物理化学实验思考题解答.docx
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物理化学实验思考题解答.docx
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物理化学实验思考题解答
物理化学实验思考题解答(SolutionstoproblemsinPhysicalChemistryExperiments)
Thinkingquestion
Experiment1.Determinationofcombustionheat
1.whatarethesystemsinthisexperiment?
Whataretheenvironments?
Isthereaheatexchangebetweenthesystemandtheenvironment?
Whataretheeffectsoftheseheatexchangesontheexperimentalresults?
Howtocorrect?
Note:
thebucketinternalmaterialandspaceforthesystem,inadditiontotheinternaltubmaterialandspacecalorimeterrestenvironment,heatexchangebetweenthesystemandtheenvironment,theheatexchangewillaffecttheaccuracyofdeterminationofheatofcombustion,theReynoldscorrectioncurvecorrectiontoreduceitsinfluence.
2.whyaresolidsamplespressedintoflakes?
Howistheamountofnaphthaleneandbenzoicaciddetermined?
Tip:
pressureintoasheettosamplethefullcombustionofnaphthaleneandbenzoicacid;Determinationoftheamountoflittleerrorislarge,toomuchisnotfullyburning,candeterminethemaximumamountofthesamplesaccordingtothevolumeofoxygenbombandinternaloxygenpressure.
3.whatarethecausesoftheburningandburningofthesample?
Tip:
presstootight,burningwirewillcauseburningintoapill;pressingtooloose,lackofoxygencancauseburningas.
Whatarethemainfactorsthataffecttheresultoftheexperimentinthe4.testanalysis?
Whatarethekeyfactorsforthesuccessoftheexperiment?
Itispointedoutthatthemainfactorsaffectingtheexperimentalresultsarewhetherthesamplecanbefullyburnedandtheheatexchangebetweenthesystemandtheenvironmentcanbeensured.Thekeytothesuccessofthisexperimentistheappropriateamountofdrugs,theappropriatetightnessofthetablet,thecorrectionofReynoldstemperature.
5.whatmattersshouldbepaidattentiontowhenusingoxygencylinderandoxygenpressurereducer?
Clew:
read"physicalchemistryexperiment"teachingmaterialP217-220
Experimenttwodeterminationofrelativemolecularmassbyfreezingpointdepressionmethod
1.whatpossiblecausestoocoldtoomuch?
Iftoocoldtoo,thefreezingpointofsolutionisloworhigh?
Istherelativemolecularweightofnaphthaleneloworhigh?
Explainwhy.
Answer:
coldagenttemperatureistoolowwillcausetoocoldtoo.Iftoocoldtoo,thefreezingpointofaliquidislow.Accordingtotheformula,itisknownthattherelativemolecularweightofnaphthaleneislowbecausethesolidificationpointofsolutionislowandTfislarger.
2.coldagenttoohighortoolow,whatiswrong?
Answer:
coldagenthightemperaturehanddoesnotappearthesupercoolingphenomenon,thisexperimentalphenomenonalsodidnotproducealargenumberofsmallcrystals,willleadtofailureintheexperiment,ontheotherhandwillprolongthetimeoftheexperiment,isnotconducivetothesuccessfulcompletionoftheexperiment;andthecoldagenttemperatureistoolowwillresultintoocoldtoo,affectedbytherelativemolecularmassofnaphthalene,seethespecificanswerquestions1.
3.howtodeterminethedissolvedmassinthesolvent?
Howmuchortoolittle?
Answer:
itshouldbebasedontheamountofsoluteinthesolventsolubilitytodetermine,becausethefreezingpointisthedecreaseofcolligativepropertiesofdilutesolution,itshouldensurethattheamountofsolutecanmakethefreezingpointloweringthevalueisnottoosmall,easytomeasure,butalsotoensurethatthepremiseisadilutesolution.Iftheamountistoomuch,ontheonehand,itwillleadtotoomuchfreezingpointdepression,whichisnotconducivetothedeterminationofthefreezingpointofthesolution.Ontheotherhand,itmayexceedtherangeofdilutesolutionwithoutthedependenceonthenumber.Toolittlewillmakethefreezingpointdropnotobvious,anditisnoteasytomeasureandtheexperimentalerrorincreases.
4.estimatetheerroroftheexperimentalresults,andexplainthemainfactorsthataffecttheresultofthemeasurement
Answer:
themainfactorsaffectingthedeterminationresultsarethedegreeofsupercoolingcontrolandstirringspeed,thetemperatureofcoldagent,etc..Theexperimentaldeterminationoffreezingpointneedtoocold,toocoldtoomuchwillcausetheresultofdeterminationofthefreezingpoint,sotheneedtocontrolthedegreeofsupercooling,onlycontactsurfaceofsolid-liquidtwo-phaseisquitelarge,liquidtoreachequilibrium.Intheprocessofexperiment,themethodofstirringsuddenlyandchangingthestirringspeedtoachievethepurposeofcontrollingthesupercoolingdegree;thetemperatureofcoldagentandtoohighandtoolowtemperatureofcoldagentarenotconducivetothecompletionoftheexperiment.
5.whatisthesignificanceoftheresultswhenthesolutehasdissociation,association,solvationandformationofcomplexesinthesolution?
Answer:
solutehasdissociation,association,solvationandformationofcomplexesinsolution,
Thefreezingpointdecreasestherelativemolecularmassdeterminationforcomplexesofsolutedissociationandassociation,solvationorformationofmolecularweight,sothefreezingpointloweringmethodforthedeterminationoftheresultsoftheactualreactionexistenceformofmaterialinsolvents.
6.inthecoolingprocess,thefreezingpointdetermineswhatheatexchangeexistsintheliquidinthetubeWhateffectdotheyhaveonthedeterminationoffreezingpoint?
Answer:
freezingpointdeterminationofliquidandairinthetube,measuringtubewall,stirringrodandtemperaturemeasuringinstrumentsensorssuchasheatexchange.Therefore,ifthestirringrodandthetemperaturesensorfrictionwillleadtothedeterminationoffreezingpointishigh.Determinationofwaterontheouterwallofthetubewillleadtothedeterminationofthefreezingpointislow.
Experimentthreedeterminationofpureliquidsaturatedvaporpressure
1.whathappensifyouunplugthepowerplugfirstwhenyoustoppumping?
Answer:
vacuumpumpoilwillflowbackward.
2.isitpossibletocheckwhetherthedeviceleaksunderheating?
Whateffectdoestheleakhaveontheresult?
Answer:
cannot.Intheprocessofheating,thetemperaturecannotbeconstant,thegas-liquidtwo-phasecannotreachtheequilibrium,andthepressureisalsonotconstant.
Theleakagewillleadtotheinstabilityoftheinternalpressureinthewholeexperiment,andthegasliquidtwo-phasecannotreachtheequilibrium,resultingininaccuratemeasurementresults.
3.whydoesthepressuregaugereadfrequentlywhenitdoesn'tleak?
Answer:
becausethesystemdoesnotreachthegasliquidequilibrium.
Underwhatconditionscantheequationof4.gramsbeapplicable?
Answer:
theapplicableconditionsofgram-Gequation:
oneisthemolarvolumeofliquidVgandVmolarvolumeofgascanbeneglectedcompared;twoistoignoretheeffectoftemperatureonthemolarheatofvaporizationofdeltavapHm,inthetemperaturerangeoftheexperimentscanbeseenasaconstant.Threeisgasasidealgas.
5.isthemolarheatofvaporizationmeasuredbythisexperimentrelatedtotemperature?
Answer:
about.
6.whatarethemainsourcesoferrorinthisexperiment?
Answer:
thetightnessofthedeviceisgood,thewateritselfcontainsimpuritiesandsoon.
Experimentfourdrawingofgasliquidequilibriumphasediagramofdoubleliquidsystem
1..Whydoestheboilingpointinstrumentneednotbewashedanddriedinthedirectionofcyclohexaneandisopropanolsystem?
Note:
theexperimentalmeasurementofboilingpoint,aslongasattheequilibriumcompositionunderdifferentphaseandliquidphasecompositioncanbe.Thetotalcompositionofthesystemisnotnecessarilyaccurate.
2.,whenthesystembalance,thetwo-phasetemperatureshouldnotbethesame?
Whataboutreality?
Howtoinsertathermometerinthesolutionofmercuryballinordertoaccuratelymeasuretheboilingpoint?
Hint:
twophasetemperatureshouldbethesame,buttheactualisnotthesame,generallythethermometermercuryballintothesolutionunderthe1/3better.
3.whatisthesizeoftheslotthatcollectsvaporcondensate?
Why?
Itissuggestedthatthesizeofsmallslotingascondensateaffectsthecompositionofgasphaseandliquidphase.
Whatshouldwepayattentiontowhenusing4.Abberefractometer?
Hint:
itisimpossibletodeterminestrongacid,strongalkaliandothersubstanceswhichhavestrongcorrosivetotheinstrument.
5.discussthemainerrorsourcesoftheexperiment.
Tip:
effectoftemperaturedetermination:
thethermometerinsertiondepth,boilingdegree;Determinationofcomposition:
backtotheliquidphaseanddeterminationofliquidbackflowofgascondensationEbulliometermovingslow
Plottingofmetalphasediagramofexperiment52component
1.whatisthedifferenceinthehorizontalcurveofthestepcoolingcurveforthemixtureofdifferentcomponents?
Answer:
purematerialstepcoolingcurveappearsatthemeltingpointofthehorizontalsection,themixtureappearsinthemeltingtemperatureofthehorizontalsection.Andtheplatformsaredifferent.
Whatarethemethodsfor2.phasediagrams?
Answer:
therearesolubilitymethods,boilingpointmethodandsoon.
3.generally,thethermaleffectofsystemwhenphasechangeisverysmall,withthethermalanalysismethodisdifficulttoobtainaccuratephasediagram,why?
WhichisthefirstturningpointinthestepcoolingcurveoftwosamplescontainingBi30%and80%?
Why?
Answer:
becausethethermalanalysisistodrawthephasediagrambystepcoolingcurve,mainlythroughthecoldcurveinflectionpointandhorizontalsection(slopechange)todeterminetheemergenceofnewphase.Ifthephasetransitionoccurs,thethermaleffectisverysmall,
Itisdifficulttogenerateinflect
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