Chemistry for CAPE® Unit 2 Chemistry for Roger Leroy CAPE® Norris Barrett Annette Maynard-Alleyne Jennifer Murray Unit 2 3 Great Clarendon Oxford It University furthers and Oxford The © Roger This published rights in means, Press, as Enquiries should must impose British Data by © the No the sent the and Barrett, of in in permitted by law, scholarship, registered other trade mark of countries and Jennifer Murrary 2012 2014 2012 Press by any of licence rights outside Department, in may in writing reprographics reproduction Oxford. asserted publication in a of research, Maynard-Alleyne Press transmitted, permission in is certain been Ltd University Oxford University this or the Annette have Oxford Rights of Kingdom excellence University Thornes appropriate to UK United the 2014 be or Oxford or by any University under terms organization. scope Oxford reproduced, form of the University above Press, at above. not this the part of worldwide. authors prior 6DP, department Oxford by OX2 objective system, expressly the in Nelson concerning be address You of retrieval with a Leroy published without or agreed Press reserved. a is publishing Norris, rights edition stored the by illustrations moral First Press Oxford, University’s University Original All the education Text Street, circulate same Library this work condition Cataloguing on in in any any other form and you must acquirer Publication Data available 978-1-4085-1746-8 10 9 8 7 Printed in India by Multivista Global Pvt. 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Boldon, every before the Lyndersay, Ltd, Wearset holders earliest Links and If Mark Wearset Oxford any in good faith responsibility website referenced for in all at Contents Introduction Module Chapter an 1 1 1 Carbon compounds: introduction in 2 1. 1 Bonding carbon compounds 1.2 Homologous 1.3 Determining formulae 6 1.4 Naming organic 8 1.5 Isomerism 10 1.6 Stereoisomerism 12 1.7 More about isomers 14 1.8 More about homologous series 2 Chapter 5 Organic acids and bases 5. 1 Carboxylic 5.2 Comparing 5.3 Amines, 5.4 Amino Chapter acids and acidity 2 50 acidities amides 52 and acyl halides 6 56 Polymers 58 4 compounds series 6. 1 Addition polymerisation Hydrocarbons 58 6.2 Condensation 6.3 Monomers 6.4 Proteins 64 6.5 Carbohydrates 66 polymerisation and 60 polymers – Module 62 1 18 Module Chapter The alkanes 18 2.2 The alkenes 20 2.3 More 2 7 Data analysis and measurement reactions of the alkenes Revision questions 3 68 16 2. 1 Chapter 54 acids Exam-style questions Chapter 50 22 7 . 1 Analysis of 24 7 .2 Accuracy 7 .3 Standards 70 scientic data in 70 measurements 72 74 A variety of functional Chapter groups 8 Titrations and 26 gravimetric 3. 1 Alcohols 26 3.2 Halogenoalkanes 28 3.3 Carbonyl 30 3.4 More 3.5 Carboxylic 3.6 Esters 3.7 Saponication 3.8 Testing for functional compounds analysis 76 8. 1 Principles of titrations 8.2 Titrimetric 76 analysis: back titrations Chapter about carbonyl compounds acids 78 32 8.3 Redox titrations 80 8.4 Some 82 8.5 Titrations 8.6 Gravimetric analysis (1) 86 8.7 Gravimetric analysis (2) 88 34 uses of titrations 36 4 and Aromatic 4. 1 Some reactions of 4.2 Methylbenzene 4.3 Phenols biodiesel compounds benzene and and dyes Revision questions groups nitrobenzene without indicators 84 38 40 42 42 44 46 48 Chapter 9 Spectroscopic methods 9. 1 Electromagnetic 9.2 Beer–Lambert’s 9.3 Ultraviolet radiation 90 90 law 92 and visible spectroscopy 94 iii Contents 9.4 More about ultraviolet Chapter 13 spectroscopy 96 9.5 Infrared 98 9.6 Analysing 9.7 Mass spectrometry 9.8 Mass spectrometry spectroscopy infrared spectra The chemical industry 13. 1 Ammonia synthesis 13.2 The 13.3 Ethanol 13.4 The impact of 13.5 The electrolysis of 13.6 The halogen impact of 138 ammonia 140 100 142 102 ethanol 144 and organic molecules 104 Revision questions 106 and brine 146 chlor-alkali industry Chapter 10 Separation techniques 108 148 13.7 The production of 13.8 The importance of sulphuric sulphuric acid 150 acid 152 Revision questions 10. 1 Introduction to 10.2 More 10.3 Applications of about chromatography chromatography 154 108 110 Chapter chromatography 14 Chemistry and the 112 environment law 10.4 Raoult’s 10.5 Principles of distillation and vapour 10.6 Azeotropic pressure mixtures 120 10.8 Solvent 122 10.9 Distillation extraction and 11 applications 11.2 Aluminium 11.3 More iv chemical Module 2 industry production about 12 aluminium Petroleum petroleum More – 124 Aluminium Locating 12.2 water purication 156 14.2 Water 158 14.3 Ozone 14.4 The 14.5 Global 14.6 The 14.7 Acid 14.8 Pollution from fuels 170 14.9 Controlling 172 14. 10 Saving 14. 11 Solid pollution in the carbon atmosphere 160 cycle 162 warming 164 126 nitrogen cycle 166 rain 168 pollution 3 11. 1 The and solvent Exam-style questions 12. 1 cycle 118 Steam distillation Chapter water and other 10.7 Chapter The 116 distillations Module 156 114 14. 1 extraction: 138 about industry petroleum fractions resources 174 128 waste and the environment Exam-style questions 128 – Module 3 176 178 130 132 Data sheets 180 Glossary 182 Index 186 134 134 136 Introduction This Study Guide has been developed exclusively with the Caribbean ® Examinations candidates, Council both in ) (CXC and out of to be used school, as an additional following the resource Caribbean by Advanced ® Proficiency Examination It prepared (CAPE ) programme. ® has been teaching and by a team examination. with The expertise contents are in the CAPE designed to syllabus, support learning ® by providing the features and for guidance this and developing On Y our answer T est of in Y ourself you problem to easier syllabus. course is an an type Do build activities to and CD Chemistry CAPE master the refer key to that includes your syllabus format! answers activities and concepts examination electronic to sample with show to to assist your the you could skill level short answers be and improved. and questions. designed questions study candidate answers understanding, specifically the examination-style example where examination inside to in remember and provide are best techniques: examination sections you interactive examiner will for questions, answering your requirements questions activities essay activities it achieve examination multiple-choice refer This the Guide from you make the Marks confidence help Revision good and feedback These of on Study Exam-style to included requirements full Inside in tools and guide so to provide helpful that experience feedback you can will revise areas. unique examination combination practice will of focused provide syllabus you with content invaluable and interactive support to help you ® reach your full potential in CAPE Chemistry. 1 1 Carbon 1. 1 Bonding compounds: Learning outcomes in carbon completion of this section, be able explain many because, more compounds once compounds formed, the than carbon to any other carbon element. (C—C) This single is covalent to: bonds carbon you partly should forms introduction compounds The variety of Carbon On an the occurrence of are very strong in comparison to other single covalent –1 Bond compounds in terms of bonds. carbon energies: C—C = –1 ; N—N 350 kJ mol = 160 kJ mol ; bonding –1 O—O understand the ‘tetravalency’ understand ‘catenation’ bonding It takes a in lot are in terms and are to hydrogen is and elements organic years ago are Berzelius Most the char (go so the form compounds chains or ring together (see is called Unit 1 catenation. Study Guide , Carbon–carbon Section vulnerability in Group carbon IV of the to attacks by other 2.5) and this chemicals. compounds it has four Periodic valence T able. It electrons exhibits in its tetravalency . outer shell, which are able to form bonds with other principle atoms. is formed by the sharing of two electrons, one A from Carbon chemicals and form four bonds because one of the each 2s electrons atom when is transferred to a 2p orbital to give the four unpaired in the into necessary for forming four bonds (Figure 1.1.1). inorganic. compounds black) can Swedish Chemist organic organic to compounds. About divided groups: their that bond electrons two bonds, atoms often carbon J. strong carbon perhaps atom. 200 in means covalent called joining non-polar reduce quantum other these of usually This some by also Hybridisation Carbon containing break ability resonance. Did you know? compounds to The of helps Carbon energy carbon bonds hybridisation of stable. compounds compounds 150 kJ mol terms and formed = burn heated. a or unpaired b electrons Most 2p inorganic chemicals just melt. 2s four paired Figure 1.1.1 unpaired electrons electrons a The electron configuration of carbon in the ground state; b The electron configuration of carbon when about to form covalent bonds. Each electron can form 3 orbitals. equivalent sp The promotion compensated other C (or thought -bonds This of H, as process of for O a electron the or being of 2s by N) energy atoms. mixed mixing so requires released The that atomic four each orbitals energy. when unlled has is But four s this C more are atomic character called is bonds than formed orbitals and p hybridisation . with can be character . These 3 mixed form orbitals single between (see Figure 1.1.2 The structure of ethane. The of bonds carbon Unit these are 1 in H, hybrid sp between and Study bonds called O Guide , ethane carbon or N atoms atoms. Section by orbitals. the 2.9). These and These Figure combination orbitals other are σ 1.1.2 of carbon bonds atoms (sigma shows separate overlap the to or bonds) formation atomic orbitals. 3 molecular orbitals formed from sp allow each bond to be a σ-bond. hybrids In ethene, one singly occupied 2s orbital and two of the three singly 2 occupied 2p orbitals in each carbon atom similar shapes to hybridise to make three 3 orbitals. form σ These bonds which approximately The 120º remaining form 2 have a π bond 2p are arranged with each orbitals (Figure a sp 2 orbitals. plane These making a sp bond orbitals angle of other . from 1.1.3). in sp each carbon atom overlap sideways to Chapter -bond 1 Carbon compounds: an introduction -bonds 2 Figure 1.1.3 Ethene has sp orbitals in one plane making σ bonds and a π bond above and below this plane Resonance In ethane and positions. more In atoms, These ethene some allowing electrons Benzene, H C 6 shows a are , is structures. said has six a single The to be localised, molecular electrons free carbon atoms of benzene. between are several structure movement arranged in the somewhere different is called a The form ↔ they are extend over a means which carbon lies in particular over these ring. three or atoms. Figure in-between. structures is resonance that the between atoms are 1.1.4(a) called actual these neither Making up a two double nor composite mesomerism . The hybrid. a Figure 1.1.4 i.e. orbitals delocalised (composite) bonds They from composite are the 6 bonds. structure electrons the representation structure single the substances, b a Two possible ways of representing benzene; b A modern representation of benzene 2 In benzene, hybrid the orbitals six carbon (one to atoms each form hydrogen a hexagon atom and with two to three localised other carbon sp 2 atoms). The three orbitals sp are arranged in a plane, so the bond angles o are . 120 These The orbitals six such as called This leaves overlap electrons benzene, aryl a single p orbital sideways involved which can have to form move this on each a of the six delocalised freely around delocalised carbon system the electron ring. ring atoms. of π bonds. Compounds structure are Exam tips compounds It is a common resonance two or They are single in many lines. A large joining atoms Most number of or ring organic the C—C of carbon carbon atoms are formed to form straight by catenation or branched – the chains bond compounds energy of s shows and and p the are stable non-polar atomic orbitals because nature results of in of this the high value of bond. the formation using a of the a with mixed Resonance is a use and of Figure can structure dashed two representing between’ of structure. shows a 1. 1.5(b) structure line. O b O RC RC O O character. Figure 1.1.5 the O O orbital of dashed RC an by ion ‘in that structures. We 1. 1.5(a) ways carboxylate of think mixtures ‘in-between’ cases Figure possible of compounds. carbon Hybridisation compounds together the to are more forms represent Key points error hybrids where the structure of a compound is a single form which a Two possible ways of is representing a carboxylate ion; b The ‘in-between’ two or more extreme structures. ‘in-between’ structure using a dashed line 3 1.2 Homologous Learning outcomes What A On completion of this series section, is a homologous be able series is a series? group of organic compounds with the same you functional should homologous group in which each successive member increases by the to: unit —CH 2 explain the meaning of A homologous functional its group is an atom or group of atoms describe the chemical and physical characteristics particular present in chemical methanol, properties. OH, CH For and example, ethanol, C 3 of formula’ write a gives a compound the and H 2 functional OH, is group —OH. 5 table below shows the names of some homologous series and series functional understand the a The homologous that series terms groups. ‘empirical Homologous ‘molecular formula’ structural formula series Functional a molecular formula other relevant Example when C= C alkene given group ethene, C H 2 4 ethanol, C H and information. alcohol —OH 2 halogenoalkane —F, —Cl, —Br or —I OH 5 chloromethane, CH Cl 3 O propanoic = carboxylic CO acid H C H 2 Each homologous A particular particular or series has general series, e.g. the following formula H C n C acid, H 2 O which for CO 5 H 2 characteristics: applies alkanes to all (where n members = in number a of 2n+2 atoms). Each successive member increases by the unit . —CH For example in 2 the alkane homologous series: CH , C 4 The members they have The carbon Empirical of The The and molecular C chemical H 3 C 8, H 4 properties. in a regular alkanes way, e.g. increases, This is because as the the number boiling present in a are shows in a the shows is given simplest whole number ratio of atoms compound. molecule formula examples the of a actual sometimes in the number of atoms of each compound. table the same as the molecular formula. below: Compound Empirical formula Molecular formula ethane CH C pentane C acid C 12 CO 6 H 5 H C 2 benzene H 2 H 5 ethanedioic of point molecular formulae 3 12 O 2 CH C dinitrobenzene C H 3 NO 2 C 2 H 4 2 H 6 4 10 group. change straight-chain for mula present empirical Some functional for mula element element in similar , 6 regularly. empirical each same very properties atoms increases The the physical have H 2 H 6 6 N 4 O 2 4 Chapter 1 Structural formulae The in a str uctural simplied for mula form. a displayed a condensed For A shows the structural for mula , showing for mula , where arrangement formula all can atoms bonds are of be and not atoms in a molecule either: bonds shown. example: H H C C H H H H CH CH 3 ethane H (displayed) H H C C ethane 3 (condensed) H H C N H H H H CH CH 3 propylamine With still chain show Hexane, (displayed) hydrocarbons , the actual CH CH 3 we can CH CH 2 CH 2 condense For 2 (condensed) formula even more and example: CH 2 the NH 2 propylamine structure. 2 CH 2 , can be written CH 3 (CH 3 ) 2 CH 4 3 Did you know? In condensed shown in formulae, side branches coming off the main chain are brackets. More are than made 100 000 each new year by compounds research H chemists. H compounds H C branches H H C C C H H H The structure of H CH (displayed) ring H these containing (side chains). are organic rings and Some also be incorporated into metals organic compounds. CH(CH 3 methylbutane of H can H Most )CH 3 methylbutane CH 2 3 (condensed) compounds Key points H C H H C A homologous series is a group C H H H H C of organic the compounds same functional with group in C H which H C H H each increases successive by the unit member —CH 2 cyclohexane (displayed) cyclohexane (condensed) The empirical formula simplest whole shows number ratio the of H atoms C H H C C C C a H C The each element molecular formula actual H of present in compound. number element of present shows atoms in a of the each molecule of H a benzene (displayed) benzene compound. (condensed) The structure compounds The ring inside the hexagon in benzene represents the delocalised ring (see Unit 1 Study Guide , Section organic be written as of displayed electrons of can or condensed formulae. 2.9). 5 1.3 Determining formulae Learning outcomes Deducing the Worked On completion should be able deduce of this section, masses masses In of or relative elements in 1 this example, we are given information about percentage (%) by mass. using Calculate absolute example you to: empirical formulae empirical formula a iodine by the that mass. empirical contains values: (A formula 8.45% C = of a carbon, 12.0, H compound 2.11% = 1.0, I of carbon, hydrogen = and hydrogen 89.44% and iodine 127.0). r compound Step deduce 1: Assume that we have 100 g of the compound, then each of the molecular formulae from percentages can be converted to mass, that is 8.45 g carbon, empirical formulae 2.11 g deduce hydrogen and 89.44 g of iodine. molecular formulae from Divide mass by to A determine number of moles of each atom in r combustion data. the compound: C H 8.45 = 2: = 2.11 mol = 1.0 Divide by lowest 0.704 number to get 2.11 the formula ratio: 0.704 = 3 = 0.704 W rite mole ______ 1 0.704 0.704 mol 127.0 ______ = 3: ______ 0.704 mol ______ Step 89.4 _____ 12.0 Step I 2.11 _____ 1 0.704 showing the simplest ratio: CH I 3 Deducing the We can determine the empirical the molar The molar Section using a Worked 6.00 g The First Step of a work formula if we know: formula of of a the compound. compound known mass volume of spectrometer example a molecular can be gas or found by: vapour (see Unit 1 Study Guide , 5.3) molecular out Divide the contains mass of empirical mass (see Section 9.7). 2 hydrocarbon relative 1: the mass mass weighing molecular formula by A 4.80 g the of carbon hydrocarbon and is 1.20 g of hydrogen. 30. for mula: : r C H 4.80 1.2 _____ ____ = 0.400 mol = 12.0 Step 2: Divide by lowest number to get 0.400 1 = 0.400 W rite the formula ratio: ______ = 3: mole 1.20 ______ Step 1.2 mol 1.0 showing 3 0.400 the simplest ratio of atoms: CH 3 Then Step 6 deduce 4: Find the the molecular empirical for mula: formula mass: 12.0 + (3 × 1.0) = 15.0 Chapter Step 5: Divide the formula molar mass of the compound by the 1 Carbon compounds: an introduction empirical mass: 30 ___ = 2 15 Step 6: Multiply deduced each in atom Step 5: in the empirical × CH 2 = C 3 Molecular formula The worked deduce the example Worked below shows formula law that temperature states and pressure example 2 of equal have how a we can compound volumes equal by the number 6 using Avogadro’s molecular Avogadro’s formula H of law use Avogadro’s using all gases numbers of law combustion at the to data. same molecules. 3 3 Propane contains carbon and hydrogen only. 3 reacts with Deduce for the Step 1: exactly the oxygen, 125 cm molecular formula W rite the information H x of 75 cm (g) + O Find the H x Deduce the (g) write → CO (so (g) ratio + of 5O y (g) 5 number of x must be equation Deduce gases (g) and → C 6 of So 4 4 (g) the use 3CO 3 (g) 1 mol 10 of the + of (g) + H law: O(l) 2 C H → 3 mol CO y 2 → 3CO water come → H (g) 3CO (g)+ react react formed the + H O(l) 2 with with carbon. hydrogen containing 8 to form hydrogen water . atoms propane. 5O 8 (g) → 3CO 2 molecular O(l) 2 2 must are from H atoms: (g) atoms atoms (g)+ 2 H 5O oxygen 3 W rite (g) 2 C 5: 5O y moles Avogadro’s volumes 2 oxygen which + number H 3 O(l) 2 2 atoms: y the H equation: 3) H 3 Step formed. balanced 3 volumes C + 2 2 volume C 4: propane is 75 cm x Step of dioxide a unbalanced 3 125 cm simplest C 1 3: carbon and 2 3 Step of propane below y 25 cm 2: 25 cm reaction. C Step When 3 formula: (g)+ 4H 2 x = 3, y O(l) 2 = 8. So formula is C H 3 8 Key points Empirical formulae elements Molecular using A a masses mass are in a molecular are found can mass Molecular formulae Avogadro’s deduced using masses or relative masses of the compound. by weighing known volumes of gases or by spectrometer. molecular formula relative present can be of be deduced from the compound deduced from the is empirical formula if the known. combustion data by applying law. 7 1.4 Naming Learning outcomes organic The We On completion of this section, IUPAC use a set be able understand organic name the carbon alkanes rules for used of tell us to with carbon atoms Stem about simple carbon The stem: in of the IUPAC by a carbon compounds may have several parts to their name: tells a us how many compound. table The carbon names atoms of the there rst are 10 along stems below. meth- eth- prop- but- pent- hex- hept- oct- non- dec- A suffix: this A is functional tells and prefix: us the for often added groups that stem, some to the end present. For example, the compound prop- tells homologous us it of is the in has stem. the the This sufx alcohol three series, the functional the bromo - in was drawn of atoms. prex before the stem. For group in the appears up tells series us that and the the compound but- tells us it is in has the four halogenoalkane carbon atoms. committee Some task examples are shown in the table below. of in 1892. The was founded in 1919 by Homologous series Sufx No. of C -ane 5 atoms Name and formula a pentane, C H 5 from universities in industry order to 12 and define alkene -ene 3 propene, C H 3 standards of naming measurements can be applied in as name (IUPAC) years. The chemists from about name Pure in Geneva of us the homologous carbon example, tells –ol naming alkane group the are 10 and Applied Chemistry begun can compounds. 9 homologous chemists carbon 8 series, compounds this bromobutanol was organic 7 International Union of of 6 rules for number structure 5 a a a 4 over the compounds chain propanol the in names 3 Did you know? by Systematic 2 the chemical compounds 1 of Naming nomenclature. atoms. shown system compounds. systematic branched main The name a compounds No. of C to called naming Simple chains rules is Naming of way to: be rules you particular should compounds chemicals chemistry throughout alcohol which the 6 and -ol 7 heptanol, C H 7 OH 15 world. carboxylic acid -oic acid 1 methanoic HCO acid, H 2 ketone -one 4 butanone, CH CH 3 Naming The branched-chain position numbering The Numbering for longest the side of the side chains carbon possible starts at chain alkanes or functional the side chain prexes The side chain is of end carbon that atoms gives the For (comes named example before) according CH — is to the the methyl, 3 formed 8 These by groups is shown by is chosen. smallest number possible chain. The propyl. 3 atoms. contains. COCH 2 groups changing are the of alkyl H groups. ‘alkane’ name. number C 2 called ‘ane’ stem to — is of carbon ethyl, 5 The ‘yl’. C atoms H 3 alkyl group — it is 7 name is Chapter Example 1 1 2 CH 3 1 Carbon compounds: an introduction 4 CHCH is CH 3 2 2–methylpentane Exam tips 3 CH 3 prefix position side Make sure is longest Example 5 4 CH 3 CH 3 2 2 the off ’ that C—C 1 CHCH 2 is CH 2 C example six More than one and is more the tetra- Example chain carefully from diagrams. bonds below carbon Remember rotate freely. than prexes for side four one di- the for the two longest In the chain is stem chain? of the atoms. C use which 5 prefix we out 3– ethylhexane 3 H 2 there work 2 CH If you chain ‘squared 6 that stem of C C C C C same alkyl groups the side chain same, tri- or for functional three the group C same same. 3 CH 3 1 2 CH 3 4 CCH 3 CH 2 3 CH 3 2,2-dimethylbutane Note: numbers are separated from each numbers are separated from words If there are Example different side chains, they 4 by by commas hyphens. are listed Example C in alphabetical order . 5 H 2 CH other I H H C C C 5 CHCHCH 3 CH 2 CH 2 H H 3 CH H Cl H 3 3-ethyl-2-methylhexane Functional The the group numbering general alkenes is Example of rules. between positions functional But note the 2-chloro -1-iodopropane groups that prex the and the 6 CH along the number CH=CHCH CH 2 chain to the follows C =C many bond of in stem. Example 3 side given 7 HOCH 3 CH 2 pent-2-ene CH 2 OH 2 propane-1,3-diol Key points The rules for stem, Suffixes, group meth-, e.g. organic eth-, –ane, prop-, -ene, -ol, carbon compounds are based on the use a etc. are added to the stem to show the functional present. Prefixes, group e.g. naming e.g. chloro-, may be added to the stem to show the functional present. Numbers are used to show the position of particular side chains. 9 1.5 Isomerism Isomers Learning outcomes atoms On completion should be define able the of this section, are are molecules arranged that have differently. the The same two molecular main types formula of but isomerism the are: you structural isomerism stereoisomerism to: term (see Section 1.6). ‘structural isomer’ understand between the chain Structural difference and isomerism position Str uctural isomers are compounds with the same molecular formula but isomers different explain about that single carbon there is free bonds in rotation chains structural formulae. There are three types of structural isomerism: of chain isomerism functional positional atoms. Chain Chain group isomerism. isomerism isomerism carbon atoms Example Butane isomerism in is where their the carbon isomers differ in the arrangement and methylpropane both have the molecular H formula H H H C C C H H H H H H C H C C C C H Methylpropane possible Example H H methylpropane is not position named for the 2-methylpropane side because there H H H H H H C C C H H H C C H C H H C The functional H H group H C H H butan-1- ol 2-methylpropan-1- ol is in the 1-position, so this is not positional isomerism. Functional Functional isomers 10 is chain. 2 H Note: H H H butane one 10 H H H only the 1 4 Note: of skeleton. is group group the isomerism isomerism same but the is where functional the molecular groups are formula different. of the Chapter Example 3 For C H 2 group (an ether). because two they and an can draw isomer isomers belong H H C C H H H we an isomer with to have with an different different —O— Positional different homologous C H 3 Cl 6 and compounds: an introduction functional group physical (an properties series. H O H H C H H H methoxymethane isomerism isomerism in — OH functional chemical ethanol Positional an Carbon 6 alcohol) These O 1 each has is where isomer . four The possible the position compound of with the the functional molecular group is formula isomers. 2 Cl H Cl H C C C H H H Cl H H H H H C C C Cl H H There is free and H H care when sure that you formulae about drawing don’t below not H H H C H Cl H rotation single the bonds. H Br C C H H Because formulae same isomers. H C 2,2-dichloropropane structural repeat are Cl H bond rotation take H Cl 1,3-dichloropropane 1,1-dichloropropane Isomerism C H 1,2-dichloropropane Cl C H of structure. They are H the H of this, different For example, same H H C C H Br you need isomers, the to making two compound. H Key points Structural different Chain atoms Functional is the Positional Know is compounds but where their the carbon with the same molecular formula but isomerism isomers each there is differ in the arrangement of the skeleton. is the functional isomerism in that in group same different are structural formulae. isomerism carbon isomers where where groups the the are molecular formula of the isomers different. position of the functional group is isomer. is free rotation about single bonds in chains of carbon atoms. 11 1.6 Stereoisomerism Learning outcomes What is stereoisomerism? Stereoisomerism On completion of this section, atoms should be able explain of the stereoisomerism structure understand the double the of in know that to a where each two other (or but more) the compounds atoms have a have the different same arrangement There are in geometrical optical in stereoisomerism: isomerism (also called cis trans isomerism) of type (cis-trans) isomerism is is free rotation around single bonds. But there is no free rotation of about asymmetry of geometrical isomerism particular types isomerism. Geometrical optical two molecules importance bond space. There due to terms isomerism bonded to: in is you a double C=C bond (or other double bonds). This can result in molecules. geometrical substituent same side Example The two isomerism . groups (cis) or Geometrical either on the side of a opposite isomerism double sides bond occurs are on the ( trans). forms of cis- and trans-dichloroethene are Cl different Cl = C C H H H cis-dichloroethene the cis-isomer isomers. H = C C In the either 1 Cl when arranged both Cl Cl trans-dichloroethene atoms are on the same side of the C =C bond. In the trans-isomer the Cl atoms are on opposite sides of the C =C bond. The two may geometric have Example some isomers chemical have different properties physical which are CH they H CH CH 2 3 3 3 = C C C C = H Optical CH H H CH 2 cis-pent-2-ene Optical and different. 2 CH Cl properties slightly 3 trans-pent-2-ene isomerism isomerism happens when four different groups are attached to a Cl central C C other . carbon They atom. are not The two identical isomers because formed they are cannot mirror be images of each superimposed r H H (matched they do up not exactly) match on up one another . exactly. An However example is you try to rotate them, bromochlorofluoromethane. mirror This Figure 1.6.1 The two optical isomers of two has four mirror different images groups (Figure attached to the central carbon and exists as 1.6.1). bromochlorofluoromethane are mirror images These but by light optical an only We rotate amount. vibrates directions. 12 isomers equal use in one an plane-polarised The light electromagnetic plane unlike instrument ordinary called a in eld opposite in light which polarimeter directions plane-polarised to vibrates measure in the all Chapter rotation which (+) of this rotates plane-polarised plane-polarised enantiomer . direction optical is The called isomer the (–) light light by in which optical a rotated enantiomer . isomers. clockwise it in The direction an 1 Carbon compounds: an introduction isomer is called the anticlockwise (Enantiomer is another word for isomer .) Did you know? The amino optical acids fortunate for are the T wo the and isomers. Our more that the optical examples central groups us correct carbohydrates bodies atom attached amino of optical not in our deal acids isomers for does to cannot and our to are their particular forms mirror carbohydrates images. we It of is get from our food bodies. isomers have bodies with be are shown carbon as below. long as Y ou it can has 4 see that different it. a CH CH 3 3 C C NH CO 2 H HO 2 2 2 H H b CH CH 3 3 Sn C Sn H 2 C 5 A a carbon chiral C 9 H 4 C 9 H 3 Figure 1.6.2 H 4 C H 2 C 7 5 H 3 7 Optical isomers of a alanine (an amino acid) and b tin tetraalkyl (or other centre . atom) Some with four molecules, different e.g. groups glucose, have attached more to than it is one called chiral centre. Did you know? The word mirror the chiral image comes from of your right the hand ancient Greek for but you cannot ‘hand’. Your superimpose left one hand is exactly a on other. Key points Geometrical isomerism double are sides each Optical to a other in A opposite carbon the either on substituent the same groups side (cis) either or on side the of a opposite two atoms happens atom, mirror compounds have a when four resulting have different in different a image. Optical the same atoms arrangement groups molecule isomers that rotate in are has bonded space. attached a non- plane-polarised light directions. centre different where the isomerism central chiral is but superimposable arranged when (trans). Stereoisomerism to bond is (in groups its most attached common to case) is an atom that has four it. 13 1.7 More about Learning outcomes Branched-chain As On completion should be able of this isomers section, the number of alkanes carbon atoms number of possible isomers draw all the isomers of pentadecane, increases longest rapidly. carbon For chain example increases, there are the 4347 to: H C 15 in you the isomers for a given of a particular alkane. The . Y ou may be asked to draw all the isomers 32 example below shows you how to do this. molecular formula draw isomers for alkenes and ring Example structures. Draw all the isomers of hexane, C H 6 1 Start 2 Draw (ve 3 the the Draw the straight-chain isomers carbon (four 4 with atoms isomers carbon with in one the with : 14 isomer fewer (six carbon carbon atom carbon atoms atoms in the in line). longest chain chain). two fewer in the longest chain atoms). For longer-chain the isomer is alkanes not one continue that H you in have this way already H H H H C C C C H H H H H until you are sure that drawn. H H H H hexane H H C H H H H H C C C C H H H H H H H 2-methylpentane H Exam tips When writing isomers, note C H H H H H C C C C H H H H H H H that: 3-methylpentane 1 A carbon chain like H this C H C C H C C H H H C C H H H H C C C C H H has five carbon atoms in C H H C H H H C H longest chain, A carbon chain C C C C C C like 2-dimethylbutane H C C C C H H H H this 2, Figure 1.7.1 is the same C 14 as C C C C this C H H not four. 2, 2 H the The five isomers of hexane 3-dimethylbutane H Chapter The isomers of C The molecular formula compounds: an introduction 8 C H 4 double Carbon H 4 containing 1 bonds suggests an alkene. Possible isomers 8 are: H H H H H C C C H C H H H C H C C H H H H H but-1-ene 2-methylpropene H H H H H C H H H C = C C C H H H = C C trans-but-2-ene cis-but-2-ene There The is also prex the possibility cyclo - is of a cyclic H H H C C H H C C H H H used H H H H H C to alkene, cyclobutane. cyclobutane indicate a ring structure which is not an aryl compound. Aryl Aryl If a compounds compounds single alkyl contain group is at least attached one to benzene the ring, ring. we do not number this group. If there is positions more by C a than giving H 2 one them b 5 alkyl the group CH i attached smallest the ring we show their possible. CH ii 3 to numbers CH iii 3 3 CH 3 CH 3 CH 3 Figure 1.7.2 a Ethylbenzene; b The three isomers of dimethylbenzene, i 1,2-dimethylbenzene, ii 1,3-dimethylbenzene and iii 1,4-dimethylbenzene Key points The larger number of the Compounds substituted Alkenes number possible containing in may of different be carbon atoms in a hydrocarbon, the greater or groups is the isomers. rings may positions isomeric with have in ring the two more alkyl ring. compounds. 15 1.8 More about Learning outcomes The A On completion should be able of this homologous section, alcohol homologous series homologous series can be series identied by: you to: the functional group it contains (and hence its typical chemical reactions) describe the the functional homologous alkanes, alkenes, series group in of a The write given aldehydes formula. alcohols, halogenoalkanes, acids, general alcohol homologous series has: carboxylic and general formulae for homologous an the —OH functional group ketones general formula C H n a OH. 2n+1 series. The table below members of the shows the alcohol Number of C names and homologous Name atoms 1 structural formulae of methanol ethanol Structural formula formula CH CH O C H 2 3 propan-1-ol C butan-1-ol O H C pentan-1-ol O 6 hexan-1-ol 7 heptan-1ol C octan-1-ol 9 nonan-1-ol C H decan-1-ol C Y ou will have end the of also notice sufx the be alcohol in H chain. other is H that a In these This if there C C H H H H in are H C is H than chain. three C O from there H H C C C C C H H H H H the are groups, OH OH H methanol functional it and a H —OH triol. H pentane-2,3-diol ethanol, group is at the group groups, For can the example: OH OH OH C C C H H H H propane-1,2,3-triol can write alkyl the group by general the formula letter R. So for for a homologous series halogenoalkanes , C by H n write RX. example, different 16 OH 21 functional two is OH 19 10 ethanol, —OH H C 22 OH 17 9 —OH If H groups We an larger the OH 15 8 H apart the H C O OH 13 7 H propan-2- ol R alcohols, because alcohols positions diol, OH all -1- ol. H C 20 10 OH 11 6 O H H C 18 9 10 O OH 9 5 O 8 H C 16 C OH 7 4 14 H H C O H 7 8 O 12 6 OH 5 3 H C H C 10 5 OH 2 H C C 8 4 5 ten 3 6 3 4 rst Molecular 4 2 the series. We can RCOR ′ alkyl write different represents groups. the alkyl groups general as formula R ′, of R″, a R″′, representing X, we can 2n+1 etc. ketone For with two Chapter The The will range of functional table need below to shows some 1 Carbon compounds: an introduction groups examples of different functional groups you know. Homologous series General formula alkanes Functional group Sufx or RH prex -ane Example propane, C H 3 alkenes RCH=CH C 2 halogenoalkanes RX (where X is —F a -ene C 8 propene, CH CH=CH 3 —Cl uoro-/ chloro-/ 2 bromoethane, C H 2 alcohols halogen) —Br —I ROH —O—H bromo-/ -ol ethanol, C H 2 carboxylic acids RCO H or O RCOOH -oic Br 5 iodo- acid propanoic OH 5 acid, 2 C C H 2 O aldehydes 5 H O RCHO COOH -al propanal, C H 2 CHO 5 C H ketones O RCOR′ -one propanone, CH C esters RCO R or C O RCOOR′ COCH 3 C -oate 3 methyl ethanoate, 2 CH C acyl chlorides O 3 C O RCOCl COOCH -oyl chloride ethanoyl CH C amines chloride, COCl 3 Cl H RNH 3 -amine methylamine, 2 N CH H amides O RCONH NH 3 -amide 2 propanamide, 2 H C C N H 2 CONH 5 2 H arenes C H 6 R R methylbenzene, 5 CH 3 Key points The functional Functional group groups (aldehydes), in alkenes containing —CO— is C =C. oxygen (ketones) and are —OH —CO H (alcohols), (carboxylic —CHO acids). 2 Halogenoalkanes Amines have have the functional the functional group group —NH —X where X is F, Cl, Br or I. . 2 The an general formula alkyl of an organic compound can be written using R— for group. 17 2 Hydrocarbons 2. 1 The alkanes Alkanes Learning outcomes On completon should be able of ths (general descrbe secton, you to: the reagents because between carbon no of areas H there and higher such as is ), only a hydrogen. or lower acids are very small They electron and unreactive towards most chemical 2n+2 alkalis. are electronegativity essentially density Details that of can some difference non-polar be so attacked important there are by reactions of halogenaton, alkanes crackng C n reagents formula and combuston are given below. of alkanes Combuston of explan the steps substtuton of n free alkanes Alkanes dioxide understand that mechansms, n alkanes radcal undergo and combustion water (in moement be oxygen For or air to form carbon example: of H 4 can excess form). reacton 2C electrons in gaseous shown by (g) + 13O 10 (g) → 8CO 2 (g) + 10H 2 O(g) 2 cured butane arrows or shhook notaton. Incomplete combustion H 2C 4 Crackng of Cracking alkanes and SiO is the and 2 O 2 (g) 9O A It carried of cracking and Cracking the is + 10H H (g) → C 28 out at of alkanes about is O(g) into shorter-chain 400–500 °C obtained. also a it a For C CH for H (g) + can the C 6 using example also H 2 propene catalyst of 3 Halogenaton of + 3 produces needed source (g) 18 octane without because alkenes H 8 CH be carried shorter-chain making many out at alkanes chemicals, (g) → CH 3 =CH 2 (g) + H 2 alkanes chlorine are mixed in the dark chlorine are mixed in the presence of can of atoms more from substitution is replaced hydrogen ultraviolet light). With the Sun), reaction : by atoms for plastics. (g) and light needed e.g. 2 and ultraviolet 700–900 °C. hydrogen: methane a another . are a A In replaced excess there variety of products reaction in which the by chlorination chlorine is one of atoms no reaction. ultraviolet be atom alkanes, ( hν light formed. or group one or represents the methane: hν CH (g) + Cl 4 With excess chlorine chlorine (g) → CH 2 more Cl(g) + HCl(g) 3 and more hydrogen atoms are atoms: CH Cl(g) + Cl 3 CH (g) → CH 2 Cl 2 (l) + 2 CHCl Cl Cl 2 (g) → (l) + Cl (l) + HCl(g) 2 CHCl 2 3 18 of 400 °C): ethene methane is catalyst (g) When This a (at 4 When (or carbon). 3 important petrol 8CO(g) (and/or 2 products tridecane is → decomposition is mixture 13 It (g) monoxide alkanes C Thermal carbon 2 thermal . + 10 alkenes. Al produces (l) + HCl(g) 3 (g) 2 → CCl (l) 4 + HCl(g) substituted by Chapter Mechansm Reaction and electron mechanisms show the steps in bond Br a moement breaking and bond : Br → Unit reactants 1 Study are converted Guide , Section to intermediates and then to products Hydrocarbons Br + Br b making H when 2 → Cl Cl (see 7.6). Figure 2.1.1 Homolytic ssion: a The bond is split so one electron goes to each A bond can break in two ways: homolytic and heterolytic ssion. atom; b Homolytic between single ssion: the two covalent The two atoms. shared Homolytic electrons ssion in can the bond occur in are split many equally types Fishhook arrows show the direction of movement of each electron of bond. + The species groups of formed atoms are with called free unpaired radicals. electrons. Free The radicals unpaired are atoms electron a or Br : Br → Br: + Br is b + represented shhook by a arrow dot. (see The movement Figure of a single electron is shown by unequally. negatively positively curly ssion: One of the charged. charged. arrow (see The two atoms The The Figure + Cl 2.1.1). Figure 2.1.2 Heterolytic → Cl a shared keeps other both atom movement electrons pairs becomes of a pair in of the bond electrons electron of are and split so decient electrons is becomes so shown atom; b A curly arrow shows the direction of movement of the electron pair is by Heterolytic ssion: a The bond is split so both electrons go to one a 2.1.2). H H Free radcal substtuton n H H C Cl → H C H The free radical substitution of hydrogen in alkanes by chlorine occurs in three steps, e.g. H Cl H or Figure 2.1.3 bromine + alkanes the reaction of chlorine with The propogation mechanism methane. Intaton H The presence break by of ultraviolet homolytic light causes the Cl—Cl bond in chlorine ssion. H Cl C → H C H hv → Cl H to Cl• + Cl H Cl• Figure 2.1.4 The termination mechanism Propagaton Free radicals methane. A are so reactive methyl free that radical, they can , CH is attack the formed relatively (see Figure unreactive 2.1.3). 3 CH + Cl• Key points → CH 4 • + HCl 3 The methyl Chlorine free free radical radicals can are then formed attack again. another So a chlorine chain form molecule. reaction occurs. Alkanes undergo carbon Crackng s the • + Cl 3 → CH 2 Cl + there is excess chlorine this to water. of alkanes to Cl• 3 shorter-chan If and thermal decomposton CH combuston doxde process can continue until all the alkanes and hydrogen alkenes. atoms in the methane have been replaced. CH Cl + Cl• → CH 3 CH Cl• + Cl• + Cl 2 → CH 2 Substtuton the Cl 2 + Cl• and so on. There bond and For radicals combine to form a by single molecule (see Figure + Cl• → CH Cl or CH 3 In • + CH 3 • → CH 3 stops nishes the when chain there reaction are no in more the propagation free or are can two radicals left step. to The react. ways break: n whch a homolytc sson heterolytc sson. reacton mechansms, of an electron par CH 3 3 s This atom another. moement • 3 nole one 2.1.4). example: CH of 2 free replacement group Termnaton T wo reactons HCl 2 reaction shown by moement by a of a shhook cured a arrow sngle and electron arrow. 19 2.2 The alkenes Alkenes Learning outcomes completon should be able descrbe wth of ths secton, you in reactive reactons hydrogen general Section than haldes of 1.1. formula Although alkanes. electron-rich to: the the C H n shown On have area This which is can alkenes because be . The structure of ethene is 2n are attacked non-polar , C =C the by they double positively are bond more is charged an reagents. alkenes and Electrophlc addton bromne An explan the steps noled n electrophile reagent mechansm of is a positively charged (or partially positively charged) the which attacks an electron-rich area of a molecule. For example electrophlc + ions H addton of hydrogen bromne bromde are good electrophiles. and to alkenes. Most the reactions other reactions a single product Addton When Exam tips is alkenes is you electron the tal where draw arrows moement, of an the passed bromoethane electron moes from and or the arrow electron head that shows The Fig t moes addition from reactions . two In reactant addition molecules and no through is mechanism of hydrogen hydrogen bromide dissolved in an inert formed. =CH + HBr → CH 2 this haldes —CH 3 electrophilic addition Br 2 reaction is shown in 2.2.1. par H shows H where wth 2 showng remember cured are formed made. CH When is reactons ethene solvent, of product H H H H + to. =C H H H :Br H C H H δ+ H H H δ Br Figure 2.2.1 The mechanism of reaction of hydrogen bromide with ethene + HBr is a partial HBr the An At charge acts as double H atom the to The Br pair of a from Br then hydrogen Br is a δ partial charge on the H atom and attacking area of high electron density in a the the double positively Br ion. atom The attacks bond gains H—Br the + in charged ethene control bond forms a bond with carbocation of the breaks carbocation electron pair in the heterolytically. and the addition product, formed. halides react in a similar way. Exam tips You A wll nd carbocaton carbon 20 the s term an carbocation alkyl atoms. They are δ atom. ethene. form time form ion the with electrophile to bromoethane, Other on an same HBr molecule bond electron the polar group often useful carryng when a wrtng sngle ntermedates n about poste organc mechansms. charge on reactons. one of ts Chapter Reacton of When the HBr double wth other bond is not alkenes products is formed. For quite the in the reaction middle of Hydrocarbons Did you know? of the alkene a mixture We of 2 HBr with propene there are can explan the reason for the two drecton n whch hydrogen bromde possibilities: adds CH +HBr CH 2 CH 2 (minor alkenes stablty product) of the n terms dfferent of the types of 3 carbocaton formed. CHCH 2 to 3 +HBr CH CHBrCH 3 (main product) most CH 3 stable 3 + CH C 3 The rule is hydrogen that the halide) more adds to electronegative the C atom in atom the (the alkene halogen which is of the connected to CH 3 the least number of H atoms. a tertiary carbocation H Reacton of alkenes wth bromne + CH C 3 Alkenes react with bromine liquid to form dibromoalkanes e.g. CH 3 a CH =CH 2 + Br 2 → CH 2 Br—CH 2 ethene secondary carbocation Br 2 H 1,2-dibromoethane + H The mechanism is similar to that for hydrogen halides (see Figure C 2.2.2). CH 3 H H H H a H primary carbocation least stable H + = C H H + H H :Br C H Br δ + Br Br Br δ Br Figure 2.2.2 The The mechanism of reaction of bromine with ethene electrophile is the Br molecule. As the Br 2 approach repels the each other , electron the pair in and ethene molecules 2 high electron the density single Br in C =C the bond bond. 2 δ+ This causes the molecule Br to be polarised Br δ – —Br so that the 2 δ+ end Br An attacks electron the pair area from of the high electron double bond density in ethene in the forms double a bond bond. with δ+ the At in and Br the the same to Br a positively time the form a charged other Br ion. Br carbocation atom The gains Br—Br is formed. control bond of the breaks electron pair heterolytically. 2 The Br ion then attacks 1,2-dibromoethane, Chlorine reacts in a is the + carbocation and the addition product, formed. similar way. Key points Most An of the reactons electrophle attacks an area The double The major addton s a of bond of postely hgh n alkenes product formed reacton or electron alkenes depends s are partly postely densty an area when on electrophlc the an of n a stablty charged reactons. speces whch molecule. hgh alkene addton electron undergoes of the densty. an electrophlc carbocaton formed. 21 2.3 More reactions Learning outcomes The completon of ths secton, bromine be able to descrbe wth water test for is very hazardous. So alkenes test for = C C the bond in we use alkenes. aqueous bromine Compounds (bromine containing to: double alkenes you water) should the bromne Liquid On of the reacton aqueous of bromne alkenes test for bonds are also unsaturated described as being unsaturated . So the test is also a compounds. (bromne On addition of bromine water to unsaturated compounds, the colour water) changes descrbe the reacton of from hot and cold descrbe wth manganate(vii) the The reaction reacton concentrated descrbe the of liquid reacton hydrogen of bromine water) is an addition reaction similar to that to occurring bromine but a mixture of colourless addition products is acd of alkenes wth concentrated sulphurc acd alkenes (ncludng is another example of an addition reaction. For example, ethene the reacts producton the alkenes sulphurc This wth of obtained. Reacton of colour acded with potassum (the alkenes colourless. wth orange/red-brown at room temperature to form ethyl hydrogensulphate, trans fats). CH CH 3 OSO 2 H. 3 H H H H Did you know? C=C + H In addton to bromne → SO 2 H H H 4 H molecules, H OSO H 3 bromne water contans bromc(i) – acd, HOBr, as well as OH ons from The electrophile is the partially charged H atom in H SO 2 the water. Bromc(i) acd s polarsed δ+ H δ– HO δ + attacks so the densty n — O — SO that area the of the Br end When hgh-electron double H 3 δ+ —Br 4 δ water alcohol) bond rst is is added formed. to the (The product sulphuric and acid the is mixture also warmed, ethanol (an reformed.) – followed by OH ons competng – wth Br ons (from Br ) to attack H H C C H H C C the 2 carbocaton to form CH BrCH 2 OH. H H + H 2 → O H H + HOSO 2 H OSO H 3 H H OH 3 The overall from water reaction across can the be thought double CH = CH 2 Reacton The wth addition reaction. It of can of as addition of the H and OH + H 2 O → CH 2 —CH 3 OH 2 hydrogen hydrogen also be to an alkene regarded as is 3 + example of of a hydrogen hydrogenation or reduction. catalyst → H 2 an addition Ni CH = CH CH the bond: CH CH 2 3 CH 2 3 150 °C propene Hydrogenation reactions Hydrogenation makes spreading digested qualities. may be Hydrogenation are in not They 22 some increase The used oils fatty unsaturated also commonly making are the produces found pies levels and of propane in or to change fats acids (they nature cholesterol which have trans pastries. less are one fatty T rans the so more (also 2.3.1). fats oils they released or acids (Figure in vegetable liquid are body , into have when = C C called These harmful leading to margarine. better fats are double trans trans to bonds). fats) fats human heart which are used health. disease. Chapter a H 2 Hydrocarbons H Did you know? = The dfference between fats and hydrocarbon C =C ols double s one of state. Ols are lqud at chain room bond They temperature can be but fats classed as are sold. saturated b (no H double (contan bonds) one or or unsaturated more double bonds). = Saturated fats tend to ncrease H cholesterol hae been leels lnked Unsaturated fats Figure 2.3.1 n to the blood heart are and dsease. healther for a A cs fatty acid. The hydrocarbon chains are on the same side of the C=C bond. b A trans fatty acid. The hydrocarbon chains are on the opposite sides of the double bond. you and are cholesterol Reacton Potassium wth potassum manganate( vii), less lkely leels and to cause heart hgh dsease. manganate(vii) KMnO , is a good oxidising agent. It is 4 commonly solution called acidied concentration Cold The potassium with and the sulphuric purple is solution converted CH acid. temperature acded dlute alkene permanganate. a colourless diol = CH 2 + (a + reaction Hot The then can when H 2 acded C=C also O reacted with → CH 2 in immediately carboxylic mixture acids of the ) 3 used to alkene carbon products (CH be oxidised or is as a depends on its with two an —OH OH—CH 2 alkene. The groups). OH 2 ethane-1,2-diol test concentrated bond ability used manganate(vii) ethene This generally oxidising compound [O] is used. potassum turns to Its It by C = CH 2 + is broken the if a and depending → for is unsaturated. manganate(vii) diol vii) on is to the formed. ketones, type of The diol is aldehydes, alkene. A example: (CH 2 ) 3 methylpropene compound a manganate( formed, 4[O] see potassum dioxide often to C = O + CO 2 + H 2 O 2 propanone Note: We can Y ou write [O] to represent the oxidising agent, KMnO 4 do not have to remember the equations for these reactions. Key points Bromne Alcohols and Hot the water used are formed product s concentrated aldehydes, Cold The to s dlute to test for when then alkenes acds potassum hydrogenaton presence react hydrolysed potassum carboxylc the wth or carbon or ols may double concentrated bonds. sulphurc acd water. manganate( vii) oxdses alkenes to ketones , doxde. manganate( vii) of fats wth of C =C oxdses produce alkenes to trans fats dols. whch are harmful health. 23 Revision Answers to 1 Which all of reaction reson questons the following of hydrogen A electrophilic B condensation C nucleophilic D elimination terms can best chloride questions be found on the describes with accompanyng CD. the 6 a Explain propene? addition b the addition Which of the statements below is correct the nature of ‘carbocation’ giving bonding Limonene of 2 term ‘electrophile’, Use c the citrus fruit, examples present their is the in the chemical main and of each. alkenes to explain activity. contributor to the fragrance its formula is shown when below: CH 2 applied to the reaction between propene and H C C 3 hydrogen bromide? A H—Br is B Br CH 3 heterolytically cleaved. + is involved in the initial attack of the propene moles molecule. C A carbanion intermediate Propene undergoes Which of the following compounds both manganate(VII) would bromine be water benzene B chloroethene phenol propane Which A A are correct double the Restricted rotation bond limonene of reacts the with products hydrogen respectively. chain hydrogen and C. reacts of n by hydrocarbon, mass. bromine the with A to D. presence A has a contains decolourises produce hydrogen A, of to a two an relative aqueous compounds palladium produce 14.2% a catalyst, gaseous Calculate the molecular empirical formula of A mass and of 56. hence bonds? about a prohibits the molecular formula. carbon–carbon b double when bromine branched its of a concerning a carbon–carbon with solution? B statements number react displayed formulae compound 4 the will molecule. solution D that acid of C reason, Write and and 7 A a hydrogenation. expected to decolourise potassium giving bromine limonene formed 3 , of is formed. D Suggest possibility Suggest the functional group present in A and of give a reason. stereoisomerism. c The atoms bonded to a double bond Explain the production are mechanism of Double The bond systems are electron double bond system consists show the of a bond and a pi 5 ii, C i, D ii, iii iii iii, iv iv Which hydrocarbon series? A C H 2 B C 2 H 3 C C D C 6 H 4 6 24 10 H 6 in the respectively, movement of using arrows electrons. With reference to c would suggest be which of these preferentially formed. bond. e B C sigma compounds ii, and decient. d i, B co-planar. to A involved system is a member of the alkene Write the name and displayed formula for D. Chapter 8 a Write the displayed formulae for the 2 Hydrocarbons – reson questons compounds A–E ethane-1,2-diol B II CH CH 2 2 A C ethene Br Br /CCl 2 4 (aq) 2 D b n E reactions conditions c n the state the reagents and used. laboratory, stages; two I–III write the reaction proceeds III equations which in two represent these stages. d State two e State the uses of B. commercial signicance of reaction I. 3 9 10 cm of a gaseous hydrocarbon were mixed with 3 100 cm room of oxygen and temperature the exploded. After resulting cooling gaseous to mixture 3 occupied 75 cm . On passing the gaseous mixture 3 through were be a solution absorbed oxygen. of and potassium the hydroxide, remaining (All volumes were gas was measured at 30 cm shown to constant pressure.) a Determine the molecular formula of the hydrocarbon. b The to hydrocarbon produce two reacts displayed formulae c With reference formed, be to deduce expected to with hydrogen compounds. Give of the these of these be formed in chloride names and compounds. respective which the carbocations compounds the greater would quantity. 25 3 A variety 3. 1 Alcohols Learning outcomes of functional Classifying Alcohols On completion of this section, have be able describe with the general formula C H n according to the position of the reaction potassium of alcohols Prmary potassium e.g. alcohols with H the reaction the of H The C —OH H of sulphuric describe may be group. the group is is attached attached to to only a carbon one other C H atom. H alcohols e.g. alcohols propan-2- ol acid H that carbon acids reaction C alcohols Secondary with They manganate(VII) carboxylic describe ROH. functional dichromate(VI) H describe or —OH propan-1- ol atom OH 2n+1 the to: H and alcohols you classied should groups iodoform The —OH group is attached to a carbon test. atom H O that attached to two other carbon H atoms. H is C C C H H H H The —OH is in the middle of the chain. water Tertary e.g. alcohols 2-methylpropan-2- ol out H The —OH atom H C that carbon to to three a carbon other atoms. in the The —OH is at a branch chain. in H C C C H OH Oxidation of Potassium + attached H point ethanol is attached H H water group is H H alcohols dichromate (K Cr 2 excess oxidising dichromate() agent. During O 2 this ), acidied with sulphuric acid is a good 7 reaction the orange dichromate ions are ions 3+ + concentrated reduced acid heat Figure 3.1.1 to Primary green ions. Cr alcohols are oxidised to aldehydes when: Apparatus for refluxing the oxidising the aldehyde agent is not in excess and the acid is fairly dilute primary alcohols to carboxylic acids. This allows heating without loss of ethanol, is distilled off immediately. which is volatile. The ethanol vapours Primary alcohols are oxidised further to carboxylic acids when: condense back into the flask. Exam tips An easy way to distinguish the oxidising the reaction agent is is carried in excess out under and the reux acid for 20 is more concentrated minutes (see Figure between H H H H O primary and secondary alcohols [O] H from their structure is to C C remember O [O] OH C H C H oxidation C C oxidation H (alcohol PAL SAM. Primary Alcohols have the H in H – at the end or Last H H no agent +H group O (oxidising H excess —OH 3.1.1). in O 2 part reflux) ethanol excess – ethanal ethanoic acid reflux) of the chain, and Secondary Alcohols (an have of the the —OH chain. group in the aldehyde) (a carboxylic acid) Middle Figure 3.1.2 Primary alcohols are converted to aldehydes at low concentrations of oxidising agent. With excess oxidising agent the aldehydes are converted to carboxylic acids. 26 Chapter Secondary alcohols H are H H H C C C oxidised to ketones. They are not + [O] H A variety of functional groups further . H H OH oxidised 3 C C O 2 H OH H H propan-2- ol (a T ertiary the alcohols O H propanone cannot be oxidised without ketone) breaking a C—C bond in alcohol. Potassium manganate( vii) potassium dichromate. Reaction of Alcohols react catalysed reversible carried alcohols with by out acts under an with carboxylic sulphuric as oxidising agent carboxylic acids to form in a similar way to acids esters. The reaction is: acid reux. O O + H R C + catalyst R R C + H Did you know? O 2 Sulphuric carboxylic alcohol acid primary For and H 3 COOH + C 7 H 2 butanoic acid may alcohols especially example: C acid also react with ester OH Y C 5 H 3 ethanol COOC 7 ethyl H 2 + H 5 if excess reaction is produce alcohol heated ethers, is to present no O 2 butanoate the to more than 140 °C. water e.g. For more information about esters see Section 3.6. 2C H 2 Reaction Alcohols the with which —OH concentrated have group at react least with one H excess sulphuric atom on the concentrated C form atom next sulphuric acid but on one to OC 5 H 2 + H 5 O 2 heating Primary alcohols are oxidised alkenes. CH CH 3 CH 2 OH → CH 2 CH=CH 3 propan-1- ol + H 2 reaction is a dehydration a water reaction from a in which water to excess carboxylic Secondary alcohols are oxidised is ketones. compound. Tertiary alcohols oxidised iodoform without cannot be breaking the reaction C—C Secondary agent) (with acids. to eliminated and 2 propene reaction: aldehydes oxidising O The H 2 Key points to This → C acid to OH 5 alcohols, which contain the group OH CH bond. Alcohols acids C 3 Hot react to form with carboxylic esters. concentrated sulphuric dehydrates alcohols An solution to acid alkenes. H are oxidised by iodine in the presence of sodium hydroxide. alkaline iodine triiodomethane formed precipitates as yellow crystals. This is known is iodofor m test . One primary alcohol, ethanol, which also used to test for as alcohols the of The contains containing the group the CH CH(OH)— 3 CH CHOH group also gives this reaction. 3 27 3.2 Halogenoalkanes Learning outcomes Classifying halogenoalkanes Halogenoalkanes On completion of this section, be able They describe primary may be general classied formula according C H X or RX (where X is a 2n+1 to the position of alcohols. For example: the halogen to: functional the n halogen). should have you the and hydrolysis group in a similar way to of primary secondary tertiary halogenoalkane halogenoalkane halogenoalkane tertiary halogenoalkanes describe nucleophilic describe the involved in H H C C H H H C C C H substitution H mechanisms Cl H H H H C H H the hydrolysis of H primary and H H I H tertiary H C C C H Br H H halogenoalkanes. chloroethane 2-iodopropane Nucleophilic A nucleophile decient atom is substitution a in a electron-decient Nucleophiles negative are charge. 2-bromo -2-methylpropane reagent that molecule. donates A new a pair covalent of electrons bond a either negatively Examples nucleophilic are charged :NH :OH substitution the nucleophile the carbon is (:Nu ) electron reaction replaces the ions :CN the electron decient a bond a bond curly electron- with the or atoms H O: than decient pair carbon in a partial halogenoalkanes: because atom (X) halogens are more δ — Br C movement with is from the nucleophile to the electron- atom is carbon an 2 halogen δ+ electronegative to formed atom. 3 In is formed between the nucleophile and the electron decient- atom is broken arrows between show the the electron-decient movement of the C atom electron and the halogen pairs. :Nu H H δ + R δ C X R H Substitution Primary in Nu + :X H primary halogenoalkanes C react halogenoalkanes with OH ions or water to form primary alcohols. CH CH 3 CH 2 Cl + OH → CH 2 Hydrolysis less with effective water is CH 3 1-chloropropane CH 2 OH + Cl 2 propan-1- ol slower than with OH ions because water nucleophile. + CH CH 3 28 CH 2 Cl 2 + H O 2 → CH CH 3 CH 2 OH 2 + H + Cl is a Chapter Ethanol is not with mix used as a solvent aqueous in these reactions since halogenoalkanes do 3 mechanism for variety Figure groups Did you know? the reaction of bromoethane with OH ions is the nucleophilic substitution shown reaction for in of functional solutions. n The A a primary 3.2.1. halogenoalkane, an intermediate chemists think is formed as that the :OH H H H δ + H C C H H C—Br H δ bond breaks and the C—OH bond forms. Br H C :Br H H H C C H H H Br H OH Figure 3.2.1 Nucleophilic substitution in a primary halogenoalkane. The OH ion attacks δ+ the C at the same time as the C—Br bond breaks. ntermediates In this mechanism: isolated, like this have not been however. δ+ the a new as OH (nucleophile) covalent the the ion C—Br Br atom bond bond takes donates between C a pair and of —OH electrons is formed to the C atom at the same time breaks both electrons in the C—Br bond and leaves as a Did you know? ion. Br The Substitution in tertiary mechanism for halogenoalkane halogenoalkanes S 2. primary hydrolysis (Substitution is called nucleophilic N T ertiary halogenoalkanes react with OH ions or water to form tertiary 2nd order). The rate-determining alcohols. step involves two species – CH(CH CH 3 )ClCH 3 + OH → CH 3 CH(CH 3 2-bromo -2-methylpropane )(OH)CH 3 + (halogenoalkane Cl 2-methylpropan-2- ol mechanism for halogenoalkane two -step mechanism for ). 3 The The and OH this reaction is shown in Figure tertiary hydrolysis is called 3.2.2. S 1. (Substitution nucleophilic 1st N order.) The CH CH 3 3 involves C Br CH one species (halogenoalkane fast + 3 step CH 3 slow CH rate-determining C :OH CH 3 C OH + Br 3 only). CH CH 3 Figure 3.2.2 CH 3 3 Nucleophilic substitution in a tertiary halogenoalkane. In the rst step a ion tertiary halogenoalkane ionises to form a carbocation. In the second step the OH attacks the carbocation. Key points In this mechanism: the C—Br bond breaks by heterolytic ssion. The bromine atom A nucleophile donates both electrons in the C—Br bond to become is a a pair of an intermediate carbocation is formed with a full charge on the atom an to form the new covalent bond. atom to Br a carbon that electrons electron-decient reagent takes OH ion (nucleophile) attacks the Hydrolysis of primary carbocation halogenoalkanes occurs in a – a new bond is formed by the electron pair donated by the OH ion. single step. t involves both the – halogenoalkane Chloro-, bromo- and iodoalkane hydrolysis Hydrolysis of and OH tertiary halogenoalkanes The reactions are similar in each case. The rate of hydrolysis is related bond strength of the carbon–halogen 2 F C 5 H 2 Cl C 5 route which by a involves bond. (i) H C occurs to two-step the ions. H 2 Br C 5 H 2 ionisation of the I 5 halogenoalkane (ii) attack by an – – faster rate weaker of hydrolysis by OH → OH ion on a carbocation intermediate. bond energy of C—halogen bond → 29 3.3 Carbonyl Learning outcomes compounds Structure Aldehydes On completion should be able of this section, describe to: the aldehydes structure and and names of ketones both aldehydes contain the and carbonyl ketones group. you In aldehydes atom and the bonded to carbonyl carbon atom has at least one hydrogen it. of ketones In ketones the carbonyl carbon atom has two carbon atoms bonded to it. describe the compounds reactions with of Brady’s carbonyl a reagent, b C c R reagent and R O C Tollens’ O C O Fehling’s H R solution Figure 3.3.1 describe the compounds reaction with of acidied The potassium a The carbonyl group; b An aldehyde; c A ketone carbonyl table below gives the names of some aldehydes and ketones. manganate(VII). Name of Structural Name of aldehyde formula ketone Structural formula methanal HCHO propanone CH COCH 3 ethanal CH CHO butanone CH 3 3 CH 3 COCH 2 3 Did you know? propanal ery are small amounts present in blood of CH and a suffering from higher Excess propanone through diabetes concentration the ‘acetone can than be lungs. This CHO pentan-2-one CH 2 CH 3 CH 2 COCH 2 3 urine. butanal People CH 3 propanone is CH (CH 3 have ) 2 CHO pentan-3-one CH 2 CH 3 COCH 2 CH 2 3 usual. exhaled called Testing for the carbonyl group breath’. We add a DNPH) present, by solution to a the of deep orange recrystallisation particular of particular for an or or is formed. its If melting present. ketone If This has a is an we aldehyde purify point, we because melting the can each point or or ketone is precipitate identify the DNPH which is compound. Distinguishing between Usng Tollens’ reagent T ollens’ is reagent (2,4-dinitrophenylhydrazine compound. determine ketone aldehyde that reagent carbonyl precipitate and aldehyde derivative Brady ’s suspected an aldehydes (sler aqueous and ketones mrror test) solution of silver nitrate in excess + ammonia. This contains the ) [Ag(NH 3 ] ion. 2 Aldehydes When warmed carboxylic ‘mirror ’ is carefully acids. seen The on with silver the T ollens’ complex side of RCHO the + reagent, ions are aldehydes reduced to are oxidised silver . A to silver test-tube. [O] → RCOOH + [Ag(NH ) 3 Note: when complex, 30 we equations can use ] + to → Ag + 2NH 2 involving [O] e 3 the oxidation represent the effect of of carbon the compounds oxidising are agent. Chapter Ketones Ketones 3 A variety groups Did you know? give no reaction with T ollens’ reagent (the mixture remains The colourless). This is because ketones cannot be oxidised to carboxylic tests for reagent solution Fehlng’s and depends using on Fehling’s the reduction of soluton complex Fehling’s aldehydes acids. Tollens’ Usng of functional solution is formed by mixing two solutions: Fehling’s A (which Section ions (see 13.4). Unit 1 Study Guide, Many chemical tests 2+ contains aqueous complexing Cu reagent ions) and an and Fehling’s B (which contains a and alkali). some analysis aspects by of quantitative spectroscopy the formation of depend complex ions on (see Aldehydes Section When warmed with Fehling’s solution, aldehydes are oxidised 9.4). to 2+ carboxylic solution acids. The changes to blue an colour of orange-red the Cu ions precipitate of in the copper( Fehling’s i) oxide. 2+ The Cu ions copper( i) oxidise the aldehyde and are themselves reduced to the state. Ketones Ketones blue). give This Usng no is reaction because potassum with Fehling’s ketones cannot solution be manganate(vii) (the oxidised or to mixture remains carboxylic acids. potassum dchromate(vi) In Section 3.1 we saw that manganate( vii) potassium alcohols can (potassium be oxidised by permanganate) acidied or potassium dichromate( vi). In each and We case using can from an aldehyde reux, also use the was rst aldehyde these is oxidising formed. With converted agents to to a help excess oxidising carboxylic us agent acid. distinguish aldehydes ketones. Aldehydes When are reuxed oxidised with to excess carboxylic CH CH 3 acidied acids. For CHO + potassium manganate( vii), aldehydes Key points example: [O] → CH 2 CH 3 propanal COOH 2 propanoic Aldehydes the The purple likely colour turns of the brownish. potassium This is manganate( because the vii) and ketones contain acid decolourises manganate( vii) ions or more carbonyl Aldehydes group, C=O. are oxidised to are carboxylic acids but ketones are 2+ reduced to ions Mn (very pale pink) or MnO (brown). 2 When reuxed with excess acidied potassium not. dichromate( vi), the aldehyde is again oxidised to the carboxylic acid having the same Brady’s to of carbon atoms. The orange colour of the potassium reagent can be used number identify a C=O group. The dichromate orange crystals formed have 3+ (oxidation number +6) changes to the green colour of Cr ions. Ketones characteristic melting depending the compound Ketones give no dichromate( vi). conditions are reaction This very is with potassium because severe and ketones C—C manganate( cannot bonds are be vii) or oxidised on points carbonyl used. potassium unless the Aldehydes form on broken. warming but ketones do Fehling’s silver mirror on reagent not. Aldehydes form precipitate a with Tollens’ an orange warming solution but with ketones do not. 31 3.4 More about Learning outcomes carbonyl Nucleophilic The On completion of this section, C=O bond be able in describe reactions of aldehydes the and oxygen ketones atom. The the reaction of closer to the oxygen describe polarised due pairs in to the the high bond are atom. carbonyl δ + compounds is electron to: drawn addition you electronegativity should compounds the with mechanism δ C NaCN/HCl O of δ+ nucleophilic addition reactions The C atom in the carbonyl group is open to attack by nucleophiles of such as and :CN HSO 4 carbonyl describe compounds the carbonyl reduction compounds A negatively The hydride addition hydrogen of platinum intermediate is formed. of by intermediate and reacts with a hydrogen ion (from dilute acid or lithium water aluminium charged present in the reaction mixture). by using :Nu a catalyst. R R δ + Nu R (H C Nu + δ O from solvent) C R C O: R R O H + H δ+ Figure 3.4.1 A nucleophile :Nu attacks the C + atom, a H ion from the solvent attacks the negatively charged intermediate. (Note: R’ can be an alkyl group or hydrogen.) The the overall reaction presence of is an hydrogen addition ions has reaction added because across the the nucleophile C =O bond, in e.g. with ethanal: CH CH 3 Nu 3 + C O + :Nu + H Nucleophilic When sodium C → H H addition of cyanide is O hydrogen acidied, the cyanide poisonous gas + NaCN The :CN ion The overall in the reaction CH weak with + acid H HCN acts as + a CH + HCN CH mechanism ketones is of shown the CN 2 → C H H The Na 3 O reaction of hydrogen cyanide OH with aldehydes below. a :CN R R δ + CN R δ CN + H C O H C H C O: O H H + H b :CN R R δ + CN R δ CN + H C R O C R C O: R + H Figure 3.4.2 32 formed: nucleophile. 2 C is is: CH 3 HCN + → HCN propanal H Reaction of HCN with a an aldehyde; b a ketone O H and Chapter In each 3 A variety of functional groups case: δ+ the C atom in the carbonyl group is attacked by the nucleophile – :CN a negatively the charged intermediate present in the intermediate reacts reaction with a is formed hydrogen ion (from dilute acid or water mixture). Did you know? The cyanide t not is a ion is danger present to us, in plants however, such since as it is sorghum, usually clover present and in cassava. very low concentrations. Reduction of Lithium aldehydes aluminium hydride and (lithium ketones tetrahydridoaluminate), LiAlH , is 4 often used as a Aldehydes reducing are agent reduced to in organic primary reactions. alcohols. For example: H H CH CH 3 + 2[H] CH 2 3 C 2 O H propanal Ketones are reduced propan-1- ol to secondary alcohols. CH For example: CH 3 3 C + O 2[H] C CH 3 CH H 3 propanone The reaction The nucleophile with propan-2- ol LiAlH is also a nucleophilic addition. 4 – is the hydride ion, H , arising from the LiAlH . 4 The reaction presence Note: We of can a can also be platinum use [H] to carried catalyst represent out (the the by adding hydrogen mechanism hydrogen here from is the in the different). reducing agent. Key points Carbonyl cyanide The compounds undergo nucleophilic addition reactions with the ion. cyanide electrons to ion acts as a the partially nucleophile positively because charged it donates carbon atom a lone in pair of aldehydes and ketones. Aldehydes or Ketones or are hydrogen are hydrogen reduced using a reduced using a to primary platinum to secondary platinum alcohols by lithium aluminium hydride by lithium aluminium hydride catalyst. alcohols catalyst. 33 3.5 Carboxylic Learning outcomes acids Introduction The On completion should be able of this section, functional group in carboxylic acids is you to: O describe the carboxylic hydroxide, reactions acids with describe the carboxylic The and describe the with table shows of reaction with —COOH names and formulae of some carboxylic acids. Structural formula acid HCOOH of PCl , acid CH COOH 3 PCl 3 and the Name methanoic acids or alcohols ethanoic carboxylic H 2 metals (esterication) —CO sodium reaction acids or C sodium hydrogencarbonate of 5 SOCl 2 propanoic acid CH CH 3 butanoic acid CH COOH 2 CH 3 CH 2 COOH 2 Exam tips The When naming carboxylic carboxylic acid group is polarised as shown below: δ acids, O remember that the number δ + of C δ + δ carbon atom atoms of the includes —COOH the carbon group. δ+ The C atom can be attacked by weak nucleophiles in the presence of + ions. H δ The O atom can be attacked by positively charged species such as + H δ+ Did you know? Many in carboxylic nature. acid) is H Acidic acids Methanoic an The are found acid irritant found (formic in atom lost when properties of Carboxylic the is acids are weak a carboxylic carboxylic acids. The acid behaves as an acid. acids position of equilibrium is over to left. bee + CH stings made and by in ants. distilling Methanoic reactions acid of t was the gives bodies some aldehydes of of the —CHO H O Y CH 2 COO + H 3 O 3 ethanoic ethanoate acid ion the because group. + ants. it They contains COOH 3 originally with are strong sodium enough hydroxide, Reacton wth Carboxylic acids and acids sodum react to show carbonates typical and acid reactive properties, e.g. hydroxde with sodium hydroxide to form the sodium water . + CH CH 3 COOH The salts + NaOH → CH 2 of CH 3 propanoic the acid sodium carboxylic acids are COO HCOO Na called 34 + H O 2 propanoate carboxylates. + is sodium methanoate, CH COO 3 ethanoate. Na 2 + reaction metals. Na is sodium salt Chapter Reacton wth Carboxylic acids 3 A variety of functional groups metals react with sodium to form a metal salt and hydrogen. + 2CH COOH + 2Na → 2CH 3 ethanoic Other reactive COO Na + H 3 metals acid also 2 sodium form salts, e.g. ethanoate magnesium ethanoate, 2+ (CH COO ) 3 Mg 2 Reacton wth Carboxylic acids water and hydrogencarbonates react carbon with dioxide carbonates are and and carbonates hydrogencarbonates. A salt, formed. + HCOOH + → NaHCO HCOO Na + H 3 methanoic Reaction of Carboxylic (usually reux acids react concentrated to distilled an sodium carboxylic prevent off the when esterification with loss the acids alcohols sulphuric of + CO is 2 methanoate with in acid). volatile reaction O 2 acid the alcohols presence The of reactants alcohols complete. and This an are esters. type acid catalyst heated The of under esters reaction is are called reaction. O O + H OH + CH H 3 Figure 3.5.1 2 CH 5 C +H H 3 2 5 O 2 The ester, ethyl ethanoate, is formed by the reaction of ethanol with ethanoic acid. The dashed line shows the bonds that are broken during the reaction. The in reaction which been can two eliminated. elimination also be molecules described have Another reaction. way This is as reacted of a condensation together describing because the and the a reaction small reaction ethanol – a reaction molecule is as molecule an rst has addition– forms an δ+ addition product Reaction by attacking with PCl , the PCl 5 Carboxylic acids phosphorus( v) . SOCl The react products or are of the group. 2 with sulphur called —COOH and SOCl 3 rapidly chloride atom C phosphorus( dichloride acid iii) chloride, oxide chlorides (acyl (thionyl chloride), chlorides). Acidic 2 fumes of HCl are also COOH CH produced. + PCl + SOCl 3 3 note: CH → CH and SOCl POCl + SO should be + HCl + HCl 2 ethanoyl 3 + 3 COCl 3 acid PCl COCl 3 2 ethanoic Safety → 5 COOH CH chloride used in a fume cupboard. 2 Key points Exam tips Carboxylic acids are Carboxylic acids react with sodium weak acids. with sodium hydrogencarbonate hydroxide to form a to form salt, a carbon salt and dioxide water and and water. You do not have equations for phosphorus Carboxylic acids react with reactive Carboxylic acids react with alcohols Carboxylic acids react with PCl metals to form a salt and 3 hydrogen chloride. PCl and 5 the chlorides or of the thionyl with carboxylic acids. You esters. should , learn reactions hydrogen. chloride to form to the SOCl to form acid chlorides and fumes know, are however, given off that and acidic that acid 2 chlorides are formed. 35 3.6 Esters Learning outcomes Introduction Esters On completion should be name able of this section, have the general structure you to: esters O and write R their ester link C O R structural formulae describe from the formation of esters from from acid alcohol alcohols describe the catalysed acid- and hydrolysis base- of The —COO— The naming group is often called an ester link (see Section 6.2). esters. alcohol The The - oic used of esters to make name begins name ends acid is is based on the name of the carboxylic acid and them. with with changed the the to alkyl part (or aryl) coming group from from the the alcohol. carboxylic acid, but - oate. O CH C 3 O CH = methyl ethanoate 3 methyl ethanoate (from (from ethanoic methanol) acid) Exam tips The Be careful sure that –oate The with you parts part of naming don’t the the get wrong name esters. the way table the comes rst alkyl relating acid (the –oate and the comes some and Structure of of different ester esters. Name of ester to the CH CH CH 2 COOCH 2 methyl butanoate 3 part from second). HCOOCH CH 2 CH CH 2 COOCH 3 propyl methanoate 3 CH 2 ethyl ethanoate ethyl benzoate 3 COOCH CH 2 water names round. 3 alcohol gives Make 3 out condenser colder CH here water COO phenyl 3 in Hydrolysis of Hydrolysis is speeded by Esters ester sulphuric ethanoate + up are the esters breakdown reacting hydrolysed a by of a compound compound heating with the with either ester water . an under acid reux It or is an with often alkali. an acid or a base. acid Heating The Reux is acid necessary or alkali because acts as a the reaction is slow. catalyst. heat and Figure 3.6.1 refluxing 36 is necessary alcohol. The to prevent vapours rise the and loss of then the volatile condense on vapours the of colder the Acid hydrolysis of an ester by the condenser . They then drip back into the ask (Figure ester parts 3.6.1). of Chapter Acd 3 A variety of functional groups hydrolyss Exam tips This is the carboxylic reverse of the preparation of an ester from an alcohol and a You acid. may nd purposes The ester is heated with diluted sulphuric The So reaction is ‘mind A For ester is carboxylic an the ester ester a revision ‘spider showing all diagram’ the reversible. not acid fully and hydrolysed. an alcohol between functional are This formed. will groups help synthesise of draw map’ reactions the useful for acid. or to it RCOOR ′ and the the carboxylic alcohol from acid the arises —OR from the RCO— a you various this to see particular section. how you can compound part by part. a three- or four-stage starting from compound. O the in another n your route particular spider diagram O + H CH C + H 3 catalyst you O CH 2 C + C 3 H 2 should include halogenoalkanes, O C 5 ketones, Figure 3.6.2 Alkalne In the carboxylic acids and esters. Acid hydrolysis of ethyl ethanoate hydrolyss base-catalysed The alcohols, aldehydes, OH H 2 alkenes, OH 5 ester is hydrolysis heated with of an aqueous ester: sodium hydroxide (or other suitable base). The reaction The ester An For is alcohol an not fully and ester RCO— is part reversible. the salt RCOOR ′, of Did you know? hydrolysed. the of a the ester carboxylic salt and of the the acid are carboxylic alcohol from Apart from their flavourings and acid the arises —OR from esters can in be perfumes, used insect damage. to some reduce part. – Some they esters are act given as out O naturally CH uses the pheromones O common formed. + C NaOH CH 3 + C C 3 H 2 by female insects to attract OH 5 the males. Spraying crops with + O C CH COOCH 3 5 synthetic + + CH 2 ethyl Na O H 2 CH NaOH COO Na males + CH 3 3 CH 3 sodium ethanoate ethanoate pheromones and they do confuses the not nd females OH 2 to ethanol mate with. So fewer offspring are produced. Figure 3.6.3 The Alkaline hydrolysis of ethyl ethanoate sodium react with sodium Some salt of sodium the carboxylic hydroxide (see acid is formed Section 3.5). because Alcohols carboxylic do not acids react with hydroxide. more equatons for HCOOCH + ester H 3 methyl CH O Y COOCH 2 HCOOH + CH 2 + 3 methanoic H OH 3 methanoate CH 3 methyl hydrolyss O Y CH 2 CH 3 propanoate acid COOH methanol + CH 2 Key points OH 3 propanoic acid methanol Esters are formed alcohols When with esters by refluxing acid. are hydrolysed + CH COOCH 3 CH 2 CH 2 + NaOH → 3 CH COO Na + 3 CH CH 3 CH 2 OH 2 by propyl ethanaote sodium ethanoate acids, the products are a propanol carboxylic acid and an alcohol. + HCOOCH CH 2 ethyl + NaOH → HCOO Na 3 methanoate + CH CH 3 sodium methanoate OH 2 ethanol When base, a esters the are hydrolysed products carboxylic acid are and the an by salt a of alcohol. 37 3.7 Saponification Learning outcomes On completion should be able describe understand of this Fats section, and oils Fats to: Long-chain The and oils are esters of long-chain carboxylic acids with glycerol. only carboxylic difference acids are between a sometimes fat and an called oil is fatty that a acids. fat is solid and saponication an by biodiesel you that biodiesel can oil is a liquid at room temperature. be made and The chain lengths of the fatty acids (carboxylic acids) in fats are from transesterication 12–18 carbon atoms. reactions understand the basic transesterication. principles The fatty acids in fats can be the same or different. of Figure make 3.7.1 a − shows triglyceride glycerol by HOOC OH an reacting with esterication three fatty acid molecules to reaction. − − − − − − O OC − H − OH + HOOC O OC − + 3 O H − OH HOOC fatty glycerol O OC − a fat acids water Figure 3.7.1 represents the alkyl side chain of the fatty acid) Saponification Saponification and is the process of making soaps by the hydrolysis of fats oils. Soaps are metal Soaps are made Sodium The by hydroxide products (soap) salts and are of long-chain boiling fats hydrolyses the sodium carboxylic with the sodium three salts of acids. or ester potassium links long-chain in hydroxide. fats. carboxylic acids glycerol. heat fat Figure 3.7.2 (or oil) shows + sodium the hydroxide hydrolysis of a fat → soap (trigyceride) + glycerol with sodium hydroxide. a C H 17 C H 17 C C 2 H 17 COOCH + 3NaOH 35 H 17 COOCH 35 C H 17 COOCH 35 C 2 glyceryl stearate + (a fat) sodium hydroxide HOCH 2 COONa + HOCH + HOCH 35 H 17 COONa 35 COONa 35 sodium (a 2 stearate + glycerol soap) b COONa COO COO + 3NaOH COONa COONa COO fat Figure 3.7.2 + sodium hydroxide soap + HO HO glycerol Soaps are formed when fats or oils are hydrolysed with sodium hydroxide; a The hydrolysis of a fat; b A simplied diagram of saponication ( alkyl side chain of the fatty acid) 38 + HO represents the Chapter supply out. For A of petroleum used as a basis for fuels will eventually this reason fuels. vegetable of functional groups r un The making variety Did you know? Biodiesel The 3 scientists Biodiesel oils from is plants a have fuel or been for fats tr ying diesel from to nd engines animals. It other that is is ways made made cleaning action of soap is due to of the attraction the soap for of different parts of from grease and water. The by ionic ‘head’ is attracted to water and transesteri cation. the T ransesterification different ester and is the reaction different of alcohol. an ester The with alkyl an group alcohol from to the form hydrocarbon ‘tail’ is attracted to grease. a alcohol water replaces the alcohol. The heat a is alkyl group reaction in is the slow ester which from a different ionic ‘head’ so: required catalyst is used to speed up the process. – e.g. originates sodium methoxide, O CH Acids, alkalis or hydrocarbon alkoxides + Na ‘tail’ are used as catalysts. 3 grease O O catalyst C H 2 COC 5 ester Figure 3.7.3 H 6 + CH 13 OH C 3 1 H 2 alcohol 1 COCH 5 + C 3 ester H 6 2 OH 13 alcohol 2 Transesterication. An ester reacts with an alcohol to form a different ester and a different alcohol. T ransesterication more complex usually results in a simpler ester being formed from a ester . grease CH COOC 3 H 12 + CH 25 OH → CH 3 COOCH 3 + C 3 H 12 off dodecanyl The has ester a is lower undergo ethanoate more + useful viscosity methanol as and a transesterication, hydroxide where fuel burns hydrolysis → because more especially also methyl it has easily. in ethanaote a Fats the lower and of surface dodecanol molar oils presence + lifted OH 25 can mass. So it also sodium occurs. Exam tips CH – O 2 CH CR CH 2 – O O 3 CR + 3CH 2 CH OH 3 O 3 CR CH 2 OH 2 CR + You CHOH do not equations CH – O 2 CR CH 2 O 3 CR CH 2 to remember the in this section. You should, OH 2 however, fat know: glycerol 1 Figure 3.7.4 have 2 the basic structure of a triester Transesterication and hydrolysis of a fat. A triglyceride reacts with (fat) methanol to form esters of lower molar mass and glycerol. R, R and R represent alkyl groups with 12–18 carbon atoms. 2 how fats The fat which has a high molar mass is converted to simpler esters molar ester link is broken when saponied of 3 lower the are how in transesterication, the mass. alkyl with group the —COOR of alkyl the alcohol group group of in the swaps the ester. Key points Fats and oils are esters of glycerol and long-chain carboxylic acids (fatty acids). Soaps are made by the hydrolysis of fats or oils by boiling with sodium hydroxide. Biodiesel Transesterication low is made relative by the process involves molecular the mass. A of transesterication. reaction different of fats ester or and oils with glycerol an alcohol of are formed. 39 3.8 Testing for functional Learning outcomes Testing for the C=C double Aqueous On completion of this section, be able bromine Compounds understand tests for water) containing is used double to test bonds for are the also C =C bond described as in being to: unsaturated. (bromine bond you alkenes. should groups that there are So the test is also a test for unsaturated compounds. specic On addition of the bromine changes bromine water to unsaturated compounds, the colour of particular functional from orange to colourless. groups describe a test for C =C double We can distinguish Alkanes do not alkenes give a from positive alkanes result by with the this bromine water test. test. bonds describe and tests for the — functional —Cl, —Br groups Halogenoalkanes describe tests to distinguish – Halogenoalkanes between alcohols, alcohols ketones and (in a solution of ethanol) react with OH ions form aldehydes, carboxylic and halide ions. acids. + CH CH 3 CH 2 Cl + – Na + + OH → CH 2 1-chloropropane The halide ions CH 3 CH 2 OH + Na – + Cl 2 propan-1- ol produced in this reaction can be identied using silver nitrate. Hydrolyse Add excess the Add a Observe suspected halogenoalkane with sodium hydroxide. – few nitric drops any bromoalkanes iodoalkanes Add a an (see carbonyl aldehyde Section Carboxylic of or 3.3 acids delocalisation in 1 can Using If T ollens’ an light n is darkens which precipitate rapidly darkens which slowly does not darken. aldehydes present give a the a ketones suspected deep positive carboxylate reagent is to and orange carbonyl compound. precipitate is formed information). reaction from (silver present, to this test because of the ion. aldehydes aldehydes aldehyde which precipitate yellow reagent between distinguish ions. nitrate. precipitate cream group not the OH ketones more do white a a silver the formed: a give ketone Dstngushng We give Brady ’s for neutralise aqueous give and solution to precipitate chloroalkanes Test for If of Aldehydes acid a and ketones mir ror silver by test) ketones three – ‘mirror ’ see is tests. Section seen on 3.3 the side of the test-tube. 40 Ketones do ‘mirror ’ is not react (the mixture remains colourless). No silver seen. Methanoic acid it gives group but can acidic properties be a positive reaction distinguished typical of from carboxylic because aldehydes acids. it has a CHO because it has the Chapter 2 Using If Fehling’s an aldehyde oxide 3 is Ketones Methanoic If do an a aldehyde green ketone Primary and this but test Carboxylic 1 of functional groups 3.3 orange-red precipitate of copper( i) a mixture positive dichromate( vi) remains blue). reaction. or potassium manganate( vii) – see is present the present acids distinguish no secondary they do and by the orange potassium potassium colour give acid a dichromate( manganate( change alcohols not carboxylic compounds) the purple will is also positive vii) observed give test a on heating. positive with vi) decolourises. result Brady ’s in reagent. halides acids from following alcohols (and many other reactions: Acidity A 2 Section an (the gives is or If can present react acid organic see variety 3.3 turns We not potassium Section is – A formed. Using solution 3 solution Reaction Bubbles of a with of carboxylic sodium carbon acid in water has a hydrogencarbonate dioxide, CO , are pH or released below sodium when the 7. carbonate acid is added to 2 a carbonate. The presence of is CO detected by bubbling the gas 2 through limewater . The limewater turns milky if is CO present. 2 Acid halides water . given The off, so a Alcohols Alcohols apart off Alcohols be fume and can from given can reaction be distinguished is can carboxylic alcohols carboxylic and should be highly used acids acidic for by adding choking these them fumes to are reactions. esters distinguished with be from vigorous cupboard carboxylic (pops very a acids lighted are all the they other react homologous with sodium. series above Hydrogen is splint). distinguished acids from because acidic from and carboxylic react with acids because: sodium hydrogencarbonate Key points are not acidic so do not react with sodium hydrogencarbonate. Alcohols which contain the group CH CH(OH) — (many secondary be 3 alcohols add and ethanol) iodine and can be sodium distinguished by the iodoform test: identied tests hydroxide Different functional used involving a precipitate alcohol or of yellow crystals shows the presence of a them with are distinguished from most other homologous be hydrolysing series by sodium the ionic hydroxide product and with their aqueous fruity can changes. secondary ethanol. testing Esters by can qualitative colour Halogenoalkanes distinguished groups silver nitrate. smell. Alcohols, can be oxidation reaction aldehydes identied by reactions with Carboxylic acidic and Brady’s acids can distinguished from their and ketones various by reagent. be alcohols by nature. 41 4 Aromatic 4. 1 Some compounds reactions Learning outcomes completion of this section, be able describe nitration explain the of the hydrocarbons ring with a based delocalised on benzene. system of π Benzene electrons has a above six-membered and below the to: plane are you planar should benzene Arenes Arenes On of bromination and of the structure of ring (see Unit 1 Study Guide , Section 2.9). This stabilises the benzene. benzene steps involved mechanism for the bromination benzene. of in nitration the Did you know? and Some arenes many centuries. This compounds. smells! In have Many rather Electrophilic and delocalised is exposed general is the than they made term the as sweet-smelling were in of π attack named the laboratory aromatic now oils from aromatic do refers to plants for (aroma-producing) not the have such structure nice of the smell. substitution ring to extracted why arenes chemistry compounds The been electrons by in in benzene benzene electrophilic has reagents. a high-electron Figure 4.1.1 density shows the mechanism. + El H C H C H C H H H C H C C H C El C C C C El + + C C + C H C H H H H H H C C C H H H + Figure 4.1.1 General mechanism of nucleophilic substitution in benzene. El represents an electrophile. The so electrophile it is A bond This T o The forms causes carbon attracted regain has reacts bromide (or a the is replaced a with charged electron system to positively a or and of the become positively the charged, benzene benzene unstable. ring. ring. One of the charged. ion is substitution hydrogen partially density electrophile hydrogen reaction iron high aromatic Bromination of Benzene the becomes stability, overall reagent positively between the atoms is to lost. reaction atom in the because benzene the electrophilic ring. benzene bromine filings and in the presence bromine). The of a catalyst overall of reaction iron( III) is: Br + Br + HBr 2 The 42 electrophilic reagent is the positively polarised bromine molecule. Chapter The highly shown. We polar say iron( III) that bromide iron( III) the causes bromide the is movement a halogen of electrons 4 Aromatic compounds as carrier . Br δ + δ + δ δ Br The mechanism is shown in Figure a 4.1.2. c b H Br Br + δ + + δ + + FeBr FeBr 3 Figure 4.1.2 HBr 3 FeBr 4 The bromination of benzene; a electrophilic attack; b intermediate formed; + ion and reformation of catalyst c loss of H Did you know? In the reaction between bromine and benzene, some books show the attacking + reagent because is, as it Br It more A An A useful to bond to the likely electrophile delocalised is conforms however, The . to forms the general bromine with pattern. The a full reaction charge shown in in this way Figure 4. 1.2 occur. (positively electrons unstable show in between the the positively polarised benzene bromine charged bromine molecule) attacks the ring. and the benzene intermediate is ring. formed. Exam tips – hydrogen ion is lost and combines with a Br from the to FeBr 4 form HBr . The catalyst FeBr is reformed. 3 Remember end in alkenes Nitration of Benzene reacts sulphuric although they do not arenes behave chemically. They do not like react benzene with acids. that -ene, a The mixture overall of concentrated reaction nitric and with bromine they are water. This is because concentrated very stable because of the is: delocalised ring electrons. NO 2 + HNO + H 3 O 2 Key points + The electrophilic reagent is the nitronium ion, NO , formed by the 2 nitrating mixture of concentrated nitric and sulphuric The of + HNO + 2H 3 The mechanism is SO 2 shown → NO 4 in – + 2HSO 2 Figure H O c of reaction arenes involves electrophilic substitution. 3 4.1.3. b mechanism + + 4 In of a main acids: the electrophilic arenes, a substitution hydrogen atom in NO 2 the H ring is replaced by Br, NO or 2 NO 2 + another suitable group. + + + NO H 2 When benzene is nitrated, + the nitronium ion, NO is the 2 Figure 4.1.3 The nitration of benzene; a electrophilic attack; b intermediate formed; electrophilic + c loss of H reagent. ion When benzene is brominated, is required. a + The electrophile (the nitronium ion, NO ) attacks the delocalised 2 halogen electrons in the benzene ring. A bond forms between carrier the nitro group, , NO and the benzene The electrophilic reagent in the ring. 2 bromination An A unstable positively charged intermediate is polarised ion is lost. This reforms the benzene is the formed. + hydrogen of sulphuric acid (H bromine molecule. – + HSO ). 4 43 4.2 Methylbenzene Learning outcomes Substituted Figure On completion should be able of this and section, 4.2.1 nitrobenzene arenes shows how we name some substituted arenes. you a to: b c CH d CH 3 CH 3 NO 3 2 1 describe the bromination NO and 2 6 nitration of methylbenzene 2 and 3 5 NO 2 nitrobenzene 4 NO 2 explain the steps mechanism of bromination and involved nitration of in the and methylbenzene Figure 4.2.1 c Some substituted arenes; a methylbenzene, b methyl-2-nitrobenzene, methyl-4-nitrobenzene and d 1,3-dinitrobenzene nitrobenzene describe the reaction of The nitrobenzene concentrated with nitration of methylbenzene Sn/ Methylbenzene HCl. it a is mixture When and slightly reacts more of isomers acids, the reactive methylbenzene sulphuric with is the is nitrated isomers 59% methyl-3-nitrobenzene 4% methyl-4-nitrobenzene 37% the it CH is mainly group in the than electrophiles as benzene but: benzene obtained. methyl-2-nitrobenzene Because same 2- and with a mixture produced 4- methylbenzene isomers is 2-, of concentrated nitric are: that are produced, we say that 4-directing. 3 This is ring. (+ because the CH group tends to release electrons to the benzene 3 the effect – intermediate Figure + I see Section formed and 5.1.) This therefore reduces the stabilises positive the charge intermediate on (see 4.2.2). CH 3 The have Figure 4.2.2 possible the intermediates positive charge on formed the C by reaction atom next at to the the 2- and methyl 4-positions group. The A methyl group tends to possible intermediates formed at the 3-position have the positive charge donate electrons to the benzene ring. The on other carbon atoms. arrow shows the direction of movement of the electrons. Bromination In the presence reagent. the Exam tips the nitronium ion 2-, of a bromine benzene again, When A and ring. A nitration of halogen atom is carrier , methylbenzene bromine substituted mixture of in isomers is reacts either obtained. 4-directing. is formed CH 3 by the reaction of nitric acid with Br sulphuric acid, the nitric acid behaves CH 3 as a Brønsted–Lowry base. + Br 2 + FeBr CH 3 3 Br 44 as the an 2- electrophilic or The 4-positions methyl group of is Chapter The nitration Nitrobenzene it is the reacts slightly rather than less it is is bromination of with the reactive reaction 3-isomer Because and at the than room mainly mainly same (it Aromatic compounds nitrobenzene electrophiles benzene 4 as benzene requires but: heating to 50 °C temperature) obtained. 3-isomer that is produced, we say that the NO 2 group This in is nitrobenzene because the is 3-directing. NO group is an electron-attracting group. It tends to 2 withdraw This at the most electrons increases 2- and the from the positive 4-positions. benzene charge So the on ring. the (– I effect – see intermediate intermediate formed Section formed, at the 5.1.) especially 3-position is stable. a b NO NO 2 2 NO 2 + + + + NO + H 2 NO 2 Figure 4.2.3 a A nitro group tends to withdraw electrons to the benzene ring. The arrow shows the direction of movement of the electrons. b The equation for the overall reaction + ion with nitrobenzene. of the NO 2 Reaction of Aromatic nitro concentrated product reaction is a nitrobenzene compounds hydrochloric complex with phenylamine alkali. is salt are acid. of With the with tin reduced by Aromatic amine. reacting amines The nitrobenzene, and an HCl with are amine is aromatic tin and formed. formed amine The from actual this by called formed. NO NH 2 2 + 6[H] + 2H O 2 Figure 4.2.4 A simplified equation for the reduction of nitrobenzene by tin and concentrated hydrochloric acid. [H] represents the reducing power of hydrogen. Exam tips You do not have 1 equations for 2 details of the to remember: the reaction different nitrobenzene and of nitrobenzene intermediates for with the tin and nitration hydrochloric and acid bromination of methylnitrobenzene. Key points When methylbenzene formed The methyl release are mainly group electrons Nitrobenzene concentrated is the in to reacts 2- with and electrophilic 4-isomers methylbenzene the benzene reduced to hydrochloric ring is of 2-, to reagents, 4-directing stabilise phenylamine the products methylnitrobenzene. by the reaction because it tends to intermediate. with tin and acid. 45 4.3 Phenol and Learning outcomes dyes Introduction Phenol, On completion of this section, be able describe with aqueous in OH, has an —OH group attached directly to the benzene 5 place of a hydrogen atom. Phenol is only sparingly soluble in to: the acid H 6 ring should C you reactions halide (acyl bromine of phenols halides), and sodium water because water molecules. as the —OH alcohols are the large The group not group —OH in (see aryl group alcohols. Section minimises does For not hydrogen always example, bonding react phenol is in the acidic, with same way whereas 5.2). hydroxide describe the formation of azo Reactions of the compounds and the reaction state Reaction some uses of —OH group in phenols coupling with alkalis and reaction with sodium azo Alcohols do not react with sodium hydroxide. However , because of to a its compounds. acidic character , (called For a phenol phenoxide) example, with does and react. It reacts with alkalis form salt water . sodium hydroxide, sodium phenoxide is formed: Exam tips + OH + NaOH O Na + H O 2 Remember that when you write phenol the ring structure compounds you may with see the of substituent structure groups, The sodium different ways. phenoxide For phenoxide is soluble in water because example, reacts with sodium 2C of writing phenol is ionic. to form sodium phenoxide and hydrogen. two – ways it written Phenol in sodium aromatic H 6 are: OH + 2Na → 2C 5 H 6 O + Na + H 5 2 OH Reaction or OH with Acyl halides PCl (see acyl (acid Section halides halides) 3.5). are Acyl (acid formed halides halides) when react carboxylic with phenols acids to react form with esters. The 5 Remember that these are the same OH bond also structure. in react the with phenol acyl in + OH → C 3 chloride Substitution A reacts lone pair This So The at So OH more the intermediates the 2-, the 4- and reaction ring are on the electron charge are HCl COOC 3 in the on with the more atom ring Alcohols + in HCl 5 the hydrogen than compared benzene. with Section aromatic is chloride ring overlaps (see intermediates stable H electrophiles oxygen density released. ethanoate aromatic aromatic the are 6 phenyl rapidly in of manner . CH 5 electrons positive Fumes similar phenol electrons increases the the of a reactions much delocalised H 6 ethanoyl Phenol broken. halides COCl CH is the 5.2). ring. reduced. with benzene (especially 6-positions). occurs under milder conditions and more positions substituted. OH Br + Br 3Br + 3HBr The reaction of phenol with bromine 2 Bromine Br 46 water reacts 2,4,6-tribromophenol rapidly is with formed. phenol. No A halogen white precipitate carrier is needed. of in Chapter Diazotisation and coupling 4 Aromatic compounds reactions Exam tips Diazotisation The Phenylamine, C H 6 NH 5 , an aromatic amine, reacts with nitrous acid reaction other the presence of of phenol with in 2 hydrochloric acid to form a diazonium salt electrophiles also occurs (general under milder conditions and with + formula TNX RN ). This process is called diazotisation more positions substituted. in For the ring example, being nitration + NH + HNO 2 + HCl N NCl + 2H 2 O 2 only phenylamine nitrous benzene acid Nitrous acid is unstable and (no diazonium is made by dilute sulphuric acid nitric is adding NaNO and HCl to acid needed) 2,4,6-trinitrophenol chloride so requires and is formed. the 2 phenylamine. the The diazonium Coupling reaction salt decomposing an orange coupling below to has to be kept below 10 °C to prevent nitrogen. reaction Benzenediazonium form mixture dye reaction . 10 °C to chloride reacts with an alkaline (4-hydroxyphenylazobenzene). The prevent temperature of decomposition the of solution This solution the is must diazonium of phenol called be to a kept well salt. + N benzene NCl OH diazonium phenol orange dye chloride Figure 4.3.1 A coupling reaction is the reaction of a diazonium salt with a phenol under alkaline conditions The positive substitutes charge into on the the diazonium 4-position of the ion ring acts of as the an electrophile and phenol. Exam tips The important aromatic HNO is points amines about and made from the diazotisation phenols NaNO 2 are and and coupling reactions are that: involved HCl 2 Key points the reaction substitution is carried of the out diazo below 10 °C compound is at the 4-position in the phenol ring Phenols groups azo compound have the N=N have Azo dyes dye formed —N=N— aromatic coloured in group amines dyes. the coupling attached and The to colour reaction two different or more directly —OH to the link. benzene The one attached is an aromatic phenols, depends on we the azo rings. can dye. By make amine and It contains using a phenolic of —OH group with NaOH with acid in phenol to form halides a salt to form reacts and esters. the different variety The ring. brightly The the electrophilic ring of substitution phenol is rapid in due compound to activation of the ring by the used. —OH group. Phenylamine reacts with Did you know? o nitrous acid below benzenediazonium Diazonium compounds are important as intermediates in organic 10 C to form chloride. synthesis. + The N with T KI NX to aromatic group produce cyanides. can be replaced substituted by a variety of iodo-compounds, other groups, reaction e.g. with CN reaction to produce A coupling when reaction diazonium phenols to form occurs salts azo react with dyes. 47 Reision Answers to 1 A all revision questions compound i reacts ii turns iii does has readily blue can the following with litmus be found on the accompanying CD. properties: bromine paper questions 6 What is the correct compounds water pink order of increasing acidity of the below? OH OH CH OH 2 not cause aqueous Which of efferescence sodium when mixed with carbonate. the following compounds most accurately CH 3 exhibits all of the aboe properties? X A C H 6 B C C C D C H 6 NH 5 H 6 2 COOH 5 H 6 2 CONH 5 Which 2 of these statements best explains the Z of A Z Y X B Z X Y C Y D X Y Z X Z weak 7 acidity A compound H The C 6 O H A, C 3 phenol? acidified – A Y OH 5 ion is a weak conjugate O, when refluxed with 8 potassium dichromate(vI) produced a base. 5 liquid B, with a sharp smell, which efferesced with – B H The C 6 O ion is stabilised ia delocalisation of 5 sodium charge into the benzene carbonate containing C C H 6 OH is a stronger acid than an two atoms, when compound heated C, with aqueous concentrated of carbon dioxide (carbonic acid). H 6 OH will efferesce with potassium sulphuric acid at temperatures of ° about C carbon 5 solution D solution. Another ring. 160 C produced a sweet-smelling gas D, which carbonate 5 decolourised aqueous bromine. C also produced solution. yellow crystals hydroxide 3 Which of the following reagents best propan-1-ol and Cr B NaOH(aq)/ /H (aq) conc. H a SO 2 D 4 of produced Explain C, Na(s) Which the following by A alkanes B alkynes C alkenes concentrated sweet-smelling and b 4 of perfumery 7 2 C the classes dehydration of of compounds is c acid B in the produced compound. E is used in the the arguments used D and the also Write of to the deduce the names compounds A, B, E. equations for B the and the sodium type of reactions of C and B, carbonate. reaction which produces D and E. a Explain the terms as ‘primary’, applied to ‘secondary’ and alcohols. arenes b There are four H formula C 4 Which compound is most likely to be formed phenol is reacted with bromine A 4-bromophenol B 2,4,6-tribromophenol C 3-bromophenol D 2,3-dibromophenol in an organic structural isomeric alcohols with O. 10 when i Write the names these alcohols and structural formulae of solent? terms ii c in a and classify laboratory between these of these them according to aboe. Describe One of 48 sodium with industry. ‘tertiary’ 5 with refluxed sulphuric structural formulae Gie and alcohols? 8 D warmed when propan-2-ol? a A 2 gently + 2– O when iodine. C differentiates presence between and isomers concentrated of when sulphuric different compounds. i State the ii Explain type the tests groups of distinguish heated acid reaction production to compounds. of with produces an excess three inoled. these compounds. Chapters 9 a Explain when alkyl b and Explain, would characteristic hydroxyl the see when ethanoyl ii an A the write aid ring of is in groups and aromatic compounds – revision questions effect bonded to an respectiely. an phenol is Functional equation, added what you to: chloride aqueous the sequence difference group, OH, benzene with i and c the the 3–4 solution of bromine structural formula for of two reactions is the shown product. below: OH NH 2 I II X Y NaOH brightly coloured i Write the ii the names compounds Write the and X structural formulae for and reagents Y. and conditions for reaction I. iii 10 Name Compare and the and phenol, equations type contrast with reactions the in reactions the following wheneer appropriate of possible I of and propan-1-ol reagents, and II. giing describing obserations: i water ii blue iii potassium iv phosphorus(v) v ethanoic litmus paper hydroxide chloride acid. 49 5 Organic 5. 1 Carboxylic acids Learning outcomes and acids K bases and values of acidity some carboxylic acids a Carboxylic On completion of this section, acids (dissociated) should be able are weak acids. They are not completely ionised you in solution. The position of equilibrium is well over to the to: left. For example, ethanoic acid COOH). (CH 3 explain the difference in acidity + CH of alcohols and understand carboxylic why substitution increasing of Cl onto the COOH + H 3 acids The table shows O Y CH 2 some K and pK a COO + H 3 values O 3 for different carboxylic acids. a the –3 carbon atom —COOH next group to Carboxylic the results acid K mol dm pK a a in –5 ethanoic stronger acid, CH understand the COOH effect of × 10 the 4.77 –5 propanoic CH acid, CH 3 conjugative 1.7 3 acidity (mesomeric) COOH 1.3 × 10 1.3 × 10 4.89 2 effect –3 and inductive effect on chloroethanoic ClCOOH acid, CH 2.89 2 determining the acidity of various –2 substituted in carboxylic acids dichloroethanoic and COOH acid, CHCl 5.0 × 10 2.3 × 10 1.30 2 alcohols. –1 trichloroethanoic COOH acid, CCl 0.64 3 The values of K and pK a equilibrium give us information about the position of a (see Unit 1 Study Guide , Section 9.3). The higher the value Did you know? of and K the lower the value of pK a Trichloroethanoic acid is used to remove skin imperfections wrinkles. The cosmetic and be as carried a chemical out supervision under because further the position of equilibrium is to the right (in favour of treatment, peel, We medical this acid treatment the greater the acidity of the carboxylic acid. must can explain these differences by referring to two effects: is corrosive. After the products) known : a The conjugative effect (also known as the mesomeric or resonance the effect). patient appears to have sunburn! The The The inductive conjugative conjugative when the single makes over the ordinary e.g. single structure at occurs rst benzene. three bond effect effect structure bonds system the effect. or more lengths bonds more The stable. molecules appears π atom and and in sight orbitals centres bond (see double bonds in carbonate the carbon–oxygen bonds in carboxylate an example: O R C O 50 bonds, Section form 1.1). The showing a usually double and delocalised The effect between effect this also effect makes are: ions acids. as and intermediate compounds carbon–oxygen acids multiple alternating bonds. the carboxylic of overlap T aking with be strengths ordinary Other to H ions derived from carboxylic Chapter Oxygen atoms hydrogen are more electronegative than carbon atoms 5 Organic The bonding shown and bases or atoms. a acids by pairs the of electrons arrows in the tend to diagram move on towards page the atoms O O as R 50. C R C O The O—H bond The carboxylate is weakened so that it is possible for a proton to be O lost. O b ion formed exists as a resonance hybrid of two R extreme forms. The actual form is somewhere in between these C two O extremes (Figure 5.1.1). + The carboxylate combine with ion it is is relatively stable, so the ability of the ion H to Figure 5.1.1 Conjugative effect in the carboxylate ion; a reduced. The extreme resonance forms; b The resonance hybrid The inductive Bonds between effect unlike atoms are polarised due to the difference H in weakest electronegativity between the atoms (see Unit 1 Study Guide , Section C acid 2.5). The more polarisation electronegative attracting such as or a is represented atom. withdrawing carbon atom. Groups effect This is on by of arrow atoms the called an can electrons the pointing also exert around inductive towards a an H 2 the H electron- particular atom Cl effect C H 2 Atoms or groups more electronegative than carbon withdraw electrons H from around the carbon atom. This is called the negative inductive Cl effect (– I effect). For example chlorine bonded to carbon. C H 2 Cl C Cl Cl Atoms or electrons effect ( groups to +I the less electronegative carbon effect). For atom. This example than is alkyl carbon called groups the tend to positive bonded to donate inductive C strongest carbon. H 2 acid Cl H CH CH 3 3 Figure 5.1.2 CH C H CH 3 C CH 3 As the number of electron- withdrawing groups on the COOH carbon C 3 atom increases, the strength of the acid H H CH increases 3 increasing +I effect Key points Comparing acidity: chloroethanoic acids – The table opposite shows the pK values of chloroethanoic acid and —COO acids a dichloroethanoic The trichloroethanoic acid. We can ion explain is stabilised in acidity of the chloroethanoic acids by the inductive The more Cl atoms that are substituted in the group CH in The acid strength the greater is the electron-withdrawing (– I) increases the COOH effect on the the C The —COOH greater the carbon and –I effect, the more the electrons are withdrawn the Carboxylic the more the electrons in the O—H bond are oxygen than The more the to atoms bonded to it. acids are alcohols stronger because of drawn effect of the conjugative and atom. inductive next electron- from the towards has group. acids the carboxylic atom of the C group withdrawing of if ethanoic 3 acid, effect. effects. acids the (mesomeric) and conjugative carboxylic by the conjugative difference in acid, electrons are drawn towards the O atom in the effects on the —COOH OH group. + bond, be the weaker the bond and the more likely it is that a H ion will formed. The greater atoms The greater the –I effect, the greater is the delocalisation of So the on of Cl the carbon next to the —COOH group, charge. the number the atom negative the substituted greater is the conjugative effect and the more likely it is that greater the acidity of the a carboxylic acid. + H ion will be formed. 51 5.2 Comparing Learning outcomes acidities Introduction Ethanol On completion of this section, form should be able explain the between difference in acidity phenols mass and the difference alcohols terms of the are soluble bonding in with water . water . This is Phenol because is only they can sparingly orbitals and water large and aryl however , ethanol. is a ring solid although Why is at reduce room its less temperature. hydrogen acidic than Its bonding ethanoic higher capacity acid is molar with more water . acidic this? in and overlap The stability acidity of compounds with —OH groups of The atomic in and Phenol, than between phenols in acids understand acidity acid hydrogen to: alcohols, carboxylic ethanoic extensive soluble and you table shows the pK values for some compounds containing the a of —OH group. The lower the value of , pK the more acidic the compound. a the phenoxide and alkoxide ions. Compound Formula pK a ethanoic acid CH COOH 4.8 3 phenol H C 6 ethanol Phenol H C is a phenoxide very weak acid. OH 10.0 5 OH 16.0 2 5 It ionises slightly in water to – H C 6 OH(s) + aq Y than is An much or water Phenol is whereas can acid by O + (aq) phenoxide weaker acid than + H (aq) 5 ethanoic ion acid but it is more acidic solution appear too weak ethanol of phenol neutral an acid nor with acid to will water has a pH narrow liberate liberate will just range carbon carbon neutralise below 7 whereas universal dioxide alcohol indicator from paper . carbonates dioxide. sodium hydroxide but does. Ethoxide, We H 6 ethanoic Neither phenol the ethanol. aqueous and a water C 5 phenol Phenol form ion. phenoxide explain the comparing and differences the in structure ethanoate acidity of the of ions ethanol, phenoxide, phenol and ethoxide and ethanoic ethanoate ions. Ethanol The charge oxygen and a CH CH 3 the on atom any ethanoate because of the electronegativity of ions formed positive the O is concentrated inductive effect of on the the ethyl group atom. O 2 This increases the negative charge on the oxygen atom. So any + ethoxide + b CH 3 CH formed is more likely to accept a ion. H O 2 Figure 5.2.1 ion There is no conjugative effect to stabilise the ethanoate ion since a The ethoxide ion has ethanol does not have a C =O group. negative charge concentrated on the oxygen; b A hydrogen ion is readily attracted to the highly charged negative ion 52 The position exists as of equilibrium undissociated is so molecules far over with to the hardly left any that the ethanoate ethanol ions. Chapter 5 Organic acids and bases Phenol In the on phenoxide the oxygen phenol An Figure The delocalised can The extra The charge the the lone with system (resonance) move over a delocalisation is spread the pairs of electrons delocalised in a p- orbital electrons in the is formed which includes the oxygen effect larger reduces over the is increased because the delocalised area. the electron whole ion density rather than on the being oxygen. conned to oxygen. The increased The conjugative of 5.2.2). conjugative electrons one overlaps ring. extended (see ion, atom conjugative movement of ring rather than The position effect the of is effect greater electrons towards in the equilibrium stabilises than the the C—O the phenoxide inductive bond is ion. effect, towards so the the phenol oxygen. is further to the right compared with ethanol. + ions H are phenoxide the not ion ethoxide as is strongly less attracted likely to form to the phenoxide undissociated ion. So molecules the than is ion. Did you know? a b c O Phenol is used to make antiseptics O O such was in as ‘Dettol’ the rst surgery. operating Figure 5.2.2 The extended delocalised ring system in phenol; a ‘TCP’. antiseptic In the 19th theatres to Phenol be used century were sprayed with The isolated p-orbitals; it. b The delocalised ring system; c and Death rates from infection were The movement of electrons in the C—O bond is towards greatly reduced by its use. We do the ring not use now Ethanoic phenol because itself for it can this cause purpose burns and acid is toxic. – Some This of the p-electrons delocalisation charge is spread in the reduces over the COO the whole group electron ion are delocalised. density rather than on the being oxygen conned (the to the Key points oxygen of the O—H group). The conjugative effect stabilises the ethanoate The conjugative effect is than ion. the ion is greater in phenol, so the stabilisation The is weakly than acidic ethanol or but more water. greater . Phenol acidic of position of equilibrium is further to the right compared with Phenol is less carboxylic acidic than acids. phenol. The acidity in phenols is due + H ions are ethanoate the not ion as is phenoxide strongly less likely attracted to form to the ethanoate undissociated ion. So molecules the than to is on the delocalisation the phenoxide of ion charge with the ion. delocalised phenol a electrons in the ring. b CH C The alkoxide ion does not have 3 CH C 3 O delocalised charge associated – with Figure 5.2.3 The delocalised electrons in the COO ion; a The isolated p-orbitals; the O atom. readily accepts form molecule. a a So the O hydrogen ion to b The delocalised electrons in the carboxylate ion 53 5.3 Amines, Learning outcomes On completion should be able of this amides state the acyl halides Introduction section, Amines are thought of compounds with the —NH functional group. Amines can be 2 you as ammonia molecules in which one or more of the hydrogen to: atoms and difference in basic has been substituted functional —CONH by group. an The alkyl group. structures Amides of some have of the these compounds 2 character aromatic of aliphatic amines and amines, are shown below. amides H CH N CH 3 explain the difference in CH CH 3 character of aliphatic CH 3 N CH 3 3 basic N 2 H amines, CH 3 H aromatic amines and amides in ethylamine terms of the inductive (a conjugative dimethylamine trimethylamine and primary amine) (a secondary amine) (a tertiary amine) effects. NH = O 2 CH C H N 3 H phenylamine (an Basic aromatic character of Amines are example, weak ethanamide amine) bases. methylamine (an amide) amines The (CH position NH 3 of equilibrium lies NH 3 Amines react with + H 2 acids to O Y CH 2 form NH 3 NH 3 The table shows the pK left. For – + OH 3 salts. + CH the 2 + CH to ). + HCl → CH 2 NH 3 values for – Cl 3 ammonia and some amines. The b lower the value of , pK the more basic is the compound. b Compound Formula pK b Ammonia NH 4.7 3 Methylamine NH CH 3 Dimethylamine ) (CH 3 Phenylamine C H 6 3.4 2 NH 3.3 2 NH 5 9.4 2 Exam tips The Remember that the values of strength of a base depends on the availability b us position the information of value about pK lower the further favour of Methylamine the equilibrium the nitrogen atom to bond to a lone pairs of ion. H is a stronger base than ammonia because: : b on the equilibrium. The of the + electrons gives of pK is position to the to of right the (in so methyl the the lone density products) group nitrogen is electron-donating (+ I effect). It releases electrons atom. pair on compared the with N atom the of the electron amine density has of a the higher N electron atom in ammonia. the greater the basicity of the the lone pair on the N atom of methylamine is better at accepting amine. + H 54 ion from water (compared with the N atom of ammonia). a Chapter Secondary amines have two alkyl groups so are stronger bases than 5 Organic acids the and bases H a : corresponding primary amines. T ertiary amines, however , are weaker CH N 3 bases than ammonia. H is phenylamine Phenylamine is a amines. is because very a very weak base weak compared with CH b base? 3 : Why ammonia and alkyl CH 3 This of the conjugative (resonance effect). Figure 5.3.1 In the phenylamine molecule the lone pair of electrons in a a Methylamine is a stronger p- orbital base than ammonia because of the + I effect on the nitrogen atom overlaps with the delocalised electrons in the of the methyl group. b Dimethylamine is a stronger base than methylamine because it ring. has two + I effects. An extended atom The (see Figure conjugative electrons delocalised The can extra system is formed which includes the nitrogen 5.3.2). (resonance) move over a delocalisation effect larger is increased because the delocalised area. reduces the electron density on the nitrogen atom. The increased The conjugative movement rather The of than conjugative effect the of the stabilises greater electrons towards position is effect in than the nitrogen equilibrium is the C—N the phenylamine inductive bond is effect, towards molecule. so the the ring atom. much further to the left compared with ammonia. Exam tips + So ions H atom from compared water with are the not as stronger strongly attracted attraction to the to N the nitrogen atom in Phenylamine ammonia. making : a b azo is the diazonium dyes. Make starting point for compounds sure that you and know c N these reactions Section by referring back to 4.3. N: N: Figure 5.3.2 The extended delocalised ring system in phenylamine; a The isolated p-orbitals; b The delocalised ring sytem; c The movement of electrons in the C—N bond is towards the ring. Key points Amides Amides are much weaker bases than amines. For example the p K ethanamide is 14.1. Amides are neutral to litmus and do not Amines react acid to form salts. This is the a p- orbital on the nitrogen atom lone atom pair carbon interacts with a p- orbital on there is which This reduces not the electrons to accept on a the proton. Amines are stronger because bases the than electron- atom considerable does because the releasing of tends ammonia adjacent bases because: as with N hydrochloric behave of b delocalisation occur ability in of ammonia the lone between or pair alkyl on the O, C and N atoms the amines. the nitrogen nitrogen atom to accept a alkyl electron group density increases on the atom. Phenylamine is a weaker base + H ion from water . than lone O a O b ammonia pair C R C because electrons the on the O nitrogen R of R atom in phenylamine is C delocalised with the delocalised + N H electrons in the aromatic ring. H H H Figure 5.3.3 a The conjugative (resonance) effect provided by the carbonyl group in Amides do not are neutral react with to litmus and acids. amides stabilises the structure; b The resonance hybrids of an amide 55 5.4 Amino acids Learning outcomes The structure of Amino On completion of this section, be able explain the amino acid–base and understand state that naturally which group will (—NH undergo ) and most the of carboxylic the reactions acid of carboxylic acids. amino acids most often found in living organisms have the —NH 2 acids the term to amino acids occurring make up the carbon atom next to the —COOH group ( α-amino acids or ‘zwitterions’ 2-amino acids properties bonded amino Amino to: The of the 2 (—COOH). amines contain acids you group should acids amino are compounds proteins. shows acids). the greatly; it general can non-polar types of Most be (see structure acidic, Figure amino amino acids of basic 5.4.2). an or exist as amino neutral. Y ou do not optical acid. The Neutral have isomers. to R R Figure group groups know details H NH vary be of polar or these acid. H a can can 5.4.1 H b C C COOH C 2 COOH NH 2 2 CH R CH 3 3 or RCH(NH )COOH 2 Figure 5.4.1 a General structure of an amino acid; b The two optical isomers of the amino acid, alanine a NH CH b COOH NH 2 CH CH COOH (CH 2 c NH CH ) 2 d COOH NH 2 NH 4 CH 2 COOH 2 CH CH 3 Figure 5.4.2 COOH 2 Amino acids with a non-polar side chain and d OH 2 an acidic side chain; b a basic side chain; c a neutral a neutral polar side chain Zwitterions The basic —NH and acidic —COOH group in amino acids can react 2 with each negative an is and In The word zwitterion parts hence the An formed. electrically different Did you know? other . the of carrying This neutral the of type species. a of species ‘molecule’ formation comes from ion is two ion with The charges, is a called a positive positive one negative negative a H A the other zwitterion ion in charges two cancel neutral. zwitterion in amino acids the + lost and zwitterion. and and positive —COOH group has + ion and the —NH group has gained a H ion. 2 the German means word hybrid. zwitterions ‘zwitter’ Substances are which H containing sometimes + called H N C COO 3 ampholytes or electrolytes. A from plants amphoteric number such as of CH chemicals 3 alkaloids form Figure 5.4.3 The zwitterion of the amino acid alanine zwitterions. Amino forces acids of ‘zwitterions’. 56 are crystalline attraction between solids the because positive of and the relatively negative parts strong of ionic adjoining is Chapter Acid–base In solution, properties of amino The —COOH The —NH acids group group amino acids show both acidic reacts with alkalis reacts with acids to 5 and to basic form form properties. a metal salt. salts. 2 Amino acid acids and Section The is In as buffer base solutions within the because same they molecule have (see a Unit supply 1 of Study weak Guide , 9.7). charge placed. side act weak on The the amino following acid depends argument on the applies for type of amino solution acids in with a which it neutral chain. solution Both the in water —NH (neutral and solution) —COOH groups are ionised: 2 – +NH —CH(R)—COO 3 + The positive charge on the NH ion balances the negative charge on 3 – the In ion. COO The solution acidic The is electrically neutral. solution acid provides hydrogen ions, e.g. from hydrochloric acid. + The lone pair on the N atom of the —NH group is already 3 + protonated positively in the zwitterion. The addition of keeps H this group charged. – The —COO The amino ion acid is is a proton positively acceptor . charged. H H + + + H N C COO + H H 3 N C COOH 3 R R Did you know? In alkaline solution Amino – The alkali provides OH ions, e.g. from sodium acids may have acidic or hydroxide. basic side chains. When dissolved in + The group —NH in the zwitterion acts as a proton donor to the 3 water, hydroxide ion since it is positively an amino acid with an acidic charged. side chain This is behaves as a weak acid. – The The group —COO amino acid is remains negatively negatively charged. charged. because —COOH —NH H there groups are and two only acidic one basic group. 2 H + H H N C COO + OH H 3 N C COO (+H 2 O) 2 NH R C COOH 2 R CH COOH 2 Key points When The amino acids which go to make up proteins have —COOH and acid —NH dissolved with a in basic water, side an chain amino behaves 2 groups which are attached to the same carbon as atom. a are weak two base. This basic NH is because groups and there only 2 The general formula for an amino acid is NH CH(R)COOH. 2 one The R group in amino acids can be acidic, basic or acidic —COOH group. neutral. H The —NH group of an amino acid interacts with the —COOH group to 2 NH C COOH 2 form a zwitterion, one end of which is positively charged and the other (CH negatively charged. ) 2 NH 4 2 57 6 Polymers 6. 1 Addition Learning outcomes polymerisation Introduction Polymers On completion of this section, are molecules should be able describe the addition polymerisation describe the formation characteristics poly(ethene), and called large molecules monomers. built The up process from of a large joining number monomers of small together to: to very you of form polymers is called polymerisation . There are two types of polymerisation: addition polymerisation condensation of polyvinyl polymerisation. chloride poly(tetrafluoroethene) from their monomers. Addition In addition the polymerisation polymerisation: monomers free join together by addition reactions (usually involving radicals) Did you know? Plastics are examples of word Greek ‘that plastic word which is derived from ‘plastikos’ can monomers the C=C the polymer In ‘that which be formed’. some have which desert been can areas, planted to usually unsaturated be real trees improve planted containing the only product of the reaction. In other examples of addition polymerisation moulded’. plastic help is ‘trees’ Poly(ethene) trap The monomers are ethene, CH =CH 2 and compounds means moisture carbon the Some words, are group polymers. The the the growth between 2 of The polymer The π -bond is called poly(ethene). The common name is polythene. them. molecule The in each form conditions required to is of cables: monomer chain needed low low-density a the or poly(ethene) high pressure high-density and H H H H C C C C H H H H + ethene bonds plastic for of with carbon depends the next atoms whether ethene long. the polymer density: high pressures + reaction for and and thousands high poly(ethene) temperature Figure 6.1.1 for density breaks many bags and temperature buckets with a and special insulation are electric bottles: lower catalyst. H H H H H H H H C C C C C C C C H H H H H H H H monomers for required poly(ethene) The formation of part of a poly(ethene) chain from three ethene monomers. The square brackets show the repeating unit. Y ou the will atoms of notice monomer . the derived rather the the Note than polymer repeating from polymer . ethene that The monomer that the consists unit the in a which repeating simplest of repeating polymer when unit repeating the joined for unit is derived smallest gives the poly(ethene) (CH ). 2 58 units is from group of structure based on Chapter Poly(tetrafluoroethene) This polymer is used as a 6 (PTFE) non-stick coating for saucepans. The most ® common commercial tetrafluoroethene, brand CF F C C F F + is ‘T eflon ’. The monomer is 2 F F C C F F + tetrafluoroethene Figure 6.1.2 PTFE =CF 2 F of F F C C F F F F F F F F C F monomers C F F F F F poly(tetrafluoroethene) The formation of part of a poly(fluoroethene) chain from three fluoroethene monomers. The square brackets show the repeating unit. Polyvinyl Polyvinyl chloride chloride monomer is is the common name for CHCl =CH chloroethene, . poly(chloroethene). Figure 6.1.3 shows a The shorthand 2 way of an writing ‘ n’ is placed number only an it of the ‘ n’ is the is polymer in them front to repeating placed repeated at be the of the monomer to show that there are a large joined unit many chain: on the bottom polymer right of is shown the repeating unit to show that times. Cl H Cl n H C C H H Exam tips Addition H H putting Figure 6.1.3 polymers systematically n the by name are named writing of the poly then monomer A shorthand way of showing the formation of part of a poly(chloroethene) brackets after this. chain from a large number ‘n’ of monomers Some more examples of Monomer Repeating unit Polymer CH propene, CH polymers 3 name Common name poly(propene) polypropylene poly(phenylethene) polystyrene poly(propenenitrile) polyacrylonitrile CH=CH 3 2 2 n C phenylethene, C H 6 H 6 5 CH=CH 5 2 2 n CN propenenitrile, CNCH=CH 2 2 n Key points Polymers are molecules Addition other The by very called the molecules polymerisation addition repeating from large built up from a large number of small monomers. is when unsaturated monomers bond to each reactions. unit in monomer a polymer which when is the smallest joined gives group the of atoms structure of derived the polymer. 59 in 6.2 Condensation Learning outcomes Condensation A On completion of this polymerisation section, condensation be able describe such the of ester and an from a the formation their and HCl, alcohol carboxylic are acid examples when is two molecules eliminated and of COOH + CH 3 of an (given alcohol condensation OH Y CH 3 ethanoic Terylene occurs or react off). and The a small formation or from an reactions. acid of For chloride example: polymerisation CH describe O H 2 characteristics condensation as to: an reaction you molecule, should reactions acid COOCH 3 methanol + H 3 methyl O 2 ethanoate water nylon-6,6 from monomers. CH COCl + CH 3 ethanoyl OH Y CH 3 chloride COOCH 3 methanol + HCl 3 methyl ethanoate hydrogen chloride Polyesters Polyesters make a a polymers carboxylic acid) are polyester , an we acid with need with to at many ester linkages, —COO—. In order to combine: least two —COOH groups (a dicarboxylic with alcohol O with at least two —OH groups O (a diol). O O C C Exam tips monomers: When C dicarboxylic writing formulae for polyesters, make sure of is round. the It O O correct should be C O the C O 2 way next ester to O the COOH polyester: group diol that O the C=O acid link carbon–hydrogen ‘backbone’ derived from the Figure 6.2.1 Making a polyester from a diol and a dicarboxylic acid. The boxes represent the carbon–hydrogen ‘backbone’ in each molecule, e.g. —CH carboxylic acid, O O C C CH 2 e.g. CH 2 — 2 Terylene T erylene The is made conditions temperature a H H benzene-1,4-dicarboxylic required are catalyst of antimony( H O III) and ethane-1,2-diol. oxide H and O C C H H acid a 280 °C. O C H of from C H O H 2 O H O H 2 O 2 b H H C H C H C C C H H O O O C C link Making Terylene; a the monomers; b unit is shown in brackets. 60 H H ester Figure 6.2.2 O part of the polymer chain of Terylene. The repeating Chapter amide is formed when a carboxylic acid or acid chloride reacts with an Kevlar amine. For is COCl + CH 3 NH 3 ethanoyl a polyamide chloride Y CH 2 CONHCH 3 methylamine + acid HCl Polyamides are polymers with many benzene-1,4-dicarboxylic with hydrogen its chloride mass, than benzene-1,4-diamine. amide linkages, —CONH—. it steel used for is ve and make a polyamide, we need to times is re protective For stronger resistant. clothing It is such as In bullet-proof to by 3 N-methyl ethanamide order made example: reacting CH Polymers Did you know? Polyamides An 6 vests and re-resistant combine: clothing. a carboxylic acid) an acid with at least two —COOH groups (a dicarboxylic with amine with at least two groups —NH (a diamine). 2 monomers: O O C C NH H dicarboxylic nylon: O O C C acid + HO O O C C OH + HN H NH H + etc. H diamine O O N C N O 2 H amide Figure 6.2.3 H H H link Making a polyamide from a dicarboxylic acid and a diamide. The boxes represent the carbon–hydrogen ‘backbone’ in each molecule, e.g. —CH CH 2 CH 2 — 2 Nylon-6,6 Nylon-6,6 is made by reacting hexanedioic acid with the diamide, 1,6-diaminohexane. Key points O O O Condensation O polymerisation H ) 2 2 NH 4 C HO (CH 2 C ) 2 OH H 4 ) 2 2 NH 4 H C O (CH 2 ) 2 C O involves 4 loss of molecule, H O 2 H 2 e.g. a H O small O or 2 2 HCl, when two types of O O O monomer Polyesters, ) N ) 4 2 C ) 4 2 N ) 4 2 polyamides, e.g. are formed H by Figure 6.2.4 and C 4 nylon H e.g. O Terylene 2 react. condensation Making nylon-6,6; a The monomers; b Part of the polymer chain of nylon. The repeating unit is polymerisation. shown in brackets. Polyesters be The ‘6,6’ in the name of nylon refers to the number of carbon atoms can made from in dicarboxylic each monomer unit. Different types of nylon can be made from acids and different diols. monomers. In the school laboratory, we can use hexanedioyl Polyamides be ClOC(CH ) 4 faster . But COCl in place of hexanedioic acid because the reaction made from is dicarboxylic 2 this method is too expensive to be can dichloride used for mass production acids and of diamines. nylon. 61 6.3 Monomers Learning outcomes and Simplifying We On completion should be draw able a of this section, to: polymer from a deduce from a a can given or simplify given writing showing by monomer structures the way of writing polymerisation reactions by: you monomer polymers monomers ‘n’ an at ‘ n’ the the drawing in front of repeating bottom each unit in monomer the right-hand continuation bonds in to polymer represent in square a large number brackets, followed corner the polymer . polymer. Example 1: Addition polymerisation of ethane: continuation bond H n C= C H Exam tips Note that water there Example are molecules (2n– 2: eliminated H C C H H H Condensation O 1) H H polymerisation n to make T erylene: O in n nHO CH 2 condensation because (2n) and (i) there (ii) are there is two one O O monomers bond fewer C CH CH 2 than the 2 polymerisation number of O +(2n – 1)H 2 O 2 monomers n which combine, monomers seven e.g. for combining bonds. every there eight are only From monomer to Addition T o draw polymers, the structure Rearrange vertically Draw single the the polymer e.g. of the structure from the poly(propene) from polymer: if necessary C =C structure of propene the bond (see monomer to make Figure but the atoms Put continuation Put square Put ‘ n’ at bonds brackets the on both through bottom right the of change ends of the the square CH n CH CH CH 3 Figure 6.3.1 b CH a the n 2 polymers structure the be H 3 H H Drawing polypropene; a Rearranging the chain; b Condensation will to brackets. H H Draw bond bonds. 3 double structure. continuation the a draw out bond. T o stick 6.3.1). of structure eliminated, the of a n The polymer polyester polymer: the e.g. e.g. H for monomers —COOH and and identify —OH the in molecule the that molecules H O 2 is 62 eliminated. Remove an an link. ester OH from the —COOH and an H from the —OH to make Chapter Put continuation bonds, square brackets and ‘ n’ around the repeat unit. 6 Polymers Did you know? a Condensation ) 2 polymers do not 4 always have different to be formed from monomers. Nylon-6 two can be b formed O (CH ) 2 heating a six-sided ring O 4 compound n little Figure 6.3.2 by called water. In caprolactam this case the with Drawing a polyester; a The monomers – identifying the atoms eliminated; unit b The polymer of the nylon is —CONH(CH ) 2 From polymer to Addition T o draw a repeating polymers, the Identify structure the —. 5 monomer e.g. of the repeating poly(phenylethene) monomer: unit in the polymer and draw this without the brackets. Remove Make the the repeating continuation single unit C C 5 C H between double H H 6 bond into bonds. H H 6 the carbon atoms in the middle of the bonds. H H C 5 6 C 5 C C C C C or H H H H H H H 6 5 C C H H n poly(phenylethene) C H H 6 5 C C H H phenylethene Figure 6.3.3 Deducing the monomer of poly(phenylethene) Condensation T o draw the Identify monomer polymers structure the of the repeating monomer: unit in the polymer and ‘break’ the bonds as follows: = O = O Key points for Add back Make the repeating OH to single unit the ester C =O bond into link group between double for and the amide H to carbon link the O atoms or in NH the group. middle of We can the showing bonds. square break draw formula for bonds the a simplied polymer repeating brackets by units and with continuation here bonds. O O C C O O C C N N N The can H H H H be (i) O O of HO C C carbon repeating monomer the the polymer single unit to in atoms bonds an double of the addition bonds, or OH (ii) by adding OH or H to the H end Figure 6.3.4 a unit polymer H unit converting between N of deduced from repeating by repeating structure N Deducing the monomers of a polyamide. The added OH and H groups are of each repeating condensation unit for a polymer. shown circled. 63 6.4 Proteins Learning outcomes Polypeptides Amino On completion of this section, aids can condensation should be able react with each other to form peptides and proteins by you reactions. The acidic —COOH group in one amino acid to: molecule reacts with the basic group —NH in another amino acid 2 identify proteins occurring units naturally- macromolecules understand the as that that amino acids condense molecule. peptide are to form and a a The link. —CO—NH— When molecule polypeptide of is two group amino water is formed acids react eliminated. is called like When this an a many amide link dipeptide amino is acids or a formed condense formed. proteins. H H H two O O H amino N C C acids H H O H O H R R H O 2 H O C C H H a O dipeptide N N C C H H O R H R amide (peptide) link Figure 6.4.1 The The formation of a dipeptide with the elimination of a water molecule C—N bond conjugative either a side in the amide (resonance) of this link link effect can (see rotate. does not Section The rotate 5.3), amide freely but the (peptide) because C—C link of the bonds also occurs in H H O polyamides C condense. H H O such In ‘monomers’ as nylon, naturally can be where occurring any of 20 two different peptides naturally and monomers proteins, occurring usually however , amino the acids. CH 3 In b H H the laboratory we can make polymers from one type of amino acid O such C as poly(alanine). stepwise CH 3 addition of Our body, various however , amino acids, makes one at polypeptides a by the time. n Proteins Figure 6.4.2 poly(alanine); The formation of a The alanine monomer; Proteins are natural polymers made from 20 naturally- occurring amino b poly(alanine) acids. Protein hormones types of Proteins chain and may found all protein. sequence. primary is Each call of of them the are these 500 sequence structure we muscle, enzymes contain The in to of has a several amino acid thousands along amino the amino antibodies. of amino acids protein acids are of in a chain part of Some different acids. particular called a the protein residues. CH R C O N H CH R C N H Part of the primary structure of a protein. R, R′ and R″ represent different amino acid side chains 64 H and sequence thousand acids are O N Figure 6.4.3 blood There specific When O R skin, proteins. protein. amino hair , Chapter 6 Did you know? It can be acids, so time-consuming their common 2-aminoethanoic of amino often acids the rst acid. names out are is use glycine, Ala letters of the the full often Biochemists e.g. Gly three writing is chemical used a e.g. glycine shorthand alanine, common Pro name names way is of of rather of amino than writing proline. This the amino the names shorthand is acid. Leu Pro Ser Phe 40 Glu 37 35 Lys Thr His 43 38 Glu 42 39 36 41 Figure 6.4.4 Part of the amino acid sequence of the blood pigment myoglobin from a sperm whale. The letters in each circle are shorthand for particular amino acids. The numbers represent the position of the amino acid residues in the chain. Exam tips You should be able to —NH—CH(R)—CO— chain. In R represents living into then a by a tripeptide tetrapeptide proteins or one organisms, proteins recognise 20 different enzymes complex four than side catalyse series (containing more repeating unit in —CH(R)—CO—NH—. This of (containing contain the of three the amino acid chain. protein unit as repeats along the chains. condensation reactions. amino one a A acids residues), residues) The of dipeptide and so individual amino is first then on. chains acids formed, a Some are called polypeptides. Did you know? Wool of is a protein bre hydrogen with a helical structure wool clothes regular is washed may by a regular arrangement bonds. hydrogen If joined then at too lose high their a temperature, shape because bonds the the hydrogen hydrogen bonds bonds break. The reform in a less way. Key points Proteins The Proteins The are naturally ‘monomers’ for are formed linkage in occurring proteins by proteins polymers. are amino sequential is the acids. condensation amide (peptide) reactions. link. 65 6.5 Carbohydrates Learning outcomes Carbohydrates Carbohydrate On completion of this section, simple should be able carbohydrates carbohydrates naturally occurring as complex C H understand that the simple monomers 12 . Even 2 For So the example, general the formula molecular for most formula for y simple carbohydrates such as glucose are quite 6 carbohydrates contain several —OH groups. For the purposes of sugars the polymerisation of carbohydrates we can write a simple which carbohydrate condense water . . molecules. understanding are O O) molecules Many with (H C x is 6 identify carbon is to: glucose means you in a simplified form as HO— —OH. to form Simple sugars such as glucose and fructose are called monosaccharides polysaccharides because identify pectin cellulose, as starch examples they contain one sugar unit (mono means one and saccharide and means sugar). Sugars containing of two simple sugar units, e.g. sucrose are called polysaccharides. disaccharides. containing Formation of H H Sugars C OH The C simple sugar units are called polysaccharides. polysaccharides polymerisation polymers many of monosaccharides (polysaccharides ) is an such example of as glucose to form condensation O H H polymerisation. W ater is eliminated. A simplified diagram of this process H is C shown OH H C C H OH OH OH HO a OH Figure 6.5.2. HO simplified monosaccharide structure a in C glucose for molecule glucose O O 2 Figure 6.5.1 A glucose molecule polysaccharide Figure 6.5.2 Monosaccharide molecules condensing to form a polysaccharide. The monosaccharide is shown as HO——OH. The C—O—C The empirical (C H 6 O 10 ) 5 i.e. linkage in formula glucose these for a with sugar polymers polysaccharide water is made called from a glycosidic glucose link. is removed. n Naturally-occurring Polysaccharides as storage in plant as a found: carbohydrate cell ‘glue’ are polysaccharides walls (starch in plants and glycogen in animals) (cellulose) between plant cell walls (pectin). Exam tips These You the are not exact expected structure of to remember are such as expected glucose. to polymerisation, know the But to form how, —OH are that water is during living organisms using enzymes as all made by condensation polymerisation. Starch a C—O—C provides us with most of the carbohydrate in our diet. It is a bond of hundreds of glucose units. It can form chains or branched eliminated. chains. 66 in groups polymer and made you Starch condense are simple They sugars polysaccharides catalysts. The glucose monomers polymerise by the —OH groups at the Chapter 1- and in position also 4-positions 6 happen leads to a is condensing always between branched a 6 5 on the the and —OH chain of b C side groups form C eliminating same at water . the the chain. 1- and Note that the group Polymerisation 6-positions. can This starch. 6 6 6 6 O 4 4 C C C 1 4 1 4 O 1 1 4 O 1 O O C 2 3 Figure 6.5.3 of 6 The simplied structure of starch; a The numbering of the carbon atoms in a glucose molecule; b A simplied diagram of part of a starch chain showing the α-1,4-linkages Did you know? Glucose isomers has of several chiral glucose. The α-D-glucopyranose. ring In centres form (see used addition for Section starch glucose 1.6). There synthesis exists in a is chain are several optical called form as well as a form. Cellulose Cellulose is responsible called the also for made this β-glucose. ring have position 6 is a In from this different not glucose polymerisation always isomer , the position on the monomers. act on —H in a and space. ‘same —OH In side’ of 1 4 atoms the (see chain that of in the are glucose position group 4 of in Figure 6.5.4). 6 O 4 enzymes isomer cellulose, 6 6 O 1 4 1 4 O 1 4 1 O O 6 6 Figure 6.5.4 The different The simplied structure of cellulose. Note that the β-1,4-linkages cause the group in the 6 position to alternate in the chain. Pectin Pectin to is make found jam between set. The methylglucuronic OH —CH group acid. at the walls monomer This is position 6 of for plant the similar in cells. It formation to glucose glucose is is used of except replaced commercially pectin by is that a the Key points —COOCH 2 group. 3 The link is a β-1,4-link as in cellulose. Polysaccharides occurring 3 3 monomers O 1 4 1 of simple sugars. O 4 1 O 4 1 O The monomers in polysaccharides COOCH COOCH 3 Figure 6.5.5 naturally- made from COOCH COOCH 4 are polymers glucose 3 The simplied structure of pectin. Note that the β-1,4-linkages cause the group in the 6-position to alternate in the chain. The or linkage between called a are glucose in the usually esters. polysaccharides sugar glycosidic units, —O— is link. Did you know? Starch and cellulose are glucose polymers. Scientists have found microorganisms. hydrogen If a this produced way of producing method could be can used be as hydrogen from modied a fuel for on cars. an cellulose industrial using scale, the Pectin is a polymer methylglucuronic of acid. 67 Exam-style Answers to all exam-style questions can questions be found on the Which a types of species heterolytic ssion of best a 1 B describe covalent Module accompanying CD. Multiple-choice questions 1 – the bond products in a of C diatomic CH CH 2 2 molecule? A electrophiles B atoms C electrophiles D nucleophiles and nucleophiles D CH 3 and free radicals and free and radicals atoms Structured questions 2 What is the UPAC name for the compound below? 6 CH C(CH 3 )ClCH 3 A 2,2-chloromethyl B 2-chloro-2-methyl C 2- D 4-chloro-4-methyl CH 2 a CH 2 Explain ii 3 pentane b A difference hydrocarbon, of pentane the between i i pentane crude oil Write has P, present as a the formula C minor of Which of the following homologous the constituent H 8 displayed formulae of three isomers P. [3] pentane ii 3 and [2] 4 methyl-2-chloro empirical structural formulae. are properties of One of these isomers, when treated with hot a acidied potassium manganate(VII), produced series? two compounds, Q (C H 3 O) and R (CH 6 O). 2 i Members can be represented by a general formula. Show the steps involved in the mechanism of ii Members possess similar the reaction between iii Members possess the iv Members differ by chemical same properties. c group. a CH Q and HCN. Use curved arrows to show the movement of electrons. empirical formulae. The product formed by the reaction in b [5] ii 2 exhibits A i, ii, iii B i, ii, iv i isomerism. State the type of isomerism and its characteristic feature. C i, ii D [2] ii ii, Draw the displayed formulae of the isomers iv involved. 4 Which of the following distinguish between reagents can compounds A be and used iii to State the [2] property which allows them to be identied. B? 7 O a i Explain [1] the meaning of addition O CH CH 3 polymerisation. C H CH A acidied ii Tollen’s iii Brady’s iv NaCN A i and B i C ii D and A, forms a polymer (polystyrene). CH manganate(VII) CH 2 reagent reagent (aq) and A dilute HCl Draw the involving iii iv and ethene, polyphenylethene B potassium Phenyl 3 ii and iii ii C CH 3 i [2] 2 of part repeating of the polymer units. [2] b Dene the term ‘condensation polymerisation’. c The a iv structure three structure, polymeric B, represents the repeating unit [2] of substance. H CH O O 3 5 On complete 0.264 g Which of of combustion carbon dioxide the following a hydrocarbon and 0.054 g compounds of produced N water. correctly C C N CH C 2 H satises H B this A analysis? i Name ii Deduce the link 2 in B. [1] 2 the monomers 68 present CH structural formulae used to form the of the polymer. [4] Module c Using your explain and d List ii knowledge the difference thermosetting two classes of of their reaction between i to heat, polymers. naturally 10 thermoplastic Eugenol from [2] is an cloves. aromatic ts 1 Exam-style liquid which structural formula can is questions be extracted represented below: OCH occurring 3 macromolecules. [2] CH 2 8 Combustion gave 2.20 g contains of of 1.00 g carbon carbon, of an organic dioxide hydrogen and and compound, 1.21 g oxygen of R, water. only. R 1.00 g a of Describe with how you would the following expect reagents, eugenol drawing to react structural 3 R occupied a volume a Calculate b Deduce c R the of at 373 cm s.t.p. empirical formula of formulae R. [5] i the reacts molecular formula with the following methanoic of R. conc. alkaline i State iodine Write dichloride ii Br iii Br State [2] 4 [3] a between the following simple laboratory pairs of R and give reasons for OH and CH CO 3 your represent the reactions two would ester of a with reagents be listed observed of the by aqueous the nal monohydric monocarboxylic distinguish H [3] 2 of and organic above. Cl and CH CH draw acid sodium is reagent alcohol hydroxide. [3] the product listed and completely Cl 2 [4] iii An to compounds: [2] to displayed formula 9 test of solution. the rst formed [2] acid name what relevant (aq) 3 iii any 2 equations with giving oxide, SOCl Describe ii R and (l)/CCl 2 conclusion. ii sulphur reagents: i the products 2 acid sulphuric the [2] b of observations. above. and [3] [2] a hydrolysed 1.63 g of the ester –2 required a 2.2 moles 10 i Calculate ii Suggest the formula of iii Draw with b × i ii the State in a the the name the the and hydroxide. mass draw of the the ester. [2] of one other was of reaction replaced industrial [1] involved by an oil signicance if the The to ester A, ester or fat. of this [1] type reaction. c ester molecular formula. type [2] structural ester. displayed formula above State sodium molecular same the of of [1] below, the following reacts with ethanol according equation: O O C H 2 OH C OH 5 OR OC H 2 5 A i Give the name of the process involved in reaction. ii d Explain When a organic i [1] its industrial mixture irradiated with of the importance. ethane ultraviolet products Give and [2] chlorine light a is number One the sh of of of the process involved in this [1] the products mechanism hook of are formed. name reaction. ii this chloroethane. involved notation electrons. is to in its describe Explain production. Use the movement [4] 69 7 Data 7 . 1 Analysis analysis Learning outcomes of and scientific Accuracy When On completion of this section, we be able apply the appropriate analysis understand ‘standard of concepts scientic to between and out chemical collecting data experiments relevant to such reaction as titrations, rates, we need gravimetric are very the terms the the ‘mean’ measurements close to the true are accurate or not. Accurate to know measurements value. can get accurate data by: and difference terms our data deviation’ understand precision to: Y ou carry or whether and data you analysis should measurement ‘precision’ repeating the measurements many times repeating the measurements using using measuring instruments which using measuring instruments carefully. different are instruments very accurate ‘accuracy’ calculate the mean and standard Precision deviation from data means how close the measurements are to each other . If the provided. measurements An idea Figure of the 7.1.1, are very close difference where the to each between results other , accuracy of different they and are precise precision titres are is shown in shown. 3 3 23 cm 23 cm true 3 3 value 24 cm 24 cm 3 3 25 cm Figure 7.1.1 25 cm The black lines across the burette in a and b show four different burette readings for the same experiment; a The results are precise but not accurate; b The results are accurate (because the average is close to the true value) but not precise. Exam tips When of n thinking shooting a the at shots about a the target are difference may precise between accuracy and precision, the idea help. but not accurate. n b the shots are accurate but not precise. a A set close 70 of to repeat the b readings true value in and chemistry be should precise. have a mean (average value) Chapter 7 Data analysis and measurement Mean value The of mean is identical average A The temperature The experiment The fuel the is results of experiments. used for to the heat a rise is the For numbers xed is volume measured repeated ve experiments Experiment of after rise/ 10.1 °C + mean + data in a number water . a set time. 2 14.2 3 12.0 + 13.5 4 14.2 + 12.7 is 5 13.5 12.7 62.5 ________________________________ The the are: 10. 1 12.0 from times. 1 Temperature taken example: _____ = = 5 12.5 °C 5 Standard deviation Standard the A deviation mean. high range. A low value The normal shows we a measure shows that standard variation chemistry, is value the use data deviation expected the of that is from ‘sample how the points only the spread data out points are spread ‘signicant’ measuring standard the are out if numbers close it to over falls The from mean. wider outside instruments deviation’. a are the used. equation the In we use is: 2 S (x = x) N n – 1 S is the sample standard deviation N x is each x is the individual piece of data mean 2 Σ is the sum n is the number The standard Worked In a of (x x) of individual deviation has pieces the same titration four titres standard data. units as the data used. example experiment to nd the 3 of of are: ; 19.6 cm concentration 3 20.0 cm of an 3 ; 20.2 cm ; alkali, the values Key points 3 19.4 cm . Calculate the deviation. 19.6 + 20.0 + 20.2 + Step 1 Find the The mean is the average of a 19.4 _________________________ 3 = mean: sample 19.8 cm of data. 4 Step 2 Find the sum of the squares of the differences from the Standard of 2 (19.6 0.04 – + 19.8) 0.04 2 + + (20.0 0.16 + – 2 19.8) 0.16 + = (20.2 – 19.8) how far 3 Divide by n – 1, i.e. 0.40 ÷ 3 (19.4 – 19.8) 0.40 = the data is a measure deviates from 2 + the mean. Precision the Step deviation mean: data refers values to how are closely grouped 0.13 together – the closer the values, _____ the 3 Step 4 T ake This could the square root: √ 0.13 = be considered quite a high standard deviation as we can 3 burette to an accuracy of at least the precision. Accuracy 0.1 cm refers to the closeness read of the greater 0.36 cm the data values to the true 3 and perhaps to 0.05 cm . A value. second example is given in Section 8.1. 71 7 .2 Accuracy Learning outcomes in measurements Errors There On completion should be able assess in the this select make of section, degree of uncertainty associated laboratory appropriate are practical three main chemistry causes of errors in practical chemistry: you to: measurements pieces of in with mistakes faults limitations in in calculations, laboratory of the including mistakes with signicant gures equipment apparatus used. apparatus apparatus measurements to Weighing depending 3 For on the degree of making up small quantities e.g. 500 cm of solutions for titrations, we accuracy need to weigh to an accuracy of ±0.01 g. For accurate gravimetric work an required. accuracy that is (mass of ±0.001 g measured of or ±0.0001 g is needed. It is always the loss of mass i.e. weighing bottle + chemical) – (mass of weighing bottle alone) Exam tips Did you know? 1 When using an accurate in weighing balance, The inaccuracies can earliest alley caused by air draughts or marks on the of a balance dates from over 4000 years ago from the ndus in present day Pakistan. Simple beam balances for accurate weighing greasy have nger record be been present in chemistry laboratories since the 19th century. The weighing modern day balance for accurate work should really be called an analytical bottle. scale 2 t is out of bad an practice to try to weigh exact solid to amount, make –3 e.g. 0. 1 mol dm . an e.g. exact than rather than an gravitational analytical balance. This is because it measures force rather mass. 1.30 g solution, Volumes Pieces of and temperatures laboratory maximum errors. glassware A have calibration calibration mark is a line marks on the which guarantee glassware that 3 shows a usually shows used particular measured some in value at typical most a of volume, particular errors for e.g. temperature some pieces of (usually class Maximum 3 B volumes 20 °C). titration are The table apparatus error 3 standard ask ±0.8 cm 3 250 cm 3 standard ask ±0.3 cm 3 50 cm 3 burette ±0. 1 cm between 3 25 cm Pieces These schools. Apparatus 1 dm . 100 cm any two marks 3 volumetric of pipette glassware such as ±0.06 cm large measuring cylinders are much more 3 inaccurate, accurately. If ±1 cm The temperatures play are a part in available only 72 e.g. read to They graduation are the to be overall which the . read nearest should marks on measured, accuracy to of be used beakers the the ±0.01 °C, degree not accuracy most measuring even of more the experiment. but Celsius. are for volumes inaccurate. thermometer Some laboratory may thermometers thermometers Chapter Overall experimental Experiments apparatus should be 7 accuracy designed to get the best accuracy out of the available. 3 Burette error masses measured volumetric The the best a The to of having nearest overall 0.5–1%. precision overall apparatus the by titres 0.01 g that and are above volumes 30 cm measured , with a pipette. concentration minimised accuracy order with is So greater to three accuracy that approximately is least a than school is the this. a point For solid It to is in of be likely nal value decimal to be in results a incorrect. depend little three only quoting would will is quoting example, gures experiment accurate. of laboratory little signicant of 1 gram in there on the piece of weighing places, if the accuracy 3 of the container 100 cm you are making a solution of the solid in is 3 accurate When to making volume of Similarly, that to prepare a solutions, solution in it a is more accurate volumetric larger smaller quantities ask of a to make than a up small substance is a large volume. more accurate quantities. solutions solution the the 1 cm weighing up prepare solute a weighing Making T o only of required known degree of concentration, accuracy and we use need a to weigh volumetric out ask the to solution. 3 T o make of 200 cm a solution of known concentration, the procedure is: 3 Tip the solid from the weighing bottle into a 200 cm beaker . 3 Add about Shake W ash Pour of 50 cm pure water . ground well out the to the dissolve the volumetric solution from solid. ask the glass stopper with beaker a little into pure the water . volumetric ask using a funnel. meniscus W ash out washings W ash with Fill Add out a the to the the any little beaker several times with pure water and add calibration the mark ask. liquid pure remaining in the funnel into the volumetric ask water . volumetric ask with pure water to just below the meniscus. 3 200 cm water dropwise until the bottom of the meniscus is on the 20 ºC calibration Put the mark. stopper (bung) on the ask and shake gently. Figure 7.2.1 A volumetric ask used to make a standard solution Key points Pipettes, known The burettes maximum overall and volumetric asks have calibration marks with a error. accuracy is dependent on the piece of apparatus that is least accurate. n to volumetric the analysis, appropriate weighing number of and measuring volumes signicant gures for the should overall be made accuracy required. 73 7 .3 Standards Learning outcomes Introduction We On completion of this section, compare values. should be able understand selecting identify We have quantities already met and terms measurements such as in standard terms electrode of standard potential to: and chemical you the criteria primary the use used in standard carbon-12 enthalpy scale. In change . Relative atomic mass is measured on the addition: standards of NaHCO Standard temperature Standard pressure is 298 K. , 3 Na CO 2 , KO 3 salts as , (COOH) 3 and primary understand preparation understand criteria for of 101 325 Pa. standards Primary is its 2 standard the use of standards used in titrations the solutions calibration In order prepare to nd the standard titrating an concentration solutions unknown of alkali of a known with solution by titration, concentrations. hydrochloric acid, For we we need example, need to to when know the curves. concentration of the acid to at least two signicant gures, e.g. –3 . 0.014 mol dm by A titrating primary it We with make a standard sure primary for use that the acid has the correct concentration standard. in titrations is a chemical with the following properties: The solid It must be stable It must be readily It must give It should Primary alkalis, must able in to obtained to a very high purity. air . preferably standards be soluble reproducible reducing Some be can be examples of a high used or water results have agents in to and in a form nd stable solution. titration. relative oxidising a the molecular exact mass. concentrations of acid, agents. primary standards Did you know? The For of the highest 99.9999% standard. All calibrated accuracy purity other against is work, used as standards silver table shows laboratory. All some of primary these standards standards are commonly available to a used high in the level of purity. a are Primary standard Used to standardise this. sodium carbonate, CO Na 2 sodium acids 3 hydrogencarbonate potassium iodide, acids sodium KO thiosulphate 3 ethanedioic acid (oxalic acid), bases (COOH) and some oxidising agents 2 potassium ‘cell’ dichromate(VI), Cr K 2 meter sodium chloride, O 2 reducing NaCl Standardising agents 7 silver solutions used in nitrate colorimetry light light filter coloured sensitive cell Colorimetry source coloured Figure 7.3.1 74 is an easy and quick way of nding the concentration of solution A colorimeter shows a solutions simplied (see Unit diagram 1 of Study a Guide , colorimeter . Section 7.1). Figure 7.3.1 Chapter The electric intensity of current light instrument, we have to it must see how concentrations making a accurate taking The a the of set be the cell on of meter a In order placed of is of proportional cell. to the Before calibrate change in known standard readings meter readings are solutions meter the light-sensitive calibrated. the of on the solutions dilution procedure Put registered falling when cell. different to the using the 7 the colorimeter , different This is done by: concentrations by solution each solution. is: containing the pure solvent used to make the solutions into colorimeter . Adjust Put a the cell meter reading containing a to zero. solution of known concentration into the colorimeter . Record the Repeat these The meter meter reading. steps readings for are other then solutions. plotted against the concentrations of the solutions. For ver y dilute proportional coloured to concentrated, concentration. of the the the Figure concentration meter We coloured solutions, can, reading from of reading solution. not nd the meter the may however, solution the the be If is likely the values of the cur ve be solutions proportional calibration to to are the concentration as shown in 7.3.2. 1.0 retem )ecnabrosba( gnidaer 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 –3 concentration/10 Figure 7.3.2 Calibration curve for a coloured solution. The concentration of the coloured –3 more information about 3 mol dm solution at meter reading 0.8 is 4 × 10 For 7 –3 mol dm . colorimetry see Section 9.2. the concentration Key points Primary or Na are substances CO 2 standards other is used as a used used to in calculate of acids, alkalis titrations. primary standard to standardise acids. 3 KO can be used to standardise sodium thiosulphate. 3 (COOH) can be used to standardise bases. 2 K Cr 2 O 2 When can making measuring When made be used to standardise reducing agents. 7 to up the measuring to a solutions required of known degree concentrations calibration curve for of concentration, asks accuracy using the a should colorimeter, be and balances selected. reference should be instrument. 75 8 Titrations 8. 1 Principles Learning outcomes and of completion of this section, titration be able is of understand used to determine unknown the amount concentration. This of is substance the present procedure in a for to: determining a titration you solution should analysis titrations Carrying out A On gravimetric the basic principles the concentration of a solution of alkali: of Fill a the acid). burette with acid of known concentration (after washing it with titration. Record Put Add an Add the a colour the the burette volume acid–base acid (end Record burette initial known the of reading. alkali indicator slowly from into to the the the flask alkali burette in until using the a volumetric pipette. flask. the indicator changes point). nal burette reading (nal – initial burette reading is called titre). Repeat the process until two or three successive titres differ by no 3 more than 0.10 cm acid Titres and standard deviation volumetric pipette For our results, we take successive titres which differ by no more than 3 0.10 cm be sure below, alkali This that the gures white . is gives the 4th, us a standard experiment 5th and 6th is deviation very titres which accurate. would be For is very example selected. The low in so the mean we can table of these 32.30. and tile indicator Figure 8.1.1 Rough titre The apparatus used in an 2nd titre 3 3rd titre 4th titre 3 3 32.85 cm 32.95 cm 5th titre 6th titre 3 32.00 cm 3 32.25 cm 3 32.35 cm 32.30 cm acid–alkali titration The standard deviation (see page 71) for these 2 (32.25 – 32.30) three titres is: 2 + (32.35 – 32.30) 2 + (32.30 – 32.30) 2 3 The standard low. If we deviation took the 2nd for to the 6th 4th to titres, 6th titres however , is 0.05 cm the , standard which is deviation very is 3 much higher: 0.31 cm Titrimetric technique Using a pipette A volumetric it is lled Have Using to the a sucking Fill the mark. 76 pipette its is designed calibration solution pipette some ller , of pipette that it again is to wash up, to mark. so the be out then deliver When used the letting liquid a xed using in a drain level volume of liquid when pipette: beaker . pipette it a is with out just the into solution the above by sink. the calibration Chapter Remove Bring the pipette from the 8 beaker . Exam tips the solution meniscus just level touches down this to the calibration mark so that the mark. When Run the contents of the pipette into the clean titration flask (or a with pure Allow with the the pipette side of pipette: When sucking up the solution, water). keep a flask 1 washed using to the drain flask completely after the by keeping solution has the been tip in contact the the tip surface of of the the pipette below solution to delivered. avoid air bubbles entering the pipette. Using a burette 2 When using a Don’t of Rinse the solution Clamp Using with burette to the a burette drain with tap and the through burette funnel, the blow out the tiny amount burette: vertically add open. make solution the a little Close sure tip and of the that be the put the tap to of a are in it then allow the the remaining in the tip of pipette. burette. beaker solution while there used solution to there no air beneath be is used still the to the liquid bubbles in burette. burette in the the tip of the burette. Fill the Adjust mark. burette. the level Make meniscus Remove of sure (see the funnel. meniscus that Figure the you take to meniscus a the denite reading graduation from the (calibration) bottom of calibration marks the 8.1.2). Figure 8.1.2 Place T urn the titration flask and its contents below the Reading a burette. Your eye should be level with the bottom of the burette. meniscus. the burette left-handed). Run to in the tap This with leaves solution your the from left hand (or other hand free the burette while right to hand shake shaking if you the the are flask. flask from side side. When doing solution approached. too high accurate from a the This value (rather burette prevents for the than one rough) drop you at a titrations, time overshooting when you the must end add point the endpoint and the end more the is getting titre. Exam tips When using a burette: 1 The titration flask 2 The meniscus is is put seen on more a white clearly tile if a to make piece of white point card is placed visible. behind it. 3 The flask is arranged so that the burette tip is just inside the mouth of the flask. Key points Acid–base colour When titrations rapidly at the processing are carried end out using an indicator which changes point. titration results, the values selected should be from two 3 or three successive titres whose values are no more than 0. 10 cm apart. 77 8.2 Titrimetric Learning outcomes completion of this section, be able is sometimes understand back back the basic principles of titrations perform In a easier back to do a titration, titration a in known reverse. amount This of a is called standard a back reagent is to: added titrations you titration. should back Back titrations It On analysis: excess are calculations based on in excess reagent useful to is the solution then titrated whose with a concentration standard we wish to nd. solution. Back titrations The when: the reaction is the substance one the very slow titrations. of the end 1 The 2 A point of is volatile, insoluble e.g. is solid, e.g. calcium carbonate ammonia difcult to a observe. back titration unknown whose concentration amount out to (in nd is moles) the reacted is with an excess of known. amount of added reagent which is excess. The number sample of of moles from the Put a of excess number mass of Add small sample Shake reagent moles calcium calculated of reagent from added carbonate the titration is originally. present in a of marble of Use the in a titration flask. –3 50 cm excess). of marble 3 an titration carried Determining the is unknown from of reagent subtracted is the an substance titration in titrated procedure another 3 be reactants Calculating General to a 0.25 mol dm volumetric contents of hydrochloric pipette the flask for acid to the marble (an this. until all the calcium carbonate has reacted. 2HCl(aq) + (s) CaCO → CaCl 3 Add more reaction Titrate hydrochloric is the solution not (aq) + CO 2 acid of known (g) + H 2 O(l) 2 concentration and volume if the complete. excess using a hydrochloric suitable Worked example A of acid acid–base with a standard sodium hydroxide indicator . 1 3 sample 0.300 g of limestone reacts completely with 50.0 cm –3 of 3 hydrochloric 0.250 mol dm acid (an excess). It required 35.5 cm of –3 Exam tips acid. Make sure that sodium 0.200 mol dm you revise mass the use of: Calculate assuming that the hydroxide mass this is the of to calcium only neutralise carbonate carbonate the in excess the hydrochloric sample of limestone present. (g) ___________________ 1 moles = Step 1: Calculate the moles of NaOH × 0.200 of HCl –1 molar mass (g mol ) 35.5 _____ mol –3 2 concentration (mol dm NaOH = –3 = 7.10 × 10 mol ) 1000 moles _____________ = Step 3 volume Take the account equation. (dm of 2: Calculate the stoichiometry of NaOH(aq) moles which react with this. + HCl(aq) → NaCl(aq) + H O(l) 2 –3 mol HCl 1 mol 78 the ) = 7.10 NaOH) × 10 mol (since 1 mol of HCl reacts with Chapter Step 3: Calculate the number of moles of HCl initially 8 added. 50.0 _____ Moles HCl = × 0.250 = 0.0125 mol 1000 Step 4: Calculate the number 0.0125 7.10 of moles of HCl that reacted with the CaCO 3 –3 Step 5: - Calculate the 2HCl(aq) + × –3 10 = number of (s) CaCO 5.40 × 10 moles → of CaCl 3 mol calcium (aq) + carbonate CO 2 (g) + H 2 which react O(l) 2 –3 5.40 × 10 ___________ –3 = = 2.70 × 10 mol 2 (since 2 mol of HCl reacts with 1 mol CaCO ) 3 –1 Step 6: Calculate the mass of CaCO (molar mass = 100 g mol ). 3 –3 2.70 Worked × × 10 example 100 = 0.270 g 2 3 A solution containing –3 45.0 cm of 0.200 mol dm hydrochloric acid was 3 added to a sample 20.0 cm concentration. The of aqueous hydrochloric acid ammonia was in of unknown excess. The excess hydrochloric –3 acid was titrated with aqueous 0.0500 mol dm sodium carbonate. It 3 required hydrochloric Step 1: of 27.5 cm acid. the sodium Calculate Calculate the the moles carbonate solution concentration of sodium of to the neutralise aqueous the ammonia. carbonate. 27.5 _____ Moles Na CO 2 = –3 × 0.050 = 1.375 × mol 10 3 1000 Step 2: Calculate Na CO 2 the (aq) moles + of HCl 2HCl(aq) which → react 2NaCl(aq) with + H 3 this. O(l) + CO 2 (g) 2 –3 mol HCl 1 mol = 2.75 CO Na 2 Step 3: Calculate × mol 10 (since 2 mol of HCl reacts with ) 3 the number of moles of HCl initially added. 45.0 _____ Moles HCl = –3 × 0.200 = 9.00 × mol 10 1000 Step 4: Calculate the number of moles of HCl that reacted with the NH 3 –3 9.00 Step 5: × 10 Calculate –3 – the 2.75 × –3 10 number of = 6.25 moles × + NH (g) → NH 3 mol of ammonia + Cl which react. – + HCl(aq) 10 (aq) (aq) 4 –3 = 6.25 × (since 10 1 mol of HCl reacts with 1 mol NH ) 3 Step 6: Calculate the concentration of the aqueous ammonia. 1000 _____ –3 6.25 × × 10 –3 = 0.313 mol dm (to 3 s.f.) 20.0 Key points n a and back titration, volume is excess added to of the one of the reagent reagents under of known test. The excess concentration reagent is then titrated. The amount originally n of substance added titrations, – moles calculations consumed substance involve in a back titration calculated from use of the the = (moles relationship: 3 concentration (in mol dm ) substance titration). 3 = amount (in mol) ÷ volume (in dm ) 79 8.3 Redox titrations Learning outcomes ntroduction Redox On completion of this section, titrations reducing should be able reagents. the basic principles calculate is the concentrations carried out in a of similar oxidising manner or to acid–base titrations. the The indicator used can be: one of reactants which acts as an indicator because it exhibits a titrations perform calculations based colour when the reaction is complete and it is in excess on redox to titration of particular used The to: understand redox are you an added redox indicator which changes colour when the reaction is titrations complete. describe the titration in use the of a redox analysis of iron tablets. Potassium Potassium manganate(VII) manganate( vii) is a good as a redox oxidising indicator agent. It can therefore be 2+ used to O H 2 calculate (hydrogen the concentration peroxide) or of reducing ethanedioic acid agents (oxalic such as ions, Fe acid). 2 burette In acidic in potassium solution, iron( ii) ions react with the manganate( vii) ions, MnO , 4 potassium manganate( vii) according to the equation: manganate () solution 2+ 5Fe – (aq) + MnO + (aq) + 8H 3+ (aq) → 5Fe 2+ (aq) + Mn (aq) + 4H 4 pale green Figure In acidified solution of deep 8.3.1 this shows O(l) 2 purple the yellow apparatus used for very this redox pale pink titration. titration: Potassium manganate( vii), KMnO , is added gradually from the 4 iron () sulphate burette Figure 8.3.1 When to the the acidied potassium solution of iron( manganate( vii) is ii) sulphate added to in the the flask. flask it loses it The titration of aqueous purple colour . This is because the purple ions MnO are changed to 4 iron(II) sulphate with potassium 2+ almost manganate(VII) When colourless just enough 2+ ions Mn by potassium reaction with manganate( vii) the Fe has ions. been added to the 2+ flask to react potassium with is indicating Did you know? the This not in is this results the added, ions, Fe manganate( vii) purplish-pink. indicator all end in the addition the point because redox the of of solution the a in the titration. potassium further drop flask Note that manganate( of turning vii) an is self reaction. Permanganate titration: worked example 2+ Potassium manganate(VII) is not Iron tablets contain Fe ions as iron( ii) sulphate. One iron tablet is 3 suitable as a primary dissolved standard in excess sulphuric acid and made up to in 100 cm a volumetric 3 flask. because, on standing, it gives A sample of 10.0 cm of this solution was titrated with a –3 0.001 00 mol dm brown precipitate of 3 potassium manganate( vii), KMnO . It required 22.5 cm 4 manganese(IV) 2+ of oxide. Hydrochloric acid should Calculate be used as the acid in manganate( vii) potassium to react completely with the Fe ions. not the mass of iron( ii) sulphate (M = 151.9) in one iron tablet. permanganate – titrations because its Cl ions get 22.5 _____ Step 1: Calculate moles of the KMnO = × 0.001 00 4 oxidised to Cl . 1000 2 –5 = 2.25 × 10 mol 2+ Step 2: Calculate (see moles of Fe using the stoichiometric above). –5 2.25 80 × 10 –4 × 5 mol = 1.125 × 10 2+ mol Fe equation Chapter Step 3: Calculate the mass of iron( ii) sulphate in the flask (from 1 8 Titrations and gravimetric analysis tablet) Exam tips –4 1.125 × –3 10 × 100/ 10 = 1.125 × 10 mol 3 We divided by 10 because n 3 10 cm of the 100 cm were taken potassium manganate( VII) for titrations, you are allowed to read titration. the burette from the top of the –3 Mass of iron( ii) sulphate = 1.125 × 10 × 151.9 = 0.171 g meniscus This is intense Potassium dichromate(VI) titrations rather because that bottom you method titration but is a similar redox to the method indicator is used added. for a potassium( Potassium vii) 2 O 2 , contains dichromate ions, Cr 7 O 2 For dichromate( time vi), that example: before 2– (aq) + Cr light In green this A + O 2 (aq) + 14H cannot is see so the doing titrations the reading colour the leave a burette little of so on the side the above the meniscus 7 burette 2+ 6Fe bottom. manganate 2– Cr K the colour properly. When permanganate The than the 3+ (aq) → 6Fe 2Cr (aq) + 7H O(l) 2 orange just is 3+ (aq) + 7 yellow deep minimised. green titration: redox indicator such as sodium diphenylaminesulphonate is added 2+ to the solution Fe obvious and in sudden the flask. colour This change is because when a we small cannot volume see of an orange 3+ solution Potassium acidied is When the to a green dichromate( vi) solution the end added colour point in has is iron( ii) of the been solution added containing gradually sulphate flask in changes the from ions. Cr from the burette to the flask. greenish to deep purple, reached. Sodium thiosulphate titrations Sodium thiosulphate, Na S 2 concentration of iodine S 2Na 2 O 2 in (aq) O 2 , is useful + I 3 (aq) The determining redox → Na 2 colourless for the 3 solution. S 2 brown O 4 rection (aq) + is: Key points 2NaI(aq) 6 colourless colourless In this type another in of titration, reaction. acidic For we are example, often the determining reduction of the iodine iodate ions released by iodide by titrations agents ions such – – (aq) + 5I (aq) + 6H+ → 3I (aq) + 3H 2 of of determining the the oxidising or sodium O(l) n many redox iodine liberated amount of in such oxidising reactions agent, titrations an 2 indicator titration involve potassium thiosulphate. 3 The as manganate(VII) solution: IO Redox such gives as us , IO a method present in one a of indicator 3 is the not added reactants by giving a because acts as an specic solution. colour In sodium thiosulphate titrations: The colour where Sodium thiosulphate is added gradually from the burette to solution of iodine in the When drops the of starch When react iodine starch. sharpens just with in This the enough all the the flask has produces end intense very pale yellow, blue–black add colour . a involved The addition has of a been further added drop to of the flask need in the disappearance of the titrations is from blue colour . A or purple colourless to to purple. titrations to an involving dichromate(VI) added redox usually indicator. thiosulphate results Redox potassium thiosulphate the in manganate(VII) few point. sodium iodine, change flask. become an excess. potassium colourless in the is (acidied) when colourless solution The amount of iron in iron is tablets can be determined by a formed. redox titration with potassium manganate(VII). 81 8.4 Some uses Learning outcomes of ntroduction In On completion of this titrations section, Section 8.3, determine should be able the describe analysis examples in the substances cleaners, aspirin, saw mass how potassium iron( ii) of manganate( sulphate present in vii) can iron be used tablets. to Many to: household we you of titrimetric quantication (vinegar, vitamin C of household Others, are products such alkaline. acid or as or medicines indigestion Titrimetric alkali present in such (antacid) analysis these can as vinegar tablets be and used to and aspirin some are acidic. household determine the cleaners amount of substances. tablets, antacids). Determining the The acid vinegar present can hydroxide indicator strong be of as base titration in vinegar found known by value, is mainly titration acid Unit the content of vinegar of 1 is a vinegar is sample acid. of The vinegar Phenolphthalein weak Study ethanoic a concentration. ethanoic (see acid acid Guide , and Section usually is sodium 9.6). diluted by a total with used acid as an hydroxide T o get factor a of in sodium is a suitable two. Did you know? Good quality vinegar from a contains great variety of by fermentation. The convert acid ethanol to Analysis of Aspirin can Hydrolysis heated CH COOC Back H a acid used by volume. inegar may rice, sugar can cane, in the fermentation acid. Although acids to two neutralisation sodium acids, happen be ethanoic present salicylic at in acid small be made palm, etc.) process is the main amounts. the acid same and time COONa + HOC 3 can be used ethanoic if the acid. aspirin is hydroxide. COOH + 2NaOH → CH procedure to quantify H 6 the amount of COONa + H 4 acid mass hydroxide of of aspirin known tablets in a flask concentration and and present. boil with volume excess for 10 minutes. Cool the mixture and titrate the excess sodium hydroxide with –3 H 0.05 mol dm SO 2 The ‘acid – Analysis of Many antacid magnesium crushing known mol of the NaOH red or phenolphthalein indicator . acid from is found by: mol NaOH used in the titration. antacid tablets tablets contain hydroxide the tablet, then (aq) 2 magnesium present concentration Mg(OH) 82 phenol 4 content’ hydrolysis using be reacting and + can hydroxide. found it with The amount hydrochloric volume: 2HCl(aq) → of by: excess MgCl (aq) 2 + 2H O(l) 2 O 2 is: known sodium plant 4 titration Put bacteria (ethanoic) natural 5% (apples, other fruits, acid hydrolysed excess 6 least aspirin and with 3 The be sources acetic acetic in vinegar, other at acid of Chapter back titrating methyl the amount added to of the Analysis of Sodium excess Many bleaches sodium excess acid magnesium tablet – mol in contain liberated adding using is can be found from: mol HCl titration chlorate( After potassium SO i), suitable NaOCl. This dilution, the is commonly bleach is treated iodide. (aq) → I 4 then starch from (aq) + NaCl(aq) + K 2 titrated indicator as SO 2 with the standard colour of sodium the (aq) + H 4 O(l) 2 thiosulphate iodine Exam tips fades. peroxide in household cleaners do household cleaners contain hydrogen peroxide. Hydrogen be determined titration with (aq) + acidied potassium by 6H (aq) + 5H O 2 adding titrating excess the manganate( vii) potassium iodine (aq) 2Mn (aq) + 8H O(l) + 5O 2 iodide liberated → 2 with under acidic sodium – 2I know vitamin C, the DCPP indicators. You or should aware, however, indicators have one reduced in the two that redox colour forms, state and one in 2+ 4 of redox to by: + 2MnO have peroxide be can not structure other Some analysis screened You Hydrogen gravimetric cleaners sodium hypochlorite. acidied iodine hydroxide and bleach 2 solution, sodium hydroxide HCl household NaOCl(aq) + 2KI(aq) + H The with Titrations indicator chlorate(I) called with the orange 8 (g) the oxidised state. 2 conditions and thiosulphate. + (aq) + H O 2 (aq) + 2H (aq) → I 2 (aq) + 2H 2 O(l) 2 Determining vitamin C Vitamin such as C (ascorbic oranges determined (DCPIP). colourless addition reduces using This in of acid) and a redox indicator its is reduced vitamin found lemons. C, It is in a indicator is blue form, in or DCPIP many good called colour pink goes if fruits, reducing especially agent. It citrus can fruits be 2,6-dichlorophenolindophenol in its the oxidised conditions colourless (or pink) form. are as It is acidic. the On vitamin C it. Key points H H H C C C O O C O The acid in vinegar determined C OH C H sodium The be titration with hydroxide. of tablets salicylic can be acid in determined The structure of vitamin C (ascorbic acid) using The by amount aspirin Figure 8.4.1 can H vitamin C content of fruit juice can be determined in the a back titration. following A back titration can be used way: to Pipette a known volume of fruit juice (suitably diluted) into a determine the amount of titration magnesium hydroxide present in flask. antacid Add 1% DCPIP solution from a burette, drop by drop to the vitamin C solution and shake the flask The The end point is when the amount blue colour of the nal drop of DCPIP household fade when added to the using titration value can be compared with the values obtained by known concentration of pure a be sodium vitamin C with the same titration. titrating a chlorine can solution. thiosulphate The available cleaners does determined not of gently. in tablets. solution itamin C can be determined of using a redox indicator. DCPIP . 83 8.5 Titrations Learning outcomes without Conductimetric titrations Some On completion of this indicators section, ions conduct electrical charge better than others. For example, the you + conductivity should be able of and H OH ions is very high compared with that of Cl to: 2– or ions. SO During a reaction where ions are produced or consumed, 4 understand the potentiometric, and principles the there thermometric conductimetric analyse of results titrations Figure by in electrical conductimetric conductivity. titration These using the changes can apparatus be shown in 8.5.1. of an acid–base titration, the base is added in small measured amounts thermometric from and changes measured In potentiometric, are conductimetric the burette to the acid in the beaker . After each addition, the meter titrations. reading shown burette is in taken. Figure T ypical results for strong and weak acids and bases are 8.5.2. meter containing alkali base strong weak ytivitcudnoc magnetic acid strong base magnetic stirring acid base mS( 1– ytivitcudnoc acid weak ) mS( 1– electrode acid strong ) conductivity strong bar weak acid weak base stirrer Figure 8.5.1 volume of Apparatus for a base volume of base conductimetric titration. The Figure 8.5.2 concentration of alkali in the burette is Changes in electrical conductivity for titrations involving strong and weak acids and bases; a With strong bases; b With weak bases about 20 times the concentration of the acid in the beaker to minimise dilution. The end graph. a point Y ou weak Strong can in these see acid–weak titrations that base acid–strong you can is shown use this by the method ‘break-point’ to nd the in end the point of titration. base: Both acid and base are fully ionised. As the + titration proceeds, ions OH combine + H with H ions: – (aq) + OH (aq) → H O(l) 2 The is conductivity an excess Weak fully of falls OH acid–strong as more ions base: and The water is formed. conductivity acid is only rises After the end point, there again. partially ionised but the base is ionised: – CH COOH(aq) + – OH (aq) Y CH 3 COO (aq) + H 3 O(l) 2 Did you know? + The Conductimetric titrations for concentrations are conductivity solution. There (when excess) is is low a to break start in with the because conductivity there are curve few H because ions OH in ions useful in are better conductors than COO CH ions. 3 determining in + precipitation reactions, e.g. Ag (aq) + Weak base–strong acid: The base is only partially ionised but the acid – Cl (aq) → AgCl(s) fully ionised: + H (aq) + + NH (aq) Y 3 NH (aq) 4 + There is a break in the conductivity curve + excess) are better conductors than NH 4 84 because H ions (when in is Chapter 8 Titrations and gravimetric analysis Potentiometric titrations Potentiometric potential, as E titrations the involve titration measuring proceeds. An a change example is in the electrode titration of , iron( ii) ions with cerium( iv) ions. 2+ Fe The used apparatus rather platinum is than is 4+ (aq) + shown a easily Ce in 3+ (aq) Figure hydrogen → Fe 8.5.3. electrode 3+ (aq) A + Ce standard because the (aq) calomel latter is electrode bulky and is the ‘poisoned’. meter 4+ Ce (aq) calomel 2+ electrode Fe (aq) platinum (Pt) electrode magnetic stirring Figure 8.5.3 magnetic bar stirrer Apparatus for a potentiometric titration 4+ The solution of Ce ions is added in small measured amounts from the 2+ to reading is the ions Fe in the beaker . After each addition, the meter llec burette 2+ At the equivalence point when the ions Fe E taken. have equivalence 4+ completely reacted with the ions, Ce there is a sharp change in the point value of E (Figure Potentiometric potassium 8.5.4). titrations dichromate are or useful when potassium coloured manganate( solutions vi) are used such as as titrants. 4+ volume of Ce Figure 8.5.4 added Change in electrode 2+ potential for the titration of Fe Thermometric titrations ions with 4 + Ce Ther mometric enthalpy or displacement added an titrations changes. in small insulated temperature It are be reactions, measured beaker is can with taken. useful applied including amounts results a reaction acid–base the an After to the each exothermic signicant redox reactions. burette stirring. for produces reactions, precipitation from continuous T ypical when to A reactions solution substance addition, and ions is in the an Key points endothermic equivalence reaction point is are shown shown by a in Figure sharp 8.5.5. break in Y ou the will notice that the curve. n potentiometric, and the thermometric conductimetric end ) C°( ) C°( erutarepmet erutarepmet break point in the is titrations, shown line of the by a sharp relevant graph. Conductimetric on the ions relative present titrations mobility as the depend of the reaction proceeds. 3 volume added (cm ) 3 volume added (cm Potentiometric on Figure 8.5.5 Change in temperature during thermometric titrations a titrations depend ) the change in E values as the for an exothermic reaction proceeds. reaction; b for an endothermic reaction 85 8.6 Gravimetric Learning outcomes analysis ntroduction Gravimetric On completion of this section, analysis be able understand which the principles gravimetric describe analyses the function equipment analysis funnel, silica describe is used in of the weighing amount a of compound one of the of known substances and ovens how main steps present. are: preliminary precipitation treatment, ltration washing drying weighing calculation e.g. dissolving or pH adjustment are some gravimetric (suction flask, crucibles, determine on based to to: The involves you composition should (1) suction the or precipitate ignition of the precipitate sintered-glass the dried precipitate (to three or four decimal places) and furnaces) gravimetric used to determine the of the amount of the element to be determined. analysis moisture Did you know? content of soils and amount of water in to nd the hydrated Theodore salts. (1914). these Richards He was developed techniques to Precipitating a A suction sintered-glass 8.6.1 base used flask shows a the rst American many of the determine accurate and filtering and funnel is sintered-glass to win techniques used a to (ground of atomic a Nobel Prize for Chemistry gravimetric masses of analysis. about 25 He used elements. sample lter and glass) wash crucible precipitates. and a Figure suction funnel filter for ltration. crucible All the solid container to suction The pump pump is Any transferred of suction the on solid water and the down is until (Buchner) to the precipitate crucible remaining stream The be turned sintered-glass b must containing a solid funnel is the liquid glass transferred no funnel into washing out the to be ltered is directed into the rod. to the remains not by funnel: used crucible in in the using beaker accurate or a gentle glass rod. quantitative work filter porcelain paper base but is useful for ltering salts which have been puried by crystallisation. with holes Washing Figure 8.6.1 a sample Two pieces of apparatus for filtration; a A sintered-glass crucible; b A suction funnel (Buchner funnel) When washing a precipitate care must be taken to prevent any redissolving. The Small W ashing in precipitate the amounts with a is of (see water makes Unit 1 for or solution precipitate redissolve washed no other longer solvent containing it less Study than an likely Guide , are ion that necessary. used. which any Section is common precipitate to one will 8.7). Drying The precipitate necessary separate of 86 so in that the the container . crucible + ppt – porous sintered-glass precipitate The mass mass of of does not precipitate crucible crucible have alone). can to be then can be oven-dried transferred be found to if a from (mass Chapter Surface at All When water heat a is or that mass Compounds day A in a place be salts, used since method nd the is free a precipitate by drying for 1–2 hrs some of the are of higher high to be air-dried. temperature temperature is carried in out decomposed The phosphorus( solids of to damp v) crystallisation in a in an furnace oven. to red several times until by heating, solid is left e.g. to dry for a the may be be soda lime hydrated lost. moisture content (s) + nH 2 mass (m or for of of soils and chloride BaCl 2 crucible gel used salts. barium O(s) → silica not heating hydrated mass empty oxide, should determine water nH but mass on used of 2 clean a precipitate crystallisation of a a at dust. water be at likely be many original Weigh heated loss of can heated obtained. dry BaCl from ‘ignited’. containing amount Water of is should to Finding the to when is which salts desiccator can it ‘ignition’ constant This removed removed say hydrated be precipitate we Drying a can 110 °C. water 8 O(g) 2 residue mass lost ). 1 Half ll the empty crucible with BaCl nH 2 Heat gently Let Reheat the at rst crucible as then cool many more strongly completely times as then necessary O and reweigh (m 2 to ). 2 red heat. reweigh. until constant mass is obtained ). (m 3 The loss in mass (m – m 2 to calculate nH BaCl 2 the O. For the is process heated prevent loss of and the residual mass (m – m 3 moles calculation of water see of Section ) can be used 1 crystallisation per mole of 8.7. 2 Determining the The ) 3 number of at is similar about organic water . moisture to 110 °C material The that to content of above. An constant from percentage being (%) of soils accurately-weighed mass. burnt. water A low The by sample temperature loss mass of in mass the is soil is due can of soil used to to the then be calculated. Exam tips Key points f Gravimetric analysis involves weighing a compound of known asked about substance to determine the amount of one of the substances The main drying Loss with and of a Drying steps in analysis are to need dry to a know precipitation, ltration, the substance: washing, 1 decomposes 2 reacts readily weighing. material common of gravimetric you present. whether how composition in precipitates is reduced by using a wash material in ion. material decomposition. washing should be carried out to a constant weight and without 3 a with readily or any drying agent used dessicator gains readily water from loses water to the the air air. 87 8.7 Gravimetric Learning outcomes analysis Determining the hydrated On completion should be able of this section, perform to: In calculations based the last moles obtained from moles of water in a salt section of water we in introduced hydrated an experiment barium chloride. to By calculate weighing the a number sample of on barium data number of you of (2) chloride before and after heating, the mass of water lost can be gravimetric found. analysis nH BaCl give examples of the use 2 of gravimetric analysis in O(s) → BaCl 2 original (s) + nH 2 mass mass of O(g) 2 residue mass lost quality control. Worked When example 0.611 g 0.521 g of chloride. of hydrated residue are values: (A 1 barium formed. Ba = chloride Deduce 137.3, Cl the = is heated formula 35.5, O to of constant hydrated mass: barium =16). r Step 1: Calculate the loss of mass Step 2: Calculate the number of water: 0.611 – 0.521 = 0.090 g 0.090 ______ of moles of water = –3 = 5 × 10 mol 18 Step 3: Calculate the moles of residue (BaCl ) 2 0.521 ______ –3 = = 2.5 × 10 mol 208.3 Step 4: Calculate the mole ratio of water to BaCl 2 –3 BaCl : H 2 So formula is O = 2.5 BaCl ·2H weighing dissolving adding The be a : 5 × 10 = 1: 2 ratio O. 2 Determination of can 10 2 2 Chlorides × –3 determined sample the nitric of the sample acid chloride chlorides in then by: solid metal chloride water excess precipitates as silver silver nitrate to the chloride solution. chloride: – Cl (aq) + AgNO (aq) → AgCl(s) + NO 3 collecting washing drying weighing Note: silver the the the The chloride chloride formed with (aq) 3 by ltration distilled water chloride the mass of experiment chloride is silver should sensitive to chloride be formed. carried out in a darkened room because light. Exam tips Calculations analysis involving usually precipitation gravimetric depend reactions. Worked example A sample Make sure 0.497 g water . that you know the Excess in the of a chloride acidied silver of a Group nitrate is I metal, added to Z, the is dissolved solution. tests for halides precipitate is ltered and dried to constant mass. The mass of and silver chloride formed is 0.957 g. Deduce which metal is present sulphates. –1 original chloride. (AgCl = 143.5 g mol ; A chlorine r 88 in The precipitation resulting reactions 2 on = 35.5). in the Chapter Step 1: Calculate the moles of silver 8 Titrations and gravimetric analysis chloride: 0.957 ______ –3 = = 6.67 × 10 mol 143.5 Step 2: Calculate the = 10 mass of Cl ions in AgCl: –3 Step 3: 6.67 Calculate 0.497 Step 4: × – the Z the is a 35.5 mass 0.237 Calculate Since × = = of 0.237 g metal 0.260 g moles Group I of of in the metal chloride: Z metal metal, present 1 mol of and Z so atomic forms 1 mol mass: of chloride ions: ZCl(aq) + AgNO (aq) → AgCl(s) + ZNO 3 (aq) 3 mass of Z ________________ So: mol Z = atomic mass of Z mass of Z 0.260 _________ atomic mass of Z ___________ = = = 38.9 –3 moles Potassium Worked Deduce is the Group example the formula I metal Z which 6.67 has an × 10 atomic mass of 39. 3 of magnesium chloride from the following information: 0.635 g of magnesium chloride, MgCl reacts with excess silver nitrate. x –1 The mass of chlorine A silver = chloride 35.5, A r formed magnesium is = 1.914 g. (AgCl = 143.5 g mol ; 24). r 1.914 ______ Step 1: Moles of silver chloride: = = 0.0133 mol 143.5 Step 2: Mass of Cl Step 3: Mass of magnesium 0.635 Step 4: Moles – ions 0.472 and in = mole AgCl: in = the 0.0133 × 35.5 magnesium = 0.472 g chloride: 0.163 g ratio: Key points 0.163 ______ mol Mg –3 = = 6.79 × 10 mol 24 –3 So mole ratio = 6.79 × 10 Calculations Mg: 1.33 × 10 gravimetric mol Cl to nd which is 1 mol Mg: 2 mol the formula is on analysis molar can be used composition of Cl particular So based –2 mol compounds. MgCl 2 Calculations gravimetric Gravimetric analysis in quality control to in Gravimetric analysis can be used determine the amount of elements such as phosphorus in conversion to insoluble determine sulphur dioxide magnesium in ammonium quality to barium the air and in wine or fruit drinks determine the a be of hydrated used water salt. analysis control to can be used determine % water in soil and in foods (by to determine the amount of sulphate) particular of can number phosphate) and conversion mole Gravimetric the the fertilisers in (by one on to: calculate based analysis chloride ions present in our water supply elements in soil and (by foodstuffs. conversion to silver chloride). 89 9 Spectroscopic 9. 1 Electromagnetic Learning outcomes The methods radiation electromagnetic Electromagnetic On completion of this section, be able explain the nature various types of electromagnetic of these types frequencies. of For and frequency × waves that have electrical directions, e.g. and light radiation are shown in waves. Figure 9.1.1. has specic light waves ranges have a of wavelengths frequency of ultraviolet 14 – 10 7.5 × 10 Hz. All these types ranges of X-rays, (UV), visible, of electromagnetic 8 travel radiation example, 14 and of particular approximate wavelength 4.5 (IR) in radiation and recall the vibrating of Each electromagnetic components to: The consists you magnetic should radiation spectrum at the same speed in air , 3.0 × radiation –1 (or 300 000 000) m s 10 infrared radio waves recall that energy levels in Speed, frequency atoms and wavelength are quantized The recall the relative energies and speed of wavelength electromagnetic by the radiation is related to frequency and equation: dangers of various types of c = f λ radiation –1 where: calculate energy equations E = hν using and c is speed in m s the f E = hc/λ is frequency (number of wave crests per second) in hertz, Hz. –1 (1 Hz λ is = the 1 s ) wavelength in m Did you know? Note: About 100 years gamma-rays ago sources (γ-rays) were emitting put pillows of some people, mistaken sleep. belief that Now we smaller it would second). often used for frequency when electrons are being the wavelength, The greater the the greater frequency, is the the frequency greater is the (the more amount waves of help transferred. So gamma-rays ( γ-rays) and X-rays carry a huge know that these amount rays is under energy them ν considered. per the symbol under The the The of energy. Because of this they are very dangerous. They can are very dangerous. easily penetrate the skin and damage cells in the body. Even ultraviolet 14 frequency v/10 Hz 4 wavelength 5 6 7 600 500 8 λ/nm 700 400 elbisiv 5 6 10 7 10 frequency 10 8 10 9 10 10 10 3 –3 10 13 10 14 15 10 10 16 10 17 10 18 10 19 10 20 10 1 wavelength Figure 9.1.1 10 –6 10 –9 10 λ/m low frequency 90 12 10 v/Hz wavelength long 11 10 The electromagnetic spectrum high frequency short wavelength Chapter rays and (UV rays) damage have to the enough eyes if energy we are to cause exposed harmful to them burns, for long skin 9 Spectroscopic methods λ cancer enough. a Energy quanta a λ In Unit have 1 Study certain 9.1.3 shows Guide, xed the Section values of 1.3, energy . movement of an we learnt These that values electron electrons are between called energy in atoms quanta. levels in only Figure an Figure 9.1.2 atom. Wavelength (λ) and amplitude (a). Wavelength is the distance between any two similar points on the a b n = 3 c wave. Did you know? n = 2 photon (radiation Although X-rays are dangerous, emitted) they are ‘see’ the still used bones in in small the ‘doses’ body to and for n = 1 sterilising hospital equipment. electron Figure 9.1.3 Movement of an electron between energy levels; a Atom in the ground state; b Excited electron; c Electron falling back to ground state Did you know? When a quantum of energy is absorbed by an electron in the ground In state atom the electron is excited to a higher energy 1906 light When an electron falls back to the ground state Einstein again, it gives out was of energy as radiation. We can also think of this energy packets as In called a The energy difference involved is given by the is we energy that the related can and called Broglie energy of a = Planck of its mass. electrons Nowadays as of waves as having well as of hν (Hz) constant –34 (6.63 × 10 of the frequency particles. radiation speed to ( J) frequency ∆E to regard properties –1 J Hz ) light Key points c ____________ frequency de equation: radiation Since: energy Louis photon. photon of 1925 a suggested particle that a photons. quantum suggested level. __ = or ν = wavelength λ Electromagnetic radiation can hc ___ we can also write: ΔE be = regarded as waves that have λ a We of a can use this particular excited limit, atom. we can equation to wavelength If the calculate or frequency calculate the the frequency of is energy radiation ionisation emitted emitted is from measured energy of the when a radiation the (see Speed The = frequency Guide , Sections 1.3 and × wavelength. convergence Unit spectrum of electromagnetic 1 radiation Study and previously at atom characteristic frequency wavelength. ranges from radio 1.4). 7 waves (10 Hz) to gamma-rays 19 Worked example Calculate the (10 energy of an electron transition which emits radiation Hz). Light waves have a frequency 14 frequency 1.01 × 4.5 Hz. 10 –34 Planck constant = 6.63 × 10 × 10 Energy into the equation ΔE = 10 12 × 1.01 we × 10 are the asked for Avogadro the value number , 6.70 × 10 J The energy per 6.02 mole × of electrons, we multiply the –22 × 10 23 × 6.02 Hz. atoms × 10 they can are only have 23 = values. 6.02 × 10 is associated given by with E = hν, a where value c 10 is the Planck 6.70 10 –22 = 23 by – energy photon If in × hν –34 × 7 .5 levels certain 6.63 14 – J s. quantized Substituting of of 12 speed of light and h is constant. –1 = 403 J mol 91 9.2 Beer–Lambert’s Learning outcomes Introduction In On completion of this section, be state use able Beer-Lambert’s given used 1 Study to the law law in The absorbed by to of a measures explain visible the origin and UV explain absorb why of the in absorption and the UV others describe the samples by steps visible understand chosen solution. A and 13.3 of the UV and spectrometer select a calibration concentration in to (Section Beer–Lambert’s molecules and we saw coloured how a colorimeter molecules 7.3). of A depend curve wavelengths for a or ions Both that particular in using a a and spectrometer narrow colorimeter Beer–Lambert’s are lter absorption substances regions. on of UV-visible specic visible band range of and law. do in the refers to light passing through a solution. Absorbance not analysing spectroscopy use law visible of to light solution passes is 7.1 concentration in refers is needed T ransmittance regions Sections the spectroscopy some light is wavelengths solution lter the colorimeter concentration species solution. UV-visible Guide , determine to: Beer–Lambert’s calculate Unit you is should law 0%. the absorbed by absorbance through a a is solution, Absorbance ( A) is solution. 0% and the If the all the to passes transmittance absorbance related light is 100% transmittance and ( T) through 100%. the by If no a light transmittance the equation: visible spectroscopy A = – T log 10 understand the use of Beer–Lambert’s complexing coloured and reagents compounds detection law states that: to form (sensitivity limits). the amount the solution the amount through In of light absorbed is proportional to the concentration of light absorbed is proportional to the distance the solution (the path length, it of travels l). symbols: Did you know? proportionality Beer–Lambert’s law is a combination concentration = absorbance of two to the laws: effect Beer’s of the law which absorbed concentration and of light refers by a to pure the Lambert’s absorbance liquid. solution light light travels law through which ε lc refers distance on constant solution of The constant, absorbance, ε, A, is called when the the molar light travels –3 without The –1 . 1 mol dm absorptivity. It has units of for 3 mol 1 cm It gives through a a value of solution the of –1 dm cm but is commonly quoted units. absorbance is also given by the relationship: I o log ∝ c I I is intensity of light transmitted through a colorimeter cell o containing I is the the If the pure intensity solution meter intensity solvent. of under readings on the the light transmitted through the cell containing test. on the detector , transmittance colorimenter are proportional to the light then: in cell with pure solvent _________________________________________ = log transmittance We 92 can use in cell Beer–Lambert’s containing law to do test simple constant solution calculations: × c Chapter Worked example 9 Spectroscopic methods 1 Exam tips When radiation cell 1.5 cm of 0.65. wavelength path Solution concentration of Rearrange X length, has of a the its 200 nm is absorption molar passed through measured absorptivity of 80. on a solution X in spectrometer Calculate a Beer–Lambert’s is the complicated solution. have Beer–Lambert’s law in to law at rst remember the absorbance the concentration A the absorbance εl path the form A = εlc so that c is is may seem sight but quite all you is: proportional to the of solution and subject: __ c Substitute the is proportional to the = length of the cell. values: 0.65 _________ c = 80 Worked –3 = example × 5.4 × 10 –3 mol dm 1.5 2 –3 A solution containing 0.025 mol dm copper( ii) sulphate (solution A) is a placed in placed 0.18. is in spectrometer 0.48. the Another same Calculate absorptivity (i) cell the of path solution under the length of 1 cm. copper same concentration copper( ii) of cell The sulphate conditions. of solution B absorbance (solution The (ii) B) of is absorbance the this ecnabrosba solution a is molar sulphate. 0.8 0.6 0.4 0.2 (i) Since absorbance is proportional to concentration if all other factors 0 0 are 0.2 0.4 0.5 constant concentration –3 absorbance of 0.48 → 0.025 mol dm copper( ii) sulphate. b 0.18 _____ So absorbance of 0.18 → 0.025 × = 0.0094 (to 2 s.f.) ecnabrosba 0.48 (ii) Rearrange Beer–Lambert’s law in the form A = ε lc so that ε is the 0.8 subject: A __ ε = lc 0.5 Substitute the 1.0 values: concentration 0.48 __________ ε = = 1 × 19.2 Figure 9.2.1 a At low concentrations a 0.025 graph of absorbance against concentration shows proportionality. It Deviation from Beer–Lambert’s follows Beer–Lambert’s law. b At higher law concentrations, Beer–Lambert’s law is not The relationship: obeyed. transmittance in cell with pure solvent _________________________________________ log = transmittance is not obeyed coloured when solutions. in high The increases. curve to in order (see concentrations For calculate Section containing absorbance concentration accurately cell this the test of solutions increases reason we less have concentration constant × c solution of to a are used, rapidly plot as a especially the calibration particular solution 7.3). Key points Transmittance Beer–Lambert’s to the distance law it Beer–Lambert’s path refers At length high and to light states travels law ε is can a passing that be of amount the expressed constant concentrations the through through of solution. Absorbance light absorbed is refers to proportional light to the absorbed by a solution. concentration of the solution and solution. as: (molar solute, a A = εlc, where A is absorbance, c is the concentration of solution, l is the absorptivity). Beer–Lambert’s law is no longer obeyed. 93 9.3 Ultraviolet Learning outcomes The UV-visible A On completion of this and visible section, single beam be able or understand describe the the understand use steps by UV detection spectrometer is spectrometer but it uses a similar diffraction to a grating colorimeter to select (see Section wavelengths in 7.3 the for UV to: samples absorption you diagram) should spectroscopy of UV in visible region rather than a lter . The procedure is: spectra Set Place the Adjust Put wavelength of light required. analysing pure solvent in the cell (water , ethanol or other organic solvent). spectroscopy about limits sensitivity the meter reading to 0 absorbance or 100% transmittance. and the sample in another identical cell and place this in the path of in UV the light. spectroscopy describe the samples by understand steps visible the in spectroscopy use Record the Repeat at A meter reading (absorbance or transmittance). analysing of other calibration selected curve wavelengths. using standard solutions can be used to relate the visible absorbance to the concentration of the substance present (see Section spectroscopy 7.3 understand complexing coloured and the use reagents to form compounds detection for details). of A (sensitivity single solution organic limits). beam spectrometer (Figure 9.3.1) molecules but can it be used cannot satisfactorily. be The to identify used to coloured distinguish wavelength is ions in between usually measured in –9 nanometres, nm (1 nm = m). 10 70 Using complexing reagents ecnattimsnart 60 Some ions may not absorb light very well in the visible or UV regions. 3+ Cr (aq) They may however be converted to more highly coloured ions by forming 50 complex 40 13.3). egatnecrep more ions These with ions sensitive to particular may the have ligands better absorption (see Unit absorption of light. 1 Study Guide ,1 characteristics. They may also Section They shift are the 30 wavelength of maximum absorption. For example: 20 2+ ions Fe in solution concentrations 10 reacted with they the are do ligand light not green absorb in colour. visible If present radiation 1,10-phenanthroline, in ver y however, low well. a When deep 0 orange–red 400 450 500 550 600 650 complex ion is for med. At the appropriate wavelength 700 2+ this wavelength/nm Figure 9.3.1 complex ions alone. The colour absorbs This radiation maximises to the a far greater precision of extent the than the Fe measurements. Absorption spectrum of a 2+ 3+ solution containing Cr of dilute copper( ii ) sulphate is due to a water–Cu ion ions complex. deep blue This is ver y complex light and blue changes in colour. the Adding wavelength of ammonia makes a maximum absorption. High High one resolution for used is shown 94 resolution UV-visible the UV about in UV-visible and one for 200–800 nm. Figure 9.3.2. spectroscopy spectrometers the A visible have regions. simplied two The diagram of separate light wavelength this sources, range spectrometer is Chapter rotating 9 Spectroscopic methods disc slit M detector S computer and light chart recorder sources R M Figure 9.3.2 A double beam UV-visible spectrophotometer. M = mirror. S = sample cell. R = reference cell. The the diffraction UV The the The and grating visible rotating cell solvent or disc to divides up containing used in detector rotates regions the test preparing compares converted to allow the beam from the whole range of so and that a it alternates reference cell between containing the solution. values percentage light produced. solution this the to be (%) of the sample transmittance and then reference to cells molar absorptivity. Cells and radiation A typical butanone can there at different the made be are of quartz two We by peaks, can organic are used because glass absorbs region. spectrum identied 275 nm. types of ultraviolet UV-absorption compounds another lenses in is one use shown their at such typical a in Figure wavelength spectra 9.3.3. absorption to of Different peaks. 190 nm distinguish For and between compound. 4 10 ytivitprosba Key points 3 10 Some molecules absorb radiation 2 10 in the UV or visible region. 1 ralom 10 This 0 gives rise to characteristic spectra. 10 0 0 200 250 300 Visible spectroscopy is limited to 350 coloured compounds. wavelength/nm Figure 9.3.3 UV spectroscopy for organic Limitations of UV-visible UV with or used molecules conjugated A is The UV-absorption spectrum of butanone visible absolute region spectrum certainty spectroscopy is not enough to carbonyl identify a substance because: Samples visible The solvents The polarity used may absorb UV radiation the solvent and pH can or are analysed spectroscopy through a by UV- by passing quartz cell signicantly. and of with bonds compounds. radiation double affect the UV detecting the radiation absorption transmitted compared with a spectrum. reference The temperature and high electrolyte concentration may interfere with the The sensitivity The method is limited to coloured compounds in UV (in visible spectroscopy) low spectroscopy compared organic compounds with conjugated double bonds such as alternating double and single bonds and carbonyl Complexing UV The width to many ions can to be increase spectroscopy). the reagents compounds added (in other methods. alkenes with with or spectroscopic detection either: are and spectrum. limits cell. of the spectrometer slit and other variables associated sensitivity and detection with limits. the spectrometer also affect the spectrum. 95 9.4 More about Learning outcomes ultraviolet Which The On completion should be able of this section, molecules absorption of The d orbitals degenerate. explain the origin explain why of UV visible radiation regions In list examples in and of the the UV others the use Guide , spectra quantization tablets, blood, of in and in ions an isolated all have transition the same element average ion are described as energy. of ligands, Section the orbitals split into two groups (see Unit 13.3). not When d energy orbital of in the lower visible energy region to a d is absorbed orbital of an electron higher energy. moves Light from is of in the visible region of the spectrum. the substances glucose cyanide element and do absorbed ultraviolet in They presence Study a in transition molecules 1 absorb light radiation? spectra some absorb UV/visible you to: spectroscopy urea (iron The wavelength between in the of split the d light absorbed depends on the energy difference levels. water). The absorption of Organic compounds radiation which in organic absorb radiation compounds in the ultraviolet (or visible) Did you know? regions When atomic molecular of the orbitals orbitals molecular energy than the overlap, two orbitals has lower conjugated exhibit bonds buta-1,3-diene, are formed. One atomic usually a resonance (alternating structure. double and the C =O group examples single bonds) are: in dienes, e.g. =CH—CH=CH CH 2 T wo in 2 aldehydes and ketones, e.g. butanone orbitals. This called has a a bonding higher orbital. The energy than the = O is other atomic CH CH 3 orbitals. This orbital these (*). is called Both σ and orbitals. There bonding contain orbitals lone an π are bonds also (n). These pairs of CCH 2 3 antibonding have non- usually electrons. When UV radiation lower radiation is used energy associated to level with passes move to a through an higher orbitals that these electron energy contain in compounds, the level. pi outer These ( π) energy electron energy from shell levels the from are a often electrons. σ* a π b antibonding π antibonding π* energy n π (n) bonding non-bonding π oxygen Figure 9.4.1 lone pair The relative energies of different orbitals π When an electron is excited by Figure 9.4.2 bonding The absorption of energy in the ultraviolet region moves an electron from a lower energy level to a higher energy level. The orbitals involved are shown for a ultraviolet light, the a diene, electron b a ketone. generally moves to the antibonding orbital. The energy energy involved levels Movements require too is from much buta-1,3-diene, ultraviolet Butanone result (n 96 → can π* and π the σ to π*). electrons cause pi at level to movements (π two movements ) to in π*, the the the n UV π* → π* σ* take place the → σ* usually For within ( π*) wavelengths. in n levels region. antibonding electrons or region. or UV which pi different of π→ in absorption bonding radiation from absorption energy cause electron from different → to bonding only are absorb two moving energy the range from in sufcient The C =O the orbitals. peaks bond Chapter a Spectroscopic methods b 1.0 1.0 ecnabrosba ecnabrosba 0.5 0.5 0 0 180 200 220 240 260 wavelength Figure 9.4.3 For a 280 group bonds, absorption as of the moves molecules, e.g. delocalisation to longer 2 CH 2 compounds, mass and the Their substance particular wavelength. concentration increases, Iron in iron are An quantifying this 260 280 300 320 (nm) the peak two of or three maximum example: CH 2 =CH–CH=CH—CH=CH 2 2 258 nm increased delocalisation → can as use in be used readily is for identify interpreted determining solution appropriate to by as the measuring calibration particular infrared amount the curve spectra of a absorbance is usually at used a to absorbance. tablets: 510 nm not present When 1,10-phenanthroline, about For one, =CH—CH=CH spectra main to 240 spectra visible particular with 217 nm spectra spectra. 220 butanone 2 ultraviolet UV alkenes wavelengths. Although 200 wavelength 171 nm Use of 180 (nm) =CH CH peak: relate 300 Ultraviolet spectra of a buta-1,3-diene and b similar double or 9 a reacted deep complex with the orange-red absorbs ligand complex radiation ion well, is so formed. can be At used for iron. Key points Glucose visible in blood: Glucose spectroscopy. If we is colourless react glucose so cannot with be excess quantied by Benedict’s solution (blue in colour) an insoluble precipitate of copper( i) oxide Organic absorb formed. The blue solution becomes less intense in colour . the colour intensity of the blue solution using radiation a we concentration glucose with Urea a can can oxidase and UV-visible in blood: Ehrlich’s be other the can The glucose measured by enzymes. spectrometer This reagent. calculate also be at a The by formed the solution suitable analysed product concentration. reacting is wavelength, adding zinc absorbs with analysed e.g. sulphate radiation visible) regions, can also measuring be the quantied absorbance by at reacting it with specic at The energy or n→ σ* Cyanide in water: CNBr , The by enzymes cyanide red in in π*, π→ moving n→ levels the UV π* causes region. Spectroscopy in the UV-visible region to and in the with water is bromine converted water . On to is used dye is formed, which absorbs of a determine particular the substance cyanogen addition in solution by measuring of the a a 340 nm. treatment p-phenylenediamine involved energy absorption and present bromide, have 435 nm. amount usually structure. electrons from 340 nm. Urea ultraviolet Glucose glucose then which the visible resonance spectrometer , in By (or measuring compounds, is radiation absorbance at a particular at wavelength. 530 nm. Iron the Did you know? can The cassava contains the plant, very tubers which small properly, is grown amounts you risk of as a root cyanide being very in ill crop its in many tuberous through parts root. cyanide If of the you do poisoning. world, not cook tablets, blood be reagents resulting and cyanide determined specic in glucose and or by in urea in water adding enzymes. The species absorb the UV-visible region. radiation 97 9.5 Infrared Learning outcomes spectroscopy Why do In On completion of this section, be able covalent molecule absorb such as infrared methane the radiation? electron clouds bonding the you C should a molecules and H atoms allow the nuclei to vibrate in two ways: stretching and to: bending explain of the infrared origin (IR) of absorption radiation Covalent A molecules molecule same describe the basic steps as analysing samples spectroscopy preparation describe the by (referring of a natural frequency of vibration. absorbs the infrared natural (IR) vibration of radiation the bonds whose in the frequency molecule. is the The associated with the vibrations is quantized (see Section 9.1). IR to The energy absorbed increases the amplitude of the vibration of the bonds. solids) limitations have involved energy in bonds by of IR Absorption of IR radiation only happens when: spectroscopy. there is some molecule is type polar of charge and separation hence has a within the molecule (the dipole) and a the vibration molecule as and H Unit Cl 2 b results (see do in 1 not a change Study in Guide , absorb in the the dipole Section moment 2.5). infrared So region of the molecules but HBr such will. 2 H Exam tips Figure 9.5.1 Vibrations in a C—H bond; You may nd it useful to think of vibrations in bonds rather like springs a Stretching vibration; b Bending vibration attached ways by to a pair of supplying atoms. You energy from can stretch and bend these bonds in several your ngers. H C Characteristics of The energy masses of absorbed the Each Different in type of C—H The IR appears types The of a result the IR the are of bond vibration of C infrared absorbs vibrations spectrum absorbed a regions bending as as an and bond particular stretching to atoms H spectrum molecular of particular spectrum, at vibrations depends on the strength. radiation in H higher a specic bonds e.g. the frequency. give rise to absorption frequencies than the absorptions due to C—H absorption shows series of the dips percentage (peaks) (%) where of radiation particular transmitted. bonds have radiation. position of the peaks is given by the wavenumber measured –1 cm frequency in hertz _____________________ wavenumber = –1 speed of light in cm s 13 So the wavenumber corresponding to a 13 9 98 due vibrations. × 10 frequency of 10 /3 × 10 9 –1 = 3000 cm × 10 Hz is: in It Chapter 9 Spectroscopic methods 100 90 )%( 80 noissimsnart 70 60 50 40 30 20 10 0 4400 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 –1 ) wavenumber (cm Figure 9.5.2 The The A typical infrared spectrum. Each of the main dips represents the absorption of IR radiation by particular bonds. infrared simplied Did you know? spectrometer structure of an infrared spectrometer is shown in Figure 9.5.3. The reference more more cell complex ways molecules there can a molecule, are in vibrate. which In the a water there detector recorder are three ways in which molecules C IR D can vibrate but in propanone there source are diffraction 24 ways. sample linear molecule n atoms there are 3n – 5 prism cell possible Figure 9.5.3 a grating containing or For ways of vibrating. Simplied diagram of an infrared spectrometer. M = mirrors. C = Comb. D = rotating disc. A beam of IR The radiation The level of compared radiation is IR with part of The diffraction of IR the is passed through radiation that The recorder The diffraction or a graph from the beam helps to of is the % a ceramic sample through prism brought plots the which grating are of coming mechanism radiation produced cell passing the this rod and heated reference through reference to the cell. 1500 ºC. cell. sample The is comb is comparison. rotated so that different wavelengths detector . Key points transmission against wavenumber . grating, prism, mirrors and cells cannot be made Infrared by glass because glass absorbs IR radiation. The cells are often made bromide or calcium uoride. These substances do IR when is the absorbed radiation the same as the natural not frequency absorb radiation molecules from is potassium (IR) from of vibration of the radiation. molecules. Preparing the sample for infrared spectroscopy Liquid two samples: discs Solid of samples: potassium This sodium for sample or (mull) analysis sample for analysis is placed as a thin lm in between for sodium is then can be two main molecules types are of vibration bending and stretching. chloride. The bromide mixture sample The sodium The analysis chloride crushed to powdered is nely (which form and a powdered do not disc. placed and absorb mixed IR two forming the discs Samples of solids for spectroscopy radiation). Alternatively, between with of or are them IR made into a by disc with KBr NaCl. chloride. In an IR spectrometer, radiation Limitations of infrared absorbed by the the sample spectroscopy is It cannot be used to identify substances that are non-polar . It cannot be used to identify substances that are electrolytes compared with a reference sample. or have ionic There the It are some limitations to components. provides information about the types of groups present, use of IR spectroscopy, e.g. including molecules such as Cl do not 2 functional groups, but not always about the structure of the molecule absorb as a IR radiation. whole. 99 9.6 Analysing Learning outcomes infrared The band Particular On completion of this section, spectra region groups such and fingerprint as C—H, O—H region and C = O absorb radiation with you –1 wavenumbers should be able deduce the region of . 1300–3000 cm Specic peaks indicate to: the in chemical groups including functional groups from information from spectra identify OH, NH IR presence region of of the homologous these groups spectrum. series In have in the this molecule. region almost We call compounds identical spectra. in this the Peaks the band same in the –1 wavenumber 600–1300 cm structure C=O, C=C, of the whole region molecule. of We the call spectrum this the tell us about fingerprint the region . This 2 region COOH and CONH can be used to distinguish between molecules with same groups from 2 functional IR group, e.g. propanone and butanone (Figure 9.6.1). spectra give examples spectra in of the use monitoring pollutants such of IR Identifying air as CO and 2 identifying known the fingerprint band region groups 2 When a specific SO values table. These according region for to the groups these are due types )%( Group from IR groups. to of spectra, Some stretching atoms alcohol we typical match vibrations; surrounding amine the peaks wavenumbers their values with given may in vary them. aldehyde/ alkene carboxylic noissimsnart ketone O—H (dips) are acid O—H N—H C =C C=O Wavenumber / 3580– 3350– 1680– 1610– 2500– 3650 3500 1750 1680 3000 –1 3000 2000 cm 1000 –1 wavenumber (cm ) b )%( The wavenumber of the C =O group may also vary according to its environment: noissimsnart 3000 2000 = O C in carboxylic C = O in aldehyde C = O in ester acid 1700–1725 1720–1740 C = O in amide 1630–1700 C = O in ketone 1680–1700 1730–1750 1000 –1 wavenumber Figure 9.6.1 (cm Another ) useful Alcohols Simplied infrared spectra and very broad Example stretch other is C—O in compounds alcohols, which are ethers highly and esters = 1000–1300 hydrogen-bonded show a –1 of a propanone and b butanone O H value vibration hydrogen-bonded OH corresponds group in an to peak between 3230 and 3550 cm 1 a This alcohol peak C—O corresponds group in an to a alcohol 100 90 )%( 80 noissimsnart 70 60 50 40 30 (CH ) 3 CHOH 2 20 propan-2-ol 10 0 4400 4000 3600 3200 2800 2400 2000 1800 1600 1400 –1 wavenumber (cm Figure 9.6.2 100 Infrared spectrum of propan-2-ol ) 1200 1000 800 600 400 Chapter Example 9 Spectroscopic methods 2 100 90 )%( 80 noissimsnart 70 60 O H 50 O stretch 40 CH 30 3 20 C =O ethanoic acid 10 stretch 0 4400 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 –1 wavenumber Figure 9.6.3 We can (cm ) Infrared spectrum of ethanoic acid identify a very wide O—H stretching vibration at –1 . 2800–3300 cm This corresponds to a hydrogen-bonded O—H group in –1 a carboxylic acid. corresponds Example to a There = O C is also group a in peak a at about carboxylic which 1730 cm acid. 3 100 )%( 90 80 noissimsnart 70 60 O = 50 40 CH C O CH 3 CH 2 3 C = O the two C O 30 ethyl ethanoate stretch stretches 20 4000 3500 3000 2500 2000 1500 1000 500 –1 wavenumber Figure 9.6.4 (cm ) Infrared spectrum of ethyl ethanoate –1 We can identify a C = O stretching vibration at 1750 cm due to the –1 = O C group in an ester . There are also two peaks at about 1050 cm and Key points –1 which 1250 cm correspond to the two C—O groups in the structure. Infrared Fourier spectra transform pollutants in the IR air and air as groups It can also be used can carbon to by wavenumbers. be used to monoxide, detect sulphur and measure dioxide their Typical typical the air . measure the concentration of carbon wavenumbers groups dioxide The method particular uses the molecules. ngerprint T o measure region the of the IR spectrum concentration of are –1 for aldehydes to –1 and identify spectra and 1680–1750 cm in be infrared for functional ozone. can identied from pollution spectroscopy such Particular ketones and 3580–3650 cm carbon for the O—H group in alcohols. monoxide: draw the polluted air through a sample A wide peak in the chamber –1 2800–3500 cm a beam sample (CO) of infrared chamber present). radiation and Any a is continuously reference decrease in chamber intensity passed (with of the no through carbon beam at a the hydrogen monoxide carboxylic is due to the presence of carbon a detector measures and the the difference amount of CO in IR radiation recorded Infrared spectroscopy between the air since different pollutants have absorbance at characteristic particular IR spectra, several pollutants at the wavenumbers, same in such carbon monoxide and sulphur this concentration of with method dioxide in the air can also can be measure used two carbon maximum is pollutants automatically dioxide. The or monoxide as chambers indicates alcohols acids. monitoring in particular wavenumber region bonding measured. time. 101 9.7 Mass spectrometry Learning outcomes The The On completion of this section, mass mass spectrometer be able and explain mass to identify be used organic to measure compounds. relative Figure atomic 9.7.1 masses shows a mass to: spectrometer can you accurately should spectrometer the basic principles spectrometer of (including a and Figure 9.7.2 shows a block diagram of the main stages involved. a electromagnet block use diagram) mass spectral determine data relative to isotopic A + masses and abundances C electron B describe how mass spectra are beam detector used to distinguish between p molecules of molecular mass. similar relative s Figure 9.7.1 The main a le electromagnet m heated cathode A mass spectrometer stages V aporisation Ionisation: are: of the sample. substance vaporised atoms from The are ions in of electric field ions accelerated are deected The ions are detected a given and electric mass the magnetic the detector . e.g. 14, m/z is an 16, eld, (z is ion is and hit Positive by an ions the with more and a heated knock ions electric by are eld cathode out one or collide more with of the formed. (through a negatively- of a magnetic eld, By on less the eld. If A) the those ions usually ratio and ion of an is with increasing mass/charge ion, charge (line C). only gradually increasing mass (line a recorded. detector . charge deected deected (bent) magnetic the 208 by and 15, ion ratio +1.) an In ion lighter doubly a the particular strength (m/z ratio) Figure than charged, is if than this, it hit 9.7.1, heavier an e.g. m/z deected as much. + Pb A 208 ion has an m/z ratio of 208, so a 2+ Pb m/z ratio of ion has 104. field A mass each spectrum ion plotted spectrum ions + of shows against the the relative m/z abundance ratio. Figure (relative 9.7.3 shows amount) the of mass germanium. of 100 recording )%( ecnadnuba Figure 9.7.2 Main stages in a mass spectrometer 80 60 evitaler 40 36.5% 27 .4% 20.5% 20 7 .8% 7 .8% 0 70 71 mass Figure 9.7.3 102 B this, magnetic detection of of twice ions from sample plate). ions charge electrons the sample. The represents deflection the of For acceleration high-energy molecules electrons charged conversion to ions or 72 73 /charge 74 75 76 ratio Mass spectrum of germanium showing the % abundance of each peak Chapter Accurate atomic and molecular 9 Spectroscopic methods masses Exam tips Relative atomic masses 1 Mass spectra element. ratios can be Different because used to isotopes each proton identify are the different detected and at neutron isotopes particular has a present in whole-number relative mass of If an you spectra can Step 1: Multiply Step 2: Add Step 3: Divide the be used each calculate isotopic gures by to mass relative by its % atomic asked Using relative abundances the can masses: abundances, up the divide abundance. together . 2 In a total by mass height Step 2: 1435 Step 3: 7263.2 that the you have abundance this number spectrum, gives the + (27.4 1972.8 / Figure 100 + = relative the of to add then in the Step 3. peak relative each isotope. × 72) 569.4 atomic of the masses from of the relative atomic mass of follows: + + (7.8 × 2701 73) + + 585 (36.5 = × 74) + (7.8 × 75) 7263.2 72.632 numbers spectrum 9.7.3, as mass is the isotopes mass chlorine weighted mean of the masses present. spectra (Figure 100 singly 9.7.4) shows peaks due to charged ions 50 evitaler mass 70) + mass Molecular The × in calculated ecnadnuba (20.5 be )%( 1: all than 1. 100. information Step of given rather example germanium Notice calculate masses m/z abundance Worked to atomic % Mass are relative doubly charged ions singly0 35 charged ions of the to the 37 Cl and Cl isotopes. The 35 18.5 The are due spectrum will doubly-charged also show small 2+ peaks peaks 37 Cl ions small and caused at 17.5 and 5 2+ by 10 15 mass Cl ionised chlorine Figure 9.7.4 20 25 /charge 30 35 40 ratio Mass spectrum of chlorine + molecules, . Cl There are 3 peaks of these molecular (up to m/z = 40) ions: 2 35 m/z 70: m/z 74 due to 35 Cl— 37 These due small m/z 72 due to 37 Cl— Cl 37 Cl— to 35 Cl peaks Cl due to the molecular ions are called the molecular ion peaks Did you know? A high-resolution of apparently relative For the isotopic example, mass same A (the SO relative relative masses and can molecular help distinguish mass. This is between because both mass have mass of a relative sulphur spectrometer is can 32 molecular and of mass measure oxygen and of SO and is measure approximately 63.944, respectively ( 16). S 2 63.962 can accurately. 16 to it molecules 2 atomic high-resolution very S 2 64 spectrometer more accurately 2 32 O = 15.995 and S = 31.972). Key points Mass the A spectrometry ions, mass of deflecting spectrum isotopes Relative High-resolution with of plotted atomic similar involves the a ions sample against mass mass relative converting in is the a of the an element spectrometry mean can atoms and shows mass/charge weighted molecular gaseous magnetic eld to ions, detecting the accelerating the relative ions. abundance ratio. of the isotopic distinguish masses. between molecules mass. 103 9.8 Mass spectrometry Learning outcomes Mass When On completion of this section, spectra of we ionise be able organic molecules compounds molecular compounds such as propanone in a mass you spectrometer , should and a single electron may be removed from the molecule. The to: + peak use data from distinguish the same explain mass spectra between relative to molecules molecular arising gives of mass ion mass patterns give information nature predict of the organic the a the spectrometer low. to the This form the molecule. mass/charge compounds, very called is For ratio relative ( m/z the ratio) of of molecule having ion propanone, abundance because fragments molecular peak , the 58 the (see m/z . It molecular Figure molecular breaks particular M up in ion the ratios. This is called fragmentation molecules identities of simple molecules explain at of is about Fragmentation The more mass ionisation mass appear many usually process the will In is this molecular peak 9.8.1). peak how fragmentation the from terms ‘base peak’ generally stable the occurs fragment, where the the bonds greater is its are weakest. abundance in the spectrum. and + ‘molecular ion’ T ertiary carbocations, e.g. ) (CH 3 C tend to be more stable than 3 + secondary carbocations, e.g. CH CH CH 3 explain the signicance of and the secondary more 3 the + stable than the primary, e.g. CH CH 3 M+1 peak in mass 2 spectra. Figure 9.8.1 shows the mass spectrum of propanone. + CH CO 43 3 100 )%( ecnadnuba 80 60 + [CH COCH 3 ] 3 molecular ion evitaler 40 58 + 15 CH 3 20 0 10 20 30 40 mass/charge Figure 9.8.1 Each ratio 50 60 (m/z) Mass spectrum of propanone fragment has a particular m/z ratio. Notice the large peaks at 15 + and 43 m/z ratios. The peak at 15 is due to a CH ion 3 + (C + 3H = 12 + (3 × 1) = 15). The peak at 43 is due to a CH CO ion 3 Exam tips (2C + 3H formed 1 interpreting for exam an need to at mass this consider the = ((2 × following 12) + (3 × 1) Remember that you you main suggest may more of ion for a ions have been O be than given These O CH C CH + 3 + CH m/z CH ratio. 3 O 3 one + type 43)). = to = only peaks. 3 able 16 way: = 2 + spectra level, the in O = When + + C CH 3 3 + For example (CH ) 3 CH and 2 The + CH CH 3 CH 2 both have an peak ratio of relative in the spectrum of the which is fragments given an is compared abundance of with the 100%. tallest This 43. called 104 abundance m/z 2 the base peak. For propanone, the base peak is at m/z 43. peak is Chapter Distinguishing Butane and between methylpropane molecules mass spectrometry to have the same distinguish molecular between these mass, 58. We molecules. are shown in Figure methods can uses of mass spectrometry are: The spectra Spectroscopic Did you know? Two use 9 testing the urine of athletes for 9.8.2. the presence of drugs + a CH CH 3 CH 2 CH b CH 2 CH 3 3 3 + CH CH 3 + CH 2 CH 2 monitoring pollutants in river + C C CH 3 CH 3 3 water. + CH CH 3 H H 2 100 100 43 43 )%( )%( ecnadnuba ecnadnuba 50 29 evitaler evitaler 58 15 50 58 0 0 40 20 ratio mass/charge ( m/z) Mass spectrum of a butane CH CH 3 the differences in the spectra CH 2 and b ( m/z) methylpropane (CH 3 especially ) 3 at m/z CH 29: + In butane m/z 29 is due to CH CH 3 100 + [CH 2 80 + [C there is no m/z 29 evitaler methylpropane peak. + So there is no CH CH 3 in methylpropane. to CH 2 butane m/z 43 is O] 5 + [C + 40 [C H H 2 OH] 5 ] 5 [M 20 + 1] 0 10 + In H 2 60 2 In OH] 2 3 ecnadnuba Notice CH 2 ratio )%( Figure 9.8.2 20 60 mass/charge due CH 3 20 30 40 50 CH 2 2 m/z + In methylpropane m/z 43 is due to CH C HCH 3 In both butane and methylpropane m/z Figure 9.8.3 3 58 is the molecular ion Mass spectrum of ethanol peak. Key points The M + 1 peak Figure 9.8.3 shows the mass spectrum of ethanol. The very small peak In a mass spectrometer, 1 compounds m/z unit beyond the molecular ion peak is called the M+1 break up into peak fragments. The M+1 peak arises because in any organic compound 1.10% of the The mass spectrometer can 13 carbon atoms are of C the isotope. We can work out the number of be carbon atoms ( n) in a molecule by using this used to identify fact. compounds from abundance 100 _____ n of M+1 if the The ion ion ____________________________ abundance of molecular ion, M molecular molecular ion peak has an abundance of 49.3% and the by the an compound abundance of 3.8%, the number of carbon atoms in The = 7C Mass of contains Cl atoms you can get a M + 2 peak and 35 peak in the spectrum. This is because Cl has two isotopes Cl For example in the compound CH Cl 2 37 M + 4 peak is due to 37 ClCH be of a determined molecular ion peak. spectra + , 2 an M + 2 peak is due to 37 37 ClCH the can be between same used to compounds molecular mass. a and 35 an its distinguish compound mass 49.3 Did you know? M + 4 can atoms from organic molecule. _____ × 1.10 an is one 3.8 100 _____ If a molecular compound = of the is: n peak loss M+1 electron from has typical patterns. produced peak their fragmentation × = 1.10 So, organic Cl The M + 1 peak can be used to Cl. deduce + the number of carbon and 2 atoms in a compound. Cl 2 105 Revision Answers to all revision questions can questions be found on the –34 h = 6.63 × 10 8 J s; c = 3.0 × 10 accompanying CD. –1 m s ; 4 a i If a solution of an analyte in 23 Avogadro’s number = 6.02 × water with –4 10 concentration examined at of 1.00 λ × mol dm 10 220 nm, a –3 the is absorbance is max 1 The diagram below shows some of the energy levels found of a hydrogen to be 1.40. If the path length of the atom. cell is 1.0 cm, what is the molar absorptivity –19 n of J ii the This analyte analyte at has this wavelength? another absorption band –19 n J at λ 268 nm. If the same solution is max examined the –19 n b J A at 268 nm, absorbance student spectrum is planning of an (ε = 900), what will be reading? to analyte record which the has UV λ = 310 nm max a An electron moves from energy level n energy change for b What is c What would for one = 1, emitting this be electron), the of of total the the n = 3 to photon. What is (ε the (each electronic in path kJ, with c A a By the energy of an X-ray transition = 6 × 10 m) with that of an What order the concentration to obtain maximum, length 2.10 0.455, is × of analyte cell with a of 1.00 cm with a concentration –3 mol dm when a be absorbance used? an 10 if an should has measured length. This in a solution absorbance measured found 0.184. in an absorbance cell is with then the a diluted same of 1.00 cm and manner, the is photon –11 (λ at in solution of path comparing 000). –3 one occurs? 2 24 prepared radiation? change, atoms same = 0.512 emitted energy hydrogen where a level process? the frequency mole energy infrared to be What is the concentration of photon x the –6 (λ 5 IR × 10 m), explain why short longer is more damaging to length human tissue than 5 wavelengths. A UV-visible the What is the energy of a photon of red (λ = lamp radiates 15 W of yellow = measurements, the and concentration from can be Identify by applying one factor Beer–Lambert ’s that can cause a law. deviation 590 nm). from What is the energy of each photon How many photons are emitted from per second? (1 W = Explain why the use law. of complexing agents the is –1 lamp Beer–Lambert ’s emitted? b ii measures substances, light a i spectrometer speci c 680 nm)? sodium (λ of light determined A absorption absorbance these c solution? = radiation b diluted sometimes required in this form of ) 1 J s spectroscopy. d Determine the frequency of: c i an X-ray beam which has a wavelength The absorption spectra is actually due to the of presence of chromophores. the ‘chromophore’? What is meant by 4.88 Å ii an iii microwaves ultraviolet ray with wavelength of 211 nm d with a wavelength of term State two limitations of UV-visible 0.211 cm spectroscopy. –10 (1 Å = –9 m; 10 1 nm = 10 m) e A solution of KMnO has an absorbance value 4 e Given that the difference in energy between –19 the 3p and 3s orbitals the wavelength of is 3.38 radiation × (in J, 10 m and what nm), of 0.508, when of 525 nm. be absorbed if an electron at a wavelength is What is the transmittance of this that solution? would measured moves from What is the % transmittance of this the solution? 3s to a 3p orbital? f The molar absorptivity of KMnO is 2240 at this 4 3 Determine the absorbance of the following a a solution with a transmittance b a solution with a % c a solution with molar of solutions: 0.314 wavelength. If the measured a cell in absorbance with a of 1.50 cm the solution path length, –3 transmittance of 42.4 of 10 what is the concentration in mol dm –3 , g dm –1 absorptivity –5 concentration of 3.25 × mol dm 10 000 and and ppm? (Molar the concentration mass KMnO , where in ppm = mass 3 absorbance 106 is measured in a is 158 g mol ; 4 –3 1.0 cm cell. volume of solution (dm )). of solute (mg) / is Chapter 6 Explain each of the following in terms of 9 electronic a The molecule CH CH 3 the UV-visible molecule CH CH 2 region CH 2 The Explain does not absorb in i how in methods each the of mass – revision the following questions processes spectrometer: vaporisation 3 above 200 nm, =CHCH=CH 2 b Spectroscopic occurs transitions: a 9 whereas the ii ionisation iii acceleration iv deection v detection. does. 2 molecule H H C b C H has two region: two spectrum H absorption UV-visible Identify H peaks λ = c H in the 320 (ε ways can be in Explain the meaning used the analysis in which data from a mass used. of of these a terms mass which are spectrum: accessible = 21) and i the m/z ratio ii the M 1 iii the base max λ = 213 (ε = 7080). + peak max c λ in the UV region is higher for the molecule peak. max CH =CHCH=CHCH=CH 2 than for the 2 10 molecule CH =CHCH=CHCH 2 a Determine a Explain why a molecule such relative a CH I would absorb i 3 The given in in the IR region, but the molecule I relative atomic b not. Explain show abundances which a 56 Fe, isotopes 2 would of stronger the bonds C–Cl or C–I 0.280% would absorption. Briey explain how a ii sample is prepared for The relative of The IR spectrum is a plot of % iii transmittance The of Fe, 5.85 and %, Fe 91.75 atomic and of relative Li mass have of isotopic wavenumber. i Dene the ii Calculate term the are ‘wavenumber’. wavenumber corresponding to b a frequency of wavelength 2.7 × 0.082 : 1.00 atomic mass 8. 18 × 10 a How could between IR the spectroscopy isomers in i mass 0. 10 CH CH 3 ii b and CH be and bands the in and positions the IR relative where used in H H C C H H the of a peak respectively. of Mg where the 25 26 Mg and Mg respectively. straight chain molecular ion alkane peak has a of to abundance 12% of and the M+1 peak has 0.55%. distinguish i How many ii What carbon atoms are there in a ii? 3 of the of major is of the this compound? molecular formula for this compound? absorption iii the following: Write the structural formula for this compound. Cyclohexanol ii where ratio of Mg, of 0. 11 the abundance relative hex-2-ene spectra and OCH 3 cyclohexane Predict i OH 2 and spectrum molecule i 2. 12% m. a 8 abundances 0.79, obtained the relative Hz 10 –6 of The is 13 have %, Li the 24 against where 58 Fe 7 Li intensities spectroscopy. d each respectively. isotopes IR mass 57 Fe, 6 c mass for i–iii. 54 radiation atomic 3 element 7 the CH 2 iv Predict four m/z H values, major fragments, that would along appear in with the their mass O spectrum C c H c The IR spectrum of this compound. C Some of the peaks of the mass spectrum for the H of the compound compound butan-2-ol 45, 15. Suggest 29 and responsible for H these have the m/z values identity of of the 74, 59, species peaks. H –7 11 An atom emits radiation of wavelength 1.5 × 10 m. H Calculate the energy of this radiation per mole H 8 of atoms. c = 3.0 × 10 has major absorption peaks in the regions –1 m s . –34 Planck constant = 6.63 × 10 3350–3500, 3000–2850 and 1600–1459. 6.02 × 10 Suggest these the identity absorptions. of the (Refer groups J s. Avogadro number, 23 . responsible for to Section 9.6.) 107 10 Separation 10. 1 Introduction Learning outcomes techniques to chromatography The theory of chromatography Introduction On completion should be able of this section, you to: Chromatography mixture. explain the theory on in chromatography is based of adsorption a mixture. and state that cellulose, silica gel are examples phase hexane explain paper, the to is separate one of the the components compounds or of a elements two different works by phases. dividing We call the this components partitioning . of a W ater do not mix. solution of They iodine form with two separate hexane, layers. most of the When we iodine goes shake hexane layer but some remains in the aqueous layer . We say into that the substances differences column, used component of iodine a Chromatography between aqueous the stationary technique and an alumina a partition and is chemistry, in mixture terms In which has been partitioned between the two layers (see Section 10.8). between thin-layer and Did you know? gas–liquid chromatography. The word writing’. separate a solute not chromatography In the early coloured days was of taken from two Greek chromatography the words technique meaning was only ‘colour used to substances. molecule adsorbed Adsorption mobile partition chromatography phase There e.g. and are two main types of chromatography, adsorption chromatography alcohol and partition chromatography. They both depend on partitioning the solute components of a mixture between two phases, a stationary phase and a molecule mobile phase. strongly solid support, e.g. Al O 2 (stationary adsorbed phase) solute b 3 in The stationar y alumina less cellulose soluble bres. components water mobile phase (aluminium of The the can be oxide) a solid, or a stationar y mixture e.g liquid, phase which silica e.g. tends are (silicon( water to hold attracted IV ) oxide) trapped to back it. or between the The greater the phase attraction, the slower is the movement of the components during chromatography. solute The mobile phase can be a liquid or a gas. The greater the solubility of a more cellulose trapped soluble water particular component in the mobile phase, the faster is the movement of fibres in (stationary water Figure 10.1.1 phase) a Adsorption chromatography; b Partition chromatography that component During phase. chromatography. chromatography, The stationary the during different phase mobile Adsorption to phase the mobile components different and phase the extents. separation chromatography: in So moves mixture some over are move the stationary attracted faster to than the others in occurs. The stationary phase is a solid. Adsorption Exam tips is the As It is important that you process the mobile the words ‘adsorb’ the means surface. That’s should means use to in this diffuse substance like a the phase bonds moves of over varying the solid to bond word with (stationary a solid phase) surface. some are adsorbed more strongly to the solid than others and occurs. at Partition chromatography: particles of The stationary phase is phase moves a liquid surrounding you a solid support. As the mobile over the section. Absorb through sponge stationary phase, stationary phase the components which are more soluble move more slowly in the liquid the taking will be held back and than those that up are more soluble in the mobile phase. This water. partition 108 strength and separation ‘absorb’. Adsorb forming distinguish components between of coefcient (see Section 10.8). difference depends on the Chapter Four types of 10 Separation techniques solvent chromatography (mobile Column phase) chromatography powdered This is a form of adsorption chromatography. Silica, alumina or a solid resin (stationary (stationary phase) is mixed with a solvent such as alcohol or phase) water components (mobile phase). The mixture is packed into a column. A mineral wool or moving down sintered glass plug at the bottom of the column keeps the stationary column phase tube in place. and The mixture then allowed then continuously to to soak be separated into the is added stationary to the phase. top of Solvent the (mobile mineral phase) is added to the top of the tube. The wool solvent plug moves through Section 10.2 Thin-layer This is a a glass near and or the the moves of plastic the 10.2 are column of A the more small to stationary for into plate. allowed components a The move of the mixture. See procedure. (TLC) paste spot phase, on the chromatography chromatography . made plate. bottom up separating on adsorption phase) solvent Section tube more chromatography form (stationary the for of the plate up the and is Silica, spread mixture placed stationary spot separates thin-layer to in the alumina in a a be thin phase. into cellulose layer separated solvent chromatography or even the over put (mobile As its is phase) Figure 10.1.2 A chromatography column solvent components. See procedure. cover Paper chromatography beaker thin This is a form of partition chromatography. The stationary phase is layer of water silica absorbed onto the cellulose of the paper . The mobile phase is usually spot organic liquid or a mixture of solvents. The apparatus (see Section on plastic an of plate 10.2) mixture is similar to stationary partition that for phase. TLC As the themselves but with solvent between paper moves the water instead up the of a paper , (stationary thin the layer of solvent components phase) and the (mobile Figure 10.1.3 (mobile phase). See Section 10.2 for more on paper phase) solvent Thin-layer chromatography chromatography procedure. Gas–liquid chromatography (GLC) solute This is a form of partition chromatography. The stationary phase is soluble high-boiling point porous solid liquid, e.g. a long-chain hydrocarbon oil less a supported on in oil a carrier inert unreactive gas, such e.g. as silica nitrogen, or alumina. helium, The argon. mobile This is phase called the is carrier gas. solute The mixture to be separated is injected into the apparatus (see gas an more Figure soluble 10.2.5, page 111). As the mixture is carried through the apparatus by the in gas, those substances that are more soluble in the oil will travel solid slowly and those that are less soluble will travel faster . See oil more Section oil 10.2 support for more on gas–liquid chromatography procedure. Figure 10.1.4 In chromatography stationary a liquid phase or to mobile separation the phase The stationary The mobile Paper, phase phase thin-layer, occurs stationary adsorption separate the moves solutes through or over a phase. Chromatographic mobile Partition in gas–liquid chromatography Key points on a can can be column solid be a a by a solute either is transferred from partition between a the gas and surface. solid, liquid and when phase or e.g. a silica or alumina or a liquid. gas. gas–liquid chromatography are used to substances. 109 10.2 More about Learning outcomes chromatography Column After On completion should be able this section, and the terms ‘retention ‘visualising agent’ ‘retention Add Allow ‘solvent the Keep the in a the basic separating mixture the using steps mixture the been to mixture adding solvent with describe has packed, the be to separated soak into to understand components R of values and f retention times quantifying are is: top of column the column. (open the tap at the it. solvent drain Don’t (mobile through let the phase) carrying column run to the the top of the components column of the and let mixture dry. involved Collect the chromatography how the the fractions of appropriate volume used in in test tubes at the bottom of column. 3 procedure bottom). front’ column time’, and the you to: understand factor’ of chromatography These may be from 3 to 1 cm 100 cm depending on the size of the column. substances. mixture solvent A B A B Figure 10.2.1 Collecting the fractions in column chromatography. The diagram shows the separation of a mixture containing two components, A and B. Thin-layer The a chromatography procedure Place Dip paper and a is spot the paper the of paper same the (or the base Allow the solvent When the for both mixture TLC below chromatography to plate) TLC be and paper separated into a on solvent. chromatography. the The base line. solvent level must be line. to solvent move front up is the near paper the (or top, TLC mark its plate). position. base Exam tips M A B C line When carrying out TLC or paper chromatography remember: b lid 1 Mark be the base line and chromatographed solvent front as in pencil. The components of ink will well! chromatography 2 solvent Put a cover over the tank or beaker. This prevents solvent loss by paper evaporation front Visualising and allows agents equilibration and of the vapour with the liquid solvent. retention value, R f M A B C solvent When chromatography tank the nished agent). Figure 10.2.2 components of chromatogram This reacts with a or mixture TLC the are plate not with colourless a coloured, we visualising components. A spray agent the (locating coloured Paper chromatography; compound is formed. The colour may sometime need to be ‘developed’ by a A mixture and three pure substances, A, warming the treated paper . Different types of visualising agents are used B, C are placed on the base line; b The chromatogram after separation. The mixture contains A and C. 110 for different give purple types of coloured compound, spots. e.g. ninhydrin reacts with amino acids to Chapter We far can the identify spots solvent the have front has components moved moved. from We on the call a chromatogram base this line the by compared retention comparing with value , how how far 10 Separation techniques Did you know? the Paper R chromatography can also be f carried distance from base line to centre of out by placing the solvent the apparatus. in spot ____________________________________ R a = trough at the top of f distance from base line to solvent front This In Figure 10.2.4 the value R of component A is 4/6 = 0.67 and the R f value of component B as called descending paper chromatography. f is 1.5/6 = 0.25. solvent Gas–liquid chromatography, GLC The for apparatus The mixture through a substance be a gas, GLC to long be liquid or shown separated spiral injected of is tube must The time injection is The components of The components leaving is Fig 10.2.5. injected containing be volatile in able to into the form The the procedure gas stationary a vapour which is: ows phase. easily, The e.g. it has to Figure 10.2.3 solid. recorded. solvent front changes in thermal the mixture the separate tube conductivity are of in the detected the gas tube. (usually coming out by measuring from A the 6 cm apparatus). 4 cm B The separated between components injection and leave detection the is tube called at different the times. retention The time . We time 1.5 cm can base identify a retention component times for by matching particular its retention substances under time the with same line known conditions. Figure 10.2.4 Calculating R values from f detector a TLC plate sample injection to chart recorder/PC carrier gas Key points variable spiral temperature paper and thin-layer chromatography, containing oven stationary In tube phase the components of identied their by the mixture R are values. f Figure 10.2.5 Gas–liquid chromatography The R value is the distance f moved by a specic component B from the distance base line moved divided by the by the solvent rotceted A front from A visualising morf langis colourless C the or the line. reagent reacts components thin-layer give base in a with paper chromatogram separated to components colour. 2 4 6 8 retention 10 time 12 14 16 18 (minutes) In gas–liquid the components retention Figure 10.2.6 chromatography, 20 are identied by times. A GLC trace. Each peak represents a different component. 111 10.3 Applications Learning outcomes Column This On completion of this of section, be able method describe how experiments using layer paper, to to carry out separate column, mixtures and state thin- chromatography some Each of of that amino fairly acids or large amounts mixtures of of material proteins. can be Columns e.g. analysed sizes. plant from proteins by Larger-sized oils such the can by columns limonene bottom be measuring quantitatively as of the analysed the be for column used with at can be purifying drugs. analysed by 280 nm. ninhydrin for purifying quantitatively absorbance reaction can or and Amino acids can measurement of of colour intensity using visible-spectroscopy . Figure 10.3.1 shows a methods analysis of separate amino acids collected from the column. analysis, forensic of natural dica purication of a the mixture using chromatography. alanine 1.5 serine valine aspartic 1.0 × fo noitartnecnoc components 2.0 m d lom quantifying steps 3– basic ) the onima understand involved e.g. collected products) advantage various products, fraction typical testing, made automatically , the (pesticide the mixtures UV-spectrometry applications chromatographic be natural be has e.g. to: can chromatography you separated, should chromatography 0 1( 3 acid 0.5 0 0 Did you know? 50 100 3 volume Columns for collected (cm ) column Figure 10.3.1 chromatography can be as wide Quantifying amino acids separated during column chromatography. The as amino acid content in each tube was determined by colorimetry. 3.2 metres These can and be as high used for as 15 metres. separating and Thin-layer purifying large amounts of and paper chromatography materials. These such methods as amino however , can be acids, completely used plant to separate pigments separate small and amounts food compounds of colourings. with similar compounds We cannot, values. R We can f use two -dimensional After it the 90º initial and different chromatography chromatography, carry out solvent we help allow chromatography (Figure to in a overcome the paper different to this dry problem. and direction then using turn a 10.3.2). = Origin Leu Leu Glu Glu Asp Asp Run in the chromatogram solvent Turn the paper 90° Run 1 Figure 10.3.2 in the chromatogram solvent 2 Two-dimensional paper chromatography of the three amino acids leucine (Leu), glutamic acid (Glu) and aspartic acid (Asp) The R values of coloured materials are easily calculated. If colourless f compounds suitable of 112 are separated, visualising materials are to agent. be the paper These identied or TLC methods but are plate are less must useful useful be when when sprayed small with a amounts quantication of Chapter large amounts made by solvent, of cutting then or Gas–liquid mass or sensitive foodstuffs often in required. Quantication removing analysing the the can, compound solution in using however , the spot be with a UV-visual from GLC spectrometer is used analyse forensic to can for separate pesticide analysis be fed directly identication. and identify concentrations to separate and into The traces in the a mass method of can be substances environment. identify in It Exam tips is particular Remember compounds, in samples and or of urine times using of in similar typical for ow is rate, given by compounds gas determine fuels. A gas concentration well-known use performance-enhancing components Quantifying A to analysing same conrmation that medicine athletes the the techniques spectrometry. arising IR and and used are spots, Separation chromatography, GLC components spectrometer very the quantitatively spectroscopy The materials out 10 are matched carrier mass have amounts gas with and those of stationary spectroscopy. similar is One retention in drugs. in testing The the blood substances the of GLC components retention and Additional limitation the separation in GLC chromatography retention known phase. that of blood the mobile is in the and depends on stationary mobility or paper the phase solubility in the phase. times. using GLC chromatogram is shown in Figure 10.3.3. hex-1-ene rotceted heptane pentan-2-one morf langis Key points 5 10 15 Column used retention time to purify natural can be products. (min) Figure 10.3.3 chromatography 20 The amount of each component The separation of three volatile organic compounds by gas–liquid in column chromatography chromatography can be calculated analysis If spectroscopic methods are not available for quantifying the amount of by samples by IR or of UV-spectroscopy. each component, Since the the peaks we are can use roughly the area triangular under in each shape, peak we as can a rough easily guide. calculate area: 1 area of triangle × = base × In gas–liquid chromatography, components of be by identied mixtures their can retention height 2 times. The computer attached to the GLC apparatus can calculate this value quite easily. We can also calculate the percentage (%) composition of The in component in the mixture as long gas–liquid each peak is well there the are peak peaks area is for all the directly components proportional in to the the mixture peak composition component be found concentration. area of under by each measuring the peak mass or by spectrometry. Chromatography in % each separated area of chromatography as: can amounts any pesticide can be used analysis, forensic A ________________________________________ = of component A testing sum of the peak areas of all the and purication of natural components products. 113 10.4 Raoult’s Learning outcomes law and vapour Vapour Figure On completion of this section, be able pressure 10.4.1 molecules state interpret a ask evaporate of water from from the Raoult’s law boiling of water an equilibrium molecules to and is established, from the in liquid O(l) Y H 2 curves of ideal has form a been removed. vapour . which is the the rate of movement same. O(g) 2 and The mixtures. pressure pressure. pressure partial exerted V apour exerted vapour vapou Liquids said to that be Liquids An We that the the each vapour varies molecules with component liquids dissolve do not liquids example say by miscible. Immiscible liquid by pressure is called temperature. in the vapour In the a vapour mixture, alone is the called the pressure Mixtures of Figure 10.4.1 air and point– H composition non-ideal which surface to: Eventually, shows you W ater should pressure is a – in An Raoult’s each dissolve form is an in of whatever is a each separate mixture mixture other , example other if of are after and solution the mixture layers hexane ideal law volumes ethanol said to be shaking added, and are water . immiscible. them together . water . it obeys Raoult’s law : Liquid–vapour equilibrium The partial vapour pressure of a component in a mixture equals its mole in a flask of water fraction, × x the vapour pressure of the pure component. A, vapour erusserp of p pressure pure A hexane mole partial p heptane p vapour ruopav of A = p° A × x A fraction A of A in in p hexane mixture mixture p For 0 an ideal mixture of two components A and B, the total vapour 1 pressure mole fraction of is: hexane o pure pure heptane hexane p Mixtures Figure 10.4.2 = p T form ideal + p A = solutions o (p × B x A ) + (p A × x B ) B if: Vapour pressure– the intermolecular forces between the molecules in the mixture are composition curve for a mixture of hexane similar to those in the pure substances and heptane there Figure are no 10.4.2 enthalpy shows the or volume effect of changes Raoult’s on law mixing. on an ideal solution (a Did you know? mixture All liquid greater mixtures or law. Those lesser that deviate to extent from more or of law are mixtures. The from boil’ two Greek and called word ‘state’. at a xed temperature. As the mole fraction the partial of the more volatile component (hexane) increases: Raoult’s pressure pressure of of the the less more volatile volatile component component increases and the decreases zeotropic comes meaning the total pressure pressures ‘to the The line = for total the experimental often use graphs. 114 heptane) less follow zeotropic words and a partial Raoult’s hexane boiling The increases so total pressure measurement points boiling that at any point the sum of the partial pressure of point is of mixtures is the a straight vapour to line. pressure mirror temperature vapour at is difcult. So we pressure–composition which the vapour pressure Chapter equals the atmospheric pressure. The molecules of a more 10 Separation techniques volatile 98 more mixture, mixture volatile the component boiling relationship Non-ideal escape points with more has vary the a as mole readily lower into boiling shown in fraction of the vapour point. Figure each For phase. an 10.4.3. So ideal There is a 69 gniliob linear a tniop the of ) C˚( component component. mixtures mole fraction Some law . mixtures The do not deviations relationship obey can between be the Raoult’s positive vapour law . or W e say negative. pressure or they deviate There boiling is not point from a and Raoult’s of hexane pure pure heptane hexane linear composition. Figure 10.4.3 Boiling point–composition curve for a mixture of hexane and heptane Exam tips will not be expected pressure–composition to do curves or ethanol and boiling based on vapour point–composition Raoult’s curves. ruopav Positive deviations from Example: calculations erusserp a You law cyclohexane. mole fraction The bonding between The between ethanol ethanol alone cyclohexane and and cyclohexane cyclohexane molecules get in the is weaker than ethanol pure pure cyclohexane ethanol alone. way of the hydrogen bonding in b ethanol The molecules So the ideal The to the in the There is mixture net are bond more breaking. likely to escape from the gniliob liquid molecules. tniop the vapour . vapour pressure of the mixture is higher than expected for an mixture. boiling point is therefore lower than expected. mole fraction ethanol Negative deviations from Example: ethyl ethanoate and Raoult’s pure pure cyclohexane ethanol law trichloromethane. Figure 10.4.4 The bonding between ethyl ethanoate and trichloromethane Positive deviation from Raoult’s law. The dashes show the line is expected if Raoult’s law is obeyed. stronger than There net The between ethyl ethanoate and trichloromethane alone. a Vapour pressure–composition curve and to So is bond molecules the the in forming. the b boiling point–composition curve. mixture are less likely to escape from the liquid Key points vapour . vapour pressure of the mixture is lower than expected for ideal Raoult’s law states that the mixture. partial The boiling point is therefore higher than vapour the b vapour tniop erusserp An ideal gniliob ruopav mixture × its of equals the pure mole fraction. obeys Raoult’s Boiling point–composition ideal mixtures show a can linear be curves drawn relationship mole fraction CHCl the composition and CHCl 3 ethyl 3 pure trichloromethane pure ethyl ethanoate pure the Negative deviation from Raoult’s law. The dashes show the line expected if Raoult’s law is obeyed. boiling point. trichloromethane Figure 10.4.5 a mixture between ethanoate a law. which pure in pressure component for mole fraction of expected. component a pressure a Vapour pressure–composition curve and b boiling point– Boiling for point–composition non-ideal positive or mixtures negative curves may show deviations. composition curve. 115 10.5 Principles Learning outcomes of distillation Simple distillation When On completion of this section, we boiling should be able need point understand which the principles distillation distillation separate below about a product 250 ºC which from a is a liquid mixture, we or solid can use with a simple to: distillation. to you are on For compounds boiling above about 180 ºC we use an air condenser . and fractional based. thermometer distillation water out flask condenser mixture water in distillate heat Figure 10.5.1 The a Simple distillation mixture lower boiling collected in of This the are time minerals salts in a be each not the in An it. in the components vapours of the mixture condenser of the will and mixture condense in with is have cooler condenser . boiling so component liquees they points do example The concentrated the their the the enough other . then points, if of other reach used present more If boiling and can vapour vaporises different as The receiver . ask method same point higher the mixture boiled. the sufciently parts is water is of the components not to the purication distils reach off rst, the of condenser of sea leaving the at water the the from mineral solution. Fractional distillation Simple other to distillation compounds separate fractional A column into used a longer contact the of glass (Figure successive separation within containing to The be used similar if the boiling narrow distillate points range of to is the boiling found one to contain required. points we In order use distillation is through 116 liquids surfaces come cannot with with liquid column the beads 10.5.2). the liquids rods or the whose a column descending vapour and or The column allows liquid with the and bulbous ascending separation vapour occurs equilibria. slower boiling the heating, points are the close better to one is the another . Chapter 10 Separation techniques thermometer water out condenser fractionating column packed water with glass boiling in point beads of pure tniop V gniliob distillate distillation (ethanol) B T (X) b L boiling flask point 0 X X 1 of pure C mole ethanol pure and B pure C fraction water of C heat Figure 10.5.3 Boiling point composition curve for a mixture of liquids B and C. Figure 10.5.2 The Fractional distillation line L represents the boiling point of the liquid. The line V represents the boiling point of the vapour. How does fractional distillation T o see two (when in components the the vapour mixture component, C, composition of the pressure is in of works X. it. this The can mixture = The we are external vapour , vapour distillate refer is to B and C. pressure), however , at Figure this shown 10.5.3. At the has its more temperature by . X In boiling mole of is other point fraction the of the volatile shown words, by the Q. Q T b q R gniliob C distillation tniop The how work? The S r liquid s mole 0 1 X X X 1 fraction of C in the vapour has X 2 1 3 increased. mole fraction pure Figure 10.5.4 When we shows heat up what the happens mixture of as we continue composition X to to distil its the boiling B pure C of C mixture. point, T : Figure 10.5.4 Boiling point composition b curve for fractional distillation The At vapour this gets boiling richer in the more , the vapour point, T by line volatile and component, liquid are in C. equilibrium. b1 Key points This The This At is shown vapour the rises up temperature the drop qQ. column is and gets represented by cooler line until it condenses. Simple points r , where the boiling point is lower , there is a new equilibrium mole fraction of C being is substances which are far used with to boiling apart from with each the distillation separate Qr . other, e.g. water from X 1 mineral At this lower boiling point, T , the vapour and liquid are in a salts. new b2 equilibrium. The This composition is of shown this by new the line mixture rR. is X , which has an even Fractional distillation obtain a complete liquids within is used to separation of greater 2 mole fraction of component C. boiling The process (mole As the continues fraction vapours = rise in this way until the vapour consists of C the column through successive equilibria, richer and richer in the more volatile component. Fractional distillation because series out of a Eventually the gets column richer and and are richer condensed. in the less The liquid volatile in the which works equilibria the up the vapour column, gets ask component. Its rich in the more boiling volatile point of they increasingly gradually of they in pass range points. occur further become narrow alone 1). in a component. increases. 117 10.6 Azeotropic Learning outcomes mixtures Azeotropic Some On completion of this section, be able interpret boiling point– curves mixtures in compare the a of from azeotropic qualitative efciency manner by simple be of the of ethanol from some ideal mixtures of liquid separated other behaviour are ethanol and because the or separation can mixtures or partly which deviate separated by widely fractional from ideal distillation. to: composition distillations mixtures compositions However , other you behaviour should and called water , be azeotropic and boiling minimum. compositions cannot ethanol point Figure of liquid separated mixtures. and shows mixtures Examples They diagram the which fractional benzene. composition 10.6.1 by boiling are HCl cannot shows point deviate distillation. a and be widely These water , separated distinct maximum composition curve for a water mixture of mixture having ethanol and benzene. Ethanol is the more volatile component. A and fractional a minimum boiling point is formed. distillation understand the advantage carrying out distillation reduced pressure. of under tniop gniliob 0 X X 1 mole fraction Figure 10.6.1 If we start X 2 1 3 of ethanol Boiling point–composition curve for a mixture of benzene and ethanol with a mixture of initial mole fraction of ethanol X and apply 1 the same ideas distillation pure a about results benzene mixture fractional distillation as in Section 10.5, fractional in: and having composition X 2. The mole fraction of ethanol represented by X is 0.54. 2 If we start with a mixture of initial mole fraction of ethanol X , fractional 3 distillation pure a results ethanol mixture in: and having composition X 2. The mole fraction of ethanol represented by X is again 0.54. The 2 minimum The boiling mixture of point is benzene 67.8 °C. and ethanol represented by X is called an 2 tniop azeotropic cannot completely gniliob Azeotropic is a mixture or of constant separate mixtures mixture a can such also boiling mixture . mixtures have trichloromethane by can fractional maximum and Y ou boiling propanone see that we distillation. points. (Figure An example 10.6.2). Ethanol distillation mole fraction of propanone When not Figure 10.6.2 118 distil pure an ethanol–water ethanol in the mixture receiver . We using get a simple mixture distillation, of water we do and Boiling point–composition curve for a mixture of trichloromethane and propanone we get ethanol. many The times process to get a is not very very high efcient. alcohol We would content. This have to does not repeat this matter too Chapter much if we because made more efcient alcohol making alcohol process. constant to alcoholic content concentrated because Fractional order are the But distillation boiling by even alcohol pure the alcohol–water the ethanol. fractional a mixture produce not a with ethanol an with as be of silica and gel. This not water of water a mole removed absorbs the The pure water . produces a %. by phrase In drinks the contains drink authorities but ‘proof This used method partly is is decompose sometimes because called the it used can to distil they in are produce distillation . can be 0.016 atm). rubber liquids reduced The to If the which to would product. value of is is (see The attached the vapour shown in completely pressure distillation purer used either atmospheric apparatus the apparatus at steam a not 70% ancient could spirit’. The that alcohol. test collect drink mean to so tax was It that on poured gunpowder. be lit, the If the spirit gunpowder was ‘proof ’. pressure distilled preference sometimes vacuum pressure (about if reduced an does applied not could under proof ’ alcoholic over Distillation ‘70% comes from shaking water techniques be more with Separation Did you know? can produce 95.6 is whisky is mixture content remaining or Ethanol which does boiling ethanol rum 100%. distillation ethanol the such to distillation, constant mixture mixture need fractional forms of beverages does 10 Section method to a It 10.7) is water pressure Figure or (1 atm). of also pump, water 10.6.3. tubing condenser to vacuum pump capillary tube 10.6.3 Apparatus for distillation under reduced pressure. The capillary tube reduces sudden movements of the liquid (‘bumping’) which often occurs in these distillations. When the reduced. distilling of pressure We can impure phenylamine 0.02 atm The is reduced, purify the phenylamine is boiling phenylamine reduced to under 77 °C reduced if the liquid 184 °C pressure. distillation dimethyl sulfoxide, (CH ) 3 reduced of point is at The carried is also 1 atm) boiling out at by point about pressure. solvent vacuum point (boiling distillation because it is SO, is commonly puried by 2 more stable when distilled under pressure. Key points An azeotropic Azeotropic minimum Fractional Distillation cannot mixtures form or mixture maximum distillation decompose under if is more at completely constant boiling reduced distilled be boiling point mixtures depending efcient pressure separated is atmospheric than used on which the repeated to distil by distillation. have either a mixture. simple distillations. compounds which may pressure. 119 10.7 Steam distillation Learning outcomes Steam distillation Immiscible On completion of this section, two should be able immiscible do not liquids mix. the understand the principles vapour pressures of the pure o how So nitrobenzene phenylamine can be puried the total steam understand distillation the use of of in simple examples distillation industries of is oils and equal to water . the For sum of components: e.g. than p B pressure The o p is higher temperature that of either than at o = p + T p H O 2 the which vapour the component oil pressure mixture alone. We boils can of either is take of and oils from of in with to distil water plant and oils have or other other substances contaminating which are compounds in calculations the application the fragrance in this steam them. give alone. lower immiscible plant distillation advantage + A vapour component therefore by is pressure o = p T distillation understand and example vapour of p steam An total to: the liquids you the This through a increased (Figure extraction process liquid and is called which the is steam distillation . immiscible mixture boils at a with When water , the temperature steam vapour lower is bubbled pressure than is 100 °C 10.7.1). plants. steam p total condenser )mta( p H 0 2 1 atm steam erusserp generator p L ruopav X 100 substance temperature immiscible (°C) heat with water water Figure 10.7.1 Vapour pressure–boiling e.g. oil in lemon peel point curves for two immiscible liquids, L oil and water. The boiling point of the mixture, X, is below that of water. 10.7.2 We Steam distillation of a plant oil can from Cut Put Bubble Condense Collect Use part of the Bhutan, a small state in the H 6 peel the Mountains, grass steam to is 120 distillation make a ask mixture plant separating distil and of plant oil such as limonene is: sections. add just enough water to cover the peel. mixture. steam oil/water a procedure small the funnel to The into through the and mixture (see plant in Section a oil. receiver . 10.8) to separate the plant oil water . distillation is used to purify and nitrobenzene, dependent perfumes. of lemon C 2 Distillation decomposition. on peel. peel into steam the NH 5 points. Himalayan a lemon the distillation orange compounds such as phenylamine, economy C of the from Steam large the steam or Did you know? A apply lemon H 6 at a lower NO 5 , which have relatively high boiling 2 temperature reduces the risk of thermal Chapter Calculations We can calculate comparing each the involving the mass component of molar of the of and mixture a liquid liquid in from present steam steam in the distillation distillation distillate. we can use techniques by Since behaves o independently, Separation steam distillation mass water 10 Raoult’s law and the equation o p p T + = H p O A 2 to develop a third equation: n p H O H 2 ____ O 2 _____ = p n A p are n partial are the pressures number of mass of liquid moles of of liquid A A A and and water water . ( m) _______________________ Since n = molar we can write mass this of liquid equation ( M) as: p m H O /M H 2 ____ O H O 2 2 __________ = p m A Worked When nitrobenzene mercury), pressure water example the of and is steam distilled distils at 10 g nitrobenzene. is of 733 mm = at 99 °C. mercury. nitrobenzene. (M A 1 mixture water /M A a At pressure this The Calculate of distillate the 1 atm temperature, (760 mm the contains relative vapour 40 g molecular of mass of 18). water Step Step 1: 2: Calculate the 760 – 733 = Substitute vapour 27 mm the pressure gures p into m nitrobenzene: the equation: /M water water _________ of mercury. water ___________________ = p m nitrobenzene 733 /M nitrobenzene nitrobenzene 40/18 ____ _____________ = 27 10/ M Key points nitrobenzene 733 18 ____ So M = × 10 ________ × = 122 Steam distillation is used to nitrobenzene 27 40 separate liquids Worked example mixtures or to of extract immiscible oils from 2 plants. Phenylamine was steam-distilled at 98.6 °C and a pressure of 760 mm mercury (1 atm). The 720 mm mercury. vapour pressure of water at this temperature Steam purify The distillate contained 25 g water . Calculate the phenylamine in the is used to high boiling point liquids mass such of distillation was as phenylamine and distillate. nitrobenzene. = (M 18, M water = 93) phenylamine Step 1: Calculate 760 – the 720 = vapour 40 mm pressure of For two total phenylamine: the mercury. immiscible vapour vapour liquids pressure pressures = of the sum the of pure components. Step 2: Substitute the gures into the equation: p m water be M phenylamine 720 masses can calculated from the moles, n, /M phenylamine phenylamine of each immiscible distillate 25/18 ____ molecular water ___________________ = p Relative /M water _________ by the liquid in the equation: ____________ = 40 m /93 p phenylamine n water water _____ _____ = p n A 25 m = A 40 ___ So ____ × × 93 = 7.2 g phenylamine 18 720 121 10.8 Solvent Learning outcomes On completion should be able of this extraction Introduction section, Solvent extraction solvent. A understand which based the solvent undertake on principles extraction simple on is based calculation partition out an describe simple experiments partitioning two be solvent used to which separate is two immiscible solutes with dissolved the rst is in used a chloride immiscible a the solutes separating solution (soluble on solute Put the in from funnel of the (see iodine water) aqueous solvent separation a using of rst Figure (very and solvent. we 10.8.1). slightly want The to extraction For soluble example, in separate water) the is to if we and iodine carried have sodium we: coefcients based of one aqueous second to: extract can you which immiscible a mixture in the separating funnel then add another is with water between good solvent for iodine, e.g. hexane. solvents. Shake The the the will sodium Run Repeat off been contents iodine The the the go of chloride bottom process removed solvent the into separating the funnel component remains in the in then which aqueous let it the is layers more settle. soluble and layer . layer . with from the (hexane) fresh solvent aqueous is until nearly all the iodine has layer . evaporated, leaving the iodine as a solid. separating funnel solution shake hexane of iodine in solution solution of of salt and in Figure 10.8.1 hexane iodine in salt water water When an aqueous solution of salt and iodine is shaken with hexane, the iodine moves to the hexane layer The distribution Solvent extraction immiscible between The immiscible concentrations equal depends solvents. two coefficient volume present. of on the amount solvents For relative of solubility solute depends example, trichloromethane, if on we the shake , CHCl which in a is of a solute in partitioned two (divided) equilibrium aqueous ammonia separating funnel, with an ammonia 3 molecules move between the two layers (CHCl NH 3 The concentration titration. The distribution of coefficient in NH layer for partition equilibrium is established. (aq) 3 each constant or Y an 3 ammonia equilibrium ) until this can be process coefficient , K determined is . called The by the value of D vary with temperature. Most values [NH are quoted at K may D 298 K. (aq)] _____________ 3 For this equilibrium K = = 23.3 D [NH (CHCl 3 Note that partition expression 122 which coefcients has the are higher )] 3 usually quoted concentration on for the the equilibrium upper line. Chapter Calculations using the distribution 10 Separation techniques coefficient Exam tips Worked example 1 In A solution of butanedioic acid (BDA) in ether contains 3 BDA ether . This solution is shaken with the mass of BDA extracted into the of water BDA(ether) Y BDA(water) 1: Calculate the concentration in each is 6.7 the to m is Step 2: the layer (4.0 × mass so Substitute m values 1000 concentration of volume are as the long same. is because So, as long are the the 1000 cancels. as the units of same, the expression volume can be 1000 [BDA(ether)] – like this. m) = × 1000 20 in is the _________ = 50 ether the units simplied m (if ignore component. ___ [BDA(water)] can layer . D Step you water . This for K 2, relating 50 cm as Calculate Step in 3 of 20 cm 4.0 g the water , this subtracted into the must from the equilibrium have mass come in from the the ether layer) expression. m ___ Exam tips 50 [BDA(water)] ____________ K = 6.7 = D [BDA(ether)] (4.0 – m) _________ Remember 20 m = the 3.8 g mass two example of extractions using single a solvents A using larger and B, small volume where of portions solvent. for K [B]/[A] of solvent We = can see are more this by efcient than comparing two we the have 15 g amount of of solute solute in 3 50 cm transferred m = of to (15 ___ 4 lot in of do not solute for as solute the rst use 3 If are calculating extracted use the using the same second you will used have in the rst. A been extraction. You removed should 4. D you 2 extraction Several if solute extractions, amount Worked that of A B – and is shake given it with 50 cm of B, the rst amount extraction removed by: in of solute MINUS the rst in the the amount extraction. m) ________ ÷ = 50 12 g 50 3 If we extract extraction the solute using two portions (15 m ___ the rst second – m) ________ ÷ = = 50 the 25 cm gives: 4 and of extraction 10 g 25 gives: Key points m (5 ___ 4 = the total extracted is m) ÷ = 50 So – _______ 10 3.3 g 25 + 3.3 = Solvent the 13.3 g in Some uses of solvent extraction two The the Ether extraction is often used in chemistry to separate products extraction relative immiscible distribution constant synthesis from water . The ether layer oats above the The evaporate useful Cosmetic cosmetic In the the is separated organic product the creams metallurgy are often different and ideas chemistry the ether behind. volatile have to they The or take use (very ammable) technique unstable account in the to of is is left immiscible relative formulation of between uses are molten ideas of used metals relative to determine and solid solubility from The how readily industrial food pollutants are taken up into the a relates of a solute how if metals. between the two of solute solvent can distribution extracted solution be by calculated coefcient is known. when Several extractions using small groundwater portions of efcient than solvent are more wastes. industry of is particular which particular uses solvent extraction to analyse the compounds in fats and aqueous using a single larger relative volume solubility coefcient a solvents. amount from deducing The another extraction on solute liquids. concentration partitioned especially heat. the a to colourings. solvent distributed Environmental is solvents hair of and product required manufacturers in impurities layer leaving when solubility ether at of aqueous the layer . based of temperature organic is solubility of solvent. solutions. 123 10.9 Distillation and solvent extraction: applications Learning outcomes Distillation Rum On completion of this section, be give of able examples the of in the the rum understand can be molasses (a by-product of sugar rening) or from sugar juice. application Y east and water are added carbohydrates for the producers particular to yeast the to molasses feed on) to (which start contains the the fermentation. Different petroleum industry use strains of yeast but many use the foam from and previous the fragrance from industry to: distillation industry, made rum you cane should is in the fermentations. industry how acids separated by and H C bases 6 O 12 (aq) → 2C 6 H 2 OH(aq) + 2CO 5 (g) 2 solvent When fermentation is complete the aqueous mixture is distilled. extraction Some select appropriate methods pot separation when given producers still and the of the and chemical components of a avours producers materials vapours. that The which are higher up use The fermentation Many rings. Did you know? of the earliest is in a give a rising cooler . the references to ‘The of too Either to high. they extract make . . . distilled, in this the is island made of vapours reach a area which condenses they like surface vapour directly rum to the its is in for is of a type pot in alcohol higher levels progressively Section of fractional stills. condensation higher the become (see This series It of than of is the the richer lled with rising the column, in alcohol the 10.5). industry are oily volatile hydrocarbon-based in nature. oils or solvent extraction for the Some oils are extraction compounds plants or contain easily steam often only denatured if distillation with very aromatic small temperature is commonly is used a hot, hellish a time to the raw extract material the is aromatic immersed in compound. the solvent Hexane and and is ether a lot are of two water , of the two solvents layers are most commonly formed – an used. aqueous If the layer plant (arising and the water present in the plant material) and an organic layer which liquor’. contains the extracted or desired from distillation. fragrance material Steam leaves and as it waxy rose is oil. Other lower low is of to of be in which extracted Ethanol is not Some remains with fragrances after ethanol, usually used solvent e.g. to can be extraction jasmine extract fresh plant water . used for plants, than compounds. ‘concrete’ can soluble stems sufciently extracting since 100 °C. prevent the oil The oils and distils fragrances off with temperature decomposition of the of the from water distillation fragrance owers, at is molecules. methods V acuum which the mixture These distillation and temperatures 124 the sugar from terrible applied fragrances. solvent contains canes is giving chief fuddling dimethyl Rumbullion Heat document from shaken (drink) are distillation. behaves large The still fragrances Many column mixture amounts In Barbados. stills). compounds evaporate. column The fragrance (1651) (pot aroma mixture. distillation. rum batches and properties Other One in alcohol the characteristic physical work of distillation: are easily This denatured can if be used fractional to extract some distillation is components used. Chapter Fractional to remove distillation: If the contaminating fragrance molecules molecules with less are stable, pleasant this is 10 Separation techniques used odours. Petroleum distillation Crude oil different is a mixture components Some of Primary the distillation fractional is separated the middle into a number of distillation: removed separates distillate, fractionation solvents to salts larger then are It of by oil simple into distillate distillation. several and groups residue) of by are discussed extract generally organic is soluble molecules tend in to further acids water . be in and in 12.1. bases Neutral insoluble Section molecules, retaw Ionic (light gases types distillation. Petroleum Using hydrocarbons. several dissolved components of by especially water . B ionic ni a as phenylamine, mixture of an organic the acid following – H C 6 If we OH Y C 5 add H 6 a slightly phenylamine, the such as phenol equilibria and an organic + + H and C 5 H 6 stronger such exist: + O base base phenylamine to a ytilibulos In NH 5 + H Y C 2 mixture remains + of H 6 phenol uncharged but NH 5 3 A molecular molecular and the 7 phenol pH becomes but the deprotonated. phenylamine The is phenol present is only present as in the form of an ionic salt Figure 10.9.1 molecules. The molecular and ionic forms of organic acids (A) and bases (B) at H C 6 OH + OH → + OH → C C 5 H 6 O + H + H 5 different pH values O 2 + H C 6 If we add an acid, phenylamine NH 5 the 3 phenol becomes H 6 remains protonated. in The NH 5 its 2 O 2 molecular phenylamine form is in but the the ionic form. + C H 6 O + H + H → C 5 H 6 OH 5 + H C 6 We can separate the NH 5 ionic + → C 2 form H 6 from the NH 5 3 molecular form by solvent extraction: A mixture solvent The An of e.g. organic acid and dichloromethane mixture is poured into a organic or base is dissolved ethoxyethane separating (an in a suitable ether). Key points funnel. aqueous solution of another acid (or base) is added to adjust Distillation fractional pH so that the molecular or ionic form you want is The water/solvent mixture is shaken and the phase containing in either the molecular form (in non-aqueous solvent) form (in the aqueous layer) is separated production and suitable method of depends of spirits such as Many perfumes extracted and fragrances or using steam solvent extraction. separation This or in whisky. distillation a used off. are Selecting is or ionic process the rum compound batch distillation present. the by the on: Acids or and bases puried using can be extracted solvent extraction. Solubility: An dissolving the Boiling be points: separated insoluble latter A by solid then mixture fractional can be separated from a soluble solid by ltering. of liquids with different boiling points can The selection method depends distillation. boiling Solubility in different solvents: Use solvent of of a suitable separating on substances properties points and such solubility as in extraction. particular solvents. 125 Exam-style Answers to all exam-style questions –34 h = 6.63 × 10 8 J s; c = 3.0 × 10 can questions be found on the – Module 2 accompanying CD –1 m s ii The equilibrium system can be represented by the equation Multiple-choice questions Br Y Br 2(H O) 2 1 The diagram hydrogen n = is 3 to shows some atom. An energy of the electron level the frequency of n = the 1, energy levels moves from emitting emitted a of a energy iii level At a temperature partition 2(CHBr above coefcient ) 3 25 ºC, would the value of change from the 66.7 . photon. What A only C ii i B i D i, and ii radiation? and iii ii and iii –19 n = 3 2.40 × 10 J 6 n The actual a food –19 amount sample was of potassium ions 4.25%. The food present sample in was J analysed by four different approaches, four different experimenters, who repeated times. The results are given experimenter’s results show each using test below. Which –19 n J 14 A 8.27 × 10 C 3.29 × 10 15 Hz B 2.93 × 10 Hz D 3.65 × 10 15 2 What is the wavelength 3.40 × Hz 15 energy of of nm? 650 a light photon and the highest degree A 5.21, 5.22, 5.21, B 5.45, 4. 11, 4.25, C 4.25, 4.24, D 4.20, 4. 15, 5.21, 5.23 4.84, 6.43 a 4.23, 4.35, 4.26, 4.30, 4.27 4.25 –29 10 J B 1.44 × D 6.63 10 J 3 –19 C 3.06 × 7 –19 10 J × 10 In a There are four types of back-titration, –3 of 25.0 cm 1.00 mol dm HCl J was 3 of precision? Hz with –36 A accuracy electromagnetic radiation in added to an agent CaCO in antacid a containing conical ask. The the active excess HCl was 3 the list –3 below: titrated with 0.55 mol dm NaOH solution and it 3 i X-ray ii infrared iii microwaves iv ultraviolet was found a that complete a volume reaction. agent CaCO , does of How the 27 .3 cm many antacid was moles required for of the active contain? 3 Which of the lists below gives the radiation in order –2 A of increasing 1.5 × –3 B 10 5.0 × 10 wavelengths? –2 C A i, iv, C iv, ii, iii B ii, iv, D iii, iii, i, ii i, ii × 10 D 7 .5 × 10 i 8 iii, 2.5 –3 A 1.5234 g sample of impure BaCO was reacted with 3 iv excess dilute hydrochloric acid. The CO liberated 2 4 For a system where a solute R is distributed between was two solvents, and R has the same absorbed both solvents, the equilibrium process may is Y solvent of to weigh the % of barium in the sample? 0. 1425 g. [Relative mass C = 12.01; O = 16.00; Ba = 137 .33] as: R Which and found be atomic represented NaOH molecular form What in by 41.94 % C 29. 19 A solution B 9.35 % D 90.65 R 1 these factors A solvent would 2 affect the value of the % % –3 9 of of KMnO molarity 0. 102 mol dm 4 partition 3 coefcient? required 30.35 cm to react completely with 3 i the mass of ii the volume iii the the of solute the originally in solvent 1 22.24 cm What solvents is MnO i and C i, ii B ii and and iii D only 1 mole of molarity ratio for the 0.348 mol dm reaction . between and X? MnO : 2 X B 2 MnO 4 iii C ii the solution X 4 temperature A A –3 of 0.4 : MnO 1 X D 5 MnO 4 iii 10 Propanone : 5 X : 2 X 4 4 shows absorption maxima at λ max 5 The partition coefcient for between Br water and 2 189 nm and λ 279 nm. What type of transition max tribromomethane at 25 ºC is 66.7 , where the bromine responsible for is in the same molecular form in both solvents a higher these i If solubility statements the is in tribromomethane. Which of true? concentration of in CHBr Br 2 , then the these 189 nm λ max 279 max A π → π* n B σ → π* σ C n → π* n D n → π* σ → → π* σ* is 3 –3 0.250 mol dm of concentration in H O is → σ* 2 –3 3.75 126 × 10 –3 mol dm absorptions? and λ has each → π* nm is Module iv Structured questions 11 a Distinguish between the terms What would drops of and ‘titrimetric analysis’. identities and the of liquid questions the rst few remaining in distillation ask, if the following mixtures [2] are fractionally b the distillate Exam-style ‘gravimetric the analysis’ be 2 distilled? A sample was prepared by mixing a number 0.79 mole fraction of 0.25 mole fraction acetone. acetone [2] of substances and the entire sample was then [2] dissolved in distilled water in a 250 ml volumetric ask. Two students, Julia and Jenny, were then 13 a UV-visible spectroscopy and IR spectroscopy are asked to determine the mass of calcium present in two of the spectroscopic methods of analysis. the 5.524 g sample by using different approaches. Compare these methods in terms of the type of Julia titrated three 25.0 ml aliquots of the solution information that can be obtained from their use. [4] –3 with 0. 100 mol dm EDTA and found that the 2+ b 3 mean titre was 37 . 10 cm The concentration of in FeSCN a solution is . Jenny placed 150 ml in a beaker and added excess Na CO 2 to be at λ determined by UV-visible spectroscopy, solution. She 3 580 nm and using a 1.00 cm cell. A max then collected, dried and weighed the precipitate, calibration curve was plotted for the system and which had a mass of 2.403 g. the [Relative atomic mass Ca = 40.078; O = molar absorptivity 3 = was found to 15.999; be C coefcient 7 .00 × 10 3 dm –1 mol –1 cm . Five students each 12.011] 3 diluted i Based on Julia’s approach, what is the mass ii in the Julia’s iii sample? Calculate What the % the iv Based of calcium in the sample from [1] identity of the of Ca in the placing 10.0 cm 100 cm water up volumetric ask of each the and the to the graduation and adding diluted results are mark. The distilled solution shown was in the then absorbance determined table below. precipitate by Jenny? on Jenny’s by 3 a Student obtained solution, [4] approach. was original of in Ca the 1 2 3 4 5 0.552 0.564 0.550 0.554 0.540 [1] approach, what is the mass sample? Absorbance [4] at λ 580 nm max v The actual mass of Ca in the sample prepared i was 1.518 g. From a consideration of Explain how coefcient, relative error, comment on the accuracy and Jenny’s results. Suggest ONE factor that could have mass obtained of molar absorptivity determined from the curve. [1] Calculate by Jenny to be the mean absorbance and use this caused to the was [2] ii vi ε, of calibration Julia’s the value the higher determine the average concentration in than –3 mol the expected value. in dm the diluted solution. [2] [1] 2+ iii 12 a Explain what is meant by the vapour pressure of liquid. a i How does the an increase boiling in point external of a pressure concentration of FeSCN in the [3] liquid? Explain why this Find the standard deviation of the students’ results. [2] [1] c c the solution? [2] affect ii is original iv b What occurs. [2] The IR spectrum for the compound ethyl ethanoate O For the two-component system acetone and carbon disulphide, an azeotrope is formed at mole CH C C CH 3 CH 2 3 fraction 0.36 of acetone, and has the boiling point –1 shows absorption bands at 3000–2850 cm , of 312 K. The boiling point of pure acetone is 329 K –1 1742 cm –1 and 1241 cm . and the boiling point of pure carbon disulphide is Identify 319 K. rise i Sketch this the boiling point intermolecular forces total volume these Would the happens of two the to of bands. bonds that most likely give [3] the: attraction liquid liquids mixing exothermic these of [3] Explain when what to type curve for mixture. ii iii composition the be process? are an mixed. endothermic [2] or [1] 127 11 Aluminium 11. 1 Locating Learning outcomes chemical industry Factors that influence the location of chemical industry On completion should be able of this section, you to: In recent the understand inuence the industrial describe the factors location some general in the of there has been aluminium much smelting discussion plants. in There the are Caribbean many about factors that that of inuence the location Nearness to ores of chemical industry, some are discussed here: an plant requirements years, building safety Metal chemical and the takes source are a of heavy, lot of raw so materials to (including transport them a water long supply): distance is expensive energy. industry. W ater is used manufacture close. This Bromine being Did you know? are The traditional chemical often found near ports easy import of raw export of plants products. The which produce such as less affected mentioned by So plants seawater , bromine used in heating water are so it near makes the In So be sea. to set addition industries most acid should the sense sea. chemical medium. sulphuric supplies located near most e.g. up a to for chemical plants rivers. network: the products away T o from transport needed. For environmental the the factory, raw good materials road and to rail the links reasons, heavy materials such as metal siting are best transported by rail rather than road, to minimise pollution. speciality metal ores are transported by ship, so the nearness to a port or pharmaceutical specially is near communications Many chemicals or is a and ores of sea as processes, ethanol. from water or many materials are and solvent the of chemical manufacturing material, a in which factory allow some manufactured raw near material production why plant as raw industry Good is a cooling, a and is is chemical as built harbour is very important. the factors Labour: here. those Employees in many chemical provide plant such Availability out at high in other the chemical areas should be of industry tend manufacturing. near enough to a to The be more location centre of skilled of than the population that can people. of cheap energy: temperatures, Many e.g. chemical smelting reactions metals. Many can only others be need carried heat to Chemical industry in the Caribbean give Cuba Trinidad Nickel and Tobago Petroleum Ammonia an economic synthesis of separation rate of ammonia processes conversion and also making require of reactants sulphuric heating, to acid. e.g. products, e.g. Purication and distillation. and Gas and oil are used often used as heat sources in industry. Although gas fertilisers and oil can be transported, it makes more economic sense to site a Pitch factory or plant near an oil renery or close to a gas pipeline. Most oil Petroleum reneries are near the coast because the petroleum is transported from Methanol the producing countries in ships. Iron Jamaica Guyana Iron Bauxite Bauxite to and and make steel the plants coke are often necessary sited for the near deposits reduction of of the coal iron which are used ore. alumina Electrolysis the of aluminium electrolyte energy is sources molten. expensive, of The If 128 it plant is (i) and power social should the is requires provided aluminium hydroelectric Environmental so oxide This or smelting close to amounts electrical plants the of energy heating. are often to keep Electrical sited near coast. factors: preferably process large by carried not out be built should in be an in area the of natural national beauty. interest Chapter (ii) there restore should the area be no alternative when the factory sites is (iii) no there longer should be is a plan to Safety in the 11 Aluminium chemical viable. industry It should affected not by be the transporting sited fumes raw so close or noise material to and a (i) centre from of the population factory (ii) that from people are Care lorries It should the be factory sited to damage minimise the the possibility environment, e.g. that waste waste products products do not from rivers and harm the area, it people were and historical makes and it the to set environment established near to production. the If up is there a is new industry factory minimised. coalelds, where already because In the there the past, were existing impact many already in country grants Political also play a and tax part on factories aluminium centres factors such as the availability the Government in the in incentives the to location develop of a of T rinidad of vapours/waste particular and T rinidad T obago near regions of coastal the to set up of an La of the ammable, pipes and chemical weakening pressure Problems town in be radioactive of the plant structure vessels. a can access to be overcome proper including and Tobago? wanted the may or of factory. smelter for Trinidad south or of safety protective and access by: clothing suits, to face oxygen aluminium and smelter harmful of corrosion masks The of which vessels An prevent: reactants/products leakage explosive the of government to get industrial taken wildlife. factors: easier be leakage gases Political to poisonous into has products. Brea. chemicals to neutralise This spillages would this be of advantage location The raw to the economy of the country. The advantages of regular checking checking materials can be sourced nearby; puried aluminium be corrosion. transported from Jamaica and bauxite ore is available the conditions of oxide pressure can for are: vessels from monitoring the working Guyana. environment It is near the sea so water is readily available and raw materials can using specic be sensors transported by ship. There is already industry present in the area – the T rinidad Lake checking that instrumentation of is working correctly. Pitch. Finance and a was loan The project port and required This available from the would provide new power were going project has from the Chinese work station to be currently Chinese company Government to for many provide was people the involved also huge in the deal available. especially amount of as a new electricity built. stalled Key points however , for various reasons: Environmentalists surrounding Some local The material arsenic people the The plant and is roads about the damage to the coastline and are worried close lines are other to the to about the about substances the site are the town smelter worried toxic leading on materials, too that people and worried location depends land. that time are The pots the in not pollution of La in needs a the fumes and replacing from the from time to cyanide, pots. suitable and scale chemical industry the Caribbean has some these are not present in a large scale. The main reserves worthwhile large-scale alumina ease production industries and natural production of metals such as nickel in gas petroleum/ in Trinidad are and Tobago. The chemical amounts to merit chemical industry is industry should and tight safety requirements extraction to on energy, environmental production have copper , raw in the Caribbean Although industry of ammonia/fertiliser important Large and important Jamaica, condition. source social factors. Bauxite are chemical available transport, and Brea. dangers the from of of the eliminate possibilities of res, processing explosions or release of toxic bauxite. materials. 129 11.2 Aluminium Learning outcomes production Introduction Aluminium On completion of this section, 7.5% should be able describe of the the crust most and abundant is present metal the processes involved slate. It aluminium is extracted oxide, e.g. from bauxite gibbsite O Al 2 in the production of its the Earth’s with silica crust. in It clay , forms shale, about granite ores, ·3H 3 which O, contain boehmite Al 2 hydrated O 2 ·H 3 O. 2 aluminium Aluminium from in combined to: and is you is obtained from bauxite in two stages: ores describe explain how why bauxite is Purication Electrolysis of bauxite to make aluminium oxide (alumina). puried of the puried alumina. aluminium impurities production requires a high energy consumption. alumina Al O 2 3 electrolysis bauxite aluminium production Did you know? NaOH cryolite electrical energy It has that been much contains known of an associated It about was 1943 recognised land the not, that and the red earth limestone however, its until signicance the Jamaica started to 1820s in Jamaica aluminous with rocks. company the since The main of extracting bauxite’ 3–25% iron( III) these has in bauxite 1–4% oxide and silica are oxides and 1–7% very of silicon, little iron. iron ‘Red and titanium. bauxite’ has silica. Alumina production the hydroxide is used to dissolve the aluminium oxide from the ore aluminium and from impurities ‘White Sodium possibility Steps in the extraction of aluminium from bauxite was Bauxite investigate Figure 11.2.1 separate the impurities. Approximately 2.5 tonnes of bauxite are rocks. needed to make 1 tonne of puried alumina, O Al 2 iron oxide O (Fe 2 (SiO ) ), titanium dioxide (TiO 3 present, ) and . In order to remove the 3 most of the silicon dioxide 2 the bauxite is treated with concentrated sodium hydroxide. 2 Aluminium oxide basic do oxides Stage is not 1: Powdered pressure amphoteric, dissolve bauxite (4 atm) in is at so it dissolves sodium mixed with 140 °C. in hydroxide This 10% sodium and are NaOH takes about hydroxide. ltered and 1–2 The off. heated hours under to complete. O Al 2 + 2NaOH → 2NaAlO 3 Silicon dioxide reaction Stage with is sodium silicate 2: The sodium aluminate settle 3: The and and sodium agitated Slow cooling H formed metal are is is during aluminate then soluble oxides ltered with either O 2 aluminate or prior to this step by hydroxide. The to Stage removed sodium contaminating + 2 sodium are removed in not. sodium The by precipitation. hydroxide impurities but are allowed off. is ‘seeded’ with pure aluminium oxide air . produces a precipitate of pure aluminium oxide trihydrate. + 2NaAlO 2 Stage 4: After 36 hours dehydrated recycled. 130 in O → Al 2 the a 4H alumina rotary O 2 kiln ·3H 3 O + 2NaOH 2 is removed by at 1000 °C. The vacuum ltration sodium then hydroxide is Chapter Electrolysis of pure 11 Aluminium aluminium oxide Exam tips Compounds molten or in electrolyte. would as it be is and solution. oxide impossible require too soluble cryolite, in solution much AlF Na considerably. the melting cryolite used is melts The alone. This cryolite calcium or is takes the very energy conduct alone high this and electricity cannot melting be used point temperature special it will aluminium 1000 °C calcium or in a when as In an (2040 °C). for containers. dissolve uoride and so uoride mixture helps a long It time Aluminium mixture calcium of to reduced about be or the aluminium lowered energy 5% reduces further than consumption. aluminium oxide So this is is the in tanks baking cathode is If it not undergo you added its will to the to read that aluminium melting true, a main purpose dissolve were not break up oxide point. Although the of dissolved, into the aluminium ions it or electrolysis. electrolyte little (cells anthracite or ‘pots’) and lined pitch. The with carbon. carbon lining This of the siphon tanks is lower could causes books adding the and to oxide. costs uoride cryolite cryolite uoride. energy many uoride. place by a maintain and containing made oxide However about aluminium Electrolysis carbon of only 6 at added point has to water . 3 This non-metals Aluminium Aluminium not molten metals nearly would oxide of (negative electrode). The anodes (positive tube electrodes) + are 20 blocks anodes into the of carbon each cell as dipping about the into 400 mm electrolysis the wide. molten The electrolyte. anodes can be Large cells lowered have + further proceeds. carbon The of cells are 40 000 amps electrolytic It linked takes a lot of for a requires about are series. required. reactions 1000 °C smelters is in and energy long to period built voltage About the rest keep of 15 kilowatt usually A the hours where 5 V one-third is time. of used to is of the keep temperature The of of a huge is of of 1 kg this of current used electrolyte electrolyte For amounts and electricity the production electricity. large used at in cathode (–) molten aluminium molten. nearly aluminium reason, electricity molten aluminium are cell oxide lining power that cheaply, station. some of e.g. The O Al 2 hydroelectric reactions at power . each Many electrode are 3+ the cathode uncertain. It their is own An electrolysis cell for the production of aluminium possible 3 O 2 aluminium have ionises: Al At smelters cryolite available Figure 11.2.2 relatively aluminium and aluminium → 3– Al + AlO 3 3 ions accept electrons and are converted to atoms: 3+ + Al The molten each cell aluminium and is which siphoned is 3e → 99.9% Al pure collects at the bottom Key points of off. At the anode a possible reaction Bauxite the 3– 4AlO → 2Al 3 O 2 + 3O 3 + is often simplied as a puried ore reaction in sodium precipitating 12e by dissolving the hydroxide, impurities and 2 then This is is: in which oxide ions form oxygen precipitating the puried by alumina from the solution. 2– loss of electrons: 2O → O + 4e 2 During anode the electrolysis, which periodically. gets The the ‘burnt carbon oxygen away ’ and dioxide produced therefore formed is reacts has led with to be away the Aluminium electrolysis calcium or process aluminium is continuous. uoride is Regular required to of fume composition. These additions are additions necessary oxide cryolite of in alumina and with the of voltage aluminium required for oxide the falls, dangerous electrolysis electrolysis anodes and cathodes. constant because when Cryolite is added uorine gas is to dissolve the the lowers the melting evolved point and using carbon alumina. This concentration a aluminium hoods. electrolyte molten replaced through maintain extracted from mixture cells The is carbon of the mixture. rises. Large amounts needed to alumina keep of energy the electrolyte are cryolite– molten. 131 11.3 More about Learning outcomes aluminium Uses of The On completion should be able of this section, uses describe relation to uses its of aluminium physical and in density: metals. used describe fuselages, properties the impact of reect its physical and chemical properties: industry on Aluminium mass is there in car lighter has one-third is and wooden in density that energy-saving bodies than lower of of of the advantages, parts ones. compared steel of ships. with same e.g. (as an alloy) Aluminium High-tension most other volume. So for ladders electricity cables it is aircraft are between the pylons aluminium Its where much aluminium to: the chemical of you Low aluminium are usually made of aluminium, since it is less dense and cheaper the than copper . These cables have a steel core because aluminium would environment. break under Good strength/ (tensile its making its aircraft, drinks than foils of relatively ratio: 7–11 many cheap. The alone. strength to 50 lightweight materials. metals the of of is aluminium So cars is the and easily similar foil so advantages readily stretching is can useful for lorries. shaped, price to aluminium aluminium Aluminium additional Aluminium pure Alloying times. Aluminium roong has 10 and other it used megapascals. ductility: and where if strength ladders and cans packaging is tensile Malleability weight mass strength) increase for own can that machined, so is be it cast it can more used is be used exible for food non-toxic and drawn and into wires. Good electrical electricity as copper), aluminium its electrical good especially Good High is mirror is It power of and few This is Aluminium is and not corroded Corrosion surface it is of metal alloys is car plane as a why is it used oxide is are bodies. It agent: is for is are agent. used conductor of conductivity with its electrical very has of low density, wiring, is well is Because of the light magnetic its if metal the not the used in the and chemical thin when oxide off. alloying roong cans a ake resistance frames, drinks because So does it elds. made reactive. because to materials food acidic. is is when paints, equipment layer of boilers, ghting. resistant window of reectance corrosion very for (92% freshly oxide corrosion useful by to the not the make also re navigational on parts silver-coloured for resistant iron, make conductivity. excellent in clothing in to thermal used forms Aluminium reducing a the T ogether signicantly less to is light aluminium. used contents good useful that oxide Unlike than it good reects Aluminium aluminium whose its metals Aluminium reactive reducing industries air . of affected aluminium aluminium and containers not corrosion. of less corrosion, Good to prevents Some and resistance: layer exposed layer is as 59% cheap. makes heat-resistant Non-magnetic: not has Aluminium because the powdered. (it lines. Aluminium one reectors silver comparatively conductivity: is Although and conductivity cookware reflectivity: nely gold overhead and reected). it in thermal cookers 132 conductivity: copper , and steel Chapter Aluminium industry Aluminium very is a useful and the metal and Did you know? environment the production of aluminium from The bauxite employs many thousands of people throughout the world. thousands making of such window others are different frames. But employed things as producing in cars, industries electrical aluminium which cables, has an use aluminium drinks price the bauxite metals cans the world bad effect Quarrying may which can either be used for and on is an area of natural beauty, e.g. forest or hilly of a world metals The quarries are unsightly, noisy and can the explosives and vehicles used to produce extract W aste rocks from the ore may produce dust and of Breaking The waste This ‘red Plants are The (furnaces) kilns The of dust of and unsightly The reaction ‘pots’ lifetime. the to the is soil by transport spoil 1980s and ores dropped of its exports badly were the led with to bauxite. The falling 25% of the workforce ore. with this business losing heaps. jobs. fumes. reaction and the remove and saturated present greenhouse also of of in get sodium sodium into hydroxide. waterways. concentrations the the gas, then high with with of sodium sludge. water carbon from the dioxide hydrated and a certain produced. alumina in the gas, uses the carbon carbon broken which of may vast amounts greenhouse producing (electrolysis When produced used quantities formed greenhouse into poisoned dust from which materials the is electrolysis therefore early alumina Considerable The other produce produces residue drain animals and Electrolysis can ore precipitated a hydroxide amount bauxite products mud’ alumina the produces and the alumina up hydroxide In fumes their Production very recession. The affected Jamaica 75% connected a area. prices from have countries agriculture connected can individual individuals. was because or ores cost: price land metal and environmental ore destroy market on rapidly. This and for there Quar rying of Hundreds on of 11 the gas of electricity. carbon dioxide are electricity. anodes with the oxygen also produces the dioxide. cells) up used or to produce recycling contain the aluminium walls/ cyanides, arsenic and as have electrodes, and other a nite dust is toxic compounds. Fluorine oxide in gas the is produced cells Peruorocarbons between uorine powerful more decreases. are produced and greenhouse the more Fluorine is during carbon a the toxic the amount gas of which electrolysis aluminium is very due to reactive. reaction electrodes. Peruorocarbons it making are very gases. Key points The properties cables, cookware The its of aluminium window frames, and drinks properties corrosion Quarrying, of the which toxic are aluminium high production affect The production and other on (or of car useful for and aeroplane overhead bodies, electricity mirrors, cans. resistance, particular make roong, the that especially strength of alumina environment potentially aluminium greenhouse are mass and by useful ratio the and are high electrolysis producing its dust low density, reectance. of alumina noise and have materials toxic). results in the production of carbon dioxide gases. 133 12 Petroleum 12. 1 The petroleum Learning outcomes Crude oil Crude On completion of this industry section, oil and (petroleum) be able describe the separating crude method the used in components of oil rst the from understand oil wells. fractions. how fractional kerosene separates crude 16 removed undergoes distillation its state the uses of obtained from and as a mixture of hydrocarbons. compounds whose It relative contains alkanes, molecular to by more simple The Each than crude has Some distillation. oil is then distillation. fraction fraction 400. has a of This dissolved ‘stripping’ transported This to separates particular components the with range an the of boiling is natural masses often oil oil done renery into boiling points gases are near where it different points e.g. the between oil while the light gas- oil fraction has components with boiling component fractions points is aromatic fractional 160–250 °C, into and to: range components you cycloalkanes should its raw 250–300 °C. the fractions crude oil materials for petrochemical between as fuels the The names 12.1.1, of which the different also shows fractions where and they their come off uses are from shown the in Figure distillation column. industry. under 40 °C bottled and bubble as gas for heating cooking cap 40–100 °C gasoline – fuel for cars (petrol) 80–180 °C naphtha – making chemicals, especially plastics 160–250 °C kerosene (paraffin) – fuel for jet aircraft and heating 250–300 °C light gas oil – fuels, including diesel, petroleum for (crude lorries, tractors oil) and cars 300–350 °C heavy gas oil – fuel for power stations, home furnace ships lubricating lubricants, and and heating oil – waxes polishes residue bitumen road sealing Figure 12.1.1 making and roofs The fractions arising from the distillation of crude oil. The diagram is simplified and does not show all the reflux pipes in the tower. 134 – surfaces Chapter The table boiling below point shows range of the Fraction Boiling approximate some of the /°C below Number of C of carbon atoms Petroleum and fractions. gas points number 12 40 1–4 gasoline naphtha kerosene gas oil residue 40–100 80–180 160–250 250–350 above 350 4–8 5–12 10–16 16–25 above 25 atoms The naphtha leads to the chemical fraction is formation syntheses, especially of e.g. important. unsaturated ethene for Further compounds making treatment which are of this important Did you know? in poly(ethene). Crude for oil has been thousands deposits of have known about years. Oily been written surface about in Separating the fractions ancient The fed crude into a oil is heated in fractionating containing bubble a furnace tower caps (see at about (column) Figure 400 °C. which 12.1.1). The contains These vapour about allow 40 is then ‘trays’ thorough this the vapour with descending liquid. In modern reneries the crude medical are replaced by jet trays which are metal sheets with oil for lighting rich used and for purposes. About 1600 years the Chinese were collecting bubble crude caps tablets. The mixing ago, of Persian depressions oil using bamboo pipes. in them. There is cooler than a temperature gradient in the fractionating tower . The top is Exam tips with the higher base. boiling Near points the base of condense. the The tower , heavier lighter hydrocarbons hydrocarbons have lower Make boiling points and so move further up the tower . As they move up sure confused tower , each hydrocarbon condenses at the point where the that temperature between tower falls just below the boiling point of the hydrocarbon. The the ascending vapour to come into contact with the The and separation theory behind occurs this is through given in successive Section trays and bubble caps allow better liquid-vapour in and Petroleum is of crude separation petroleum oil. Petrol used as is a fuel equilibria. 10.5. mixing petrol. name for cars. It is its fraction The and descending a fraction liquid get words tower another allows don’t the in petroleum the you the of better name to as remember it by crude oil gasoline. the components. After a component condenses on a particular tray it moves down to the Key points tray below. whose When the temperature ascending is below the vapour reaches boiling point a of tray the containing vapour , the liquid vapour starts to condense. As it condenses, the vapour heats the liquid in Fractional separates tray and the more volatile components in the liquid evaporate. The components pass up the tower with the remaining process occurs in each tray, the least volatile vapour condensing most volatile evaporating. The result is that each tray has a boiling components with a narrow range of boiling The main fractions points. and with lower components relative with molecular higher mass relative products molecular move mass up move The under from vacuum. the crude Lowering oil the which pressure has not reduces passed the up tower boiling is point distilled the components distil below their decomposition Section oil. petroleum reduced residue is pressure distilled to form lubricating oil and bitumen and Fractional distillation separates temperatures the (see and fuel fractions. ensures kerosene residue the residue are gasoline, the under The gases, down. Separating the obtained distillation So naphtha, tower into ranges fraction petroleum components distinct points. by fractional containing components and the the having vapour . of This of more fractions volatile distillation the crude oil into fractions by a 10.6). series which of gas-vapour are adjusted temperature equilibria as the decreases up the column. 135 12.2 More about Learning outcomes petroleum fractions Cracking Most On completion of this section, But should be able describe the some fractions are more we get useful from than the distillation others because of petroleum there is a are greater useful. demand to: for of you catalytic cracking and them. from the We use more fractional gasoline distillation (petrol) of and diesel petroleum (see than Figure can be supplied 12.2.1). reforming Petroleum describe the impact of companies hydrocarbons, petroleum industry on solve this problem by breaking down larger , less useful the to smaller , more useful hydrocarbons. They do this by a the process called cracking. Cracking is the thermal decomposition of alkanes. environment. When large alkane alkene molecules alkane can molecules are undergo are formed. cracking cracked, T wo of the smaller many alkane possible molecules ways that and an are: 50 supply from refinery H C 10 demand from 40 customers → C 30 H 10 C 22 → H 6 dodecane C 22 + H 5 C 14 + H 4 hexane 8 butene C 12 H 2 + C 4 H 3 6 % dodecane pentane ethene propene 20 The alkanes formed, e.g. C H 6 are used to make more gasoline. The 14 10 alkenes seudiser lio leuf leseid enesorek ahthpan sag /enilosag yrenfier 0 their a used double making as are or chemical bonds. many fuel in new for They are products making the including H 2 They starting ammonia) C Figure 12.2.1 synthesis. → can C 6 are compounds plastics also H 2 very be and reactive (feedstock) ethanol. produced + because by of for Hydrogen cracking (used ethane. H 4 2 Demand and supply for ethane ethene hydrogen some petroleum fractions How is cracking Naphtha Figure using or gas 12.1.1, a catalyst cracking is oil p. carried out? from 134) in called a fractional are the catalytic catalytic distillation feedstocks. cracking cracking . in an Cracking unit The (cat oil is renery usually cracker). vapours from This the (see carried type gas- oil out of or cracked alkanes and alkenes kerosene aluminium be dirty oxide continuously This catalyst fractions frees the are at passed through 400–500 °C. recycled catalyst to the from The cat any a catalyst catalyst cracker carbon of is a silicon( ne through deposited a on iv) oxide powder and regenerator its surface. and has to tank. Modern reactor catalysts include compounds called zeolites which are aluminosilicates. (cat cracker) The main products Renery A gas of catalytic containing cracking ethene and are: propene. powdered catalyst liquid with aromatic higher a high yield hydrocarbons. grade of branched-chain This is used to alkanes, make more cycloalkanes petrol and (especially petrol). catalyst clean A high-boiling point residue. This is used as fuel oil for ships and regenerator catalyst home heating. long-chained Long-chain alkanes can also be cracked at a high temperature (between alkanes 450 Figure 12.2.2 and 800 °C). This type of cracking produces a larger percentage of Simplified diagram of a alkenes and is called thermal cracking. catalytic cracking unit Reforming Refor ming arenes. 136 is the conversion of alkanes to cycloalkanes or cycloalkanes to Chapter When the gasoline and naphtha fractions are passed over a catalyst above 12 Petroleum CH 3 500 °C, the process is straight-chain alkanes are converted to ring compounds. This CH 2 called cyclisation. See Figure 12.2.3. CH CH 2 The catalyst aluminium is platinum oxide. The or Pt vi) molybdenum( or oxide catalyses MoO the deposited 3 onto dehydrogenation CH while CH 2 2 3 the aluminium oxide catalyses any rearrangement of the carbon skeleton. CH 2 More modern diameter plants deposited use onto bimetallic metal aluminium clusters between 1–5 nm in oxide. CH 3 A catalyst containing platinum and iridium atoms converts straightCH chain alkanes to arenes. CH CH 2 2 + H 2 CH CH 3 CH 2 CH 2 CH 2 CH 2 + 3 4H 2 CH CH 2 2 CH 2 A catalyst from containing platinum methylcyclohexane to and form rhenium atoms remove hydrogen methylbenzene. CH 3 CH CH 3 + 3H 3 2 + 3H 2 Petroleum Crude oil and industry its rened and the products are environment responsible for various types of Figure 12.2.3 Cyclisation pollution. Oil Oil spills Did you know? spillages from oil wells or tankers can kill wildlife, especially sea birds The and sh. T ar on the birds’ feathers reduces their ability to y and rig their insulation and ability to oat on water . Even a thin layer of worst oil sea results in a large reduction of oxygen in the water spill from took underneath, of place in April Mexico die. Birds, sh and other animals also die through ingesting drilling the when 2010 a in the drilling rig so exploded. The sh a on Gulf the oil reduces oil gushed out for toxic three months. Tens of thousands of components. sea Incomplete combustion birds were jobs. Incomplete combustion of petroleum products results in toxic and sh taken So and many large was the being hydrocarbons. Section formed The as latter well two as can carbon particles contribute to and lost oil their slick that carbon countries monoxide died, shermen ill in the Caribbean were on unburnt photochemical smog (see high alert in case the oil reached the region. 14.8). Lead Key points Lead compounds agent in gasoline from the (petrol) addition can result of tetraethyl in damage lead( to the iv) as an nervous ‘antiknock’ system in children. Although most gasoline does not now contain lead Cracking of fractions many people are worried that the arenes put into petrol to less useful oil compounds, replace it produces more useful are alkanes and alkenes. The alkanes poisonous. are Acid used alkenes rain to to products The in sulphur the are present air to form burnt in vehicle in acid trace rain. amounts The engines in nitrogen also fuels reacts oxides contribute to with formed acid rain oxygen when (see and fossil Section make make petrol a wide including and the range of plastics. water fuels 14.7). Reforming chain converts hydrocarbons cycloalkanes or straight- to arenes. Plastic Plastics made from petroleum products cause problems in terms of Crude oil products disposal in the environment and their effect on wildlife (see Section and its rened their can be responsible for 14.11). various types to accidents or transport of pollution during due extraction Metals Some of the metals used as catalysts in the petroleum industry into the air during catalyst as a result of can combustion escape or of fuels. change. 137 13 The 13. 1 Ammonia chemical Learning outcomes industry synthesis The Haber Ammonia On completion of this section, be able outline by the Haber Process. The stages in this are: to: manufactured you process should is Process the steps in A mixture of nitrogen (1 volume) and hydrogen (3 volumes) is the compressed. manufacture of ammonia from its The compressed contains gases pass into a converter (reactor vessel), which elements describe the Haber the of catalyst: Process including trays The catalyst is iron (Fe) or a mixture of iron and III) iron( oxide (the manufacturing oxide gets reduced by the hydrogen to iron). The iron is porous, so conditions it understand the Haber Process has a large of chemical for the gases to react on. A promoter potassium hydroxide) is added to increase the equilibrium effectiveness and area in (usually terms surface of the catalyst. kinetics. The temperature The pressure (but 200 atmospheres Under these converted to in in the the conditions converter converter up is to is can usually range about from common). 15% of the nitrogen and N (g) + 3H 2 The here The they (g) Y 2NH 2 passes not (g) into condenses. unreacted are are ∆H –1 = 92 kJ mol 3 mixture and hydrogen ammonia: Ø 400–450 °C 25–200 atmospheres an The nitrogen expansion ammonia and is chamber . removed hydrogen are The as a returned ammonia cools liquid. to the converter so wasted. unreacted N (g) 2 and H (g) 2 recycled N (g) expansion 2 chamber H (g) 2 converter packed liquid with Figure 13.1.1 Exam tips Different chemical synthesis of plants for ammonia use the The conditions. If you are an exam for the answer is: conditions, 200 atm materials for the hydrogen Haber is from made the either fractional from natural distillation natural gas by reaction with steam of 450 °C of gas or crude by cracking oil. It can ethane also in the presence of a be made nickel catalyst. pressure, heat temperature Process the from best An outline of the Haber Process asked obtained in ammonia catalyst slightly The different raw Fe and Fe (g) CH + + Ni O(g) → CO(g) H 4 + 3H 2 (g) 2 catalyst. The carbon Process is monoxide removed by which can reaction CO(g) + H poison with O(g) the more → CO 2 The nitrogen distillation hydrogen. 138 of for the air). Haber The Process oxygen catalyst (g) + 2 is from in the Haber air is H (g) 2 extracted the used steam. from the removed air by (by fractional reaction with Chapter The best Effect of conditions for the Haber 13 in pressure The production pressure formed. Section fewer shifts This 8.5) is higher favoured because the they plant. are by used increase Le the in pressure. right. Chatelier ’s shifts pressure Although not to pressure A an towards according the molecules. on yield is equilibrium increasing gaseous depending the the between pressures More and above An Haber in (see Book favour 200 atm is rst is A lot lot At more more 1, is used, 200 atmospheres early to the compressors. pressures would withstand the the have to extra reaction be spent vessels to are make less them safe. strong A This lot named Fritz after Haber, the give a catalysts costs is in a who in improved testing order result the process the century. The German Bosch after ones. As power is this twentieth process because: required chemist chemist Carl of to nd the the thousands the of best process’s full Haber–Bosch Process. a money. higher money energy Process discovered name industry increase product Principle equilibrium 25 chemical Did you know? Process German Ammonia The Haber and Nobel prizes for Bosch were their awarded work. more enough to pressure. Effect of temperature Ammonia the production reaction is favoured decreases the For by an value lower temperature. exothermic of so K reaction decreases the This an is because increase yield of 100 200 °C in ainomma temperature is exothermic. the p forward Le reaction, Chatelier ’s i.e. the yield of ammonia. This is because according to principle: 80 300 °C 60 fo decrease the energy in temperature reaction goes in the decreases direction the in energy which of the energy dleiy surroundings is released % is released in the exothermic reaction. This favours 40 400 °C 20 500 °C the reactants. 0 50 0 Effect of A at catalyst which catalyst does the not 150 100 200 pressure /atmospheres affect product the yield (ammonia) of is ammonia but does increase the rate Figure 13.1.2 The yield of ammonia depends on both the temperature and the formed. pressure The best Figure When conditions overall 13.1.2 the shows how temperature the is yield varies with temperature and pressure. increased: Key points the rate of reaction the equilibrium increases yield decreases. Ammonia Haber There is a decreases which conict with between increase increases with in the between temperature increase in the and best the temperature. equilibrium best So rate we use of yield, a temperature of about 420–450 °C is used with an iron catalyst to give a N reaction (g) + 3H 2 (g) Y 2NH 2 (g) 3 The conditions of the Haber at reasonable yield at a are 200 atm, 450 °C and fast catalyst. rate. Removing ammonia by condensing it also helps improve the yield. The because removing equilibrium to the ammonia right in as favour a liquid of fewer shifts the position molecules. yield of ammonia decreases This as is the compromise Fe enough by Process: Process 200 atmospheres manufactured which conditions; is the temperature increases. of The of rate of production ammonia temperature The increases conditions Haber Process between a and rate high as increases. used are high of a in the compromise equilibrium yield reaction. 139 13.2 The impact Learning outcomes of The ammonia uses of Ammonia On completion of this section, be able describe describe uses and the ammonia 85% of the on a huge ammonia scale and produced has is many used to uses (see make Figure 13.2.1). fertilisers. to: the agriculture made you About should is ammonia of ammonia other in industry impact industry of on uses cleaners including and nitric the making household nylon dyes acid the making fertiliser (ammonium environment. and Figure 13.2.1 Apart The main uses of ammonia from making Making Nitric other acid nitrogen As As In a In T o to of make in pH main of as a textiles of ammonia compounds, cleans cleaners without on source a of large shiny scale, nitrogen fermentation (especially for and leaving for and dye acid. organic industries. surfaces for nitric many ‘streaky ’ e.g. are: especially explosives pharmaceutical household the uses fertilisers, the especially fermentations treating make Ammonia refrigerant, the the nitrogen-containing used compounds ovens. adjust is fertilisers, components and salts nitrate) such as glass marks. cooling ice microorganisms rinks. and to mixture. cotton and wool) to alter their properties. dyes. Manufacturing fertilisers Plant roots absorb plants convert When farmers not usually depleted into in soil, nitrates. future to When This Ammonia Exam tips readily nitrate, When writing equations for formation of ammonia, remember ammonium the are are be the from the used soil. as So grow and as such back more nitrates. needed taken of for up as the are should. manure soil minerals nitrogen, so plant soil fertilisers plants plants grow to and (mainly in ammonium the the compounds relevant USA) such as phosphate but (aq) + HNO 3 as a product. it evaporates are used. acid. 2NH (aq) + H 3 SO 2 (aq) SO 2 NO (aq) 3 ammonium nitrate (aq) + H PO 3 (aq) 4 → (NH ) 4 PO 3 (aq) 4 (aq) 4 ammonia 140 NH 4 acid → 3 ) 4 nitric 4 3NH (NH (aq) → 3 e.g. ammonia and ammonium water NH is formed are grow. faster e.g. no modern available salts from that back the not is becomes put In are for the the minerals) The growth. by years, they to of yield. fertiliser sulphate are other well essential provide crop form number (and as ammonium ammonia a nitrogen other the nitrogen fertilisers add a Over in which the nitrates not to soil proteins soil. and used ammonium made to nitrates the crops, natural increases can from the will quantities fertilisers bigger . to Unless crops provide from their to industry, sufcient used nitrates harvest returned agricultural in the nitrogen phosphoric acid ammonium phosphate These Chapter The solutions blown. the Hard soil. each are evaporated pellets Fertiliser other of the and sprayed fertiliser factories often are have into a formed. several tower These into which dissolve chemical plants air is slowly next nitric by Trinidad to is fertilisers the Haber chemical of the in the largest from largest nitrate or phosphate fertilisers phosphorus plant are and and is exporters 3-plant ammonia ammonia fertilisers from the ammonia and nitric acid. central Trinidad of Most of Process and fertiliser factory exporter the Caribbean world’s of fertilisers. The acid industry Did you know? one ammonia The in making: 13 called NPK potassium, fertilisers all three of because which they are contain needed for its at Savonetta exports nearly in 99% production. nitrogen, healthy growth. water air Ammonia and the phosphate rock environment natural gas sulphuric acid Eutrophication Overuse excess of fertilisers quantities overgrowth organisms. of of algae The causes eutrophication . fertilisers and stages pollute bacteria rivers leading to This and the is process lakes death and of by cause which an aquatic ammonia phosphoric factory acid factory are: potassium Rainwater elds dissolves into rivers fertilisers and and the solution runs off (leaches) chloride from compound lakes. nitric acid fertiliser The concentration of nitrates and phosphates in the river or factory lake factory increases. Algae algal The in the bloom dense water use covering growth of these the nutrients. surface algae of blocks the They grow very fast causing an water . sunlight ammonium from reaching plants nitrate below factory the water surface. NPK These plants die from lack of sunlight. The algae also die when the fertiliser nutrients Bacteria The Without are feed bacteria used on up. the use up dead the plants oxygen and algae dissolved and in multiply the rapidly. water . ammonium oxygen, sh and other water animals die. nitrate fertiliser Other Smog: effects of Ammonia sulphur oxides contribute Human to ammonia in from the atmosphere vehicles and can combine industry to with form ne nitrogen and particles which Figure 13.2.2 A ow chart for making NPK fertilisers smog. health: Ammonia itself can irritate the lungs and inhibit the Key points uptake of oxygen Ammonia salts. can These by react exist as haemoglobin by with the acids small in particles altering the pH atmosphere (particulates). to of the form When blood. ammonium breathed in Most ammonia is used to make over fertilisers. a period of time, these can cause bronchitis, asthma, coughing ts and ‘farmer ’s Fertilisers replace Soil acidication: When ammonia in the atmosphere reacts with the soil it is converted to added to nitrogen the taken soil up to by plants and to increase crop + ions. NH the water crop + in are lung’. NH 4 ions are also present in 4 yield. + fertilisers. Excess ions NH are converted by bacteria to nitrites, nitrates 4 + and ions. H + The H ions make the soil acidic and plants may not The on able to grow main impact of fertilisers be the environment is well. eutrophication. Changes to plant diversity: Ammonia gas can settle on plant leaves and stems and cause damage because of its alkalinity especially in Ammonia can react with acids in alpine the air can be to form particulates which plants. damaging to health. 141 13.3 Ethanol Learning outcomes The production of alcoholic beverages Fermentation On completion should be able of this section, you to: The drinks example explain the importance in fermentation and distillation exports. manufacture of industr y is Jamaica, the big business r um in industr y many is parts worth of the about world. For 45 million Alcoholic drinks include beer, wine and spirits such dollars as r um, in whisky the in of and gin. Fer mentation has been used by humans for centuries alcoholic to produce alcohol. Fer mentation is the conversion of carbohydrates to beverages alcohols describe the fuel in uses of ethanol as the organic acids using yeast or bacteria in the absence of air. a Almost and or any vegetable material can be used as starting materials as long pharmaceutical as industry. they sugars acts contain such on as sugar or glucose. glucose or starch In the sucrose in which can production the absence be of broken down alcoholic of air to to drinks, produce simple yeast and CO 2 ethanol. From glucose: C H 6 From sucrose: C O 12 H 12 (aq) → 2C 6 O 22 H 2 (aq) + H 11 OH(aq) + 2CO 5 (g) 2 O(l) → 4C 2 H 2 air OH(aq) + 4CO 5 (g) 2 lock (CO can escape but 2 air cannot fermentation Figure 13.3.1 Glucose between is T oo mixed and T oo low a high proteins Exam tips higher It Remember example occurs a of in absence student (aerobic If oxygen error were respiration), might is oxygen). to is plant yeast control temperature the a will possibility temperature will have the temperatures, important to and water (according keep of is to material, water) air and the alter the at a temperature alcoholic bacterial cell structure proteins of of enzymes unwanted out left type will work to to too slowly and fermentation. structure of catalyse become apparatus to the the yeast and reaction. At denatured. prevent: (it It oxidation of unwanted ethanol to ethanoic acid is side reactions due to bacterial action in the presence of air . suggest involves present Fermented used in the drinks are generally fermentation. For classied according to the plant example: ethanoic be formed of beverage important: incorrect the the cause will rather Beers Wines are Mead made from cereals and other starchy than and ciders are made ethanol. 142 liquor ( yeast, an respiration of alcoholic fermentation oxygen. acid anaerobic the common that that fermentation with 40 °C T emperature increases in) vessel fermentation sugar, back Simple fermentation apparatus 15 required). get is made from honey. from fruit juices. material. material Chapter 13 The chemical industry Distillation There is a limit fermentation. than 15% it will fermentation alcohol by the is kill in the some to characteristic Other the pot producers still use and alcohol In the column a can made by in distillation of batches alcohol and produced rises distilling alcoholic than in be content suitable higher the work that alcohol are reaches much avours the Spirits it is ethanol. rum its when producers directly of when yeast. spirits volume rum, amount because mixture content 35–40% make to This (pot wines the more the content. beers, fermented stills). aroma or by to Heat is compounds The e.g. liquor to applied giving the evaporate. distillation. See Section 10.9 for further information. T wo important Rum from Whisky Uses of Ethanol The has Ethanol use cereal or sugar cane juice. grains. of ethanol ethanol of sugar is as fuel a fuel or industry cane in residues. In a fuel the additive world. the USA, It for is vehicles. produced ethanol is Brazil by largely made (maize). can Ethanol used fermented molasses a fuel largest corn fermented ethanol fermentation from are: distilling from as main the spirits either be used containing for vehicles on 4.9% that its own water run on is as a fuel produced ethanol or by mixed with gasoline. distillation. This Did you know? is only. It W ater is removed by an adsorbent, such as a zeolite or starch, is thought that the word rst ethanol for mixed petrol-ethanol engines is came uses of Alcoholic In the Ethanol in It is paints is a beverages acid As an As an language an Arabic word in ‘al-ghul’. above). to make halogenoalkanes, esters, ethers, amines. (usually as methylated spirits) as an industrial solvent adhesives. commonly evaporates (see industry and used and English ethanol chemical ethanoic into the required. 1543 from Other alcohol if used solvent in perfume industry because it rapidly. antiseptic: antidote it to is used in poisoning medical by other wipes and alcohols, antibacterial e.g. ethylene hand gels. glycol poisoning. Key points Fermentation In order mixture to is Ethanol make can has perfume used to produce alcoholic drinks alcoholic such as drinks. rum and whisky, the fermentation distilled. Ethanol from material is the fermentation be used other as uses of sugar cane residues or other plant a fuel. including as a solvent, as an antiseptic and in manufacture. 143 13.4 The impact Learning outcomes of The ethanol effect of Although On completion of this section, be able social describe impact the of occasions, in alcoholic ethanol is beverages classed as a tends to make psychoactive people drug relax (one which to: acts ethanol body you on should the ethanol on the social ethanol and economic production and we the view small As consumption on central things, amounts the nervous understanding, we amount system of may get alcohol a in and and in behaviour). feeling the results of general bloodstream changes If we in drink well-being increases mood, alcohol and how in relaxation. (measured as –3 blood describe the changes caused alcohol content, BAC, in ), g dm the ethanol has a progressively physiological bad by effect on us. The short term effects are: alcohol –3 consumption BAC 0.5 g dm : feeling of relaxation, increased talkativeness, impaired judgement. describe the impact of the –3 ethanol industry on BAC 1.0 g dm : difculty moving properly, giddiness, feeling of not the being in control, nausea, vomiting, symptoms of intoxication, e.g. environment. slurred speech, aggressive behaviour . –3 BAC 3.0 g dm : Not knowing what is happening to oneself, loss of consciousness. –3 At blood alcohol concentrations of above about , 1 g dm ethanol acts as a Did you know? depressant, it lowers the activity of particular parts of the brain. At blood –3 alcohol The Latin saying ‘in vino veritas’ blood wine, the truth) suggests that concentrations to more likely to tell the the truth have had a glass of wine leading to loss of decreases consciousness and the ow of eventually –3 or death at concentrations above 4 g dm effects of excessive consumption of alcohol (alcoholism) can two lead to brain, when Long-term they ethanol 1.4 g dm people possible are above (in to many social and health problems. Although small amounts of drink! ethanol energy, can one be carcinogenic body may Excessive metabolised product (causes result in alcohol alcohol syndrome various birth The of the in cancer). liver the alcohol A and can buildup of be is such used as ethanal toxic a source and this substances of is in the cancer . consumption in body metabolism which the in pregnant child of the women can alcoholic result mother in foetal can have defects. social and economic impact of ethanol Did you know? These When used as a solvent about methanol is often added to include: 10% Social killed to ‘denature’ the alcohol consequences so that as a not t for drinking. This is called methylated alcoholics, afford however, alcoholic to can drinking result in death. More methylated blindness Because manufacturers of now add methylated emetics up spirits the to of the families driver under of those the of individuals help from the who have an alcohol habit and who community. of in hospitals expensive required. liver In many transplants countries required due to in the world long-term consumption is increasing rapidly. Many working hours are lost when people do not turn up for impact on production work this, of a ‘hangover ’. This has an economic methylated to there is nobody to take their place. the make people production and the environment alcohol. When It ethanol helps used 144 a spirits. Ethanol vomit for of and if spirits more treatment number because some or drinks, eventually injured judgement drink. isolation require alcohol This individuals impaired who the resort the spirits. cannot of Long-term may Some of alcohol mixture result it inuence is for ethanol as is made conserve an by the fermentation: world’s alternative fuel. diminishing supply of crude oil as it is Chapter The process is ‘carbon neutral’. The sugar cane absorbs CO as 13 The chemical industry it 2 grows and, although this is CO returned to the atmosphere when 2 ethanol just burns, puts the into CO two the processes are atmosphere, in see balance. Section (Burning fossil fuels 14.4.) Did you know? 2 CO (a greenhouse gas) is produced when harvesting, transporting and still and 2 processing better and for the the sugar cane and environment fractionally distilling distilling than it. But extracting this is petroleum cheaper from the ground Ethanol wood it. When combusted gases. an But engine relatively petrol The or the as engine. less Food much These Some can crop be more The of are destroy displace decrease There are of for or low forests people the level as of cane or plant living carbon or in get made from sawdust Enzymes cellulose have and other which been in produce sugars which can used then to be fermented. with of to for a petrol activity to expensive. cane make food, in or diesel the smog. increased sugar or approximately with leading more feed The in recent and biofuels. food years. vegetable will If oils crop become scarcer . other may plants areas of habitats these sinks so has (maize), ethanol other formed produces comparison produces compared photochemical instead or also in be greenhouse amounts It particulates ozone, areas the diesel. engines animal some than or ethanol corn food, and car produces also straw, oil. ethanal decrease as less and undergo biofuels in sugar animal in such such as are ethanol (petrol) crude and production grow Comparing might either grown destruction ethanol biofuels increased to from aldehydes expensive cleared formed methanal plants engine, monoxide generating used plants of car gasoline derived production production on carbon diesel atmosphere the amounts running combustion twice in in material. digest can cellulose (see lead to being more countryside and lead land grown. to is being The likely species’ increased to: extinction areas Section 14.4) and cause soil erosion. methods two main fermentation hydration of ways of ethane producing CH = CH 2 ethanol: (g) + H 2 O(g) → CH 2 CH 3 OH(l) 2 Key points When have comparing to consider these the methods and their effect on the environment we following: Ethanol which Fermentation Hydration of is a psychoactive depresses the drug nervous ethene system. Easy to set up Complex to set up Drinking of Requires low temperatures, e.g. 15–40 °C Requires temperature of control, other natural catalyst ( yeast) Requires phosphoric acid ethanol concentration so of about 15% distillation Produces very pure are plants alcohol period not being vomiting of and intoxication. can to excess lead to over a death. required The use rather materials nausea, symptoms Drinking long ethanol Raw to feeling of catalyst Produces leads 300 °C in Requires alcohol giddiness, feeling and yeast Raw materials from distillation of ethanol than as gasoline a fuel or diesel is of better for the environment as petroleum less CO is produced in making 2 ethanol Y ou can see that the energy requirements for the production of ethanol making hydration more of ethene are (greenhouse CO likely gas) is to be higher likely to be than for fermentation by fermentation than in by petrol or diesel. and emitted. 2 145 13.5 The electrolysis Learning outcomes The of brine electrolysis of The diaphragm On completion should be able of this section, to: describe the Brine involved in chemical is a concentrated from electrolysis using describe the of chlorine diaphragm the describe sodium diaphragm economic production cell the solution dissolving of sodium rock salt in chloride. water . It is The of brine Fig is 13.5.1 used to shows produced a chlorine, diaphragm cell hydrogen used to and sodium electrolyse brine. cell advantages by the production of by The cell is divided The electrolyte The anodes The cathodes A is into a a series of concentrated cathode solution and of anode brine compartments. (sodium chloride). method hydroxide electrolysis or of hydroxide. brine aqueous seawater processes electrolysis the cell you obtained brine by of are titanium are steel rods. grids. the porous diaphragm separates the cathode and anode compartments. brine. This can is made pass of a through a mixture the asbestos and polymers. W ater and ions diaphragm. b chlorine X Ti of out hydrogen out anode brine in porous diaphragm perforated NaOH/NaCl solution electrolyte diaphragm Ti steel anode Figure 13.5.1 (+) cathode (–) A diaphragm cell; a The arrangement of the electrodes from above; b A simplified diagram of the cell across X-X in a The ions present in the electrolyte are: + Sodium, Na Chloride, Hydrogen – Cl + ions, H , from the self ionisation of water – Hydroxide ions, , OH from the self ionisation + H O(l) Y H of water . – (aq) + OH (aq) 2 The At electrode the reactions anode – Both Cl This is – and OH – ions move to the anode. Only Cl ions undergo oxidation. – because chlorine gas is they are pumped in off far greater from the concentration top of the anode – 2Cl than the OH ions. The compartment. – (aq) → Cl (g) + 2e 2 At the cathode + Both Na This is + and H because electrochemical from the top of + ions move hydrogen series) the is cathode. lower than cathode to in sodium. the Only H discharge The ions hydrogen compartment. + 2H (aq) – + 2e → H (g) 2 + The 146 Na ions remain in the cathode undergo series compartment. gas (and is reduction. the pumped off Chapter Formation of sodium hydroxide 13 The chemical industry Did you know? + The removal of H ions causes the following equilibrium to shift to the A more modern way of making right. chlorine + H O(l) Y H and sodium chloride is – (aq) + OH to (aq) use a special ion-permeable 2 membrane rather Membrane cells than a diaphragm. + As more and more H ions are removed, the concentration of OH ions in produce a higher + the cathode compartment increases. So Na and OH ions, the components concentration of sodium hydroxide are present. The electrolyte level in the is kept higher than in the cathode compartment. diaphragm that the ow of electrolyte is towards the cathode compartment reduces the possibility of NaOH moving to cathode H are enough, the solution containing 10% NaOH and by mass is run off from the cathode compartment. This evaporated more soluble The economic A lot of and NaOH sodium as the a NaCl 50% removed weight/ advantages of hydroxide and by volume chlorine crystallisation solution cell (Castner cell) see ‘Did you possibility also reduced the membranes are longer is than the diaphragms. the still cell manufactured Exam tip using a You mercury is solution. a diaphragm is leaving mixing 2 lasting partially in 15% and NaCl costs reduced. The and Cl 2 concentrated so NaCl/NaOH compartment. of When cells the and mixture so hydroxide This concentrating ensures sodium anode than compartment of know?’ do not have to know the box. details of the mercury overvoltage. You Did you know? on the economic diaphragm cell cell should or about concentrate advantages over the of the mercury cell. In the mercury cell method, puried brine flows through the cell in the same direction as the mercury. Cl is formed at the Ti anode. At the mercury cathode 2 + Na + ions are discharged in preference to H ions because of a high overvoltage. The mercury/ sodium mixture (amalgam) is then sent to an amalgam Mercury cell Diaphragm cell decomposer, where the sodium reacts with water to form a solution of sodium hydroxide. Expensive titanium to cheaper to construct Works at 4.5 Works (more expensive (slightly to run) expensive chlorine anode saturated brine at 3.8 less to out run) brine Toxic waste mercury mercury Much construct in sodium No must toxic mercury amalgam be removed decomposer No asbestos diaphragm The diaphragm advantages and cell has several disadvantages advantages are over summarised the in mercury the cell. Asbestos diaphragm The needs table. to renewed often be quite and asbestos dust is Key points toxic The diaphragm cell has Ti anodes and steel cathodes and an electrolyte of Sodium brine (concentrated aqueous hydroxide In the diaphragm cell Cl Sodium NaCl). is formed at the anode and H 2 at the purer hydroxide less cathode. 2 pure The solution from which in the the cathode NaOH is compartment is a solution of NaOH and NaCl separated. Needs The diaphragm does not cell contain works toxic at a lower mercury. voltage than the mercury cell and purity work high brine Works to brine low with of fairly purity 147 13.6 The halogen Learning outcomes The The On completion of this section, be able importance of the manufacture chlor-alkali describe the industrial importance of the halogens and their chlorine industry . materials solvents different compounds of industry chlor-alkali and sodium industry Both chlorine hydroxide and sodium together is hydroxide known are as the to: starting chlor-alkali you the should and the describe the uses of the halogens end and for aerosols many chemical amongst chlorine-containing of the last century , chlorine due to solvents and plastics. the other compounds there increased Before processes things. was use of this a which There which huge are was about used growth chloro - organic there produce are in plastics, 15 000 commercially! the demand compounds always an excess such of At for as NaOH in making bleaches, PC, produced by the mercury diaphragm cells. The uses of chlorine and sodium halogenoalkanes, solvents, hydroxide produced by the chlor-alkali industry are shown in Figure 13.6.1. aerosols, refrigerants and anaesthetics The describe the impact of the chlor- use of decreasing chlorine because environmental in of making the problems solvents toxicity (see of and the halogenoalkanes products made is now and below). alkali industry on the environment. Uses of the a chloroethene for halogens PVC Fluorine propene oxide T o make uranium T o make sulphur hexauoride for the production of nuclear ‘fuel’. solvents hexauoride, which is an inert medium for some inorganics electrical e.g. work. HCl, T o make PTFE, which is a ‘non-stick’ T o make hydrouoric T o make hydrouorocarbons plastic for cooking pans, etc. NaOCl halogenoalkane water acid for etching glass. purification, for anaesthetics. insecticides, anaesthetics Chlorine b chemicals NaCN, Na T o make bleaches, which often contain sodium chlorate( I) (sodium O 2 2 hypochlorite). paper T o make vinyl chloride, the monomer for the plastic, polyvinyl neutralisation chloride (PVC). soap, oil T o make halogenoalkanes T o make anaesthetics T o make for chemical syntheses. detergents refining rayon (which often have uorine in them as well). and aerosols (although the production of chlorine-containing acetate fibres aerosols other of recently due to their effect on the ozone layer). T o make solvents such as trichloroethane (the production of these is purification also bauxite decreasing layer). Fig 13.6.1 decreased uses, e.g. has Some of due to these their toxicity solvents are as still well as their used in dry effect on the ozone cleaning. Uses of a chlorine and b sodium hydroxide T o make refrigerants. Chlorine- (chlorouorocarbons) in recent make years T o Sterilisation (see good Section insecticides in are and and uorine-containing refrigerants but their use hydrocarbons has declined 14.3). dyestuffs. swimming pools and water treatment works. Bromine Polymers Making pesticides, Making bromoethene to 148 containing combust bromine dyes properly and as in a an atoms some are ame pharmaceutical antiknock car good engine agent to (although retardants. products. allow gasoline becoming (petrol) rarer). Chapter Iodine As 13 The chemical industry Did you know? a catalyst in the production of ethanoic acid by the Monsanto Salt (sodium chloride) was very process. important As an additive to the feed for cows, sheep and pigs (nutrient to the preserving food Romans for and tanning leather. supplement). The T o disinfect Often water added to and table in salt water (to treatment. help prevent Romans soldiers the disease called salary goitre). money ‘salt’ ‘connected chlor-alkali Chlorine-containing chlorine may Mercury Mercury the can is toxic. and cell and escape sh compounds an impact of and the as well the as About which mercury into the poison the method of production one-third has a of compounds air or people water . who the owing eat chlorine mercury formed Even the produced cathode during small the (see is made Section operation amounts of of mercury using the can cell kill ‘Minamata mercury after sh. used be in the changed diaphragm regularly. of the When it diaphragm dries out, cell (see asbestos into the air . Tiny amounts of these bres can cause the in which breathing becomes very increased risk of lung Minamata the hydroxide environment base and some hence in evaporation alter the difcult of the the banned in 1997 This litter may is used industries. and and an in (see was of leak from process. water the cell Sodium or get into poisonous hydroxide sufciently to cause is a of the was central nervous by people in the was area eating as tetrachloromethane solvents, are aerosols and ozone-destroying destroy huge is ozone. poisonous death to (For and refrigerants chemicals. details see were Other Section 14.3). Key points amounts not in the biodegradable Section recycling dioxins the 14.11). PVC construction, so is waste PVC sometimes packaging and contributes burnt to Chlorine and as a source of energy. These and acidic hydrogen chloride into used PC, to make halogenoalkanes, in processes the is bleaches, aerosols, refrigerants can anaesthetics. atmosphere. Environmental the problems chlor-alkali related industry emissions include efuents from the paper industry, which can use chlorine as mercury bleaching agent, may contain halogenocarbon compounds (which asbestosis depletion) and dioxins (which are very and ozone non- may biodegradability ozone poisoning, a depletion, cause In unknown reported. This containing to The by sh. an strong Dioxin of mercury. the and put absorbed ‘epidemic solvents, waste 1932. The there (PVC) PVC landll controlled since layer they also chloride plastic other used because halogenoalkanes Polyvinyl pH chlorouorocarbons, 1,1,1-trichloroethene Bay water . Depletion of the ozone Many ethanal water cancer . occasionally the can organisms the leaks can from waste made into in lung sh Sodium Minamata which seeping of named are caused hydroxide of was Section bres system’ Sodium (a form Mercury-containing a factory disease an town been 1956 ‘asbestosis’ disease’ poisoning) chemical is meaning with’. Did you know? in to condition ‘arius’ word ‘sal’ 13.5). from asbestos released latin of had has the environment. Asbestos 13.5) and their salt. The environment Japan. The buy gave waste Castner Mercury have industry to comes from meaning The sometimes of PC. poisonous). 149 13.7 The production Learning outcomes On completion should be able describe of this section, manufacture of Most sulphuric the Contact manufacture terms of equilibria acid is acid sulphuric made by the acid Contact Process . The raw materials you for this process sulphur are: to: understand in sulphuric The of sulphuric the Contact the and (from sulphur deposits beneath the ground, from sulphide Process for ores the of or from hydrogen sulphide from petroleum or natural gas) acid air (from water . the atmosphere) Process chemical kinetic factors There involved. are three conversion stages and in the absorption. sulphur sulphur process: These sulphur are shown burning, in Figure sulphur dioxide 13.7.1. dioxide 98% H SO 2 as + air + 2% 4 H O 2 absorber recycled air beds water sulphur converter burner sulphur trioxide 99.5% H SO 2 4 H SO 2 4 for Fig 13.7.1 The manufacture of sulphuric acid by the Contact Process Sulphur A spray burning of molten sulphur is burned S(l) + O in (g) a → furnace SO 2 The gas sulphur mixture dioxide which and Sulphur dioxide This a is the reaction (usually key of out oxygen of by converter a current (the in the vanadium( V) the The oxide dioxide of the reaction catalyst by heat air . (g) burner contains about The sulphur converter is catalyst, converted V to dioxide contains 10% O , on a + O (g) Y 2SO 2 is (g) is passed several silica into layers support. In 5 sulphur trioxide. Ø (g) 2 Since dry volume. process. converter). sulphur 2SO of conversion reaction vessel four) comes 10% in 2 2 the industry –1 ∆H = –98 kJ mol 3 exothermic, exchangers. the The heat is removed percentage between conversion of each layer to SO SO 2 is between 3 96–99.5%. Did you know? Absorption The idea Process was not behind was discovered until demand for the Contact much high in later, quality 1831. when and The It the This sulphur ceramic very water. concentrated sulphuric acid that it was is is absorbed tower The because called sulphur a mist developed on trioxide reacts with into an a trioxide of 98% absorber. is cor rosive solution The not of tower absorbed sulphuric sulphuric is packed directly acid is acid. with into for med water and this does not condense when ver y an The sulphur trioxide scale. a 150 a was easily. industrial in material. This sulphur required, trioxide happens thick liquid called oleum. dissolves in the 98% sulphuric acid to for m Chapter SO (g) + H 3 SO 2 98% (l) → H 4 S 2 sulphuric acid O 2 oleum is mixed with a little water , The of this acid is returned to the Exam tips 98% sulphuric acid is run off an exam, absorber . The rest is as concentrated sulphuric make sure that to between a question be asks for the best conditions acid. for converting SO to SO 2 H S 2 O 2 (l) + H 7 O(l) → 2H 2 SO 2 which (l) to best asks for the conditions for the Contact Process the Contact the former high The key reaction in the Contact Process pressure answer is low the answer temperature, and to O catalyst. 5 latter is 450 °C, is: atmospheric pressure and O 2 Ø 2SO (g) + O 2 Effect of Sulphur When right. shifts however , slightly the for At operate is 1 Study extra very higher corrosive in either percentage the formed. at yield The (g) 5 –1 ∆H = –98 kJ mol catalyst. Guide, of Section pressure. the there the is is are moist in Le the molecules. or at pressure. shifts to increasing pressure This increase according 8.5) to the Chatelier ’s pressure Most plants, temperatures only because: very increased use an equilibrium gaseous reaction plants by of because fewer requirements pressures, of is atmospheric of scale nature favoured position This marginally energy large be the favour atmospheric pressure. Only Unit will increased equilibrium above The is product (see the 2SO 3 production pressure More principle Y pressure trioxide the (g) 2 one conditions Process. The 2 The and 3 actual 4 in The you reformed. that used industry (l) 7 distinguish Some chemical oleum In When 13 high yield needed to pressures additional without would not produce above increasing compensate higher pressure. atmospheric problems because pressure. of the gases. Effect of temperature Sulphur because increase trioxide the in production reaction is is favoured exothermic. temperature decreases For the by lower an temperature. exothermic value of so K This reaction decreases is an the yield of p the forward The the reaction, temperature reaction temperature Effect of The the rate range the in the exothermic, so that the yield of sulphur converter heat is between exchangers catalyst is within trioxide. are its 450–580 °C. used to working try to Because decrease the range. catalyst catalyst below is i.e. at does which about not it is 370 °C. affect the formed. It works yield The best of sulphur vanadium( at about trioxide V) oxide but does catalyst is increase Key points inactive 410 °C. The key Process The best reaction (g) + O 2 the temperature is increased: The the rate of reaction the equilibrium conditions yield of no point in yield trioxide is high at atmospheric pressure, extra energy pressurising the converter . of rate is maintained in the in the 450 °C, and region at about where 450 °C the so catalyst that is there most is a vanadium(V) Sulphur trioxide oxide. there is absorbed in The sulphuric acid rather than good water reaction are pressure catalyst 98% temperature (g) 3 decreases. sulphur wasting 2SO increases is Y used Process atmospheric the (g) 2 Contact Since the Contact conditions overall 2SO When in is to make oleum. More efcient. sulphuric add a acid little is then water to made the by oleum. 151 13.8 The importance Learning outcomes Sulphur About On completion of this section, be able 0.1% in describe the importance industrial of used compounds of The describe dioxide the use in food of describe acid the sulphuric the salt preservation compounds of Earth’s crust consists of sulphur domes in the USA and sulphur . Mexico and It is found associated as the with of the the various production sulphur other parts 10% is is of rst used of sulphuric burnt to processes Europe. to make and in About acid. make 90% In of the for sulphur production sulphur chemicals the other dioxide of (see agriculture, mined is sulphuric Section 13.7). dyestuffs, in vulcanisation. and Vulcanisation: manufacture impact acid in woodpulping sulphur sulphuric in acid, sulphur of some acid to: minerals and sulphuric you element should of rubber to ‘accelerator ’ the industry. In make is powder: as and Carbon manufacture tyre also Sulphur vines the the harder . added This is to of The speed used as a tyres, rubber up the sulphur is becomes added less to the sticky. An process. fungicide for dusting on plants such strawberries. disulphide: This used for making the polymers rayon and cellophane. Pharmaceuticals: e.g. Some drugs and medicines are sulphur compounds, sulphonamides. Organic sulphur compounds: Some dyes and agrochemicals contain sulphur . Exam tips When answering questions about The the uses of the concentrate compounds, on a few important ones so a detail, of that uses of the most you can Sulphuric more e.g. rather acid is burnt the make drugs’, answer a ‘sulphur better is used answer ‘sulphur make compounds sulphonamide are drugs’. of air to produce sulphuric acid by the the sulphur Contact dioxide for the to used preservation to Sulphur any as dioxide bacteria wine and general, such it as which is dried is may used present. be The to preserve Sulphur fruits sulphites packaged released. such such meats caused sulphur by as as and food dioxide sodium bacterial be in drinks. added order sulphite, ready-made dioxide and can apricots the it is The + wood dioxide pulp. It damaged Other is 2 agent. is 2H by acid agent, drink (aq) used as especially stronger (in killing them. added to such In foods conditions, sulphur dioxide (g) O(l) is → SO + H a 2 food) sulphur reacting action of is are acidic by drinks dioxide with the also acts as an antioxidant, air . sulphur dioxide bleach useful during for bleaches the bleaching such as manufacture silk, wool of and paper straw from which chlorine. uses Sulphur SO and preserve 2 ion reducing bleaching Sulphur are a food this to + (aq) sulphite preventing to In does bacteria. 3 Because It directly which meals. fermentation, kills 2– SO 152 required Process. would Food be in than manufacture given manufacture give Sulphur bit sulphur dioxide just dioxide used as was an formerly inert used solvent. as a Sulphur refrigerant. dioxide gas In is chemistry a good liquid reducing Chapter The uses of sulphuric acid 13 paints The chemical plastics and industry phosphate fertilisers Figure 13.8.1 Among to shows other make the things, main uses sulphuric phosphoric acid. of acid sulphuric is acid. used: Sulphuric acid is added to calcium other uorophosphate rocks to produce the acid. Phosphoric acid is used to cleaning fibres make phosphate metals fertilisers other soaps to make ammonium fertilisers sulphate which is a and uses fertiliser detergents as a cleaning agent for metal as the as a to make detergents. to make dyes to make corrosion-resistant surfaces Figure 13.8.1 electrolyte catalyst in in lead/acid various and car chemical Many of processes these are sulphonates Did you know? paints concrete. Jābir ibn called The impact of the sulphuric acid industry general the are sulphuric sulphur a In the the (or acid which are Sulphuric acid can in result The Acid eyes The can acid of acid hydrogen sulphide. used not be acid environment to make allowed rain from causing are (see escape Section various death of toxic sulphuric to about is sometimes discovering 1200 years is sulphuric ago. However , sulphuric cause lakes dioxide minerals as acid, into 14.7). industrial animals and sulphur by can cause acidication of soils. This leaching. dioxide in the atmosphere can lead to irritation throat. in a metals sulphuric acid the re hydrogen industry the and toxic. with who of Chemistry’ sensitive. present of into rivers not of must and is as processes) toxic sulphur of present contact Since of and aerosols acid and loss presence the escaping acidify such trioxide are corrosive, production other they liberation Process as dioxide the atmosphere may although compounds sulphur Sulphuric of in sulphur or plants used itself, dioxide processes of Contact sulphur oxides number acid Hayyān, ‘the father credited acid In The uses of sulphuric acid batteries is with gas a sulphuric which used contributes atmosphere which include gaseous sulphur hazard. to could make indirectly acid spill explode phosphate to can and result cause fertilisers, eutrophication (see in the res. the sulphuric Section 13.2). Key points Sulphur of is burnt sulphuric Other uses to make sulphur dioxide, which is used in the production acid. of sulphur are vulcanisation of rubber, making polymers and in agriculture. Sulphur dioxide manufacture The main Sulphuric is and use of acid is used as a as sulphuric used a food preservative, in sulphuric acid bleach. to acid make is in making fertilisers. detergents and dyes and for cleaning metal surfaces. The impact formation of of the acid sulphuric acid industry on the environment is largely the rain. 153 Revision Answers to 1 all List four factors industrial 2 revision questions a Give b i chemical the from name which What that ii that is determine name some how By writing dioxide d Why its e is is is an 7 List two bauxite ores 8 its of red in i the impurity showing the b i added to show is the occur at the electrolysis f Why must g Why is the cathode of the and anode be electrolytic bauxite the plants in two anode aluminium the i reactions during during that out a List three effects the by Explain iv Why as aluminium industry of the What that are the allow properties aluminium (physical to be used or are the in stated to a List make the b Explain of i overhead ii food iii cooking iv fire fighter ammonia. Include required for under the a process balanced the a which using the principle pressure and process ammonia Haber state yield is Process. the temperature maximum answer in c conditions c i not ii of that ammonia above. used for exactly dictated in four electricity uses by in the line process, with Le Chatelier’s c the principle, ii? 10 a pots is crude oil the process b name of the process by eutrophication in and the role contributing to Write a balanced What is separated into its of name equation glucose of the to showing produce enzyme process in a used the ethanol. in the above? which c is of process. fermentation clothing the ammonia. cables packaging What of ammonium-based fertilisers fermentation i Process chemical) this a Haber environment. following: 4 the has 9 b on process. your stated as on nitrogen produce this iii the Caribbean? that has answer. industrially conditions 3 industry required for methane? your Le Chatelier’s would the carried of conditions conditions periodically? not the the Using using replaced equation for hydrogen in produced oxide. process is State ii equations for petroleum obtained? c electrolysis? Write How silicon oxide the production the equation bauxite. aluminium balanced obtained from is how a How ii equations, that environment. colour? above effects Write bauxite. the three a extracted. impurity the balanced of and formula removed from cryolite of the bauxite the removed from c location accompanying CD. plant. aluminium gives be found on the the and formulae the Describe can questions Theoretically, higher temperatures would components increase the rate of production of ethanol using called? this ii Describe the principles upon which process, method mentioned in a lower temperatures are the chosen. Give separating however i above a reason for this. is d State two other conditions (besides the based. temperature b List four fractions of crude oil and state the a i Define ii Why ‘cracking’ do process b presence of the enzyme) are required for the fermentation process. each. e 5 the uses that of and An alkane and petroleum of state the companies two types. carry out of the of 12 carbon cracking hydrocarbon with to 10 produce carbon a process ethanol by which produced the concentration by fermentation is f List three a Why b State uses of ethanol. atoms 11 undergoes the the increased. cracking? consisting Name is ethanol classified as a drug? saturated atoms and three short-term effects of ethanol on the an body. unsaturated hydrocarbon. i equation c Write an to show this State two long-term effects of ethanol on the reaction. body. ii Name the unsaturated hydrocarbon formed. d 6 a What b Why is is reforming? reforming petroleum 154 a State of useful industry? process in the one social ethanol. and one economic consequence Chapters 12 Write the the equations for anode and production 13 a Why is of the cathode in reactions the chlorine from the industry 11–13 Aluminium, taking diaphragm place cell for petroleum and the chemical industry – revision questions at the brine. called the chloro-alkali industry? b State c Why does have to d Under of 14 four Sodium The iii Polyvinyl Dioxins three of equations for a Explain c State a List two b List four c State on stages used the the diaphragm basis? discuss on the the impact environment: principle of sulphur answer uses uses the temperature yield of in industrial acid. Write balanced stage. conditions two products. chloride and your the chlorine sulphuric maximum b in regular headings, of Le Chatelier’s pressure used a its layer each production 16 on or hydroxide ozone iv of asbestos production i Using chlorine the following the the of changed ii State a the be preparation 15 uses in of would produce above. the industrial dioxide. sulphuric of conditions trioxide. sulphur effects that the trioxide. used for sulphur of a state the acid. sulphuric acid industry environment. 155 14 Chemistry and 14. 1 The cycle water Learning outcomes The On On completion of this section, the be able describe water the importance of the cycle describe purication cycle planet, ice water caps only or stays when in the stored in same place aquifers when (huge frozen in natural reservoirs surface of and a methods for absorbed in the water into porous atmosphere cycle (Figure is rocks). The constantly water on evaporating the and the condensing to form 14.1.1). energy wind carries clouds water falls as (desalination, fractional rain, distillation, or explain the dissolved importance oxygen to hail transpiration electrodialysis) and Earth purifying solar water of to: water water you permanent should and water our environment snow respiration of aquatic clouds life. water into evaporation from aquifers sea, land, lakes water and in rivers rivers returns to sea wells water waste in Fig 14.1.1 Fresh The water When water The In is into rivers this home kept get carried or and lakes onto nds the seas, by colder larger sea and from condenses falling way, is reaches and the water and air cools droplets back purified for human works evaporates vapour this vapour The sewage treated use or in industry The water cycle water its of or falls back into in the sea seas, air , water surface. the to Some the through the Earth’s colder of snow. on soil. the or droplets drains water the across rain some land way amount as and masses tiny fall and the winds land to lakes water form of the clouds. water falls land. the to soil start the into the streams cycle atmosphere again. and land constant. Did you know? Dissolved oxygen If the is too total dissolved gases in Aquatic high sh can get ‘gas affects is rather deep like sea of and can block the blood this through eventually gas form in life such as sh, the oxygen crabs (DO) and for plankton respiration. (tiny If animals there is not in the sea) sufcient ‘bends’ dissolved in the water , aquatic animals will die. Oxygen gets into divers. rivers, Bubbles life dissolved oxygen which aquatic bubble need disease’. This and water the and the sea by: blood the flow vessels. lakes of It blood can diffusion through diffusion from be fatal. over waterfalls the water bubbles or from of surface air from trapped in photosynthesis the air fast-owing of aquatic water as it goes plants. –3 At 20 °C amount 156 The and of at DO DO atmospheric in water decreases pressure depends as on there several temperature is about 9.5 mg dm DO. The factors: increases and as pressure decreases. Chapter Salt water Degree of has less DO agitation of than the freshwater . water 14 Chemistry owing Stagnant water has less The and Tobago of bacteria and water plants removing oxygen from in eutrophication (see Section in amount example survive of sh DO such than huge needed as small trout by an and organism salmon invertebrates. The depends need plant and it is one the Americas. The of plant the is 13.2). located The a the largest e.g. has water . number water environment DO desalination the Did you know? surface. Trinidad than and on relatively minimum DO the species. higher level For amounts to support the to near water purposes an can as industrial be well used for as for estate so industrial drinking a water. Water is taken in from the –3 healthy sh population is . 4–5 mg dm When the DO levels fall below this, sea and has to be pre-treated –3 aquatic life is put under stress. At DO below sh 1–2 mg dm will die. extensively is Purifying Pure water brackish for of or (slightly salts fresh seawater drinking water removal where water from water is the in this water is can be expensive countries where over of one of is 60% end of all a it water , large compartments from a from seawater important e.g. having those in low by or Desalination especially of are warmed. each of by fractional energy. cheap. water exchangers) At obtained desalination . seawater lot supplies and (heat lower . is be is before there which is desalination. This a has sedimentation lot to of be silt in the removed and ltration. the countries rainfall. and ash distillation desalinated tank it by supply, requires energy can water) short obtained as the successively industry salty Fractional distillation Pure because in It the stages, is distillation most suited distillation world. then where these Flash the is This Seawater pumped of produces is fed through pressure some and the but to a in at series temperature seawater turns seawater to steam and condenses again, so forming pure water (see Figure 14.1.2). Electrodialysis + Electrodialysis is used to transport the ions in salt purified (Na and Cl ) from one water solution of a a to another voltage. positively The through ions Cl charged an ion-exchange move towards anion-exchange the membrane anode. membrane under These but are ions the pass prevented through waste migration to the anode by the negatively charged water from Fig 14.1.2 further out inuence Simplied diagram of a ash cation-exchange distillation unit (* shows where the water + membrane. The ions Na move to the cathode but are prevented migrating condenses) further one Ion by part an of anion-exchange the cell leaving membrane. the other part So the ions depleted in are concentrated in ions. exchange Ion-exchange columns have been used in commercial and household Key points water an purication ion on the units resin for swaps many with years. an ion These in are solution. based In on order the to idea that remove sodium and chloride ions from water a series of three columns is The amount atmosphere, one which acts as the desalination column and another two which maintain a specic balance of anions and is Reverse osmosis kept a region forced of low membrane, solution by gets from a solute region high concentration applying more of a pressure concentrated solute as concentration through on the the a high water in the and constant by the the cycle. Dissolved aquatic is seas cations. water W ater water the serve land to of used, selectively (salt from side. The is essential for to permeable concentration passes solution) oxygen life. salt Temperature, bacteria it. oxygen Water all salt affect dissolved can be and the in number amount of of water. desalinated by Freeze desalination distillation, When salty water freezes, the ice separates leaving a solution with a exchange, concentration of salts. The ice is taken from the solution and repeating this process several times, ice free of salts is ion reverse osmosis and re-melted. freeze By electrodialysis, high desalination. formed. 157 14.2 Water pollution Learning outcomes The sources of W ater On completion of this section, pollution be able describe the pollution heavy sources (nitrates, metals cyanide, water phosphates, (lead trace of and metals, mercury), rivers them. end herbicides, petroleum suspended particles) describe experiments selected pollutants sites. lead and, in the of wastes chemical are often or biological discharged often also Material pollutants treated, contains may also still have synthetic leach into toxic into substances seas detergents rivers in which from waste may disposal include: from the leaching of fertilisers (see Section 13.2). residues, Phosphates: to test for phosphates from from the leaching of fertilisers and sewage disposal including detergents. (nitrates, ions, metals: e.g. mercury from the chlor-alkali industry, lead from old cyanide) pipes the effect of and from anti-knock agents from petrol, cadmium from the aquatic water batteries. from metal extraction industries, e.g. silver , gold, the iron and environment steel describe and pollutants Cyanides: industry and from the discharge of material from the preparation of treatment. organic Other chemicals. metals: leaching into e.g. through Pesticides and paints from reaching plant of T oxicity levels of in are washes extraction, from these from trace elements by industry. crops and leaches them in the water of clay sites, the fertiliser and other quarries and material storm such as sewers. environment can may disturbs inorganic mercury reduce inhibit food the amount of photosynthesis chains run- off Phosphates waste. and the world. with (see from and in the even lead water . Section sewage sunlight and and 13.2) can lead detergents to also consequent effect on spillages. If effect Section they on of result leak in food into wildlife, 12.2). water Diseases the metals are concentrations poisonous, can reach e.g. high water . herbicides can heavy Their e.g. is responsible such contaminated water harmful of contamination in Many lead. bodies in (see particles This through pesticides presence Oil 12.2). aquatic organisms. associated Many Small This enclosed Microbial sickness clay discharges eutrophication. cadmium, rain Section plants. death. death cause from from construction solids water Eutrophication the or and the Suspended to (See particles: washed Pollutants soil herbicides: residues: Suspended aluminium the rivers. Petroleum 158 sewage sea. electroplating introduction turbidity describe on the Industrial although Common water to water . pesticides, Heavy phosphates, and the Domestic up Nitrates: into to: and due pollution you materials should is water as cholera, for 80% of typhoid all and the malaria water . are the halogenated death chain) water , seals as of well as petroleum can be hydrocarbons. invertebrates infertility residues blinded and (and in Their its birds. may birds have may a die Chapter Testing for selected 14 Chemistry and the environment pollutants Nitrates Add aqueous zinc powder ammonia sodium or gas hydroxide aluminium is released to the powder (see Unit (or 1 suspected nitrate Devarda’s alloy). Study Guide , and On Section then either warming, 14.3). Phosphates Acidify with molybdate. gently Lead concentrated The nitric formation indicates that a of a acid and bright phosphate is add yellow a little ammonium precipitate on warming present. ions Did you know? –3 Add 1 mol dm redissolves hydrochloric in hot water acid. The indicates that presence lead is of a white present. A precipitate that conrmatory test Mangroves is to add aqueous potassium iodide to the acidied water . A bright kinds precipitate indicates the presence of are areas where various yellow of trees grow in several feet lead. of water tropical along and the coast subtropical in some areas. In Cyanide mangrove Add If a iron( ii) deep sulphate blue to complex the ion solution is then formed, acidify cyanide with ions hydrochloric are acid. present. is needed some swamps in the high water young sh from preserve the turbidity to protect predators and ecosystem. Turbidity T urbidity simplest through use a a to to the column using greater scattering a the and cloudiness measure to detector the the measure number of turbidity containing nephelometer particles The refers way on of greater to the under light same suspended the test. scattered side of the particles, detector matter measure liquid the the suspended is A by a liquid. as The transmitted better the tube the in light method is to suspended the greater light is beam. the reading. Water treatment W ater this has to process be to treated purify to make dirty it water safe for drinking. The main steps in Key points are: Screening: Aeration: Removes large oating Common include Removes volatile substances such as hydrogen sulphide nitrates, metals, Flocculation and together sedimentation: and are then The water removed after is agitated. Small particles Filtration: Removes nely suspended particles from the Coagulation: There ne Iron sulphate suspended or particles aluminium clump sulphate are Disinfection: Chlorine is added to specic chemical added to phosphates, tests lead help and cyanide. together . are nitrates, ions very particles. water . for pesticides, and settling. phosphates, cyanide, residues suspended clump water oils. petroleum in and heavy volatile pollutants objects. kill bacteria and Turbidity is measured by the other ability of a suspension to scatter microorganisms. light. Adsorption: Activated charcoal is used to adsorb organic chemicals which might give a bad odour and taste to the Water is treated processes Oxidation: Undesirable substances, e.g. are oxidised with ozone to form less harmful Desalination: (see Section the of aeration, ltration, disinfection and products. charcoal using cyanide-containing coagulation, compounds, by water . adsorption. 14.1). 159 14.3 Ozone in Learning outcomes the Ozone The On completion of this atmosphere section, in the stratosphere atmosphere is the part of the atmosphere about 20–50 km above the you Earth. Ozone, , O is present in the stratosphere in a ‘layer ’ which varies in 3 should be able to: thickness. explain ozone how in the the concentration atmosphere of per The million, ozone absorbs which is harmful present at ultraviolet a concentration (UV) radiation of about from the 10 parts Sun. is maintained The understand the importance of the ozone The ‘photodissociation’ ozone light describe the signicance describe of CFCs some free reactions in human health layer reaches is important surface of for human health because if too much UV Earth: environmental in the ozone layer layer to term the radical there is the people we an skin increased ages are risk of sunburn and skin cancer faster more likely to get cataracts in their eyes upper may have reduced resistance to some diseases. atmosphere describe the effects of ozone on Ozone formation human life (referring stratosphere and to in the stratosphere the troposphere). In the on stratosphere, oxygen. light (usually enough free This (see ozone a to cause which Section is formed naturally photodissociation ultraviolet energy radicals, ssion is light) causes oxygen are very bond molecules reactive. by the reaction a action is The dissociate an of reaction breaking. to This – to example UV in UV light form of light which has oxygen homolytic 2.1). UV light 2O•(g) (g) → O 2 oxygen An oxygen radical can react with O (g) an + oxygen O•(g) → molecule O 2 Ozone is oxygen also free broken radical down are by UV Dutch scientist Martin the absence was the rst person to distinctive machinery later found smell was to when due to of ozone is ozone ‘ozein’ comes from which means to the Sun. Oxygen an factors (g) + O•(g) 2 in balance decomposing with the rate of the ozone, the breakdown. rate So of the of ozone in the atmosphere remains constant. was ozone. The chemicals the Greek smell. Chlorofluorocarbons toxic and are atmosphere reach the A cycle Section (CFCs) unreactive for Highly involving 2.1). We of reactive use the free as refrigerants normal years. where initiation, shall used under hundreds stratosphere, molecules. After UV many light radicals CFC by Initiation: not the The C—F F UV light is strong enough to break the UV CCl F 2 2 light → Cl• + •CClF 2 not the may these homolytic CCl bond. in molecules ter mination chlorouorocarbon, are persist decompose formed and aerosols They years, can are propagation the and conditions. 2 160 and light (g) → O other Ozone-depleting word from electrical working. This be any (g) record amount a of ozone. van formation Marum light 3 In 1785 form 3 UV In to formed. O Did you know? radical ssion. occurs as an (see example. 2 C—Cl bond but Chapter Propagation: Cl free radicals can Cl• + then O → attack ClO• ozone + + result of these reactions is O → Cl• ozone (g) → + In Cl• these 100 000 radicals to radical chain ozone high jet present Earth’s Other in surface) may low the can because chlorine before a of it radical 2O converted is to constantly may termination CFCs and in the break oxygen. reaction compounds to ozone being down reformed. about between atmosphere trichloroethane. contribute two therefore may also Nitrogen free leads have oxides this from depletion. level ozone troposphere be e.g. (g) chloro - organic also environment 2 catalyst a presence aircraft effects of Ozone a tetrachloromethane ying The The depletion . e.g. as molecules occurs. ozone effect, acts reactions, is 3O 3 The the 2 that 2O and 2 3 The Chemistry O 3 ClO• molecules, 14 toxic to (the plant layer and of the animal atmosphere life. It next to can: Exam tips irritate the respiratory been linked have a to system increased and cause incidences of breathing asthma and difculties. It has bronchitis. The bad affect cholesterol-like cardiovascular on the heart compounds problems and to such blood form as in vessels. the It lungs. atherosclerosis may These cause may (hardening effect depletion cause of the the of CFCs of the production troposphere as on the ozone of a layer ozone result in of and the the arteries). interaction Ozone is dioxide one from reactions and in of the car the nitrogen factors exhausts presence dioxide is contributing (see of Section UV light. to photochemical 14.8) can Ozone is undergo formed smog. Nitrogen examples photolytic during this cycle sure that related UV NO + nitric dioxide oxide + → O chain you to light nitrogen are reactions. know and these with exhausts the both Make initiation, termination steps reactions. We rst O• came nitrogen O• car light → 2 of propagation regenerated. NO of UV oxides from oxygen across these in Section 2. 1. free radical O 2 3 ozone NO + O → NO 3 When hydrocarbons disrupted organic and ozone radicals. photochemical and/or reacts These smog are (see + O 2 carbon with 2 monoxide unsaturated responsible Section for are present, this hydrocarbons many of the to cycle gets produce harmful effects of 14.8). Key points The concentration involving free radical Photodissociation CFCs can radicals deplete and Stratospheric Tropospheric nitrogen is the ozone ozone oxides ozone in the atmosphere is maintained by a cycle reactions. the initiated of of breaking ozone by layer and be a by ultraviolet protects can of bond catalytic light, usually UV reactions light. involving free light. humans from produced subsequent by by the the reaction harmful UV photochemical of an rays of the Sun. decomposition oxygen free radical with oxygen. Ozone is harmful to plant and animal life. 161 14.4 The carbon Learning outcomes cycle Carbon The On completion of this section, oceans, be able explain the importance maintaining carbon explain of the dioxide the sources atmosphere carbon and rocks reservoirs or all contain carbon sinks . carbon. The We call amount of these carbon to: in the you carbon should sinks balance in the carbon equilibrium of of cycle in is terms of these because carbon atmosphere concepts each This from mainly as reservoirs there these carbon is a has not balance reservoirs. dioxide, is changed between The the much the reservoir one which of over uptake carbon can millions and in the undergo of release years. of atmosphere, most rapid changes. and reforestation. Releasing There are several Respiration: complex dioxide oxygen carbon This series is ways is of the into H 6 CO when of the process the O 12 to which produce (aq) to + do 6O into food such This CO is energy. the atmosphere. oxidised During Aerobic in this the body process respiration by a carbon removes this. (g) → 6CO 2 2 (g) + 6H 2 as coal, wood escapes into O(l) 2 and the hydrocarbons atmosphere. produce When this 2 happens, be in gets atmosphere. Fuels burn. atmosphere carbon 6 fuels: they which atmosphere C Combustion by reactions released from into the due oxygen to is human also removed activity (e.g. from for the atmosphere. transport) or natural Combustion activity (e.g. can forest res). Other decompositions: atmosphere From by oceans: the Small amounts breakdown When of dissolves CO of carbon vegetation in in are released into the swamps. seawater various equilibria are set 2 up involving hydrogencarbonate and carbonate ions, e.g. 2– (aq) 2HCO Y CO 3 (g) + H 2 O(l) + gases water in are the less soluble oceans gets in (aq) 3 hydrogencarbonate Most CO 2 carbonate water warmer as the temperature bubbles CO out of increases. solution and When the 2 equilibrium The above is uptake of There are two atmosphere: to the right. carbon from the main ways in which photosynthesis Photosynthesis: during shifted Plants photosynthesis remove to (g) 6CO and + 6H 2 carbon by the carbon make atmosphere dioxide is removed from the oceans. dioxide from the atmosphere carbohydrates. O(l) → C 2 H 6 O 12 (aq) + 6O 6 (g) 2 glucose The energy pigment By in oceans: for this plants is CO reaction traps quite the comes from sunlight soluble in and water sunlight. acts and as a large Chlorophyll, amounts 2 from the atmosphere when it dissolves in oceans: + CO (g) 2 162 + H O(l) 2 Y HCO (aq) 3 + the green catalyst. H (aq) are removed Chapter Balancing uptake and 14 Chemistry and the environment release of CO 2 Exam tips The complete carbon cycle is shown in Figure 14.4.1. The carbon two most features in important regulating dioxide atmosphere of the carbon cycle are 100 respiration and photosynthesis. 100 3.5 that increases the other 125 120 of drastically extent these to takes reduces which place will or one or upset decay the 1 carbon cycle. respiration burning (as Anything fossil methane) fuels photosynthesis warmer water dead marshes oceans organisms numbers show the organisms carbonate of carbon year transferred in thousands millions of Did you know? amount 2– rocks sediments every HCO of tonnes in sea. After the to two processes which keep Respiration this cycle releases in CO balance into the are air respiration and takes and up Photosynthesis takes up from CO the air and puts oxygen air . These two processes are carbonate cycle approximately balanced so that sea animals can be they (plankton) die, bed. Over plankton content of the air remains fairly constant. In addition, the is dead millions of rocks, taken organisms form e.g. out limestone. This of the carbon unless the carbonate rocks are the heated CO tiny back 2 the the these carbon 2 into by The carbon cycle photosynthesis. oxygen. ions 3 up years The and CO taken fall Figure 14.4.1 ions 3 to make lime. large 2 amount of taken CO up by the oceans is balanced by that released from 2 the oceans. Upsetting the The burning dioxide into of fossils the If burnt would we there are fuels only atmosphere respiration. So balance fossil putting fuels not were be more a releases compared being into small the formed problem. CO a with But the as fossil amount amount fast as fuels of they are carbon released were not by being being formed. atmosphere. 2 Many people are worried that an increase in the amount of CO in the 2 atmosphere warming will (see put the Section carbon cycle out of balance and increase global Key points 14.5). As the world’s population increases, many forests are being The carbon level because of an increased need of land for agriculture, cycle quarrying or of carbon deforestation means that less is CO being removed from dioxide the in the housing. atmosphere This keeps cleared relatively constant. the 2 atmosphere and to by photosynthesis. respiration replace those is altered. lost) is That So is important the why in balance between reforestation maintaining photosynthesis (replanting this of The carbon into trees the balanced dioxide released atmosphere respiration balance. dioxide in by in living the uptake the of is carbon photosynthesis. Burning fossil fuels deforestation the by organisms carbon may cycle and cause to become unbalanced. Reforestation the carbon helps to rebalance cycle. 163 14.5 Global warming Learning outcomes The The On completion of this section, be able explain effect’ the and terms ‘greenhouse ‘global if it describe absorbed effect by the is a the energy from the temperature were heated of the directly the by which and Earth’s by re-radiation of the region infrared simplied diagram of thermal re-radiated surface radiation the some into process atmosphere in radiation all from directions the so and from the atmosphere is higher than Sun. warming’ A is to: that greenhouse effect you Sun should greenhouse greenhouse effect is shown shorter energy in wave Figure rays 14.5.1. – atmosphere. escapes visible into the space energy the radiated Earth infrared as + UV Sun from long wave rays carbon energy dioxide + water absorbed in by from the atmosphere greenhouse gases warms the atmosphere energy near Figure 14.5.1 In the water it not is Earth’s surface Simplied diagram of the greenhouse effect greenhouse and absorbed the vapour exposed Ultraviolet effect, to and wavelengths. gases prevent the the Sun’s visible The in the Earth rays. It radiation visible atmosphere from cooling works from radiation like the and such down as carbon too dioxide rapidly when this: Sun some have of the relatively UV short radiation pass Did you know? through The term named ‘greenhouse because a similar in a greenhouse, radiation way it in effect’ appears to the letting through but to glass was so air short-wave trapping by warming up the air When idea relating the surface the gains Earth’s without radiation being hits absorbed the Earth’s by carbon surface so dioxide. that the energy. surface absorbs the short wavelength rays it heats the Energy is lost from the surface as radiation with a longer wavelength. inside. The The rst atmosphere wavelength up. heat the short Earth’s work and The radiation emitted is in the infrared region. insulating Infrared radiation can be absorbed by greenhouses gases such as CO 2 properties of the atmosphere were and put forward by Joseph Fourier but these ideas were experimentally until Some of the greenhouse of fossil fuels effect was to in space The heat than were is re-radiated and some would not absorbed the atmosphere. back escapes to into Earth and space. the Less lower layers radiation of escapes be the case if greenhouse gases such as carbon present. radiation raises the temperature of the atmosphere. Svante natural 1896. warming. 164 in the This Arrhenius present to burning naturally 1859 person dioxide relate the atmosphere into by John Tyndall. The rst are not the proved which in 1824 water , raising of the atmospheric temperature is called global Chapter Global 14 Chemistry and the environment warming Exam tips Global that the war ming arises Earth reected from be The atmosphere, the to the increase the in more global the up carbon heat is effect. If than and absorbed of the There we because rather dioxide because more. temperature cold, surface more heats in extremely atmosphere atmosphere rise greenhouse from atmosphere. and the the would away is is of did the the not have water re-radiated greenhouse enhanced by back So is to and in the the must Earth by A greenhouse absorbs main Water and spectrum. naturally- occurring The distinguish greenhouse effect the then the way Earth’s close re-emitted radiation. Global refers to the radiation surface to range greenhouse the as Earth’s longer warming temperature the is and increase greenhouse effect. gases gas electromagnetic to atmosphere arising from Greenhouse to terms relates surface, warming). able the absorbed the (an be global warming. The effect the warming You between be the there effect. global warming, would absorbed vapour atmosphere global radiation being and Earth’s gases This radiation absorption greenhouse greenhouse vapour: emits The gas, is naturally may shown in present contribute in the infrared spectrum from of Figure in the about part carbon of the dioxide, a 14.5.2. atmosphere 30–60% of are: the vis greenhouse present in Carbon the by especially atmosphere the water dioxide: in the lower small layers amounts, of the which atmosphere. are kept It is relatively cycle. is CO in ecnabrosba constant effect naturally present in the atmosphere. Although 2 it is only present contributing Methane: to in at This is low least concentrations, 30% found in of the the it is a potent greenhouse atmosphere at greenhouse gas effect. much lower 2 3 10 concentrations than , CO but it absorbs relatively more IR and may contribute Methane is formed as by 4 10 10 radiation 2 wavelength much the as 5–10% action of of the bacteria greenhouse in the (nm) effect. digestive system of Fig. 14.5.2 The absorption spectrum of carbon dioxide animals paddy Ozone, and by the bacterial decay in marshes as well as from rice elds. CFCs and nitrogen oxides are also effective greenhouse gases. Key points Enhanced global warming and climate change Over the past 150 years the amount of CO in the atmosphere has The greenhouse effect is a been 2 process increasing stations because and for of the increased transport. The burning present of fossil percentage fuels of in in CO by which thermal power radiation the is absorbed by the 2 atmosphere The is nitrogen oxides atmosphere in concentration warmer melting of 0.039%, of other years for greenhouse can ice rainfall 50 ozone, the gases affect caps low-lying the whereas greenhouse tropospheric recent of polar reducing of and atmosphere ooding about concentrations and our same leads years gases, have been reasons. to climate hence ago it such was as about increasing The increased atmosphere 0.031%. methane so and in Earth’s the is increased global warming. A areas so sea levels leading to increased increasing the rate of increasing species Global the the weather the such more violent temperature as corals. An of the and unpredictable oceans increased than by re-radiated and if it of the atmosphere were heated radiation from leading amount of to the death will CO be of also some be warming A is temperature atmosphere formation deserts making surface higher the some and temperature the Sun. areas in the directly by: raising that which greenhouse greenhouse emits part the rise the in Earth’s arises from effect. gas radiation of the of in absorbs the and infrared electromagnetic 2 released from the oceans leading to an even further increase in global spectrum. warming. 165 14.6 The nitrogen Learning outcomes On completion should be able of this The section, cycle nitrogen Nitrogen gas chemical reactivity. describe explain forms 78% of the atmosphere by volume, but it has low you Nitrogen can be recycled at a sufcient rate in the to: atmosphere cycle the how nitrogen the cycle diagram of to allow the plants nitrogen to grow. Figure 14.6.1 shows a simplied cycle atmospheric N in air 2 concentrations of the oxides of N + O/NO/NO 2 NH 2 /NH 3 nitrogen may be 4 altered. in air in air fertilisers agriculture vehicles industry sea creatures dissolved N run-off from and fertilisers compounds sediments Figure 14.6.1 Much of the catalysed are Simplied diagram of the nitrogen cycle shown catalysed nitrogen cycle conversions in by Figure in is dominated microbes, 14.6.2. Many by plants of the reactions and involving animals. reverse These reactions can enzyme- reactions be microorganisms. de d en tr mmoni cay/a fic tion fica at io n amino proteins N NH 2 NO 3 nitrogen nitrogen NO 2 ammonia acids in amino + animals acids/ 3 nitrites nitrification nitrates nitrification proteins in plants assimilation fixation Figure 14.6.2 Exam tips Reactions The nitrogen You need cycle is very Some biological oxidations and reductions involving nitrogen compounds which Denitrication: reactions biological learn below the rather conversions nitrogen Denitrifying into the bacteria occur atmosphere under both aerobic and complex. anaerobic only release conditions in the soil and in the oceans. They use organic basic than of all compounds to reduce compounds are nitrates to nitrogen gas. The organic the oxidised to carbon dioxide. ammonia + O(aq) 5CH to + 4NO 2 proteins. (aq) + 4H (aq) → 2N 3 (where CH O is a (g) + 5CO 2 simplied formula for a (g) + 7H 2 O(l) 2 sugar) 2 The nitrates remains or Ammonium oxidation largely animal in The of 166 sea. The and which for fertilisers fertilisers, decomposition nitrogen gas fertiliser This nitric run oxides can ammonium ammonium ammonia and of Nitrogen and remove Process : atmosphere make oxidation: the Haber from conversion ammonia remains Reactions arise from ions be ions animal by arise by bacteria. from and plant nitrates. reformed anaerobic This decaying occurs plant off. nitrogen from the removes nitrogen synthesis. acid. of into The atmosphere directly nitrogen is from then the used to and Chapter Lightning: nitrogen further which The to reactions dissolve Nitrogen be aerobic by nitrifying nitrates Car or to in Nitrogen the the bacteria The are called or into in soil. emitted to oxygen which and the environment and can removed then combine. from show the that then be undergo as nitrates exhaust of gases. convert bacteria to nitrates a car This of engine can oxides mixture gases are Some found 14.6.2). nitrogen different Did you know? can dissolved Figure inside mixture several the (see pressure A can converted absorb proteins and algae nitrogen-xing can and temperature NO nally blue-green The Plants acids to cause formed, being ammonia amino oxygen are or ammonia. the lightning Chemistry groundwater . bacteria The in high and which sometimes sea Certain synthesise of oxides atmosphere, anaerobic. nitrogen formed, temperatures nitrogen engines: cause in xation: atmospheric high combine. 14 is is in swellings beans and swellings Farmers beans formed: nitrogen-xing are on because the are plant roots clover plants. These called root sometime or bacteria clover they nodules. plough back into increase crops the the of soil nitrogen x content N (g) + O 2 N (g) High temperature causes The The nitrogen (g) + 2O balance of the atmosphere remains main more parts of has or the nitrogen atmosphere amount from exhausts and affect amounts by the removed removed not for the of industry very air due working nitrogen Oxides of Nitrous nitrogen oxide, N to is to form days balanced The in these nitrogen these put by is of its furnaces oxides. the natural of the is atmosphere 14.7 as that the the also from present of from same oxides the Sections processes nitrogen presence the by nitrogen about at process, nitrogen More the concentration Haber nitrogen the (see of now processes cycle, into so the removal xation. formation problems of xation fertilisers being being vehicle time may increasing by and vehicles and 14.8). atmosphere recycled added temperature nitrogen, the the nitrogen in the are of nitrogen the the oxides O were of (g) cycle roughly particular Nitrogen oxides high sink Although of 2NO combine atmosphere. bacterial industry . poses was the → 2 Before cycle production by the large constant. into to nitrogen which back (g) The oxygen nitrogen microorganisms, put a less soil. 2NO(g) 2 furnaces: and the 2 2 → of in to the the atmosphere atmosphere by by natural processes. denitrication 2 reactions. Nitric oxide, NO, and nitrogen dioxide, NO , are produced 2 during thunderstorms: Key points (g) N + O 2 (g) → 2NO(g) and N 2 (g) + 2O 2 (g) → 2NO 2 (g) 2 Nitrous oxide passes from the lower atmosphere to the stratosphere, Processes from it is converted to and N NO by photolytic reactions initiated by UV that remove nitrogen where the atmosphere include light: 2 the N O(g) → NO(g) + Haber process, lightning and N•(g) 2 nitrogen xation. O(g) N → N 2 (g) + O•(g) 2 Nitric oxide can form by the reaction of N O with the oxygen free radicals to 2 formed by the latter reaction or from the decomposition of Processes ozone: the that add nitrogen atmosphere denitrication include and ammonia oxidation. O(g) N + O•(g) → 2NO(g) 2 The NO formed can catalyse the decomposition of ozone. Some NO The concentration oxides also react with either oxygen free radicals or ozone to form acidic of nitrogen can in the atmosphere is NO 2 increasing which can contribute to acid rain (see Section part of the nitrogen cycle is of concern to many scientists are affecting it to a considerable nitrogen produced extent (see Sections by vehicle because emissions humans of 14.7). oxides This because 14.7 and high temperature and furnaces. 14.8). 167 14.7 Acid rain Learning outcomes What Rain On completion of this section, be able the describe the products of containing explain naturally rain? air . This slightly rain effects of the combustion of fuels If acid the rain. acidity This atmosphere is of pH due of to carbon about 5.6. dioxide But this reacting is not with classed water as rain caused by with falls below oxides water of about sulphur pH 5, and the rain nitrogen is acid in called the vapour . sulphur how oxides nitrogen. acidic a the reacting acid rain is formed Acidic oxides from has to: rain. acid you in should is is of sulphur in the air and Coal also and before to natural contain the fuel sulphur gas small is contain amounts sold. dioxide, When which some of is these an S(s) sulphur sulphur , fuels acidic + are → third of are the Nitrogen natural oxides temperature nitrogen a sulphur can also furnaces. dioxide is source dioxide an formation Figure 14.7.1 of acidic acid shows get rain it for is transport removed sulphur is oxidised (g) dioxide. pollutes the oxide air the from and They produce nearly a atmosphere. car nitric exhausts oxide are and not from acidic high but gas. acid these the Fuels of 2 sulphur into Nitrous The formation of The of which burnt, SO 2 V olcanoes most gas: (g) O impurities. although rain involves two stages: oxidation and deposition. stages. 2– SO 4 + oxidation H H O SO 2 4 2 SO 3 dry SO reaction burning vehicle acidified exhausts surfaces reactions by atmosphere. trioxide and of 2 fossil fuels dioxide Oxidation in the nitrogen Sulphur nitric nitric in the atmosphere atmosphere dioxide: dioxide oxide. oxide SO The with (g) + is This reacts oxidised can with nitrogen oxygen NO 2 (g) in → take then: 2NO(g) O (g) 2 a place dioxide the is variety fairly catalysts. quickly dioxide then of to in form reformed the sulphur by air . SO 2 + by nitrogen (g) + NO(g) 3 sulphur 168 deposition The formation of acid rain Oxidation Sulphur wet NO 2 Figure 14.7.1 deposition → trioxide 2NO (g) 2 nitric oxide Chapter The NO which is reformed can go on to oxidise another SO Chemistry and the environment molecule. 2 This 14 2 process can be repeated to oxidise many more molecules. SO The 2 acts NO as a catalyst. 2 Oxidation in the involving atmosphere free and radials: so do These not reactions occur until often the SO take has place moved higher up to 2 these levels. Examples Oxidation with are: oxygen SO free (g) + radicals O 2 Oxidation to formed the O (H by + O• → → ozone: SO 3 sulphates action (g) or by of OH• O• (g) + O 3 radicals. radicals (g) 2 The from OH• ozone radicals with are water 2OH•). 2 several OH•(g) + SO (g) → HSO 2 Nitric oxide radicals or from ozone car to exhausts form the can H react gas, with nitrogen SO 2 → also acidic steps •(g) 3 either 4 oxygen, dioxide, free NO 2 NO(g) + O•(g) → NO (g) or NO(g) + O 2 Acid formation Wet deposition: atmosphere form acid a dilute with solution trioxide or of and dissolve NO (g) + O 2 (g) 2 small water acid. particles vapour This of in falls sulphates the with in the atmosphere the rain to to form rain. (g) + H 3 Nitrogen dioxide atmosphere to in the from a 2NO Some sulphur sulphurous (g) + H of O(l) These nitric may when Small or it → such as and with water vapour react in the (aq) + HNO (aq) 2 directly with water to form raining. (g) + H O(l) → H 2 particles dry plants (aq) 4 acid. HNO of acid sulphates reacts and SO and SO 2 (aq) 3 and with SO 2 surfaces SO 3 also is sulphuric compounds reacts nitric 2 deposition: H 2 SO when → 2 atmosphere solution dioxide acid O(l) 2 2 air in sulphuric SO Dry → (deposition) Sulphur react (g) 3 nitrates ammonia gases can be can in form the in the atmosphere. deposited on moist 3 wet buildings to form acids. Key points The effects of acid rain T rees may forest have their leaves and roots damaged. This can lead to When fuels are burnt, containing sulphur sulphur dioxide is death. formed. Lakes Soil and rivers become acidic. Some aquatic organisms may die. may leached become out of too the acidic to grow crop plants and minerals may be Sulphur dioxide atmosphere Buildings Metals made from structures carbonate such as rocks bridges may and be eroded. railings may 200 km may fall trioxide from far and their from the nitrogen sources. source oxides So the of pollution. can effects be carried on the Sulphur by be obvious radicals the and Sulphur trioxide close to the to form or sulphur sulphates. vapour reacts to form with dilute dioxide, winds as environment far will sulphuric as acid in the rain. not always dioxide trioxide water rain sulphur by free in corrode. Acid oxidised soil. nitrogen is Nitrogen oxides can be oxidised sources. to form nitrogen dissolves nitric in dioxide, water vapour which to form acid. 169 14.8 Pollution from fuels Learning outcomes Primary and Atmospheric On completion of this section, be able (particulates) describe the difference and secondary describe the effect of pollutants: monoxide fossil of combustion as environment describe the and on of liquid or tiny particles of and on are released directly from a process, e.g. from fuels, car exhausts, particulates sulphur released dioxide from released erupting from volcanoes a waste product of animal digestion. Other or primary resulting from human activity include: the nitric carbon of oxide lead and volatile the dioxide nitrogen from dioxide lime kilns from and car from exhausts combustion of fossil in car fuels lead organic and compounds These humans effects compounds and droplets air . of pollutants hydrocarbon fuels the the methane products gases, pollutants burning be with between carbon primary can mixed to: Primary pollutants pollutants you solids should secondary and lead small compounds particles of from combustion reactions engines paints environment humans volatile organic compounds e.g. unburnt hydrocarbons from vehicle engines explain the term ‘photochemical smog’. CFCs from Secondary primary arising refrigerants pollutants: pollutants from sulphur ozone human nitrogen organic particles the These undergo trioxide in from and salts now formed in the reactions. atmospheric from oxygen formed formed banned). atmosphere Secondary when pollutants include: troposphere dioxide are further activity compounds of (although in (see in oxidation the Section smog the of sulphur photochemical (see 14.3 dioxide cycle and involving below) below) atmosphere, e.g. nitrates from NH 3 and acids Burning in air . hydrocarbon fuels Incomplete When the combustion hydrocarbon formed, which present, is a fuels hydrocarbon monoxide, CO, is undergo greenhouse fuels formed H 2C 4 (see undergo as (g) complete gas + well 9O 10 combustion Section 14.4). incomplete as (g) soot → carbon not particles + 10H 2 of dioxide enough combustion. (small 8CO(g) If air is is Carbon carbon). O(l) 2 Exam tips 2C H 4 Some well pollutants as can secondary example, NO is be primary pollutants. a primary as Particles haem, For pollutant of the present in soot are oxygen red (g) + 5O 10 irritants. carrying blood (g) → 8C(s) + 10H 2 cells. Carbon group It O(l) 2 in monoxide the prevents protein oxygen is toxic. It combines haemeoglobin from binding to which haem with is and 2 when emitted from but a is secondary car exhausts, pollutant can lead to when Unburnt formed in the atmosphere from ozone. between So when nitric oxide answering an hydrocarbons not enough oxygen on primary and make sure that context understand the pollutant being formed. released into the atmosphere if there smog in combines with oxygen in the high temperature of car engines to you which oxides of nitrogen ). (NO In the presence of hydrocarbons from car x the exhausts, smog. 170 be them. exam form is also burn secondary Nitrogen pollutants, to and Photochemical question may the is reaction death. ozone This is and made sunlight, worse in this cities mixture where a reacts layer to of form warm photochemical dry air traps a Chapter layer dry of air cooler allows air beneath the it (temperature maximum amount of inversion). UV light to The be layer of warm 14 Chemistry and a the environment warm air transmitted. cooler Figure 14.8.1 shows how a photochemical smog air NO forms. CO Nitrogen dioxide from car exhausts can undergo photolytic reactions in C H n the presence dioxide is of UV light. Ozone is formed during this cycle and regenerated. UV b UV NO O• + NO O + O → NO hydrocarbons Ozone and/or reacts + monoxide these carbon 2 3 more CO O 2 carbon with + O 2 3 O 3 disrupted. + O• NO → 2 NO radiation light → 2 When 2n+2 nitrogen + C H n 2n+2 2 are present, compounds this to cycle produce gets organic c radicals such as O• CH and HCO•. These combine with nitrogen oxides NO 3 + O x to form cause may aldehydes, irritation also higher be of peroxides the present, molar eyes, and breathing including masses. The organic some nitrogen nitrates. difculties nitrates, dioxide, These and asthma. aldehydes which compounds is an and aldehyde Particulates ketones higher concentrations, gives the smog a brownish irritant and + C H n 2n+2 + nitrates with toxic Figure 14.8.1 in + CO 3 can colour . The formation of photochemical smog; a Early morning: temperature inversion prevents the dispersion of NO , CO and hydrocarbons; x Lead compounds and the environment reacts with O b Slightly later: NO 2 form ozone. Lead and lead compounds are toxic. They can affect the heart, bones and reaction of O 3 kidneys. Lead particularly permanent paint fuel harmful containing V olatile ozone nervous is tetraethyl layer . the system aqueous of environment children. problems. and VOCs combustion (VOCs) methanal children. get Lead and Methane It gets can into is , NO and hydrocarbons to x form smog. cause the of as by leakage by evaporation from cleaning by evaporation from paints refrigerants the fuel burn more engines. environment compounds methanal, the can a make such with low membranes affect the greenhouse of as the immune gas and methane, boiling points. eyes, nose system, CFCs deplete the atmosphere: of products the is to vehicle are and irritate effects into in and the compounds allergic (added combustion compounds have in in burnt compounds organic especially and behavioural lead lead chlorocarbon lungs, the undergoes Chlorocarbons and to and containing Organic atmosphere when: smoothly) CFCs, the learning environment in to 2 c Late morning and afternoon: paints from and old glues in building materials refrigerators products and used which contain them glues. Key points Primary pollutants pollutants Combustion of CO gas, – a toxic Photochemical nitrogen Lead are are formed and smog and volatile burn may is formed vehicle a process. pollutants lead photochemical organic or directly from primary hydrocarbons oxides from when fuels released when to Secondary react further global warming, in the the air. emission of smog. when ozone reacts with hydrocarbons and exhausts. compounds evaporate into the can be released into the atmosphere air. 171 14.9 Controlling Learning outcomes pollution Introduction Many On completion of this section, of the fuels environment should be able describe and methods preventing of controlling atmospheric pollution describe rain. the design more electric importance of carbon is transit in describe and as coal and such as petrol, pollute increased the global also preventing the and fuels are emissions. better for so that powered being For the by helps fewer to pollutants batteries do developed example, make than are are warming as a chemical For carbon cleaner alcohol the and formed. produce which making environment not engine and production by and example, dioxide. and fuel plant reduce fermentation use of cleaner fuels, technology sequestering washers such problems technology efcient vehicles petroleum improved use, cause Improved Alter native alternative and to: acid we you and pollution importance of agents, lters, scrubbers fractions (see Section 13.4). mass Hydrogen only cells is a product. used to non-polluting Hydrogen power can some fuel. be When used vehicles as it a burns fuel (Figure in in oxygen, water is hydrogen–oxygen the fuel 14.9.1). in electron flow porous controlling porous negative positive pollution. electrode electrode coated coated V with with platinum platinum + H hydrogen oxygen water electrolyte (acid) membrane Figure 14.9.1 Carbon A hydrogen–oxygen fuel cell emissions mass transit individual can also using be reduced vehicles such by: as buses and trains rather than cars using simpler forms using alternative of transport, energy sources, such e.g. as cycles solar power , wind power , wave power . Improved technology fuels be may electric cars needed and Catalytic Catalytic oxides, to to not make make solve the all the problems. electricity hydrogen for fuel to converters platinum–rhodium nitrogen hydrocarbons are and tted and catalyst gas and carbon to carbon cars recharge causes carbon + to reduce nitrogen oxides monoxide may 2CO(g) → to also (g) N the Once 2NO (g) + 4CO(g) 2 Sequestering 172 from the the fossil batteries in N to be reduce + nitrogen the converted dioxide. the 2CO of up, to Unburnt nitrogen oxides. (g) 2 (g) + 4CO 2 (g) 2 agents agents air . → emissions warmed carbon 2 or example, cells. monoxide. monoxide 2NO(g) Sequestering For converters hydrocarbons harmless does They are agents often that form remove complexes particular with metal ions ions from (see solution Unit 1 Chapter Study Guide , Section 13.4). They can be used to remove metals ions 14 Chemistry and the environment from 2+ the soil, from contaminated water or from the air . For example and Cu Exam tips 2+ ions Ni agents such removed then as adding be be mixture so separated such that using water EDT A waste surfactant pH from of industrial a the removed a from adjusting then can the by and adding chitosan. products as a by is mixture Heavy adding long-chained complex methods a a separate metals The in polar removed from removes these and water ions non-polar by as adding an solvents. sodium insoluble can acid of You be agent and complex molecules 2+ solubility sequestering sequestering carboxylic uncharged. which of do details not of converters can You different have to how fuel or should, importance know cells, scrubbers however, of these precise catalytic work. know in the reducing 2+ and Ca Mg ions hexametaphosphate can be pollution. which complex. Scrubbers Scr ubbers scrubbers high remove work pressure the tank the cleaned or in a particles rather against spiral. air sometimes, like the The escapes from waste gases spin dryer . The a side of dirty from a cylindrical water the in runs top. factory. gases tank. down This a waste The the process sprayed water side is Modern are of the called at moves tank wet up and scrubbing washing. Flue-gas desulphurisation Flue-gas process, desulphurisation acids, harmful waste substances gases moving alkalis in bed sulphite of in power solid formed is or is an other waste gases. stations calcium either and + of scrubbing reactions Sulphur furnaces carbonate dumped (g) SO example chemical or (s) into → SO (g) + can oxide. CaSO (s) + to be the removed CaO(s) → CaSO this from through a calcium acid. CO 3 2 In neutralise gases The sulphuric 3 washing). used passing calcium made CaCO 2 or dioxide by (air are (g) 2 (s) 3 Filters Filters are chemical of long drawn used to plants polyester though 14.9.2). opposite The remove and some ‘socks’, the lter lters is direction dust which and cleaned and and power particulates stations. allow the gases dust the by dust from lters through, collects periodically collecting Air on the passing as a the waste consist but not outside air of gases a in to chimney number dust. Air is (Figure through in the air solid. sucked through polyester Washing ‘sock’ dust collecting Materials the such as metal contaminating dust ores and undergo clays. high pressure W ashing may washing also to remove dirty air in remove soluble dust contaminants from a substance. removed Figure 14.9.2 A bag lter used to collect dust from waste gases Key points Pollution ethanol, by can be reduced improving means Pollution of mass can be by using technology, transport, reduced by cleaner fuels e.g. e.g. more buses using such efcient and as hydrogen engines and or by travelling trains. sequestering agents, lters, washers and scrubbers. 173 14. 10 Saving resources Learning outcomes Reduce, reuse, Reduction of On completion should be able of this section, to: understand W aste reuse and terms reduction describe the in reduction waste and plastic, steel describe importance and to such steel involved glass, reduce and Reuse Repairing of of (waste created. minimisation) Examples glass, the use of second-hand is the prevention of waste are: broken of products. items instead of replacing them, e.g. mending a cup. Designing paper, aluminium as broken recycling how materials plastic, processes the reusing being reduce, recycle understand the waste you material recycle plastic products shopping Avoiding the Cleaning Designing use of articles to be reusable (using cotton shopping bags instead plastic cutlery. bags). disposable before products, e.g. disposable recycling. paper, products that use less material to achieve same purpose, aluminium. e.g.lighter same aluminium drinks cans or lighter steel frames with the strength. Reducing Improving rather excess the than paper or durability plastic of an packaging. item, e.g. making a sieve of aluminium plastic. Reuse Reuse means purpose and to use something sometimes Rellable drinks for bottles a more than different (glass or once, purpose. plastic) sometimes Examples which can for the same are: be rewashed and reused. Using a glass Retreading Reusing jar to rubber metal put owers in. tyres. shipping containers or wooden chests for removals. Recycling Recycling prevents of fresh from is raw sure that you difference between reduction: reduce, and can apply know the the Rs 3 different product reuse these to and glass, are materials of waste process paper that have of to and plastic. recycling means chemical or that there is reduces energy either use produce converted into paperboard requires be into materials, and fresh products. reduces the reduces pollution This consumption arising sorted It also from transport and time usually a new recycled paper). to and the supply paper) The a the same produce a slightly disadvantages recycling energy produces of or are centres, required product of for lower of the the quality. paper, recycling that some reprocessing Glass of W aste the it materials recycle Remember physical (e.g. used useful landll. can is recycling. Examples of metals and materials (e.g. of potentially materials, material recycling Make processing of incineration Recyclable Exam tips the waste glass can be sorted then melted and either used to make new glass material. objects up to or added 30% as energy glass saving ‘cullet’ and a to glass 20% being reduction freshly in made. There emissions CO can made be by 2 recycling glass carbonate. 174 compared with making glass from sand, lime and sodium Chapter Recycled glass to make as an as a as an can new be in component abrasive, Chemistry and the environment used: glass aggregate 14 bottles or concrete of e.g. glass or astroturf in for display making and counters new golf-bunker ceramics ‘sand’ glasspaper . Paper Recycled paper household in the cut world, down. water can waste. so paper from is is paper about 35% used scrap production recycling Recycling pollution Recycled come Paper to from important reduces to 35% the making quality or of from the by of about paper paper, trees number emissions with lower mills for reduce carbon compared make paper accounts felled trees 75% from and trees. cardboard and paperboard. Plastic Most of the plastics recycled are thermoplastics – those that melt when heated. Recycling making the plastic plastic same type recyclable. PET plastic a type polyester bins HDPE (high plastic furniture. and density Poly(styrene) picture again. The by Many recycled terephthalate)) of rubbish emissions monomers. about 70% plastics plastics are compared not formed with recycled are into often not are: (poly(ethene bottles, of carbon their Examples produce reduces from can bre containers used plastic recycled to are melted fabrics, new and recycled to containers, furniture. poly(ethene)) be for is recycled make clothes to make rulers hangers, and ower pots and frames. Steel Scrap and iron cast girders. and The steel steel and iron steel pipes iron or reduces from from can steel carbon haematite steel be plates, used is to beams, make melted and emissions by new columns, steel added about to a 60% old car products furnace. bodies, such as Recycling compared with iron making ore. Key points Waste reduction is the Did you know? prevention Some archaeologists down scrap bronze have or suggested other that metals, for some ancient example, from civilisations old axe being melted heads, for reuse. the for Aluminium Scrap aluminium aluminium window and cans frames, added to a from is aircraft used roong furnace to fuselages, make and then new car bodies, aluminium aluminium cans. degassed remove to cycles, products The cookware such aluminium hydrogen. It is is Recycling aluminium reduces carbon emissions by 95% consumption of as by 95% compared with making used use purpose is something sometimes for and sometimes purpose. the processing materials into fresh products. melted then Describe how to reduce the use and aluminium materials such as glass, paper, from plastic, bauxite to once, different Recycling of energy material and recast. means than same a waste created. Reuse more of steel and aluminium. ore. 175 14. 11 Solid waste Learning outcomes completion of this section, be able avoid too describe wastes the on impact the glass, solid plastic, reference and biodegradable materials before non- it Some and and waste the environment, possible (see we should Section generate 14.10). The the options and heat improper techniques for including or in shown in recycled the Figure but we 14.11.1. may be Much able to of get our solid energy from ground. steam waste can gaseous of to for be burnt products. its in This original run a special can volume. turbine disposing of incinerators reduce to the The produce some to energy of a waste solid solid released electricity. hazardous form volume This such residue waste can be method as to up used to to is biological and disposal dumps waste. One problem with this method is that organic compounds and such sanitary to waste are reused dumped one-thirtieth proper materials is be Incinerating medical of solid management cannot practical disposal damage of to lead, waste describe waste waste it paper, biodegradable nuclear of terrestrial environment. With iron, much amount to: for environment you smallest should the Introduction T o On and as dioxins, furans and polyaromatic hydrocarbons are formed. These landlls. are toxic waste and may (heating temperature) containing best it in CO stay in under sealed and the atmosphere pressure solid which H with vessels is for many limited can burnt be to years. oxygen used to produce at a make Pyrolysis of high carbon and a gas electricity. 2 prevention Solid waste and the environment reuse Solid waste may harm organisms as well as the environment. recycling Glass: energy and recovery Broken animals. It particles of glass does is not glass sharp and degrade are may very produced. cause quickly. These cuts and When may abrasions glass remain in breaks, the air in tiny for some disposal worst time option and lenses, Fig 14.11.1 Options for waste management Paper: soil Printing as wind, so get lungs. as Did you know? and of the a waste in the sea by may be as million kg of much plastic be gets a of glass leading meals and such to as substances paper is easily can also act as res. cadmium organochlorine toxic addition danger stuck dies. action in In Pieces heating heavy bleaches potentially plastic of nets in wildlife, and compounds may leach blown gullet, leach readily and down and into few are they and years. sh from sea the animal from out they plastics a when the microorganisms), after especially suffocate organisms also Biodegradable seas to or the Many may decompose creatures cause contain wet. lungs. into away by in the the litter . in break the cannot to the not in the are many (break environment materials plastics, which the any Since biodegradable biological particles into ingest crocodiles Biodegradable microscopic Animals gets plastics. remain other life. plastic may such however , be harmful rivers. is in Many metals are alloys. When they are thrown away, they may as react 10 000 do of and decompose time. simply Metals: plastic. There gets additive not the long may These therefore T oxic rays residual can plastic do wood may to 80% These If plastics for paper tangled affected. down inks as spreading Plastics: food well irritation light quantities. when may cause focusing arsenic small can with water and air and corrode to form soluble compounds which the diffuse into the soil or water . Iron rusts and may form unsightly pools of oceans. red waste metals from This and 176 which such as lead aluminium waste reduce with growth cadmium smelting reacts hydrogen. or plant may water as (from still well car being batteries) contain forming as high ammonia unsightly. are poisonous. amounts and Some of W aste aluminium. ammable acetylene Chapter Nuclear waste: This may contain radioactive isotopes with very long 14 Chemistry and the environment half 129 lives, cause as I e.g. has radiation well as a half burns, causing Disposing of life of skin animals solid 17 million damage to and become years. Radioactive damage to the waste immune may system sterile. waste Landll W aste Some can poorly be buried landlls, a landll site however , consist of managed Wind can in site blow may away create paper a such as mounds number and an of of plastic unused rubbish quarry (waste environmental bags into the or mine. dumps). A problems: surrounding areas. waste T oxic or harmful liquids may drain through the soil or rocks gas to cover contaminate Gases such released as groundwater as a methane, result of and soil. carbon organic dioxide waste and hydrogen breaking down in sulphide the are absence of solid oxygen. Some of these gases are foul-smelling and may kill wastes surface rock/ vegetation. Others (methane and ) CO are greenhouse lining gases. 2 soil Organic W aste material may attract rats and other vermin. Figure 14.11.2 of In a the dumps may rubbish can well-managed The waste The site is has take up large area and be unstable because landll (sanitary lining of to landll) prevent clay, it plastic site: moving or or blowing rubberised Did you know? away. material which Nuclear minimises drainage of liquids into the soil or rocks The gases are extracted (the gases are either burnt waste can off immediately used for other 137 burnt The site is Because smaller in it a controlled covered is so way that compacted, it to generate does the not waste is reprocessed purposes. For or example, are be below. and A modern landll site some move. compacted a a 90 Cs and Sr can be electricity). attract more rats stable and and other separated from other substances and used food bacteria. radioactive vermin. conned to a to kill to irradiate area. Composting Organic plant material and animal waste can be composted and returned Key points to the soil materials as in a fertiliser . the Fungi, presence of bacteria and worms help break down the oxygen. Iron, glass, metals Nuclear waste plastic, may all environment if paper harm not and the disposed of correctly. This requires completely the special isolated methods used treatment and cannot so that escape the into radioactive ground substance water or air . is Amongst are: Incineration energy solid Vitrication: allowed glass is to stored Adsorption: waste which The cool. to is waste The in steel Iron( iii) adsorb mixed is glass heated does cylinders hydroxide and with in or concentrate cement then not safe an the then mixed dissolve with or places solution. into with glass water . A resin sludge drums and is is going of waste reduce to can the provide amount of landll. and The underground. ion-exchange put molten react and A good landll drainage added to loss the formed of of site liquid will to greenhouse prevent the soil gases to and the air. stored Nuclear waste can be disposed underground. of Above ground disposal: (Low level waste). The waste is put into a by vitrication followed cylinder . An inert gas is added. The steel cylinder is then placed or adsorption steel in by encasement in a cement. concrete cylinder and stored. 177 Exam-style Answers to all exam-style questions can questions be found on the – Module accompanying CD iv Multiple-choice questions To separate hydroxide 1 Which the of the following reaction electrolysis which of half occurs equations at the Al(l) Al (aq) → Al (aq) C Al(l) + brine used from the sodium cathode during A i only produced. B i and C i, ii D i, ii, the ii only alumina? + 3e and iii only 3e 3+ B the represents 3+ A 3 iii and iv → Al(l) 3+ (l) → Al + 3e 6 During the Contact Process, sulphur trioxide is 3+ D 2 Al (l) Which of emitted + 3e → Al(l) the following into the are pollutants atmosphere during that the produced by shown the following by rening carbon hydrogen iii oxides 2SO (g) + O (g) Y equation: 2SO 2 (g) ∆H = –196 kJ mol 3 of the following of in the yield iv chlorofluorocarbons A i and iii only Low B i and iv only C i, ii D i, iii B and iii and temperature, High C Low only iv is D manufactured combining this nitrogen reaction is during and shown the Haber + 3H 2 (g) Y hydrogen. The equation 7 below: 2NH 2 High of a maximum trioxide? pressure and high (g) ∆H The is = of of concentration crucial low pressure and low and low and high oxygen. high pressure oxygen. low pressure oxygen. Which to of the of dissolved existence the following of oxygen aquatic causes a in water life forms. decrease in the –92 kJ mol represents the temperature and of dissolved oxygen in water bodies? ideal A of of 3 the following conditions high temperature, concentration Which produce Process –1 (g) would sulphur oxygen. temperature, concentration only of temperature, concentration concentration Ammonia of nitrogen concentration N pressure for Low temperatures and an increase in aerobic the respiration. production of ammonia using this process? B A Low temperature and high High temperatures and an increase in aerobic pressure. respiration. B High C Low temperature and low pressure. C temperature and low Low temperatures and a decrease in aerobic pressure. respiration. D High temperature and high pressure. D 4 Which of the following production of are necessary for ethanol from High the temperatures and a decrease in aerobic respiration. the fermentation of 8 A yellow precipitate was produced when a sample sugars? of A Carbon dioxide, yeast and river water B Aerobic conditions, C Anaerobic yeast and tested by adding iodide yeast of the following pollutants is and in this sample of water? water. A NO B PO ions 3 Carbon dioxide, anaerobic conditions and yeast. 3– ions 4 5 During the the production diaphragm What is cell, a of chlorine from porous brine diaphragm is using To C CN D Pb used. ions 2+ ions its function? 9 i separate the liberated hydrogen and Which of the following gases. To separate sodium iii To 178 liberated hydroxide separate sodium the the gas from hydrogen from produced. A RCl B O C Cl• D ClO• the produced. liberated hydroxide chlorine species reacts with chlorine stratospheric ii ions most water. present conditions, was to water. it. Which D as sulphide A for oxygen monoxide ii by with –1 of increase 3 dioxide oil? Which i sulphur are 2 crude reacting 2 the ozone causing its depletion? likely Module 10 Fires are waste a in major produced from A hazard when landlls. Which landlls of is disposing of the following responsible for solid d gases Why are being these res? e O hydrogen allowed to and 3 Exam-style nitrogen questions puried before react? [1] Suggest ONE reason why the ammonia is removed from the system as soon as it is formed? [2] 2 B CO f State ONE use of ammonia in EACH of the 2 following C H D CH industries: 2 i Agriculture [1] ii Chemical [1] 4 Structured questions 13 11 Aluminium is extracted by the electrolysis of The chlor-alkali industry refers to the industrial molten production of the alkali sodium hydroxide and chlorine aluminium oxide. This oxide is found in bauxite along by the electrolysis of a concentrated solution of with oxides of iron and silicon which are the main sodium chloride (brine). One method of production impurities. involves the use of the diaphragm cell as shown below. a Write the formulae for the chlorine i iron ii silicon found and as hydrogen + oxides impurities in aluminium oxide. [2] A b i State the silicon ii Use in acid–base a your how oxide an of the oxide of above. answer this include i nature is ionic [1] in b i above to explain removed from equation in the your bauxite, E explanation. C [4] c Explain why aluminium and describe electrolytic d i dissolving oxide Write how the Explain cryolite in economically it achieves this the benet in half State ONE property for Complete ii Describe equation for the anode. why the anode the in reaction iii [2] must be property periodically aluminium packaging food that and ONE allows it to iv Ammonia by is manufactured [2] combining nitrogen and during the Haber + 3H 2 (g) Y 2NH 2 How is the are produced cell. [5] the reaction anode. [2] Carbon is not used to make the anode (B) and Why is the diaphragm environmental used in this particular [3] cell, hazard? [1] c State a Using ONE use of chlorine. [1] hydrogen. (g) ∆H = 14 balanced equations explain how the –92 kJ mol 3 concentration a chlorine, Process –1 (g) N which hydroxide equation for the [3] from and explain why carbon is not used. b an 12 E materials that the anode and cathode are made used products. half at by sodium diaphragm the and the cathode (D) in this particular cell. State the physical be Write process and occurring [2] chemical the labels A, C the hydrogen [2] at of i the replaced. e a molten benecial process. occurring ii is nitrogen for the Haber of ozone is maintained in the Process stratosphere. obtained? b b i State [5] [1] the source of the hydrogen used in i Using the data below, describe the trend in the the Process. concentration of stratospheric ozone over [1] time. ii Write TWO hydrogen is equations to show obtained from the how [1] the source Year mentioned c i State used the to in b i above. temperature manufacture and pressure ammonia that using [O are ] Why iii the temperature Explain stated in your c i above is 2000 260 240 160 110 108 why the trend described in b i above Using considered to be a the concern. is relevant [2] equations, explain why the answer trend in 1990 [2] cause for Explain: 1980 the Process. ii 1970 3 ii Haber 1960 [4] described in b i is occurring. [4] compromise iv Outline ONE prevent this step that can be taken to temperature. Why this compromise temperature is used. trend from continuing. [1] [2] 179 Data Selected sheets bond energies Selected electrode potentials Ø Diatomic molecules Polyatomic molecules –1 Electrode –1 Bond 436 C—C 350 Mg N≡N 994 C=C 610 Al O=O 496 C—H 410 V F—F 158 C—Cl 340 Zn Cl—Cl 244 C—Br 280 Fe Br—Br 193 C—I 240 V I—I 151 C—N 305 Ni H—F 562 C—O 360 Sn H—Cl 431 C=O 740 Pb H—Br 366 N—H 390 2H Bond H—H energy/kJ mol energy/kJ mol E /V + Bond Bond reaction + K e Y K –2.92 2+ + 2e Y Mg –2.38 3+ + 3e Y Al –1.66 2+ + 2e Y V –1.2 2+ + 2e Y Zn –0.76 2+ + 2e Y 3+ Fe –0.44 2+ + e Y V –0.26 2+ + 2e Y Ni –0.25 + 2e Y Sn –0. 14 + 2e Y Pb –0. 13 2+ 2+ + + 2e Y H 0.00 2 2– H—I 299 N—N 160 O S 4 2– + 2e Y 2S 6 O 2 +0.09 3 2+ O—H 460 Cu + O—O 150 VO 2e Y Cu 2+ +0.34 + + 2H 3+ + e Y V + H O +0.34 2 + I 2e Y 2I +0.54 2 3+ 2+ + Fe e Y Fe +0.77 + + Ag e Y Ag + +0.80 + + VO 2H 2+ + e Y VO + H 2 + Br O +1.00 2 2e Y 2Br +1.07 2 2– O Cr 2 + Cl + + 14H 3+ + 6e Y 2Cr + 7H 7 O +1.33 2 2e Y 2Cl +1.36 2 – 4 180 + + MnO 8H 2+ + 5e Y Mn + 4H O 2 +1.52 sheets Data 0.571 301 rL muicnerwal ]262[ 0.371 201 oN muilebon ]952[ 9.861 101 dM muivelednem ]852[ 3.761 001 mF muimref ]752[ 9.461 99 sE muinietsnie ]252[ 5.261 89 fC muinrofilac ]152[ 9.851 79 kB muilekreb ]742[ 3.751 69 mC muiruc ]742[ 0.251 59 mA muicnema ]342[ 4.051 49 uP muinotulp ]442[ ]541[ 39 pN muinutpen ]732[ 2.441 29 U muinaru 0.832 9.041 19 aP muinitcatorp ]132[ eC munec 1.041 09 hT munoht 0.232 901 tM muirentiem ]86 2 [ muimso 2.091 801 sH muissah ]962[ muinehr 2.681 701 hB muirhob ]462[ netsgnut 8.381 601 gS muigrobaes ]662[ mulatnat 9.081 501 bD muinbud ]262[ fH muinfah 5.871 401 fR muidrofrehtur ]162[ 75 aL munahtnal 9.831 98 cA muinitca ]722[ 65 aB muirab 3.731 88 aR muidar ]622[ 74.58 55 sC muiseac 9.231 78 rF muicnarf ]322[ 85 rP muimydoesarp muidiri 2.291 aT 27 95 dN muimydoen 1.591 W 37 06 mP muihtemorp munitalp eR 47 16 mS muiramas dlog 0.791 sO 57 26 uE muiporue yrucrem 6.002 rI 67 36 dG muinilodag muillaht 4.402 tP 77 46 bT muibret dael 2.702 uA 87 56 yD muisorpsyd htumsib 0.902 gH 97 66 oH muimloh ]902[ lT 08 76 rE muinolop bP 18 86 muibre ]012[ iB 28 96 mT muiluht enitatsa oP 38 07 bY muibretty nodar ]222[ tA 48 17 uL muitetul nR 58 73 bR 68 rS 01.93 muidibur 83 26.78 Y 80.04 muitnorts 93 muirtty rZ 69.44 19.88 04 22.19 bN 78.74 muinocriz 14 muiboin oM 49.05 19.29 24 49.59 cT 00.25 munedbylom 34 ]89[ uR 49.45 muitenhcet 44 1.101 hR 58.55 muinehtur 54 9.201 dP 39.85 K muissatop muidohr 64 aC muiclac 4.601 gA 96.85 cS muidnacs muidallap 74 iT muinatit revlis dC 55.36 V muidanav 9.701 84 rC muimorhc 4.211 nI 93.56 nM esenagnam muimdac 94 nori muidni nS 27.96 eF 8.411 05 oC tlaboc nit bS 16.27 iN lekcin 7.811 15 uC reppoc 8.121 eT 29.47 cniz ynomitna 25 nZ 6.721 I 69.87 aG muillag muirullet 35 eG muinamreg enidoi eX 09.97 sA cinesra 9.621 45 eS muineles nonex 0 8 . 38 rB enimorb 3.131 rK notpyrk 13.42 02 210.9 muihtil 149.6 3 iL eB 4 muillyreb 11 91 99.22 12 92 22 03 cimota 21 32 13 42 23 52 33 62 43 89.62 72 53 90.82 82 63 79.03 evitaler 70.23 aN muidos yeK )notorp( cimota eman cimota rebmun lobmys ssam 54.53 gM muisengam 800.1 59.93 lA muinimula 31 iS nocilis 41 P surohpsohp norob 18.01 51 S nobrac 10.21 61 ruhplus 10.41 71 lC enirolhc negortin 81 rA nogra negyxo B 00.61 C eniroufl N 5 00.91 O 6 noen F 7 81.02 eN 8 9 negordyh 01 muileh 1 H 300.4 2 eH 181 Glossary -1 Band region The Chromatography 1300–3000 cm Method of separatng A waenumber Absorbance absorbed Accurate ery Acid by a percentage close to (%) ther acdc oxdes SO Addition n reaction and NO A sngle and product other Adsorption bonds Air lter a dust gases power and s Base ths peak of regon tallest path used to plants Mode one or more Aldehyde A compound —OH Aliphatic chans formula C Brine that wth A a bonds s s concentraton one up of and smplest and of the down n relate a to ols engnes made and has of the but and (gen atom not the compounds reaction and When a small showng the n Alternative fuels more cleanly reduce Amide carbon An CONH Fuels than whch burn hydrocarbons an To aqueous atoms measurement emssons. organc soluton or wth the readngs those of of a effect molecules lengths Contact by standards. functonal hang a group. NH An organc functonal compound hang an group. acid hang An an organc NH compound functonal chan, R, whch group can be Carbocation postely group, of a n 2 COOH functonal and a acdc, sde C, for alkalne C or wth and and Occurs multple effect cyclc rngs delocalsed that wth hae one or delocalsed n n some bond the e.g. bond strengths between boiling bonds, ordnary double mixture sngle bonds. See mxture. Process ths Sulphurc process, whch of a relates of SO substance e.g. UV to SO a carbon atom s O made the usng a V 3 O 2 temperature a The salt wth phenol to form Cracking The nto 450 reacton of an alkalne an thermal of 5 C. a soluton azo dye. decomposton shorter-chan alkanes of and alkenes. molecule where 2:1. The smple a Coupling reaction alkanes charged. A and dazonum organc s to o catalyst of n acd refers the consstng H and general O are formula carbohydrates Cryolite Compound alumna durng and the lower used ts to dssole meltng electrolyss of pont alumna. s O) 2 y cycle through water Compounds rng structure that based hae on benzene. and A mxture that of wdely from Raoult’s law whch carbon acid A n cracking of SO Catenation The lng keeps the ar the and Al contanng usng a A remoed Delocalised can more reacton Electrons oer whch two Denitrication whose three moement than n water (elmnated). extend allowng O 2 Dehydration s group. Crackng ablty thngs, constant. compound the COOH functonal catalyst and carbon atmosphere, rocks of Carboxylic Catalytic mixture The ow the 2 deates whch ntermedate where rato amount compounds Azeotropic changes makes ordnary conerson cure property, An and most (H Carbon Compounds electrons. Aryl Ttratons of D neutral. more H the x Aromatic A concentratons partcular Carbohydrate 2 Amino a chemstry 2 Amine to curve absorbance. compound attached conductty. ntermedate correlate nstrument known and an bonds. Conductimetric titrations azeotropc Calibration 2n of each C standard H two off ). 2 general formula C or molecule A formula compound Constant the geometrc mxture. react benzene. The or fats. chlorde. general one a elmnated Conjugative desel concentrated sodum solublty 6 chans. contans One n electrcal aromatc See Condensed formula carbon a atoms H A fuel for Calibrate double soluton bonds 2n+2 that Component molecules of contan the isomerism elements mass n somersm. nolng The Biodiesel of branched Hydrocarbon more a H n or or Hydrocarbon Alkene contanng molecule. a amount of braton from egetable group. Compounds carbon Alkane has groups. compound CHO functonal that n as dfferences charge. organc where hydrocarbon, C Alphatc The the 6 Alcohol the such other. Benzene statons. by to bond brates the and n peak cis-trans the groups length. molecule Apparatus and/or by Condensation law absorbed Bending partculates from ndcate and C=O The compounds the spectrum. Specc partcular proportonal the of formng of spectrum. lght molecules surface. chemcal n presence Beer–Lambert’s s formed. process sold n whch product reactant (industrial) remoe waste The wth , 2 two electromagnetc C—H, O—H produces ranwater. formed from no are true alues. Burnng fossl fuels deposted lght peaks measurements 2 are of soluton. Accurate rain the The regon or of orbtals more atoms, electrons oer atoms. The reducton of ntrates 3 of carbon atoms to N gas by bactera. 2 has a maxmum pont. Also or called mnmum a constant bolng bolng mxture. to form Chain the chans by isomerism jonng. The arrangement of Desalination somers the dffer carbon n atoms water, The remoal usually from Diazonium salt A of salts from seawater. salt of general + Azo dye The reacton wth an dye formed between alkalne a by a couplng dazonum soluton of a salt phenol. n ther Chiral carbon centre wth four t, A skeleton. carbon dfferent creatng the somers. Some (or formula other groups possblty atom) attached of molecules, to optcal e.g. glucose, RN Diazotisation dazonum aromatc ≡NX The formaton salt by amne the wth Displayed formula of a reacton ntrous A formula of an acd. showng B hae Back titration reagent soluton reagent 182 s to s A known added be n amount excess to estmated. The then ttrated. of the excess more than one Chlorofluorocarbons contanng C, Cl responsble for layer. chral centre. (CFCs) and F that depletng Molecules are the ozone all the atoms Distribution bonds. coef cient equlbrum dstrbuton mmscble and constant of solent solutes. The for the between two Glossary Initiation E The rst photochemcal Electrodialysis where ons soluton Method are to step n a G of desalnaton transported another, usng from one Gas–liquid chromatography radcals Chromatography n whch the Iodoform statonary phase s a lqud and the an reacton n whch free are formed. reaction contanng Compounds CHOH the CH group are 3 on-exchange moble phase s a gas. membrane. oxdsed by and I NaOH to form a 2 Electromagnetic whch hae radiation electrcal Geometrical isomerism Waes and groups ether sde of a double bond are magnetc arranged ether on the same sde (cis) or components. Electrophile partally that a A postely postely attacks an charged charged on the opposte sdes (trans). or reagent electron-rch area of Global warming yellow Isomers Molecules formula Formula arranged smplest rato of atoms of n the that hae but the the same atoms are dfferently. The rse n temperature K Determnng the A compound contanng a CO amount of a substance present n a each functonal element trodomethane. of the atmosphere due to the Gravimetric analysis showng of molecular formula Ketone the precptate greenhouse effect. molecule. Empirical Two substtuent group between two carbon compound by methods nolng compound. atoms. Ester Compound contanng weghng. the Greenhouse effect O The process by whch thermal radaton s absorbed by the functonal C O C M group. C atmosphere and re-radated n all M + 1 peak Small peak n a mass drectons. spectrometer Esterication The reacton of an Greenhouse gas wth a carboxylc acd to the an molecular Eutrophication The polluton of rers leadng to the death ratio The process for makng and H 2 Mass usng an ron 2 catalyst. F Alkane n whch one or more H atoms are substtuted by A soluton dstngush aldehydes The breakng of a bond so that the two shared electrons n the bond are splt unequally between Fermentation (alcoholic ) Makng the two atoms. One of the atoms keeps from sugars by usng yeast both the electrons and so becomes anaerobc condtons (no becomes postely charged. See ar region The Homologous series A group of organc regon 600–1300 cm of spectrum. Peaks n unt. ncreases by a CH regon tell us about the whole The breakng of a bond molecule. so that the two shared electrons n the Fraction A group of compounds that bond are splt equally between the two separate from a mxture wthn a atoms, one electron gong to each atom. narrow range of bolng ponts. Hybridisation Fractional distillation A process The process of mxng separate mxtures of lquds used dfferent bolng Compounds contanng The breakdown of a n a Hydrolysis compound n a partcular way as of cars. the data n numbers dentcal experments. Mesomerism oer Makng from liquids one up seeral a composte dfferent Lquds able to mx another. phase the Molecular the The phase statonary formula actual element that phase moes n present ion formula of n peak arsng electron Monomer The breakdown of a A number a atoms showng of molecule each of a compound. one ponts. carbon and hydrogen only. Fragmentation such transportaton nddual the masses compounds. ehcles for aerage spectrum of Hydrocarbons slghtly trans from Molecular used atomc orbtals. to on chromatography. 2 structure Homolytic ssion the taken Mobile the group n whch each successe member electromagnetc of an atomc organc Usng than The wth compounds wth the same functonal waenumber ths of m/z Instrument relate dentfy and Miscible lter. –1 Fingerprint charge structures. present). (industrial) to transit structure negately charged. The other atom Filter Mass Mean from ketones. oxygen ts spectrometer rather used Heterolytic ssion under by calculate buses halogen atoms. solution to and Halogenoalkane ethanol mass mass anmals. ammona from N to In the of Haber Process and Fehling ’s unt peak. H dded fertlsers plants on ester. spectrometry, by m/z emts nfrared radaton. Mass/charge make one A gas that absorbs and beyond alcohol trace from Small together to The from a peak the a mass of molecule. molecules form n remoal that jon polymers. compound wth water. The rate of mass spectrometer. reacton s often ncreased by reactng Free radical Atoms or groups of atoms N the compound wth an acd or an alkal. wth an unpared Frequency The electron. number of Nitration waes In organc chemstry, the I passng Fuel cell whch a gen An O pont per electrochemcal and H 2 react to substtuton second. cell atoms Ideal produce s group that ge An a group same atom Raoult’s group of ts propertes. isomerism formula but or compound chemcal molecular the H atom by an A soluton whch NO group. obeys Nitrogen cycle law. The ow of ntrogen 2 partcular The solution Immiscible Functional a 2 n water. Functional of the of the functonal dssole Inductive atoms or somers groups liquids n each effect to exert around a an do not effect of groups on the of electrons atom. Radaton through the atmosphere, lng thngs, water and rocks that keeps the amount ablty electron-attractng partcular (IR) whch other. The wthdrawng Infrared Lquds of waelength of N n the ar constant. 2 Nitrogen xation The conerson of N 2 the ar to ammona by bactera. Nucleophile A reagent that donates a par of electrons to an electron- 6 are dfferent. about 700–10 nm. decent atom n a molecule. 183 n Glossary Nucleophilic substitution A reacton n Primary pollutant Pollutant released S drectly from whch the nucleophle bonds wth or Primary ‘attacks’ the poste or partally propertes molecule (usually a carbon atom) deducng attached to t. acds process. standard poste charge of an atom n a resultng n the replacement of a group a the and A make chemcal t Saponication whose soaps sutable for concentraton of other A cyclc seres of reactons n whch free radcals react wth molecules or atoms to form dfferent radcals and O Proteins Optical isomerism This occurs different groups are polymers made from of only Compounds sngle hydrogen Scrubber usng bonds can Part a be of so that that a central carbon and a of more added. chemcal partcles from spray contan no plant waste naturally occurrng amno Secondary that gases water. acds. (referrng to alcohols and attached halogenoalkanes) The OH to makng of fats when 20 four Natural process hydrolyss ols. remoes dfferent molecules or atoms. The the Saturated alkals. Propagation by atom. The two attached to a carbon attached to two or Cl atom s whch s Q isomers formed each mirror images of Quanta other. Ozone depletion amount caused Ozone are of The ozone n decrease the n ozone the an layer Energes whch can be of xed alues absorbed or only, emtted Secondary by atom. An stratosphere wthn has a remoes the atoms. Pollutant formed pollutants undergo agent Agent partcular whch ons from soluton R relately or from hgh Radical of carbon reactons. Sequestering area that concentraton pollutant prmary further by CFCs. layer when other See free Solvent law The partal apour extraction a component n a mxture = because × apour of separaton dfferences n of a ts ts solublty mole fracton The pressure solute of ar. radcal. ozone. Raoult’s the pressure n two solents. of Solvent front The leadng edge of the P pure component. solent that progresses along the Partial vapour pressure The pressure Reaction mechanisms These show the surface where the separaton of the exerted by each component n the steps n bond breakng and bond mxture (chromatography) s occurrng. apour alone. makng when reactants are conerted Standard deviation Partition coefcient See dstrbuton to ntermedates and then to spread coefcent. Recycling The processng of out Ddng the components materals nto new a mxture between two dfferent Redox titration data measure s from of the how mean. phase In chromatography, a products. sold of the used Stationary Partitioning A products. These are used or lqud that remans xed n to poston. phases. calculate the concentraton of Steam distillation Phenol Compound contanng one or oxdsng or reducng olatle more —OH to aromatc groups attached drectly Reforestation compound from rng. formed when smog A smoky fog and hydrocarbons, ozone usng react n ntrogen the presence absorbs more CO Reforming the same lght. lght Polyamide The breakng (usually UV Polymers but the wth of a Relative abundance atoms hae n lght). many Mode Polymers amde brate one the wth many unit ester atoms n a monomer, molecule bult The smallest group up from molecules. n the polymer whch structure Resonance process dered from of when the joned of formng hybrid structure of a monomers. synthess of The Polymer of smple sugar Retention time In unts. the isomerism The poston of tme n and ts a a smpled form. isomers same Compounds molecular formula wth but made up of structural formulae. a reaction A reacton n dfferent forms. gas between compound showng n ges one atom or group of atoms s chromatography, replaced Positional atoms composte molecule seeral A formula of polymer. whch Polysaccharide bond a Substitution polymers from a a plane. arrangement dfferent The of n of the Polymerisation atoms commonest speces n a mass spectrum. Repeating —COO—. Large small dfferent of braton where Structural many a of one speces compared wth the —CONH—. lnkages, hae other space. molecule molecule Polymer each The relate amount the Polyester to from the ar. Structural formula lnkages, compounds bonded The conerson of alkanes to Stretching by Two cycloalkanes or cycloalkanes to arenes. Photodissociation bond more steam. atoms arrangement of UV a Replenshes the wood resource and 2 oxdes of mmscble replace depleted forests or woodland. Stereoisomerism Photochemical an Plantng of young trees to mxture an Dstllaton agents. njecton of by another. a detecton. T the functonal group s dfferent but Retention value, R In chromatography f the molecular formula s Potentiometric titration nolng measurement electrode Precise measurements Primary of changes n Precse close to each to a attached to only the dstance Reuse n alue. (referrng dstance from base are ery attached 184 the Ttraton moed base of lne, the by a compound dded by solent front from the use once for somethng the same or a more than dfferent to alcohols carbon one and or Cl atom, other Reverse osmosis s whch carbon desalnaton s through from a a n Method whch regon of concentraton. hgh to reacton combne n whch to form two a molecule. (referrng to alcohols halogenoalkanes) The attached to a carbon attached to three OH or atom other and Cl s whch s carbon atoms. of water sem-permeable A radcals Tertiary lne. To Termination free the purpose. halogenoalkanes) The OH atom. same. potentals. (precision) other the s forced membrane low salt Tetravalency The quantum shell. These form four other outer has four alence n wth ts atom electrons atoms. prncpal bonds Glossary Thermometric titrations Ttratons U nolng measurement of changes Ultraviolet temperature. Thin-layer chromatography chromatography phase s phase a Tollens’ lqud thn n used of the the the form of moble statonary sold. Ammonacal for dstngush whch and layer reagent ntrate to a A sler aldehydes (UV) waelength Unsaturated Radaton between Compounds contanng test wth dfferent an The alcohol ester and a form of an atmosphere them saturated. passng Turbidity matter The n a through a cloudness lqud. (%) and Wavenumber Vacuum distillation reduced speed Dstllaton of In s of n whch the the Earth and constantly condensng. IR spectroscopy, of braton dded the by the lght. under pressure. Vapour pressure of soluton. of eaporatng surface of created. process n the preenton Z a dfferent percentage The the The beng carbon–carbon bonds). Hydrogen can The pressure exerted by apour molecules n a closed system. The cycle frequency alcohol. Transmission Water materal on from reacton to reduction waste water V Transesterication lght Waste 4–400 nm. double or trple bonds (usually ketones. ester of about be added to these compounds to make sler mrror W n suspended Visible (vis) about Radaton waelength 400–700 nm. Visualising agent to speces charge An wth n electrcally a two poste dfferent neutral and negate parts of the on. Chemcal chromatography spots of Zwitterion make used n colourless coloured. 185 Index Key n terms the are n bold and are also lsted barum base glossary. chlorde peaks bases 46, bauxte absorbance 50–7 , see also A 74, accuracy acd 70, haldes 164, 98 conductty 41, benzene 3, 46, 137 , 37 , manganate (vii) conjugative constant effect boiling 50–1 mixtures 5, 15, 42–5 Contact Process 150, 118 151 38, 83, 39 corroson 152 coupling resstance reactions 132 47 23 97 , 144 ponts 115, acds 27 , 34–5, 41, 120, 125 cracking 18, crude 134–5 ol 136 2–3, 11, 40 cryolite 131 50–1 branched-chan 74, 117–18, 125 bonds alkanes 8–9, 14–15 cyandes 32–3, 97 , 158, 159 76–85 brine haldes 92–3 168–9 50–7 , carboxylc ttratons law 54 bolng acyl 84 132 141 potassum 22, 60–1 72–3 blood acds 35, 5 conductimetric titrations 133 bending bleach rain condensed formulae 165 biodiesel acid 125 62–3 reactions 92–3 150–1, acdcaton acded 76–85, titrations ore polymers condensation Beer–Lambert’s absorpton condensaton 87 104 46, 146–7 54 bromne 21, 22, 42–6, 148 D addton polymers addition 62, reactions adsorpton 159, adsorption 63 20, bromoalkane 32–3, 58–9 burettes hydrolyss 29 data 77 177 analyss/measurement dehydration chromatography 108 delocalised reactions electrons 70–5 27 3 C aeraton of air lters ar water ethanol alkals calcum 101, 16, 141, 26–7 , 52, aldehydes alkalne 167–8, 35, 118–19, 30, 31, hydrolyss 39, 170–3 41, 124 alkanes carbonates 37 alkenes 8–9, 14, 2–3, 15, 20–3, alternative fuels 128–33, alumnum oxde amides 54, amines 54–5 55, acids ammona tablets CFCs asbestos salts 170 doxn 30–3, 34–5, 40 41, 151, 172 DO 47 152, 168–9 149 oxygen dryng 146 of 156–7 124–5, coefcients bonds ductlty 5 (DO) 116–21, (dssoled double 2 131, 150, dssoled 136 147 47 displayed formulae 50–1 169 173 146, emssons distribution 139, ran 159 39 dstllaton cracking oxygen) 156–7 40 samples 86–7 132 160–1, 165 E chiral 156–8 isomerism centres chlor-alkal 44 compounds 3, chlordes 42–9 chlorne 15 10 electrcal 13 ndustry 148, conductty electrodialysis 149 electrolyss 88–9 hydrolyss 131, 133, acds electromagnetc 29 electrons 51 132 157 electromagnetic 148 chloroalkane 149 146–7 radiation spectra 90 19 82 chlorofluorocarbons atmospherc carbon atmospherc ntrogen uptake oxdes ozone mass electrophiles 20, 42, empirical formulae 108–13 43 4, isomerism 12, 22, enantomers 23 6 12–13 products energy 83 91, 128 103 clmate Aogadro’s law azeotropic mixtures change engnes 165 167 7 coagulaton enronment 159 156–79 118 coefcients of distribution azo dyes 165 160–1 cleanng atomc 160–1, 167 cis-trans atmospherc (CFCs) 162–3 chromatography alumnum 122–3 128–9, 133 47 colormetry column ammona 74–5 chromatography 109, 110, 112 141 chlor-alkal ndustry 149 B combuston back titrations bactera 100 18, 137 , communcatons complexng 173 regions 186 78–9 167 bag lters band 143, 108 177 162, networks reagents components compostng 150, 94 170–1, 128 176 ethanol 144–5 petroleum errors n 137 measurement esterication esters 36–7 , 35, 41, 72 39 60, 157 122–3 67 chloroethanoc asprn diazonium desel (chlorouorocarbons) chain 82–3 compounds cathodes cellulose 166 enronments 42–3, 140–1 cells doxdes 162–5, 27 , daphragm diazotisation 109 136, catenation 64–5 138–9, 2–17 167 gases catalytic 56–7 , 78 162–3 acids engnes catalysts 146 aromatic car 41, compounds carboxylic acd 157 , desulphursaton hydrocarbons cycle of desalination 66–7 35, 166 132 deposton 20 doxde carbonyl carrer oxdaton arenes 62 131 anodes aquatc 58–9, 61 54–5, 131, carbon carbon 175 ammonum antacd 62 172 alumnum amino 18–19, halogenoalkanes densty 75 75 compounds see also bases 4, curves carbohydrates 40–1 78 instruments calibration carbon see also carbonate calibrated carbocation 142–5 33, 46 see also aryl denitrication 173 polluton alcohols 159 62–3 90 Index ethane 62 hydrated ethanoate ethanoc ethanol ethene ons acd 52, 2, ethoxde 52, 53 53 3, 58, 142–5 59 52 eutrophication 88 141 methylbenzene miscible 18–25, mobile 170–1 22–3 hydrogen bromde hydrogen chlorde hydrogen cyande 35, haldes peroxde content molecular 41 molecular 45 hydrogen 114 chromatography moles ion 108 87 6–7 104 103 88 monomers 20–1 4, peaks mass phases analyss molecular formulae 21 32–3 hydrogen 44 liquids mosture hydrogen hydrogencarbonates F fats 87 , 145 hydrocarbons 118–19, ons salts hydraton 58, 62–3 83 38 hydrolysis fatty acds 22, 23, hydroxde Fehling’s solution fermentation 29, 36–7 N 38 31, 142, groups 46, 52 ntrates 41 158, nitration 145 159 43, 44, 45 I fertlsers lters 173 ltraton ideal 86, ngerprint xaton ash of 159, ntrogen dstllaton ue-gas uorne 173 regions occulaton food ntrobenzene 140–1 nitrogen 114 liquids 100 ncomplete combuston 167 ndcators 157 inductive 159 desulphursaton 173 80, 124, infrared (IR) 114, 18, 137 , 170 152 nuclear 51 128–9, 130–7 , spectroscopy odne fractional distillation 116, 117 , 124, 157 reactions 98–101, 134–7 96, hydrolyss ndustry radicals 19, 124 IR 160–1, 169 reactions 157 , 38, 137 27 isomerism desalnaton 157 spectroscopy 98–101 157 97 isomers 90–1 IUPAC (Internatonal Unon of Pure 131, cells 172 Appled Chemstry) 39, 143, 162, group 168–9 168 156–7 160–1, 165 170–1 ozone depletion functional 166, 167 , 8 ozone fuels 159, 165, and oxygen fuel 26–7 , 10–15 oxdes frequencies 12–13 133 oxdaton freeze 42 159 (nfrared) ron 28–9, 61 29 osmoss free 32–3 19 ore fragrance 29, substitution O odoalkane ons 167–9 115 177 28, 149 iodoform 104 waste nucleophilic optical fragmentation 167 165, mxtures nucleophiles 138–55 ols fractions 166–7 oxdes nylon-6,6 initiation 4–7 ntrogen non-deal 100–1 preseraton cycle 45 nitrogen xation 120 84–5 effect ndustry 148 formulae solutions immiscible 44, isomerism 161 10–11 K ozone functional see also groups 4, hydroxide 9–11, 17 , 26–41, layer 149, 161 52 ketones groups 30, 31, 33, 40–1 P L G gas–liquid 111, chromatography 109, 174–5, global landlls lead 113 geometrical glass (GLC) isomerism 12, 22, 23 137 , lght 159, see lquds 164–5 175, paper chromatography 176 methods 114–15 partial vapour pressure 110–11, 114 partition chromatography partition coefcients partitioning glucose 109, 112–13 167 99, paper 171 spectroscopic lghtnng 176 warming 177 108 122–3 108 97 pectn gravimetric analysis 76, 86–9 67 M peptdes greenhouse effect greenhouse gases 64 164 M + 1 peaks 105 pestcdes 158 165 magnetsm 132 malleablty PET 132 (poly(ethene petroleum 125, terephthalate)) 134–7 , 175 158 H mass Haber Process 138–9, halogenoalkanes halogens HDPE heatng heay 18, (hgh of samples 102–5, 175 densty resoluton UV-sble poly(ethene) (HDPE) 175 spectroscopy series homolytic ssion hybridisation 16–17 carboxylc 3 144, 160 128–33, acds chlor-alkal sold 35 176 polluton methane 158 165 methylamne 175 ndustry 137 waste water 19 141, 2 4–5, phenylamne 63 158, phosphorus (iii) phosphorus (v) chlorde smog (π) bonds p (π) orbtals plant 35 35 141, 161, 170–1 160 162 76–7 p 2, 58, polluton 3 50 dersty plastcs 54–5 159 chlorde photodissociation ppettes 53 55 photosynthess 149 53 52, photochemical petroleum 94–5 47 , ons phosphates 149 alumnum hgh 46, phenoxde phenylethene metals 19 hgh health 102–5 71 mesomerism 158 homologous phenols 102 172 mean values mercury 87 132 ratios spectrometry mass transit poly(ethene)) 158 heterolytic ssion human mass 40 148–9 densty metals herbcdes 28–9, 87 , mass/charge 166 141 137 , 101, 175, 141, 176 158–9, 167–8, 170–3 187 Index polyamides 61 resources 174–5 T polyesters 60, poly(ethene) poly(ethene 62–3 respraton 58 162 retention time terephthalate) (PET) 175 111 retention value Teon ) (R 110–11, 112 59 temperature 72, 139, 151 f polymerisation polymers 58–69, polypeptdes reusable 58–61 149, poly(propene) R poly(styrene) groups rng 63 rum 66–7 termination 157 5, 15, 46 benzene ndustry tertiary halogenoalkanes (PVC) (PTFE) thermal 59, 149 110, 10, 47 , 87 , 88, 157 , dchromate (vi) potassum manganate (vii) 41, 23, 81 31, tn saturated 23 scrubbers 173 41, chlorde ttratons secondary samples analysis alcohols 26, 109, 35 74, 76–85 reagent 30–1, 40 27 85 transesterication secondary halogenoalkanes secondary pollutants 39 28 86 transton element ons 96 170 70 turbidity sedmentaton (TLC) 45 Tollen’s potentiometric titrations 85 chromatography 38 80–1 prexes 132 112–13 thonyl 31, 29 159 11 potassum 28, 2 conductty thin-layer S saponication precision of 27 62 tetravalency 124 59 salts isomerism of 60, 26, 19 alcohols thermometric titrations chlorde precptatng reactions tertiary Terylene 175 poly(tetrauoroethene) positional 174 16 compounds see also 62 polysaccharides polynyl reverse osmosis 175 64 poly(phenylethene) resources 159 159 8 separaton preseraton of food technques 108–27 , 135 152 U sequestering pressure 114, 119, 139, sgma primary alcohols primary halogenoalkanes primary pollutants (σ) standards reactions unknowns spectroscopy calculatons 94–7 78–9 dstllaton plants 116 unsaturated 128–9 urea 22–3, 40 97 141, 161, 170–1 UV light 94–7 19 38 sodum 46 sodum carbonate V 64–5 (poly(tetrauoroethene)) (polynyl chlorde) 59, controls 41 59 (i) vacuum distillation sodum chlorate sodum chlorde 83 sodum hydrogencarbonate apour 146 sodum hydroxde sodum thosulphate 34, 147 , 41 149 ttratons 87 , 141, 124 pressure negar 82 (vis) visualising solublty 125 solutons 73–5, 165 114 light spectroscopy 94–5, 96 169 91 133 solvent 114, vapour visible 81 89 sol quarryng 119, 149 Q quanta 40 62 proteins qualty ultraviolet 30–1, 74 soap PVC 2 28–9 smog PTFE test 170 smeltng propene bonds mrror smple propagation 172–3 26 sler primary agents 151 tamn C 114 extraction trcaton 122–5 solvent front 110 spectroscopc methods agents 110 83 177 olatle organc olume 72 compounds (VOCs) R radaton 96–101 see also ran 137 , standard deviation ultraviolet spectroscopy 168–9 Raoult’s law standard starch 114–15 solutons 71, 90–107 olumetrc asks 76 66–7 stationary W chromatography phases washng raw materals 128, 138 mechanisms 19 steam distillation 120–1, 174–5 steel 80–1 stems pressure dstllaton 119 reduction 57 , 88, reactons 33 stereoisomerism stretching waste 174 12–13 strong acd–strong base ttratons 158–9 132 structural formulae cycle 163 structural 5 isomerism 90–1 10 wavenumbers reforming relative relate 136–7 substitution abundance atomc 102 mass 103 42, reactions 18, 19, resdue units resonance resonance 188 58 separatons 135 3 hybrids weak acd–strong weak base–strong base ttratons 84 acd ttratons 84 46 sufxes 8 sulphur dchlorde sulphur doxde sulphurc 3 98–101 28–9, weghng repeating 157 156 waelengths reforestation 156, 84 water reectty 165 87 98 purcaton reduction of 174 128, crystallsaton polluton reducton 97 , 8 of reduced 173 176–7 175 water redox titrations 149, 124 waste recycling 86, 108 waste reaction 73 74–5 acd suspended oxde 150, 22, 35 152 27 , partcles 72 Z 150–3 158 zwitterions 56 171 Chemistry for Unit 2 CAPE® Achieve your potential Developed guide in will CAPE® Written exclusively provide by an designed ● ● in learning to Engaging the with additional experienced syllabus information ● the Caribbean Examinations support to Council®, maximise your this study performance Chemistry. Chemistry key you with an and team enhance activities teachers examination, easy-to-use outcomes of from your that this study double-page the study help syllabus of you the and guide format . and the in such the covers Each contains subject , develop experts a CAPE® all topic range the essential begins of with features as: analytical skills required for examination Examination tips with essential advice on succeeding in your assessments Did You Know? boxes to expand your knowledge and encourage further study This study choice also questions examiner sample to build a fully interactive examination skills Examinations Thornes subjects includes and answers confidence at to CSEC® produce and a Council series (CXC®) of of incorporating with in O x f o rd has Study multiple- accompanying preparation for the CAPE® worked Guides exclusively across a wide with range of CAPE®. How Pa r t CD, examination. 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