Post on 29-Mar-2023
CHEM162:LAB2IntermolecularForcesDemonstration
OVERVIEWThislabwillbeconductedonlineandisexpectedtotake3–4hourstocomplete.Studentswilllearnabouttheinformationtypicallykeptinageneralchemistrylaboratorynotebook.Severalformatsforlaboratorynotebookswillbesharedandstudentsareinvitedtochooseastyletheyprefer.Studentswillobservetheimpactofintermolecularforcesonphysicalpropertiesofsurfacetension,viscosity,solubility,andevaporativecooling.TECHNIQUESTOLEARN
• Howtowriteascientificobjective.• Howtosummarizeaprocedure.• Howtoanticipatethedatathatwillbecollectedandcreatedatatablesandgraphsbeforeperformingthelab.• Howtowriteahypothesisandanalyzedatatosupportorrefuteahypothesis.• Howtorecordobservationsanddatainalaboratorynotebook.
MATERIALS
• Notebook,scratchpaper,ortabletforwriting.• 2differentcoloredpens(blueandblack,orsimilar)• Noteaboutvideos:allvideoslinksforthislabwillbelistedinthisdocumentandtheywillbeembedded
inthecanvasassignmentpage.
CRITERIAFORSUCCESS
Studentsattempteachquestioningoodfaith.Shortanswerresponsesareformattedincompletesentences.
Allworkisshownforcalculationswhenrequested.Thesemaybeembeddedintheassignmentsubmittedorattachedseperatelyifnecessary.
Studentdemonstratesmasteryofthelab'slearningobjectives.Someerrorsmaybepresentintheassignment,about85%oftheanswersarecorrectwithnolargegapsinknowledgepresent.Theassignmentisformattedasalaboratorynotebook.Mistakesarelegibleandtheworkishandwritten.Scientificobjectiveiswrittenfromtheperspectiveofascientist(notstudent),anddescribesthegoalofthelabratherthenthetasksthatwillbecompleted.Studentsdemonstrateunderstandingofformatingalabnotebook,recordingobservations,andtheeffectofintermolecularforcesonphysicalproperties.Twocolorsofpenareused.Oneisusedtopreparethenotebookbeforewatchingthedemonstrationvideosandanothercolorisusedtorecordobservations.Theprocedureissummarizedbrieflyinthestudentsownwords.Observationsincludephysicalappearances,changes,andmeasurements.PartDtableisproperlyformattedandeasytoread,itincludesobservationsofintialtemperature,finaltemperature,andtime.CalculationsareshownforpartDConclusionparagraphaddressesintermolecularforcesforeachdemonstration.
Lab2:LabNotebooks&IMFDemo
General
Lab2
INTRODUCTIONThislabwillbeconductedonline.Tocompletethelabyouwill:
1) Readtheintroductionandwatchavideoabouthowtokeepalaboratorynotebook.2) ReadtheIMFDemoprocedureandusinganotebookorloosepaperpreparea“labnotebook”before
watchingtheDemovideos.3) Watchthedemovideosandrecordobservationnotesinthe“labnotebook”pages.4) Reflectonyourobservationsinaconclusionsparagraph.
LABORATORYNOTEBOOKSThescientistsgoalinkeepingalabnotebookistohavearecordofeverythingthathappenedinthelab.EVERYTHING.Thismeansthatmistakes,questions,observations,andmeasurementsareallrecorded.Havingasystematicwayofrecordinginformationmakesiteasierforascientisttofindinformation,analyzedata,andultimatelycommunicatetheirfindings.Inthisclassyouwillpracticelabnotebookskills.Thesearethesectionsyourlabnotebookmustincludeforthisclass.Boldedsectionswillbeincludedinalllabsregardlessofthelab’sprocedure.
• Name• Date• Labnumberandtitle• ScientificObjective• Pre-labnotes:Theseshouldbeincludedasnecessarybasedonthelabprocedure.
o Hazards&Safetyinformationo Wastedisposalinformationo Listofchemicals,amounts,physicalpropertieso Chemicalreactions
• Proceduresummary• Spaceforobservations• Spaceforcalculations(ifthelabrequirescalculations)• Datatablescreatedandreadyforinformationtoberecorded.(ifthelabrequiresrecording
measurementsinatable)• Spaceforgraphs,ifpossiblecreateaxisandtitlebeforestartinglab(ifthelabincludesgraphingdata).• Spaceforconclusions
ScientificObjectives.In1–2sentencesstatethepurposeofthelabfromtheperspectiveofascientistratherthanastudent.Oftenscientificobjectivesletthereaderknowwhatthefinalcalculationswilldeterminefromcollecteddataorwhatquestionisbeingansweredbytheexperiment.Thesemayincludethetechniquesthatareusedinthelabbutnoproceduraldetailshouldbementioned.PleaseseeAppendixAofthislabforexamplescientificobjectives.ProcedureSummary.Thepurposeofsummarizingtheprocedureistwo-fold:1)studentscommunicatetheyarepreparedtoconductthemselvessafelyinlabbydemonstratingtheyhavecarefullyreviewedtheprocedure.2)Asummarycancreateashortroadmapoftheexperimentthatcanbereferencedwhilerecordingobservations.Thiscanreducetheamountoftimeittakestowriteyourobservationsinyournotebook,allowingthestudenttorecordmoredetails.PleaseseeAppendixBformoreinformationaboutformattingalabnotebook.Observations.Allobservationsmustbemadeinpen.Ifamistakeismadeasinglelineshouldbedrawnthroughanobservationtoindicatetheinformationisincorrect.Thecorrectinformationcanthenbewritten.Thegoalistorecordmistakesaswellasyoursuccesses,somistakesmuststillbelegibletothereader.Observationsshouldnotethephysicalappearanceofasolution,changesthatareobserved,measurementsofphysicalproperties
thatareperformed,andpossibleproceduralmistakesthataremadealongthewaythatshouldbeconsideredwhenanalyzingdatalater.FormoreinformationaboutobservationspleaseseeAppendixB.Conclusions.Attheendofanexperimentstudentsshouldrecordtheirinitialimpressionsoftheirwork.Reviewingthelabquestionsthatfollowtheprocedureandmakingafewnotesafterbeingseepedintheworkofthelabforhourswillmakeiteasiertorecalldetailsofthelabdaysorweekslater.Thiscanreducetheamountoftimespentansweringthequestionsafterthedatahasbeenanalyzed.INTERMOLECULARFORCESThestructureofamoleculeinformshowitwillinteractwithothermolecules.Overallpolarity,thepresenceofH-F,H-N,orH-Obonds,thesize,theshape,andthechargealldictatetheintermolecularforcesthatwillexistbetweenmolecules.Themoreintermolecularforcesthatexist,thestrongertheinteractions.Thephaseofthesubstance(solid,liquid,andgas)affecthowclosethemoleculesaretooneanother.Thecloserthemoleculesthestrongertheinteractions.Intermolecularforcesarelistedbelowinorderofincreasingstrength.LondonDispersionForces(weakestIMF)
Theseexistbetweenallmolecules(withanelectroncloud).Thisinteractionarisesfromtemporaryandspontaneousdipolemomentsthatarecreatedwhenelectronsfromonemoleculecomeclosetoelectrons,andrepelthem,inanothermolecule.
Dipole-DipoleInteractions Theseexistonlybetweenmoleculesthathaveoveralldipolemoments.Thepartialpositiveendofamoleculewillalignwiththepartialnegativeendofanothermolecule.
HydrogenBonding TheseexistonlybetweenmoleculeswithH-F,H-N,andH-Obonds.TheHydrogenatomhasalargepartialpositivechargeandtheF,N,orOhasalargepartialnegativechargeandlonepairsthatarecapableofinteractingwiththelargepartialpositivechargeofaHydrogenonanothermolecule.
Ion-DipoleInteractions(strongestIMF)
Theseexistinmixtureswhenacationinteractswiththepartialnegativeendofapolarmoleculeorananioninteractswiththepartialpositiveendofapolarmolecule.
Thislabwillincludeacomparisonofthephysicalpropertiesofpuresubstances.Reviewthechemicalstructuresofthemoleculesthatwillbecomparedineachpartoftheexperiment.Whatintermolecularforcesexistwithinapuresampleofeachcompound?
LAB2ACTIVITYInthisactivityyouwilllearnfirstaboutlabnotebooksandprepareyourownforaseriesofintermolecularforces(IMF)demos.YouwillthenwatchtheIMFdemosandrecordyourobservationsinthenotebookpagesyouprepared.Finally,youwriteaconclusionsparagraphusingtheprovidedquestionstoguideyourdiscussion.First,watchthenotebookvideolinkedbelowabouthowtopreparealabnotebookbeforeconductinganexperiment.Thevideowillalsoincludeinformationabouthowtorecordobservations.Thevideowillshowanexampleofhowtosetuplabnotebookpages,thisexperimentisnotthesameasthosecompletedinthislab.Usethisinformationandtheinformationprovidedintheintroductiontocompletequestion1oftheactivity.ThedocumentsshowninthevideocanbedownloadedfromtheLab2canvasassignmentpage.
WatchtheNotebookVideohere:https://youtu.be/BvpvyqpAX-o(about30minutes)Q1.Createyourprelabnotebookpages.Useanotebook,piecesofscratchpaper,oratablettopreparealabnotebookpagesfortheexperimentsdescribedintheprocedurethatfollowsthisquestion.Thisshouldbedonebeforewatchingthedemonstrationvideos.Yourpagesshouldinclude:
• Includeyourname,date,andalabtitle.• Writeascientificobjectiveforthelab.(ReviewingQ4canhelpyouwriteyourobjective)• Reviewtheprocedurebelowfortheintermolecularforcedemonstrationsandsummarizeitasa
shortparagraphorbulletpointswithspaceforobservations.• Leavespaceforyourobservations.• Createatablefortheevaporativecoolingexperiment.Thetableshouldincludeinitial
temperature,finaltemperature,time,andcalculatedrate.• Leavespaceforevaporativecoolingratecalculations.• Leavespaceforconclusions.
PartA: Water CookingOil(unsaturatedtrigylceride)
PartC: Isopropanol PropyleneGlycol Glycerol
PartD: Water Isopropanol Acetone
Q2.Recordobservations.Foreachexperimentdescribedintheprocedurewatchashortvideolinkedbelow.Recordyourobservationsinyourlabnotebookpagespreparedinquestion1.Pleaseuseadifferentcoloredpensoitiscleartomehowyoupreparedyournotebookandhowyourecordedobservations.
A. Solubility:https://youtu.be/sWxLhkhbGhoB. SurfaceTension:https://youtu.be/Qvi6dm9QeEIC. Viscosity:https://youtu.be/977wNbFiYlc?t=226(thevideowillstartatminute3:46)D. EvaporativeCooling:https://youtu.be/xqardSvsPOU?t=109(thevideowillstartatminute1:49)
Thedataiscollectedatthefollowingtimesinthevideo:Water:minute2:30 IsopropylAlcohol:minute3:55 Acetone:minute5:05
PROCEDUREFORIMFDEMOS
A.Solubility1. Pour50mLofoil(nonpolarbuthighmolecularweightmolecules)intoa250mLerlenmeyerflask.2. Add150mLofwatertothesameerlenmeyerflask.3. Addafewdropsofgreenwatersolubledye.4. Dothewaterandoilappeartoformahomogenoussolutionwithoutagitatingthemixture?5. Addaalkaseltzertablettotheflask.Thecarbondioxidebubblesformedasthetabletdissolvesin
waterwillagitateandmixthesolution.6. Dowaterandoilappeartoformahomogenoussolutionwhenagitatingthemixture?
B.SurfaceTension
7. Fillabowlwithtapwater.8. Carefullyplaceaneedle(withahigherdensitythenthewater)onthesurfaceofthewater.9. Doestheneedlefloatorsink?
C.Viscosity
10. Obtainthree100mLgraduatedcylinders.Eachwillbefilledwith100.0mLofadifferentsolvent.11. Fillthefirstgraduatedcylinder(tothefurthestleftinthevideo)withisopropanol,C3H8O.12. Fillthesecondgraduatedcylinder(inthemiddle)withpropyleneglycol,C3H8O2.13. Fillthethirdgraduatedcylinder(furthesttotherightinthevideo)withglycerol,C3H8O3.14. Atthesamestartingtimedropthreeweightedballsintothegraduatedcylindersandobservethe
relativeratetheyfalltothebottom.15. Inwhichliquiddoestheballtravelthefastest?Andtheslowest?
D.EvaporativeCooling
16. Obtainthree100mLbeakers.Eachwillbefilledwith50.0mLofadifferentsolvent.17. Fillthefirstbeaker(leftinthevideo)withwater,H2O.Fillthesecondbeaker(middleinvideo)with
isopropanol,C3H8O.Andfillthethirdbeaker(rightinthevideo)withacetone,C3H6O.18. Useathermometerthatcanautomaticallyrecordtemperaturemeasurementstwiceinonesecond.
Dipthethermometerintothesolutionandremoveitsoitisexposedtotheair.19. Oncethethermometerhasbeenremovedfromthesolutionrecordthetemperatureevery0.5
secondsuntilthetemperaturenolongerdecreases.20. Foreachliquidrecordtheinitialtemperature,thelowesttemperature,andtheamountoftime
(seconds)thatpassestoreachthelowesttemperature.
Q3.CalculatetheevaporativecoolingrateforeachsolventinpartDofthedemonstrations.Showyourworkinyournotebookpagesbelowyourobservations.ThenrecordyourcalculatedratesinthetableconstructedtocollectmeasurementsinyourobservationsfordemonstrationD.
𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑖𝑣𝑒𝑐𝑜𝑜𝑙𝑖𝑛𝑔𝑟𝑎𝑡𝑒 = ∆01234
unitsshouldbe°C/sQ4.Writeaconclusionparagraphthatsharesyourinitialthoughtsabouteachexperiment(A-D)andtheroleintermolecularforcesplayintheobservedphysicalproperties.Thequestionsbelowcanhelpguideyourdiscussion.(pleaselimitresponsestoapageorlesswithinyournotebook)
a. Dowaterandoilmix?Howcanintermolecularforcesexplainyourobservationofsolubility?b. Iftheneedleisdenserthenwater,whydoesitfloatratherthansink?c. Dothedifferencesinviscosityobservedforisopropanol,propyleneglycol,andglycerolmatchyour
expectationsbasedonthestrengthoftheintermolecularforcesforeachmolecule?d. Explainthedifferencebetweenevaporativecoolingratesofwater,isopropanol,andacetonein
termsoftheintermolecularforcesorstructuralfeatures(likeweight)ofeachmolecule.Tosubmitthisassignmentpleasetakeapictureofyourlabnotebookpagesandconvertthemtoapdffile.ThepdffilecanthenbeuploadedontheLab2assignmentpage.Ifyouhaveanyquestionsabouthowtogenerateapdffileorhowtosubmitanassignmentincanvaspleaseemailyourinstructor.Someusefulstrategiesinclude:
• Downloadingapdfscannerappontoasmartphone.Irecommendcamscanner.Theseappswilltakeapictureofadocument,orofmultipledocuments,andconvertittoapdfthatcanbeemailedtoyourself.Camscannerhastheabilitytouploadtocanvasaswellifyouusethecanvasphoneapp.
• Takeapicturewithacameraorphonecamera.Thenyouhaveafewoptions:o Opentheimageinimageviewingsoftwareandexportasapdf,saveasapdf,orprintto
pdf.o EmbedtheimageinaprogramlikeMicrosoftwordandprinttopdf.
Lab2AppendixA:ScientificObjectives
ExamplesofScientificObjectives:1) ThescientificobjectiveforanexperimentstandardizingtheconcentrationofNaOHcouldbe:
BAD“ThescientificobjectiveofthisexperimentistotitrateNaOHsolutionwithastrongacid.”
GOOD“ThescientificobjectiveofthistitrationistodeterminetheconcentrationofanunknownNaOHsolutiontofoursignificantfigures.”(Whyisthisanswerbetter?Itidentifiesthequantitybeingdetermined(concentration),thesolutioninquestion,andthemethodused.)
2) Thescientificobjectiveforanexperimentthatmeasuresthechangeinfreezingpointofasolutionwhen
lauricacidisdissolvedinbenzoicacid;thisinfoisusedinthepost-labtocheckthemolarmassoflauricacid:BAD“Thescientificobjectiveofthisexperimentistomeasurethefreezingpointoflauricacidandbenzoicacid.”
GOOD“Thescientificobjectiveofthisexperimentistodeterminethemolarmassoflauricacidusingitsfreezingpointdepressioninabenzoicacidsolution.”(Whyisthisanswerbetter?Itcorrectlyidentifiestheendresultofthelab(molarmassdetermination)ratherthanjusttheintermediatedatathatiscollected.)
3) Thescientificobjectiveforanexperimentthatmeasureshowethanol’svaporpressurechangeswith
temperature,andwhichresultsinquestionsabouttheenthalpyofvaporizationofethanol:BAD“Thescientificobjectiveofthisexperimentistovarythevaporpressureastemperaturechanges.”
GOOD“Thescientificobjectiveofthisexperimentistodeterminetheenthalpyofvaporizationofethanolbyvaryingitstemperatureandmeasuringvaporpressure.”(Whyisthisanswerbetter?Itcorrectlyidentifiesthephysicalquantitybeingdetermined,thechemicalitisdeterminedfor,andthemethodused.)
Lab2AppendixB:PreparingyourLaboratoryNotebooksTheGeneralStructureofYourLaboratoryNotebookBeforeyoucometolab,youmustprepareyournotebook.Thismaytakequitesometime.Inprinciple,aneducatedpersonwhoisfamiliarwithchemistryshouldbeabletoreproduceyourexperimentbasedsolelyonwhatyouwriteinyournotebook,bothbeforeandduringlab.Keepinmindthatyouarewritingforsomeoneelse.Useplain,straightforwardlanguageandincludeasmanydetailsaspossible.Agoodlaboratorynotebookshould:
• sayexactlywhatwasdone,whenitwasdone,andwhyitwasdone;• makeclearwhodidit;• enablesomeoneelsetodothesamethingatsomefuturedate.
InChemistry161,youweregivenpre-formatteddatatablesforeveryexperiment.InChemistry162,youwillrecordallofyourdatainablanknotebook.Thiswillrequiremorepreparationonyourpart.Suchnotebooksarethetruerecordofthesciencedone,eventhoughmostotherscientistswillencountertheworkinanotherform,suchasapublishedresearcharticle.Introduction.Theintroductiontoyourexperimentalreportshouldhavethefollowing:
• YourNameandyourlabpartner’sname• TitleoftheExperiment.Thisshouldalsoappearonanyaddedpiecesofpaper,graphs,whatever,thatare
tapedintothenotebook.• ScientificObjective.Whyareyoudoingthisexperiment?Whatdohopetofind/show?Thisisthesame
objectivethatisrequiredforthepre-lab.• TheDate.Inindustryorresearchthisisexceedinglyimportant,butitisgoodpracticeforundergraduates
also.Writethedateunambiguouslyandincludetheyear-forexample:2July2000.Pre-LabLectureNotes.Leaveyourselfsomeroomtorecordnotesduringthepre-lablectures.Procedure. Although the lab manual for this course includes detailed instructions for the experimentalprocedure,youneedtowriteabriefsummaryoftheprocedureinyournotebook.Thepurposeofthisistomakeyouthinkaboutalloftheexperimentalpartsbeforeyousetfootinthelab.Remember:knowledgeispower.Donotcopytheprocedureinthemanualverbatimintoyournotebook.Thereisnoneedtodothis,sinceyouwillbe allowed to bring your labmanual with you to lab.What you should focus on are themajor stepsof theexperiment, not the tiny details. Write your procedure as a numbered list, using simple, direct statements.Comment on any special features of the materials to be used, such as special handling or waste-disposalprocedures.ExperimentalObservations. Theobservationsyoumakeand thedata that you recordwill lead to theacceptance or rejection of your hypothesis, and will decide what future experiments may be done. Theobservationsanddataarethereforecentraltothewholeexercise.Observationsareyournotesaboutcolorchanges,gasesorprecipitatesformed,solidsdissolving,colorsofsolutions,solids,liquidsorgases,meltingorboiling,heatevolvedorabsorbed(exothermicorendothermicreaction),rateofreaction(slow,moderate,fast,explosive?),soundsorsmells.Youshouldalsorecordany
problemsyouencounteredwithequipmentorchemicalsandhowyouaddressedthem.Ifyoudeviatedfromthelaboratorydirections,besuretorecordwhatyoudidinmoredetail.Acorrectlywrittenobservationincludesenoughinformationtoputtheobservationincontext.Itidentifiesthechemicalsreacting,theequipment,thechangeobserved,andthetime-frameinwhichitoccurred.Forexample:“StepIIparta.When6Mnitricacidwasaddedtothecalorimeter,thesolutionimmediatelybecamewarmtothetouch.”Eveninexperimentsthataremostlyquantitativeinnature,therearealwaysqualitativeobservationsthatshouldbemade,suchasdescriptionsofthesubstancesusedorchangestoprocedure.SometipsforrecordingObservationsandData:
• DOrecordobservationsanddatahonestly.Ifyoumessedup,youmustrightdownyourmess-upsothatyoucantroubleshootbaddatalater.
• DOrecordobservationsanddataasyougoalong,inthenotebook,inink,immediately.• DONOT trustyourmemory,notevenforaminute. It isveryeasyto forgetwhatyouhave justdone.
Further,youdonotwantyourmindoccupiedwithtrivialthingsandsmalldetails.Youneedtokeeptheoverallexperimentalplaninmind.
• DONOTuseoddscrapsofpapertorecordobservationsanddata.• DOrecordobservationsanddataascompletelyasispossible.Don'tworrytoomuchaboutinterpreting
thedataasyougoalong,anddon'tworryifsomeoftheobservationsappearbanal.• DO use good penmanship. Take care with numbers…DONOT over-write an incorrect value with the
correctone.Simplycrossouterroneousmaterialwithasinglelineandre-writethecorrectdatanexttoit.
• DONOTusewhite-out.• DO leavewhite space in your notebook for comments, notes, corrections, and redrawn tables. Your
notebookhasmorepaperthanyouwilluse.HandPlots.Aspartofyourfinalizedlabreport,youwillinmanycasespreparecomputer-generatedplotsofyourexperimentaldata.However,itisalwaysagoodideatoplotdatabyhandinyournotebookbeforeyouleavethelab.Lookingatyourdatagraphicallycanrevealerroneousvaluesthatyouwon’tnecessarilynoticesimplybylookingatadatatable.Thisgivesyouthechancetomeasurethatvalueagain,ifnecessary.But,justbecausethesearehandplotsisnoreasontoskimponproperformatting.Therefore,allhandplotsarerequiredtohave:
• Apropertitle,includingthetrialnumberifapplicable.• Appropriatelyscaledaxesthatallowthedatato“beitself.”• Properlylabeledaxes,includingunitsinparentheses.
DataTables.Youshouldknowwhatdatayouwillbecollectingbeforeyoucometo lab,andthereforeyoushouldknowwhatyourdatatablewilllooklikebeforeyoucometolab.Yourtablesmustbewritteninverticalcolumns,witheachcolumnheadedwith thequantityand theappropriateunits.Therows inyour tablesmayrepresenttrials,time-steps,volumeadded(asinatitration),etc.Theappropriaterowdesignationwilldependonthe particular experiment, but generally speaking, all the numbers in a given row should be related in somefashion.Insomecasesyoumayalsowanttoincludecolumnsfortheresultsofcalculationsusingtherawdata.