考试真题化学

UNIVERSITYOFCAMBRIDGEINTERNATIONALEXAMINATIONS

GCEAdvancedSubsidiaryLevelandGCEAdvancedLevel

MARKSCHEMEfortheMay/June2007questionpaper

9701/31

9701CHEMISTRY

Paper31(AdvancedPracticalSkills1),umrawmark40

Thismarkschemeispublishedasanaidtoteachersandcandidates,toindicatetherequirementsoftheexamination.ItshowsthebasisonwhichExaminerswereinstructedtoawardmarks.ItdoesnotindicatethedetailsofthediscussionsthattookceatanExaminers’meetingbeforemarkingbegan.

AllExaminersareinstructedthatalternativecorrectanswersandunexpectedapproachesincandidates’scriptsmustbegivenmarksthatfairlyreflecttherelevantknowledgeandskillsdemonstrated.

Markschemesmustbereadinconjunctionwiththequestionpapersandthereportontheexamination.

CIEwillnotenterintodiscussionsorcorrespondence onnectionwiththesemarkschemes.

CIEispublishingthemarkschemesfortheMay/June2007questionpapersformostIGCSE,GCEAdvancedLevelandAdvancedSubsidiaryLevelsyllabusesandsomeOrdinaryLevelsyllabuses.

GenericMarkSchemeforPapers31and32

Skill

Breakdownofmarks

Manipulation,measurementandobservation

16marks

Successfulcollectionofdataandobservations

8marks

Decisionsrelatingtomeasurementsorobservations

8marks

Presentationofdataandobservations

12marks

Recordingdataandobservations

5marks

Disyofcalculationandreasoning

3marks

Datalayout

4marks

ysis,conclusionsandevaluation

12marks

Interpretationofdataorobservationsandidentifyingsourcesoferror

6marks

Drawingconclusions

5marks

Suggestingimprovements

1mark

Question

Sections

Indicativematerial

Mark

1(a)(i)

PDO

Tabulatesinitialandfinalburettereadingsandvolume

[1]

Layout

addedineachofthetables

Tabulationmaybeverticalorhorizontal.

Ignoreabsenceofunits

DoNOTawardthismarkifanyfinalandinitialburette

readingsareinvertedor50isusedastheinitialburette

reading

()

PDO

Bothburettereadingsinthedilutiontableandfinaland

[1]

Recording

initialburettereadingsforallaccuratetitresinthetitration

3

tablerecordedtothenearest0.05cm.

Treatalltitresas“accurate”unlesslabelledroughor1st

titreistolowerprecisionthansubsequenttitres

(i)

MMO

Followsinstructions–Roughplussufficientaccurate

[1]

Collection

titrations

AwardthismarkiftherearethreeormoretitresOR

wheretwotitresonlyhavebeenrecorded

theyarewithin0.20cm(neitherlabelledasrough).

Thefirsttitredoesnothavetobelabelledrough

(iv)

MMO

Hasatleasttwouncorrectedtitreswithin0.1cm3

[1]

Decisions

Accuracy(v)and(vi)

Give2marksifdifferencetoSupervisoris0.3orless

[2]

Give1ofthesetwomarksforadifferenceof0.3+to0.5Give0marksforadifferencegreaterthan0.5

[6]

(b)

ACE

Interpretation

Candidateselects/calculatesappropriate“average”from

3

anyuncorrectedtitrevalueswithin0.20cm.

[1]

[1]

(c)(i)and()

ACE

Interpretation

Examinercheckseachofthefirstfourstepsofthecalculation.

Awardtwomarksifallstepsarechemicallycorrect.Withhold1markforeachchemicalerror–nonegativemarks.Count pletedstepsaschemicalerrors.

voldiluted

x0.50

1000

xtitre250

x1x1000

2 25 (Potential2errors)

x106

Workingshownineachstepattempted

3or4significantfiguresinfinalanswergivenforeachofthefirstfoursteps

Answertolastsectioniscorrectlyevaluatedto3sfusingcandidate’svalueto4thstep.

(Answermaybefromfinalanswertostep4orusenumbercarriedoncalculator)

[2]

(i)

(iv)

PDO

Disy

[1]

[1]

(v)

[1]

[5]

Question

Sections

Indicativematerial

Mark

(d)

ACE

Interpretation

Smallestdivisioncorrectlyreadfrommeasuringcylinderanderrorestimatedat½smallestdivision

Both%errorscorrectlycalculated

[econdmarkecffromsmallestdivisionandestimatederror]

[1]

[1]

[2]

(e)

ACE

Conclusions

Drawsappropriateconclusionfrom(d)–supportedby(experimental)evidence

comparesconsistencyoftwotitresperformed

commentsonlowertitrethanin1stexperiment

compares%errorformeasuringcylinderandpipette

referstoliquidremaininginthemeasuringcylinder(allowedforinpipette)

measuringcylinderhaslargeerror–volumesaddedwillvary(eachtime)leadingtovariabletitres

[1]

[1]

(f)

ACE

Improvement

CandidatesuggestsheatingsolutiontodriveoffCO2(acceptuseofhotwateronlyiflinkedtodecreasedsolubilityofcarbondioxide)

[1]

[1]

[Total:16]

Question

Sections

Indicativematerial

Mark

2(a)

PDO

Layout

PDO

Recording

MMO

Collection

Tabulatesallexperimentalreadingsforatleastoneexperiment.

(massofemptyweighingbottle,massofbottle+solid,massofbottle+residualsolid,initialtemperature,finaltemperature)

and∆Tandm

Tabulatedvaluesareinasingletablecoveringbothexperiments

Tablehascorrectlabelsandunits(onlygandoC)

Allweighingsrecordedwithconsistentprecisiontoatleast1dpandalltemperaturereadingsrecordedto1dponly.

[1]

[1]

[1]

[1]

[4]

(b)

MMO

Collection

Giveonemarkifdifferencweencandidate’s∆T/mvalues,iswithin0.1oCg1

Giveonemarkifthedifferencweenmean∆T/mvalueforSupervisorandcloser∆T/mvalueofcandidate,is

o 1

within0.1Cg

[1]

[1]

[2]

(c)

MMO

Decisions

Candidatereferstohis/herexperimentalvaluestoarriveatanappropriatecommentastowhethertheexperimentshouldbefurtherrepeated

[Theanswermustbebasedonthereliability(consistency)ofthetwoexperimentsperformed]

[1]

[1]

(d)

ACE

Interpretation

Examinercalculatesto3sfthemean∆T/mvaluefromthecandidate’s∆T/mvaluesforeachexperiment.

Give1markifthecandidate’sanswerto(d)iswithin1%ofexaminercalculatedmean∆T/mx61.59.

[1]

[1]

[Total:8]

Question

Sections

Indicativematerial

Mark

FA6issolidbasicz carbonate,FA7issolidcopper()chloride

3(a)

PDO

Layout

MMO

Collection

MMO

Decisions

ACE

Conclusion

TabulatesobservationsforFA6andFA7

ObservesandrecordsblueorgreensolutionwithFA7andcolourlesssolutionwithFA6

SelectslimewaterintestforgaswithFA6

Identifiescarbondioxideasgasevolvedfromtestwithlimewater

EvidenceforCO2mayalsobefoundintheconclusionfortheanionandcanbeawardedretrospectively

[1]

[1]

[1]

[1]

[4]

(b)

PDO

Layout

PDO

Recording

MMO

Collection

Tabulatesobservations

Thistableshouldshowclearlyrows/columnsforNaOHandNH3asreagentsandFA6/FA7.

Thetabledoesnotneedlinestobedrawn–clearlylaidoutandheadedblocksoftextareacceptable

Allobservationsinasingletable

Thekeyfeaturetolookforisreagentinformation–itshouldonlyappearonceforeachreagentandcoverFA6andFA7

Fullobservationsforreagentstoexcess

RecordswhitepptsolubleinexcessNaOHandexcessNH3forFA6

ForFA7recordsabluepptwithNaOHandalighter/palerbluepptwithammonia

ForFA7records(blue/whiteonly)pptsolubleinexcessammoniatoformadeep/darkbluesolution.

[1]

[1]

[1]

[1]

[1]

[1]

[6]

Question

Sections

Indicativematerial

Mark

(c)

ACE

Conclusions

CationinFA6

2+

SummarisesevidenceforZn froms