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8810-6105 13 pages

N10/4/CHEMI/SP2/ENG/TZ0/XX

Thursday 11 November 2010 (afternoon)

CHEMISTRYSTANDARD 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 one question 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.

1 hour 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 24.821222324

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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(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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(ii) Statetheassumptionmadeinpart(b)(i).

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

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(c) Thecolourofthesolutionchangedfrombluetocolourless.Deducetheamount,inmoles,ofzincwhichreactedinthepolystyrenecup.

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(d) Calculatetheenthalpychange,inkJmol–1,forthisreaction.

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(e) Anexperimentwasdesignedtoinvestigatehowtheenthalpychangeforadisplacementreactionrelatestothereactivitiesofthemetalsinvolved.Thefollowingmetalsinorderofdecreasingreactivitywereavailable.

Magnesium most reactive

Uranium

Zinc

Iron

Copper

Silver least reactive

Excessamountsofeachmetalwereaddedto1.00moldm–3copper(II)sulfatesolution.Thetemperaturechangewasmeasuredandtheenthalpychangecalculated.

(i) Suggestapossiblehypothesisfortherelationshipbetweentheenthalpychangeofthereactionandthereactivityofthemetal.

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[1]

(ii) Sketchagraphonthediagrambelowtoillustrateyourhypothesis. [1]

Enthalpychangefor

M(s

Cu

aqC

u(s

Maq

)(

))

()

+→

++

+2

2

+

0

–

Mg U Zn Fe Cu Ag

Metal

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2. Thealkenesareanexampleofahomologousseries.

(a) Statethenameofthealkeneshown. [1]

Key:

Carbonatom

Hydrogenatom

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(b) Brominewater,Br2(aq),canbeusedtodistinguishbetweenthealkanesandthealkenes.

(i) Describethecolourchangeobservedwhenthealkeneshowninpart(a)isaddedtobrominewater.

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[1]

(ii) Drawthestructuralformulaandstatethenameoftheproductformed.

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[2]


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(c) 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]

(c) Calculatethenumberofelectronsintheion56Fe2+.

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(d) Describethebondinginironandexplaintheelectricalconductivityandmalleabilityofthemetal.

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SECTION B

Answer one question. 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. Ethene,C2H4,andhydrazine,N2H4,arehydridesofadjacentelementsintheperiodictable.

(a) (i) DrawLewis(electrondot)structuresforC2H4andN2H4showingallvalenceelectrons. [2]

(ii) State andexplain theH–C–Hbondangle in etheneand theH–N–Hbondangleinhydrazine. [5]

(b) Thepolarityofamoleculecanbeexplainedintermsofelectronegativity.

(i) Definethetermelectronegativity. [2]

(ii) Compare the relative polarities of the C–H bond in ethene and the N–H bondinhydrazine. [1]

(iii) Hydrazine is a polarmolecule and ethene is non-polar. Explainwhy ethene isnon-polar. [1]

(c) The boiling point of hydrazine is much higher than that of ethene. Explain thisdifferenceintermsoftheintermolecularforcesineachcompound. [2]

(d) Hydrazineisavaluablerocketfuel.

Theequationforthereactionbetweenhydrazineandoxygenisgivenbelow.

N H g O g N g H O g2 4 2 2 22( ) ( ) ( ) ( )+ → +

UsethebondenthalpyvaluesfromTable10oftheDataBooklettodeterminetheenthalpychangeforthisreaction. [3]

(e) State thenameof theproductand identify the typeof reactionwhichoccursbetweenetheneandhydrogenchloride. [2]

(f) 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]

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5. Considerthefollowingsequenceofreactions.

RCH RCH Br RCH OH 3 2 2

reaction reaction reaction1 2 3 → → → RCOOH

RCH3isanunknownalkaneinwhichRrepresentsanalkylgroup.

(a) Thealkanecontains81.7%bymassofcarbon.Determineitsempiricalformula,showingyourworking. [3]

(b) Equal volumes of carbon dioxide and the unknown alkane are found to have thesamemass,measuredtoanaccuracyoftwosignificantfigures,atthesametemperatureandpressure.Deducethemolecularformulaofthealkane. [1]

(c) (i) Statethereagentandconditionsneededforreaction 1. [2]

(ii) Statethereagent(s)andconditionsneededforreaction 3. [2]

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

(e) Themechanisminreaction 2isdescribedasSN2.

(i) StatethemeaningofeachofthesymbolsinSN2. [1]

(ii) Explainthemechanismofthisreactionusingcurlyarrowstoshowthemovementofelectronpairs,anddrawthestructureofthetransitionstate. [3]

(f) Propan-1-olhastwostructuralisomers.

(i) Deducethestructuralformulaofeachisomer. [2]

(ii) Identifytheisomerfrompart(f)(i)whichhasthehigherboilingpointandexplainyourchoice.Refertobothisomersinyourexplanation. [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) Explaintheeffectofincreasingthetemperatureontherateofreaction. [2]

(b) Fertilizersmaycausehealthproblemsforbabiesbecausenitratescanchangeintonitritesinwaterusedfordrinking.

(i) Defineoxidationintermsofoxidationnumbers. [1]

(ii) Deducetheoxidationstatesofnitrogeninthenitrate,NO3–,andnitrite,NO2

–,ions. [1]

(c) Thenitriteionispresentinnitrousacid,HNO2,whichisaweakacid.Thenitrateionispresentinnitricacid,HNO3,whichisastrongacid. Distinguishbetweenthetermsstrongandweak acidandstatetheequationsusedtoshowthedissociationofeachacidinaqueoussolution. [3]

(d) Asmallpieceofmagnesiumribbonisaddedtosolutionsofnitricandnitrousacidofthesameconcentrationatthesametemperature.Describetwoobservationsthatwouldallowyoutodistinguishbetweenthetwoacids. [2]


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(e) Astudentdecidedtoinvestigatethereactionsofthetwoacidswithseparatesamplesof0.20moldm–3sodiumhydroxidesolution.

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

(ii) The following hypothesis was suggested by the student: “Since nitrous acidis aweak acid itwill reactwith a smaller volumeof the 0.20moldm–3 sodiumhydroxidesolution.”Commentonwhetherornotthisisavalidhypothesis. [1]

(f) Thegraphbelowshowshowtheconductivityofthetwoacidschangeswithconcentration.

Conductivity

Acid 1

Acid 2

0.05 0.10Concentration/moldm–3

IdentifyAcid 1andexplainyourchoice. [2]

(g) Nitricacidreactswithsilverinaredoxreaction.

__ ( ) __ ( ) ____ __ ( ) __ ( ) ____Ag s NO aq Ag aq NO g+ + → + +− +3

Usingoxidationnumbers,deducethecompletebalancedequationforthereactionshowingallthereactantsandproducts. [3]

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