22096108isite.lps.org/sputnam/LHS_IB/IBChemistry/IBChemExams/ChemHL2a_… · CHEMISTRY HIGHER lEvEl...

2209-6108 19 pages

M09/4/CHEMI/HP2/ENG/TZ1/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. Biodiesel makes use of plants’ ability to fix atmospheric carbon by photosynthesis.Many companies and individuals are now using biodiesel as a fuel in order to reducetheir carbon footprint. Biodiesel can be synthesized from vegetable oil according to thefollowingreaction.

vegetableoil methanol glycerol biodiesel

(a) Identifytheorganicfunctionalgrouppresentinbothvegetableoilandbiodiesel.

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[1]

(b) For part of her extended essay investigation into the efficiency of the process,a student reacted a pure sample of a vegetable oil (whereR=C17H33)withmethanol.Therawdatarecordedforthereactionisbelow.

Massofoil =1013.0g Massofmethanol = 200.0g Massofsodiumhydroxide = 3.5g Massofbiodieselproduced= 811.0g

Therelativemolecularmassoftheoilusedbythestudentis885.6.Calculatetheamount(inmoles)oftheoilandthemethanolused,andhencetheamount(inmoles)ofexcessmethanol.

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[3]

(This question continues on the following page)

3CH3OH(l)(l)+ (l)+3

H C

C

H

O

H

CH

H

O

O COC

R

OC R

R

O

CH3 O C RO

H C

H

OH

CH OH

CH OH

H

NaOH(s)(l)

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(Question 1 continued)

(c) The reversible arrows in the equation indicate that the production of biodiesel is anequilibriumprocess.

(i) Statewhatismeantbythetermdynamic equilibrium.

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[1]

(ii) Using the abbreviations [vegetable oil], [methanol], [glycerol] and [biodiesel]deducetheequilibriumconstantexpression(Kc)forthisreaction.

[1]

(iii) Suggestareasonwhyexcessmethanolisusedinthisprocess.

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[1]

(iv) Stateandexplaintheeffectthattheadditionofthesodiumhydroxidecatalystwillhaveonthepositionofequilibrium.

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[2]

(d) Thereactantshadtobestirredvigorouslybecausetheyformedtwodistinctlayersinthereactionvessel.Explainwhytheyformtwodistinctlayersandwhystirringincreasestherateofreaction.

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[2]


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(e) Calculatethepercentageyieldofbiodieselobtainedinthisprocess.

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[2]

(f) Whenbiodieseliscombusteditproducescarbondioxide.Explainwhytheuseofbiodieselasafueldoesnotsignificantlycontributetoglobalwarming.

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[1]

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2. (a) ThepKavalueforpropanoicacidisgiveninTable15oftheDataBooklet.

(i) Statetheequationforthereactionofpropanoicacidwithwater.

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[1]

(ii) Calculatethehydrogenionconcentration(inmoldm–3)ofanaqueoussolutionof0.100moldm–3propanoicacid.

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[2]


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(b) Thegraphbelowshowsacomputersimulationofatitrationof25.0cm3of0.100moldm–3hydrochloricacidwith0.100moldm–3sodiumhydroxideandthepHrangeofphenolredindicator.

pH

14.0

12.0

10.0

8.0

6.0

4.0

2.0

00 5 10 15 20 25 30 35 40 45 50

Volumeof0.100moldm–3NaOH(aq)added/cm3

Sketchthegraphthatwouldbeobtainedforthetitrationof25.0cm3of0.100moldm–3

propanoicacidwith0.100moldm–3potassiumhydroxideusingbromophenolblueasanindicator. (ThepH rangeofbromophenolblue canbe found inTable16of theDataBooklet).

pH

14.0

12.0

10.0

8.0

6.0

4.0

2.0

00 5 10 15 20 25 30 35 40 45 50

Volumeof0.100moldm–3KOH(aq)added/cm3

[3]

red

yellowindicatorrange

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3. TwostudentswereaskedtouseinformationfromtheDataBooklettocalculateavaluefortheenthalpyofhydrogenationofethenetoformethane.

C H (g) H (g) C H (g)2 4 2 2 6+ →

JohnusedtheaveragebondenthalpiesfromTable10.MaritusedthevaluesofenthalpiesofcombustionfromTable12.

(a) CalculatethevaluefortheenthalpyofhydrogenationofetheneobtainedusingtheaveragebondenthalpiesgiveninTable10.

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[2]

(b) Determinethevaluefortheenthalpyofhydrogenationofetheneusingthevaluesfortheenthalpiesofcombustionofethene,hydrogenandethanegiveninTable12.

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[2]

(c) SuggestonereasonwhyJohn’sanswerisslightlylessaccuratethanMarit’sanswerandcalculatethepercentagedifference.

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[2]


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(d) Johnthendecidedtodeterminetheenthalpyofhydrogenationofcyclohexenetoproducecyclohexane.

C H l H g C H l6 10 2 6 12( ) ( ) ( )+ →

(i) Usetheaveragebondenthalpiestodeduceavaluefortheenthalpyofhydrogenationofcyclohexene.

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[1]

(ii) Thepercentagedifferencebetween these twomethods (averagebond enthalpiesandenthalpiesofcombustion) isgreater forcyclohexene than itwas forethene.John’shypothesiswasthatitwouldbethesame.Determinewhytheuseofaveragebond enthalpies is less accurate for the cyclohexene equation shown above,thanitwasforethene.Deducewhatextrainformationisneededtoprovideamoreaccurateanswer.

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[2]

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4. Thepercentageof iron(II) ions,Fe2+, inavitamin tabletcanbeestimatedbydissolving thetablet indilute sulfuric acid and titratingwith standardpotassiummanganate(VII) solution,KMnO4(aq).Duringtheprocessiron(II)isoxidizedtoiron(III)andthemanganate(VII)ionisreducedtothemanganese(II)ion,Mn2+(aq).Itwasfoundthatonetabletwithamassof1.43grequired11.6cm3of2.00× 10–2moldm–3KMnO4(aq)toreachtheend-point.

(a) (i) Statethehalf-equationfortheoxidationoftheiron(II)ions.

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[1]

(ii) Statethehalf-equationforthereductionoftheMnO4–ionsinacidicsolution.

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[1]

(iii) Deducetheoverallredoxequationforthereaction.

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[1]

(b) (i) Calculate the amount, in moles, of MnO4– ions present in 11.6 cm3 of

2.00× 10–2moldm–3KMnO4(aq).

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[1]

(ii) Calculatetheamount,inmoles,ofFe2+ionspresentinthevitamintablet.

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[1]

(iii) DeterminethepercentagebymassofFe2+ionspresentinthevitamintablet.

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[2]

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5. Sodiumoxide,Na2O,isawhitesolidwithahighmeltingpoint.

(a) Explainwhysolidsodiumoxideisanon-conductorofelectricity.

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[1]

(b) Molten sodium oxide is a good conductor of electricity. State the half-equation forthe reaction occurring at the positive electrode during the electrolysis of moltensodiumoxide.

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[1]

(c) (i) Statetheacid-basenatureofsodiumoxide.

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[1]

(ii) Statetheequationforthereactionofsodiumoxidewithwater.

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[1]

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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.

6. (a) DrawtheLewisstructures,statetheshapeandpredictthebondanglesforthefollowingspecies.

(i) PCl3 [3]

(ii) NH2– [3]

(iii) XeF4 [3]

(b) ConsiderthefollowingBorn-Habercycle:

K + KBr

a = 90.0 c = 112

b = 418 d = 342

K+(g) + Br–(g)

e = 670

(s)(s)

(g) (g)K Br

Themagnitudesforeachoftheenthalpychanges(atoe)aregiveninkJmol–1buttheirsigns(+or–)havebeenomitted.

(i) Statethenamesfortheenthalpychangescandd. [2]

(ii) Deducewhichtwooftheenthalpychangesatoehavenegativesigns. [1]

(iii) Determinethevaluefortheenthalpyofformationofpotassiumbromide. [2]

(iv) Explainwhythequantitativevalueforthelatticeenthalpyofcalciumbromideislargerthanthevalueforthelatticeenthalpyofpotassiumbromide. [2]


12 2Br l( )

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(c) (i) Compare the formationof a sigma ( )σ and a pi (π) bondbetween two carbonatomsinamolecule. [2]

(ii) Identifyhowmanysigmaandpibondsarepresentinpropene,C3H6. [2]

(iii) Deduceallthebondanglespresentinpropene. [2]

(iv) Explainhowtheconceptofhybridizationcanbeusedtoexplainthebondinginthetriplebondpresentinpropyne. [3]

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7. (a) Anelectrochemicalcellismadefromanironhalf-cellconnectedtoacobalthalf-cell:

voltmeter

Co

V

Fe

Co2+(aq) Fe2+(aq)

The standard electrode potential for Fe (aq) 2e Fe(s)2+ −+ is –0.45V. The totalcell potential obtainedwhen the cell is operatingunder standard conditions is 0.17V.Cobaltisproducedduringthespontaneousreaction.

(i) Define the termstandard electrode potentialandstate themeaningof theminussigninthevalueof–0.45V. [3]

(ii) Calculatethevalueforthestandardelectrodepotentialforthecobalthalf-cell. [1]

(iii) Deducewhichspeciesactsastheoxidizingagentwhenthecellisoperating. [1]

(iv) Deduce the equation for the spontaneous reaction taking place when the ironhalf-cellisconnectedinsteadtoanaluminiumhalf-cell. [2]

(v) Explainthefunctionofthesaltbridgeinanelectrochemicalcell. [2]

(b) Deducetheoxidationnumberofcobaltinthefollowingspecies.

(i) [Co(H2O)6]2+

(ii) Co2(SO4)3

(iii) [CoCl4]2–

[1]

[1]

[1]


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(c) Anelectrolyticcellismadeusingaverydilutesolutionofsodiumchloride.

(i) Drawa labelleddiagramof thecell. Useanarrow toshowthedirectionof theelectronflowandidentifythepositiveandnegativeelectrodes. [3]

(ii) Givetheformulasofalltheionspresentinthesolution. [2]

(iii) Predicttheproductsobtainedateachelectrodeandstatethehalf-equationfortheformationofeachproduct. [3]

(iv) Deducethemolarratiosoftheproductsobtainedatthetwoelectrodes. [1]

(d) Predicttheproductsbygivingtherelevanthalf-equationforthereactionoccurringateachelectrodeiftheelectrolyteofthecelldescribedinpart(c)waschangedto:

(i) concentratedsodiumchloride

(ii) moltensodiumbromide

[2]

[2]

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8. (a) (i) Describeandexplaintheoperationofamassspectrometer. [5]

(ii) State three factors that affect the degree of deflection of ions in amassspectrometer. [3]

(iii) Strontiumexistsasfournaturally-occurringisotopes.Calculatetherelativeatomicmassofstrontiumtotwodecimalplacesfromthefollowingdata.

isotope Percentage abundanceSr-84 0.56Sr-86 9.90Sr-87 7.00Sr-88 82.54

[2]

(b) Thegraphofthefirstionizationenergyplottedagainstatomicnumberforthefirsttwentyelementsshowsperiodicity.

Firstionizationenergy/kJmol–1

2500

2000

1500

1000

500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Atomicnumber

(i) Define the term first ionization energy and state what is meant by thetermperiodicity. [2]

(ii) Explainhow information from thisgraphprovidesevidence for theexistenceofmainenergylevelsandsub-levelswithinatoms. [4]

(iii) Statewhatismeantbythetermsecond ionization energy. [1]


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–17–

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(iv) Sketchandexplaintheshapeof thegraphobtainedfor thesuccessiveionizationenergiesofpotassiumusingalogarithmicscaleforionizationenergyonthey-axisagainstnumberofelectronsremovedonthex-axis. [4]

(c) (i) Statethefullelectronicconfigurationsofcopper,Cu,andthecopper(I)ion,Cu+. [2]

(ii) Explain why copper(II) compounds in aqueous solution are coloured whereasscandium(III)compoundsinaqueoussolutionarecolourless. [2]

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9. (a) But-1-ene and 1-aminobutane (1-butylamine) can both be prepared from1-bromobutane.

(i) State the equation (using structural formulas) and the necessary reagents andconditionsforthepreparationofbut-1-enefrom1-bromobutane. [3]

(ii) Identify the type of reaction and explain themechanism for the preparation ofbut-1-enefrom1-bromobutaneusingcurlyarrows to represent themovementofelectronpairs. [3]

(iii) Statetheequation(usingstructuralformulas)forthepreparationof1-aminobutanefrom1-bromobutane.Statethenecessaryreagentsandconditionsofthereaction. [3]

(iv) Explainthemechanismforthepreparationof1-aminobutanefrom1-bromobutaneusingcurlyarrowstorepresentthemovementofelectronpairs. [4]

(b) 2-bromobutaneand2-bromo-2-methylpropanearetwoisomersof1-bromobutane.

(i) Draw the structures of the two mirror images of the isomer that can exhibitopticalisomerism. [2]

(ii) Describe how the two optical isomers can be distinguished practically usingplane-polarizedlight. [2]

(iii) Explainwhythemechanismofthereactionwillbedifferentif1-bromobutaneisreplaced by 2-bromo-2-methylpropane to form 2-amino-2-methylpropane in thereactioninpart(a)(iv). [3]


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(c) Oneformofnylonhastherepeatingunit:

N (CH2)6 N

H H

C

O

(CH2)8 C

O

(i) Identifythecircledfunctionalgroup. [1]

(ii) Deducethestructuresofthetwomonomersusedtomakethisformofnylon. [2]

(iii) Nylonisacondensationpolymer.Anothercondensationpolymercanbeformedbyreactingethane-1,2-diolwithbenzene-1,4-dicarboxylicacid.

H C

OH

H

C

OH

H

H

HO C

O

C

O

OH

ethane-1,2-diol benzene-1,4-dicarboxylicacid

Deducetheequationforthisreactionusingnmolesofeachreactant. [2]

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