Chemistry for ® CSEC Anne Elizabeth Tindale Ritchie Dianne Sarah Luttig Chapman Jennifer Anna Murray Bowman s s er P ytisrevinU dr o f x O I N C LU D E S fo Edition CD t r aP 2nd Chemistry for ® CSEC Anne 2nd Tindale Edition Elizabeth Ritchie Dianne Sarah Chapman Jennifer Anna 1 Luttig Murray Bowman 3 Great Clarendon Oxford It University furthers and the Oxford The by © Anne moral rights published edition rights in means, Press, of by No retrieval as the the concerning sent the address You must impose British Data to the of have of other Dianne in law, reproduction trade mark of countries Sarah Chapman 2014 2014 2014 Press by any of rights the 2014 be reproduced, form or Oxford licence outside Department, in may in writing reprographics Rights scholarship, asserted publication by Oxford. registered Luttig, Press transmitted, in a of research, certain been permission in is in Ltd University Oxford University this or the Kingdom excellence Ritchie, permitted should and United University Oxford appropriate Enquiries be UK Thornes part prior expressly with the system, of worldwide. authors by 6DP, department Oxford the OX2 objective Elizabeth Nelson reserved. a a in © published without or agreed Press Tindale, This stored is publishing illustrations First All Press University Original Oxford, University’s education Text Street, or by any University under terms organization. scope Oxford the above University of Press, at above. not this circulate same Library this work condition Cataloguing on in in any any other form and you must acquirer Publication Data available 978-1-4085-2503-6 10 9 8 7 Printed in India by Multivista Global Pvt. 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Contents Introduction A5.5 1 Str ucture Key Section A1 A Principles States of of chemistry 2 matter Practice The A1.2 Evidence proper ties of solids par ticulate nature of matter 86 exam-style questions 88 Chemical for t he equations and reactions 89 2 A6.1 Writing and balancing chemical par ticulate equations t heor y of matter The t hree states Key concepts of matter Types of exam-style questions A2.1 and their Elements, separation compounds A2.2 Solutions, A2.3 Solubility 96 concepts 99 questions The mole concept 101 and mixtures colloids A7.1 The mole and mass 101 A7.2 The mole and gas 106 A7.3 The mole and concentration 16 volumes 19 of 22 solutions A2.4 Separating mixtures A2.5 Extraction of sugar Key sucrose A7.4 The mole and chemical formulae 1 1 1 A7.5 The mole and chemical reactions 1 13 Key concepts from cane 30 exam-style questions structure The str ucture A3.2 The electronic A3.3 of atoms Key configuration Acids, bases The periodic A4.1 A4.2 and table radioactivity reactions of acids 121 A8.2 Proper ties and reactions of bases 128 A8.3 Strengt h A8.4 Salts A8.5 Neutralisation A8.6 Volumetric questions 45 and periodicity 46 of elements in A4.4 Trends Group 46 II of t he A9 in Group VII of Period 55 3 of t he Structure concepts A5.2 Formation A5.3 Writing ionic A5.4 questions bonding Chemical bonding of ionic chemical bonds formulae compounds Formation metallic of 148 152 questions 154 and reactions reduction 156 – an Oxidation Oxidising Key 156 numbers and 159 reducing agents concepts Practice 164 170 exam-style questions 171 62 exam-style A5.1 Oxidation A9.3 60 and 145 analysis exam-style A9.2 periodic A10 A5 reactions introduction t he table in Practice 132 135 Oxidation–reduction A9.1 periodic table Key alkalis t he table in periodic and concepts Practice 51 Trends acids 40 table A4.3 of 44 Arrangement Trends 121 and 37 exam-style periodic salts Proper ties Key A4 and A8.1 of concepts Practice 120 34 atom Isotopes questions 34 A3.1 an exam-style 33 A8 Atomic 1 19 32 Practice A3 108 25 concepts Practice 100 16 and suspensions exam-style 15 A7 Mixtures reactions 14 Practice A2 chemical 9 Key Practice 89 4 A6.2 A1.3 80 2 A6 A1.1 and concepts covalent bonds Electrochemistry 173 64 A10.1 The 65 A10.2 Electrical 65 A10.3 Electrolysis 69 A10.4 Quantitative A10.5 Industrial of 72 and 76 electrochemical series conduction 173 176 179 electrolysis applications 188 of electrolysis 191 Key 195 concepts Practice exam-style questions 197 iii Contents A11 Rates of reaction A11.1 Measuring A11.2 Factors Key 198 rates of affecting reaction rates of reaction concepts Practice exam-style questions C18 Reactivity, 198 metals 202 C18.1 The reactivity 209 C18.2 The extraction 210 C18.3 Uses Energetics 212 A12.1 Energy A12.2 Calculating Key changes during energy reactions changes concepts Practice questions of B Organic chemistry Introduction to organic B13.1 Organic B13.2 Homologous 217 C19 chemistry – and Sources Alkanes: alkanes C questions and extraction Metals 224 B14.3 Alkenes: C Key alkenes in living systems Alcohols, corrosion of The impact metals H and alkanoic Alkanoic Esters: C20.2 Chemical proper ties questions acids C H and esters OH 2n acids: 239 of uses C20.5 Harmful and of C H COOH 2n Key 253 non-metals of 324 non-metals compounds 326 chemistr y 330 concepts 334 exam-style questions 336 255 Water 338 C21.1 The unique proper ties C21.2 The treatment of water 338 260 of water for pur poses 342 269 questions concepts 345 271 exam-style questions 346 Qualitative analysis polymers concepts C22.1 Identification of cations questions chemistry of C17.1 Physical C17.2 Chemical C22.2 Identification of anions 351 C22.3 Identification of gases 354 281 concepts Reactions of of metals 283 compounds concepts Practice 282 and metals metal exam-style 356 questions 358 periodic table 360 282 of proper ties exam-style 282 metals proper ties reactions 347 275 279 exam-style Inorganic 347 272 The iv uses 1 polymers Condensation Key 318 and 263 exam-style Characteristics C17.3 non-metals preparation effects t heir Green Practice C17 of 321 The Key – 316 and 272 Practice C non-metals gases C20.4 C20.6 C22 Section of 255 concepts Addition Key 315 1 Polymers B16.2 questions proper ties Laborator y Practice B16.1 31 1 313 316 Physical Key B16 environment exam-style C20.1 C20.3 251 RCOOR Practice living concepts domestic Key 309 on Non-metals 246 n B15.3 t he metals 2n n B15.2 of 2 exam-style Alcohols: the 237 C21 B15.1 and The Practice B15 308 309 Practice 239 concepts Practice questions C19.2 226 242 2n n 307 C19.1 of H n 302 236 hydrocarbons B14.2 299 alloys 230 exam-style B14.1 t heir 226 series concepts Hydrocarbons metals and exam-style reactions B14 of 294 226 compounds Practice metals environment C20 Key of concepts Practice Key B13 of metals systems Section uses 212 223 exam-style and 294 Key A12 extraction 288 291 questions 293 Index 361 Introduction To the Chemistr y you student for achieve experienced for you The to CSEC® your is best teachers master Chemistr y Principles t he a t he who course examination. have included It designed has been features to to help written make it by easier is divided Chemistry, into Section B, t hree sections; Organic Section Chemistry, A, and Section C, Inorganic Chemistry. Chapters 1–12 of t his book cover topics in Section Chapters 17–22 A, Chapters cover topics 13–16 in the The cover Section topics in Section B, and writing t he of Chemistr y CSEC® syllabus It for are Caribbean provides a for presented chapters based grasp on impor tant dened met, CSEC® has been driven by experienced each in t he t he in and is of of order topics concepts, each t hat coverage t he chapter units, and content is appropriate and students. complete material teaching, C. teacher Caribbean science educators to ensure t hat bot h t he requirements of relevant concepts. syllabus of comprehensive in key To of t he for t hen which t he t he CSEC® syllabus. you syllabus syllabus as a and To help teacher broken down develops one of t he to into wit h divided students manage several t hese t he into your clearly impor tant Key terms are highlighted t hroughout t he text to help you to ‘home concepts. in’ on t he key concepts. Impor tant denitions and which you Each laws chapter also facts to All must be able to quote are given in Key fact boxes. to includes Did you know? boxes which contain impor tant be able identify your interest, and Exam help you pass your examination. tip boxes You will also which contain valuable tips range in a large number of clear diagrams denitions quote are and given laws in which ‘Key fact’ t he students boxes for are expected students to and and t hen clearly learn. to A nd to stimulate t he of practical syllabus can activities be found which closely t hroughout relate t he to text. t hose You suggested can use t hese colour to help you develop a practical approach to your teaching and also to photographs to enliven and enrich your learning, and a wide assess range of different designed your use to help learning some practical of you using t hese (SBA) skills. Each chapter a activities. develop your ‘hands-on’ activities to These practical approach. assess your activities skills Your and have to teacher School-Based enhance may also Assessment Clear, The learning beginning of broken down objectives t he unit so into for t hat several each you unit can see clearly are dened clearly what you given are are units. at t he expected in t he unit. These learning objectives relate fully to t he to found Assessment (SBA) skills of your students. you help in all diagrams students and gain a colour better photographs understanding which of each are topic chapters. know?’ boxes wit h facts to stimulate t he student’s interest, and ‘Exam tip’ boxes containing valuable tips to prepare students for t heir examination appear t hroughout t he text. to Each learn School-Based explanator y designed ‘Did is t he been unit begins wit h a list of learning objectives for students to specic clearly see what t hey are expected to master in t he unit. These relate objectives given in t he syllabus. Each unit t hen ends wit h a selection fully to t he specic objectives in t he syllabus. of summary questions to test your comprehension of t he material covered in t he Revision unit. questions designed At t he to help end of each chapter you will nd a list of t he key is followed two to by revise a t he variety exam-style impor tant of content of multiple-choice questions to help you to t he chapter. questions apply t he are provided students to at t he consolidate end of t heir each unit knowledge which of t he are key concepts material you for This and usually knowledge found in t he unit. list you A list of key students concepts revise t he is key given at content of t he t he end of each chapter to help chapter. gained in t he chapter to answer t he different question types t hat you Multiple-choice, str uctured and extended response questions similar will encounter during your examination. The rst of t he exam-style to questions is a str uctured question requiring shor t answers and t hose chapter your CSEC® Examination you will be given spaces on t he on t he CSEC® Examination are included at t he end of each in for students to test t heir knowledge and understanding of question t he mater ial covered in t he chapter and hone t heir examination paper for your answers. The second is an extended response question skills. requiring a greater element of essay writing in your answers. The A marks allocated for t he different par ts of each question are complete 60-question multiple-choice test wit h answers is to clearly be found on t he CD. This will enable your students to test t heir given. knowledge and understanding of t he material covered in t he entire On t he CD you will nd a complete multiple-choice test composed of text. 60 questions to test your knowledge and understanding of material A Data Analysis section on t he CD provides information on answering taken from all sections of t he syllabus. If you work t hrough all t he test you t he Data Analysis question toget her wit h t hree practice questions for end of chapter will be well On t he questions and t he complete multiple-choice students prepared for your The CD you will also nd a section on Data Analysis you wit h det ails CD about t he Data Analysis question be required allocations you for infor mation School-Ba sed you of read study. t his to you answer to as practise. about what Assessment section before t he skills required in answering t his question. well as There is also required (SBA). you t hree is It is questions a section from you extremely embark on your wit h whic h in includes for a students section which to an gain provides detailed understanding of information what t hem over t heir two-year programme of is required study. mark gives ter ms impor t ant two-year also SBA you from will develop whic h about provides to examination. of t hat course Chemistr y Each activity SBA may for CSEC® practical may section be adopts activity be used provides used for t he a practical begins as a t he wit h basis for location different a SBA. in types approach suggestion The t he of table book of wherever indicating which t he possible. how t he follows t he activities which assessment. 1 Section A States of matter A1 Chemistry is the study of the structure and behaviour of Objectives By the be able end of this topic you matter. will Everything has ● give a ● give the denition four of main matter ideas both beings of us is made of matter. Matter explain theory why particulate of and of and volume. animals are all Air, water, matter. sand, Matter human exists in states. The three main states of matter are solid, matter scientists theory mass the various particulate ● around to: nd the liquid and gas. matter useful identify ● the three main states the relationship of A1.1 The particulate nature of matter matter explain ● Matter between temperature and the As motion of far bac k idea a t hat piece half Exam is important definitions Chemistry. provided boxes of that you key terms These for you know in the the ‘Key in how for par ticles. called example, many cuts a will t hought He Democr itus piece you t hat of have it asked gold, to ended t his developed in make at question: half and before some t hen you point, ‘f t he cut can t he you cut cut it it smallest in no and t hat building t hese bloc k s of smallest matter. bits of Today matter, scientists or particles , have added would to be bits t he Democr itus’ of matter. book. particulate particulate t heor y is theory theory ver y of useful of matter because matter states it t hat helps all us matter to is explain made bot h of par ticles. t he physical fact proper ties of matter and also t he differences between t he t hree states of matter. We Matter is anything occupies that has will Key that looking at t he t hree states of matter in detail in Unit A1.3. space. par ticulate matter is t heor y ● all made ● t he ● t here are spaces ● t here are forces par ticles are of of in matter has four main ideas: par ticles constant, random motion fact particulate states be mass The The philosopher of fact’ This ! Greek idea and now descr ibe matter and its proper ties using t he par ticulate t heor y are The and a Democr itus matter, basic the used definitions throughout Key matter, again, The ! BC consisted tip of It 460 matter of fur t her?’ ✔ as particles. all theory matter is of between t he par ticles matter made up of attraction between t he par ticles. of particles. matter of The is made par ticles par ticles Figure constant 1.1.1 par ticulate The particulate t heor y of are theory matter in there motion of can are between spaces par ticles matter be used to explain many physical phenomena t hat we obser ve in our ever yday lives. Examples of some of t hese are 2 given on t he next page. t explains: States of The ● and How is it can Why ● e.g. e.g. be t he States density rise in liquid freezer can smelt at t he get of of cause forms gas harder between it vibrate in in t he e.g. why matter pebbles change into a solid, e.g. when water side of you a room, t he e.g. when chicken is fr ying, kitchen. wit h an increase in temperature, drive. become crisper when soaked in water, liquids, e.g. cer tain in insects can ‘walk’ on water. Figure 1.1.2 Figure 1.1.3 Pebbles sink in water matter common in to increases as vegetables tension t hese Par ticles gases, of potatoes. of most and nature ice. Matter can exist in various forms or t he liquids t hroughout ot her a solids, particulate water. can it move pressure cer tain raw a a tyres Surface ● in smell car Why ● a in bubbles cooling placed Why ● The difference sink ● matter states t he t heir liquid are lies solid xed state t he solid, in t he state have energy have position states. The t hree states of matter t hat are liquid t he and medium and and least t hey amount are amounts gaseous states. arrangement packed of of of t hey difference par ticles. energy, closely energy, The t he t hey toget her. move simply Par ticles about slowly and t hey have small spaces between t hem. Par ticles in t he gaseous state have t he greatest spaces The energy par ticles in its t he faster of hanging a t hey will can is g reater t his directly This substance The move study change temperature. substance. t hey energy, You par ticles matter temperature t he of t hem. of and changing t he amount between one change of and detail to t he physical state t he kinetic rapidly greater related from increases t he about in energy t hey Unit to of par ticles large of anot her because energ y t he have 1.3. temperature state occurs kinetic in t he by increasing t he par ticles possess, t he move. state by changing temperature is a physical change. A physical change occurs when t he form of t he substance is changed wit hout changing its chemical t he same gaseous composition, chemical state, i.e. Summary 1 State 2 If a the water example, as water of main ideas potassium of the colour spreads of particulate theory of Explain 4 What are 5 What is as a liquid particulate manganate( VII ) purple 3 t he solid, i.e. state and ice, as has exactly water in t he three the the water vapour. water, evidence in states The of drinks illustrate the matter questions three crystal for par ticles is theory dropped throughout matter does this the of matter. into water. a beaker What observation of features provide for? why scientists the the three nd states relationship the of particulate theory of matter useful. matter? between temperature and the movement of particles? 3 Evidence for the particulate theory of matter A1.2 Objectives By the be able end of States this topic you Evidence for the particulate theory of of matter matter will n t he previous unit we mentioned t hat scientists nd t he par ticulate t heor y to: of matter ver y useful because it allows t hem to explain t he physical proper ties explain ● evidence which of supports the particulate matter. suppor t of ● t he t heir same ideas. time There t hough, are simple scientists practical have to provide activities evidence involving to d iffusion matter explain ● At theory the processes diffusion and describe experiments and osmosis and movement which we can perform to provide evidence for t he existence of of par ticles. osmosis which Diffusion demonstrate diffusion and osmosis explain ● sugar and We the to uses control preserve of salt and garden food have into pests items. a all freshener. t he smell t hrough of had baker y, All matter air are Key Diffusion particles t hese to is in concentration ! cosmetic of seems t he experience a smells travel as a one of being or are of t he air. of and a smell, into at a This d iffusion. motion lower aware climbing produced t hrough result constant to of shop a point move t hat in process Diffusion will whet her car t he of shop t he occurs from a it is walking contains or smell air but travelling because region an car, par ticles of higher concentration. fact is the movement from an area concentration to an concentration until of area they of higher of Investigating lower are the particulate theory of matter evenly Your teacher may use this activity to assess: distributed. ● observation, recording ● analysis interpretation. Y ou will be potassium and supplied with and a manganate( VII) reporting straw, a beaker containing distilled water and a crystal. Method 1 Place the bottom 2 Drop the moving 3 Very straw of the vertically crystal the in the beaker of water until it touches the beaker. of potassium manganate( VII) into the straw without straw. carefully remove the straw trying to disturb the water as little as possible. 4 ✔ Exam tip the 5 It is very important questions in distinguish and to must your or while what you If examinations the If what are would experiment, you are you purple colour immediately begins to spread throughout water. Leave the colour has beaker and spread observe conclusion can throughout after you draw all a the few days. water in Note the that beaker. the purple What about: asked then is a the spaces b the movement between the water particles you of the potassium manganate( VII) particles? and used being asked conclude then the would experiment you to observations you how answering observations, describe performed. when between conclusions. give see tests Observe to state from must the The potassium illustrated in manganate(VII) Figures 1.2.1 and cr ystal 1.2.2 are t he bot h water composed in of t he experiment minute particles. give The par ticles in t he cr ystal are packed closely toget her and t hose in t he water what you can deduce from the have observations. A deduction is ver y minute by using data from the small spaces between t hem. When t he cr ystal is in t he water, t he made cr ystal par ticles slowly separate from each ot her and diffuse into t he experiment spaces between t he water par ticles. This continues until all t he par ticles have to arrive at a conclusion. separated 4 from t he cr ystal and have diffused between t he water par ticles. States of matter Evidence for the particulate theory of matter straw beaker of water the potassium water purple becomes colour a throughout manganate(VII) crystal The cr ystal solution Figure 1.2.1 Potassium crystal being placed gradually where diffusion is in t he t he manganate(v II) and colour an solvent. aqueous Figure solution 1.2.3 is illustrates water particles random spaces with moving crystal small from between a while the throughout i.e. process particles each diffuse purple the water a of other into the the separate and spaces water particles particles packed manganate(VII) After formed, t he between crystal potassium 1.2.2 spreads experiment. water at Figure water d issolves water occurring in closely together crystal before dissolving after dissolving Investigating Your teacher diffusion may use in this observation, recording ● analysis interpretation. Y our and teacher will perform and the 1.2.3 Explanation of diffusion gases activity ● Figure to assess: reporting following experiment: Method 1 Place 2 Soak a Seal 4 Allow 5 Use During them the time your t he for called t he as off of the of the a at gas to air The what in of the t he and 1.2.4 and glass stands. ammonia solution and concentrated hydrochloric acid and tube. t he tube to vapours during and ammonia react retort stoppers. happened gas ammonium glass chloride Figures The two concentrated hydrogen gas. in between rubber ammonia collide in end with and chlor ide t he wool explain called length each illustrated t hey chlor ide . in tube ammonia t hrough meet, ammonium 1 m cotton glass hydrogen diffuse par ticles glass pieces experiment gives par ticles least observations off gas at simultaneously ends solution a tube separate place 3 glass the 1.2.5, diffuse. and t he a each white forms a any changes. ammonia acid hydrogen towards Observe experiment. hydrochloric form chloride to ot her. solid ring gives chloride When known inside t he tube. 5 Evidence for the particulate cotton theory wool in wool matter soaked hydrochloric cotton of in acid a chemical involved, (g) equation NH The glass Figure 1.2.4 chloride (g) a gas gas Ammonia diffuse and (g) and and (s) (s) solid: a indicate t he each wool soaked hydrochloric cotton wool other in acid faster state of t he chemicals This of soaked ● chloride NH t he forms because chloride experiment ammonium chloride l(s) 4 acid t hrough chloride Hl(g) ammonium hydrogen hydrogen towards hydrogen hydrochloric tube cotton t he par ticles. air t han Therefore, t he provides closer t he to ammonia t he hydrogen following t he cotton par ticles are ammonia chloride wool soaked lighter t han par ticles move in t he much par ticles. evidence for t he par ticulate t heor y matter: Par ticles are par ticles must able to move – t he ammonia and hydrogen chloride ammonia ● There are between t hem white where indicating 3 in matter ammonia ammonia of We can represent t he reaction between t he ammonia and hydrogen chloride as soaked States Figure 1.2.5 ring to have spaces t he air, move moved between par ticles ammonia between towards and each each – ot her t here hydrogen to must form have chloride t he been white ring. spaces par ticles to allow ot her. forms After a while a white ring Osmosis forms inside the glass tube Osmosis water region ! Key is wit h of water solution the from movement a region molecules, or a case of t hrough lot differentially substances is molecules special of water a diffusion, which d ifferenti ally molecules to a involves permeable region wit h t he movement membrane fewer water of from a molecules. fact A Osmosis a molecules pure e.g. water, of with a to pass t hrough membrane but not is a ot hers. membrane You may also t hat nd allows t he some membrane water a lot being called membrane dilute a to permeable a semi-permeable t hat surrounds or selectively biological cells is permeable membrane. differentially The cell permeable. region A differentially permeable membrane contains minute pores. Water molecules with fewer water molecules, e.g. a are concentrated solution, through able ot her differentially permeable to pass t hrough t hese pores. However, t he par ticles of many a substances, which may be dissolved in t he water, are unable to pass membrane. t hrough. When concentrations, two are t he water molecules t he more dilute molecules, solutions, e.g. separated by will diffuse solution however, do to not t he sucrose a differentially t hrough more move solutions, t he t hey have permeable pores in concentrated because which are t he membrane, membrane solution. unable different to The pass from sucrose t hrough t he pores in t he membrane. The volume of t he more dilute solution decreases and t he volume of t he more differentially concentrated permeable solution increases. membrane sucrose cannot molecule pass through the differentially permeable membrane water molecule diffuses the through differentially permeable membrane dilute sucrose concentrated solution Figure 1.2.6 Theoretical explanation net of 6 osmosis sucrose solution movement water of molecules States of matter Evidence Investigating Your teacher may ● manipulation ● analysis Y ou will lled be with osmosis and use and in this green activity for the particulate theory of matter paw-paw to assess: measurement interpretation. supplied distilled with water a piece and of one green beaker paw-paw lled with (the experiment concentrated may sodium be done chloride with potato or yam), one beaker solution. Method 1 Cut 2 Measure 3 Place 4 Allow 5 Remove 6 Measure 7 Explain the piece and three containing the distilled 8 the Explain chloride in to length into remain from record the in solution of which strips the for Feel placed equal containing chloride each of length. strip. solutions beakers. the distilled water and place the other three strips into the beaker solution. one hour. strips and take note of the texture of each strip. strip. in water distilled water molecules become move, from more the rigid and paw-paw have into increased the distilled in length water or from the paw-paw). strips (consider or each sodium the six beaker strips paw-paw length into of the length paw-paw into the in the the direction water why the concentrated the the paw-paw strips strips and decrease the strips why green record of the (consider of from the the placed in direction sodium concentrated in which chloride the solution sodium water into chloride molecules the solution move, become from the oppy and softer paw-paw into the and sodium paw-paw). distilled water concentrated beaker sodium chloride paw-paw solution Figure 1.2.7 Paw-paw strips in strips concentrated distilled paw-paw increase Figure the 1.2.8 After concentrated a chloride water strips in while sodium size the strips chloride in water solution increase decrease sodium chloride strips in t he experiment of t he illustrated paw-paw cells act in as Figures length 1.2.7 differentially and those in Did and 1.2.8, permeable t he can pass t hrough t he cell membranes, eit her into or out of t he works cells as If sweat a the concentration) than the paw-paw cells, therefore water moves in takes place into the cells out sodium chloride osmosis, have a higher solution, resulting in t he water t herefore paw-paw content water strip t han moves out becoming t he of same in lowers water cells the you water. paw-paw in does This Distilled water has a higher water content (or lower sodium chloride The it the way in paw- cells: by osmosis, resulting in the paw-paw strip becoming longer and more rigid. ● know? cell paw. ● you membranes. your Water solution length Osmosis membranes concentrated size ? During and sodium decrease in water solution paw-paw in distilled of your your blood and lot and starts cells. you For lose amount of osmosis to this pull water reason it is concentrated t he shor ter cells and very important on hot to drink lots of water by a day or when you exercise. sof ter. 7 Evidence for the particulate theory of matter States Practical We use garden t he pests and many t han of and snails, t hemselves being of moist to to dehydrate snails in our and dissolves. is in food various ways. These include controlling items. herbivores, The ot her by die. skin water We using Figure 1.2.9 sodium serious of t hese This garden pests means evaporating make use sodium Snails deliquescent, When are animals. prevent and gardens chloride osmosis plants. most t hem Sodium of pests precious skin matter osmosis preser ving garden our t he of principles Controlling Slugs uses of of are serious which chloride lot to garden pests sprinkled it bodies absorbs on slugs ravage permeable need control salt). t hat more t heir facts which t hey (table means is a t hat from t hese chloride is pests to keep causing slugs water and and readily snails, it absorbs some of t he moisture surrounding t heir bodies and dissolves forming a concentrated solution. This causes water inside t heir bodies to move out and into t he solution by osmosis. f t he slugs and snails lose more water t han t heir bodies Preserving can food ot h sodium sh, fr uits cr ystallised t he ● same tolerate, to and sugar vegetables. fr uits, way die from dehydration. items chloride and t hey guava We jelly preser ve are used are and all glacé to preser ve familiar cherries. food wit h ot h items, salt salt sh, and e.g. meat, salt pork, sugar work in foods: They withdraw water from the cells of the food items by osmosis. This makes the water unavailable for the chemical reactions in cells which cause decay. Without these reactions occurring, the food items do not decay. ● They also decay, wit hdraw e.g. growing bacteria and water and causing from fungi. t he food t he This microorganisms prevents items to (a) 8 t hese t hat bring organisms about from decay. (b) Figure 1.2.10 (a) Salt sh and (b) crystallised fruits are examples of preserved food items States of matter The Summary 1 For each of particulate a If a b If the experiments theory the bottles of 2 State of 3 Why 4 When 30 do a we 5.0 cm Explain its of how to control to preserve You have and gas. The ammonia bottles. long raw potato was is case was have theory chloride a to of the placed to a of the evidence: beaker of each other, and a white diffusion. diffusion? in water to and left 5.5 cm. explain for Use your this. used: garden sh. three states already t hree t hat st ates proper ties. obser ved or subst ance. of of matter matter Objectives matter exists have in t hree st ates: noticeable solid, differences liquid in By the be able Physic al measured Shape, properties wit hout volume, c hanging density, are c haracter istics t he c hemical compressibility, t hat of this and boiling physical point are proper ties all of examples t he t hree of physical st ates can be you will explain the difference be of between the matter terms three states of a in of energy and particles, and melting proper ties. explained of The forces different topic to: t heir can composition solubility, end arrangement point matter concentrated to increased matter into osmosis of feature(s) provides ● physical of water. and next between special chip found particulate in a the dropped placed differences is is solution the two state experiment throughout and and length slugs lear nt spreads osmosis sodium b The that below, the opened between the a A1.3 are which manganate(v II) colour acid say minutes, described for potassium similarities knowledge 5 matter concentrated forms any of purple hydrochloric cloud states questions crystal water, three by of attraction between t he particles par ticulate t heor y of matter. ● Table 1.3.1 and t he We can summarises arrangement t he of physical par ticles in proper ties t he t hree of t he t hree states of matter account for properties states. matter in the of terms arrangement use t he arrangement of par ticles in t he t hree states of matter t he physical proper ties of t he different three of of states of energy and particles, and to forces explain physical the of attraction between states: particles ● Solids have a xed shape because t heir to out par ticles are arranged in a regular ● way ● and Solids t heir any t hey have a are xed par ticles closer unable are volume packed move and ver y are of ver y closely t heir xed difcult toget her to explain the state terms changes compress and cannot be pushed in arrangement because ● understand of ow ● Liquids can because t heir par ticles are able to move past each energy and particles boiling, condensation, Liquids of melting, evaporation, toget her. ● of positions. freezing and ot her. sublimation be compressed slightly because t heir par ticles have small ● spaces between t hem enabling t hem to be pushed closer understand heating ● Gases t heir take t he par ticles attraction shape move between and volume freely t hem, and of t he rapidly. t herefore container They t hey have spread t hey only out to and interpret toget her. are in weak ll cooling curves. because forces any and of available space. ● Gases are between easy to t hem, compress t herefore because t hey can t heir be par ticles pushed have closer large spaces toget her. 9 The three states of matter States T able 1.3.1 The properties Property Shape of the three states Solid and volume of Solids have and a a fixed Gas Liquids fixed a volume. fixed they do not shape, have volume. a the container of and always Gases fixed definite shape occupy have but Liquids the is the part that the A take gas will space of is they is, horizontal. of Most solids have a high density. Compressibility Solids to The density usually are very difficult compress. density of Liquids can is of the The particles particles packed together, regular Forces of between attraction the The particles in. volume volume in a strong and attraction have between of the and movement are very of Arrangement in small kinetic particles fixed not those Particles particles a solid have amounts energy. vibrate position. of gas a the of shape the entire in. a low are easy to pressure particles and of the spaces as attraction strong Particles in a kinetic The as large weak attraction the spaces them. particles very are arranged have between particles between have forces of between them. solid. liquid have Particles energy particles particles about The small a The are them. of than their shape compress. randomly particles more The in Gases very arranged forces between them. Energy have The of it The is have the density. be particles between forces Gases up container solids. when randomly usually is the it a volume. take therefore, and have or applied. The pattern. particles very are closely liquids than compressed slightly Arrangement of lower not the placed and surface do shape container Density matter matter Liquid shape of in a large solid. energy. move move slowly. in a gas amounts The about of have kinetic particles freely and rapidly. of particles Changing Did ? you Matter A SCUBA fact to divers that compress. SCUBA 2250 T o of use very of average tank holds this, milk think cartons be of consequently sized order about we of can change changed state is, from one t herefore, state air. a need changes change change to changing milk hold to a remove its of water heat are t he into chemical state in kinetic ice we of diving milk, tank therefore, holds the a anot her by energy. to a by change in is a Figure of put hanging composition summarised energy need heating in or cooling. temperature t he t he t he par ticles. water state physical of For and into a example, t he freezer, substance change. The in i.e. wit hout different 1.3.1. one add litre to caused the easy compressed understand Most are An diving litres carton. make gases state know? heat SCUBA same volume evaporates/ of air as 2250 empty milk cartons! melts boils LIQUID SOLID freezes GAS condenses sublimates sublimates Figure of 1.3.1 Summary of the changes remove state We will changes 10 now in look state in in more Figure detail 1.3.1. at heat each of t he processes t hat cause t he States of matter The three states of matter Melting When more a solid is heated, vigorously. t he par ticles Eventually t he gain kinetic par ticles are energy able to and begin overcome to vibrate t he Key ! strong Melting forces of attraction between t hem and t hey move more freely and fact point is the constant fur t her temperature at which a solid apar t forming a liquid, i.e. t he solid melts. The temperature remains constant changes into a liquid. while t he solid is melting because all t he heat energy being supplied is used to overcome t he temperature forces is of known attraction as t he between melting t he solid par ticles. This constant point Evaporation When Some a liquid of t he is heated, par ticles t he near par ticles t he gain surface of kinetic t he energy liquid and move faster. have enough kinetic t hem and able Did ? When energy to overcome t he forces of attraction between are t he liquid par ticles and t hat become leave t he a vapour. liquid take These par ticles lots energy of are wit h said to t hem, of t he and the evaporates water from in our evaporate. leading to it takes energy with it causing cooler. If we a our cooling sweat sweat skin, The we know? to the leave you bodies to feel put liquid. alcohol even on faster our skin, than it evaporates water because Boiling it When a liquid where it star ts to kinetic energy wit hin t he while t he is boil. and liquid liquid overcome heated t he temperature is At at boiling of known temperature t his star ted and forces is its point to move its because t he liquid fast surface. attraction as t he t he eventually heat between boiling par ticles enough The reaches to have change temperature energy t he being liquid a cer tain gained into a enough gas remains supplied point has a water. even lower This differs from evaporation in oiling place ● occurs at any oiling place a specic our skin when we than feel sweat. bot h is par ticles.This used to constant Key ! fact point two point temperature ways. temperature, whereas evaporation can is at into a the constant which a liquid gas. take temperature. takes only at than point constant changes ● makes colder Boiling oiling boiling at place t he t hroughout surface of t he t he liquid, whereas evaporation takes ✔ liquid. If Exam you are tip asked to give a difference Condensation between When t he temperature of a gas is lowered, t he par ticles lose kinetic two things, it is essential energy that you describe the of using specific and begin to move more slowly. The forces of attraction between t he par ticles property become liquid, stronger i.e. t he causing liquid t he par ticles to move closer toget her forming a condenses. ‘whereas’ describe each, to link just the the two. word Do not one. Freezing When t he temperature of a liquid is lowered, t he par ticles lose kinetic energy and begin to move more slowly. The forces of attraction between t he par ticles become stronger causing t he par ticles to move even closer toget her ! Key forming Freezing a solid, i.e. t he liquid freezes. The temperature at which t his occurs fact is point temperature t he freezing freezing point, e.g. at the which constant a liquid point changes The is called point water of has a a pure substance melting point has and a t he same freezing value point of as t he into a solid. melting 0 °. Sublimation When t he forces of attraction between t he par ticles in a solid are weak, t he addition of a small amount of heat can cause t he solid to change directly into a gas, wit hout passing t hrough t he liquid state. f t he gas is t hen cooled it will change directly back to t he solid a a to a to gas or gas solid. solid it When is said a to substance changes directly from a sublime 11 The three states of matter States Examples Figure 1.3.2 Solid air fresheners substances (known balls camphor balls releasing t heir or sublime of dioxide as ‘dr y which ice’), are undergo sublimation ammonium made of fragrances chloride and napht halene. into t he are of iodine, carbon napht halene. Solid air matter Mot h fresheners also air. sublime (a) cotton wool Observing est sublimation in iodine tube Your may observation, ● iodine teacher use this recording activity and to assess: reporting. crystals iodine vapour Y ou will cotton be supplied wool and a with pair a of test tube, a small iodine crystal, a piece of tongs. Method 1 Place the 2 iodine mouth Hold the Bunsen the the tube of the test in crystal test tube the into the test tube and place the cotton wool into tube. with ame tongs of a at a Bunsen 45° angle burner and until all heat the the bottom iodine of crystal has burner sublimed. (b) iodine crystals 3 Observe what 4 Remove the 5 Observe what During the heated, it happens tube from the happens experiment sublimes and as the iodine ame as the tube illustrated forms and in purple is heated. let is it cool. cooling. Figure iodine 1.3.3, vapour as the which iodine diffuses cr ystal up the is test tube. The top of the tube is much cooler and when the vapour reaches the top, Figure 1.3.3 heated and Iodine (b) sublimes when cooled (a) when it sublimes back Heating f t he on a The state graph water and a solid, forming cooling temperature changes is to cur ve a against shown increases. in shows of a pure liquid time, Figure t hat However, temperature 12 to a ring of iodine cr ystals around the inside of the tube. remains curves solid and a is t hen heating measured to a gas, curve is at inter vals and t he as it is heated temperature obtained. The is heating and plotted cur ve for 1.3.4. as t he heating graph constant occurs, has for a t he two temperature horizontal period of time of t he sections even substance where t hough t he heating States of matter continues. state is water These where melting is of 0 °. temperature t he happen melting point t his The occurs t here and t he substance The second remains substance when has e.g. t he at for t he a change of temperature until change constant boiled, is all of t he state is t his where point is The remains substance boiling water state. of has change constant melted, boiling t he rst occurs substance at three states of matter of t he e.g. for and t he until all 100 °. 140 )C°( 120 gas and liquid boiling 100 point erutarepme T 80 60 liquid 40 20 solid and liquid melting 0 20 solid point (ice) 40 Time Figure 1.3.4 The as heating heat is curve added for water f t he temperature of a gas is measured at inter vals as it is cooled and changes state to a liquid and t hen to a solid, and t he temperature is plotted on a graph against shown time, in a cooling Figure curve is obtained. The cooling cur ve for water is 1.3.5. 140 gas (steam) )C°( 120 gas and liquid boiling 100 point erutarepme T 80 liquid 60 40 20 melting 0 point solid 20 40 Time Like Figure heating 1.3.5 cur ves, The as heat cooling cooling is removed curve cur ves for have water two horizontal sections. The rst is where t he state changes from gas to liquid and t he second is where it changes from liquid to solid. Summary 1 Complete what is the of Name state Gas Solid 3 4 below. The rst row is completed as an example of given to change state Melting Energy added change state or removed to Added gas liquid to to What liquid to to Liquid 2 of to Liquid table required. Change Solid questions solid gas are a Explain b Give Explain the main what three what differences occurs during examples of a curve heating between evaporation and boiling? sublimation. solids which undergo sublimation. shows. 13 The three states of matter States Key matter concepts ● Matter ● The is dened proper ties matter, which matter states made – t he – t here are spaces – t here are forces par ticles Matter ● The exists are in difference energy of t he energy anyt hing matter all The is as of – ● ● of constant, mass states: between random t he attraction t hree has explained and by occupies t he space. particulate theory of par ticles between of t hat be t hat: of in can t he motion par ticles between solid, t hree t he liquid states is par ticles. and gas due to t he arrangement and par ticles. of t he par ticles is directly related to t he temperature of t he par ticles. ● Diffusion t heor y ● of Diffusion and osmosis provide evidence to suppor t t he par ticulate matter. is t he concentration movement to an area of of par ticles lower from an area concentration of until higher t hey are evenly distributed. ● Osmosis lot of wit h is t he water fewer water differentially ● The ● The and energy account for of of e.g. a molecules, permeable principles chloride movement molecules, molecules solution e.g. are food and arrangement t he physical can change from solid ● Matter can change from gas ● The names given are to t he melting, of to region water, solution, of processes to wit h to a a region t hrough to pests chloride solids, t hree wit h and a liquids and gases states. wit h t he addition solid wit h t he removal cause boiling, sodium sugar. gas which evaporation, in t he liquid liquid garden sodium par ticles to to control wit h proper ties Matter anot her a pure concentrated used items ● to a from or membrane. osmosis preser ve water dilute t he change of of from condensation, heat. heat. one state freezing and sublimation. ● Melting point ● wit h weak When t he changes against ● When against 14 t he of from a time, in attraction of solid heating from a temperatures known as t he melting respectively. at any gas state t hrough temperature state specic occurs change temperature state t he liquid passing forces time, changes a at point, temperature and leads to t he liquid. is wit hout occur boiling of t he Sublimation versa, ● of boiling t he Evaporation cooling ● and and of a pure is liquid is t heir substance to from state. gas, a t solid to occurs a in gas, or vice compounds molecules. is and measured t he as it is temperature heated is and plotted obtained. pure liquid curve straight between liquid curve to cooling a to t he substance to solid, is and obtained. measured t he as it is temperature cooled is and plotted States of matter Practice i) Practice exam-style State what t he level funnel Which is of made t he of following provide(s) evidence t hat af ter t he expect 30 sucrose to have solution happened in t he minutes. Explain t he reason for your (4 iii) b Decomposition Diffusion , Name A second t he process and occurring in t he and and D only substance t hrough t he X as liquid it t he was state temperature heated to t he from (1 mark) of an t he gaseous solid state. are plotted in Figure 2. Use t he Her information in only t he C measured marks) apparatus. results student unknown state mark) obser vations. Osmosis A t histle (1 matter par ticles? B of questions ii) 1 would questions questions to Multiple-choice you exam-style Figure to answer t he following questions. only 80 2 Par ticles in a solid: 70 are packed B are capable C have large spaces between D have weak forces of A t he differ of random from par ticles toget her in t hem attraction gases a movement in liquid between t hem. t hat: can move more freely 60 50 erutarepme T Liquids closely )C°( 3 A t han 40 30 20 10 t hose in a gas 0 B t he par ticles in a gas are closer toget her t han t hose in 10 a liquid 20 C t he par ticles t han D t he t hose in in par ticles a a in liquid possess more kinetic energy 0 t hem a gas t han have t hose weaker in a The forces of conversion of Figure a gas to a 2 liquid is described during Graph 12 14 showing heating 16 18 20 22 24 26 (min) the against temperature of substance time as: What Over state what is X in at 68 °? temperature (1 range does X exist C condensation D boiling. iii) From take Which show of t he following lists consist of substances iv) which sublimation? A Aluminium B Ammonium chloride, iodine, C Ammonium chloride, napht halene, D Aluminium chloride, sulfate, iodine, carbon carbon dioxide, t he (2 time until it X has Describe, in par ticles, what star ts to melt, completely terms is of how long melted? a energy and happening to v) monoxide. Using draw iodine. X napht halene. o to represent a par ticle par ticles as t hey of n order to a investigate student set t he up par ticulate t he nature apparatus of shown (2 1 below and lef t it for 30 glass Extended a response Describe thistle b funnel Water of T WO can level of sucrose marks 15% sucrose sucrose exist differences t hem solution y reference for EAH i) 35% of steam to investigate the a of evidence solid, t heir and to suppor t t he a (4 liquid t hese t heir and t hree par ticles, par ticles, t he can permeable membrane ii) a cr ystal shape. used of matter. kinetic a gas. states forces in of marks) Explain terms attraction energy. explain clearly (6 t he marks) reason following: be conver ted to liquid water by solution beaker differentially as of between to reducing Apparatus pieces solution c particulate its of temperature potassium chloride (3 has a ver y marks) denite (2 marks) nature Total of 15 question t heor y arrangement between original 1 in marks) minutes. t he Figure it X, appear 15 °. par ticulate as marks) in 7 Figure of X substance would it mark) behaviour substance (3 T WELE at does question matter, glass t he marks) (1 melts. dioxide. carbon state? Total Structured 6 mark) in evaporation liquid 5 10 melting ii) B 8 attraction i) A 6 liquid. X 4 4 Time between 2 gas 15 marks matter 15 A2 Mixtures Elements, and compounds their and separation mixtures form a part of our Objectives By the be able ● end of this topic you everyday will distinguish between substances and pure foil we explain an When we wrap our food in aluminium the difference element, a are our food using we are an element. eating a When we compound. place When salt we on drink a mixtures cold ● lives. to: soda we are drinking a mixture. It may be useful to between compound and a know how to separate some of these mixtures into their mixture component ● give examples compounds ● explain a the of and mixtures difference homogeneous heterogeneous parts. An example of this is the purification elements, and of drinking water. between a mixture. A2.1 Elements, compounds and mixtures Matter can be classied into two main groups: pure substances and mixtures. Pure substances ● They have ● Their ● The a xed, proper ties component physical Mixtures ● They ● Their t he following constant are xed par ts of characteristics. composition. and a general constant. pure substance cannot be separated by means. have have a t he following variable proper ties individual ● have are general characteristics. composition. variable since t heir components retain t heir own, proper ties. The component parts of mixtures can be separated by physical means. Pure substances Mixtures can be heterogeneous breakdown of can be fur t her fur t her mixtures . t hese classied into classied into The diagram tree elements and homogeneous in Figure compounds. mixtures 2.1.1 shows and t he groups. matter pure mixtures substances elements Pure A 2.1.1 homogeneous heterogeneous mixtures mixtures Classication of matter substances pure substance following 16 Figure compounds xed is composed of only one type of material proper ties: ● a shar ply dened, constant melting ● a shar ply dened, constant boiling ● a constant density. point point or freezing point and has t he Mixtures and their separation Elements, compounds and mixtures To determine if a substance is pure or not, its melting point or boiling point is determined. Any impurities in a pure substance will usually lower its melting Did ? point and usually cause raise it t he to melt boiling over point a of wider a pure temperature substance range. and mpurities cause it to boil over In a many ice wider temperature will produce only one (Unit single 2.4) spot may on a also be used. f a chromatogram. substance f it is not is pure pure it is it t han one will The and Your ● may observation, Y our boiling points of pure water and teacher the the snow the and roads in the (sodium chloride) roads melt dissolves the use this perform activity and the to its to in surface the freezing the of the film the point temperature ice starts freezing 18 °C, saturated recording will on about sodium solution teacher on lowers lower the salt salt water below chloride on ice, spot. this Comparing where problem rock spread ice. of more a range. chromatography produce know? countries pose winter, Paper you will to the melt. point the sodium of to ice Salt of can water freezing chloride to point of solution. assess: reporting. following demonstration. Method 3 1 Place 2 cm 2 Place an open end 3 Place 4 Half a of distilled inverted facing water closed in end a test tube. capillary tube into the test tube with the downwards. thermometer in the tube. 3 ll a 250 cm assembly is 5 Heat the ensure of in beneath the the oil bubbles indicates bath surface beaker that beaker is emerges that the so of over even. from water a and the the place surface Bunsen test of burner, heating capillary the the above the test water tube in the test tube oil. Continue the in oil that level gently heating with tube. tube is stirring until This a constantly rapid stream to stream of bubbles boiling. thermometer 6 Remove last 7 the bubble heat emerges the oil Record the temperature Repeat the 9 This and is the the reading boiling using the capillary repeat the procedure observe a stream tube, cooling after sodium of record process each point of trial the chloride When the more. average three capillary tube tube oil in place distilled water sodium chloride or of conclusion sodium can chloride you draw about the boiling points of pure solution heat water solution? Figure An element anyt hing is t he simpler chemical means’ simplest by form ordinar y to of matter. chemical exclude nuclear or t cannot physical reactions. be broken means. The We down say smallest 2.1.2 of t hat has t he same proper ties as t he element is an Determining the boiling liquid fact element is a pure substance into that cannot be broken any simpler substances down into ‘ordinar y par ticle atom. by any in ordinary element a Key ! Elements an rod beaker point An end stirring test all water. solution closed temperature. twice and distilled bubbles. water. What and the bath and from Reheat temperatures. 8 source chemical or physical Each means. element is composed of only one kind of atom. 17 Elements, compounds and mixtures Mixtures Examples copper of elements (Cu), which are is iron (Fe), composed which of is only and composed copper of atoms their only and separation iron atoms, oxygen (O ), 2 which is composed of only oxygen atoms. Compounds Key ! fact Compounds are A compound is a pure contains types of element together or and properties more which chemically proportions their two in in of more than chemically, one t hey are kind of always atom. These present in atoms t he by mass and t hey cannot be separated by physical same means. A different are bonded a compound elements fixed such have composed toget her substance propor tions that are combined way that can t hat combined, be t he e.g. represented compound t he chemical by is chemical a made up formula of of formula , and water t he is H which ratio in indicates which t hey t he have O. 2 changed. Examples oxygen of in compounds a ratio of are 2 : 1, water, sodium which chloride is composed (NaCl), of which sodium and chlorine in a ratio of 1 : 1 and met hane (CH hydrogen is and composed of ), which is composed 4 of carbon and hydrogen in a ratio of 1 : 4. The proper ties of a compound are xed and are different from t he proper ties of t he individual hydrogen is a and elements oxygen are t hat bot h for m gases at t he room compound. temperature, For example, however, water liquid. Mixtures Key ! fact Mixtures A mixture consists substances in two (elements compounds) together of more and/or physically varying or means. combined are combined, will be Some component of t he investigating of two t heir physical in or more substances components Unit met hods 2.4, are can for which be separating ltration, are not separated chemically by mixtures, evaporation, physical which we cr ystallisation, proportions. distillation, Each composed t herefore retains its fractional distillation and chromatography. n a mixture t he own component par ts are not in a xed ratio and t hey retain t heir own, individual independent properties and has physical undergone with any no other chemical proper ties. reaction substance in the Homogeneous mixtures mixture. A homogeneous are uniform mixture t hroughout distinguished from each is one t he in which mixture. ot her. A t he The solution is a proper ties and component composition par ts homogeneous cannot be mixture. Examples of homogeneous mixtures are air, salt dissolved in water and metal alloys such as brass, Heterogeneous a mixture which t he component can be eye. Suspensions copper and zinc. mixtures A heterogeneous mixture in of distinguished is a non-uniform mixture, for example, a mixture par ts from are each in different ot her, states. alt hough not The component always wit h t he par ts naked (a) Examples muddy Figure heterogeneous are heterogeneous mixtures are salt mixtures. and sand, mayonnaise, and water. The diagrams can be in Figure distinguished ● f t here is ● f t here are 2.1.3 (a) Gold is an only 2.1.4 by one show looking kind of at how t he atom, elements, par ticles t hen it is compounds t hat an make up and t he mixtures substance. an element, (b) copper sulfate is water is of an a compound example of a or more kinds of atoms element. joined toget her in t he same ratio, and (c) it is a compound. an ● example two example t hen of 18 colloids (c) (b) of and f t here is a combination muddy mixture. t hen it is a mixture. of two or more elements and/or compounds, Mixtures and their separation Solutions, suspensions and colloids n Figure 2.1.4, elements are represented in diagrams D, E and H, compounds are represented diagrams A, atoms not are F in diagrams and . is arranged a B, and mixture regularly A C G and and not among t he B a mixtures compound green Summary 1 Copper is 2 What is a 3 What are 4 What is A2.2 example, described blue D the E diagrams shown I the F atoms Figure of 2.1.4 as an element. What does this tell us about are the differences difference suspensions bot h Elements, compounds and mixtures copper? water is a between between a a pure substance homogeneous suspensions and colloids solution, form muddy mixture and par t water of is a and mixture? and a heterogeneous colloids our Objectives ever yday suspension mixture? lives. For milk and and By the be able ● fog different compound? the sea t he in questions Solutions, Solutions, because C H represented atoms. In G are end of this topic you will to: explain the terms solvent, colloids. solute ● and identify solution different types of Solutions solutions A solution is known is as a homogeneous t he solvent and mixture. t he minor The major component component is known of as a solution t he solute. Some solutions may contain more t han one solute, e.g. sea water. The solute and a solvent liquid, salt is can t he t he be gases, liquid solute is and liquids always water is or solids. t he solvent, t he solvent. When a gas e.g. a mixture in or a solid of dissolves salt ● in a ● in 2.2.1 gives examples of various between suspension describe some water, solution, a T able 2.2.1 Examples of different types Solvent Example Components solid liquid sea sodium of liquid soda solid solid brass water carbon of chloride the in give in water examples dioxide in Key liquid white gas gas air rum a a of and solutions, colloids. fact water solution is a homogeneous copper mixture liquid of and solution A zinc the properties solutions. ! gas solution, solutions Solute water a colloid colloid types of of a suspension suspensions and distinguishing ● Table distinguish ethanol in water components, usually oxygen, water vapour, consisting argon and carbon dioxide in a one of of two or which more is liquid. nitrogen 19 Solutions, suspensions and colloids Mixtures A saturated at a solution par ticular study is one t hat temperature saturated solutions in in contains t he more as much presence detail in of and solute as can undissolved Unit their separation be dissolved solute. You will 2.3. Suspensions A suspension cont aining (a) Figure 2.2.1 (a) Soda water brass are examples of par ticles mixture whic h can Key is a par ticles The be eye. f in a lef t are undisturbed, suspension components separated by of eventually a suspension ltration. Examples of suspensions Dust air which minute, but is are dispersed in in a suspension of a solid visible, in particles naked heterogeneous ● in t he fact suspension mixture to solutions settle. A heterogeneous and t he (b) ! a (b) visible is minute a gas. another substance, usually a liquid. Figure 2.2.2 Muddy water is an Powdered chalk in water is an example ● example of a suspension of a suspension of a solid in a liquid. Muddy ● water is anot her example of a solid suspended in a liquid. Colloids A colloid is A size The in a par ticles colloid one is in a The those larger the are particles of dispersed in substance, dispersed than than of usually particles a are a you of a ● Smoke ● Fog also but solution. 10 1 Solution very size in of mixture in air Do out the by 20 proper ties of a a a microscope, colloid are t hat are suspension. and if lef t and t hose of a inter mediate suspension. is a colloid of a solid in a gas, also known as a solid aerosol. and sprays liquid in air are colloids of a liquid dispersed in a gas, aerosols. mayonnaise as Gelatine as are colloids of a liquid dispersed in a liquid, also emulsions. and jelly are colloids of a solid dispersed in a liquid, also known gels. comparison colloids is 2.2.2 of given t he in distinguishing Table proper ties of solutions, suspensions and 2.2.2. T able A comparison be of the properties of solutions, (less than one nanometre diameter) than are visible and 1000 that to of a the solution naked nanometres in but eye they (between diameter) heterogeneous transparent usually and suspensions Suspension greater not colloids opaque, large to enough the 1000 naked so eye that they (greater nanometres in are visible than diameter) heterogeneous some are translucent opaque no no yes no no yes filtration? components after the mixture standing for a Transmission solution Colloid small generally components separated a aerosol known homogeneous Appearance the wit h of colloids 1 Can The even par ticles t hose millimetre Particle of seen and millimetres nanometres Property T ype settle. cont aining solution know? 6 nanometre of and Milk ● A 1 000 000 not be a liquid. as 1 do cannot of smaller suspension, those Examples ● Did t hey t hose known ? colloid mixture t hose heterogeneous which substance another between fact between mixture heterogeneous in undisturbed Key ! a inter mediate separate has been while? of light transmits light appearing transparent will scatter light does not transmit light; it is opaque Mixtures and their Comparing a separation the Solutions, properties of a solution, a suspension suspensions and colloids and colloid Your teacher may ● observation, ● manipulation Y ou will be use this recording and supplied activity and to assess: reporting measurement. with two beakers, a lter funnel held in a retort stand, (a) lter and paper, distilled water, calcium hydroxide powder, copper( II) sulfate gelatine. Method 1 Half 2 Place mix 3 ll the a beaker large with spatula water. full of calcium hydroxide powder into the water and vigorously. Hold the mixture up to the light and look through it. Is it transparent or opaque? (b) 4 Place the lter paper in the lter funnel and place the second beaker below it. 5 Filter half Leave the settle out? Using your the mixture. other half of Could the you separate mixture for two the components hours. Does the by ltering? Figure (b) 2.2.3 (a) mayonnaise is a answers solution, a from 3, points suspension or a 4 and 5, decide whether the Repeat sure the that experiment you stir each with Y ou may of the the need to colloids colloid suspension colloid. copper( II) mixtures sulfate until there and is gelatine, heat the gelatine no longer particle size making any solid Figure of remaining. of mixture increasing 7 and examples mixture solution 6 Milk are 2.2.4 particles in A comparison solutions, of the colloids size and gently. suspensions 8 Record your ndings Summary 1 2 3 How does the particle a solution b a suspension of the a does b can be c will not Classify not a table. questions a Which in compare transmit separated settle of a mayonnaise b chalk c fog d white dust in with compare following each size out the is of: that with true of a that of a suspension of a colloid? solution, a suspension or a colloid? light by ltration after standing? following as a solution, a suspension or a colloid: water vinegar. 21 Solubility Mixtures A2.3 Objectives By the be able end of this topic you dene ● explain The the term what a their separation Solubility will to: ● and solubilit y dissolve in a we nd of a xed solute mass of is an indication solvent at a of how par ticular muc h of t he temperature. solute For can example, solubility can t he solubility of sodium c hlor ide in water by deter mining saturated 3 how solution muc h sodium explain the effect dissolve in of 10 cm water at temperature describe the substance on When no more solute can be dissolved in t he a par ticular solvent, t he of solution ● can is temperature. ● c hlor ide reac hes saturation point and we say t he solution is saturated . f solubility solubility from a of any more and will solute is added to t he solvent, t he solute will remain in solid of a for m a be mixed wit h t he saturated solution. The solubility solute in solubility water is usually measured as t he mass of solute t hat will saturate 10 0 g of curve water. perform ● calculations using solubility and will is saturate given the mass 100 g of of solute a solvent at effect a speci c solubility at a solute and in t he a solvent is determined by t he str ucture of t he temperature. of temperature on solubility For most solid solutes in water, solubility increases as temperature increases. This means will saturate which form as a that fact saturated which has temperature. Key A of solvent, temper ture ! combination fact The Solubility solvent temperature. solute Key and curve. The ! solute a given solubility Eac h solution contains can be as undissolved in a much dissolved temperature, is the at a is t hat a as will not saturated since t he xed less of temperature mass be at water. saturated one t he of at increases, A a solution higher temperature solute can is dissolve a is a cr ystals lower mass of solute saturated temperature, cooled, at greater which and of if t he a at one solution solute will temperature. solution You learnt earlier in t his unit t hat solubility in water is usually measured as solute t he mass of solute which will saturate 100 g of water. The unit for solubility given presence of is solute. g n per 100 g water . determining However, solubility of a it is not solute in practical water in to weigh t he 100 g laborator y, of water. we make −3 use of t he fact t hat pure water has a density of 1 g cm . n ot her words, 3 1 cm 3 of water has a mass of 1 g, or 1 g of water has a volume of 1 cm . )retaw 3 This 70 means t hat 100 g of water has a volume of 100 cm , and it is easy to 3 measure g 001 60 100 cm of water in t he laborator y. 50 When we plot solubility of a solute against temperature, we draw a graph rep 40 known as a solubility curve . The solubility cur ve for potassium chlorate(V), g( 30 ytilibuloS KClO , is shown in Figure 2.3.1. 3 20 Looking at t he solubility cur ve in Figure 2.3.1, you can see t hat t he solubility 10 of potassium chlorate(V) increases wit h an increase in temperature. 0 Solubility 0 10 20 30 40 50 60 T emperature Figure 2.3.1 Graph 70 80 90 of potassium as t his can be used to obtain any temperature various useful for pieces of example: the ● solubility such 100 information, (°C) showing cur ves The solubility of a solid at wit hin t he range of t he chlorate( V) graph. against temperature Example ✔ Exam tip What Before reading ensure that any graph you is t he Solubility scale of you each can axis. interpret the 22 two axes will The not of KClO of potassium chlorate(V) at 78 °C? scales at 78 °C 35 g per 100 g water 3 the of ● the solubility must necessarily The temperature at which cr ystals would just star t to form if an be unsaturated solution point it containing same. where is just saturated. a xed mass of solute is cooled to t he Mixtures and their separation Solubility Example At what temperature would cr ystals just begin to form if an unsaturated solution of potassium chlorate(V) containing 20 g of potassium chlorate(V) dissolved in 100 g Temperature at of water which is 20 g cooled of from KClO 80 °C? saturates 100 g of water 55 °C. 3 ∴ ● temperature The mass of at which solute temperature is t hat cr ystals would just begin cr ystallise to out form of a 55 °C saturated solution if its decreased. Example What mass solution is of decreased At potassium containing 64 °C, from 25 g of chlorate(V) 100 g 64 °C to KClO of water would when cr ystallise t he out temperature of of a saturated t he solution 22 °C? saturates 100 g of water. 3 At 22 °C, 7 g of KClO saturates 100 g of water. 3 ∴ mass of KClO cr ystallising out of a saturated solution containing 100 g 3 of ● The is water mass of 25 g solute 7 g to be 18 g added to resaturate a solution if its temperature increased. Example What mass of potassium chlorate(V) must be added to resaturate a solution containing increased At 32 °C, 250 g from 10 g of water 32 °C of to KClO if t he temperature of t he saturated solution is 82 °C? saturates 100 g of water. saturates 100 g of water. 3 At 82 °C, 38 g of KClO 3 ∴ mass of KClO to be added to resaturate a solution containing 100 g 3 of and water mass of 38 g KClO 10 g to be 28 g added to resaturate a solution containing 3 28 ____ 250 g of water 250 g 70 g of water required 100 ● The a minimum given mass to dissolve a xed mass of solute at temperature. Example What is t he minimum mass of water required to dissolve 40 g of potassium chlorate(V) At 74 °C, at 32 g 74 °C? of KClO saturates 100 g of water. 3 100 ____ ∴ 40 g of KClO saturate 40 g of water 125 g of water. 3 32 Minimum mass of water required 125 g 23 Solubility Mixtures Investigating Your teacher may ● observation, ● manipulation Y ou will be supplied water the bath), a a use this recording and placed with effect of temperature activity and to on and their separation solubility assess: reporting measurement. in groups boiling by tube, burette, a a your teacher thermometer, balance and and a each beaker potassium group with will be water (for a nitrate. Method Each group potassium teacher your 1 will will tell results Using determine nitrate, you with the the varying the the temperature from mass 6 g that to at 16 g, your which just group a specic saturates is to use. mass 10 g Y ou of will of water. then Y our share class. balance, weigh your group’s mass of potassium nitrate. 3 2 Using is 3 the burette, equivalent Add the using the Carefully all the nitrate heat T ake 6 Observe the the boiling the easiest 7 Note 8 T o it 9 to the see that and your outlined on Mass of distilled water solution the in the boiling carefully water has just dissolved. out as of the you at at water stir the it boiling tube (this to tube and, dissolve as much which temperature by bath and as and it of stirring stir cools. the it constantly the solution Look tube as for that gently. signs is until of where it is forming. the is temperature board bath, bottom temperature the two the to the crystals your weighed in especially the T emperature stir nitrate the you solution tube note Average of possible. temperature ensure again as solution crystallisation, 10 cm nitrate thermometer, potassium 5 place 10 g). potassium potassium 4 to your crystals just accurate, at which readings teacher start reheat the and to the crystals record (the table 6.0 8.0 is it form. solution just in start the given and to cool form. table below). (°C) KNO saturating 10 g of water (g) 10.0 12.0 14.0 16.0 3 Solubility of KNO (g per 100 g water) 3 10 Once and all water 11 the at each the On sheet of the of Record graph class have potassium temperature, temperature. a from mass each Summary 24 results calculate paper, i.e. the these draw been nitrate solubility recorded, that of potassium solubilities in a curve solubility copy dissolved your in the table 100 g nitrate of at table. for potassium nitrate. questions 1 Dene 2 What effect does 3 What is unit solubility. the temperature used for have measuring on the solubility solubility? of solids in liquids? Mixtures and A2.4 Since their separation Separating mixtures mixtures into form t heir a Separating mixtures par t of our component Objectives ever yday par ts is lives, t he impor tant. separation Examples of t hese include By the be able of drinking water and t he making of lter coffee. f you end of on a deser t island wit hout any drinking water, your topic you will identify suitable techniques to were separate stuck this to: t he ● purication mixtures knowledge the components the types of of mixtures separating mixtures could help you to make pure water from sea water. ● Mixtures physical are type means. component e.g. a met hods of proper ties The par ts par ticle of is size, matter met hod t he by boiling by point, t hat you component t he which determined separation of where a t he components can mixture be physical solubility. will par ts be allows 2.4.1 of into t hese wit h mixtures to t he be by its each met hod. T able 2.4.1 A summary of the methods used to separate by evaporation, simple t he physical and separated a method Physical properties of component describe the involved in A mixture liquid. of The a solid and components a liquid are where mixtures by solid based does on not their dissolve different in the particle and A mixture the of liquid of the is a solid lower which solid. The than is that dissolved of the in components solid. are a liquid The where methods the separated based only boiling on allow point their for ltration, A liquid of is collected. a solid lower The which than is that dissolved of components the are in solid. a liquid Both separated where the liquid and the different based on their boiling the funnel explain the residue and terms explain the ltrate, distillate boiling point solid different separating of ● mixture the a fractional chromatography miscible distillation crystallisation, collection points. Simple processes separating distillation, distillation, ● crystallisation funnel sizes. and Evaporation fractional separating parts the separated crystallisation, mixtures simple Filtration mixtures chromatography evaporation, Separation of ltration, distillation, distillation, ● by describe separated par ts, summarises toget her t he separated separated properties Table studying, t hat can be difference and between immiscible of can liquids. be boiling points. Fractional distillation A mixture points, of i.e. two there completely. The (or is more) a miscible difference components in are liquids volatility. which have Miscible separated based different liquids on are their boiling ones different that mix boiling points. Separating funnel A mixture of Immiscible separated Chromatography A mixture (or based of components and two liquids more) are on their dissolved are attraction to immiscible liquids different liquids do not which mix. have The different components densities. are densities. substances separated the which which based on will their travel through different a material. solubilities in a The solvent material. Filtration Filtration does a not is used to separate a mixture of a solid and a liquid where t he solid dissolve suspension. in t he Filtration liquid, makes i.e. it use is of used lter to separate paper to t he components separate t he solid filter paper filter funnel of from t he liquid. The lter paper works like a sieve, keeping back t he solid par ticles. The solid par ticles are too big to pass t hrough t he lter paper, whereas t he the in liquid par ticles are small enough to pass the The par t residue. t he of t he The mixture par t of t he t hat stays mixture behind t hat solid the remains filter paper as t hrough. passes in t he lter t hrough t he paper lter is called paper is residue t he called suppor t ltrate Filtration is one of t he steps used in t he purication of drinking water. Most the simple water purication devices t hat you might use in your homes liquid through: ltration as t heir solid impurities form of lter main from paper to met hod t he water. separate of A purifying coffee t he t he machine coffee granules water. makes from They use t he of separate a lter coffee. in filters use called t he it the is filtrate t he Figure 2.4.1 Filtration apparatus 25 Separating mixtures Mixtures and their separation Evaporation solvent evaporates quickly Evaporation is used to separate a solution of a solid dissolved in a liquid, but it into the air only allows the solid to be collected. During evaporation, the solution is boiled allowing boiling the liquid to vaporise into the air. The solute is left behind in the solution container. Evaporation is a fairly rapid process and if all the liquid evaporates, the solid remaining lacks any cr ystalline str ucture . The method is not suitable if heat the solid to be collected is decomposed by heat. Evaporation is useful to obtain the sodium chloride from a sodium chloride solution. Crystallisation solute is left Like evaporation, crystallisation is used to separate a solution of a solid dissolved behind in Figure 2.4.2 a liquid, and it only allows the solid to be collected. Unlike evaporation, the Evaporation solution is not boiled, it is left in a container at room temperature for the liquid to vaporise into the air. Crystallisation is a slow process and the solid remaining has solvent a distinct water slowly at of structure. crystallisation is t required. is used Water if of a hydrated solid crystallisation is containing water that is room incorporated temperature this filter crystalline evaporates paper impurities to in Unit within 8.4. the crystalline Crystallisation is structure useful to and obtain you will learn hydrated more copper(II) about sulfate prevent entering crystals (CuSO .5H 4 O) from a copper(II) sulfate solution. 2 solution evaporating basin Simple Simple crystals of the distillation distillation is also used to separate a solution of a solid dissolved in a solute liquid. t allows both the solid and the liquid to be collected. Simple distillation is are left behind an appropriate method of separation only if the liquid has a lower boiling point Figure 2.4.3 Crystallisation t han key The ● t he solid, i.e. components met hod The by mixture vaporisation ● The vapour condenser down ● The t he poured of Figure 2.4.4 Apparatus for which is t he t he heated up cools and t he vapour in before distillation apparatus distillation if distillation condenses and of when an solute t he a used distillation in and condenser into becomes apparatus t he solid. is a Liebig works is as ask until and it it One of follows: boils and t he most is ask back collected solution of evaporating t he in as and a t he t he liquid basin to as passes liquid. The lef t t he Liebig passes d istillate distillation has into liquid ask vaporised, to t he cr ystallise gradually solution to obtain can required. distillation thermometer boiling point liquid of Liebig condenser distillation water out flask anti-bumping granules assist smooth boiling receiver cold water in distillate heat 26 be cr ystals simple records t he condenser. occurs. rises it liquid t he concentration increases t he of Mixtures and their separation The t hermometer t he condenser. t he pure liquid, Distillation t he f solid distilled is a and used t hen ver y t he water is t he to monitor temperature t he distillate useful liquid from Separating tap is met hod af ter water t he temperature remains of t he vapour at t he boiling entering point of pure. of separation separation. and constant can be if you However, used to it need is obtain to also pure collect used water to bot h make from ✔ n bot h t hese cases, any solution remaining in t he distillation Exam ask is very since it is not important to draw separation Fractional which are line you diagrams are of the required. apparatus Fractional that is able discarded tip sea It water. mixtures used in the different processes. distillation distillation miscible is and used have to separate different a mixture boiling points of two that or are more close liquids together. Miscible liquids are liquids that are able to mix. The apparatus used in fractional distillation is similar to that used in simple distillation. However, a fractionating column is attached between a round-bottomed ask and the Liebig condenser. Fractional distillation can be used to separate a solution of ethanol and water since the boiling point of ethanol is 78 °C and that of water is 100 °C. The fractionating surface by area. many liquid the with top of of times fractionating the on column. the the has Vaporisation condensation place column lowest column a the Vapours boiling of of The temperature constant the each the point and 2.4.5 a Fractional fractionating distillation column thermometer. takes surface first using followed vapour Figure large at liquid the as remains boiling it distils point of separately reach enter water the out condenser Liebig condenser cold water distillation in flask receiver. A fresh receiver anti-bumping is used to granules each catch distillate heat ? Did The The met hod by which t he apparatus for fractional distillation works is you process of know? fractional as distillation is used in several follows. industries come ● The mixture boils and vapours of bot h liquids enter and move up across. ● As the mixture increasingly lower column of vapours richer boiling where in point column consists into the condenser, The vapour the t hey moves more (ethanol), only of the condense up volatile until more condenses the the is vaporise fractionating component, vapour volatile and and column, i.e. the reaching component. collected as the many the This top of t he less volatile liquid, i.e. t he one with t he (water), condenses in t he fractionating column and separate the (Unit 15.1), have in the fermentation of the vapour higher and in passes industry to different fractions kerosene Also the rum ethanol the mixture separate petroleum and liquid air into crude such diesel can (Unit be oxygen as oil into gasoline, 14.1). fractionally and nitrogen boiling returns to which have various uses t he (Unit round-bottomed to from gases point used the distillate wit h is becomes distilled ● It might times. it one you t he industry fractionating that 20). ask. 27 Separating mixtures Mixtures ● When almost temperature reaching second ● Once of t he top t he to of container t he liquid, all begins t he and liquid Separating is volatile showing column liquid t hat and a has distilled mixture distilling of over. their over, bot h This is separation t he vapours is collected in a discarded. temperature t hat more rise, and reaches t hen t he boiling distilled into a point t hird of t he less volatile container. funnel A separating funnel is used to separate a mixture of liquids that are immiscible and have different densities. Immiscible liquids are liquids which are unable oil liquid to mix. A separating funnel is a container that has a tap at the bottom, allowing interface water oil one liquid reduce water to the are be drained amount two of liquids off before liquids that lost are the at other. the t is usually interface immiscible and of they the have conical two in shape liquids. different Oil to and densities. f a mixture of oil and water is placed in a separating funnel, the oil with a lower density The ● ● oats met hod The tap r un into The tap by is of Figure 2.4.6 separating Separation runs ● The t he a is tap you Chromatography is their use it work. to forensic For analyse presence of from example, body illegal they fluids drugs, to for the to explosives. crime scenes, are detect If the colourless, a on the with the them t he liquid wit h again (oil) a to to second whic h t hrough a wit h t he is as follows: higher density (water) to interface almost reaches it and t he rst second. allow r un a into container ver y t he are small amount container and of t he t hen liquid closed. wit h The discarded. are is used coloured to mater ial, e.g. or separate can lter be a mixture paper. coloured, of The and dissolved substances whic h are will separated on: how soluble how strongly and, residues spots that locating are t hey in are t he solvent attracted to used t he paper. inks and food colourings are mixtures of two or more dyes, which can at separated by paper chromatography. by which from form agent chromatogram. colourless t hey analyse The met hod paper chromatography works is as follows: is A drop of the dye mixture is placed 1 cm from the bottom of a rectangular This of absorbent paper, e.g. lter paper. The paper is then hung in a spots, containing solvent so that the lower edge is below the surface of coloured. the ● ● ● ● solvent The and solvent t hem different rates. The dyes t hat t he paper The dyes t he paper Once to paper, known as dr y. each a above. t he paper and dissolves t he However, t he different dyes most least soluble and and will be a in its t he a solvent in travel and t he up mixture, t he paper least attracted to most attracted to at and distance. movement par t dyes distance. solvent least pattern representing chromatogram t he fur t hest t he completed There in t he soluble slowest has one is fastest t he t he solvent it. t he t he are travel allowed t he are dye up wit h travel t hat t he the moves carr ying is 28 liquid works chromatography beaker making funnel density. below. chromatog raphy piece reacts t he ● ● sprayed opened ● be airports, t he higher scientists Many blood as a separating allow replaced has used based in to which know? travel by t he container density of substances extensively is is contents funnel Paper Did which closed lower Paper ? water out funnel using the opened t he container water on of of up t he different t he paper, t he coloured mixture. This paper dyes on pattern is Mixtures and their separation Separating mixtures Your may teacher use Separating using this mixtures chromatography activity to assess: drop of dye mixture, ● observation, ● manipulation be recording and Y ou will two water-based supplied and datum measurement. with a markers piece of e.g. ink reporting of lter different paper, colours a beaker, and food a capillary line solvent tube, colouring. Method solvent edge 1 Measure the length your depth of the beaker with a ruler. The depth will be the front of – solvent fastest moving of lter paper. different dye coloured 2 Cut the lter paper into a rectangular strip, 4 cm wide and the length as dyes slowest measured in 1 point above. datum line moving dye 3 Draw the a pencil line at line 1 cm across intervals the strip with a 2 cm pencil up from the bottom and mark dot. Figure 2.4.7 Separation using paper chromatography 4 Attach the 5 Make with to 6 a top a with drop enough the its second place hung of with dot the Place is the beaker strip lower one of the marker of food water the beaker, but the coloured a glass just the the on second colouring the rod on beaker bottom so above markers on into in to edge the rst third that the it the in beaker. Make a dot capillary tube dot. the be suspended the dot. Use pencil will be of pencil dot. when strip can bottom pencil the so of that the strip of lter immersed in paper the ? water, dots will be above the Did Using 7 Hang the bottom and strip of the spread of lter paper up the paper and lter in the watch paper beaker the as so colours the water that in the rises the water three up the wets dots the Compare colours 9 If the in separate that plants, known actually paper. any of Which What as 3 a For is on the them of into your used with common made two markers. Did they contain any and green as of it can be pigment in chlorophyll, is three pigments, different orange, yellow green. different theirs with to coloured see if markers different from coloured you, markers had yours. questions a of the components separation main separation each class results in properties deciding 2 the your colours Summary 1 from the common? members compare results know? chromatography shown coloured 8 you water. the their of a mixture are considered when technique? difference between using distillation and evaporation method? following mixtures, component a a mixture of salt, b a mixture of oil, black sugar explain how you would separate parts: pepper and and water water. 29 Extraction of sucrose from sugar cane A2.5 Objectives By the be able end of Mixtures this topic you Extraction of sucrose from and sugar their separation cane will Sugar to: cane was rst introduced to t he Caribbean by t he Dutch in about 1625 and has been a ver y impor tant par t of its economy ever since. The production ● describe the extraction of of sucrose from t he sugar cane plant is an industrial process t hat makes use of sucrose from sugar cane several ● draw a ow diagram the steps the separation sugar which are of separation involved sucrose in from The processes The sugar and cut The pieces to The The cane clarier t he ● juice, of sucrose from sugar cane are as The and from way or Sugar cane in one or under to t he water acidic into t he juice. knives cr ushers produces t he boiler which and Figure The out, t he i.e. rotar y insoluble is factor y, cleaned shredder. water lter mud 85% is juice sprayed and where is water, lower pressures boils t he at and boiling about successively t he juice process. 35% is Andrew’s Sugar Factory t he cane it is on t hem bre, burnt The and or to goes into t he a t hat as juice ltration factor y elds. of occurs. t he juice temperatures. from but t he causes larger, series d istillation so and into produces to t he calcium continuous This lower Barbados enters juice concentrated water. in in conver ted returned successively it heated where vacuum next is acids are impurities. factor y about any t hey where by t he impurities, juice evaporators containing 2.5.3 as to t he furnace ower in cane contains occurs. neutralises The evaporates caramelised syr up is which moves juice, t he to taken precipitate claried are in is remove boilers t he t hick 2.5.2 to claried four boilers Sugar added to transpor ted revolving This which t hen place by precipitation The juice har vested, boilers. par ticles. or 2.5.1 is t he insoluble mud ● for are present. bagasse impurities takes 30 separation crushed sugar where hydroxide Figure t he pieces t hen t he heat stalks small are dissolve supply ● cane into bagasse. in cane. ● Figure involved follows: ● techniques. showing not last t hree These passes n t his charred boiler is a Mixtures and their separation Extraction ● The t hick place. soon t he t he t he are The syr up added molasses. sugar basket. speed. ● The tumbled in evaporated as is for in of is of molasses are and t he sugar sugar t hen The cr ystals. separated a is t he by perforated revolves sugar As and massecuite. contains in As called viscous forms cane takes sugar. sugar, and t his holes centrifuge. wit h of t hick centrifuge t hrough t he grains formation basket from crystallisation massecuite t he sucrose saturated small and Each in out dr um t he where becomes cr ystals placed forced outer it t he syr up centrifuges. are unrened of molasses is until exceeded, nuclei mixture t he cr ystalliser remaining t he t he t hrough sugar (1) in t he point and molasses behind damp, is massecuite collected The The in into ser ve t he cr ystals The remain to form, centrifugation are moves saturation cr ystals called ● Here as ‘seed’, syr up of at high basket and cr ystals basket. sugar heated cr ystals are collected and dried by being air. cane shredder (2) crushers bagasse (fibre) (3) clarifier (4) cane filter juice heat water molasses seed cr ystal thick syrup (8) collectors (6) (5) boiler cr ystalliser heat raw sugar (7) Figure 2.5.4 Summary 1 Draw a Why is it from sugar diagram of the various stages in the extraction of sucrose questions simple separation 2 Flow centrifuge of ow diagram sucrose important to from use a of the sugar steps which are involved in the cane. series of boilers in the extraction of sucrose cane? 31 Extraction of sucrose from sugar cane Mixtures Key Matter can ● A substance pure constant be Pure ● An element is a of is a propor tions its cannot be pure in of proper ties be any a are into t hat ordinar y are one separated substance such substances only classied which and pure substance by pure element into composed can substances compound types is par ts substances simpler ● classied composition, component ● A their separation concepts ● ● and t heir t constant has and a xed, t he means. and compounds broken or contains toget her t hat and be mixtures material. physical cannot t hat of elements chemical bonded way xed by and type down physical two or more chemically proper ties in have into any means. different xed changed. A mixture consists of two or more substances combined together in varying proportions. Each component retains its own independent properties and has undergone no chemical reaction with any other substance in the mixture. The components of mixtures can be separated by physical means. ● Mixtures can be heterogeneous ● A homogeneous composition cannot ● A classied be are solution is a are mixture is t hroughout A heterogeneous ● A suspension par ticles A are colloid is substance dispersed t han ● Solubility of 100 g ● A saturated ● at The as wit h is each in which t he t he sample proper ties and t he and components ot her. mixture usually is a consisting a liquid. non-uniform heterogeneous in anot her are in mixture of The two or more par ticles in a solution anot her smaller mixture. in which substance, mixture in usually which substance, t han t hose of minute, a t he a visible, liquid. par ticles usually but a of one liquid. The suspension, but larger solution. measure at a of given t he mass of solute which will saturate temperature. The unit of solubility Possible simple given also is a solution contains as much temperature, t hat in affects solubility. temperature increases. is a g per curve is a graph t he The showing presence solubility how t he of solute as undissolved of most solubility solids of a The proper ties t he met hod separation distillation, extraction processes: of by t he component which met hods are fractional of sucrose cr ushing, cr ystallisation 32 can be solute. in water solute a par ts mixture ltration, distillation, can of be a mixture evaporation, a are used and from sugar precipitation, separating centrifugation. cane involves ltration, to separated. cr ystallisation, funnel and chromatography. ● xed temperature. physical determine ● a a a solubility varies mixture a solution Temperature A which dispersed solvent increases ● is and water dissolved ● is par ticles of mixture from heterogeneous are t hose mass of dispersed a mixtures small. ● ● a homogeneous one extremely homogeneous uniform distinguished components, into mixtures t he vacuum following distillation, Mixtures and their separation Practice iv) Practice exam-style At 1 t he temperature and Y t he same? Which of components t he solubility v) What is vi) What mass following is of a mixture can be separated mixture contains two or more pure Figure 2 D The Y from X would at 46 °C? cr ystallise 100 g 62 °C to t he main steps combined sugar cane. shows (1 mark) (1 out of a mark) saturated of water if t his 24 °C? solution (3 mixture has a xed component melting par ts in t he marks) extraction of substances from toget her. Step A of containing cooled sucrose chemically C of means. b A of by is B solubilities correct? solution physical t he questions A The are questions questions X Multiple-choice what exam-style of a 1 Step 2 Step 3 Step 4 point. mixture are in a xed ratio. Cutting and Precipitation 2 3 The solubility of a solid in water A increases as temperature increases B increases as temperature decreases C remains D decreases The constant as following as temperature temperature are all crushing usually: increases Step increases colloids 6 Step 5 except: Vacuum A Centrifugation fog distillation B air C milk D mayonnaise Figure from 4 The process of fractional distillation depends on in Flow chart showing the extraction of sucrose cane a i) difference 2 sugar Complete t he char t by labelling t he boxes in 3 A melting B densities points C solubilities D boiling of t he components of t he of t he components of t he and 5. (2 marks) mixture ii) Describe t he process taking place in step 2. mixture (2 of t he components of t he mixture in points of t he components of t he Why is it necessar y best sand is way to separate sodium chloride solution boilers B carefully C ltering simple pouring t he lower pressures in step 4? off t he sodium chloride (1 mark) 15 marks solution Extended response question mixture Chemical substances mixtures, t he can combine in various ways to form distillation various Structured under Total evaporation a t he and 7 6 have by: A D to mixture successively The marks) water iii) 5 steps t he: components of which can be separated by means. question Figure 1 solids, X shows t he solubility cur ves for two a What do you b Solutions, understand by t he term ‘mixture’? ionic (2 and following Y. Use t his information to answer marks) t he suspensions and colloids are examples of questions. mixtures. mixtures 90 lef t to Explain in terms stand and t he of differences par ticle size, transmission of between t hese t hree sedimentation light. (6 when marks) )retaw Y 80 c You are given sodium g 001 70 The a mixture chloride, solubilities lead of of t hree chloride t hese t hree solid and chlorides: silver chlorides chloride. in water are 60 X rep given in t he table below. 50 g( Compound 40 Solubility in cold Solubility ytilibuloS water in hot water 30 sodium chloride soluble soluble insoluble soluble insoluble insoluble 20 lead chloride 10 silver chloride 0 0 10 20 30 40 50 60 70 80 i) T emperature Use t he devise Figure 1 Solubility curves for ionic information substances X and a scheme i) Dene t he solubility iii) term Temperature Explain of ‘solubility’. has t he which how you greatest (2 effect on at your marks) t he compound? arrived ii) Draw a pieces (1 answer to in separate t he t he table to mixture into mark) to par t ii) (2 marks) par ts. labelled of scheme. (5 diagram apparatus you to show used in one your of marks) t he separation (2 Total above. its Y component ii) given (°C) marks) 15 marks 33 A3 Atomic For a long structure time, people believed that all matter Objectives By the be able end of this topic you will consisted water. give ● the atomic symbols of common elements describe the structure of give relative charge of an dene a proton, a elements: earth, fire, air and the represent know that the smallest identifying is of matter an atom. matter. into Atoms On a mixtures are the basic macroscopic and pure scale we substances; we going to investigate matter on a microscopic by looking at the structure of the atom. atomic mass atoms matter blocks now scale terms and now neutron electron number ● basic and are ● of classified the mass and four Scientists building an atom ● the the particle ● of to: number by A3.1 nuclear The structure of atoms notation Regardless interpret ● nuclear determine the number particles in an metals of atom an have is the element the the one gram of gold identifying can and be one masses is kilogram, will broken par ticle classied non-metals smallest that same can one exhibit gram t he or same are into of an into smaller element metals given in and Units is par ts, an it non-metals. 4.4, 17 .1 and represented The and The in 3.1.1 by atomic an atomic symbols of symbol, some of which t he represents commonest Tables and 3.1.2. properties T able 3.1.1 The atomic symbols of the common metals element. Element Atomic Aluminium Al symbol Element Atomic Lithium Li Barium Ba Magnesium Mg Beryllium Be Manganese Mn Calcium Ca Mercury Hg Chromium Cr Nickel Ni Cobalt Co Potassium K Copper Cu Silver Ag Gold Au Sodium Na Iron Fe T in Sn Lead Pb Zinc Zn T able 3.1.2 The atomic symbols of the common symbol non-metals Non-metals is Exam essential atomic 34 that and with care, form your letters tip you symbols elements atom still of a For be gold. proper ties Each of that making capital know all you sure and the Element Atomic Element Atomic Argon Ar symbol Neon Ne Boron B Nitrogen N Bromine Br Oxygen O Carbon C Phosphorus P Chlorine Cl Silicon Si Fluorine F Sulfur S Helium He Hydrogen H the common write that them you common Iodine I Krypton Kr correctly. one of element atom elements still It will 20.1. Metals ✔ one proper ties. atom. component exist chemical be element. as have t hese fact can An if smallest Elements Key you all atom. The ! whet her element, of example, subatomic of notation par ticular to symbol are of t he given Atomic We structure cannot t hic kness see of a The atoms because human hair, t hey an are atom is incredibly more small. t han a Compared million times to structure of atoms t he smaller. Did ? you know? 7 The average t hat, on diameter average, However, t here an are of an atom atom is 25 par ticles is about million t hat are 2.5 times even 10 mm, smaller smaller whic h t han t han a an means millimetre. atom. These The atomic the elements Latin fundamental par ticles are called subatomic particles and atoms are name of t hese the and copper Subatomic Cu, particles is are of of some of from the derived the element. Latin name For for iron is par ticles. ferrum Atoms are made example, up symbols made up of t hree subatomic par ticles: protons, neutrons is lead Pb, the symbol cuprum is and and plumbum silver is for its and iron is Fe, symbol its is symbol argentum, and symbol Ag. electrons. Protons ● and neutrons are found in t he centre of an atom in an area electrons known as t he nucleus. Protons and neutrons are collectively known the nucleons. Electrons ● around Nearly are t he t he found nucleus (sometimes but all just volume of t hat involved are Mass and Protons are at in called movement an t he of atom. in mass quite a a series t he an atom distance of shells). t he levels Most electrons When charge of is from t he known of t he t he reactions in nucleus, as atom around chemical concentrated energ y is in occur, it nucleus. spinning empty space, constitutes is t he t he electrons reaction. of subatomic particles the positively charged par ticles and electrons are negatively nucleus charged. contains The size of electron. t he charge Neutrons are on a proton electrically is equal neutral so to t he have size no of t he charge. charge In an on atom, an and of protons an is electrically atom is always t he neutral same and as has t he no number of electrons. protons neutrons t he number nucleus shells fact nucleus its orbit as Figure 3.1.1 The structure of an atom Therefore, charge. The mass of a proton is equal to t he mass of a neutron. The mass of a proton is 24 extremely small, Comparing t he 1836 times The proper ties Table only mass heavier 1.67 10 g. of proton to t han of a a an The mass t hat of of an an electron electron, a is even proton smaller. is about electron. proton, neutron and electron are summarised in 3.1.3. T able 3.1.3 Subatomic The properties particle of a Relative Proton proton, a neutron charge and Relative 1 1 Neutron 0 1 Electron 1 an electron mass 1 _____ 1836 Atomic number ! The is number unique world t hat to of a protons in par ticular have t he same an atom element, is known i.e. t here atomic number. means t hat For as are t he no atomic two example, number elements t he atomic in t he number hydrogen The 20 atomic is 1, whic h number of calcium is ever y 20, hydrogen t herefore, atom ever y has calcium 1 fact Atomic number protons in of of Key and an the is the nucleus number of one of atom element. proton. atom has protons. 35 The structure of atoms Atomic In an atom, protons, Mass ! Key t he since t he number number of of electrons electrons is equal is to always t he equal atomic to t he structure number of number. number fact The number of protons and neutrons in an atom is known as t he mass number. The mass number is not unique to a par ticular element, for example Mass number is the total number polonium of protons nucleus of and neutrons one atom of in an and astatine bot h have a mass number of 210. the element. The number of neutrons can be calculated by subtracting t he atomic number from t he mass number Nuclear number, of i.e. neutrons mass number atomic number notation We can represent an atom (or ion) of an element using the nuclear notation: A X Z where This X atomic notation protons, is symbol, ver y neutrons A useful and mass number because electrons number of protons ● The number of neutrons is equal to A ● The number of electrons is equal to t he Examples T able to allows us Z to atomic calculate number. t he number of atom. The to equal it an ● equal is in and Z Z number of protons, which is Z are 3.1.4 given The Element in Table number Nuclear of 3.1.4. subatomic particles Number of Protons (Z) in the atoms of three elements notation Neutrons (A–Z) Electrons 14 Nitrogen N 7 7 7 AI 13 14 13 Cl 17 20 17 7 27 Aluminium 13 37 Chlorine 17 The nuclear elements on notations page Summary 1 Which a 2 Dene of the the 3 For each electrons of elements in the 36 B and 5 is/are be found responsible b mass following in t he periodic table volume for the: of the atom? give the number number. nuclear notations, neutrons. 11 a can terms: number, the atom atom following atomic all questions particle(s) mass for 360. 40 23 b Na 11 c Ca 20 of protons, of Atomic structure A3.2 The Electrons spin energ y The electronic around shells. Each t he configuration nucleus energy shell of is a an atom xed in a of an series distance of from atom levels and t he electrons in t he same shell have t he t he same known nucleus amount of configuration of as By the be able end electrons represent t he are arranged arrangement in of t he energy electrons in shells an in atom, a specic known as way. t he (or str ucture), using anot her scientic atom of this topic you will t he give the maximum number of energy. We allowed in the rst can three energy shells work out electronic of an atom electronic ● conguration an to: electrons The of Objectives ● atom electronic the model. conguration electron of the rst 20 elements proton represent ● the conguration × electronic of an atom in writing represent ● the conguration energy shells shell an atom by a diagram explain ● electronic of the term valence electron. neutron nucleus × In t his Figure scientic around t he 3.2.1 Model model, nucleus, but t he as of the arrangement energy t his is shells only a of are electrons drawn model, t his is in as an atom concentric not how t hey circles actually Did ? look. The is The shell shells are closest number 2, to and numbered t he so according nucleus is to assigned t heir distance number 1, t he from next t he you know? nucleus. fur t hest away on. The maximum number that an shell energy of can electrons hold is 2 Each ● ● ● shell shell shell shell 8 can hold number number number 1 2 3 up can can to a cer tain hold hold may be a a maximum maximum of maximum considered of to 2 8 number of electrons: given by is the shell 3 can, therefore, of maximum more numbers conguration of an electrons, hold since atom you wit h but will more it not t han a is maximum not have 20 number can of of necessar y to work to out know t he t heir 32 electron electrons. have by negative an electrons electrostatic around are force constantly of attraction . t he nucleus and energy t hey possess. Electrons energy t han t hose can only occupy a in t he t heir distance in shells specic being shell t he if The t hey have t he closest from to electrons from shells fur t her attracted t he t he t he positive maintain nucleus to t he required t heir because nucleus nucleus. nucleus In fact, spin of t he have less chemical in an proper ties atom of of t hat an element element, in depend par ticular, on t he shell the t he outermost energy where Shell actually 2 n number hold a and shell electrons number (up maximum However, 3, When in 4. 4 to been electrons number placed after these placed any 10) 8 are Only are when something shell electrons have number a number number electrons shell hold placed next in remaining placed in shell 3. electrons energy. t he arrangement number of Key fact of electrostatic force of electrons attraction in , electrons happens. been shell An electrons 18 electrons. in ! The 4 up 3, 2 The 2n electrons filling hold number. maximum unusual shells formula electrons electrons. Fur t her the is the force that exists shell. between two oppositely charged particles. 37 The electronic configuration of an atom Atomic Shell Key ! by an electronic atom is electrons diagrams fact The The structure the in configuration arrangement the energy drawing a conguration shell diagram or of in an atom writing of an using element can numbers. In be represented order to draw a of shell of shells electronic of diagram of an atom, t he following steps must be followed. the 1) Determine t he number of protons, neutrons and electrons in t he atom atom. 2) using t he Draw a atomic small neutrons 3) Work electrons, up 4) shell circle inside out t he in 2, Represent number for t his and t he order, so t he nucleus number and (Unit write t he 3.1). number of protons and circle. electronic and mass i.e. ll conguration up shell 1 rst by and, lling when up t hat t he is shells full, star t wit h to ll on. electronic conguration by drawing concentric circles around t he nucleus. The number of circles you should draw is determined by t he number of shells t hat you are going to ll or par tially ll. Use crosses or dots as a to pair. contains represent t he Draw electrons 5 or t he more electrons. in Draw t he t he ot her 2 electrons shells as in pairs shell number when t he 1 shell electrons. Examples 12 1 The str ucture of a carbon atom, C. 6 × ×× A carbon 6 6p × atom has: protons × 6n 6 neutrons 6 electrons. (12 6) × 12 T able 3.2.1 Determining the electronic conguration of a carbon atom C carbon, 6 Shell Figure of a 3.2.2 carbon Electronic number Maximum number of electrons Number of electrons in carbon conguration atom 1 2 2 2 8 4 The t he electronic symbol shell of conguration t he separated element by of a carbon followed commas, i.e. C by atom t he can be number written of by electrons writing in each (2,4) 39 2 The str ucture of a potassium atom, K. 19 × ×× A potassium atom has: ×× 19 20n ×× ×× ×× ×× 19p protons 20 neutrons 19 electrons. T able 3.2.2 (39 19) Determining the electronic conguration of a potassium atom ×× Shell number Maximum number of electrons Number of electrons in potassium ×× 1 2 2 2 8 8 3 8 8 4 not 39 potassium, K 19 Figure of a 3.2.3 Electronic potassium conguration atom The 38 electronic necessary conguration 1 of a potassium atom is K (2,8,8,1) Atomic structure 3 str ucture The Examples given in of t he The of ot her t he configuration congurations diagrams in Figure 3.2.4 of atoms and are of ot her written × an atom Table are 3.2.3. ×× 8p × 5p 0n elements in Element Electronic hydrogen H (1) boron B (2,3) oxygen O (2,6) 6n 8n sodium Na argon Ar calcium Ca T able 3.2.3 (2,8,1) (2,8,8) (2,8,8,2) Written congurations × 1 of electronic the atoms shown in × Figure 11 H configuration ×× × 1p hydrogen, of atoms. electronic shell electronic boron, 16 B oxygen, O 5 1 3.2.4 8 × × ×× ×× ×× ×× ×× 20n ×× ×× ×× Ar Exam tip It important that is shell Ca calcium, diagrams numbers Figure 3.2.4 Shell diagrams showing the electronic congurations of atoms Valence draw of 1 to 20, i.e. atomic hydrogen in the periodic to table. electrons example, The can atoms elements The electrons in t he outermost energy shell are known as For you of calcium different of 20 18 11 ✔ 40 40 argon, Na ×× 20p ×× 23 sodium, ×× ×× ×× 22n ×× 18p ×× ×× 12n ×× ×× ×× ×× 11p potassium outer most (2,8,8,1) e le c t ro ns are has t he one valence on es t h at valence electrons . electron. are involve d in c h emical reactions, i.e. t he va le n ce e le ct ro n s. A dia g ram o f an a tom can b e drawn t h at shows only t he va le n c e e le ct ro n s. × ×× × Figure B Diagrams electrons Summary 1 What 2 Represent using is the 12n O boron, sodium, maximum oxygen, a number electronic shell magnesium, For each of 18p 20n sodium Na and argon, argon atoms Ar showing the only of electrons conguration diagram and the of allowed each of in the shell b elements 2? atoms writing: chlorine, 20 c Cl neon, 17 in number following 35 Mg 12 3 ×× 11p 24 a 3.2. 5. questions the both of Fig ure ×× oxygen, 3.2.5 valence in ×× × g ive n ×× 8n boron, ×× × 6n a re × 8p × 5p E xa mple s question 2, Ne. 10 give the number of valence electrons. 39 Isotopes and radioactivity Atomic A3.3 Objectives By the be able end of this topic you Isotopes and structure radioactivity will Isotopy to: The dene ● the terms isotope atomic number is unique to an atomic number a particular element. For example, all atoms and of magnesium have of 12, i.e. they all have 12 protons and, isotopy therefore, ● dene ● explain relative atomic 12 electrons. The number of neutrons in atoms of the same element mass is not unique. For example, most magnesium atoms have 12 neutrons, however, what is meant by a some radioactive have number describe ● 13 neutrons and others have 1 4 neutrons. Atoms the uses of protons and electrons but different numbers of neutrons same called isotopy isotopes. In ot her words, numbers. Key the are of isotopes. The occurence of these different isotopes is known as radioactive ! with isotope fact ● isotopes Isotopes have t he same atomic number but different mass have: the same chemical properties and electrical properties because they have the same number and arrangement of electrons, e.g. if the different isotopes Isotopes are different atoms of the of magnesium react with oxygen, the chemical reaction would be the same same element that have the same ● number but of protons different and numbers slightly different of neutrons. neutrons, different Most Key ! are fact of the the is the same same electrons occurrence element number but of that of have The isotope abund ance t he proper ties different because isotopes of of t he different magnesium have numbers slightly of of more unstable an t he t han ones element one decay in a isotope, into sample but ot her of t he not all isotopes. element of The is t hese isotopes percentage referred to as of t he isotope. have protons different atoms e.g. masses. elements stable. each Isotopy physical electrons of and numbers Examples of 1 Carbon neutrons. Carbon, atomic number 6, has three naturally occurring isotopes, one with a mass number of 12, one with a mass number of 13 and one with a mass number of 1 4. There are two main methods of representing these isotopes: ● Using nuclear C By 14 C 6 ● notation: 13 12 C 6 6 name: carbon-12 or C-12 carbon-13 or C-13 carbon-14 or C-14. Carbon-12 has 6 neutrons, carbon-13 has 7 neutrons and carbon-1 4, which is unstable, has 8 neutrons. Carbon-12 is the most abundant carbon isotope. In fact 98.89% of all naturally occurring carbon is the carbon-12 isotope. Did ? you 2 know? Hydrogen Hydrogen The is deuterium heavier since it made of from normal heavy used than has an normal extra hydrogen This nuclear of is has three naturally in known heavy reactors Water place as water to is slow H thus the fast-moving enabling a isotopes. hydrogen 1 down occurring hydrogen neutron. deuterium water. in isotope neutrons, sustained 2 or protium H 1 3 or deuterium 1 H or tritium 1 chain Figure 3.3.1 The three isotopes of hydrogen reaction. Hydrogen is the only element that has different names for its isotopes. These are given in Figure 3.3.1. Protium, or normal hydrogen as it is usually 40 Atomic structure Isotopes and radioactivity called, has a single proton in its nucleus. It is the most abundant hydrogen isotope, making up 99.985% of all naturally occurring hydrogen. 3 Chlorine 35 Chlorine has two naturally occurring Cl, isotopes, or chlorine-35, and 17 37 Cl, or chlorine-37 . Approximately 75% of naturally occurring chlorine 17 is t he chlorine-35 Relative Chemists mass of smaller system ensure in To t he To could unit t hat a t hese ratio t his t he units mass of a gram t he 6 or t he atom. is t he t hat chlorine-37 carbon-12 of isotope. of of but They atoms. t he because needed They wit h, but a t he much designed t hey mass of each chosen as a had atom a to and atoms. t he has was chose number unit as assigned t he basis to work nature. t hey mass new was one-twelf t h in mass, a t his atom atoms, work abundance dened carbon-12 of to isotope and carbon-12 Therefore, mass easier of clumsy. representative masses stability They mass ver y t he are representative A t he becomes measure are because neutrons. amu. 1.00 to actual great 12, 25% measure it numbers numbers as its be to small, numbers to and grams so us and mass system of carbon-12 mass a t han because protons is gives same make use atom t hat carbon-12 of atomic an design from isotope mass number 12, i.e. one-twelf t h a of t he of mass a of it t he 12.00 carbon-12 for has 6 mass atomic atom has Key ! fact amu. Relative atomic mass, A , is the r The mass of carbon-12 Relative an atom atom atomic was of an t hen mass is element assigned given t he compared a value symbol to one-twelf t h known as relative t he mass atomic of a average mass mass . element compared the A mass of of an one atom to atom of an one-twelfth of carbon-12. r Relative atomic mass, t herefore, compares t he mass of an atom of an element to one-twelf t h value, When relative t he mass atomic calculating of mass t he a carbon-12 has no relative atom. Because it is a comparative units atomic mass of an element, t he of each isotope is taken into account. For example, fact relative A abundance Key ! t he radioactive isotope has an relative unstable nucleus which decays atomic mass of chlorine, which is 35.5, is t he average mass of t he two isotopes spontaneously of chlorine according to gas, approximately 75% and 25% t he consists of t heir of relative t he abundance. sample chlorine-37 consists of In a t he 75 atomic mass of chlorine and atomic neutrons) isotopes when not a whole real atom of mass an gives atom has. calculating number, carbon e.g. has a rough idea However, relative t he of chlorine-35 isotope form by to emitting a more stable particles and radiation. 25 t he because atomic relative 12.01 1 chlorine ____ ( 35 ) 37 ) 35.5 100 number we mass, atomic ( 100 Relative of isotope. ____ Relative sample are t he mass of of nucleons looking at relative atomic carbon is a (protons mixture but you know? of mass 12.01 1, Did ? The three and radiation main types of particles is no nucleons. isotopes • by radioactive are: alpha ( ) consist of neutrons Radioactivity emitted particles, which 2 and protons and have a 2 charge of 2 Some isotopes have unstable nuclei. These are known as rad ioactive isotopes . • beta ( ) particles, which These isotopes undergo radioactive decay by spontaneously ejecting par ticles consist and radiation from t heir nuclei. Radioactive isotopes eject t hese become different more stable and in t he process t hey may produce an an electron atom of a element. • charge gamma is a form of time taken for half of t he nuclei in a sample of a radioactive isotope ( ) of radiation, high radioactive decay is known as t he half-life of t he which energy radiation and to has undergo have 1 electromagnetic The and par ticles a to of neither mass nor a charge. isotope. 41 Isotopes and radioactivity Uses of radioactive Carbon-14 dating Carbon-14 d ating up to about archeological carbon-14 All living mass. is of sites. 5700 is t he When to determine old, which use contain in ratio a of t he have age of been plant and discovered t he fact t hat carbon-14 and carbon-12 or as living constantly living animal remains, isotopes makes same (animals) a It structure t he in places half-life of such as radioactive years. present organism food used years organisms This carbon-14 t he is 60 000 Atomic in organism dioxide organism’s takes carbon carbon in molecules dioxide dies, body it in in t he decays, a specic ratio atmosphere. it is containing replaced carbon in As by t he because t he form (plants). stops taking in t hese carbon containing molecules and t he carbon-14 is not replaced as it decays. The ratio of carbon-14 to by carbon-12, comparing expected Figure to 3.3.2 determine Carbon-14 the age of dating some is used fossils of t herefore, ratio carbon-14 t he ratio for t hat was half decreases. of carbon-14 organism of The t he if age to it a specimen carbon-12 was expected of alive. amount, in For t he can be specimen example, t hen t he determined if wit h t he specimen t he amount would be 5700 years old, if it was a quar ter of t he expected amount, t hen t he specimen would be 1 1 400 years old. Radiotherapy Radiotherapy tumours are sensitive to uses radiation composed damage of by to cure rapidly or control dividing radiation. They cancer. cells can and be Cancerous these cells controlled are or growths or particularly eliminated by irradiating the area containing the growth with external or internal radiation. External irradiation radiation Internal gamma a tiny from beta Figure treat 3.3.3 Radiotherapy cancerous growths is used can involves emitter, protective be carried radioactive irradiation or cancerous a into capsule tumour. For or out cobalt-60 eit her t he wire injecting target (a example, by directing source area, a radioactive a t he placing seed) is beam a isotope, radiation directly used to of cancerous radioactive or iodine-131 at at treat t he gamma growt h. usually source site t hyroid of a in t he cancer to and radioactive seeds containing iridium-192, palladium-103 and iodine-125 are used to treat breast and prostate cancer and brain tumours. Tracers Radioactive isotopes are used as tracers in the medical eld as a diagnostic tool. These tracers generally have a short half-life so they do not remain in the body for ver y bloodstream long. and as A small it moves amount around of the the tracer body it is usually emits injected gamma rays into the which can be obser ved using special equipment. This allows the physician to obser ve the functioning of specic organs. Examples of medical tracers are: ● Technetium-99 studies of skeleton, ● most is used organs lungs, Iodine-131 t hyroid is liver, used to to in gall produce t he body, bladder image images and and especially and carr y carr y t he out brain, functional hear t muscle, kidneys. out functional studies of t he gland. Another example of the use of radioactive tracers is in determining the uptake of atmospheric carbon dioxide by plants. Plants can be grown in an environment containing radioactive carbon dioxide, i.e. carbon dioxide that has been made by 42 replacing the carbon-12 atoms in the molecules with carbon-1 4 atoms. Atomic structure Isotopes and radioactivity Using a Geiger counter (a machine that detects radiation) the parts of the plant that absorb the radioactive carbon dioxide can be identied. Energy generation Radioactive isotopes are used to generate electricity in nuclear power stations. The isotopes they undergo smaller an it splits of of split ones two that ssion, Nuclear either into amount are nuclear nuclei. atom also used power i.e. smaller The releasing atoms or more large the use releases neutrons neutrons and amounts nucleus splits, uranium-235 plutonium-239 and released ver y when stations uranium-235 energy. release two can is or usually by a free neutrons strike This energy sets when into two plutonium-239. str uck three then energy. or of other up a If neutron, and atoms, chain a large which reaction which releases enormous amounts of energy. Did ? you know? Ba 3 One energy 235 type of atom bomb derives U neutrons Ba Kr its destructive force from nuclear 1 fission. Only two atom bombs have neutron Ba 235 235 energy U been used during warfare, both by U Kr the USA War Kr II. towards The first, the a end of uranium World fission Ba 235 bomb, U code named ‘Little Boy’, energy was Kr city Figure 3.3.4 The chain reaction in splitting a uranium exploded of The fission t he chain reaction is controlled, t he energy produced can be used electricity. If t he chain reaction is not controlled, it results Heart A explosion as occurs in an atom hear t. It connected in the Man’, was in plutonium named detonated Japan three over days later. bomb. is to is a medical implanted t he hear t device under muscle t hat t he by is skin used just to regulate below t he t he collar beating bone of and is early 1970s, some Did ? you pacemakers were developed that were powered by is to thought 100 that people pacemakers radioactive decay, it emits energy. In the pacemaker batter y, this energy is used by generate an electric powered current by which chemical delivers batteries about have a 0.2 milliwatt lifespan of of about power. 10 only living that plutonium-238 use for Pacemakers know? electrodes. batteries containing plutonium-238. As the plutonium-238 undergoes natural to a code a It In Japanese August, pacemakers pacemaker t he such second, bomb, Nagasaki nuclear 6 to ‘Fat generate the on atom 1945. If over Hiroshima was never several about today are powered batteries. really reasons, 50 have Their developed one of the years. main ones being the reluctance of To replace the batteries, the pacemaker has to be surgically removed and then people replaced. Since the half-life of plutonium-238 is about 87 years, to have by plutonium-238 batteries should be able to deliver current for lifetime Summary 1 Dene a 2 the without having to be the sodium, following in their body replaced. terms: b similarities and Na-23 Na-22. 3 Explain why 4 Explain what 5 How is plutonium life. questions isotope Give containing a for patient’s device pacemakers radioactive powered a and relative a differences atomic radioactive carbon-14 used in mass between has isotope the relative no atomic the two mass. isotopes of units. is. dating of fossil samples? 43 Isotopes and radioactivity Atomic Key ● concepts Atoms are t he identifying ● Atoms basic par ticle consist par ticles: ● structure Protons known of and an t hree protons, as building of of are nucleus. and found Protons matter. t hat fundamental neutrons neutrons t he blocks element has An t he par ticles, atom is proper ties known as t he of smallest t he element. subatomic electrons in the and centre of neutrons t he are atom in an collectively area known as nucleons ● Electrons levels ● amount of Protons are neutrons ● are The an found known size as at quite energ y a distance from t he shells. Electrons in t he charged, electrons are nucleus same in shell a series have of t he same energy. positively have of no t he electron. charge In an negatively charged and charge. on atom, a proton t he is equal number of to t he protons size of equals charge on t he t he number of An electron electrons. ● The mass of a proton is equal to t he mass of a neutron. has a 1 ____ mass of t he mass of a proton or a neutron. 1836 ● Protons are and neutrons responsible ● The number ● The total mass ● The as ● of are t he protons number of responsible volume in an protons of an atom and for t he mass of an atom. Electrons atom. is known neutrons as in t he an atomic atom is number known as t he number electrons t he Each for are arranged electronic electron in t he energy shells in a specic way known conguration shell can hold up to a cer tain maximum number of electrons. ● Shells ● The closest electronic using Electrons ● The electrons in Isotopes are They Isotopy t he of have is same or t he chemical number ● in t he nucleus ll conguration numbers ● ● to by a shell outermost proper ties t he atoms different protons an t he same atomic t he occurrence of atom are can known element be represented in writing t he of valence depend same but number atoms protons as on t he electrons arrangement of element. of electrons t he number an of diagram. atoms and rst. shell of of up and different but of element t he have numbers different same electrons t hat but mass of t he same neutrons. numbers. element t hat different have numbers of neutrons. ● ● Isotopes of physical proper ties. The an relative element atomic have mass, t he A , is same a chemical number t hat proper ties compares but t he different average r mass ● of Some an atom isotopes wit h have one-twelf t h unstable t he nuclei. mass These of are a carbon-12 known as atom. rad ioactive isotopes ● Radioactive dating, 44 isotopes have radiot herapy, many tracers, uses. energy Some of t hese generation are and carbon-14 pacemakers. Atomic structure Practice Structured Practice exam-style 1 If t he of mass atomic in t he number a i) of an of t he following table by lling in t he gaps. atom nucleus question Complete questions number neutrons questions questions 6 Multiple-choice exam-style is t he 59 and atom t he is Particle number 32, t hen t he Mass Atomic Number Number number number of of neutrons electrons is: 56 A 27 B 32 C 59 D 91 Fe 26 58 Fe (7 ii) A sample 39 2 A potassium atom is written as of 56 K. Which of of t he iron was found to contain a marks) mixture 58 Fe and Fe in a ratio of 7 to 3. Calculate t he 19 following statements about I It has an atomic II It has 20 neutrons. III It has 19 electrons. IV The A I and IV only B II and III only C I, II total number number a potassium of atom are relative tr ue? D I, III III and Students were information protons and electrons is Which of sample of iron. asked given questions in t he based table on marks) t he below. Mass Atomic Electron number number configuration A 25 — 2,8,2 B 17 8 — only IV t he t he 39. only The 3 of (2 b of mass 19. Element and atomic following is t he electronic conguration following statements were taken from one of of t he student’s exercise books. These statements 19 uorine, F? 9 are A INCORRECT. In each case, explain why t he 2,8,8,1 statement B 2,8,1 C 2,8 D 2,7 is incorrect and t hen give t he correct A 2 statement. i) INCORRECT ‘The 4 Isotopes of an element I t he same atomic II t he same number of III has have: number of but different electrons but mass different numbers numbers ii) neutrons t he same physical proper ties but different B I I 2 STATEMENT: number valence – Explain – Give ‘The chemical it – Explain – Give t he correct element is because statement is incorrect. statement. (3 conguration has a why mass t he of number statement element of marks) is B is 2,8,7 17 .’ incorrect. only and II t he correct statement . (3 C II and D I, II III and of 15 marks only III Extended Which marks) only Total 5 it STATEMENT: electron because of electrons.’ why t he INCORRECT proper ties A atomic t he following is not a use of response question radioactive 7 a The following nuclear notations refer to atoms of isotopes? aluminium A energy generation B carbon dating C chemot herapy D radiot herapy and uorine: 19 27 Al and F 13 9 Draw b shell diagrams atom A occurring naturally 21 X i) 15% ii) t he uorine element str ucture of atom. X an (4 consists of marks) 85% X. can you Determine What is Explain – deduce a relative element atomic mass of X. radioactive occurring isotope? marks) naturally (2 marks) (2 marks) how: carbon-14 and naturally (2 t he uranium-235 – about X? occurring i) show a 10 What element ii) and 22 and 10 c to aluminium animal is is used used to remains. to generate determine electricity t he age of (5 Total plant marks) 15 marks 45 The A4 periodic table and periodicity Elements are arranged in the periodic table in increasing Objectives By the be able ● end of this topic you will order of atomic number. The arrangement of the to: describe the historical development of the elements in wealth information of specific rows and about columns the provides properties of a elements periodic in the same group and in the same period of the table ● explain how arranged in elements the periodic are ● identify is the ability to metals, in explain the groups and non-metals the periodic difference and an element based on give the elements give the elements explain in in the same the the in same of the periodic the chemical properties of a its location in the table. of elements in the periodic group Ever yone is the labs one of a have familiar on wit h t he t he wall. period ic The table periodic of table elements is a as most chemistr y classication of all t he elements and it is incredibly impor tant to chemists. It shows t he symbol, full period down table of properties change along of group name, t he mass number elements and t heir into and atomic columns and number rows of based each on element t he and str ucture of it organises t heir atoms proper ties. period. arranged and in in t he periodic order chemically wit h Key predict Arrangement Elements ! values table the conguration how elements and in conguration similarities electronic ● main periods similarities electronic ● the between A4.1 ● of table metalloids ● One modern table periodic table. similar of table show increasing similar proper ties to each recur period icity. atomic ot her number, occur per iodically When all elements at regular t hroughout t he t hat elements are inter vals, t he are physically i.e. t hose series. fact Historical Periodicity is the recurrence elements with chemical properties similar development of the periodic table of physical and Early in t he 19t h centur y, scientists star ted to tr y to classify elements based on at regular t he similarities between t hem. Four scientists made impor tant contributions intervals in the periodic table. to t he development Newlands, Johann In Dmitri of t he modern Mendeleev and periodic Henr y table: Johann Döbereiner, groups of John Moseley. Döbereiner 1829, Johann Döbereiner noted that certain three elements possessed similar chemical and physical properties, e.g. he found that lithium, sodium the and three potassium elements in were a all group soft, were reactive metals. arranged in He order also of observed increasing that if relative atomic mass, then the relative atomic mass of the middle element was close to the average of the other two elements. He called these groups T able 4.1.1 Elements and Döbereiner’s their relative triads of atomic elements masses lithium sodium potassium 7.0 23.0 39.0 calcium strontium barium 40.0 88.0 137.0 chlorine bromine iodine 35.5 80.0 127.0 Average 23.0 88.5 81.25 46 triads relative atomic mass The periodic John In 1865, atomic John periodicity mass had and ever y arranging t he sodium similar Newlands t hat recurred Arrangement of elements in the periodic table put for ward discovered discovered eighth t he t hat element. elements was Be Figure Dmitri been in his at of time similar For Octaves. in order element and of and arranged order wit h atomic lit hium of physical star ting relative bot h He increasing chemical example, increasing eight h L aw t he and t he 56 relative proper ties lit hium mass, he sodium and found showed proper ties. Li and Newlands elements t hat table B 4.1.1 C N Newlands’ O F octaves of Na Mg Al Si P S Cl elements Mendeleev In 1869, Dmitri Mendeleev published his ‘ Periodic Classication of Elements ’ in which he elements arranged with elements similar in chemical increasing and relative physical atomic properties mass and together in placed vertical columns. His table was widely accepted at the time for two reasons: ● he lef t been ● he gaps switched families. For group as his e.g. 1914, of wit h order he suggested to placed atomic better 127 , so bromine, by elements relative classify tellurium, mass and was predicted able t he had all of atomic t hem relative t hat periodic to predict proper ties Mendeleev Moseley is not yet into atomic iodine which fell mass chemical mass in 128, t he showed same similar t he of credited proper ties gallium, wit h being of t he which t he missing was creator not of t he table. modern rearranged instead similar modern of t heir chemical periodic periodic atomic table number. t he elements relative in atomic proper ties all t he table masses. fell in t he In based t his same on new t heir order, groups. table consists A copy of of 103 t he elements periodic arranged table can in be order found of on 360. Elements in non-met als . Unit 4.4. r uns from t he t he Henr y increasing page t he chlorine 1875. numbers elements The corresponding Moseley atomic The t he elements Mendeleev he until version Henry t hat proper ties. table, discovered relative uorine, chemical elements, ignored example, iodine, rst seemed adjacent before Using it discovered occasionally and In when t he moder n The Looking above met als excluding and per iodic proper ties at t he per iodic aluminium t he hydrogen of (H), are t able (Al) non-met als. t able can met als in be and Figure stepping divided into non-met als 4.1.2, down All t he elements met als and t he to to t he solid ast atine t he elements to met als are and given line (At) in whic h divides lef t of t he t he r ight line, of t he 47 Arrangement of elements in the periodic table The line, including border t he inter mediate include (Sb), hydrogen, line are known between are as t hose boron (B), silicon tellur ium (Te) and non-met als. met alloid s . of (Si), met als Some The and ger manium polonium periodic of table t he proper ties periodicity elements of non-met als. (Ge), and The ar senic whic h met alloids are met alloids (As), antimony (Po). metals 0 non-metals 1 H I II III Li Be Na Mg IV V VI He VII 2 3 transition 4 5 B C N O F Ne Al Si P S Cl Ar metals K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb T e I Xe Cs Ba La Hf T a W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 6 metals Elements on metalloids; metallic Figure 4.1.2 Metals and non-metals in the periodic The Did ? The you periodic most table textbooks found consists in of periodic T o date, elements have discovered Elements up californium, exist to synthesised nuclear cases in number rest few been table rows are is divided called periods ver tical Eight t he of last proper ties including have laboratories very have some into ver tical columns called groups and columns t hese are of elements. numbered There using are Roman 18 groups numerals in t he from periodic group being Group 0. Elements in t he same group I show to VII, similar synthesised. accelerators. only element or and the and characteristics. actually atomic naturally, non-metals however, wit h been are Groups table. 118 line some 103 Groups elements. this have table horizontal know? near characteristics non-metallic or they In 98, and, because of t his, some groups have been assigned special names: been ● Group I – alkali metals ● Group II ● Group VII – ● Group 0 noble or – alkaline ear t h metals some atoms of the halogens synthesised. Between – Groups transition gases. II and elements or III t here transition are ten groups of elements called t he metals. Periods Did ? you know? Periods are horizontal rows of elements numbered using Arabic numerals from 1 Naming newly discovered to 7 . Moving along a period, the properties of the elements gradually change or from metals on the left-hand side to non-metals on the right-hand side. synthesised by the Pure elements International and (IUPAC). Applied Many are is controlled Union of Chemistry named Electronic configuration and the periodic table after Looking at t he electronic conguration of t he elements in t he periodic table, famous scientists or places, immediately e.g. einsteinium and between 48 we can see similar ities between californium. elements in t he same period. elements in t he same group and The periodic table Figure 4.1.3 in periodic t he and periodicity summarises t he Arrangement electronic conguration of t he rst 20 of elements in the periodic table elements table. Figure 4.1.3 The electronic Groups conguration I II III IV V VI VII of the rst 20 elements 0 in H the periodic table He 1 (1) (2) sdoireP Li Be B C N O F Ne (2,1) (2,2) (2,3) (2,4) (2,5) (2,6) (2,7) (2,8) Na Mg Al Si P S Cl Ar (2,8,1) (2,8,2) (2,8,3) (2,8,4) (2,8,5) (2,8,6) (2,8,7) (2,8,8) K Ca (2,8,8,1) (2,8,8,2) 2 3 4 Groups The similarities group ● all are as elements t heir (Ca) t he are all all shell electronic of conguration in (Na) (S) has Group has two 2, any i.e. group six 0 of elements a t his can shell again t he each above it. t he all same in hold, element t he is same shell one is more calcium for example, maximum electrons in hold. electron (Li) for VI t he eight can in valence electrons shell, has of number, Group which lit hium and valence in (Ne) t his has 1 electrons group electron neon example, of number (Mg) two t he and number maximum For as outermost shell number t he have same electrons full in same have magnesium t hey is valence have t he t hey (Be), and electrons group, t hree have shell, electrons once directly has group ber yllium same electrons down element same electron valence sulfur number Moving sodium t he t he of (He) number t he example, in elements helium t he for number example, ● in outermost electrons, ● in follows: has two shell t han shells and shells. Periods The similarities period ● all are as elements same electrons t he in electron aluminium ● in t he t he (Al) in number are shell of (Ca) along has any element electrons and electronic number and all period in is four t he of elements in electrons in t he same the as each (P) of element For ve an number, ● t he number of valence ● the number of occupied and i.e. period contain it. has shells, electronic period valence (Na), period t he t hat before conguration t he same same period, t heir sodium magnesium t hey all have t he (Mg) and t heir valence 3 shells directly have electron t he phosphor us Determining The conguration example, occupied calcium t he for number electrons, t han same shell, contain Moving electronic follows: t he electrons has valence electron for and more silicon can t he shells shells t hat it is in Period valence has 4. electron four valence electrons. be same is of example, (Si) configuration atom is one example, remembering electrons number number, of determined atoms from t he group t hat: as the t he same group as the number period number. 49 Arrangement of elements in the periodic table The For Exam ✔ example, periodic tip if you know table, you can electrons Correctly representing electronic the configuration str ucture of and of a elements is extremely is used to reactivity of bonding in when it determine of an an atom atom forms a will the be know type can involved t hat sesaercni increases s a s e F s e s a e r c in e r tu e r tu a n cillatem ic ll ta e m Fr metallic nature increases cillatem-non erutan e r c erutan sesaercni nature in n reactive its number electronic electronic t hat Group shells. V and atom Period has Therefore, 3 ve t he of t he valence electronic (2,8,5). and period conguration conguration calcium In Unit you on t he 3.2 are be (Fr) is the most in learnt arrangement number number of an element is is in Group of II a known. calcium For can example, and Period atom 4 of is be if you (2,8,8,2), t he you periodic of of in proper ties in t hat trends t he summarised down a a t he are same t he table. as in t he t hey way t hat elements directly group table chemical electrons such of periodic electrons valence arranged These the and properties atoms have. t here in a of t he The are related to in an element, trends in same in in t he group electronic t he element elements par ticular elements of or depend par ticular, t he periodic physical in a and par ticular congurations period. These of trends follows. ● Moving ● Moving down a group, the non-metallic nature of the elements ● Moving along a period, t he metallic ● Moving along a period, t he non-metallic group, t he metallic nature of nature t he of elements t he nature increases elements of t he decreases decreases elements increases These It is trends are impor tant Their Francium if t he trends can o group General elements n in compound. period. a t he determine chemical n electron is is phosphor us periodicity the and table ic ll ta e m - a and atoms t he non-metallic atom t hat table important. determined It phosphor us occupied phosphor us Alternatively, of t hree t hat determine periodic atoms all shown to note have in Figure t hat full 4.1.4. elements outer in electron Group shells 0 are and, chemically because of unreactive. t his, t hey have a stable electronic conguration. Atoms of all ot her elements do not have full metal outer electron shells and are, t herefore, unstable. In order to become stable, t hey need to attain t he electronic conguration of a noble gas, i.e. a full outer Fluorine (F) reactive non-metal Figure 4.1.4 is the Trends in most electron the shell. They can do t his by losing or gaining valence electrons. periodic The willingness of an atom of an element to lose or gain valence electrons is table a strong valence shell indication electrons when t hey of its and metallic or non-metals non-metallic tend to gain nature. Metals electrons into tend t heir to lose valence react. When atoms lose or gain valence electrons t hey form positively or negatively Key ! fact charged par ticles known as which An ion is an electrically atoms or formed gains when gain ions. They are said to have ionised. The ease wit h valence an atom how reactive t hey electrons, known as ease of ionisation , are. loses electrons. In ● general: The ease group wit h and t herefore, along ● The a a increases wit h and going along period. will units. r ight going which t herefore, a metal from atoms to lef t down lose electrons along a a group period. and increases The going going reactivity from right down of to a metals, lef t period. ease group which going metals, You 50 or charged determines particle lose be non-metal from lef t increases studying t he to atoms r ight going reasons along up for gain a a electrons period. group t his in and more increases The reactivity going detail going from in lef t t he up of non- to right next t hree The periodic table Summary 1 Name three What a 3 is the Group For scientists For a it b is the in Give How A4.2 Group in in of ber yllium, Trends made to Period I the of 3 the of metallic along a contributions elements in c VII periodic table, periodic to chemically all ver y the periodic Group state but give the similarities table, give the similarities and of an atom of potassium, given that 4. and period number is S (2,8,6). nature of elements of change sulfur, when given that moving its down a period? in Group periodic table II is calcium, of the periodic composed strontium, of t he barium table following and Objectives elements: radium. By the be able metals which display ver y similar proper ties. end reactive t hey are and so are collectively reactive, t hey are known never as found alkaline naturally are The always found elements in in nature Group II combined are listed wit h in ot her Figure t heir symbols, atomic numbers and electron this topic you will give the general properties of are II elements the chemical earth in give properties of t heir elements 4.2.1, of to: These They II elements in compare the reactivity of Group toget her II wit h table and ● compounds. periodic table? Group free the 0 ● Because of the Group metals. II conguration. arrangement Period number magnesium, are Group conguration. the conguration the following Group electronic and group t he II important ● elements in table. electronic electronic the and Group their Trends II given their Group does group in in electronic 6 who periodic b elements Give the name elements differences 5 of II differences 4 periodicity questions development 2 and elements with oxygen, water arrangements. and ● beryllium Be dilute predict hydrochloric the properties unknown elements based group in acid of Group II 4 (2,2) ● on explain why trends elements in magnesium Group II show similar chemical Mg 12 properties (2,8,2) ● calcium explain Group Ca going 20 why II the reactivity elements down the of increases group. (2,8,8,2) strontium Sr 38 (2,8,18,8,2) barium Ba 56 (2,8,18,18,8,2) radium Ra 88 (2,8,18,32,18,8,2) Figure 4.2.1 Group II elements and their electronic congurations 51 Trends in Group II of the periodic table The General Group A Key cation frmed elements ● They are fairly ● They are shiny, as ! II properties t hey react t he have sof t of t he Group following layer on ● They have ● Their atoms have ● Their atoms lose table and periodicity elements general proper ties in common. metals. silver y-white wit h II periodic t he surface when oxygen of t he in freshly t he air. cut, This but turn reaction dull forms ver y a quickly dull oxide metal. fact is a when positively a metal charged atom fairly high melting points valence electrons. and boiling points. ion two loses t heir valence electrons readily to form metal cations electrons. 2 wit h a Going ● it charge down becomes Chemical Group II of t he 2, e.g. group, easier for t he have They react wit h oxygen ● They react wit h water ● They react wit h dilute chlorides The ease (see with hydrochloric as the Unit reactivity is, of the and of to t he lose Group form form and the metal. metal two 5.2). radii) valence increase and electrons. elements acid proper ties (see to Unit and form in common. 8.2). hydrogen salts known gas. as metal gas. react for rank Unit (atomic hydroxides different we (see oxides hydrogen If t heir II basic metals Ba atoms chemical hydrochloric however, 2 Ca following to to 8.4) which acid of t he ● , radii atoms reactivity elements Mg t he 2 with the the oxygen, different metals water metals from the and and most is dilute known reactive to the least reactive, based on how fast or how vigorously they react, the reactivity increases going reactive Comparing Your ● teacher the may observation, Y ou will dilute be reactivity use this recording supplied hydrochloric with acid of magnesium activity and test and and to down the group. Ber yllium, at the top of the group, is the radium, and at the bottom of the group, is the most least reactive. calcium assess: reporting. tubes, strips distilled of freshly cleaned magnesium two tubes. ribbon, pieces of freshly cleaned calcium, water. Method 3 1 Pour 2 cm tube and of a dilute piece of hydrochloric calcium to acid the into each second of tube. test Compare the Add a strength piece of magnesium of effervescence of magnesium ribbon occurring in to the the rst two tubes. 3 2 Pour a Y ou 3 2 cm piece of might Based on consider 4 If you more 5 If you more 52 of distilled water calcium to need leave the is to relative more added or less barium vigorous or the to each of for vigorous dilute two a while or hydrochloric than with than with tubes. the and Add observe that a strength you piece of them effervescence ribbon occurring in to the the rst two tube and tubes. periodically. observed in steps 1 and 2, which metal would you calcium? acid and distilled water, would you expect the effervescence to be magnesium? hydrochloric vigorous test Compare effervescence magnesium dilute of tube. tubes strength to less into second reactive, beryllium vigorous added the acid and calcium? distilled water, would you expect the effervescence to be The A periodic table compar ison wit h oxygen, and of of are Similar given. and a bar ium. solid and in (aq) a t he water Examples t he You periodicity reactivity and dilute c hemical c hemical indicates an of magnesium, hydroc hlor ic equations equations have Trends can already be aqueous t he wr itten come equation. for In across t hese solution, acid calcium is given reactions for (g) t he and equations, i.e. a and barium to solution II of the periodic table 4.2.1. magnesium wit h indicate (l) Group bar ium Table wit h reactions (s) and in in indicates where calcium a gas a and liquid water is t he solvent. T able 4.2.1 Reactions Reaction Oxygen (or air) of magnesium, calcium Magnesium (Mg) Reacts to slowly exposure flame, to air. Calcium form If producing a coating ignited, white, of magnesium magnesium solid burns magnesium oxide with a (MgO) blinding on Reacts white coating oxide. (CaO) if magnesium oxygen magnesium O (g) readily of on Very to form calcium calcium a Reacts oxide exposure ignited, a brick to form air. burns a (Ba) very oxide (BaO) to If air. readily coating of on to barium exposure ignited, red flame, barium burns with an apple flame, producing green 2MgO(s) 2 producing calcium Water Barium oxide with 2Mg(s) (Ca) clean magnesium reacts producing magnesium hydroxide very slowly with ) (Mg(OH) cold and Reacts water, hydrogen gas (H 2 ). cold white, solid oxide. solid vigorously water, with barium Reacts producing with very cold white, oxide. vigorously water, 2 calcium hydroxide producing barium hydroxide (Ba(OH) magnesium magnesium water hydrogen (Ca(OH) ) and hydrogen 2 ) and 2 hydroxide gas (H ). hydrogen gas (H 2 Mg(s) Dilute hydrochloric acid Reacts O(l) 2H Mg(OH) 2 vigorously to (aq) produce magnesium chloride H 2 ). 2 (g) 2 (MgCl ) and Reacts very vigorously to Reacts violently to 2 hydrogen gas (H ). produce calcium chloride produce barium chloride 2 (CaCl ) and hydrogen gas (BaCl 2 hydrochloric magnesium hydrogen (H ). (H 2 acid Mg(s) From t he trends in t he reactivity MgCl (aq) t he Group II metals, H 2 of t han vigorously barium, calcium, but and less t han t he magnesium, reactivity vigorous t han of radium gas ). we (g) 2 can predict t he Did ? less hydrogen 2 reactivity of ber yllium, strontium and radium. We would expect ber yllium to react and chloride 2HCl(aq) ) 2 magnesium to strontium react to even be more more you know? vigorously vigorous t han Group II metals fireworks barium. air or oxygen flames. brick and red Group e.g. a a II bright metals strontium chloride they red is used burn to light produces a Compounds may also carbonate colour produces an in in coloured used white calcium colour. crimson often producing Magnesium produce effect are because and be of used, produces barium apple green colour. Figure 4.2.2 Compounds of Group II elements are often used as reworks 53 Trends in Group II of the periodic table The An explanation of the trends in periodic Group table and periodicity II Elements in Group II all have ver y similar c hemical proper ties because t heir atoms all have ionise by losing ions, i.e. Since t hey Group t he ● ● t he t he number t he ver y of atomic radii attractive pull The less valence t he easier for to t he t herefore, get of combination attracted of of atoms atoms, t herefore, t he of t he extra become shell react now full. electrons to moving As lled fur t her a lose, down t hey c harged however, t he i.e. g roup, electron away shells, from t he more shielded from t he positive nucleus factors nucleus t heir down t he reactive means going valence t he t hat down t he t he electrons. valence g roup The electrons and ease of it are becomes ionisation, g roup. smallest, ionise Group element. II t he least easily. Radium Ber yllium atoms, most being is, t he reactive Group element. str ucture of t he rst t hree elements in Group II is ×× electronic Figure ×× The given 4.2.3. × × × ×× ×× ×× ×× Ca × ×× ×× Mg × ×× ×× × Be ×× ×× Figure 4.2.3 Summary 1 What 2 a is the Does b 3 Give Compare diagrams of the rst three elements in Group II questions reactivity down the Shell collective the going 54 2, down result: largest, ionise t he most easily. Radium is, t herefore, t he II is Moving increases. t hey positively shells. two lose electron increases. when for m nucleus become going being least to and number shells due metals, proper ties, elements positive t hese to same electrons positive increases Ber yllium t he bigger t he outer c hemical electron t he t he Being electrons t heir electron valence full t his, have electrons extra electrons. valence similar occupied t he t he doing reactivity t herefore, by In two elements have II valence t heir c ations. all all two the reason the name of the for the elements elements in in Group Group II group? for reactivity your of answer beryllium to a and above. calcium. II? increase or decrease in The periodic A4.3 Group table and Trends VII in t he periodicity in Trends Group periodic table VII is of the composed periodic of t he table following in Group VII of the periodic table Objectives elements: By the be able end of this topic you will to: uorine, chlorine, bromine, iodine and astatine. These elements are all non- ● give the general properties of metals. They display similar proper ties and are chemically ver y reactive. They Group are collectively known as t he halogens. The elements in Group VII are Figure 4.3.1, toget her wit h t heir symbols, atomic numbers and elements listed ● in VII give the chemical properties of electron Group VII elements arrangements. ● explain Group uorine why VII chemical F elements show in similar properties 9 ● (2,7) explain why the elements in going the reactivity Group VII of the increases chlorine up group Cl 17 ● describe displacement (2,8,7) reactions bromine Group Br 35 ● (2,8,18,7) of elements in VII explain the term oxidising strength ● predict the properties of iodine unknown elements based group in Group VII I 53 on trends. (2,8,18,18,7) astatine At 85 (2,8,18,32,18,7) Figure General Group VII 4.3.1 Group properties elements ● They are ● They exist ● They are have poisonous as VII of t he elements Group following and their VII electronic congurations elements general proper ties common. elements. non-polar, diatomic molecules, e.g. F , Cl 2 generally in soluble in non-polar solvents , Br 2 and and I 2 2 slightly soluble in water. ● They have low ● Their ● Their atoms readily accept an electron into their valence shells to form non- atoms melting have points seven valence metal anions with a charge of ● They share an electron and boiling ! Key fact electrons. 1, e.g. F readily points. with , Cl other , Br and I non-metal (see Unit 5.2). atoms (see Unit An anion ion formed gains is a negatively when a charged non-metal atom electrons. 5.4). Group VII elements have different colours and states at room temperature, as summarised T able 4.3.1 in Table Some 4.3.1. physical temperature the rst four State fluorine gas pale chlorine gas yellow bromine liquid red-brown solid room of Element iodine at properties elements in Group VII Colour yellow green – the liquid temperature forming grey-black the heated – forming solid a evaporates an orange sublimes purple readily at room vapour readily when vapour 55 Trends in Group VII of the periodic table The Chemical Group VII reactivity elements react of Group wit h most VII metals periodic table and periodicity elements to form ionic compounds (Unit 5.2) and t hey react wit h most ot her non-metals to form covalent compounds (Unit 5.4). Examples 1 2 Chlorine reacts Sodium 2Na(s) Chlorine reacts Hydrogen H reactivity Fluorine, bottom An at of t he Cl of to form sodium sodium (g) chloride. chloride 2NaCl(s) 2 wit h t he top hydrogen gas to chlorine Cl t he sodium chlorine (g) 2 The wit h form hydrogen hydrogen (g) chloride gas. chloride 2HCl(g) 2 Group of group, explanation t he is t he of VII elements group, least the is t he increases most going reactive and up t he group. astatine, at t he reactive. trends in Group VII Elements in Group VII all have ver y similar chemical proper ties because t heir atoms all have seven valence electrons. Being non-metals, when t hey react t hey ionise by gaining one valence electron and t hey form negatively charged ions, i.e. Since all all have t he anions. t he ● reactivity t he electron of of pull valence t he inner have t he elements atoms get t herefore, of t he of outer same electron number proper ties. increases. As smaller t he positive of is electrons However, Moving a shell up now to gain, moving t he full. group, i.e. up t he 1, t hey Group VII number of result: due to valence t he decrease electrons in become number closer of to lled t he nucleus become electron combination t heir decreases. electrons full t his, chemical shells t he t he The t he shells, attractive ● similar electron radii doing elements ver y occupied In less shielded from t he positive nucleus by shells. t hese two factors means t hat t he valence electrons are more attracted to t he positive nucleus going up t he group, as are any electrons being gained by t he atoms. It becomes easier for t he atoms to gain an electron Key ! fact into t heir valence shell going up t he group. The ease of ionisation, t herefore, Electronegativity of how strongly an is a measure atom increases going up Fluorine atoms, t he group. attracts being t he smallest, ionise t he most easily. Fluorine is, electrons. t herefore, t he Group F Cl t he largest, VII most ionise least Group easily. VII element. Astatine is, Astatine t herefore, atoms, t he least being reactive element. The tendency The electronegativity Fluorine reactive t he is for t he atoms of most to attract t he electrons atoms, is t herefore, electronegative known as increases element and electronegativity . going up astatine Group is t he VII. least electronegative. The Figure two 56 4.3.2 elements Shell in diagrams Group VII of the electronic rst Figure 4.3.2. str ucture of t he rst two elements in Group VII is given in The periodic table The melting points explained t he by smallest weakest, which t he lowest. t he boiling at Trends points relative t he t hat Astatine, means t he t he t he Group t he as VII elements molecules. molecules. The and atoms, t he large forces melting point boiling has t he astatine and can Fluorine, intermolecular point largest between t hat t he of known melting having forces of size smallest molecules, means which t he has small intermolecular strongest, are and atoms, t hese The periodicity looking between are and of largest of VII of the periodic table be having are t he uorine molecules. molecules boiling Group attraction forces , point also in point are of t he astatine highest. F F fluorine (F ) 2 Cl Cl chlorine (Cl ) 2 Br Br bromine (Br ) 2 I I iodine (I ) 2 Figure 4.3.3 Displacement A d isplacement t he place of Comparing the sizes of the rst four halogen an element molecules reactions reaction anot her occurs element in a when compound. A in more its free reactive state takes element will displace a less reactive element from a compound containing t he less reactive element. element However, from a a less reactive element will not displace a more reactive compound. For example, if chlorine gas is bubbled into a solution of potassium bromide, t he chlorine will displace t he bromine from t he potassium bromide forming potassium chloride chlorine Cl (g) 2 However, will not if potassium bromide 2KBr(aq) bromine determine and colour t he and colour. from a of colourless, and a t he e.g. different is a is iodide Chlorine brown added potassium halogen potassium occurs is chlorine whet her of all t he solution are a bromine: displace bromine To and to potassium and wit h resulting (KI) are halogen a chloride reaction a solution is chloride all it bromine grey-black is (aq) 2 t he occurred, potassium obser ved. (KCl), can Br solution, has or colourless. forms, bromine bromine reaction reaction sodium occurs: no displacement potassium to no chloride mixed chloride 2KCl(aq) yellow-green, solution potassium If be a aqueous solution halide potassium solutions bromide displacement identied red-brown precipitate The an halide and by its distinctive iodine depending on (KBr) reaction will t he range amount produced. 57 Trends in Group VII of the periodic table The Investigating Your teacher may observation, ● Y ou will be bromine, displacement use this recording supplied iodine, with activity and test potassium reactions to periodic of the table and periodicity halogens assess: reporting. tubes and chloride, aqueous potassium solutions bromide of and chlorine, potassium iodide. Method 3 1 Pour 2 cm 3 of potassium potassium iodide solution each to bromide solution tube and into solution another into test a test tube. tube and 2 cm Carefully add chlorine shake. Observe any colour chloride solution into a changes. 3 2 Pour 2 cm 3 of potassium potassium iodide solution each to solution tube and into another test test tube. tube and Carefully shake. Observe any colour chloride solution into a 2 cm add Pour 2 cm bromine potassium potassium bromide solution each 4 Record 5 Using From ● 3 of t he to your your results, chlorine and in a the and another test Observe elements above bromine chloride into shake. test tube. any tube and Carefully colour 2 cm add of iodine changes. table. place activity displaces potassium solution tube results practical Chlorine of changes. 3 3 of we can from in see increasing order of reactivity. t hat: potassium bromide producing bromine: potassium bromide 2KBr(aq) potassium chloride bromine Br (aq) 2 Cl (aq) 2 2KCl(aq) potassium red-brown bromide chlorine solution ● Chlorine displaces iodine from potassium iodide producing potassium solution chloride and chlorine iodine: potassium iodide potassium chloride iodine I (aq) 2 Cl (aq) 2KI(aq) 2 2KCl(aq) brown ● solution of bromine potassium chloride Bromine displaces bromide and bromine iodine from potassium iodide producing potassium iodine: and potassium iodide potassium bromide 2KBr(aq) iodine I (aq) 2 (aq) Br 2 Figure added 4.3.4 to Chlorine potassium solution bromide 2KI(aq) brown is solution ● No displacement reaction occurs between bromine and potassium chloride. ● ✔ Exam No From If a question displacement reactions occur wit h iodine. tip asks you to t he trends in t he displacement reactions involving chlorine, bromine describe and iodine, we can predict t hat uorine, at t he top of Group VII, will displace a chemical reaction, you must all t he ot her halogens from compounds containing t hem. However, astatine, provide all observations, including at any colour t he t heir 58 bottom of Group changes. compounds. VII, will not displace any of t he ot her halogens from The periodic table and Displacement Displacement oxidising a reactions of of how can t he easily substance. The oxidising moving t he g roup up increases moving Trends reactions strengt hs measure periodicity up be one oxidising explained Group VII of t he by t he takes t he Oxid ising electrons from in Group to by gaining ionise VII of the periodic table relative strength elements ability Group strength consider ing elements. substance strengt h because t he and in VII is anot her increases an electron g roup. Key ! fact An oxidising the oxidation agent of brings another about reactant Comparing t he relative oxidising strengt hs of chlorine, bromine and iodine, by we see t hat chlorine has t he strongest oxidising strengt h and iodine has causing reactant weakest. We say t hat chlorine is t he strongest oxid ising agent and iodine to atom lose or ion electrons. in In that the is process, t he an t he the oxidising agent gains weakest. electrons. A stronger agent. oxidising This is why agent will chlorine accept displaces electrons t he from bromide a ions weaker in t he oxidising potassium bromide. Each chlorine atom in a chlorine molecule accepts an electron from a bromide (Cl ion) t hen ion and pair to ion). (Br each form chlorine a As a result, each bromide ion bromine molecule: forms a chlorine bromine bromide chloride ion ion (aq) 2 Chlorine is said displacement iodide. You Again, from bromine will be a Group stronger What will is Group 2 Two a chloride bromine ion atoms bromine 2Cl a oxid ised bot h lot trends more in we t he can (aq) t he chlorine about molecule (aq) 2 potassium and bromine oxidation displacement predict Br t hat bromide. oxidised reactions reactions uorine, at in In t he t he Unit involving t he top of ot her potassium 9. chlorine, Group VII, oxidising agent t han chlorine and astatine, at t he bottom of be a weaker oxidising agent t han iodine. questions similar in the electronic conguration of the elements in VII? a Does b Give the going What 4 List 5 a What b Give is the up the 3 to (aq) have iodine, Summary 1 to learn t he and VII, 2Br reactions, will atom. forms molecule Cl atom reactivity the by elements would a for the in you potassium the elements in Group VII increase or decrease group? reason meant of term Group for answer VII if in above. strength’? order an a to ‘oxidising observe iodide reason your of increasing aqueous solution oxidising of strength. chlorine is added solution? your answer to a above. 59 Trends in Period 3 of the periodic table The A4.4 Objectives By the be able end of this topic you Trends give Period the properties of 3 how the properties elements change along Period explain the why the to along Period Did Silicon is abundant oxygen, the is a in making the on up It is which are from silicon a Physical Earth of led found The following elements: sulfur, chemical proper ties of t hese chlorine elements devices 4.4.1 Moving from lef t to right, t he metallic change nature in decreases and metals, t he t hose non-metallic to or t he right are nature increases. non-metals and The elements silicon, in properties of metals and non-metals have t he following solid at room physical are ● They have high melting ● They have high densities. ● They are good ● They are shiny ● They are malleable, proper ties temperature, points and except boiling in common. mercur y, which is a liquid. points. Trends conductors of heat and electricity. in appearance. i.e. t hey i.e. can be t hey can drawn be out hammered into into different shapes, and wires. its ● They are sonorous, chip t hey make a ringing sound when hit. have t he following physical proper ties in common. ● its They are bromine usually is a gases at room temperature, however, some are solid and liquid. debut forms ● They have low melting ● They have low densities. points and ● They are ● In t he solid state t hey are dull ● In t he solid state t hey are brittle. ● In t he solid state t hey make boiling points. the computer not in i.e. silicon electronic made would number its invention exist Period poor conductors of heat and electricity. today. summar y of t he trends of a t he in appearance. dull sound elements in when hit. Period 3 is given in Table 4.4.1. 3 Na Mg Al Si P S Cl Ar I II III IV V VI VII 0 11 12 13 14 15 16 17 18 (2,8,1) (2,8,2) (2,8,3) (2,8,4) (2,8,5) (2,8,6) (2,8,7) (2,8,8) loses loses loses shares gains gains gains none configuration Loses/gains/shares 1e 2e 3e 4e 3e 2e 1e electrons at 25 °C Electrical conductivity solid solid solid conductor conductor conductor solid solid solid gas gas semi- insulator insulator insulator insulator non-metal non-metal non-metal non-metal conductor 60 Metal/non-metal metal Ease increasing of ionisation t he metalloid. They computer without Electronic State of after calculators modern and period. the to of first silicon number Atomic and ● A Group t he semiconductor, has chips of technology T able of phosphor us, most 28% pocket The foundation silicon, from moving manufacture which 1961. such composed know? second computers. using is 3. element crust. devices to physical semi-metal Non-metals chips table aluminium, properties change non-metal you property in periodic t he are ductile, use The along lef t Metals a table 3 elements metal Earth’ s t he elements t he middle, ? periodic moving to of the of t he ● of periodicity non-metals describe the in magnesium, argon. moving ● 3 and metals and and Period table will to: sodium, ● in periodic metal ease of ionisation metal metalloid increasing ease of ionisation The periodic table and periodicity Trends (a) (b) Figure An As 4.4.1 you Metals along learnt to it. t he As a t he t he radii positive to 3. ease and one electrons has more of its of the periodic table around or to elements t heir volcano vent and (c) chlorine gas 3 atoms tend a lose or gain valence non-metallic gain electrons. decreases non-metallic nature. Moving because nature t heir increases increases. valence moving electron sulfur metallic t he and (b) which t heir 3 (c) Period non-metals nature However, in wit h of decreases 3 sparklers, trends t he gain Period in Period electrons from and one lef t in t he to more same electron right along proton t han t he t he shell, period, element result: number electrons 4.1, metallic ability has the electrons t he in burning indication electrons number causing ● 3, element before Unit lose lose element of strong to t heir shell each in a Period because Each is tend ability ● Magnesium explanation electrons i.e. (a) in of to of positive attraction get t he protons between in t he t he nuclei positive of t he atoms nucleus and gets t he greater, valence stronger atoms protons in get t he smaller nucleus, to t he increasing pulling due t he outer number electrons of closer to t he nucleus. The combination more attracted harder gain for t he Since t he is t he Aluminium Figures reactive. ionisation t he protons i.e. 17 . Argon has a is t he a t heir by t he smallest and atoms and by non-metals period. Phosphor us its nucleus. most non-metal shell stable is full, and electronic t he is found i.e. it two and easily gaining t he is least t he to t he contains t he of t he and its least and nucleus, and t he has t he is i.e. t he 13 most reactive. t he atoms two least of period. nucleus. ease chlorine t hree and is in easily t he its to ot her 3. ionisation t herefore, sulfur smallest and more reactive. of increases has 15 protons, Chlorine reactive. right eight conguration, is electrons, easily most most t hem In Period in are becomes for along protons protons t he and largest t he of It period. along ease 1 1 easier t he decreases has more ionises phosphor us, is t he electrons period. and along increases electrons, least Chlorine ionises easily has valence t he electrons aluminium atoms t he along moving elements Sodium t he t hat going valence losing and ionises means shell t he t hree 4.4.3). ionise of t he in is of factors nucleus valence ionise largest 4.4.2 of t he electron lose magnesium Phosphor us ionises to t heir Aluminium Non-metal along atoms sodium, Sodium (see into two positive electronegativity metal metals t hese t he atoms electrons words, of to it of chlorine. electrons. does not However, Because ionise and it of is its valence t his, argon chemically unreactive. 61 Trends in Period 3 of the periodic table The Silicon of sodium Na 12p found reacts usually ionise. magnesium M Group IV and non-metallic by electronic 13p in and usually The 11p is metallic sharing str ucture a electrons of 14p is metalloid proper ties. t he wit h elements 15p It because has ot her in periodic four table it has 3 a valence non-metal Period and is combination electrons atoms. given periodicity in It does Figure 16p 17p 18p silicon phosphorus sulfur chlorine argon Al Si P S Cl Ar 4.4.2 Electronic conguration of the elements in Period not 4.4.2. aluminium Figure and 3 0.20 )mn( 0.18 suidar 0.16 0.14 cimotA 0.12 0.10 0.08 Na Mg Al Si P S Cl Ar the elements Element Figure Summary 1 Chlorine of 2 the 4 5 62 Trends in the atomic and magnesium periodic table. One are is both a one is the metal? b Which one is the non-metal? does 3 Which b Give is the a Which b Give Which the metallic change a is the of from more more in for for Period 3 Give in Period and the which one is a reasons THREE are found 3 or answer for your reasons non-metallic or answer has the a for your nature of above. chlorine? to a above. greatest Period 3 answer. magnesium? to in non-metal. right? sulfur your and THREE sodium your reactive, reason element to reactive, reason Give nature left elements metal Which How radii questions a Period 3 4.4.3 metallic nature? answer. elements in The periodic Key table Scientists ● Dmitri ● t he star ted Period icity The The elements All periodic All ● The in This two ● Group dilute ● The of ● II The The proper ties Group of the periodic table II all ability t he t he 19t h creator centur y. of t he rst version elements wit h in t he table similar physical periodic are and table. arranged in order of of ver tical columns called groups and same have same of an in have have as t he as t he t he same t he element similar number group are valence of occupied electron number. determined t he of number. number period par ticular, ver y same number proper ties of by t he valence because electrons. t hey all have have reactions wit h oxygen, water and of II elements, t heir II being metals, valence electrons. elements increases t heir atoms to lose depends going t heir down valence on t he t he ability group electrons increases VII have ver y similar proper ties because t hey all have electrons. of t heir reactivity similar acid. group. Group reactivity t he early electrons. valence of t he being periodic t he electrons, Group in is t he of Group atoms of VII to Group ability of elements, gain VII t heir an being electron elements atoms to non-metals, into t heir increases gain an depends valence going up electron on t he shell. t he group increases going up group. elements reactive in Group element containing ● is reactivity down in inter vals group period lose because t he t he Group ability ● 3 periods same to seven ● modern of t he wit h of regular called elements Elements The at atoms going ● Period 1869. consists t he of reactivity because ● in number. hydrochloric t heir The in valence credited in number in chemical Elements t he number arrangement ● Trends elements recurrence table This elements shells. in rows elements electrons. ● t he atomic horizontal ● is is table proper ties increasing ● classifying Mendeleev period ic chemical ● periodicity concepts ● of and t he Displacement will less reactions strength a of how undergo reactive oxid ising measure VII displace of of t he easily a a less d isplacement reactive reactions . element from a A more compound element. Group VII elements, substance elements where takes depend oxidising electrons on t he relative strengt h from is anot her substance. ● The oxidising strengt h of Group VII elements increases going up t he group. ● Going along elements ● Going ● The to decreases along elements Period from lef t because Period increases 3 3 from because electronegativity of to t heir lef t to t heir right, t he ability to right, t he ability elements in to metallic lose nature electrons non-metallic gain Period 3 electrons increases of t he decreases. nature of t he increases. going from lef t right. 63 Practice exam-style Practice questions The exam-style periodic table and periodicity questions N Multiple-choice questions Na 1 Elements in t he modern periodic table are arranged Mg Si Cl in Ca order of Br A chemical B atomic C mass reactivity The periodic table showing the position of some elements number a i) Name two elements which occur in t he same number period. D relative atomic State t he An element of atomic number 20 is expected to in Group II of t he periodic t he reason same for placing t hese two period. (1 a transition i) Name two elements which occur in t he same in Period 4 of t he periodic State a A I reason same group. for placing t hese two mark) elements (1 and III Element I, II and IV I, III D III and IV 3 valence IV element X electrons in its and correct 4 electron position in above. (1 Give t he electronic conguration of a calcium atom. only (1 e Which element shows ver y similar chemical Bot h magnesium and calcium react acid. barium? i) A Which element would you expect to react B (1 mark) aluminium ii) C sulfur D magnesium f X is an element periodic I II III react table. ver y ionise react below X calcium would be vigorously more slowly readily wit h in Group expected wit h t han cold II of t he ii) to: A I only B I and C II and D I, II Explain What g of potassium Explain i) Explain reason for to above. (2 obser ve added to an if an aqueous bromide? your t he (1 obser vation to right elements for t he along fact Period decreases and t hat, 3, when t he t he mark) in (2 reason marks) aqueous above. lef t t he t he is i) marks) moving metallic nature non-metallic increases. (3 marks) only III and which expect solution Total only 15 marks III Extended In you to e chlorine nature II would answer of from acid your solution f water calcium hydrochloric i) of 5 more sodium vigorously? 4 mark) wit h proper ties hydrochloric to t he mark) only d and has Place only gure C X only shells. 3 in mark) metal c B t he table t he IV (1 element ii) III in mark) table group. II mark) elements be: b I (1 mass ii) 2 Kr increasing: group of t he periodic table are t he response question halogens 8 a Outline t he contributions of Döbereiner and found? Mendeleev A Group to t he development of t he periodic (4 B Group II C Group VII b The reactivity table D Group 0 Which of t he following is t he most of increases statement and 6 by calcium elements going reference wit h in down to Group t he t he oxygen, II group. of reactions water and t he of hydrochloric (6 silicon C sulfur D phosphor us Element X potassium reaction i) Place X, Structured position gure in to iodide t he be to displace solution, potassium following found chlorine, but iodine was chloride elements going iodine, of cer tain elements in t he periodic Explain, in terms was to displace able marks) down from found to have no solution. in order Group as VII: uorine. t hey element t he gure answer t he below. Use following t he information questions. of oxidising (2 iodine strengt h, marks) from t he why X potassium table iodide given found question ii) The was wit h would 64 t his magnesium chlorine B is periodic electronegative? c 7 marks) Suppor t acid. A table. I in solution. (3 marks) t he Total 15 marks A5 Most substances Structure occur as compounds in and bonding n a t u re . Objectives Compounds a re chemically with a re a re formed each when o t h e r. atoms The combine compounds By the be able m o re stable than the f re e of explain elements why chemical w e re . The noble gases a re an exception to do occur in n a t u re as atoms. The state e l e c t ro n i c of the noble gases is the their will atoms form bonds how atoms form chemical name the three types of re a s o n chemical behind you bonds ● configuration topic this; ● they this to: which ● formed end s t a b i l i t y. describe ● chemical work ● of out binary bonding three types of formulae the empirical compounds formulae from their names. A5.1 Chemical Introduction When atoms to bond bonding chemical wit h eac h bonding ot her, only t he o u t e r m o st electrons, k n ow n a s va l e n c e e l e c t r o n s , a r e u s u a l ly i nvo lve d i n t h e p r o c e s s . A t o m s c o m b i n e He wit h eac h 3.2). The shell is is t his noble t heir are t he st a b l e g i ve s ga s st a b l e a to m s t hem a electron configuration electronic because st a b l e configuration. o u t e r m o st electronic m o st t heir electronic A to m s , shell of configuration t he o u t e r m o st or electron configuration. t h e r e fo r e , valence f i r st ( Un i t t hree bond shell. noble This wit h eac h Fi g u r e 5 .1.1 ×× Ne ×× fill att ain ga s e s and t he t he to ×× to s h ow s noble full called ot h e r ot h e r ga s e s . ×× A to m s ga i n n e a r e st st a b i l i t y noble ga s to if t h ey t hem in att ain t he t he noble per iodic ga s t able, configuration i.e. t he element of t he t hat is ×× c l o s e st is by neon and n e a r e st Fo r noble e xa mp l e , ga s to t he n e a r e st c hlor ine is noble argon. ga s This is to sodium ×× i l l u st r a t e d ×× ×× ×× ×× ×× × Ar ×× 5 .1. 2 . ×× Fi g u r e t he n u m b e r. ×× in a to m i c ×× ×× ×× ×× share or more more valence ×× ×× structure argon gas conguration valence valence electrons ×× ×× and This can occur electrons electrons wit h in of sodium by and bonding three ways. chlorine wit h They to anot her atom from anot her atom anot her Ar to ×× ● one or noble ×× gain one a change. electronic ×× achieve chemical the neon ×× a gases, ×× can during Comparing noble ×× Atoms ● ×× 5.1.2 nearest donate Cl ×× Figure ● × Ne ×× ×× ×× ×× ×× Na Figure of 5.1.1 helium, The neon electronic and structures argon their ot her atoms can: atom. 65 Chemical bonding Structure During ! Key fact are A chemical attraction results their bond is between from the chemical involved. a force atoms of These caused toget her. by bonding, bonds t he There chemical are forces redistribution are three main bonds of of t heir types are formed attraction of between between electrons, chemical and and t he t hey bonding t he atoms join atoms which t he atoms bonding: that redistribution ● ionic bond ing , which occurs when a metal ● covalent bond ing , which occurs when ● metallic bond ing , which occurs wit hin bonds wit h a non-metal of two or more non-metals bond electrons. onic and covalent bonding bot h metals. result in t he formation of chemical compounds. Chemical Just by as elements ionic or Chemical are in compound. ● are The can be covalent a There are are be impor tant as well various formula , atoms compound. by can atomic because as t he types symbols, represented of by t hey ratio tell us between chemical compounds chemical which t he formulae. formed formulae . elements elements The in t hree t he main below. molecular of compounds represented compound given number of bonding formulae found types formulae For of which each uses element example, t he subscripts present molecular in to one formula give t he actual molecule of water of is a H O, which 2 means atom. one molecule Ot her of molecular water contains formulae 2 hydrogen include CO for atoms carbon and 1 oxygen dioxide and 2 C H 6 ● O 12 The for 6 structural molecule bonds. atom The of For OCO ● glucose. t he which and t he between compound empirical which compound example, t he shows carbon empirical ratio formula , us t hat formula diagrammatic lines between formula t here are for two representation t he atoms carbon bonds to one represent dioxide between of is each oxygen atom. which elements consists using a str uctural formula , t he is of for in gives t he multiples of magnesium t he simplest compound t hese smallest chloride is whole using number subscripts. units. MgCl , For which The example, tells us t he t hat 2 magnesium and chlorine are present in a ratio of 1 to 2. Example The t hree types of chemical ● Molecular formula: ● Str uctural formula: C formula: et hane are:. 6 H Empirical for H 2 ● formulae H H C C H H H CH 3 ! Key fact Writing Valence number (valency) is A maximum number of bonds can form other atoms. when it binary bonds t he of binary compounds compound empirical is composed formulae of of two binar y different elements compounds using only. t he We can concept of with valence atom 66 formulae an write atom empirical the number can form. or valency, which is t he maximum number of bonds an Structure and bonding Chemical bonding The number of valence electrons an atom has determines its valence number. This is because of chemical in forming electrons it is t he bonds. bonds, an valence Since t he atom electrons atoms valence has to lose, number lose, gain which gain or can or par ticipate share be share t heir t hought during in t he formation valence of as t he bonding. electrons number The of valence number of an element is related to its position in t he periodic table as shown in Table T able Group 5.1.1 Valence number Valence n 5.1.1. number ot her numbers I II transition 1 2 variable, metals often 2 III IV V VI VII 0 3 4 3 2 1 0 words: ● valence number of elements in Groups ● valence number of elements in Groups V Since bot h same number element types in of t he of atom valence forming a electrons, compound must be to V to V compound t he sum of t he 8 must t he group t he lose, number group gain valence or number. share numbers of t he each equal. Example The chemical formula of aluminium oxide is Al O 2 ● ● ● Number Valence Sum i.e. To of t he write of atoms number t he of of t he each each valence sum t he of element element: 3. 3 (Group ), 2 (Group V). O 3 numbers a 2, O 2 of O formula 3 Al Al numbers: Al valence chemical present: of 3 2 t he binar y 6, 6, two elements compound, is follow equal. t he steps given below. 1) Determine 2) Write 3) Write down symbol Write 5) Write Points of t he t he symbol to t he of t he of t he element. rst symbol of valence t he t he of t he valence 1 as subscript two elements element. f a present. metal is present, write its t he of second element t he rst element directly as a af ter element as a subscript t he af ter t he subscript. subscript af ter t he element. must of be t he no spaces number (see is between one, example transition valence number of by Roman numeral placed copper(II) example indicates t hese t hat t he write symbols only t he and subscripts. symbol wit hout t he number 2). metals The e.g. t he note f a of rst second number second ● Some symbol number There ● numbers valence ● a valence rst. t he symbol 4) t he have is in more t han indicated brackets copper has in af ter a one t he valence name t he of name valence number. t he of compound t he number of metal, 2 (see 3). 67 Chemical bonding Structure ● The ● To valence write t he simplest number of empirical form, t hen hydrogen formula, cancel to if its and t he t he transition ratio simplest of t he form element, subscripts (see and is example bonding silver, is not its in 1. 4). Examples 1 Magnesium ● nitride Determine t he ● Write down ● Write t he t he valence t he symbol valence symbol of numbers t he of number rst t he of of rst t he element: t he two elements element: second present: Mg 2 (Group ), N 3 (Group V). Mg element as a subscript af ter Mg 3 ● Write t he symbol of t he second element: Mg N 3 ● Write t he symbol valence of t he number second of t he element: rst Mg The empirical formula of element as a subscript Potassium ● ● t he magnesium 2 nitride is Mg N 3 2 af ter N 3 2 sulde Valence numbers Empirical of formula t he of elements: potassium K 1 (Group ), S 2 (Group V). sulde is K S 2 3 ron( ) ● ● bromide Valence numbers Empirical of formula t he of elements: iron () Fe 3 (given Br 1 (Group bromide is FeBr in t he name), V). . 3 4 Carbon ● ● dioxide Valence numbers Empirical of formula t he of elements: carbon C 4 (Group V), O 2 (Group V). dioxide is CO . 2 simplest Summary Explain why atoms form compounds. 2 Explain how atoms form compounds. 3 Name the 4 Using your a O 2 is cancelled to 4 questions 1 following (C ratio.) three periodic binary sodium types of chemical table to help bonding. you, write the formula of each of the compounds: oxide b copper(II) c tetrachloromethane, bromide a compound formed between carbon and chlorine 68 d aluminium e ammonia, sulde a compound formed between nitrogen and hydrogen. its Structure and bonding Formation A5.2 Formation of ionic bonds atoms. Compounds formed by ionic ionic bonds Objectives onic bonding involves t he transfer of valence electrons from metal atoms to non-metal of bonding are known as By the be able end of this topic you will to: ionic ● explain the principles of ionic compounds bonding The principles of ionic bonding are explained as follows. ● ● Metals are valence noble ● found to electrons. gas t he f lef t t hey of lose t he periodic t heir table valence and most electrons have t hey can 1, 2 or attain 3 Non-metals are found to t he right of t he periodic table and most how cations and form a conguration. explain metal atoms non-metal form atoms anions ● name ● describe ionic compounds the formation of ionic have bonds 5, 6 or 7 valence electrons. f t hey gain electrons into t heir valence shell ● t hey can attain a noble gas represent shell ● When an atom loses or gains electrons it forms an ion. The ions now charged number of When metal par ticles electrons as because t he t hey number of no longer contain t he t han ● a atom electrons. When a The non-metal electrons t han loses ion electrons, has atom protons. using a gains The ion has formed charge electrons, ion a the of compounds ionic empirical formulae protons. t he positive deduce same ● ● bonding diagrams formed ● are ionic conguration. and t he ion negative is has more called formed charge a describe sodium the structure chloride of a crystal. cation has and protons is more called an anion Examples 1 Lithium When now is in Group bonding has one wit h more of a t he periodic non-metal, proton t han table lit hium electron. and has loses its one valence valence Therefore it electron. electron carries a and single positive charge, , and is represented as Li . t is known as t he lit hium ion or Li ion. 3p 3p 4n 4n lithium atom lithium an electron ion Li (2,1) Li (2) 2 Figure Nitrogen is electrons. When and now in has 5.2.1 Group V Formation of bonding t hree more t he of a lithium periodic wit h a table metal, electrons t han ion, Li and nitrogen protons. has ve gains valence t hree Therefore it electrons carries a 3 triple negative charge, 3 , and is represented as N . t is known as t he 3 nitride ion or N ion. 3 7p 7p three electrons 7n nitrogen 7n atom nitride ion 3 N (2,5) N (2,8) 3 Figure 5.2.2 Formation of a nitride ion, N 69 Formation of ionic bonds Structure When Key ! naming electrons, fact t he t he negative name changes anions from formed t hat of when non-metal atom. The t he name and bonding atoms of t he gain anion 2 always Ionic bonds created by are the chemical bonds and of t he attraction between charged negatively ‘ide’. bromide For ion example, (Br t he chloride ion (Cl ), t he oxide ion (O ) ). t he cations charged anions compounds formed by ionic bonding, t here are strong electrostatic the forces positively in electrostatic n forces ends of attraction between t he positive cations and negative anions. and in These ionic forces of attraction are known as ionic bonds and t hey hold t he ions toget her. The strengt h of t he ionic bonds accounts for t he proper ties of ionic compounds. compounds (Unit Examples to 5.5). show The formation of and potassium nitride cross the sodium by formation chloride, ionic of magnesium bonding is ionic compounds uoride, shown next aluminium by means of oxide dot and diagrams. Sodium chloride Sodium is positive sodium a metal wit h one valence electron. t loses t his electron to form a is a non-metal negative chloride atom atom accept t herefore, Figure in seven ion t hat a single valence which loses t his has has one electron. positive electrons. a single electron The t charge, gains negative t here empirical will one formula . Chlorine to i.e. be Cl to . For one sodium form a each chlorine chloride is, shows how to use shell diagrams to represent t he ionic bonding chloride. – + ×× ×× ×× ×× Cl ×× ×× ×× ×× Na Na ×× sodium of Na electron charge, need × 1 i.e. NaCl 5.2.3 sodium which wit h sodium to ion Cl ×× atom 1 chlorine atom 1 sodium ion 1 chloride ion + (Na) Did ? you term (Na ) (Cl ) know? The (Cl) ‘lattice’ refers Figure 5.2.3 Ionic bonding in sodium chloride to t is important to note that NaCl is not a separate, individual entity. NaCl simply a regular, three-dimensional represents arrangement of the ratio of Na ions to Cl ions in sodium chloride, i.e. it is the particles. empirical formula. t can also be called the Sodium c hlor ide formula unit of sodium chloride. t hat we spr inkle on our food is composed of tiny cr yst als t hat are cubic in shape. Eac h − = − Cl of t hese cr yst als is made up of millions of Na ions − + and millions one Cl of Cl ions in a ratio of one Na ion to − way; ion. t hey These occur ions are ar ranged alter nately in in rows a ver y and regular columns. + + = Na Eac h + − Na ion is bonded + to six Cl ions and eac h Cl ion is bonded to six Na ions by strong ionic bonds. − This t hree-dimensional, for ms strong ionic charged ordered ar rangement lattice. + − oppositely ions 70 cr yst al bonds − between a Figure 5.2.4 Crystal lattice of sodium chloride of ions Structure and Magnesium Magnesium bonding Formation of ionic bonds fluoride is a metal wit h two valence electrons. t loses t hese electrons to 2 form a positive magnesium ion which has a double positive charge, i.e. Mg Fluorine to form For is a each negative atoms one uoride non-metal is, to wit h uoride magnesium uorine accepts a atom accept electron. t herefore, seven ion t hat t hese The valence which loses two has two electrons. a single electrons electrons empirical formula gains negative one i.e. need be will each uorine formula unit of . electron charge, t here since or t to atom F . two only magnesium MgF 2 – F F × 2+ × ×× ×× × ×× ×× ×× ×× Mg Mg – ×× ×× F F × 1 magnesium 2 atom, atoms, fluorine 1 magnesium 2 fluoride 2+ Mg Figure 5.2.5 Aluminium Ionic F ion, bonding in magnesium Mg ions, F uoride oxide Aluminium is a metal wit h three valence electrons. t loses t hese electrons to 3 form a positive Oxygen is a aluminium non-metal ion wit h which six has valence a triple positive electrons. t charge, gains two i.e. Al . electrons to 2 form a negative oxide ion which has a double negative charge, i.e. O each has total six aluminium to gain of six two electrons electrons. t herefore, The Al O 2 To as simplify in Figure atom has electrons, and to lose two t hree empirical t hree electrons aluminium oxygen formula or atoms atoms will formula and will be unit each be oxygen needed needed of . Since to to gain aluminium atom lose a t hese oxide is, . 3 t he diagrams, sometimes only t he valence electrons are shown, 5.2.6. 2– × O O × 3+ × Al Al 2– × × O O 3+ × × Al Al 2– × × O O × 2 aluminium 3 oxygen 2 aluminium ions, 3 oxide 3+ atoms, Figure Al 5.2.6 atoms, Ionic O bonding Al in aluminium ions, 2– O oxide 71 Writing chemical formulae of ionic compounds Structure Potassium Potassium and bonding nitride has one valence electron. t loses t his electron to form a positive potassium ion wit h a single positive charge, i.e. K electrons. t gains t hree electrons to form a . Nitrogen has negative nitride ve ion valence which has 3 a triple t hree of negative electrons potassium charge, to one nitride i.e. N . nitrogen is, Three atom. t herefore, K potassium The atoms empirical are formula needed or to lose formula unit N 3 + K K 3 + × K N × × + K 3 K potassium 1 nitrogen 3 potassium ions, 1 nitride + atoms, K atom, Figure 5.2.7 Summary 1 Explain 2 Use bonding in potassium ion, 3 K N nitride questions what shell Ionic N happens diagrams a sodium b magnesium and to during ionic represent oxygen to form bonding. the ionic sodium bonding oxide, Na between: O 2 and nitrogen to form magnesium nitride, Mg N 3 3 4 the be able ● end this topic you ● ionic the name b Give the formula Describe the of compound the unit structure Writing will the the names common and formulae cations and with uorine. compound. of of the the compound. crystal chemical lattice of sodium formulae of chloride. ionic compounds onic compounds formula of an compound. anions ● an Give to: give of of forms a A5.3 Objectives By Calcium 2 work out ionic compound the formula write the name compound of from of from an the an the name ionic ● ionic are ionic There represented compound are using is impor tant also empirical known points to as note formulae . t he The formula when writing empirical unit of t he formulae of compounds. Metals generally generally gain lose electrons electrons forming forming positive negative cations. Non-metals anions. formula. ● The magnitude of the charge on an ion is the same as the valence number. Therefore, when writing formulae of ionic compounds, the magnitude of the charge on the ion can be used in place of the valence number. ● Not all atoms were 72 ions are bonded formed from toget her. previously known one These as atom. ions radicals). are Many ions known as are made from polyatomic several ions (t hese Structure ● When bonding writing t he Writing formula positive charges types of atom or group same number of electrons. The in and names Tables T able and 5.3.1 5.3.1 Monovalent must formulae and of equal of of an t he atoms t he ionic sum compound, of t he bonded ions t hat toget her you are of must required lose to of ionic compounds t he since or bot h gain know t he are given cations cations Divalent cations Trivalent hydrogen H lithium Li sodium Na magnesium Mg calcium Ca barium Ba Ag aluminium Al 3 2 iron(II) Fe copper(II) Cu zinc Zn tin(II) Sn lead(II) Pb silver Fe 2 K Cu 3 iron(III) 2 copper( ) cations 2 2 2 ammonium sum charges, formulae 5.3.2. Common potassium t he negative chemical 2 NH 4 2 T able 5.3.2 Monovalent Common anions anions Divalent anions Trivalent anions 2 fluoride F oxide O chloride Cl sulfide S 3 nitride N phosphate PO 2 3 4 2 bromide carbonate Br CO 3 2 iodide sulfite I (sulfate(IV)) SO 3 2 hydride sulfate H (sulfate(VI)) SO 4 2 hydroxide dichromate(VI) OH Cr O 2 nitrite (nitrate(III)) 7 ✔ Exam tip NO 2 Success nitrate (nitrate(V)) in chemistry depends on NO 3 being manganate(VII) able to write the names and MnO 4 formulae hydrogensulfate of compounds. Knowing HSO 4 hydrogencarbonate HCO ethanoate CH the formulae important 3 this of step ions is towards a very achieving success. COO 3 n order to write t he chemical formula of an ionic compound from t he name, follow 1) t he steps below. Write down t he formulae of t he two ions t hat are involved from Tables 5.3.1 and 5.3.2. 2) Rewrite 3) Write t he t he formula outside Write formula of magnitude of required, 4) given t he place t he t he of cation. t he bracket formula t he cation, t he f it charge is a polyatomic (see of on t he polyatomic cation example t he omitting anion in its charge. anion as cation brackets a subscript and and more write af ter t han t he t he one is subscript 4). directly af ter t he subscript, omitting its charge. 5) Write t he formula required, outside magnitude of t he place t he of anion. t he bracket t he f it charge is a polyatomic (see on t he polyatomic anion example in cation as anion brackets a subscript and and more write af ter t han t he t he one is subscript 5). 73 Writing chemical formulae of ionic compounds Structure Points ● f to t he f t he bonding note magnitude subscript ● and (see ratio simplest of of t he charge examples t he form 2 and subscripts (see example is one, do not write t he number 1 as a 3). is not in its simplest form, t hen cancel to its 6). Examples 1 Aluminium sulde 3 ● Write down t he ions ● Write down t he formula ● Write t he t he involved: magnitude formula of t he of of t he t he cation: Al 2 , S cation charge wit hout on t he its anion charge: as a Al subscript af ter Al 2 ● Write t he formula of t he anion wit hout its charge: Al S 2 ● Write t he t he magnitude formula of t he of t he anion: charge Al formula unit of t he cation Al S Calcium a subscript af ter aluminium 3 sulde is 2 2 as S 2 The on 3 iodide 2 ● ons involved: ● Magnitude ● Formula Ca , 2 of unit t he of charges: calcium Ca iodide is 2, 1 CaI 2 3 Sodium phosphate ● ons involved: Na 3 , PO 4 ● Magnitude of t he charges: Na 3 1, PO 3 4 ● Formula unit of sodium phosphate is Na PO 3 4 Ammonium sulfate ● ons involved: NH 2 , SO 4 4 ● Magnitude of t he charges: NH 2 1, SO 4 ● Formula 4 unit of ammonium 2 4 sulfate is (NH ) 4 SO 2 4 (The polyatomic ammonium ion, NH , is placed in brackets wit h 4 subscript 5 outside.) Copper(II) nitrate 2 ● ons involved: ● Magnitude Cu , NO 3 2 of t he charges: Cu 2, NO 1 3 ● Formula unit of copper () nitrate is Cu(NO ) 3 (The polyatomic nitrate ion, NO , is placed 2, in 2 brackets 3 subscript 6 outside.) Magnesium carbonate 2 ● ons involved: Mg 2 , CO 3 2 ● Magnitude of t he charges: Mg 2 CO 2 3 ● Formula unit of magnesium carbonate is MgCO 3 (Mg (CO 2 74 ) 3 is 2 cancelled to its simplest ratio.) wit h t he t he Structure and Naming The name bonding ionic of an Writing chemical formulae of ionic compounds compounds ionic compound is built from t he cation and anion names. Examples 1 Al(OH) is composed of t he aluminium cation and hydroxide anion. ts 3 name 2 K O is is aluminium composed of hydroxide. t he potassium cation and t he oxide anion. ts name 2 is 3 potassium Ca (PO 3 f t he is is by composed of t he calcium cation and phosphate anion. ts magnitude of 2 calcium cation charge its ) 4 name oxide. is phosphate. t hat looking of at a t he transition subscript metal, af ter t he determine t he anion use and t his to its determine name. Examples 1 FeCl 2 ● The subscript af ter ● The magnitude of t he t he chloride charge ion on is t he 2. iron ion must be 2. be 3. 2 2 ● The cation ● The name Fe(NO must of t he be t he iron (II) compound is ion, Fe iron (II) chloride. ) 3 3 ● The subscript ● The magnitude af ter ● The cation ● The name of t he t he nitrate charge ion on is t he 3. iron ion must 3 of Summary 1 2 Write the must chemical iron(III) b calcium c sodium d ammonium e silver f zinc g potassium h copper(II) a iron (III) compound is ion, Fe iron (III) nitrate. formula of each of the following ionic compounds: sulde hydroxide sulfate phosphate oxide nitrate (PO 3 AgCl c ZnI d Al(HCO for each of the following compounds: ) 4 b manganate( VII) carbonate names Mg t he questions a Write t he be 2 2 ) 3 e 3 FeBr 3 f FeSO g Cu 4 O 2 h Pb(NO ) 3 2 75 Formation of covalent and metallic bonds A5.4 Objectives By the be able ● end of this topic you Covalent describe the covalent bonds using Formation formation shell of Covalent metal covalent covalent and metallic bonding bonds bonding bonding bonding atoms. covalent involves t he Compounds sharing formed of by valence covalent electrons bonding between are non- known as compounds diagrams Non-metals write ● of and will to: represent ● Structure formulae of are found to t he right of t he periodic table and have 4, 6 or shell 5, to covalent 7 valence electrons. They need to gain electrons into t heir valence compounds attain describe ● metallic the formation a noble gas conguration. of bonds Since all t he atoms involved in covalent bonding need to gain electrons, t hey ● relate the properties to bonding of metals achieve t his by approaching each ot her so t hat t heir outermost electron shells the in metals. overlap. are Any t hen valence shared, in electrons pairs, pair of electrons forms a are Key ! known orbiting electron covalent bond is a a pair formed of covalent bond bond ing pair. Each not two in pairs in overlapping t he original atoms. Each atoms shared and t he electrons in a covalent bond bonding shell by the electrons around and is each stable. nucleus. Two Each pair atoms atom spends may now share has one, a wit h bot h completed time outer two or t hree pairs of chemical electrons bond a were t he fact atoms, A as t hat between sharing between between t hem. of two Two or more non-metal atoms can bond toget her by sharing electron atoms. pairs. When molecules. The electrostatic ! Key bonding fact molecule more atoms bonded is a group which together are of two or may behave chemical as a reaction. atoms of pairs bond t hey wit hin form a attraction of molecule between electrons. toget her by separate, Atoms covalent are t he of individual held toget her nuclei t he entities same of t he by known t he atoms element or of as strong and t he different bonding. covalently strongly single t his, or enough Examples to do forces pair elements A t hey unit in to show the formation of covalent a substances The by formation means Chlorine of of dot a variety and cross of substances by covalent bonding is shown next diagrams. gas Chlor ine is a non-metal wit h se ven valence electrons. t needs one more electron to ll its valence electron shell and attain a noble gas conguration. Dur ing t he for mation of a chlor ine molecule, two chlor ine atoms come close enough pair of for t heir outer electrons for ming a chlor ine is electron between single shells t hem. covalent The bond to overlap. shared between pair t he The two orbit two atoms around atoms. The share bot h 2 ×× ×× ×× ×× ×× Cl ×× ×× ×× ×× 2 chlorine atoms, Cl 1 ×× Cl ×× ×× ×× ×× ×× Cl × chlorine Cl molecule, Cl 2 76 Figure 5.4.1 Covalent bonding in chlorine atoms for mula Cl ×× one for Structure and bonding Formation of covalent and metallic bonds Water Water is a its t is a compound non-metal valence needs atoms water more needed hydrogen for electron two are wit h atom is H formed one shell. to provide shares one hydrogen electron. Oxygen electrons to from valence is ll t he a its and valence wit h one wit h atoms. more six electron electrons pair oxygen needs non-metal two electron t valence shell. required t he oxygen Hydrogen electron Two by to hydrogen oxygen. atom. ll electrons. The Each formula O 2 H O H O H H 2 hydrogen 1 oxygen 1 water molecule, H O 2 atoms, H atom, Figure 5.4.2 O Covalent bonding in water Methane Met hane is a compound formed from carbon and hydrogen. Carbon is a non- metal wit h electron Four Each formula valence electrons. Hydrogen hydrogen carbon. The four shell. atoms are hydrogen for needs needed atom met hane is t one needs four electron to shares to provide one electrons ll t he its to valence four ll electrons electron pair wit h valence electron its valence electron t he shell. required carbon by atom. CH 4 Oxygen gas Oxygen needs formation for t heir of two an outer electron electrons between oxygen O is electrons oxygen shells t hem, to ll molecule, to its two oxygen overlap. forming a The double atoms two atoms covalent shell. come During close share bond . two The t he enough pairs formula of for 2 H × × ×× ×× × C H × H O O × × × H 1 methane molecule, CH 1 oxygen molecule, O 4 Carbon Figure 5.4.3 bonding in methane and oxygen dioxide Carbon needs valence electron four required wit h carbon t he dioxide is electrons shells. electrons carbon Covalent 2 by and oxygen oxygen carbon. atom, CO Two Each forming a needs atoms oxygen double are two electrons needed atom to shares covalent two bond. to provide ll t he electron The t heir four pairs formula for . 2 77 Formation of covalent and metallic bonds Structure and bonding Nitrogen Nitrogen is electrons to molecule, a non-metal ll two its wit h valence nitrogen ve electron atoms valence shell. come electrons. During close t he t needs formation enough for t heir t hree of more a nitrogen outer electron shells to overlap. The two atoms share t hree pairs of electrons between t hem, forming a triple covalent bond . The formula for nitrogen is N 2 ×× ×× × × ×× × × O × × × 1 carbon dioxide molecule, CO 1 nitrogen molecule, N 2 The Figure drawing simplied shell of by 5.4.4 dot Covalent and showing diagram are bonding cross only shown in in carbon diagrams t he to valence Figure dioxide represent electrons. and nitrogen covalent bonding Examples of t his can be type of 5.4.5. O C N O 2 N O H Exam ✔ 1 It is very important that you are draw dot and cross water molecule show the bond compounds. T o first the decide ionic is or if from a this, you compound covalent. formed formation do If the metal carbon dioxide molecule 1 nitrogen molecule Figure 5.4.5 Covalent bonding in water, carbon dioxide and nitrogen showing diagrams valence to 1 able to H tip only in must is Str uctural covalent compound and electrons formulae bond str uctural is may also shown formulae of be by a used line molecules are to represent between given in t he molecules two Figure in atoms. which each Examples of 5.4.6. a H non-metal formed it will from be ionic, non-metals if it is only it Cl will be metal covalent. usually Remember has 1, 2 or 3 that Cl H O H C has 4, 5, and 6 or a non-metal 7 valence electrons. chlorine Valence Number bonds 1 1 of 1 1 chlorine 1 1 formulae of chlorine, water, carbon methane, dioxide oxygen, nitrogen carbon dioxide nitrogen Unit 5.1 bonds you with learnt other that the atoms is number known of as bonds its that valence an atom can number. form This is when shown clearly by these dot and cross diagrams. Hydrogen has a valence number of one and the diagrams number bromine Structural oxygen covalent it fluorine 5.4.6 methane formed n hydrogen N H water Figure and number N usually Element O valence H electrons H a of two show and it the forming diagrams one covalent show it bond. forming Oxygen two has covalent a valence bonds. The 1 1 valence numbers and number of covalent bonds formed by the common non- iodine 1 1 oxygen 2 2 sulfur 2 2 nitrogen 3 3 carbon 4 4 metals when bonding to form covalent compounds are given in Table 5.4.1. Polar and Molecules t he T able 5.4.1 number of Valence covalent number bonds and formed atoms atom 78 atoms may in be t he attracts polar or molecule. electrons. covalent non-polar as molecules a result Electronegativity Oxygen, nitrogen, is a of t he electronegative t han atoms of uorine ot her electronegativity measure and by strongly non-metal non-polar elements. of how strongly chlorine are of an more Structure ● n a and polar electrons of the bonding molecule, in the molecule negative Formation the atoms bond with has slightly charge. a Water (H at each different positive O), side of charge ammonia (C H 2 OH) and covalent The and (NH 2 ethanol a strengths. ), result one bond is side hydrogen attract that has one a of covalent glucose (C H 6 O 12 ) metallic bonds the side slightly chloride (HCl), 3 5 and δ molecules are all polar. 6 O ● n non a attract have polar molecule, electrons any wit h charged t he equal sides. atoms at strengt hs Oxygen (O each such ), side t hat nitrogen t he (N 2 carbon dioxide (CO ) and met hane The formula each of element formula. of of n elements a covalent one some are molecule ), same, ) and met hane (CH 3 (Cl (CH ) not H H δ ), δ 2 molecules are all non-polar. Figure 5.4.7 A polar water molecule compound of gives t he compounds e.g. water t he exact compound, t he (H O), molecular carbon number i.e. it is formula dioxide of t he atoms and (CO of molecular ), t he Prefix Number mono 1 di 2 tri 3 tetr 4 pent 5 hex 6 of atoms ratio ammonia 2 ). n t hese compounds t he molecular and empirical 4 formulae are molecular t he same. formula of n ot her glucose is compounds C H 6 The does chlorine 2 (NH bond compounds molecule covalent t he covalent 4 covalent in a 2 2 Formulae of name formula. placed of This a is before prexes are covalent done t he given compound by name in O 12 using of Table t he t he but t hey its are not empirical t he same, formula is e.g. t he CH O. 6 2 can sometimes prexes element to di, tri, indicate tetr, which and t hey are its so molecular on. These referring. are These 5.4.2. T able in 5.4.2 naming Prexes covalent sometimes used compounds Examples ● CO is t he formula for carbon monoxide. ● SO is t he formula for sulfur dioxide. is t he formula for sulfur trioxide. 2 ● SO ● CCl 3 is t he formula for carbon tetrachloride, more correctly known as 4 tetrachloromet hane. ● N O 2 t is a you is t he formula for dinitrogen tetroxide. 4 good come names, idea to across e.g. learn t hem, ammonia t he molecular especially (NH ) and formulae since some met hane (CH 3 of covalent cannot be compounds derived from as t heir ). 4 positive Metallic ions bonding – – – – + Metals type of have ver y bonding distinct t hat chemical occurs and between physical t he metal proper ties atoms. as The a result type of of + t he bonding – + between metal atoms in a metal is known as metallic bond ing – The atoms in a metal are packed ver y closely together to form a – – – – metal lattice. + Because of this tight packing, the outer electron shells overlap and the valence electrons become par ticular atom. delocalised, These i.e. delocalised they are electrons, no also longer associated known as mobile with any ‘delocalised’ a belong ‘sea’ to of the electrons lattice as a which whole. move around Positive within metal the cations metal are electrons electrons, form + lattice formed Figure 5.4.8 The structure of metals and from the metal atoms when the electrons become delocalised. The metal lattice is held ! together by the strong electrostatic force of attraction, known as the Key fact metallic bond, which exists between the positive cations and the moving, delocalised, The negative bond created force of t is electrons. impor tant to Figure note 5.4.8 t hat illustrates metals are the still bonding made up in of metals. atoms and not metallic t he valence even electrons t hough t hey have are no not been longer lost. They attached to a are still t here par ticular is the attraction in cations the chemical electrostatic between and the the moving, t he delocalised str ucture by ions positive because bond negative electrons. atom. 79 Structure and properties of solids Structure The way in which understand explained ● have strong forces high of amounts Metals t he of metal t he atoms are proper ties of bonded metals in metal given in lattices Unit bonding helps 4.4. us These to are below. Metals Large ● some and have melting points attraction of high heat and between energy densities are boiling t he required because points cations t he to and because separate atoms are of t he delocalised t he packed electrons. atoms. ver y closely toget her. Metals ● are electrons ● allows Metals are Metals t he an good moving carried are breaking Use shell t he electricity moving current act of as to be heat heat because electrons carried because carriers, t he act delocalised as t hrough of t he charge t he carriers, metal. delocalised which allows electrons. heat to be metal. and t herefore, atoms t he of The conductors malleable can roll metallic Summary 1 move. electrons type, t he to electric t hrough same metal, conductors free which These ● good are ductile all of over because t he same each t he size. ot her atoms f into in force new a is metal are applied positions to all of t he wit hout bond. questions diagrams a hydrogen, c hydrogen to represent covalent H bonding b phosphorus d carbon in the following: triuoride, PF 2 3 bromide, HBr disulde, CS 2 2 Draw the chlorine shell and 3 Explain the 4 Explain why diagram give the terms of the formula covalent of ‘delocalised metals are the bonding electron’ electrical between carbon and compound. and ‘metallic bond’. conductors. Objectives By the be able end of this topic you will A5.5 ● describe the examples ● relate the chloride ● Structure and properties of solids to: of its the examples of and give crystals properties to describe structure ionic of structure proper ties atoms, sodium structure simple The molecules individual chemical and give molecular of an or ions, par ticles. bond element This between or compound, depend means t he on t hat par ticles. t he t he n whet her forces of is composed attraction proper ties addition, it depend t he between on t he proper ties of t he type depend of on t he arrangement of t he par ticles, for example, if t he par ticles are packed ver y tightly toget her, t he element or compound will have a high density. crystals When ● distinguish between ionic t he simple molecular describe the way structure and of giant ● describe the diamond and relate of their ● the structure of and and graphite the crystals because pattern ● ionic ● simple ● giant identify are bonded four different wit hin t he str uctures solid. They based are on known t heir par ticles t hroughout t he are arranged str ucture. The in four a t hree-dimensional, types of solid are: cr yst als ● met allic molecular term molecular cr yst als cr yst als cr yst als. to allotropy. We have We will unit. 80 can uses structures explain we par ticles graphite properties diamond solids, t he molecular crystals ● which give ordered examples in crystals as ● considering and already be studied studying t he t he str ucture str ucture and and proper ties proper ties of of t he metals ot her in Unit t hree in 5.4. t his Structure Ionic Ionic is solids composed in represented by sodium n are a Unit ionic as a result lattice in repeating, of an which called formulae have of ionic t he bonding. cations t hree-dimensional attraction empirical bonding and properties of solids or ionic formula ionic cr ystal and An ionic anions are arrangement by bonds. units. onic All str ucture, cr ystals compounds for example, chloride. structure form an forces by ionic of formed regular, electrostatic formed The Structure crystals toget her strong are bonding crystals cr ystal held and 5.2 you sodium and studied chloride. properties t he ionic You may of bonding sodium between remember t hat t he chloride sodium and sodium chloride chlorine to cr ystal lattice is composed chloride ions or of Cl millions ions held of sodium toget her ions by or strong Na ions ionic and bonds. millions Also t hat of t he ions are in formula a ratio unit for of 1 Na sodium ion to 1 chloride Cl is ion and t hat t he empirical formula or NaCl. ionic Figure 5.5.1 Crystal lattice of Na Cl ion ion bonds sodium chloride a) The i.e. proper ties t he Table of sodium arrangement and 5.5.1 Properties of Property Explanation High The melting – about 801 °C high the bonding of to weaken and The to sodium melting sodium solid Hard can be its explained par ticles, by as its Solid sodium chloride str ucture, summarised in – + – + + – + – – + – + 5.5.1. T able point chloride ions point and these chloride is due to chloride forces and the ions. very A strong large separate the electrostatic amount ions of from heat each forces energy other, between is needed allowing the melt. sodium and chloride ions are closely packed and held together by strong + brittle electrostatic crystal forces lattice, the making ion the solid hard. layers move slightly charges come to When with pressure respect to is applied each to other the – – and + ions with the same between the like charges and the lie next lattice to each breaks other. apart, i.e. Repulsion it is occurs brittle. + Soluble in When sodium chloride is added to water the ions can separate resulting + in – – – water sodium water chloride molecules being soluble attract the in water. negative The partial chloride ions positive and the ends of partial the polar negative + ends attract the positive sodium ions. This pulls the ions out of the – lattice + and the crystal molecules water a and dissolves. new The forces of ions become attraction surrounded now exist by the water between the ions and the molecules. Conducts For electricity particles substance when are which b) to are conduct able to an electric move. In current molten it must (melted) contain sodium Sodium chloride dissolved charged chloride, the ions – + i.e. molten, NaCl(l), or no longer sodium held chloride together to by conduct ionic bonds electricity in and the they liquid are state. able to When move allowing sodium water + Na Cl dissolved in water, chloride an dissolves aqueous in solution water, of the sodium ions move chloride to freely throughout conduct an the electric water, allowing molecule current. i.e. Figure 5.5.2 What happens when NaCl(aq) sodium chloride dissolves in water 81 Structure and properties of solids Structure Simple Simple molecular molecular and bonding crystals crystals are solids composed of small molecules. Each molecule is composed of only a few atoms bonded toget her by strong covalent bonds. These molecules are t hen arranged in a regular, t hree-dimensional way to create weak a simple forces These of intermolecular formulae are Examples of ● molecular attraction ice, used to simple composed lattice . between forces hold represent water t he simple molecular of The t hem small as wit hin t he lattice intermolecular molecules molecular cr ystals molecules, molecules known toget her. have forces . Molecular cr ystals. include: molecular formula H O 2 ● iodine, composed of iodine molecules, molecular formula 2 ● dr y ice, composed of carbon dioxide molecules, molecular formula CO 2 ● glucose, composed of glucose molecules, molecular formula C H 6 Distinguishing between ionic and simple O 12 6 molecular solids onic t he and simple different summarised T able way in 5.5.2 Property molecular in which Table solids t heir have ver y par ticles different are proper ties bonded. These Comparison Ionic of the properties of ionic and solids simple Simple NaCl, KBr molecular molecular Examples: I , CO 2 of chemical bond Ionic bonds These are are very found between ions. strong. bonds atoms the of in very molecules. point Have the a high strong ions. A melting ionic large needed to separate allowing amount weaken the the point bonds ions of heat these from solid to because between of the energy bonds each Have of is and other, a the low between much melt. the simple when Due to and negative in being polar are solvents, insoluble e.g. Do not strong the ionic move. water because together they are free Follow are do held and solvents, to or ions not by free electricity dissolved are no in longer ionic bonds and move, which allows current to be in solid together conduct the by when are the but solvents. carried. not are is from solid the because forces Not needed and to separate other, melt. solids e.g. forces weak. each to the bonds between point forces rule Some sublime iodine ‘like e.g. and in in dissolves substances solvents, like’. polar e.g. in dissolve iodine tetrachloromethane. conduct because move. dissolves dissolve glucose Non-polar charged to found energy non-polar state Intermolecular substances dissolves Do These dioxide. Polar water. between molecules. heated, soluble solvents, organic (melted) held positive water, electricity bonds They of are tetrachloromethane, ions molten electric e.g. other when an 82 and most non-polar conduct because to in kerosene, gasolene Conductivity composed ions, occur molecular carbon O intermolecular these the H melting molecules allowing Solubility are the heat weaken solids 2 These weak solids molecules. strong. attraction , 2 Covalent are Melting of are 5.5.2. Examples: T ype because differences electricity they particles do not which in any have are free any Structure and bonding Investigating ionic Your and teacher may observation, ● manipulation will (simple be in solubility use and supplied this conductivity properties of solids of solids activity and electrical and to assess: reporting measurement. with sodium solids), solvent) Figure and molecular recording molecular (non-polar shown the simple ● Y ou Structure and chloride distilled the water (ionic (polar to solid), glucose solvent), apparatus used test of chloride, and iodine tetrachloromethane electrical conductivity 5.5.3. Method 1 Investigate following the the solubility instructions sodium iodine and glucose by below. 3 ● Place 5 cm ● Add small of a glucose Shake ● Repeat ● in the of water into sodium second tube thoroughly each chloride and and a of to three the crystal observe of if test rst tubes. tube, iodine each to a small the spatula third switch tube. substance A not. experiment using tetrachloromethane instead of water. Investigate shown distilled tubes or the distilled 2 to the dissolves of spatula the electrical Figure 5.5.3 conductivity and by of following solutions the using instructions the apparatus beaker below. carbon electrodes Make ● three solutions by adding three small spatulas of sodium solution 3 chloride to 25 cm of distilled water, three small spatulas of glucose 3 to to of distilled water and one crystal of iodine to 25 cm Place the If electric current, the conduct them, and 3 Draw up 4 What can a in electrodes switch. not ammeter an test table you three into if it electric the to the sodium record not a two all beakers. chloride reading, register current. other conclude separate registers does a Remove solutions your the the for the solution and solution reading, Figure then conducts the electrodes electrical close solution and the type of solid (ionic ● the type of solid and strong covalent a gi ant or its t hroughout t he bonds does conductivity. simple molecular) and its solubility ? conductivity? in a composed regular, such of non-metal t hree-dimensional The covalent t hat a giant bonds bonded arrangement exist molecular atoms between cr ystal is to t he also by Did macromolecule, i.e. formula is of giant ● diamond, ● graphite, is form atoms known as it is a molecule composed of millions of atoms. used to represent giant molecular in type of and sand. occurs molecular composed of cr ystals carbon silicon composed dioxide, empirical of carbon atoms, composed of silicon and as formula empirical oxygen a quartz. Earth’ s of crust. almost the main all Quartz It every is a rock component of this crystalline forms large These ornamental precious C formula silica form that is known almost and atoms, are beautiful very stones gemstones. is purple popular and For semi- example, quartz, citrine is C orange and rose quartz is a empirical pink formula known abundant The yellow ● also most cr ystals. include: atoms, the is amethyst also the Almost in crystals. Examples know? dioxide, silica, pure empirical you component as a solution results. electrical are lattice . lattice a crystals crystals molecular measure of clean mineral molecular to an as Gi ant Apparatus conductivity the Silicon molecular 5.5.3 electrical about: ● Giant tested of tetrachloromethane ● be 3 25 cm to rose-red variety. SiO 2 83 Structure and properties of solids Structure Structure Diamond to four is carbon consists t hroughout t he t he bonds, The proper ties in Table T able of Properties word which Greek means diamond diamond is another known the as cut using make is covalent hard be bonds. and has explained melting about covalent amount from hard of each Diamond bonds heat other, is the is of covalent useful industry as the by carbon needed allowing hardest strength in the between energy the bonds diamond to solid naturally not conduct The valence Carbon electrons does not have of the any diamond, is a you diamonds were formed is atoms to years as of point. summarised occurring often are these very strong. forces and A very separate large the atoms solid. the used The carbon in hardness atoms. cutting and is This due to the property is high very carbon atoms electrons are to all shared drilling. conduct an between electric the atoms. current. a corner cutting, polished to gems create used to (b) Figure 5.5.4 (a) A cut diamond and (b) ago at in the an we see (if depths below molten mantle where temperature Powerful brought Earth’ s of bonds billions) about the Earth’ s rock are the of the atom pressure both magma the diamond today not carbon Earth’ s uncut know? millions kilometres surface then strengt h melting str ucture, of anot her melt. covalent high. t he high cr ystal technique powder sparkling hard, the After then Most and of A one jewellery. Did 150 ver y it. to covalently from of around bonded Because a its weaken between ‘free’ (a) ? atoms bonded ‘adámas’, so using diamond beautiful, comes word bruiting. diamond tetrahedron carbon is ‘unbreakable’. Because of a atom know? ‘diamond’ ancient can Each diamond The – electricity the of Very high strong diamond in t hese extremely Explanation Does The by is of diamond atoms. arranged bonding 5.5.3. 5.5.3 Extremely you atoms cr ystal of carbon millions diamond 3550 °C Did of of Property point ? properties composed ot her diamond and and extremely eruptions diamonds to the surface. Structure Graphite is and also Figure 5.5.5 properties composed of Structure of carbon of diamond graphite atoms. Each atom is bonded covalently to three other carbon atoms, forming hexagonal rings of atoms which link up to form at sheets or layers of carbon atoms. The four th electron of each atom is not bonded to another atom and becomes delocalised. These layers of carbon atoms then atoms in weak forces str ucture, 84 lie the as on top layers of of are each ver y attraction. summarised other. strong, The in The covalent however, proper ties Table 5.5.4. of the bonds layers graphite between are can held be the carbon together explained by by its Structure and bonding Structure Property Explanation Very The high point – melting about 3600 °C from in Soft covalent amount and each weak over Good of conductor electricity other, The fourth the crystal. Because molten act These this, the between as a of the carbon needed the in a to solid metals, resulting electron of is allowing for other can between energy forces each graphite bonds heat containers The lubricating of to e.g. melt. are these very strong. forces Because of and this, A very separate graphite 5.5.4 the can of carbon crystal atoms which allow feels the slippery. layers to Because slide of this, lubricant. each moving graphite carbon atom electrons is used as can is delocalised carry allowing electricity electrodes during it through to the move within crystal. electrolysis. Did Constructing fit together models may manipulation of sodium chloride, diamond use and this activity to Figure with similar 5.5.6 Structure of graphite ✔ Exam tip It important assess: is that you can draw measurement. supplied (or of and and plasticine form layers graphite be stable graphite layers will more diamond. forces between Y ou a atom weak ● is than know? bond carbon teacher you layer covalent Your graphite used carbon how of solids atoms be Graphite graphite Properties of large ? one properties crucibles. layers ‘soft’ atoms weaken T able and toothpicks round, soft and material small, to use different as coloured atoms or pieces of describe sodium chloride, graphite ions). their the and that properties structure diamond you and can uses of and relate to their Method structures. Using the show their diagrams ● sodium ● diamond ● graphite. Use the Unit 5.5 to help you, make models of the following to chloride plasticine represent in structure: the to bonds represent between atoms or ions and the toothpicks to them. 85 Structure and properties of solids Structure and bonding Allotropy Key ! fact Diamond t hey Allotropes are different are of same physical the same bot h graphite made are out of known t he as same allotropes element, of carbon. carbon, This is but, in t he occurence of t hese because solid state, structural t heir forms and element in carbon atoms are known as bonded differently. The different the allotropes state. is allotropy Because diamond and graphite are bot h composed of carbon atoms, t hey have t he Key ! same different Allotropy is the existence structural forms t hey proper ties. have physical different However, cr ystal t heir atoms str uctures are which bonded result in differently, t hem having proper ties. of Several different chemical t herefore, fact of ot her elements exhibit allotropy. These include sulfur and the phosphor us, when in the solid state, and oxygen, when in the gaseous state. same element in the same physical state. Summary 1 Did ? you Converting to diamond dream the of high its to bonding that the and force consuming and long crystal is Potassium structure does each of the following have? b Iodine c Ice d Graphite e Calcium bromide held extremely carbonate temperatures carbon to have 2 Why 3 Compare 4 Why are diamonds 5 Why can graphite can sodium chloride dissolve in water? change meant extremely the melting points of an ionic solid and a simple molecular solid. time- extremely hard? energy-intensive. Consequently it achieved any with a the structure process of a graphite throughout However, pressures required been scientists world. type know? inexpensive has What questions has not real yet been conduct an electric current? success. Key ● concepts Atoms bond wit h conguration, ● Atoms can electronic ● There are each i.e. lose, t hat gain ot her of or to t he share attain nearest a more noble valence stable electronic gas in t he periodic electrons to attain a table. stable conguration. t hree main types of chemical bonding: ionic, covalent and metallic. ● A chemical t he ● ● redistribution Chemical can be There are V alence form Ionic t hree Metal form 86 force t heir by main formulae number ot her of atoms form negative of valency a result chemical t hat results from is t he positive of ionic or covalent bonding formulae: molecular formulae, formulae. t he number number composed called atoms formulae. Valence forming ions as empirical involves between electrons. types atoms. atoms, attraction formed and or of chemical compounds bond ing non-metal ● of a compounds wit h formulae ● is represented str uctural ● bond of transfer two of of can bonds be used different electrons an to atom write can empirical elements. from metal atoms to ions. ions called anions cations and non-metal atoms Structure ● n ionic t he ● A ● onic ions lattice metal Atoms forces n to or The strong electrons Four ● The ● Simple in a ions t he of as attraction ionic solids between bonds, made arrangement empirical hold shar ing from of shared of formula par ticles. or formula present. several polyatomic in held a atoms bonded ions . electrons pair of are between electrons bonded chemical toget her nuclei electrons cations non- for ms a of by t he toget her strongly reaction. t he strong electrostatic atoms and t he bonding become delocalised and are able which remain. These delocalised to move electrons are electrons. force of attraction cations forms between t he t he metallic delocalised bond which holds toget her. metals solid of are due str uctures bonded wit hin t he result t he and from t he crystals be solid t he bonding identied str uctures arrangement bonding. and anions composed t hree-dimensional wit hin based t he on way to forces depend of They are t he are held arrangement are intermolecular t he metal t he way lattice. t he solids. ionic cations to can different par ticles molecular Weak which t he t hree-dimensional regular, lattice. an A unit are between positive of which repeating, ● t he t heir atoms single molecule lattice are in of a electrostatic crystals lattice using as t he regular of are known molecules. mobile proper ties Ionic ratio involves as metal different between t he forces known of electrons. proper ties par ticles are valence as and metal ● represented group a of t he known The anions, properties lattice. compounds for m a t he also ● is pairs metals, t he cr ystal give ions attraction between ● are behave wit hin of electrostatic t hree-dimensional ionic to a strong negative and bond molecule pair a bond ing atoms enough ● in t he and in which These covalent ● of ions Covalent A is compounds toget her. ● cations toget her bot h Many Structure compounds, cr ystal unit, ● bonding positive t hese ● and by of create strong a in ionic a bonding of an ionic regular, bonds. molecules simple t he t he composed toget her small between on par ticles. arranged molecular molecules hold t hem toget her. ● onic and ● Simple polar ● cr ystals t hey molecular solvents Gi ant bonds in molecular high melting electricity cr ystals and molecular covalent giant have conduct t hey have do crystals a Diamond and graphite are ● Diamond and graphite are ● carbon, Diamond is ver y are also ● element, not regular, lattice, but t heir hard, has points, when most molten low or melting conduct dissolve points, electricity composed of as examples a of allotropes. solvents water. dissolve any in non- state. atoms arrangement bonded to form by a macromolecule. giant They atoms are a melting high polar in most in non-metal t hree-dimensional known in dissolved molecular are bonded cr ystals. composed of t he same differently. point and does not conduct electricity. ● Graphite conduct is ‘sof t’ and lubricating, has a high melting point and does electricity. 87 Practice exam-style questions Structure 7 Practice exam-style Multiple-choice 1 Which of calcium t he Ca (PO 2 4 B Ca(PO ) A isotopes B isomers C allotropes following is t he correct formula for D allomers carbon of of carbon carbon Structured 3 question The table gives t he mass number and atomic number of 4 Ca (PO 3 X of 2 four The are: carbon questions 8 2 of PO 3 D graphite questions ) 4 Ca and bonding phosphate? A C Diamond and Y elements. ) 4 2 formula and different of would t he compound formed between Element Mass number Atomic fluorine 19 9 neon 20 10 aluminium 27 13 phosphorus 31 15 number atoms be: a i) Which element would not be capable of forming compounds? ii) b A XY B X Give Two an ionic Name (1 reason elements form i) a in for t he your table answer. are (2 capable of mark) marks) bonding to compound. t hese elements. (1 mark) Y 3 ii) C Give t he formula of t his compound. (1 mark) XY 3 iii) D X By means bonding A two B a occurs c between: Two and a i) non-metal ii) metalloid and a 4 two An atom cross diagram, show wit h an atomic number of 15 and an atom a in covalent Name Give formed. table are (3 capable of atomic number A form a B form an elements. formula of t his compound. Draw a dot and cross diagram to show C form a D not of 9 covalent bonding in ionic metallic bond aqueous wit h solution A water B electrons mark) t his Describe t he compound. (2 marks) i) Why is bonding aluminium in able aluminium. to conduct an (2 marks) electric compound can Total only conduct electricity when 9 conduct become free a electricity when t hey free when t hey t he lattice are are response Wit h in i) aqueous ii) become in aqueous b marks when t hey are in question of a sodium diagram in EACH case, describe chloride reference each sodium to of t he of: graphite. Wit h i) free aid str ucture explain become 15 in solution protons mark) ot her because: molecules ions (1 lattice each solution D mark) (1 compound compounds t he (1 would: Extended C to t he current? onic marks) bonding compound. t hese t he is t he wit h ii) 5 how non-metals d an and non-metal iii) D compound elements form metals metal a dot 3 t his onic C a Y 7 3 of t he t he str ucture and type of (3 marks) (3 marks) bonding, following: chloride is able to conduct electricity aqueous when molten (2 marks) solution ii) 6 Which of t he molecular following is/are t he proper ties of a simple They are usually They conduct They have A iii) soluble electricity in in water. any state. is able to conduct electricity in state compound? graphite (2 bot h sodium melting c Some t he types chloride and graphite have points. of sand high (3 consist of silica, SiO . solid marks) marks) Silica is 2 and low melting points. relatively hard, state has and C and D high not conduct melting electricity point. in Describe any t he only bonding B a does which you would expect to nd in silica. only (2 and Total 88 only mark) only 15 marks Chemical equations and A6 reactions Chemical equations use symbols and formulae to Objectives represent chemical standards for change. writing There chemical are universal equations which make By the be able for chemists all over the world to interpret of this the understand the conventions equations written by others. The theory behind is very important in the chemical you will different used when writing chemical chemical reactions topic to: it ● possible end industry. It ● write equations balanced chemical equations reduces the risk of accidents, can improve productivity ● and can increase the yield of chemicals. ● A6.1 A Writing chemical using formed The equation symbols reactants, and and are t he and any all on t he reactions, i.e. are representation The lef t chemical chemicals side t he of t he by an are or write a compound insoluble balanced in ionic is water equations. equations a chemical are reacting, equation products, separated of t hat whether soluble and shown t he on t he reaction i.e. t he chemicals right side. arrow: products Understanding that shor t hand products reactants Chemists a formulae. shown during reactants is balancing predict use person the chemical same reading a equations conventions chemical when equation writing will chemical understand equations exactly so what it means. The conventions used when writing chemical equations are as follows: ● ● The symbol side of on t he An arrow The ● A plus A and ● means ( ) on is t he and solid is The liquid gas (aq) aqueous conditions above about each separate or reactant formula t he state is placed on t he of each product reactants from t he catalyst. wit hout A are a a used 1 1.2. t he solution for is a up t he as lef t is placed products. and t he symbol where t he or state water reaction to temperature, t he each right product. it means formula of t he The ‘and’. of each reactants follows: chemical in on physical are specic For and af ter used required e.g. catalyst being Unit brackets i.e. reactant wit h’ indicates symbols arrow, each ‘reacts in This which in separate solution, t he catalysts to means written specic to used a is lef t (l) reaction used of symbol ‘produces’. (g) or t he product. products. written a ) (s) Any formula and side. symbol reactant chemical ( sign sign state or equation right arrow plus ● t he a is occur solvent. can specic substance reaction. t he You which will be pressure speeds learn up more example, 898 °C CaCO (s) CaO(s) CO 3 This shows decompose (g) 2 t hat into calcium calcium carbonate oxide and requires carbon heating to 898 °C for it to dioxide. 89 Writing and balancing chemical equations Chemical ● f t he reaction NH is reversible, Cl(s) NH 4 ● will The equation balance When learn on more must each t he AgNO (g) an about arrow ( ) in so t he t he t hat arrow sections equation, following (aq) of each reactions t he is number t he t hat par t in same. For example, of 6.2. atoms will or ions learn of how each to follow. represents a word or a statement. example: KCl(aq) AgCl(s) KNO (aq) 3 equation chloride used. Unit You 3 The is reactions HCl(g) reversible balance side equations reading Consider double and 3 You element a equations reads solution as to follows: ‘silver produce solid nitrate silver solution chloride reacts and wit h potassium potassium nitrate solution’. Balancing You should chemical have noticed equations t hat in t he t hree chemical equations above, t he atoms are not changed during t he reactions. The way in which t he atoms are bonded to each ot her changes, but t here is t he same number of atoms of each element created on nor bot h sides destroyed When writing atoms of each a of in each chemical element equation. chemical equation, on t he n ot her reactions, right you side t hey must of words, are ensure t he atoms only t hat equation are neit her rearranged. is t he t he number same as of t he number on t he lef t side. A chemical equation t hat conforms to t his is known as a balanced You learnt about understand 2H ● 2H ● H chemical how represents represents equation . writing to chemical balance two one formulae chemical atoms of hydrogen, molecule of in equations, not hydrogen, Unit 5. consider bonded To t he help you to following: toget her consisting of two atoms of 2 hydrogen ● 2H bonded represents toget her two molecules of hydrogen and, in total, four atoms of 2 hydrogen H 2 ● 3CO represents t hree molecules of carbon dioxide. n total, t he number which consists 2 of ● atoms Ca(NO of ) 3 each element represents one is 3C and formula 6O unit atoms of calcium nitrate, 2 2 of one Ca ion and two NO ions; t herefore, t he number of atoms of 3 2H 2 each ● element 2Ca(NO ) 3 Figure 6.1.1 Different atoms and 1Ca, 2N represents and two 6O. formula units of calcium nitrate. n total, t he 2 representations number of is of atoms of each element is 2Ca, 4N and 12O. molecules The number in front of each formula in t he list above is called t he A coefcient equations. to produce formulae H as (g) of is not t he hydrogen written. reaction chloride Coefcients between gas. We are used hydrogen can gas summarise when and t his balancing chlorine reaction gas using follows: Cl 2 Studying one Consider coefcient. (g) HCl(g) 2 t his equation we can see t hat t here are two atoms of hydrogen on t he lef t side, but only one atom on t he right side. Also, t here are two atoms of chlorine on t he lef t side, but only one atom on t he right side. The equation is, t herefore, not balanced. f a coefcient, 2, is placed in front of t he formula 90 Chemical for of equations hydrogen chlorine H (g) chloride, on t he Cl 2 The t ver y cannot be t he elements writing write should Write now two atoms of hydrogen and two balancing chemical equations atoms balanced. t he of t heir The of t hat when number t he of always balancing balancing atoms coefcient in remain balanced and be note must of front t he t he of a t he elements formula. formulae can The only be subscripts same. chemical chemical equations equations equations, t he guidelines outlined followed. correct t he – Seven to changing When note gives and 2HCl(g) changed. by to ● now Writing side: (g) is How below t his right impor tant changed af ter reactions 2 equation is and chemical formula for each reactant and product, taking following: t he free common st ate. These elements are H , involving any of t hese exist N 2 , O 2 , as F 2 elements, , diatomic Cl 2 wr ite , Br 2 t he molecules and 2 . n when in reactions 2 for mula for t he diatomic molecule. – n reactions atomic wr ite involving symbol of t he ot her elements element, e.g. if in a t heir free reaction st ate, wr ite involves t he magnesium, Mg. ● Separate t he ● Separate each ● Write ● Star t t he reactants and reactant state and symbol balancing t he products each af ter in an product each elements by by reactant t he arrow. a plus and product sign. product. immediately af ter t he arrow rst. ● Any polyatomic ion which appears unchanged from one side to t he 2 ot her can be balanced as a unit, e.g. if SO appears at bot h sides, 4 consider ● f any it as a single compounds unit (see contain Example hydrogen ✔ Exam It essential or oxygen, balance is from last and balance oxygen last (see Examples 2 and f any elements balance, e.g. occur Fe, Ca, in Cl , t heir Use of coefcients each in element t he leave t hese until t he ver y last to of the each lef t and formula right to sides. balance The t he number formulae must of not atoms reactions Always same 2 front on state, O 2 ● free you chemical can write equations for 3). all ● that hydrogen balanced second tip 4). of check type each you that and arrow, and the correct you on that encounter. have number element the will of both you the atom sides have of given be state symbol for each changed. reactant ● Check t hat t he coefcients are in t he lowest possible and product. ratio. Examples 1 Write a balanced chemical equation for the reaction in which magnesium burns in oxygen to form magnesium oxide as the only product. Write t heir each t he chemical state element Mg(s) formulae symbols. on O Af ter each (g) of t he doing side of reactants t his, t he and determine products t he toget her number of wit h atoms of arrow: MgO(s) 2 Reactants Products Mg 1 Mg 1 O 2 O 1 91 Writing and balancing chemical equations Chemical O does not balance. Mg(s) O Balance by placing a 2 in equations front of t he and reactions MgO 2MgO(s) (g) 2 Reactants Now Products Mg 1 Mg 2 O 2 O 2 Mg does 2Mg(s) not O balance. Balance by placing a 2 in front of t he Mg 2MgO(s) (g) 2 Reactants The 2 gas a (C 2 Mg 2 O 2 O 2 Write t heir is now balanced H 3 on Mg equation Write Products ) and balanced. chemical oxygen to equation form t he each C chemical symbols side H 3 of (g) t he O 8 formulae and of t he determine reaction and between propane steam. of leaving (g) CO 2 (g) H 2 C 1 H 8 H 2 O 2 O 2 elements oxygen t he products atoms of toget her each O(g) CO balance. in . its free Balance Balance state t he t he until H by 1 3 carbon last. and Balance placing a 4 in hydrogen t he C front by of H 3 (g) O 8 t he H still (g) 3CO 2 (g) 4H 2 O(g) 2 C 3 C 8 H 8 O 2 O 6 not 3 Products H does a O 2 Reactants O rst, placing 2 C wit h element Products 3 of of 2 t he and number C t he front reactants t he arrow: Reactants in t he dioxide 8 state None for carbon balance. Balance by 3 placing 4 a 5 10 in front of t he O 2 C H 3 (g) 5O 8 (g) 3CO 2 The 3 4H C 3 C 3 8 H 8 O 10 O 6 t he is now ) 3 (aq) 4 10 balanced. following Ca(HCO O(g) 2 Products H equation Balance (g) 2 Reactants equation: HCl(aq) 2 CaCl (aq) CO 2 (g) H 2 O(l) 2 Determine the number of atoms of each element on each side of the arrow: Ca(HCO ) 3 (aq) HCl(aq) 2 CaCl (aq) 92 Ca 1 H 2 CO 2 1 (g) 2 Reactants 3 Ca 1 H 2 1 C 2 C O 6 O 2 Cl 1 Cl 2 1 H O(l) 2 Products 3 Chemical Star t equations by arrow. front and balancing Ca of t he balances, t he reactions Writing elements but Cl does in t he not product balance. immediately Balance af ter placing ) 3 (aq) 2HCl(aq) CaCl 2 (aq) CO 2 Ca 1 Ca 1 H 2 C 2 H 2 C O 1 6 O Cl 2 2 Cl 2 Balance t he carbon front t he CO Ca(HCO . ) 3 2 and 4 hydrogen Balance t he H next. by Balance placing a 2 t he in C by front (aq) 2HCl(aq) CaCl 2 (g) 1 H 2 C 2 O Cl equation of (aq) ) 3 t his is O(l) 3 placing t he 2CO H a 2 in O 1 H 4 C 2 6 O 4 2 Cl 2 2 (aq) (g) 4 2H O(l) 2 2 6 balanced. equation NaOH(aq) Al(OH) 3 (s) NaNO 3 t he 2 now reaction, H Products Ca following Al(NO n in 2 1 2 Ca t he 2 2 Reactants Balance equations Products 2 4 chemical t he a 2 Reactants The balancing HCl Ca(HCO of by and NO and t he OH ions are (aq) 3 polyatomic ions which 3 remain unchanged treated as element single at each Al(NO ) 3 from units side (aq) one when of t he side to t he ot her. determining t he They number of t herefore, atoms NaOH(aq) Al(OH) 3 (s) NaNO 3 Al NO 1 3 of (aq) 3 Products Al NO 3 1 1 3 Na 1 Na 1 OH 1 OH 3 Start with the product immediately after the arrow. Balance by placing a 3 in front of the OH does not balance. NaOH. Move on to the next product. does not balance. Balance by placing a 3 in front of the NaNO 3 3 Al(NO ) 3 (aq) 3NaOH(aq) Al(OH) 3 Al NO State 3NaNO 1 3 Al NO 1 3 3 Na 3 Na 3 OH 3 OH 3 is now symbols (aq) 3 Products 3 equation (s) 3 Reactants The each arrow. Reactants NO are, of balanced. ionic compounds n Unit 5.5 you learnt t hat most ionic compounds are soluble in water. Some ionic compounds involving ionic compound is are, however, compounds, soluble or it insoluble is ver y insoluble in in water. impor tant water. f it to is When know writing equations whet her insoluble, t hen t he it ionic would 93 Writing and balancing chemical equations always be given t he state t he solubility T able 6.1.1 Solubility All and All of state (aq). ionic Solubility symbol Table (s). 6.1.1 compounds of ionic e.g. f it gives in is equations soluble would t he it solubility and reactions usually r ules for be given determining water. compounds rule compounds soluble, t he symbol Chemical in water Exceptions of Group I compounds metals of are lithium, None. sodium potassium. ammonium Most nitrates compounds and are ethanoates soluble. are None. soluble. Silver ethanoate (CH COOAg) is only slightly soluble. 3 Most chlorides, bromides and iodides are Those soluble (PbCl of ) lead and and silver lead(II) are insoluble. bromide (PbBr 2 soluble Most sulfates are soluble. Those in of (CaSO ) hot All Exam hydrogencarbonates are soluble. Lead(II) are chloride moderately water. lead and and silver barium are sulfate (Ag 4 ✔ ) 2 insoluble. SO 2 ) are Calcium slightly sulfate soluble. 4 None. tip Most carbonates and phosphates are Those of Group I metals and ammonium are soluble. Those of Group I metals and ammonium are soluble. insoluble It is essential that you learn the Most solubility rules so that you metal hydroxides are insoluble. can Barium hydroxide (Ba(OH) ) is moderately soluble, 2 give the correct state symbols calcium hydroxide (Ca(OH) ) is slightly soluble and 2 when This writing is chemical particularly magnesium equations. important ionic metal oxides t hey Those Example of a is very slightly ions a For in only result, t he end known may a ion may be conver ted ● an element in its be ionised. Write t he 2) Rewrite t he atoms up in join to Group to I metals, form the calcium equivalent and barium, react hydroxides. a or ions which different state actually from take t he one par t in in a which to state should an insoluble atom, may be but compound an be i.e. compound may when equation show composed it conver ted followed chemical equation, form wit hin precipitate covalent free balanced individual precipitate steps a as an 1) form may two following of water example, solution solution, ions show as ● any for ions to t hat molecules discharged an ion, writing t he of be i.e. ionic it may equations. reaction. are present in solution in solution as ions. solution 3) Delete bot h not 4) 5) t any sides take ions of par t which t he in t he t he ionic change, i.e. t hose Cancel is t he unchanged, These are i.e. called which are spectator ions and t hey equation which showing actually to t he only take lowest to note t hat when (HNO (aq)) and sulfuric t he par t in possible acids, acid such (H 3 as SO 2 atoms t he or ions which reaction. ratio if necessar y. hydrochloric (aq)), are in acid (HCl(aq)), aqueous solution 4 t hey ionise to form on do reaction. coefcients impor tant acid remain equation. Rewrite nitric 94 soluble. equations ● The a and, star ted. t he 6.1.2 ionic equations two ● in insoluble. with reaction formed are equations. onic Figure ) when Writing (Mg(OH) 2 Most writing hydroxide hydrogen ions, or H ions, and negative anions. Chemical equations and reactions Writing and balancing chemical equations Examples 1 Write t he ionic equation chloride solution 1) t he Write Pb(NO ) 3 2) Rewrite to balanced (aq) for t he produce chemical between lead lead chloride nitrate and 2NaCl(aq) PbCl (s) 2NaNO 2 t he equation solution sodium 2NO showing (aq) sodium solution. ions (aq) 3 present in solution as individual (aq) and nitrate equation: 2 2 Pb reaction insoluble 2Na ions: (aq) 2Cl (aq) PbCl 3 (s) 2Na (aq) 2NO 2 (aq) 3 3) Delete t he Na (aq) and NO (aq) ions since t hey remain unchanged: 3 2 Pb (aq) 2Cl (aq) PbCl (s) 2 2 4) Rewrite t he ionic equation: Pb (aq) 2Cl (aq) PbCl (s) 2 2 Write t he SO (H 2 1) ionic (aq)) to equation produce for t he 2KOH(aq) H SO 2 between sulfate (aq) K 4 2K SO 2 2) reaction potassium and potassium hydroxide and sulfuric acid water. 4 (aq) 2OH (aq) 2H 2H O(l) 2 (aq) 4 2 (aq) SO (aq) 2K 2 (aq) SO 4 2OH (aq) 2H 2 (aq) (aq) 2H 4 O(l) 2 2 2H O(l) 2 4) 2OH (aq) 2H (aq) 2H O(l) 2 5) OH (aq) H (aq) H O(l) 2 3 Write t he (HCl(aq)) ionic to equation produce for t he Key ! reaction magnesium between chloride and magnesium hydrogen and hydrochloric acid It is give 1) Mg(s) 2HCl(aq) MgCl (aq) H 2 2) Mg(s) 2H 2 (aq) 2Cl (aq) Mg the that you correct (g) 2 extremely important gas. fact (aq) 2Cl (aq) H state symbols when writing ionic (g) 2 equations 3) Mg(s) 2H and 2 (aq) (aq) H that (g) the equations 2 balance 4) Mg(s) 2H 2 (aq) Mg (aq) H (g) 2 Summary 1 Write questions balanced a Aluminium b N c CH (g) H 2 (g) The The to f 2 State reaction the Na b KOH(aq) CO 2 between between Ba(NO H O(g) 2 potassium and aluminium hydrogencarbonate Na 3 hydrogen water carbon and to are ) hydroxide and equations HCl(aq) (NH 4 and then ) 4 write NaCl(aq) or (NH ) (aq) SO 2 Na (aq) 4 SO 2 K SO 2 (aq) 4 (aq) (s) in equation H water: for each reaction: O(l) 2 (g) 3 4 (HCl(aq)) 4 NH 4 BaSO acid steam. insoluble ionic (g) hydrochloric PO 3 the CO and water. 2 2 potassium produce soluble KMnO 3 and to 3 3 produce dioxide oxygen compounds CO 2 following (aq) chloride, following ) 4 c (g) 2 between the Fe(NO a oxide (g) CO aluminium reaction Balance reactions: gas. 3 3 NH (g) reaction whether AgI following aluminium 2 produce The the 3 O hydrogen e for oxygen 2 (g) 4 d equations NaNO H O(l) 2 (aq) 3 95 Types of chemical reactions Chemical A6.2 Objectives By the be able end of this topic you identify Chemical the seven main t ake ● chemical give ● write the of reactions reactions place in for m our an integ ral bodies, suc h as par t of our respiration lives, whic h from reactions c hanges energy, to complex reactions, whic h produce glucose phar maceutical reactions examples types chemical reactions types into of of and will to: t hat ● Types equations of the chemical balanced different products. There are descr ibed below. se ven main types of c hemical reactions whic h are main reactions equations types of for chemical Synthesis reactions reactions. Synthesis reactions are reactions in which two or more substances combine chemically to single A reaction synt hesis form A Examples of a is O generally B synt hesis 2Mg(s) product. symbolised by: AB reactions are as follows: (g) 2MgO(s) (g) 2FeCl 2 2FeCl (s) Cl 2 Decomposition Did ? you down being islands coral largely of When the started in of the islands, calcium sugar are composed carbonate. industry Barbados, and carbonate roasted calcium into a first coral compound or was if an juice in lime kilns The calcium used during the to state or is at one from to clarify current dissolved decomposition time A was island a cane, major (Unit in if t he in a single reactant reaction will is broken occur is passed is t hrough solution heated t he (t hermal if t he compound decomposition) when in t he liquid (electrolysis). reaction is generally A symbolised by: B B of decomposition reactions are as follows: cane heat (s) CaO(s) 3 which CO (g) 2 heat industry ) (s) 2PbO(s) 2 4NO (g) O 2 (g) 2 2.5). Single A single displacement d isplacement in its of (displaces) will free ● state always reactions A metal This and a be may t he type of of Mg(s) reaction a element less divided displace single t his involves The in reactive into from t he type CuSO of (aq) single 2HCl(aq) from a free A between state more an takes reactive compound. element t he place element Displacement from a compound or it may acid. reaction AX can generally MgSO (aq) reaction Cu(s) 4 ZnCl (aq) 2 be symbolised B displacement 4 Zn(s) its compound. metal an BX reaction in types. displacement t he element element two anot her hydrogen A Examples reactions compound. anot her displace can displace 96 which decomposition compound aqueous of 3 the A oxide 2Pb(NO within reactions island, produce the extraction sugar are products. unstable, CaCO sucrose more quarried oxide. then reactions or electric Examples was two Caribbean, A calcium reactions know? Decomposition Many (s) 3 2 H (g) 2 are as follows: by: Chemical equations Writing t hese and as reactions ionic Types Cu 2H reactions insoluble solid 2 (aq) Mg Zn(s) chemical equations: 2 Mg(s) of (aq) Cu(s) 2 (aq) Zn (aq) H (g) 2 n t he above appears ● A examples, above non-metal This type of may single X An example Cl (g) of magnesium hydrogen in displace t he anot her displacement AY t his of single 2KBr(aq) more reactive series non-metal reaction AX type is reactivity can t his Ionic Ionic be displacement 2KCl(aq) Br (g) as an ionic a and zinc compound. generally symbolised by: reaction is as follows: (aq) 2Br equation: (aq) 2Cl (aq) Br 2 n from copper 18.1). 2 t his Cl t han Unit Y 2 Writing (see (aq) 2 example, chlorine precipitation precipitation is more reactive t han bromine. sometimes referred reactions reactions are to as double d isplacement reactions . They usually involve two compounds which are in solution, An ionic AX where t he compounds precipitation BY reaction AY exchange is ions. generally symbolised by: BX To have a successful ionic precipitation reaction, one or bot h of t he products must be because incapable t hey form of one undergoing product t he which reverse is reaction. insoluble, known This as a is generally of ionic precipitation reactions are as precipitate that follows: forms result AgNO (aq) KBr(aq) AgBr(s) KNO 3 BaCl of a in is a an solution, chemical often as a reaction. (aq) 3 (aq) Na 2 Writing fact precipitate A Examples Key ! SO 2 t hese as (aq) BaSO 4 ionic (s) 2NaCl(aq) 4 equations: Ag (aq) Br 2 Ba AgBr(s) (aq) 2 (aq) SO BaSO (aq) Neutralisation Neutralisation acid. The acid are a salt An example and reactions reactions is (s) 4 4 are neutralised reactions by t he between base (or a alkali) base (or and t he an alkali) products and an formed water. of a NaOH(aq) neutralisation reaction HCl(aq) is: NaCl(aq) H O(l) 2 Writing t his as an ionic equation: OH (aq) H (aq) H O(l) 2 Redox Redox in reactions reactions, or oxidation–reduction which one reactant reactions will be is covered reduced in more and t he detail in reactions, ot her Unit are chemical reactant is reactions oxid ised. Redox 9. 97 Types of chemical reactions Chemical Reversible Reversible can be reactions direction. f reaction a is occur easily, again. one and reactions reactions reversed reactants equations Most i.e. when t he a direction products reactions reversible, t he are not double can react reversible; arrow of to a produce t hey ( ) chemical is can t he only used. n change original proceed a in reversible reaction, we refer to t he for ward reaction as proceeding from lef t to right and t he A reverse reversible A For ring of backward reaction B NH is C example, ammonia white or for ms near symbolised ammonium hydrogen Cl(s) proceeding from right to lef t. by: D chloride NH 4 ammonium as generally when and reaction (g) chloride is heated, it decomposes into gases: HCl(g) 3 chloride the top f t he ammonia temperature) NH (g) and t hey hydrogen react to chloride form HCl(g) gases ammonium NH 3 are cooled (or mixed at room chloride: Cl(s) 4 ammonium The chloride reaction is, t herefore, reversible and t he equation can be written as follows: NH Cl(s) NH 4 n Figure 6.2.1, hydrogen is Bunsen much cooler many t he and can 6.2.1 chloride HCl(g) t he ammonium gases, and which when t he chloride diffuse gases up reach is heated t he test here, it forms tube. t hey The react ammonia top and Heating ammonium chloride reversible same time products. enter backward reached or f 1 dynamic t he t he are a inside t he occurs stage equal. is of reaction reaction reaction t hen reactions Balance t hat t he leave, around reactions, such Summary form t he a and tube can always in a ring of directions at tube. proceed contains sealed reached The t he system where reaction t he in a bot h mixture where rates of not stop and classify the reactions the Mg(NO ) 3 b Fe(s) following equations, single then displacement, (s) MgO(s) Zn(s) ionic NO 2 precipitation (g) or Cl (g) FeCl HCl(aq) NaOH(aq) AgNO (aq) 3 O (g) (s) 3 H ZnCl SO 2 e substances for ward said to and have (aq) (aq) 4 MgBr (aq) (g) 2 Na SO 2 2 H (aq) 4 AgBr(s) H O(l) 2 Mg(NO ) 3 (aq). 2 as synthesis, neutralisation 2 2 d 2 2 c is reactants questions reactions: a no t he does of equilibrium decomposition, 98 of bur ner n Figure as chloride ammonium (g) 3 Chemical Key ● equations ● Chemical The reactants ● state of each solid, (l) for a balanced of are a equations Writing and, of chemical reactions any determine of chemical reactions using for lef t r ules in an product gas and equation on of bot h sides in which given (aq) for must of t he front Formulae water. is t here placed equation can These be its aqueous be t he products formula on using (s) solution. same formulae. never used are af ter t he number of equation. of must and to useful be They determine in are used changed. t he solubility determining state compounds. show as a only result, t he end atoms up in a or ions which different actually situation take from t he par t one in in star ted. ionic showing ● ionic t hey (g) t he and numbers solubility of at equations. compounds reaction which ● are There symbols representations reactant element balancing Ionic shown liquid, when ionic are chemical each Coefcients of ● are The n Types formulae. right. atoms ● equations and t he for ● reactions concepts symbols ● and equations involves ions t hat are which ions do Spectator ions are t herefore, remain t he writing present not ions in change which unchanged. do These t he full solution in any not are as rst, but ions to way. take lef t equation individual par t out of in a t he reaction nal and, ionic equation. ● There are seven main decomposition, redox ● A and ● A A its An ionic A of A a is to redox a is any synt hesis, precipitation, neutralisation, in which two or more reactants reaction where a single reactant is products. reaction compound is any where reaction to insoluble reaction t he between element an element displaces anot her usually produce solid a t hat involves two compounds in precipitate. forms in a solution, of ten as a reaction. reaction salt reaction reaction more reacting an a reactions: ionic compound. chemical form chemical product. or precipitation neutralisation alkali) ● t he any reaction two and solution precipitate result ● state from aqueous A into is single d isplacement free element ● a of displacement, reactions. reaction form down single in ● to decomposition broken ● reversible synthesis combine types single and occurs occurs when an acid reacts wit h a base (or water. when one reactant is reduced and t he ot her is oxidised. ● A reversible can be reaction reversed reactants easily, occurs i.e. t he when t he products direction can react of to a chemical produce change t he original again. 99 Practice exam-style questions Chemical Equations Practice exam-style questions Write Which of t he following a correctly represents The sulfuric reaction acid to between produce sodium sodium and NaOH(aq) H SO 2 B 2NaOH(aq) (aq) NaSO 4 H b (aq) H 4 SO 2 (aq) Na 4 reaction 2NaOH(aq) H SO 2 (aq) SO The reaction (H O(l) (s) 2H 4 Na each of t he aluminium chloride as and t he chlorine only to product. SO between (aq)), aluminium which oxide produces and sulfuric aluminium sulfate 4 2 2 4 between aluminium 2 SO 2 and water. The reaction and hydrochloric O(l) 2 c C for and water? acid A equation t he hydroxide sulfate chemical reactions. produce chemical reactions write balanced following a 1 and questions 6 Multiple-choice to equations between potassium carbonate solution (aq) 4 2H acid (HCl(aq)) to produce O(l) 2 potassium D Na(OH) (aq) H 2 SO 2 (aq) NaSO 4 chloride, carbon dioxide and water. (aq) 4 d The reaction between et hane (C H 2 2H (g)) and oxygen to 6 O(l) 2 make 2 Which of t he following compounds is soluble in copper(II) B magnesium C zinc sulfate The reaction nitrate and aqueous potassium The reaction and ammonium sulfate solutions to make of lead(II) lead(II) sulfate nitrate. between potassium Aqueous solutions react of which of t he following sodium B zinc to form a chloride sulfate precipitate when and and copper(II) magnesium ammonia hydroxide to form solution potassium C potassium D lead hydroxide nitrate and chloride and sodium ammonium The reaction between (HCl(aq)), which h The reaction between hydroxide following water. calcium makes and hydrochloric calcium sodium and chloride and and water to produce hydrogen. nitrate The reaction between magnesium carbonate hydrogencarbonate t he and hydrogen. i nitrate gas mixed? sodium Consider solution compounds acid A sulfate phosphate g 4 steam. hydroxide calcium would between potassium and sulfate, 3 and carbonate f D dioxide water? e A carbon solution and nitric acid reaction: (HNO (aq)), which produces magnesium nitrate, 3 Mg(HCO ) 3 (aq) 2HCl(aq) MgCl 2 (aq) carbon 2 2CO (g) 2H 2 The best ionic equation for t his reaction dioxide and water. O(l) 2 j is: The reaction and sulfuric and water. between acid (H 2 2 A Mg (aq) 2HCO (aq) 2H 2 (aq) Mg sodium SO (aq)) hydroxide to make solution sodium sulfate 4 (aq) 3 2CO (g) 2H 2 O(l) 2 7 Write balanced f, and ionic equations for B 2HCO (aq) 2H (aq) 2CO 3 (g) 2H 2 O(l) 2 C HCO (aq) 2H (aq) CO 3 (g) H 2 O(l) 2 D HCO (aq) H (aq) CO 3 5 What to type H of reaction would you O(l) 2 consider t he following be? 2Al(s) 3H SO 2 100 (g) 2 (aq) Al 4 A a neutralisation B a single C a double D a synt hesis (SO 2 reaction displacement reaction displacement reaction reaction ) 4 (aq) 3 3H (g) 2 g, i j in question 6 above. t he reactions in c, e, A7 Chemistry often The involves mole determining the concept amount of a Objectives substance how required much to ammonia produce and nitric a product. acid are For example, required By the be able mass to of 1 kg an devise of the atom is another fertiliser so ammonium small method that of nitrate? chemists measuring have the of this method uses the had dene the mass, relative and amount mole and dene atomic, will relative atomic molecular formula relative mass mass molecular and masses the terms mole and mass ● give ● perform Avogadro’s constant mass moles, Relative you mole. molar The terms relative calculate ● of ● A7.1 topic The formula substances; this to: to ● produce end molecular and formula calculations masses and involving number of masses particles. Yo u lear nt in Unit scientists use known relative t he A as mass of a an carbon-12 amu, 1.0 0 3. 3 m uc h atomic ato m atom t herefore, t ha t be cause s malle r m a ss . wit h wa s unit t he ma ss t han They a on e -t welf t h t he a atoms to designed on e -t we lf t h assign e d of g ram t he mass mass of of a a is ex t remely compare s y st e m ma ss of 12.0 0 a wh ic h s mal l, mas s es , c ompares carbo n - 12 a tomic carb o n - 12 t h eir mass a tom has a tom. un i ts a or ma s s of amu. Relative atomic element to mass, compara tive valu e , mass t he is t herefore, one-twe lf t h given t he re la tive s y mb ol compares ma ss of a to mic a t he mass carbo n - 12 mass has no of an a tom. units. atom B ec au se Relative of it an is a a to mic A r n t he denition of relative atomic mass given in t he Key fact box, we use t he word ‘average’ because relative atomic mass takes into account t he Key ! fact relative Relative atomic mass, A , is the r abundance nearest same each whole example, When of t he number, relative calculating logic isotope. by can The be atomic t he found mass masses comparing relative of t heir of in atomic t he periodic calcium covalent masses to mass is and t he 40 an table and ionic of of element, on page uorine compounds carbon-12 to t he 360. For is we 19. average mass element compared the use elements composed of and compounds formed by of an one atom to atom of an one-twelfth of carbon-12. t he atom. Key ! Molecular mass of covalent bonding fact are Relative molecular mass, M , is r molecules. We use t he term relative molecular mass to the compare t he mass of a molecule of a molecular element or compound t he mass of a carbon-12 atom. Relative molecular mass is symbol Compounds of formed by ionic bonding use t he term relative formula mass ionic an element compound wit h are represented by formula units. an molecule or compound one-twelfth determine t he one-twelf t h relative toget her t he relative t he molecular atomic the mass Since values, have mass of a carbon-12 Key ! atom. mass or relative formula mass, masses of all t he elements present in relative no molecular and formula masses are fact formula mass is the we mass of one formula unit t he a compound compared to one- comparative twelfth t hey carbon-12. We of compound. of to compare t he mass of a formula unit of average add to atom Relative To one M r an of given compared t he mass wit h of one-twelf t h average the mass of an atom of units. carbon-12. 101 The mole and mass The mole concept Examples 1 Calculate t he relative molecular mass of nitrogen, N 2. N consists of 2 atoms of N. 2 ∴ relative molecular mass of N (2 14) 28 mass of glucose, 2 2 Calculate t he relative molecular C H 6 C H 6 O 12 ∴ consists 6 atoms of H, 12 atoms of H and 6 6. atoms of O. 6 relative C H 6 3 of O 12 molecular O 12 (6 mass 12) of (12 1) (6 16) 180 6 Calculate t he relative formula mass of magnesium carbonate, MgCO 3. MgCO consists of 1 atom of Mg, 1 atom of C and 3 atoms of O. 3 ∴ relative formula MgCO (1 mass 24) of (1 12) (3 16) 84. 3 The mole We use different terms to represent a xed amount of somet hing, e.g. a dozen apples same can be mole ! Key mole is used of is to number sized par ticles. 12 apples used in describe atoms large or a and a pair anyt hing, mole is, and chemistr y. of of The e.g. a molecules. t herefore, used gloves represents mole represents mole of apples, However, mainly as a a a a two mole mole gloves. xed The number. of represents measurement t gloves, of a a ver y atomic fact Like A represents concept the amount of relative atomic mass, t he mole has been dened using t he carbon-12 a isotope because of its high abundance and stability. t was found t hat 12.00 g substance that contains number particles the same 23 of of as there carbon-12 contains 6.0 10 atoms of carbon-12. One mole represents are 23 t he atoms in 12.00 g of number of atoms in 12.00 g of carbon-12, i.e. 6.0 10 . This number is carbon-12. known as A vogadro’s constant , or N A 23 n ot her words, par ticles of Looking at t he t he ‘amount’ ● ● a ‘par ticles’ can same t he denition can if t he is amount of a substance t hat contains 6.0 10 substance. substance n mole refer t he to a to t hat mole mass substance refer way of t he is a atoms, it was in of a t he Key fact substance box: or t he volume of a gas molecules, found formula t hat units 12.00 g of or ions. carbon-12 contains 23 6.0 10 carbon-12 atoms, it was found t hat: 23 ● 40 g of calcium (Ca) contains 6.0 10 Ca atoms 23 ● 28 g of nitrogen (N ) contains 6.0 10 N 2 molecules 2 23 ● 180 g of glucose (C H 6 O 12 ) contains 6.0 10 C 6 H 6 O 12 molecules 6 23 ● 84 g of magnesium carbonate (MgCO ) contains 6.0 10 MgCO 3 formula f we look numerical is t he NB 102 mass When 3 units. at t he value of masses as one t he mole writing t he given relative of above mass par ticles mole as a of we of t he unit, it see t he t hat each element or mass has compound t he and substance. is usually abbreviated to mol same each The mole Molar The concept The of one mole of a substance is known as its a compound molar mass, or ! M Key Molar molar mass of an element or is given t he unit mass mole or g mol mass, grams, . For example, because 12.00 g of carbon fact M, is the mass, in grams 1 per and mass mass The mole of one mole of a substance. contains 23 6.0 10 carbon atoms, or 1 mol of carbon atoms, t he molar mass of carbon 1 is 12 g mol The molar t hough apples are mass t hey will bot h a different, of are be as Calculating Looking at t he different dozen. just different all t he This t he elements mass from is molar of t he an and one compounds mole, mass because mass ndings of t he of a is as will t he g rapes of atoms t he different from be different mass dozen mass apple just of even of t he one t hough each mass even dozen t hey element of a is g rape. mass above, it can be seen t hat: 23 ● because 40 g of calcium contains 6.0 10 Ca atoms, or 1 mol of 1 Ca atoms, t he molar mass of calcium is 40 g mol 23 ● because 28 g of nitrogen contains 6.0 10 N molecules, or 1 mol of 2 1 N molecules, t he molar mass of nitrogen is 28 g mol 2 23 ● because 180 g of O of glucose contains 6.0 10 C H 6 O 12 molecules, or 1 mol 6 1 C H 6 12 molecules, t he molar mass of glucose is 180 g mol 6 23 ● because 84 g of formula units, magnesium carbonate contains 6.0 10 MgCO 3 or 1 mol of MgCO formula units, t he molar mass of 3 1 magnesium carbonate is 84 g mol Therefore, t he molar mass of an element or compound is t he relative atomic, molecular More or formula mass amount expressed in grams per mole. examples 1 M(H O) (2 ) 64 ) (3 ) (2 1) 16 18 g mol 2 1 M(CuSO 32 (4 16) 160 g mol 40) (2 31) (8 14) (8 1) 4 1 M(Ca (PO 3 ) 4 16) 310 g mol 2 1 M((NH ) 4 Moles Molar mass t he of an 12 (3 16) 96 g mol mass gives us t he relationship element or compound. number of moles or 3 and mass mass CO 2 of an between We can element t he use or number t he molar of moles mass to and t he calculate compound. Examples 1 Calculate t he number of moles in 10 g of calcium carbonate, CaCO 3 First calculate t he molar mass of CaCO 3 1 M(CaCO ) 40 12 (3 16) 100 g mol 3 i.e. mass of 1 mol CaCO 100 g 3 10 ____ ∴ number of moles in 10 g mol 0.1 mol 100 103 The mole and mass The 2 Calculate t he mass of 0.2 mol of sulfuric acid, H calculate t he molar mass of H SO 2 performing 1 SO 2 chemistry, involving the including mole, it ) (2 1) 1 mol H 32 you show each (4 is essential step of i.e. mass of SO by statement. You down of a set making must not numbers a what you are 98 g mol 98 g mass of 0.2 mol of H SO 0.2 98 g 19.6 g 4 clear just put without Moles stating 4 2 clearly 16) your ∴ working 4 those 2 that 4 calculations M(H in 4 tip First When concept SO 2 Exam ✔ mole and number of particles calculating. 23 The number can calculate t hat t he ● t he t he type of f a in number par ticle substance f a are one of in of f is an mole is par ticles a always in substance element, individual substance compound, ● par ticles any 6.0 10 number depends on . of t he Using t his moles. type of fact is e.g. a e.g. bonding and t he noble gases, t hen t he atoms molecular water, metals element, t hen t he e.g. par ticles oxygen, are or a molecules covalent made up atoms a substance par ticles are is an ionic formula compound, units made up e.g. of sodium chloride, t hen t he ions. Examples 1 Calculate t he number of atoms 10 in 0.5 mole of copper, Cu. 23 1 mol Cu contains 6.0 atoms. 23 ∴ 2 0.5 mol Calculate Cu t he contains number 0.5 of 6.0 moles of 10 23 atoms carbon 3.0 dioxide, CO , 10 atoms t hat contain 2 23 2.0 10 carbon dioxide molecules. 23 1 mol CO contains 6.0 10 molecules. 2 23 number of moles in 2.0 2.0 10 6.0 10 __________ 23 ∴ 10 molecules mol 23 We can extend number ● of 1 mol our moles of calculations or water, par ticles H O, of moles inside consists of: a and 1 mol of 2 H ● atoms 2 mol and of 1 mol potassium 0.33 mol par ticles compound. H O For to or t he molecules, or 2 mol of 2 of O atoms carbonate, K CO 2 units, at example: consists of: 2 mol 4 mol of K of K 3 CO 2 3 2 formula look ions and 2 mol of CO ions. 3 ✔ Exam It essential tip Example is correct in your unit that you after place each calculations, the value given especially Calculate t he number of hydrogen atoms in 1.5 mol of met hane, CH 4 your 1 mol CH contains 4 mol H atoms. 4 final answers. have no units The are only values relative that atomic, ∴ 1.5 mol CH contains 1.5 4 mol H atoms 6 mol H atoms 4 molecular and formula masses. 23 1 mol Your answer wrong the 104 unit value is or for incorrect no unit, relative if it has unless mass. it H atoms contains 6.0 10 atoms. the is 23 ∴ 6 mol H atoms contains 6 6.0 10 24 atoms 3.6 10 we Remember substance. par ticles ● of atoms in The mole concept Moles, We can mass now number The of and combine number our of mole and mass particles calculation of moles and mass, and moles and par ticles. Examples 1 Calculate t he number of molecules in 1.8 g of water, H O. 2 1 M(H O) (2 1) 16 18 g mol 2 i.e. mass of 1 mol H O 18 g 2 1.8 ___ ∴ number of moles in 1.8 g mol 0.1 mol 18 23 1 mol H O contains 6.0 10 molecules 2 23 ∴ 0.1 mol H O contains 0.1 6.0 10 molecules 2 22 6.0 10 molecules 23 2 Calculate t he mass of 1.5 10 molecules of hydrogen chloride, HCl. 23 1 mol HCl contains 6.0 10 molecules 23 1.5 number of moles in 1.5 10 __________ 23 ∴ 10 molecules mol 0.25 mol 23 6.0 10 1 M(HCl) 1 35.5 i.e. mass of 1 mol ∴ mass of 0.25 mol 36.5 g mol HCl 36.5 g HCl 0.25 36.5 g 9.13 g 3 3 Calculate t he oxide, O Al 2 number of aluminium ions, Al , in 40.8 g of aluminium 3 1 M(Al O 2 i.e. ) (2 27) (3 16) 102 g mol 3 mass of 1 mol Al O 2 3 moles in 102 g 40.8 _____ ∴ number of 40.8 g mol 0.4 mol 102 3 1 mol Al O 2 contains 2 mol Al ions. 3 3 ∴ 0.4 mol Al O 2 contains 0.4 2 mol Al ions 3 3 0.8 mol 3 1 mol Al Al ions 23 ions contains 6.0 10 ions 3 ∴ 0.8 mol Al 23 ions contains 0.8 6.0 10 ions 23 Summary 1 Calculate a mass of Calculate a 3 20 g of Calculate 10 ions of: sodium sulfate, Na the number of moles b number of 1.2 mol of glucose, 4 C H 6 O 12 6 in: neon the b SO 2 2 questions the 0.25 mol 4.8 molecules in 63.0 g of 1.5 mol magnesium of hydrogen carbonate. chloride, HCl. 23 4 Calculate Ca (PO 3 5 the mass of the number 2.5 10 formula units of calcium phosphate, ) 4 2. Calculate of molecules in 34 g of ammonia, NH 3 6 Calculate the number of chloride ions in 6.8 g of zinc chloride, ZnCl 2 105 The mole and gas volumes The A7.2 Objectives By the be able end of this topic you The state gas volumes Gases have ver y small masses because of t heir low densities, so chemists have Avogadro’s ● dene molar ● perform relationship occupied by t he between t he number of moles of a gas and t he gas. volume calculations and t he law volume moles and concept will to: investigated ● mole mole volumes involving of gases. n 181 1, Amedeo Avo ga dro notice d t h at a ll gase s un d er t h e same c on d iti on s of temperature t he same and number pre ssure, of an d mo le cules. o cc u pying He propose d t he same volume, A vogad ro’s con t ain law 3 As ! Key at fact an a example, using temperature of Avogadro’s 25 °C and law, we pressure can of say t hat 101.3 kPa 100 cm has t he of same oxygen gas number of 3 molecules Avogadro’s law states that as of 100 cm nitrogen gas at 25 °C and 101.3 kPa. equal 23 volumes same and of all gases, conditions pressure, number of of under the temperature contain the same f t he number 1 mol must of all of molecules gases occupy t he under same in t he each gas same is 6.0 10 conditions of , i.e. 1 mol, it temperature follows and t hat pressure volume. molecules. Molar The volume volume of one mole of a gas is known as its molar volume, or V m ! Key fact Molar volume is, t herefore, t he volume of a gas which contains 23 Molar volume, V is the volume 6.0 10 molecules of t he gas. m occupied by 1 mol of a gas. Since temperature volume of ● will and depend pressure on bot h of bot h t hese. affect t he Chemists volume mostly of a work gas, wit h molar two sets conditions. Stand ard temperature and pressure , or stp, which equates to a o temperature of 0 C (273 K) and a pressure of 101.3 kPa 3 Molar ● Room volume at stp temperature temperature of is 22.4 dm and 25 °C and a 22 400 cm or rtp, which pressure of Molar t he volume volume volume number of of at r tp gives a gas. moles of us is a atmosphere). 24 000 cm relationship can use t he to (1 3 or t he We a 24.0 dm equates 101.3 kPa 3 Molar atmosphere). 3 or pressure , (298 K) (1 between molar volume t he to number calculate of moles t he and volume or gas. Examples 1 Calculate t he volume occupied by 0.25 mol nitrogen, N , at stp. 2 3 Volume of 1 mol of N at stp 22.4 dm 2 3 ∴ volume of 0.25 mol of N at stp 0.25 22.4 dm 3 5.6 dm 2 3 2 Calculate t he number of moles in 2.4 dm of oxygen gas, O , at r tp. 2 3 Volume of 1 mol of O at r tp 24.0 dm 2 2.4 _____ 3 ∴ number of moles in 2.4 dm of O at r tp mol 0.1 mol 2 24.0 We can moles, 106 now mass, combine volume our and calculations number of wit h par ticles. t hose in Unit 7 .1 to involve The mole concept The mole and gas volumes Examples 1 Calculate t he volume occupied by 6.4 g of oxygen, O at stp. 2 Calculate t he molar mass of O gas. 2 1 M(O ) 2 16 32 g mol 2 i.e. mass of 1 mol of O 32 g 2 6.4 ____ ∴ number of moles in 6.4 g mol 0.2 mol 32 3 volume of 1 mol O at stp 22.4 dm 2 3 ∴ volume of 0.2 mol O gas at stp 0.2 22.4 dm 3 4.48 dm 2 3 2 Calculate t he mass of 600 cm of carbon dioxide, CO , at r tp. 2 3 Volume of 1 mol CO at r tp 24 000 cm 2 600 _______ 3 ∴ number of moles in 600 cm mol 24 000 0.025 mol 1 M(CO ) 12 (2 16) 44 g mol 2 i.e. mass of 1 mol CO 44 g 2 ∴ mass of 0.025 mol CO 0.025 1.1 g 44 g 2 3 3 Calculate t he number of molecules in 6.72 dm of ammonia, NH , at stp. 3 3 Volume of 1 mol NH at stp 22.4 dm 3 6.72 _____ 3 ∴ number of moles in 6.72 dm mol 22.4 0.3 mol 23 1 mol NH contains 6.0 10 molecules 3 23 ∴ 0.3 mol NH contains 0.3 6.0 10 molecules 3 23 1.8 10 molecules 22 4 Calculate chloride t he gas, volume HCl at occupied by 4.5 10 molecules of hydrogen r tp. 23 1 mol HCl contains 6.0 10 molecules. 22 number of moles in 4.5 4.5 10 6.0 10 __________ 22 ∴ 10 molecules mol 23 0.075 mol 3 volume of 1 mol HCl at r tp 24 dm 3 ∴ volume of 0.075 mol HCl at r tp 0.075 1.8 dm 24.0 dm 3 Summary 1 Calculate questions the ammonia, mass, volume and number of molecules in 2.5 mol of NH 3 3 2 Calculate the number 3 Calculate the volume of of atoms 16 g of in 4.8 dm sulfur of neon dioxide, gas SO , at at rtp. stp. 2 3 4 Determine the mass of 840 cm of oxygen gas, O , at rtp. 2 107 The mole and concentration of solutions A7.3 Objectives By the be able end of The this topic you The You explain what is meant of a have already explain the terms a solution solutions come and across saturated. ways of describing However, we can solutions express such t he as dilute, concentration in more solutions. precise The ways, which concentration allow of a us to perfume solution is a calculations measure of t he mass quantity concentration of solution involving ● concentration by of concentration and concept will to: concentrated ● mole mole and of a solute dissolved in molar a xed volume 3 of solution usually used is 1 dm of t he solution. The volume 3 , i.e. 1000 cm concentration dene ● the term Concentration standard of a solution can be expressed in two ways. 3 solution perform ● ● calculations involving Mass of concentration , solution. The unit which for gives mass t he mass of concentration solute is dissolved grams of solute in 1 dm per cubic 3 concentrations of solutions. decimetre ● Molar of solution or concentration , g dm which gives t he number of moles of solute 3 dissolved in 1 dm of solution. The unit for molar concentration is moles 3 of solute per cubic decimetre of solution or mol dm t is ver y impor tant to note t hat concentration is expressed as t he quantity of 3 solute in 1 dm 3 of solution and not in 1 dm of solvent. Example A solution of sodium hydroxide contains 10.0 g of sodium hydroxide 3 Did ? you dissolved know? in 1 dm of 3 g dm Molar concentration may solution. Express t he concentration of t he solution in 3 and mol dm also 3 The be called molarity molarity. is M. A The unit solution solution contains 10.0 g of NaOH in 1 dm for with 3 a Therefore, mass concentration 10.0 g dm 3 concentration be or described ‘1 M of 1 mol dm as a ‘1 may molar To solution’ determine hydroxide solution’. t he molar concentration, nd t he number of moles of sodium present: 1 M(NaOH) Key ! i.e. mass of 1 ∴ number 23 mole 16 1 40 g mol NaOH 40 g fact 10 ___ of moles in 10.0 g NaOH mol 40 A standard solution is one whose concentration is known 0.25 mol accurately. 3 Therefore, A molar standard concentration 0.25 mol dm solution A solution whose concentration is known accurately is referred to as a standard solution. A standard solution is made in a volumetric ask as shown in Figure meniscus of the solution 3 7 .3.1. These asks come in various sizes, e.g. 100 cm , 3 250 cm 3 , 500 cm and 3 etched line 1 dm indicating . A known mass of solute is added to the ask and distilled water is then 3 volume, e.g. 250 cm added until the solution reaches the mark on the neck of the ask. 3 To make mass volumetric a fixed flask volume of a standard solute solution required must which be does not calculated have a volume of 1 dm , rst. contains of solution Example when the the meniscus etched 3 e.g. is on line, Determine t he mass of potassium carbonate which must be dissolved in 250 cm 3 distilled water to make 250 cm concentration of 0.2 mol dm of potassium carbonate solution wit h 3 3 108 Figure 7.3.1 A volumetric ask 1000 cm 3 (1 dm ) of t he required solution contains 0.2 mol K CO 2 3 a t he The mole concept The mole and concentration of solutions 0.2 _____ 3 ∴ 1 cm of t he required solution contains mol K CO 2 3 1000 3 and 250 cm of t he required solution contains 0.2 _____ 250 mol K CO 2 0.05 mol K 3 CO 2 3 1000 Therefore 0.05 mol K CO 2 is required to make t he solution. 3 1 M(K CO 2 i.e. ) (2 39) mass of 1 mol K CO 2 ∴ 12 mass 16) 138 g mol of Therefore 0.05 mol t he mass 138 g 3 K CO 2 of Making Your a K CO may manipulation use and 138 g 6.9 g required is 6.9 g 3 standard teacher 0.05 3 2 ● (3 3 solution this activity to assess: measurement. 3 Y ou are going Y ou will be to make 250 cm 3 of sodium carbonate solution with a concentration water, balance, of 0.1 mol dm 3 supplied with sodium carbonate, distilled a a sheet of weighing paper, a 100 cm beaker, 3 a glass rod and a 250 cm volumetric ask. Method 1 Calculate the mass help you.) above to 2 Weigh a 3 Weigh the 4 Carefully 5 Add 6 Transfer 7 Rinse 8 of mass of the sodium the distilled the rod to with distilled water three Add distilled water to until Place the the bottom stopper on of stir the the the ask. determined to the beaker, with over transfer line meniscus make the solution. (Use the calculation given in the example the in your calculation making glass rod sure until all it is the on all the sheet of weighing paper. transferred. sodium carbonate has dissolved completely . ask. water the to balance. solution and below required you volumetric times just a carbonate distilled with on carbonate and the carbonate paper sodium water solution glass sodium weighing transfer some drop 9 sheet of is Holding in the on the the beaker these and washings volumetric the transfer to the ask. the ask Add washings each the nal to the ask. Wash the beaker time. quantity of distilled water drop by line. stopper in place, invert the ask three times to mix the solution. Calculations We can extend our calculations involving solutions as shown in t he examples below. Examples 1 Calculate t he molar concentration of a solution of hydrochloric acid, 3 HCl, which has a mass concentration of 9.125 g dm 1 M(HCl) 1 i.e. mass of ∴ number 35.5 1 mol 36.5 g mol HCl 36.5 g 9.125 ______ of moles HCl in 9.125 g mol 0.25 mol 36.5 109 The mole and concentration of solutions The mole concept 3 i.e. number of moles HCl in 1 dm 0.25 mol 3 Therefore, 2 Calculate which molar t he concentration molar contains 6 g 0.25 mol dm concentration of sodium of a solution hydroxide of sodium dissolved in hydroxide distilled water to 3 make 200 cm Calculate of t he solution. molar mass of sodium hydroxide, NaOH. 1 M(NaOH) i.e. mass of ∴ number 40 g mol 1 mol of NaOH 40 g 6 ___ of moles in 6 g NaOH mol 0.15 mol 40 3 200 cm of solution contains 0.15 mol NaOH 0.15 ____ 3 ∴ 1 cm of solution contains mol NaOH 200 0.15 3 and 1000 cm ____ 3 (1 dm ) of solution contains 1000 mol NaOH 200 0.75 mol NaOH 3 Therefore t he molar concentration 0.75 mol dm 3 3 Determine how many moles of sodium sulfate are present in 250 cm of a 3 sodium sulfate solution which has a molar concentration of 0.2 mol dm 3 1 dm of solution contains 0.2 mol Na SO 2 , 4 3 i.e. 1000 cm of solution contains 0.2 mol Na SO 2 3 ∴ 4 0.2 _____ 1 cm of solution contains mol Na SO 2 4 1000 0.2 _____ 3 and 250 cm of solution contains 250 mol SO Na 2 4 1000 0.05 mol Na SO 2 Therefore, 4 You wish number to make of a moles sodium of sodium chloride sulfate solution present wit h a 4 0.05 mol molar 3 concentration chloride. of What Calculate t he 0.25 mol dm is t he molar , maximum mass of but you volume sodium only of have 1 1.7 g solution chloride, you of sodium can make? NaCl. 1 M(NaCl) 23 35.5 i.e. mass of 1 mol ∴ number 58.5 g mol 58.5 g. 1 1.7 _____ of moles in 1 1.7 g mol 58.5 0.2 mol 3 Required solution has a molar concentration of 0.25 mol dm , 3 i.e. 0.25 mol NaCl is contained in 1 dm of solution 3 or 0.25 mol NaCl is contained in 1000 cm of solution. 1000 _____ ∴ 1 mol NaCl is contained in 3 cm of solution 0.25 1000 _____ and 0.2 mol NaCl is contained in 3 0.2 cm of solution 0.25 3 800 cm of solution 3 Therefore, the maximum volume of solution which can be made is 110 800 cm The mole concept The Summary 1 Dene 2 Calculate the mole and chemical formulae questions terms the ‘molar mass concentration’ concentration and and ‘standard molar solution’. concentration if 2.8 g of potassium hydroxide is dissolved in 3 distilled water to make up 500 cm of solution. 3 3 What mass of calcium chloride, CaCl , needs to be weighed to make a solution of volume 200 cm and 2 3 concentration 0.1 mol dm ? 3 4 How many moles of sodium carbonate are present in 400 cm of sodium carbonate solution, which has a 3 concentration A7.4 The Empirical n terms of of 0.25 mol dm mole and and ? chemical molecular moles, a chemical formulae Objectives formulae formula shows how many moles of By the be able each ● element combine to form one mole of t he compound. For example, H O n Unit 2 mol 5.1 you of hydrogen learnt t hat atoms combined chemical formulae wit h can 1 mol be of oxygen written in atoms. t hree We The ● will be considering empirical ratio between formula , t he atoms two of which or t hese gives ions in ways t he t he here. simplest whole number this explain the terms molecular atoms onic t he of each element compounds ratio of Covalent t he formula , are ions which present always wit hin compounds are gives in one mole represented t he actual ● by of number t he of moles will formula and composition the molecular formulae empirical of and a compound mole compound. t he you empirical determine determine the composition The ● topic molecular percentage main ● ways. of to: formula, 2 represents end percentage of a compound. of compound. empir ical formulae , which give compound. represented by molecular for mulae . The empir ical and molecular for mulae of covalent compounds may be t he same, e.g. water (H O), ammonia (NH 2 ) and met hane be a simple molecular whole for mula of we we know can use molecular and its To we butene know is multiple C H t hese to work t he of a molar of out t he t he and of or its t he t he molecular empir ical for mula for mula, for mula is e.g. 2 elements, empirical by mass, formula is mass compound, t he t he CH 8 compound of empir ical different of from we in a t he t he can compound, compound. empirical use t his to t hen f t he formula work out formula. determine of propor tions formula molecular moles of t he t his ), 4 number 4 f (CH 3 may t he each empirical element formula, present and we t hen need to calculate determine t he t he number simplest mole of ratio elements. Examples 1 A sample of potassium, empirical mass (g) molar mass a solid 4.34 g is of formula decomposed chromium of t he and and found 5.34 g of to contain oxygen. 6.52 g What is of t he compound? K Cr 6.52 4.34 O 5.34 39 52 16 1 (g mol ) 6.52 4.34 ____ number of moles simplest mole ratio 2 5.34 ____ 39 0.167 ____ 52 1 0.083 0.333 16 4 111 The mole and chemical formulae The The empirical formula is K of 2 To each On determine element analysis, 6.7% a by t he t he sample hydrogen and 4 simplest smallest of concept CrO 2 Note: mole mole glucose 53.3% ratio, number, was oxygen. found The divide i.e. t he number of moles 0.083. to contain molar mass 40.0% of t he carbon, compound is 1 180 g mol . f of t he each mass Determine t he element mass t he sample can be (g) is molecular assumed expresses in formula to be of 100 g, glucose. t hen t he percentage of grams. C H 40 6.7 O 53.3 12 1 16 1 molar mass (g mol ) 40 6.7 ___ number of moles simplest The mole ratio empirical 53.3 ___ ____ 3.3 12 6.7 1 1 2 formula of glucose is 3.3 16 1 CH O 2 To determine t he molecular formula, calculate t he molar mass of CH O: 2 1 M(CH O) 12 (2 1) 16 30 g mol 2 1 M(glucose) 180 g mol 180 ____ Ratio between M(glucose) and M(CH O) 6 2 30 ∴ t he The molecular molecular formula formula of is 6 t he glucose is empirical C H 6 Percentage The by of composition each composition of . 6 composition percentage mass, O 12 formula. element water in shows of the what a compound compound. percentage indicates For of the the example, mass of a the percentage, percentage water molecule is made up of hydrogen and what percentage is made up of oxygen. f we mass, know of t he each 1 mol of 1 mol of t he t he formula element of a compound, present compound and can t he be t he percentage calculated mass which by each composition, calculating element t he by mass of contributes to compound. Examples 1 Calculate t he percentage composition of hydrogen 1 M(H O) (2 1) 16 18 g mol 2 i.e. mass of 1 mol H O 18 g 2 Mass of hydrogen in 1 mol H O 2 1 2 2 ___ ∴ percentage hydrogen 100% 18 Mass of oxygen in 1 mol H 11.11% O 16 g 2 16 ___ ∴ percentage oxygen 100% 18 112 88.89% 2 g and oxygen in water. The 2 mole concept Calculate t he phosphate, The percentage, (NH ) 4 by mass, of nitrogen in mole and chemical reactions ammonium PO 3 4 1 M((NH ) 4 i.e. PO 3 mass ) (3 14) of 1 mol (NH ) 4 Mass of (12 1) 31 (4 14 g 16) 149 g mol 4 nitrogen in PO 3 149 g 4 1 mol (NH ) 4 PO 3 3 42 g 4 42 ____ ∴ percentage nitrogen 100% 149 Summary 1 On analysis Determine 2 A liquid 28.19% questions a compound the used empirical in rocket was found formula fuel is of to contain the found to 11.64 g of sodium, 16.20 g of sulfur and 12.15 g of oxygen. compound. consist of 3.04 g of nitrogen and 6.94 g of oxygen. The acid, SO molar mass of the 1 compound 3 Calculate is 92 g the mol . Determine percentage the composition molecular of formula hydrogen, sulfur of the and compound. oxygen in sulfuric H 2 4 Determine the percentage, by mass, of carbon in aluminium carbonate, Al (CO 2 A7.5 The n The Law Un i t mole of 6 .1 yo u lear nt reactions, c hemical e qu a t i o n of This Key is t he t hat t h ey t he e qu a t i o n summed fact chemical Conservation c hemical side and up in a to m s are o n ly number m u st t he of be L aw of neit her rear ranged, a to m s same of as created and eac h t he d e st r oye d when element number C o n s e r vat i o n nor t hat of ) 3 3 Objectives Matter are of t he reactions 4 on on t he M at te r in wr iting t he lef t g i ve n By the be able ● ● in the t he ● this Law topic you will of Conservation Matter apply the mole balanced side. b ox . of to: state of a r ight end concept chemical using masses apply the to equations mole concept to mole concept to ionic equations Since all t he atoms t hat were present at t he beginning of t he reaction are ● apply the present at t he end of t he reaction, it follows t hat t he total mass of t he products balanced must We be can water. t he same prove The as t his t he using balanced total t he mass of reaction equation for t he original between t he and oxygen to make ● using volumes of apply the concept balanced is: using 2H (g) O 2 This (g) 2H 2 molecules on a reactant chemical to equations concentration of solutions. O(g) of H 1 molecule of O bigger and 2 molecules of H 2 scale, t he product. The coefcients equation, O 2 show t he t herefore, number of moles of each means: ! 2 mol of H 1 mol of O 2 2 mol of 2 H we now take t his a step Key O fur t her and use our mole/mass relationship, means: Law 1) g of H 1(2 16) g of 2 4 g of H 2 O 2[(2 1) 16)] g of 2 32 g of O H Conservation states neither be a that created chemical matter nor of can destroyed reaction. O 2 36 g 2 of Matter during 2(2 fact 2 The it gases 2 2 f mole means: 2 Or, equations reactants. hydrogen reaction chemical of H O 2 113 The mole and chemical reactions The We can total We clearly mass can of see t he use t hat t he original balanced mass of reactants, chemical t he water hydrogen equations produced and to is oxygen, determine mole t he i.e. t he concept same as t he 36 g. quantities of unknown reactants and products in a reaction. f t he quantity of one reactant or product ot her is known, reactants Mass and and it is possible to calculate t he quantities of any of t he products. chemical reactions When answering questions involving masses of reactants and products, you will always be given the mass of one reactant or product and be asked to determine the mass of another reactant or product. To do this we use our mole/mass relationship and the mole ratio from the balanced equation for the reaction. The 1) steps Calculate its 2) involved given t he whose Use t he t he unknown 3) Use 1), of 4) t he and t he t he 3), write f number number and you t he its molar and have of found in product using The known reactant or product is t he 2), of of t he been to whose t he or calculate unknown equation t he reactant its you are product t he or ratio products. The calculating. found number product of in step moles found in mass equation before mole and/or mass reactant determine given chemical determine to t he question. reactants known step t he one product. not in to or mass, follows: or unknown t he as reactant given is are known reactant moles problems t he equation product ratio of mass. been t he moles molar balanced moles have or of mole of mass–mass chemical known reactant t he step its you unknown Use Note: and mass balanced between solving number mass one in for you t he begin reaction, your you must calculation. Examples 1 Calculate t he magnesium The mass in balanced 2Mg(s) of excess magnesium O formed by burning 12 g of oxygen. equation oxide for t he (g) reaction is: 2MgO(s) 2 The mass of t he magnesium 1) Find t he reactant, oxide, is number Calculate t he to of magnesium be moles molar is known. The mass of t he product, determined. mass of of Mg using its mass and molar mass: Mg. 1 M(Mg) 24 g mol i.e. mass 1 mol ∴ number of Mg 24 g moles in 12 g 12 ___ of of Mg mol 0.5 mol 24 2) Use t he balanced between 2 mol ∴ 3) Mg 1 mol Use to t he and form Mg Mg chemical forms t he equation to determine t he mole ratio MgO: 2 mol number calculate 0.5 mol 114 Mg of MgO. 1 mol moles number forms MgO of of 0.5 mol Mg from moles MgO of 1), and MgO t he mole produced: ratio from 2), The mole 4) concept Use t he The number determine t he of moles mass of of MgO MgO from 3), and its molar mass, mole and chemical reactions to produced. 1 2 M(MgO) 24 i.e. mass of 1 mol ∴ mass of 0.5 mol Determine of sodium t he 16 mass chloride, of MgO of of The equation CO 2 The (s) 40 g sodium acid. Na MgO when hydrochloric balanced 40 g mol t he for 0.5 carbonate sodium t he 40 g 20 g required carbonate reaction 2HCl(aq) to mass of wit h 2NaCl(aq) CO (g) H 2 t he product, sodium sodium carbonate, is chloride, to be 23.4 g excess is: 3 reactant, produce reacts is known. O(l) 2 The mass of t he determined. 1 1) M(NaCl) 23 35.5 i.e. mass of 1 mol ∴ number NaCl 58.5 g mol 58.5 g 23.4 _____ of moles in 23.4 g mol 0.4 mol 58.5 2) 1 mol Na CO 2 forms 2 mol NaCl. forms 0.4 mol 3 1 __ 3) 0.4 mol Na CO 2 NaCl 0.2 mol Na 3 CO 2 3 2 1 4) M(Na CO 2 i.e. ) (2 23) mass of 1 mol Na CO 2 ∴ 3 mass Determine of 0.2 mol t he magnesium The 12 (3 16) 106 g mol 3 decrease carbonate balanced MgCO equation (s) 0.2 in is 106 g 3 106 g mass heated for t he t hat decrease nd t he would until its reaction MgO(s) CO 3 The 21.2 g occur mass when remains 21.0 g of constant. is: (g) 2 in mass decrease in is due mass, to t he t he loss mass of of carbon carbon dioxide, dioxide t herefore, produced to must be mass of determined. The t he mass of t he product, reactant, carbon magnesium dioxide, is to be carbonate, is known. The determined. 1 1) M(MgCO ) 24 12 (3 16) 84 g mol 3 i.e. mass of 1 mol MgCO 84 g 3 21.0 _____ ∴ number of moles in 21.0 g mol 0.25 mol 84 2) 1 mol MgCO forms 1 mol CO 3 3) 0.25 mol 2 MgCO forms 0.25 mol CO 3 2 1 4) M(CO ) 12 (2 16) 44 g mol 2 i.e. mass of 1 mol CO 44 g 2 ∴ mass of 0.25 mol CO 0.25 44 g 11.0 g 2 Therefore, We four can also t he decrease apply t he in mass mole is 11.0 g concept to ionic equations using t he same steps. 115 The mole and chemical reactions The mole concept Example Calculate t he mass of lead(II) hydroxide t hat could be produced when a solution containing 3.4 g of hydroxide ions reacts wit h a solution containing excess The lead ionic ions. equation for t he reaction is: 2 Pb (aq) 2OH (aq) Pb(OH) (s) 2 The of mass t he of t he product, hydroxide lead(II) ions present hydroxide, is to in be t he solution is known. The mass determined. 1 1) M(OH ) 16 i.e. mass of ∴ number 1 1 mol 17 g mol OH ions 17 g 3.4 ____ of moles in 3.4 g mol 0.2 mol 17 2) 2 mol OH ions form 1 mol Pb(OH) 2 3) 0.2 mol OH ions form 0.1 mol Pb(OH) 2 1 4) M(Pb(OH) ) 207 (2 16) (2 1) 241 g mol 241 g 2 i.e. mass of 1 mol Pb(OH) 241 g 2 ∴ mass of 0.1 mol Pb(OH) 0.1 24.1 g 2 Gas Exam ✔ volumes used must pay very careful reactions to determine the conditions under involving i.e. rtp, stp or the to correct gases ensure value and volume t he of mole a reactant ratio from or t he product using balanced t he equation t he reaction. occur, that for unknown relationship which for reactions t he attention mole/volume use chemical A balanced chemical equation for a reaction which involves gases can also be You to and tip you When answering questions involving volumes of gases, use t he same four molar steps as are used in solving mass–mass problems. volume. Example Nitrogen reacts wit h hydrogen to produce ammonia. Calculate t he minimum 3 volume of hydrogen t hat would be required to react completely wit h 6.0 dm of nitrogen The at balanced N (g) r tp. equation 3H 2 The t he (g) reaction 2NH 2 volume reactant, for of is: (g) 3 t he hydrogen, reactant, is to be nitrogen, is known. The volume of t he ot her determined. 3 1) Volume of 1 mol N at r tp 24 dm 2 6.0 ____ 3 ∴ number of moles in 6.0 dm mol 0.25 mol 24 2) 1 mol N reacts wit h 3 mol H 2 3) 0.25 mol 2 N reacts wit h 3 0.25 mol H 2 0.75 mol H 2 2 3 4) Volume of 1 mol H at r tp 24.0 dm 2 3 ∴ volume of 0.75 mol H at r tp 0.75 24.0 dm 3 18.0 dm 2 Problems can also be solved involving bot h mass and volume using t he same four 116 steps. The mole concept The mole and chemical reactions Example Calculate t he volume of sulfur trioxide gas formed at r tp when 9.6 g of oxygen reacts The wit h excess balanced 2SO (g) sulfur equation O 2 dioxide. for t he (g) reaction 2SO 2 is: (g) 3 The mass of t he reactant, oxygen, is known. The volume of t he product, sulfur dioxide, is to be determined. 1 1) M(O ) 32 g mol 2 i.e. mass of 1 mol O 32 g 2 9.6 ____ ∴ number of moles in 9.6 g mol 0.3 mol 32 2) 1 mol O forms 2 mol SO 2 3) 0.3 mol 3 O forms 2 0.3 mol SO 2 0.6 mol SO 3 3 3 4) Volume of 1 mol SO at r tp 24.0 dm 3 3 ∴ volume of 0.6 mol SO at r tp 0.6 24.0 dm 3 14.4 dm 3 Molar concentration and chemical reactions A balanced chemical equation for a reaction which involves a solution whose volume t he and mass same of four molar t he steps concentration ot her reactant, as solving for or are t he mass known mass and or can also volume volume be of used a to determine product, using t he problems. Examples 3 1 To prepare t he salt, sodium sulfate, a student adds 50 cm of sodium to excess 3 hydroxide sulfuric The solution acid. wit h Calculate balanced equation 2NaOH(aq) H a t he for SO 2 The are volume known. and The 3 1) 1000 cm mass t he (aq) sulfate SO 2 t he product, t hat would form. of (aq) 2H 4 t he reactant, sodium O(l) 2 sulfate, sodium is to be hydroxide, determined. 3 (1 dm 1 cm 2.0 mol dm is: Na concentration of of sodium reaction ) NaOH(aq) contains 2 mol NaOH 2 _____ 3 ∴ of 4 molar mass concentration NaOH(aq) contains mol NaOH 1000 2 _____ 3 and 50 cm NaOH(aq) contains 50 mol NaOH 0.1 mol NaOH 1000 2) 2 mol NaOH forms 1 mol Na SO 2 4 1 __ 3) 0.1 mol NaOH forms 0.1 mol Na SO 2 0.05 mol 4 Na SO 2 4 2 1 4) M(Na SO 2 i.e. mass of ) (2 23) 1 mol Na SO 2 ∴ mass of 32 (4 16) 142 g mol 4 0.05 mol 142 g 4 Na SO 2 0.05 142 g 7.1 g 4 117 The mole and chemical reactions The 2 What volume when 20 cm reacts wit h of carbon dioxide, measured at stp, would be mole concept produced 3 The (CO 2 ) is (s) acid aluminium equation 3 volume acid, hydrochloric excess balanced Al The 3 of for wit h a concentration t he reaction 6HCl(aq) is: 2AlCl (aq) 3CO 3 and molar The concentration volume 1.5 mol dm carbonate? 3 known. of of t he of t he product, (g) 3H 2 reactant, carbon O(l) 2 hydrochloric dioxide is to be determined. 3 1) 1000 cm HCl(aq) contains HCl. 1.5 _____ 3 ∴ 1.5 mol 1 cm contains mol HCl 1000 1.5 _____ 3 and 20 cm contains 20 mol HCl 0.03 mol HCl 1000 2) 6 mol HCl form 3 mol CO 2 ∴ 2 mol HCl form 1 mol CO 2 1 __ 3) 0.03 mol HCl forms 0.03 mol CO 0.015 mol CO 2 2 2 3 4) Volume of 1 mol CO at stp 22.4 dm 2 3 ∴ volume of 0.015 mol CO at stp 0.015 22.4 dm 2 3 Summary 1 Ethene (C C H 2 If 2 2.8 g ) burns (g) the oxygen following 3O 4 of in to form carbon (g) 2CO 2 ethene (g) 2H 2 burn in excess of moles in 2.8 g b calculate the number of moles of carbon c calculate the mass carbon d calculate the volume carbonate heated. Carbon gas. of carbonate monoxide the dioxide carbon decomposes Calculate Calculate of is gas the O(g) oxygen, number calcium steam 2 the of and equation: calculate Calcium dioxide 4 to a when 3 questions H 2 according 0.336 dm of ethene dioxide formed formed dioxide into mass of formed calcium carbon at oxide dioxide stp. and carbon released dioxide when 300 g heated. reacts volume with and oxygen mass of gas to carbon form carbon monoxide gas dioxide required to 3 produce 4 4 dm Potassium of carbon carbonate dioxide reacts with gas at nitric rtp. acid (HNO ) to produce potassium 3 nitrate, carbon dioxide and water. Calculate the mass of potassium 3 chloride formed when 40 cm of potassium carbonate solution 3 concentration 118 of 0.5 mol dm reacts with excess nitric acid. with a The mole Key ● concept mole and chemical reactions concepts Relative masses of The a atomic of carbon-12 ● Relative ● A mole mass, atoms, par ticles t he as and mass and formula formula units mass wit h compare one-twelf t h t he t he mass atom. atomic is molecular molecules mass, molecular amount t here are of a mass substance atoms in and t hat 12.00 g of formula contains mass t he have same no units. number of carbon-12. 23 ● The number A vogadro’s of par ticles number or in a mole is 6.0 10 , which is also known as N A ● Molar ● The mass is t he mass, in molar mass of an molecular mass or formula grams, element or mass of one mole compound amount of is a t he substance. relative expressed in atomic grams per mass, mole. 1 Molar ● mass is A vogadro’s conditions given law of t he states unit t hat temperature g mol equal and volumes pressure, of all gases, contain t he under same t he same number of molecules. ● Molar molar volume volume temperature is is t he t he and volume same occupied for all gases by one under mole t he of same a gas. The conditions of pressure. 3 ● Molar volume at standard ● Molar volume at room ● The temperature and pressure (stp) is 22.4 dm 3 concentration dissolved in a xed of temperature and a a solution volume of is t he pressure measure (r tp) of t he is 24 dm quantity of a solute solution. 3 ● Mass concentration gives t he mass of solute dissolved in 1 dm of 3 solution. ● Molar Mass concentration concentration gives is t he given t he number of unit g dm moles of given t he solute dissolved 3 ● ● of solution. A stand ard A standard The The f solution t he t he of atoms atoms of t hen formula molar of a mass or one its a using concentration a a volumetric t he gives present formula by is mol dm known accurately. ask. t he gives in simplest be from known, t he one mass, can different compound is unit mole ratio compound. compound elements, is is compound in of empirical t he whose element t he compound of of ions each of concentration made formula propor tions known, is is formula molecular moles ● Molar solution empirical between ● in 3 1 dm in actual mole a of its t he f empirical molecular of compound. compound determined. t he number are t he molecular formula formula and can t he be determined. ● The by ● percentage mass, The L aw created ● The of element in t he a product and is a states chemical chemical t he can it and indicates t he percentage, t hat matter can neit her be reaction. equation give t he mole ratios products. products known, reactants compound compound. Matter a equations reactants ot her of balanced and of t he during reactants chemical or in Conservation t he unknown reactant composition destroyed coefcients Balanced any each of nor between ● of is be in used a to determine reaction. possible to f t he quantities quantity calculate t he of of one quantities of products. 119 Practice exam-style questions The b Practice exam-style Calcium hydrogencarbonate Ca(HCO ) 3 questions (s) The mass of 0.25 mol of potassium carbonate 2HNO t he following nitric (aq) Ca(NO an ) 3 investigation in t he (aq) 2CO 2 (g) laborator y, O(l) 2 8.1 g of calcium a hydrogencarbonate student to excess 24.75 g B 34.5 g C 38.5 g i) acid. Determine t he number hydrogencarbonate D of used moles by t he of calcium student. 552.0 g (2 A 2H 2 is: nitric 2 acid equation: 3 added A to 2 During 1 wit h concept questions according Multiple-choice reacts mole mass of 32 g of ii) oxygen: Determine 23 A contains 6.0 oxygen 10 B contains 2 mol of C contains 6.0 10 D contains t he same 35.5 g chlorine dioxide atoms iii) oxygen of molecules of of at oxygen molecules of oxygen c as number of moles of marks) carbon made. Determine 23 number t he (2 t he volume of carbon dioxide r tp. marks) made (1 Magnesium reacts wit h produce magnesium anot her investigation, hydrochloric chloride and acid mark) to hydrogen. n 3 a student reacted 20 cm 3 3 What is t he A 0.88 g B 224 g C 448 g D 880 g mass of 448 cm of carbon dioxide at stp? of hydrochloric acid wit h a concentration of 3 1.5 mol dm i) Write a wit h excess balanced magnesium. chemical equation for t he reaction. ii) (2 Calculate acid t he number of moles of marks) hydrochloric used. (1 mark) 3 4 You are required to make 250 cm of a solution of iii) sodium hydroxide which has a concentration Determine t he number of moles of magnesium of chloride produced. (2 marks) 3 0.1 mol dm . What mass of sodium hydroxide would iv) you need to weigh Calculate t he mass of magnesium chloride out? produced. A (2 d B 1.0 g C 4.0 g On analysis 24.45 g of empirical D a compound iron and formula was 10.55 g of t he found of to oxygen. contain Determine compound. A t he (2 marks) 15 marks 25.0 g Total 5 marks) 0.1 g compound W combined of W of t he is 40 was found wit h and t he 7 g of to consist Z. relative f t he of 30 g relative atomic mass of element atomic of Z is mass 14, Extended 8 following is t he correct empirical formula response question which for a i) What do you understand by t he term ‘standard t he solution’? (1 mark) compound? 3 ii) A WZ B W You wish to carbonate prepare solution 250 cm of of potassium concentration Z 2 3 0.8 mol dm C W t he laborator y. Determine 3 mass W of potassium carbonate required. Z 3 2 (3 6 Hydrogen reacts wit h oxygen according to t he iii) following Name make equation: 2H (g) O 2 (g) 2H 2 b O(g) A volume oxygen of reacts steam wit h could excess 8.96 dm B 12.8 dm of apparatus solution wishes to you would in. make a be produced at stp if (1 sample of t he to mark) lead(II) chloride, in t he laborator y. insoluble Determine 12.8 g mass reacting wit h 3 of a a lead(II) solution chloride which solution containing could containing excess be made 23.4 g of lead() sodium by nitrate chloride. (6 3 C marks) use hydrogen? 3 A piece your student t he of t he 2 salt, What t he Z 2 D in marks) 17 .92 dm 3 D c 25.6 dm Ammonium extensively wit h Structured question in t he This question is concerned wit h t he mole and By in and ammonium gardeners nitrogen growt h. nitrogen 7 nitrate by t hey as need calculating each of t he sulfate fer tilisers to t he make to protein percentage, fer tilisers, are supply by determine used plants for use mass, of which its would be t he better same per kilogram. value for money if t hey bot h cost application. t he a Give a denition for t he term ‘mole’. (1 marks) 15 marks mark) Total 120 (4 A8 The concept of Acids, acids, bases and salts bases has been and salts around Objectives for As a very our long time; knowledge as of early as the chemistry has 17th century. developed, By the be able of a compound as an acid, a base or a salt explain when has been refined. Acids, bases and salts are used in of our lives. Properties was have not always and until somet hing substance a in few known hundred common, t hat reacts reactions t hat a vinegar years t hey wit h of acids ● ago bot h base and t hat contain to form a it lemon was acids. salt juice taste discovered An and acid sour, t hat can be but t hese it in t heir anhydrous an give you ionisation acid have dened as a form, i.e. not dissolved ● water. in the in in acids describe the acids will of acids water terms of are composed with properties reactive carbonates, and describe which the can dene of reactions hydrogencarbonates acids water, general aqueous metals, ● Acids the dissolved dene of People topic protons ● A8.1 this all ● aspects of to: the ● classification end be acid ways in bases classied anhydride and give of examples of acid anhydrides covalent molecules and t hey may be solid, liquid or gas at room temperature. ● Solids include citric acid, tar taric acid and ascorbic acid (vitamin C). give examples of acids in living Liquids systems. include sulfuric acid and nitric acid. Gases include hydrogen chloride All acids have hydrogen in t heir formulae, e.g. nitric acid, HNO gas. and sulfuric 3 acid, H SO 2 . Table 8.1.1 gives t he names and formulae of some common 4 acids. T able 8.1.1 Some Name acid HCl acid H SO 2 nitric acids Formula hydrochloric sulfuric common acid 4 HNO 3 phosphoric acid H PO 3 methanoic ethanoic acid 4 HCOOH acid CH COOH 3 (a) Figure (b) 8.1.1 (a) Some common laboratory acids, (b) some common household acids 121 Properties and reactions of acids Acids, Ionisation When an of acid is acids added in to bases and salts water water, t he acid molecules ionise, i.e. t hey for m ions. Acids always ionise to for m hyd rogen ions , or H ions, and negative anions. The H ions t hen become att ac hed to t he polar water molecules for ming hyd ronium ions or H O ions (sometimes called hydroxonium 3 ions). Using an t he ionisation of hydrogen chloride gas to form hydrochloric acid as example: HCl(g) water H (aq) H t he Cl (aq) (aq) overall H O(l) H 2 O (aq) 3 reaction can be hydronium ion summarised as: HCl(g) H O(l) H 2 For simplicity, it O (aq) Cl (aq) 3 is usual to represent t he reaction as follows: in water HCl(aq) Ot her examples t hat H show t he (aq) Cl ionisation (aq) of acids are: HNO (aq) H (aq) NO 3 (aq) 3 H SO 2 (aq) 2H 2 (aq) SO 4 (aq) 4 H PO 3 (aq) 3H 3 (aq) PO 4 (aq) 4 CH COOH(aq) CH 3 COO (aq) H (aq) 3 1 A hydrogen atom, H, has one proton in its nucleus and one electron spinning 1 around single ! Key proton electron, acid is nucleus in since it t he is rst energy formed by a shell. A hydrogen hydrogen atom ion losing is, its t herefore, one a valence fact an An t he a proton acid leaving to only donate its t he nucleus hydrogen containing ions, or t he protons, one to proton. anot her The ability reactant can of be donor. used to When dene an dissolves an an acid in aqueous acid as reacts, water, can solution being t he be of a proton hydrogen given to donor. ions, t he hydroc hlor ic ot her acid or protons, react ant. reacts for med For wit h when example, sodium it when hydroxide, t he hydroc hlor ic acid gives its H ions, or protons, to t he OH ions of t he sodium hydroxide, for ming water. This can be summar ised by t he following ionic equation: OH (aq) H (aq) H O(l) 2 General properties of aqueous acids The presence of H ions in aqueous solution gives acids t heir proper ties. Aqueous solutions of acids are described as being have 122 t he following ● t hey have a ● t hey change ● t hey have a sour common taste blue pH proper ties: litmus value of to red less t han 7 characteristic acid ic and t hey Acids, bases and salts Properties ● t hey are corrosive ● t hey are electrolytes, Chemical Since all form a in acid The form reactions hydrogen an reactions acids common ions salt. A is in is, Acids react Acids, except nitric Reactive of (see This can reactive When as produce t is acid dioxide is i.e. impor tant nitric be to ), are wit h current. aqueous n metal all ions formed detail solution, of or t hese acids t he have reactions, ammonium when ammonium t he ions hydrogen to ion ion. below. reactive above metals to produce hydrogen in t he potassium, by t he acid sodium, following salt wit h and reactions it acids, t he are t hat metals not in an acids a salt reactivity calcium, and series magnesium, lead. react wit h or t hose i.e. evolved, and ion react remember reacts (NO in compound summarised t he by of acids reactants. replaced a electric reactions metals and an when ot her discussed 18.1), iron ions metal acid, metals gas heat, are metal reactive hydrogen a metals Unit zinc, reaction by reactive hydrogen. aluminium, are conduct aqueous cer tain acid acids with of t herefore, replaced of t hey hydrogen wit h t he salt reactions metals i.e. and effervescence described acid produces word equation: hydrogen reactions nitric general as become being does not oxides of (bubbling) hotter is seen because t hey exothermic react in t his nitrogen, way. e.g. When nitrogen hydrogen. 2 Example Magnesium reacts wit h sulfuric acid to produce magnesium sulfate and hydrogen: Mg(s) H SO 2 The ionic (aq) MgSO 4 equation for t his reaction Mg(s) 2H (aq) H 4 (g) 2 is: 2 (aq) Mg (aq) H (g) 2 Acids react with metal carbonates and hydrogencarbonates Acids react wit h metal carbonates and metal hydrogencarbonates to produce a salt, carbon dioxide and water. These reactions can be summarised by the following general word equations: carbon metal carbonate acid salt water water d ioxide metal carbon acid salt hydrogencarbonate When metal effervescence carbonates is seen as d ioxide and carbon hydrogencarbonates dioxide gas is react wit h acids, evolved. 123 Properties and reactions of acids Acids, bases and salts Examples 1 Potassium nitrate, K CO 2 The carbonate carbon reacts dioxide (aq) 2HNO 3 ionic wit h and nitric (aq) 2KNO for 2 t his (aq) 2H reaction (aq) CO (g) H O(l) 2 is: CO hydrogencarbonate chloride, ) 3 ionic 2 (g) H 2 Ca(HCO The potassium (aq) calcium produce 3 3 Calcium to 3 equation CO 2 acid water: carbon (aq) reacts dioxide wit h and O(l) 2 hydrochloric acid 2HCl(aq) CaCl 2 (aq) 2CO 2 equation for t his reaction to produce water: (g) 2H 2 O(l) 2 is: HCO (aq) H (aq) CO 3 Did ? you know? Acids react Acids react with bases wit h bases neutralisation Any reactive metals, that react salts the and with appear salt insoluble acids to to H to reactions. produce t is a salt impor tant O(l) 2 and water. to note by t he t hat These are base a a is known metal a metal hydroxide. soluble because These reactions can be summarised following general word equations: dissolves. metal metal When bases oxide acid salt water hydroxide acid salt water react exothermic wit h acids, t he reactions become warmer because t hey reactions. Examples 1 Copper(II) and oxide reacts wit h sulfuric acid to produce copper(II) sulfate water: CuO(s) H SO 2 onic (aq) CuSO 4 (aq) H 4 O(l) 2 equation: CuO(s) 2H 2 (aq) Cu (aq) H O(l) 2 ✔ Exam tip n t his and It is extremely important that a reaction, blue t he solution black copper(II) forms. This is oxide because appears soluble to dissolve copper(II) slowly sulfate is you 2 can write balanced equations acids. T o for help word equations that you products for to do memorise given know each produced chemical reactions you idea so to the good the the in it is a general this of the must also common learn the t he solution contains blue 2 Sodium hydroxide chloride and ions. reacts wit h hydrochloric acid to produce O(l) water: NaOH(aq) HCl(aq) NaCl(aq) formulae H 2 reaction. equation: of acids. OH (aq) H (aq) H O(l) 2 124 Cu section general type and of this, onic You as oxide bases form dissolve produced insoluble or carbonates (g) 2 sodium are Acids, bases and salts Investigating Your teacher Properties reactions may use this of observation, recording ● analysis interpretation. Y ou will be copper(II) acid, and supplied with carbonate, nitric acid, and lime to water, of acids assess: reporting magnesium calcium reactions acids activity ● and ribbon, hydroxide, test tubes zinc, copper( II) and a sodium oxide, wooden hydrogencarbonate, hydrochloric acid, sulfuric splint. Method 1 Reactions between an acid and metals: 2 a Place 2 cm of magnesium if b it becomes Place of a 2 Repeat Reaction splint gas. pop the acid Observe the in a test tube reaction. Feel and the add a piece bottom of of the tube to see hotter. burning hydrogen squeaky c hydrochloric ribbon. If and at the ame experiment between an the mouth hydrogen is will using acid and be a a of being the test tube produced, to the test for splint the will presence make a extinguished. small piece of zinc. hydrogencarbonate: delivery tube 3 a Place 2 cm of sulfuric acid in a test cork/bung tube and add a spatula hydrogencarbonate. of test tube sodium Observe the reaction. b Cork the running test tube through with the a delivery cork into a tube test tube dilute sulfuric of colourless Figure 8.1.2, lime to water, test for as the shown acid in presence lime sodium of carbon dioxide. If carbon dioxide (calcium hydrogencarbonate is water hydroxid solution) being produced, a white precipitate will form 3 in the lime Reaction between a Place 2 cm and add b T est for c Observe Figure 8.1.2 sulfuric acid Reaction between water. an acid and a and sodium hydrogencarbonate carbonate: 3 4 Reactions a of sulfuric spatula the of colour between an in a copper( II) presence any acid of test tube carbonate. carbon dioxide changes occurring acid bases: and Observe as in step during the the reaction. 2 reaction. 3 a Place 2 cm hydroxide. tube b Shake the Repeat the experiment all your hydrogen 6 Write 7 Explain a changes time any and you shake felt in and observe a the spatula add the a spatula reaction. Feel of calcium the bottom of the tube of copper( II) periodically oxide until no instead further of calcium changes changes. for each equation changes steps tube reaction, including the results of the tests dioxide. chemical colour test and using colour carbon a hotter. observations balanced any becomes This Observe in tube if Record it acid see occur. for nitric to hydroxide. 5 of you 1a for each observed and in reaction. steps 3c and 4b, and any heat 4a 125 Properties and reactions of acids Acids, During and f t he experiment, carbon dioxide hydrogen is you learnt how to test for t he bases presence of and salts hydrogen gases. produced in a reaction, it causes a burning splint to make a squeaky pop and to be extinguished. The ‘pop’ is t he sound of a small explosion as t he hydrogen 2H (g) O 2 f carbon (g) 2H is lime calcium produced water. hydroxide, and (aq) Acids can be Inorganic ● of compounds geological do not origin. contain exceptions Organic An of plants and the and ● carbon compounds biological animals. carbon to form steam: a reaction, is because carbon and dioxide water. it forms t he reacts The a lime white water wit h calcium precipitate is t his a when solution forming carbonate of white, forms t he (g) CaCO of and (s) H 3 O(l) 2 acids in organic a variety of ways. acids and be classied as acid inorganic contains a acids or organic non-met allic acids. origin, e.g. as well as Most organic acids it are hydrogen. Examples of element inorganic or polyatomic acids are given in 8.1.2. is t he acids contain hydrogen at t he t he carboxyl end of t he group, i.e. carboxyl COOH. group n t hese which forms t he ion when t he acid dissolves in water. Examples of organic acids are from given contain t he CO classied inorganic Table H mainly can g roup carbonates, hydrogencarbonates dioxide. air are Most carbon, being t he know? Acids Inorganic in 2 Classification ? in O(g) This carbonate 2 you oxygen precipitate: Ca(OH) Did wit h 2 d ioxide into insoluble white explosively 2 bubbled calcium reacts They always most contain in T able Table 8.1.2 8.1.3. Common inorganic acids T able 8.1.3 Common organic acids hydrogen. Acid hydrochloric nitric acid acid Formula Acid HCl methanoic HNO ethanoic 3 sulfuric acid H phosphoric acid H acid lactic 4 H carbonic acid H CH CH(OH)COOH acid C H citric acid C O 8 H 6 6 O 8 7 3 CO 2 dibasic COOH SO 2 Monobasic, CH 6 2 acid acid acid ascorbic 4 HNO sulfurous HCOOH 3 PO 3 nitrous acid 3 SO 2 Formula 3 and tribasic acids Acids ! Key fact per can also molecule be classied when according dissolved in to water, t he number known as of t heir H ions t hey produce basicity. Basicity is produced when it the per ● number of H molecule of acid dissolves in A monobasic acid produces one H ion per molecule when it dissolves ions in water. Hydrochloric acid (HCl), nitric acid (HNO ) and et hanoic acid 3 (CH water. COOH) are examples of monobasic acids. 3 ● A d ibasic water. acid Sulfuric produces acid (H two SO 2 ) H is ions an per molecule example of a when dibasic it dissolves in acid. 4 ● A tribasic water. acid produces Phosphoric acid t hree (H PO 3 126 H ) 4 is ions an per molecule example of a when tribasic it dissolves acid. in Acids, bases Dilute Acids A ● and can and salts Properties concentrated also d ilute be acid one reactions of acids acids classied is and based t hat on t he contains a quantity lot of of water, water e.g. Did ? present. hydrochloric you know? acid, A concentrated acid is always 3 which has a concentration A concentrated acid ● of 0.1 mol dm , is dilute. diluted to is one that contains very little water, e.g. hydrochloric 3 on reaction i.e. Strong and weak the can when t he also be A ● strong acid A ● weak e.g. We and is classied be is fully sulfuric acid is carbonic will dissolved acid based on t he degree of ionisation t hat a is slowly When lot to of an acid water , heat the energy , exothermic. spattering ionised slowly when dissolved in water, e.g. only at can This be of hydrochloric to water If the can the acid water , is the absorb added larger volume the heat energy is compound produced. par tially and and occurs water. acid. acid looking in ionised et hanoic strong and when dissolved in water, acid. weak acids in more detail in Unit 8.3. Key ! Acid acid added off reaction cause dangerous. acid water . being gives the acids can Acids adding distilled ionises , is concentrated. acid, which has a concentration of 12 mol dm the by fact anhydrides An Cer tain compounds react wit h water to form an acid. These are known acid which as anhydride reacts with a water to form an acid. acid anhydrides Acid anhydride literally means ‘an acid wit hout water’. Many acid anhydrides are acidic oxides of non-metals. Carbon dioxide (CO ), sulfur dioxide 2 (SO ), sulfur trioxide (SO 2 ) and nitrogen dioxide (NO 3 ) are examples of acid Did ? 2 you know? anhydrides: Nitrogen CO (g) 2 H O(l) H 2 CO 2 in carbonic the (g) 2 H H O(l) H 2 (g) SO 2 3 O(l) H 2 (aq) 3 SO 2 acid H O(l) HNO 2 reacts with the it air it forms HNO 2 rain can buildings acid nitric living to with come Table of across t hese variety in of our 8.1.4 Acid acid vitamin H O 8 acids ever yday Acids in living C In many fruits, foods, West ) sweet Methanoic In acid ant (HCOOH) Important e.g. Indian citrus A shortage Lactic 6 acid O them to It acidic make as it can for soluble also certain make living organisms. These are We also to aquatic survive. use summarised in peppers, points of to vitamin note C exposure to heat, in e.g. the diet during can lead cooking, to scurvy. vitamin C is destroyed by being oxidised. tomatoes, the leafy Sodium hydrogencarbonate is ) sometimes texture. This vitamin Causes itching, added to fruits and vegetables to improve their appearance and vegetables venom of bee and neutralises any redness, swelling C and present, pain reducing around the the vitamin C content. sting. stings Produced during in muscle strenuous cells If can be treated by hydrogencarbonate. too much lactic acid applying These builds a paste both up it of sodium neutralise prevents the hydrogencarbonate or calamine lotion which contains acid. muscles from contracting and the person collapses. activity 3 Ethanoic (CH calcium cherries, zinc H in activities. Stings 3 of dissolve 6 green (C made slowly systems On 6 This statues systems organic Occurrence Ascorbic (C cause 8.1.4. T able or a acids then nitrate. too organisms some vapour rain. acid water We the (aq) calcium in water acid in vehicles. 3 reacts acids present motor acid (aq) nitrous of also When carbonate Examples is of and 2 naturally lightning 4 sulfuric (g) it fumes in (aq) and exhaust acid 2NO made when acid sulfurous SO is atmosphere occurs SO dioxide (aq) 3 acid COOH) In vinegar Vinegar is enzymes used that to preserve cause decay food and items. inhibits Being the acidic, growth of it has a low bacteria pH, and which denatures (destroys) the fungi. 3 127 Properties T able and 8.1.4 of bases Acids, Occurrence Citric acid (C O H 8 In citrus fruits, Important e.g. limes Lime ) (Fe 7 juice O 2 ) in points is used the rust to to stains (s) 3 iron(III) rust making 6H stains a from soluble clothes. Summary Write and the Give three 4 Give the 5 terms Write ‘acid’ which properties, products metal and ‘acid show how the other that are than formed chemical equations reaction between zinc b the reaction between c the reaction between 6 How does 7 Why is able vinegar sodium of work for magnesium aluminium to preserve hydrogencarbonate the a dene an of with the the iron( III) oxide clothes: the (aq) stain removed 3H O(l) acids ionise when placed in water: sulfuric acid, hydrochloric acid topic you base in terms of which react are typical of aqueous acids. with: following: and hydrochloric sulfuric some used of as nitric acid acid. the a acid and foods we treatment eat? for ant Properties stings? and reactions of bases will base and dene 2Fe hydrogencarbonate and A ● acids A8.2 this to: ● reacts out carbonates. hydroxide Objectives be juice acid reactions, when b oxides balanced end lime washed 3 (aq) from following their the the the be anhydride’. a By in can acid. 3 a acid which questions equations nitric The compound 2 oxide (rust) 2 salts note remove O 2 Dene and 3 Fe 1 bases (continued) Acid 6 reactions can be water. dened Bases are as a substance normally metal which reacts oxides and wit h metal an acid to form hydroxides. a salt However, protons ammonia is also classied as a base. Examples of bases include magnesium alkali oxide (MgO), copper(II) oxide (CuO), magnesium hydroxide (Mg(OH) ) and 2 give ● the general properties of copper(II) hydroxide (Cu(OH) ). 2 ● aqueous alkalis describe the with acids ● dene ● classify an reactions and of bases ammonium amphoteric oxides into salts substance acidic, You learnt protons t he acid and Unit t he and 8.1 base, t his fact t hat when forming can be a base water. used to reacts The wit h base dene a has base an acid, accepted as a t he t he proton acid donates protons from acceptor. basic, Using amphoteric in to t he same example as in Unit 8.1, when hydrochloric acid reacts wit h neutral. sodium hydroxide, ions, protons, from following ionic by or t he t he OH t he ions of t he hydrochloric sodium acid hydroxide forming water, accept as t he H summarised equation: Key ! A base is OH fact a ! proton acceptor. in alkali water (aq) H O(l) bases known as or ions. OH are soluble alkalis. When in water, t hey ot hers dissolve in are insoluble. water, t hey a base which form a OH ions. dissolves solution common hydroxide (Ca(OH) ), alkalis (NaOH), which is include which are potassium fully moderately soluble soluble. hydroxide in For water, NaOH(s) 128 bases hydroxide water Na (aq) OH (aq) (KOH) and example: 2 containing Soluble form are ions, fact is to H Alkalis The An 2 Some Key (aq) and calcium sodium hydroxide Acids, bases and salts Properties and reactions of bases When ammonia gas is added to water it reacts wit h water to form ammonium hydroxide (NH OH), which is also an alkali: 4 NH (g) H 3 O(l) NH 2 Potassium oxide (aq) OH (K O), sodium oxide (Na 2 react wit h water (aq) 4 to O) and calcium oxide (CaO) also 2 form t he equivalent hydroxide. For example: Na O(s) H 2 Like on ● acids, t he A alkalis degree strong A weak e.g. of 2Na can be classied ionisation alkali hydroxide ● O(l) (aq) 2OH (aq) 2 and alkali is fully sodium is only t hat into strong occurs ionised when when alkalis t he and alkali dissolved in is weak alkalis dissolved water, e.g. in based water. potassium hydroxide. par tially ionised when dissolved in water, ammonia. We will be looking at strong and weak alkalis in more detail in Unit Figure 8.2.1 These products contain 8.3. bases General properties of aqueous alkalis The presence of OH ions in aqueous solution gives alkalis t heir characteristic proper ties. solutions t hey have Aqueous t he following ● t hey have a ● t hey change ● t hey have ● t hey are corrosive ● t hey are electrolytes, ● t hey feel a bitter red pH Chemical alkalis are described as being alkaline and proper ties: taste litmus value soapy of common to of i.e. when blue more t hey t han 7 conduct an electric current touched. reactions of bases Since bases contain oxide or hydroxide ions, bases have common reactions with certain other reactants. The reactions of bases are discussed in detail below. Bases Bases react react These with wit h acids reactions, following Remember to which general base acids word produce you looked salt when salt at and in water. Unit 8.1, can be summarised acids, t he reactions by t he equation: acid t hat a bases water react wit h become warmer because t hey are exot hermic reactions. Also, any insoluble bases which react to produce soluble salts, appear to dissolve. Examples 1 Magnesium chloride oxide and MgO(s) reacts wit h hydrochloric acid 2HCl(aq) MgCl (aq) H 2 onic to produce magnesium water: O(l) 2 equation: MgO(s) 2H 2 (aq) Mg (aq) H O(l) 2 2 Potassium sulfate hydroxide and 2KOH(aq) H SO 2 onic reacts wit h sulfuric acid to produce potassium water: (aq) K 4 SO 2 (aq) 4 2H O(l) 2 equation: OH (aq) H (aq) H O(l) 2 129 Properties and reactions of bases Acids, Bases Bases react react base n order wit h to with ammonium ammonium ammonium react, t he and salts salts salts to produce salt reactants bases salt need to be a salt, ammonia ammoni a and water: water heated. Examples 1 Copper(II) chloride, oxide reacts ammonia CuO(s) wit h and 2NH ammonium Calcium sulfate, hydroxide ammonia Cl(s) CuCl Ca(OH) (s) reacts ammonium (NH Your ● teacher will paper, be a may wit h SO 2 2NH (g) H 3 ammonium sulfate (s) CaSO 4 reaction use this recording supplied dry copper(II) O(l) 2 to produce calcium (s) 2NH 4 between (g) 2H 3 calcium O(l) 2 hydroxide and chloride observation, Y ou ) 4 the produce water: 2 Investigating (s) 2 and to water: 4 2 chloride test with tube activity and calcium and to assess: reporting. hydroxide, ammonium chloride, red litmus tongs. Method 1 Place 2 Add mix Did ? you litmus it paper reacts form gas causes to with turn the ammonium moist (g) H 3 the small blue water because present hydroxide O(l) heat paper ammonia hydroxide ammonium OH(aq) 4 4 Look at 5 Write a 6 Explain Some substance substance which both and can with react strong is chloride the and test tube. shake the tube to mixture If the and while mouth ammonia gas of is heating the tube hold to produced test a piece for the the litmus any water of moist presence paper will red of turn blue. the sides of the test tube to see if droplets form. balance the chemical formation of oxides equation the water and for the reaction. droplets. hydroxides metal wit h oxides acids and and also hydroxides behave as can acids behave as because t hey bases because can react t hey can wit h strong amphoteric oxides a with alkalis. These substances are referred to as being amphoteric alkalis. The following and hydroxides ● The general word equations summarise ● The amphoteric amphoteric strong alkali The amphoteric how react. substance reacting as amphoteric oxide or hydroxide 130 in fact amphoteric acids of calcium is react An the across gas. Amphoteric ! spatulas of to which NH 2 Key spatulas solids. Carefully litmus red alkaline: NH two small know? 3 Ammonia two substance reacting as a base: an acid salt and hydroxides are water acid: amphoteric oxide or hydroxide oxides listed in Table salt 8.2.1. water Acids, bases T able and 8.2.1 Amphoteric aluminium salts Properties Amphoteric oxides oxide oxide oxide reactions of bases hydroxides Formula Amphoteric Al aluminium O 2 zinc and and hydroxide Formula hydroxide Al(OH) 3 3 ZnO zinc PbO lead(II) hydroxide Zn(OH) 2 lead(II) oxide hydroxide Pb(OH) 2 Examples 1 Aluminium aluminium hydroxide chloride Al(OH) (s) reacts and wit h hydrochloric 3HCl(aq) AlCl 3 2 Aluminium to produce acid to (aq) 3H 3 hydroxide sodium NaOH(aq) reacts wit h aluminate Al(OH) produce water: t he and O(l) 2 strong alkali, sodium hydroxide, water: (s) NaAlO 3 (aq) 2H 2 O(l) 2 sodium aluminate 3 Zinc oxide reacts wit h hydrochloric acid to produce zinc chloride and water: ZnO(s) 2HCl(aq) ZnCl (aq) H 2 4 Zinc oxide sodium reacts zincate 2NaOH(aq) wit h and t he strong sodium hydroxide, to produce water: ZnO(s) alkali, O(l) 2 Na ZnO 2 (aq) H 2 O(l) 2 sodium zincate Classification So far in t his Anot her unit type t herefore, be of oxides Acid ic oxides a salt you are and oxides have oxide classied Acidic form of as for of across exists, acidic, oxides water, come also acidic, known basic, cer tain as basic a and neutral amphoteric non-metals and amphoteric oxide. oxides. Oxides can, neutral. which react wit h alkalis to Key ! example, Acidic 2NaOH(aq) CO (g) Na 2 CO 2 (aq) H 3 O(l) oxides SO (g) also H 3 react wit h water O(l) H 2 to SO 2 form an acid, for (SO ) and nitrogen Basic oxides for dioxide (NO ), sulfur dioxide (SO ), 2 ). 2 are oxides of metals which 2HNO (aq) react Cu(NO 3 wit h acids to form a salt and ! ) 3 (aq) H 2 O(l) few basic alkalis, K for O(s) 2 oxides which react oxides also react wit h water to form a hydroxide, i.e. t hey and are with oxides acids to of metals form a water. are H O(l) 2KOH(aq) 2 Examples ) fact example, 2 O Key Basic salt 2 alkalis water. example, CuO(s) (Fe and certain oxides water, A salt of with (aq) 3 Basic a oxides react example, 2 trioxide form are which 4 Examples of acidic oxides include carbon dioxide (CO sulfur oxides non-metals 2 to Acidic fact of and basic oxides copper(II) include oxide magnesium oxide (MgO), iron(III) oxide (CuO). 3 131 Strength of acids and alkalis Acids, Basic oxides which are alkalis include potassium oxide (K bases O), and sodium salts oxide 2 (Na O) and calcium oxide (CaO). 2 Amphoteric ! Key Amphoteric acids Amphoteric of oxides fact certain oxides metals are which the and oxides strong are alkalis t he to oxides form a of salt cer tain and acids and strong form a and water. alkalis which react wit h bot h example, with PbO(s) 2HNO (aq) Pb(NO ) 3 (aq) H 2 O(l) 2 to 2NaOH(aq) salt for oxides react 3 both metals water, PbO(s) Na PbO 2 (aq) 2 H O(l) 2 sodium plumbate The t hree amphoteric oxides are aluminium oxide (Al O 3 and lead(II) Neutral ! Key Neutral oxide ), zinc oxide (ZnO) 3 (PbO). oxides fact oxides are oxides Neutral oxides are acids or alkalis. These oxides (NO) and of cer tain include non-metals carbon monoxide which (CO), do not nitrogen react wit h monoxide of dinitrogen monoxide (N O). 2 certain react non-metals with acids which or do not alkalis. Summary 1 Dene 2 Give the three aqueous 3 Write questions terms ‘base’, properties, ‘alkali’ other and than ‘amphoteric their substance’. reactions, which are typical of alkalis. chemical equations a the balanced reaction between magnesium for b the reaction between calcium c the reaction between sodium the following: hydroxide oxide and hydroxide and nitric ammonium and zinc acid nitrate hydroxide. Objectives 4 By the end of this topic you Calcium calcium be ● able ● the strong give difference acid and examples of a a basic oxide. Explain, using a chemical equation, why basic. strong acid and Strength of acids and alkalis acids explain the difference between Aqueous a is between weak A8.3 weak ● is oxide to: explain a oxide will strong alkali and a solutions of both acids and alkalis can be classied as strong or weak weak based on the degree of ionisation which occurs when they are dissolved in water. alkali You ● give examples of strong must not confuse this with concentration. The concentration of an acid or and alkali is based on the quantity of water present in the solution (see Unit 8.1). weak ● alkalis explain the relationship Strong between the pH acidity, alkalinity and weak acids and scale When an acid dissolves in water, its molecules ionise to form hydrogen ions, ● ● give the pH acids, weak alkalis and values acids, weak explain how to pH solution for strong or a Strong determine give the colours in negative anions. acids strong acid is fully ionised when it dissolves in water. This means t hat of acidic acid molecules ionise and t here is a high concentration of H ions certain and solution. Hydrochloric acid is an example of a strong acid: alkaline HCl(aq) H (aq) Cl (aq) solutions. Ot her strong acids include nitric acid (HNO ) 3 132 all t he t he indicators and the of ● ions, strong alkalis A of H and sulfuric acid (H SO 2 ). 4 in Acids, bases Weak acids A weak and acid is salts only Strength partially ionised when it dissolves in water. This of acids and alkalis means that the solution contains a mixture of acid molecules which have not ionised and ions produced from the molecules which have ionised. The solution has a low concentration of H ions. Ethanoic acid is an example of a weak acid: CH COOH(aq) CH 3 COO (aq) et hanoate At any i.e. t he H (aq) 3 one time, solution only about contains 1% 1% of ion et hanoic et hanoate ions acid (CH molecules COO ) and are ionised, hydrogen ions 3 (H ) and 99% et hanoic acid molecules (CH COOH). 3 Most organic (HNO ), acids sulfurous are acid weak. (H 2 Strong When and an Strong weak alkali is ions, or hydroxide A SO 2 Weak ) and inorganic carbonic (H include CO 2 nitrous acid ). 3 alkalis added OH to water, it ionises to form positive cations and ions. alkalis strong a acid 3 alkali is fully ionised when contains a high concentration of OH of acids strong it dissolves in water. The solution ions. Sodium hydroxide is an example alkali: NaOH(aq) Potassium Weak Na hydroxide (aq) (KOH) is OH (aq) anot her example of a strong alkali. alkalis A weak alkali is only par tially ionised when it dissolves in water. The solution contains a low concentration of OH ions. Ammonia is an example of a weak alkali: NH (g) H 3 Measuring The strengt h The pH scale solutions a of pH stronger ● A t han t he t he strong (HNO ) aqueous pH 7 less are as also t han a neutral t he A weak or wit h 7 are considered tells lower of acid scale OH (aq) acids and alkali measured is numbers considered to be solution. alkalis ranging to alkaline. Distilled be An us how strong t he acidic t he stronger t he acid, using from acidic 0 or is pH 14. scale. Aqueous t hose wit h a solution wit h a neutral. alkaline and t he to and aqueous water pH, t he solution higher t he is. pH, n t he alkali. acid and has a pH sulfuric close acid to (H 3 ● (aq) strength number dened scale general, an wit h pH The of a greater is NH 4 the is pH 7 O(l) 2 1, SO 2 acid has a pH of e.g. hydrochloric acid (HCl), nitric acid ). 4 about 4 or 5, e.g. et hanoic acid (CH COOH). 3 ● A neutral substance has a pH of 7 , e.g. distilled water (H O). 2 ● A weak alkali has a pH of about 9 or 10, e.g. aqueous ammonia (NH OH). 4 ● A strong and alkali potassium has a pH close hydroxide to 14, e.g. sodium hydroxide (NaOH) (KOH). 133 Strength of acids universal pH and alkalis Acids, indicator There are two main met hods t hat are solution. One is used in bases t he and salts laborator y to paper measure ot her 0 is t he a pH pH of a universal indicator and t he meter. very acidic hydrochloric 1 Universal ● acid indicates 2 lemon ind icator t he pH of is a a chemical solution by substance colour, i.e. which its colour juice acidic orange changes depending on t he pH of t he solution. form or solution Universal juice 3 indicator can using paper, be in paper form. When vinegar t he a small piece of paper is dipped into t he 4 solution and its colour is compared wit h a pH colour char t. slightly black 5 coffee Figure acidic 8.3.1 different shows pH t he colour of universal indicator paper at values. rainwater 6 A ● pure pH meter is an electronic instr ument. t consists of a neutral water 7 measuring sea probe connected to an electronic meter, which water 8 baking soda milk magnesia of displays t he met hod for pH reading. A pH meter is a more accurate slightly determining t he pH of a solution t han universal alkaline 9 soap indicator paper. 10 11 Other 12 washing soda acid–alkali indicators alkaline There are ot her acidic solution ind icators which change to one colour in an 13 oven impor tant sodium Figure 8.3.1 The pH you is may met hyl you colour note t hat t hese in an indicators alkaline solution, t hey only indicate do not solution. measure t t he is pH a if it is acidic or alkaline. scale Litmus Did anot her to alkaline hydroxide of and very cleaner 14 an example come orange, across of in t his t he type of indicator. laborator y phenolpht halein and include Ot her indicators met hyl bromot hymol orange, blue. These which screened are used in know? neutralisation experiments to indicate t he neutralisation point (see Unit 8.5). ? The compounds which and are the and be in fruit in They colour of skins. extracted anthocyanins acidic purple-blue conditions. for called red T able parts, Anthocyanins cabbage, and acid–alkali naturally is made certain e.g. from the used indicator. occurring by of 8.3.1 Indicators t heir colours in acidic and used in the alkaline solutions laboratory Indicator Colour can litmus red blue as a of in acidic solution Colour red yellow red green phenolphthalein colourless pink bromothymol yellow blue in alkaline solution crude Litmus is indicator dyes orange red screened methyl orange a which from blue lichens. Investigating Your teacher observation, ● manipulation will be universal orange the may ● Y ou 134 and 8.3.1. these leaves extracting species indicators Table flowers methyl plant in responsible many easily common given conditions alkaline are are use this recording and supplied indicator and acidity and alkalinity activity and to of various solutions assess: reporting measurement. with paper, samples pH phenolphthalein. of colour solutions chart, red to be and tested, blue test litmus tubes, paper, methyl Acids, bases and salts Salts Method 1 Y ou the are going colour and of to measure each the indicator phenolphthalein when pH in of each the each of the solution. solution you solutions Only are use and methyl testing is investigate orange colourless. 3 a Place b Dip c d 2 cm a of piece tube and chart to Dip a piece the second Place of If there each meter 3 Record 4 Classify weak a of drops each alkali Summary a neutral 2 Name 3 Describe the of alkaline 4 acidic, Give difference three the values strong pH colours for the a the the four test solution colour with in the tubes. the pH rst colour blue litmus paper into the solution in colours. orange use each into of solution. other that each two the you and phenolphthalein, tubes. meter rinse to the Observe their determine measuring the colours. pH probe of of the reading. table. as a strong acid, a weak acid, a strong alkali, a substance. questions What the of in paper of their methyl after in the piece Ensure results tested Compare of available, water 1 is the substance or a each solutions. your pH and be indicator Observe meter to colour. the of into distilled all its red tube. pH the in universal observe two is of solution determine respectively, 2 the each between acids scale, and of of and the strong three giving the neutral methyl a acid weak range and a weak acid? acids. of the scale and the pH values solutions. orange and phenolphthalein and the pH following: a aqueous ethanoic c aqueous ammonia acid b sodium d aqueous hydroxide solution hydrochloric acid. Objectives A8.4 You Salts have molecule one already when hydrogen learnt t hey ion t hat all dissolve per in molecule acids form water, and e.g. sulfuric at least one hydrochloric acid (H SO 2 hydrogen t hey are ions hydrogen reactant, can known a ions salt as are is be replaced by ot her positive replaceable hydrogen replaced metal by or hydrogen ions . ions (HCl) forms two. the be able end of ● dene ● distinguish the between be of classied or term salt salt acid a normal These when acids acids ions react react from an salt and and t he and ● explain water of crystallisation ● distinguish between salt anhydrous t he a hydrated ot her and decide an on method all will forms only of the most salt appropriate preparing a salt salts ● can you formed. Classification whet her topic per ● Salts this to: 4 When ammonium ) acid ion By into some two of groups, t he normal hydrogen ions salts are and acid replaced: salts, based on describe of ● ● the preparing describe the everyday life state some different methods salts uses of the of salts in dangers of salts. 135 Salts Acids, Normal Key ! fact and salts salts Normal salts are formed when by bases metal or ammonium ions. all of the hydrogen ions in an acid are replaced For example, when sodium hydroxide (NaOH) reacts with sulfuric acid (H SO 2 ), if all of the H ions in the acid are replaced by 4 A salt is a compound formed when Na ions, the normal salt, sodium sulfate (Na SO 2 some or all of the hydrogen ions 2NaOH(aq) H SO 2 an acid are ammonium replaced ions. by metal ), is formed: 4 in (aq) Na 4 SO 2 (aq) 2H 4 O(l) 2 or All acids can Acid salts Acid salts replaced form are by normal formed metal or salts. when the hydrogen ammonium ions. ions in an For example, the H acid when are only sodium partially hydroxide reacts with sulfuric acid, if only one of ions in the acid is replaced by a Na ion, the acid salt, sodium hydrogensulfate (NaHSO ), is formed: 4 NaOH(aq) H SO 2 Only The dibasic type of quantity of 2 mol was of and salt produced. 1 mol The of tr ibasic formed each sodium acids by However, acid, can For acid and acid 1 mol only salt phosphoric of in two different hydroxide, it can acid form H 1 mol was acid salts. t he For salts. acids t he of depends two acid sodium on reactions reacted, t he relative above, a hydroxide when normal reacted salt wit h produced. (H PO ), can produce one normal salt 4 example, normal O(l) 2 sulfuric 3 and (aq) tribasic example, and when an form dibasic reactant. acid, NaHSO 4 hydroxide sulfuric tribasic (aq) 4 salt, in t he sodium reaction phosphate wit h (Na sodium PO 3 ), when 4 all t hree H ions are replaced. t can also form two H t he two acid salts, sodium hydrogenphosphate (Na HPO 2 ) when ions are replaced and sodium 4 dihydrogenphosphate (NaH PO 2 3NaOH(aq) 2NaOH(aq) NaOH(aq) Again, you which salt Table 8.4.1 T able can is H H H see PO 3 shows 8.4.1 acid acid one (aq) PO 3 Na (aq) PO t hat Na t he (aq) Salts salts formed HCl HNO acid acid PO 2 relative (aq) 4 NaH quantity by formed common Salt(s) by t he (aq) 4 of t he common replaced: 3H 2H H two O(l) 2 O(l) 2 O(l) 2 reactants determines CH H 2 acids. acids formed Anion T ype present salt chlorides Cl normal salt NaCl nitrates NO of Example normal salt NaNO COO normal salt CH 2 normal salt 3 3 COOH ethanoates 3 sulfuric (aq) HPO 4 t he is 4 2 3 ethanoic ion PO 3 4 3 H 4 4 Formula hydrochloric when produced. Acid nitric ) CH 3 3 SO sulfates 4 SO 4 hydrogensulfates COONa Na SO 2 acid HSO salt 4 NaHSO 4 carbonic acid H CO 2 carbonates 3 4 2 normal CO salt 3 hydrogencarbonates Na CO 2 acid HCO salt 3 NaHCO 3 phosphoric acid H 3 PO phosphates 4 3 3 normal PO salt 4 hydrogenphosphates acid salt 4 dihydrogenphosphates H 2 136 Na PO 3 2 HPO Na 4 HPO 2 PO 4 acid salt 4 NaH 2 PO 4 Acids, bases Water Some ions of salts in a cr yst al water of cr ystallisation CuSO Salts contain t heir following ● salts crystallisation containing of and xed number lattice, known cr yst allisation can be given in water as are t he molecules water refer red of between cr ystallisation . to as of t he salt as sulfate. The formula for mula hyd rated salts . shown t he Salts Water in t he examples. .5H O represents 4 2 for ever y hydrated copper(II) 2 t hat of shows 2 mole of Cu and moles of water SO ions wit hin t he cr ystal lattice, 4 ● t here are ve CoCl .6H 2 .7H 4 FeSO ● and .7H of O represents O represents cr ystallisation sometimes becomes copper(II) heated cobalt(II) chloride. hydrated magnesium sulfate. hydrated iron(II) sulfate. 2 cr ystallisation it hydrated 2 4 Water represents 2 MgSO ● O molecules. t he is removed powder y sulfate t hey is essential colour, and by its cr ystals become of to colour t he may bright and develop cr ystals heating, are white t he solid also blue t he cr ystalline containing loses its change. and have it. str ucture, t his cr ystalline For a f example, regular water of str ucture, hydrated shape. When powder y: heat CuSO .5H 4 O(s) CuSO 2 (s) 5H 4 O(g) 2 white blue cr ystals powder Salts wit hout water Preparation We use later be in salts t his in When of all unit. produced, cr ystallisation are known as anhydrous salts salts aspects There some deciding of of on of are which a our many we lives. Some different will preparation be of t hese met hods discussing met hod, it in is uses by will which t his be discussed t hese salts can section. impor tant to know t he solubilit y of t he salt t hat is to be produced and t he solubilit y of t he compounds whic h may be used to prepare t he salt. Met hods of prepar ing insoluble salts differ You from can t hose nd a table Preparation Insoluble t he of salts cations t he of salt. used insoluble can This is prepare summarising of t he to be salt prepared being known as soluble t he salts. solubility r ules in Unit 6.1. salts by reacting prepared ionic and two t he solutions, ot her precipitation . n one containing an ionic containing t he anions precipitation reaction, t he two soluble salts in solution react to form an insoluble salt, i.e. a precipitate, wit h and sodium nitrate soluble salt. solution For to example, form barium insoluble nitrate barium solution sulfate and reacts sodium solution: ) Ba(NO 3 onic a sulfate (aq) Na 2 SO 2 (aq) BaSO 4 (s) 4 2NaNO (aq) 3 equation: 2 Ba 2 (aq) SO (aq) 4 BaSO (s) 4 137 Salts Acids, bases and salts Method The 1) following two soluble salt t he ot her and 2) Dissolve 3) Mix 4) Filter 5) Wash When t he t he t he t he barium t hat sodium one t he form collect for preparing containing water to wit h used to anions make t he t he distilled t he cations salts. required to make t he required. solutions. insoluble salt precipitate water insoluble while as a as t he it is precipitate. residue still in t he lter funnel dr y. t he all to two salts nitrates c hoose above to are would use in your soluble, be a preparation, as nitrate and a preparation are to all supply sodium it sodium t he salt is impor tant salts. cations, to supply to Therefore, i.e. t he bar ium anions, sulfate. prepare Your solution to t he in and residue it salts in salts solutions c hoosing best T o two salts, is containing mixture leave nitrate e.g. t he two remember nitrate met hod Choose and adding general an teacher may ● observation, ● manipulation Y ou will two beakers, be insoluble use recording and supplied a this lter salt by activity and ionic to precipitation assess: reporting measurement. with solutions funnel and of lter barium nitrate and sodium sulfate, paper. Method sodium to 3 sulfate 1 Place 10 cm of sodium sulfate solution into a small beaker. solution 3 2 Add 3 Using 4 Wash 10 cm allow Figure 8.4.1 insoluble Preparation salt, barium of of the lter the residue it to 5 Record 6 Write all your both reaction sulfate are a ● direct ● t he ● t he a Salts by sulfate 138 precipitate lter distilled and paper, water swirl lter while to mix. the mixture. it still is in the lter funnel and observations as you chemical prepare equation the and sample an ionic of the salt. equation for the of barium of the insoluble soluble main met hods salt that you have prepared. salts for preparing soluble salts: combination reaction between base reaction and a an between reactive metal, an insoluble carbonate or an acid a soluble base, i.e. an alkali, and an acid, known as combination composed reacting The name titration. Direct A with balanced and three insoluble 8.4.2 and solution the There Figure funnel nitrate dry. Preparation barium metal anions. two of two simple elements, supplies t he a ions, metal cations such and of a t he as metal chlorides, non-metal, salt and t he directly can be wit h non-metal prepared each ot her. supplies t he Acids, For bases and example, passing glass a salts aluminium stream tube as Salts of dr y shown in chloride chlorine Figure can gas be prepared over heated a fume cupboard foil in a by long 8.4.3. aluminium dry in aluminium foil chlorine unreacted in chlorine out heat Figure The 8.4.3 Preparation equation 2Al(s) for t he 3Cl of aluminium reaction (g) is: 2AlCl 2 Since is an t he anhydrous Reactions Many soluble carbonate ● occurs salt. chloride with or in This and is absence par ticularly anhydrous salts can be of any moisture, suitable iron(III) prepared base wit h reactive metal Mg(s) t he e.g. an an ● cannot potassium is Reacting too an preparing formed anhydrous by reacting acid as a or reactive shown in t he metal, insoluble examples below. and an acid, e.g. to prepare magnesium chloride: 2HCl(aq) met hod acid salt chloride. MgCl (aq) H 2 This for t he acids insoluble Reacting a (s) 3 reaction aluminium chloride be sodium (g) 2 used to prepare salts, because salts t he of ver y reaction of reactive t hese metals, metals wit h violent. insoluble carbonate and an acid, e.g. to (aq) prepare calcium nitrate: CaCO (s) 2HNO 3 ● Reacting an (aq) Ca(NO 3 insoluble CuO(S) H SO 2 ) 3 base and an (aq) acid, e.g. CuSO 4 (g) H 2 to (aq) CO 2 prepare H 4 O(l) 2 copper(II) sulfate: O(l) 2 n t hese reactions, t he nal product will only be a pure solution of t he required salt if t he achieve to t he t he reaction t his acid is by until reactant to has reached using some react a completion reactant remains. wit h and, which This is and indicates since it is no acid insoluble. t here is insoluble, remains. This no t he One reactant more acid excess way is will to added lef t for remain ✔ undissolved in t he solution of t he Exam tip salt. Being able to describe the Method methods is very used to important prepare for salts exams. If The following general met hod is used to prepare soluble salts using reactions you wit h asked Choose the appropriate reactive metal, insoluble carbonate or base to provide the prepare cations and the appropriate acid to provide the t he excess used. 3) acid solid This speed into a remains indicates up t he beaker and t hat reaction and add t he effer vescence all t he when acid has using a metal, stops if reacted. metal or a carbonate a metal Heating or or base until carbonate may a soluble be with an is required idea to the salt acid using and insoluble cations reactants, choose the you a can a carbonate it doesn’t the and it is a good appropriate carbonate since to supply reaction an acid the between is rapid, base. need heating and visible Dip a piece of blue litmus paper into t he solution to ensure all t he acid has effervescence reacted. The litmus Remove t he excess, should remain unreacted stops when the blue. reaction 4) how anions choose Place to describe insoluble reaction 2) to acids. to 1) are solid by has reached completion. ltration. 139 Salts Acids, 5) Collect the ltrate a salt hydrated is bases and salts and evaporate the water over a beaker of boiling water. f required, evaporate some of the water to concentrate the solution and leave the concentrated solution to cr ystallise. T o prepare Your a teacher may ● observation, ● manipulation Y ou will beaker, be an soluble use salt this recording and supplied by reacting activity and to a base with an acid assess: reporting measurement. with evaporating samples dish, a of lter copper( II) funnel oxide and lter and sulfuric acid, a paper. Method Add the the copper(II) sulfuric heating more acid gently, will oxide to 3 1 Place 2 Add 20 cm of sulfuric acid into the beaker. while until no copper( II) oxide to the acid a spatula at a time, heating and stirring dissolve gently, 3 until oxide in Using the excess 4 Pour 5 Place more lter funnel ltrate of a piece of lter i.e. until you can see excess copper( II) all 7 Write balanced 8 T o heat paper and over the the it the mixture Place the solution remove crystallise evaporating becomes evaporating to to the ltrate. dish. until leave lter the evaporating observations chemical anhydrous evaporating paper, collect dish and dish a concentrated. containing form over the hydrated crystals. Record your lter and and solution sulfate produce the water 6 a react, and oxide into boiling concentrated copper(II) will beaker. copper( II) the beaker no the dish over as you equation copper( II) a prepare beaker for the sulfate, of the reaction. you boiling salt. can water heat until the all ltrate the water in the has evaporated. Filter off the excess copper(II)oxide Titration Potassium, sodium and ammonium salts cannot be prepared by the method which you have just learnt for two reasons. Firstly, potassium and sodium react in a violent way with acids making the reactions too dangerous. Secondly, potassium, sodium and ammonium carbonates and hydroxides are all soluble, T o produce copper(II) so hydrated sulfate allow when the excess solid crystals days. to T o form over a of boiling over a Figure 8.4.4 preparation sulfate of has alkali reached until t he solution involved hydrated in is completion. added to and no more acid remains, the For is just potassium example, neutral, hydroxide to indicating prepare t hat solution potassium t he reaction until t he sulfate, resulting sulfuric solution is the copper( II) just neutral: crystals 2KOH(aq) H SO 2 The colour point. to The change a of xed solution (aq) K 4 technique neutralise carbonate 140 completion beaker water Steps reached sulfate acid has and the solution of the salt will then not be pure. Potassium, sodium and ammonium salts are prepared by adding an acid to an copper(II) aqueous evaporate dissolves few produce anhydrous reaction the an indicator used to volume may SO 2 also used determine of be is aqueous used (aq) in 2H 4 O(l) 2 to determine t he exact alkali place of is t he volume known t he neutralisation of as aqueous a acid needed titration. alkali. A Acids, bases and salts Salts Method The 1) general Choose and 2) an met hod an for performing appropriate appropriate alkali acid to or a titration soluble supply t he is as follows. carbonate to provide t he cations anions Measure a xed volume of t he aqueous alkali or carbonate using a pipette. Run e.g. it into a conical ask and add a few drops of indicator solution, phenolpht halein. 3) Place 4) Add t he t he point is 5) Take a 6) Repeat acid acid in to a burette t he and aqueous take an alkali or initial burette carbonate reading. until t he neutralisation reached. nal burette reading and determine t he volume of acid added. 3 of t he each titration ot her. until Average you t hese have t hree volumes volumes to of acid determine t he wit hin volume 0.1 cm of acid needed. 7) Add t his volume of acid to t he xed volume of aqueous alkali or carbonate wit hout 8) t he Evaporate T o t he prepare Your indicator. water a teacher soluble may ● observation, ● manipulation from use salt this recording and t he solution. by titration activity and to assess: reporting measurement. 3 Y ou will be supplied with 3 0.1 mol dm sodium hydroxide solution, 0.1 mol dm hydrochloric acid, phenolphthalein 3 solution, a 25 cm pipette, a conical ask and a burette. Method 1 Rinse the 2 Rinse the burette with some hydrochloric acid and ll it with the acid. 3 pipette 3 Add 4 T ake 5 Slowly a pipette and few an run it with into drops initial add colourless. of the the sodium conical reading, hydrochloric The hydroxide solution remembering acid neutralisation solution. Measure 25 cm of sodium hydroxide solution in the ask. phenolphthalein burette the to of some to the point to to the conical take conical is the the ask, point ask reading swirling where the and from swirl the contents. bottom constantly, colour the until changes of the the meniscus. solution after the just addition turns of from just one pink drop acid. 6 T ake 7 Discard the 8 Repeat your a nal burette reading contents of the and determine conical ask the and volume rinse the of hydrochloric ask acid thoroughly added. with This distilled is your rough titration. water. 3 titration until you have three volumes of acid which are within 0.1 cm . Each time you can add the 3 acid tap rapidly and until you have added the acid drop by add about drop until less 1 cm the than you neutralisation added point is in your rough titration, then almost close the reached. 3 9 Average the three volumes of acid, which are within 0.1 cm . This is the accurate volume of acid needed to 3 neutralise 10 Repeat 25 cm your determined 11 Place the of the titration, in step solution 9, sodium but this add into an hydroxide time the acid do not drop evaporating solution. add by dish the drop and Y ou can now prepare phenolphthalein until you carefully have solution. added evaporate the all the the salt. When correct water you approach the volume volume. to obtain sodium chloride. 141 Salts Acids, 12 Record your results in a table like the one opposite. Burette 13 Write a chemical equation for the Titration number Rough 1 bases and salts reading 2 3 reaction. 3 Final reading/cm 3 Initial reading/cm 3 Volume of acid added/cm safety burette filler these allow fill valves you and the to empty when pipette pipette is these filled to this graduations mark measure it contains how exactly much solution 3 25 cm of solution has been added tap conical flask (a) Figure 8.4.5 hydroxide (a) Using solution hydrochloric and a pipette (b) using to a measure burette a to xed add a volume varying of sodium volume of acid Figure 8.4.6 pink (b) to added Preparation You learnt wit h of earlier sulfuric acid in acid t his (H SO 2 The formation of 2NaOH(aq) a H SO 2 The formation of an NaOH(aq) H ● to at t he produce hydroxide ● to produce hydroxide f t he acid a SO 1 mol an acid t he same, changes hydroxide 0 .1 mol dm (a) acid is solution sodium hydroxide (NaOH) reacts salt: Na SO NaHSO salt, t he t he O(l) 2 (aq) H t he t hese of O(l) 2 two reactions: reactants is 2 mol of sodium acid ratio sulfuric can for ratio sulfuric of we 2H 4 equations of salt: (aq) of (aq) 4 of reactants is 1 mol of sodium acid. sodium a p p ly t he hy d r ox i d e ratio to solution vo l u m e s . and Fo r t he sulfur ic e xa mp l e , 3 use from hydrochloric possibilities: 2 salt, 1 mol concentrations are two 4 normal to when are (aq) acid balanced to t hat t here 4 2 Looking sodium when 4 normal to Phenolphthalein colourless salts unit ) (b) if we 3 sodium hy d r ox i d e solution and 0 .1 mol dm sulfur ic acid: 3 ● to produce a normal salt, we would react 50 cm of sodium hydroxide 3 solution wit h 25 cm of sulfuric acid 3 ● to produce an acid salt, we would react 50 cm of sodium hydroxide 3 solution wit h 50 cm of sulfuric acid. Comparing t he two, to prepare t he acid salt we would need of 142 acid t hat we used to prepare t he normal salt. double t he volume Acids, bases and salts Salts Method The as ● general Determine volume ● met hod for preparing t he acid Repeat of of t he sulfuric t he volume sodium titration acid of sulfuric hydroxide wit hout acid sodium needed solution hydrogensulfate, is t he using indicator to a neutralise a xed titration. and adding twice t he volume determined. Evaporate t he water from Summary of salt preparation ● salt, follows. t he solution. You have just learnt t hat t here are several met hods t hat can be used to prepare salts and it is impor tant t hat you choose t he correct met hod. The ow char t in Figure 8.4.7 outlines a series of questions to ask which will help you decide which met hod to choose. Use reactive or an a metal insoluble acid carbonate Is NO the acid or an base an insoluble salt Is acid anhydrous NO the salt a chloride? YES potassium, sodium Is YES Use or the direct ammonium salt YES combination salt soluble ? in Use water? NO a titration Use ionic precipitation Figure Uses 8.4.7 of Flow chart salts in for the preparation everyday of salts life Salts play an extremely impor tant par t in our ever yday lives, from t he sodium chloride as t hat washing T able we soda. 8.4.2 use to Table Uses of avour 8.4.2 our gives food to t he sodium some of t he uses carbonate t hat we use salts. salts Salt Use Explanation Sodium An Baking hydrogencarbonate in (NaHCO powder ) of ingredient baking powder is used to hydrogencarbonate and in the the cake mixture, make an cakes acid. two rise. When It contains mixed compounds with react the forming sodium liquid carbon 3 dioxide: Figure 8.4.8 Washing soda is a salt HCO (aq) H (aq) CO 3 The carbon heating Sodium carbonate (washing T o soda) soften hard water Hard dioxide causing water calcium forms the does and cake not ) added, the H in the O(l) 2 cake which which expand some of us have in our homes on rise. with salts. soap. When It is caused sodium by dissolved carbonate is 2 and Ca bubbles to lather magnesium 2 (NaCO (g) 2 Mg ions precipitate out as insoluble 3 calcium and magnesium 2 Ca carbonate: 2 (aq) CO (aq) CaCO 3 The Calcium carbonate (limestone) (CaCO ) water Manufacture T o of quantities cement make becomes cement, of and calcium other (s) 3 soft will lather carbonate materials such as is with soap. heated silicon with dioxide small (sand) in 3 for use in the construction a kiln to forming about 1400 °C. calcium oxide The calcium carbonate decomposes (quicklime): industry CaCO (s) CaO(s) CO 3 The calcium inside small the (g) 2 oxide is then kiln to form amount of calcium blended clinker. The sulfate with the clinker is (gypsum) other then to materials ground make with a cement. 143 Salts Acids, T able 8.4.2 ? you Magnesium know? (Epsom (MgSO Epsom salt derives its sulfate salt) .7H 4 O) Use Explanation Various Added medicinal relax the uses strain, town of to the where salt in The in healing a bitter power saline of spring heal the spring. waters chloride and were realised news of in these (NaCl) Sodium preservation and fish, that the from rapidly . Epsom salt is pain used and inflammation, to ease aching help cure stress limbs, skin and ease muscle problems T aken orally, Epsom salt is used as a and saline to help also chloride by is eliminate used to toxins from withdrawing water is preserve the water unavailable withdraws water from for the food body. their items, cells reactions from the from growing. such by as meat osmosis that microorganisms cause which so decay. cause about preventing them powers Sodium spread cuts. and Food decay, 1618 reduce back first It the Epsom soothe Surrey , was Sodium discovered water, name Epsom the bath body, help laxative England salts 2 help from and (continued) Salt Did bases nitrate Food Sodium nitrate preservation chloride to and sodium nitrite are often used with sodium quickly ) (NaNO and preserve meat. They destroy certain bacteria that 3 developed into a spa town and sodium people travelled from far and wide to nitrite (NaNO cause ) severe rancidity. food Sodium poisoning nitrite and gives an retard the attractive development red colour to of the 2 visit Epsom and ‘take the meat, waters’. Sodium H (C 6 benzoate COONa) e.g. Food Sodium preservation e.g. ham and benzoate fizzy drinks bacon, is used and fruit and to adds preserve juices. At a flavour. foods pH of benzoate is converted to benzoic acid (C H 6 Calcium sulfate (gypsum) Did ? you .2H 4 inhibits the Manufacture Plaster of of which of plaster O) Paris, and back it was centuries gypsum By than used through many the 9000 parts 1700s, of the became known years used bones as the of when plaster a broken paste and is building centre as Paris for the were time, made plaster the of walls the of its to of Paris fate as houses was make Fire of did not and 1666. heated plaster) to is about made 300 °C of to calcium sulfate remove the in and, by to suffer in are then impregnated with water the Paris powder. When water is added to the dry bandage, forms then law, heat wrapped Plaster an of to is around orthopaedic Paris the given is dry also the off. The damaged bandage, limb, with where it its hardens cast. used plaster to as a building make a paste material. Water which used is is to and coat ceilings. of salts been implicated the in causing various healt h problems. Table 8.4.3 summarises so of t hese dangers. same T able 8.4.3 Dangers of salts Great Salt Dangers Sodium chloride Sodium nitrate (NaCl) (NaNO ) Excessive and May consumption increase a person’ s can lead risk of to hypertension developing (high blood pressure). cancer. 3 sodium nitrite (NaNO ) Have been implicated in causing brain damage in children. 2 Sodium H (C 6 benzoate COONa) Explain the 2 What water 3 Name salts. is the In prepare May increase difference of most each the implicated a in increasing person’ s risk of hyperactivity developing and asthma in children. cancer. magnesium anhydrous Describe, Describe appropriate salt c and full starting we calcium c magnesium a normal method the write a two salt and for an preparing compounds balanced chloride details, with use the sulfate sulfate. how you magnesium following you chemical chloride giving how name iron( III) a between acid salt. crystallisation? case a carbonate 5 been questions 1 4 Has 5 Summary 144 a paste, While salts play such an impor tant role in our ever yday lives, some have also cover fireproof the and Paris used them had Bandages it London which Paris. some that COOH) 5 microorganisms. had use plaster wood Paris of forming material the Dangers At of (gypsum been crystallisation. walls become growth Paris has added world. pH, sodium plaster more in of which setting date low 4.5, 2 is origins a know? (CaSO The with below 5 each equation b lead( II) d potassium would of would the following choose for the to reaction: sulfate prepare nitrate. magnesium nitrate. salts in b our everyday sodium lives: hydrogencarbonate Acids, bases A8.5 and salts Neutralisation Neutralisation n Unit 6.2 you learnt t hat a a base and an acid. n a reactions Objectives neutralisation reaction is any reaction between neutralisation reactions reaction a salt and water are By the be able end of this topic you will to: always ● explain ● describe a neutralisation reaction formed. how When a strong alkali reacts wit h a strong acid, t he reaction is complete when neutralisation neit her an alkali nor acid is present in excess. At t his point pH of 7 , i.e. t hey are neutral. This point is known as t he or end t he products have a neutralisation point point. indicator, temperature ● describe to a neutralisation reaction between an aqueous alkali and an acid, t he reaction hydrogen ions remain occurring ions in of t he solution is between acid. as These spectator t he ions ions. hydroxide react For to ions form example, of t he water t he alkali and t he reaction meter using and change how we use reactions in our t he daily actual out reactions pH neutralisation n carry lives. and ot her between sodium hydroxide solution and hydrochloric acid can be summarised by t he following chemical NaOH(aq) equation: Key ! HCl(aq) NaCl(aq) H O(l) A 2 fact neutralisation reaction reaction between a base is a and an The OH ions from the sodium hydroxide and the H ions from the hydrochloric acid to form a salt and water. acid react to form water, as shown in the following ionic equation: OH (aq) H (aq) H O(l) 2 Key The Na and Cl ions remain in solution as spectator ! ions. The reaction between t he hydroxide and hydrogen ions is described as being The an point exothermic can a make use reaction of t his fact (see Unit when 12.1) because determining t he it produces heat neutralisation energy. point of We such neutralisation in where an the neither reaction. fact point acid–alkali reaction acid nor is alkali is the reaction complete is and present in excess. Determining acid–alkali The the acid point in an reaction neutralisation aqueous neutralisation is point of deter mined a by reaction between perfor ming a an aqueous titration. alkali Dur ing t he and an titration, t he volume of one solution required to neutralise a xed volume of anot her solution of three c hange. using is deter mined, ways: We using will now temperature Using an n Unit in an an and t he neutralisation indicator, look at using two of a pH t hese point meter ways, is or identied using using an in one temperature indicator and c hange. indicator 8.3 you acidic learnt solution t hat and an ind icator anot her is colour a in substance an which alkaline has one colour Did ? performing solution, usually indicator are a t he added. titration alkali, The is using placed ot her an in indicator, a a conical ask solution, usually t he know? solution. The When you xed and acid, a is volume few of drops added one of t he from t he neutralisation determined instead is of added using an in point can a meter pH indicator. small One quantities, be solution e.g. 3 2 cm , to a fixed other solution volume of the burette and t he indicator will change colour at t he neutralisation point. This point is determined when t he colour changes on t he addition of a solution drop of solution from t he and the pH of the single changes sharply to 7 at the burette. neutralisation point. Phenolpht halein and met hyl orange are t he most commonly used indicators to determine t he neutralisation point in a titration. 145 Neutralisation reactions Acids, Using temperature When using a xed a of and salts change temperature volume bases one change solution is to deter mine placed in an t he neutralisation insulated point, container, e.g. a polystyrene cup, and its temperature is recorded. The ot her solution is added 3 in small t he is quantities, solution is recorded. in e.g. 2 cm quic kly The temperature , from stir red af ter procedure have been is t he burette. eac h continued recorded. Using addition until This is t he and several known t her mometer, t he temperature successive as a drops thermometr ic titration A graph added To draw t are and of is t hen from t he An one t hrough intersection example of of showing temperature against t he volume of solution burette. graph, drawn, one drawn t he t he t he t he a points t hrough points two graph are t he plotted points where lines is which t he the and t hen where t he temperature neutralisation might two be straight temperature is lines is of best increasing decreasing. The point point. obtained when hydrochloric acid 3 is added to 25 cm of sodium hydroxide solution is shown in Figure 8.5.1. 3 The graph shows t hat 1 1.0 cm of hydrochloric acid is needed to neutralise 3 25 cm of sodium hydroxide solution. neutralisation the temperature point increases acid is as more added the temperature decreases )C°( acid is as more added erutarepme T 0 2 4 6 8 10 12 14 16 18 of hydrochloric 3 Volume Figure 8.5.1 Graph of hydrochloric showing acid temperature added against (cm ) volume acid 3 added to 25 cm of sodium hydroxide solution The reaction between t he OH in t he hydrochloric acid ions in t he sodium hydroxide and t he H produces ions heat: OH (aq) H (aq) H O(l) 2 The temperature being added to when all OH This is reasons; 146 t he t he no increases react wit h ions heat is acid at lower solution heat is and reacted being being acid OH point. completion, a more t he have neutralisation more as is ions. and The t here produced to t he The because are because is more temperature none temperature temperature lost added t hen t he being environment. H stops lef t in t he decreases reaction added ions solution. for has which are increasing t hree reached cools t he Acids, T o bases and salts determine Your teacher the may observation, ● Neutralisation neutralisation use this recording activity and to point by using temperature change assess: reporting manipulation ● and measurement 3 Y ou will be supplied polystyrene cup, a with and a analysis ● and interpretation. 3 1.0 mol dm burette reactions sodium hydroxide solution, 3 1.0 mol dm sulfuric acid, a 25 cm pipette, a thermometer. Method 1 Rinse the burette with some sulfuric acid 2 Rinse the pipette with some sodium hydroxide and ll it with the acid. 3 pipette and run 3 Using 4 Keeping the solution with the it into the thermometer, polystyrene measure and solution. Measure 25 cm of sodium hydroxide solution in the cup. record the temperature of the sodium hydroxide solution. 3 thermometer the in the thermometer sodium and hydroxide record its solution, maximum add 2 cm of acid from the burette. Quickly stir the temperature. 3 5 Immediately 6 Repeat step quickly as 7 Record your 8 Use your added. add 5 another until you 2 cm have of hydrochloric recorded four acid, quickly successive stir drops the in solution and temperature. record It is its maximum essential that temperature. you do this as possible. results results Draw to two in a table. draw a straight graph lines showing of best the temperature of the solution against the volume of sulfuric acid t. 3 9 10 11 Use determine the volume of sulfuric acid needed (use an why the temperature of the solution increased b why the temperature of the solution stopped c why the temperature of the solution decreased. Suggest ant T able Where reasons why this neutralisation already and 8.5.1 used Antacids studied bee neutralisation to a have treat graph to neutralise 25 cm of sodium hydroxide solution. Explain: Using We your stings. method of ionic equation to help is less you) increasing determining the neutralisation point accurate than using an indicator. reactions how neutralisation Table 8.5.1 reactions summarises t hree can be ot her used ways to we use reactions. Using neutralisation reactions Action Antacids are [Mg(OH) ] taken to treat indigestion and acid reflux. They may contain sodium hydrogencarbonate (NaHCO ), magnesium hydroxide 3 2 excess T oothpaste Acid, aluminium hydroxide [Al(OH) , ], magnesium carbonate (MgCO 3 hydrochloric produced by acid in bacteria the in ) or calcium carbonate (CaCO 3 ). They work T wo active the ingredients in mouth, causes toothpaste, tooth sodium reacting with the hydrogencarbonate decay by and sodium calcium hydroxyapatite [Ca monofluorophosphate (PO 4 (Na ) the The sodium hydroxide ions hydrogencarbonate in the calcium neutralises hydroxyapatite any acid forming in the calcium mouth. The fluoroapatite fluoride ions (PO [Ca 10 Ca (PO 10 Acids Soil treatment Most do plants ) 4 not (OH) 6 grow (s) 2F (aq) Ca 2 react best (PO 10 with calcium if the soil fluoroapatite is neutral. hence Finely ) 4 the F 6 (s) the 2OH 6 in F the sodium ] in tooth 2 ), help reduce 3 monofluorophosphate displace ]: 2 (aq) 2 tooth ground ) 4 (OH) 6 FPO 2 decay. neutralising stomach. 10 enamel. by 3 enamel calcium does not carbonate decay. (limestone, CaCO ) or lime in the form of calcium oxide 3 (quicklime, CaO) or calcium hydroxide (slaked lime, Ca(OH) ) can be added to soil to neutralise any acids present. However, lime cannot 2 be added beneficial at the effects same of time an ammonium fertiliser because the two react to make a salt, ammonia gas and water which eliminates the both: CaO(s) as 2NH 4 2 (aq) Ca (aq) 2NH 3 (g) H O(l) 2 147 Volumetric analysis Acids, Summary 1 What 2 Outline a By the be able end of an this topic you a how three 4 Why should time to salts you would reaction? perform a neutralisation b indicator Give and questions neutralisation 3 A8.6 Objectives is bases uses of lime neutralisation and an reactions ammonium reaction temperature using: change. in our daily fertiliser not be lives. added at the same soil? Volumetric analysis will Volumetric analysis involves performing a titration to determine t he exact to: volume of one solution, usually an acid, required to neutralise a xed volume ● explain ● determine volumetric analysis of the mole ratio anot her t he which ● reactants determine the concentration concentration used in a solution, usually an aqueous alkali or carbonate. The results of in titration can t hen be used quantitatively in one of two ways: combine ● to determine t he mole ● ratio to determine t he molar of t he in which t he two reactants combine mass and of concentration and mass concentration of one molar one reactants. reactant titration. Determining The mole ratio mole in ratios which reactants combine can be determined using a titration if t he mass or molar concentration of bot h reactants is known, i.e. if t hey are bot h standard solutions. Example 3 During a titration it was found t hat 25 cm of potassium 3 concentration 0.6 mol dm hydroxide of molar 3 was neutralised by 10 cm of sulfuric acid of 3 molar concentration reactants . 0.75 mol dm Determine t he mole ratio t he number of moles of potassium hydroxide t hat 3 concentration 3 i.e. 1000 cm ∴ 1 cm of KOH(aq) 0.6 mol dm 3 (1 dm ) KOH(aq) contains 0.6 mol KOH. 0.6 _____ 3 KOH(aq) contains mol KOH 1000 0.6 _____ 3 and 25 cm KOH(aq) contains 25 mol KOH 1000 Calculate t he number of moles of 0.015 mol sulfuric acid KOH t hat reacted: 3 Molar concentration of H SO 2 3 i.e. 1000 cm (aq) 0.75 mol dm 4 3 (1 dm ) H SO 2 (aq) contains 0.75 mol 4 H SO 2 0.75 _____ 3 ∴ 1 cm H SO 2 (aq) contains mol 4 H SO 2 4 1000 0.75 _____ 3 and 10 cm H SO 2 (aq) contains 10 mol H 4 SO 2 4 1000 0.0075 mol H SO 2 148 which combine. Calculate Molar in 4 4 reacted: t he Acids, Use bases t he and salts number 0.015 mol of KOH Volumetric moles reacts of each wit h reactant 0.0075 mol to H determine 2 mol KOH react wit h 1 mol H SO 2 mole ratio: SO 2 ∴ t he analysiss 4 . 4 The mole ratio in which t he reactants combine is 2 mol potassium hydroxide to 1 mol sulfuric acid. Determining The t he concentration concentration mass or standard t hat you molar solution. followed of one reactant concentration This in is done your of by used t he a titration can ot her in reactant is following calculations in t he Unit same be determined known, four steps, i.e. i.e. if it is 1) to if a 4), 7 .5. Examples 1 A student solution performed of a titration hydrochloric acid. to determine The student t he used concentration a standard of a solution of 3 potassium hydroxide wit h a concentration of 0.1 mol dm and added 3 t he hydrochloric The results of t he acid to 25 cm experiment of are Titration Burette t he potassium shown in t he hydroxide solution. table. number reading Rough 1 2 3 21.5 20.5 41.0 20.4 0.0 0.0 20.5 0.0 21.5 20.5 20.5 20.4 3 Final reading/cm 3 Initial reading/cm 3 Volume of acid Determine Calculate added/cm t he t he molar average concentration volume of of t he hydrochloric hydrochloric 20.5 acid 20.5 acid. used: 20.4 __________________ average volume of HCl(aq) ( 3 ) cm 3 3 20.5 cm 3 i.e. it takes 20.5 cm 3 of hydrochloric acid to neutralise 25 cm of potassium 3 hydroxide solution, which has a concentration of 0.1 mol dm The balanced chemical KOH(aq) equation HCl(aq) for t he reaction KCl(aq) H is: O(l) 2 1) Calculate t he number of moles of potassium hydroxide t hat reacted: 3 Molar concentration 3 i.e. 1000 cm ∴ 1 cm of KOH(aq) 0.1 mol dm 3 (1 dm ) KOH(aq) contains 0.1 mol KOH. 0.1 _____ 3 KOH(aq) contains mol KOH 1000 0.1 _____ 3 and 25 cm KOH(aq) contains 25 mol KOH 1000 2) Use t he KOH balanced and 1 mol equation to 0.0025 mol determine t he KOH mole ratio between HCl: KOH reacts wit h 1 mol HCl. 149 Volumetric analysis Acids, 3) Use to t he number calculate 0.0025 mol 4) Use t he t he of moles number KOH number reacts of of of KOH wit h moles from moles of of 1) and HCl from 3) mole ratio and from salts 2) reacting: 0.0025 mol HCl t he bases HCl and t he volume used to 3 calculate t he number of moles of HCl in 1 dm : 3 Volume of HCl(aq) used 20.5 cm 3 i.e. 20.5 cm ∴ 1 cm HCl(aq) contains 0.0025 mol HCl. 0.0025 _______ 3 HCl(aq) contains mol HCl 20.5 0.025 3 and ______ 3 1000 cm (1 dm ) HCl(aq) contains 1000 mol HCl 20.5 0.122 mol HCl 3 Therefore, molar concentration of HCl(aq) 0.122 mol dm 3 2 A student found t hat 20.0 cm of hydrochloric acid of unknown 3 concentration were required to neutralise 25 cm of sodium carbonate 3 solution wit h a concentration The balanced Na CO 2 concentration of t he 0.12 mol dm hydrochloric chemical (aq) of equation . Calculate t he mass acid. for t he 2HCl(aq) reaction 2NaCl(aq) is: CO 3 (g) H 2 O(l) 2 3 1) Molar concentration of Na CO 2 3 i.e. (aq) 0.12 mol dm 3 3 1000 cm (1 dm ) Na CO 2 (aq) contains 0.12 mol Na 3 CO 2 3 0.12 _____ 3 ∴ 1 cm Na CO 2 (aq) contains mol Na 3 CO 2 3 1000 0.12 _____ 3 and 25 cm Na CO 2 (aq) contains 25 mol Na 3 CO 2 3 1000 0.003 mol Na CO 2 2) 1 mol Na CO 2 3) 0.003 mol reacts wit h 2 mol 3 HCl. 3 Na CO 2 reacts wit h 2 0.003 mol HCl 3 0.006 mol HCl 3 4) Volume of HCl(aq) used 20.0 cm 3 i.e. 20.0 cm ∴ 1 cm HCl(aq) contains 0.006 mol HCl. 0.006 ______ 3 HCl(aq) contains mol HCl 20.0 0.006 3 and 1000 cm ______ 3 (1 dm ) HCl(aq) contains 1000 mol 0.3 mol HCl 20.0 HCl 3 Therefore, molar concentration of HCl(aq) 0.3 mol dm 1 M(HCl) 1 i.e. mass of 1 mol ∴ mass of 0.3 mol 35.5 HCl HCl 36.5 g mol 36.5 g 0.3 36.5 g 10.95 g 3 Therefore, 150 mass concentration of HCl(aq) 10.95 g dm Acids, T o bases and salts determine the hydrochloric Your teacher Volumetric concentration of a solution analysis of acid may ● manipulation ● analysis use and and this activity to assess: measurement interpretation 3 Y ou will be supplied hydrochloric acid with of 0.2 mol dm unknown sodium concentration, hydroxide methyl solution, orange indicator, a 3 25 cm pipette, a conical ask and a burette. Method 1 Rinse the 2 Rinse the burette with some hydrochloric acid and ll it with the acid. 3 sodium 3 Add the 4 a with hydroxide few drops some solution of sodium in methyl the hydroxide pipette orange to and the solution. run it conical into Measure the ask 25 cm conical and swirl of ask. to mix contents. Carry This out time orange much 5 pipette a titration add on as described the acid until the adding one drop of in the practical solution acid. If just it activity turns turns red from you on page yellow have 141. to added too acid. Record your results in a table as outlined in the practical activity on page 3 6 142 and average Use this volume concentration help or vitamin C packaged iodine to of three volumes calculate the the of acid molar hydrochloric which were concentration acid. Use the within and 0.1 cm . mass examples above to you. Determining The the vitamin (ascorbic fr uit solution. juices odine C acid) can acts content content be as of vitamin determined an by oxid ising C tablets, fresh performing agent (see a Unit fr uit juices titration using 9.3) during t he titration and oxidises t he ascorbic acid to dehydroascorbic acid. The ascorbic acid is acts as a C H 6 O 8 During xed is (aq) t he t he longer starch it to is of t he of (aq) C brown juice immediately where a all since in of The iodine or a t he O 6 iodine (aq) of t he 1 mol colour t he fr uit of by colour. ions. The reaction ascorbic is added vitamin ascorbic has in t he The end 2H(aq) acid from C acid just to of burette As t he colourless reacted, solution point t he tablet. and t he iodine reacts a ions. will wit h titration to iodine is no t he when forms. iodine juice a acid remains just of t he ascorbic iodine to 6 solution solution reduced t he blue-black blue-black acid H 6 concentration calculated reduces equation: 2 fr uit produce ascorbic and dehydroascorbic reduced. permanent f agent following titration, point be t he acid volume added At in 6 ascorbic a reducing summarised solution or solution acid reacts is known, of wit h a t he vitamin 1 mol of concentration C tablet can be iodine. 151 Volumetric analysis Acids, T o determine Your teacher may ● manipulation ● analysis and be the Y ou will e.g. grapefruit 1% starch vitamin use and this C content activity to of a fruit bases and salts juice assess: measurement interpretation. supplied with a sample of a fruit juice without pulp, 3 juice, iodine solution of concentration 0.005 mol dm , 3 indicator solution, a 25 cm pipette, a conical ask and a burette. Method 1 Rinse the burette with some iodine pipette with some of solution and ll it with the iodine solution. Summary questions 3 2 3 1 A volume sodium of 40 cm carbonate of solution of 3 Rinse the juice in the Add ten pipette drops of and run starch it the into fruit the indicator to juice. Measure conical the 25 cm of the fruit ask. conical ask and swirl to mix the 3 concentration 0.2 mol dm contents. 3 reacts with 20 cm of nitric 4 acid of Carry out a titration as described in the practical activity on page 141. concentration This time add the iodine solution until the rst permanent trace of a blue- 3 . 0.8 mol dm Determine black the mole ratio in which combine. A of is obtained. the 5 reactants colour Record on your page results 142 and in a table average as the outlined three in the volumes of same practical iodine solution activity which 3 2 volume sodium 30 cm hydroxide 3 of were solution within 0.1 cm . of 6 Use this volume to calculate the molar concentration and mass Use the 3 concentration 0.4 mol dm concentration of ascorbic acid in the grapefruit juice. examples 3 were neutralised by 20 cm of on sulfuric acid. Determine concentration of the pages 149–50 to help you. the sulfuric You could adapt t he experiment which you have just performed to determine acid in: 3 a 3 b t he effect of heat on t he vitamin C content of a fr uit juice. Planning and mol dm designing experiments is discussed in more detail in t he School-Based g dm Assessment Key section on t he CD. concepts ● An in acid An ● Aqueous ● acid red, is substance dibasic An ● We which use a forms of acids react water; hydrogen ions (H ) when dissolved across a some be or of t hese 7 taste, and metals wit h bases change conduct to as to form that organic organic form organic concentrated; compound variety of sour hydrogencarbonates classied a a t han reactive react dilute is donor. have less and and may tribasic; of wit h carbonates of proton value anhydride come make pH acids or acid a acids and Aqueous as solutions wit h dioxide ● dened have Aqueous react ● a water. ● to 152 is in in a salt and form salt strong with living our colour electric a or litmus hydrogen; carbon water. monobasic, weak. water to form organisms ever yday of current. salt, and inorganic; and reacts acids acids or a to t he an an and acid. we activities. Acids, ● A ● An bases base and salts analysis is dened as a proton donor. alkali is a base which dissolves in water to form a solution containing hydroxide ions (OH ● Volumetric ). Aqueous solutions of alkalis have a bitter taste, change the colour of litmus to blue, have a pH value greater than 7 , conduct an electric current and feel soapy. ● Bases react with acids to form a salt and water and react with ammonium salts to form a salt, ammonia and water. ● Amphoteric substances ● Oxides ● Strong acids and alkalis are fully ionised when dissolved in water. ● Weak acids and alkalis are partially ionised when dissolved in water. ● The strength of an acid or alkali is measured using the can be classied as acidic, basic, amphoteric and neutral. ranges from ● can react with acids and strong alkalis. pH scale which 0 to 1 4 The stronger the acid, the lower the pH. The stronger the alkali, the higher the pH. ● Neutral substances have a pH of 7 . ● Universal indicator or a pH meter is used to measure pH. ● Other acid–alkali indicators have one colour in an acidic solution and another colour in an alkaline solution. ● A salt is a compound formed when some or all of the replaceable hydrogen ions in an acid are replaced by metal or ammonium ions. ● A normal salt replaced. An is formed when all the hydrogen ions in an acid are acid salt is formed when only some of the hydrogen ions are replaced. ● Some salts contain water molecules trapped between their ions in the cr ystal lattice. This is known as water of crystallisation ● nsoluble salts can be prepared by ionic precipitation. ● Anhydrous binar y salts can be prepared by direct combination. ● Potassium, sodium and ammonium salts can be prepared using a titration. ● Other soluble salts can be prepared by reacting a reactive metal, an insoluble carbonate or an insoluble base with an acid. ● Salts play an extremely important part in our ever yday lives, but can also be dangerous. ● A neutralisation reaction is a reaction between a base and an acid to form a salt and water. ● The neutralisation point is the point in an acid–alkali reaction where the reaction is complete and neither acid nor alkali is present in excess. ● The neutralisation point of an acid–alkali reaction can be determined during a titration by using an indicator, a pH meter or temperature change. ● Neutralisation reactions are used in various aspects of our daily lives. ● Volumetric analysis involves performing a titration to determine the exact volume of one solution required to neutralise a xed volume of another solution. ● Results of a titration can be used to determine the mole ratio in which the two reactants combine or to determine the concentration of one reactant. ● The vitamin C content of a vitamin C tablet or fr uit juice can be determined using a titration. 153 Practice exam-style questions Acids, 9 Practice exam-style Multiple-choice 1 Which of t he Magnesium sulfate can be prepared bases and salts by: questions reacting magnesium carbonate reacting magnesium nitrate reacting magnesium wit h A and B and C , D wit h wit h sulfuric sulfuric acid acid questions following is not a proper ty of sulfuric acid. hydrochloric only acid? A t turns a blue B t is C t reacts strong t reacts 2 Which of magnesium and form carbonate dioxide following and is/are to form sodium They react and wit h They have a They react wit h acids pH less to water. proper ties form t han a of aqueous salt and hydrogen. 7 . ammonium salts only to form a Which of t he following neutralisation alkalis? magnesium 10 sodium carbon t he to water. wit h chloride, only red. electrolyte. wit h chloride D litmus point an alkali? A An B A t hermometer C A pH D An in cannot a be reaction used to determine between an acid t he and anemometer meter indicator salt, 3 11 ammonia and A volume of of 25 cm a carbonate solution of water. 3 concentration A and C , and D 3 A neutralised by 20 cm of 3 acid of concentration 0.5 mol dm . The mole ratio in only which was only an B 3 0.2 mol dm and t he reactants combine is: A 1 mol of carbonate to 1 mol of acid B 1 mol of carbonate to 2 mol of acid C 2 mol of carbonate to 1 mol of acid D 3 mol of carbonate to 1 mol of acid. A volume only weak acid A is B ionises C has D does is one which: dilute fully in aqueous solution 3 12 a low concentration of of 10 cm of sulfuric acid of unknown ions H 3 concentration not ionise in aqueous neutralised 25 cm of sodium solution. 3 hydroxide 4 A solution which has a pH of solution concentration A is more B is less alkaline t han a of concentration . 0.4 mol dm The 1 1: solution wit h a pH of of t he acid is: 12 3 alkaline t han a solution wit h a pH of A 0.1 mol dm B 0.25 mol dm C 0.4 mol dm D 0.5 mol dm 9 3 C is more acidic t han water 3 D is less alkaline t han a sodium hydroxide solution of 3 t he 5 The same actual hydroxide concentration. change which solution occurs reacts wit h when sodium sulfuric acid is: Structured A 2Na question 2 (aq) SO (aq) Na 4 SO 2 (aq) 4 B OH C 2NaOH(aq) (aq) H (aq) D NaOH(aq) H H 13 O(l) A titration is used to determine t he volume of one 2 H SO 2 Na 4 SO 2 (aq) SO 2 (aq) Na 4 2H 4 SO 2 (s) O(l) solution Which of t he following acids is found in 4 an O(l) solution. Met hanoic B Et hanoic neutralise Titrations a xed volume of can be used as a means of soluble salts and in volumetric analysis t he concentration of one of t he solutions acid During a titration, t he neutralisation point C Lactic D Hydrochloric determined by using an indicator. acid a acid What is meant by t he neutralisation point of titration? of is acid usually Which to sting? used. 7 anot her preparing 2 ant determine A to 2 (aq) H cer tain 6 needed t he following is not an amphoteric Lead(II) B Aluminium C ron(III) D Zinc marks) substance? b A a (2 n order to determine t he solution, student concentration of a sodium oxide hydroxide a is provided wit h two hydroxide solutions labelled X and Y. oxide hydroxide – X is aqueous sulfuric acid wit h a mass 3 concentration 8 A pure sample of lead(II) chloride can be prepared of 19.6 g dm by – Y is a sodium hydroxide solution of unknown reacting: concentration. A lead B lead(II) wit h hydroxide dilute hydrochloric C lead(II) nitrate wit h dilute acid hydrochloric acid To determine t he concentration of Y, t he student 3 solution wit h sodium chloride titrates t he solution X against readings 25.0 cm from t he of Y. burette The gure before and 3 D 154 lead(II) carbonate wit h hydrochloric acid. titration using 25.0 cm of solution Y. shows af ter each Acids, bases and salts Practice c 0 17 2 19 4 Salts can be prepared i) your 20 5 t he before wit h answer a you would copper(II) copper(II) a balanced prepare sulfate a in variety carbonate. chemical pure t he 1 after titration nclude would before to your (5 met hod prepare be hydrated different if i) Using t he t he table in for copper(II) 2 marks) you sulfate after titration (1 mark) 15 marks 3 Total Burette sample equation cr ystals? titration of laborator y reaction. How wanted after by 23 ii) before how anhydrous star ting 3 laborator y met hods. Describe of 18 t he questions 22 different 1 in exam-style readings information from t he gure, complete below. Titration number 1 2 3 needed to 3 Final burette reading/cm 3 Initial burette reading/cm 3 Volume of solution X used/cm (3 ii) Calculate t he volume of X marks) neutralise 3 25 cm iii) of Y. Calculate (1 t he concentration of sulfuric mark) acid in 3 solution iv) X Calculate used v) in Write in t he t he a mol dm (1 number of moles of sulfuric titration. balanced for t he Determine t he number of moles mark) reaction. (2 vi) acid (1 equation mark) of marks) sodium 3 hydroxide vii) Calculate in t he t he of 25.0 cm concentration solution of Y used. (1 mark) (1 mark) sodium 3 hydroxide c How in b i) would t he in solution student Y use in t he mol dm . titration carried to prepare a pure dr y sample of sodium sulfate (2 ii) to prepare a pure sodium Total 14 a An as response acid a can proton be (1 mark) 15 marks question dened acceptor. as a proton Explain t he donor reason and for denition. b a acid However, t hey and sulfuric have acid different are pH bot h values. base EACH (4 Carbonic marks) hydrogensulfate solution? Extended out above: marks) acidic. You are 3 supplied wit h a solution 1.0 mol dm i) Suggest a pH ii) Explain t he value for EACH reason for t heir of each solution. different (2 pH Give one way suggested pH you could values are use to nd correct. out if marks) values. (2 iii) acid. marks) your (1 mark) 155 Oxidation–reduction A9 reactions Oxidation and reduction reactions form a very important example, in batteries, Objectives By the be able end of this topic you will part of our everyday photography, ● describe the oxidising and action of common in all these dene ● oxidation terms identify of and electron the photosynthesis reactions electrons and are the rusting being of cars. transferred. It In was and reduced using the discovery of oxygen that the chemistry the behind oxidation–reduction A9.1 Oxidation reactions was understood. reduction transfer reactant oxidised after everyday activities in for reducing only substances ● lives, to: being reactant electron and reduction – an introduction being transfer. The discover y stepping when metals oxides. and stone The in are laborator y chemistr y. burned, term preparation Antoine t hey oxid ation combine was used of oxygen Lavoisier wit h later to was a (1743–94) oxygen dene ver y from any impor tant discovered t he air reaction to in t hat form which a reactant gains oxygen. An example, according to t his denition of oxidation, is t he reaction gained between oxygen, 2Mg(s) forming O magnesium and magnesium oxide: (g) oxygen where t he magnesium has 2MgO(s) 2 The removal reaction of oxygen because reduction was t he used from metal to a metal oxide dene any was oxide was reduced reaction in to described t he which a pure as a metal. reactant reduction The loses term oxygen. An example, according to t his denition of reduction, is t he reaction between iron(III) oxide and carbon where t he iron(III) oxide has lost oxygen to form iron: 2Fe O 2 These (s) 3C(s) 4Fe(s) 3CO 3 (g) 2 denitions were later extended to include reactions involving hydrogen. Hydrogen is chemically opposite to oxygen, therefore, oxidation was dened as a loss of hydrogen and reduction was dened as a gain of hydrogen. With the discovery of protons, neutrons and, most importantly, electrons, scientists rened their denitions of oxidation and reduction, and the denitions were rened again using the concept of oxidation number or oxidation state. You will be studying these denitions in detail later in this unit. Oxidation and We encounter, our ever yday Action of Bleach is and lives. reduction make We use will of, look in our many at everyday oxidation some of t hese and activities reduction added bleaches and oxygen to are clothes chlorine bleaches to remove bleaches containing coloured containing hydrogen stains. The sodium peroxide most Figure the has 9.1.1 statue oxidation 156 of started The copper Marcus to turn from Garvey green is which made because stain to remove their stains colourless by oxidising form, hence the the coloured stain (H O summarises how the chlorate(I) ion (ClO The ). or (aq) coloured dye Cl Both dyes, equation ) in a chlorine bleach works: of ClO (NaClO) (aq) colourless types 2 chemicals, disappears. commonly chlorate(I) 2 bleach in bleaches used of reactions below. dye in the below Oxidation–reduction reactions Oxidation and reduction – an introduction Rusting When iron and its a lloy, ste el, co me into con t ac t w it h oxyg en an d mo isture t he iron xH O), is oxidised by t he oxygen to fo r m hydra te d ir on (I II) oxid e (Fe O 2 ot her wise known as r ust . Given sufficient t ime a nd 3 ex po su re to 2 oxygen r ust and and moist ure , Browning of As cer t ain so on suc h t he as air. a ny iro n ob j ec t w ill even tu ally oxid ise e n tir ely to disinteg ra t e . as cut f ruits and fr uit s pot atoes, a re Enzymes in suc h pee led t he vege tab les as or plan t a pple s cut , c ells an d t he on cu t t he ban an as, su r f ac e su r f ac e is of or cer t ain veget ables ex p ose d to t he or fr u it oxyg en in ve get ab le begin to oxidise cer t ain c hemica ls in t he ce lls to brown Figure on known tur n n as melanins . These melanins c a us e t he cut or b ec au se it 9.1.2 da maged su r f ac e exposure cases, appearance, b rown in g flavo ur, is qualit y un desirab le and t aste. Th e me la n ins cau se s for med c h an ges a re not in Did ? in some case s t h e ir pro ductio n is use f u l sinc e it con tr ib u tes turns in the brown air you colour and flavour of ite ms suc h as raisins, pr u n es, coffee, t ea and are pigments to of eyes skin, of hair, and scales, animals. ultraviolet for the light feathers Exposure stimulates the preservation production Sodium sulfite enhance and flavour, discolouration pot atoes bacter ia dr ied brown responsible coc oa. and being dark t he colour Food know? tox ic to black and of fo o ds shr imp. oxidising de stroyed pot ato s ulfur pre s e r ve by The bre at halyser test t he te st , dic hromate(VI) do is t he as t his sh r imp to acid. used c r y st a ls Any (K et h an o l by to O ) t he in to c hemicals fr u it s, Th ey C b r own ing in of dic hromate(VI) io n tur ning t he cr yst a ls g re en (se e dr ie d oxidation invo lve reactio n s electrons electrons to was was t hat sai d said to to a in ) Un it lo ss of invo lved h ave produc e d leve l have of in t he oran ge be e n b reat h and reduc t ion being t he loss t he dr ive r ’s acidified b reat h w ill wit h reduce to t he green c h romium(III) io n t he (Cr ), 9.3). Key can fact electrons ele c tron s. a b ee n be en of electrons of p ot assi um tran sfer Th ey of oxid ised develo ped ele c tron s. and a A a mo d el su b st an c e subst ance t hat for by an is the element element in a loss in its free state or an compound. t h at gained reduced . be d ef ined in t er ms of ele c tron Key fact t ran s fer, Reduction oxidation of dur in g ! Oxidation skin 7 and h ave why ju ic e Oxidation seemed is fr u its , By t h e tur n of t he 2 0t h ce nt ur y, c he mists realise d t h at ox id atio n reac tion s always which sunlight. p reven t fr u it ! Oxidation–reduc tion skin, in 3 O 2 human darkens pigments 7 vapo ur s (Cr in melanin dr ied 2 orange to and of for m. sample whic h spoilage dr ie d vit amin a lco h o l a preservative s preven t ox id atio n . t he p reven t reducing food or j u ices, p reven t test 2 fr u it c olo u rle ss blow s Cr as r ed u c e p reven ting a lso by t h eir dr ive r use d and and They 2 sulfur ic are wine , vine ga r ba c k te st n to a nd pro c e ss breathalyser dr iver s. suc h ox idat io n . produc t s browning diox ide fre sh ne ss Th ey win e The lost apple oxygen to Melanins t he cut to brown. many and A compounds electrons and re duc tio n b ein g t he gain is the gain of electrons of by an element in its free state or an electrons. element in a compound. 157 Oxidation and reduction – an introduction Oxidation–reduction reactions A substance will not lose electrons unless t here is anot her substance available ✔ Exam to tip gain t he electrons, i.e. for ever y oxidation reaction t here will always reduction reaction. These oxidation–reduction reactions are known as You must oxidation electron be able and define reduction transfer. remember to these remembering An in easy reactions. terms way definitions two words: is of to t he The oxid ation electrons is Oxidation Is RlG Reduction half known t hat equation as t he only and shows t he reduction t he loss equation half of t hat electrons only is shows t he OlL gain as of equation RlG of redox reactions Loss Is 1 Gain Burning magnesium 2Mg(s) in oxygen: O (g) 2MgO(s) 2 The Key ! redox oxide (MgO) reaction is a Each consisting magnesium in reduced and which the one of Mg in atom t he reaction is an ionic 2 ions loses and two O ions. electrons to During form a t he reaction: magnesium ion. chemical Magnesium reaction produced 2 compound ● A magnesium fact reactant other is (Mg) is oxid ised: is 2 oxidised. Mg This is 2e more Mg correctly written as: 2 Mg The ✔ Exam Mg overall oxidation 2e half equation is: tip 2 2Mg(s) When and writing balanced reduction half oxidation equations ● you 2Mg Each oxygen form an atom oxide in ion. (s) t he 4e oxygen Oxygen (O ) molecule is gains two electrons to reduced: 2 must always include state symbols 2 O and the it is important number balance at of to ensure atoms each side and of 2e O that charges The overall reduction half equation is: the 2 O (g) 4e 2O (s) 2 equation. 2 Adding zinc Zn(s) to copper(II) CuSO sulfate (aq) solution: ZnSO 4 The zinc sulfate displaces and copper Writing in t he t he During ● t he Each Cu Cu(s) copper(II) ionic 2 Zn(s) 4 t he copper. (aq) equation sulfate to for reaction: t he form zinc 2 (aq) Zn (aq) Cu(s) reaction: zinc atom loses two electrons to form a zinc ion. Zinc (Zn) is oxid ised: 2 Zn(s) ● Each Zn copper (II) ion (aq) gains two 2e electrons to form a copper atom. The 2 copper(II) ions (Cu ) are reduced: 2 Cu 3 Bubbling Cl (aq) chlorine (g) 2e gas 2Cu(s) t hrough 2KBr(aq) potassium 2KCl(aq) bromide Br 2 The t he (aq) displaces chloride t he and bromine bromine. in t he potassium Writing t he reaction: (g) 2 158 gas potassium Cl solution: 2 chlorine form 2Br¯(aq) 2Cl¯(aq) Br (aq) 2 ionic bromide to equation a redox known by Examples OlL equation be for Oxidation–reduction During t he Each ● reactions Oxidation numbers reaction: bromide bromide ions ion (Br loses ) are 2Br¯(aq) one electron to form a bromine atom. The oxid ised: Br (aq) 2e 2 ● Each chlorine form a atom chloride in ion. t he chlorine Chlorine (Cl ) molecule is gains one electron to reduced: 2 Cl (g) 2e 2Cl¯(aq) 2 onic the bonding non-metal always atom. involves Any a transfer reaction in of electrons which ionic from bonds the are metal formed atom is a to redox reaction. Using the reaction between sodium and chlorine as an example: 2Na(s) Cl (g) 2NaCl(s) 2 Each ● is sodium atom loses one electron to form a sodium ion. Sodium (Na) oxid ised: 2Na(s) Each ● a 2Na chlorine chloride atom ion. in (s) t he Chlorine 2e chlorine (Cl ) is molecule gains one electron to form reduced: 2 Cl (g) 2e 2Cl (s) 2 Summary 1 Dene 2 State questions oxidation whether and each reduction of the in terms following half of a transfer equations of electrons. shows oxidation or reduction: 3 a Fe 2 (aq) 3e b Fe(s) Fe c Br (aq) 2Br (aq) 3 (aq) Fe (aq) e 2 d 2e Cu 2e Cu(s). 2 3 In the has following been Br redox reaction, state what Why A9.2 Redox (aq) 2KI(aq) an apple turn Oxidation chemistr y 2KBr(aq) For water, and what I (aq) is no when it is cut in half? numbers in Objectives fur t her reactions example, t here brown developed oxidation–reduction for m oxidised 2 does electrons. been reduced: 2 4 has t he did when not reaction change in t he chemists always between number of involve recognised t he hydrogen valence transfer and the be able end t he atoms, ● dene ● determine on any i.e. t here is no transfer of valence electrons. However, t he ● reaction is denitely a redox reaction because t he reaction involves and (g) O 2 The of development Oxidation as a result (g) 2H 2 model will oxidation number oxidation numbers formulae dene oxidation terms of and oxidation reduction of oxidation–reduction t he concept indicates chemical identify redox number change in identify the reactions using a O(g) 2 number of you oxygen: ● 2H topic bot h in hydrogen this to from of of to: of oxygen electrons By t hat of t he bonding. reactions oxid ation number of was number electrons expanded or lost, by oxid ation gained or t he state. shared ● oxidation reactant oxidised and reduced using oxidation the a number being reactant change being in number. 159 Oxidation numbers Oxidation–reduction Oxidation Key ! oxidation fact sign The oxidation element that an have if atoms it were was is the atom all in the the ionic number of theoretical of the and the is placed 1, always 2, can of an before and be t he t here positive, element, is number always negative unless a to t he or zero. number indicate number af ter impor tant role if it t he is When zero, is a positive sign, i.e. writing plus or t he or t he minus negative, number 1 is written. would between compound e.g. charge element bonds composed an numbers number reactions the containing Oxidation numbers compounds as you play will an learn in sections t hat in t he naming of cer tain follow. compound entirely of ions. Rules Before for you determining can learn how to oxidation recognise numbers redox reactions using t he concept of oxidation number, you must learn how to determine t he oxidation numbers of ● elements. The For To do oxidation t his, a set number of of r ules each need atom of to an be followed. element in its free state is zero. example: oxidation number of an oxidation number of each Al atom N in atom Al in 0 N 0. 2 ● The oxidation to t he in Al number charge on t he of each ion. For simple ion in an ionic compound is equal example: 3 O 2 : oxidation number of each Al ion 3 ion 2. 3 2 oxidation ● number The oxidation number of of each O hydrogen when present in a compound is always 1 except when bonded to a metal in a metal hydride where its oxidation number is 1, e.g. in sodium hydride (NaH) and calcium hydride (CaH ). 2 ● The 2 oxidation except in number of peroxides oxygen where it when is 1, present e.g. in in a compound hydrogen is peroxide always (H O 2 ● The sum of t he compound is atom add oxidation zero. For numbers example, of in all H elements O, t he present oxidation in ). 2 a number of each in t he 2 must up 2(oxidation ● The sum of OH ion, 0 (2) 0 (2) (2) 0 number oxidation ion t he zero: 2(1) t he polyatomic to is equal oxidation (oxidation of H) numbers to t he of O) (2) of all charge number number (oxidation of elements on each number t he ion. atom (oxidation of O) present For must a example, add number in of up H) (1) to 1: 1 1 Following these r ules, the oxidation number of any element can be determined from the formula of the compound or polyatomic ion in which the element occurs. Examples 1 Determine t he oxidation number of sulfur in sulfur dioxide (SO ). 2 (oxidation number of S) 0 (oxidation number of S) 2(oxidation 2(2) 0 (oxidation number of S) (4) 0 4 ∴ The compound sulfur dioxide number oxidation (SO ) can be of number called O) of S sulfur( IV) oxide 2 because 160 t he oxidation number of sulfur in t he compound is 4. Oxidation–reduction 2 Determine t he reactions oxidation Oxidation number of nitrogen in t he nitrate ion (NO numbers ). 3 (oxidation number of N) (oxidation number of N) 3(oxidation 3(2) 1 (oxidation number of N) (6) 1 5 ∴ The nitrate ion (NO ) is more number oxidation correctly of number called t he O) of N 1 nitrate( V) ion 3 because 3 t he Determine carbon in oxidation t he number oxidation met hane (CH of nitrogen number in t he ion is of ). 5. C 4(1) 0 C (4) 0 ∴ C 4 4 The 4 oxidation Determine number t he manganese in of oxidation t he carbon is number MnO ion 4 of and name Mn 4(2) 1 Mn (8) 1 7 4 t he The ∴ ion. oxidation number manganate( VII) in 5 t he t he chromium oxidation in K Cr 2 name of manganese because of t he is 7. The oxidation ion is called number of t he manganese ion. Determine of ion Mn t he O 2 number 2(1) 2Cr 7(2) (2) 2Cr (14) 0 2Cr 12 Cr 6 and 7 compound. ∴ The oxidation The compound oxidation 6 number is called number Determine t he of of chromium potassium chromium oxidation in number is 0 6. d ichromate( VI) t he because of t he compound. of S 3(2) 2 S (6) 2 4 2 sulfur in t he sulte ion (SO ) and 3 suggest The be an alternative oxidation called t he Oxidation Cer tain t his elements, name. and when it is is its T able give 9.2.1 containing Compound of done ions, sulfur more impor tant is ion. 4. ∴ The ion can S also a to naming compounds t han possible one compound include by placing in Roman t he t he ion and naming for name t he t he or ion oxidation oxidation numerals always oxidation t hat in ends in number. contains number number brackets ‘ ate’. any as of par t t he af ter Tables of For t hese of t he element, its name. 9.2.1, 9.2.2 examples. Names of compounds manganese Oxidation T able ions Name 9.2.2 Names containing Compound of compounds and nitrogen Oxidation T able ions Name 9.2.3 Names containing Compound Oxidation number number of of of Mn manganese(IV) N NO 2 nitrogen(II) NO 4 nitrogen(IV) oxide SO 2 of compounds and sulfur number 4 2 have charge, naming 9.2.3 MnO number This wit hout When number sulfate( IV) elements reason, name Name S 4 sulfur(IV) oxide 6 sulfur(VI) oxide 4 sulfate(IV) ion 6 sulfate(VI) ion oxide 2 KMnO 4 7 oxide SO 3 potassium 2 NO 3 nitrate(III) ion SO 5 nitrate(V) ion SO 2 3 manganate(VII) 2 NO 3 4 161 Oxidation numbers Oxidation–reduction Redox Key ! reactions and oxidation reactions number fact f we consider t he loss or gain of electrons and a change in oxidation number, we Oxidation is the increase in number of an in state an element its free or can see a clear link between t he two. the oxidation element in Whenever ● a an same time, atom forms atom its or ion oxidation loses electrons number it has increases. been For oxidised. example, At when a t he sodium compound. increases a sodium from 0 to ion 1. it loses The one sodium electron atom has and its been oxidation number oxid ised: Na Key ! oxidation Reduction is the decrease in oxidation number of an in state an element its free or the Whenever ● element in time, a its forms compound. a an numbers: atom oxidation chloride decreases from 0 or ion is Exam easy to reduction number, ion to it gains 1. is remember a you electrons decreases. The one it has been example, electron chlorine For and atom its has e reduced. when a t he same chlorine atom oxidation been At number reduced: Cl (0) (1) tip when make it it that decrease because anything, Na (1) gains number numbers: By considering t he It e (0) Cl oxidation ✔ fact in oxidation you reduce is possible to change in oxidation number of each element in a reaction determine if it is a redox reaction. f it is a redox reaction, t he oxidation number of one element will increase and t he oxidation number of anot her element will decrease. less Consider t he 2Mg(s) following O reaction (g) again: 2MgO(s) 2 We can write magnesium t he ions half and equation show t he for t he oxidation conversion number of of each magnesium to below: 2 2Mg(s) 2Mg (0) (2) Looking atom We can and at has t his, we increased write show t he t he can see from half (s) 0 t hat to t he 2. equation oxidation 4e for numbers oxidation Magnesium t he number (Mg) has conversion of of each been magnesium oxid ised oxygen to oxide ions below: 2 O (g) 2 4e 2O (0) Looking in t he (s) (2) at t his, oxygen we can see molecule t hat has t he oxidation decreased from number 0 to 2. of each Oxygen oxygen (O ) has atom been 2 reduced t is impor tant to note t hat in writing t he oxidation number of each element we disregard number of a any Recognising Changes in electrons. subscripts single atom redox oxidation The or or ion t he are not numbers We element reactions number oxidation coefcients. of of using always are writing t he oxidation only. oxidation brought elements in about covalent numbers by a transfer substances of can also change when t hey react to form ot her covalent substances. For example, when hydrogen and oxygen react 2H (g) 2 oxidation 162 numbers: (0) to form O (g) 2 (0) water: 2H O(g) 2 (1) ( 2) Oxidation–reduction ● The has oxidation increased reactions number from 0 of to Oxidation each 1. hydrogen Hydrogen atom (H ) in has t he been hydrogen numbers molecule oxid ised 2 ● The oxidation decreased number from 0 to of 2. each oxygen Oxygen (O ) atom has in been t he oxygen molecule has reduced 2 Redox don’t reactions involve which a number by 1) Write t he balanced 2) Write t he oxidation not need ions 3) 5) to is t he t he f t here which is a no in number t he which of has increase in each electrons be and also recognised an been shows been a t hose using which oxid ation reaction. in a brackets of below elements in it. You do polyatomic reaction. increase in its oxidation number. oxidised. decrease in its oxidation number. This reduced. oxidation number t he numbers during shows has for element oxidation element which of can equation unchanged oxidation redox transfer below. chemical element which element decrease not remain a electrons outlined element Determine is steps of determine which Determine This 4) t he involve transfer of number anot her of one element element, t hen and t he a reaction is reaction. Examples 1 Determine been which reduced in CuO(s) (2)( element t he H has reaction been oxidised between (g) Cu(s) H 2 (0) 2) and copper(II) which oxide element and has hydrogen. O(g) 2 (0) (1)( 2) reduced oxidised ● The oxidation number of each hydrogen atom in the hydrogen molecule has increased from 0 to 1. Hydrogen (H ) has been oxidised. 2 2 ● The oxidation decreased 2 number from Determine which reduced t he in CH to (g) 0. element reaction 4 ( 2 of 2O t he Cu ion Copper(II) has been between oxide (g) t he CO 2 and and (g) has oxide been which has reduced. has been oxygen. 2H 2 (4)( copper(II) (CuO) oxidised met hane (0) 4)(1) in O(g) 2 2) (1)( 2) oxidised reduced ● The has oxidation increased number of t he carbon 4 to 4. Met hane number of each from atom in (CH t he met hane has been ) molecule oxid ised. 4 ● The has oxidation decreased from 0 to 2. oxygen Oxygen atom (O ) in has t he been oxygen molecule reduced. 2 3 Determine whet her 2AgNO (aq) 3 (1) Because t he following MgCl NO (aq) is a redox 2AgCl(s) 2 (2)( t he reaction ion 1) remains (1)( unchanged 1) reaction Mg(NO or ) 3 not. (aq) 2 (2) in t he reaction, i.e. it of t he nitrogen and is one of oxygen in 3 t he spectator t he ion None This do of is t he not ions, not a t he need to elements redox oxidation numbers be considered. has undergone a change in oxidation number. reaction. 163 Oxidising and reducing agents Oxidation–reduction 4 Determine which reduced t he in Mg(s) element reaction ZnSO has been between oxidised and which magnesium and zinc (aq) MgSO 4 (0) (aq) been sulfate. Zn(s) 4 (2) has reactions (0) (2) oxidised reduced 2 Because t he SO ion remains unchanged in t he reaction, t he oxidation 4 numbers of t he sulfur and oxygen in t he ion do not need to be considered. The ● oxidation Magnesium number (Mg) has of t he been magnesium has increased from 0 to 2. oxid ised. 2 The ● oxidation from 2 to 0. number Zinc of each sulfate Zn (ZnSO ion ) has in t he been zinc sulfate has decreased reduced. 4 Summary questions 1 Dene 2 Determine the a copper in b sulfur c carbon oxidation in and reduction oxidation in number terms of oxidation number. of: CuO H S 2 in each of CO, CO , H 2 d nitrogen in each of NH e chlorine in each of AlCl , CO 2 Mg 3 N 3 , and C 3 H 2 and NH 2 4 NaClO and KClO 3 3 Use oxidation reactions. If they oxidised and a Cl (g) number are the to 3 determine redox reactant whether reactions which 2KI(aq) has give 2KCl(aq) I 3O (g) 2Al 2 Mg(s) reactant are which redox has been reduced: (aq) O 2 2HCl(aq) (s) 3 MgCl (aq) H 2 d following 2 4Al(s) c the the been 2 b 4 Cl BaCl (aq) H 2 SO 2 (aq) (g) 2 BaSO 4 (s) 2HCl(aq). 4 Objectives By the be able end of this topic you will A9.3 n ● dene the reducing terms agent oxidising dene in terms any redox of ● One terms oxidising in terms oxidation One This oxidising as t he reactant as t he can brings about oxid ising brings occur simultaneously. t he oxidation of t he ot her reactant. This is reduction of t he ot her reactant. This is agent about reducing generally oxidised and of compounds A oxidised can oxidising reduction t he agent be B symbolised is t he as reactant follows, t hat has where been A is t he reactant reduced: agents examples which and and been reducing oxidation number recognise give agents of known ● reducing and ● agent reaction, reactant known the reducing ● and and electrons ● Oxidising to: act as agent both and a B C D reduced an reducing n t he above reaction: agent ● 164 describe tests oxidising and to ● A must have been oxidised ● B must have been reduced by B. B is t he oxidising A is t he reducing agent. identify reducing agents. by A. agent. t hat has Oxidation–reduction reactions Oxidising and reducing Consider example t he 2Al(s) of Oxidising aluminium (g) 3Cl agents 2AlCl 2 ● The in terms reacting of has been wit h chlorine each atom because has lost t hree to form an aluminium ion (Al agents fact An oxidising the oxidation by 3 electrons Key ! gas: (s) oxidised reducing electrons 3 aluminium and causing agent of an brings another atom or about reactant ion in that ): reactant to lose electrons. 3 2Al(s) The 2Al chlorine Chlorine atoms (Cl ) is (s) brought t he 6e about oxid ising t his loss by taking t hese electrons. agent 2 ● The chlorine gained one 3Cl has been electron (g) reduced to form 6e a because chloride 6Cl each ion atom (Cl in t he molecule Key ! ): A (s) fact reducing agent brings about 2 the The aluminium atoms brought about t his gain by donating Aluminium (Al) is t he reducing a oxid ising reducing agent, agent Oxidising t herefore, causes and causes anot her reducing anot her reactant to agents reactant gain in another reactant causing an atom or ion in that agent. reactant An of t hese by electrons. reduction to lose electrons to gain electrons. and electrons. terms of oxidation Exam ✔ tip number It Consider t he example of magnesium burning in oxygen can learn 2Mg(s) O (g) (0) (2)( agent 2) to reduced magnesium has been oxidised because t he oxidation number magnesium atom has increased from 0 to 2. confusing Oxygen (O ) is well as reducing them know out that electrons of to try to oxidation those of agent. It when Oxidation (OIL). An and oxidising is better needed. Is the oxidising Loss agent of must each as and work Y ou of The very definitions reduction oxidised ● the 2MgO(s) 2 (0) be again: cause this loss by taking these t he 2 electrons. oxid ising agent because it is t he reactant t hat caused t he increase The oxygen has atom been reduced because t he oxidation number of has decreased An ion agent, anot her number of because from it is 0 t he to 2. Magnesium reactant t hat (Mg) caused t he is of in an t herefore, atom or to ion causes increase. in A anot her t he oxidation reducing reactant number agent to of causes an t he atom reducing which agent in CuO(s) (2)( reactant t he H is t he reaction oxdising between decrease (g) Cu(s) 2 (0) 2) agent and copper(II) (0) H which oxide is and Is the reducing cause The this gain reducing by agent giving itself electrons. Key fact An oxidising the oxidation agent of brings another about reactant t he by causing the oxidation an atom ion in number of hydrogen. O(g) or that reactant to increase 2 (1)( A or Examples Determine (RIG). oxidation ! 1 must electrons. loses reactant Reduction electrons t he decrease number. oxid ising in agent that each agent reducing oxidation itself electrons. know Gain oxygen agent number. Y ou ● oxidising in gains oxidation The 2) reduced oxidised Key ! ● Copper (II) t he oxide hydrogen atom to by increase (CuO) is causing from 0 t he t he to oxid ising oxidation agent number because of each it hydrogen A reducing reduction 1. causing ● Hydrogen (H fact oxidised agent of the brings another about reactant oxidation the by number of ) is the reducing agent because it reduced the copper(II) 2 an atom or ion in that reactant to 2 oxide by causing the oxidation number of the Cu ion to decrease from decrease 2 to 0. 165 Oxidising and reducing agents Oxidation–reduction 2 ✔ Exam Determine reducing tip Zn(s) It is better to work out which agent H of oxidising t he SO 2 is t he reaction oxdising between (aq) ZnSO 4 agent zinc (aq) 4 and and which sulfuric H is t he acid. (g) 2 the (0) definitions reactant in reactions agent (1) (0) (2) and oxidised reducing of agent oxidation need using number the concept when reduced you them. Sulfuric ● acid (H SO 2 If you remember that involves an increase number, an oxidising oxidation in zinc oxidation agent from this 0 causing to ) is t he oxid ising agent because it oxidised t he 4 t he oxidation number of t he zinc atom to increase 2. must Zinc ● cause by (Zn) is t he reducing agent because it reduced t he sulfuric acid increase. by If you remember that involves a decrease in number, a reducing agent oxidation number of each H ion to decrease from 1 0. oxidation must 3 this t he reduction to cause causing s iron(III) it reacts oxide behaving as an oxdising agent or a reducing agent when decrease. wit h Fe O 2 carbon (s) 3CO(g) 3 (3)( monoxide? 2) (2)( 2Fe(s) 3CO (g) 2 (0) 2) (4)( 2) oxidised To determine t he carbon t he behaviour monoxide has of iron(III) been oxide oxidised or we need to look to see if reduced. The carbon monoxide has been oxidised. The iron(III) oxide (Fe O 2 ) is 3 behaving as an oxidising agent because it caused the oxidation number of the carbon atom in the carbon monoxide (CO) to increase from Substances reducing There are agents. Sulfur can behave as both act as oxidising and agents some Their compounds that 2 to 4. compounds behaviour which dioxide, can which depends behave in can on t his t he bot h ot her way are oxidising reactant. given and reducing Examples of two below. SO 2 Sulfur dioxide usually acts as a it reacts wit h SO (g) 2 reducing agent. This is seen, for example, when chlorine: Cl (g) 2 2H O(l) H 2 SO 2 (aq) 4 2HCl(aq) (0) ( reduced by 1) SO 2 The sulfur each dioxide chlorine When it sulde, reacts sulfur 2H S(g) 2 ( reduced atom in wit h a dioxide SO t he t he chlorine chlorine stronger behaves (g) reducing as an 3S(s) 2 by causing molecule agent oxidising to 2H t he oxidation decrease t han from itself, 0 such number to of 1. as hydrogen t he oxidation agent: O(l) 2 (0) 2) oxidised by SO 2 The sulfur dioxide oxidised t he hydrogen sulde by causing number of t he sulfur atom in t he hydrogen sulde molecule to increase from 2 166 to 0. Oxidation–reduction reactions Oxidising and reducing agents Acidified hydrogen peroxide, H /H O 2 2 Acidied hydrogen peroxide is hydrogen peroxide solution to which sulfuric acid has been example, added. when 2K(aq) ( it t usually reacts H O 2 wit h (aq) H 2 behaves SO 2 oxidising (aq) 4 hydrogen oxidation it agent. This is seen, for 2 (g) K SO 2 4 (aq) 2H O(l) 2 (0) by H O 2 When an iodide: 1) oxidised The as potassium peroxide number reacts of wit h oxidised t he a 2 ion stronger to t he potassium increase oxidising from agent iodide 1 to t han by causing t he 0. itself, such as acidied potassium manganate(VII), acidied hydrogen peroxide behaves as a reducing agent: 2KMnO (aq) 5H 4 O 2 (aq) 3H 2 SO 2 (aq) K 4 SO 2 (aq) 5O 4 (g) 2MnSO 2 (7) reduced by H t he hydrogen oxidation T ests There O(l) 2 O 2 The (aq) 8H 4 ( 2) for are chemical peroxide number reduced of t he oxidising cer tain in a agents ver y potassium manganese chemicals reaction t he 2 to and which distinct from reducing undergo way, manganate(VII) decrease e.g. to by causing 2. agents oxidation they 7 may or reduction change to a in a distinct colour, they may form a par ticular precipitate or they may give off a par ticular gas. Chemists use these chemicals to determine whether unknown substances are oxidising agents or reducing agents. They do this by reacting the unknown substance with these chemicals and obser ving the products. These chemicals form the basis of tests for oxidising agents and reducing agents. Examples Potassium iod ide solution, Potassium iod ide solution agent. There is brown when t he because ( ) t he which a distinct K (aq) is potassium oxidising dissolves used colour agent forming in t he change iodide is laborator y in t he oxidised. oxidises t he a solution. brown to test solution The colourless for from colour iodide an oxidising colourless change ion ( ) to occurs to iodine 2 ( (aq) 2 (aq) 2 2e (0) 1) oxidised The potassium iodide is, itself, a reducing agent. Acid ied potassium manganate(VII) solution, H /KMnO (aq) 4 Acid ied test for from The a potassium reducing purple colour to manganate(VII) agent. colourless change There is when t he occurs a because solution distinct is potassium t he used colour in t he change in laborator y t he manganate(VII) reducing agent reduces is to solution reduced. t he pur ple 2 manganate(VII) ion (MnO ) to t he colourless manganese(II) ion (Mn ). 4 2 MnO (aq) Mn (aq) 4 (7) (2) reduced The acidied potassium manganate(VII) is, itself, an oxidising agent. 167 Oxidising and reducing agents Oxidation–reduction T ests for oxidising Table 9.3.1 chemicals These chemicals T able 9.3.1 Reducing for agents summarises which can are, t he be agents used agent iodide as used Visible test Potassium names used t hemselves, Reducing agent reactions solution colour reactants reducing to test change is and t he for changes to test of for t he main oxidising two agents. agents. the when presence of an oxidising agent Explanation oxidised Colourless to brown The (KI(aq)) colourless iodine (I ) iodide which ion (I dissolves ) is oxidised forming a to brown 2 solution 2 Iron(II) Figure 9.3.1 Potassium iodide sulfate solution Pale green to yellow-brown The (aq)) to 4 colourless to brown green iron(II) ion (Fe ) is oxidised 3 (FeSO from pale turns the yellow-brown iron(III) ion (Fe ) when oxidised There are reactions, oxidising T able several agent. 9.3.2 Reducing ot her alt hough These Other chemicals t hey are are common agent given sulfide in Visible gas (H S(g)) A which usually reducing is Hydrogen not Table behave used to as test reducing for t he agents presence in of an 9.3.2. agents change when agent Explanation oxidised yellow precipitate forms Yellow insoluble sulfur (S) is 2 produced Concentrated hydrochloric acid A yellow-green gas is evolved Yellow-green chlorine gas (Cl ) 2 is (HCl(aq)) Others: hydrogen gas (H ); carbon (C); carbon monoxide (CO); reactive produced metals 2 T ests for reducing Table 9.3.3 chemicals These summarises which chemicals T able 9.3.3 Oxidising agents can are, used agents for test potassium manganate(VII) as used and t he colour reactants oxidising to Visible is Acidified names used t hemselves, Oxidising agent t he be test for change changes to test of for t he main reducing two agents. agents. the presence when agent of a reducing agent Explanation reduced Purple to colourless solution The manganate(VII) purple (MnO ) is reduced to ion the 4 (H /KMnO (aq)) colourless manganese(II) ion 4 2 (Mn Acidified potassium dichromate(VI) Orange to green ) The orange solution (H dichromate(VI) ion 2 /K 2 Cr 2 O (aq)) (Cr 7 2 O ) is reduced to the 7 3 green Figure 9.3.2 (a) manganate( VII) Acidied turns colourless when potassium dichromate( VI) orange to green potassium from purple reduced. when (b) to Acidied turns from reduced (a) 168 (b) chromium(III) ion (Cr ) Oxidation–reduction reactions Oxidising and reducing agents There are several ot her chemicals which behave as oxidising agents, alt hough t hey are are not given T able in usually Table 9.3.4 Oxidising used to Other common oxidising agent sulfate for t he presence of a reducing agent. These 9.3.4. Visible is Iron(III) test solution agents change when agent Explanation reduced Yellow-brown to pale green The yellow-brown iron(III) ion 3 (Fe (SO 2 ) 4 (aq)) ) (Fe is reduced to the pale 3 2 green Dilute or (HNO (aq)) concentrated nitric acid A brown gas is evolved Brown (NO 3 Hot iron(II) ) ion (Fe nitrogen is ) dioxide gas produced 2 concentrated sulfuric acid A pungent gas is evolved Sulfur dioxide gas (SO ) is 2 H SO 2 (l)) which turns acidified potassium produced 4 manganate(VII) Others: sodium chlorate( ) solution (NaClO); oxygen colourless gas (O ); chlorine gas (Cl 2 T o investigate Your teacher the may reactions use this activity ● observation, recording ● analysis interpretation. Y ou will be and supplied dichromate( VI), with and oxidising to manganese(IV) oxide (MnO ) 2 agents and reducing agents assess: reporting aqueous potassium of ); 2 iodide, solutions iron( II) of acidied sulfate and potassium acidied manganate( VII), hydrogen peroxide acidied and ve potassium test tubes. Method 3 1 Place 2 cm solution, of acidied shaking as potassium you add the manganate( VII) solution, until solution you see no into the further rst test colour tube. Slowly add 3 2 Place potassium iodide change. 3 2 cm of acidied potassium manganate( VII) solution into the second test tube, 2 cm of acidied potassium 3 dichromate( VI) iron(II) as sulfate you add 3 Record in 4 Explain the T ables 5 Dene a 2 In in and on the each of reducing into the the until original for 9.3.3 the third fth you behaviour tube. see colour colour above tube, to of Slowly no of the 2Fe b 2NO(g) each O Give an agent acidied colour you iodide solution hydrogen into peroxide the fourth solution to tube and 2 cm each tube, of shaking change. and the observed hydrogen nal in colour each after reaction. mixing. Use the information given in peroxide. questions of the oxidising agent and b electrons following reactions reducing in terms identify the (s) agent of oxidation oxidising number. agent and the 3C(s) 3CO (g) 4Fe(s) 2 2CO(g) N (g) 2CO 2HCl(aq) (g) 2 MgCl (aq) H 2 3 add solution that acidied 3 Mg(s) potassium you. 2 c of further change help 3 2 cm agent: a 2 the terms terms the reason 9.3.1 into solution, table Summary 1 solution the a Comment solution example and as a of a compound reducing which (g) 2 can act both as an oxidising agent. 169 Oxidising and reducing agents Oxidation–reduction Key ● concepts We encounter, our ever yday of fr uits, and breat halyser and make make use of Many Oxid ation or an Oxidation oxidation ● dened element is and involve as in dened element in and reduction r usting bleaches, food and reactions t he in browning preser vation and t he a t he a a known transfer loss of of as redox reactions electrons. electrons by an element in its free compound. as in are t he gain of electrons by an element in its free compound. reduction can also be dened using t he concept of number. Oxid ation would in reactions reactions is Reduction state ● an t hem t hem test. ● or oxidation encounter ● state of, We Oxidation–reduction redox use lives. ● ● reactions number have containing if it all t he were is t he t heoretical bonds ionic between and t he charge t he t hat atoms compound in was an atom t he of an element compound composed entirely of ions. ● n any redox numbers ● Oxid ation in ● its free free An is A oxid ising ● An ● A ● An will always be a change in t he oxidation an an as an as a is t he in a in a in oxidation number of an element compound. decrease element agent increase element in oxidation number of an element reactant t hat brings about t he oxidation of agent is t he reactant t hat brings about t he reduction of reactant. oxidising reducing agent agent oxidising causes causes agent t he t he causes ot her ot her t he reactant reactant oxidation to to lose gain number electrons. electrons. of anot her element to increase. ● A reducing agent causes t he oxidation number of anot her element to decrease. ● The distinctive reduction when ● ● of to for for 170 a presence iron (II) presence potassium of changes are t hat compounds and t he dichromate(VI) presence t he iodide test Acidied colour cer tain testing Potassium used in compound. reactant. reducing anot her or dened or t here elements. dened is state anot her ● reaction two state Reduction its ● of of accompany allow sulfate of an reducing agent. are or agents and reducing to or be used agents. agents which can be agent. acidied which oxidation compounds reducing oxidising manganate (VII) oxidising t hese oxidising t he can be potassium used to test for t he Oxidation–reduction reactions Practice 8 Practice exam-style n t he following 4HNO is: a gain of oxygen a gain of electrons a decrease A only B and C , D in B oxidation number C D only following undergoes Copper ) (aq) statements oxidation A 2 B 4 C 6 D 8 number of sulfur in t he O S ion Copper Copper n its oxidation tr ue? oxidation and its oxidation reduction and its oxidation oxidation and its oxidation increases. undergoes increases. experiments, acidied acidied following obser ved solutions sulfur of potassium pairs in Colour dioxide potassium name of t he BrO ion was bubbled dichromate(VI) t he of manganate(VII). correctly describes t he Which colour of t he changes experiment? potassium Colour of potassium manganate(VII) is: A orange to green colourless B orange to green pur ple C green to orange colourless D green to orange pur ple When acidied to pur ple bromite(I) bromate(I) C bromite(V) to colourless to to pur ple colourless bromate(V) 10 4 is and 3 and B D copper O(l) 2 decreases. undergoes separate into is: 3 A about 2H reduction d ichromate(VI) The (g) 2 only 2 3 2NO 2 decreases. undergoes number 9 The t he number 2 2 of Copper number and Cu(NO 3 number (aq) questions A Oxidation reaction: 3 which 1 questions questions Cu(s) Multiple-choice exam-style Consider t he hydrogen peroxide solution is added to following: iron(II) sulfate solution: 2 M(s) n t he reaction represented has been has increased has A only B and C and D , (aq) M metal M: oxidised gained above, in oxidation number 5 6 Which of t he C t he oxidation D t he acidied Structured following causes an B t causes a C ts D t increase loss oxidation which iron(II) green solution ion is number formed of hydrogen to t he t he iron(III) iron(II) peroxide is ion ion decreases acting as a agent question a The gure and mineral below shows t he of is tr ue in about oxidation a reducing supplement information agent? has been label bottle. on a multivitamin lef t Much of t he out. number. electrons. number increases. electrons. of t he following reactions does t he oxidation Each number is oxidised t n pale only A gains t he electrons 11 and a B reducing only A of nitrogen show t he greatest tablet contains increase? …………………………… A 2NO(g) (g) O 2NO 2 B 4NO (g) O 2 (g) 2 (g) 2H 2 …………………………… O(l) 4HNO 2 (aq) …………………………… 3 Potassium C N (g) 3H 2 (g) 2NH 2 iodide 0.1 mg (g) 3 …………………………… D 2NH (g) 3CuO(s) N 3 (g) 3Cu(s) 3H 2 O(l) 2 …………………………… 7 Which A of t he 2Na(s) following 2H reactions O(l) is not a redox 2NaOH(aq) H 2 B Fe(s) C MgO(s) FeCl (aq) 2 H SO 2 A (g) (aq) H (g) A 2 MgSO 4 (aq) 4 H C(s) O (g) 2 and mineral supplement bottle solution hydrogen O(l) CO is made of peroxide is one of added t he to tablets t he and acidied solution. 2 i) D multivitamin 2 2HCl(aq) reaction? State what you would expect to obser ve. equation to represent (1 mark) (g) 2 ii) Write an ionic half reaction. iii) Wit h a b Three (2 reason, represents redox t he state whet her oxidation reactions are or t he marks) reaction reduction. represented by (1 mark) t he 171 Practice exam-style questions equations given substance which give t he reason Oxidation–reduction below. has for For been your EACH reaction, oxidised. choice n based name EACH on t he case, oxidation number. i) Zn(s) 2HCl(aq) ZnCl (aq) H 2 (g) 2 (2 2 ii) 2Fe marks) 3 (aq) Cl (g) 2Fe (aq) 2Cl (aq) 2 (2 iii) (g) 2NH 3CuO(s) N 3 (g) marks) 3Cu(s) 2 3H O(l) 2 (2 c One type of potassium i) For t he breat halyser dichromate(VI) what pur pose is test uses marks) acidied cr ystals. t he breat halyser test used? (1 ii) Describe t he iii) test what is Explain would obser ve if t he t he (1 chemistr y Using oxidation ClO ion. involved in (2 suggest a of mark) t he test. number, mark) result positive. breat halyser d you name for marks) t he (1 mark) 15 marks 2 Total Extended 12 a Dene i) ii) b response oxidation question in terms of: electrons oxidation Suppor t reference Cl number. EACH to (g) t he (2 denition given following 2Br in a above marks) by reaction: (aq) 2Cl (aq) Br 2 (g) 2 (4 c ‘Metals are oxidising Use your i) agents and non-metals marks) are agents.’ EACH whet her reducing of t he t he answers 2PbO(s) reactions above based below statement on is oxidation C(s) to determine tr ue. Pb(s) Give reasons for number. CO (g) 2 (2 ii) The reaction sulfate d You are an respectively. Describe what and wit h are two agents tests told you about bottles agent are a and carr y Y. X Y agent, liquids. out to conrm (4 Total 172 marks) and reducing colourless could X labelled and marks) copper(II) (3 oxidising Bot h T WO you magnesium solution. provided containing between marks) 15 marks reactions A10 Electrochemistry is Electrochemistry the study of the relationship Objectives between An chemical reactions electrochemical reaction and is electrical one which energy. By the be able electrical energy or requires electrical energy give of in order in a to proceed. From the reactions that to produce an electrolysis of aluminium electric current, the the to to the is important in produce our you electrochemical determine reaction will series metals if a will and displacement occur their between compounds aluminium, based electrochemistry topic common metals oxide this occur ● battery of to: either ● produces end lives. on positions their in relative the electrochemical series ● determine displace A10.1 The electrochemical if a metal hydrogen on its position electrochemical electrochemical series of an acid series based The will from in the series metals ● give the electrochemical series n Unit 5.2 you learnt t hat when atoms bond ionically, t he metal atom always of loses electrons to form a t han ot hers. positive metal cation. Some metals lose more which t hey easily When metals are placed in order of ease electrons, i.e. ease wit h which t hey ionise, a series determine known A electrochemical section of t he series of metals electrochemical is if a displacement will occur non-metals The 10.1.1. more forms. n easily Metals conver t which t his back are at to easy Since metals when t hey a table, metal t he top atoms. to lose react t he series atom of t he Metals conver t of t he common ionisation ionises, t he at bottom t he to increases more form metals is given their compounds their relative ver y stable stable of t he going are ions series based positions in on the in series. upwards. t he ions which form are t hat it hard to unstable ions T able 10.1.1 The series of common the electrochemical metals atoms. when ot her of series back electrons wit h ease and created. electrochemical Table between as certain t he non-metals wit h reaction lose common electrons ● much some t hey ionise, substances, i.e. t hey t hey act give as reducing electrons to agents t he Metal Cation potassium K calcium Ca sodium Na magnesium Mg aluminium Al zinc Zn iron Fe lead Pb hydrogen H copper Cu silver Ag ot her 2 reactant. The more easily t hey give electrons, t he stronger t heir reducing power. The strengt h as a reducing agent, t herefore, increases going up 2 t he series. 3 Potassium is highest in t he series, which means t hat it ionises t he most 2 easily, forms t he most stable ions and is t he strongest reducing agent. Silver is t he lowest in t he series, which means t hat it ionises t he least easily, forms t he least stable ions and is t he weakest reducing 2 agent. 2 We can make chemical use of t he electrochemical series of metals to predict cer tain reactions. 2 Displacement A met al from a met al ions of t he been displace compound is of will a stronger t he lower lower of a metals met al t hat cont aining reducing met al. met al are As is t he agent, a it in met al. t herefore, result, conver ted below lower t he to electroc hemical readily higher atoms, t he This is gives met al i.e. t he because are ser ies higher electrons ionises ions t he to and t he said to t he ions have d ischarged 173 The electrochemical series Electrochemistry Examples 1 Will a reaction copper(II) occur sulfate Magnesium is magnesium can Magnesium is if a strip of magnesium ribbon is placed in solution? higher t han copper in t he electrochemical series, t herefore, 2 a displace stronger t he Cu ions reducing from agent, t he copper(II) t herefore, it 2 t he Cu ions The magnesium d ischarged Mg(s) forming CuSO ionises copper (aq) ionic equation MgSO Mg(s) copper(II) sulfate to 2 Mg ions and t he Cu (aq) Cu(s) 4 is: 2 blue forming atoms: 4 The electrons 2 ions. are gives sulfate. Cu 2 (aq) Mg (aq) Cu(s) solution The transfer of electrons is shown in t he ionic half equations: magnesium 2 Mg(s) Mg Cu(s) (aq) 2e 2 Cu colourless As t he ● The (aq) reaction 2e proceeds magnesium t he ribbon following gradually are gets obser ved: smaller as it ionises and t he magnesium 2 sulfate pink Figure 10.1.1 Mg solution copper Magnesium is added to ions ● A ● The pink dissolve solid blue in builds colour t he up in solution. t he solution of t he copper (II) ions are discharged as copper sulfate is solution formed. gradually fades as 2 copper( II) sulfate t he solution 2 Will a blue Cu reaction occur if some iron from lings t he are solution, placed in a forming solution copper. of zinc nitrate? ron is lower than zinc in the electrochemical series. Displacement of No reaction will occur. hydrogen Metals above ions an in hydrogen acid, in forming t he electrochemical hydrogen gas (H ). series Metals will below displace hydrogen t he will H not 2 displace t he H ions. Metals above hydrogen are stronger reducing agents and will readily give electrons to t he H ions of t he acid. Metals below hydrogen are weaker reducing agents, so will not reduce t he H ions. Examples 1 Will a reaction Zinc is zinc can higher occur t han if zinc is hydrogen placed in t he in hydrochloric electrochemical acid? series, t herefore, displace t he H ions from t he hydrochloric acid. Zinc is a stronger reducing agent, t herefore, it gives 2 zinc ionises hydrogen forming gas (H Zn electrons to t he H ions. The ions and t he H ions are d ischarged forming ): 2 Zn(s) 2HCl(aq) ZnCl (aq) H 2 The ionic equation is: Zn(s) 2H (g) 2 2 (aq) Zn (aq) H (g) 2 The transfer of electrons is shown in t he ionic half equations: 2 Zn(s) Zn (aq) 2e 2H (aq) 2e H (g) 2 2 Will a reaction Copper will 174 is lower occur. occur t han if some copper hydrogen in turnings t he are placed electrochemical in sulfuric series. No acid? reaction Electrochemistry The The electrochemical When non-metal electrons to electrons atoms form much a series bond ionically, negative more easily of series non-metals t he non-metal t han electrochemical ot hers. non-metal anion. When atom Some always gains non-metals non-metals are gain placed in order of ease wit h which t hey gain electrons, i.e. ease wit h which t hey ionise, a A series known section Table The of 10.1.2. easier forms. hard t he n a electrochemical t his ions, when at back which non-metals agents table, non-metal conver t unstable electrochemical t he Non-metals to Since as are ease atom t he to gain t hey t he top series series of t he t he series form Non-metals easy conver t electrons react wit h back when ot her at stable ver y t he to t hey is created. non-metals increases more atoms. to non-metals some ionisation ionises, of of of going are stable bottom is t he ions ions, of given in upwards. t he t hat which series substances, t hey i.e. t hey act as are form oxid ising remove T able 10.1.2 series of The some electrochemical non-metals Non-metal Anion fluorine F chlorine Cl bromine Br iodine I it atoms. ionise, electrons from t he ot her reactant. The more easily t hey remove electrons, t he stronger t heir oxidising power. The strengt h as an oxidising agent, t herefore, going up t he Fluorine is forms t he lowest in least We can cer tain highest most t he stable in series, ions make and use chemical non-metal series from higher will a t he stable series, ions and which is of which is t he means means t hat strongest t hat it ionises t he weakest oxidising t he electrochemical it ionises oxidising t he t he agent. least most easily, odine easily, is t he forms t he agent. series of non-metals to predict reactions. Displacement A increases series. of non-metals displace compound non-metal is a a non-metal containing stronger which the is lower oxidising below it in the non-metal. agent, electrochemical This therefore, is because readily the removes electrons from the ions of the lower non-metal. As a result, the higher non-metal ionises, and the ions of the lower non-metal are discharged forming atoms. Examples 1 Will a reaction occur if chlorine gas is bubbled into sodium iodide solution? Chlorine is higher than iodine in the electrochemical series of non-metals, therefore, chlorine can displace the ions from the sodium iodide. Chlorine is a stronger oxidising agent, therefore, it removes electrons from the ions. The chlorine discharged ionises forming iodine ( forming Cl ions and the ions are ): 2 Cl (g) 2Na(aq) 2NaCl(aq) 2 The ionic equation (g) 2 is: (aq) 2Cl (aq) 2 (aq) 2 transfer Cl (aq) 2 Cl The (g) of electrons 2e is shown 2Cl in t he ionic half equations: (aq) 2 2 (aq) (aq) 2e 2 175 Electrical conduction Electrochemistry 2 Will a reaction potassium Bromine will If is lower zinc is Explain b Give c a What the able end of occur: topic you the b silver c iodine d bromine Which chlorine a solution reaction added to a solution of in t he electrochemical series. No reaction of copper( II) nitrate, a reaction occurs. occurs. chemical of metal lead(II) equation colour of and a balanced ionic equation for the copper( II) nitrate solution? Explain to in of the a displacement reaction solution. electrochemical zinc when three series will release hydrogen acid? displace occurred Arrange not solution iodide the to or solution hydrochloric found whether solution chloride metals was ease nitrate potassium added predict nitrate sodium displacement of the following, the X to calcium when A10.2 this of aluminium order be is occurs. a solution. By in a happens will no Objectives why this each A solution questions balanced For gas 4 bromine reaction. why 3 t han placed a the 2 if occur. Summary 1 occur chloride? it from was metals, X, zinc added zinc nitrate to and solution magnesium magnesium in but nitrate decreasing ionisation. Electrical conduction will n Unit 5 you learnt t hat in order for a substance to conduct an electric to: current, it must contain charged par ticles which are able to move t hrough t he ● distinguish conductor between and a a substance. non- can conductor ● distinguish between electrolytic distinguish between electrolyte, a and a give Conductors weak a strong can include electrolyte examples electrolytes, be are substances solids, metals, compounds of can based be on eit her t heir electrons or ions. ability to conduct electricity to pass Materials an electric liquids which graphite, and aqueous or allow solutions. molten acids ionic and Examples of t hrough. compounds, conductors solutions of ionic alkalis. Non-conductors are substances which do not allow an electric current strong weak pass t hrough. Non-conductors can be solids, liquids, solutions electrolytes and gases. Examples of non-conductors include non-metals (except non-electrolytes. graphite), 176 par ticles groups non-electrolyte to and two metallic ● ● charged into conduction They ● These classied current. ● and be plastics, covalent substances and solid ionic compounds. Electrochemistry T o Electrical investigate the electrical conductivity of conduction various substances Circuit 1 switch Your teacher may ● observation, ● manipulation Y ou will be sulfate a and e.g. hydrochloric with rod, and to assess: reporting circuit wire, a sodium acid, activity A measurement. copper graphite crystal, this recording supplied substances, crystal, use components, magnesium plastic chloride ethanol and ruler, a samples ribbon, sodium solution, of various aluminium chloride copper( II) foil, crystal, sulfate an a iodine copper( II) solution, solid to be tested dilute kerosene. Circuit 2 Method 1 switch Draw up a table ‘Prediction’ with and three ‘Results’. columns In the headed rst ‘T est column substance’, write down the name of A each test column a substance ll in your that you prediction have of been whether supplied the with. substance In is the a second conductor or non-conductor. beaker 2 Connect the circuit as shown in Figure 10.2.1. If the test substance is a carbon solid use Circuit 1 and if it is a solution or a liquid use Circuit electrodes 2. solution 3 Record 4 Compare the results of your experiment in the third column of your to table. your predictions with the Figure 10.2.1 When and ionic created electrolytic compounds contains ions melt and of a solid and to test a liquid the conduction or is circuits tested results. conductivity Metallic T wo be dissolve known in as water, an t he liquid electrolyte. or solution Electrolytes are conductors. There are cer tain differences between conduction in a metal, known Key ! as metallic electrolytic conduction , and conduction in an electrolyte, known An conduction electrolyte that forms aqueous Metallic n a fact as ions is a compound when molten or in solution. conduction metal, t he delocalised valence electrons, electrons known as of t he mobile atoms are electrons, delocalised. are able to These move t hroughout t he metal. Metals are able to conduct an electr ic cur rent because t hese mobile electrons is of a non-metal, delocalised, During ionic an conducts an mobile electrons (see conduction, t he electr ic Unit metal cur rent because of t he presence 5.5). remains chemically ions no unchanged conduction ionic bonds can move t hroughout t he metal. Alt hough graphite also metallic Electrolytic When it and compound t hey melts, become free t he to move are longer t hroughout t he held toget her by liquid: heat NaCl(s) Na (l) Cl (l) 177 Electrical conduction Electrochemistry Similarly, when an ionic compound dissolves in water, t he ionic bonds break and t he ions are free to move t hroughout t he solution: water NaCl(s) These of Na electrolytes mobile ions (aq) conduct which are Cl an able (aq) electric to current move because t hroughout t he of t he liquid presence or aqueous solution. During electrolytic chemically T able 10.2.1 Metallic Mobile through The Metallic electrons the metal electrolyte and electrolytic conduction carry remains can is decomposed, i.e. it is the electric current Mobile the chemically of an between ions Strong electrolytes Strong electrolytes strong of in t he are alkalis concentration unchanged The ions conduction carry the electric current through electrolyte electrolyte decomposes electrolyte distinguish of compared Electrolytic metal. concentration acids, t he conduction Strength We conduction, changed. fully and ions strong in and weak electrolytes based on t he electrolyte. ionised soluble solution. when ionic For dissolved in compounds. water, These e.g. have strong a high example: HCl(aq) Molten Weak Weak e.g. H ionic (aq) compounds are Cl also (aq) classied as strong electrolytes. electrolytes electrolytes weak solution. acids For and are only weak parti ally alkalis. These ionised have a when low dissolved concentration in of water, ions example: CH COOH(aq) CH 3 T able 10.2.2 Examples Strong Acids COO (aq) H (aq) 3 of electrolytes electrolytes Hydrochloric acid Weak (HCl(aq)) electrolytes Carbonic acid (H CO 2 Nitric acid (HNO (aq)) Ethanoic 3 Sulfuric acid (H Alkalis Potassium Sodium Salts Molten Sodium Molten hydroxide 178 solution solution (NaOH(aq)) (NaCl(aq)) bromide bromide (KOH(aq)) (NaCl(l)) solution potassium Potassium (aq)) chloride chloride COOH(aq)) 4 hydroxide sodium (CH 3 SO 2 acid (aq)) 3 (KBr(l)) solution (KBr(aq)) Aqueous ammonia (NH 3 (aq)) in Electrochemistry Strong Electrolysis electrolytes are much better electrical conductors t han weak Summary questions electrolytes. The strengt h of an electrolyte can be tested wit h a simple circuit which has a light bulb (or light emitting diode (LED)) connected to a batter y 1 and two electrodes which are dipped in t he electrolyte. The greater Distinguish a strengt h of t he electrolyte, t he more brightly t he bulb will between: t he a conductor and a non- glow. conductor A non-electrolyte liquid any state ions. or is a substance dissolved in Non-electrolytes which water. are The remains liquid or non-conductors. as molecules solution Examples when does of not in the b metallic contain and electrolytic conduction non-electrolytes c a strong and a weak include liquids such as kerosene and gasoline, molten covalent substances such electrolyte. as wax and solutions of covalent substances such as ethanol and glucose. 2 Classify as Pure water a each strong weak of the following electrolyte, electrolyte or a a non- electrolyte: Pure water is an extremely weak electrolyte. Water undergoes spontaneous ionisation into H ions and OH ions. At any one time, approximately one a potassium b a c aqueous d kerosene e aqueous chloride solution 8 in ever y 5.56 10 water molecules is ionised: solution of sucrose ethanoic in water acid H O(l) H (aq) OH (aq) 2 7 The concentration of H ions and OH As next you will learn in t he unit, ions in pure water is 1 10 t his is of par ticular 3 mol dm signicance when . 3 electric current is passed t hrough an aqueous When an Why is pure decomposed current into is simpler passed t hrough substances, i.e. an it electrolyte, undergoes a t he electrolyte chemical is By the be able as ● ● takes electrolytic A batter y Two or place cell has ot her electrodes in a piece three d.c. of main power connected, apparatus supply via known as an electrolytic cell. ● components. of this topic you will to: dene the terms wires, t hat take t he electric current into anode, cathode, electrolysis, identify ions anion present and cation in electrolytes provides t he to t he batter y and out of or electric power current. ● t he predict the ion drift will electrode during to which an electrolysis supply, ● which end electrolysis Electrolysis An an electrolyte? change ● known water weak Objectives Electrolysis electric acid. electrolyte. extremely A10.3 nitric an electrolyte. They discuss the electrolysis of molten must electrolytes be able to conduct an electric current and are usually made of an iner t ● material such as graphite (carbon) or platinum. The anode is explain of to t he positive terminal of t he batter y and t he cathode is connected negative The electrolyte, compound mobile discharge discuss the electrolysis of certain terminal. aqueous ● preferential ions to ● t he the connected or a which is solution a molten electrolytes. ionic containing ions. battery Key ! fact Electrolysis which is is occurs passed the chemical when through an an change electric current electrolyte. electrolyte Key fact The anode is The cathode ! anode Figure 10.3.1 An electrolytic cell the positive electrode. cathode is the negative electrode. electrodes 179 Electrolysis Electrochemistry electrons around from flow the Mechanism of electrolysis circuit anode to e e During Light electrolysis bot h anions and cations are d ischarged, i.e. bulb: cathode glows t hey brightly lose or gain electrons to form neutral atoms. This occurs as e battery if the is electrolyte follows. strong e e glows the e dimly if The ● electrolyte anions (negative ions) are attracted to t he anode is (positive electrode). The anions lose electrons to t he anode weak e e and anode () cathode ( form atoms, i.e. t hey are discharged: ) n n C C n n A A A ne n C n n A C n A Oxid ation occurs at t he anode (OL). The anode electrolyte, n C n C n CA(l A n A → A or aq) acts as t he oxid ising The electrons, agent ne n C n A n C ne → C n n A ● C lost by t he anions circuit to t he positive at t he anode, travel n C n A n n C n C C t hrough n Figure 10.3.2 Mechanism of ● ✔ tip The cations electrode). atoms, It can be confusing to try to of t he t hen re-enter t he circuit from t he negative batter y. terminal of electrolysis t he Exam terminal A They t he (positive The i.e. batter y ions) cations t hey are and travel are gain to t he attracted t he cat hode. to electrons t he cat hode from t he (negative cat hode forming discharged: learn n which electrode which is is negative. positive It is C and better it out, remembering C to Reduction work ne that occurs at t he cat hode (RG). The cat hode acts as t he reducing the agent electrodes which • are You are named attracted know negative that to after anions charge. the ions them. have Anions a must Electrolysis be attracted electrode. must be to The called the positive the You know positive that electrode cations charge. molten electrolytes Molten electrolytes contain only two different ions, one cation and one anode anion. • of positive have Cations Bot h are discharged during electrolysis. a must Example be attracted electrode. electrode to The must the negative negative be called Electrolysis of molten (fused) le ad(II) bromide using inert g raphite the electrodes cathode 2 The At ions the present in t he molten lead(II) bromide are Pb (l) and Br (l). anode: The Br lose electrons ions immediately 2Br move to towards t he bond (l) anode t he covalently Br (g) anode forming where bromine forming t hey are atoms. bromine discharged, Pairs of i.e. bromine t hey atoms molecules: 2e 2 Brown At the fumes of bromine are evolved at t he anode. cathode: 2 The Pb gain ions move towards t he cat hode where t hey are discharged, i.e. t hey electrons to form lead atoms: 2 Pb Molten 180 (l) lead 2e forms Pb(l) around t he cat hode and drips off. Electrochemistry T o Electrolysis electrolyse (T eacher molten lead( II) bromide using graphite electrodes demonstration) + Your teacher may observation, ● use this recording activity and to assess: reporting. anode Y our teacher will perform the − following () ( ) cathode experiment. bromine gas The experiment must be performed in a fume cupboard. molten lead Method 1 Place 2 Heat 3 Connect the circuit 4 Observe the product 5 Write ionic some the lead( II) lead( II) bromide bromide as into until it shown a crucible. melts. in Figure bromide 10.3.3. heat formed at each electrode. an Electrolysis During those the of half of equation aqueous electrolysis the for solute. of an the occurring at each Figure electrode. lead( II) 10.3.3 Electrolysis of molten bromide solutions aqueous Because reaction water solution, the undergoes ions present spontaneous are not only ionisation, an aqueous solution always contains H ions and OH ions from the ionisation of water molecules as well as the ions from the solute. As a result, aqueous solutions always contain at least n t he will be electrolysis of discharged in two different cations and an aqueous preference solution, to t he two different anions. one ot her. type This is of ion of known as each charge preferenti al d ischarge. Preferential discharge of anions There are three main factors which inuence t he preferential discharge of t he anions The t hat you position Considering at t he top of will be the ion of t he t he studying: in the electrochemical electrochemical series are t he series most of stable series anions and given t he in hardest Table to 10.3.1, ions discharge. ons at t he bottom of t he series are t he least stable and t he easiest to discharge, i.e. t he ease of discharge increases T able 10.3.1 series of The electrochemical anions Anion downwards. F 2 The lower t he ion in t he electrochemical series, t he more likely it is to be discharged. SO 4 NO 3 Cl This is seen, for example, when we look at the electrolysis of dilute sulfuric Br acid, dilute sodium chloride inert electrodes; the OH solution and copper(II) sulfate solution using ion is preferentially discharged from each solution. I OH The concentration The concentration preferentially to be of the electrolyte t he discharged. preferentially solutions of electrolyte There discharged. containing halide ions, is a has However, i.e. an tendency Cl impact for t his ions, Br t he r ule on more really ions and which ions are concentrated ion only applies to ions. 181 Electrolysis Electrochemistry This is seen when we compare t he electrolysis of dilute sodium chloride solution wit h t he electrolysis of concentrated sodium chloride solution, bot h using iner t discharged electrodes. n but concentrated in t he t he dilute solution, t he solution, OH ion is preferentially Cl ion is preferentially t he discharged. The type of electrode The type of anode chosen for t he electrolysis can affect t he reaction occurring at t he anode. f t he anode is inert, for example graphite or not affect t he reaction occurring. However, if t he anode is copper, it happens This is can at t he seen an iner t When an iner t active There is cations T able 10.3.2 series of Cation The in t he compare anode wit h is electrolysis main you t he of factor will be t he its used, anode, discharge one t hat we anode copper Preferential par t process it does active, for example and t his affects what anode. when using an take platinum, electrolysis electrolysis t he OH anode ion of copper(II) using is an sulfate active preferentially solution copper anode. discharged. Wit h ionises. cations which inuences t he preferential discharge of t he studying: electrochemical cations The position of the ion in the electrochemical series K Considering t he electrochemical series of cations given in Table 10.3.2, ions 2 Ca at t he top of t he series are t he most stable and t he hardest to discharge. ons at Na 2 Mg t he bottom t he ease of of t he series discharge are t he increases least stable and t he easiest to discharge, i.e. downwards. 3 Al The lower t he ion in t he electrochemical series, t he more likely it is to be 2 Zn discharged. 2 Fe This is seen, for example, when we look at t he electrolysis of dilute and 2 Pb concentrated sodium chloride solution; t he H ion is preferentially H discharged in bot h. Also when we look at t he electrolysis of copper(II) sulfate 2 2 Cu solution; t he Cu ion examples referred is preferentially discharged. We will now look at Ag to above in greater detail. Examples 1 Electrolysis Ions of d ilute sulfuric acid using inert electrodes present: From t he H SO 2 : H 2 (aq) and SO 4 (aq). 4 From t he H O: H (aq) and OH (aq). 2 At the anode: 2 The SO ions and t he OH ions move towards t he anode. The 4 OH ions are preferentially electrochemical 4OH series of (aq) discharged 182 occurs 2H as t hey are lower anions: O(l) 2 Effer vescence because oxygen O (g) 4e 2 gas is evolved at t he anode. in t he t he Electrochemistry At the Electrolysis cathode: The H ions move towards t he cat hode where t hey are discharged: 2H (aq) 2e H (g) 2 Effer vescence Relative volumes Comparing from are occurs t he t he anode of hydrogen gases two to as is evolved at t he cat hode. produced: equations, t he gas for cat hode, ever y 1 mol of 4 mol of oxygen electrons and transferred 2 mol of hydrogen produced: 4OH (aq) 2H O(l) O 2 (g) 4e 2 4H (aq) 4e 2H (g) 2 1 volume Changes of in oxygen the is produced for ever y 2 volumes of hydrogen. electrolyte: The sulfuric OH ions acid are becomes discharged more from concentrated it, i.e. water because is being H ions removed and from t he electrolyte. Because electrolysis of T o electrolyse (T eacher of sulfuric t he discharge acid dilute is of referred sulfuric t he to acid as H ions t he using and OH electrolysis inert ions, of t he water . electrodes demonstration) oxygen Your teacher may use this activity ● observation, recording ● analysis interpretation. Y our and teacher will perform and the to hydrogen assess: reporting following experiment. Method platinum foils 1 Set up the sulfuric Hoffmann’s acid 2 Observe 3 T est the as the gas the as shown in Figure 10.3.4, using dilute anode electrolyte. relative given voltameter volume off at the of gases anode to given off see it if at is each splint. The splint should glow brighter oxygen or (–) electrode. by using a Figure 10.3.4 showing glowing cathode (+) re-light if the gas the Hoffmann’s electrolysis voltameter of dilute is sulfuric acid oxygen. 4 T est a the gas burning given splint. extinguished 5 if off The the at the splint gas is cathode should to see make a if it is hydrogen squeaky pop by and using ? be Did Oxygen gas glowing splint relight why oxygen b why hydrogen c why the was produced at the anode (include an 6 What volume would you of produced hydrogen expect to at the was happen cathode greater to the the electrolyte an equation) volume as to the glow it brighter supports or the equation) (include than causes because combustion, was know? hydrogen. Explain: a you the of i.e. burning, of the splint. oxygen. reaction proceeds? 183 Electrolysis Electrochemistry 2 Electrolysis Ions of d ilute sod ium chloride solution using inert electrodes present: From t he NaCl: Na (aq) and Cl (aq). From t he H O: H (aq) and OH (aq). ions move 2 At the The are anode: Cl ions and preferentially lower in t he 4OH t he OH discharged electrochemical (aq) 2H towards t he because t hey in series anions: O(l) of O 2 Effer vescence At the occurs as dilute OH ions solution and are 4e 2 oxygen gas is evolved at t he anode. Na ions and preferentially series a The cathode: The (g) are anode. of t he H ions discharged move because towards t hey are t he cat hode. lower in t he The H ions are electrochemical cations: 2H (aq) 2e H (g) 2 Effer vescence Relative volumes Comparing from are occurs t he t he anode produced, of gases two to i.e. as gas is evolved at t he cat hode. produced: equations, t he 1 hydrogen for cat hode, volume of ever y 1 mol of oxygen is 4 mol of oxygen electrons and produced 2 mol for transferred of ever y 2 hydrogen volumes of hydrogen. Changes in the electrolyte: The ions 3 sodium and chloride OH Electrolysis inert Ions ions of solution are becomes discharged concentrated from sod ium more concentrated because H (brine) using it. chloride solution electrodes present: From t he NaCl: From t he H Na (aq) and Cl (aq). O: H (aq) and OH (aq). ions move 2 At the The ions anode: Cl ions are and t he OH preferentially concentrated 2Cl discharged towards because t he t hey anode. are The halide Cl ions in a solution: (aq) Cl (g) 2e 2 Effer vescence At the occurs as Na gas is evolved at t he ions and preferentially series chlorine of t he H ions discharged move because towards t hey are t he lower cat hode. in t he The H cations: (aq) 2e H (g) 2 Effer vescence occurs as hydrogen gas is evolved at t he ions are electrochemical 2H 184 anode. cathode: The yellow-green cat hode. Electrochemistry Relative volumes Comparing from are Electrolysis t he t he in to i.e. the gases two anode produced, Changes of produced: equations, t he for cat hode, equal ever y 1 mol volumes of of 2 mol of electrons chlorine chlorine and and transferred 1 mol hydrogen of are hydrogen produced. electrolyte: The electrolyte becomes alkaline because H ions and Cl ions are discharged form from sodium it leaving an excess of Na ions and OH ions, which hydroxide. test T o investigate the effect the preferential of the concentration of tubes the electrolyte electrolyte (T eacher Your on of ions demonstration) teacher may use this activity ● observation, recording ● analysis interpretation. Y our discharge and teacher will perform and the to assess: reporting following experiment. anode cathode Method 1 Set up an electrolytic electrodes 2 Place an and dilute inverted cell as shown sodium test tube in chloride lled with Figure 10.3.5, solution dilute as using the sodium inert graphite electrolyte. chloride solution over each electrode to collect the gas evolved at Figure 10.3.5 concentrated 3 T est the gas in 4 T est the gas in the tube the over tube the over anode the for cathode oxygen for Electrolysing each. using hydrogen a glowing using a splint. (brine) in the sodium chloride solution laboratory burning splint. 5 Repeat 6 T est the the experiment gas in the using tube over concentrated the anode for sodium chloride chlorine using a solution. piece of Did ? moist and blue then litmus paper. If the gas is chlorine the paper should turn Chlorine white. litmus 7 T est the gas in the tube over the cathode for hydrogen using a a form piece of red litmus paper into the electrolyte. it How were your observations in the two turns red moist and reacts then with hydrochloric chloric( ) acid Cl H (g) 2 9 know? acid the similar b different? Which the were in the dilute b in the concentrated each Which case, ions Explain were why electrolyte sodium explain experiments? 12 preferentially a In 11 ions the in chloride why and preferentially Give a reason litmus step discharged sodium (HClO): O(l) HCl(aq) 2 at the acids turn chloric( ) litmus acid red HClO(aq) and oxidises it to colourless. anode: solution chloride include solution? the discharged and paper to and experiments: The 10 white water (HCl) a blue burning splint. Dip gas paper because 8 you red a relevant at relevant changed the equation. cathode in both equation. colour when dipped into the 8 185 Electrolysis Electrochemistry 4 Electrolysis Ions of copper( II) sulfate solution using inert electrodes present: 2 From t he CuSO : Cu 2 (aq) and SO 4 (aq). 4 From t he H O: H (aq) and OH (aq). 2 At the anode: 2 The SO ions and t he OH ions move towards t he anode. The 4 ions OH are preferentially electrochemical 4OH series of (aq) discharged 2H O(l) O 2 Effer vescence At the occurs as are lower in t he (g) 4e gas is evolved at t he anode. cathode: Cu ions t hey 2 oxygen 2 The because anions: ions are and t he preferentially electrochemical H 2 ions move discharged series of towards because t he t hey cat hode. are lower The Cu in t he and t he cations: 2 Cu A pink (aq) 2e deposit of copper increases Changes in in Cu(s) builds up around t he cat hode because t he blue cat hode size. the electrolyte: 2 The electrolyte becomes paler blue Cu ions are 2 discharged from it. t also becomes acidic because Cu ions ions are discharged leaving an excess of H and OH 2 ions and SO ions, which 4 form 5 sulfuric Electrolysis acid. of copper( II) sulfate solution using active copper electrodes Ions present: 2 From t he CuSO : Cu 2 (aq) and SO 4 (aq). 4 From t he H O: H (aq) and OH (aq). 2 At the anode: 2 The SO ions and t he OH ions move towards t he anode. However, 4 t he anode, being made of copper, is active and t he copper atoms ionise, 2 forming Cu ions, t his requires less energy t han discharging t he OH ions. 2 Cu(s) Cu (aq) 2e 2 The ✔ Exam in size. At the you are ions go the The writing reactions t he electrolyte and t he ions towards anode gradually decreases cathode: Cu are ions and t he preferentially H 2 move discharged because t he t hey cat hode. are lower The Cu in t he and t he equations electrochemical for into 2 tip ions When Cu occurring at series of cations: the 2 anode always and cathode, include the remember correct Cu to (aq) 2e A pink deposit of symbols increases 186 Cu(s) state in size. copper builds up around t he cat hode cat hode Electrochemistry Changes in Electrolysis the electrolyte: The electrolyte remains unchanged. For ever y 2 mol of electrons transferred 2 from anode to cathode, 1 mol of Cu ions enter the electrolyte at the 2 anode and 1 mol of Cu T o investigate on the the ions is discharged at the cathode. effect electrolysis of of using copper( II) inert and sulfate active electrodes solution anode (T eacher Your teacher may use this activity ● observation, recording ● analysis interpretation. Y our () ( ) cathode demonstration) and teacher will perform and the to assess: reporting following experiment. oxygen pink gas builds is copper up evolved around at cathode the the Method anode 1 Set up an electrolytic cell as shown in Figure 10.3.6, using graphite graphite electrodes 2 Observe the electrode. blue and Repeat 4 Observe 5 Classify 6 How anode Also litmus 3 copper( II) the as and the cathode, taking the colour the into the experiment the solution observe paper the sulfate anode electrodes note of what electrolyte and occurs dip a at each piece of the as copper cathode inert or anode electrodes. and the colour of the your observations in () ( ) cathode electrolyte. active. the were electrodes electrolyte. electrolyte. using and of the the two anode experiments: pink becomes a b similar different? copper builds thinner up around 7 Why was the reaction experiments? 8 Why did 9 Why was the Include litmus there experiment a but occurring the paper change not in relevant change in the at the anode in the two of in the step copper 2? electrolyte in the rst Figure 10.3.6 sulfate solution Dene 2 Give the term 3 formula a molten b dilute Draw a 4 sodium labelled Describe solution using 5 the inert means the anode a of and By a and sulfuric electrolysis using of copper( II) graphite and electrodes state the in the electrolysis graphite graphite of sulfate differences an of chloride copper( II) when symbol acid diagram the of Exam tip electrolysis. It the Electrolysis questions ✔ 1 electrodes second? copper Summary the cathode equations. colour colour different of the ions present c copper( II) d potassium apparatus solution used using electrolysis of concentrated in each sulfate in of graphite dilute sodium is line important diagrams that to you show can draw electrolytic cells solution laboratory inert sodium following: solution bromide the the for the electrodes. chloride chloride solution electrodes. equation in copper( II) anode each sulfate case, show solution b a is the reaction electrolysed copper occurring at using: anode. 187 Quantitative electrolysis Electrochemistry A10.4 Objectives By the be able end of this topic you Quantitative electrolysis will The volumes of gases and masses of substances produced during electrolysis to: can be calculated using t he mole concept t hat you studied in Unit 7 . Michael ● dene ● calculate and the Faraday the masses produced constant volumes of of gases (1791–1867) quantity t he quantity symbol Q Each you of of and electrons Did t he rst person to propose t hat t he mass of a electricity passing t hrough t he electrolytic cell. electrolysis. The ? was substance produced at an electrode during electrolysis is directly propor tional to substances during Faraday ow electron electricity, is measured from t he owing or in quantity units anode t hrough of called to t he t hese electrical coulombs, cat hode wires has an charge, C. is During given t he electrolysis, t hrough electrical electrical charge wires. which is know? extremely small. n fact, t he electrical charge on one electron is so small t hat 18 when The electrical charge on 1 C of electrical charge ows t hrough a circuit, 6.25 electrons 10 one have owed. 19 electron means is 1.6 that 1 C 10 of C. This electrical charge The quantity of electricity or electrical charge owing t hrough an electrolytic 1 ___________ is equivalent cell to during electrolysis depends on two factors. 19 1.6 10 electrons. ● The the rate of ow symbol I of and the is electrical measured charge, in units i.e. the called current, amperes which (also is given known as 18 amps), A. owing ● The A for quantity t he following of 1 amp is equivalent to 1 C, or 6.25 10 electrons, 1 s. lengt h The current of of time, t, t hat electricity t he or current electrical ows for, measured charge can t hen be in seconds, calculated s using formula: quantity of electrical charge (C) current Q I i.e. (A) time (s) t Example Calculate t he ows circuit Time seconds in can for of electrical charge t hat ows when a current of relate electrons 20 60 electrical t his has. to The Faraday of the of electrons, constant electrical charge is on the size one mole if we 10 charge moles You will if owing we consider recall t hat 2 t he 1 mol 1200 C electrical of 2400 C charge electrons is which 1 mol equivalent to 19 electrons. have 96 500 C. 2.0 A 1200 s 23 6.0 of 20 min. 2.0 A quantity We ! quantity of fact a Current ∴ Key in 1 mol This of The charge electrons, value is known on one t hese as t he electron electrons Farad ay is 1.6 would 10 have a C, total t herefore, charge of constant 1 i.e. 96 500 C mol . Dur ing electrolysis, discharged at t he a cation cat hode wit h a according to single t he positive following charge, i.e. M , is equation: M e M This and shows form t hat 1 mol 1 mol of M of or, electrons applying is required t he Faraday to discharge constant, 1 mol 96 500 C of is M ions required to discharge discharging 96 500 C 188 is 1 mol 1 mole of of required. M ions anions and wit h form a 1 mol single of M. negative This also charge at applies t he when anode, i.e. Electrochemistry The to following calculate and examples t he electrolysis. of will volumes You volumes Quantitative will of recall show gases t he how and we can masses following of use t he Faraday substances quantities t hat constant formed relate electrolysis moles during to mass gases. Molar mass, M mass Molar volume, V of 1 mol volume of of a substance. 1 mol of a gas. m 3 At stp, V 22.4 dm 3 , at r tp, V m 24.0 dm m Examples 1 Calculate of 5 5.0 A t he ows mass of lead t hrough produced molten at lead(II) t he cat hode bromide for when 16 a current minutes and seconds. Determine t he quantity Current Time seconds ∴ in t he electricity t hat ows: 5.0 A quantity Write of of (16 60) electricity equation for t he 5 965 s (5.0 965) C reaction at t he 4825 C cat hode: 2 Pb From (l) t he 2 mol of 2e Pb(l) equation: electrons ∴ 2 96 500 C i.e. 193 000 C ∴ 1 C are required form form 1 mol 1 mol to form 1 mol Pb. Pb Pb 1 ________ forms mol Pb 193 000 1 ________ ∴ 4825 C forms 4825 mol Pb 193 000 0.025 mol Pb 1 M(Pb) 2 207 g mol i.e. mass of 1 mol ∴ mass of 0.025 mol f an 2 hours electric 34 produced current minutes at Determine t he t he Time seconds ∴ for 4OH 207 g Pb of 0.025 2.5 A and anode 24 at is 207 g passed seconds, 5.175 g t hrough calculate dilute t he sulfuric volume of acid for oxygen r tp. of electricity t hat ows: 2.5 A quantity Equation quantity Current in Pb of (2 60 electricity t he (aq) reaction 60) (34 (2.5 9264) C at t he 2H 60) 24 9264 s 23 160 C anode: O(aq) 2 O (g) 4e 2 189 Quantitative electrolysis Electrochemistry From t he 4 mol equation: electrons are lost in forming 1 mol O 2 ∴ 4 96 500 C form 1 mol O 2 i.e. 386 000 C form 1 mol O 2 1 ________ ∴ 1 C forms mol O 2 386 000 1 ________ ∴ 23 160 C forms 23 160 mol O 2 386 000 0.06 mol O 2 3 Volume of 1 mol O at r tp 24.0 dm 2 3 ∴ volume of 0.06 mol O 0.06 24.0 dm 3 1.44 dm 2 3 A solution of Determine t hrough copper(II) t he t he Determine solution t he Time seconds ∴ for is mass 32 of electrolysed of t he minutes anode and electricity 10 t hat using if a copper current of electrodes. 4.0 A passes seconds. ows: 4.0 A quantity Equation in quantity Current in sulfate decrease for of (32 60) electricity t he reaction 10 1930 s 4.0 1930 C at t he anode: 7720 C 2 Cu(s) From t he Cu (aq) 2e equation: 2 2 mol electrons are lost in forming 1 mol Cu ions. 2 ∴ 2 96 500 C i.e. 193 000 C ∴ 1 C form 1 mol Cu ions 2 form 1 mol Cu ions 1 ________ forms 2 mol Cu ions 193 000 1 ________ ∴ 7720 C forms 2 7720 mol Cu 0.04 mol ions 193 000 21 2 M(Cu Cu ions 1 ) 64 g mol i.e. mass of 1 mol ∴ mass of 0.04 mol 2 Cu ions 64 g 2 Therefore, 4 A steel decrease spoon Calculate the electroplate Calculate needs ions in mass to be length the t he Cu of spoon number of 0.04 t he anode electroplated time that when of a of as the 2.56 g 2.56 g wit h current placed moles 64 g 13 g of of 15 A cathode chromium of which produced: 1 M(Cr) 52 g mol i.e. mass of 1 mol ∴ number Cr 52 g 13 ___ of moles in 13.0 g mol 52 190 chromium. would 0.25 mol have the to ow electrolytic need to be to cell. Electrochemistry Equation for Industrial t he reaction at t he applications of electrolysis cat hode: 3 Cr From (aq) t he 3 mol ∴ 3 i.e. 289 500 C ∴ 0.25 form 96 500 C Therefore, Calculate quantity Cr(s) equation: electrons 3e 1 mol form form t he t he of 1 mol 1 mol 289 500 C electricity 72 375 C ∴ of taken 15 A 0.25 mol Cr electricity for (C) Cr Cr. form quantity time Cr. time 72 375 C required 72 375 C current to (A) ow 72 375 C using time a current of 15 A: (s) (s) 72 375 ______ time s 15 t would take Dene 2 Calculate 3 the 1 hour Faraday when chloride for rtp How to 20 a a of magnesium 40 volume current must for a of Electrolysis is extracting ● purifying metals 25 25 seconds seconds that ows and chlorine 2.5 A to ows electroplate the spoon. of 10.0 A of copper would 28 ow at ways t heir in deposited molten on the magnesium seconds. through and be through 50 that would be produced concentrated at the anode sodium seconds. through the a solution of copper( II) cathode? applications many from 5.0 A minutes 25.6 g Industrial in of current produce used of minutes 51 A10.5 ● minutes minutes current hours solution long sulfate 2 the when chloride 20 constant. mass cathode at hour questions the Determine 4 4825 s 1 Summary 1 industr y of electrolysis Objectives By the be able i.e. plating one metal describe wit h anot her, i.e. used coating a metal wit h its oxide, i.e. now look at will how each of t hese in to electrolysis can extract metals from ores describe be will you anodising. ● We topic electroplating their ● this electrorening be ● of to: ores ● metals, end including: more used how to electrolysis purify can metals detail. ● describe the process of electroplating Extraction of metals ● Ver y few metals are found in t heir free state in t he Ear t h’s cr ust. Most describe the process of are anodising. found bonded Minerals from to ot her which elements metals can in be ionic compounds extracted are known known as as ores. minerals. The process 191 Industrial applications of electrolysis Electrochemistry of extracting atoms, i.e. it metals is a from t heir reduction ores involves conver ting t he metal ions to process: n M Metals ions. high This reason from in t hese t heir t he electrochemical t hat metals ores. and is where example oxide (Al O 2 need ions a to of is t he ), using series ver y the ionise t heir molten easily difcult to met hod of molten ore aluminium from t he are of extract series t hey are powerful Electrolysis electrolysis cat hode t heir used electrochemical During An M means reduction t he ne and and reduce form to reduction is a ver y atoms. to extract powerful metals above stable For t his t hem met hod of aluminium in ores. ore, t he metal ions move towards t he discharged. extraction iner t of aluminium graphite from its molten ore, aluminium electrodes. 3 The aluminium ions move towards t he cat hode where t hey are discharged to form molten aluminium: 3 Al (l) The molten and it be sinks 3e aluminium to discussed t he in is which bottom more Purification Electrolysis Al(l) of of detail forms t he in is denser electrolytic Unit t han cell and t he is molten tapped electrolyte off. This will 18.2. metals ver y useful in t he production of pure metals from impure samples of t he metal. This process is known as electrorening. The principles of ● electrorening The impure terminal of The cat hode ● The electrolyte ● The ● anode, The metal metal ● The t he negative is as is follows. made t he anode, i.e. it is connected to t he positive batter y. a ver y is an t hin sample aqueous of t he solution pure which metal. contains ions of t he metal puried. electrolyte electrode, metal t he ● being positive are being where ions which are are ionises, join t he discharged builds electrolyte anode active, t hey up at around remains removed and ot her t he t he t hey are of t he metal enter t he ions. cat hode where t hey metal ions form t he pure cat hode. unchanged as ions metal since t he discharged at t he entering it at cat hode. power electrode, the anode, a bar supply ● the of impure Any insoluble impurities present in t he anode fall to t he bottom of t he cathode, copper a (1) thin sheet (2) of cell forming a sludge which can be removed. pure copper An example of electrorening is t he purication of copper . This is illustrated in Figure 10.5.1. The impure copper is t he anode (1) and t he cat hode is a t hin 2 sheet of sulfate sludge copper(II) containing The pure copper (2). The electrolyte copper anode of copper Cu(s) Cu (aq) copper(II) 2e 2 ions, The Cu ions enter t he electrolyte (aq) forming 10.5.1 The electrorening pure copper: of 2 192 i.e. ionises: 2+ Cu copper ions, solution. 2 solution flow Figure Cu sulfate impurities contains Cu (aq) 2e Cu(s) and are discharged at t he cat hode, Electrochemistry Electrore ning hydrogen in t he ions, in being is t he ser ies hydrogen Industrial only suitable for electroc hemical would lower in not t he be pur ifying ser ies. disc harged ser ies, would Any at be t he metals metal whose ions cat hode preferentially ions are above since applications of electrolysis below hydrogen t he hydrogen disc harged, for ming gas. Electroplating Electroplating involves anot her Electroplating metal from object be metal. made of principles The ● corrosion, appear t he more any of metal, to negative be The anode ● The electrolyte The is used The metal metal The ● t he As a for anode, electrolyte ● pure is ions t he sample an to t hat made similar made to t he of one eit her appearance usually is layer out object ver y or is of to t hose of cat hode, on top t he make cheap being brass, metal protect a metal electroplated copper or of original steel. can The electrorening. i.e. it is connected to batter y. of aqueous active, t hey are t he metal solution electrolyte ionises, join t he discharged builds up as remains removed electrorening, electrochemical of t hin which which is being contains used ions for of plating. t he metal plating. being are is are its The electroplated where which anode wit h it a carried improve but terminal ● ● to is valuable. electroplating object being depositing series a at t he coating t hey only be are of t he cat hode since where t he t he whose for metal enter t he ions. at ions t hey form t he pure object. metal discharged metals used ions metal around unchanged as can and ot her ions t he are entering it at cat hode. below hydrogen in t he plating. Examples of electroplating are chromium plating, silver plating, gold plating and nickel plating. Chromium plating , look as as as t he well cat hode, solution of or chrome protecting t he t hem anode is chromium(III) plating, from pure sulfate chromium [Cr (SO 2 The chromium anode gives steel corrosion. ) 4 and objects The t he steel a shiny, object electrolyte is is silver placed usually a ]. 3 ionises: 3 Cr(s) Cr (aq) 3e 3 The Cr ions enter t he electrolyte and are discharged at t he cat hode forming a layer of chromium on t he Figure 10.5.2 Chrome plated taps object: 3 Cr The (aq) 3e electrolytes solutions of Cr(s) used nickel(II) in nickel sulfate plating (NiSO ) and and silver silver nitrate plating (AgNO 4 ). are usually During t he 3 + silver process of silver plating illustrated in Figure 10.5.3, t he silver anode ionises: nitrate the object electrolyte Ag(s) Ag (aq) e being plated The Ag a layer (cathode) ions enter t he electrolyte and are discharged at t he cat hode forming of silver on t he silver object: anode Ag (aq) e Ag(s) Figure 10.5.3 Electroplating with silver 193 Industrial applications of electrolysis Electrochemistry Anodising On a exposure layer of to air, aluminium aluminium oxide immediately (Al O 2 unreactive a result The it and adheres protects t hickness objects it can of be t he t he rmly metal ) on wit h surface. t he This oxygen layer is to form relatively 3 to t he metal from attack aluminium oxide ar ticially its reacts increased by by below and does oxygen and moisture layer a on process t he not surface known as ake of in off. t he As air. aluminium anod ising. This makes t he objects, such as window frames and saucepans, even more resistant to ● corrosion. The The aluminium hydroxide ● The t he ● The ● As anodising solution cleaned terminal electrolyte as to to t he is be clean aluminium positive soon ar ticle process of anodised and ar ticle t he usually a electrolytic involves etch is is following pre-treated t he made t he steps. using sodium surface. t he anode, i.e. it is connected dilute cell is solution of connected sulfuric up, t he acid. aluminium anode 3 begins to ionise, forming to batter y. Al 2 ions, and at t he same time t he SO ions 4 and t he OH ions in t he electrolyte move towards t he anode. The OH 3 ions react surface of wit h t he t he Al ions forming a layer of aluminium oxide on t he aluminium: 3 Al(s) Al (aq) 3e 3 2Al (aq) 3OH (aq) Al O 2 The silver-grey attractively aluminium oxide (s) 3H (aq) 3 coating readily absorbs dyes cathode anode () article to e.g. a – be Figure Summary Explain why Describe 3 the Give ( 4 electrolysis how series you anodising is would for used from the to their purify occurring equations 194 chromium What is ) of – dilute acid aluminium questions reactions the The at a the extract metals high plating anodising? in the ores. sample anode reactions that of silver. and the occur Include b nickel the equations cathode. at the during: a be frame 10.5.4 electrochemical for can coated, window sulfuric 2 it aluminium electrolyte 1 so coloured. plating. anode and cathode Electrochemistry Key ● The electrochemical The t heir A atoms higher ionises ● metal ● Metals can The A a above of how higher it from not t he from can a t he an in t he electrolysis Electrolytes are to a list of metals in order of how is t he ions non-metals in gain t he stronger series is gas; from more easily series a list displace metals an it from a of t he below acid. non-metals in electrons. electrochemical are its non-metal containing to t he electrochemical hydrogen hydrogen of electricity pass in electrochemical t he a it series, powers. metal. forming atoms displace allow electricity below t he series compound Conductors is reducing lower acid, t heir and metals electrochemical its metal non-metal ionises of t he are displace easily non-metal in hydrogen electrochemical allow ● displace is containing will series ● stronger hydrogen easily ● metal ions order ● of electrons. t he hydrogen The series lose t he and compound ● applications concepts easily ● Industrial oxidising below t he pass it lower t hrough. series, t he more powers. in t he electrochemical non-metal. Non-conductors do not t hrough. compounds t hat form ions when molten or in aqueous solution. ● Electrolytes ● When conduct electricity electricity passes because t hrough an t hey contain electrolyte, t he mobile ions electrolyte decomposes. ● Metals ● When ● Strong of ● conduct electricity electricity ions. passes electrolytes Weak of Pure ver y is t hrough fully electrolytes concentration water are because a a t hey metal, ionised; are contain t he t hey par tially mobile metal contain ionised; electrons remains a high t hey unchanged. concentration contain a low ions. weak electrolyte due to t he ver y low concentration of H ● and ● is of t he are anode lose electrons. The cathode Molten Bot h t he chemical t hrough used is and t he during positive Oxidation is t he gain which occurs when an electric electrolyte. electrolysis to conduct electrode. occurs at Anions t he electricity in to and move negative electrode. Cations Reduction occurs contain discharged during one type towards t he anode and anode. electrons. electrolytes are change an electrolyte. The cat hode ● is passed Electrodes out ● ions. Electrolysis current ● OH of move at cation t he and towards t he cat hode. one type of anion. electrolysis. ● Aqueous ions electrolytes from t he preference ● Factors ● The t he which position t he to of water. of solute type of ions ion of as well each as H charge ions will be and OH discharged in ot her. anion solution position preferential One inuence t he aqueous contain t he in t he preferenti al t he electrochemical and whet her cation discharge of in t he t he d ischarge series, anode is of active electrochemical anions t he or series are t he concentration of iner t. determines t he cations. 195 Industrial applications of electrolysis Electrochemistry ● When dilute produced ● When if t he at sulfuric t he sodium solution concentrated, at ● ● t he solution oxygen dilute, chlorine in copper (II) bot h is sulfate solution at it, Copper is produced at t he of passing t hrough ● The quantity ● The quantity charge, i.e. Q t The I gas electrolysis of of t he Farad ay or is t he using t he iner t at t he electrodes, oxygen is cat hode. electrolysed produced produced produced volume is is at at using t he anode. iner t anode, electrodes, if it Hydrogen is is produced cases. is The electrolysed hydrogen chloride oxygen during ● is and is cat hode When acid anode if mass t he cat hode of a directly electricity , electricity constant I, is is electrolysed, in is made bot h substance Q, t he if t he anode copper, it is iner t, ionises. cases. to t he at an electrode quantity of electricity cell. is measured dependent and of produced propor tional electrolytic current, is anode t he size time of on t he t he in coulombs, t he rate current electrical of C. ow ows charge of for, on electrical t, i.e. one mole of 1 ● electrons, i.e. ndustrial uses ores, 196 t he 96 500 C mol of electrolysis purication of . include metals, t he extraction electroplating and of metals anodising. from t heir Electrochemistry Practice Practice exam-style Multiple-choice 1 Metal X was containing questions to displace sulfate of Y. metal Y However, from X did a solution not displace anode metal t he Z from a following A X B Z is solution is higher containing Z sulfate. Which cathode of correct? in t he electrochemical series t han Z. copper(II) is a stronger C Y is higher D Y is a in reducing t he stronger agent t han electrochemical reducing agent series t han Which of t he following lists consists t han X. Z. of Electrolytic State, sodium B hydrochloric chloride, magnesium, C aqueous sodium D kerosene, et hanol, copper, et hanoic State, electrolysis, potassium t he giving a a what you relevant reason, chloride, tap t he electrolyte. would obser ve equation. (3 what you would obser ve f current reaction which takes (2 a place at 40 of 5.0 A seconds ows t hrough for determine t he increase Give differences t he 2 hours 8 minutes in electrolytic mass of t he cell, cat hode. t he B reduction C oxidation D a current t hrough would electrolytic cell made t he anode made t he cat hode. a be A 2.7 g B 5.4 g of 5.0 A silver ows nitrate deposited at for 16 minutes solution, t he what and mass 5 i) seconds of Give and ii) silver you would obser ve if and t he t he copper electrode graphite C 10.8 g D 27 .0 g T WO ONE (2 a 0.75 mol sodium of electricity chlorine use response Electrolysis of of between (2 of anodising. molten is during is needed t he to produce electrolysis of answer molten b chloride? Using t he is a 72 375 C discuss chemical B 96 500 C products C 144 750 C The of EACH Use t he show Which of t he can following A ron B Anodising be puried is used statements by to is incorrect? c marks electrolysis Suppor t your and wit h of iner t t he (4 marks) concentrated electrodes, following on t he electrolysis. position of ions aluminium items from layer concentration process t hem items more appearance Electroplating t hin The The metal electrolysis. protect corrosion. of can be used to coat steel items wit h in t he electrochemical Magnesium of of t he electroplating wit h a layer resistant and to make steel of made of layer nickel followed can be anot her corrosion, t hem Cutler y electrolyte. (2 marks) (2 marks) is to coat metal to make improve appear of ten used more t heir valuable. electroplated wit h a a of by a layer of silver. silver. i) D 15 193 000 C ii) C mark) how equations. dilute solutions effect of of to process. ionic electrolysis t he process. bromide relevant chloride A i) chemical potassium wit h sodium a marks) (1 question series. 6 was marks) electroplating Total 8 quantity differences anode? electrolysis What D in was electrode anodising. Give Extended 5 t hat decomposition c f T WO displacement t he 4 marks) is: iv) A in marks) (4 anode at marks) water and During reason, acid iii) 3 a nclude aluminium hydroxide, molten anode. graphite ii) acid, giving cell conductors? t he A sulfate solution X. i) 2 questions questions found t he exam-style can be extracted from its ore Draw a labelled diagram to show t he apparatus by you could use to electroplate a steel spoon wit h electrolysis. nickel using nickel sulfate solution (NiSO (aq)) as 4 Structured 7 a b Dene An electrolyte. use as Clearly indicate what you would question t he term electrolytic wit h t he cell copper(II) graphite ‘electrolysis’. (1 anode was sulfate and a set up, as solution copper ii) mark) shown as t he cat hode. in t he gure, electrolyte, a How t he long anode must t hrough t he 9.44 g nickel? of and a t he steady electrolyte cat hode. current to coat (3 of 4.0 A t he spoon (4 Total marks) ow wit h marks) 15 marks 197 A11 Rates of reaction Chemical reactions reactions can proceed at different speeds. Some Objectives By the be able end of this topic you will while ● take years, such as the rusting of cars, to: dene what is meant by rate of others explosion. happen Other in less reactions than take a second, place at such varying as an speeds reaction between ● explain how reaction ● explain the can the be rate of which measured collision these two extremes. Knowing the speed at a theory reactions occur is extremely important in industry for to maximise productivity while minimising costs and the reactions ● interpret rate curves risk for of accidents. reactions. A11.1 The t he Measuring study rate of of t he concentration increases. speed reaction , f of we t he can is rates at which called increase in concentration t he decrease or increase The rate of a reaction to can, chemical of occur, we in can be t he in product, t herefore, decrease as decrease a reaction kinetics. decreases t he t he reaction chemical reactants measure a of occurs, During a concentration concentration and know determine t he determined by: concentration of a of how rate known reaction, of a a products reactant long of as t he it took or for reaction. reactant ____________________________________ rate of reaction time increase taken in for t he decrease concentration of a product ____________________________________ or rate of reaction . time ! The Key rate change fact of in reaction the is a measured concentration of Changes in are property products, or product with time at t hat changes can be are not which measured always depend to increase easy on to t he determine measure. nature t he rate of of a However, t he t here reactants reaction. and Some of t hat can be measured are: if one of t he products is a gas, t he volume of gas produced over time temperature. can ● ● be measured metal and if of one an t he products reaction between if a if mass precipitate t here is reaction e.g. ● if t here of a a is t he gas syr inge, a gas, if t he reaction carbonate for ms, t he e.g. a reaction between a reactive t he gas can and be an appearance reaction between is allowed measured to escape, over t he time, e.g. a acid of t he sodium precipit ate t hiosulfate can be and acid c hange between is reaction a a acid in hydroc hlor ic ● using decrease measured, 198 changes, t he a ● stated concentration for a t he reactant ot her taken in colour pot assium distinct proceeds, c hange any of intensity, iodide in t his and pressure, t hese can be can be acidi ed measured, hydrogen temperature measured or over pH as time. e.g. t he peroxide t he Rates of reaction Collision Chemical Measuring theory reactions and t he formation take place, all of for t he new t he breaking bonds following the reactant particles must ● of reaction reactions involve of rates in must t he of original products. bonds in order for n t he a reactants reaction to occur: collide with each other in order to break the original bonds in the reactants so that new bonds can form in the products the ● reactant activation reactants and products (see t he ● par ticles energ y reactant energy in enable Unit to break collide Unit the with 12.1), par ticles to to enough break have energy, the known original enough as bonds energy to in the form 12.1) par ticles produced order must (see by must t he collide collision wit h can t he be correct passed on or ientation to t he so t hat original t he bonds t hem. Not all collisions occur wit h t he required activation energy or wit h t he correct orientation of par ticles. Therefore, not all collisions result in a reaction occurring. Collisions which result in a reaction are called effective collisions . The For rate of a reaction example, 2H (g) in O 2 The t he depends reaction (g) on 2H break will t he t hen (H ) and oxygen atoms, collisions. and oxygen must collide to form (O ) molecules new between covalent forming water bonds to atoms form wit hin wit h t he between covalent new must break H H O O H t he must O O 2 Figure 11.1.1 To be effective an to molecules Rate f a The and reaction t he t he between each covalent molecules This hydrogen and form H O H 2H 2 collision, break ot her covalent bonds 2H each molecules. molecules. bonds H t he H energy water: O(g) oxygen bonds original H hydrogen effective 2 covalent allow of 2 2 to number between 2 hydrogen t he hydrogen and collision bonds must be O 2 oxygen must wit hin correctly generate t he enough hydrogen orientated to activation and each oxygen ot her. curves measured proceeds and proper ty t he is plotted proper ty on changes, a a graph rate against curve is time as t he reaction obtained. gas syringe volume measures of the hydrogen Examples 1 The reaction between magnesium and hydrochloric acid: dilute Mg(s) 2HCl(aq) MgCl (aq) H 2 (g) 2 hydrochloric f magnesium ribbon is added to hydrochloric acid, t he volume acid of magnesium hydrogen gas given off can be measured in a gas syringe at regular inter vals using t he apparatus shown in Figure 1 1.1.2. f t he volume of Figure of is t hen plotted against time, t he cur ve in Figure 1 1.1.3 may be 11.1.2 Investigating the rate gas reaction between magnesium and obtained. hydrochloric acid. 199 Measuring Figure rates 11.1.3 gas reaction Graph Rates of volume of released against time of reaction 50 45 mc( 3 ) hydrogen of 40 sag 35 negordyh 30 25 fo 20 emuloV 15 10 5 0 0 60 120 180 240 300 Time We can use reaction at t he values different on t he stages graph in t he increase to determine reaction in 360 420 480 (s) by volume of t he using average t he rate general of formula: hydrogen ______________________________ rate of reaction time To ● determine t he average taken rate of for t he t he increase reaction in t he rst minute (60 s): 3 volume of gas produced in t he rst minute 28 cm 3 28 cm _______ ∴ average rate of reaction in t he rst minute 3 0.47 cm 1 s 60 s To ● determine t he average rate of t he reaction in t he second minute: 3 olume of gas produced in the second minute 3 (38 28) cm 10 cm 3 10 cm _______ ∴ average rate of reaction in t he second minute 60 s 3 This clearly decreases. graph. t he The discuss 2 wool to The can t hat as t he also be seen gradient reaction becomes cotton shows This is shallower t his in reaction is rapid. steep reaction at more detail between in as calcium at t he beginning t he t he t he proceeds, looking t he However, indicating by of reaction reaction next is t he 0.17 cm rate of gradient t he graph progresses, slowing t he or 1 s reaction slope of t he indicating t he down. gradient We will section. carbonate and hydrochloric (aq) acid: stop CaCO (s) 2HCl(aq) CaCl 3 f some hydrochloric balance, be cur ve in calcium at acid regular Figure is poured carbonate is inter vals. 1 1.1.5 may be into a added, f t he (g) H 2 conical t he mass ask, mass is of t hen O(l) 2 which t he is on reaction plotted a can against time, obtained. )g( calcium acid carbonate noitcaer hydrochloric (marble and measured t he CO 2 chips) fo ssaM direct-reading balance Time on Figure 11.1.4 reaction and 200 Investigating between hydrochloric calcium the rate Figure 11.1.5 Graph of (s) mass of reaction against time of carbonate Looking at reaction proceeds, t he gradient of t he graph we can also clearly acid t he rate of t he reaction decreases. see t hat as t he Rates of reaction Measuring Explanation We can steep at of the see that both the beginning shape rate of cur ves the of rate have reaction a of reaction curves ver y and rates similar gradually shape. The becomes gradient shallower is until the cur ve eventually becomes horizontal. This shows that the rate of a reaction changes as the reaction proceeds. We will now look at the reasons for this. ● The gradient is steepest at the beginning of the reaction indicating that the rate of the reaction is at its highest. This is because the concentration of the reactant particles is at its highest at the beginning of the reaction. The frequency of collision between the particles is at its highest at the beginning. ● As the reaction proceeds, the gradient becomes shallower indicating that the rate of the reaction is decreasing. This is because the concentration of the reactant particles is decreasing as the reaction proceeds. The frequency of collision between the particles is decreasing as the reaction proceeds. ● After a period of time the cur ve becomes horizontal, i.e. the gradient becomes zero, indicating that the reaction has reached completion and has stopped. One of the reactants has been used up and there are no more of its particles left to collide. The reactant which is used up in a reaction is known as the limiting reactant. The quantity of the limiting reactant determines the quantity of the products produced. T o investigate reaction Your the change in rate of a reaction as the proceeds teacher may ● observation, ● manipulation ● analysis and use this recording and activity and to assess: reporting measurement interpretation. 3 Y ou will be supplied hydrochloric acid, through a it to a gas with 4.0 g conical syringe, of calcium ask, a a cork measuring carbonate with a crystals, delivery cylinder and a tube 0.3 mol dm running stopwatch. Method 1 Place the calcium carbonate crystals in the conical ask. in the measuring 3 2 Measure 3 As quickly conical 4 30 cm as ask of possible with in hydrochloric syringe, as Record the volume remains Record your the Figure volume pour cork the gas acid which 11.1.2. of acid At in has the the into a conical delivery same gas the time, syringe tube start every cylinder. ask and running the 15 cork to the the gas stopwatch. seconds until the ✔ 5 constant results in a for three table and consecutive use them to Exam plot a graph of volume of When drawing obtained gas against time. Draw a curve of best t between the from Using your graph, rst minute calculate the average rate of the reaction the b the second minute. Explain than in why the the average second rate of the reaction is higher in the Explain why the you rst line of necessarily data it draw a is curve best join curve or line smooth or straight of all fit. You the best fit do points. must be minute and must pass minute. between 8 that straight not A 7 using for: or a graphs experiments, points. important 6 tip readings. curve of your graph eventually becomes horizontal. close as the points possible to so all that the it is as points. 201 Factors affecting rates of reaction Rates Summary Dene 2 Give two ways 3 Give two methods of reaction changes Objectives By the be able end of this topic you 4 What 5 Explain the rates explain affect ● that between a of reaction. the rate student magnesium of a reaction. could use ribbon and to determine dilute how the hydrochloric rate acid time. the how rate calculating collision the rate Factors The a theory of a for a reaction reaction changes affecting state? as rates the of reaction proceeds. reaction will rate factors which of of reaction describe different rates changing the a will is dependent be st udyin g on several whi c h can factor s. a f fec t There t he r ate are of four a main r eacti on . are: of ● concentration ● temperature ● sur face ● presence factors reaction experiments determine we reaction how the t hat affect These ● of by to: identify the meant A11.2 facto r s ● is with does reaction questions 1 what of effect factor to area (par tic le size) of on the rate or absen c e of a ca t aly st . of Light and pressure also affect t he rate o f c e r t ain re act ion s. For e xa mple , t h e a reaction reaction between met h a n e a n d c h lor ine (se e Unit 14.1) a n d p h otosynt h esis ● interpret graphical are representations of bot h t he obtained in initiated by ligh t , an d as t he lig h t in ten sity in c rease s, t he r ate of data studying rates reaction incre a s e s. Ch emic al re ac tio n s wh ic h are in it ia ted or sp eed ed of up by light are kn own as photochemic al re actions . reaction. Pressure affects pressure on meaning Did ? you know? is possibly the most in the world. which important green It is the plants effective carbon water. plants make by food dioxide use sunlight reaction. animals and to would both bring W ithout no oxygen rea c t a n t gase ou s t h eir p ar ticle s p er st ate. volume un it f t he dec reas es , vo lume. As a t he collis io n s , N (g) reactio n t h ereby b etwee n increasing n itrog en t he and rate of t he hyd rogen to re a c t io n . for m This is a mmon i a: the 3H (g) 2NH 2 (g) 3 will now look in det ail at h ow eac h of t he ot h er four factor s affects t he and of a reaction. When co nsider ing a p ar ticu la r f ac tor, it is of a assu med t h at energy about ot her factor s a re ke pt co nst a nt . the no and food animals to eat Concentration would The have t he photosynthesis, have plants in 2 all from mo re in in c rease d , by rate The are r eac t an ts is reactions process We combining t h e re bet we en react ants one seen of t hat gaseous result, t h e par ticl e s c o llide mo re fre quen tly an d t h is inc rease s t h e c h an c es of Photosynthesis re a c t io n s t he for gene ral r ule is t h at t he higher t he concentration rea ct a nt , t he respiration. higher This is t he rate applies in creased, volume. t he As a c hances of t he reaction. par t ic ula rly t his me an s result , of t he to so lution s. t ha t t h ere pa r t icles e ffe c t i ve f a re c o llide co llisio n s, t he con c en tratio n mo re r eac t an t mo re frequen tly t h erefore, t he of a par ticle s r ate w h ic h of t he r eac t an t per unit inc r eas es r eac tion increases. f we measure t he rate of a rea ctio n a t differen t con c en tratio n s o f on e o f t h e react ants, and plot t h e rat e a gain st c on c en tratio n , we g et a g raph similar to t he one in Figure 1 1. 2.1. The g raph 202 cle arly sh ows t h at a s t h e con c en trati on Rates of reaction t he rate increases. t also shows t h at, for t h is reac tio n , t he r ate of 1 reaction is directly propor tional to t he rates of reaction s( t he affecting ) increases Factors concentrat io n . noitcaer fo etaR 3 T o investigate Your teacher the may ● observation, ● manipulation ● analysis effect use this recording and and Figure of Rate of reaction concentration activity and 11.2.1 to on against the Concentration concentration rate of a will ) reaction assess: reporting measurement interpretation. 3 Y ou (mol dm be supplied of acidied with 0.005 mol dm 3 potassium iodide solution, 0.01 mol dm sodium thiosulfate solution, a 3 solution hydrogen peroxide 3 25 cm and starch with a hydrogen peroxide concentration of 0.085 mol dm , two 3 measuring cylinders, one 10 cm measuring cylinder, a burette, a small beaker and a stopwatch. Method 1 Place the sodium thiosulfate solution into the burette. 3 2 Measure sodium 25 cm 3 of thiosulfate potassium solution iodide from the solution burette in a and measuring swirl to cylinder mix the and pour it into the beaker. Add 1 cm of solutions. 3 3 Measure 4 Add the piece 5 of 25 cm of acidied mixture to the white Observe the hydrogen beaker and at peroxide the same and time starch start mixture the in another stopwatch. measuring Swirl the cylinder. beaker and place it on a paper. solution in the beaker from above and as soon as a blue-black colour begins to appear stop the stopwatch. 6 Record the time 7 Repeat the experiment table 8 taken for the four blue-black more times colour using to the start to volumes appear. of potassium iodide solution and water given in the below. Calculate the concentration of potassium volume of iodide solution for each of KI(aq) using the following formula: Kl(aq) _______________ concentration experiment 3 0.005 mol dm 25 9 Calculate the rate of reaction for each experiment using the following 1 ______________________________________ rate of reaction Record your against the Volume results a Volume iodide of of distilled 3 solution/cm taken table concentration of potassium in 1 s time 10 formula: for similar the blue-black to the potassium Concentration potassium of dm appear below solution. Volume of and Draw sodium thiosulfate 3 solution/mol to outlined iodide iodide 3 water/cm one colour a plot a graph straight Volume of hydrogen to of show best acidified peroxide 3 solution/cm line Time and the t rate of between taken blue/black the the for colour Rate mixture/cm 25 0 1 25 20 5 1 25 15 10 1 25 10 15 1 25 5 20 1 25 of reaction/ 3 starch reaction points. 1 to appear/s s 203 Factors affecting rates of reaction 11 What 12 Explain 13 Use your and 0.0044 mol dm can you the deduce effect Rates about that the effect increasing the of concentration concentration has on the rate of the reaction? on the rate of the reaction. of reaction 3 graph to determine the rate of the reaction at potassium iodide concentrations of 0.0022 mol dm 3 double. Did information the rate given . In of theory, your below to if the reaction help concentration double? If it of a didn’t reactant double, doubles, can you the rate suggest of a reaction reasons why? should Use also the you. During t he potassium experiment, iodide to t he iodine hydrogen molecules peroxide ( oxidises t he ions in t he ): 2 2 (aq) (aq) 2e 2 As soon back to as an iodine molecule is formed t he sodium t hiosulfate reduces it ions: (aq) 2e 2 (aq) 2 When all t he sodium t hiosulfate has reacted, iodine molecules remain in t he solution and react concentration t he same, iodine time t he has t he volume blue-black been taken wit h and for concentrations made t he of starch of colour each same produce time. n of iodide a blue-black t hiosulfate star ts quantity potassium to sodium to appear your solution when t he experiment iodine to be colour. used same you Since each quantity determined produced t he time using is of t he different solution. T emperature The general r ule is t hat t he t he f higher t he t he rate of temperature par ticles gain t he at kinetic t he par ticles move ● t he par ticles collide sufcient Combining effective which energ y ● wit h higher t he temperature at which a reaction occurs, reaction. faster, wit h activation t hese two collisions a has t herefore more as occurs t he t hey energy, energy effects, increase, reaction which for t he is collide temperature t herefore the rate of to collisions occur react. increases, t he reactant frequently more par ticles t he effects: more t herefore t he increased, following t he reaction chances increases. of For some chemical reactions which occur at room temperature, if t he temperature increases f we 10 °C, measure against The by the t he rate temperature graph reaction clearly rate of we a but it t he reaction reaction get shows increases, of a at graph that as shows different similar the that approximately to temperatures the one temperature the rate doubles is and shown in increases, not directly the 1 ) s( noitcaer fo etaR 204 Figure 11.2.2 Rate of (°C) reaction against the rate rate 1 1.2.2. of the proportional temperature. T emperature plot Figure temperature to Rates T o of reaction Factors investigate Your teacher the may ● observation, ● manipulation ● analysis effect use this recording and and of temperature activity and to on the rate of a will be rates of reaction reaction assess: reporting measurement interpretation 3 Y ou affecting supplied with 1.0 mol 3 dm hydrochloric acid, 0.05 mol dm sodium thiosulfate solution (Na S 2 O 2 (aq)), 3 3 a small conical ask, a 50 cm measuring cylinder, a burette, a thermometer and a stopwatch. Method 1 Using a black pen, draw a cross on a piece of white paper. Do not make the cross too dark. 3 2 Measure 50 cm 3 Pour hydrochloric the of sodium acid thiosulfate into the solution using the measuring cylinder and pour it into the conical ask. burette. 3 4 Add mix 5 1 cm the When Look 6 of the two down 7 the before 8 the to the and to the are conical the ask mixed, ask conical on a the ask of the precipitate and record top stop the and at of sulfur same slowly stopwatch temperature the time start the stopwatch. Swirl the ask to cross. of the as forms soon mixture as in which the the gradually cross conical is no ask obscures longer and the cross. visible. record the time taken disappear. experiment, adding Repeat the acid place measure cross Repeat and reactants into Immediately for hydrochloric solutions the but this hydrochloric experiment three time heat the sodium thiosulfate solution in the conical ask to about 40 °C acid. more times, heating the sodium thiosulfate solution to about 50 °C, 60 °C and then 70 °C. 9 Record your results in a table and calculate the rate of the reaction at each temperature using the following formula: 1 ______________________________ rate of reaction s time 10 Plot t a graph between 11 What 12 Explain 13 Use can double, Given can chemical deduce graph that that to rate about of for the if the suggest products equation for the cross to reaction effect increasing determine double you the the taken disappear against the nal temperature of the mixture. Draw a curve of best points. effect approximately 14 show the you the your to 1 the the the the temperature temperature rate of the temperature reasons of of why? reaction is reaction the the rate of the reaction? on the rate of the reaction. 40 °C and 50 °C. at increased Use are has on by 10 °C. information sodium chloride, Did given the In rate below sulfur, water to theory, of help and the your rate of reaction a reaction double? If it should didn’t you. sulfur dioxide, write a balanced reaction. During t he experiment, t he sodium t hiosulfate reacted wit h t he hydrochloric acid to form Na S 2 Since each t he O 2 (aq) each sulfur, which slowly 2HCl(aq) built 2NaCl(aq) up and S(s) obscured H 3 t he O(l) t he and cross time. n concentration disappeared your of when experiment t he t he you two solutions same were quantity (g) 2 used of cross: SO 2 volume time, made insoluble was t he same sulfur had been determining t he time taken sulfur for t he same quantity of sulfur to be produced at different temperatures. precipitate cross Figure 11.2.3 thiosulfate Following solution and the reaction hydrochloric between sodium on drawn paper acid 205 Factors affecting rates of reaction Rates Surface area The general rate of This a size only to par ticles n of t he our oxygen t he T o t he size) smaller in t he t he t he ot her par ticles of a reactant, t he higher t he ne coal same solid solid. mass of par ticles reactant. t he As state. Small large have a chances mines, e.g. which par ticles investigate t he t he solid a par ticles. t he effective solids par ticles greater result, of When solid react, t he have f surface t he area par ticles a larger par ticle exposed collide collisions, more t herefore, t he increases. spark, air t he in of smaller increases and Any surface t han reaction mills reactants t he t he which ammable. of area of to on decreased, frequently rate t hat applies occurs surface is is reaction reaction. reaction total r ule (particle of of could our the t he from a be and effect nely divided cigarette, explosive can our and initiate because of a coal are reaction t he large highly wit h surface t he area coal. of surface area on the rate of a reaction Your teacher may ● observation, ● manipulation ● analysis Y ou will be use this recording and and activity and to assess: reporting measurement interpretation. supplied with 5.0 g of small calcium carbonate crystals, 5.0 g of 3 large calcium ask, a cork measuring carbonate with a crystals, delivery cylinder and a tube 0.3 mol dm running hydrochloric through it to a gas acid, a conical syringe, a stopwatch. Method 1 Place the small calcium carbonate crystals in the conical ask. 3 2 Measure 3 As 30 cm quickly conical as ask with as Record the volume remains 5 Repeat the 6 Record your of gas the 7 8 volume cork of gas constant results time of in for At in the of the into a measuring the conical delivery time, syringe every use cylinder. ask tube start consecutive large and set in same gas three table each has the the for calculate the small crystals b the large crystals. the acid which using a acid and running the 30 cork to the the gas stopwatch. seconds until the readings. crystals. them crystals. to plot Y ou a can graph plot of both volume curves axes. graph, why the 11.1.2. a Explain pour experiment set your the Figure against same Using in hydrochloric possible syringe, 4 of average the rate of average the rate reaction of is the reaction higher for for: the small crystals. 9 Explain of 206 gas. why both sets of crystals produced almost the same volume on Rates of reaction Presence Cer tain t he Factors or absence chemical reaction. substances These of a can chemically in substances industr y unchanged to at be are added to reactions to known as catalysts and increase t he end alter t he t hey rate are of of t he t he rate of reactions. Key ! catalysts providing an activation of t he t he added to alternative energy collisions increases For are t han occur number example, normal wit h hydrogen up pat hway t he of speed are reaction. t he for 2H O 2 into water peroxide oxygen: 2H O(l) (aq) reaction O O 2 ) a reaction. reaction for in a Unit t he which 12.1). As par ticles given They lengt h decomposes ver y work requires a result, to react, of time. slowly fact catalyst alters the reaction of (see energy (H and 2 t he collisions 2 temperature rate pat hway sufcient effective of used Catalysts any Most rates catalyst A extensively affecting is a rate substance of a without permanent which chemical itself undergoing chemical change. by less more which at room 2 (g) 2 The reaction can be speeded up considerably by adding manganese(IV) oxide (MnO ). The manganese(IV) oxide acts as a catalyst and it is chemically 2 unchanged mass of of t he at t he end of manganese(IV) t he oxide reaction. is When exactly t he t he same reaction has as at it was nished, t he t he beginning reaction. Enz ymes are biological catalysts made of protein molecules. They are present in t he t hat cells would of all living ot her wise organisms occur too where slowly t hey for life speed to up chemical reactions exist. Did ? catalytic you know? conver ter CO 2 T etraethyl lead(IV) was first mixed N 2 with H gasoline in the 1920s as an 2 inexpensive way to increase engine gases performance and fuel economy by from preventing engine uncontrolled combustion ceramic known suppor t ‘honeycomb’ cavities in matrix through which it as Because gases Pt and covers Pd Figure few of the knocking’. as Hence ‘antiknock’. compounds, toxic inter nal fuel has the nature been use of of lead phased leaded out almost area react A known pass catalyst large surface ‘engine became 11.2.4 A together catalysts catalytic forming are converter harmless added in a car exhaust allows harmful pollutant gases to worldwide. This in in the USA phasing the out started mid-1970s. products to slow down the rate of a reaction. These are known as negative catalysts or inhibitors. They work by providing an alternative pathway ✔ Exam tip for the reaction which requires more activation energy than the normal pathway. This decreases the number of effective collisions in a given length of time. An example of a negative catalyst is tetraethyl lead(IV) ((C H 2 ) 5 Pb), If are asked to particular factor affects to be added prevented to gasoline uncontrolled (petrol) for combustion use of in the internal gasoline combustion so that the how rate a of which chemical the reaction, your answer engines. must t explain 4 a used you engine be based on the collision ran theory for reactions. more smoothly. Effect The be effect shown Figures used changing of changing on 1 1.2.5 remains is of t he and rate in a any factor curve 1 1.2.6, unchanged. up factors t he for and rate which t he t hat of t he determines curves alters reaction. number Remember reaction on t he rate n each moles limiting t he of t he of of of reaction t he is t he products can graphs limiting reactant quantity a in reactant one which produced. 207 Factors affecting rates of reaction Rates B A Original B Rate rate curve tcudorp increased A fo one ytitnauQ the a the a or temperature reaction, adding by: concentration reactant, solid an caused the decreasing of rate increasing of reaction curve showing increasing of of or the particle reactant, size or catalyst. Time Figure a 11.2.5 Figure of changing graph ● 1 1.2.5, A cur ve any B has higher rate B cur ve time ● curve showing the effect of any factor which increases the rate of one is single t he original factor as cur ve and indicated. B cur ve Looking shows carefully t he at effect what t he shows: cur ve a rate reaction n ● A to bot h been a becomes reach cur ves made reactant steeper – hor izontal – t his sooner – is because t his is t he reaction because t he is occurring reaction takes at less completion become t his was gradient is not horizontal because t he when the original same quantity number of of moles product of t he has limiting changed. A Original C Rate rate curve tcudorp decreased curve showing rate a caused by: A decreasing the concentration C fo of ytitnauQ one of the a the reaction, increasing of reactant, decreasing solid adding a the or temperature or particle reactant, negative size or catalyst. Time Figure a 11.2.6 n Figure of changing graph ● ✔ tip ● is extremely important that interpret graphs which cur ve of C C A cur ve any has at one is single a a shallower slower becomes time bot h to cur ves made t he effect original factor as gradient of any factor which decreases the rate of cur ve indicated. and cur ve Looking C shows carefully at reaction is t he effect what t he hor izontal reach – t his is because t he rate later – t his is because t he reaction takes completion – become t his is horizontal because reaction. reactant 208 the when the same quantity of product has show been rates showing you ● can curve shows: cur ve more It rate 1 1.2.6, occurring Exam A reaction was not changed. t he original number of moles of t he limiting Rates of reaction Factors Summary 1 2 3 Explain how b decreasing c increasing What Explain Key ● is Describe particle ● of reaction a the the the the particle size of concentration a catalyst experiment size following increases the rate of a reaction: a of reactant a reactant. catalyst? how an of temperature on the rate alters you of a the could rate of a perform reaction. to determine the effect of reaction. concepts The rate of reaction reactant or product The collision collide, and ● An ● A ● All ● The t he t he effective rate of a a t he when factors temperature, time be is at t hat must t he t he a to occur one t hat same as t he area of a of required t he reactants activation must energ y in t he formation plotted against of t he product. time. shape. t he reaction wit h of concentration orientated. time reactant rate t he par ticles results (par ticle in temperature. t he proper ty decreases affect react, wit h basic limiting change stated correctly changes rate surface measured measured reaction and completion main have a states must shows cur ves rate Four t heor y collision curve rate is wit h collisions par ticles beginning ● each increasing a rates questions a b affecting a is proceeds. until used chemical size) t he t is fastest reaction at t he reaches up. reaction: concentration, and t he presence reactant, t he higher or absence of a catalyst. ● The higher t he concentration t he temperature, of a t he rate of a reaction. ● The higher ● The smaller ● A catalyst wit hout ● Most ● A t he is a itself size, substance if present, catalyst, if higher t he rate of a reaction. t he higher t he rate of a reaction. which undergoing catalysts, negative par ticle t he any speed present, alters t he rate permanent up t he slows rate down of a chemical chemical of t he a reaction change. reaction. rate of a reaction. 209 Practice exam-style questions Rates 6 Practice exam-style A mass of 5.0 g of powdered zinc will react of t he reaction slowest questions wit h: 3 A Multiple-choice 3 30 cm questions of 0.1 mol dm of 0.2 mol dm of 0.3 mol dm of 0.4 mol dm 3 B 20 cm C 20 cm D 10 cm 3 1 Which of t he following would not result in an increase 3 in t he rate sulfuric of acid reaction and between excess magnesium of 0.1 mol dm carbonate cr ystals acid sulfuric acid 3 3 3 25 cm sulfuric 3 sulfuric acid sulfuric acid 3 at 28 °C? A ncreasing t he temperature of t he acid to Structured 38 °C. question 3 B ncreasing C Using t he volume of t he acid to 40 cm 7 t he same mass of magnesium a An experiment was set up to investigate what effect carbonate changing various factors has on t he rate of reaction powder. between D ncreasing t he concentration of t he acid calcium carbonate and hydrochloric acid. to The reaction was carried out at 30 °C in a conical 3 0.2 mol dm ask 2 An aqueous solution of hydrogen peroxide t hat calcium was was placed carbonate on was a balance. placed in A mass t he ask of 10.0 g and of excess 3 decomposed a gas t he and syringe. total t he Which volume of oxygen of t he produced following oxygen as was collected graphs measured at hydrochloric in represents various time of concentration added. The ask and its regular inter vals and t heir as inter vals? acid shown in t he contents mass was 1.0 mol dm were weighed plotted against at time, gure. 306 )g( emuloV noitcaer emuloV A B ssaM Time 304 303 fo Time 305 302 301 300 emuloV emuloV 0 0 30 Time Time C D i) The rate catalyst A speeds B slows C takes D alters is best described as a substance of of proceeds. A 90 120 150 Time Mass 3 60 against reaction Using determine which: a reaction t he t he 180 210 time decreases data average 240 (s) from rate of as t he t he t he reaction graph, reaction 1 up t he down no t he par t t he rate in rate of rate a of a of chemical a chemical chemical a reaction reaction chemical : in g s reaction ii) reaction – in t he rst – in t he second Why is second 4 The rate of a chemical reaction independent of t he size of rate minute. faster in (4 t he rst minute minute? marks) t han (2 t he marks) is: iii) A t he minute t he par ticles of a What effect would repeating rate t he t he reaction at 40 °C solid have on t he of reaction? (1 mark) reactant iv) B independent of t he concentration of t he By referring explain C dependent on D unaffected by t he to t he collision t heor y for reactions, reactants your answer to par t iii) above. temperature (3 a v) 5 f t he wit h temperature sodium following at which t hiosulfate is hydrochloric raised by acid 10 °C, of What effect, if any, would using excess 3 reacts which hydrochloric t he occurs? A The rate of t he reaction is increased by a factor of 10. B The rate of t he reaction is decreased by a factor of 10. C The rate of t he reaction is doubled. D The rate of t he reaction is halved. b i) ii) 210 marks) catalyst have on your answer. What is Explain t he a acid rate of of concentration t he reaction? 0.5 mol dm Give a reason (2 catalyst? how a catalyst (1 works. (2 Total for marks) mark) marks) 15 marks Rates of reaction Extended 8 The response graph which below was reaction acid Practice between varies over out t he to results n of determine magnesium time. questions question shows carried exam-style t he an experiment how ribbon t he and experiment, rate of a hydrochloric excess 3 magnesium ribbon was added to 25 cm of hydrochloric o acid at 35 regular C and t he volume of gas was measured at inter vals. mc( 3 ) sag fo emuloV Time a i) ii) b Write a balanced Account Draw a could for labelled be set up t he (min) equation shape diagram to carr y of to out for t he reaction. cur ve. show t he t he how t he (2 marks) (4 marks) apparatus experiment. (3 c i) Copy on t he your graph expected at 25 °C. your ii) f graph draw results Make onto if a your second t he sure answer cur ve experiment t hat you paper to show was distinguish between (2 experiment was repeated again t he repeated cur ves. t he marks) and marks) wit h o magnesium powder what effect, if – t he maximum – t he rate Explain of any, instead would volume evolution your answer of in of t his of have gas t he each ribbon at 35 C, on: evolved gas? case. (4 Total marks) 15 marks 211 A12 Energetics Chemical energetics is the branch of chemistry that Objectives By the be able end of this topic you will deals and ● with distinguish between exothermic reaction an chemical accompany and give and examples of exothermic endothermic explain physical processes bond reactions. all Energy chemical changes reactions. In usually fact, in some reactions the energy produced is more important than the products of the chemical reaction, reactions exothermic endothermic on during reaction e.g. ● changes an chemical endothermic ● energy to: reactions breaking the burning of fuels. Energy changes can take many and and based forms, e.g. changes in heat, light and electricity. bond forming A12.1 ● explain what enthalpy ● explain is meant change, H exothermic endothermic enthalpy changes during reactions Exothermic and Whenever is endothermic reactions and reactions t here a chemical reaction, t here tends to be a change in energy based of on Energy by t he system. The energy changes in chemical reactions are usually in t he change form of heat energy, however, t hey may also be in t he form of light, electrical ● draw energy prole or diagrams for exothermic nuclear on endothermic show the t he energy effect of adding can distinguish which between two types of reaction based occur. If t he reaction using energy produces heat, causing t he reaction mixture and its a surroundings catalyst We changes reactions ● ● energy. and to get hotter, t he reaction is said to be an exothermic prole reaction. Exot hermic reactions transfer energy to t heir surroundings. diagrams. ● If the its reaction reaction. ! An Key to its reaction surroundings to get ! heat, causing colder, Endothermic the reactions the causing reaction absorb is the said energy to reaction be from an mixture their surroundings. causing investigate fact teacher exothermic may ● observation, ● manipulation and endothermic reactions use this recording and activity and to assess: reporting measurement. 3 Y ou An endothermic energy from causing and endothermic hotter. Your Key get releases surroundings, T o the to fact exothermic energy absorbs surroundings the its reaction will be supplied with 3 2.0 mol dm hydrochloric acid, 2.0 mol dm absorbs sodium hydroxide pellets, ammonium solution, zinc metal, potassium nitrate, sodium hydroxide surroundings, surroundings to chloride, distilled water, a polystyrene cup supported in get a beaker, two measuring cylinders and a thermometer. colder. Method 3 1 Measure pour it 25 cm into the of hydrochloric polystyrene cup. acid using Record a the measuring cylinder temperature of the and acid. 3 2 Measure cylinder and 25 cm and record of add the it sodium to the hydroxide acid. maximum or Stir solution the minimum in solutions the other with the measuring thermometer temperature. 3 3 Measure another polystyrene amount 212 of cup. zinc. 25 cm Record Stir and of hydrochloric the acid temperature record the of and the maximum or pour acid it and into add minimum the a cleaned small temperature. Energetics Energy changes during reactions 3 4 Measure pour it water 25 cm into and Repeat or step ammonium Make sure 6 Record 7 Classify of distilled cleaned add maximum 5 the a small 4 using you your amount minimum chloride each sodium reaction of a cleaned cup. measuring Record potassium hydroxide place the in in the nitrate. cylinder temperature Stir and and of the record the temperature. in wash results water polystyrene a of the pellets potassium polystyrene cup and again nitrate between in using each each case. experiment. table. as exothermic or endothermic. zinc is added sodium polystyrene hydroxide cup solution hydrochloric Figure 12.1.1 solution is Sodium added to acid hydrochloric hydroxide Figure hydrochloric 12.1.2 hydrochloric Zinc is acid added to acid acid Examples of exot hermic ● burning of ● neutralisation between reactions include: fuels reactions sodium ● reactions ● respiration, between hydroxide between which and acids and bases, hydrochloric reactive metals releases energy and e.g. t he reaction acid acids from food in t he cells of all living organisms ● dissolving sulfuric Examples ● t he cer tain substances in water, e.g. sodium hydroxide and acid. of endot hermic decomposition decomposition, decompose into ● photosynt hesis ● dissolving of e.g. reactions compounds calcium calcium in cer tain include: oxide and plants, which salts water, in when carbonate heated, must carbon absorbs e.g. known absorb as heat thermal in order to dioxide sunlight ammonium energy chloride and potassium nitrate. Bond breaking and bond forming In Unit 1 1.1 you learnt t hat a chemical reaction involves breaking t he original bonds in t he reactants ● When t he original ● When new bonds bonds are is making bonds are reactants energy and broken absorbed are new broken formed in t he bonds in t he in t he products. reactants, products, energy energy is is absorbed released products bonds are energy is formed released 213 Energy changes during reactions Energetics In ● Did ? you an know? t he Average bond found chemical in energies data can be amount of energy in new absorbed during can be a bonds In an the all up bonds the the in bond bonds in in new t he the for and products following change energies all bond in the sum in extra of t he to break released energy is in t he released surroundings existing forming to t he increases. reaction , is t he greater energy t han absorbed t he to break energy released t he energy is in existing forming in t he and products. t he The temperature extra of t he absorbed surroundings from t he decreases. Ever y chemical bond has a specic amount of energy, no matter what and it is in, known as its bond energ y. The amount of energy which formula: of reactant energies The absorbed energy all for has energy t he temperature reactants bonds compound applying products. t he energy t han by energies reactants the t he less chemical calculated the t he endothermic surroundings adding in and is books. t he reaction reaction , reactants released bonds or t he surroundings ● The exothermic bonds the all bond sum to be released absorbed when to t hat break bond is t hat bond is t he same as t he amount of energy formed. of products Enthalpy The energy symbol but change it H. is content The of energy possible to a substance content measure reaction. This is known as of t he a is called its substance change in enthalpy change enthalpy cannot ent halpy be and is given measured t hat occurs t he directly, during and is given t he symbol a H and 1 is usually The expressed ent halpy change ent halpy i.e. in of change H kilojoules, of In an i.e of reaction t he reaction kilojoules summarised per mol, by t he kJ mol following (total ent halpy of products) (total ent halpy of reactants) . formula: H reactants H energy t he ent halpy of t he products is less t han t he reactants: H products extra is or reactions H Therefore, a products exothermic ent halpy reaction H reaction Exothermic a kJ, reactants has is a value released which to t he is less t han zero, surroundings and i.e. t he H is negative. temperature of The t he surroundings increases. Anot her way to t hink of t his is t hat since t he reaction loses energy, H is negative, i.e. H energy of ve. content reactants ygrenE H ve energy of Progress An example value of H of is an Figure 12.1.3 exot hermic given af ter t he An of content products reaction exothermic reaction is t he reaction combustion of met hane (t he equation): 1 CH (g) 2O 4 The is 214 value (g) CO 2 for completely H tells burned (g) 2 us in t hat 891 kJ oxygen. 2H O(g) H 891 kJ mol 2 of energy is lost when 1 mol of met hane Energetics Energy Endothermic In an t he i.e. of t he H reaction t he ent halpy of t he products from is greater reactants t he surroundings and t he H is positive. Energy temperature of t he surroundings decreases. Anot her way to t hink of t his is t hat since t he reaction H is positive, i.e. H of ygrenE H energy of example of an Figure content products ve content reactants Progress and gains energy, ve. energy An t han H Therefore, H has a value which is greater t han zero, i.e. absorbed reactions reactants: products is during reactions endothermic ent halpy changes 12.1.4 endot hermic An of reaction endothermic reaction is t he reaction reaction between hydrogen iodine: 1 H (g) I 2 The value hydrogen by t he (s) 2HI(g) H 26.5 kJ mol for H iodide reaction tells is us made t hat 26.5 kJ during represented in t he t he of energy reaction. equation is The would gained overall be when energy double t his 1 mol since Reversible In a it shows of It may a reaction of hydrogen iodide being be very confusing value, which causes to think an increase of i.e. made. temperature as having and vice that an a of its surroundings negative versa. Try value to for H remember reactions reversible reverse 2 mol tip absorbed in 53 kJ, Exam ✔ 2 reaction , reaction is if t he for ward endot hermic and reaction vice versa. is exot hermic, The H value t hen given t he for a losing and exothermic energy if you minus it, to lose i.e. its reaction anything H is is surroundings –ve. you are Similarly, the reversible reaction is for t he for ward reaction, i.e. t he reaction which proceeds endothermic from lef t to right. For example, t he reaction between nitrogen and form ammonia is gaining hydrogen energy to reaction from its surroundings and is: if you gain anything you are plus it, 1 N (g) 3H 2 (s) 2NH 2 (g) H –46.1 kJ mol i.e. 3 H is ve. This shows t hat t he for ward reaction which produces ammonia is exot hermic. Therefore, 1 mol of t he reverse ammonia is reaction made is endot hermic. during t he reaction, It also 46.1 kJ shows of us energy t hat is when released. ! Energy profile Key fact diagrams Activation The energy change in a chemical reaction can be illustrated wit h an energ y amount must prole d i agram. The diagram shows t he energy content or ent halpy of and products, H and t he activation energy. Most reactions energy to get t hem star ted. This minimum amount of energy is given, normally activation energ y . This activation energy can be t hought of the minimum reactants excess possess, in of what order bonds to start breaking in the called reactants t he in is that need for some energy energy t he they reactants be of as and products to start t he forming. energy The for amount t he The barrier of of reaction are reaction. activation reaction general a and energy shown is prole in energy not does included diagrams Figure not in of affect t he an t he overall calculation exot hermic of and energy t he an change value of H. endot hermic 12.1.5. 215 Energy changes during reactions Energetics (a) (b) activation energy tnetnoc tnetnoc AB + C reactants activation ygrenE ygrenE –ve H A + BC products energy H A + BC AB + C products Course Figure (a) An 12.1.5 When Energy exothermic Drawing you impor tant of prole energy are you Course an an endothermic energy include t he formulae of t he reactants ● t he formulae of t he products ● arrows ● t he An value example hydrogen is of H. of how shown t his in prole activation can be Figure reaction. diagram following t he t he energy done for a and t he specic on your reaction it is diagram: H reaction between nitrogen and 12.1.6. tnetnoc (g) + 3H 2 for information activation N reaction diagrams ● indicating of diagrams. (b) profile drawing t hat reactants reaction reaction, +ve energy (g) 2 ygrenE –1 = H – 46.2 kJ mol 2 NH (g) 3 Course Catalysts In Unit rate has is of a Figure and 1 1.2 a energy you because t hat prole a of activation energy t han a catalyst reactant par ticles reaction provides activation have speeds t hat result in t he The effect of using up an t he because of catalyst for is a the a formation substance reaction same t he of t he can are to more products) be shown t hat which ammonia for when effective in on t he pat hway. react t he can a wit hout pat hway normal energy t here in reaction alternative t han required formation a energy, energy t he diagram catalyst terms less reaction diagrams In requires t he Energy profile learnt reaction. lower 12.1.6 of a is reaction As a t hey lengt h prole t he used catalyst. This which result, more collide, collisions same energy increase catalyst and (collisions of time. diagrams. It is impor tant to note that although the reaction has a lower activation energy, as shown in the diagrams in Figure 12.1.7 , the energy values for the reactants and products 216 remain unchanged, therefore, the value for H remains the same. Energetics Calculating activation energy activation activation without a without a energy catalyst activation a changes energy catalyst with energy energy catalyst with a catalyst reactants tnetnoc tnetnoc ygrenE ygrenE H ve H ve products reactants Course Figure (a) an of 12.1.7 reaction Energy exothermic Summary 1 Explain Course prole reaction, diagrams (b) an with and endothermic without a of reaction catalyst. reaction. questions what is meant by an exothermic reaction and an endothermic reaction. 2 Explain exothermic a bond b enthalpy 3 Give 4 Draw breaking the a fully on and endothermic bond reactions by reference to: forming change. formula Indicate and used labelled your to calculate energy diagram enthalpy prole what diagram effect change. for adding a the following catalyst reaction. would have. 1 2H (g) O 2 (g) 2H 2 O(g) H 241.8 kJ mol 2 Objectives A12.2 Calculating energy changes By the be able ● In t he can laborator y, be t he deter mined reaction, known by as energy c hange, measur ing t he he at of t he or ent halpy heat re action . c hange We c hange, t hat cannot in occurs a t he or ent halpy, of t he react ants and products directly. dene calculate t he heat of reaction by measur ing t he c hange occurs dur ing a the terms unit you will heat of give the formula of neutralisation to calculate heat change of a calculate heat reaction changes from reaction. learn neutralisation of solution how to determine heats of reaction such as explain why data the and t he heat of solution experimentally. In heat of t he neutralisation heat heat and experimental t his specic heat temperature ● In will we ● whic h you t he However, in topic capacity, the can this energy ● content, of to: reaction dur ing measure end for the reaction t hese between a strong acid and experiments you will measure t he change in temperature which accompanies strong t he neutralisation reaction between a strong acid and a strong alkali and of a solid in water. You can t hen use what is known as t he describe capacity to determine t he change in ent halpy for t he speci c heat capacity of a substance, c, is t he the same experiments determine the heat of reaction. neutralisation The always specic to heat is t he ● dissolving alkali quantity of heat and heat of required solution to raise t he temperature of a unit mass of t he substance by 1 °C or 1 K. We ● usually take t he unit mass of t he substance as 1 g and measure give the when in deg rees Celsius. This being t he case, speci c heat capacity is given joules per g ram per deg ree Celsius or J g calculating . Using water as neutralisation speci c heat capacity of water is and heat of an solution t he heat 1 °C 1 example, made the t he of 1 units assumptions temperature 4.2 J g o from experimental 1 C . This means data. t hat it takes 4.2 J of heat energy to raise t he temperature of 1 g of water by 1 °C. 217 Calculating energy changes Energetics If Key ! we heat fact t he The specific heat capacity know of substance heat energy is quantity required temperature substance the of by a to unit 1 °C temperature q, of t he substances from t he specic change, T, using reacting, heat t he m, capacity following we of can t he determine substances, c, t he and formula: m c T of raise mass or mass of q a t he reaction, the of the Measuring 1 K. To measure heats t he heat apparatus known container whic h sur roundings being The a general xed be heat reaction t he is out is and used. released of if a t he heat A by exot her mic, reaction made met hod volume it into of maximum or of solution calor imeter a reaction or heat reaction polystyrene above determining water reactants minimum to or calorimeter The temperature given for solution t he t hermometer. The neutralisation c alor imeter is cup is a an piece escaping from t he into t he sur roundings endot her mic. because of insulated A simple polystyrene is a insulator. pouring a by can of a reaction prevents t he absorbed calor imeter good if as of are to can t hen t he t hen heat of of be reaction used measuring temperature change calculate and heats be t he its mixed reached in involves t he t he calculated cylinder, temperature calorimeter reaction and measuring measuring initial in in a used is using and t he measured. in t he determine t he formula reaction. Assumptions In t he experiments you will be carr ying out to heat of neutralisation and heat of solution, you will make t hree assumptions in your calculations. ● The density of a dilute aqueous solution is t he 3 1 g cm ● The This specic means heat t hat ● i.e. 4.2 Negligible J g heat surroundings Heat ! Key of t he capacity 1 water, same as water, i.e. 3 . of a mass of dilute 1 cm of aqueous solution solution is is 1 g. t he same as 1 °C is lost during to t he t he surroundings or absorbed from t he reaction. neutralisation fact The neutralisation reaction between a strong acid and a strong alkali is an exot hermic reaction. The amount of heat produced per mole of water formed The heat heat of change 1 mol of neutralisation which water is occurs produced is the when in in t he between an acid is known as t he heat of neutralisation of neutralisation, a In reaction reaction and calculating t he heat t he initial temperature of an bot h solutions must be measured and averaged to determine t he initial alkali. temperature, must be and t he number of moles of water produced in t he reaction calculated. Example 3 A volume of 50 cm of sodium hydroxide solution of 3 1.0 mol dm concentration 3 and temperature 26.0 °C is added to 50 cm of hydrochloric 3 acid t he of concentration maximum neutralisation 218 temperature and and 1.0 mol dm draw an of t he temperature solution energy prole is 33.2 °C. diagram for 27 .0 °C. Af ter Determine t he mixing, t he reaction. heat of Energetics The Calculating balanced equation NaOH(aq) for t he reaction HCl(aq) energy changes is: NaCl(aq) H O(l) 2 Determine t he number of moles of water made in t he reaction: 3 1000 cm of NaOH(aq) contain 1.0 mol NaOH 1.0 _____ 3 ∴ 50 cm of NaOH(aq) contain 50 mol NaOH 0.05 mol NaOH 1000 3 And 1000 cm of HCl contains 1.0 mol HCl 1.0 _____ 3 ∴ 50 cm of HCl(aq) contain 50 mol HCl 0.05 mol HCl 1000 From t he 1 mol equation: NaOH reacts wit h 1 mol HCl forming 1 mol H O 2 ∴ 0.05 mol NaOH reacts wit h 0.05 mol HCl forming 0.05 mol H O 2 i.e. 0.05 mol H O is produced in t he reaction. 2 Determine t he heat of neutralisation: 3 Total ∴ volume mass of of solution solution, m 50 50 100 cm 100 g 26.0 27 .0 ___________ Average initial temperature, T °C 26.5 °C 1 2 Final temperature, T 33.2 °C 2 ∴ temperature increase, T T – T 2 (33.2 – 26.5) °C 1 Specic Using q heat heat m c evolved capacity in of t he 6.7 °C 1 solution, c 4.2 J g 1 °C T, forming 0.05 mol H O (100 4.2 2814 J 2.814 kJ 6.7) J 2 2.814 ______ ∴ heat evolved in forming 1 mol H O kJ 2 0.05 56.28 kJ 1 i.e. The heat t herefore, The heat of neutralisation, neutralisation t he energy of reaction prole was is H negative 56.28 kJ mol because t he temperature increased, exothermic diagram is shown NaOH(aq) HCl(aq) below: activation energy tnetnoc ygrenE 1 H 56.28 kJ mol NaCl(aq) H O(l) 2 Course of reaction 219 Calculating energy changes Energetics T o determine Your teacher the may ● observation, ● manipulation ● analysis heat use this recording and and of neutralisation activity and to assess: reporting measurement interpretation. 3 Y ou will be hydroxide and a supplied solution, with a 3 1.0 mol dm calorimeter sulfuric (polystyrene acid, 2.0 mol dm cup), a potassium measuring cylinder thermometer. Method 3 1 Measure the 2 dry 50 cm of sulfuric acid in the measuring cylinder and pour it into calorimeter. Measure and record the temperature of the acid using the thermometer. 3 3 Measure 50 cm measuring 4 Pour the solution Record 6 Calculate 7 to the that the the reaction calculation The an the hydroxide of solution temperature the initial density as prole for cleaned the calorimeter the and temperature stir the change. reached. of the heat the and to for the the two solutions and use increase. acid diagram neutralisation into specic page in temperature. watching calculate sulfuric previous its temperature and water, solution record while temperature between energy heat the same on hydroxide and thermometer average calculate both 9 Measure maximum are Draw the the Assuming 8 potassium potassium with 5 this of cylinder. capacity heat of potassium help the of the solution neutralisation hydroxide. for Use the you. reaction. reaction should be approximately 1 56.3 kJ mol . If your value is lower than this, can you suggest reasons why? The heat of neutralisation for t he reaction between any strong acid and any acids and 1 strong alkali is always about 56.3 kJ mol . This is because strong strong alkalis are fully ionised in aqueous solution and t he common reaction t hat releases heat in all cases is: OH (aq) H 1 (aq) H O(l) H 56.3 kJ mol 2 The equation for t he neutralisation reaction between sodium hydroxide and sulfuric acid is: 2NaOH(aq) H SO 2 (aq) Na 4 SO 2 (aq) 2H 4 O(l) 2 In this reaction, 2 mol of water are produced. The heat of neutralisation is still 1 about 56.3 kJ mol in the The equation heat of is , however, the overall heat change for the reaction shown about 1 12.6 kJ, neutralisation thermometric temperatures titration of t he acid can i.e. also explained and double be in alkali t he heat determined Unit must 8.5. be In of neutralisation. from t his t he results met hod, measured and t he t he of a initial point of intersection of t he two lines of best t on t he graph represents t he maximum temperature 220 recorded during t he reaction. Energetics Heat When Calculating of a energy changes solution solid, liquid or gas dissolves in a solvent, t here is usually a change in Key ! fact ent halpy. This ent halpy change which occurs when 1 mol of solute dissolves The in In a solvent is known calculating be measured t he and as heat t he heat of of solution solution, exact t he quantity initial of heat change temperature solute dissolving of t he must water be of solute t he number of moles of solute can be solution of solvent is occurs dissolves in the heat when such 1 mol a volume must known that further dilution by the so solvent t hat of which produces no further heat calculated. change. Example 3 A student water. The minimum heat for dissolves initial 5.35 g of of solution of t he solution process. t he ammonium temperature temperature Determine of 16.4 °C ammonium number of t he is of water recorded chloride of moles chloride NH and Cl is by in 100 cm 22.5 °C. t he draw student. an of Af ter energy distilled mixing, Determine prole a t he diagram dissolved: 4 1 M(NH Cl) 53.5 g mol 4 i.e. mass of 1 mol NH Cl 53.5 g 4 5.35 _____ ∴ number of moles in 5.35 g mol 0.1 mol 53.5 Determine t he Mass heat of Initial of water, solution: m 100 g temperature, T 22.5 °C 1 Final temperature, T 16.4 °C 2 ∴ temperature decrease ( T) T – T 1 22.5 4.2 – 16.4 °C 1 Specic Using q heat heat m capacity c absorbed of t he 6.1 °C 2 solution, c J g 1 °C T, in dissolving 0.1 mol NH Cl 100 2562 4.2 6.1 J 4 J 2.562 kJ 2.562 ______ ∴ heat absorbed in dissolving 1 mol NH Cl kJ 25.62 kJ 4 0.1 heat of solution, H Exam ✔ 1 i.e. 25.62 kJ mol It is essential tip that you give The heat of solution is positive because t he temperature decreased, t herefore, the t he reaction was correct unit energy the heat of endothermic neutralisation The for prole diagram is shown below: are for or calculating producing dissolving solution. the heat 1 mol 1 mol of of (aq) Cl (aq) 4 you change water solute, NH Since or the unit 1 will tnetnoc It is always also be J mol essential 1 or that kJ mol you . indicate activation whether energy 1 H or ygrenE your Cl(s) reaction by is exothermic putting a 25.62 kJ mol negative NH the endothermic or positive sign before value. water 4 Course of reaction 221 Calculating energy changes Energetics T o determine Your teacher may ● observation, ● manipulation ● analysis Y ou will use and of this solution activity and to assess: reporting measurement interpretation. supplied calorimeter heat recording and be the with (polystyrene potassium cup), a nitrate, measuring distilled cylinder water, and a a balance, a thermometer. Method 3 1 Measure into the 100 cm dry 2 Measure 3 Using the water in 4 Stir the of distilled water in the measuring cylinder and pour it calorimeter. and record balance, the the temperature weigh 12.1 g of of the water. potassium nitrate and add it to the calorimeter. solution with the thermometer while watching the temperature change. Summary questions 5 Record 6 Calculate 7 Assuming as 1 Dene the the water, the a heat of neutralisation b heat of solution Is specic heat made in the heat of capacity solution of of the solution potassium is the nitrate. same an on a the previous potassium reason for your page nitrate to an help Use the you. exothermic or endothermic reaction? answer. Draw an energy prole diagram for the bonds breaking and solution process. assumptions 10 to the heat capacity. 9 are decrease. specic calculate dissolving Give What the reached. following: 8 2 temperature temperature that calculation c minimum By reference for the to bonds forming, explain the reason experiment determine the heat enthalpy change which occurred when potassium nitrate of dissolved in water. neutralisation? 3 Why is the heat of When neutralisation between and the for sodium hydrochloric same as the the ● hydroxide solute Bonds the acid heat a dissolves in a solvent t he following events occur. reaction break between surroundings. which break, bonds between e.g. In the the when par ticles case of sodium of the ionic solute; this compounds, chloride dissolves it in absorbs is the water energy ionic it is from bonds the ionic of neutralisation for the potassium sulfuric It was found that of the Cl ions which break. In the case substances, it is the intermolecular forces between the of molecules break, e.g. between when the ethanol ethanol dissolves molecules in water that it is the intermolecular break. when ● 4.0 g and acid? forces 4 ions hydroxide that and Na reaction covalent between the ammonium The intermolecular also absorbs forces between t he solvent molecules also break; t his nitrate energy from t he surroundings. 3 dissolved in 50 cm of distilled water, temperature ● the Attractions t he decreased from 27.4 °C Determine solution for the heat draw an energy energy reaction is for the absorbed ions or process to t he molecules is called of t he solute solvation and and it surroundings. exot hermic if more energy to break if more t he bonds energy is in t he is released solute absorbed process. solvent 222 t he This during solvation t han and solvent. The reaction is prole endot hermic diagram between solvent. nitrate is and t he of The ammonium formed of to releases 21.6 °C. are molecules t han is released during solvation. to break bonds in t he solute and Energetics Key ● Exothermic reactions mixture its and Endothermic t heir ● bonds are an an The The energy t han energy an broken in heat to in get t he in of energy forming reaction, energy t he released a change t han The H exot hermic The H is zero, A proceed to The ● The The of ● t he energy in t he of To m energy from is absorbed. can When new to break bonds is less absorbed called new to break bonds is bonds. enthalpy and is given t he reaction be measured and is given t he H < H , t herefore, H is less t han reactants H > H , t herefore, H is greater reactants positive. in t he by heat a chemical is t he reaction minimum from heat c in a of can be illustrated amount of energy by an required for a a of is can determine in t he route required for t he for a reaction to substance in t he quantity mass be enables us to determine temperature. of heat heat from t he capacity using energy substance calculated T, of t he t he by required 1 °C masses of t he or of to 1 K. t he substances, c, formula: T in solution produces energy alternative specic neutralisation dissolves a unit t he activation energy. change q, m, of an temperature, produced of less capacity reaction , amount providing capacity reacting, of is heat solvent is requires change heat solute ● reaction bonds. forming a reaction, temperature heat water The t he absorb reactants energ y change specic q ● t hey d i agram occur which substances and H reduces specic raise to occur. to ent halpy ● energy H change activation catalyst The reaction negative. prole reaction ● i.e. ent halpy reaction ● causing absorbed is reaction endot hermic energ y ● t he transfer released. new substance in products i.e. an is products ● t hey i.e. energy energy products In energy colder, reactants products reaction, content zero, ● causing i.e. H. H In energy hotter, H reaction ● get absorb released t he ent halpy symbol ● are formed endot hermic symbol ● heat to surroundings exot hermic t he greater ● reactions its bonds In produce surroundings surroundings. t han ● and When In changes surroundings. mixture ● energy concepts t heir ● Calculating is such no a is t he a heat of heat change between change volume fur t her heat t he reaction heat of an which acid which solvent occurs and occurs t hat an when fur t her when 1 mol alkali. 1 mol dilution of by t he change. neutralisation or heat of solution we assume 3 t hat 1 cm of a heat capacity dilute aqueous solution has a mass of 1 g 1 negligible ● The heat which heat of is is lost t he to, same or neutralisation as water, absorbed for t he i.e. from, reaction 4.2 t he J g and a specic 1 °C , and t hat surroundings. between a strong acid and a 1 strong alkali is always t he same, about 56.3 kJ mol 223 Practice exam-style questions Energetics 3 6 Practice exam-style When 0.2 mol water, t he t hat Multiple-choice sodium nitrate dissolved in 100 cm of questions t he questions temperature specic 1 4.2 J g heat decreased capacity of by 7 .2 °C. t he Assuming solution is 1 °C , t he heat of solution of sodium nitrate is: 1 1 Which of t he following statements best describes an A 604.8 J mol B 3024 J mol C 15.12 kJ mol 1 endot hermic reaction? 1 A The ent halpy of of B Energy released C The ent halpy D The temperature is t he t he ent halpy reactants is greater t han t he 1 products. to t he change of is t he D 151.2 kJ mol surroundings. Structured negative. surroundings decreases. 7 a The a 2 When sodium hydroxide is added to question water at 28 °C, gure reaction below and shows t he an effect energy of a prole catalyst on diagram t he for reaction t he pat hway. temperature t he B energy C t he D t he ent halpy is change released reaction more solution is energy to is increases to 40 °C because: positive t he surroundings tnetnoc A of endot hermic is absorbed to break t he ionic bonds during 3 Which I II of t he Na ion and OH ions t han is released solvation t he breaking following of solvation a of processes releases B C ygrenE between A energy? bond an ion Course III formation A I only B I and of a Energy i) II II and State, III III wit h a prole reason, diagram if t he reaction is exot hermic endot hermic. (2 Identify t he par ts labelled A, B, and C on diagram. The diagram below shows t he energy prole diagram How (3 does a catalyst work to speed up t he reaction. Which letter in t he diagram represents necessar y for t he reaction to take (2 of a marks) t he b energy marks) rate of reaction? a t he only iii) 4 marks) only ii) D reaction only or C of bond The dissolving of ammonium nitrate in water may be place? represented by t he (s) following equation: NH NO 4 A water NH 3 (aq) 4 D NO (aq) H ve 3 tnetnoc In order to distilled 16.0 g water of H, a student of ammonium nitrate in 75 cm at room temperature (30.0 °C). of He ygrenE C stirred at t he regular t he Course of room i) following sodium equation hydroxide H PO 3 and for t he reaction phosphoric (aq) Na 4 O(l) PO H (aq) 4 168.9 kJ t he following A The reaction B The heat C The reactants D The temperature is statements is incorrect? exot hermic. 1 of neutralisation have more is 168.9 kJ mol energy t han t he On erutarepme T 2 of between recorded all t he The t he t he its mixture largest initial temperature solid had had dissolved returned difference temperature he and temperature t he axes in was t he below, show t he 15 °C. sketch solution a graph temperature to wit h time. acid 3 3H Which of temperature. variation )C°( 3NaOH(aq) and until reaction solution t he mixture inter vals temperature obser ved between value 3 dissolved to Consider t he B and 5 determine 50 40 30 20 10 products. 0 224 of t he surroundings would increase. Time (min) (2 marks) Energetics ii) Practice Calculate t he assuming t hat energy t he change specic 1 solution iii) t he t hat Determine t he reaction, capacity °C . number of moles of heat (2 of solution of 8 a i) ii) Dene (2 ‘heat Account for of neutralisation’. t he fact for strong acid and Give relevant t hat t he any t he reaction strong ionic (2 heat A student between alkali equation is to determine between She was marks) t he any same. suppor t your (2 was required t he heat of potassium provided marks of answer. b marks) 15 question neutralisation a marks) ammonium Total response t he marks) ammonium nitrate. Extended of (2 dissolved. t he questions 1 4.2 J g Determine nitrate iv) is for heat exam-style to carr y out an neutralisation hydroxide wit h t he and in t he sulfuric following marks) experiment to reaction acid. materials and equipment: 3 50 cm of potassium of sulfuric hydroxide solution 3 50 cm acid of concentration 3 0.6 mol dm a t hermometer a polystyrene She recorded solutions, recorded mixed t he temperature Initial Initial initial t hem temperature in maximum recordings temperature solution i) cup. t he are potassium of sulfuric Determine t he t hat State in From your of heat t he ot her your specic Draw t he a and reached. Her hydroxide fully acid for t he heat 37 .1 °C reaction, capacity . of (3 assumptions to i) given in i) t he above, t hat t hat labelled energy you marks) have above. (2 calculate t he t he sulfuric reactant. reaction. 29.5 °C mixing 1 calculation answer limiting af ter change °C 4.2 J g neutralisation t he iv) T WO made two cup below: of 1 iii) given temperature is t he 29.5 °C temperature solution of polystyrene temperature Maximum assuming ii) t he heat acid (4 prole marks) diagram (2 Total is marks) for marks) 15 marks 225 Section B Introduction Objectives the end be able of Organic this topic you will chemistry compounds give is the containing branch carbon of chemistry atoms, in known which as organic to: compounds, ● organic chemistry B13 By to examples of are studied. Studying organic compounds organic is very important since they are all around us and form compounds ● give the main containing an compounds integral oil, ● give the carbon ● structure of and can form illustrate double bonds, single daily lives, for example plastics, diesel and alcohols. Organic compounds that form and of fats are a the major food part we of eat. the bodies Proteins, of living organisms carbohydrates and all organic compounds. unbranched branched chains and structures explain identify the term certain represent using our bonds, B13.1 Organic compounds All compounds functional functional groups ● gasoline, also group ● of a atom carbon ringed ● electron understand chains, part carbon organic contain carbon. Most also contain hydrogen and many contain oxygen. Ot her elements may also be present such as nitrogen, sulfur and phosphor us. Organic compounds which contain only carbon and organic molecular, compounds fully hydrogen are known as hydrocarbons displayed A vast number of organic compounds exist and t hey are used in all aspects of and condensed structural our lives. Some examples of organic compounds t hat we use in our ever yday formulae. lives ● are given Met hane, below. CH , is t he main component of natural gas which is used as 4 a ● fuel to generate pur poses and as Et hanoic acid, electricity, a fuel CH for as a fuel vehicles COOH, is t he in for domestic some main heating and cooking countries. component in vinegar which is 3 used ● to preser ve Et hanol, C H 2 ● Glucose, C ● H Protein is an and is for The great , is an of of t he carbon ● metal ● fossil ● carbohydrates, ● organic ● diamond dioxide of a basis of bot h plants of and of in wines and spirits. and animals as one of t heir atom. (see Unit man-made polymer bags and compounds Carbon which which cling is in t he found in: monoxide oil, and natural lipids ascorbic graphite 16) is used by grow. hydrogencarbonates cr ude as a to sandwich organic proteins such polymer t hem is widely used wrap. compounds carbon and as natural enable carbon such and by example carbonates acids, to carbon ● fuels, used example, abundance chemistr y t he energy. example as plastic, food. 6 of Polyet hene a forms animals Formation 226 O 12 sources plants ● OH, avour 5 6 main and which (fats acid are gas and pure and and coal oils) citric acid carbon. world is because of t he Introduction The atomic and has to organic number chemistry of carbon is Organic 6. A carbon atom t herefore has six compounds electrons × an electronic conguration of C (2,4). The shell diagram of a carbon ×× atom is shown in Figure 13.1.1. 6p × × 6n Looking This can at t he means form electron t hat four str ucture, carbon covalent can a carbon share four wit h ot her bonds atom has electrons atoms. four wit h These valence ot her ot her electrons. atoms, atoms i.e. it × include 12 hydrogen, oxygen, nitrogen and t he halogens. carbon, C 6 It is impor tant to note t hat not all carbon-containing compounds are organic Figure 13.1.1 Electron structure of carbon compounds. Carbon dioxide, carbon monoxide, metal carbonates and metal hydrogencarbonates are classied as inorganic compounds Did ? Bonding As a result wit h vast in of ot her organic carbon carbon number of having atoms different Carbon compounds four in valence an almost organic electrons, unlimited compounds carbon way. exist compounds. The simplest of t hese is met hane (CH atoms Because compared to can of bond t his, a inorganic ). If we look at t he met hane you is the know? sixteenth abundant element crust the and element after neon by sixth mass hydrogen, and in Earth’ s most in the helium, nitrogen. most the abundant Universe oxygen, It is is the present in 4 molecule in t he ball and stick model in Figure 13.1.2, we can see t hat carbon all forms most is bonded to four hydrogen atoms arranged in a tetrahedron around it. angle Organic between covalent molecules, bonds t herefore, is life and abundant element second by mass in The the bond of human body after oxygen. 109.5°. have ver y distinctive t hree-dimensional str uctures. When carbon Single bonds atoms bond wit h each ot her a variety of str uctures can form. Figure 13.1.2 Ball and stick model of methane Single a bonds carbon can atom leaves t hree ot her atoms. form shares ot her For between one pair electrons example, of adjacent per carbon et hane (C H 2 carbon atoms, represented by carbon electrons t he wit h atom ) has a atoms. anot her available single H bonds Double bonds a carbon leaves atom two can containing saturated form shares ot her two pairs For atoms, represented example, per et hene two two H H ) 6 single of adjacent electrons carbon (C H 2 by t he bonds between adjacent carbon compounds between electrons atoms. only Double as between This wit h (C known bond bonding H C C H 2 compounds for bond, atom. H et hane are single line: or atoms a 6 single H Organic In carbon ) atom has a carbon wit h atoms. anot her available double for bond In a double carbon bonding between bond, atom. wit h two This ot her carbon 4 lines: 227 Organic compounds Introduction (C H 2 chemistry C C H et hene organic H H or to H ) 4 Organic compounds containing one or more double bonds between adjacent carbon atoms Unbranched known chains butane (C of H 4 single bonds as unsaturated compounds chains Unbranched example, are carbon ) is an atoms of different unbranched chain of lengt hs four can carbon form. atoms For wit h 10 between adjacent atoms: H H H H H C C C C H H H H butane (C H H 4 Branched ) 10 chains Branched chains of carbon atoms of different lengt hs can form. For example, met hylpropane (C H 4 ) is a chain of t hree carbon atoms atom t he wit h t he four t h 10 branching off from t he middle H H atom carbon of chain: H H C C C H H H H C H H met hylpropane (C H 4 ) 10 Rings Rings of carbon atoms can form. For example, cyclohexane (C H 6 of six carbon ) is a ring 12 atoms: H H H H C C C H H H C H H H C C H H cyclohexane (C H 6 ) 12 The ability of carbon atoms to form covalent bonds wit h ot her carbon atoms forming It is t he long chains impor tant drawings to note above Functional compounds a par ticular two of wit h each carbon t he atoms exception molecule in is known of t he as ball catenation. and two-dimensions stick models, only. groups group between rings t hat, show Organic is and contain atom, carbon a atoms one or more par ticular wit hin functional group t he of groups . atoms, molecule. or The a A functional par ticular functional bond group determines t he chemical proper ties of t he compound containing it. Organic 228 Introduction to compounds on t he organic are chemistry classied functional into group Organic groups t hat t hey known contain as homologous (see Unit 13.2). Table 13.1.1. series Some based of T able groups we will be studying are given in Functional groups t he Name functional 13.1.1 compounds of Structure functional group of functional group carbon–carbon The simplest organic compounds t hat you will be studying can be t hought of single bond C as ● being t he composed of hydrocarbon two C par ts: part which is composed of carbon and hydrogen carbon–carbon atoms ● t he only. double functional bond group hydroxyl group O H or Formulae of The of organic carboxyl formulae organic OH compounds compounds can be written in a variety of group O different C ways. Using butanoic acid as an example, t he most common met hods are: O ● The molecular each for element butanoic formula . in one acid is atoms ● The chemistr y are fully joined H compound O 8 since form (Figure t he . of compound. number formulae The of atoms molecular have a limited don’t give any information about formula use or t he how group O t he C formula . atoms COOH in molecule. structural are This shows arranged in in one H of ester t he how t he Molecular actual 2 t hey wit hin d isplayed diagrammatic shows molecule C 4 organic This or two-dimensional molecule of O COO t he 13.1.3). H H H O The fully displayed formula has t he limitation t hat it is a two-dimensional C C C drawing of a t hree-dimensional molecule, i.e. t he molecule is straightened out and t he actual attened. The molecule ball in and stick model t hree-dimensions. in Figure However, 13.1.4 you represents would not H required ● The to draw condensed arrangement t hat t he shown of nature wit hout t his. atoms and separately bonded to it. in The formula . one position actually written Figure 13.1.3 formula structural and molecule of in t he sequence, t he followed CH 3 CH 2 t he sequence compound of t he molecule. str uctural CH of shows attachment drawing condensed This Each by formula in t he for carbon ot her a of may atoms t he be and shor tened total molecule, fur t her number of by atoms is t hat acid are is: COOH Figure 13.1.4 How 2 What is a 3 What is the many Ball and stick model of showing t he atoms in total t he number of hydrocarbon acid carbon par t of i.e. H 3 1 structural acid 2 hydrogen C Summary displayed is butanoic This Fully butanoic way group atom butanoic H and such functional H be COOH 7 questions bonds can a carbon atom form with other atoms? hydrocarbon? difference between a saturated and an unsaturated organic compound? 4 What 5 Give and is a the functional condensed molecular group? structural formula of formula H H H H H C C C C H H H H this H compound: H 229 Homologous series Introduction Objectives By the end be able of B13.2 this topic you organic chemistry series will We can classif y compounds into groups based on t he functional group which to: t hey dene ● Homologous to the term contain. These groups are known as homologous series homologous series list ● of the a the given write ● of a general series formula homologous the formulae given Characteristics of The a of characteristics for straight of common determine series to chain the All members of t he series ● All members of the series ● Each from its ● compound name or member dene All members isomer given below. have t he same functional group. can be represented by the same general formula. series by differs relative from t he molecular member mass of before or af ter it by a 14. of a series as molecule increases. All molar members as of a possess mass series similar increases, show a i.e. chemical as gradual t heir molar mass melting point, boiling t he change increases. point In proper ties. number in t heir general, and of density as Reactivity carbon atoms per physical molar mass increase. and ● structural t he and decreases increases, structural of group proper ties formula ● are 2 members ● belongs series series homologous a homologous ● homologous which of a series ● series members homologous name the homologous series CH ● a characteristics homologous write ● general All members of a homologous series can be prepared by t he same general isomerism met hod. explain ● can be name ● how structural isomers formed branched chain Naming straight Because t he chain members of a homologous series isomers. of great variety of organic compounds, a set of r ules for naming t hese compounds has been developed by t he International Union of Pure and Applied Key ! is fact Chemistr y known as nomenclature A of homologous organic series compounds is a that group is no the same is ambiguity to as ensure to The process nomenclature . t hat which when chemical a of naming The main person reads compound it chemical function a compounds of chemical chemical name t here refers. all The possess (IUPAC). chemical functional names of straight chain members of a homologous series consist of group. two ● par ts: The rst present par t, in compounds ● or one prex, is molecule. up to ten related Table carbon to t he 13.2.1 total gives number t he of carbon prexes for atoms organic atoms. The second part which is based on the homologous series to which the compound belongs and relates to the functional group present. For example, if the compound belongs to the alkane series, its name ends in ‘-ane’. T otal T able 13.2.1 organic Prexes for number of carbon atoms Prefix 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec- naming compounds Table 13.2.2 gives t he main homologous series you will be studying, toget her wit h 230 an example of a member of each series containing two carbon atoms. Introduction T able Name to 13.2.2 organic The main chemistry Homologous homologous series series of Example General Functional group Condensed homologous Naming formula containing C carbon–carbon H n Structural formula formula carbon Alkane two present series single bond prefix atoms ethane ane CH 2n2 H CH 3 H 3 or C C C C H H 2 6 H Alkene C H n carbon–carbon double bond prefix 2n ethene ene CH CH 2 H H H H H 2 or C H 2 Alcohol or C H n hydroxyl OH group prefix ethanol anol 4 CH 2n1 CH 3 alkanol O H OH H 2 H or C OH C H 2 OH 5 H Alkanoic acid or C H n carboxyl COOH group prefix anoic ethanoic acid acid CH COOH H 3 2n1 H O carboxylic acid O C C H O H O H COOH Determining homologous The homologous series t hat you are name of out t he deduce given t he formula of its if name a a compound t he compound compound you series have if been you belongs or have given its its to can formula. been given be determined You its can name also or if work you can from t he formula. Examples ● To determine name, par t look of t he at t he homologous t he name second is ‘-ene’ ser ies par t of t hen t hat t he t he a compound name. For compound belongs example, belongs if to to t he t he second alkene series. ● To work out determine t he prex butane of t hen carbon formula t he t he t he it name. belongs atoms. of t he homologous The For to to alkane formula from which example, t he general compound series if t he series. of an it t he name, belongs name Its of t he prex alkane is and is butane must be C ‘but-’ To determine formula, t he look t he functional belongs to t he so it The has four formula 2n2 10 homologous and . at is H 4 ● look compound H C n of rst t hen see group what present alcohol ser ies t hat functional is t he a compound group O H is belongs present. group, For t hen to from example, t he t he if ✔ It series. is can ● To deter mine deter mine and t hen t he t he look name of t he homologous at t he tot al compound ser ies to number from whic h of t he t he carbon for mula, compound example, if t he for mula of t he atoms compound is C in H t he 2 very to t he alkanoic acid ser ies so t he second be ‘-anoic acid’. It has a tot al of t hree if its that name so t he pre x must be ‘prop-’. The name you you have of a been or you can given deduce t hen name of a compound if you it 5 of t he been atoms in of t he given the formula. T o do name of these, you must be able to t he compound the homologous series to is which propanoic that formula molecule. identify molecule the belongs COOH par t carbon out compound either must important work have belongs tip r st the For Exam compound the compound belongs. acid. 231 Homologous series Introduction Structural ! Key organic str uctural Structural isomers compounds isomers which formula compounds formulae, have the each element, but t he same molecules molecular contain t he formula same but different number of but t hese atoms are bonded toget her atoms differently. are called structural isomers and t his phenomenon These is called isomerism formulae. Str uctural isomers homologous Key If ● fact t hey Structural isomerism occurrence of compounds two with is the or more the same have organic contain If ● formula but ver y bonded t hey can belong to t he same homologous series or to different series. homologous t he same series. similar contain functional Because chemical differently t hey different t hey group have proper ties, have must same physical groups t hey belong functional however, different functional t hey t he because to t he group, t heir same t hey atoms are proper ties. belong to different different homologous structural have t heir different structural molecular i.e. same compounds ! chemistry are of structural organic fact Many molecular to series. Because of t his t hey have different chemical and formulae. physical Each different Str uctural by proper ties. t he isomers chain functional Forming Carbon str uctural of group chains straight carbon has chain atoms a different name. molecules becoming can branched be or formed by t he in two position ways, of t he atoms. For changing. isomers example, of isomer by can pentane branching have (C side H 5 ) branches has t hree of one isomers, or more one of carbon which is t he straight 12 chain isomer and two of which are formed by branching of t he carbon chain as is shown given in Figure below t he 13.2.1. The condensed str uctural formula of each H H C H H H C H H H H H C C C H C H H CH 3 Figure 13.2.1 Isomers of pentane H CH 2 Straight It is always twisted a CH 2 bent version C C C H H H H H H H C H CH CH 3 3 CH(CH 2 )CH 3 CH 3 note t hat t he when longest Care of t he straight of t he straight drawing t he continuous must c hain also be isomer. c hain isomer CH CH C(CH 3 Branched hor izontally . versions H C isomer to H H H compound, drawn H C H H H CH 2 chain impor tant organic is H CH isomer isomer. chain t aken For of CH 2 3 isomers str uctural c hain ) 3 of not to example, pentane for mula carbon draw t he and, of an atoms bent is or following t herefore, is incor rect: CH 3 2 CH 2 2 CH 3 Forming isomers by changing the position of the functional group The functional group is usually situated at t he right-hand end of t he molecule. However, 232 t he position of t he functional group can change. Introduction to organic chemistry Homologous series Examples Butene (C H 4 double ) has two isomers because t he position of t he carbon–carbon 8 bond can change as H H H shown in Figure 13.2.2. H H H H C C H C C C C H H H H H H Figure 13.2.2 Isomers of butene When drawing t he str uctural formulae of alkenes, t he carbon–carbon double H bond is always alkenes in Butanol Unit (C H 4 group ( drawn hor izontally. You will learn more about t he isomers C 14.2. OH) has two isomers because t he position of t he hydroxyl 9 OH) can H change as shown in Figure branched chain H C C H H H H H H H H C C O H 13.2.3. C Naming H of H isomers H H The side chains which branch off from t he longest chain of carbon atoms in a H molecule C H n known Alkyl as groups alkyl are groups. named by These adding groups t he have sufx t he ‘ -yl’ general to t he formula prex. Figure T able name t he of rst a branched par t chain indicates t he molecule number of is made t he up carbon of t hree Isomers of butanol atom to par ts: which t he is Naming alkyl groups of the Name attached alkyl t he 13.2.3 side Formula chain ● 13.2.3 2n1 The ● . are second par t is t he name of t he side chain, i.e. t he alkyl group – group CH methyl 3 ● t he t hird par t compound is derived belongs and from t he t he homologous longest series continuous to chain which of t he carbon – C – C 2 atoms. 3 To name should 1) be Find branched chain molecules, t herefore, t he following four H ethyl 5 H propyl 7 steps used. the number of the carbon atom to which the side chain is attached. 2) Determine t he name 3) Determine t he homologous and 4) t he total number carbon chain. Put information t he separating of t he t he of from number side chain. series carbon steps from 1) t he to which atoms to 3) name in t he t he toget her by a compound longest to belongs continuous name t he compound, hyphen. Examples 1 Determine t he name of t he following branched chain isomer of C H 5 H H C H H C C H 12 H H C H C H 233 Homologous series Introduction 1) Find t he Number t hat longest t he t he side continuous carbon chain atoms is at chain from t he lowest H H C H of t he carbon end to organic atoms closest to in chemistry t he t he str ucture. side chain so number: H H C C H H H C H 2) The side chain is attached The side chain is an methyl 3) The The 4) 2 to t he longest name The is, has only alkane group atom wit h one number carbon 2 atom. It is t he of t he t he carbon–carbon bonds. Therefore, it carbon chain has four carbon atoms in it. Its butane compound name single series. continuous t herefore, name Determine carbon group. compound belongs alkyl to of t he is 2-methylbutane following branched chain isomer of C H 6 H H C H H C C H 14 H H C H C H 1) Number t hat t he t he carbon atoms side chains are at in t he H t he longest lowest H C continuous carbon chain so numbers: H H C C H H H C H C H There are two side chains. One is attached to carbon atom number 2 and one is attached to carbon atom number 3. When writing t he name we write 2,3- because bot h side chains are t he same, i.e. CH 3 2) Bot h t he ‘di-’, 234 side chains met hyl i.e. we are group write alkyl and groups because d imethyl wit h t here one are carbon two of atom. t hem we They use are t he bot h prex Introduction 3) The to compound belongs The 3 to t he longest name 4) organic The is, has t he t he carbon–carbon bonds. Therefore, it carbon chain has four carbon atoms in it. Its butane compound name single series series. continuous of Homologous only alkane t herefore, name Determine chemistry of t he is 2,3-d imethylbutane following branched chain isomer of C H 4 8 H H H H H H 1) Number t hat t he t he carbon side chain atoms is at t he in t he longest lowest continuous carbon chain so number: H H H H H H The 2) side chain is attached to carbon The side chain is an alkyl group wit h atom number 2 one carbon atom. It is t he methyl group. 3) The compound has a carbon–carbon double bond; t herefore, it belongs to t he The longest name 4) The Ot her alkene is, series. continuous t herefore, name of examples t he are carbon chain has three carbon atoms in it. Its propene compound given is 2-methylpropene below: H C H H H H C C C C H H H H CH H C CH 3 CH 2 CH 2 2 3 H CH 2 H C CH 3 H 3-ethylhexane 2,2,3-trimethylpentane 235 Homologous series Summary 1 Give four 2 Give the 3 Introduction characteristics name an alcohol c an alkanoic a C the and with of a homologous condensed one acid following carbon with three b 6 4 Dene 5 Name formula structural series. of each of the following atom carbon C H 4 the chemistry atoms straight chain isomers: b an alkene with four carbon atoms d an alkane with two carbon atoms. c CH compounds: H 3 organic questions a Name to OH 9 d C 4 H 2 COOH 5 isomerism. following isomers: a H H C H H H C C C CH b 3 H CH CH 3 H H H C CH 3 3 H CH 3 C H 6 Draw the structural formula of 2,3-dimethylhexane. Key concepts ● Organic ● All many A carbon ● Carbon ot her and A atoms carbon ● ● The a two based on a t he are can represented two par ts, carbon of rst atoms functional wit h Each t he t he isomers t he t he or and straight a ot her and atoms. double chains, par ticular atoms wit hin chemical by condensed into group all same bonds wit h branched a t hat chains molecular known of atoms or a molecule. proper ties t hey general group t he str uctural groups possess members prex, molecule is t he same compounds chain t he different a series chain isomerism Str uctural of by par t, in The by hydrogen of t he formula, a fully formula. as homologous contain. t he same formula functional and have group, cer tain of which and a is t he homologous related second to series t he par t total which consist of number is related group. formulae. position contain characteristics. straight t he Structural single atom, t he classied homologous common names also wit h represented or functional of The compounds Most bonds form carbon be formula compounds be form determines Members all to also par ticular can ways, 236 group str uctural compounds ● is between compound t he ● group An of ● can it. Organic organic carbon. covalent ability They containing organic of str uctures. functional ot her ● t he four compound series ● study contain form have bond displayed ● can atoms. functional par ticular t he oxygen. atom ringed is compounds contain ● ● chemistr y organic of of occurrence molecular are known of two formula as or but more organic different structural straight chain molecules can carbon atoms becoming branched functional str uctural group isomer be changing. has a different str uctural isomers name. formed or in by two t he to Introduction to organic chemistry Practice 6 A compound has t he formula C H 3 Practice exam-style 1 Members of a I have similar have t he chemical same series: proper ties molecular differ from The name of 7 A et hanoic B propanoic C propanol D butanoic is: acid succeeding acid acid formula 7 III compound questions homologous II COOH. questions questions t he Multiple-choice exam-style members by Which of t he following is t he correct formula of CH 2 pentanol? A I and II B I and III only A C B C C C H 5 H 5 C II and III I, II and 1 1 H OH 12 III D C H 5 2 OH only 5 D OH 10 only To which A alkanes homologous B alkenes C alcohols D alkanoic series does C H 4 OH 13 belong? 8 8 What is t he name of t he following isomer? CH 3 3 CH acid Isomers always: A have t he B have similar CH 3 3 CH CH 3 C D 4 have have Which same similar chemical physical different of t he functional A 2,2,3-trimet hylbutane B 2,3,3-trimet hylbutane proper ties proper ties str uctural following 3 group formulae formulae do not C 2,3,3-trimet hylheptane D 2,2,3-trimet hylheptane represent isomers? I II H C H H H Structured H C H H 9 H a The question fully displayed compounds C str uctural formulae of ve organic H C H H C C H H are given below: H H H H H H H H C H H C C H H H H H H H A III H IV H B H H O H C H H C H C H H H O H H C C C H H C H C H H H C H A I and II B I and III H H H H D H H H H H C C C C C H H H H H H H H E C II D III and III and IV i) 5 The general A C B C H n C C D C alkane Which compounds homologous is: ii) Name t he belong to t he same series? homologous (1 series to which mark) compounds you named in a i) belong t he and reason for placing t hem in t he same give a series. 2n2 H n an 2n1 H n of 2n H n formula 2n3 (2 marks) 237 Practice exam-style questions iii) Give t he names iv) Give t he name Introduction of compounds B and D (2 formula carbon same of t he atoms and fully displayed compound in its homologous which molecule series as has and marks) str uctural FOUR belongs to (2 v) Draw t he isomers isomer b Name t he following t he fully fully of displayed compound E. you have str uctures Give of any name series to str uctural which belongs formula EACH and of marks) T WO of (4 compounds displayed t he drawn. homologous organic t he compound D EACH marks) of t he draw EACH compound: i) ii) propene 2,2-dimet hylpentane. (4 Total Extended 10 a response Explain fully marks) 15 marks question how t he electronic conguration of 12 t he carbon atom, C, can account for t he fact t hat 6 carbon can form such a wide variety of organic compounds. b Organic (5 compounds homologous i) List can be classied series. FOUR characteristics of a homologous (4 ii) A compound has t he formula H C 2 – To which homologous compound – c i) Give What t he do Explain t he why same chemical physical COOH 5 does t he of t he compound. understand by t he term (2 (2 str uctural homologous proper ties, proper ties. isomers series but of have t hey marks) ‘str uctural marks) members ver y have of similar different (2 Total 238 series. marks) belong? name you series isomerism’? ii) marks) into marks) 15 marks to organic chemistry Hydrocarbons – alkanes B14 and alkenes Hydrocarbons are organic compounds which consist Objectives By the be able end of this topic you entirely will of carbon hydrocarbons identify ● and hydrogen. The majority of to: natural petroleum as gas and natural of sources dead are marine naturally organisms formed under by the the decomposition effects of high of pressures, heat and converting them bacteria deep under the sea, hydrocarbons describe ● the distillation fractional of the main fractions the oily liquids or gases. Hydrocarbons petroleum are list ● into uses of obtained fractional one of the most important energy sources on Earth. the from distillation of B14.1 Sources Sources of and extraction of hydrocarbons petroleum ● describe the thermal catalytic cracking of and alkanes. hydrocarbons Hydrocarbons atoms only. hydrocarbons. under t he organic or Natural compounds include Naturally Ear t h’s petroleum, drilling are They oil, where and t he exist gaseous in bot h form, carbon alkenes hydrocarbons t hey t he containing alkanes, occurring surface cr ude t he are t he as hydrogen t he extracted liquid known and and from form, natural ringed deep known gas rig Natural gas is a mixture of four alkanes: met hane (CH ), et hane (C 4 impervious H 2 ), 6 rock propane (C H 3 natural as gas. ) and butane (C 8 H 4 ). Met hane makes up about 80% 10 gas of natural gas and t he ot her t hree hydrocarbons make up 20%. The petroleum propane and butane are removed before natural gas is sold commercially. water Commercial impervious et hane. Figure 14.1.1 Diagram showing of petroleum and natural be This the surface of the natural piped t herefore, is a mixture of met hane and to gas homes can and t hen used be for used to cooking generate and electricity, heating, or it can it be gas liqueed under gas, the can occurrence natural rock under pressure to produce liqueed natural gas, or LNG. LNG Earth is Af ter and used in removal, used ‘bottled to place t he and petrol propane produce gas’ of of vehicles and liqueed many in you butane petroleum use it for in some are also gas, or countries, liqueed LPG. LPG e.g. Germany. under is also pressure known as cooking. Petroleum ? Did you know? Petroleum is an hydrocarbons, Petroleum renewable the is a finite, resource existing supplies crust will be have once which and is a complex ringed mixture hydrocarbons. of The many smallest within gaseous hydrocarbons t he liquid. been and t he largest solid hydrocarbons are dissolved in all oily The mixture can contain hydrocarbons wit h as many as 70 must be the used more carbon atoms in t heir molecules. To be useful, petroleum they separated not liquid alkanes non- and or Earth’ s oily mainly into its different components, or fractions, as t hey are called. This replaced. is done by fractional Fractional When it is have is to be heated t he removed Before it removed. to lower distillation rst impurities. about par t d istillation of can from be Once 400 °C a of at an and under t he liquid fractionating ground, into impurities t he rener y. petroleum separated t he oil its have and tower . petroleum components, been vapour The contains t hese removed, t he produced fraction are which many impurities petroleum piped remains into as a 239 Sources and extraction of hydrocarbons refinery bubble Hydrocarbons viscous gas liquid at 400 °C sinks to t he bottom of t he – alkanes tower and and is alkenes tapped off caps forming bottled bitumen or asphalt. gas 25 °C and chemicals The petrol (gasoline) petrol tray kerosene jet oil (paraffin) vapours larger hydrocarbons caps in wit h t he t he temperature t he lower lower tower of wit h par t of boiling and t he t he pass tower higher t he tower, points rise t hrough decreases boiling and series points t hose fur t her a and of upwards. of bubble The condense t he on smaller condense at caps vapours t he and of t he bubble hydrocarbons higher levels. The fuel tower. diesel produced Gases diesel oil t hat tapped off from t he trays at t he different do not condense at t he temperatures renery gas at of t he tower. wit hin levels t he in t he as t he top tower are fuel Each fuel are oil removed crude up The liquids heated rise trays. oil, and fraction boiling lubricating waxes Petrol is points is a mixture wit hin tapped off a of hydrocarbons specic from t he temperature top trays, of similar range kerosene as molecular shown and in diesel size Table oil and 14.1.1. are tapped are tapped oil off from t he off from t he middle trays and fuel oil, lubricating t he fractions oil and waxes 400 °C fuel for ships lower trays. bitumen Table 14.1.1 distillation roads T able Name of Refinery Petrol 14.1.1 Uses of the fraction Diesel different fractions Number carbon below (paraffin Boiling gas oil roofing point/°C obtained of 14.1.2 from and oil, lubricating oil Fuel for domestic for internal 170–250 10–14 Fuel for cooking, 250–350 14–20 Fuel for diesel 350–400 18–30 Fuel waxes oils into are Lubricating Waxes above 400 more than 30 Road are ? you Lake natural world. Located the lake is over 75 m a tourist in T rinidad deposit in covers e.g. heating, engines, smaller used oils as are used are obtained by fractional uses. petroleum cooking to kerosene e.g. and engines, cars, heating. e.g. lamps lorries, cars and T o and jet buses, manufacture light aircraft. engines. trains, a variety As Cracked trucks and of petrochemicals. solvents. into smaller hydrocarbons. generators. hydrocarbons. fuel used for to make factory boilers, lubricate polishing ships mechanical waxes, wax and power parts paper, in stations. machinery petroleum and jelly vehicles. and candles. Roofing. hydrocarbons petroleum problems Pitch largest of which t heir know? When The use, combustion surfacing. Cracking Did distillation of Uses Fuel Bitumen some atoms 1–4 oil) and petroleum Cracked Fuel Fractional 5–10 oil 25 Figure petroleum 25–170 (gasoline) Kerosene and summarises of of is deep. attraction 40 The and is in ● distilled into its different fractions, two arise. The fractions which contain the smaller hydrocarbon molecules, e.g. petrol, are in much greater demand in today’s world than the fractions and serves also the T rinidad, hectares lake fractionally the asphalt south-west about is containing the larger hydrocarbon molecules, e.g. diesel oil. However, the as distillation of petroleum produces an excess of the larger hydrocarbons mined and insufcient of the smaller ones to meet modern demands. for its asphalt. Sir Walter Raleigh was ● introduced guides in to the 1595 recognised its lake and by he Most of t he carbon single his potential ships with release energy, and the we to use Bot h fact t hese is long-chain the process by hydrocarbons which are into known as shorter-chain are fairly manufacture ever y day, which t he t hey have petroleum and, unreactive. great need To variety to be apar t be have from used of ot her conver ted carbon–carbon can molecules only carbon– burning in t he in air to petrochemical organic be into overcome smaller, double by more into compounds more reactive bonds. breaking useful down molecules t he by a larger process cracking can be carried hydrocarbons. catalytic 240 from molecules broken Cracking down t hey problems hydrocarbon Cracking obtained t heir started compounds Key in tar . t hat ! bonds immediately industr y caulking hydrocarbons Amerindian cracking out in one of two ways, thermal cracking and Hydrocarbons Thermal During larger to thermal alkanes break. fairly alkanes and alkenes Sources cracking into Thermal are high temperatures smaller ones. cracking broken of Under an in a fairly propor tion of alkene above t hese alkane up of 700 °C conditions, molecule random and way molecules. t he always so For pressures long-chain forms thermal a octane t hree of H H H H H H H H H H H H C C C C C C C C C C C C H H H H H H H H H H H H H t hese are illustrated in Figure to 70 alkane shor ter-chain cracking example, up always (C H 8 ways, and extraction of hydrocarbons cracking molecules a – atmospheres molecules alkane gives ) can a be are used vibrate and at of cracked in break strongly least mixture to one t he enough alkene. The products containing a of variety different 18 14.1.3. H H C C H H H C H H octane C H H H pentane H 8 C 18 H H H H H H H propene H 5 H C 12 H 3 H H H H 6 H H C C C C C C C C C C C H H H H H H H H H H H H H C C H H C C H H octane C H butane H 8 C 18 butene H 4 C 10 H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H H 4 H H C C 8 H H H C H H octane C Figure 14.1.3 Catalytic C 18 Thermal cracking of H H propene H 3 H H propane H 8 H C 8 et hene H 3 C 6 H 2 4 octane cracking During catalytic cracking t he long-chain alkanes are heated to temperatures of about catalysts dioxide of 500 °C are known petrol and Natural at fairly normally as raw gas low pressures synt hetic zeolites. Catalytic materials and for oil in in mixtures t he t he of presence cracking is t he petrochemical the of aluminium most a catalyst. oxide and impor tant The silicon source industr y. Caribbean The Republic of Trinidad and Tobago is t he leading Caribbean producer of oil and natural gas, wit h t hese accounting for about 40% of gross domestic product and a large percentage of expor ts. The oil rener y in Trinidad is found at Pointe-à-Pierre and accounts Figure 14.1.4 Pointe-à-Pierre oil for renery most of t he prosperity domestically. ammonia More plants Summary 1 Name two of t han and to t he region. two-t hirds t he All of electricity t he it is natural piped to gas produced met hanol, is used urea and Did ? sector. List the natural main The Pointe-à-Pierre only oil sources of with a refinery wildlife uses of three of of the fractions obtained from the Wild 4 Describe what is meant and Give formulae catalytic and by ‘cracking’ cracking names of of and distinguish between thermal alkanes. two products which could be and cracking reserve. Fowl to The T rust environmental pentane (C H 5 to is is the co-exist Pointe- a not-for- organisation environmental conservation waterfowl. It and 25 about of education wetlands consists of hectares two of and lakes land within obtained the by refinery world petroleum. cracking the oil the fractional dedicated 3 in hydrocarbons. profit distillation know? questions à-Pierre 2 you oil refinery . ). 12 241 Alkanes: C H n Hydrocarbons 2n B14.2 Objectives Alkanes: C the end be able of this topic you form a homologous series wit h t he general formula C H n Alkanes the alkenes 2n 2 to: give and will Alkanes ● alkanes H n By – 2 names and are saturated hydrocarbons . This means t hat t hey 2n 2 contain only structural single bonds between carbon atoms. Alkanes are relatively unreactive because formulae of unbranched and of branched alkanes up to t he t he carbon ● ● the to presence describe reaction ● carbon–carbon single reactivity the of describe of of alkanes single Alkanes bonds combustion series given substitution named by using t he prex in do not Figure show str uctural names and in number of formulae are ) et hane H C C C H H (C H 2 ) H H propane H (CH H met hane H to H H alkanes H (C 6 H 3 ) 8 properties ● Their H C C H 4 their total of t he H C H undergo reactions uses indicates the alkanes H why H relate bonds reactions halogens explain with which isomerism. alkanes substitution ● carbon–hydrogen 14.2.1. ● and carbon atoms in t he molecule and t he sufx ‘ -ane’. The rst t hree alkanes in t he alkanes are H of bonds molecules. atoms relate the strong six describe the production Alkanes biogas. from page H H H H Figure 14.2.1 Structural formulae of the rst three alkanes of H H 4 C C C C H H H H 233 14.2.4 (C wit h t heir for show ), four or ability more to naming t he pentane carbon form atoms branched branched chain names and str uctural (C and hexane 10 H 5 ) show Figures formulae H 6 isomerism Following isomers, (C 12 str uctural chains. of t he steps 1) 14.2.2, resulting to 4) 14.2.3 isomers of on and butane ). 14 H H H C H pentane H H H H H H H H C C C C H H H H H H butane C H H H H C H H H H C C C H C C Figure 14.2.2 2-met hylpropane The structural isomers of butane (C H 4 ) 10 H H H H H H 2-met hylbutane H H H H H H H C C C C C H H H H H H C H H H C C C C H H H H H H C H H H H C H H H H H C H hexane 2-met hylpentane H H C H H H C H H H H C H H H H H 2,2-dimet hylpropane C H Figure 14.2.3 pentane (C The H 5 structural isomers H H H C C Figure H ) 12 hexane 14.2.4 (C H 6 The C structural isomers C C C H H C C C C H H of C H of H H H H H H H H H H H H C H H H H H H ) 14 3-met hylpentane 2,2-dimet hylbutane The melting and boiling points of t he alkanes 2,3-dimet hylbutane increase wit h an increase in t he size of t he molecules, i.e. wit h an increase in molar mass. The rst four alkanes, met hane, 242 et hane, propane and butane, are gases at room temperature. Hydrocarbons – alkanes and alkenes Alkanes: C H n 2n 2 Alkanes wit h 5 to 16 carbon atoms in t heir molecules are liquids, while t hose wit h 17 or more carbon atoms are solids. Alkanes become less volatile as t heir molecular size Did ? namely are relatively combustion, described in know? increases. The Alkanes you Unit unreactive and substitution 14.1. We will only and now undergo cracking. look at t he a The few types cracking ot her two of of reaction, alkanes was reactions. prefix reactions of when chain isomers. called alkanes used name isomer Combustion ‘normal’ sometimes of naming The butane normal Similarly, or the ‘n-’ before is the the straight straight is chain sometimes butane straight or n-butane. chain isomer Alkanes burn ver y easily in air or oxygen. The reaction is exot hermic producing of large amounts fuels. The oxygen supply. combustion, When of heat products if f it alkanes energy, of t he is t he oxygen limited, burn which t hey is why combustion supply t hey do is wit h a are used extensively var y depending plentiful, t hey undergo undergo so alkanes reaction incomplete clear blue on as remains to to carbon give t he dioxide ame a or carbon yellow, or a ver y low Complete soot content. combustion of Alkanes are and because no appearance. regarded as called normal n-pentane. complete t he ratio unreacted The ame, ✔ Exam tip It important that of is clean you can fully displayed structural and names unbranched give the formulae carbon of and t herefore, branched has be combustion. ame monoxide smoky pentane can t he carbon to hydrogen atoms in t he molecules is low. All t he carbon is t herefore conver ted pentane burning chain isomers of any fuels. alkane containing atoms if you are up to given six its carbon molecular alkanes formula. When t he undergo of oxygen supply complete alkanes are combustion CH of (g) H 2 carbon met hane 2O 4 2C plentiful, combustion . always is and The (g) (g) 7O is CO 2 6 products dioxide et hane alkanes and 2H 2 (g) t he in as t he completely, complete steam. O(g) H t hey combustion The following i.e. complete ✔ equations: Exam Balancing ve (g) 6H 2 combustion of t he oxygen combustion. carbon The O(g) H is shown supply and in is of Begin balancing by followed as incomplete steam. following alkanes The undergo combustion incomplete incomplete of alkanes are combustion of until last. and the you have atoms equation: Leave (g) 3O 4 by (g) 2CO(g) 4H 2 O(g) H the After the be difficult. the carbon hydrogen oxygen balancing hydrogen, on an odd the coefficient 2CH can ve 2 limited, t he water t he alkanes alkanes products monoxide met hane combustion of atoms. When the reactions atoms Incomplete tip 2 4CO 2 of water shown (g) burn if you of multiply (including the carbon find number right, atoms the that oxygen each unwritten ve 2 1) by 2, before balancing the oxygen. Substitution reactions Under conditions, t he right molecules, hydrogen t he carbon atoms of alkanes atoms possible. alkanes are When a can react bonded reaction to wit h t he occurs halogens. maximum between an n alkane number alkane of and a halogen, t he hydrogen atoms are replaced by halogen atoms. These reactions are of known t he time. as They Energy in works takes place ● Light ● The form t he in atoms also reactions t he of light required but and is of ten t he speed brighter of t he halogen Fluorine, odine being does for sunlight t he of t he – not is t he t he t he more most react atoms one A take hydrogen reactions sufcient. reaction light, t he t he halogen molecules, halogenation – reaction. because alkane called stages reactivity in be best, intensity reaction. rapid ● can t he light t he substitution hydrogen to occur. depends on three t he reaction. reactive t he halogen, wit h halogen, alkanes to has any place at a Ultraviolet substitution faster reactive t he atom reaction factors. t he t he faster most extent. The reactivity of the alkane – the smaller the alkane molecule, the faster the 243 Alkanes: C H n Hydrocarbons 2n – alkanes and alkenes 2 reaction. This No is Methane, being the smallest molecule, has the most rapid reaction. seen in reaction light a slow t he reaction occurs in t he substitution one between dark. n reaction replaced by chlorine produces chloromet hane bright occurs atom and met hane at a light in The chloride H reaction is rapid. one hydrogen rst stage of n atom t he dim being reaction gas: Cl UV H chlorine. t he stages, time. hydrogen and C H light H H H H met hane chlorine monochloromet hane hydrogen chloride or U CH (g) Cl 4 light (g) CH 2 Cl(g) HCl(g) 3 As t he reaction continues, t he hydrogen atoms are replaced one by one until tetrachloromet hane (CCl ) is produced: 4 U CH Cl(g) Cl 3 light CH (g) Cl 2 2 (l) HCl(g) 2 dichloromet hane U CH Cl 2 (l) Cl 2 light CHCl (g) (l) HCl(g) 3 2 trichloromet hane Did ? you know? U CHCl (l) Cl 3 Trichloromethane (or light CCl (g) (l) HCl(g) 4 2 chloroform) tetrachloromet hane and tetrachloromethane carbon tetrachloride) are (or both The volatile, At one used ‘sweet’ time, as a because smelling trichloromethane general the reaction can was be U CH anaesthetic vapours overall summarised by t he following (g) 4Cl 4 light (g) CCl 2 (l) 4HCl(g) 4 depress The products of t he halogenations of alkanes are called the nervous system, tetrachloromethane in fire extinguishers equation: liquids. haloalkanes or alkyl and was and used as halides a The reaction of bromine vapour or bromine solution wit h met hane is similar, solvent in dry cleaning. Their uses but were discontinued when it since slowly. discovered how toxic they bromine is less reactive t han chlorine, t he reaction proceeds more was Once again, energy in t he form of ultraviolet light is required for t he of t he both reaction to proceed. were. During t he reaction between bromine and any alkane, t he colour bromine slowly fades from red-brown to colourless. The rst step in t he reaction between et hane H and bromine is shown t he equation H UV H in C C H H et hane Br C C H H light H bromine H below: H monobromoet hane hydrogen bromide 244 Hydrocarbons – alkanes and alkenes Alkanes: C H n Uses of of alkanes, related t heir Alkanes are burn – t hey release t he t hey – t hey to a for several amount of low an a variety given of uses. The main uses of below. reasons: of energy alkane fuels, soot easily have are ignited burning ver y used dissolve heptane parafn Biogas as is an i.e. when t hey undergo exot hermic t hey burn combustion, reaction wit h a clear blue ame content liquids in containers, which makes t hem easy glues a as solvents. variety used and of as ot her are non-polar non-polar solvents ot her solid Alkanes in t he adhesives, solutes. molecules For manufacture petroleum jelly t herefore example, of is hexane fast-dr ying oil dissolved in alkane. production of any a are wax, refers absence crop fuels when large stored are lacquers, from 2 transpor t. t hey Biogas a clean has are Alkanes and as easily alkanes proper ties, combustion are which t heir used t hey – ● proper ties, to – i.e. alkanes Because ● 2n to a gas oxygen. organic residues, t produced is matter sewage, a by the renewable including garden breakdown energy manure waste, food of source and other waste organic which and matter can farmyard organic be in the produced animal waste waste, from food industries. The organic occurring oxygen waste is anaerobic into biogas. put into a sealed microorganisms, Biogas is a anaerobic e.g. mixture of bacteria, digester digest approximately it where in 60% the naturally absence methane, of 40% carbon dioxide and traces of other contaminant gases such as hydrogen sulde. Summary The exact composition depends on the nature of the original organic matter. Biogas can can be or it be by removal used directly conver ted to as a fuel almost to pure provide heat met hane, and of ten generate called electricity 1 Give the names t he ot her gases. This biomet hane can t hen be piped to natural gas or liqueed under pressure to produce liqueed natural for use in vehicles designed to r un on lef tover indigestible material and structural isomers Write a balanced dead microorganisms, known can t hen be used as a fer tiliser. The production of biogas on non-renewable fossil fuels, equation show the complete recycles soil nutrients and of butane. reduces 3 demands formulae hexane. as combustion d igestate, of LNG. to The three gas 2 (LNG) fully homes of wit h and biomethane, displayed of questions Propane reacts with chlorine reduces gas. t he amount of waste going to garbage dumps and landlls. a What condition necessary to slurry and manure b for is the reaction occur? What is the name given to power gas grid this c anaerobic biogas food Use of reaction? structural formulae to biomethane digester show the rst step in the reaction. and amenity type waste d Name rst transport the step products in the of the reaction. fuel digestate crops and residues 4 Explain why the main use of heat alkanes Figure 14.2.5 Production of is as fuels. biogas 245 Alkenes: C H n Hydrocarbons B14.3 Objectives Alkenes: C the be able ● end of recognise give you the alkenes of a form Alkenes the names of a homologous series up and to six presence describe are unsaturated C the of of a atoms alkenes Alkenes carbon carbon– t he bond are series given named atoms in do in not Figure by t he show H Their bond total rst names number two and alkenes formulae of in are H H H C H with the hydrogen, hydrogen H H (C H ) propene (C 4 H 3 ) 6 the Figure 14.3.1 Structural formulae of the rst two alkenes halides Alkenes wit h four or more carbon atoms show str uctural isomerism. Str uctural reactions to which distinguish and the double carbon–carbon reactions water alkane one t he The undergo an indicates ‘ -ene’. H C C 2 used isomerism. H et hene be sufx addition describe which t he alkenes describe halogens, contain 2n C prex and str uctural H alkenes They why reactions their C combustion alkenes addition relate formula 14.3.1. explain t he of using molecule C C ● general bond: H and t he hydrocarbons . structural carbon reactivity double reaction ● wit h unbranched to of 2n between two carbon atoms, i.e. t heir functional group is t he double the the by carbon–carbon relate carbon ● alkenes will bond alkenes ● and n formulae ● topic Alkenes double ● this to: presence ● alkanes H n By – 2n an uses isomers can between ● alkene of alkenes t he of alkenes change position to of however, in result from position t he t hat of t he t he functional carbon–carbon t he bond must following: double always group, bond be (it i.e. is t he change impor tant to in note, horizontal) properties. ● branching When H H C C H H ● number t he molecule. isomers carbon of alkenes: atoms in t he longest chain from t he end closest to H C C t he double bond so t hat t he double bond is closest to t he lowest number and indicate t he position of t he double bond in t he name using t he H ● but-1-ene (or naming t he H H of lowest possible follow steps 1) number to 4) on page 233 for naming branched chain isomers. 1-butene) Using H H H H H r ules above, t he str uctures H 4 H C C C C H H t he branched isomers of butene (C isomers of hexene (C H 6 ) are and names ) and pentene (C 8 of H 5 given in Figures 14.3.2, t he unbranched and ) and t he unbranched 10 14.3.3 and 14.3.4. 12 H but-2-ene H (or 2-butene) H H H H H H H H H C C C C C H H H H H H H H C C H H C C H H C C H C H H H H H H H H H pent-1-ene pent-2-ene 2-met hylbut-1-ene H C C C H (or 1-pentane) (or 2-pentene) (or 2-met hyl-1-butene) H H H 2-met hylpropene H H Figure 14.3.2 butene (C H 4 The structural isomers H H H H C C H H H of H ) 8 H C C H H C C H C C H Figure 14.3.3 pentene (C H 5 246 The ) 10 structural isomers of 3-met hylbut-1-ene (or 3-met hyl-1-butene) H 2-met hylbut-2-ene (or 2-met hyl-2-butene) Hydrocarbons – alkanes and alkenes Alkenes: C H n H H H H H H H H H H H C C C C C H H H H H H H H C C C C C H H 2n H C C C C H H H C H H H H hex-1-ene (or H 1-hexene) hex-2-ene H (or H 2-hexene) H hex-3-ene The presence of t he double bond makes alkenes more reactive t han (or Figure 3-hexene) 14.3.4 The straight isomers of hexene (C H 6 Alkenes looking undergo at are a variety combustion of different and reactions. addition The ones t hat we will reactions of burn ver y easily in air an alkene produces carbon Exam tip important that alkenes or oxygen. The complete is dioxide and water as steam. The unbranched exot hermic, combustion of producing et hene is a large shown in amount t he of heat equation energy. The complete below: containing atoms. you It can is H 2 (g) 3O 4 (g) 2CO 2 (g) 2H 2 O(g) H require more oxygen cor responding alkane wit h t he alkenes higher ratio of have a not carbon and bur n as steam. wit h a wit h soot As smoky clean and for complete same number carbon a ames. sometimes result of t he atoms combustion of to carbon t han t he When carbon because atoms atoms in formula. hydrogen presence t hey bur n monoxide of t he soot t hey as in well t he release as if atoms t heir unreacted carbon ame, can are reactions wit h one called molecule. hydrogen The of of 14.3.5, two reaction, t he t he in addition a t he single of to given It not essential is name the its branched any six are Hexene you (C H 6 involve t he double reactions substitution reaction where atoms which A–B or covalent bond adding extra atoms to bond being broken in t he Alkenes as because two reactions, t he an represents small bond double forming atom t he at carbon reaction alkene a groups between bond a one molecules alkene of A also undergoes molecule atoms and B breaks. saturated side atom undergo to with a react does not wit h in a breaks The a is to form lose any summarised single covalent molecule. and one double of bond is compound and A has thirteen the chain three isomers Figure 14.3.4 and ten of t he original double chain isomers. For could see many how practice, of and at t he ot her each This The atoms carbon always in t he atom following at a nickel ● a pressure ● a temperature you draw. t he C C C C A B in conver ted small saturated B bonded product becomes Figure 14.3.5 Summary of addition side. addition eit her an reaction hydrogenation, hydrogen of alkenes side molecule of t he wit h t he breaks original hydrogen single and bond one double gas atom bond known between in is t he bonded t he alkene. alkane conditions ● of During produces you these in bonds becomes bond shown branched bond During t he ) 12 hydrogen type hydrogenation. hydrogen of process. reactions Addition you t he to that isomers molecule carbon bonded carbon molecular know? isomers, alkene to up you Did can carbon–carbon to unbranched bur n atoms. between that displayed dioxide alkenes alkenes alkenes bond Unlike addition Figure any carbon alkenes. in one of isomers containing unbranched They six ame reactions molecules, to fully formulae branched structural Add ition up important the alkene ? Addition name ve molecules. Because of t his higher ratio of carbon to hydrogen atoms, alkenes do of 2 and Alkenes also draw structural C can isomers reaction alkene is you combustion the of 12 reactions. It Alkenes ) be ✔ Combustion chain alkanes. are required for t he reaction: catalyst of about of 5 atmospheres about 150 °C. 247 Alkenes: C H n Hydrocarbons For Did ? you example, et hene reacts alkanes wit h hydrogen to fats is used and in oils, industry i.e. H H H catalyst H C atm, 150 their melting points. H margarine hydrogenating can the be H For et hene example, H °C H by alkenes et hane: H 5 ‘harden’ increase and H Ni Hydrogenation form know? H to – 2n hydrogen et hane made carbon– or carbon double bonds in vegetable Ni oils. This hardens the oils making C H 2 (g) H 2 2 5 the margarine it also If margarine butter, has it more possible is used reduces spreadable health in animal atm, 150 (g) 6 °C and benefits. place of the amount fats in Addition the reaction with halogens of Alkenes saturated catalyst H 4 undergo a type of addition reaction wit h halogens known as diet. halogenation. atoms in t he During molecule halogenation, breaks and t he one single atom is bond between bonded to each t he halogen carbon atom at eit her side of t he original double bond in t he alkene. This always produces a haloalkane n contrast reaction to does temperature. reaction For t hat t he not halogenation need The reaction occurs example, light wit h reactions energy; is also a it can rapid which take alkanes place reaction in in undergo, t he dark contrast to at t his room t he slow alkanes. propene reacts wit h bromine vapour to form 1,2-dibromopropane: H H H H H C C Br Br H C C Br Br H H H H propene bromine 1,2-dibromopropane or C H 3 n t his reaction, bot h cases, wit h it. Addition Alkenes Br with (HCl) 3 can be in bromine t he is hydrogen addition chloride H 2 bromine undergo produce + red-brown reactions hydrogen to t he (g) 6 of a (l) 2 vapour decolour ised as or a t he solution. alkene n reacts halides reactions and form rapidly Br 6 wit h hydrogen hydrogen bromide halides, (HBr), at for room example, temperature haloalkanes For example, ethene reacts with hydrogen chloride to form monochloroethane: H H H H H H Cl C H et hene hydrogen H 2 248 H 4 H H monochloroet hane chloride or C Cl 2 Cl(l) 5 Hydrocarbons – alkanes and alkenes Alkenes: C H n Addition Alkenes steam a reactions undergo known hydrogen t he as double bond carbon atom The in at type and atom following is t he t he of of a catalyst t he ● a pressure ● a temperature alkene ot her example, 60–70 of During oxygen to and side. are phosphoric of addition bonded conditions ● For a water hydration. atom hydrogen with 2n reaction atom t he t he This in in t he carbon for sand of water at OH in t he t he bonds molecule one side group produces t he water one atom remaining always required acid wit h hydration, an is of form of between breaks t he and original bonded to t he alcohol reaction: (silica) atmospheres about ethene 300 °C. reacts with water, in the form of steam, to form ethanol: H H H H H H PO 3 O ethene H C 70 H 300 °C catalyst 4 atm, 300 + °C H 60–70 atmospheres steam H H phosphoric(V) acid catalyst et hene water et hanol cooling unreacted of or gases gases recycled H PO 3 C H 2 (g) + catalyst 4 H 4 H 2 2 70 atm, 300 OH(l) 5 °C ethanol to Et hanol and ver y to is steam low produced using so increase t he preparation Addition t he of yield. i.e. example, et hene ow t he is addition above. recycled diagram in reaction The back Figure yield into 14.3.6 between of t he t he et hene reaction reaction shows t he is ethanol vessel industrial acidified an an by potassium addition The t he alcohol et hene Figure 14.3.6 preparation solution. oxidised d i alcohol, For with undergo is The by listed et hanol. manganate(VII) alkene conditions unreacted reaction Alkenes industrially t he acidied wit h reacts two wit h is a wit h redox potassium –OH The of industrial ethanol manganate(VII) reaction reaction turns liquid acidied reaction in manganate(VII) potassium which to t he form a groups. acidied potassium manganate(VII) to form et hane-1,2-diol: H H H H H H O [O] 2 H C H H et hene from oxidising H et hane-1,2-diol agent or Exam ✔ C H 2 (g) + H 4 H 2 2 (OH) 4 2 It is very write Dur ing t he changes colour and reduces reaction, from t he t he purple pur ple potassium to colourless. manganate(VII) The manganate(VII) alkene ion tip (l) acts (MnO solution as ) a to for that the you can addition rapidly reducing t he important equations reactions of can the alkenes and that you agent state conditions required colourless 4 for the reactions to occur. 2 manganese(II) ion (Mn ). 249 Alkenes: C H n Hydrocarbons Reactions Did ? – alkanes and alkenes 2n you to distinguish between an alkane and an know? alkene Alkenes in can addition also add reactions. These very molecules large to themselves You polymerisation reactions but make known have slow We will be more detail in Unit learnt t hat saturated bot h whereas reactions alkanes alkenes because t hey and are alkenes are unsaturated. contain only hydrocarbons, Alkanes undergo carbon–carbon single as looking at whereas alkenes undergo rapid addition reactions because of t he this presence in are substitution bonds polymers. already alkanes of a carbon–carbon double bond. 16. The difference bet we e n t he re ac tion s of a lk an es a n d a lken es w it h bro min e solution or laborato r y see if t he acidifie d to p ot a ssium dist in g uish compo un d man gan ate(VI I) b etwee n c o nt ain s a t he t wo. solutio n B ot h c arbon – c arb o n is r eac tio n s dou ble u se d a re in t he t est in g bo n d , i. e. if to it is uns aturated The tests used to distinguish between an alkane and an alkene are summarised in T able 14.3.1 Distinguishing between an Table alkane Observations and and 14.3.1. an alkene explanation T est Alkane Add acidified potassium manganate(VII) The Alkene solution remains purple. The solution solution changes colour rapidly from purple to colourless. Alkanes do not react with acidified potassium Alkenes rapidly reduce the purple MnO ion to the 4 2 manganate(VII) Add a water solution (bromine of bromine water) or in The solution remains colourless red-brown. The in tetrachloromethane under standard conditions Mn solution ion. changes colour rapidly from red-brown to colourless. Alkanes laboratory solution. do laboratory not react with bromine solution under standard conditions. t ● is impor tant n t he in water brown ● to note presence or to of alkanes red-brown and ultraviolet and due light, to t he to t he decolour ise t his reaction to rapid addition conditions, alkanes slowly slow react colourless. due a any reaction including with bromine darkness. following. alkenes to light rapidly reaction under ultraviolet colourless from Alkenes undergo solution tetrac hloromet hane Bot h in t he Alkenes substitution wit h bromine Alkanes slow t he does cause c hange slowly not due need solution colour light, reaction t he bromine red- occur r ing. c hanging decolour ise to of from reaction vapour, substitution vapour a rapid t herefore t he it vapour occur r ing. addition it will occur laborator y tests in darkness. These reactions distinguish T o teacher will be and test and use with acidied tubes. an this recording supplied cyclohexene, however, between may observation, Y ou 250 alkane distinguish Your ● an are, not usually used as alkene. an alkane activity and to and an alkene assess: reporting. samples potassium of two hydrocarbons manganate( VII) cyclohexane solution, bromine and solution to Hydrocarbons – alkanes and alkenes Alkenes: C H n 2n Method 3 1 Place 2 cm A B. and of cyclohexane into each of two test tubes. Label the tubes of cyclohexene into each of two test tubes. Label the tubes 3 2 Place C 3 and Add A 2 cm a D. few and drops of acidied Shake 5 Add 6 Shake and 7 Which hydrocarbon of a a and few of Alkenes solution to tubes observe drops any of colour bromine observe any is changes solution colour to which test occur. tubes B and D. changes. saturated and which is unsaturated? alkenes are wide manganate( VII) C. 4 Uses potassium extremely range of reactions due to example, t hey are impor tant chemicals t he starting because presence of of t he mater ials t heir for ability t he to manufacture undergo carbon–carbon double addition bond. Did ? The used to manufacture et hanol and ot her alcohols you combustion undergo addition reactions wit h steam and to of alkenes is an because exothermic t hey know? For manufacture reaction, therefore, various alkenes could be used as fuels. haloalkanes because of t heir addition reactions wit h halogens and hydrogen However, they are far too important halides. They are also used to manufacture antifreezes, such as et hane-1,2-diol as and synt hetic t hemselves plastics. r ubbers. t hey You will Give the straight 2 names Describe b Give to more t hey can undergo manufacture about plastics a in wide Unit addition variety reactions of starting materials for making wit h polymers, other organic them by products to waste or using them as fuels. 16. questions chain a used learn Summary 1 are Because and fully isomers what you of displayed structural formulae of the three hexene. would observe when bromine solution is added to ethene. 3 4 Give a the balanced conditions a hydrogenation b hydration Describe an distinguish Key ● of under of to experiment between which ethene ethane an for to the the that following produce produce you alkane reaction structural reactions formulae. occur: ethane ethanol. could and using an perform in the laboratory to alkene. concepts Hydrocarbons hydrogen are atoms ● Natural ● Natural gas et hane, propane ● equation gas Petroleum and is is organic petroleum composed a compounds composed of carbon and sources hydrocarbons. only. and are mainly natural of met hane of wit h small amounts of butane. complex mixture mainly of alkanes and ringed hydrocarbons. 251 Alkenes: C n H Hydrocarbons – alkanes and alkenes 2n ● Separation of distillation ● The of ● ● main an uses petroleum of oil the are as The larger molecules can be Thermal Catalytic catalyst in surfacing down cracking its fractions fuels, and broken in into components is done by fractional rener y. lubricants molecules ● petroleum at obtained the uses the of fractional distillation petrochemicals, as roads. produced into from manufacture during smaller, high fractional more useful temperature distillation molecules and pressures by to of petroleum cracking break the down. cracking to break of an ● Cracking ● Alkanes ● Alkanes with four ● Alkanes burn in ● The are uses the fairly high molecules alkane produces saturated temperatures, low pressures and a down. at least hydrocarbons one with alkene. the general formula C H n ● air more or carbon oxygen combustion of produces carbon dioxide produces carbon monoxide Alkanes of ● complete or undergo atoms with a clear alkanes and water and substitution display is as blue an str uctural ame. exothermic steam. 2n2 isomerism. The reaction incomplete and combustion steam. reactions with halogens in the presence light. Substitution replaced ● Alkanes ● Biogas ● Alkenes by are is a reactions one halogen used mainly renewable are take place atom as unsaturated at fuels source in of a stages, one hydrogen atom being time. and organic solvents. methane. hydrocarbons with the general formula C H n ● Alkenes have the ● Alkenes with four ● Alkenes burn in ● The complete produces ● Alkenes the ● addition an ● The a carbon oxygen of and addition the t with a water is as with a an in functional str uctural 2n group. isomerism. ame. exothermic which in is nickel their reaction and steam. bond hydrogen requires as display smoky alkenes one bond atoms reactions process reaction double the other double known catalyst, as a atoms bond are added hydrogenation pressure to breaks. of 5 atm and and a 150 °C. reaction with the halogens is known as halogenation and it haloalkane. ● The addition reaction with the hydrogen halides also forms a haloalkane. ● The addition hydration catalyst, ● Alkenes a ● Alkenes Alkenes a wide it from are addition of an the colour to of the t and of a as star ting of a steam temperature solution of known for their as acid in sand 300 °C. red-brown whereas to alkanes do manganate (VII) alkanes materials because of from potassium whereas is phosphoric conditions, acidied chemicals form requires bromine colourless, mainly reactions. in laborator y colour other water alcohol. 60–70 atm standard pur ple used range of the under with forms pressure change solution ● reaction and change colourless 252 n of addition forms or dioxide alkane. temperature more combustion undergo forms or air carbon molecule. The it carbon–carbon do the not. manufacture ability to of undergo not. Hydrocarbons – alkanes and alkenes Practice 7 Practice exam-style The process Natural sources of hydrocarbons include: petroleum natural gas coal A and B and C only 2 , and of cracking 3 4 t he and B propene C butane D met hane, What following could not be obtained by hexane? are and and t he fuel pentene be hydrogenation hydration addition A and B and C and D , only only and only Which of t he following could propane from best be used to distinguish propene? A Burn bot h B React bot h wit h bromine C React bot h wit h hydrogen D React bot h wit h acidied air. vapour. gas. potassium manganate(VII) solution. propane propene main As a B To manufacture and C As a roong D As a lubricant different in et hane A separated and uses for surfacing and as fractions and a 9 bitumen? to which and surface roong fully displayed as a up A str uctural and B are formulae given of fuel. H H H H H C C C C C H H H H H H H H cr ude oil are H H C C C C C H H H H H H t heir different melting B t heir different boiling C t heir different densities D t heir different solubilities B points points a To which homologous reacts wit h in water b bromine vapour which of is/are does EACH compound Draw (2 THREE str uctures to represent isomers A. marks) of (3 marks) t he c following series belong? compound et hane H on: A When two below: roads. material. make The question hydrocarbons, roads. petrochemicals material based of Structured et hene A 5 can met hane The et hane only Which A to only 8 D et hene as: questions 1 conver ting questions questions described Multiple-choice of exam-style A and B bot h react wit h chlorine but under different tr ue? conditions. a substitution reaction occurs i) t he bromine is rapidly Give ONE condition necessar y for B to react chlorine. only A one product is (1 Draw t he fully displayed str ucture of t he only compound B and C and formed when A reacts wit h chlorine. only (1 and Draw t he following are all str uctural isomers of pentene H H displayed H H H H H produced reaction except: d H fully str ucture of t he organic only product The mark) only iii) 6 mark) produced ii) D wit h decolourised H Describe a chemical distinguish during between B and test between A t hat and t he rst step of chlorine. could be t he (1 used B. marks) to (1 marks) H e C C C C C C C C Give t he reagent and t he reaction conditions H necessar y to conver t A to B. (2 marks) H f H H H H H Bot h and B ii) H H H H Write t he f equal which C C C H H oxygen. balanced chemical combustion equation volumes of A of B. for or B (2 t he are burnt marks) separately, would Give a you expect reason for to your produce choice. t he more (2 marks) C H Total 15 marks H H H or H soot? C air H H C in B complete H burn H i) A A C H C H H C H H D 253 Practice exam-style Extended 10 a response One of man is i) t he is Name iii) main Hydrocarbons a sources of hydrocarbons used by i) dentify fractions fractional distillation main of uses (1 obtained of from petroleum each. of too few t he hydrocarbons t he demands supplies alkanes of are represent smaller of today ’s t hese one petroleum world. smaller cracked. give (4 distillation alkanes and an way to ii) marks) cracking iii) t he can be and reaction used to conver t: – compound A to compound B – compound A to compound D. Describe what would formation of Under right wit h larger to t he be obser ved compound C from (4 during compound A conditions, compound D Name t he – Write a rst type of chemical step in t he reaction equation reaction. taking to study t he reaction answer t he questions CH CH OH which scheme below (3 follow. (g) 2 2 2 CH CH CH 2 B A CH CH 3 CHBrCHBr 3 C CH 2 D 254 CH 3 3 t he marks) marks) and Br CH 3 mark) reacts place. represent Total Carefully marks) t he chlorine. – hexane. (2 b alkenes (1 meet increase equation of t he reagents which produces hydrocarbons, Write possible To mark) t he and Fractional of suitable conditions hydrocarbon? T WO – question petroleum. What ii) questions 15 marks Alcohols, alkanoic acids B15 and Alcohols, alkanoic acids and esters esters are organic Objectives compounds contain that oxygen, because of the all contain their way oxygen. properties the oxygen Although and they reactions atoms are all differ bonded By the be able of molecules. Because of their varied properties have members widespread of these uses in three industry homologous and our daily you will of the by the hydroxyl and group, reactions, topic alcohols presence the this to: identify ● in end series give ● –OH the names formulae lives. alcohols of and structural unbranched with up to six carbon atoms B15.1 Alcohols: C H n OH relate ● the solubility Alcohols have are t he also known hydroxyl as group, alkanols. –OH, as They t heir are organic functional compounds which general formula of alcohols which group. contain one of presence and alcohols of the to polar the –OH group describe ● The volatility 2n 1 hydroxyl group the reactions of is ethanol C H n OH. This can also be written R–OH, where R represents C 2n 1 H n , 2n 1 explain ● i.e. an alkyl Alcohols are named by using t he prex which indicates t he total number t he atoms in t he molecule plus t he ending ‘ -anol’. The rst two series given do not show str uctural isomerism. Their names and describe fermentation the by in Figure H H H describe H H (CH involved OH ) et hanol (C 3 Figure Alcohols wit h isomers three 15.1.1 or H 2 Structural more rum H C C O H H met hanol Str uctural change position ● of branching of formulae carbon of the atoms OH alcohols of hydroxyl t he result t he from t he functional group, the in processes wine rst two show alcohols Exam ✔ str uctural isomerism. must not confuse group, i.e. t he change group in alcohols that present with is in hydroxides. –OH molecule. H H H and indicate group t he t he so longest t hat position t he of chain group t he from is at hydroxyl t he t he end H H H follow steps 1) to 4) on page 233 for naming group branched in t he propan-1-ol name chain t he r ules above, t he str uctures and names of propan-2-ol 1-propanol) Figure 15.1.2 (C of propanol (C H 3 given in Figures OH) and butanol 7 15.1.2 (C H 4 and H H H H OH H OH H H H H C C C H H H C C C O H H H H H H butan-1-ol (or 1-butanol) butan-2-ol (or 2-butanol) of H C H H H C C C C H H H isomers H H H H C C C C O H H H H structural OH) 7 OH) H H 2-propanol) 9 15.1.3. H C H H The H 3 are (or t he propanol isomers H isomers. Using OH lowest (or ● H C C C H H closest functional in H atoms number carbon H H alcohols: of isomers –OH ion in t he –OH OH to t he the the following: number and tip H C C C O H ● making ) naming of position t he is manufacture. When in ethanol carbohydrates 5 You t he from 15.1.1. H C O H which formulae ● ● the alcohols produced are of test process in principles breathalyser of ● carbon the group. 2-met hylpropan-1-ol (or 2-met hyl-1-propanol) 2-met hylpropan-2-ol (or 2-met hyl-2-propanol) Figure 15.1.3 structural of The isomers butanol (C H 4 OH) 9 255 Alcohols: C H n OH Alcohols, alkanoic acids and esters 2n 1 H H H H The H C C C C H H H H straight given in H H chain isomers of pentanol (C H 5 are Figures H H 15.1.4 and H H H H C C C C H H H H OH) and hexanol (C 1 1 H 6 OH) 13 15.1.5. H H H H H H C C C C C H H OH H H pentan-1-ol (or 1-pentanol) H H H H H H H H H hexan-1-ol (or C C C C hexan-2-ol 1-hexanol) (or H H H H OH 2-hexanol) H H H H H H C C C C C H H OH H H H H pentan-2-ol (or H H 2-pentanol) H H H hexan-3-ol H (or C C C C 3-hexanol) H Figure 15.1.5 The straight chain isomers of hexanol (C H 6 H H OH H OH) 13 H pentan-3-ol General (or Figure 15.1.4 isomers of The straight pentanol (C H 5 chain OH) Alcohol Recall molecules t hat is Exam tip important that bot h you a are alcohols polar polar molecule has slightly molecule negative It of due to is covalent a t he presence of t he molecule in polar –OH which one group. par t of 11 t he ✔ properties 3-pentanol) can charge. related to a The t he positive volatility polar of nature charge alcohols of t heir and and anot her t heir par t has solubility a in slightly water are molecules. name Volatility the unbranched isomers alcohol containing atoms. It you can is also draw structural up to of six important the fully formulae of any carbon that displayed unbranched Alcohols number higher point are of less carbon t han of volatile t hat up to of six any alcohol carbon containing atoms. is not name It the 89 °C. et hanol This between essential that you can alkane branched isomers of is t he i.e. corresponding (C t he H OH) is t he corresponding of boiling 78 °C and point of an alkane. t he alkanes alcohol For boiling wit h is always example, point of t he t he et hane alcohol As much (C H 2 t he polar molecules a same boiling 5 because molecules. t heir atoms, 2 isomers t han result, –OH to all be groups cause stronger alcohols are t han eit her t he forces between liquids or ) is 6 of attraction t he non-polar solids at room alcohols. temperature. The boiling point of alcohols molecules increases. molecules increase Solubility in The general This as t he is increases because size of t he as t he t he number of carbon intermolecular molecules forces atoms in t he between t he increases. water r ule on solubility states t hat polar solutes dissolve in solvents. Water is a polar solvent, t herefore alcohols, being polar, are in water. The completely of carbon soluble atoms Reactions Alcohols (–OH) of of as alcohols, in t he a variety n of met hanol, t he et hanol solubility and decreases soluble propanol, as t he are number increases. reactions t his however, contain t he as however, molecules group. et hanol, all water, such ethanol undergo t hey decreases 256 in functional reactions since small polar number t he of section t he ot her hydroxyl carbon due we to will be alcohols group. atoms t he in The t he presence looking undergo strengt h alcohol of t he hydroxyl specically similar of t he molecules at t he reactions reactions increases. Alcohols, alkanoic acids and esters Alcohols: C n Combustion of H OH 2n 1 ethanol Ethanol burns ver y easily in air or oxygen producing carbon dioxide and water as steam. The reaction is exothermic, producing a large amount of heat energy. The complete combustion C H 2 OH(l) 3O 5 in dioxide t he and Reaction Et hanol (g) 2CO 2 Et hanol burns wit h a atoms of ethanol is shown in the equation below: of clear blue ame molecule no reacts is low. unreacted ethanol All t he carbon with wit h (g) 3H 2 O(g) H ve 2 because t he ratio of carbon to hydrogen carbon remains is to t herefore produce conver ted When effer vescence of sodium between 2C a sodium piece occurs as et hoxide to et hanol and H 2 OH(l) of t he in carbon sodium produce sodium et hoxide (C H 2 hydrogen. to soot. sodium metal hydrogen alcohol sodium is is gas is is evolved formed. given The into and a ONa) colourless equation for and 5 et hanol steady solution t he reaction below: 2C 2Na(s) dropped H 2 5 H ONa(alc sol) H 5 sodium (g) 2 C C H 2 O . et hoxide is The displayed fully an ionic compound str ucture of containing sodium t he et hoxide et hoxide The is represented in 15.1.6. reaction sodium and Figure 15.1.6 structure between water. n sodium bot h and et hanol reactions, Na t he is similar sodium to t he reaction d isplaces H ion, 5 Figure O et hoxide H Sodium H of The fully sodium displayed ethoxide between hydrogen from t he et hanol or t he water, forming hydrogen gas. However, t he strengt h of t he reaction between Dehydration When et hanol heated in one to of two is passing t he bot h i.e. a t he t he of wit h 170 °C, et hanol oxide is much concentrated is more vigorous sulfuric dehydrated excess where vapour acts as a functional atom of water a met hods, formation carbon wit h et hanol hydroxyl hydrogen t he mixed t he et hanol aluminium n water (see Unit 17 .2). to acid et hene. and This t he can mixture be is achieved ways: temperature ● and ethanol 170 °C, heating ● of sodium is a concentrated t he over acid acts heated as sulfuric a acid catalyst aluminium in at t he oxide, a reaction where t he catalyst. molecule is group removed from carbon–carbon removed is from removed t he ot her double each from carbon bond et hanol one carbon atom. between This t he molecule, atom and results two in adjacent atoms. The equation acid is given for t he dehydration of et hanol using concentrated sulfuric below: H H conc. H H H H H SO 2 4 C 170 H H O °C H H et hanol et hene water or conc. H SO 2 C 4 H 2 H 5 2 170 4 (g) H O(g) 2 °C 257 Alcohols: C H n OH Alcohols, alkanoic acids and esters 2n 1 Oxidation When of et hanol potassium solution, can ethanol be is heated t he et hanol represented C H 2 wit h manganate(VII) OH(l) is by powerful oxid ised t he to following 2[O] 5 a solution or oxidising acidied et hanoic such acid. The as acidied dichromate(VI) oxidation of et hanol equation: CH COOH(aq) 3 et hanol agent, potassium from et hanoic H O(l) 2 acid oxidising agent n t he above reaction, et hanol is behaving as a reducing agent. f t he reaction occurs wit h changes acidied from pur ple potassium to manganate(VII) colourless because t he solution, et hanol t he reduces solution t he purple 2 manganate(VII) ion (MnO ) to t he colourless manganese(II) ion (Mn ). f 4 t he reaction solution occurs changes wit h from acidied orange potassium to green dichromate(VI) because t he solution, et hanol reduces 2 orange dichromate(VI) (Cr Reaction Et hanol of reacts discussing T o investigate Your ● teacher may observation, Y ou will be the oxidation use this recording supplied with of activity and ethanol wit h t his in with ) to t he green chromium(III) ion (Cr ). 7 alkanoic alkanoic greater t he 3 O 2 t he acids detail in acids to form Unit an ester and water. We will be 15.3. ethanol to assess: reporting. ethanol, acidied potassium dichromate( VI) solution and a test tube. Method 3 1 Place 2 Add 3 Observe about an 2 cm equal the of ethanol volume colour of of into acidied the the test tube. potassium solution dichromate( VI) periodically The The for about solution 15 of breat h. acidied dichromate(VI) The to mix. test potassium colour change is used in t he driver’s shake minutes. breathalyser reduction and driver cr ystals. blows f dichromate(VI) and t he accompanying breathalyser test to test t he alcohol content of a t he over a sample of breat h contains driver’s orange acidied et hanol potassium vapour, t he 2 et hanol will reduce t he orange dichromate(VI) ion (Cr O 2 ) to t he green 7 3 chromium(III) ion Production (Cr of ). As a ethanol result, by t he cr ystals turn green fermentation Fermentation is t he chemical reaction in which carbohydrates are conver ted into et hanol oxygen. down yeast Yeast any t hen simple 258 is yeast a anaerobic fungus carbohydrates produces into under unicellular complex sugars anaerobic by anot her et hanol respiration , into enzyme and releases conditions, which carbon energy i.e. produces simple called sugars, which This t he t he absence t hat of break mainly glucose. The which conver ts t he zymase dioxide. in enzymes process, yeast cells also use. known as Alcohols, alkanoic acids and esters Alcohols: C H n The equation for t he fermentation zymase C H 6 O 12 in of about 14%, given below: ✔ 2C H 2 glucose t he is yeast (aq) 6 When glucose OH(aq) 2CO 5 (g) H 2 Exam et hanol concentration it begins stops. fractional et hanol is tip ve to of et hanol destroy t he in t he fermentation zymase enzyme and mixture t he reaches fermentation It is a line very used important diagram to carry distillation reaction OH 2n 1 The et hanol d istillation collected at can (Unit 78 °C t hen 2.4). and is be separated During about t he 96% from t he distillation mixture process, to that show you the can out fractional the laboratory . in draw apparatus by t he pure. conical cork flask T o prepare a sample of ethanol glucose, (T eacher Your demonstration) teacher may observation, ● use this recording activity and to water lime and water yeast assess: reporting. Figure 15.1.7 Production of ethanol by fermentation Y our teacher will perform the following experiment. Method thermometer 3 1 Place and 2 10 g mix Make a of to glucose make paste a into a glucose with 1g of 3 250 cm conical ask. Add 100 cm of water solution. dried yeast and a small quantity of water. Add water the paste to the glucose out solution. condenser 3 Place a cork on the ask with a delivery tube leading to a beaker fractionating containing lime water. Ensure that all the connections are properly column, sealed. The bacteria lime which water can acts cause as the an airlock formation to of prevent ethanoic the entry acid of aerobic (vinegar). packed with The water glass in beads lime the water also formation shows of a when white the production of carbon dioxide starts by precipitate. distillate 4 Leave 5 Pour the the reaction mixture until into a fermentation distillation has ask stopped. and fractionally distill it, point of fermentation collecting the fraction which distils at 78 °C, the boiling ethanol. mixture containing ethanol heat Fermentation such as wine produced r um is used and during making in in r um. t he more t he t is also process detail production used makes in t he in t he next of different baking dough alcoholic where rise. We t he will beverages carbon look at dioxide wine and sections. Figure 15.1.8 fractional Separation of ethanol by distillation Winemaking Wine to is form wine made a t he primarily mixture skins of are from pulp, grapes skins removed. in and The a winer y. juice vintner The known grapes as are ‘must’. (winemaker) To t hen rst cr ushed make adds white yeast ? Did must in fermentation tanks and t he yeast ferments t he sugars or et hanol skins removed and carbon dioxide. When fermentation is complete and t he wine is ltered to clarify it. The wine is t hen red storage wines is tanks or between oak 10% barrels and before bottling. The et hanol content of most are 14%. colour. from vary Great care must be taken t hroughout t he winemaking process to and are the used to grape present throughout aged fermentation in grapes wine any skins are black present make forming know? to Red t he you White ‘white’ in to give wine grapes, colour from the is wine made which green its mainly actually to pale minimise yellow. t he exposure of t he wine to air. This is because cer tain aerobic bacteria may 259 Alkanoic acids: C H n COOH Alcohols, alkanoic acids and esters 2n 1 be present in t he air, in t he t hese wine from bacteria t he original oxid ise t he aerobic C H 2 OH(aq) O 5 grapes et hanol to and, et hanoic Rum Rum t hen acid, CH COOH(aq) t he wine to become H 3 causes or to oxygen vinegar: O(l) 2 acid sour and undrinkable. manufacture is which acid exposure bacteria (g) 2 et hanoic The on et hanoic made is from produced t he black during t he treacle-like extraction substance of sugar from known sugar as molasses, cane (Unit 2.5). The molasses is rst diluted wit h water and yeast is added. The yeast ferments t he sugar in t he molasses forming et hanol produced is t hen sent to t he still where it is a distillate wit h an et hanol content of and carbon dioxide. The fractionally d istilled between 70% and mixture to produce 95%. The distillate is then diluted and transferred to oak barrels to be aged. This process can take 20 years or more. The oak barrels are charred on the inside to impart a variety of avours to the rum, give it a smoother taste and add colour. More water is then added to reduce the ethanol content to about 40% and a master blender Figure of the 15.1.9 oak A master blender Summary 2 Explain how 3 Ethanol burns 4 Ethanol can be a Give the conditions b Draw be the a responsible for blending various rums of different names and the the displayed functional in oxygen and/or from different group with a structural of blue the formulae alcohols ame. Give of affects a three their balanced straight solubility equation chain and for isomers boiling the of pentanol. points. reaction. dehydrated. fully balance fully required displayed chemical for the structural equation for reaction. formulae the of the products fermentation of formed glucose and in the give reaction. two ways in which the reaction may used. B15.2 Objectives Alkanoic acids: C H n By the be able end of this topic you acids are also known as carboxylic acids . They are organic to: compounds identify the COOH 2n 1 will Alkanoic ● ages questions Give Give is front barrels to produce the unique brands of the different rum manufacturers. 1 5 in barrels alkanoic presence of acids the group. by The which have carboxyl t he group carboxyl can also be group, –COOH, represented as t heir functional as: O carboxyl C –COOH group, O H ● give the names formulae alkanoic of and structural unbranched acids with up to The six is general C H n carbon atoms C H n ● relate the volatility of of , i.e. acids part of the the polar functional the ethanoic acid. contain one R–COOH, carboxyl where R group represents an alkyl group. acids of are carbon named atoms by in using t he t he prex molecule plus which t he indicates sufx ‘-anoic t he total acid’. to remember t hat t he functional group contains one t is carbon group reactions which must be taken into account when naming alkanoic acids, i.e. of t he by prex adding formula is not 1 to CH derived t he directly value COOH 3 260 which written –OH atom describe be also to impor tant ● acids can and alkanoic presence alkanoic 2n 1 number the of This 2n 1 Alkanoic solubility formula COOH. is of ‘ n’. et hanoic from For ‘ n’ in t he example, acid and not general t he formula, name met hanoic of t he acid. it is acid derived wit h t he Alcohols, alkanoic acids and esters Alkanoic acids: C H n COOH 2n 1 The names and formulae of t he straight chain isomers of t he rst six alkanoic acids are shown in Figure 15.2.1. H ? H C C C C O H Organic H H H H et hanoic (HCOOH) (CH propanoic acid (C COOH) H 2 3 acid butanoic COOH) (C 5 H 3 H H H H hexanoic COOH) (C 9 H 5 be natural Figure 15.2.1 Structural formulae of the rst six COOH) of alkanoic Alkanoic acid molecules are throughout Methanoic bee in the stings venom while gives vinegar O H acid, found the acid of ant is ethanoic and its sour acid taste. in citrus three carboxyl acid, found fruits, Citric groups has and tartaric acid in tamarinds, has COOH) 1 1 alkanoic acids functional acetylsalicylic reduce Properties found world. 7 two or H 4 H acid one groups O H C C C C C C O H containing functional acid (C H H H H H H pentanoic H O H C C C C C H H H H H acids carboxyl found H know? H can acid you O H more H met hanoic Did O H C O H H C C C H O O H C O H H H C H H O acids pains, fever has groups. acid, and one Aspirin, which relieve carboxyl is or used aches to and group. polar due to the presence of the polar –OH part of the carboxyl functional group. Like alcohols, the volatility of alkanoic acids and their solubility in water are both related to the polar nature of their molecules. Volatility Alkanoic same acids number always much boiling point ethane (C are of less higher of volatile carbon than atoms, i.e. than that of ethanoic acid (CH their the the corresponding boiling point corresponding COOH) is 1 12 °C of alkanes an alkane. and with alkanoic For the example, boiling the acid is the point of 3 H 2 ) is 89 °C. This is because the forces of attraction between the 6 polar alkanoic acid molecules are stronger than between the non-polar alkane molecules. All alkanoic acids are either liquids or solids at room temperature. The in boiling t he point molecules of molecules increase Solubility in Alkanoic such as soluble as t he acids increases because size of t he t he as t he number intermolecular molecules of carbon forces atoms between t he increases. water acids, being met hanoic in alkanoic increases water, atoms in t he When alkanoic polar, acid, however, molecules acids are soluble et hanoic t he acid in water. and solubility The propanoic decreases as small acid t he alkanoic are acids completely number of carbon increases. dissolve in water, they also ionise to a very small degree to form hydrogen ethanoic acid (H ) dissolves ions, in hence water they about are 1% weak of the acids. For ethanoic example, acid when molecules ionised at any one time, i.e. the solution contains 1% ethanoate ions (CH are COO ) 3 and hydrogen ions (H ) and 99% ethanoic acid molecules (CH COOH). 3 The ionisation of et hanoic acid is shown in t he following equation: CH COOH(aq) CH 3 COO Reactions Aqueous acids of aqueous solutions such oxides, (aq) H (aq) 3 et hanoate as metal of alkanoic hydrochloric hydroxides ethanoic acids acid and ion react when metal acid in they a ver y react carbonates. similar with The way reactive reactions to inorganic metals, are metal slower than they would be with inorganic acids because the alkanoic acids are weak acids. 261 Alkanoic acids: C H n COOH Alcohols, alkanoic acids and esters 2n 1 n t his acid. all section we However, t he contain number Salts of t he Reaction Reactive Using by with Mg(s) group. et hanoic react reaction 2CH looking alkanoic atoms reactive metals t he be carboxyl carbon formed will ot her in The t he acid specically acids strengt h molecules are at undergo known of t he reactions similar t he of reactions reactions et hanoic since decreases t hey as t he increases. as ethanoates metals wit h et hanoic between acid magnesium to produce and (CH COOH(aq) COO) 3 3 a salt et hanoic and acid as Mg(aq) gas. example: H 2 magnesium hydrogen an (g) 2 et hanoate t is important to note that since the magnesium has displaced the H ion from the –COOH functional group, it is written in the place of this H ion in the formula of the salt. However, in the name of the salt, the metal still comes rst. Reaction Metal with oxides metal react wit h reactions are oxide et hanoic and ZnO(s) oxides et hanoic neutralisation acid 2CH as an acid to reactions . produce Using a t he salt and reaction water. These between zinc example: (CH COOH(aq) COO) 3 3 zinc H Zn(aq) 2 H O(l) 2 et hanoate O Reaction C with metal hydroxides O Metal Na hydroxides react wit h et hanoic acid to produce a salt and water. These H are Figure 15.2.2 The fully also neutralisation hydroxide structure of sodium reactions . Using t he and et hanoic acid as an CH CH COOH(aq) COONa(aq) sodium fully Figure the name following a C H 3 of each of C an displayed H Reaction of sodium et hanoate is represented in with metal carbonates carbonates and why acid. methanoic As part of acid your as water. an Using write chemical a in Why ethanoic CaCO acid acid water. than between to produce calcium (s) 2CH (CH COOH(aq) a salt, carbonate COO) 3 3 Ca(aq) carbon and 2 calcium dioxide et hanoic acid CO (g) H 2 O(l) 2 et hanoate Esterification Alkanoic acids react with alcohols to produce an ester and water. The reaction acid less is known acid volatile et hanoic which methanoic ionises is wit h reaction balanced equation how t he example: 3 shows react COOH 11 answer 3 str ucture 15.2.2. COOH Explain is O(l) 2 7 5 2 H et hanoate the compounds: Metal b sodium questions The Give 3 3 1 between example: ethanoate NaOH(aq) Summary reaction displayed and as esterication heat in order to and take it requires place. Since a catalyst two of concentrated molecules are reacting sulfuric together ethane? with the loss of a water molecule from between them, the reaction may also be 4 Give a balanced chemical referred to as a condensation reaction. The alkanoic acid and alcohol must be equation for the reaction between ethanoic in the pure liquid form and not in aqueous solution for the reaction to occur. acid and: Using a calcium b potassium t he reaction between et hanoic acid conc. H the conditions the reaction example: acid C H 3 OH(l) 4 CH 7 acid COOC 3 propanol propyl H 3 (l) 7 et hanoate H O(l) 2 water between and et hanoate ethanol. t he 262 an heat Propyl ethanoic necessary et hanoic for as SO 2 COOH(l) 3 Give propanol carbonate. CH 5 and oxide next unit. is an ester. We will be looking at esters in more detail in Alcohols, alkanoic B15.3 acids Esters: and esters Esters: RCOOR RCOOR Objectives By the be able end of this topic you will An ester is a compound formed when an alkanoic acid reacts wit h an alcohol. The smaller sweet bot h esters fr uity are smells. animals and volatile Esters plants, liquids are which widespread especially in usually in have nature owers and ver y where fr uits, distinctive t hey giving occur t hem in identify ● of t heir are esters of long-chain alkanoic acids and an alcohol called esters ester describe ● glycerol. the by the presence functional group, –COO– distinctive smells and avours. Naturally occurring animal fats and vegetable oils to: how esters are formed Esters are used extensively as ar ticial perfumes, food avourings and write ● essences, e.g. ar ticial avourings such as banana, strawberr y and of are esters. solvents from They for t he are also making reaction of used paints fats in t he and wit h manufacture varnishes. of soap Biod iesel is and an as ester have group can t he also ester be names and formulae esters industrial ● explain the hydrolysis ● explain the saponication of esters produced of met hanol. fats Esters the apple group, –COO–, represented as t heir functional group. The ester and oils distinguish ● soapless as: between soapy and detergents. O C O Did ? The general formula of a simple ester is C H n COOC 2n 1 H x where ‘n’ ‘x’ may be t he same or different numbers. This can also be written R–COO–R , Some where in R and R represent alkyl groups which may be t he you same or different. esters animal produce play of chemical same are made by a condensation reaction known as esterication. an alkanoic sulfuric acid acid. is The heated wit h reaction is an alcohol reversible in and t he presence produces in For an natural of the these are 3-methylbutyl of which of is the the main banana aroma, water. reaction can be summarised by t he following general word H also the equation: a conc. the honeybee. bee is acid alcohol ester ● it acts ● it is a as a increases Using catalyst powerful produced sulfuric t he yield str uctural speed is ester formulae t he attacked released by a of when which for two aggression in predator the other to bees provokes them to sting. reasons: reaction agent, reaction of added up dehydrating during t he to acid is water heat concentrated It pheromone 4 trigger alkanoic alarm SO 2 The of ester is The Some example, component and called trigger members species. ethanoate, concentrated signals which role Animals During esters. esterication, important esters responses Esters an communication. pheromones Formation know? and 2x 1 t herefore, which favours it removes t he t he for ward water reaction and produced. to represent t he reaction between et hanoic acid and et hanol to produce et hyl et hanoate, we can see t he str ucture of t he et hyl et hanoate t hat is formed. H C C O H + H H C C O C C H H O H H H et hanol equation COOH(l) 3 + H heat for t he et hyl reaction is conc. SO H 2 CH H H O 4 acid chemical H H SO 2 lost 2 et hanoic The O H H O C C H H H conc. H H O H C H 2 OH(l) given water below: 4 CH 5 et hanoate COOC 3 H 2 (l) 5 H O(l) 2 heat et hanoic acid et hanol et hyl et hanoate water 263 Esters: RCOOR Alcohols, Formulae O H H H writing comes from t he alkanoic formed t he ester. The name of t he names When t hat H and an str uctural ester is of also acids and esters esters formula acid alkanoic and of t he derived an ester, second from t he t he par t rst par t comes alkanoic of t he from acid and formula t he t he alcohol alcohol. H C C O C C C H H H H H propyl Figure propyl par t To ethanoate 15.3.1 Structural formula of of t he acid Formula: tip writing reaction and an the ending ‘anoate’. str uctural of the an always acid for alkanoic write first. In of rst; when ester, you you write will the part t he alkanoic acid. alcohol par t second. rst of wit h t he propyl ending et hanoate ‘yl’; is acid shown par t in second Figure wit h 15.3.1 Some prepare more examples of t he formulae and names of esters are given in Figure this H write COOCH 5 HCOOC 3 H 4 C 9 H 3 COOC 7 H 2 5 of the propanate butyl methanoate ethyl butanoate a sample of ethyl Figure 15.3.2 Other examples of esters ethanoate demonstration) water teacher may use this activity to out assess: condenser observation, Y our an first. (T eacher ● as 15.3.2. the Your t he the acid formula always par t formula methyl T o from t his. 2 acid par t alcohol C the derived Name: The equation between alcohol, formula way, is summarise: example When name ethanoate Exam ✔ However, t he rst par t of t he name is derived from t he alcohol and t he second teacher recording will perform and the reporting. following reflux water experiment. in the position in Method 3 1 Place 10 cm 3 of ethanoic acid into a round-bottomed ask. Add 10 cm of mixture of ethanol 3 ethanol and 2 Attach a 3 Gently boil 4 Pour the 2 cm of condenser the concentrated to mixture the mixture into ester formed by a its the for ask 5 in sulfuric the acid. reux and position as shown in Figure of the acid 15.3.3. minutes. small beaker half characteristic lled odour with and cold oily water and appearance identify on the Figure of surface ethanoic 15.3.3 ethyl Preparing a sample ethanoate water. The reaction proceeds between relatively et hanoic slowly. As acid t he and et hanol reaction is to produce heated, bot h et hyl et hanoate reactants and any ester produced boil forming vapours which must be retained. The condenser is placed et hanol in condense are dense 264 reux et hyl and returned resulting dissolve t he and return for in t he t han to fur t her mixture is it t he reaction Et hyl oats i.e. ver tically, vapours ask. poured water. water, position, et hanoate into n t his and t he way, no an is t hat et hanoic on et hanoic acid is unreacted slightly layer t he condenser et hanoate any only oily so t he t he et hyl water, et hanoate forming enter and lost. acid soluble t he where of t hey et hanol When and and, surface acid, being t he t he alcohol less water. Alcohols, alkanoic Hydrolysis During of and esters reaction molecules by reacting wit h Esters be hydrolysed can products Acid of Esters: RCOOR esters hydrolysis The a acids are broken down into smaller water. by hydrolysis molecules heating depend wit h on a dilute whet her acid or an aqueous acid or an alkali an is alkali. used. hydrolysis During dilute acid alkanoic Using hydrolysis, hydrochloric acid t he and acid or an t he ester sulfuric is acid. heated The wit h an products of acid acid catalyst such hydrolysis are as an alcohol. hydrolysis of et hyl et hanoate as an example: H CH COO 3 2 et hyl Alkaline During H (l) H 5 ions CH O(l) COOH(aq) 3 2 et hanoate et hanoic C H 2 acid OH(aq) 5 et hanol hydrolysis alkaline hydrolysis , hydroxide solution. potassium salt of an The t he ester products alkanoic acid of is heated alkaline and an wit h sodium hydrolysis alcohol. The are or potassium t he reaction sodium occurs in or two stages. Using t he alkaline hydroxide Stage 1: hydrolysis solution et hanoic as acid an of et hyl and et hanol are OH CH COOC 3 et hyl Stage 2: to CH (l) COOH(aq) overall is H 2 is (l) it t hen in COOH(aq) acid sodium hydrolysis: C H 2 acid neutralised NaOH(aq) OH(aq) 5 et hanol by t he sodium CH COONa(aq) hydroxide in t he following NaOH(aq) O(l) 2 et hanoate equation: CH COONa(aq) 3 et hanoate H 3 wit h et hanoate: shown 5 as 3 sodium COOC 3 et hyl CH acid reaction reacting ions O(l) acid sodium by rst et hanoic 3 CH H 2 et hanoic form et hanoic The 5 formed et hanoate t he solution H 2 et hanoate example: sodium C H 2 et hanoate OH(aq) 5 et hanol ? Saponification of esters Glycerol for S aponi c ation refers animal veget able of fats soap. and Dur ing t he to t he alkaline oils. Did hydrolysis Saponi cation manufactur ing process, is of large used fats and in esters t he oils found you is the know? common propane-1,2,3-triol name or in 1,2,3-propanetriol. The formula is structural manufacture are boiled of glycerol drawn for you wit h below: concentrated sodium The salts ot her pot assium of or long-c hain product of t he sodium hydroxide alkanoic reaction is acids, t he solution also alcohol, known to as glycerol, produce fatt y C H 3 t he for mula shows, glycerol is an alcohol wit h t hree hydroxyl t he (OH) 5 H acid s . . As 3 functional g roups. A simplied equation for t his reaction is: heat H fat or oil NaOH sodium salt of a long-chain alkanoic acid glycerol 265 Esters: RCOOR Alcohols, alkanoic acids and esters Example One example of a fat is glycer yl octadecanoate ((C H 17 Glycer yl acid (C octadecanoate H 17 is an ester of COOH) and glycerol (C 35 by boiling octadecanoate wit h (C H 17 octadecanoate is one form t he H 3 hydrolysed sodium is fatty (OH) 5 acid COO) 35 known as C 3 H 3 ). 5 octadecanoic ). When glycer yl octadecanoate 3 concentrated COONa) and sodium glycerol hydroxide are solution, produced. Sodium 35 of soap. heat (C H 17 COO) 35 glycer yl C 3 H 3 (l) 5 3NaOH(aq) 3C H 17 octadecanoate sodium COONa(aq) 35 C H 3 octadecanoate (fat) (OH) 5 (aq) 3 glycerol (soap) When t he soap has been produced, t he mixture is added to saturated sodium chloride solution to precipitate out and solidify t he soap. O CH CH 3 Figure 15.3.5 Model of a CH 2 Figure T o CH 2 CH 2 15.3.4 prepare CH 2 A a CH 2 soap CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 + Na C O CH 2 2 molecule sample of soap soap (T eacher demonstration) molecule Your ● teacher may observation, Y our teacher use this recording will perform activity and the to assess: reporting. following experiment. Method 3 1 Büchner Place 3 10 cm of cooking oil into a beaker and carefully add 15 cm of funnel 3 ethanol and 15 cm mixture thoroughly. 3 of 5.0 mol dm sodium hydroxide solution. Stir the soap filter paper perforated plate 2 Continue stirring about 30 minutes and must it doesn’t cork much. to vacuum the – mixture the fairly overheat T op or thick. foam mixture while mixture up During and a no the it gently longer heating, that with heating must make volume solution on a hot separate sure that doesn’t containing plate into the two mixture decrease equal for layers too volumes of pump ethanol 3 Büchner be the When and thick, water let if the necessary. mixture cool for a while, but do not let it cool flask completely. 3 4 filtrate Add stir Figure 15.3.6 separate Suction soap from ltration the the to mixture to precipitate 100 cm out the of saturated sodium chloride solution and soap. to reaction 5 mixture Filter the mixture paper as the Rinse the using suction ltration and collect the soap in the lter residue. 3 6 during soap with two separate ltration and continue the 10 cm suction portions ltration of to iced dry distilled the water soap. 3 7 Place a distilled 266 small portion water. Place of a the cork soap on in the a test tube, tube shake and add about thoroughly and 4 cm of observe. Alcohols, alkanoic Soapy and A detergent surfaces wit h ● and two One hating. ● The a t he say t his is end of t he of carbon in substances t he or is ‘head’, are as oils is as of from RCOOR long is readily grease. end We oil-loving. molecules dissolves and in oil- head covalent This clot hing, proper ties. water-loving ionic ‘tail’, and and or atoms. dir t composed ionic t he and and remove str uctures t he hydrogen water-hating hydrocarbon to molecule, such to hydrophilic referred and water different t he end to molecules ver y of ten composed hydrophobic added molecule, t hat end opposite have Esters: detergents Detergent which This organic esters chemical oors. of We and soapless is ends end water. acids say This and readily t hat end is is dissolves t his end referred is to as tail Dirt often consists of oily or greasy substances that do not dissolve in water. This makes them difcult to remove. Detergents help to remove this dirt by lowering the surface tension of water, loosening the dirt molecules and dispersing them in the water, i.e. they help to make the greasy dirt mix with the water. When a detergent is added to oily or greasy dir t on fabrics or t he skin, t he hydrophobic (oil-loving) tail of t he detergent molecule dissolves in t he greasy dir t and t he hydrophilic (water-loving) head sticks out. The head dissolves in t he water This is Figure and helped 15.3.7 t he by dir t is lif ted agitation shows how from such greasy as t he fabric occurs dir t can in be a or skin washing removed and is washed away. machine. from fabric. detergent molecule greasy dirt fabric The hydrophobic molecules The in hydrophilic the tails dissolve in of the the heads detergent greasy remain The dirt. off greasy the dirt is lifted The fabric. by dissolved water. greasy into smaller with water. which Detergent t heir molecules be classied into soapy or soapless soap. They can is surrounded molecules droplets This be depending and that forms washed an broken can mix emulsion away. Figure How 15.3.7 detergent remove greasy molecules dirt on str ucture. Soapy detergents Soapy detergents animal fats hydroxide soap can dirt detergent or solution, molecule Soapy is of ten as calcium do just oils known wit h described shown detergents dissolved are vegetable in not and in Figure lat her as concentrated t he previous are made potassium section. The by or boiling sodium str ucture of a 15.3.4. easily magnesium in salts hard such water. as Hard calcium water and contains magnesium hydrogencarbonate (Unit 21.1). The calcium and magnesium ions in t he hard water displace t he sodium ions in t he soap forming an insoluble precipitate of calcium or magnesium octadecanoate. This precipitate is known as scum 2 2C H 17 COONa(aq) 35 soap Ca (aq) (C H 17 COO) 35 Ca(s) 2 2Na (aq) Figure 15.3.8 Scum forms when soap scum and hard water react 267 Esters: RCOOR Alcohols, Scum removes t he soap from t he solution which alkanoic prevents acids and from doing it esters t he job of removing greasy dir t. t is only when all of t he calcium and magnesium ions have been precipitated out of t he water as scum t hat any remaining soap molecules will Soapless detergents Soapless called form detergents detergents. soapless a detergent lat her are and also They t heir known are molecule do as formed is shown job of removing synt hetic from in dir t. detergents petroleum. Figure t he and The of ten str ucture just of a 15.3.9. O + CH CH CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 O S O CH 2 2 Na 3 O Figure Soapless 15.3.9 A soapless detergents detergents. t herefore, This t hey is do detergent lat her much because not t heir form molecule more easily calcium and wit h hard water magnesium t han salts are soapy soluble, scum. Apar t from t heir different lat hering abilities in hard water, soapy and soapless detergents T able Soapy They they do not are broken Soapy differences and soapless which lather a easily etc. grey, and in by greasy therefore, they sewerage systems lakes rivers. and not or layer detergents Instead wastes around they do do not not contain lather their they the are Some environment, in hard calcium foaming waterways, in e.g. phosphates, are up foam makes oxygen therefore, Some can damage non-biodegradable the environment and are manufactured resource, and oils i.e. will fats not and run Most contain improve compare on hard ● not form salts scum are soluble. the treatment for of aquatic the cause foam waterways. difficult and organisms modern phosphates cleaning environments them on prevents resulting soapless to This in detergents biodegradable. their rapid These and growth turns which ability. by of are causing green added Phosphates eutrophication, algae waterways to pollute (Unit green 20.5). and eventually stagnant. of teacher will soft be renewable supply of They fats the effects of are manufactured resource, will may use a this recording supplied water, pipettes. a The a i.e. eventually soapy from petroleum. run and The a non-renewable supplies of petroleum out. a soapless detergent water observation, Y ou from oils. out. T o Your 268 do soapless They are They magnesium systems sewage dissolving however, makes 15.3.10 and sewerage death. They pollution. in Eutrophication detergents water. non-biodegradable. build i.e. Figure 15.3.1. sinks, aquatic Table detergents since their cause in compared They are, They summarised clothes. i.e. in cause on water. which discolours bacteria do hard scum biodegradable, down are Soapless unpleasant forms showers, They 15.3.1 ot her detergents form soap, have with sample of activity and a assess: reporting. soapy hard to detergent, water, four a soapless boiling tubes detergent, and two a sample dropping Alcohols, alkanoic acids and esters Esters: RCOOR Method 3 1 Label the boiling tubes A, B, C and D. Place 20 cm of soft water into 3 each 2 Using in 3 of a tube Allow Observe Place test 6 Record 7 Compare to form a 2 Name a the C the H 3 Give lather ● for of adding mixture in a hydrolysis Compare and a of the and lather in contents the number each is no to the 10 lather many water seconds. permanent how C to for permanent note D. lather, forms. drops of lather. and soapless of each tube of drops when a of detergent an ester. needed tube. necessary for the formation of esters: C H 2 of butyl of COOC 5 H 3 7 for: ethanoate ethyl from methanoate ethanoic using acid sodium and butanol hydroxide solution. saponication? a soapy effects hard detergent and a soapless detergent by referring to on: b water the environment. concepts Alcohols have t he general formula C H n ● The ● Alcohols ● Alcohol ● Alcohols are t he nature ● a and detergent permanent detergent C vigorously there until of table. equation the 5 form soapy If 2 step soapy b b What of shake minute. to 3 balanced is 1 the required COOCH formation Key and repeating formed following the a drop each questions a their one tube into D. conditions 4 water the stand appearance 7 a 4 to and permanent the 3 2 were results Summary Give to hard add on Continue B your permanent cork appearance steps of 20 cm pipette, tube 2. the detergent 1 and a detergent Repeat to B, dropping A. step soapy 5 and the repeat 4 A The functional wit h molecules polar smaller polar group t hree less are t he of t he alcohols more is t he carbon hydroxyl atoms group, display –OH. str uctural isomerism. polar volatile of alcohols nature of or OH 2n 1 t han t heir corresponding alkanes because of molecules. are completely molecules. soluble Solubility in water decreases as because t he of t he molecular size increases. ● Ethanol dioxide burns and in air water ● Et hanol reacts ● Et hanol can wit h be concentrated as or oxygen steam. sodium dehydrated sulfuric wit h The to to a clean reaction form is sodium et hene by blue ame to form carbon exot hermic. et hoxide being heated and to hydrogen. 170 °C wit h acid. 269 Esters: RCOOR Alcohols, ● Et hanol can be oxidised manganate(VII) ● The reaction The reduction and t he t he produces of breat halyser acidied Et hanol reacts wit h ● Et hanol can it acidied wit h acidied potassium acid and potassium colour alkanoic ● Fermentation is conver ted into et hanol ● Wine r um are ● Alkanoic ● The ● Alkanoic acid ● Alkanoic acids produced acids reacting of ● t he The polar smaller polar t he by acids by from have t he to orange produce reaction yeast by group of under solution. to cr ystals by green used is et hanol in an are less of general alkanoic t he are and water. in which anaerobic carbohydrates are conditions. formula acids is C H COOH 2n 1 t he carboxyl group, –COOH. polar volatile t he ester fermentation. alkanoic molecules of potassium fermentation. chemical made nature nature esters water. n functional and dichromate(VI) dichromate (VII) change acids test. ● and or et hanoic accompanying be by solution alkanoic t han t heir corresponding alkanes because molecules. acids are completely molecules. Solubility soluble in decreases water as t he because of molecular t he size increases. ● Alkanoic acids ● Aqueous ethanoic hydroxide ● Et hanoic ● An ester and acid is a par tially ionise acid metal reacts in reacts wit h carbonates wit h compound water in alcohols formed making reactive t he to metals, same way produce when an t hem an as weak metal oxides, inorganic ester alkanoic acids. and acid metal acids. water. reacts wit h an alcohol. ● The as reaction which esterication. t makes an requires ester a is a catalyst condensation of reaction concentrated sulfuric known acid and heat. ● Esters of ten vegetable ● The ● Acid ● Alkaline have oils are functional distinctive esters group hydrolysis of an hydrolysis of of esters ester of sweet an fr uity long-chain is t he forms ester smells. alkanoic ester an group, alkanoic forms t he Animal acids salt and glycerol. –COO–. acid of fats and and an an alcohol. alkanoic acid and an alcohol. ● Saponication hydrolysis is Soapless ● Soapy detergents scum. Soapless Soapy detergents not detergents contain some are t he animal ● ● 270 of do process fats are not or do not which produced lat her detergents phosphates. by vegetable do easily pollute and is made by t he alkaline in in petroleum. hard t hey detergents t hey water, instead t hey form water. because Soapless non-biodegradable from lat her soap oils. are can contain biodegradable cause and pollution phosphates. do because Alcohols, alkanoic acids and esters Practice a Practice exam-style Draw t he fully scheme When type 1 and 2 refer answering of t he to t he following question, select types t he of most reaction. Name i) ii) A fermentation B reduction c 1 substitution oxidation The process by which et hanol is produced process d by shown in of each t he of reaction A State to which et hanol is of reaction involved in marks) t he of: Glucose to A. C. t he reaction to conditions and any (1 mark) (1 mark) reagents conver t: i) A to B (2 ii) C to A (2 marks) iii) D to A (2 marks) Write a and B balanced between The D marks) from carbohydrates. 2 and (4 type necessar y D C above. t he conversion appropriate reaction. C A, questions b Questions str uctures questions questions compounds Multiple-choice displayed exam-style conver ted to B and chemical equation magnesium and for name t he reaction compound E et hanoic (3 marks) acid. Total 3 During t he et hanol on breat halyser a driver’s test to breat h, detect t he t he presence oxidises t he green to t he orange Cr O 2 reduces t he orange C reduces t he green Cr O 2 ion to t he green Cr t he orange Cr 8 a Describe t he orange Cr O ion of 7 et hanol ion t he green Cr ion laborator y. 7 and Concentrated sulfuric acid is used in t he et hanoic acid and a could prepare suitable a pure sample carbohydrate name et hanol nclude t he an most equation suitable for t he in t he met hod reaction of obtaining of et hanol from t he fermentation mixture. as: (5 A a reducing B an C a catalyst D a neutralising Acid oxidising b agent Fats oils and agent hydrolysis of met hyl et hanoate will and are oils are esters A met hanoic acid B met hanoic acid, C et hanoic acid D et hanoic acid, and of sodium t he consist of soaps. long-chain and carbon t he str ucture of general following will and a fat is represented by not react wit h aqueous write t he C a balanced formation B propanoic C et hyl met hanoate represented D olive oil carbon ii) acid Calculate would question be t he chemical of a soap number present in i) in of t he above equation from t his hydrogen R if group t hat to of information soap. is a The given in t he following you t he group t he questions which fat contains (1 by-product formula of in t he expect glycerol to B has been identied for is be C H (OH) 5 or in water? Give a reason for your H 12 O Mg A (glucose) 6 B (CH 3 COOH) Describe glycerol E + H what reacts would wit h expect sodium. to Give a (an alkene) D (a when balanced State fat or to T WO oil represent ways differs in t he which from a reaction. a soap soapless (3 prepared marks) from a detergent. (2 C marks) obser ve (g) equation A you 2 v) + answer. you. yeast 6 . 3 soluble follow. iv) C 18 mark) manufacture glycerol (2 Compound marks) t hat reaction insoluble answer (2 atoms 3 and represent fat. atoms. Glycerol of Would t he t he formula, water et hanol scheme and acids met hanol met hanol A Study fatty O dioxide iii) 7 Fats produce: hydroxide? Structured manufacture glycerol. f R Which to et hanol et hanol and used which following 6 marks) agent i) 5 a reaction sample between you from 3 O 2 4 how 2 to 2 oxidises ion 7 ion 2 D question 3 3 Cr response ion 7 2 B Extended 2 ion Cr marks of et hanol: 3 A 15 Total marks) 15 marks sweet smelling compound) 271 B16 Polymers Polymers are very large molecules known as Objectives By the be able end of this topic you macromolecules. will They can be natural or synthetic, i.e. to: man-made. ● dene ● explain the term the polymer process of of natural Proteins, polymers, starch and whereas cellulose are polystyrene, examples PVC, addition terylene and nylon are examples of synthetic polymers. polymerisation ● show the how alkenes structure of a are linked in Synthetic polymers give examples ● state of uses of called plastics. the chemistry of polymers is important polyalkenes as the collectively polyalkene Understanding ● are it allows us to use and recycle them efficiently. different polyalkenes. B16.1 Addition The carbon can form atom is unique long-chain macromolecules polymers are among molecules known as all elements known as polymers. t hat are found macromolecules. Polymers are in nature. Some made It of t hese from small molecules known as monomers which are linked toget her, usually in chains. A polymer The molecule reaction may which contain produces t housands a polymer of monomers. from monomers is known as polymerisation Addition polymers are synthetic, i.e. man-made, polymers which are made by addition polymerisation . Addition polymerisation occurs when monomers containing ! A Key fact polymer is a a form a each alkene single carbon–carbon polymer. For this molecule covalent bonds to double occur, breaks. The between bond, one of i.e. molecules adjoining alkenes, the bonds then carbon are in bond atoms linked the to to together double one form a to bond another of by polymer. macromolecule Polyalkenes formed more by linking small monomers, together molecules, usually in 50 known chains. or as Addition known only The polymers as have single bonds carbon–carbon toget her derived is T able known from examples produced polyalkenes. of t he between single as an name Names of alkenes t he are some are carbon bond alkane of polyalkenes 16.1.1 from Polyalkenes (–C–C–) monomer in addition polymerisation compounds t hey t he which The from Table links specic each name monomer unit which it of was a polymer formed. polyalkenes ethene propene monochloroethene Polymer polyethene polypropene polychloroethene will now look at t he is Some 16.1.1. Monomer We are because atoms. linkage. given by saturated formation of polyet hene and polypropene in more detail. Formation of polyethene Polyethene is formed and it wit h by placing et hene (C H 2 heating et hene 272 molecule a catalyst. breaks and One t he of t he saturated ) in a pressurised container 4 bonds in polymer, t he double bond polyet hene, is of each formed. Polymers The Addition addition polymerisation high of et hene can be represented by t he polymers following: pressure et hene polyet hene catalyst, heat In t he formation of polyet hene, t housands of et hene molecules join toget her. We can represent t he reaction using str uctural formulae as in Figure 16.1.1. alkane linkage H H H pressure, C C C C H catalyst, H high C C H n + C C n H H H H H H H H H heat H n many et hene many Figure Formation 16.1.1 of Polypropene polyet hene molecules molecules et hene The formation of polyethene polypropene is formed by placing propene (C H 3 and heating it wit h toget her to form In to show order we must two redraw carbon shown in B a catalyst. Thousands of ) in a pressurised container 6 propene molecules t hen join polypropene. t he t he atoms polymerisation propene joined by of molecule t he propene shown double bond using in are A str uctural below drawn so formulae, t hat only horizontally. t he This is below. H CH H H 3 C H H H A We can now str uctural show C H H how B propene can polymerise to form polypropene CH H CH 3 CH CH H 3 n n pressure C C catalyst, H H H C C C H H H heat H H propene H 3 H 3 high many using formulae: many n propene polypropene molecules Figure molecules 16.1.2 The formation of polypropene If t he monomer contains ot her atoms, groups of atoms or functional groups, e.g. chlorine, uorine or t he et hyl group, t hen t he monomer and t he resulting polymer can represented in Figure H where C C H 16.1.3. X C C n as X H be H H X is Cl, F , C H 2 etc. 5 H n monomer In ● Figure addition t he polymer 16.1.3 Formation of a polyalkenes polymerisation: polymer makes it atoms from is t he possible only for between product t he – t he monomers breaking to link of t he toget her double wit hout bond losing any t hem 273 Addition polymers Polymers ● t he monomers ● t he empirical it ratio atoms Examples Table T able 16.1.2 Examples Monomer of monomers H H their addition in of t he atoms t he two monomers are is polymer lost t he and polymer is are t he during its all t he same same as t he formation, monomer t herefore, t hat t he same. t heir addition polymers are given in t he polymers Cl H F F H F F chloroethene ethene no t he 16.1.2. H H H and since of make formula formed of which H CH H H H C H 5 H propene tetrafluoroethene H 6 3 styrene Polymer H H H Cl F F H CH H C 3 C C H H C C H H n ? know? polystyrene, C H 6 structure shown of six is a C H H addition polymers C C H H 5 n are n polypropene more polychloroet hene is polytetrauoroet hene is polystyrene commonly commonly commonly known by ot her known as polyvinyl knowºn as PTFE and names, for chloride or polystyrene ringed 5 carbon F polytetrafluoroethene example, PVC, In F C n polychloroethene Some you C n polyethene Did C H 6 is atoms of ten called styrofoam. as below. Uses of polyalkenes H Because polyalkenes can be moulded easily into different shapes, are light in C weight, are coloured easily, can be made to be exible or rigid, are good thermal C C C C and electrical insulators and are durable, i.e. they do not corrode or decay, they have a great many uses. Table 16.1.3 summarises some of these uses. T able 16.1.3 Uses of some polyalkenes C Name This can also be represented as: of polymer Uses Polyethene T o make wrap, plastic bags, packaging plastic materials bottles, and sandwich moisture bags, barriers cling used in construction. or Polychloroethene (PVC) T o make and Polytetrafluoroethene (PTFE) As a T o fittings, for non-stick make Polypropene pipe insulation coating low-friction make water electrical ropes, on pipes, wires guttering, and kitchen plastic windows cables. and garden utensils and to bearings. plastic toys, carpets and plastic food containers. Polystyrene (styrofoam) T o make As a in Figure used 274 16.1.4 to make Polyvinyl guttering chloride is fast food protective walls and containers packaging and vending material and an cups for drinks. insulation material roofs. Figure make 16.1.5 ropes Polypropene is used to Polymers Condensation Summary 1 What 2 Explain 3 For is a questions polymer? what each polymers of happens the during following addition polymers, monomer that formed the a H Cl H Cl H Cl C C C C C C H H H H H H polymerisation. draw the structural formula of the polymer: b H H 4 Give of H C C C C C C H H H H H H three examples of addition polymers and give two uses of each them. B16.2 Condensation Condensation Condensation polymers are polymerisation polymers made by involves Objectives condensation linking By the be able monomers toget her in by eliminating a small molecule from between of this adjacent The molecule is of ten water (H O), where one you will explain the process of monomer condensation units. topic to: long ● chains end polymerisation . hydrogen atom polymerisation (H) 2 ● comes from one monomer unit and an oxygen and a hydrogen atom show how linked come from t he adjacent monomer. Instead of water, ot her small in the also be eliminated such as hydrogen chloride (HCl) or structure are of a molecules polyester, can monomers (OH) ammonia (NH a polyamide and a ). 3 polysaccharide The elimination link up of a small molecule makes it possible for t he monomers to ● in give examples polyesters, In contrast to addition polymerisation, during condensation natural polymerisation: t he polymer synthetic polyamides is not t he only product made – polymerisation always forms two products, t he polymer and state the uses made of small polymer is of ten different discuss the harmful effects molecules of t he of polymers anot her ● ● and condensation condensation compound and polysaccharides ● ● of chains. made from more t han one different type of synthetic polymers on the environment. monomer ● t he empirical since In atoms order fo r molecules (–OH) lost types h ave c a r b ox yl of of t he during monomer s m u st and/or d i f fe r e n t formula are to polymer t he fo r m t wo is different formation g roups t he condensation functional condensation of p o ly m e r s , t he p o ly m e r s , g roups, (–COOH). from We monomer polymer. e.g. will t he monomer hy d r ox yl be p o lye st e r s , g roups st u d y i n g t hree p o lya m i d e s and p o ly s a c c h a r i d e s . 275 Condensation polymers Polymers Polyesters O C Polyesters are synthetic condensation polymers that are formed from the condensation reaction between an alkanoic acid and an alcohol. The acid and C X H O O OH the a alcohol H O O H Y acid is, therefore, The number represent a Figure diacid 16.2.1 and a must both have two functional groups in their molecules. The diacid dialcohol Structural of t he known carbon carbon as a diacid atoms chain in to and t he the acid which alcohol and t he t he is known alcohol functional can groups as a dialcohol. var y, are so we can attached by X or Y. The str uctural formulae in Figure 16.2.1 show t he two monomers t hat formulae of are a involved in t he formation of a polyester. dialcohol When t hese eliminated two from molecules between react t hem wit h and an each ot her, ester functional a water molecule group is (–COO– O or –OOC–) forms which links t he two toget her. The str ucture of t he ester C O functional Figure 16.2.2 The ester or ester is shown in Figure 16.2.2. functional A group group polyester forms by linking t housands of t hese monomers toget her linkage alternately in chains, wit h an ester functional group between adjacent monomers. Therefore, we say t hat polyesters are polymers where t he linkages between monomers are ester linkages Figure 16.2.3 uses a diacid molecule and a dialcohol molecule to give a simple representation of how t hey can be condensed to form a polyester ester functional group O C H Figure X C Y 1 O O molecule. (linkage) O X C C O Y O H 16.2.3 H O lost 2 A section of a polyester molecule An or is example by brand formed of a polyester names from a such diacid is as in polyet hylene Ter ylene which X or has terepht halate, Dacron. t he formula C H 6 which Y has t he formula C also known Polyet hylene and as PET, terepht halate a dialcohol in 4 H 2 4 O C N Polyamides H Figure group 16.2.4 or The amide amide Polyamides all contain the amide functional group functional The linkage str ucture Some of the polyamides looking at bot h amide are types functional synt hetic in t his group while is (–CONH– or –NHCO–). shown ot hers in occur Figure 16.2.4. naturally. We will be section. H N NH or 2 Synthetic polyamides H The amino Synthetic polyamides functional two The amino functional str uctural involved in are made from a diacid and a diamine. A diamine has groups formulae t he in formation shown Figure of a in 16.2.6 synt hetic Figure show O C formulae of a diacid and a diamine monomers a diacid N H H 276 Structural Y OH 16.2.6 two H N X HO Figure t he polyamide. C 16.2.5. O as 16.2.5 group Figure H diamine t hat are Polymers When Condensation t hese eliminated which t hese two links t he between two monomers group between polymers Figure molecules from 16.2.7 toget her. toget her adjacent where t he uses a react t hem A wit h and monomers. diacid a by water we say are diamine an molecule group linking wit h monomers and a functional forms chains, Therefore, between molecule in ot her, amide polyamide alternately linkages each an t hat amide molecule is forms t housands amide polymers of functional polyamides are linkages to give a simple representation of how t hey can be condensed to form a synt hetic polyamide molecule. O X C H C 1 O O Y N N X C H H O C Y N H H H H O lost amide 2 functional group Figure An 16.2.7 example diacid in A of section a which of a polyamide synt hetic C X has t he polyamide formula C is H an a which dialcohol is in formed which Y from has a t he 8 12 are natural acids functional of and 6,6, polyamides Proteins amino nylon H 6 Natural (linkage) molecule 4 formula N group amino polyamides toget her. acid and is Amino one given formed acids carboxyl in Figure are by linking molecules functional monomers which group. The have known one str uctural as amino formula 16.2.8. H O C H N C H In t he which amino may acid molecule, contain ot her R atoms amino represents such Figure 16.2.8 Structural formula of an O H R as a variable nitrogen, hydrocarbon oxygen and sulfur, acid molecule group as well as carbon and hydrogen. There are 20 different groups, t herefore t here are 20 different Figure of t he amino 16.2.9 acids uses which two condensation make amino of acid amino up molecules acid H protein molecules. to molecules give to a simple form a molecule. H O N C C H R H H representation protein H O N C C H R9 H N C C 1 H O N C C H H O R H R9 H O lost 2 amide Figure Like 16.2.9 synt hetic amide Formation of a protein polyamides, linkage. In proteins, (linkage) functional group molecule proteins t his functional group contain amide t he linkage is amide also known as t he or peptide linkage Examples collagen such as many of proteins which is ligaments hormones include found and are in keratin t he tendons. also made which connective of is found tissue Haemoglobin, in t hat hair makes enzymes, and up nails and str uctures antibodies and proteins. 277 Condensation polymers Polymers Polysaccharides Polysaccharides as are natural monosaccharides glucose, fr uctose formula C H 6 Starch is as Examples galactose. These are by of all linking monomers monosaccharides isomers wit h t he known include molecular 6 polysaccharide polymerisation. written toget her. and formed O 12 a polymers The follows, formed simplied where n is when glucose chemical t he undergoes equation number of for t his repeating condensation reaction glucose can units in be t he polysaccharide: nC H 6 O 12 (C 6 H 5 glucose The O 10 ) 5 nH n O 2 starch str uctural formula of a glucose molecule is given in Figure 16.2.10. If we t hink of two of t he –OH groups of a glucose molecule as being functional H groups, H C O H t hen we can represent t he glucose molecule X represents t he rest of t he glucose molecule, i.e. C as H 6 H–O–X–O–H, O 10 where . Figure 16.2.1 1 uses 4 two glucose molecules to give a simple representation of t he condensation of glucose O H C molecules to form a starch molecule. H H ether functional C C C H HO OH C H OH group (linkage) X O OH X O H O X H H O O O H X lost 2 Figure 16.2.10 glucose Structural formula of a Figure 16.2.11 Formation of a starch molecule molecule Polysaccharides contain Ot her polysaccharides which is Uses Like found of in plant bres. t hem molecules These ver y ether cell bres useful summarises synt hetic are some are condensation of long strong, t he t he (– O or –) between animal t he starch monomers. and cellulose polymers extremely in linkage glycogen walls. condensation polyalkenes, Their t he include and light in production uses of bot h polymers one of weight of a have t heir and variety synt hetic a variety main uses durable, of and of to which fabrics. natural is Table uses. make makes 16.2.1 condensation polymers. T able T ype of 16.2.1 Uses polymer Polyester of some Name polymer Polyethylene (PET , Polyamide of condensation terephthalate T erylene Nylon or Dacron) polymers Uses T o make bed make PET T o make fishing e.g. Protein T o ✔ Exam is the very important uses of soft cells, and and hair carpets stretch activity and and is and required, wear. nails. T o make some hormones. the that you different Starch Used to produce in living to glucose. energy organisms during respiration after first being as food digested know types Stored a reserve of organisms. polymers. Polysaccharide 278 clothing, carpets. drinks. seatbelts, where antibodies outdoor sails tip Polysaccharide It for lines, stockings body enzymes, boat bottles especially nylon build especially towels, T o clothing, Polyamide clothing, sheets, Cellulose Used to build cell walls of plant cells. in living Polymers Condensation Environmental Synt hetic harmful given ● polymers, effects on t he released from ● ot her wise living synthetic known systems manufacture into t he Many t he plastic of Most plastics items and as polymers plastics, t he are can environment. aquatic organisms, causing suffocation. can lead immune to air Many ● Plastics Their (a) have a variety Some of t hese of are during of ten use persistent, for a great pollution. leading to of t hese and i.e. many They They t heir toxic chemicals continue when t hey to be are released disposed remain in t he years. build are up in t he par ticularly deat h by being environment harmful ingested to or by (b) dense smoke and damage, and poisonous serious cancer healt h and gases when problems, damage to t he burnt. such as ner vous These ast hma, and systems. plastics are water pollution system reproductive ● and variety of are non-biodegradable. to produce a Some t hemselves damage leading Plastics plastics, chemicals doing land of environment. t hese environment ● of below. During of. impact polymers are made ammable. from manufacture is As a petroleum result t hey which contributing to t he is a pose re hazards. non-renewable world wide resource. depletion of petroleum. Summary questions Figure (a) 1 Explain 2 Give what two happens differences 16.2.12 terephthalate during condensation between addition boat sails is Polyethylene used and (b) to make PET bottles polymerisation. polymerisation and condensation polymerisation. 3 Draw the partial monomer 4 Draw the structure of a polyester which is made from four units. structural formulae of the two monomer units in the following polymer: O O O C N H 5 Give two example polymer examples of a of natural synthetic O C N H H condensation condensation polymer. H polymers Give two and uses one of each named. 279 Condensation polymers Polymers Key ● A concepts polymer small ● a Polymers can polymers are ● The ● Add ition reaction form of by are alkene molecule monomer form identical are t he Polyalkenes contain ● Polyet hene, polypropene, examples polyalkenes. Polyalkenes have ● Condensation t he known t he variety polymers of condensation of necessarily monomer are Polyesters ● Polyet hylene Synthetic Proteins ● All a Synt hetic polymerisation polymerisation . molecules adjoining is Alkenes carbon–carbon t he t hen polymer, formulae of double bond carbon t he to one atoms. all t he polymer and polyalkenes linkage (–C–C–) between (PVC) and monomers. polystyrene by involves small condensation linking are molecule polymerisation . monomers from toget her between an t he a in adjacent t he polymer produced, and t he anot her compound monomers formulae of t he condensation polymers formed are not polymer and t he and ester of a of are diacid polyamides of a are amino natural polyamides a by t he dialcohol. linkage (PET), (–COO–) also between known as monomers. Ter ylene or Dacron, is polyester. example are t he are empirical diacid polyamides condensation ● a terepht halate of condensation Natural and synt hetic of contain example ● more different. are ● is The as t he product formed molecules identical condensation Nylon in empirical polymerisation small are Polyesters ● or units. composed an 50 uses. eliminating In add ition polychloroet hene long by toget her chains. natural. known between as alkane polymerisation chains is bond only t he or in plastics breaks. Condensation monomer ● a linking usually same. polymers ● by one bonds and ● of as polymer when Alkenes ● a covalent by man-made, formed ● ● i.e. polymerisation are formed monomers, known forms polymers single addition as synt hetic, polymers monomers t he be known which each anot her In macromolecule collectively addition bond ● is molecules, condensation and a polymers formed by t he diamine. synt hetic polyamide. condensation polymers formed by t he acids. polyamides. contain t he amide linkage (–CONH–) between monomers. ● Polysaccharides condensation ● Polysaccharides ● Starch, ● Condensation ● Synt hetic are contain and t he condensation t he ether cellulose polymers polymers and natural polymers formed by t he monosaccharides. glycogen systems 280 of can have have are a a environment. linkage (–O–) examples variety variety of of of between monomers. polysaccharides. uses. harmful effects on living Polymers Practice Use Practice exam-style t he information to answer exam-style t he questions following questions questions. i) Multiple-choice 1 Which of t he type of polymerisation formation What of EACH following is not an addition ii) polymer? Draw unit A polystyrene B ter ylene C polyet hene D polypropene t he of A Amide linkages involved are found polymer? str uctural and iii) Name t he iv) Name ONE could be of formula of EACH I proteins ter ylene (2 unit naturally (1 occurring represented which of B. by C makes and up nylon A I and B II only C I D I, and II b The two polymer name t he t he polymer you O only O and F, illustrated below, O C 3 Amino and have marks) polymerisation. X C HO Y OH O E II mark) t hat (2 compounds, E only III marks) in: undergo III t he marks) monomer named. II in (3 B. monomer monomer 2 is questions F III acids are so called because i) t hey: group A contain t he NH B contain t he COOH C turn D contain Using of F, T WO show molecules how t he of E and T WO compounds are molecules linked 2 blue litmus t he toget her group red NH ii) group and t he COOH group Name in In a condensation polymerisation par t i) form type monomers 2 4 to t he in a of t he above polymer. linkage polymer and (2 formed name you t he between have type t he polymer has a different t he drawn of reaction, polymer. A marks) empirical formula to (2 marks) t he iii) Give a named example of t he type of polymer monomer drawn B one product is formed C t he polymer is always in i) above and state T WO of its uses. (3 monomer D water is formed from one type Total only always The monomer of starch fr uctose B sucrose C galactose D glucose Which of t he following response Polymers is not tr ue about are are What b Polymers They are question can polymers and in ever y aspect of our daily named be (1 classied into condensation addition two groups, polymers. polymer and Briey ONE discuss named plastics? B They are easily C They are good D They are easily your condensation polymer. You should include answer: biodegraded. i) The str ucture of t he monomer units of EACH insulators. polymer. (2 Appropriate monomers str uctures are linked to to show form how EACH t he polymer. question (4 a The marks) moulded. ii) 7 mark) addition ammable. in Structured lives. polymers? synt hetic A found a ONE 6 marks is: 8 A 15 produced Extended 5 marks) of str uctures A, B and C represent t hree types marks) of iii) The name of t he type of linkage formed between polymers. t he H H H H H C C H CH C C H CH C C H CH c T WO Addition addition 3 3 uses of EACH polymers EACH polymer. are polymer. formed polymerisation formed Give O in and by a process H O H T WO by condensation N C C N CH C H C CH 3 marks) called condensation polymers differences between t he two types N H 3 of O C C d Give T WO synt hetic H marks) (2 polymerisation. polymerisation. B (2 3 are H units H iv) A monomer (2 disadvantages polymers of t he (plastics) in extensive today ’s use of world. CH 3 (2 C O marks) X Total marks) 15 marks 281 Section C Characteristics of metals C17 Most elements in the periodic table are metals. In fact, Objectives By the be able end of this topic you will metals table. ● describe the properties physical of relate of for about 80% of all the elements study of metals, in the the metals metal physical to atoms Metallurgy, oldest applied the sciences, dating back to is one 6000 BC of the with the way are discovery of gold. Metals have a variety of physical to play properties in which bonded in and chemical properties which enable them an the extremely metallic i.e. metals the ● account to: important part in our daily lives. lattice. C17.1 Physical Metals are usually 1, table and elements 2 or 3. whose Most between properties atoms metals Groups are have found and as a of metals small in number Groups t he , transition of valence and of electrons, t he periodic metals. n Unit 5.4 you learnt t hat t he type of bonding between metal atoms in a metal is known as proper ties of metal t hat t he t he The as a result cations lattice between as metallic t he way in of t his held positive and t hat bonding. surrounded is metallic bond ing by toget her cations a and Recall ‘sea’ by t he t he metals of have t hat a ver y metal delocalised, strong lattice mobile electrostatic delocalised, distinct composed electrons force negative is physical of and attraction electrons known bond which t he metal atoms are bonded in metal lattices helps us to understand t he physical proper ties of metals. We will consider some of t hese in detail Metals The below. have high melting electrostatic forces points of and boiling attraction between negative, delocalised electrons are relatively of heat metals. energy All exception Metals The Figure 17.1.1 Because good conductors used to make of frying metals heat pans they are are mercur y good delocalised and allowing an heat required metals of position as are are separate found in which is electrons free to move. solid state metal These heat atoms electricity t he to t he t he positive and at in order room to melt or temperature, boil t he wit h t he and lattice moving be carried to be heat are not electrons t hrough carried t he t hrough held act as any charge metal. t he in They metal xed carriers also act when, for are are example, a ame, Metals one t he end ot her have a of a end shiny piece of of t he metal metal is placed quickly in a heats hot environment, up. lustre Lustre is t he shininess of a metal. Metals generally have a ver y shiny, metallic lustre. This is because t he mobile electrons reect t he photons of light back from t he metal surface before t hey 282 cations strong. As a result, large amounts liquid of in current allowing t he a conductors electric carriers to points are Figure allowed 17.1.2 to This penetrate silver cup far has a into shiny t he surface. metallic lustre such as Characteristics Metals are Metals are a is force can be of metals hard, bent meaning malleable considered applied to and t hat Chemical to be t hem. and hammered t hey can be and reactions of metals ductile hard They properties because are, into drawn t hey however, different out into are not easily malleable shapes. wires. They This is damaged meaning are also because when t hat t he t hey ductile, atoms in t he metal are all of t he same type, t herefore t hey are all t he same size. f force is applied to t he metal, t he atoms can roll over each ot her into new positions wit hout breaking Metals The Figure have metallic 17.1.3 high density substance t he This gold ring demonstrates the malleability of metals densities of any its volume. by bond. substance is Metals calculated have high by dividing densities t he because mass t heir of t he atoms are packed ver y closely toget her. This means t hat t here are as many metal atoms as possible in a given Summary 1 Explain 2 Why 3 Explain why are malleable 4 Why do C17.2 Because by losing metals have good terms and metal. high melting conductors ‘malleable’ and of points and electricity ‘ductile’. boiling and Explain points. heat? why metals are ductile. metals have a high density? Chemical properties and reactions of metals metals electrons, of questions metals the volume are usually t hese elements 1, 2 or valence 3, whose t hey atoms form electrons. This have positive can be a small cations in number of chemical summarised as Objectives By the be able As a M ● result, metals describe various form ionic behaves as a reducing agent it ot her compounds when t hey react and t he the water and name the reactant to gain electrons metal water We will dilute now an metal’s look at indication position t he dilute of oxygen, acids products balanced various gives with formed by reactions write ot her substances, e.g. oxygen, water and acids. The way in which a par ticular t he will (RG). equations to reactions metals Some metals are relatively stable while ot hers react violently when exposed to reacts you since it gives electrons to t he ot her reactant, i.e. ● related topic metal the t he this ne ● causes of to: reactions follows: n M end valence in of its t he reactions of reactivity. periodic cer tain The reactivity of a metal is for metals and chemical the reactions with dilute of oxygen, acids. table. metals wit h oxygen, water and acids. 283 Chemical properties and reactions of metals Characteristics The reactions Some metals t he oxygen and see be in to stored barrier, be t he around exposure to can air of exposed air. us. some t he with air of metals e.g. metals so t he to and t hat wit h sodium. into great we oxid ises vigorously coming any ones metals potassium from reacting include ot her react metals oxygen wit hout metals surface parafn, preventing to These The and under metals of use regularly oxygen t hey parafn wit h t he This metal Figure stored 17.2.1 under Sodium parafn has to to be prevent Table it acts with oxygen in the of 17 .2.1 summarised oxygen shows Potassium exposed Reacts very potassium t he metal what happens following the reaction T able 17.2.1 Description of Reactions the of metals when cer tain to readily dry air when forming Burns oxide heated in vigorously oxygen Reacts very metals Reacts wit h oxygen in Products formed when heated and equation with a lilac Forms a white powdery solid, potassium oxide: flame readily forming Burns oxide O (g) 2K vigorously with an orange Forms a 4Na(s) O(s) 2 white powdery solid, sodium oxide: flame readily calcium react reaction O (g) 2Na 2 Calcium metal equation: air 2 sodium word oxide with 4K(s) Sodium general air. Metal when by a air Description be as from t he reacting can on have air. When metals react wit h oxygen, t hey form ionic compounds known as oxides. wit h immediately The contact extent to form coating of oxide Burns very easily with a brick red Forms a 2Ca(s) O(s) 2 white powdery solid called calcium oxide: flame O (g) 2CaO(s) 2 Magnesium Reacts of slowly to magnesium form a coating oxide Burns easily with a bright white Forms a white powdery solid, magnesium oxide: flame 2Mg(s) O (g) 2MgO(s) 2 Aluminium Reacts coating slowly of to form aluminium a thin Burns oxide when especially if heated strongly, Forms a white powdery solid, aluminium 4Al(s) 3O (g) 2Al 2 Zinc Reacts coating very of slowly zinc to form oxide a thin Burns when especially oxide: powdered if heated strongly, Forms a 2Zn(s) O 2 white powdery solid, (s) 3 zinc oxide, which is yellow when hot: powdered O (g) 2ZnO(s) 2 Iron Does not react with dry air Burns when especially if heated strongly, Forms a 3Fe(s) black powdery solid, 2O (g) Fe 2 Copper Does not react with dry air Does not does form iron(II, III) oxide: powdered burn an when oxide heated, coating but Forms a 2Cu(s) O 3 black solid, copper(II) (s) 4 oxide: if O (g) 2CuO(s) 2 heated Silver Does not react with dry air Does not heated f very t he react, very water to form form oxides form at potassium, and hydroxide, hydroxide which calcium reactions example, is and sodium calcium slightly hydroxide can 284 t he reacts reacts All t he water, reacts wit h wit h Potassium alkalis. t he reactions are of calcium found in metals and Groups wit h oxygen magnesium and of are t he periodic table. in t he t he most periodic lef t of t he table. n general, t he reactivity of metals across in oxide oxide oxide soluble. are dissolve potassium t he wit h water water to hydroxide, ot her oxides in insoluble. sodium, metals t hese For potassium hydroxide are in alkaline. sodium hydroxide Looking produced is soluble soluble 17 .2.1 These when solution calcium sodium Table even strongly metal resulting to strongly air we see reactive table, i.e. t hat metals. to t he far decreases from lef t to right Characteristics The of reactions Metals can also metals t hat are to metals be of Chemical metals added ver y to with water reactive wit h to properties and reactions of metals water determine oxygen are t heir highly reactivity. reactive n general, when exposed water. When a metal produced. The reacts wit h reaction water, can be t he metal summarised hydroxide by t he and hydrogen following general are word equation: metal water metal hydroxide hydrogen When a metal reacts wit h steam, t he metal oxide and hydrogen are produced. The reaction metal Table into 17 .2.2 be wit h 17.2.2 Metal summarised steam shows contact T able can what water Reactions Reacts water t he metal very happens or of Description Potassium by the when a with water reaction vigorously producing oxide general word equation: hydrogen cer tain metals are allowed to lilac with cold or steam Products formed and Potassium hydroxide equation and hydrogen: flame 2K(s) 2H O(l) 2KOH(aq) H 2 Sodium Reacts water, vigorously producing come steam. metals of following with an cold orange Sodium (g) 2 hydroxide and hydrogen: flame 2Na(s) 2H O(l) 2NaOH(aq) H 2 Calcium Reacts moderately with cold Slightly (g) 2 soluble calcium hydroxide and hydrogen: water Ca(s) 2H O(l) Ca(OH) 2 Magnesium Reacts water very and slowly slowly with with cold hot W ith water water: hydroxide Mg(s) (aq) very and vigorously with steam W ith 2H slightly soluble O(l) steam: Mg(s) H Does not water. react Reacts with with cold or hot Aluminium magnesium Mg(OH) (aq) magnesium oxide O(g) and MgO(s) not water. react Reacts with with cold or hot hydrogen: 2H oxide and hydrogen: 3H O(g) Al Zinc oxide O 2 and (s) Does not react Reacts with with H hydrogen: O(g) ZnO(s) H cold or hot Iron(II III) not (g) 2 oxide 4H and hydrogen: O(g) Fe 2 Does (g) 2 steam 3Fe(s) Copper 3H 3 2 water. (g) steam Zn(s) Iron (g) 2 2 2 Does H 2 steam 2Al(s) Zinc (g) 2 2 Aluminium H hydrogen: 2 Reacts 2 react with water or react with water or O 3 (s) 4H 4 (g) 2 steam Silver Does not steam t can water. to be react water. most seen They from do, means Once Table however, t hat again, vigorously t hey 17 .2.2 react are less potassium, wit h t hat wit h some steam. reactive sodium of t he The t han and metals fact t he t hat ones calcium do not t hey t hat are react require react metals wit h steam wit h t hat cold react water. When potassium and sodium react wit h cold water, t hey bot h roll into a ball and move rapidly around on t he surface of t he water as t hey decrease in size. As t hey move, a lilac ame forms around t he ball of potassium and an orange ame forms around t he ball of sodium. The lilac ame around t he potassium is shown in Figure 17 .2.2. Figure 17.2.2 around potassium cold A lilac ame when it forms reacts with water 285 Chemical properties and reactions of metals Characteristics Investigating (T eacher Your ● teacher teacher Great of metals with metals water demonstration) may observation, Y our reactions of care use this recording will perform must be activity and the taken to assess: reporting. following when experiment. reacting potassium and sodium with water. Method 3 1 2 Place about clean magnesium Look for 2 cm signs of of distilled ribbon. water Leave effervescence into a test undisturbed and dip a tube for piece and one of add a piece of hour. red litmus into the solution. 3 3 4 Place about piece of Look for by 5 Half a a Look for surface a of 7 9 the Which Table t hat 17 .2.3 286 is a with at gas for water surface Note the the the of the mouth and the effervescence with of with a a test tube and add a as potassium of the the place a presence tube. very Dip small of a hydrogen piece piece of red of water. the colour small potassium of the ame disappears, piece sodium, test burning splint. reacted We and by is the chemical of most of for sodium. the dip If a presence vigorously can react again are with ver y When moves that a around forms piece ame of of on the around the red does litmus not hydrogen water t he and form by which touching reacted word metal t he reactions. acids except nitric metals reactive on four dilute salt happens a the acids, t hat general depends what chloride. wit h acid produced for with see also following metal acid. equations metals metals water t he shows hydrochloric formed another solution. reactive oxygen salt into vigorously? reactive The of reactions summarised the water. ball hydrogen. wit h trough balanced general, and 6 metal least Write The n the sodium the When around the solution. trail step test into the Repeat the 8 into and splint onto potassium. paper water burning large potassium 6 distilled effervescence paper ll of calcium. placing litmus 2 cm wit h acid, which acids. are The to form ver y a salt reactive reaction can be equation: hydrogen metal used when cer tain reacts wit h and t he metals acid. react hydrochloric wit h acid dilute t he salt Characteristics T able 17.2.3 of metals Reactions Chemical of Metal Description Potassium An extremely metals of the violent with hydrochloric reaction reaction occurs properties and reactions of metals acid Products formed Potassium chloride and and equation hydrogen: 2K(s) 2HCl(aq) 2KCl(aq) H (g) 2 Sodium A violent reaction occurs Sodium chloride and hydrogen: 2Na(s) 2HCl(aq) 2NaCl(aq) H (g) 2 Calcium A fairly violent reaction occurs Calcium chloride and hydrogen: Ca(s) 2HCl(aq) CaCl (aq) H 2 Magnesium A very vigorous reaction occurs Magnesium chloride and hydrogen: Mg(s) 2HCl(aq) (g) 2 MgCl (aq) H 2 Aluminium A vigorous reaction occurs Aluminium chloride and hydrogen: 2Al(s) 6HCl(aq) 2AlCl (g) 2 (aq) 3H 3 Zinc A fairly vigorous reaction occurs Zinc chloride and hydrogen: Zn(s) 2HCl(aq) ZnCl (aq) H 2 Iron A very slow reaction occurs Iron(II) chloride and hydrogen: Fe(s) 2HCl(aq) FeCl Does not react with dilute acids – Silver Does not react with dilute acids – Looking t hat at t he reactions potassium, of sodium, metals wit h calcium hydrochloric and magnesium acid are we t he can again most (g) 2 (aq) H 2 Copper (g) 2 (g) 2 see reactive Did ? you know? metals. It The reactions between t he metals and dilute sulfuric acid are ver y similar is unadvisable reactions t he reactions which occur wit h dilute hydrochloric acid. However, when reacts wit h sulfuric acid, t he salt formed is a the Your teacher reactions may use this of activity ● observation, recording ● analysis interpretation. Y ou will zinc, be iron tubes and supplied and and a with copper, wooden metals and the sodium with an acid because and these dilute metals react reactions are so violently that dangerous. acids assess: reporting samples dilute to with perform potassium, sulfate. three Investigating of a calcium metal to to of the metals hydrochloric acid, magnesium, dilute sulfuric aluminium, acid, ve test splint. Method 3 1 Carefully ve 2 test Label place about 2 cm of dilute hydrochloric acid into each of the tubes. each tube with the symbol of the particular metal that will be added. hydrogen 3 Add a small piece of metal to each tube so that each tube contains lighted 4 different metal Observe each test the gas as indicated tube for for by signs its of presence of hydrogen the tube feel by If effervescence placing a lighted is seen, splint at the mouth of and splint label. effervescence. the the bottom of the tube to see if Figure 17.2.3 If no effervescence is seen, heat the tube gently. the presence If effervescence is holding mouth pop’ seen on gas production can be of conrmed warm. by 5 The it hydrogen becomes gas a heating, test the gas for of hydrogen. Make of a the sound lighted test will splint tube. identify A near the ‘squeaky the gas as sure hydrogen. that acid you do boils. source of not confuse effervescence Effervescence heat, boiling continues does with after bubbling the tube is that occurs removed if the from the not. 287 Reactions of metal compounds Summary 1 Write a Characteristics questions balanced 6 Repeat for method using dilute hydrochloric acid. Record observations sulfuric acid in place of metals dilute chemical 7 equation the of each of your in a table, noting if the reaction needed the heating. following reactions: a calcium b zinc c reacting with reacting with hydrochloric acid iron with reacting 8 oxygen Did the metal even sulfuric 9 In metals reacted when what differ the in their most reactivity vigorously with and the which acids? If showed they no did, which reaction at all, heated? ways were the reactions between the metals and the 17.2.3 until two acids acid. similar? 2 How do the products of 10 reactions differ when Aluminium with water and reacts with balanced each steam? chemical Write Which seems reactive, equation iron seem reactive, metals to be or to be the balanced dilute sulfuric t he react in T able the test why? chemical equations for the reactions of the metals with acid. Group or the end of I metals, transition Group II metals? from topic you t he is metal reactions oxides, sulfate. the reactions of carbonates possibly t he test discovered tubes were t hat aluminium heated. This is did because wit h These wit h a t hin acids lm oxide salts when of for ming dissolve cold. aluminium soluble and t he When oxide heated, aluminium aluminium t he whic h acids prevents c hlor ide is t hen or able react wit h aluminium to react wit h Reactions of metal compounds have will already review come t hese across and some look at of t he some reactions new of metal reactions in compounds. t his unit. The of hydroxides with describe you until acids. we will be looking at include metal oxides, metal hydroxides, and metal carbonates coated aluminium You the acids will to: describe t he reacting C17.3 this exper iment, wit h compounds ● suggest least We ● described you copper? Objectives the as Can more t he able react for it be not heated. Write aluminium Which By did were reaction. not 4 differences? a Dur ing 3 any when 11 it there magnesium tubes reacts Were the carbonates and metal nitrates. acids decomposition metal and Reactions nitrates, of metal oxides hydroxides. Metal oxides summarised metal This a react by oxide reaction is wit h t he to form general acid known base t hat neutralises reacts wit h an acid acids following as a t he t he a salt word salt acid to form a reaction salt becomes water. The reaction can be water neutralisation reaction and equation: and since water. warmer t he When because it is metal a oxide metal oxide exot hermic. Examples 1 Copper(II) sulfate oxide and reacts H SO 2 During Figure oxide 17.3.1 slowly Black powdery disappears in sulfuric acid to produce soluble copper(II) water: CuO(s) wit h t he (aq) CuSO 4 reaction, (aq) H 4 t he black, powder y O(l) 2 copper(II) oxide disappears copper( II) slowly and sulfate is a blue solution forms. This is because soluble copper(II) sulfuric 2 acid as it copper( II) 288 reacts sulfate to form soluble, produced which blue speeded up by heating it. contains blue Cu ions. The reaction is can be Characteristics 2 of metals Magnesium oxide magnesium chloride MgO(s) Reactions reacts wit h and hydrochloric acid to O(l) white, acid to 2HCl(aq) powder y form Reactions Metal can MgCl is a of metal also summarised metal (aq) t he and exot hermic, is it also a of H soluble 2 disappears magnesium wit h acids following to acid t he form general acid becomes to a as it reacts wit h t he chloride. salt word salt neutralisation it compounds hydroxides neutralises t herefore oxide solution react by hydroxide reaction base magnesium colourless hydroxides be This a metal water: 2 The produce of a water. The reaction water reaction form and equation: since salt and t he metal water. hydroxide The reaction is warmer. Examples 1 Copper(II) nitrate hydroxide and reacts Cu(OH) (s) 2HNO 2 During t he solution wit h nitric acid to produce soluble copper(II) water: (aq) Cu(NO 3 reaction, forms due t he to blue t he ) 3 copper(II) production (aq) 2H soluble O(l) 2 hydroxide of 2 disappears copper(II) and nitrate a blue which 2 contains 2 Zinc blue Cu hydroxide chloride and ions. reacts wit h hydrochloric acid Zn(OH) (s) 2HCl(aq) ZnCl 2 The to white, form a Metal The powder y of metal When carbon a can zinc react be metal soluble zinc (aq) 2H disappears zinc O(l) 2 at it reacts wit h t he acid chloride. carbonates wit h carbonate is of acids summarised carbonate dioxide hydroxide solution metal carbonates reaction produce 2 colourless Reactions to water: to by form t he acid reacts a salt, salt wit h carbon following an acid, dioxide general carbon word and d ioxide effer vescence water. equation: is water seen as t he evolved. Examples 1 Calcium nitrate, carbonate carbon CaCO (s) reacts dioxide During t he calcium solution nitric acid to (aq) fairly quickly of produce soluble calcium CO water: Ca(NO 3 reaction, carbonate colourless and 2HNO 3 wit h ) 3 vigorous as it reacts (g) H 2 effer vescence disappears calcium (aq) 2 occurs, wit h t he O(l) 2 and t he acid to white form a nitrate. 289 Reactions of metal compounds Characteristics 2 ron(II) carbonate carbon dioxide FeCO (s) reacts and H 3 Fairly SO a acid (aq) FeSO 4 to produce green (aq) CO 4 effer vescence and sulfuric iron(II) metals sulfate, water: 2 vigorous disappears wit h of occurs. solution The forms H 2 green due to iron(II) t he O(l) 2 carbonate production of quickly soluble 2 iron(II) sulfate which Decomposition Many metal contains of green metal compounds Fe ions. compounds decompose when t hey are heated. Table 17 .3.1 summarises t he effects of heat on metal nitrates, metal carbonates and metal hydroxides. T able 17.3.1 The effect Metal of heat on metal nitrates, metal carbonates and metal hydroxides compound Metal Nitrates Potassium Carbonates Decompose to form the metal nitrite and Do oxygen: not The Sodium 2NaNO (s) 2NaNO 3 Decompose Calcium dioxide (s) O 2 and to form the metal Hydroxides decompose. carbonates are Do stable. not The decompose. hydroxides are stable. (g) 2 oxide, nitrogen Decompose oxygen: and carbon to form the metal oxide Decompose dioxide: water (as to form the metal oxide and steam): Magnesium 2Mg(NO ) 3 Aluminium 2Cu(NO 3 Zinc (s) 2MgO(s) 4NO 2 ) (g) O 2 (s) 2CuO(s) 4NO 2 (g) MgCO 2 (g) O 2 (s) MgO(s) CO 3 (g) CuCO 2 (g) Mg(OH) 2 (s) CuO(s) CO 3 (s) MgO(s) H 2 (g) Cu(OH) 2 O(g) 2 (s) CuO(s) H 2 O(g) 2 Iron Lead Copper Sliver Decomposes dioxide and 2AgNO to form the metal, silver, nitrogen oxygen: (s) 2Ag(s) 2NO 3 (g) O 2 Silver carbonate is unstable. too does not exist since it Silver too hydroxide does not exist since it is unstable (g) 2 When some metal compounds are heated and they decompose, are obser ved. For example, when the compounds of copper colour changes are heated they change colour from blue or blue-green to black because black copper(II) oxide is formed in each reaction. When compounds of lead are heated, they change colour from white to yellow because yellow lead(II) oxide is produced. Tests given in Table 22.3.1 on page 354 can be used to identify the oxygen, nitrogen dioxide, carbon dioxide and water vapour produced when metal compounds decompose. Looking at t he decomposition of metal compounds we can see t hat potassium and in Investigating Your ● teacher will be and dry test this recording with hydroxide, tubes, one activity and water, tted form of stable t he which decomposes ver y to of metal compounds nitrates, are too easily only unstable and which do decompose to completely exist not decompose slightly. or, when in on However, t he case of heating silver silver nitrate, heated. compounds assess: with of sodium nitrate, a wooden splint, a cork which has calcium nitrate, sodium a piece of blue litmus a delivery tube running carbonate, paper, a copper( II) piece through it. of cobalt carbonate, chloride or, forms reporting. samples lime case compounds decomposition use supplied magnesium 290 may observation, Y ou the sodium t he paper Characteristics of metals Reactions of metal compounds Method 1 Place still 2 3 a spatula heating Repeat to fumes. If Place end a of 1 step begins be have Repeat step 5 Place a spatula paper across Describe 7 Which 8 Explain 9 Write 2 3 Write 3 of the balanced a sodium saw did chemical piece into a the each you saw equations for chemical equation reaction between magnesium between copper( II) c the reaction between zinc and explain oxide is Write balanced into metal a calcium b potassium zinc test tube nitrate. litmus should tube. strongly glowing do Place until the lime in test the the cork water see slowly time into this you splint This paper containing place in a of test copper( II) tube was Explain you the for reaction lead( II) in when the d blue you compound the c a sodium a for brown fume into (see vigorous into the oxygen gas. effervescence. While tube. when T ake a care brown not to gas inhale the cupboard. the mouth Figure of the 8.1.2). tube Heat the with test the other tube and carbonate. heat strongly. Place a piece of dry cobalt chloride tube. b following test hydroxide a put of moist into heat heated. why. heated copper( II) decomposition carbonate. reactions. questions balanced Describe of and inserting available, decompose? change tube by place carbonate when not test water. magnesium you colour lime of in carbonate leading the mouth compound a a oxygen cupboard copper( II) tube into of nitrate Place fume using the what Summary 1 of nitrate presence calcium observe 4 6 a delivery and the produced. you the sodium for using spatula strongly of test the sulfuric chemical and which to following: and and sulfuric heated equations the hydroxide change and of carbonate oxide colour acid each nitric acid hydrochloric acid acid. occurs when copper( II) gently. show the effect of heat on the compounds: carbonate nitrate hydroxide nitrate. 291 Reactions of metal compounds Characteristics Key ● Metals are reactions A metal elements usually by The is whose 2 or 3, t hese atoms and valence composed of have t hey a small form number positive of valence cations in chemical electrons. metal cations surrounded by a ‘sea’ of electrons. electrostatic negative 1, losing lattice delocalised ● metals concepts electrons, ● of attraction electrons, known between as t he positive metallic cations bond, and holds delocalised t he metal lattice toget her. ● ● n general, have densities. The high Metals of form a behave ● Metals react ● f ● Potassium, metal Ot her and ● ● as ● are and chemical ionic agents to form in calcium except points lustre, explained in form dissolve sodium, be cations t hey hydroxide and and boiling malleable by relating points, and conduct ductile t hem to and t he in and by losing valence reactions. metal water reactions compounds oxides. t hey form magnesium alkaline react solutions. wit h water to form hydrogen. copper, react wit h steam to form t he metal oxide Metal metals react oxides react hydroxides is a Metal hydrochloric acid and sulfuric acid to form a wit h acids to form a salt and water. The reaction is a reaction. Metal also wit h hydrogen. neutralisation ● can oxygen can melting shiny lattice. reducing wit h metals, a hydrogen. Reactive salt metals metallic result oxides high have positive As Metals metal of t he ● t he heat, proper ties electrons. ● have and str ucture ● metals electricity react neutralisation carbonates react wit h acids to form a salt and water. The reaction reaction. wit h acids to form a salt, carbon dioxide and water. ● The t he ● nitrates metal The ● ● t he Silver of nitrate oxygen. The carbonates to carbonates form t he and sodium decompose when heated to form oxygen. oxide, when and metals, except nitrogen decomposes and The and ot her metal decomposed ● potassium nitrite nitrates form of silver, dioxide when hydroxides heated of decompose and to when heated to oxygen. form potassium silver, and nitrogen sodium are dioxide not heated. of ot her metals, metal oxide and except carbon silver, dioxide. decompose Silver when carbonate heated does not exist. ● The t he 292 hydroxides metal oxide of metals, and water except as silver, steam. decompose Silver when hydroxide does heated not to exist. form Characteristics of metals Practice i) Practice exam-style Complete t he table by exam-style writing in t he ii) Using All solid lose at room electrons form A B symbols A and B, as shown above, write balanced equations temperature when t hey react t he reaction between A and steam – t he reaction between B and hydrochloric – t he between A and oxygen. acid reaction (5 and and i) When following B When nitrates are heated, one or two may be given off. From t he nitrates of only statements are all tr ue metals calcium reacts hydroxide and ron more reacts wit h cold calcium, sodium, zinc and copper, except: select A most only t he The marks) only gases 2 t he – soluble basic oxides when they react with oxygen b D t he for only and C marks) in following: metals: are t he (3 questions table 1 missing questions information. Multiple-choice questions water it forms ONE nitrate t hat: calcium – gives off – gives off ONE gas hydrogen. vigorously t han zinc wit h T WO gases. (2 marks) hydrochloric ii) Write t he equation for t he reaction which acid. gives C Magnesium burns readily in c D 3 When silver Metals can A t he atoms B t he cations C t here nitrate conduct an decomposes electric it forms current An t he metal t he gases metal, Z, above. was (2 found to react marks) in a ver y silver. similar way of on heat to t he magnesium. How carbonate Z of would differ t he from action t he because: of heat on sodium carbonate? vibrate Give in T WO unknown action in off air. metal lattice are mobile between t he atoms t he relevant equation(s) given t hat Z forms 2 t he are lattice D some small which of t he spaces allow electricity electrons in t he to pass metal in t he Which of t he A Metals B All C react metal wit h and Copper is a are reacts in t he air readily to when wit h form when decomposes dioxide Total Zinc liberates hydrogen gas acidic oxides. 8 a response Metals heated. into magnesium heated. hydrochloric have common. acid. cold are high melting are malleable metals, physical good and points. explain ductile By t he proper ties conductors and reference reason for of in electricity, t hey to have t he EACH bonding of listed. Zinc carbonate, copper(II) oxide and water sulfuric A B hydroxide are nitric in acid each and and C , D t hree treated wit h separate excess dilute experiments. reaction using t he following sub-titles: only and obser vations on adding dilute nitric acid only explanation of t he equation t he obser vations iii) for reaction. (9 When sodium nitrate but t hey melt B t hey form a brown, C t hey form a gas D t hey evolve a Structured The do cr ystals A not a causes squeaky table A below gives and and Charge on Metal B, some t heir glowing a lighted splint splint to be pop information about two reactions. the Action metal of water on the Does not react with cold does react with steam Action of on metal dilute metal ion but a question metals, 2 marks heated: gas relights which wit h are 15 decompose acidic which gas extinguished B marks) only Total A Discuss acid i) a marks) magnesium steam ii) 7 t he (6 from: EACH 6 marks question cer tain They t hey in b 15 mobile proper ties 5 marks) statement? decompose carbonate carbon tr ue oxygen hydroxides Magnesium oxide D following (3 t hrough lattice Extended 4 ion. Z metal or hot hydrochloric acid Action the water Burns if Reacts of air when on the heated metal strongly, especially powdered violently 293 Reactivity, extraction and C18 uses Metals of vary metals considerably in their reactivity. Some are Objectives By the be able end of this topic you will so reactive with ● discuss ● describe the reactivity of metals oxygen metal between metals must be stored out of contact unreactive. explain the basis series of the reactivity of of order moisture The in reactive the air. metals Others occur in are the extremely Earth’s ionic compounds from which they are extracted. compounds are known as ores. The unreactive the occur in the Earth’s crust in their elemental state. metals Metals of metals experimental in These ones deduce or and compounds reactivity ● they displacement crust reactions ● that to: based on of the are used things we extensively by man see us and around to make this many makes their results. extraction C18.1 t is The possible reactions. from ● t he t he extremely to The determine reactive strengt h of hydrochloric how ● displacement will now Strength dilute t heir t he of each metals least dilute series is reactive wit h are a of list metals of based oxygen, sulfuric by metals on t he water looking arranged at in t heir order following: and dilute acid decomposed between of metals reactivity compounds at of reactions reactions look of or t he series to t heir acid ● We easily reactivity reactivity most important. t he metals when and heated metal compounds. t hese. reaction with oxygen, water and acids You studied t he reactions of a variety of metals wit h oxygen, water and dilute acids ● ● in Unit Potassium, metals sulfuric acid. Copper is from oxygen, potassium, nally n Unit easily 4 its ionises, t hese calcium wit h least or at reactive dilute and oxygen, acid. we see cer tain magnesium water metal Silver can and wit h does trends. appear to hydrochloric oxygen not react and it wit h be t he most not react and does oxygen, water or acids. Star ting wit h t he steam dilute Looking sodium, reactive wit h ● 17 .2. potassium, water sodium, and t he strengt h dilute calcium, acid of t he decreases magnesium, reaction in t he zinc, of t he metals following iron, copper order: and silver. you atoms t he learnt t hat ionise, more t he known reactive it reactivity as is. ease Of t he of of a metal ionisation . metals is determined The studied, more by easily potassium is a how metal t he most reactive metal because it ionises t he most easily and silver is t he least reactive because 294 it ionises t he least easily. Reactivity, extraction and Decomposition uses of of metals metal The reactivity of metals compounds We studied t he decomposition of metal compounds in Unit 17 .3. Looking at t hese ● reactions The ver y we reactive compounds. not The compounds and of Compounds of from and trends. and sodium, hydroxides and t he easily t he t heir aluminium, iron, it can be of seen form are nitrates so are fairly stable stable t hat t hey decomposed are only t he t hat unstable unstable decompose t he ease following nally t he less too such to t hat exist silver and silver nitrate heated. metals and The are calcium, in lead compounds. extremely when ot her compounds increases t his are hydroxide compounds its potassium heated silver silver ver y are cer tain carbonates when decomposes From see slightly. carbonate ● again metals, Their decomposed ver y ● can of order: when heated. Star ting decomposition calcium, of t he magnesium, zinc, copper. more reactive reactive t he t he metal metal is, is, t he t he less more stable stable are its compounds and t he more easily t hey decompose. This is because t he reactive metals ionise compounds t he ions easily ver y t hey and t he stable. form are ions The t hey less unstable. form reactive This are ver y metals means t hat stable. do not t heir This makes ionise t heir easily compounds are and also unstable. Displacement A d isplacement reactions reaction occurs when a metal in its free state (chemically uncombined) takes t he place of (displaces) anot her metal from a compound. A more reactive metal will always displace a less reactive metal from its compounds. f a more reactive reactive metal, reactive metal t he reactive less This of ten metal t he will more be off placed d ischarged metal drops is reactive will into form t he in a solution metal to on will form t he solution atoms. surface when containing ionise As of and a more and ions ions result, t he disturbed t he a of of less less precipitate reactive t he a t he more of metal. reactive metal gradually decreases in size. Depending on t he nature of t he solution, it may also undergo Displacement difference t he A in a colour reactions t he change are reactivity of as t he reaction exothermic t he two proceeds. reactions . metals, t he more The heat is greater t he produced in reaction. displacement reaction can be summarised by t he following general equation: A BX more less reactive reactive t han B t han AX B A n ● A is more reactive t han B. A ionises to form A ions: n A A ne t han A. n ● B is less reactive The B ions are discharged to form B atoms: n B ne B 295 The reactivity of metals Reactivity, Displacement Did ? you acts know? as a reactive It is by a possible placing solution a of to make coil of silver a ‘silver copper nitrate. tree’ wire reactions reducing metal. reducing are agent The more also redox extraction reactions . because it gives reactive t he metal and copper(II) The electrons is, t he and more to t he more uses of metals reactive ions of powerful metal t he it less is as a agent. into Copper is Example more it reactive displaces silver than the nitrate silver, silver and therefore, from after a The the while reaction between magnesium Mg(s) CuSO (aq) MgSO 4 is deposited forming a on the beautiful copper sulfate solution: silver (aq) Cu(s) 4 wire ‘tree’. Magnesium is more reactive t han copper, t herefore, t he magnesium ionises 2 and t he Mg ions enter t he solution. 2 Mg(s) Mg (aq) 2e 2 The Cu copper ions in t he copper(II) sulfate solution are discharged forming atoms: 2 Cu A pink t he (aq) 2e precipitate solution Cu(s) of when copper builds disturbed. The up on t he magnesium magnesium becomes and drops smaller and off into t he blue 2 colour The of t he overall solution ionic gradually equation for fades t he Figure into a 18.1.1 solution When copper containing is Cu is deposited on the blue Cu ions are discharged. is: 2 (aq) Mg (aq) Cu(s) placed silver ions, Investigating silver t he reaction 2 Mg(s) as displacement reactions copper Your teacher may use this activity ● observation, recording ● analysis interpretation. Y ou will and be supplied approximately sulfate the solution, with same zinc and sulfate assess: reporting clean size: to samples of magnesium, solution, the following zinc copper( II) and metals copper, sulfate of magnesium solution and six test of two test tubes and 5 cm tubes. Method 3 1 Place about 5 cm magnesium sulfate solution into each 3 tubes, of 2 Add a each. 296 of shake If a 10 tube. If sulfate off of zinc and a into the into another last two two tubes. Measure and record solution. magnesium to to the the piece of zinc sulfate magnesium copper to and the sulfate the copper( II) and the magnesium sulfate copper( II) sulfate and solutions. each tube metal from minutes, the solution solution each displacement displaced After of piece sulfate dropping 4 a solutions zinc Gently the sulfate piece sulfate the zinc temperature solutions, 3 of copper( II) the 3 5 cm periodically reaction deposited the metal measure temperature of on into and occurs, the the observe it should metal you solution the temperature any tube what be the increases, in to added when of occurs possible and see possibly shaken. contents calculate of the each increase. Reactivity, 5 extraction Observe about 6 30 Record similar was the uses colour of of the metals The copper( II) sulfate solution in each tube reactivity of metals after minutes. your to not and observations the one carried appropriate outlined out. If no and any below. temperature The reaction increases indicates occurred, place a in that a the cross in table reaction the place. Observations on adding Magnesium Magnesium dash Zinc Copper sulfate solution Zinc sulfate Copper(II) 7 Using so the that metal 8 9 10 Why solution sulfate most appears the at in sulfate solution? a the why the copper( II) balanced Explain a from reactive the table, metal draw occurs at up the a list top of the three and the least metals reactive bottom. temperature placed Write – information the was – solution increase sulfate chemical greater solution than equations for when when each it magnesium was placed reaction that was in zinc occurred. following: reaction occurred between magnesium and copper( II) sulfate solution b why no c why the zinc and reaction blue occurred colour copper( II) of between the sulfate solution copper faded and in the zinc sulfate reaction solution between solution. most reactive potassium zinc magnesium sulfate sulfate solution copper(II) solution sulfate sodium solution calcium magnesium aluminium zinc iron lead (hydrogen) Figure 18.1.2 The displacement reactions of various metals with metal copper salts mercury silver The reactivity series of metals gold The reactivity strengt h t he of ease t he of series of reactions some of of t he decomposition of t he common metals t he wit h metal metals, oxygen, drawn water compounds and and up from dilute t he acids, least reactions, is given in Figure 18.1.3. reactive displacement Figure 18.1.3 The reactivity series of metals 297 The reactivity of metals Reactivity, Potassium, at t he top, is t he extraction and uses of metals most reactive. t ionises t he most easily and forms t he most stable ions which are ver y hard to discharge. Gold, at t he bottom, is ✔ Exam tip t he It is the really order important that of reactivity the reactivity you of learn in reactive. t ionises wit h great difculty and forms ver y unstable ions are ver y easy to discharge. the We metals least which can use t he reactivity series of metals to make cer tain predictions series. ● We can series predict is known. magnesium water will how and also it For will dilute not any metal example, react acids displace less but will if a react metal vigorously more calcium if its occurs t han vigorously but will position in between calcium t han displace t he reactivity calcium wit h and oxygen, magnesium. magnesium The from metal t heir compounds. ● We can t he way predict it vigorously wit h to zinc displace magnesium below position what reacts is known. dilute from sulfate a For metal hydrochloric zinc sulfate solution, will example, occupy if acid t he in metal t han solution t hen a but metal t he is zinc not must reactivity found and is to series react also if more found magnesium from occur zinc above but magnesium. f two metals are ver y similar in t he way t hey react, t hen it is easy to determine which is higher in t he series by carr ying out displacement reactions between t he two t he lower metals Hydrogen We can and metal is use t heir from its included t he compounds. The higher metal will always displace compounds. in t he position of reactivity hydrogen series to even predict t hough how it is metals a non-metal. will react wit h acids ● ✔ Exam if since a metal is important that you know how ● to of deduce metals the order based on of or above t he hydrogen hydrogen in t he ion, H : data if a t he acid metal is because below it displaces reactivity hydrogen in t he series, t he hydrogen reactivity in t hen t he it will react series, it acid will not react wit h reactivity t he acid because t he higher it will not displace t he hydrogen in t he acid experimental ● results is contain tip wit h It acids up t he metal is in t he series, i.e. t he fur t her it be an is away from supplied. hydrogen, t he Summary 1 Why is 2 Why don’t when 3 a If a a t he reaction will wit h acid. questions sodium more reactive potassium a reaction piece sulfate b vigorous than carbonate copper? and sodium carbonate decompose heated? Would a more clean of occur clean if: magnesium ribbon was placed copper placed into into copper( II) solution piece reaction of occurs, was explain why and give sodium a sulfate balanced solution? equation for the reaction. 4 Explain metals 5 Metal react C in the A will with their reactive. 298 benet even a of though react with solution correct including it is a a solution containing order hydrogen of in the reactivity series of B will non-metal. containing ions reactivity of ions metal from the C. of metal Write most but metals reactive to A, B the not and least Reactivity, extraction C18.2 The ver y state, The silver uses of metals extraction unreactive e.g. and metals and gold, occur and of in The metals t he can, Ear t h’s of metals Objectives cr ust t herefore, extraction be in t heir mined free elemental directly from By the be able end of this topic you will to: t he ● explain how the position of a Ear t h. Most metals, however, occur combined wit h ot her elements in impure metal in the reactivity series ionic compounds and t hey t hen have to be extracted from t hese compounds. determines Compounds from which metals can be extracted are known as ores. its extraction The method most impor tant ores are metal oxides, suldes and carbonates. ● The extraction positive of metal a metal cations from have its to ore be is a reduction discharged to process form because atoms by t he describe the extraction of extraction of aluminium gaining ● describe the iron. electrons: n M ne M The actual met hod used depends on t he position of t he metal in t he reactivity series. ● Metals high in magnesium reduce. They met hod ● is and Metals lower They the ions need is a a less a of form in are the i.e. potassium, ver y met hod molten stable of sodium, ions which reduction. ore . This The met hod calcium, are difcult most uses to powerful t he most expensive. t he reactivity easier powerful reducing This series, powerful most down with hydrogen. t he which need ore reactivity aluminium, electrolysis energy stable t he and met hod to met hod agent uses series, reduce of such less i.e. t han zinc t hose and high below, in reduction which as carbon carbon, energy t han t he form involves heating monoxide electrolysis less series. and is or less expensive. Extraction of Aluminium is silicon, t he is and extracted oxide, Al is O 2 Guyana. t he t hird most 3 O. most abundant abundant known xH as metal. bauxite. There are in t he The Bauxite large Ear t h’s main is bauxite ore cr ust from impure, reser ves af ter t hen t he bauxite aluminium expor ted, extracted The by hydrated aluminium in bot h Jamaica has oxide, been also mined, known as it is puried alumina, Al mainly to Canada and t he USA , where to O . form and The pure, alumina 3 t he aluminium is electrolysis electrolysis (graphite), and aluminium 2 is oxygen which 2 Af ter anhydrous aluminium of which alumina forms takes an place in electrolytic a large cell. steel The tank carbon lined with lining carbon acts as the negative cathode in the electrolysis process. n the middle of the tank there are huge An blocks of carbon, electrolytic Figure cell hung used from for above, t he which extraction act of as the positive aluminium is anode. shown in 18.2.1. carbon blocks (positive anode) steel bubbles oxygen carbon of alumina + gas lining molten (negative cell in dissolved molten cryolite molten aluminium can tapped aluminium cathode) – be off Figure 18.2.1 Extracting aluminium by electrolysis 299 The extraction of metals Reactivity, The 1 extraction The at pure about process alumina 950 °C. involves t he (aluminium Cr yolite following oxide) is extraction and uses is dissolved extremely poor much t he high, conductor. reduced 2 is molten i.e. By meaning better in dissolved is sodium aluminium t he cr yolite because 2050 °C, dissolving less energy conductor cr yolite, its of and it is in t he in molten uoride, ions required are free melting formed cr yolite, and Once to t he liquid molten electricity. metals steps: cryolite Na AlF 3 alumina of t he t he when its it of solution The alumina melts melting alumina . 6 point is point produced has a is is dissolved a in move. The molten cryolite/alumina solution is electrolysed in the electrolytic cell: ● The aluminium reduced to ions form move towards aluminium t he cat hode where t hey are atoms: 3 Al Did ? you extraction of The molten and is The oxide aluminium since it is an requires 3e Al(l) aluminium expensive energy to tapped off. ions t is t hat move t hen forms made collects towards into at t he sheets t he anode or bottom of t he cell where blocks. t hey are oxidised to by form electrolysis know? ● The (l) oxygen gas: process melt 2 the 2O (l) O (g) 4e 2 cryolite, it uses huge amounts of The electricity is and replacing the oxygen gas t hat forms is released as bubbles. t forms carbon anodes dioxide by reacting wit h t he need be replaced since carbon anodes, and over time t he anodes costly. to Extraction of The from main ores Haematite is t hey disintegrate oxide which impure Fe O 3 ores A using blast . t he iron iron(III) The is extracted oxide, extraction reducing for shaped hot result Fe O of iron are and agent, t he tower carbon haematite magnetite its ores extraction t hat can be monoxide , of iron up to is and is reaction. magnetite. impure involves hot waste iron(II, reducing t he a blast in furnace. Figure 18.2.2. t is tall. iron ore, and coke waste they air in shown 30 m released are that limestone gases used enters to carbon released; heat the iron(III) oxide air t he 3 from gases hot of 4 furnace chimney a iron 2 III) as the furnace meets monoxide is hot blasted into air is blasted the into the furnace furnace molten slag can slag from and molten drained 300 reaction calcium iron off iron the be Figure 18.2.2 A blast furnace used for is tapped extracting off iron oxide of silicon dioxide a Reactivity, extraction The extraction The following 1 A mixture t he to mixture 2 Hot 3 At steps of air t he a is iron The of metals involved ore, blown as in of is and is made ‘t he charge’. t he furnace, extraction coke calcium from coke is of coal of iron added carbonate bottom t he O (g) CO 2 t he The extraction of metals t he burns its t hrough and which from is coke ores. t he is t he mainly top of name carbon. The furnace. in t he hot air forming dioxide: C(s) The t he t hat t hrough t he in limestone limestone known bottom carbon are substance is uses process furnace. given and reaction furnace is at (g) ΔH ve 2 exot hermic about and 1900 °C. keeps The t he carbon temperature at dioxide fur t her rises t he bottom up of t he furnace. 4 n t he form middle carbon CO (g) of t he furnace, t he carbon dioxide reacts wit h more coke to monoxide: C(s) 2CO(g) 2 The 5 n carbon t he monoxide upper part of t hen t he rises furnace, fur t her t he up carbon t he furnace. monoxide t hen reduces t he Did ? iron ores to The Fe O 2 (s) 3CO(g) 2Fe(l) 3CO 3 iron or the from O (s) 4CO(g) 3Fe(l) 4CO 4 blast of molten iron r uns to t he bottom of t he This as furnace where it is iron contains a fairly high percentage of carbon (about 4%), to ot her impurities such as silicon and phosphor us, and is iron’. alloy Most Figure These The ron of bottom of t he pig iron is t hen main into branch channel. a off puried and conver ted the way a These litter that of the suckling piglets into each other when they lie are from a sow. This is why the as that is tapped off from the blast steel, is known as ‘pig iron’. iron. 18.2.3 ‘Pig moulds function ore the as known furnace an of flows tapped iron ‘pig out that resemble in feeding well moulds the moulds next off. runs furnace (g) 2 piglets The that (g) series 3 know? 2 of Fe you iron: iron’ gets resemble of the contains a a its litter name of from suckling the moulds in which liquid iron collects. piglets. limestone lot of impurities, mainly silicon dioxide (sand), which would eventually build up and ‘clog up’ t he blast furnace. Limestone is added to ● remove The t he heat silicon in carbonate t he to CaCO upper part decompose (s) 3 dioxide. The of steps t he blast forming CaO(s) involved furnace calcium CO are as causes oxide and follows: t he calcium carbon dioxide: (g) 2 301 Uses of metals and their alloys Reactivity, The ● to calcium form oxide, calcium being silicate, basic, then CaSiO . reacts Calcium extraction with the silicate is and acidic also uses of silicon known metals dioxide as slag: 3 CaO(s) SiO CaSiO (s) (l) 3 2 slag The slag forms used n t he in it steel 1 2 3 Why are from their different b Outline the named in the diagram What it can is be Por t Lisas, associated to use to Trinidad, as a is t he and carbon uses use into the reduce product gases of tapped ground agent wit h waste bottom and nely possible vapour ot her the iron reducing water and to furnace separately. mixed or t he no coke, with ore, where t is in for place such atmosphere, is harmful as t he are of example, Hydrogen ot her it then cement. hydrogen iron hydrogen. and of t he blast off ideal gases. release avoided of wit h hydrogen. methods used to extract aluminium and iron ores? Name a of or t he in down molten questions a The t he the iron as problems dioxide use of plant carbon r uns building produces Pollution Summary road and above monoxide spat since melts layer extraction carbon t he a are ore from which process a by aluminium which is extracted. aluminium is A extracted from the ore above. shows the a blast three furnace: materials that are added to the top of the blast iron ore reduced furnace at b What removed A in the c Explain d The e Why extraction of iron? to is why air at is B and blown iron C? into the blast furnace. molten the 4 Write carbon iron( III) is the it monoxide oxide. easy What to balanced acts as does remove the chemical a reducing this agent when it reacts iron with mean? slag? equation hot to show air hot air how C iron(III) oxide is converted to iron in the blast furnace. B Objectives C18.3 By the be able end of this topic you Metals ● describe the uses of lead and are metals and uses of iron to their extensively proper ties, by man. especially ● explain what ● explain why t hey an are and strong ductile, and have last a high alloy metal ● and relate in the lead the and place uses of of the metal is directly linked Metals are to used relatively of long and time. can They conduct are also shiny, electricity All of t hese proper ties make metals par ticularly useful. Metals can and also alloys. This is done to improve or modify proper ties of t he metals. metals aluminium, Uses alloys uses lead of metals aluminium, alloys to t his unit their and properties. 302 a proper ties. are n iron of is alloys t he used describe use physical densities be mixed wit h ot her metals to make often The its properties heat. iron alloys aluminium, malleable ● their iron the and used par ticular because relate lead of aluminium, its ● Uses will to: iron. we will look at t he uses of t hree metals, aluminium, lead Reactivity, extraction and uses of metals Uses of metals and their alloys Aluminium Aluminium aluminium it ver y is resistant produce a par ticularly oxide on to louvred its useful surface. corrosion windows This (Unit and metal layer 19). because adheres Because window of frames, it to has t he t his, a t hin metal aluminium which can layer and resist is of makes used to corrosion when t hey are exposed to oxygen and moisture in t he air. Anot her major use of aluminium and is to make aluminium cans used as containers to store food drink. Figure make 18.3.1 louvred Aluminium is in power overhead a Aluminium is used to Figure are windows good conductor cables. These of electricity cables have a 18.3.2 used to which steel Aluminium store enables core cans Figure drinks to it down to t he be t hem. Aluminium it make saucepans. useful to protected by t he t hin, is also a good Aluminium unreactive layer conductor foil of is used of heat for aluminium which cooking oxide to Did it it is has a There was reective surface t hat allows it period of to reect heat back into t he food, it warm for a longer has t he disadvantage t hat it is not t he strongest of metals. For t his reason it is usually alloyed wit h ot her metals to make it stronger. We will be discussing some of t he uses of used know? was a time Napoleon when more III was aluminium precious than believed have held a banquet where time. the Aluminium be t hus to keeping you considered gold. highly can makes since and Aluminium saucepans used centre ? strengt hen 18.3.3 make aluminium alloys in t he next honoured aluminium the other gold section. guests utensils guests to were eat were given with only while given utensils. Lead As one of t he rst metals to be discovered, lead has been used for several t housand years. The largest use of lead today is in lead–acid batteries because it is highly batter y made resistant used of lead(IV) in lead to motor alloyed oxide (PbO ) corrosion vehicles wit h a and an and conducts consists small of six quantity electrolyte of of electricity. cells. Each antimony, sulfuric acid. A typical cell a has 12-volt an cat hode Chemical anode made of reactions 2 occurring t he in batter y each can be cell produce electricity. Since t he reactions are reversible, recharged. Anot her impor tant use of lead is as a radiation shield around X-ray equipment and nuclear reactors because X-rays and nuclear radiation do not penetrate t hrough wear it. Whenever which shields you you have from an t he X-ray taken harmful you effects of are given a t he X-rays. lead apron Figure 18.3.4 A lead–acid battery to Iron Today, iron is t he most widely used of all met als because of its high abundance, low cost and high strengt h. However, because pure iron is quite 303 Uses of metals and their alloys Reactivity, sof t Did ? you know? to The word plumbing from the lead. Plumbing ancient and Latin plumbum, was civilisations Greek as was they derived meaning originated such as and baths, historians the was due getting to into causing of lead the Roman from water widespread ✔ Exam tip It important that the uses of metals actually their physical of and made t han wrought t hese items have wrought iron. or nament al railings. of mild it wrought Most steel wit h iron, str uctures, items because carbon has suc h descr ibed it is easier as as for m used steel . for fur niture, wrought and lighting iron c heaper Pure centur ies today to produce iron. t he The descr iption wrought bent and appearance shaped iron is of still items used because for merly made that Empire water pipes supply lead and poisoning. you and can Figure 18.3.5 Wrought iron gates relate their alloys uses of metals and t he proper ties t hat make t hem par ticularly suitable properties for each T able use are 18.3.1 summarised Properties Metal Use Aluminium • to • to and in uses Table of 18.3.1. metals Properties make cables overhead (with make a electrical steel • core) good conductor corrosion, saucepans • good light attractive • to make food aluminium and cans to store • drink weight, • to make window • to make foil for resistant frames cooking manufacture • to make car • as of aluminium lead–acid alloys batteries, e.g. a resistant • unreactive to to make shield Wrought weights, keel • manufacture • to produce highly easily alloyed good conductor • e.g. weights of lead fishing for to weight, non-toxic, light in the aluminium oxide does not react with food, reflective with other of metals electricity, resistant to high density • high • easily • malleable of steel prevents radiation from through density, malleable sailboats alloys ornamental manufacture to therefore • iron work used) • in corrosion • iron (rarely to corrosion radiation weights, resistant light corrosion, (due penetrating • heat, resistant ductile appearance • batteries of non-toxic, to non-toxic, • electricity, weight, malleable coating), Lead of in conductor corrosion, 304 to been water The to var iety alloying as metals by is a gates by known of Some speculated the make are hardened uses Roman drinking systems. have decline usually and developed piped drainage is commercially xtures, of public it iron, extraction • alloyed with and shaped, easily resistant to easily other ductile, metals therefore welded, strong easily therefore stress alloyed with carbon and other metals Reactivity, Alloys extraction and and their uses of metals Uses of metals and their alloys uses There are many situations where metals are not used in t heir pure form. More atoms t han one metal may an alloy. Sometimes To make an be a combined to produce non-metal may also metals heated, a be mixture of metals known as cooled so pur pose of of original added. atoms t hat t hey making alloy, solidify an alloy t he again. is to are Alloys improve are t he solid mixed t horoughly metallic solutions. proper ties the metal of t he metals and The or to modify of alloying Figure 18.3.6 Structure of an the element alloy t heir proper ties. Alloys are usually harder, stronger and more resistant to corrosion t han The t he original atoms of metals. t he Did ? metals t hat are mixed are usually of different sizes. t hey are changed when a metals only slightly and it makes it force is applied. different more This in size, difcult is why for t he t he alloys regular atoms are to harder packing slide and of over atoms each stronger is ot her t han t he of is zinc. It now look at t he alloys of aluminium, lead and is electrical pins is and produce to aluminium of ten of mixed wit h different duralumin are duralumin 18.3.2 and and copper, alloys. magnesium, Two of t he magnalium. magnalium are The given manganese, most common Composition, alloy Duralumin uses and properties Composition Uses About aluminium, In with aircraft 4% 94% copper amounts and and Magnalium composition, in Table of aluminium uses and Did ? having very being good you of small magnesium the Properties construction and precision to 95% 5% of was by a make tools than so withstand it can greater aluminium stress, as Alfred Originally Stronger weight aluminium Construction magnesium and of automobile as German it make and aircraft Stronger, parts, and metallic scientific more mirrors to instruments W ilm a lightweight and is used to The name by a Dürener of duralumin ‘Dürener’ In 1917 during and World I, Hugo Junkers, a German resistant corrosion than construct designer, pioneered the use than lighter of in duralumin the aluminium J 7 in fighter Did can the to construction know? alloyed form specialist of plane. you be metals as and made called harder of strong 1909. company contraction Iron is in only in ? Duralumin and metallurgist aluminium aluminium, weight 18.3.7 developed German was Metallwerke. light aircraft to know? 18.3.2. War with what steels. a variety are For known example, aircraft titanium steel titanium, is an alloy manganese of steel iron is and an alloys alloy of cobalt The is alloys manganese About and Iron to it make properties. ‘Aluminium’. Figure due to of is since and silicon alloys called Aluminium plugs copper instruments patented T able 30% manufacture iron. Duralumin consisting and alloys Aluminium proper ties to for than acoustic zinc alloy copper used malleable Aluminium copper 70% stronger alone. will a about musical We know? Even Brass if you building industr y makes extensive use of iron, usually in t he form Steel is an alloy of iron wit h carbon or various ot her metals. There and is manganese an alloy of and iron and of cobalt. steel. iron steel Each steel has specialist are uses; titanium steel can withstand quite a few different types of steel. Steels formed by alloying iron wit h carbon very are known as between 0.1% and 1.5%. As t he carbon content increases, t he harder but less malleable and ductile and t herefore becomes make and harder to spacecrafts, is cobalt used steel magnetised easily so is used to more make brittle so steel is becomes temperatures carbon steels. Generally t he amount of carbon in carbon steels to varies high magnets. weld. 305 Uses of metals and their alloys Reactivity, The are composition, given T able Iron Mild in Table 18.3.3 alloy uses and proper ties some Composition, uses and properties Contains less than 0.25% In the motor common between 0.25% to store made a T o carbon nails items, thin of alloys metals of iron alloys of so ‘tin and stronger malleable easily and shaped, than ductile easy to weld and ‘tin of iron, T o and steel Harder cans’ coated tin to corrosion. make bits, of food i.e. layer prevent 1.5% iron ships vehicles. wire, other in and some bridges, cans’ are Contains of construction make carbon uses Properties buildings, and steel t he Uses carbon High of and 18.3.3. Composition steel of extraction cutting knives and tools, drill Harder masonry more cooking Hard, sinks, more than mild steel, but brittle nails Stainless steel T ypical 70% and Figure 18.3.8 Steel is widely used values iron, 10% are 20% about T o chromium make utensils, nickel cutlery, kitchen strong hospital equipment, (rusting) catering equipment steels. than Has construction a to much corrosion carbon shiny, in attractive the and resistant industry but to is appearance, more expensive produce than carbon steels. Cast iron Contains about 4% T o carbon make e.g. small manhole railings, blocks castings, grates, in Inexpensive covers, cast cylinder engines and saucepans into Hard, but steel, therefore shatter when Lead alloys Lead is of ten common lead and solder t he is By 40% being lead tin. so lead 2 What used t hat it tin, into t he between be is 4 What are 5 Discuss and the an items higher t he harder of lead and joint toget her. t han solder t hat of t han make t he t he has a brittle it than tends than making make electrical alloys, suitable To about do items. One 60% t his, On t he cooling points of t he solder. lower melting point lead. for give the use it useful for: cables two uses of lead and in each case explain given. alloy? the two to bend alloys. of melting lead to hit. toget her. The produced stronger aluminium overhead What t he to rather composed ows saucepans? 3 is items making is copper metallic making lead or solder more easy shapes. questions properties than Lead join b Other antimony solder. to joining must also tin, lead a why 306 is is wit h is Summary 1 t joined and wit h lead solidies, alloying t han of melted solder metals mixed alloy and exact advantages named uses of of alloys each. using of an alloy aluminium rather by than referring a to pure the metal? composition Reactivity, Key ● t extraction and uses of metals Uses of metals and their alloys concepts is possible t heir to reactions decomposed determine wit h when t he oxygen, heated, reactivity water and and series dilute of metals acids, displacement how reactions by looking easily t heir between at t he strengt h compounds t he metals and of are metal compounds. ● The more ● n d isplacement a reactive t he metal, t he reaction , a more more stable its reactive compounds. metal displaces a less reactive metal from its compounds. ● The is: reactivity potassium, copper, ● The ● ● mercur y, position metals will The ver y e.g. silver Most of and metals gold, occur metal ● The extraction ● Metals high aluminium, Metals are of a to ● Aluminium ● Bauxite to reduce. be metals metal t he They t he cr ust can During ● ron is extracted impure, extracted ● its ions need Ear t h’s be is t he lead least reactive (hydrogen), to in t heir compare how cer tain from wit h t hese are free from ot her elemental t he state, Ear t h. elements in impure ionic compounds. known as ores. The most impor tant is i.e. a reduction potassium, which of process. sodium, are difcult the molten series, i.e. zinc to calcium, reduce. magnesium They need a and powerful ore . and a less powerful met hod its ore, bauxite, by below, of form less reduction, stable i.e. ions heating which the ore from aluminium oxide, electrolysis. Al O aluminium as impure its t he ores, forms t he haematite reducing iron( III) at agent oxide, Fe cat hode and in O a xH 3 O. 2 and magnetite blast and oxygen by forms reducing at t he t he anode. ores using furnace. magnetite is impure iron(II, III) oxide 3 O 3 ● used directly extracted 2 Fe be cr ust mined combined be ore series, reactivity hydrated from monoxide Haematite to iron, agent electrolysis, carbon reactive zinc, carbonates. electrolysis t he can 2 ● most aluminium, series extracted and from stable i.e. in t herefore, suldes in reactivity occur reactivity down is t he Ear t h’s have reduction, reducing is t he ver y from acids. can, which a form lower easier with of t he in metals in metals magnesium, gold. and oxides, in common calcium, dilute t hey from are met hod wit h and Compounds t he silver, unreactive ores ● of hydrogen react compounds ● series sodium, 4 Molten iron and molten slag, calcium silicate (CaSiO ), are produced in t he blast furnace. 3 ● The physical ● The main frames, ● The shields The ● An ● Alloys ● use and main alloy more is are a ● is an iron mixture of ten more to are cans make to t hem make and foil is to make is to manufacture and of alloy of metals useful corrosion for lead–acid ver y useful overhead to man. electrical cables, saucepans, window cooking. batteries. t is also used to make radiation alt hough t han t han magnalium steel. t he t he are sometimes pure pure alloys metal a non-metal because t hey can are be added. harder, stronger and metal of aluminium. Their main use is in t he aircraf t. of iron different proper ties Solder an is metals storage lead of resistant Duralumin Steel of of aluminium weights. use constr uction ● of aluminium main ● proper ties uses alloy of wit h and carbon or ot her elements. Different types of steel have uses. lead and tin. t is used to join metal items. 307 Practice exam-style questions Reactivity, iii) Practice exam-style Explain your What would precipitate Which most A of t he following reactions is likely B Mg(s) Pb(NO C Mg(s) Cu(NO (aq) Mg(NO ) (aq) take Zn(NO ) (aq) ) 3 (aq) v) place (aq) ) 3 (aq) met hod determined t he used Mg(NO 2 to (aq) ) 3 extract a metal from How if Pb(s) Cu(s) t he point t he position C t he solubility t he of electrical (aq) Zn(s) vii) of t he t he of its ore in conductivity is extracted from molten t he of reactivity t he molten reduction of alumina alumina alumina of t he zinc rod molten D electrolysis of alumina occurring in Anot her student order in lead, iron of rate of t he reaction be t he following extraction haematite, of replaced t he same wit h a piece of dimensions? answer to a (1 vi) (2 in is carried to out determine experiments t he relative 1 and limestone, carbon haematite, air, and an 1: A unknown piece cr yolite in list of t he t he using molten raw lead(II) of of metal metal nitrate. materials A appearance Use t he most cr yolite 2: piece iron(II) of of X X, was Metal X in metal sulfate. metal which has D coke, X placed became into air, carbon dioxide, limestone, haematite, t he constr uction order of X was placed There was no given to place reactivity, lead, star ting an metal X (2 ionic equation for t he reaction mild magnetite, How marks) between and t he lead(II) nitrate solution. would you expect metal X to react following silicon is coke acid? 15 marks most widely used in t he Extended response question a Chemical and electrolytic reduction are t he two steel met hods used to extract metals from t heir ores. steel ONE factor t hat determines t he met hod t hat duralumin be employed in t he extraction of metals from solder Structured A student places copper(II) hours, The t he a sulfate gently of zinc below t he rod solution shaking diagrams star t several ores. Explain met hod to be Outline t he how t his factor determines used. t he (3 marks) question b a mark) industr y? t heir 6 (1 dioxide should D marks) wit h coke dentify C and t he monoxide main B a in iron wit h reactive. Write into change used 7 stainless a coated Total air, a X. information hydrochloric A 2 reactivity lead. metal dissolved a of solution carbon alumina limestone, C of mark) marks) iron? B Which mark) affected 2. Experiment iii) 5 mark) t he (2 A t he (1 reaction was of your below i) of of of ore by: using dissolved electrolysis t he bottom series monoxide C in t he ore of Which in hours? is ii) 4 mark) solid metal metal t he reduction carbon seen t he (1 Explain wit h Aluminium B (1 of 2 solution A was several type would Experiment 3 colour by: melting B t he t hat af ter magnesium valency D t he 2 of A Name vi) 2Ag(s) b The be 2 Mg(NO 2 3 2 ii). metals 2 Mg(NO 2 ) 3 ) 3 3 Mg(s) of beaker. 2AgNO 3 D to readily? Mg(s) to a uses questions beaker 1 answer and questions iv) Multiple-choice extraction t he show in a and beaker leaves solution what experiment and containing it for iron several include occasionally. t he student t hen again saw from involved iron(III) relevant silicon oxide. in Your equations. dioxide, is t he extraction answer Details removed are of not Stainless ii) steel, how alloy of iron, is used to is Suggest an alloy? T WO make (1 reasons cooking why utensils stainless instead of steel is solid mark) used iron. rod d solution sulfate marks) make (2 copper(II) t he required. utensils. What to an of must (7 c i) zinc ore, steps at af ter cooking rod its THREE impurity, hours. zinc main precipitate Aluminium Name ONE is anot her alloy of metal used aluminium to and make give marks) alloys. its main use. solution start of the experiment experiment several (2 after hours Total i) Explain during why t he equation ii) What to zinc suppor t change solution? 308 t he rod experiment. would decreased Give your you marks) a in size relevant answer. expect to ionic (3 marks) obser ve (1 in t he mark) 15 marks Metals in living systems and C19 the Some metals are extremely environment important in the lives of Objectives plants and poisoning animals, if while consumed others and can can cause have severe harmful By the be able the environment. Conversely, the environment can explain metals have devastating effects on metals and can of lead to ● give for ● ● corrosion of what the Metals, especially to its occurs reaction t hose when wit h used t he c hemicals in will when explain explain to what necessary corrode happens when corrodes what happens when metals outdoors, surface happens conditions metals iron Cor rosion you corrode aluminium The topic their corrosion. C19.1 this to: effects ● on end of t he t he tend metal to undergo g radually environment, cor rosion . wears mainly rusts. away due oxygen and moisture, and it is speeded up by t he presence of cer tain pollutants. n some cases it may cor rode, lead t hey e.g. carbonates The rate at general, are nor mal aluminium will The On of now for med t he iron at exposure to aluminium a off from and fur t her aluminium reactivity f a in of to shiny t he air of linked t he to faster cor rode quite while of metal wit h sodium wit h corrosion carbon to bot h t he it will at an c hlor ide different t he metal’s t he of t he Al piece of . layer O relatively corrosion. less aluminium see t he section again process ar ticially shiny to and This aluminium t hese by to dyes, added making t han atmosphere. t he iron in rate n t hat corrosion is of detrimental. more detail. adheres immediately to t he metal forms below, a layer does not 3 unreactive. t is As because reactive is a of t han scratched metal become renews which thickened advantages absorbs salts, Met als faster result, t his is it protects aluminium predicted by t he aluminium oxide its layer position its and t he underneat h. dull as oxide t he oxide t layer does aluminium not is t hat in t he so by t he t he reacts aluminium; anodised advantages, cookware such it objects anodised as pots of t he (Unit can oxide 10.5). makes t he be pans layer The to has on oxide surface coloured aluminium and ver y wit h it long t he is for oxygen lm. t hickness electrolysis removed, take Aluminium can be made even more resistant to corrosion by is metals for m reactivity. cor rode. results; metals When also dioxide. even in corrosion t hese object. sometimes aluminium fresh oxide , appears tend is t he They series. piece possible t hat is reaction metal, will of oxides. cor rode t he 2 peel t he benecial of air, by presence t he corrosion t heir corrode mostly look sea t he destr uction to met als reactive of and is tot al most to because Aluminium We are more close t he oxid ised whic h t he used to are anod ising. This t he aluminium layer harder gives and attractively. a great protecting many satellites it is added readily Because uses, from of from space debris. 309 The corrosion of metals Metals The On corrosion exposure to immediately Fe O 2 xH 3 O, Figure 19.1.1 Rust formation on a begin systems and the environment iron oxygen which living to and moisture corrode has an to in form t he air mainly orange-brown iron and hydrated colour. steel objects iron(III) Hydrated iron(III) oxide , oxide is 2 commonly known n order iron t does for not damaging of in forms on to occur and t he as rust. r ust, if bot h only costly. surface Corrosion Unlike of oxygen one is t he of iron and water present. The adherent aluminium, and r ust steel or known moisture r usting coating does is not of of as must iron be can aluminium adhere to rusting t he present. be bot h oxide t hat iron below. The newly padlock Rust akes exposed t he T o investigate Your teacher may observation, ● Y ou will be what use conditions this recording supplied with activity and and t hen exposes r usts fresh and t he iron to process oxygen and moisture. and gradually continues wears away iron. are to off iron needed for rusting to occur assess: reporting. three steel nails, some calcium chloride, some oil and three test tubes with corks. Method 1 Place one 2 Place the The 3 some test tube the Leave 5 Record 6 What 7 Which 8 Did 9 What the water nail any to nails in into nails it three the a signs you could on the What of Add oxygen of for a the few layer conditions rusting? whether a to water small the half in the allow it completely water. days cover amount air and to Cork and of the nail calcium and cork chloride If the so, to the third to cool the quickly. the nail. Place Gently carefully observe any what condition nail rusts in this was necessary more absent for quickly in nail some in dry rusting? in sea water or air of oil water nail calcium chloride 1 19.1.2 T est tube Investigating 2 the tube. oil the case? water 310 third changes each boiled Figure the pour case? layer the tube? present air tube cork into T est conditions tube 3 needed for rusting tap water. another down tube. air T est and tube. tube. cover were conditions steel steel the table. oil about a from water top suitable draw test tube. tubes adding enough moisture boiled layer a add dissolved this test in test any the most? no can of tube, dry of forms the show you a remove purpose rusted test absorbs observations the how rst enough that conclusion Explain nail add so your was the chloride and tube 4 into second calcium Boil of 10 nail nails. the side Metals in living systems Summary 1 What 2 Y ou a are given Which 3 What 4 Explain 5 Suggest a metal deep C19.2 four metal The impact of metals on to would be aluminium than for of the the iron on the present effects on zinc reactive Why is and than of iron iron for position in the to of the occur? differently. tend to rust more at the bottom the of tend the of to rust very slowly when found water. metals on living systems Objectives environment t heir compounds are extremely impor tant to By the be able However, same cer tain living metals and organisms t heir and compounds also on t he can have end of metals and their a vital role in the functioning e.g. calcium, referred to as for good potassium, sodium and topic you will explain the metals and importance of their compounds in environment. organisms discuss the harmful effects of compounds of living organisms. Some of these ions are required by the human body in amounts in excess of 100 mg per day, this living metals play of to: harmful ● ions environment this? rusting corrode shipwrecks surface and importance Metal the aluminium. its living The and top. impact t he systems following. The and iron, less suggest? and made at below copper, appear ● organisms. living corrodes? metals must railings metals environment rusts? reasons Pieces a tends series why railing Many the conditions Metal b when metal reactivity b the questions happens Which and magnesium. These are on and living their compounds organisms and the environment. sometimes macro-minerals. Others are recommended in smaller amounts health, molybdenum, these include selenium and manganese, chromium. iron, These zinc, are cobalt, referred to copper, as micro- minerals or trace minerals. Plants also require cer tain metal ions for healthy growth. Some of organometallic Table 19.2.1 the ions required compounds , summarises t he for by plants example, impor tance and animals chlorophyll of cer tain are and used to make haemoglobin. metal ions in living organisms. T able Metal 19.2.1 ion Magnesium The importance Importance Magnesium Chlorophyll plant so parts that in the are the their and can for pigment given 6H the Chlorophyll is its (g) 2 shortage known as own a and teeth, of chlorophyll chloroplasts food in plants by organisms of to in green plant trap cells. the plants. It gives sunlight photosynthesis. The green energy equation for energy O(l) C H 6 magnesium ions body play living causes by the chlorophyll leaves of O 12 (aq) 6O 6 (g) 2 glucose plants to become yellow, a condition chlorosis Magnesium human the 2 of in below: absorbed A in essential sunlight 6CO compounds formation found manufacture is their organisms necessary green colour. plant photosynthesis metals living ions is of vital role in are since in the also they the required are for essential production transmission of of more for energy nerve than the 300 biochemical functioning in cells, impulses in and of the in many reactions enzymes. formation the of in strong contraction of the The ions bones muscles. 311 The impact T able of metals 19.2.1 on living systems and the environment Metals in living systems and the environment (continued) Metal ion Importance Iron Iron the ions red body. with are in living pigment The C found oxygen energy. The H 6 organisms necessary O 12 is for in then for 6O 6 formation red used equation (aq) the the blood by the of haemoglobin cells. body respiration (g) is It is cells in given 6CO 2 in essential animals. to carry respiration to Haemoglobin oxygen provide around is the the body the body, below: (g) 6H 2 O(l) energy 2 glucose A shortage tiredness Calcium Zinc fact the is natural release of the contamination environment unpleasant by and of and ions The know? of too phrase ‘mad was coined during as a hatter’ the 1800s the for clot leads the to important part and in the in and play contraction of number known strong of as of red calcium bones blood cells in anaemia and phosphate teeth. in the Calcium body. ions are also may also cut. which cell ions a bones an the production build at in in condition to condition of of metals toxic Other Many effects same become high. them. The to a a potassium and reduction needed blood wounds, and is calcium play of impulses harmful health you ions a necessary the rickets, to energy, and the the becoming become functioning tissue an teeth legs growth important of the and role soft and weak. It bowed. immune system, in the repair. in the transmission of nerve muscles. the Some Did Zinc of of harmful substances. ? to are for shortage lead Sodium potassium leads lack phosphate healing Sodium Pollution a Calcium A Key iron Calcium necessary ! of and metals required to the same metals, not required these are in a by living living by group and their organisms organisms living known compounds when organisms, as heav y to maintain their can levels also metals, their become be toxic which to mainly includes the transition metals and some of the metalloids. All of these metals occur naturally in ionic compounds, however, their concentrations within the when mercury was used in the environment production used by felters levels of felt, felters were of to which make exposed mercury. was hats. daily This to The trace Heavy metal compounds in of them their dementia to to pollution you become par ticularly combining Table effects on T able 19.2.2 t he ion Harmful wit h 19.2.2 human effects Sources toxic organic when t hey compounds, summarises Minamata disease discovered in some Disused in car the of the 1956. release industrial was environment batteries, car T oxic using leaded exhaust petrol, lead fumes based city It of was Lead damages and kidneys, of methyl wastewater from into mercury local shellfish when population, mercury and fish eaten by resulted poisoning the with the cells leading in of body and the brain. normal to particular It nervous also formation anaemia. the system, interferes of It red is blood especially to young IQ and children causing potentially learning disorders. permanent Disused and thermometers from hospitals Mercury damages the central nervous gradually in the in 1700 industry, extraction gold, severe over laboratories, lights, the Cadmium and Disused refining Arsenic e.g. smoke, of of of of fossil sodium certain and burning fossil of metals, as impairing hearing, touch sight, known muscular speech as and coordination, the Minamata sense of disease. Cadmium e.g. causes respiratory extraction of and paint can also bones damage system, cause become to kidneys osteoporosis weakened the and liver. where It the and fragile. and skin PVC. especially purification fuels, coal, such batteries, fuels, e.g. of system hydroxide. manufacture plastics, extraction metals industry, metals, certain Mining of fluorescent combustion refining nickel–cadmium combustion and disused manufacture cigarette deaths. 312 variety Minamata and in and have a Mercury up lead can mercury methyl which, a organs, bones especially Minamata, factory bay, t hat caused Bay. built ions effects tissues first chemical This organometallic tetraet hyl metals reduced in form e.g. metal harmful the activities. body. paints. by man’s know? when in by (madness). Lead Japan, caused symptoms Metal Did due bodies develop ? ions by mercur y. harmful causing increasing gradually met hyl accumulated are then of gold, metals, especially coal. Arsenic can problems. system, It cause also heart cancer damages and blood the nervous vessels. Metals in living systems Heav y metal ions are persistent, organic and the environment The impact of metals on t hey pollutants. living remain They also in t he have environment t he potential to and do build not up in decay t he like Did ? organisms, especially fatty tissue, and t hey concentrate harming mercury sh t his eat in t he of top sh, humans plankton. mercur y general consumers such as than especially due f to t his gradually Larger large mercur y up in is t he major concentrating plankton builds sh, contains t he sh t hen eat t he up small bodies smaller food in chain t heir to t he bodies ver y t hroughout sh, large, t heir long-lived of source t he food sh of ingested chain. amounts t he know? women need since more they of such as This haemoglobin Also women they get zinc during each lose iron during must month in menstruation. adequate ensure that supplies of mercur y, building continues sharks, bodies Small t hroughout constantly lifespan. sh you men their marlin, pregnancy since it is t heir up for growth of the cells and t he tissues mercur y environment humans. essential lifetime. the food from Consumption and tissues up iron chains, systems are par ticularly harmful in t he environment because t hey i.e. In of living up t he tuna and of the foetus. swordsh. Disposal of solid since t hese waste includes: waste metals should ● lead–acid ● t hermometers ● compact uorescent mercur y vapour batteries not from be motor containing nickel–cadmium ● containing light heavy metals allowed to poses enter t he a serious problem environment. This vehicles mercur y bulbs from and hospitals ot her and uorescent laboratories bulbs containing batteries. These items should not be disposed of in landll sites because of t he possibility of contaminating incinerated t he metal groundwater because ions into of t he t he and nearby possibility air. The of soil. releasing problem of t heir They should harmful disposal also gases can be not be containing solved to a Figure light large extent by recycling Summary all What is haemoglobin? 2 What is chlorophyll? 3 Why 4 a zinc Name b 5 why swordsh heavy uorescent mercury vapour metals. Why Why is calcium different is it important it important important metals to whose in to our bodies? plants? humans? ions have negative effects on the body. Describe Explain and three human containing Compact contain questions 1 are items 19.2.1 bulbs or some of it be may the negative dangerous effects to of each consume metal large sh named such in a as marlin. 313 The impact of metals on living systems and the environment Key Metals, ● Corrosion its and moisture, When form fur t her The ● When it is corrode, living systems and the environment t he outdoors, surface chemicals of in tend t he t he speeded up t hey oxidised are by to undergo metal gradually environment, t he presence to corrosion. t heir of wears mainly cer tain oxides and away oxygen pollutants. sometimes salts. tend to corrode much faster t han t hose t hat are lower in which is series. aluminium relatively ● wit h and metals reactivity When used when reaction metals Reactive t hose occurs to t he ● especially due t hey ● in concepts ● ● Metals corrodes unreactive and it forms adheres a to layer the of aluminium metal below, oxide protecting it from corrosion. layer of iron aluminium corrodes it oxide forms can be t hickened hydrated iron (III) by anod ising oxide, also known as rust ● n order for iron to r ust, bot h oxygen over time exposing and water or moisture must be present. ● Rust The akes gradually ● Metal of off newly exposed wears ions t hese play are iron away a t hen t he vital iron and t he to oxygen process and moisture. continues and iron. role combined fresh r usts in wit h t he functioning organic of compounds living to organisms. form Some organometallic compounds ● Macro-minerals of 100 mg per day. macro-minerals ● healt h. needed Calcium, by t he human potassium, body sodium in amounts and in excess magnesium are t he needed. Micro-minerals good are are Two of required t he in most small amounts impor tant by t he human micro-minerals are body iron for and zinc. ● One ● Metals are impor tant in can a ● The have group transition The most ● Heavy decay such are by on of t he t hese harmful due to include harmful in up plants living metals, some concentrate is magnesium. organisms. which mainly Many of includes t hese t he metalloids. heavy metals pollution lead, t he food wit hin caused mercur y, t he man’s cadmium environment chains, by because harming t he activities. and arsenic. t hey top do not consumers humans. of sh, humans Disposal of solid t hese especially due waste metals includes bulbs Waste effect heav y metals in light 314 of mercur y waste required increasing ions t hey Consumption since ● metal as and harmful and as is ion negative concentration ● ● a known metals environment ● metal large mercur y containing should lead–acid and to not be containing heavy metals heavy allowed batteries, nickel–cadmium sh, is t he major concentrating metals to mercur y up poses enter t he be a recycled. of food serious ingested chain. problem environment. t hermometers, batteries. should source t he This uorescent Metals in living systems and the environment Practice Extended Practice exam-style a questions Most Which of t he following must be present for iron to t he case undergo t his of can iron it corrosion. be n benecial can be t he to harmful case t he of metal and while costly. What happens when a metal corrodes? (1 carbon Explain why t he corrosion of aluminium is dioxide benecial while t he corrosion of iron is not. A only B and of C and D , ‘Metal corrosion ions include and t heir reference to t he proper ties. products are extremely impor tant (6 to By reference to magnesium, iron and calcium, provide evidence to suppor t t his statement. (6 Which of t he following is not a benet to be gained corrosion t causes of Cer tain metals Explain why position to be less reactive t han forms in be C D t he reactivity oxide coloured The t an oxide forms a harmful to living organisms. layer series on t he are released formed relatively metals into t he are so harmful environment when by human predicts. aluminium, which (2 Total akes off unreactive marks) can attractively. layer t hese its activities. t are aluminium? aluminium t hey B marks) from c t he marks) living only organisms.’ and should only b A Your moisture answer 2 mark) oxygen ii) question r ust? i) metals aluminium in 1 questions questions 7 Multiple-choice response exam-style 15 marks easily. oxide layer on t he aluminium. 3 Which of t he following metals is a constituent of chlorophyll? 4 A magnesium B zinc C calcium D iron Which human 5 6 of t he body following for A calcium B potassium C zinc D magnesium Which of t he good following are harmful to t he A arsenic, iron, B arsenic, cadmium, C cadmium, D arsenic, rickets B anaemia C cancer D Minamata of is a mercur y, cadmium, A a human large trace mineral needed by t he list of heavy ions t hat lead mercur y mercur y, lead magnesium, sh metal body? lead, calcium, Consumption is healt h? is most mercur y likely to cause: disease 315 C20 Non-metals Most elements in the periodic table are metals, the Objectives By the be able end of this topic you will rest make metals. give ● the general properties of the specic properties oxygen, physical side group of elements known as the non- of state where nitrogen, sulfur the non-metals table. Many are found on right-hand non-metals the are found naturally their elemental state, mostly as gases or solids. are also found combined with other non-metals chlorine, covalent compounds and combined with metals in sulfur hydrogen, chlorine, occur of They hydrogen, nitrogen, and The physical in carbon ● a non-metals in give ● up to: oxygen, carbon and ionic compounds. man. However, Non-metals because the are used properties extensively of the by different naturally. non-metals vary significantly, their uses also vary quite considerably. C20.1 Physical Non-metals valence , , are and The bonding you learnt and elements electrons, 0 of usually t he graphite. t he 6, 7 of t he diatomic of atoms or 8. non-metals usually Most have non-metals a large are number found in of Groups table. non-metal bonding Several Each whose 5, periodic between about molecules. properties in atoms t he ot her in two a non-metal allotropes non-metals molecule is made of are up varies. carbon, two Unit 5.5 diamond of d i atomic composed of n i.e. atoms of t he non- metal bonded covalently. Weak intermolecular forces t hen exist between t he diatomic molecules. hydrogen (H in ), Non-metals oxygen (O 2 Group ), composed nitrogen (N 2 of t he ) of diatomic and all t he molecules halogens, include i.e. t hose 2 periodic table including uorine (F ), chlorine (Cl 2 bromine (Br ) and iodine ( 2 exist as individual between t he Because t he physical ✔ It important is the way of in due ot her which of non-metals t he have to having full non-metals t he non-metal different t he valence electron shells. Bonding varies. atoms non-metals following general are also bonded var y physical to differs, some t he extent. proper ties: tip that differences physical atoms atoms proper ties However, Exam ), 2 ). The non-metals in Group 0, i.e. t he noble gases, 2 you can between properties of ● t hey have low ● t hey are poor ● t hey are dull ● t hey are weak ● t hey have melting points conductors of and heat boiling and points electricity give the metals in appearance when in t he solid state and and brittle when in t he solid at room state non-metals. Many of t he low densities. non-metals are gases temperature because of t he weak forces of attraction between t he diatomic molecules or atoms, e.g. hydrogen, oxygen, nitrogen, uorine, found a room The liquid specic given 316 as in at proper ties Table 20.1.1. chlorine temperature and and and all t he characteristics t he noble ot her of gases. non-metals some of t he Bromine are is solids non-metals are Non-metals T able Physical 20.1.1 Properties Non-metal Hydrogen and Properties (H ) A characteristics and colourless, of some odourless of non-metals non-metals characteristics tasteless, properties Occurrence gas Occurs in the compound water (H 2 O), in hydrocarbons and in most other organic 2 compounds The lightest Acts Oxygen (O ) A as a of all elements reducing colourless, agent tasteless, odourless gas Occurs in the Occurs in water, elemental state as O 2 Nitrogen (N ) A as an oxidising colourless, agent tasteless, odourless gas and carbon and in very Occurs in in oxides dioxide, many the in other of metals metal in the air. non-metals, It carbonates and metal e.g. makes metal up about sulfates, in ores, 21% many silicon of the dioxide air. organic (sand) compounds elemental state as N molecules in the air. It makes up about 78% of the air. 2 One it (Cl and compounds 2 Chlorine molecules 2 Acts ) is A of the least considered yellow reactive non-metals; relatively green Occurs in proteins, Occurs combined Occurs in the Occurs in all metal nitrates and ammonium compounds inert gas in metal chlorides, e.g. sodium chloride (table salt) 2 Has Carbon a strong Poisonous to Acts as oxidising Has two an graphite (Unit a very A Y ou will copper, bulb, a be and as light the soft, has a flaky, very conducts reducing yellow use supplied of this with two in elemental carbon state as diamond compounds, in and metal graphite carbonates and metal hydrogencarbonates and dioxide solid. opaque, high dark melting electricity. agent of two activity and to Occurs in the Occurs in metal metals and elemental sulfides two state, and e.g. metal near hot springs and in volcanic regions sulfates non-metals assess: reporting. of two metals, non-metals, samples e.g. graphite conducting organic point. solid recording samples switch, a a It and hard, sparkling melting properties may observation, is solid. Acts ● extremely high point teacher an colourless, has diamond 5.5) It grey Your is agent allotropes, transparent, Graphite Comparing humans main Diamond Sulfur odour wire and two e.g. aluminium and crocodile roll foil sulfur, a and cell, a clips. Summary questions Method 1 Set up a circuit crocodile clips non-metal In 2 each in as turn case, Classify using each the shown cell, in between does metal the bulb, Figure the bulb switch, 20.1.1. crocodile light connecting Attach clips following to metal close the 1 2 or Is it properties of Name seven diatomic non-metal 3 be Where would you nd oxygen tested the in nature? criteria: 4 ● ve hydrogen. and switch. List elements. metal and according and up? to non-metal each and wire shiny or Compare graphite, ● Is it malleable ● Is it a or conductor diamond and bulb dull? brittle? or and a the giving the differences similarities between them. non-conductor? cell 3 Record your ndings in table. switch a Figure 20.1.1 conductivity A circuit to test electrical 5 By the means of a properties those of table, of compare metals with non-metals. 317 Chemical properties and reactions of non-metals C20.2 Objectives By the be able end of Non-metals this topic you will the reactions of reactions of with oxygen and non-metals the products valence formed of whose atoms usually have a large number electrons, reactions usually wit h 5, 6, metals 7 by or 8, t hey gaining for m negative electrons into anions t heir in valence by electron reactions elements metals chemical state are non- of metals the and non-metals Because ● properties to: describe ● Chemical shell. non-metals n with oxygen explain ● the and metals oxidising N properties ne N and As reducing of a result t hey form ionic compounds when t hey react wit h metals. The non- non-metal behaves as an oxidising agent since it gains electrons from t he metals. metal, i.e. it causes Non-metals can t he also metal react to lose wit h electrons each ot her. (OL). n t hese reactions t hey share valence electrons forming covalent compounds and may behave as oxidising and We reducing will metals, agents. now and look at Reactions Non-metals oxides. is in contrast Most t he reactions cer tain of non-metals with wit h form oxygen non-metal wit h non-metal and of oxidising react These at t he metal oxides to oxides oxides are reducing are acidic, compounds are e.g. of wit h oxygen and non-metals. oxygen usually which non-metals proper ties gases solids carbon at at known room room dioxide as non-metal temperature. This temperature. (CO ), sulfur dioxide 2 (SO ), sulfur trioxide (SO ) 2 and nitrogen dioxide (NO 3 known acidic as acid A few These oxides are also 2 anhydrides solutions. ). (Unit non-metal 8.1) since oxides are t hey react neutral, e.g. wit h water water (H to O), form carbon 2 monoxide or Did ? you and nitrogen (NO). They don’t react 20.2.1 T able summarises 20.2.1 Reactions Non-metal Reaction Hydrogen Hydrogen t he of reactions some with acids of non-metals cer tain with non-metals wit h oxygen. oxygen oxygen burns with a very pale blue, almost colourless, flame forming water as forming nitrogen know? 2H destruction airship an killing of 35 infamous the A passengers example of combustion of hydrogen. Hindenburg was a (g) O 2 Hindenburg mixture The luxurious Nitrogen of feet long feet decks and tall. for Inside were passengers sixteen hydrogen to gas cells make it and air or oxygen explodes when lit. with oxygen if the temperature is high enough, oxide): airship (g) O (g) 2NO(g) 2 and This 135 O(g) 2 (nitrogen(II) 2 804 2H hydrogen reacts monoxide N measuring (g) 2 the Nitrogen reaction occurs during lightning storms and in the engines of motor two and filled Carbon crew with lighter than Carbon If the burns oxygen forming supply is either carbon limited, monoxide carbon or monoxide carbon is dioxide. produced: air. 2C(s) (g) O 2CO(g) 2 As it was coming to land in New If Jersey on 6 May at the 1937, a the oxygen supply is plentiful, carbon O (g) CO 2 and ship within was 34 rear of seconds consumed in dioxide is produced: flame C(s) appeared the ship the entire Sulfur Sulfur burns with (g) 2 a blue flame forming flames. S(s) O 2 318 wit h steam: The is monoxide alkalis. Table (CO) (g) SO 2 (g) sulfur dioxide (sulfur(IV) oxide): vehicles. Non-metals Chemical Investigating (T eacher Your ● of non-metals with and reactions of non-metals oxygen demonstration) teacher may observation, Y our reactions properties teacher use this recording will activity and to assess: reporting. perform the following piece carbon experiment. Method 1 Place 2 Carefully a begins small to observe Repeat 4 Compare 5 burn. violence of Non-met als react a a metal and in a to a Bunsen burning, 2 and Which products Reactions Once 1 the spoon on place deagrating burner it into a spoon. ame gas until jar full the of carbon oxygen and happens. steps oxygen. What the what 3 with heat of using sulfur of reaction the seems were more formed in wit h metals is a to place of carbon. carbon with oxygen and sulfur reaction? with for m redox of reactive? each non-metals non-met al in metals ionic reaction compound s . because t he A reaction metal loses between electrons, i.e. it is oxidised, and t he non-met al gains t hese electrons, i.e. it is reduced. The non-met al ● acts Hydrogen e.g. as an reacts Ca(s) oxid ising wit h H agent metals to (g) in form CaH 2 Oxygen reacts e.g. wit h 2Mg(s) of metal t hese reactions. hydrides, (s) 2 calcium ● all metals O to hydride form (g) metal oxides, 2MgO(s) 2 magnesium ● Nitrogen e.g. reacts wit h 3Mg(s) metals N to form (g) metal Mg 2 N 3 magnesium ● Chlorine e.g. reacts wit h 2Al(s) metals 3Cl to form (s) reacts e.g. wit h Fe(s) metals to form Non-metals behave can (s) chloride metal suldes, FeS(s) iron(II) as chlorides, 3 S(s) Non-metals (s) 2 2AlCl aluminium Sulfur nitrides, nitride metal 2 ● oxide oxidising as bot h sulde and reducing oxidising agents agents and reducing agents. They generally behave as oxidising agents, however, some non-metals can also behave as reducing agents, for example, hydrogen, carbon and sulfur. 319 Chemical properties and reactions of non-metals Non-metals Non-metals ● All to as oxidising non-metals form ionic e.g. behave agents as oxid ising compounds. 2Zn(s) O They agents remove (g) when t hey electrons react from t he wit h metals metal atoms, 2ZnO(s) 2 2Fe(s) 3Cl (s) 2FeCl 2 Mg(s) ● Chlorine and Whenever oxidising S(s) oxygen t hey react (s) 3 MgS(s) are par ticularly wit h anot her powerful element or oxid ising compound S(s)O (g) SO 2 2KBr(aq) Oxygen caused the reaction. oxidation Non-metals ● as Hydrogen , wit h the Cl (g) 2KCl(aq) oxidation number reducing a 2H ver y to Br O C(s) O number removed increase sulfur powerful (g) act as O oxidising (g) 2H (g) CO ● t hese oxygen (g) Hydrogen metal and oxides. e.g. in t he t he O 2 (s) the second 4 in causing reaction. agents when t hey react (g) (g) non-metal oxygen also H in to ions agent, act t he to as caused decrease reducing metal ions (g) to Cu(s) t he from oxidation 0 agents to number of 2. when t hey react wit h atoms, H 2 2Fe 0 Br O(g) SO reduce CuO(s) to the 2 carbon They 1 increase from 2 reactions, atom to 2 2 each sulfur reducing 2 of electrons from 2 S(s) (aq) agents and 2 each 0 (g) 2 Chlorine carbon oxygen, e.g. n from as 2 2 their act agents, e.g. rst agents. t hey O(l) 2 3C(s) 4Fe(s) 3CO 3 (g) 2 2 Hydrogen oxide to caused t he decrease oxidation from 2 to number 0 in t he of t he rst Cu ion reaction. in t he Carbon copper(II) caused t he 3 oxidation number 3 t he to 0 in Summary 1 What 2 When is 4 produced carbon 320 reacts determines b Write balanced different ion in with non-metal oxygen which it oxide iron(III) oxide to decrease from chemical with form oxygen? one of two different oxides. equations to show the formation following reactions: of the oxides. chemical equations between aluminium b the reaction between sodium non-metal agent. reacts produced? reaction a t he can is the When balanced a a oxidising 5 Fe reaction. when What Write each questions a two 3 of second reacts Explain Certain non-metals agents. Name answer by Include balanced one can with the act as to two equations both for the non-metal different always acts as an this. oxidising can the chlorine hydrogen. metal, that for the and and reason non-metal reference a for agents behave reactions reactions. as of and both the reducing and support named your non-metal. Non-metals Laboratory C20.3 Laboratory preparation and uses of gases Oxygen, carbon dioxide and ammonia are all gases which, if required, can be made ver y wit h relative impor tant ease uses in in t he laborator y. today ’s These same gases also have t he considering following t he By the be able of t he to be gas used need to to prepare be a gas in t he The solubility of t he gas in water to determine if t he gas can be end bubbling it t hrough The reactivity of t he ● The agents density met hod of used Laboratory Oxygen is peroxide be t he gas to wit h different relative collect prepared you will how and oxygen, ammonia in relate methods the the carbon can be laboratory collecting the of drying gases to dr ying agents to determine properties which explain the uses carbon dioxide of oxygen and used. t he to dr y preparation solution topic water. gas can gases collected ● dr ying this prepared their ● of describe and by of to: dioxide laborator y, considered: ● ● uses some world. met hod proper ties and Objectives ● When preparation in t he using a t he density of air to determine t he based on their properties. gas. of oxygen laborator y catalyst of by t he decomposition manganese(IV) oxide. of hydrogen The hydrogen oxyge peroxide decomposes according to t he following equation: MnO 2 2H O 2 (aq) 2H 2 O(l) O 2 (g) hydrogen 2 peroxide The oxygen which ● f t hat depends dr y Figure lls on oxygen bubbling it is produced whet her not gas since jar, t he can dr y water water t hen into oxygen t hen oxygen required, t hrough 20.3.1, t he is is an not level in be is t he collected required gas upside ver y t he can be down soluble jar or one of two solution ways water not. collected gas in drops. in jar, as water. This is by shown As t he known in oxygen as manganese(IV) downward full. The having ● f dr y d isplacement oxygen been it as shown in in t he t he Figure Laboratory Carbon usual in wash 20.3.2. The dr y is following CaCO (s) be of t he is can to be react it can wit h whet her ● f dr y since when of water dried preparation carbon it in when vapour it is absorb directly t he due jar to is reacting t hrough t he into denser problem jar it calcium oxide, concentrated slightly The t he passing or compounds carbon by by chloride carbonate 2HCl(aq) dr y soluble see water oxide is it catalyst Figure 20.3.1 a water t han wit h jar air t his The laboratory oxygen a or sulfuric gas of by acid, vapour by and sinks met hod is an The full. dioxide a carbonate wit h wit h hydrochloric CaCl (aq) CO 2 carbon to acid acid. as shown equation: t he bubbling be collected 3 As easy containing t hese prepared calcium is preparation upwards. determined it contains calcium t hen air air way bottle All gas and water. t hen preparation d ioxide met hod t he a displacing cannot t his anhydrous d isplacement jar, it in water t hrough required, t hrough oxygen. upward t hat is containing bubbling in bubbled oxygen U-tube collected of dioxide t hrough water. of dioxide is oxygen, is not water However, t he required required, into t he an met hod or H of O(l) 2 collection depends on not. t hen upside carbon (g) 2 t he gas down dioxide can gas be jar collected since collected will it is by not ver y contain vapour. 321 Laboratory preparation and uses of gases Non-metals f ● ✔ Exam tip it It is can very important draw line apparatus carbon that drawings used dioxide dr y carbon t hrough to and of the prepare wit h oxygen, ammonia in dioxide U-tube t hrough oxide you a a wash cannot it. The be dr y d isplacement is bottle used gas of required, containing to is air t hen containing dr y t hen since t he gas can is be dried calcium t han passing into or sulfuric carbon directly denser by chloride concentrated because collected it it anhydrous a acid. dioxide gas jar by it bubbling Calcium reacts by upward air. the laboratory. hydrochloric acid carbon dioxide concentrated sulfuric calcium t is be Figure 20.3.2 impor tant used to calcium acid carbonate The to note produce sulfate. laboratory t hat carbon This forms preparation calcium dioxide a layer of dry carbon carbonate since t he around dioxide and sulfuric reaction t he calcium acid produces cannot insoluble carbonate cr ystals, which prevents t hem from continuing to react wit h t he acid and t he reaction quickly ammonium and stops. Laboratory preparation Ammoni a be of ammonia chloride calcium can prepared in t he laborator y by reacting an alkali wit h an hydroxide ammonium salt, for example, calcium hydroxide and ammonium chloride ammonia as shown in t he Ca(OH) following (s) 2NH 2 equation: Cl(s) CaCl 4 (s) 2NH 2 (g) 2H 3 O(g) 2 The solid calcium hydroxide and ammonium chloride are mixed toget her in heat a calcium boiling tube tube. placed They are t hen horizontally, as heated shown using in a Bunsen Figure burner 20.3.3. Since wit h t he boiling ammonia is ver y oxide soluble in water, it cannot be collected over water. The gas is dried by passing it t hrough calcium Figure 20.3.3 The of dry U-tube or nor up a dr ying tower concentrated containing sulfuric acid can calcium be used oxide. to Neit her dr y t he gas laboratory since preparation a chloride ammonia reacts wit h bot h of t hem. ammonia The ammonia since it less is collected dense t han air in a and gas jar rises to by downward t he top of t he d isplacement jar, displacing of air t he air downwards. t is possible to determine when t he gas jar is full of ammonia by placing a piece of moist red litmus paper at t he mout h of t he jar. f t he litmus turns blue, t he jar is full. Table 20.3.1 summarises t he met hods used to prepare oxygen, carbon dioxide and 322 ammonia in t he laborator y. Non-metals T able Laboratory 20.3.1 Gas Summary Usual Oxygen a the methods reagents Hydrogen and of Solubility peroxide catalyst used Slightly of to of prepare gas soluble. in Can gases in the Drying collected over agent(s) Anhydrous calcium Calcium dioxide hydrochloric Calcium and Slightly acid The of gases Upward soluble. Can be collected over Anhydrous sulfuric gases of collecting displacement denser than the of dry gas air. Oxygen air. Carbon is air. calcium acid chloride Upward water. dioxide hydroxide and Very chloride to soluble. form cannot Uses of oxide carbonate ammonium chloride slightly Concentrated Ammonia uses oxide Concentrated Carbon Method water. Calcium manganese(VI) and laboratory water be preparation Ammonia ammonium be reacts hydroxide, collected over with water Calcium sulfuric displacement is slightly of denser than air. acid oxide Downward therefore, Ammonia displacement is less dense of air. than air. water. gases which we can make in t he laborator y also have many impor tant uses. We will look at some of t he uses of oxygen and carbon dioxide based on t heir Uses proper ties. of oxygen Oxygen is essential for all living organisms to make energy during t he process of aerobic breat he. respiration . Oxygen is also Humans essential obtain for t his oxygen combustion to from t he occur. air when Because of we t hese two proper ties, which ● are given Oxygen and humans is also found a variety of uses for oxygen, some Figure 20.3.4 in ease hospitals cer tain for patients medical who disorders, have e.g. difculty breat hing re emphysema, Summary extinguisher chronic bronchitis Oxygen is and hear t Describe on how you could disease. prepare carried questions ast hma, 1 ● A of below. used to have aeroplanes and submarines for breat hing dry oxygen in the pur poses laboratory. in emergencies. 2 ● Nearly pure ● Oxygen oxygen is used in spacesuits for astronauts to Ammonia the is used in oxyacetylene and oxyhydrogen can be prepared laboratory by heating torches to burn or hydrogen and produce extremely high-temperature are used to weld and cut ammonium Write hydroxide a chloride. balanced equation Liquid oxygen is used to burn the fuel that generates the lift in spaceships. for b Uses of carbon Carbon the d ioxide Pressurised Name a agent for has cer tain proper ties t hat make it useful to c humans. What liquid carbon dioxide is used in re extinguishers. valve of t he extinguisher, When is suitable reduced by opening t he t he the drying gas. method to would collect the be dry gas t he and pressure reaction. dioxide used ● calcium metals. a ● of ames and t hat a t he mixture acetylene in breat he. why is this method carbon used? dioxide t han is air, released. so it The smot hers carbon t he dioxide ames, is non-ammable keeping out t he and oxygen in denser t he d air. Why is ammonia collected ● Solid carbon industr y. items t dioxide sublimes extremely cold (‘dr y at ice’) is 78.5 °C, and leaves used as a refrigerant t herefore, no liquid it can when it be in t he used to sublimes not water? food keep to a food 3 a What method collect gas. in ● over the dry is used carbon to dioxide laboratory? Carbon dioxide is used to make carbonated soft drinks. The solubility of b the gas increases as the pressure increases. The carbon dioxide is dissolved in the drink under pressure. When the pressure is released by opening the 4 Why Explain is this why method oxygen is used? used: bottle or can, its solubility decreases and bubbles form causing the drink a in hospitals b in welding. to ‘zz’. The carbon dioxide also adds a pleasant taste to the drink. 5 ● Carbon cer tain dioxide is used foodstuffs, as such an as aerosol whipped propellant cream, in cans because it is Explain why used re carbon dioxide is containing relatively in extinguishers. iner t. 323 The uses of non-metals Non-metals C20.4 Objectives By the be able end of this topic you The non-metals only a small number of elements in t he periodic table are non- to: metals, list of will Alt hough ● uses the uses metals and of various their non- t hem compounds. play metals t hese a and T able elements are par ticularly t heir 20.4.1 used impor tant compounds The uses of are carbon Uses Carbon • in • to cut and • in the tips • diamond • as • to • as • to make • to soften • in the • as a • as an • in Carbon (graphite) Sodium carbonate (Na ) CO 2 3 Sodium a wide role given and Non-metal/compound (diamond) in its in in range of industr y. Tables applications. The uses of Some some of non- 20.4.1–20.4.6. compounds jewellery the powder in and other diamonds is used as an abrasive for polishing and fine grinding pencils electrodes solid glass drills ‘lead’ make a engrave of for use in industry lubricant carbon hard fibres manufacture raising to strengthen plastics water agent of in glass baking powder hydrogencarbonate (NaHCO antacid ) 3 Figure been 20.4.1 Did ? This reinforced you Vulcanisation hardening is heated is racquet carbon the process The sulfur has make Figure T able 20.4.2 20.4.2 Carbon The in uses the of form sulfur Non-metal/compound Uses Sulfur • to • in of and diamond its is used to make jewellery compounds of rubber to extinguishers bre know? rubber. with tennis with fire it vulcanise the (harden) manufacture rubber, e.g. of medicinal of fungicides of matches for car drugs tyres and ointments to treat fungal infections stronger, more resistant to elastic chemical and more attack. • This in the manufacture garden is achieved cross-links chains of is discovery history of the sulfur between the Goodyear its by the rubber. in 1839, stabilising credited with however, the rubber Sulfur dioxide (SO 324 1600 attacks • to make the heads ) • to manufacture • as a food • as a bleaching sulfur dioxide preservative, e.g. and in sulfuric jams and acid fruit agent in the manufacture of juices paper dates acid (H 2 to fungal 2 Sulfuric back prevent polymer Charles generally to plants forming SO ) • in the • in lead–acid manufacture of fertilisers, e.g. ammonium 4 BC batteries, e.g. car batteries sulfate on crops and Non-metals T able The 20.4.3 The uses of phosphorus and its Uses Phosphorus • to make the • to make flares, striking Did surface of safety you to make • in the fireworks and of phosphoric acid to supply of the for acid (H PO 3 ) • to manufacture ) 4 • e.g. P fertilisers, e.g. ammonium to the that growth. elements one soil they or require Three needed more of by the plants sulfides, as • to a PO 3 phosphate are ] nitrogen (N), phosphorus (P) 4 rust make and remover the heads of potassium supply mainly known as (K). Fertilisers these which elements are matches NPK fertilisers. 3 T able Figure 20.4.4 20.4.3 The The uses of heads of chlorine Non-metal/compound Uses Chlorine • to treat • to make these and its matches contain a phosphorus sulde compounds drinking water solvents and to destroy dry-cleaning fluids, • to make pesticides, • to make antiseptics, • to make monochloroethene, window • to frames manufacture e.g. and e.g. tetrachloroethene (C Cl chlorate( ) (NaClO) and chlorate( ) • as • to [Ca(ClO) used to ) TCP and Dettol which is used Did ? to make PVC for Chlorine guttering chlorate(I) and calcium you know? pipes, poison chlorate(I) gas gas was during trenches in used as World a War I in Europe. 20.4.5 sterilise agents releases The uses as of ‘free nitrogen Uses Nitrogen • liquid • to fill • in food • and its nitrogen light aerobic ) water chlorine’ and which swimming is toxic to pool water – the compound bacteria disinfectants Non-metal/compound (NH drinking ] • Ammonia is bleaches calcium 2 T able bleaching Chlorine chlorine 4 the Sodium 20.4.4 DDT e.g. sodium Figure manufacture bacteria 2 elements with S 4 added 4 [(NH Phosphorus phosphate are plants healthy major Phosphoric know? explosives pesticides manufacture non-metals matches Fertilisers • of compounds ? Non-metal/compound uses is bulbs compounds used to quick together packaging to with provide freeze foods argon an inert atmosphere which prevents decay in the manufacture • in household • to manufacture of ammonia cleaners, e.g. oven and window cleaners 3 fertilisers, e.g. ammonium nitrate (NH 4 ammonium sulfate [(NH 4 [(NH ) 4 Nitric acid (HNO ) PO 3 ) SO 2 ] and ammonium NO ), 3 phosphate 4 ] 4 • in the manufacture • to manufacture of nitric fertilisers, acid e.g. ammonium 3 nitrate (NH 4 NO ) 3 • to manufacture explosives and Figure 20.4.5 Ammonia is often used dyes in cleaning agents 325 Harmful effects of non-metals and their compounds Non-metals T able 20.4.6 The uses of silicon Non-metal/compound Uses Silicon • in the Silicon (SiO dioxide (quartz) to • • • its compounds manufacture pocket • and calculators make silicone to make a in jewellery, in the silicon chips used in electronic devices from computers implants silicon e.g. of to steel for alloy amethyst plastic in is the and steel purple reconstructive surgery industry quartz ) 2 manufacture of glass – silicon manufacture of cement dioxide is the main ingredient of glass Metal silicates • in • mixed the • to make roof Summary 1 Which 2 What is used to of 3 four with cement ceramic tiles, floor and aggregate products, tiles, building such to as bricks make concrete pottery and and sewer porcelain products, pipes questions compounds mean by of non-metals ‘vulcanisation vulcanise rubber and of are used rubber’? explain what to Name make the happens fertilisers? non-metal during the that is process vulcanisation. Discuss some of the uses of the following non-metals and their compounds: a C20.5 Objectives By the be able end of this topic you Harmful will c chlorine effects of silicon. non-metals and their compounds to: While discuss ● b carbon the harmful non-metals and t heir compounds are extremely useful to humans, effects some compounds of t he same non-metals can have harmful effects on living of non-metals and their systems compounds on living t hese and the and t he environment. Like cer tain metals, t he concentrations of systems non-metal compounds wit hin t he environment are increasing due environment. to pollution caused by man’s activities. These harmful substances are called pollutants We will t hese now environment will look pollutants also be in T able 20.5.1 Non-metal Harmful effects of some compounds of some Table discussed at and of t heir t he 20.5.1. in more Figure sources negative Some detail 20.5.1 of some effects of t hese af ter Pollution on t he harms of t he effects table. the environment non-metals compound/ Sources in the environment Harmful effects pollutant Sulfur dioxide (SO ) Combustion of fossil fuels, especially coal and Sulfur dioxide causes respiratory problems in humans, 2 heavy oils, e.g. in industry and power stations e.g. bronchitis. dissolves as Carbon monoxide (CO) Incomplete in motor combustion vehicles of fossil fuels, mainly acid Carbon readily (see reaching mental in binds oxygen the growth forming later monoxide dizziness, 326 reduces rainwater rain than oxygen and in It this body and solution haemoglobin a reduction tissues. awareness, headaches, acidic plants known unit). with causing an of causes This in much the reduces visual more amount of respiration impairment, unconsciousness and even death. Non-metals T able Harmful 20.5.1 Non-metal effects of non-metals and their compounds (continued) compound/ Sources in the environment Complete combustion Harmful effects pollutant Carbon dioxide (CO ) of fossil fuels, e.g. in Carbon dioxide, together with other gases, builds up in 2 motor vehicles, industry, power stations and the aeroplanes upper effect and About 25% by oceans the increase Hydrogen sulfide (H S) Decay of organic matter in garbage dumps, atmosphere global in of such produce and Hydrogen warming the carbon leading acidity shellfish contributing as is to expected maintain is sea their the later dioxide ocean oysters, sulfide (see to in greenhouse this released unit). is absorbed acidification. to affect urchins the and This ability corals of to shells. extremely toxic. Like carbon 2 landfills and petroleum farmyards. Released from monoxide, refineries. reduces it combines cellular headaches, of nitrogen (NO and NO ) Combustion at high temperatures in motor Oxides of respiration with and unconsciousness concentrations Oxides readily irritate nitrogen the are haemoglobin, causes and eyes even and extremely death. Low respiratory toxic which dizziness, causing system. lung 2 vehicle engines nitrogen and and power oxygen in the stations air to causing damage. react system. the of growth Used as a refrigerant refrigerators aerosol Carbon particles (C) and in a air-conditioners propellant in and CFCs some fires break Earth’ s of and fossil fuels, e.g. in (see atmosphere sprays Combustion Bush as rain industry. blacken and sulfur ions ) (NO and phosphate Fertilisers ions used in agriculture, especially in These drivers e.g. ions role dissolve layer trees skin, in in in to the eyes die, and reduce development rainwater the forming upper light to reach the unit). reducing combine smog, aircraft bronchitis, cause leaves this They form and cause ultraviolet in blacken the major ozone buildings. irritate unit). more later to a and this the (see dioxide for problems, in allowing particles and visibility Nitrate down also play smog later surface Carbon cigarettes. They plants, photochemical acid (CFCs) concentrations respiratory of Chlorofluorocarbons Low which pilots asthma (see water causes and and eutrophication photosynthesis with vapour poor respiratory lung disease. later in this unit). 3 3 intensive ) (PO farming. Synthetic detergents. 4 Pesticides, e.g. insecticides, fungicides and Used herbicides in control agriculture and vectors of control disease, for of pest control, weeds. e.g. Used disease Pesticides to consumers control mosquitoes. useful as which are concentrate (see well as later up in harmful essential for food this chains unit). They organisms, pollination harming top can harm for are also example, being killed bees by insecticides. Acid Acid of rain rain is nitrogen when t hey SO formed are react (g) wit h H 2 when released pollutant into the rainwater O(l) H 2 t hey SO 2 (g) H 2 O(l) such form as sulfur These acidic dioxide oxides solutions, are for and oxides acidic and example: (aq) 3 sulfurous 2NO gases atmosphere. acid HNO 2 (aq) HNO 2 nitrous (aq) 3 acid nitric acid These acidic solutions t hen fall to Ear t h as acid rain which can have a serious effect t he on soil, corrodes causes plants, animals, damages crops, buildings, lakes, organisms, streams such as cars, and sh. t he trees soil and and machiner y rivers to water. ot her Acid plants and become rain and historical acidic decreases harms and t he animals. monuments unsuitable for pH t of also and it aquatic Figure 20.5.2 corroded by A limestone acid statue rain 327 Harmful effects of non-metals and their compounds The greenhouse When t he Non-metals fossil fuels are atmosphere, greenhouse monoxide burnt a including gas. (N effect O) Ot her and and number carbon passes The infrared gases form by a t his layer, surface t hen radiation. absorbed warming are produced Carbon include and dioxide water released is into known vapour, as a dinitrogen ). 4 t hrough Ear t h’s gases gases (CH 2 Greenhouse of dioxide. greenhouse met hane global t he Some layer around reaches t he radiates of t his greenhouse t he t his heat radiation gases Ear t h. Ear t h’s Radiation surface back into goes back t he Ear t h. around and t he into from warms Sun Ear t h. atmosphere space The t he t he and some greenhouse as is gases t hen re-emit t his radiation. Some of it is re-emitted into space, however, most of it is re-emitted known as the back towards greenhouse the Figure on 20.5.3 The effects of acid t he Ear t h as heat. The heat causes a warming effect Earth heat rain radiates back into space trees some is radiation absorbed radiated into radiation space from CH the Sun the Earth H warms 4 O 2 CO 2 absorb CO some radiation 2 H O O H 2 2 400 CO CH space 2 4 CO O noillim 2 is radiated back towards Earth atmosphere 380 H O CO 2 2 CH 4 rep 360 straP Figure 20.5.4 The greenhouse effect 340 An increase warming 1960 1970 1980 1990 2000 of greenhouse warming Figure levels 20.5.5 in the Average carbon atmosphere from 1960 to ooding weat her is of fossil fuels, Ear t h’s is especially resulting surface as a in result carbon t he of dioxide Ear t h caused getting increasing by warmer. t he The concentrations gases in causing t he atmosphere polar ice caps is called and global glaciers to warming. melt, sea This of levels global low-lying coastal areas, global climate changes and to more rise, severe patterns. Ozone you of t he gases, dioxide 2012 Did greenhouse 2010 Year ? in combustion 320 H 2 layer depletion know? Ozone (O ) is a gas found in the upper atmosphere which shields the Ear th from 3 In 1800 the average concentration was about (ppm) or in 280 the about had risen In 316 ppm dioxide atmosphere parts 0.028%. was carbon per and by million 1960 the in in figure 2012 dangerous about 394 ppm. aerosol is currently sprays, about 2 ppm per This which, refrigerators and ozone until layer recently, air-conditioners. is becoming were These used CFCs depleted extensively are iner t and it damaging the ozone layer. Depletion of the ozone layer means that more light is reaching the Ear th and this is leading to more and more people increasing developing at radiation. (CFCs) The U concentration (U) insoluble in water causing them to accumulate in the atmosphere where they are to ultraviolet chlorouorocarbons skin cancer, cataracts and depressed immune systems. year. Eutrophication Eutrophication is the rapid growth of green plants and algae in waterways such as lakes, ponds and rivers caused by nitrates and phosphates entering the water. Nitrate and phosphate ions are needed by green plants to make proteins so they can grow. When their concentrations increase, it promotes the growth of 328 plant life, especially algae. This rapid growth causes the water to turn Non-metals green. and Harmful Underwater the algae decomposed plants start by to die aerobic then due begin to to die due overcrowding. bacteria which to reduced The multiply dead and light plants use up all effects of non-metals and their compounds penetration and the algae are dissolved oxygen. This leads to the death of other aquatic organisms such as sh. Effects of Pesticides pesticides are chemicals used to destroy pests. They are used especially in agriculture and in t he control of vectors of disease such as mosquitoes. There are different types of pesticides: herbicides are used to kill weeds, insecticides are used Some are to kill insects pesticides persistent, have t he absorb are i.e. fungicides par ticularly t hey potential toxic and do for substances not are harmful break used in down bioaccumulation at a faster rate to t he in destroy environment t he which t han t hey because environment. occurs excrete Figure 20.5.6 Eutrophication occurs fungi. when t hem. t hey They when there green algae is uncontrolled in growth of water also organisms For example, if fat soluble pesticides such as DDT are absorbed by living organisms t hey are stored in fatty tissues of t he organisms where t hey gradually accumulate. The concentration moving up are of ten ver y of food t he harmed, Disposal of Plastics organic are pesticides chains. As a in especially solid t he result, fatty tissues consumers birds of of at animals t he top of t hen t he increases food chain prey. waste compounds composed of t hey are organic compounds, most plastics are non-metals. Even t hough non-biodegrad able , i.e. t hey cannot be broken down by microorganisms and t herefore t hey remain in t he environment waste ● Plastics t hat to ● for ver y containing make more accept Some up and all danger ● Plastics and ● of and healt h where leading problem recycling all of 1 Explain to how of time. This all solid waste being used up chemicals plastics gases of to are if of burnt t hey are makes going t he to extend by of being are of in disposal landlls, and build groundwater which ver y can of solid meaning landlls harmful can be to or in wit hin t here and lead of of ten ingested plastics persistent landlls disposed plastics par ticularly deat h disposal which disposed when properly, t hey made are contaminating problems t heir t he items Summary toxic toxic disposed oceans of ten The not is chemicals produce serious When 25% of problem. plastics. When t hese periods serious land release environment. a about more t hese plastics long plastics to nearby air up aquatic soil. pollution in to a water ways organisms, causing solved t he t he incinerators. land by is suffocation. large extent by plastic. questions carbon dioxide contributes to global warming and suggest some of the consequences of global warming. 2 Name 3 What 4 a What b Why 5 What two are which pesticides is is are gases can and why eutrophication eutrophication some of the form are and a acid rain they harmful what is problem problems of it in and discuss to caused aquatic disposing of some organisms of at the the effects top of of food acid rain. chains? by? environments? plastics? 329 Green chemistry Non-metals C20.6 Objectives By the be able end of this topic you Green chemistry will Green chemistry is also known as sustainable chemistry . Green chemistr y to: involves designing chemical products and processes t hat reduce or eliminate ● dene ● outline green chemistry t he the principles of use or generation of substances t hat are hazardous to living organisms green and t he environment. The principles chemistry. when The for t hey principles economic and t he Key Green chemistry set of use fact of a or eliminates is the principles the use utilisation that or reduces a hazardous the design, application and substances chemical processes. on new t he provide materials, development development chemical variety of at t he a framework products, of same They create usually costs processes reagents, and heavy chemistr y sustainable time as for chemists processes and designs protecting to use systems. which human allow healt h including pressures yields associated usually and raw solvents. purication below wit h take 100%, place They has to generate materials, energy in several of ten take require place at substantial usage steps and and elevated each waste, waste step. incur disposal generation manufacture of focus temperatures and of green designing environment. Trad itional ! of are have a negative impact on t he environment. in and products Green chemistr y is doing chemistr y t he way nature does chemistr y; using renewable, biodegradable materials which do not persist in t he environment or harm Using t he t he environment. technologies of green chemistr y provides a number of benets including: ● reduced wastage ● reduced pollution ● safer ● reduced ● improved The are and, to toget her follow at ‘It’s term t he wit h principles Prevent and principles The working twelve energy natural of principles twelve systems. while of competitiveness chemists and 1 use twelve There for products when ‘green United John are chemical of of designing States chemistry chemistr y, new chemistr y’ below manufacturers. green green Warner, stated resources was which materials, coined Environmental he developed wit h a provide shor t by products, Paul twelve road in Agency principles. explanation of map processes Anastas Protection t he a 1991 (EPA) These each. waste better to prevent waste than to treat or clean up waste af ter it has been created.’ Chemical waste 2 as Maximise atom methods mater ials used materials in few, if should be designed to produce as little hazardous economy ‘Synthetic Chemical 330 processes possible. in should be designed maximise process into processes which incor porate into any, t he nal wasted the to the products atoms. nal the incorporation of all product.’ most should be or all used. of t he This star ting would t hen result Non-metals 3 Green Design less ‘Wherever generate hazardous practicable, substances chemical synthetic that possess chemistry syntheses methods little or should no be toxicit y designed to which human use health and and the environment.’ Chemical least risk harmless 4 Design processes to All safer still 5 be Use chemicals products minimising new healt h products effective designed t he using reactants environment and which which pose t he produce for t heir ‘The use auxiliar y they should be made chemical agents. waste. use The of and specic perform their desired functions Many to uses, be but safer. have These products minimum should toxicity. auxiliaries substances or which designed innocuous t hese totally designed be processes separating eliminated be products toxicity.’ should solvents of and should their safer Many be and by-products. ‘Chemical while should human use of should when auxiliar y t hese are substances t hey be should minimised wherever possible and used.’ substances hazardous should be be such and reduced replaced wit h as lead to less solvents to a and considerable minimum, hazardous alternatives. 6 Increase ‘The energy synthetic if energy efficiency requirements methods of should chemical be processes conducted at should ambient be minimised temperature and and pressure possible.’ Chemical processes of f energy. (surrounding) amounts of should possible, temperature energy be designed processes and associated should to be pressure wit h use to using t he carried avoid higher minimum out at t he t he need amounts ambient for temperatures large and pressures. 7 Use renewable ‘Raw mater ials whenever The as waste feedstocks feedstock Whenever materials such or should be rene wable rather than depleting practicable.’ term process. feedstocks which refers are ot her any raw material chemical renewable. pur pose-grown from to possible, crops, These wood used processes include chips, in an should industrial use agricultural processed solid raw products waste and processes. The use of non-renewable raw materials should be reduced to a minimum since t hey are rapidly r unning out. Non-renewable raw materials include t hose and obtained t hose from which are fossil fuels, mined such from t he as petroleum, Ear t h, such as natural gas and coal, ores. 331 Green chemistry Non-metals 8 Reduce derivatives ‘Unnecessar y derivatisation Derivatisation processes. waste, 9 Use involves Since t his should minimised temporarily requires derivatisation be should modifying additional be or avoided physical reagents avoided or if and possible.’ and can chemical generate minimised. catalysts ‘Catalytic reagents Catalysts are not reaction itself. are up used are super ior used up in to reactions Stoichiometric and t he stoichiometr ic reaction since reagents of ten take forms reagents.’ t hey do par t in not t he unwanted or take par t reaction in so hazardous t he t hey by- products. Catalysts reaction t he 10 should occurs reaction products of by-products. for ‘Chemical products persist in Analyse life t he in into when the of t he or any t he and several reasons. it conversion reduces The needed t he of for reactants production be so they break down into innocuous environment.’ designed down into to be so t hat harmless at t he end products of t heir which do not be is pollution developed minimise chemical chemical should to a the process complete to allow for formation should and to of real-time, in-process hazardous always detect be t he substances.’ monitored formation to of any by-products. for used accidents in chemical accidents, processes including which explosions, minimise res and the toxic releases always to The show by in chosen to reduce t he risk of chemical action understand year, awards be minimum. way our for temperature atmosphere.’ Each chemistr y to potential The which the prevent reaction chemistry Awards. reagents in should Green various to hazardous the for accidents best t he improves designed break control reagents Reagents action. of it be should real-time progress potential wastage processes reduces environment. and Minimise chemical catalyst energy, persist t hey methods ‘Choose 332 not products unwanted 12 do monitor ing know saves should ‘Analytical The in t he degradation that functional used reducing products Chemical 11 which to Design be faster, t he US t he potential Environmental including The Presidential following are how effective small environmental t he a businesses few examples green larger chemistr y Green of application and challenges. of Protection Agency Chemistr y award-wining of is t he cor porations to (EPA) it in Challenge innovations principles is see sponsors of beginning to green solve Non-metals ● irent Green Energy gasoline, plants. Systems diesel The process economically ● with resource so Eastman Chemical esters use uses for and products Battelle and their in enzymes acids ● and and photocopiers carbohydrates paper than star ting also the place traditional lower from corn. allowing considerable oil toner which the of a energy, than for protein are made from be easily and are a to renewable avoids of make method using traditional to strong undesirable by- methods. printers together easier to of compete Their laser much energy can method production and make petroleum. new toner to cellulose Plants is paper amounts a on temperatures soya and products. saves the developed This toners care which minimises at energy and petroleum. developed personal esters have made from from method starch dependence has and catalytic sugar, external reduce solvents, materials, saves little Company par tners the produced helps make takes its water-based, from requires cosmetics to a fuel fuels use organic and use jet chemistry with remove from petroleum-based recycled. reduces ts the production use of petroleum. ● Buckman derived order from to and means recycled saves natural make stronger This nternational paper. of paper, the thus signicant carefully sources, Paper higher that has to can of using than be conser ving amounts modify made quality paper selected the paper energy and bres modied made using natural designed cellulose these made and by less reduces in bres wood is traditional wood resources. enzymes, The the bre use of methods. and process in much more also additional chemicals. ● Seventh Generation products, diapers, such body as washes phosphate- and materials its in produces laundr y and and green cleaning, dishwasher lotions. chlorine-free The paper and detergents, company ingredients in uses its personal paper care towels, baby biodegradable products and and recycled packaging. Figure 20.6.1 Seventh biodegradable and Generation phosphate- products and use chlorine-free ingredients Summary 1 Dene 2 Suggest 3 Outline questions ‘green chemistry’. some six benets principles of of using green the technologies of green chemistry. chemistry. 333 Green chemistry Non-metals Key ● concepts Non-metals valence ● n general, not a ● and Many few ● Carbon ● Diamond ● Graphite ● Non-metals ● and has is is is two a a are low at nitrogen yellow green allotropes, are have points dull, weak and and temperature. transparent, sof t, aky, into colourless, and opaque, dark anions t heir in valence sulfur and colourless, negative electrons are gas diamond share valence covalent a large number of boiling brittle points, in t he do solid Bromine is a liquid and tasteless is a and yellow odourless solid. graphite. sparkling grey solid. solid. chemical electron reactions shell. As a wit h metals result t hey by form electrons react wit h oxygen ● Non-metals react wit h metals ● All ● Oxygen non-metals and ot her Hydrogen, when t hey react wit h each ot her compounds . Non-metals ● melting room ● wit h usually 8. compounds forming ● atoms or heat, gases and a form Non-metals wit h 7 densities. oxygen chlorine gaining 6, solids. Hydrogen, ionic low 5, have electricity have whose usually non-metals are gases, elements non-metals conduct state ● are electrons, behave chlorine as to form form oxid ising always non-metals or carbon sulfur and to act as non-metal ionic agents oxides compounds when oxidising t hey agents react when wit h t hey metals. react compounds. act as reducing agents when t hey react oxygen. Hydrogen and carbon act as reducing agents when t hey react wit h metal oxides. ● Oxygen can hydrogen ● ● dioxide with acid, an Ammonia Calcium used ● Dr y air, ● ● to Two impor tant metals. Carbon dioxide sof t Non-metals jeweller y and in carbon is to and in in re as to and make t he laborator y and decomposition by oxide reacting hydrochloric laborator y by are by and reacting of catalyst. a carbonate acid. an ammonium concentrated collected downward are alkali wit h sulfuric acid may be in an hospitals aerosol have plastics, by to insecticides, upward displacement and as a for of welding refrigerant, organisms and and t heir t he compounds environment. and to make propellant. a great many strengt hen matches, can of air. uses r ubber fer tilisers, including used in tyres, bleaches, glass ceramics. Non-metals an chloride. displacement extinguishers, compounds strengt hen the by manganese(IV) laborator y. dioxide and a hydroxide oxygen used t heir t he oxide t he collected drinks and bres calcium in of carbonate calcium of laborator y prepared calcium made is t he presence prepared uses cutting in 334 and in t he be e.g. ammonia making ● be salt, gases oxygen dr y can chloride, dr y in usually can carbonated ● prepared Carbon ammonium ● be peroxide have a negative effect on living Non-metals ● The Green concentration wit hin t he of t hese environment is harmful non-metals increasing due to and t heir pollution chemistry compounds caused by man’s activities. ● The most carbon harmful non-metal monoxide, carbon chlorouorocarbons, compounds ● Acid rain in compounds dioxide, carbon include hydrogen par ticles, sulfur sulde, nitrate and dioxide, oxides of phosphate nitrogen, ions and pesticides. forms when sulfur dioxide and oxides of nitrogen react wit h rainwater. ● Carbon dioxide is contributing to the greenhouse effect and global warming ● Chlorouorocarbons are atmosphere more ● Nitrate ● Pesticides ● Disposal ● and allowing phosphate of solid Green chemistry eliminates t he manufacture ● Using t he use of is use and t he or energy and natural There twelve are harming should plastics be of green of set chemical of green top upper surface. consumers. serious principles problem. and provides pollution, and t hat substances products chemistr y resources principles a hazardous reduced a t he recycled of of poses t he in Ear t h’s chains, wastage, manufacturers. t he food utilisation chemical layer reach eutrophication generation of ozone to causing application reduced t he light are containing plastics technologies including ● waste containing up down ultraviolet ions concentrate Waste breaking safer improved a in reduces t he or design, processes. number products, of benets reduced competitiveness of chemistr y. 335 Practice exam-style questions Non-metals 9 Practice exam-style Acid 1 Which A B 2 of Most They t he have are They are D Most have of metals A at high all C Which questions following solid hydrogen, C uorine, D oxygen, of nitrogen carbon A only B and C and D , Most A is of room a list of and temperature. 10 gaseous diatomic The increase neon, to cause A depletion of t he B changes in C melting of D ooding 4 amphoteric D neutral n which behaving A Zn(s) B 2K(aq) a following reducing PbO(s) 2Mg(s) layer weat her polar ice patterns caps of low-lying coastal areas are: 11 a The question diagram used to below prepare shows a dr y t he apparatus sample of t hat oxygen in could t he reactions is t he X non-metal ZnS(s) Cl (g) 2KCl(aq) (aq) 2 (g) H atmosphere except: helium Pb(s) H 2 D t he chlorine 2 C in following agent? S(s) levels t he laborator y. t he as of ozone global liquid of dioxide all non- be basic carbon predicted nitrogen hydrogen, non-metals C in are acidic B only nitrogen hydrogen, nitrogen, of only electricity. points. bromine, oxygen, oxygen, oxides dioxide monoxide non-metals? Structured 3 by: temperature? oxygen, B at melting following room chlorine, tr ue non-conductors low caused dioxide densities. usually t he is is sulfur Multiple-choice rain questions O(l) 2 O (g) 2MgO(s) 2 5 Oxygen can be prepared in t he laborator y by t he dry decomposition of hydrogen peroxide. Manganese(IV) oxygen oxide is also usually A a source of B a catalyst C an t he used in t he preparation solid as: solid oxygen i) oxidising a reducing Y dentify t he State t he role Write an of t he following is used as t he dr ying agent in of dr y ammonia in t he A calcium oxide B calcium chloride v) Name C calcium D concentrated sulfuric t he t he suitable following to prepare pairs a of reactants sample of would carbon be dioxide Give A calcium B magnesium C copper(II) D calcium form ONE re ii) carbonate and carbonate carbonate carbonate dioxide is dilute and and and used can nitric dilute C D and show how oxygen Y. t hat could be Z marks) and reason for and collecting name t he t he state marks) oxygen met hod. (2 react wit h bot h metals and by t he marks) non-metals dilute dilute in all of t he f balanced water, oxygen acid hydrochloric sulfuric a zinc to acid equation and followed is by added reacts obser ve? to wit h Give for t he reaction oxygen. a a few t he (2 drops oxide sulfur, reason blue formed what for of would your when you (2 following non-metal hydrogen can behave expect answer. acid The marks) litmus as bot h marks) an except: agent and a reducing agent. Write T WO extinguishers sof t one to show hydrogen behaving as an drinks oxidising agent reducing agent. and one to show it behaving as a hospitals aerosol (2 marks) sprays Total 336 mark) is (2 compound shown solution, acid sulfuric Write equations, B X to oxides. oxidising A marks) (1 (2 between in laborator y? Carbon (2 role. Oxygen i) t he c 8 Y. acid to of solid carbonate b least by ONE met hod Which t he laborator y? its 7 and solid Y. t he iv) preparation t he equation produced Which of agent iii) 6 liquid X agent ii) D Z 15 marks Non-metals Practice Extended 12 a The response Four t h Annual Assessment ntergovernmental Change published t he next par tially gases i) in is likely two in to t he 2007 be decades. attributed Name to This on predicts about t he Repor t Panel t hat 0.2 °C global of t he per overall decade warming increase in United Climate has main Explain how iii) Discuss t he greenhouse t he gas. greenhouse (1 effect Over t he a This possible years studies signicant Your of has been c some answer t he of global linked ozone ‘Non-metals extensively shown t he wit h for of t he t he t here extensive many and man.’ provide has layer. use of of reference t his to depletion. t he function (3 t heir compounds By reference evidence on marks) years. consequences include t hat ozone layer. by non-metals, statement. of must have marks) warming (3 depletion chlorouorocarbons Discuss effects mark) works. environment. been been greenhouse (4 b global for atmosphere. t he ii) t he questions question Nations warming exam-style to are to marks) used T WO suppor t different t his (4 Total marks) 15 marks 337 C21 Water Water makes up between 60% and 70% of the human Objectives By the be able ● end of this topic you will body describe some properties of of the unique a liquid explain of it covers 71% of the Earth’s surface. Water is why water and the can harmful at it exists room on temperature Earth in all three and pressure, states, solid however, (ice), liquid water and ● and to: gas (water vapour or steam). Water has certain properties have unique useful effects on properties that make it essential for life on Earth. living These properties help us to understand such things as systems ● discuss the ● the consequences solvent distinguish types of properties between water of the of water how the water becomes bottom of lakes polluted when the and why top is life can exist at frozen. two hardness. C21.1 Pure The water, i.e. unique water tasteless and standard pressure. has a side negative positive shown t hat charges Figure a The and does liquid Water has charge. in t hat odourless properties molecules par tial two t he not contain t hat boils are positive hydrogen oxygen of any at charge atom has and meaning and in a impurities, 100 °C polar, atoms water a par tial t hat side each is a colourless, freezes at each t hat has molecule negative 0 °C at molecule a par tial have par tial charge. This is 21.1.1. oxygen partially hydrogen negative partially side + of positive molecule side of hydrogen molecule + Figure The 21.1.1 par tial A polar positive water molecule hydrogen atoms and par tial negative oxygen atoms of O H + t he water molecules are attracted to each ot her. This attraction forms what H is + known as t he hydrogen bond. Hydrogen bonds are usually stronger hydrogen O H t han ot her intermolecular forces which gives water several properties . exist between molecules and t his bonds H + O + unique We will now look at some of t hese t he mass H proper ties + H O and at t heir signicance to living organisms. H + H + The + maximum density of water occurs at 4 °C O Density H is a measure of how compact a substance is. t is dened as + of H a substance divided by its volume, i.e. + mass ________ density Figure 21.1.2 Hydrogen bonding in . volume water f t he f its of a xed increases, When most liquids of solid is t he solid is, liquid 338 volume volume it less t herefore, sinks. mass its are cooled t han of density t he denser a substance and become volume t han decreases, its density increases. decreases t he of solids t he liquid t hey liquid and if contract. from it is which placed The it in volume forms. more of The t he Water The Somet hing cooled However, until it of t he forms. if to it is freezes volume t han slightly down is below This from water why ice happens contracts 0 °C. water liquid This it cooled at t he different 4 °C and 4 °C it means which from oat star ts t hat it which cubes in to t he forms. it in t he case becomes expand cold water. Solid of ice and just and volume formed a of denser, it When like continues ice is, is to greater t herefore, oats on water ot her t he unique properties of water is liquids. expand t han less t he dense liquid as it drink. 1.0000 m c g( 3 ) 0.9995 ytisneD 0.9990 0.9985 0.9980 0 2 4 6 8 10 12 14 T emperature When a Figure pond or 21.1.3 lake The freezes, maximum ice density forms at t he 16 18 20 (°C) of water surface occurs and at t he 4 °C denser, Figure 21.1.4 Ice oats in water warmer water remains below t he ice. This enables aquatic organisms to sur vive under t he ice. ice summer Figure 21.1.5 has a Water n Unit t he 12.2 amount substance, requires t hat ver y a water changes, The or, t he t heir ● As to of body sur vive in heat 1 °C. a lot ot her living of extremes of 4 °C of to of of in heat t he heat water its for two changing capacity a high and of not of a in its by a winter substance unit specic temperature main mass heat 1 °C. of t he ver y of is t he capacity, This temperature change it means changing surroundings much. This is of reasons. between absorb ver y summer temperature contain can in wit hout t he does heat has energy when lake temperature water increase a capacity specic temperatures temperature of change much. large not water a much. 60% lot of This and heat 70% water. energy means t hey wit hout can temperature. not do 3 °C 4 °C organisms t he environments 2 °C 5 °C raise organisms temperature ver y to words, living environmental t he organisms living t his, 1 °C 6 °C Because energy absorb in t hat needed by 0 °C 7 °C specific temperature bodies Because heat 8 °C temperature learnt 1 g, of can signicance ● of lot much high you e.g. The winter bodies This change, of water means experience t hat e.g. from such as winter lakes organisms extreme to and living uctuations in summer, seas in does aquatic temperature. 339 The unique properties of water Water Water The a heat liquid gas has due t hat of a to t he large is high gas. not water A amount ver y of a has melting is energy ice of a is t he t he met hods high and t he to a a cooling boiling due required change high heat of change water This to a means vaporisation, organism This to liquid molecules. living organism. of size ener
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