88106102 - WordPress.com · – 12 – N10/4/CHEMI/HP2/ENG/TZ0/XX 5. Consider the following sequence of reactions. RCH RCH Br RCH OH 3 2 2 reaction 1 reaction 2

8810-6102 16 pages

N10/4/CHEMI/HP2/ENG/TZ0/XX

Thursday 11 November 2010 (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 2010

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SECTION A

Answer all the questions in the spaces provided.

1. Thedatabeloware fromanexperiment tomeasure theenthalpychange for the reactionofaqueouscopper(II)sulfate,CuSO4(aq)andzinc,Zn(s).

Cu aq Zn (s Cu (s Zn aq2 2+ ++ → +( ) ) ) ( )

50.0cm3of1.00moldm–3copper(II)sulfatesolutionwasplacedinapolystyrenecupandzincpowderwasaddedafter100seconds.Thetemperature-timedatawastakenfromadata-loggingsoftwareprogram.Thetableshowstheinitial23readings.

A B C D E F G H1 time / s Temperature / °C2 0.0 24.83 1.0 24.84 2.0 24.85 3.0 24.86 4.0 24.87 5.0 24.88 6.0 24.89 7.0 24.810 8.0 24.811 9.0 24.812 10.0 24.813 11.0 24.814 12.0 24.815 13.0 24.816 14.0 24.817 15.0 24.818 16.0 24.819 17.0 24.820 18.0 24.821 19.0 24.822 20.0 24.823 21.0 24.824 22.0 24.8

Linear fit for selected data.T = – 0.050t + 78.0T Temperaturet time

0 100 200 300 40020

40

60

80

time / s

Tem

pera

ture

/ °C

Astraightlinehasbeendrawnthroughsomeofthedatapoints.Theequationforthislineisgivenbythedataloggingsoftwareas

T t= - +0 050 78 0. .

whereTistheTemperatureattimet.

(This question continues on the following page)

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(Question 1 continued)

(a) Theheatproducedbythereactioncanbecalculatedfromthetemperaturechange,DT ,usingtheexpressionbelow.

Heatchange=VolumeofCuSO4(aq)́ SpecificheatcapacityofH O2 ×∆T

Describetwoassumptionsmadeinusingthisexpressiontocalculateheatchanges.

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[2]

(b) (i) Use the data presented by the data logging software to deduce the temperaturechange,DT , which would have occurred if the reaction had taken placeinstantaneouslywithnoheatloss.

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[2]

(ii) Calculatetheheat,inkJ,producedduringthereactionusingtheexpressiongiveninpart(a).

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[1]

(c) Thecolourofthesolutionchangedfrombluetocolourless.Deducetheamount,inmoles,ofzincwhichreactedinthepolystyrenecup.

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[1]

(d) Calculatetheenthalpychange,inkJmol–1,forthisreaction.

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[1]


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(e) Anexperimentwasdesignedtoinvestigatehowtheenthalpychangeforadisplacementreaction relates to standard electrode potentials. The standard electrode potentials ofsomehalfreactions,M aq M sn ne+ −+( ) ( ) ,arelistedinTable14oftheDataBooklet.The following metals were available: copper, iron, magnesium, silver and zinc.Excessamountsofeachmetalwereaddedto1.00moldm–3copper(II)sulfatesolution.Thetemperaturechangewasmeasuredandtheenthalpychangecalculated.

(i) Suggest a possible hypothesis for the relationship between the enthalpy changethatoccurswhenthemetal,M,isaddedtocopper(II)sulfate(aq)andthestandardelectrodepotentialforthehalfreactionM aq M sn ne+ −+( ) ( ) .

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[1]

(ii) Sketchagraphonthediagrambelowtoillustrateyourhypothesis. [2]

Enthalpychangefor +

0

–

–4 –3 –2 –1 0 1 2

StandardelectrodepotentialforM aq M sn ne+ −+( ) ( ) /V

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2. (a) But-2-ene is a straight-chain alkenewith formulaC4H8. Themolecule contains bothσandπbonds.

HH

HH

HH

HH

C(3)C(2)

C(4)

C(1)

(i) Explaintheformationoftheπbond.

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[2]

(ii) Foreachofthecarbonatoms,C(1)andC(2),identifythetypeofhybridizationshown.

C(1): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C(2): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[1]

(b) But-2-eneshowsgeometricalisomerism.Drawthestructuralformulaandstatethenameoftheothergeometricalisomer.

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[2]


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(c) Identify the structural formula of an isomer of but-2-enewhich does not decolourizebrominewater,Br2(aq). [1]

(d) The polymerization of the alkenes is one of the most significant reactions of thetwentiethcentury.

(i) Outlinetwo reasonswhythepolymersofthealkenesareofeconomicimportance.

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[2]

(ii) Statethetypeofpolymerizationreactionshownbythealkeneinpart(a).

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[1]

(iii) Deducethestructureoftheresultingpolymershowingthreerepeatingunits. [1]

(iv) Explainwhymonomersareoftengasesorvolatileliquids,butpolymersaresolids.

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[2]

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3. Iron has three main naturally occurring isotopes which can be investigated using a massspectrometer.

(a) Thefirst stage in theoperationof themass spectrometer is vaporization. The iron isthenionized.

(i) Explainwhytheironisionized.

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[2]

(ii) Explainwhyaverylowpressureismaintainedinsidethemassspectrometer.

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[1]

(b) Asampleofironhasthefollowingisotopiccompositionbymass.

Isotope 54Fe 56Fe 57Fe

Relative abundance / % 5.95 91.88 2.17

Calculatetherelativeatomicmassofironbasedonthisdata,givingyouranswertotwo decimal places.

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[2]


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(c) Describethebondinginironandexplaintheelectricalconductivityandmalleabilityofthemetal.

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[4]

(d) StatethefullelectronicconfigurationsofaCuatomandaCu+ion.

Cu: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cu+: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]

(e) Explain the origin of colour in transition metal complexes and use your explanationto suggest why copper(II) sulfate, CuSO4(aq), is blue, but zinc sulfate, ZnSO4(aq),iscolourless.

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[4]

(f) Cu2+(aq)reactswithammoniatoformthecomplexion[Cu(NH3)4]2+.Explainthisreaction

intermsofanacid-basetheory,andoutlinehowthebondisformedbetweenCu2+andNH3.

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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.

4. Magnesium is the eighth most abundant element in the earth’s crust. The successiveionizationenergiesoftheelementareshownbelow.

Ionizationenergy/kJmol

–1

200000

150000

100000

50000

0 1 2 3 4 5 6 7 8 9 10 11 12

Ionizationnumber

(a) (i) Definethetermfirst ionization energyandstatetheequationforthefirstionizationofmagnesium. [3]

(ii) Explainthegeneralincreaseinsuccessiveionizationenergiesoftheelement. [2]

(iii) Explainthelargeincreasebetweenthetenthandeleventhionizationenergies. [3]

(b) Magnesiumcanbeproducedfromtheelectrolysisofmoltenmagnesiumchloride,MgCl2.

(i) Explainhowmoltenmagnesiumchlorideconductsanelectriccurrent. [2]

(ii) Identify the electrode where oxidation occurs during electrolysis of moltenmagnesiumchlorideandstateanequationforthehalf-reaction. [2]

(iii) Explain why magnesium is not formed during the electrolysis of aqueousmagnesiumchloridesolution. [1]


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(c) ThelatticeenthalpyofmagnesiumchloridecanbecalculatedfromtheBorn-Habercycleshownbelow.

MgClª(s)

Mg (s) + Clª(g)

Mg (g) + Clª(g)

Mg (g) + 2Cl (g)

I = +148 kJ

II

V = _642 kJ

III = +738 + 1451 kJ IV

MgÛ±(g) + 2eÑ + 2Cl (g)

MgÛ±(g) + 2ClÑ(g)

ëHlatÀ(MgClª)

H

(i) IdentifytheenthalpychangeslabelledbyIandVinthecycle. [2]

(ii) Use the ionization energies given in the cycle above and further data from theDataBooklettocalculateavalueforthelatticeenthalpyofmagnesiumchloride. [4]

(iii) Thetheoreticallycalculatedvalueforthelatticeenthalpyofmagnesiumchlorideis+2326kJ.Explainthedifferencebetweenthetheoreticallycalculatedvalueandtheexperimentalvalue. [2]

(iv) TheexperimentallatticeenthalpyofmagnesiumoxideisgiveninTable13oftheDataBooklet. Explainwhymagnesiumoxidehasahigher latticeenthalpy thanmagnesiumchloride. [2]

(d) (i) State whether aqueous solutions of magnesium oxide and magnesium chlorideareacidic,alkalineorneutral. [1]

(ii) Stateanequationforthereactionbetweenmagnesiumoxideandwater. [1]

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5. Considerthefollowingsequenceofreactions.

RCH RCH Br RCH OH 3 2 2

reaction reaction1 2

RCH3isanunknownalkaneinwhichRrepresentsanalkylgroup.

(a) Thealkanecontains82.6%bymassofcarbon.Determineitsempiricalformula,showingyourworking. [3]

(b) A1.00ggaseoussampleofthealkanehasavolumeof385cm3atstandardtemperatureandpressure.Deduceitsmolecularformula. [2]

(c) Statethereagentandconditionsneededforreaction 1. [2]

(d) Reaction 1 involves a free-radical mechanism. Describe the stepwise mechanism,bygivingequationstorepresenttheinitiation,propagationandterminationsteps. [4]

(e) Themechanisminreaction 2isdescribedasSN2.Explainthemechanismofthisreactionusingcurlyarrowstoshowthemovementofelectronpairs,anddrawthestructureofthetransitionstate. [3]

(f) There are four structural isomers with the molecular formula C4H9Br. One of thesestructural isomers exists as two optical isomers. Draw diagrams to represent thethree-dimensionalstructuresofthetwoopticalisomers. [2]

(g) All the isomers can by hydrolysed with aqueous sodium hydroxide solution.When the reactionof oneof these isomers,X,was investigated the followingkineticdatawereobtained.

Experiment Initial [X] / mol dm–3

Initial [OH–] / mol dm–3

Initial rate of reaction / mol dm–3 min–1

1 2 0 10 2. × − 2 0 10 2. × − 4 0 10 3. −×

2 2 0 10 2. × − 4 0 10 2. −× 4 0 10 3. −×

3 4 0 10 2. −× 4 0 10 2. −× 8 0 10 3. −×

(i) Deducetherateexpressionforthereaction. [3]

(ii) Determinethevalueoftherateconstantforthereactionandstateitsunits. [2]

(iii) StatethenameofisomerXandexplainyourchoice. [2]

(iv) Stateequationsforthestepsthattakeplaceinthemechanismofthisreactionandstatewhichofthestepsisslowandwhichisfast. [2]

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6. TheHaberprocessenablesthelarge-scaleproductionofammonianeededtomakefertilizers.

(a) TheequationfortheHaberprocessisgivenbelow.

N g H g NH g2 2 33 2( ) ( ) ( )+

Thepercentageofammoniaintheequilibriummixturevarieswithtemperature.

PercentageofN

H3in

equilibriummixture

Temperature

(i) Usethegraphtodeducewhethertheforwardreactionisexothermicorendothermicandexplainyourchoice. [2]

(ii) Stateandexplaintheeffectofincreasingthepressureontheyieldofammonia. [2]

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

(iv) Amixtureof1.00molN2and3.00molH2wasplacedina1.0dm3flaskat400 °C.

Whenthesystemwasallowedtoreachequilibrium,theconcentrationofNH3wasfoundtobe0.062moldm–3.Determinetheequilibriumconstant,Kc,ofthereactionatthistemperature. [3]

(v) IronisusedasacatalystintheHaberprocess.StatetheeffectofacatalystonthevalueofKc. [1]

(b) Ammoniacanbeconvertedintonitricacid,HNO3(aq),andhydrocyanicacid,HCN(aq).ThepKaofhydrocyanicacidis9.21.

(i) Distinguishbetweenthetermsstrongandweak acidandstatetheequationsusedtoshowthedissociationofeachacidinaqueoussolution. [3]

(ii) Deduce the expression for the ionization constant,Ka, of hydrocyanic acid andcalculateitsvaluefromthepKavaluegiven. [2]

(iii) Useyouranswerfrompart(b)(ii)tocalculatethe[H+]andthepHofanaqueoussolution of hydrocyanic acid of concentration 0.108moldm–3. State oneassumptionmadeinarrivingatyouranswer. [4]


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(c) Asmallpieceofmagnesiumribbonisaddedtosolutionsofnitricandhydrocyanicacidofthesameconcentrationatthesametemperature.Describetwoobservationsthatwouldallowyoutodistinguishbetweenthetwoacids. [2]

(d) Astudentdecidedtoinvestigatethereactionsofthetwoacidswithseparatesamplesof0.20moldm–3sodiumhydroxidesolution.

(i) Calculate thevolumeof thesodiumhydroxidesolutionrequired to reactexactlywitha15.0cm3solutionof0.10moldm–3nitricacid. [1]

(ii) Thefollowinghypothesiswassuggestedbythestudent:“Sincehydrocyanicacidis aweak acid itwill reactwith a smaller volumeof the 0.20moldm–3 sodiumhydroxidesolution.”Commentonwhetherornotthisisavalidhypothesis. [1]

(iii) UseTable16oftheDataBooklettoidentifyasuitableindicatorforthetitrationofsodiumhydroxideandhydrocyanicacid. [1]

(e) Thegraphbelowshowshowtheconductivityofthetwoacidschangeswithconcentration.

Conductivity

Acid 1

Acid 2

0.05 0.10Concentration/moldm–3

IdentifyAcid 1andexplainyourchoice. [2]

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7. Hydrazine,N2H4,isavaluablerocketfuel.

(a) (i) DrawtheLewis(electrondot)structureforN2H4showingallvalenceelectrons. [1]

(ii) StateandexplaintheH–N–Hbondangleinhydrazine. [3]

(b) Hydrazine and ethene, C2H4, are hydrides of adjacent elements in the periodic table.Theboilingpointofhydrazineismuchhigherthanthatofethene.Explainthisdifferenceintermsoftheintermolecularforcesineachcompound. [2]

(c) Theequationforthereactionbetweenhydrazineandoxygenisgivenbelow.

N H l O g N g H O l2 4 2 2 22( ) ( ) ( ) ( )+ → +

(i) The enthalpy change of formation,DH fÖ, of liquid hydrazine is 50.6kJmol–1.

Usethisvalue,togetherwithdatafromTable12oftheDataBooklet,tocalculatetheenthalpychangeforthisreaction. [3]

(ii) UsethebondenthalpyvaluesfromTable10oftheDataBooklettodeterminetheenthalpychangeforthisreaction. [3]

(iii) Identify the calculation that produces the most accurate value for the enthalpychangeforthereactiongivenandexplainyourchoice. [3]

(iv) CalculateDSÖforthereactionusingthedatabelowandcommentonitsmagnitude. [3]

Substance S / JK mol1 1Ö - -

O2(g) 205

N2(g) 191

H2O(l) 69.9

N2H4(l) 121

(v) CalculateDGÖforthereactionat298K. [2]

(vi) Predict, giving a reason, the spontaneity of the reaction above at both high andlowtemperatures. [2]


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(d) ThereactionbetweenN2H4(aq)andHCl(aq)canberepresentedbythefollowingequation.

N H aq HCl aq N H aq Cl aq2 4 2 622 2( ) ( ) ( ) ( )+ → ++ −

(i) Identifythetypeofreactionthatoccurs. [1]

(ii) PredictthevalueoftheH–N–HbondangleinN2H62+. [1]

(iii) SuggestthetypeofhybridizationshownbythenitrogenatomsinN2H62+. [1]

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88106102 - WordPress.com · – 12 – N10/4/CHEMI/HP2/ENG/TZ0/XX 5. Consider the following sequence of reactions. RCH RCH Br RCH OH 3 2 2 reaction 1 reaction 2