARK
b magnesium oxide
c sulfur dioxide
a sodium
¬-ARK
b iron
c zinc
d magnesium
Write down two substances needed to make iron metal from its ore.
¬-ARKS
4
Zinc is reacted with sulfuric acid. Bubbles form. What gas is this?
¬-ARKS
5 6
7
b carbon dioxide
c hydrogen
Mg ¬-ARK
Sodium carbonate is added to a flask containing hydrochloric acid and a few drops of universal indicator. A small excess of sodium carbonate was added. Explain what happens to the colour in the flask.
¬-ARKS
The diagram below shows four different metals reacting with sulfuric acid solution.
¬-ARKS
E
F
• Describe any observations you might make during the reactions.
¬-ARKS
16 In an experiment a student reacted metals with solutions of sulfates of the
other metals. One metal, X, was unknown. These are the results:
d chlorine
1 g of metal carbonate dissolves completely in acid, but 2 g does not dissolve. How many grams do you add to the same volume of acid to make a salt?
D
how salts are made using sulfuric acid and calcium and its compounds as an example. • You should use equations to illustrate your answer
3
a oxygen
¬-ARK
15 alts can be made by reacting acids with a variety of other substances. Show
d silicon dioxide
Which metal is most reactive?
¬-ARK
14 Methanoic acid, HCOOH, is a weak acid. Define the term weak acid.
G
Fe ✗
MgSO4 FeSO4
✓
CuSO4
✓
✓
XSO4
✓
✗
Cu ✗ ✗
¬-ARKS
X ✗ ✓ ✓
✗
Describe where X lies in the reactivity series, giving reasons.
¬-ARKS
Most demanding
a Determine the order of decreasing reactivity for metals D to G.
17 Solid magnesium carbonate, MgCO3, was added to an aqueous solution of
nitric acid in a conical flask.
b Explain what makes one metal more reactive than another.
a State two observations that could be made. b Write a balanced chemical equation for the reaction, including state symbols. mild fizzing
no fizzing
copious quantities of fizzing
Going further
carbon and other materials such as limestone and sand. a Write a balanced equation for the reaction of tin(IV) oxide with carbon.
8
Estimate the pH of hydrochloric acid solution.
¬-ARK
9
Which metal oxide can be reacted with carbon to produce the metal?
¬-ARK
a aluminium oxide
¬-ARKS
18 Tin is present as tin(IV) oxide, SnO2, in cassiterite ore. The ore is heated with
in between D and F for fizzing
b sodium oxide
c iron(III) oxide
d magnesium oxide
10 Explain why solid lead bromide cannot be electrolysed.
¬-ARKS
11 Describe the stages of making pure zinc sulfate salt crystals from sulfuric acid.
Give equations where appropriate.
¬-ARKS
c Part of the reactivity series is as follows: K, Na, Mg, Al, C, Zn, Fe, Sn, Pb, H2, Cu, Ag, Au. Explain why it is not necessary to use electrolysis to extract tin.
• Zinc was added to copper(II) sulfate solution. Copper was deposited.
¬-ARKS
19 Aqueous potassium hydroxide is added to a solution of phosphoric acid, H3PO4
a State the type of reaction and write the balanced ionic equation including state symbols. b The concentration of the phosphoric acid solution was 0.243 mol / dm3 Calculate the mass of phosphoric acid required.
12 Some experiments were carried out on metals and solutions of metal salts.
¬-ARKS
20 An aqueous solution of calcium iodide was electrolysed.
• Metal X was added to zinc sulfate solution. Zinc was not deposited.
a Predict the products at the electrodes.
• Metal X was added to copper(II) sulfate solution. Copper was deposited. Place the metals in order of reactivity. Justify your answer.
b Explain what is happening in terms of oxidation and reduction.
b Write the half equations occurring at the electrodes.
¬-ARKS
¬-ARKS
4OTAL ¬ ¬-ARKS
170
AQA GCSE Chemistry: Student Book
End of chapter questions
171
There are questions for each assessment objective (AO) from the final exams. These help you to develop the thinking skills you need to answer each type of question. AO1 – to answer these questions you should aim to demonstrate your knowledge and understanding of scientific ideas, techniques and procedures. AO2 – to answer these questions you should aim to apply your knowledge and understanding of scientific ideas and scientific enquiry, techniques and procedures. AO3 – to answer these questions you should aim to analyse information and ideas to: interpret and evaluate, make judgements and draw conclusions, develop and improve experimental procedures.
How to use this book
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Chemistry
ELEMENTS, MIXTURES AND COMPOUNDS s¬ MIXTURES¬CAN¬BE¬SEPARATED¬EASILY¬BY¬l¬LTERING¬AND¬OTHER¬ WAYS s¬ %LEMENTS¬CANNOT¬BE¬BROKEN¬DOWN¬BY¬CHEMICAL¬MEANS s¬ #OMPOUNDS¬ARE¬MADE¬FROM¬ELEMENTS¬CHEMICALLY¬COMBINED
ATOMS AND THEIR STRUCTURE s¬ %LECTRONS¬HAVE¬A¬NEGATIVE¬CHARGE ¬ s¬ !TOMS¬HAVE¬A¬NUCLEUS¬WITH¬A¬POSITIVE¬CHARGE s¬ %LECTRONS¬ORBIT¬THE¬NUCLEUS¬IN¬SHELLS
SOME ELEMENTS AND THEIR COMPOUNDS s¬ (ELIUM¬IS¬UNREACTIVE¬AND¬USED¬IN¬BALLOONS s¬ 3ODIUM¬CHLORIDE¬IS¬USED¬TO¬m¬AVOUR¬AND¬PRESERVE¬FOOD ¬ s¬ #HLORINE¬IS¬USED¬TO¬KILL¬BACTERIA¬IN¬SWIMMING¬POOLS
METALS IN THE PERIODIC TABLE s¬ 'OLD ¬SILVER¬AND¬PLATINUM¬ARE¬PRECIOUS¬METALS ¬ s¬ -ERCURY¬IS¬A¬LIQUID¬METAL s¬ :INC ¬COPPER¬AND¬IRON¬ARE¬USED¬TO¬MAKE¬MANY¬USEFUL¬ OBJECTS
METALS AND NON-METALS s¬ 'OLD ¬IRON ¬COPPER¬AND¬LEAD¬ARE¬METALS¬KNOWN¬FOR¬ CENTURIES s¬ /XYGEN¬AND¬NITROGEN¬ARE¬GASES¬OF¬THE¬AIR s¬ 3ULFUR¬IS¬A¬YELLOW¬NON METAL
12
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WHAT MODEL DO WE USE TO REPRESENT AN ATOM? s¬ %LECTRONS¬l¬LL¬THE¬SHELLS¬AROUND¬THE¬NUCLEUS¬IN¬SET¬PATTERN¬ ORDERS ¬ s¬ 0ROTONS¬AND¬NEUTRONS¬MAKE¬UP¬THE¬NUCLEUS s¬ %LECTRONS¬CAN¬BE¬LOST¬FROM¬OR¬GAINED¬INTO¬THE¬OUTER¬SHELL
HOW DID THE MODEL OF THE ATOM DEVELOP? s¬ !TOMS¬USED¬TO¬BE¬THOUGHT¬OF¬AS¬SMALL¬UNBREAKABLE¬SPHERES s¬ %XPERIMENTS¬LED¬TO¬IDEAS¬OF¬ATOMS¬WITH¬A¬NUCLEUS¬AND¬ ELECTRONS s¬ %LECTRONS¬IN¬SHELLS¬AND¬THE¬DISCOVERY¬OF¬THE¬NEUTRON¬CAME¬LATER
WHY CAN WE USE CARBON DATING? s¬ !TOMS¬OF¬AN¬ELEMENT¬ALWAYS¬HAVE¬THE¬SAME¬NUMBER¬OF¬ PROTONS s¬ 4HEY¬DO¬NOT¬ALWAYS¬HAVE¬THE¬SAME¬NUMBERS¬OF¬NEUTRONS s¬ %LEMENTS¬EXIST¬AS¬DIFFERENT¬ISOTOPES
C
C
Spot the difference in these isotopes
WHY IS HELIUM SO UNREACTIVE AND SODIUM SO REACTIVE? s¬ 4HE¬OUTER¬SHELL¬OF¬HELIUM¬CAN¬TAKE¬NO¬MORE¬ELECTRONS s¬ 4HE¬OUTER¬SHELL¬OF¬SODIUM¬HAS¬ ¬ELECTRON¬WHICH¬IT¬NEEDS¬TO¬ lose s¬ -ETALS¬NEED¬TO¬LOSE¬ELECTRONS ¬NON METALS¬DO¬NOT
WHAT DO TRANSITION METAL COMPOUND SOLUTIONS LOOK LIKE? s¬ 4RANSITION¬METALS¬ARE¬HARDER¬AND¬STRONGER¬THAN¬'ROUP¬ ¬METALS ¬ s¬ 4RANSITION¬METALS¬ARE¬OFTEN¬USED¬AS¬CATALYSTS s¬ 4RANSITION¬METAL¬COMPOUNDS¬OFTEN¬FORM¬COLOURED¬SOLUTIONS
Atomic structure and the periodic table
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Chemistry
Elements and compounds
KEY WORDS
Learning objectives:
balanced compound element equation symbol
sÂŹ IDENTIFYÂŹSYMBOLSÂŹOFÂŹELEMENTSÂŹFROMÂŹTHEÂŹPERIODICÂŹTABLE sÂŹ RECOGNISEÂŹCOMPOUNDSÂŹFROMÂŹTHEIRÂŹFORMULA sÂŹ IDENTIFYÂŹTHEÂŹELEMENTSÂŹINÂŹAÂŹCOMPOUND
All the elements are listed in the periodic table. The elements in the formulae of any compound, no matter how large, can be identified by using the periodic table.
Elements and compounds !NÂŹelementÂŹISÂŹAÂŹSUBSTANCEÂŹTHATÂŹCANNOTÂŹBEÂŹBROKENÂŹ DOWNÂŹCHEMICALLY !ÂŹcompoundÂŹISÂŹAÂŹSUBSTANCEÂŹTHATÂŹCONTAINSÂŹATÂŹLEASTÂŹ TWOÂŹDIFFERENTÂŹELEMENTS ÂŹCHEMICALLYÂŹCOMBINEDÂŹINÂŹ lXEDÂŹPROPORTIONS
1 1
PERIODIC TABLE ELEMENTS 1-20
H
hydrogen
7 3
Li
lithium
23 11
9 4
Be
beryllium
24
Na 12 Mg
sodium magnesium
39 19
K
40 20
11 5
B
boron
27 13
Al
12 6
C
14 7
N
16 8
O
4 2
19 9
F
carbon
nitrogen
oxygen
fluorine
28 14
31 15
32 16
35 17
Si
P
aluminium silicon phosphorus
S
sulfur
He
helium
Cl
chlorine
20 10
Ne
neon
40 18
Ar
argon
Ca
potassium calcium
&IGUREÂŹ ÂŹTwo sections of the periodic table. Can you ďŹ nd magnesium and oxygen?
+ &IGUREÂŹ ÂŹMagnesium (metal) reacts with oxygen (gas) to make magnesium oxide (white powder).
+ x z y
&IGUREÂŹ ÂŹThe reaction of the elements in Figure 1.2 can be represented by models of their atoms. 1
Identify the following substances as elements or compounds. copper
2
14
copper chloride
copper sulfate
Name the elements in beryllium chloride.
AQA GCSE Chemistry: Student Book
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Compounds and elements
1.1
#OPPER¬IS¬AN¬element ¬)T¬CANNOT¬BE¬BROKEN¬DOWN¬INTO¬ANY¬ OTHER¬SUBSTANCES ¬BUT¬SALT¬CAN 4HE¬CHEMICAL¬NAME¬FOR¬COMMON¬SALT¬IS¬SODIUM¬CHLORIDE ¬ 3ODIUM¬CHLORIDE¬IS¬A¬compound ¬3ODIUM¬CHLORIDE¬CAN¬BE¬BROKEN¬ DOWN¬TO¬MAKE¬SODIUM¬AND¬CHLORINE ¬BUT¬THIS¬IS¬NOT¬EASY¬TO¬DO¬ BECAUSE¬THE¬SODIUM¬AND¬CHLORINE¬ARE¬CHEMICALLY¬COMBINED ¬ 7E¬NEED¬TO¬USE¬ELECTRICITY¬TO¬MAKE¬SODIUM¬AND¬CHLORINE¬FROM¬ SODIUM¬CHLORIDE 3ODIUM¬AND¬CHLORINE¬CANNOT¬BE¬BROKEN¬DOWN¬ANY¬FURTHER ¬ 3ODIUM¬AND¬CHLORINE¬ARE¬ELEMENTS 4HERE¬ARE¬ONLY¬ABOUT¬ ¬ELEMENTS¬BUT¬THESE¬CAN¬JOIN¬TOGETHER¬ CHEMICALLY¬TO¬MAKE¬AN¬ENORMOUS¬NUMBER¬OF¬COMPOUNDS ¬4HEY¬ NEED¬CHEMICAL¬REACTIONS¬TO¬DO¬THIS 3
Identify the elements in potassium bromide.
4
Predict the products when lead iodide is split by electricity.
KEY INFORMATION When chlorine reacts to make a compound it chemically combines and becomes a chloride. Similarly, bromine reacts to become a bromide and oxygen reacts to become an oxide.
Making the element copper into a compound !¬CHEMICAL¬REACTION¬IS¬NEEDED¬TO¬MAKE¬COPPER¬ AN¬ELEMENT ¬INTO¬ A¬COMPOUND ¬)F¬COPPER¬IS¬BURNED¬IN¬OXYGEN¬IT¬FORMS¬COPPER¬OXIDE ¬ #HEMICAL¬REACTIONS¬ALWAYS¬INVOLVE¬THE¬FORMATION¬OF¬ONE¬OR¬MORE¬ NEW¬SUBSTANCES ¬AND¬OFTEN¬INVOLVE¬A¬DETECTABLE¬ENERGY¬CHANGE
DID YOU KNOW? Compounds can only be separated into elements by chemical reactions. To get the element copper back, the oxygen needs to be chemically removed. This is done using hydrogen. The oxygen combines with the hydrogen to make water, another compound. copper oxide + hydrogen â&#x2020;&#x2019; copper + water &IGURE¬ ¬Copper (an element) burning in oxygen (an element) to make copper oxide (a compound). This is normally done by heating the copper in crucibles. 5
What is the name of the compound made from sodium and oxygen.
6
Oxygen can be removed from iron(III) oxide by carbon monoxide. Identify the element and compound produced.
7
Substance D reacted with hydrogen to form zinc and water. Explain whether substance D is an element or compound. Google search: 'unusual periodic table (images)'
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