Write a conclusion paragraph for this lab (Volumetric Analysis). The conclusion should restate the objective and hypothesis of the lab, summarize key data and results, and summarize the experimental portion of the lab.

Write a conclusion paragraph for this lab (Volumetric Analysis). The conclusion should restate the objective and hypothesis of the lab, summarize key data and results, and summarize the experimental portion of the lab. A clear conclusion should be made about the lab overall and should relate back to the hypothesis and concepts learned in class.

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Stoichiometry:VolumetricAnalysisPurposeThepurposeofthisexperimentistodeterminetheconcentrationofanunknownacidsample.LearningObjectivesUseaprimarystandardtodeterminethepreciseconcentrationofasodiumhydroxidesolutionbytitra-tion.Determinethemolarconcentrationofanunknownacidsolutionbytitratingagainstastandardizedsolutionofsodiumhydroxide.Determinethepercentbymassofanunknownacidinasolidsamplebytitratingagainstastandardizedsolutionofsodiumhydroxide.LaboratorySkillsUseaburetCarryoutanacid-basetitration.Standardizeasodiumhydroxidesolution.Equipment30mLbeaker250mLbeaker250mLErlenmeyerFlaskBalanceRingstandBuret25mLvolumetricflaskBuretclampWeighingpaperWash/waterbottleWhitepapersheetSpatulaChemicalsPhenolphthaleinindicatorsolution~0.1MNaOHDrypotassiumhydrogenphthalate,(KHC8H4O4),alsoknownasKHPSolidorsolutioncontaininganunknownconcentrationorpercentageofamonoproticacid(,aceticacid,NaHSO4,benzoicacid.)ordiprotic(maleicacid,malonicacid.oxalicacid,tartaricacid).CatalystEducationOERLabsarelicensedunderaCreativeCommonsAttribution-NonCommercial-ShareAlike4.0license.Toaccessourfulllistofexperimentsvisithttps://links.labflow.com/OER.LabVersionVARelease3.28.VA.1

VolumetricAnalysisIntroductionAchemicalanalysisthatisperformedprimarilywiththeaidofvolumetricglassware(e.g.,pipets,burets,volu-metricflasks)iscalledvolumetricanalysis.Foravolumetricanalysisprocedure,aknownquantityoracare-fullymeasuredamountofonesubstancereactswithato-be-determinedamountofanothersubstancewiththereactionoccurringinaqueoussolution.Thevolumesofallsolutionsarecarefullymeasuredwithvolumetricglassware.Theknownamountofthesubstanceforananalysisisgenerallymeasuredandavailableintwoways:1.Asaprimarystandard:Aprecisemass(andthus,moles)ofasolidsubstanceismeasuredonabalance,dissolvedinwater,andthenreactedwiththesubstancebeinganalyzed.Notallsubstancescanbeusedasprimarystandards.Tobeusefulasaprimarystandard,asubstancemustbeavailableinahighdegreeofpurity,witharelativelylargemolarmass,benon-hygroscopicandmustreactinapredictableway.2.Asastandardsolution:Ameasurednumberofmolesofsubstanceispresentinameasuredvolumeofsolution-asolutionofknownconcentration,generallyexpressedasthemolarconcentration(ormo-larity)ofthesubstance.Ameasuredvolumeofthestandardsolutionthenreactswiththesubstancebeinganalyzed.Thereactionoftheknownsubstance(standard)withthesubstancetobeanalyzed(analyte),occurringinaqueoussolution,isconductedbyatitrationprocedure.Thetitrationprocedurerequiresaburettodispenseasolution,calledthetitrant,intoaflaskcontainingtheanalyte(FigureVA.1a).Aburetisusedbecauseitallowsfortheprecisemeasurementofdispensedvolumes.Thetitrantcanbeasolutionofknownorunknownconcentration.Theanalytemaybeasolutionwhosevolumeismeasuredwithapipetoritmaybeadissolvedsolidwithaveryac-curatelymeasuredmass.Thisexperimentinvolvestwotitrations.Thefirstdeterminesthepreciseconcentrationofasodiumhydroxidesolutionusinganacidthatisaprimarystandard.Thesecondtitrationusesthatsodiumhydroxidesolution(nowstandardized)todeterminetheamountofacidinanunknownsample.Inbothcases,thetitrantisasodiumhydroxidesolution,andtheanalyteisanacid.VA.2

VolumetricAnalysisFigureVA.1:(a)Titrantintheburetisdispensedintotheanalyteuntil(b)theindicatorchangescoloratitsendpoint.(c)Tipsforcarryingoutasuccessfultitration.Areactioniscompletewhenstoichiometricamountsofreactants,amountsthatreflectthemoleratiointhebalancedchemicalequation,arecombined.Inatitration,thispointiscalledthestoichiometricpointorequiv-alencepoint.Inanacid-basetitration,theequivalencepointisoftendetectedusinganacid-baseindicator,whichisasubstancethathasastructureinacidicsolutionthathasadifferentcolorthanitsstructureinbasicsolution.Thepointinthetitrationatwhichtheindicatorchangescoloriscalledtheendpointoftheindicator(FigureVA.1b).Theindicatorusedinthisexperiment,phenolphthalein,iscolorlessinacidicsolutionandturnspinkinbasicsolution.Notethatthecolorintheimagein(FigureVA.1b)ismuchdarkerthanthepalepinkcolorofthetrueendpoint.Thetrueendpointoccursatthefirstdropoftitrantthatresultsinapersistentcolorchange.VA.3

VolumetricAnalysisStandardizationofaSodiumHydroxideSolutionSodiumhydroxidesolutionsarefrequentlyusedastitrantsinacid-basetitrations.However,solidsodiumhydrox-ideisveryhygroscopic(absorbswatervaporreadily),whichmakesitimpossibletomeasureitsmassaccuratelyenoughtobeusedtoprepareaprimarystandardsolution.Inaddition,sodiumhydroxide,NaOH,reactswithcarbondioxide,CO2,intheatmosphereformingsodiumcarbonate,Na2CO3,alesssolublesalt(ReactionVA.1).CO2(g)+2NaOH(aq)−−−→Na2CO3(s)+H2O(l)(ReactionVA.1)Consequently,aNaOHsolutionmustbestandardizedbytitratingitagainstanacidthatisaprimarystandard.Inthefirstpartofthisexperiment,drypotassiumhydrogenphthalate,KHC8H4O4,isusedastheprimaryacidstandardfordeterminingthemolarconcentrationofasodiumhydroxidesolution.Potassiumhydrogenphthalateisawhite,crystalline,acidicsolidthatisavailableathighpurity,hasahighmolarmassandisonlyslightlyhygroscopic.ThenumberofmolesofKHC8H4O4usedintheanalysisiscalculatedfromitsmeasuredmassandmolarmass(204.22g/mol)asshowninEquationVA.1:molKHC8H4O4=mass(g)KHC8H4O4×1molKHC8H4O4204.22gKHC8H4O4(EquationVA.1)Thebalanced,netionicequationforthereactionindicatesthatonemoleofKHPreactswithonemoleofNaOH,asseeninReactionVA.2:HC8H4O4−(aq)+OH−(aq)−−−→H2O(l)+C8H4O42−(aq)(ReactionVA.2)Intheexperimentalprocedure,anaccuratelymeasuredmassofdrypotassiumhydrogenphthalateisdissolvedinDIwater.ApreparedNaOHsolutionisthendispensedfromaburetintotheKHC8H4O4solutionuntilthestoichiometricpointisreached,signaledbythecolorchangeofthephenolphthaleinindicatorfromcolorlesstopink.AtthispointthedispensedvolumeofNaOHisnotedandrecorded.ThemolarconcentrationoftheNaOHsolutioniscalculatedusingEquationVA.2molarconcentration(M)NaOH(molL)=molNaOHLNaOHsolution(EquationVA.2)Oncethemolarconcentrationofthesodiumhydroxideiscalculated,thesolutionisstandardized.Thesodiumhydroxidesolutionisclassifiedasasecondarystandardsolution.VA.4

VolumetricAnalysisMolarConcentrationofanAcidSolutionThestandardizedsodiumhydroxidesolutionisnextusedtodeterminetheconcentrationofananacidsolutionorthepercentagebymassofanunknownacidinasolid.Ineithercase,theNaOHsolutionisusedtotitrateanaccuratelymeasuredvolumeoftheacid,oranaccuratelymeasuredmassofunknownsolid,tothestoichiometricpoint.Then,EquationVA.3isusedtodeterminethenumberofmolesofNaOHusedintheanalysis:volume(L)×molarconcentration(molL)=molNaOH(EquationVA.3)Themolesofacidneutralizedinthereactioniscalculatedusingthestoichiometryofthereaction,whichisde-terminedbythetypeofunknownacid.Acidsusedinthisexperimentmaybemonoprotic,HA,diprotic,H2Aortriprotic,H3A.ExampleVA.1showshowtocalculatethemolarconcentrationofaunknowndiproticacidsolutionandExampleVA.2showhowtodeterminethepercentbymassofamonoproticacidsample.ExampleVA.1:CalculatingtheMolarConcentrationofanUnknownDiproticAcidYourassignmentwastotitrateanunknownsolutionthatcontainsanacidtypeH2A,adiproticacid.YouhaverecordedthevolumeandconcentrationoftheNaOHsolutionusedinthetitration.Solution:CalculatethenumberofmolesofNaOHusedtoneutralizetheunknownsolution(EquationVA.3)andusethatnumbertodeterminethenumberofmolesoftheacidpresentinthetitration.Thefollowingchemicalequation,ReactionVA.3isthechemicalequationforthereactionofNaOHandadiproticacid.EquationVA.4givesthemoletomolerationeededtodeterminethemolesofacidinthesamplefromthetitration.H2A(aq)+2NaOH(aq)−−−→Na2A(aq)+2H2O(l)(ReactionVA.3)molH2A=molNaOH×(molH2A2molNaOH)(EquationVA.4)Noticethatthenumberofprotons(hydrogenions)presentintheunknownacid(H2A)solutionisthenumberofmolesthatneedtobeneutralized.InthisspecificexamplethereisonemoleofH2Apresentforevery2molesofNaOHusedinthetitration.Calculatethemolarconcentrationoftheunknownacidusingthethemolesoftheacidthatwereneutralizedinthetitrationandthemeasuredvolumeoftheacidsample.ThisisshowninExampleVA.1:MH2A=molH2ALH2A(EquationVA.5)VA.5

VolumetricAnalysisExampleVA.2:CalculatingthePercentagebyMassofanUnknownMonoproticAcidYourassignmentistodeterminethepercentagebymassofanunknownsolidthatcontainsanacidtypeHAwithamolarmassof204.22g/mol(monoproticacid).Solution:CalculatethenumberofmolesofNaOHusedtoneutralizetheunknownsolution(EquationVA.3)andusethatnumbertodeterminethenumberofmolesoftheacidpresentinthetitration.ReactionVA.4isaneutralizationequationforamonoproticacid.ThemoletomoleratiofromthatequationisgiveninEquationVA.6.HA(aq)+NaOH(aq)−−−→NaA(aq)+H2O(l)(ReactionVA.4)molHA=molNaOH×(molHAmolNaOH)(EquationVA.6)Noticethatthenumberofhydrogenionspresentintheunknowntypeacid(HA)solidisthenumberofmolesthatneedtobeneutralized.Inthisspecificexamplethereis1moleofHAforeach1moleofNaOHusedinthetitration.CalculatethemassofacidinthesolidmixtureusingthemolesofacidthatwereneutralizedandthemolarmassoftheacidusingEquationVA.7gHA=molHA×(gmolHA)(EquationVA.7)ThepercentagebymassoftheacidcanbecalculatedusingEquationVA.8:%bymass=(gHAgsample)×100%(EquationVA.8)VA.6

VolumetricAnalysisProcedureMaintainatleastthreesignificantfigureswhenrecordingdataandperformingcalcula-tions.StandardizationofaSodiumHydroxideSolutionCarryoutthestandardizationuntilyouachievethreetrialswithin±1%reproducibility.1.Obtainthreeclean125-or250mLErlenmeyerflasks.2.Obtaintheprepared~0.1MNaOHsolution3.CalculatethemassofKHC8H4O4thatwillrequireabout15-20mLofyour~0.1MNaOHsolutiontoreachthestoichiometricpoint.Showyourcalculationonthereportsheet.4.Measuretheamountyoupreviouslycalculated(±0.010g)ofKHC8H4O4onweighingpaperandtransferittoalabeledErlenmeyerflask.Prepareatotalofthreesampleswhileyouareoccupyingthebalance,recordingtheexactmassesusedforeachsample.5.DissolveeachKHC8H4O4sampleinabout50mLofpreviouslyboiled,DIwaterandadd2to5dropsofphenolphthalein.6.Obtainaburetandcleanitfollowingthesesteps:RinsetheburetwithtapwaterandrinseseveraltimeswithDIwater.Rinsetheburetwiththree5mLportionsoftheNaOHsolution,wettingtheentireinnersurfacewiththesolutioneachtime.Draineachrinsethroughtheburettip.Discardeachrinseinthe“WasteBases”container.7.Usingacleanfunnel,filltheburetwiththeNaOHsolution.Readthevolumebyviewingthebottomofthemeniscuswiththeaidofablacklinedrawnonawhitecard(theburetcanberemovedfromthestandormovedupordownintheburetclamptomakethisreading;youdonotneedtostandonachairtoreadthemeniscus).Recordthisinitialvolumeusingallcertaindigits(fromthelabeledcalibrationmarksontheglassware)plusoneuncertaindigit(thelastdigitwhichisthebestestimatebetweenthecalibrationmarks).VA.7

VolumetricAnalysisPlaceasheetofwhitepaperbeneaththeErlenmeyerflask.Havetheinstructorapproveyourburetandtitrationsetupbeforecontinuing.8.SlowlyaddtheNaOHtitranttothefirstKHC8H4O4solutionpreviouslyprepared.Swirltheflaskaftereachaddition,watchingastheinitialpinkcolorfades.AtfirstyoucanaddtheNaOHsolutionin1-to2mLincrements,makingsurethatyouoccasionallyrinsethewalloftheflaskwithasmallamountofDIwater.Whenyounoticethatthepinkcolorbeginstofademoreslowly,youarenearingthestoichiometricpoint.YouwillneedtoaddtheNaOHmoreslowly,eventuallyonedropatatime.ContinueadditionoftheNaOHtitrantuntiltheendpointisreached,whichiswhenapalepinkcolorpersistsfor30seconds.ReadandrecordthefinalvolumeofNaOHintheburet.9.RepeatthetitrationtwomoretimeswiththeotherKHC8H4O4solutions,makingsurethatthereissufficientNaOHintheburetatthestartofeachtitration.10.CalculatethevolumedispensedandusethattocalculatethemolarconcentrationoftheNaOHsolution.ThemolarconcentrationsoftheNaOHsolutionfromthethreeanalysesshouldbewithin±1%.KeepthisNaOHsolutiontouseinthenextprocedureorprocedures.11.Ifnecessary,prepareadditionalKHC8H4O4solutionstorepeatthetitrationuntilyouhaveachievedgoodagreementamongthreetitrations.12.DisposeoftheneutralizedsolutionsintheErlenmeyerflasksinthe“WasteAcids”container.MolarConcentrationofanAcidSolutionYouwilldeterminethemolarityofanacidsolutionofeitherHAorH2Aacidtype.Youwillbegiveninformationregardingtheacidtype.1.Obtainthreeclean125-or250mLErlenmeyerflasks.2.Measure25.00mLoftheunknownacidsolutionusinga25.00mLvolumetricflask.TransferthemeasuredsolutiontoacleanErlenmeyerflask.Add2dropsofphenolphthaleinandswirl.3.FilltheburetwiththestandardizedNaOHsolution.Readandrecordtheinitialvolume.TitratetheacidVA.8

VolumetricAnalysissampletothephenolphthaleinendpoint.Readandrecordthefinalvolumeoftitrant.4.Titratetwoadditionalsamplesoftheacidsolution.5.Calculatetheaveragemolarconcentrationofyouracidunknown.6.Disposeoftheneutralizedsolutionsinthe“WasteAcids”container.PercentagebyMassofanAcidinanUnknownSolidAsolidsamplecontaininganunknownamountofeitherHAorH2Aistobeanalyzed.Youwillbegiveninfor-mationregardingtheacidtypeanditsmolarmass.1.Obtainthreeclean125-or250mLErlenmeyerflasks.2.Weighoutapproximately1.25gofyoursolidmixtureonweighingpaper.Recordthemass.TransferthesolidsampletoacleanErlenmeyerflaskanddissolvewith50mLofDIwaterandadd2dropsofphenolphthalein.3.FilltheburetwiththestandardizedNaOHsolution.Readandrecordtheinitialvolume.Titratetheacidsampletothephenolphthaleinendpoint.Readandrecordthefinalvolumeoftitrant.4.Weighandtitratetwoadditionalsamplesofthesolidunknown.5.Calculatethepercentagebymassofyouracidunknown.Calculatetheaveragepercentbymassoftheacidunknown.6.Disposeoftheneutralizedsolutionsinthe“WasteAcids”container.7.Cleanup:Rinsetheburetseveraltimeswithtapwateranddiscardrinsesappropriately.RinsetwicewithDIwater.Clamptheburetupsidedowntodripdryatyourdesk.CleantheErlenmeyerandvolumetricflasksfollowingthesameprocedure.Checkandcleanthebalancearea.ReturnallunknownstoyourLabInstructor.VA.9

VolumetricAnalysisVA.10

ReportSheet:VolumetricAnalysisName:Section:Date:StandardizationofaSodiumHydroxideSolutionApproximatemassofKHC8H4O4needed(g)Showcalculations.ReportTableVA.1:TitrationofKHC8H4O4Trial1Trial2Trial3MassofKHC8H4O4(g)MolesofKHC8H4O4(mol)InitialburetreadingofNaOH(mL)FinalburetreadingofNaOH(mL)VolumeofNaOHdispensed(mL)ConcentrationofNaOH(mol/L)AverageconcentrationofNaOH(mol/L)ShowcalculationsforTrial1.CatalystEducationOERLabsarelicensedunderaCreativeCommonsAttribution-NonCommercial-ShareAlike4.0license.Toaccessourfulllistofexperimentsvisithttps://links.labflow.com/OER.LabVersionVARelease3.28.VA.1

VolumetricAnalysisReportSheetMolarConcentrationofanAcidSolutionAcidtype:Unknown#BalancedequationforneutralizationofacidwithNaOH:ReportTableVA.2:TitrationofUnknownAcidSolutionSample1Sample2Sample3Volumeofacidsolution(mL)InitialburetreadingofNaOH(mL)FinalburetreadingofNaOH(mL)VolumeofNaOHdispensed(mL)Concentrationofacidsolution(mol/L)Averageconcentrationofacidsolution(mol/L)ShowcalculationsforSample1.VA.2

VolumetricAnalysisReportSheetPercentagebyMassofAcidinanUnknownSolidAcidtype:Unknown#BalancedequationforneutralizationofacidwithNaOH:ReportTableVA.3:TitrationofUnknownSolidSample1Sample2Sample3Mas

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