22096114 past papers - subject...22()gn ()gh2 2og() at equilibrium, the concentration of no –3was...

2209-6114 15 pages

M09/4/CHEMI/HP2/ENG/TZ2/XX+

Monday 18 May 2009 (afternoon)

CHEMISTRYHIGHER lEvElPaPER 2

INSTRUCTIONS TO CANDIDATES

• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Section A: answer all of Section A in the spaces provided.• Section B: answer two questions from Section B. Write your answers on answer sheets.

Write your session number on each answer sheet, and attach them to this examination paper and your cover sheet using the tag provided.

• At the end of the examination, indicate the numbers of the questions answered in the candidate box on your cover sheet and indicate the number of sheets used in the appropriate box on your cover sheet.

2 hours 15 minutes

Candidate session number

0 0

© International Baccalaureate Organization 2009

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Section a

Answer all the questions in the spaces provided.

1. Aspirin, one of the most widely used drugs in the world, can be prepared according totheequationgivenbelow.

OH

COOHC

H3C O

O

CCH3

OOCOCH3

COOH

+ + CH3COOHH+

salicylicacid ethanoicanhydride aspirin ethanoicacid

(a) Statethenamesofthethree organicfunctionalgroupsinaspirin.

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[3]

(b) A student reacted some salicylic acid with excess ethanoic anhydride. Impure solidaspirinwas obtained by filtering the reactionmixture. Pure aspirinwas obtained byrecrystallization.Thefollowingtableshowsthedatarecordedbythestudent.

Massofsalicylicacidused 3.15±0.02g

Massofpureaspirinobtained 2.50±0.02g

(i) Determinetheamount,inmol,ofsalicylicacid,C6H4(OH)COOH,used.

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[2]

(This question continues on the following page)

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(Question 1 continued)

(ii) Calculatethetheoreticalyield,ing,ofaspirin,C6H4(OCOCH3)COOH.

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[2]

(iii) Determinethepercentageyieldofpureaspirin.

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[1]

(iv) State the number of significant figures associatedwith themass of pure aspirinobtained,andcalculatethepercentageuncertaintyassociatedwiththismass.

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[2]

(v) Another student repeated the experiment and obtained an experimental yieldof150%.Theteachercheckedthecalculationsandfoundnoerrors.Commentontheresult.

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[1]


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(vi) Thefollowingisathree-dimensionalcomputer-generatedrepresentationofaspirin.

C2

C3

C4

C1

C6

C5

H2

H3

H4

H5

C7

C8

C9

H1

H8

H7

H6

O3

O4

O1

O2

A third studentmeasured selected bond lengths in aspirin, using this computerprogramandreportedthefollowingdata.

Bond Bond length / × 10–10 m

C1–C2 1.4C2–C3 1.4C3–C4 1.4C4–C5 1.4C5–C6 1.4C6–C1 1.4C2–O3 1.4

Thefollowinghypothesiswassuggestedbythestudent:“Since all the measured carbon-carbon bond lengths are equal, all the carbon-oxygen bond lengths must also be equal in aspirin. Therefore, the C8–O4 bond length must be 1.4 × 10–10 m”.Commentonwhetherornotthisisavalidhypothesis.

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[2]


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(vii) The other product of the reaction is ethanoic acid,CH3COOH. Define an acidaccordingtotheBrønsted-LowrytheoryandstatetheconjugatebaseofCH3COOH.

Brønsted-Lowrydefinitionofanacid:

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ConjugatebaseofCH3COOH:

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[2]

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2. Someofthemostimportantprocessesinchemistryinvolveacid-basereactions.

(a) (i) Calculate the Ka value of benzoic acid, C6H5COOH, using Table 15 in theDataBooklet.

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[1]

(ii) Based on its Ka value, state and explain whether benzoic acid is a strong orweakacid.

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[2]

(iii) DeterminethehydrogenionconcentrationandthepHofa0.010moldm–3benzoicacidsolution.Stateoneassumptionmadeinyourcalculation.

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[4]

(b) Describetheacid-basecharacteroftheoxidesofeachoftheperiod3elements,NatoCl.

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(c) Stateone exampleof an acidic gas, producedby an industrial process or the internalcombustionengine,whichcancauselarge-scalepollutiontolakesandforests.

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[1]

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3. (a) (i) Drawtheshapeofthepzorbitalusingthecoordinatesshown. [1]

y

z

x

(ii) StatetheelectronconfigurationofFe3+.

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[1]

(iii) Definethetermligand.

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[1]

(iv) Explainwhythecomplex[Fe(H2O)6]3+iscoloured.

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[3]

(v) Theelementselenium( )Z = 34 haselectronsinthe4s,3dand4porbitals.Drawanorbitalboxdiagram(arrow-in-boxnotation)torepresenttheseelectrons.

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[1]

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4. Considerthefollowingreaction.

2 23 2 2 6 2CH OH g H g C H g H O g( ) ( ) ( ) ( )+ → +

(a) The standard enthalpy change of formation forCH3OH(g) at 298K is –201kJmol–1

andforH2O(g)is–242kJmol–1.UsinginformationfromTable11oftheDataBooklet,

determinetheenthalpychangeforthisreaction.

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[2]

(b) The standard entropy for CH3OH(g) at 298K is 238JK–1mol–1, for H2(g) is

131JK–1mol–1andforH2O(g)is189JK–1mol–1.UsinginformationfromTable11of

theDataBooklet,determinetheentropychangeforthisreaction.

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[2]

(c) Calculate the standard change in free energy, at 298K, for the reaction and deducewhetherthereactionisspontaneousornon-spontaneous.

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[3]

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Section B

Answer two questions. Write your answers on the answer sheets provided. Write your session number on each answer sheet, and attach them to this examination paper and your cover sheet using the tag provided.

5. Nitrogenandsiliconbelongtodifferentgroupsintheperiodictable.

(a) (i) Distinguishintermsofelectronicstructure,betweenthetermsgroupandperiod. [2]

(ii) Statethemaximumnumberoforbitalsinthen = 2energylevel. [1]

(b) Draw the Lewis structures, state the shapes and predict the bond angles for thefollowingspecies.

(i) SiF62– [3]

(ii) NO2+ [3]

(c) Thegraphbelowshowstheboilingpointsofthehydridesofgroup5.Discussthevariationintheboilingpoints. [4]

Period

2 3 4 5

Boilingpoint/

° C

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

SbH3

NH3

AsH3

PH3


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(d) Explain,usingdiagrams,whyNO2isapolarmoleculebutCO2isanon-polarmolecule. [3]

(e) Describethestructureandbondinginsilicondioxide. [2]

(f) ConsiderthemoleculeHCONH2.

(i) Statethenameofthecompoundanddrawitsstructuralformula,showingallthebondspresent. [2]

(ii) Explainthetermhybridization. [1]

(iii) Describehowσandπbondsform. [2]

(iv) StatethetypeofhybridizationofthecarbonandnitrogenatomsinHCONH2. [2]

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6. (a) Considerthefollowingequilibrium.

2SO (g) O (g) 2SO (g) = 198kJmol2 2 31+ − −

ë ÖH

(i) Deducetheequilibriumconstantexpression,Kc,forthereaction. [1]

(ii) Stateandexplaintheeffectofincreasingthepressureontheyieldofsulfurtrioxide. [2]

(iii) State and explain the effect of increasing the temperature on the yield ofsulfurtrioxide. [2]

(iv) Statetheeffectsofacatalystontheforwardandreversereactions,onthepositionofequilibriumandonthevalueofKc. [3]

(b) When amixture of 0.100molNO, 0.051molH2 and 0.100molH2Owere placed ina1.0dm3flaskat300K,thefollowingequilibriumwasestablished.

2 2 22 2 2NO g H g N g H O g( ) ( ) ( ) ( )+ +

Atequilibrium,theconcentrationofNOwasfoundtobe0.062moldm–3.Determinetheequilibriumconstant,Kc,ofthereactionatthistemperature. [4]

(c) (i) Outline twodifferencesbetweenanelectrolyticcellandavoltaiccell. [2]

(ii) Explainwhysolidsodiumchloridedoesnotconductelectricitybutmoltensodiumchloridedoes. [2]

(iii) Molten sodiumchloride undergoes electrolysis in an electrolytic cell. For eachelectrode deduce the half-equation and state whether oxidation or reductiontakesplace.Deducetheequationoftheoverallcellreactionincludingstatesymbols. [5]

(iv) Electrolysis has made it possible to obtain reactive metals such as aluminiumfrom their ores, which has resulted in significant developments in engineeringandtechnology.Stateonereasonwhyaluminiumispreferredtoironinmanyuses. [1]

(v) Electroplatingisanimportantapplicationofelectrolysis.Statethecompositionoftheelectrodesandtheelectrolyteusedinthesilverelectroplatingprocess. [3]

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7. (a) (i) Definethetermrate of reaction. [1]

(ii) State an equation for the reaction of magnesium carbonate with dilutehydrochloricacid. [1]

(iii) Therateofthisreactionin(a)(ii),canbestudiedbymeasuringthevolumeofgascollectedoveraperiodoftime.Sketchagraphwhichshowshowthevolumeofgascollectedchangeswithtime. [1]

(iv) The experiment is repeated using a sample of hydrochloric acid with doublethevolume,buthalf theconcentrationof theoriginal acid. Drawa second lineonthegraphyousketchedinpart(a)(iii) toshowtheresultsinthisexperiment.Explainwhythislineisdifferentfromtheoriginalline. [4]

(b) Nitrogen monoxide reacts at 1280°C with hydrogen to form nitrogen and water.Allreactantsandproductsareinthegaseousphase.

(i) Thekineticsofthereactionwerestudiedatthistemperature.Thetableshowstheinitialrateofreactionfordifferentconcentrationsofeachreactant.

experiment [no (g)]/ mol dm–3 × 10–3

[H2(g)]/ mol dm–3 × 10–3

initial rate/ mol dm–3 s–1 × 10–5

1 5.00 2.00 1.252 10.00 2.00 5.003 10.00 4.00 10.00

Deduce the order of the reactionwith respect toNO andH2, and explain yourreasoning. [4]

(ii) Deducetherateexpressionforthereaction. [1]

(iii) Determinethevalueof therateconstantfor thereactionfromExperiment3andstateitsunits. [2]


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(c) Thegas-phasedecompositionofdinitrogenmonoxideisconsideredtooccurintwosteps.

Step1: N O g N g O(g)2 2

1( ) ( )→ +

k

Step2: N O g O(g) N g O (g)22 2

2

( ) ( )+ → +k

Theexperimentalrateexpressionforthisreactionisrate= k [ ]N O2 .

(i) Identifytherate-determiningstep. [1]

(ii) Identifytheintermediateinvolvedinthereaction. [1]

(d) The conversion of CH3NC into CH3CN is an exothermic reaction which can berepresentedasfollows.

CH3–N≡C transitionstate CH3–C≡N

Thisreactionwascarriedoutatdifferenttemperaturesandavalueoftherateconstant,k, wasobtainedforeachtemperature.Agraphoflnk against1/Tisshownbelow.

0.0018 0.0019 0.0020 0.0021 0.0022

lnk

–5

–6

–7

–8

–9

–10

–111/T(K–1)

(i) Definethetermactivation energy,Ea. [1]

(ii) Construct the enthalpy level diagram and label the activation energy, Ea,theenthalpychange,∆H,andthepositionofthetransitionstate. [3]

(iii) Describe qualitatively the relationship between the rate constant, k, and thetemperature,T. [1]

(iv) Calculate the activation energy, Ea, for the reaction, using Table 1 of theDataBooklet. [4]

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8. In some countries, ethanol is mixed with gasoline (petrol) to produce a fuel for carscalledgasohol.

(a) (i) Definethetermaverage bond enthalpy. [2]

(ii) UsetheinformationfromTable10oftheDataBooklettodeterminethestandardenthalpychangeforthecompletecombustionofethanol.

CH CH OH g O g CO g H O g3 2 2 2 23 2 3( ) ( ) ( ) ( )+ → + [3]

(iii) The standard enthalpy change for the complete combustion of octane, C8H18,is–5471kJmol–1. Calculate theamountof energyproduced inkJwhen1gofethanoland1gofoctaneisburnedcompletelyinair. [2]

(iv) Ethanolcanbeoxidizedusingacidifiedpotassiumdichromate,K2Cr2O7, to formtwodifferentorganicproducts.

CH CH OH3 2Cr O

HCr O

H2 7

22 7

2−

+

−

+ → →a B

State the structural formulas of the organic productsa andB and describe theconditionsrequiredtoobtainahighyieldofeachofthem. [4]

(v) Ethenecanbeconvertedintoethanolbydirecthydrationinthepresenceofacatalystaccordingtothefollowingequation.

C H g H O(g CH CH OH(g2 2 3 24 ( ) ) )+

Forthisreaction,identifythecatalystusedandstateoneuseoftheethanolformedotherthanasafuel. [2]

(b) Deduce a two-step synthesis for each of the following conversions. For each step,statethestructuralformulasofallreactantsandproductsandstatetheconditionsusedinthereactions.

(i) Ethanoltoethylethanoate. [2]

(ii) Propenetopropanone. [2]


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(c) Thereagentsusedinaneliminationreactionareshownbelow.

CH3

C Br

CH3

H3C + NaOCH2CH3

Explainthemechanismofthisreactionusingcurlyarrowstorepresentthemovementofelectronpairs. [3]

(d) (i) Describegeometrical isomerism. [1]

(ii) Drawthegeometricalisomersofbut-2-ene. [2]

(iii) Drawthetwoenantiomersofbutan-2-ol. [2]

22096114 past papers - subject...22()gn ()gh2 2og() at equilibrium, the concentration of no –3was...

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