AQA A LEVEL CHEM PRACTICALS - PAPER 3
Measuringme.m.f.mofmelectrochemicalmcellsm-
m"ACCURATEmANSWER"mmThemstandardmcellmpotentialmismtheme.m.f.mbetweenmtwomhalfm
cellsmmakingmupmthemcell,mmeasuredmundermstandardmconditions.
cleanmpiecemofmeachmmetal,me.g.mcoppermandmzinc.mdegreasemusingmpropanone,
placemcopperminmambeakermwithmaroundm50cm₃m1moldm⁻³mcoppermsulfatemsolution,mplace
mzincminmamseperatembeakermofmsamemconcentrationmandmvolumemzincmsulfatemsolution
joinmthemtwombeakersmwithmfiltermpapermcoatedminmNaCl/potassiummnitratem-
mactsmasmamsaltmbridge
connectmonemendmtompositivemterminalmofmvoltmetermandmthemothermelectrodemtomthem
negativemterminal,mensuringmthemreadingmismpositivem-
mifmitmismnegative,mreversemthemconnectionsmtomthemelectrodes
recordmthemreadingmofmthemvoltmeter,mwritingmwhichmelectrodemismconnectedmtomthempo
sitivemandmnegativemterminals
standardmsolutionm-m"ACCURATEmANSWER"mm-
mplacemamknownmmassmofmamsampleminmambeaker,maddm100cm³mmofmdistilledmwatermto
mbeakermtomdissolvemsample,mrecordmmassmtom2md.p.
-musemamglassmrodmtomstir
-mpourmthismsolutionmintomamgraduatedmflaskmviamamfunnel
-mrinsembeakermandmfunnelmusingmdistilledmwatermandmaddmwashingsmtomvolumetricmflask
-mmakemupmtomthemmarkmwithmdistilledmwatermsomthatmthemmeniscusmsitsmonmthemline
-minvertmflaskmseveralmtimesmtomensuremuniformmsolution
Titrationm-mknownmconcentrationminmburette,munknownmconcentrationminmconicalmflaskm-
m"ACCURATEmANSWER"mm-
mrinsemburettemwithmdeionisedmwatermandmthenmwithmthemsolutionmyou'remusing
-
mfillmthemburettempastmthemmarkm(usingmfunnel)mandmemptymthemburettemuntilmmeniscus
mismonmthemline
-mremovalmfunnelmsomnommoremsolutionmcanmenter
-
mrinsempipettemwithmdeionisedmwatermandmthenmwithmthemsolutionmyou'remusing.mwhenm
fillingmpipettemgompastmthemlinemthenmemptymuntilmmeniscusmismonmthemline
-rinsemconicalmflaskmwithmdeionisedmwater
-mpipettem25cm³mofmrequiredmsolutionmintomconicalmflask
-maddmrequiredmindicator
-mswirlmtommix
-
mtitratemthemsolutionmfrommthemburette,maboutm1cm³matmamtime,muntilmindicatormchange
smcolour
*anymdropsmormsplashesmupmthemsidemofmthemflaskmshouldmbemwashedmwithmdeionisedm
water
*repeatmtitrationmaddingmsolutionmdropwisemwhenmreachingmendmpointm-
mrecordmallmtom2.d.pmbutmonlymendingminm0morm.5mrepeatmuntilmresultsmaremconcordant
m(withinm.1)
Whatmmaymgomwrongmwithmtitration?m-
m"ACCURATEmANSWER"mmmaymlosemsomemsolutionmbeforemitmstarts
don'tmremovemfunnelmsomsomemdropsmfallmduringmtitration
maymrinsemconicalmflaskmwithmsolutionmsomyoumhavemaddedmmoremsolutionmtomthemflask
maymnotmincludemallmofmthemwashings
, Whichmindicatormshouldmbemused?m-m"ACCURATEmANSWER"mmstrongmacidm-
mstrongmbasem=meithermmethylmorangemormphenolphthaleinm(mpinkmtomcolourless)
weakmacidm-mstrongmbasem=mphenylphthalein,mstrongmacidm-
mweakmbasem=mmethylmorangem(myellowmtomred/orange)
Indicatormmustmchangemsharplymatmthemequivilancempoint,msomthempHmrangemofmthemindi
catormshouldmfallmwithinmthem'verticalmsection'm(regionmofmrapidmpHmchange)
Whatmhappensminmanmacid-basemtitrationm-
m"ACCURATEmANSWER"mmsolutionmofmalkalimofmknownmconcentrationmaddedmfrommambur
ettemtomammeasuredmamountmofmanmacid.mindicatormusedmtomfindmendmpointm-
mfrommvolumemofmbasemrequired,mconcentrationmofmacidmcanmbemcalculated
Howmcanmnumbermofmmoleculesmofmwatermofmcrystallisationmbemdeterminedminmampractic
al?m-
m"ACCURATEmANSWER"mmtitratemthemaqmsolution,mwithmknownmvolumeminmamconicalmflas
kmandmacidminmburette,mrepeatmtitrationmuntilmconcordantmresultsmfound.
Usemaddedmvolumemtomworkmoutmmolesmusingmmolarmratio.
calculatemmrmusingmknownmmassmandmnumbermofmmolesmfoundm-
mthenmcalculatem'x'musingmfoundmmrm-
mmrmofmeachmmoleculeminmsubstance,mdividedmbym18mtomfindmnumbermofmH2Ommolecul
es
Acid-basemtitrationm-m"ACCURATEmANSWER"mm-
mpipettem25cm³macidmandmaddmindicatir,mplacembeakermonmammagneticmstirrermandmplace
mmagnetminmthembeaker,mfillmburettemwithmbase
-
mrinsemelectrodemwithmdistilledmwatermasmreadingsmmaymhavemchangedmovermtime,mdipmi
tmintomthemacidminmthembeaker,mrecordingmpH
-switchmonmstirrermandmensuremmagnetmdoesntmstrikemthemelectrode.
-maddm5cm³mbasemandmtakemreadingsmofmpHmandmindicator
-
mcontinuemaddingmbasemtakingm5cm³mreadingsmeachmtimemthenm1cm³maroundmendmpoint,
mthenm5cm³mutilmmostmbasemhasmbeenmadded
-mplotmamgraphmofmpHm(Ymaxis)magainstmvolumemofmbasemadded
Usingmhess'smlawmtomdeterminementhalpymchangemofmamreactionm-mcalculatingm∆1m-
m"ACCURATEmANSWER"mmThismismanmexothermicmreactionmsomamcoolingmcurvemshouldmb
emdrawn.
-mweighmamknownmmassmofmanhydrousmcoppermsulfatem(sample)
-
musingmmeasuringmcylinder,mplacem25cm³mdeionisedmwatermintompolystyrenemcup,mplacemt
hisminmambeaker
-
usemthermometermtomrecordmtemperaturemofmdeionisedmwatermeverymminutemform15mmin
utes,mstirringmconstantlym(usemstopwatch)m
-
matmFOURTHmminute,maddmanyhdrousmsamplemrapidlymandmcontinuemtomstir,mrecordmtem
peraturematm5mminutesmthenmeverymminutemuntilm15mmins.
plotmgraphmofmtempmonmYmagainstmtime,mdrawmtwomseperatembestmfitmlinesmandmusemt
hemgraphmtomdeterminemthemtemperaturemchangematmthemfourthmminutem(riseminmtemp)
musemthismvalueminmq=mc∆t
Usingmhess'smlawmtomdeterminementhalpymchangemofmamreactionm-mcalculatingm∆2m-
m"ACCURATEmANSWER"mmthismismanmENDOTHERMICmreactionmsommaxmandmminmtemperat
uresmshouldmbemrecordedm
-
mweighmoutmmassmofmhydratedmcoppermsulfate,musingmmeasuringmcylindermplacem25cm³m
Measuringme.m.f.mofmelectrochemicalmcellsm-
m"ACCURATEmANSWER"mmThemstandardmcellmpotentialmismtheme.m.f.mbetweenmtwomhalfm
cellsmmakingmupmthemcell,mmeasuredmundermstandardmconditions.
cleanmpiecemofmeachmmetal,me.g.mcoppermandmzinc.mdegreasemusingmpropanone,
placemcopperminmambeakermwithmaroundm50cm₃m1moldm⁻³mcoppermsulfatemsolution,mplace
mzincminmamseperatembeakermofmsamemconcentrationmandmvolumemzincmsulfatemsolution
joinmthemtwombeakersmwithmfiltermpapermcoatedminmNaCl/potassiummnitratem-
mactsmasmamsaltmbridge
connectmonemendmtompositivemterminalmofmvoltmetermandmthemothermelectrodemtomthem
negativemterminal,mensuringmthemreadingmismpositivem-
mifmitmismnegative,mreversemthemconnectionsmtomthemelectrodes
recordmthemreadingmofmthemvoltmeter,mwritingmwhichmelectrodemismconnectedmtomthempo
sitivemandmnegativemterminals
standardmsolutionm-m"ACCURATEmANSWER"mm-
mplacemamknownmmassmofmamsampleminmambeaker,maddm100cm³mmofmdistilledmwatermto
mbeakermtomdissolvemsample,mrecordmmassmtom2md.p.
-musemamglassmrodmtomstir
-mpourmthismsolutionmintomamgraduatedmflaskmviamamfunnel
-mrinsembeakermandmfunnelmusingmdistilledmwatermandmaddmwashingsmtomvolumetricmflask
-mmakemupmtomthemmarkmwithmdistilledmwatermsomthatmthemmeniscusmsitsmonmthemline
-minvertmflaskmseveralmtimesmtomensuremuniformmsolution
Titrationm-mknownmconcentrationminmburette,munknownmconcentrationminmconicalmflaskm-
m"ACCURATEmANSWER"mm-
mrinsemburettemwithmdeionisedmwatermandmthenmwithmthemsolutionmyou'remusing
-
mfillmthemburettempastmthemmarkm(usingmfunnel)mandmemptymthemburettemuntilmmeniscus
mismonmthemline
-mremovalmfunnelmsomnommoremsolutionmcanmenter
-
mrinsempipettemwithmdeionisedmwatermandmthenmwithmthemsolutionmyou'remusing.mwhenm
fillingmpipettemgompastmthemlinemthenmemptymuntilmmeniscusmismonmthemline
-rinsemconicalmflaskmwithmdeionisedmwater
-mpipettem25cm³mofmrequiredmsolutionmintomconicalmflask
-maddmrequiredmindicator
-mswirlmtommix
-
mtitratemthemsolutionmfrommthemburette,maboutm1cm³matmamtime,muntilmindicatormchange
smcolour
*anymdropsmormsplashesmupmthemsidemofmthemflaskmshouldmbemwashedmwithmdeionisedm
water
*repeatmtitrationmaddingmsolutionmdropwisemwhenmreachingmendmpointm-
mrecordmallmtom2.d.pmbutmonlymendingminm0morm.5mrepeatmuntilmresultsmaremconcordant
m(withinm.1)
Whatmmaymgomwrongmwithmtitration?m-
m"ACCURATEmANSWER"mmmaymlosemsomemsolutionmbeforemitmstarts
don'tmremovemfunnelmsomsomemdropsmfallmduringmtitration
maymrinsemconicalmflaskmwithmsolutionmsomyoumhavemaddedmmoremsolutionmtomthemflask
maymnotmincludemallmofmthemwashings
, Whichmindicatormshouldmbemused?m-m"ACCURATEmANSWER"mmstrongmacidm-
mstrongmbasem=meithermmethylmorangemormphenolphthaleinm(mpinkmtomcolourless)
weakmacidm-mstrongmbasem=mphenylphthalein,mstrongmacidm-
mweakmbasem=mmethylmorangem(myellowmtomred/orange)
Indicatormmustmchangemsharplymatmthemequivilancempoint,msomthempHmrangemofmthemindi
catormshouldmfallmwithinmthem'verticalmsection'm(regionmofmrapidmpHmchange)
Whatmhappensminmanmacid-basemtitrationm-
m"ACCURATEmANSWER"mmsolutionmofmalkalimofmknownmconcentrationmaddedmfrommambur
ettemtomammeasuredmamountmofmanmacid.mindicatormusedmtomfindmendmpointm-
mfrommvolumemofmbasemrequired,mconcentrationmofmacidmcanmbemcalculated
Howmcanmnumbermofmmoleculesmofmwatermofmcrystallisationmbemdeterminedminmampractic
al?m-
m"ACCURATEmANSWER"mmtitratemthemaqmsolution,mwithmknownmvolumeminmamconicalmflas
kmandmacidminmburette,mrepeatmtitrationmuntilmconcordantmresultsmfound.
Usemaddedmvolumemtomworkmoutmmolesmusingmmolarmratio.
calculatemmrmusingmknownmmassmandmnumbermofmmolesmfoundm-
mthenmcalculatem'x'musingmfoundmmrm-
mmrmofmeachmmoleculeminmsubstance,mdividedmbym18mtomfindmnumbermofmH2Ommolecul
es
Acid-basemtitrationm-m"ACCURATEmANSWER"mm-
mpipettem25cm³macidmandmaddmindicatir,mplacembeakermonmammagneticmstirrermandmplace
mmagnetminmthembeaker,mfillmburettemwithmbase
-
mrinsemelectrodemwithmdistilledmwatermasmreadingsmmaymhavemchangedmovermtime,mdipmi
tmintomthemacidminmthembeaker,mrecordingmpH
-switchmonmstirrermandmensuremmagnetmdoesntmstrikemthemelectrode.
-maddm5cm³mbasemandmtakemreadingsmofmpHmandmindicator
-
mcontinuemaddingmbasemtakingm5cm³mreadingsmeachmtimemthenm1cm³maroundmendmpoint,
mthenm5cm³mutilmmostmbasemhasmbeenmadded
-mplotmamgraphmofmpHm(Ymaxis)magainstmvolumemofmbasemadded
Usingmhess'smlawmtomdeterminementhalpymchangemofmamreactionm-mcalculatingm∆1m-
m"ACCURATEmANSWER"mmThismismanmexothermicmreactionmsomamcoolingmcurvemshouldmb
emdrawn.
-mweighmamknownmmassmofmanhydrousmcoppermsulfatem(sample)
-
musingmmeasuringmcylinder,mplacem25cm³mdeionisedmwatermintompolystyrenemcup,mplacemt
hisminmambeaker
-
usemthermometermtomrecordmtemperaturemofmdeionisedmwatermeverymminutemform15mmin
utes,mstirringmconstantlym(usemstopwatch)m
-
matmFOURTHmminute,maddmanyhdrousmsamplemrapidlymandmcontinuemtomstir,mrecordmtem
peraturematm5mminutesmthenmeverymminutemuntilm15mmins.
plotmgraphmofmtempmonmYmagainstmtime,mdrawmtwomseperatembestmfitmlinesmandmusemt
hemgraphmtomdeterminemthemtemperaturemchangematmthemfourthmminutem(riseminmtemp)
musemthismvalueminmq=mc∆t
Usingmhess'smlawmtomdeterminementhalpymchangemofmamreactionm-mcalculatingm∆2m-
m"ACCURATEmANSWER"mmthismismanmENDOTHERMICmreactionmsommaxmandmminmtemperat
uresmshouldmbemrecordedm
-
mweighmoutmmassmofmhydratedmcoppermsulfate,musingmmeasuringmcylindermplacem25cm³m
