第39届国际化学奥赛实验试题莫斯科.docx
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第39届国际化学奥赛实验试题莫斯科.docx
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第39届国际化学奥赛实验试题莫斯科
The39thInternationalChemistryOlympiad
Chemistry:
art,scienceandfun
PREPARATORYPROBLEMS
(Experimental)
July15-24,2007
Moscow,Russia
The39-thInternationalChemistryOlympiad–Preparatoryproblems
TABLEOFCONTENTS
RULESTOBEFOLLOWEDINLABORATORIES................................................................3
LISTofR-andS-PHRASES...................................................................................................4
Problem29.TITRIMETRICDETERMINATIONOFFEINDIFFERENTOXIDATION
STATES.....................................................................................................................................6
Problem30.ASYMMETRICAUTOCATALYSIS–THENUMERICALEXPERIMENT...10
Problem31.OSCILLATINGREACTIONS...........................................................................13
Problem32.DETERMINATIONOFTHEACIDITYCONSTANTOFBROMOCRESOL
BLUE(3′,3′′,5′,5′′-TETRABROMO-M-CRESOLSULFONEPHTHALEIN,BCB)................15
Problem33.ACIDORANGE7..............................................................................................18
Problem34.DETERMINATIONOFMOLECULARWEIGHTOFAPROTEINUSING
GELFILTRATION..................................................................................................................20
2
RULESTOBEFOLLOWEDINLABORATORIES
AsmentionedinthePreface,wepaygreatattentiontosafetyofexperimentalwork.
BelowyouwillfindalistofrulestobefollowedduringlaboratoryexamatIChO-2007.
Wealsohopeyouwilltakethisinformationintoaccountwhilepreparingforthe
Olympiad.
·Studentshavetobringtheirownlaboratorycoats.
·Priortotheexam,studentswillbegivenSafetyinstructionsintheirmothertongue.
Eachstudentmustcarefullyreadthetextandthensign.
·Whenstudentsenterthelabtheymustfamiliarizethemselveswiththelocationsof
emergencyexits,safetyshower,fireblanketandeyewash.
·Laboratorycoats,eyeprotectionsandclosedshoesmustbewornwhilestayingin
thelaboratory.
·Coatsandbagsareforbiddeninthelaboratory.Thosehavetobedepositedinthe
cloakroom.
·Eating,drinkingorsmokinginthelaboratoryortastingchemicalsarestrictly
forbidden.
·Pipettingbymouthisstrictlyforbidden.
·Organizersdotheirbesttoavoidharmfulchemicalsattheexam.Allpotentially
dangerousmaterials(ifany)willbelabeledbyinternationalsymbols.Eachstudentis
responsibleforrecognizingthesesymbolsandknowingtheirmeaning.
·Donotdisposeofchemicalsdownthesink.Followalldisposalinstructionsprovided
byOrganizers.
·Donothesitatetoaskyourlabinstructorifyouhavegotanyquestionsregarding
safetyissues.
Nobodycancreaterulesthatwillcoverallsituations,whichmayhappeninreality.We
dorelyonyourcommonsenseandresponsibility.
Goodluckduringpreparationsandattheexam!
R-PHRASES
The39-thInternationalChemistryOlympiad–Preparatoryproblems
LISTofR-andS-PHRASES
forthereagentsusedinExperimentalproblems
R5:
Heatingmaycauseanexplosion
R8:
Contactwithcombustiblematerialmaycausefire
R9:
Explosivewhenmixedwithcombustiblematerial
R10:
Flammable
R11:
Highlyflammable
R20:
Harmfulbyinhalation
R22:
Harmfulifswallowed
R23:
Toxicbyinhalation
R25:
Toxicifswallowed
R34:
Causesburns
R35:
Causessevereburns
R36:
Irritatingtoeyes
R37:
Irritatingtorespiratorysystem
R40:
Limitedevidenceofacarcinogeniceffect
R43:
Maycausesensitizationbyskincontact
R50:
Verytoxictoaquaticorganisms
R61:
Maycauseharmtotheunbornchild
R20/21/22:
Harmfulbyinhalation,incontactwithskinandifswallowed
R23/24/25:
Toxicbyinhalation,incontactwithskinandifswallowed
R36/38:
Irritatingtoeyesandskin
R36/37/38:
Irritatingtoeyes,respiratorysystemandskin
R50/53:
Verytoxictoaquaticorganisms,maycauselong-termadverseeffectsinthe
aquaticenvironment
S-PHRASES
S2:
Keepoutofthereachofchildren
S7:
Keepcontainertightlyclosed
S16:
Keepawayfromsourcesofignition-Nosmoking
S17:
Keepawayfromcombustiblematerial
S22:
Donotbreathedust
4
The39-thInternationalChemistryOlympiad–Preparatoryproblems
S23:
Donotbreathegas/fumes/vapor/spray(appropriatewordingtobespecifiedbythe
manufacturer)
S24:
Avoidcontactwithskin
S26:
Incaseofcontactwitheyes,rinseimmediatelywithplentyofwaterandseek
medicaladvice
S28:
Aftercontactwithskin,washimmediatelywithplentyof...(tobespecifiedbythe
manufacturer)
S30:
Neveraddwatertothisproduct
S35:
Thismaterialanditscontainermustbedisposedofinasafeway
S36:
Wearsuitableprotectiveclothing
S37:
Wearsuitablegloves
S38:
Incaseofinsufficientventilationwearsuitablerespiratoryequipment
S45:
Incaseofaccidentorifyoufeelunwellseekmedicaladviceimmediately(showthe
labelwherepossible)
S60:
Thismaterialanditscontainermustbedisposedofashazardouswaste
S61:
Avoidreleasetotheenvironment.Refertospecialinstructions/safetydatasheet
S1/2:
Keeplockedupandoutofthereachofchildren
S36/37:
Wearsuitableprotectiveclothingandgloves
S36/37/39:
Wearsuitableprotectiveclothing,glovesandeye/faceprotection
S37/39:
Wearsuitableglovesandeye/faceprotection
5
The39-thInternationalChemistryOlympiad–Preparatoryproblems
Problem29.TITRIMETRICDETERMINATIONOFFEINDIFFERENTOXIDATION
STATES
Somemethodsofirondeterminationintheoxidationstates+2and+3arediscussedin
Problem12.Youareinvitedtotestonemoreapproachtosolvingthatproblemin
practice.
Reagentsandsolutionsrequired
KIO3(R9,R22,R36/37/38,S35),reagentgrade,solid
Ascorbicacid,solid
KI(R36/38,R42-43,R61;S26,S36/37/39,S45),5%aqueoussolution
HCl(R34,R37,S26,S36,S45),conc.and2M
HNO3(R8,R35,S1/2,S23,S26,S36,S45),conc.
Sulfosalicylicacid,25%aqueoussolution
NH3(R10,R23,R34,R50,S1/2,S16,S36/37/39,S45,S61),10%aqueoussolution
EDTA(R36,S26),standardsolution,about0.05M(theexactvaluewillbegiven)
1.PreparationofaprimarystandardsolutionofKIO3
1.1.Calculatewiththeaccuracyof0.0001gtheweightofKIO3necessaryforthe
preparationof200.0mLof0.01000MKIO3solution.
1.2.UsinganalyticalbalanceweighoutaccuratelyaportionofKIO3.Theweightofthe
portionmaydifferfromthecalculatedonenomorethanby0.05ganditshouldbe
measuredwitha0.0001gaccuracy.
1.3.Transfertheportioninto200.0mLvolumetricflask,dissolveitinwater,dilutetothe
markandmix.
1.4.Calculatetheexactconcentrationofthesolutionpreparedinmol/L.
6
The39-thInternationalChemistryOlympiad–Preparatoryproblems
2.Preparationofthetitrantsolution–ascorbicacid
2.1.Calculatewiththeaccuracyof0.01gtheweightofascorbicacidnecessaryfor
preparationof200mLof0.1Msolution.
2.2.Usingtechnicalbalanceweighoutaportionofascorbicacid.Itsweightmaydiffer
fromthecalculatedonenomorethanby0.05g.
2.3.Dissolvetheportionin~200mLofwater,mixwell,transferthesolutionintoavessel
andcloseittightlywithastopper.
3.Standardizationoftheascorbicacidsolution
3.1.Fillinaburettewiththeascorbicacidsolution.
3.2.Withapipettetransfer10.00mLofstandardKIO3
solutionintoa100mL
Erlenmeyerflask,add20mLof5%KIsolutionand5mLof2MHCl.
3.3.Titratethemixturewiththeascorbicacidsolutionuntiltheiodinecolordisappears.
Note.Whentitratingiodinewithsolutionsofreducingagents,starchisusuallyaddedas
anindicator.Hereitisnotrecommendedtodosobecausethereactionratedecreases
significantlyinpresenceofstarch.
3.4.Repeatthetitrationuntilthreetitrantvolumesdiffernomorethanby0.10mL.
3.5.Calculatetheaveragetitrantvolume.
3.6.Calculatetheascorbicacidconcentrationinthesolutioninmol/L.
Questions
1.Writedownthebalancedequationsofallthereactionstakingplaceduring
standardizationofascorbicacidsolution.AscorbicacidC6H8O6isbeingoxidizedto
dehydroascorbicacidC6H6O6.
7
2.KIO3
The39-thInternationalChemistryOlympiad–Preparatoryproblems
inpresenceofexcessofKIcanbeusedasaprimarystandardforHCl
standardizationaswell.Themethodissimilartothatdescribedabovewiththeexception
thatnoHClisaddedtothetitratedsolutioninthiscase.Whichcompound(s)canbe
usedasanindicator(s)forthattitration:
□
□
□
□
starch
sulfosalicylicacid
methylorange
methylorange+Na2S2O3(inexcess)
4.DeterminationofFe(III)byascorbimetrictitration
4.1.FromyourinstructorobtainasamplesolutioncontainingFe(II)andFe(III)(in100.0-
mLvolumetricflask).Dilutethesolutiontothemarkwithwaterandmix.
4.2.Fillintheburettewiththestandardizedascorbicacidsolution.
4.3.Withapipetteplace10.00mLofthesamplesolutionintoa100mLErlenmeyer
flask,add40mLofwaterandheatnearlytoboiling.
4.4.Intothehotsolutionadd4-5dropsof25%sulfosalicylicacidsolutionasan
indicator.
4.5.Titratethesolutionwiththeascorbicacidsolutionuntilthevioletcolordisappears.
Duringthetitrationandespeciallyneartheendpointthesolutionmustbehot.Youmay
needtoheatitadditionally,ifnecessary.Neartheendpointtheascorbicacidsolution
shouldbeaddedslowly.
4.6.Repeatthetitrationsuntilthreetitrantvolumesdiffernomorethanby0.10mL.
4.7.Calculatetheaveragetitrantvolume.
4.8.CalculatetheweightofFe(III)inthesamplesolutiongiventoyou.
8
The39-thIn
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