CHEMISTRY Candidate session number HIGHER LEVEL ... PAST PAPERS - YEAR/2011...(b) The IR spectrum,...

42 pages

M11/4/CHEMI/HP3/ENG/TZ2/XX

Tuesday 10 May 2011 (morning)

CHEMISTRYHIGHER LEVELPAPER 3

INSTRUCTIONS TO CANDIDATES

• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Answer all of the questions from two of the Options.• Write your answers in the boxes provided.

1 hour 15 minutes

Examination code

2 2 1 1 – 6 1 1 5

Candidate session number

22116115

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Option A — Modern analytical chemistry

A1. Selected regions of the electromagnetic spectrum are represented in order of increasingfrequencybelow.

Gamma-rays

X-raysUltraviolet

Visible

InfraredMicrowave

106 108 1010 1012 1014 1016 1018 1020 1022 1024

Frequency/Hz

(a) IdentifyregionA. [1]

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(b) Identify the atomic or molecular processes associated with microwave andultravioletradiation. [2]

Microwave:

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Ultraviolet:

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(c) Explain why the absorptions in infrared (IR) spectroscopy occur at much higherfrequencythanthosein1HNMRspectroscopy. [2]

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A2. Infraredspectroscopyiscommonlyusedasananalyticaltechniquebyinorganic,physicalandorganicchemists.

(a) ExplainwhyhydrogenbromideisIRactivewhereasbromineisIRinactive. [1]

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(This question continues on the following page)

(Question A2 continued)

(b) TheIRspectrum,massspectrumand1HNMRspectrumofanunknowncompound,X,ofmolecularformulaC5H10O2,areasfollows.

IRspectrum%Transmittance

0 I4000 3000 2000 1500 1000 500

Wavenumber/cm–1

Massspectrum

Relativeintensity

010 20 30 40 50 60 70 80 90 100

m/z1HNMRspectrum

16 14 12 10 8 6 4 2 0Chemicalshift/ppm

[Source:SDBSWeb:http://riod01.ibase.aist.go.jp/sdbs/(NationalInstituteofAdvancedIndustrialScienceandTechnology)]

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(i) IntheIRspectrum,identifythebondresponsiblefortheabsorptionlabelledI. [1]

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(ii) In the mass spectrum, deduce which fragments the m/z values at 102 and 57correspondto. [2]

/ 102m z = : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

/ 57m z = : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iii) Identifythepeakat11.5ppminthe1HNMRspectrum. [1]

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(iv) State what information can be obtained from the integration traces in the1HNMRspectrumaboutthehydrogenatomsresponsibleforthepeakat1.2ppm. [1]

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(v) DeducethestructureofX. [1]

(vi) HCOOC(CH3)3 is an isomer ofX. For the1HNMR spectrum of this isomer,

deduce the total number of peaks (excluding theTMS peak at 0 ppm) and theratioofpeakareas.Foreachpeak,deducewhetheritisasinglet,doublet,triplet,quartetorshowsamorecomplexsplittingpattern. [3]

Numberofpeaks(excludingtheTMSpeakat0ppm):

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Ratioofpeakareas:

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Splittingpatterns:

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(vii) CH3CH2COOCH2CH3 is another isomer of X. For the 1HNMR spectrum ofthisisomer,deducethetotalnumberofpeaks(excludingtheTMSpeakat0ppm)andtheratioofpeakareas.Foreachpeak,deducewhetheritisasinglet,doublet,triplet,quartetorshowsamorecomplexsplittingpattern. [3]

Numberofpeaks(excludingtheTMSpeakat0ppm):

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Ratioofpeakareas:

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Splittingpatterns:

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A3. Nuclearmagneticresonance(NMR)spectroscopyisthebasisofadiagnosticmedicaltechniquecalledmagneticresonanceimaging(MRI).Theinstrumentusedinthistechniqueinahospitalisshownbelow.

[Source:http://en.wikipedia.org/wiki/File:Modern_3T_MRI.JPG]

ExplaintheroleofNMRinthistechniquewhichcanbeusedtoobtainathree-dimensionalviewoforgansinthehumanbody. [2]

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A4. Gas-liquidchromatography(GLC)isapowerfulanalyticaltechnique.Outlinetheprinciplesofthistechnique,fromtheinjectionofthesample. [5]

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Option B — Human biochemistry

B1. Triglycerides are one of three types of lipid found in the human body. The followingequationrepresentstheformationofatriglyceride.

3RCOOH triglyceride 3+ +X Y�

(a) IdentifythecompoundsXandY. [2]

X: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Y: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Draw the structural formula of a triglyceride formed from one molecule each ofoctanoic acid, lauric acid and stearic acid. The formulas of the acids are shown inTable22oftheDataBooklet. [1]

(c) Explainwhetherthetriglycerideinpart(b)isasolidoraliquidatroomtemperature. [3]

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(Question B1 continued)

(d) Identifythetypeofreactionthatoccursduringtheformationofatriglyceride. [1]

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B2. (a) Amixture of the amino acids serine (Ser), glutamic acid (Glu) and lysine (Lys)wasseparatedusingelectrophoresisandabufferofpH5.7.Adropcontainingthemixturewasplacedinthecentreofthepaperandapotentialdifferencewasapplied.Theaminoacidsweredevelopedandthefollowingresultswereobtained.

(i) Describehowtheaminoacidspotsmayhavebeendeveloped. [1]

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(ii) PredictwhichaminoacidispresentatspotC.Explainyouranswer. [3]

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(iii) TheaminoacidatspotBisatitsisoelectricpoint.Describeonecharacteristicofanaminoacidatitsisoelectricpoint. [1]

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(b) Explain,usingequations,howtheaminoacidglycine(Gly)canactasabuffer. [2]

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B3. Copperionsareusedinelectrontransport.Onereactionthatoccursistheoxidationofglucose,C6H12O6, toformcarbondioxide,CO2. Statethehalf-equationsfortheoxidationofglucoseandtheassociatedreactioninvolvingcopperions. [2]

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B4. (a) DNAandRNAbothcontainapentosesugar.

(i) Statethenamesofthesugarsineachnucleicacidandoutlinehowtheirchemicalstructuresdiffer. [2]

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(ii) StateoneotherstructuraldifferencebetweenDNAandRNA. [1]

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(b) (i) OutlinethestepsinvolvedinDNAprofiling. [5]

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(ii) StateoneuseofDNAprofiling. [1]

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Option C — Chemistry in industry and technology

C1. Aluminiumanditsalloysarewidelyusedinindustry.

(a) Aluminiummetalisobtainedbytheelectrolysisofaluminadissolvedinmoltencryolite.

(i) Explainthefunctionofthemoltencryolite. [1]

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(ii) State thehalf-equation for the reaction that takesplace at thepositive electrode(anode). [1]

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(b) Outlinetwodifferentwaysthatcarbondioxidemaybeproducedduringtheproductionofaluminium. [2]

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C2. Catalystsmaybehomogeneousorheterogeneous.

(a) (i) Explain how a heterogeneous catalyst may increase the rate of the reactionbetweencarbonmonoxide,CO(g),andnitrogenmonoxide,NO(g). [2]

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(ii) Outline one disadvantage of using a heterogeneous catalyst rather than ahomogeneouscatalyst. [1]

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(b) Discuss two factors which need to be considered when selecting a catalyst for aparticularchemicalprocess. [2]

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(Question C2 continued)

(c) (i) StatethetypeofreactionforwhichaZiegler-Nattacatalystisused. [1]

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(ii) DescribethecompositionofaZiegler-Nattacatalyst. [2]

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C3. Liquid-crystaldisplaysareusedindigitalwatches,calculatorsandlaptops.

(a) Describe the liquid-crystalstate, in termsofmoleculararrangement,andexplainwhathappensastemperatureincreases. [3]

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(b) Discuss three properties a substance should have if it is to be used in liquid-crystaldisplays. [3]

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(Question C3 continued)

(c) Kevlarisacondensationpolymerthatisoftenusedinliquid-crystaldisplays.Asectionofthepolymerisshownbelow.

(i) Describetheliquid-crystalpropertiesofKevlar. [3]

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(ii) ExplainthestrengthofKevlarintermsofitsstructureandbonding. [2]

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(iii) Explainwhyabullet-proofvestmadeofKevlarshouldbestoredawayfromacids. [2]

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Option D — Medicines and drugs

D1. Morphineisastronganalgesicwhichisadministeredparenterally.

(a) Explainwhymorphineisnormallyinjectedintravenously. [1]

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(b) Diamorphine (heroin) is amore effectivepainkiller thanmorphine. The structuresofmorphineanddiamorphineareshowninTable20oftheDataBooklet.Explainatthemolecularlevelwhydiamorphineisabsorbedintofattytissuemorerapidlythanmorphine. [2]

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D2. Caffeineandnicotinearetwocommonstimulants.

(a) Describetwoeffectsoflargeamountsofcaffeineonthehumanbody. [2]

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(b) (i) Statethenameofthefunctionalgroupcircledonthestructureofcaffeine. [1]

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(ii) Deducewhichfunctionalgroupiscommontobothnicotineandcaffeine. [1]

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D3. Duringdrugdevelopment,trialsareconductedtodeterminethetherapeuticwindow.

(a) Explain the meaning of the term therapeutic window and discuss its importance indrugadministration. [4]

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(b) Explaintheuseofplacebosinclinicaltrialsonhumans. [3]

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(c) Identifyoneothereffectofadrugwhichmustbedeterminedduringclinicaltrials. [1]

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(Question D3 continued)

(d) Inthe1950s,thalidomidewasgiventopregnantwomentoalleviatemorningsickness.Many of the children born to thesewomen had deformed limbs. State the structuralfeatureofthalidomideresponsibleforthesedifferenteffectsandexplaintheeffectthatthiscasehashadonthedevelopmentofdrugs. [2]

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(e) Sorafenib, a drug used to treat kidney and liver cancer, was produced usingcombinatorialtechniques.Thestructureofsorafenibisshownbelow.

F3C NH

(i) Describehowcombinatorialchemistrymayhavebeenusedtosynthesizesorafenib. [3]

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(ii) Stateoneadvantageofsolid-phasechemistryduringcombinatorialsynthesis. [1]

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D4. Severalmind-alteringdrugsexhibitsimilaritiesintheirstructures.SomeoftheseareshowninTable20oftheDataBooklet.

(a) State one structural similarity and one difference between lysergic acid diethylamide(LSD)andpsilocybin. [2]

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(b) Describetwoshort-termmindalteringeffectsoftetrahydrocannabinol(THC). [2]

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Option E — Environmental chemistry

E1. Carbondioxide,methaneandchlorofluorocarbons(CFCs)arewell-knowngreenhousegases.Nitrogentrifluoride,NF3,isthousandsoftimesmoreeffectiveatwarmingtheatmospherethananequalmassofcarbondioxide.NF3canbeusedinthemanufactureofcomputerchipsandthin-filmsolarphotovoltaiccells.

(a) Identifytwo greenhousegasesnotmentionedabove.Oneofthegasesthatyouidentifyshouldcontainanitrogenatom.Foreachgas,stateitssource. [4]

Greenhousegas1:

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Source:

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Greenhousegas2:

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Source:

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(b) The methane produced by sheep and cows can contribute to global warming.InAustralia, it is considered that sheepandcowsproduce approximately14%of thecountry’stotalgreenhouseemissions.Explainhowthismethaneisformed. [1]

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(Question E1 continued)

(c) The following graph shows the annual increase in the concentration of atmosphericcarbondioxiderecordedatMaunaLoa,Hawaii.

ConcentrationofCO

2/partspermillion

1960 1970 1980 1990 2000 2010Year

[Source:http://scrippsco2.ucsd.edu/graphics_gallery/mauna_loa_record/mauna_loa_record.html]

Explainwhythegraphisnotsmoothbutinvolvesannualfluctuations(showningrey). [1]

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(d) Stateoneeffectofglobalwarming. [1]

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E2. Freshsuppliesofwaterareofmajorimportancetosocietytoday.

(a) Both mercury and polychlorinated biphenyls (PCBs) can potentially cause serioushealtheffectswhenpresentinwater.Stateonesourceforeachofthesetwopollutants. [2]

Mercury:

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(b) Fresh water can be obtained from sea water by using multi-stage distillation andreverseosmosis.Evaluatethesetwoprocesses.Youranswershouldincludeadescriptionofeachprocess. [5]

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E3. (a) Industrialeffluentisfoundtobehighlycontaminatedwithsilverandleadions.Asampleofwatercontains 38.0 10−× moldm–3Ag+and 21.9 10−× moldm–3Pb2+.Ontheadditionofchloride ionsbothAgCl 10( 1.8 10 )spK −= × andPbCl2

5( 1.7 10 )spK −= × precipitate fromthesolution. DeterminetheconcentrationofCl–neededtoinitiatetheprecipitationofeachsaltanddeducewhichsaltprecipitatesfirst. [5]

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(b) (i) Statewhatismeantbytheterm cation-exchange capacity (CEC). [1]

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(ii) Describetwochemicalfunctionsofsoilorganicmatter(SOM). [2]

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(Question E3 continued) (iii) DiscusshowchangesinsoilpHaffectstheavailabilityofnitrogenandphosphorus

forplants. [3]

Nitrogen:

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Phosphorus:

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Option F — Food chemistry

F1. (a) Rancidity is the perception of flavours in lipids that our senses perceive as offbecauseofadisagreeablesmell,taste,textureorappearance.Theprocessesthatcreatetheoff-flavoursmaybehydrolyticrancidityoroxidativerancidityinlipids.

(i) Predicttheproductsofhydrolyticrancidityoffats. [2]

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(ii) The hydrolysis of milk products is used in the making of cheese. State twoconditionswhichincreasetherateofhydrolysisoffatsinmilk. [2]

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(iii) Potato chips (crisps) are cooked in oils made from unsaturated fatty acids.Explain in terms of chemical processes why potato chips are purchased insealed,opaque,nitrogen-filledfoilpacksandtastebestwhenfreshlyopened. [3]

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(Question F1 continued)

(b) Initiation,propagationandterminationstepsoccurinthefree-radicalchainmechanismduringoxidativerancidity.Foreachstep,stateonerelatedequation. [3]

Initiation:

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Propagation:

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Termination:

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F2. (a) Antioxidants are substances that slow the rate of oxidationof foods andmay also beconsumedtoprovidehealthbenefits.Twotraditionalfoodswithantioxidantpropertiesare green tea and oregano. Green tea contains epigallocatechin-3-gallate (EGCG)and oregano contains rosmarinic acid. The structures of these two compounds areshownbelow.

OHEpigallocatechin-3-gallate(EGCG)

Rosmarinicacid

(i) ExplainwhybothEGCGandrosmarinicacidhaveantioxidantproperties. [1]

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(ii) Listtwohealthbenefitsofconsumingfoodssuchasgreenteaandoregano. [2]

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(b) Anthocyaninsarenaturallyoccurringpigmentsresponsibleforthecolourofblueberriesandcranberries.ThestructuresoftwoformsofanthocyaninsareshowninTable22oftheDataBooklet.

(i) Using the abbreviations QB for quinoidal base and FC+ for flavylium cation,stateanequationtodescribehowpHaffectsthecolourofanthocyanins. [1]

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(ii) Suggestwhyblueberriesshouldnotbestoredinaluminiumcans. [2]

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(c) Comparethestructuresofthenaturalpigments,chlorophyllandhemeBusingTable22oftheDataBooklet. [4]

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F3. Carvone is a member of a family of compounds called terpenoids. Carvone occurs intwoenantiomericforms.(S)-(+)-carvoneistheprincipalcomponentofcarawayseedoiland(R)-(–)-carvoneistheprincipalcomponentofspearmintoil.

(a) Identifythechiralcentreincarvone,withanasterisk,*. [1]

(b) ExplainthemeaningoftheRandSnotationandhowthisdiffersfromthedandlnotation. [2]

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(c) Thestructurerepresentedis(S)-(+)-carvone.Explainhowthishasbeendeduced. [2]

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Option G — Further organic chemistry

G1. Benzene, C6H6, is a planar compound which differs from the non-planar structure ofcyclohexane, C6H12. The structures of benzene and the most stable form of cyclohexanearerepresentedbelow.

Benzene Cyclohexane

(a) With reference to the compounds benzene, cyclohexane and 1,3-cyclohexadiene,statewhichcompoundwouldcontaintheshortestcarbon-carbonbondlength. [1]

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(b) Explain why it is more common for benzene to undergo substitution reactions thanadditionreactions. [1]

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(Question G1 continued)

(c) Suggest why chloromethylbenzene, C6H5CH2Cl, reacts with warm aqueous sodiumhydroxide,NaOH,easilywhereasforchlorobenzene,C6H5Cl,strongerconditionssuchashightemperature(e.g.350°C)areneeded. [2]

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G2. (a) Draw the structural formulas of themajor organic products formed in the followingreactions.

(i) 3 2H CCH CH ICl= + → [1]

(ii) 3H CCHO HCN+ → [1]

(iii) 3H CCHO +

→ [1]

(iv) 3

1.H CCHO2.H OCH MgI → [1]

(Question G2 continued)

(b) Drawthestructuralformulaoftheotherproductofthereactioninpart(a)(i). [1]

(c) Identify each of the types of reaction in (a) as elimination, nucleophilic addition,electrophilicaddition,acid-base,addition-eliminationorGrignard. [4]

Reaction Type

(a)(i)

(a)(ii)

(a)(iii)

(a)(iv)

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G3. (a) Identifyallthemajorproducts,A–D,inthefollowingreactions.

(i) 3 3 2 2CH COCl CH CH NH+ → +A B [1]

(ii) 2

+ + + →2 3 2 22HNO C D H OH SO4 [1]

(b) CandDareisomers.Explainthemechanismofthereactionin(a)(ii),formingoneofthesetwoisomers,usingcurlyarrowstorepresentthemovementofelectronpairs. [3]

G4. Benzenereactswithethanoylchloride,CH3COCl, in thepresenceofanaluminiumchloridecatalyst,AlCl3,inanacylationreaction.Explainthemechanismofthereaction,usingcurlyarrowstorepresentthemovementofelectronpairs.Includetheformationoftheelectrophile. [4]

G5. Deduceatwo-stepreactionpathwaywhichcanbeusedtoconvertbutan-1-ol,CH3(CH2)3OH,into 1,2-dibromobutane, CH3CH2CHBrCH2Br. State the reagents used in each step andidentifytheproductformedinstep1. [3]

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