EXPERIMENT #16 CHEMICAL EQUILIBRIUM AND LE CHATELIER'S PRINCIPLE化學(xué)平衡與勒夏特列原理

PAGEEXPERIMENT#16:CHEMICALEQUILIBRIUMANDLECHATELIER'SPRINCIPLEPURPOSE: TostudychemicalreactionsatequilibriumandtheirresponsestostressasdescribedbyLeChatlier'sPrinciple.INTRODUCTION: Youwillstudythreedifferentequilibriumsystemsinvolvingionsinsolution.Thefirstsystemistheconversion oftheindicatorthymolbluefromitsblueformtoitsyellowform.Theextenttowhichtheforwardreactionis favoreddependsupontheconcentrationofhydrogenions,[H+],insolution:thymolblue(blueform)+H+(aq)?thymolblue(yellowform) Thesecondreactioninvolvesthelightyellowiron(III)ion,Fe3+,andthiocyanateion,SCN–,whichformsthe coloredcomplex,FeSCN2+:Fe3+(aq)+SCN-(aq)?FeSCN2+(aq) Thethirdsysteminvolvesthehydratedcobalt(II)ion,Co(H2O)62+,whichcanbeconvertedtothechlorinated complexion,Co(H2O)4Cl2:Co(H2O)62+(aq)+2Cl–(aq)?Co(H2O)4Cl2(aq)+2H2O(l) Youwillstudytheeffectsofchangingthetemperatureonthissystem.Yourdatashouldallowyoutopredict whethertheforwardorreversereactionisendothermic.PROCEDURE:(Includewithyourlaboratoryreport,orrefertothispage)PARTI:ThymolBlueEquilibrium 1. Cleantwo125mLErlenmeyerflasks.Toeachflask,addapproximately20mLofdistilledwaterand5drops ofthymolbluesolution.Recordthecolorofthissolutioninthedatasection. CAUTION:Hydrochloricacid(HCl)andsodiumhydroxide(NaOH)areextremelycorrosive.Handlethese solutionswithcare. 2. Tothefirstflask,addasingledropof0.1MNaOH.Swirlthecontentsoftheflaskandcontinuethedrop- by-dropadditionuntiladefinitecolorchangeisobserved.Thesecondflaskservesasacontrol.Compare thesolutioncolors.Recordthenewcolorofthesolution. 3. Tothefirstflask,add0.1MHCldrop-by-dropuntiladefinitecolorchangeisobserved.Recordthenew color.PARTII:Ferro-thiocyanateIonEquilibrium 4. Place5dropsof0.2MFeCl3intoa100mLbeaker.Recordthecoloroftheiron(III)chloridesolution. Recordthecolorofa0.2MKSCNsolution,andthenadd5dropsofthepotassiumcyanatetothebeaker containingtheFeCl3.Swirlthemixtureandnotethecolor. 5. Addenoughdistilledwatertothesolutiontodilutetheintensecolortoalightambercolor(50to70mL). 6. Pourapproximately5mLofthissolutionintoeachoffivetesttubeslabeledAtoE.7. TotesttubeA,add10dropsofdistilledwater.TesttubeAwillserveasacontrol. 8. TotesttubeB,add10dropsof0.2MKCl. 9. TotesttubeC,add10dropsof0.2MFe(NO3)3.10. TotesttubeD,add10dropsof0.2KSCN. 11. TotesttubeE,add10dropsof6.0MNaOH. 12. RecordthecolorofthesolutionaftertheadditionofdropstotesttubesBthroughE;comparetothe controltesttubeA.PARTIII:HydratedCobalt(II)ChlorideEquilibrium13. Placeasmallcrystal(approximately0.2g)ofcobalt(II)chloridehexahydrate,CoCl2·6H2O,intoeachof two100mLbeakers. CAUTION:CoCl2·6H2Oisverypoisonous,andcanbefataliftakeninternally.Donotgetanyinyour mouth,andwashyourhandsattheconclusionofthislab.14. Usinga25mLgraduatedcylinder,add10mLof6.0MHCltothefirstbeaker.Recordthecolorofthe resultingsolution.15. Tothesecondbeaker,add10mLofdistilledwater.Recordthecoloroftheresultingsolution.16. Graduallyadddistilledwatertothesolutioninthefirstbeakeruntilitappearstobethesamecolorasthatin thesecondbeaker.Recordthecolor.17. Set-upringstandassemblyandlightBuddyBunsen.Gentlyheatthefirstbeakeroveralowflame.Aftera definitecolorchangeisobserved,shutofftheburner.Removethebeakerfromtheringstand,andrecord thecolorofthesolution.18. Set-upacool-waterbathina250mLbeaker,fillwithapproximately50to100mLoftapwater,andlowerthe firstbeakerintothebath.Asitcools,recordanychangesincolor.PRE-LABQUESTIONS:(Willbecompletedonaseparatepagepriortobeginningthelab.)1. WriteanequationfortheequilibriumreactioninPartI.2. Writetheequationfortheequilibriumreactioninvolvingtheformationoftheiron(III)thiocyanateionfromPartII. 3. Writetheequationfortheequilibriumreactionbetweenthehydratedcobalt(II)ionandthehydratedcobalt(II) chlorideionfromPartIII. 4. InPartI,whatisthepurposeofaddingthymolbluetotwoErlenmeyerflasksifadditionalreagentsareonlyto beaddedtothefirstflask? 5. WhatprecautionsshouldyouobservewhenheatingthecobaltchlorideandacidsolutioninPartIII? 6. WhatisthepurposeofaddingdistilledwatertothebeakerinPartII? 7. Whatisthefunctionoftesttube“A”inPartII? 8. Writeandbalancetheequationforthereactionbetweenhydrogenionsandhydroxideions. 9. Referringtoyouranswertoquestion#8,howmightthehydrogenionconcentrationbedecreased? 10. Whatisaspectatorion?EXPERIMENT#16:EquilibriumandLeChatelier’sPrinciple(continued)DATAANDOBSERVATIONS:(Recordonaseparatepage)PARTI:Ferro-thiocyanateIonEquilibrium a) Initialcolorofthymolbluesolution: ________________________ReagentAddedStress(ionadded)ColorObservedEquilibriumShift(forwardorreverse)b)NaOH(aq)c)HCl(aq)PARTII:HydratedCobalt(II)ChlorideEquilibrium d) Colorof0.2MFeCl3solution: ________________________ e) Colorof0.2MKSCNsolution: ________________________ f) Colorofmixture;FeSCN2+complex: ________________________ (testtubeA)ReagentAdded(testtube)StressIonSpectatorIonObservedColorEquilibriumShift(forwardorreverse)g)distilledwater(ttA)h)KCl(ttB)i)Fe(NO3)3(ttC)j)KSCN(ttD)k)NaOH(ttE)PARTIII:HydratedCobalt(II)ChlorideEquilibrium l) ColorofCo(H2O)4Cl2solution: . m) ColorofCo(H2O)62+solution: pink.StepStressObservedColorEquilibriumShift(forwardorreverse)n)Step16o)Step17p)Step18POST-LABDISCUSSION: TheequilibriumsysteminPartIcanbeaffectedbytheadditionofanyreagentsupplyingH+orOH-.Hydrogen ionsarecharacteristicofacidsandhydroxideionsarecharacteristicofbases.Theadditionofanacidshould favortheconversionintotheyellowformoftheindicator. AnotherfactortoconsiderinexplainingyourobservationsisthefactthatH+willreactwithOH-toformwater molecules.Asaresultoftheformationofwater,theconcentrationsofH+andOH-intheequilibriumreactionare reduced. InreviewingyourdatafromPartII,itisimportanttonotethattheformationofFeSCN2+isheavilyfavoredoverthe reversedecompositionreaction.Dilutingthesolutionwithwaterallowsyoutoobservesmallchangesinthe equilibriummorereadily.Inexplainingyourobservationsofthisequilibrium,rememberthatspectatorionsdonot participateinthenetreaction. Instep11ofPartII,younotedtheformationofaprecipitate.Inthiscase,theprecipitateisFe(OH)3.In explainingyourresults,rememberthattheformationofthisprecipitatereducestheFe3+concentrationofthe solution. ForthereactioninPartIII,recallthatincreasingthetemperatureofanequilibriumreactionfavorstheendothermic reaction.Fromyourobservations,youshouldbeabletopredictwhichofthetworeactions,forwardorreverse,is endothermic.QUESTIONS:(Answeronaseparatepage) 1. InPartI,howwoulddecreasingthemolarityoftheNaOHsolutionfrom0.1Mto0.05Maffectthenumberof dropsrequiredfortheobservedcolorchange?Explainyouranswer. 2. ApplyLeChatelier'sPrincipletoexplaintheresultsyouwouldexpecttoobtainwhen6.0MNaOH(aq)was introducedintotheiron(III)thiocyanateion(FeSCN2+)equilibriumsystem.Explainyouranswer. 3. Ifthehydratedcobalt(II)ionc