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M09/4/CHEMI/SP2/ENG/TZ1/XX+

Monday 18 May 2009 (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 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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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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(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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(d) Thereactantshadtobestirredvigorouslybecausetheyformedtwodistinctlayersinthereactionvessel.Explainwhytheyformtwodistinctlayersandwhystirringincreasestherateofreaction.

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(Question 1 continued)

(e) Calculatethepercentageyieldofbiodieselobtainedinthisprocess.

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[2]

(f) Whenbiodieseliscombusteditproducescarbondioxide.Explainwhytheuseofbiodieselasafueldoesnotsignificantlycontributetoglobalwarming.

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2. TwostudentswereaskedtouseinformationfromtheDataBooklettocalculateavaluefortheenthalpyofhydrogenationofethenetoformethane.

C H (g) H (g) C H (g)2 4 2 2 6+ →

JohnusedtheaveragebondenthalpiesfromTable10.MaritusedthevaluesofenthalpiesofcombustionfromTable12.

(a) CalculatethevaluefortheenthalpyofhydrogenationofetheneobtainedusingtheaveragebondenthalpiesgiveninTable10.

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[2]

(b) MaritarrangedthevaluesshefoundinTable12intoanenergycycle.

C2H4(g) + H2(g) C2H6(g)

3O2

2CO2(g) + 3H2O

–141

1kJmol

–1

–286

kJmol

–1

–1560 kJ m

ol–1

(hydrogenation)

(l)

Calculatethevaluefortheenthalpyofhydrogenationofethenefromtheenergycycle.

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[1]

(c) SuggestonereasonwhyJohn’sanswerisslightlylessaccuratethanMarit’sanswer.

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[1]

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ë ÖH

1 22

O

312

2O

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(Question 2 continued)

(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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3. 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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4. (a) Defineoxidationintermsofelectrontransfer.

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[1]

(b) Chlorine can be made by reacting concentrated hydrochloric acid with potassiummanganate(VII),KMnO4.

2KMnO (aq) 16HCl(aq) 2MnCl (aq) 2KCl(aq) 5Cl (aq) 8H O(aq)4 2 2 2+ → + + +

(i) StatetheoxidationnumberofmanganeseinKMnO4andinMnCl2.

KMnO4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MnCl2 ........................................................

[2]

(ii) Deducewhichspecieshasbeenoxidizedin thisreactionandstate thechangeinoxidationnumberthatithasundergone.

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[2]

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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.

5. (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

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(Question 5 continued)

(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) State the electron arrangement of argon and explain why the noble gases,helium, neon and argon show the highest first ionization energies for theirrespectiveperiods. [3]

(iii) A graph of atomic radius plotted against atomic number shows that the atomicradiusdecreasesacrossaperiod.Explainwhychlorinehasasmalleratomicradiusthansodium. [1]

(iv) Explainwhyasulfideion,S2–,islargerthanachlorideion,Cl–. [1]

(v) ExplainwhythemeltingpointsoftheGroup1metals ( )Li Cs→ decreasedownthegroupwhereas themeltingpointsof theGroup7elements ( )F I→ increasedownthegroup. [3]

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6. (a) (i) Draw the Lewis structures for carbonmonoxide, CO, carbon dioxide, CO2 andmethanol,CH3OH. [3]

(ii) List,with an explanation, the three compounds inorderof increasing carbon tooxygenbondlength(shortestfirst). [2]

(b) Predicttheshapeandbondanglesforthefollowingspecies:

(i) CO2

(ii) CO32–

(iii) BF4–

[2]

[2]

[2]

(c) (i) DefineaBrønsted-Lowryacid. [1]

(ii) Deducethetwoacidsandtheirconjugatebasesinthefollowingreaction:

H O (l) NH (aq) OH (aq) NH (aq)2 3 4+ +− +

[2]

(iii) Explainwhythefollowingreactioncanalsobedescribedasanacid-basereaction.

F (g) BF (g) BF (s)3 4− −+

[2]

(d) Ethanoicacid,CH3COOH,isaweakacid.

(i) Definethetermweak acidandstatetheequationforthereactionofethanoicacidwithwater. [2]

(ii) Vinegar,whichcontainsethanoicacid,canbeused tocleandepositsofcalciumcarbonatefromtheelementsofelectrickettles.Statetheequationforthereactionofethanoicacidwithcalciumcarbonate. [2]

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7. (a) Three compounds with similar relative molecular masses are butane, propanal andpropan-1-ol.

(i) List the three compounds in order of increasing boiling point (lowest first) andexplainthedifferencesintheirboilingpoints. [4]

(ii) Predict, with an explanation, which of the three compounds is least soluble ormiscibleinwater. [2]

(iii) When propan-1-ol is oxidized using a warm acidified solution of potassiumdichromate(VI)twodifferentorganicproductscanbeobtained.Deducethenameandstructuralformulaforeachofthesetwoproducts. [3]

(iv) Propan-2-olisanisomerofpropan-1-ol.Drawthestructureofpropan-2-ol. [1]

(v) Identifytheclassofalcoholsthatpropan-2-olbelongstoandstatethenameoftheorganicproductformedwhenitisoxidizedbyanacidifiedsolutionofpotassiumdichromate(VI). [2]

(b) Ethanolcanbeformedfrometheneinatwostepreaction:

H

C

H

C

H

H

H C

H

H

C

Br

H

H H C

H

C

H

OH

H

H(g) (g) (l)step 1 step 2

(i) Statethenameofthereagentusedforstep1. [1]

(ii) Statethenameofthereagentandtheconditionsusedforstep2. [2]

(iii) Themechanisminvolvedinstep2isSN2.Explainhowthereactionproceedsusingcurlyarrowstorepresentthemovementofelectronpairs. [3]

(iv) Outlinehowethanolismanufacturedfrometheneinindustryandstateoneimportantcommercialuseofethanol. [2]

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