內(nèi)容教程說明

Page

PAGE

2

MarkScheme

Syllabus

Paper

GCEAS/ALEVEL–May/June2014

9701

34

?CambridgeInternationalExaminations2014

Question

Sections

Indicativematerial

Mark

Total

1 (a)

PDO

Layout

IUnambiguousheadingsfor2balancereadingsand

3

volumeofFB2addedbetween47.5and48.5cm

1

MMO

Collection

IIInitialandfinalreadingsandtitrevaluegivenforroughtitre

andinitialandfinalreadingsfortwo(ormore)accuratetitrations(minimumof2×2box)

1

PDO

Recording

IIIAppropriateheadingsandunitsforallaccuratedata.

and

volumeFB3addedrecordedforeachaccuratetitre.

Headingsshouldmatchreadings.

initial/start(burette)reading/volume

final/end(burette)reading/volume

titreorvolume/FB3used/added(not“difference”)

unit:/cm3or(cm3)orincm3orcm3foreachentry

1

MMO

Decisions

3

IVAllaccurateburettereadingsrecordedto0.05cm.

Theneedtorecordto0.05appliesonlytotheburettereadingsandnottotherecordedtitres.

Donotawardthismarkif:

50(.00)isusedasaninitialburettereading

morethanonefinalburettereadingis50.(00)

anyburettereadingisgreaterthan50.(00).

1

3

VHastwouncorrected,accuratetitreswithin0.1cm

Donotincludeareadinglabelled‘rough’.

Donotawardthismarkif,havingperformedtwotitres

3

within0.1cm,afurthertitrationisperformedthatismore

3

than0.1cmfromthecloserofthetwoinitialtitresunless

3

furthertitrationswithin0.1cmofanyotherhasalsobeen

carriedout.

Donotawardthemarkifany‘a(chǎn)ccurate’burettereadings(apartfrominitial0)aregiventozerodp.

1

3

Roundanyburettereadingstothenearest0.05cm.

Checkandcorrectsubtractionsinthetitretable.Examinerthenselectsthe“best”titreusingthehierarchy:

3 3

twoidentical;titreswithin0.05cm;titreswithin0.1cm;etc.

Candidatescaledtitrecalculatedas:

Candtitre×Cand{(Vadded/500)1.6×mass/100.1)}

Scaledtitre=

Supervisor{(Vadded/500)1.6×mass/100.1)}

ExaminercomparescandidatescaledtitrewithSupervisor’stitre.

(a)

MMO

Quality

AwardVI,VII,VIIIandIXforδ≤0.40cm3

3 3

AwardVI,VIIandVIIIfor0.40cm<δ≤0.80cm

3 3

AwardVIandVIIfor0.80cm<δ≤1.20cm

3 3

AwardVIonlyfor1.20cm<δ≤2.00cm

3

Ifthe“best”titresare≥0.50cmapartcanceloneoftheQ

marks.

4

[9]

Page

PAGE

3

MarkScheme

Syllabus

Paper

GCEAS/ALEVEL–May/June2014

9701

34

?CambridgeInternationalExaminations2014

Question

Sections

Indicativematerial

Mark

Total

(b)

ACE

Interpretation

Candidatemustaveragetwo(ormore)titresthatareall

3

within0.20cm.

Workingmustbeshownorticksmustbeputnexttothetwo(ormore)accuratereadingsselected.

Themeanshouldnormallybequotedto2dproundedtothenearest0.01.

Twospecialcaseswherethemeanmaynotbeto2dp:allowmeanto3dponlyfor0.025or0.075e.g.26.325;allowmeanto1dpifallaccurateburettereadingsweregivento1dpandthemeaniactlycorrect.e.g.26.0and

26.2=26.1iscorrectbut26.0and26.1=26.1isincorrect.

Note:thecandidate’smeanwillsometimesbemarkedascorrectevenifitisdifferentfromthemeancalculatedbytheExaminerforthepurposeofassessingaccuracy.

1

[1]

(c)(i)&(ii)

(iii)

(iv)

(v)&(vi)(vii)

(2marks)

ACE

Interpretation

PDO

Disy

0.200×25 3

Correctlycalculates 1000 =5×10 in(i)

andgives5×103in(ii)

250

Uses(ii)× in(iii)

(b)

2.00×Vdiluted

Correctexpression 1000 in(iv)

Correctexpressions(iv)–(iii)in(v)and

(v)÷2in(vi)

V(vi)×100.1(allow×100)in(vii)

(answer÷correctmassFB1)×100in(vii)

Answerstosteps(iii)to(vii)givento3or4sf

minimumnumberofstepsattempted=4toaccessthismark

1

1

1

1

1

1

1

[7]

(d)(i)(ii)

ACE

InterpretationConclusion

smallest=48.40,largest=48.60

CorrectlinkbetweenvolumeofFB2used/inexcess/concentrationofremainingFB2andtitre

orbetweenconcentration/volumeFB3/HClremaining/inexcessandtitre.

(highervolume/concentrationgivessmallertitreora)

Correctreferencetostudent(s)Xand/orY

1

1

1

[3]

Qn1

Total

[20]

Page

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4

MarkScheme

Syllabus

Paper

GCEAS/ALEVEL–May/June2014

9701

34

?CambridgeInternationalExaminations2014

Question

Sections

Indicativematerial

Mark

Total

2 (a)

PDO

Recording

Headingswithunitsforallfourbalancereadingsaretabulatedclearly.

massofcrucible

massofcrucible+FB5

massofcrucible+contents/residue/solid/FB5afterheating/cooling

massofcrucible+contents/residue/solid/FB5afterre-heating/re-cooling/2ndheating/2ndcooling

Mass/g,(g),ing,ingrams

Ifunitsareomittedfromtheheadingsthentheymustappearnexttoeachentryinthetable.

Recordsallbalancereadingstoaconsistentnumberofdp(minimum1dpandminimum3balancereadings)

andrecordsmassofFB5(atstart)andmassofsolidremainingowtte

Headings for the two masses of solid must beunambiguous.

1

1

[2]

(b)(i)(ii)

(iii)

ACE

Interpretation

PDO

Disy

ACE

Interpretation

Correctmasslossfromresultsin(a)

(i)×100.1

Showscorrectuseof100.1and44: 44

ans(ii)

calculatesmass ×100

FB5

1

1

1

[3]

(c)(i)

ACE

Conclusion

Thermal positionislessaccuratebecausenotallcarbonatehas posed.

Temperatureusednothighenoughto posesolidPercentageofCaCO3ismuchlessinQuestion2

1

(ii)

Improvement

Heattoconstantmass.

Useagas/Bunsenburner/furnace

Ifcandidatesachieveconstantmassandgivetitrationlessaccurateasmorestepsthenaward1mark.

1

[2]

Qn2

Total

[7]

Question

Sections

Indicativematerial

Mark

Total

FB6isMgSO4+HNO3(aq);FB7isZnCO3(s)+KI(s)

3 (a)

MMO

Collection

ACE

Conclusion

MMO

DecisionsCollection

ACE

Conclusion

WhitepptwithNH3insolubleinexcess

Novisiblereaction/nochange

and

Whiteppt

2+ 3+ 2 2

Mg andAl andSO4and/orSO3 in(iv)

SelectsNaOHin(v).

(AllowKI/HCl/H2SO4/K2CrO4ifPb2+in(iv))

Whitepptinsolubleinexcess(NaOH)(AllownoreactionwithKIifPb2+in(iv))

(not