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EXPERIMENTB7:GREENCRYSTAL

LearningOutcomesUponcompletionofthislab,thestudentwillbeableto:

1) Synthesizeaninorganicsaltandpurifyitusingthemethodofrecrystallization.

2) Testthepurityofthesynthesizedcrystals.3) Analyzethesynthesizedcrystalsandpredictitsformulausingmethods

suchas:titration,spectrophotometry,anddeterminationofpercenthydrate.

IntroductionOneofthemostexcitingaspectsofchemistryistheabilitytosynthesizenewmaterials.Thesesyntheticmaterialsareinavarietyofconsumerproductsandcanbefoundinproductssuchasfood,healthandbeautysupplies,andpharmaceuticals.Chemistsemployconceptualchemicalmodelstoformulaterelativelysimpleprocedurestosynthesizesuchsubstancesreliablyandinhighyield.Oncesynthesized,thesubstancesmustbepurifiedandanalyzedtoconfirmthechemicalidentity.Thisensuresthequalityandeffectivenessoftheproductinquestion.Accordingly,synthesis,purification,andanalysisarethreeessentialmethodologieseverychemistmustbefamiliarwith.InthisexperimentaGreenCrystalwillbesynthesizedfromiron(III)chlorideandpotassiumoxalateandthenpurifiedviarecrystallization,acommontechniqueinsyntheticprocedures.Theexactchemicalformulaofthecrystalwillinitiallybeunknown,thoughthegeneralformulacanbewrittenasKwFex(C2O4)y(H2O)z.Titrationandspectrophotometrywillbeusedanalyzethepurifiedmaterialsinordertodeterminethepreciseformulaofthecrystal.Part1:SynthesisofGreenCrystalAqueoussolutionsofiron(III)chloridehexahydrateandpotassiumoxalatemonohydratewillbereactedatatemperatureofaround90°CtoproducetheGreenCrystal.Theunbalancedchemicalequationfortheprocessmaybewrittenasfollows:

FeCl3!6H2O(aq)+K2C2O4!H2O(aq)"KCl(aq)+KwFex(C2O4)y!zH2O(s)

Coolingthereactionmixturewillresultintheformationofgreencrystals.Thecrystalsobtainedinthisstepareconsideredasthe“crudeproduct”astheyarenotpure.Thesolidproductwillbeseparatedfromtheaqueoussupernatantby

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decantingtheliquid,andthenthecrudeproductwillbepurifiedinthenextstepoftheprocess.Part2:PurificationoftheGreenCrystalThepurificationoftheGreenCrystalisdonethroughaprocesscalledrecrystallization.Inrecrystallization,thecrudeproductisdissolvedinasmallamountofhotsolvent,completelydissolvingtheentiresample.Atthisstageboththeimpuritiesandthedesiredproductaredissolved.Thechoiceofsolventissuchthat,thepureproductismuchlesssolubleinthecoldsolvent,causingthemtosolidify(recrystallize)asthesolutioncools,whiletheimpuritiesshouldremaindissolved.Theliquid,containingtheimpurities,canthenberemovedviafiltration,leavingthepuresolidproductbehind.Inthisexperiment,themostlikelyimpuritiescombinedwiththepureproductarethestartingmaterials.Accordingtothesolubilityrules,chloridesalts(suchasFeCl3!6H2O)andpotassiumsalts(suchasK2C2O4!H2O)arehighlysolubleinwater.Thedesiredproduct,theGreenCrystal(KwFex(C2O4)y!zH2O)isasparinglysolublesaltthatonlydissolvesinwaterathightemperatures.Therefore,waterisagoodsolventchoicefortherecrystallizationprocess.Thequalityofthecrystalsisimprovedifthecoolingisdoneslowly.Giventhis,itisnotrecommendedthatthecoolingbedoneovericeinitially.Itisbesttoallowthesolutiontocooltoroomtemperatureslowlyandthenplacethesolutioninanicebathonlyifnecessary.Thepercentagepurityoftherecrystallizedproductcanbegreatlyincreasediftheprocessisrepeatedmorethanonce.Whilemultiplerecrystalliztionsincreasethequalityoftheproduct,eachiterationalsodecreasesthequantityofproductthatcanbeisolated,resultinginanoveralldiminishedpercentyield.Giventhisconcernonlyoneortworecrystallizationsaretypicallycarriedoutinatypicalsyntheticscheme.Part3:AnalysisofthePercentofOxalateintheGreenCrystalThepercentofoxalate(C2O42-)intheGreenCrystalwillbeanalyzedbytitration(seeexperimentsA7andA9forareviewoftitration).Oxalatereactswithpermanganateinanacidicmediumaccordingtothefollowingequation:

2MnO4−(aq)+5C2O42-(aq)+16H+(aq)"2Mn2+(aq)+10CO2(g)+8H2O(l)

Theabovereactionisanexampleofaredoxtitration.TheMnO4−isreducedtoMn2+andtheC2O42-isoxidizedtoCO2.Anintroductiontooxidation-reduction(redox)reactionscanbefoundintheTypesofReactionschapterofanyGeneralChemistrytextbook,whileamoredetailedtreatmentmaybefoundinthelater

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electrochemistrychapter.BothofthesesectionswillbediscussedoverthecourseoftheGeneralChemistryseries.Theprimaryfocusforthepresentisthefactthataccordingtothestoichiometryofthereaction,2molesofMnO4−willcompletelyreactwith5molesofC2O42-.Duringthistitration,aknownmassoftheGreenCrystalwillbedissolvedinwarmacidicwater.Thissolutionwillbecolorlessinitially.Astandardizedpermanganatesolution(whosemolarityispreciselyknown)willbeslowlyaddedfromaburetintoasolutioninwhichsomeoftheGreenCrystalwasdissolved.Thepurplecolorofthepermanganatewilldisappearasitreactswiththeoxalateinthereactionflask.Justpasttheequivalentpoint,whenalltheoxalatehascompletelyreacted,additionofonemoredropofthepermanganatewillleaveanexcessofpermanganateinthesolutionandthereforeapalepurplecolorinthereactionflask.Thisistheendpointofthetitration.Thevolumeofpermanganatesolutionneededforthetitrationandthemolarityofthepermanganatewillbeusedtodeterminethemolesofpermanganateusedforthetitration.Fromthestoichiometricrelationshipbetweenthepermanganateandtheoxalate,themolesoftheoxalatetitratedcanthenbedetermined.Thisisthenusedtocalculatethemasspercentofoxalateinthesample.Part4:AnalysisofPercentofIroninGreenCrystalTheanalysisofthepercentageofironintheGreenCrystalwillbedoneusingthemethodofspectrophotometry.SpectrophotometryandBeer’slawhavebeenextensivelydiscussedinpreviousexperiments(seeExperimentsB4andB6).TheironintheGreenCrystalhasanoxidationstateof+3.TheanalysisisgreatlyfacilitatedbyconvertingalltheFe(III)toFe(II).Inordertoreducetheironfromits+3to+2oxidationstate,severalstepsarerequired.Thesampleisfirstplacedinanammoniumacetatesolution,whichactsasabuffertostabilizethepHofthesolution.ThereductionofFe(III)toFe(II)isdonebyaddinghydroxylaminehydrochloride.Finally,thereagentortho-phenanthrolineisaddedtotheFe(II)togivethesolutionanorangecolor.Ortho-phenanthrolineactsasaLewisbasehere,donatingelectrondensitytotheironcation,formingtheLewisadduct[Fe(phen)3]2+,called“ferroin.”ThisorangecoloredcomplexiscommonlyusedforthephotometricdeterminationofFe(II)concentrations.Theorangecoloredferroincomplexhasawavelengthofmaximumabsorbance(λmax)at510nm.Therefore,spectrophotometricanalysisofthesampleiscarriedoutat510nm.

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InthepreviousdiscussionsofspectrophotometryandBeer’slaw,thecalculationoftheconcentrationofasamplewhoseabsorbanceisknownusestheformula:

A=ε×C×l

Intheaboveformula:Aistheabsorbanceofthesample,Cistheconcentration,listhepathlengthoftheinstrumentandεisthemolarextinctioncoefficientofthesubstancebeinganalyzed.Theaboveformulacanonlybeusedifthemolarextinctioncoefficientofthesampleisknown.Intheabsenceofthisinformation,additionalstepsmustbeemployedtodeterminetheconcentrationoftheunknownsample.Oneofthesimplestmethodsinvolvesconstructingastandardcurveusingknownconcentrationsoftheunknown.Thisstandardcurveisaplotoftheabsorbanceofknownconcentrationsoftheanalyte,andisoftenreferredtoasa“Beer’sLawPlot.”Aplotofabsorbance(y-axis)vs.concentration(x-axis)shouldresultinacurvewhoseregressionequationcorrespondstothatofastraightline,y=mx+b.Uponmeasuringtheabsorbanceoftheunknownsample,theregressionequationobtainedfromthestandardcurvewillbeusedtocalculatetheconcentrationoftheunknown(concentrationx=(y–b)/m).Ineffect,theslopevalueobtainedinthisgraphshouldequaltheproductofthepathlengthandthemolarextinctioncoefficient,ε×l.Ifdesired,thevalueofthemolarextinctioncoefficientcanbedeterminedatthispointaswellbydividingtheslopebythepathlength.Bywayofexampleastohowthiswouldbeemployedinanexperiment,assumethatastocksolutionoftheanalytewithaconcentrationof1mg/mlhasbeenprovided.Theknownsolutioncanbedilutedtoobtainasetofsolutionsofknownconcentrationssuchas:0.2,0.4,0.6,0.8,and1.0mg/ml.Theabsorbancemeasurementofeachofthesesolutionsandtheunknownsolutionmayresultinadatasetsuchasispresentedbelow:

Solution(mg/ml) Absorbance0.0 0.0120.2 0.2220.4 0.3800.6 0.6120.8 0.7901.0 0.995

Unknown 0.585

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Inordertoascertaintheconcentrationoftheunknown,astandardcurvemustbeconstructed.Asmentionedbefore,thestandardcurveisaplotofabsorbance(y-axis)vs.concentration(x-axis).Thegraphbelowisthestandardcurveobtainedfromtheabovedata.Theequationofthebest-fitline(seeExperimentB2)isalsoshowninthegraph.

Sincetheabsorbanceoftheunknownsampleis0.585,itsconcentrationiscalculatedusingtheequationofthelineasfollows:

€

y = 0.9787x + 0.0125

x =y − 0.01250.9787

x =0.585 − 0.0125

0.9787= 0.58 ≈ 0.6mg

ml Part5:AnalysisofPercentHydrateinGreenCrystalFromtheformulaoftheGreenCrystal,KwFex(C2O4)y!zH2O,itshouldbeapparentthatthesubstanceisahydrate.AswasdiscussedinExperimentA3,hydratesareinorganiccompoundswithwatermoleculesboundtothem.Inahydratedcompoundafixednumberofwatermolecules,calledthewaterofhydration,arechemicallycombinedwiththemetalion.Inthispartoftheanalysis,themasspercentofwaterinthehydratedGreenCrystalwillbedeterminedusingmethodsoriginallydescribedinExperimentA3.The

y=0.9787x+0.0125R²=0.99857

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Absorbance

Concentration(mg/ml)

StandardCurve

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procedureinvolvesmeasuringthemassofthesubstancebeforeandafteritisdehydratedbyheatinginordertodeterminethemassofwaterlostintheprocess.Part6:AnalysisofPercentPotassiuminGreenCrystalThedeterminationofmasspercentsofiron,oxalate,andwaterwasdiscussedinParts3,4,and5,respectively.Themasspercentofpotassiumisthencalculatedbydifference.Noseparateanalyticalprocedureisneededforthisdetermination.

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ExperimentalDesignThisexperimentwillbeperformedoveraperiodoffourlaboratorydays.Day1:Iron(III)chloridehexahydrateandpotassiumoxalatemonohydratewillbecombinedinanaqueousmediumatatemperatureof90°CandcooledtoobtainthecrudeproductoftheGreenCrystal.ThecrudeproductwillthenberecrystallizedusingwaterasthesolventandcooledovernighttoobtainthepureformoftheGreenCrystal.Day2:ThemasspercentofoxalateinthepurifiedGreenCrystalwillbedeterminedbytitrationwithstandardizedpotassiumpermanganate.Day3:ABeer’sLawPlotwillbeconstructedandthemasspercentofironinthepurifiedGreenCrystalwillbedeterminedbyspectrophotometricanalysis.Day4:ThemasspercentofwaterinthepurifiedGreenCrystalwillbedeterminedbymeasuringthemassofthehydratedanddehydratedsalt.ReagentsandSuppliesSolidIron(III)chloridehexahydrate,solidpotassiumoxalatemonohydrate,0.04MStandardizedKMnO4,3MH2SO4,Standardironsolution(0.05mg/ml),10%hydroxylaminehydrochloride,3%o-phenanthroline,1MammoniumacetatesolutionFilterpaper,filterflask,Hirschfunnel,25-mLburet,hotplate,seven10-mLvolumetricflasks,two25-mLvolumetricflasks,Spectrophotometer,cuvettes,microcrucible(SeepostedMaterialSafetyDataSheets)

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ProcedurePART1:SYNTHESISOFGREENCRYSTAL1. Obtainahotplatefromthestockroom.2. Measure3-4gramsofiron(III)chloridehexahydrateandtransferittoa250-mL

beaker.Recordtheexactmass.3. Add15mLofdeionizedwatertotheiron(III)chloridehexahydratetodissolve.

Warmslightlyifnecessary.4. Measure8-9gramsofpotassiumoxalatemonohydrateandtransferittoa250-

mLbeaker.Recordtheexactmass.5. Add30mLofdeionizedwatertothepotassiumoxalatemonohydratetodissolve.

Heatthesolutiontoboiling.6. Transfertheiron(III)chloridehexahydratesolutiontothebeakercontainingthe

boilingpotassiumoxalatemonohydrate.7. Heatthemixturetoabout90°C.8. Whenthemixturereaches90°C,fromheatusingtongs.Placethebeakeronared

tileandallowittocoolslowlyforfiveminutes.9. Prepareatraywithice.10. Placethebeakercontainingthemixtureofreagentsoniceandallowittocoolfor

30-40minutes.11. Oncecrystallizationiscomplete,slowlydecantthesupernatantanddiscardthe

liquidintoanappropriatewastecontainerprovidedbytheinstructor.12. Thesolidcrystalsarethecrudeproduct.Taketheseforwardtothenextstep.

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PART2:PURIFICATIONOFTHEGREENCRYSTAL1. Heatapproximately25mLofdeionizedwatertonearboiling.2. AddacoupleofmLofhotwaterfromStep1tothecrudeproductfromPart1

andheatthismixturealongwiththedeionizedwater.Continueaddingsmallincrementsofhotwatertothemixturecontainingthecrudeproductuntilthecrudeproductiscompletelydissolved.Makesurenottoaddtoomuchwater.[NOTE:Inorderfortherecyrstalizationtobesuccessful,thecrudeproductmustbedissolvedinaminimumamountofhotsolvent.]

3. Coverthebeakerwithawatchglass.4. Placethebeakercontainingthedissolvedcrudeproductinsidethelocker.

Purifiedcrystalswillformasthesolutioncools.5. ThisisagoodstoppingpointforDay1activities.Day26. Coolasquirtbottlecontainingdeionizedwaterinanicebath.7. ObtainthebeakercontainingthepureGreenCrystalsfromthelocker.8. SetupavacuumfiltrationusingaHirschfunnelandafilterflask.9. TransferthecrystalsfromthebeakertothefilterpaperontheHirschfunnel.

Scrapeanycrystalsstucktothebottomofthebeaker.10. Rinsethebeakerwithtwosmallaliquotsofice-coldwaterandaddthistothe

crystals.11. RemovethefilterpapercontainingthecrystalsfromtheHirschfunnelandplace

onawatchglass.12. Allowthecrystalstoairdry.13. WhilethecrystalsaredryingstartworkingonPart3andreturntoattendtothe

crystalswhentheyarecompletelydry.14. Obtainthemassofthedrycrystals.Besuretoweighallthecrystalssynthesized.15. Transferthecrystalsintoalabeledbeakerandplacetheminthelockeruntilthe

endoftheexperiment.

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PART3:ANALYSISOFTHEPERCENTOXALATEINTHEGREENCRYSTAL1. Obtainabout20mLofstandardizedKMnO4solution.Recordtheexactmolarity

oftheKMnO4.

2. Obtaina25-mLburetandahotplatefromthestockroom.3. Setupaburetstandandclamptheburettothestand.Turnonthehotplate.4. RinsetheburettwicewithdeionizedwaterandconditiontheburetwithKMnO4.5. FilltheburetwiththeKMnO4solutionandrecordtheinitialburetreading.6. Measure0.1to0.12gramsofpureGreenCrystals.Recordtheexactmass.7. Transferthecrystalstoa125-mLErlenmeyerflask.8. Addabout12.5mLofdeionizedwaterand2.5mLof3Msulfuricacidtothe

Erlenmeyerflask.Addaboilingchipintotheflask.9. GentlyheattheErlenmeyerflaskonthehotplateuntilthecrystalsdissolve

completely.10. PlacetheErlenmeyerflaskcontainingthehotsolutionbelowtheburet

containingtheKMnO4solutionandbegintitrating.Constantlyswirltheflasktothoroughlymixthecontents.Stopthetitrationattheappearanceofapermanentpalepurplecolor.

11. Recordthefinalburetreading.12. Repeatsteps6to12anadditionaltwotothreetimes,asneeded.Youshould

have2trialsinwhichthemasspercentagreeswithin10%.13. Discardallthewasteinanappropriatewastecontainerprovidedbythe

instructor.

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PART4:ANALYSISOFPERCENTIRONINGREENCRYSTALNOTE:Thispartoftheexperimentwillbeperformedingroupsoftwo.Theinstructorwillobtainthedataforthestandardcurvethatwillbeusedbytheentireclass.Bothmembersofthegroupmustpreparetheirownsampleforanalysis.1. Eachgroupshouldobtaintwo10-mLvolumetricflasksandtwo25-mL

volumetricflasksfromthestockroom.2. Obtaintwocuvettesandaspectrophotometer.Powerupthespectrophotometer

andallowtheinstrumenttowarmupfor10minutes.Theinstructorwilldemonstratetheproperuseofthespectrophotometer.

PreparationofStandards(Steps3-9willbedonebytheinstructor)3. Labelfive10-mLvolumetricflasksas1,2,3,4,and5andaddthefollowing

reagentsintotheflaskusingelectronicpipetsfordispensingthereagents.Flask Iron-standard,

µLAmmoniumacetate,µL

Hydroxylaminehydrochloride,µL

O-phenanthroline,µL

1 100 100 100 1002 200 100 100 1003 300 100 100 1004 400 100 100 1005 500 100 100 1004. Fillthevolumetricflaskswithdeionizedwateruntilthecalibrationmark.Iftoo

muchwaterhasbeenadded,discardthissolutioninthewastecontainerandredothepreparation.

5. Capthevolumetricflask,ensurethatthecapissecure,andthoroughlymixthe

contentsoftheflaskbyinverting.6. Preparefive“Blank”solutionscorrespondingtoeachstandardsolutionby

substitutingtheIron-standardwithanequivalentamountofdeionizedwater.7. Measuretheabsorbanceofthesamplesat510nm.8. Addtheblanksolutiontooneofthecuvettes.Placethecuvettecontainingthe

blankinsidethesamplecompartment,aligntheguidemarkonthecuvettewiththeguidemarkatthefrontofthesamplecompartment,closethelidandadjusttheabsorbancereadingtozero.

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9. Addthestandardfromvolumetricflask1toacuvette.Nowplacethecuvettecontainingthestandardinsidethesamplecompartment,aligntheguidemarkonthecuvettewiththeguidemarkatthefrontofthesamplecompartment,closethelidandrecordtheabsorbance.

PreparationofSamples(individually)10. Measure0.01gramsoftheGreenCrystal.RecordtheexactmassoftheGreen

Crystal.Transferthecrystalstoasmallbeaker.11. Add10mlofdeionizedwatertothebeaker.12. Add0.5mlof3Msulfuricacid,usingamicroburet.13. Heatthebeakertillallthesaltdissolves.14. Transferthecontentsintoa25-mLvolumetricflask.Rinsethebeakerwith

deionizedwaterandtransfertherinsesolutionintothevolumetricflaskaswell.15. Fillthevolumetricflaskwithdeionizedwateruntilthecalibrationmark.Iftoo

muchwaterhasbeenadded,preparethesolutioninthisflaskagain.16. Capthevolumetricflask,ensurethatthecapissecure,andthoroughlymixthe

contentsoftheflaskbyinverting.17. Carefullytransfer0.50mLoftheabovesolutionintoa10-mLvolumetricflask

labeledas“sample”.Useamicroburetforthemeasurement.18. Tothe10-mLvolumetricflaskcontainingthesamplealsoadd(useelectronic

pipets):

a. 100µLammoniumacetateb. 100µLhydroxylaminehydrochloridec. 100µLO-phenanthroline

19. Fillthevolumetricflaskwithdeionizedwateruntilthecalibrationmark.Iftoo

muchwaterhasbeenadded,preparethesolutioninthisflaskagain.20. Capthevolumetricflask,ensurethatthecapissecure,andthoroughlymixthe

contentsoftheflaskbyinverting.Thiswillbethe“Sample”.MeasurementofAbsorbance21. Setthewavelengthofthespectrophotometerto510nm

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22. Inalargetesttubepreparea“Blank”solutionbyaddingthefollowing,followedbythoroughmixing:

a. 100µLammoniumacetateb. 100µLhydroxylaminehydrochloridec. 100µLO-phenanthrolined. 10mLofdeionizedwater

23. Measuretheabsorbanceofthe“Sample”(fromStep20)accordingtomethods

describedinSteps7-9.Usethe“Sample”insteadofthe“Standards”forthemeasurement.

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PART5:ANALYSISOFPERCENTHYDRATEINGREENCRYSTAL1. Obtainamicrocruciblefromthestockroom.2. Heatanemptymicrocrucibleandbringittoaconstantmass(±0.0010g).In

ordertodothis,recordthemassoftheemptycrucible.Thenheatthecruciblefor3-4minutes.Oncethecrucibleiscool,recorditsmassagain.Repeattheheating-cooling-weighingprocessuntilthemassrecordediswithin1mgofthepreviousmeasurement.

3. AddsomeGreenCrystaltothemicro-crucible(scoopasmallamountwitha

spatula,approximately0.1000grams).Measurethemassofthemicro-cruciblewiththesolid.

4. Heatthemicro-crucibleoveraBunsenburner(useayellowflame).Continuethe

heatingprocessforaboutfiveminutes.Makesurethatthesaltdoesnotturnblackincolor(whichisanindicationofdegradationoftheproduct).

5. Coolthemicro-crucibletoroomtemperatureandmeasurethemassofthe

micro-cruciblewiththeanhydrouscompound.6. Inordertoensurethatallthewaterofhydrationhasbeenevaporatedfromthe

solid,themicro-cruciblecontainingtheanhydroussolidshouldbeheatedovertheflameonceagain.

7. Onceagain,coolthemicro-crucibleandmeasurethemassofthemicro-crucible

containingtheanhydrouscompound.8. Theheating-cooling-weighingofthemicro-cruciblewiththeanhydrous

compoundmustberepeateduntilthemassofthemicro-cruciblecontainingtheanhydrouscompoundiswithin1mgofapreviousmeasurement.

9. Discardthecontentsofthemicro-crucibleintheappropriatewastedisposal

container.

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DataTablePART1:SYNTHESISOFGREENCRYSTALMassofIron(III)chloridehexahydrate,grams

Massofpotassiumoxalatemonohydrate,grams

PART2:PURIFICATIONOFTHEGREENCRYSTALMassofpureGreenCrystalsynthesized,grams

PART3:ANALYSISOFTHEPERCENTOXALATEINTHEGREENCRYSTALMolarityofstandardizedKMnO4

Trial1 Trial2 Trial3

InitialburetreadingofKMnO4(mL)

FinalburetreadingofKMnO4(mL)

MassofpureGreenCrystals(grams)

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PART4:ANALYSISOFPERCENTIRONINGREENCRYSTALMassofGreenCrystal(grams)

Concentrationofstockironsolution

Absorbance Absorbance

Standard1

Standard2

Standard3

Standard4

Standard5

Sample

PART5:ANALYSISOFPERCENTHYDRATEINGREENCRYSTAL Trial1 Trial2 Trial3

Constantmassofemptymicro-crucible(grams)

Massofmicro-crucible+GreenCrystal(grams)

Massofmicro-crucible+anhydrousGreenCrystal(followingfirstheating)(grams)

Massofmicro-crucible+GreenCrystal(followingsecondheating)(grams)

Massofmicro-crucible+GreenCrystal(followingthirdheating)(grams)

Massofmicro-crucible+GreenCrystal(followingfourthheating)(grams)

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DataAnalysisPART3:ANALYSISOFTHEPERCENTOXALATEINTHEGREENCRYSTALMolarityofstandardizedKMnO4

Trial1 Trial2 Trial3

InitialburetreadingofKMnO4(mL)

FinalburetreadingofKMnO4(mL)

VolumeofKMnO4(ml)

VolumeofKMnO4(L)

MolesofKMnO4(Molarity×Volume)

Molesofoxalate(usestoichiometry)

MolarMassofoxalate(grams/mole)

Massofoxalate(grams)

MassofpureGreenCrystals(grams)

Masspercentofoxalate

Averagemasspercentofoxalate

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PART4:ANALYSISOFPERCENTIRONINGREENCRYSTAL1. CalculatetheconcentrationofironineachoftheStandardsamples1through5.

Concentrationofstockironsolution=NOTE:Eachsamplewasdilutedtoafinalvolumeof10.0mL.Forinstance,Standard1waspreparedbydiluting100µLor0.10mLofstocksolutiontoafinalvolumeof10.0mL

ConcentrationofIron

AverageAbsorbance

Standard1

Standard2

Standard3

Standard4

Standard5

Sample

Unknown

2. PlottheStandardCurve(Plotofabsorbance(y-axis)vs.concentration(x-axis))

andobtaintheequationofthebest-fitline.

Equationofbest-fitline:

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3. Calculatetheconcentrationofironinthesample.4. Theabovenumberistheconcentrationoftheironinthe10-mLvolumetricflask

samplepreparedinStep13oftheprocedure.Thissamplewaspreparedbydiluting0.5mLoftheoriginal25.0mLsampletoafinalvolumeof10.0mL.UsingtheconcentrationcalculatedinStep3above,calculatetheconcentrationofironinthe25.0mLsample.

5. Calculatethegramsofironinthesample.NOTE:Thevolumeofthesampleis

25.0mLandtheconcentrationofironisthenumbercalculatedinStep4above.6. CalculatethepercentageofironintheGreenCrystal.NOTE:Themassofthe

GreenCrystalisinthedatatable.

€

% Fe = Mass of Iron (g)

Mass of Green Crystal×100

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PART5:ANALYSISOFPERCENTHYDRATEINGREENCRYSTAL

Trial1Trial2

Trial3

Massofemptymicro-crucible(grams)

Massofmicro-crucible+GreenCrystal(grams)

MassofGreenCrystal(grams)

Constantmassofmicro-crucible+anhydrousGreenCrystal(followingfinalheating)(grams)

MassofanhydrousGreenCrystal(grams)

PercentageofwaterinGreenCrystal(grams)

AveragepercentageofwaterinGreenCrystal

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PART6:ANALYSISOFPERCENTPOTASSIUMINGREENCRYSTAL

Percentoxalate

Percentiron

Percenthydrate

Thereforepercentpotassium

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PART7:DETERMINETHEEMPIRICALFORMULAOFTHEGREENCRYSTALAssumethereare100gramsoftheGreenCrystal:

Grams

MolarMass(grams/mol)

Moles

RelativeMoles

Oxalate(C2O42-)

Iron

Hydrate(H2O)

Potassium

EmpiricalFormulaofGreenCrystal:

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PART8:DETERMINATIONOFPERCENTYIELDOFTHEREACTION1. ObtainthecorrectformulaoftheGreenCrystalfromtheinstructor.

FORMULA:2. WriteacompletebalancedchemicalequationforthesynthesisoftheGreen

Crystal.3. Basedontheexactmassesofthetwostartingmaterialsusedforthesynthesis

(DataTable:Part1),calculatethetheoreticalyieldoftheGreenCrystal.Besuretoconsiderthelimitingreagent.

4. BasedonthemassofthepureGreenCrystalobtained(DataTable:Part2),

calculatethepercentyieldofthereaction.

€

% Yield = Experimental Yield

Theoritical Yield×100