Compounds & Elements - Department of ChemistryCompounds & Elements Electrolysis of Water Equipment Hoffman apparatus, platinum electrodes, AC-DC rectifier, 100 DC "house current"

Compounds&ElementsElectrolysisofWaterEquipmentHoffmanapparatus,platinumelectrodes,AC-DCrectifier,100DC"housecurrent".ReagentsDilutesulfuricacid.Presentation

1. Filltubewithdilutesulfuricacid.Becertaineachofthesidetubesiscompletelyfilledwiththesolution.2. Connecttheterminalstothecurrent.Thepowersupplyshouldbesetanywherebetween6-12volts,dependingupon

howfastyouwishtheelectrolysistoproceed.3. Allowreactiontooccur.Thehydrogentubewillfillattwicetherateoftheoxygentube.

HazardsBecausesulfuricacidisbothastrongacidandapowerfuldehydratingagent,itmustbehandledwithgreatcare.Thedilutionofconcentratedsulfuricacidisahighlyexothermicprocessandreleasessufficientheattocauseburns.Therefore,whenpreparingdilutesolutionsfromtheconcentratedacid,alwaysaddtheacidtothewater,slowly,withstirringandcoolingthereceivingbeaker.Hydrogenandoxygengaseswillbeproducedincloseproximitytooneanother.Thisisanexplosivecombinationandanysparkcouldsetoffthisreaction.DiscussionTherearetwoelectrochemicalreactionstakingplace:oxidationisoccurringattheanodeandreductionisoccurringatthecathode.

Cathode:2H2O(l)+2e-®H2(g)+2OH-Anode: 2H2O(l)®O2(g)+4H+(aq)+4e-Tokeepthenumbersofelectronsbalanced,thecathodereactionmusttakeplace,twiceasmuchastheanodereaction.Ifthecathodereactionismultipliedby2andthetworeactionsareaddedtogetherweget:

6H2O(l)+4e-®2H2(g)+O2(g)+4H+(aq)+4OH-(aq)+4e-IfwecombinetheH+andOH-toformH2Oandcancelspeciesthatappearonbothsidesofthearrow,wegettheoverallnetreaction:

Net:2H2O(l)®2H2(g)+O2(g)Sinceequalmolesofgasesatequalpressuresoccupyequalvolumes,thefactthatthevolumeofhydrogenistwicethatoftheoxygenconfirmsthattherearetwiceasmanymolesofhydrogenasoxygenbeingproduced.

References:AlyeaandDutton,p.222.

ThermodynamicsThermiteReactionEquipmentTwoclayflowerpotswhosetopsare2.5inchesindiameterandwhichhaveapproximately1cmdiameterholesintheirbottoms,durable,non-combustiblecontainerfilledtoadepthofapproximately2.5cmofsand.Thediametershouldbelargeenoughtocatchthemolteniron,whichwillflowfromtheflowerpots.Alargeringstandwitharingthatwillsupporttheflowerpots.Asafetyshield,barbecuelighter,andtongs.Reagents40-50gramsofthermitemixture.Thethermitemixtureisacombinationoffinelypowderedaluminumandiron(III)oxide(alsocalledferricoxide)inamassratioof1:3respectively,a5-7.5cmlengthoffireworkssparkler.Presentation

1. Plugtheholeinthebottomofoneoftheflowerpotswithapieceofpaperortape.2. Fillthisflowerpotapproximately2/3fullwiththethermitemixture.Thiswilltake40-50grams.3. Pushthesparklerdownintothethermitemixtureinthecenterofthepot.Pushitintoadepthsuchthatitisfirmly

heldinplace,somewherebetween1/4and1/2ofitslengthissufficient.Gentlytapthebottomofthepotontoahardsurfacetoinsurethateverythingiswellpacked.

4. Nestthefilledflowerpotintotheemptyflowerpot.Theinnerflowerpotinevitablycracksandtheouterflowerpotcontainsit.

5. Placetheflowerpotsintotheringandadjusttheringheight,sothatthepotsareclearlyvisibletotheaudience.6. Makesurethesandcontaineriscorrectlypositionedtocatchthemoltenironthatwillflowfromthepots.7. Placethesafetyshieldbetweentheaudienceandthepots.

8. Lightthetopofthesparklerwiththebarbecuelighterandstepback.

HazardsThisreactionproducesalargeamountofheatflyingsparksandmolteniron.Allcombustiblematerialsshouldberemovedfromthevicinityofthedemonstrationandafireextinguishershouldbereadilyavailable.Watershouldnotbeusedtoputoutanyfiresortocoolthemolteniron.Themoltenironcandecomposewaterintohydrogenandoxygenwhichcanbeanexplosivemixture.Moltenirondroppedintowatercanshatterwithagrenadelikeeffect.Themoltenironcancauseverysevereburnsandshouldonlybehandledwithtongsafterithassolidified.DiscussionThechemicalreactionthatisoccurringinthisdemonstrationisasfollows:

Fe2O3(s)+2Al(s)®Al2O3(s)+2Fe(s)Theenthalpychangeforthisreactionis-849kJ/molofiron(III)oxide.Togivesomeideaofwhatthisreleasedheatisdoing,keepinmindthatironmeltsat1,530oC.Theamountofthermiteusedinthisreactionissuitableforalargelecturehall.Theamountmaybescaleddownforsmallerroomswhilestillprovidingaspectaculardemonstration.Afterthepotshavecooled,separatethemandthrowtheinnerpotaway.Theouterpotshouldbesuitabletobeusedastheinnerpotinthenextdemonstration.Therearenumerousmethodslistedintheliteratureforsettingoffthisreaction,magnesiumribbon,sulfuricacidandpotassiumchlorateandsugar,potassiumpermanganateandglycerine.Noneofthesemethodsisasconvenient,safe,orreliableasthemethoddescribedherein.ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.1,p.85-89

TemperatureDependenceofSilverOxideFormationEquipmentBunsenburnerorpropanetorch,lighter.Ifartificialtarnishingisnecessary:5voltpowersupplyandleads,containertoholdsilverobject.ReagentsPieceoftarnishedsilver.Weuseapitcher,butanyitemlargeenoughtobevisibletotheaudienceshouldwork.Silveroxidepowderwillalsowork,thoughitdoesn'thavethesameimpactasafamiliarhouseholditem.Ifartificialtarnishingisnecessary:1MsodiumhydroxidesolutionofsufficientquantitytodipsilverobjectintoitPresentation

1. Gothroughthefreeenergycalculationsandshowthetemperaturedependenceofthesilveroxideformation.2. Displaythetarnisheditemtotheaudience,notethetarnishedblackenedappearence.Ifyourobjectisnottarnished

sufficiently,followthetarnishingproceduresbelowbeforethedemonstration.3. LightthetorchorBunsenburnerandheataportionofthetarnishedobject.Theblacksilveroxidewillbereplacedby

metallicsilverwhereverthetemperaturehasbeenraisedsufficiently.Applytheheatcarefullysoasnottomeltyourobject.

ElectrochemicalTarnishingProcedure1. Makeupenough1Msodiumhydroxidesolutiontoimmerseasignificantportionofyouritemin.2. Mechanicallypolishyouritemuntilitissmoothandshiny.3. Immerseyouriteminthesodiumhydroxidesolution.4. Connectthepitchertothepositiveleadofthepowersupply.Connectthenegativeleadtoalargecounterelectrode

(graphiteworkswell).5. Turnonthepowersupplyandadjustthevoltageuntiltheitemblackens,thisshouldrequirelessthan5volts.6. Allowtheitemtotarnishforapproximately10minutes.7. Turnoffthepowersupply,disconnectthepowersupplyleads,removetheitemfromthesolution,andrinse

thoroughlywithdeionizedwater.

HazardsEitherthepropanetorchortheBunsenburnercanproduceanintenseandveryhotflame.Severeburnscanresulteitherdirectlyfromtheflameorbytouchingobjectsheatedinthem.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.DiscussionSilvermetalwilloxidizespontaneouslyuponexposuretofreeoxygen.Thisprocessiscommonlyreferredtoas"tarnishing".Thechemicalreactiondescribingthisprocesisshownbelow.4Ag(s)+O2(g)®2Ag2O(s)Silvermetalisagrayishwhitecolor,silveroxideisablackcolor.Thiscontrastincolorsmakestarnishedsilverappearmuchdifferentinappearencethanuntarnishedsilver.Thisexplainswhysomuchphysicalandchemicaleffortisspentinremovingthetarnishfromsilverobjects.ThermodynamicConstantsofCompoundsofInterest[1]

Compound DHof(kJ/mol) DGof(kJ/mol) So(J/mol.K)Ag(s) 0 0 42.6O2(g) 0 0 205.2Ag2O(s) -31.1 -11.2 121.3

Thestandardstateenthalpy(DHorxn)andentropy(DSorxn)changesforthereactionare-62.2kJand-0.133kJ/Krespectivelyascalculatedfromthethermodynamicdataintheabovetable.Thesevaluestellusthatthereactionisexothermicandthattheentropyofthereactionisnegative.Thedecreaseinentropyistobeexpectedwhentherearefewermolesofgaseousproductsthanthereweremolesofgaseousreactants.Theentropyandenthalpytermsareinconflict.Theenthalpytermfavorsthereactionbeingspontaneous,buttheentropytermfavorsthereactionbeingnon-spontaneous.Whenthetermsconflictinsuchamanner,thetemperatureatwhichthereactionoccurswilldeterminethespontaneity.ThefollowingequationwillallowthestandardGibb'sfreeenergy(DGorxn)ofthereactiontobecalculated.

DGorxn=DHorxn-TDSorxnEq.1Substitutingthepreviouslycalculatedvaluesforthestandardstateenthalpyandentropychangesandthestandardstatetemperatureof298Kintothepreviousequationyields:

DGorxn=-62.2kJ-(298K)(-0.133kJ/K)DGorxn=-22.6kJ

SinceDGorxn<0,thereactionisspontaneousatroomtemperature.Thisagreeswithourexperiencethatsilverdoesspontaneouslytarnishasitsitsinair.ByrearrangingEq.1wemaydetermineatwhattemperaturethereactionwouldbeatequilibrium(DGorxn=0).NOTE:ItisnotentirelyaccuratetousestandardstatethermodynamicquantitiesawayfromT=298K,sincetheydohaveatemperaturedependencetothem,butthisusuallyintroducesanacceptablysmallerrorintheresultingcalculations.

T=DHorxn/DSorxnT=(-62.2kJ)/(-0.133kJ/K)

T=468KForT<468Kthereactionisspontaneous,forT=468KthereactionisatequilibriumandforT>468Kthereactionwouldbenon-spontaneous(orthereversereaction,seereactionbelow,wouldbespontaneous).Inordertoremovethetarnishfromoursilverobjectallweneeddoisraisethetemperaturetoabove468K.TheanimatedGIFbelowshowsthetemperaturebeingraisedbyapplyingapropanetorch'sflametothesideofabadlytarnishedsilverpitcher.

2Ag2O(s)®4Ag(s)+O2(g)ReferencesElectronicversion,CRCHandbookofChemistryandPhysics,81sted.

EndothermicReactionofSodiumBicarbonatewithHydrochloricAcidEquipmentSBI,temperatureprobe,400mLbeaker,magneticstirbar,stirplate,small3fingerclampandringstand.Reagents33.3mLof3Mhydrochloricacid,8.4gofNaHCO3.PresentationLoggerProsettings:Useatemperaturerangeof10-25°C,collectdatafor100secondsatarateof2samplespersecond.

1. AddtheNaHCO3tothebeaker,placethestirbarinthebeaker.2. Placethebeakeronthestirplate.Someinsulatingmaterialbetweenthebeakerandthestirplateishelpful.3. Clampthetemperatureprobetotheringstand,lowertheprobeintothebeakeruntilitisalmosttouchingbottom.

Placetheprobesothatitistotheside,outofthewayofthestirbar.4. ConnectSBItothecomputer.5. StartLoggerProprogramandsetparameters.6. Startdatacollection.7. Addhydrochloricacidslowlytothebeaker,sothatthereactiondoesnotoverflowthebeaker.

Note:RemovethetemperatureprobefromthesolutionassoonasdatacollectioniscompleteandrinsewithDIwater.HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.DiscussionThestandardstateenthalpyofthefollowingreactionis+28.5kJmol.-1

NaHCO3(s)+H+(aq)®Na+(aq)+CO2(g)+H2O(l)ThestandardstateGibb'sfreeenergyis-41kJmol-1.Sincethereactionisspontaneous,itmustbeentropydriven.Thisintuitivelymakessensebecauseoneofthereactantsisasolidandoneoftheproductsisagas,sotheoverallentropyhasincreased.Acalculationrevealstheentropyincreasetobe230Jmol-1K-1.

DustExplosionEquipment25x20cmcanwithtightlyfittingcoverandabulbfunnelattachmentfordispersingpowder,candleorgas,8cmfunnel,watchglass,barbecuelighter.Reagents2mLofdrylycopodiumpowder.Presentation

1. Placesmallpileoflycopodiumpowderonawatchglass.2. Trytoignitethepilewiththelighter.3. Placelycopodiumpowderinfunnel.4. Letthepowdersettlebeforelightningthecandleorgas.5. Placepluginholeusedforlightingthegasorcandle.6. Coverthecansecurely.7. Pressbulbtodispersethepowder.8. Explosionshootscoverinairandflamerisestoaroundaheightof2meters.

HazardsStandbacktoavoidtheflyinglidandflames.Lycopodiumpowderisveryflammable.Lowhazardmaycauseeyeand/orskinirritation,maycausegastrointestinalirritation(nausea,vomits,diarrhea),ifingestedmaycauserespiratoryirritation,ifinhaledpossibleasthmaticattack.DiscussionLycopodiumpowderisthesporefromclubmoss.Thisdemonstrationillustratestheincreaseinareactionratewithanincreaseofsurfacearea.Withthelycopodiumwasinapile,theexposedsurfacewasrelativelysmallandtheratewassoslowastobenon-existent.Whenthepowderisblownoutofthefunnel,thesurfaceareaishugeandthecombustionreactionrateissofastthatitbecomesexplosive.ReferencesAlyeaandDutton,p.8(2-17).

HClCannonEquipmentOne250-mLErlenmeyerflask,a#6stopperwith3holes,twographiteelectrodesofadiametertofitthestopperholesandalengthtoreachnearlytothebottomoftheflask,powersupplycapableofapproximately6voltsand2amperes,100-mLclearplasticgraduatedcylinder,withendspoutcutoff,2-holestoppertofitthegraduatedcylinder,corktofitthegraduatedcylinder,plastictubingandglassbendstochannelgasesandacameraflaskorsomeothersourceofintensewhitelight.Optional:redandbluefilters.Reagents250mLof6MHCl,250mLof6MNaOHPresentation

1. PourtheHClsolutionintotheflasksothatthelevelisabout5cmfromthebottomofthestopper.2. Placethestopperwithelectrodesandthegasoutlettubefirmlyontotheflask.3. Placethestopperwiththegasinletandoutlettubesfromtheflaskfirmlyintothegraduatedcylinder.4. PlacetheoutletfromthegraduatedcylinderintotheNaOHsolutionTheNaOHwillreactwithanyescapingchlorine

convertingitintohypochlorite.5. Connecttheoutputofthepowersupplytotheelectrodesandturnonthepowersupply.6. Adjustthepowersupplytobetween5and6volts.Thisshouldproduceacurrentofapproximately2amperes.

Hydrogenandchlorinegasbubblesshouldstartformingonthesurfacesoftheelectrodes.Theamountofchlorineformationmaylooksmallatfirst,butthechlorineissolubleinwaterandsosomeofitisbeingdissolvedinthesolution.Thesolutionwillbecomepalegreencoloredfromthisprocess.

7. Allowtheelectrolysistocontinueuntilthecontentsofthegraduatedcylinderaredistinctlygreencoloredfromthechlorine(probably15-20minutesdependingupontherateofelectrolysis).

8. Turnoffthepowersupply.9. Quicklyreplacethestopperwiththeinletandoutlettubeswithacork.Thecorkshouldbepressedonlyvery

gentlyintothegraduatedcylindertopreventthecylinderfromrupturinguponignition.10. Clampthegraduatedcylinderintotoaringstand,sothatthecorkwilltravelinahigharcovertheaudience.11. Wearingeyeandearprotection,chargeacameraflashandflashitnexttothetube.12. Thefiltersmaybeplacedoverthelightsource.Theredfilterwillnottransmitlightofsufficientenergytoinitiatethe

reaction.Thebluefilterwilltransmitlightofsufficientenergytoinitiatethereaction.

HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.Thecorkispropelledwithsufficientforcetocauseinjuryifsomeoneishitatblankrange.Thecylindermayshatterifthecorkisseatedtoofirmly.Thecylinderweakenswitheverydemonstrationandwillusuallyburstafter3-4uses.Thedemonstratorshouldwearsometypeofhearingprotectionandtheaudienceshouldbecautionedtocovertheirears.Discussion

Cl2+light(500nm)®2Cl•(initiation)Cl•+H2®HCl+H•(propagation)H•+Cl2®HCl+Cl•(propagation)2Cl•®Cl2(possibletermination)H•+O2®HOO•(possibletermination)Cl•+O2®ClO2•(possibletermination)radical+containerwall(possibletermination)

ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1983,Vol.1,p.121-123.ReactionofMagnesiumwithDryIceEquipmentBarbecuelighter,Screwdriver,Handheldpropanetorch,Gloves,Tongs,InsulatingpadortowelReagents5lbslabsofdryice(2),30gofMgturningsPresentationPreparation

1. Usingaflatheadscrewdriver,gougeaholeinthemiddleofoneoftheslabsofdryice.Theholeshouldbeahemisphere,roughly3-4cmindiameter.

2. Usingaflat,polishedmetalsurface,polishonesideofeachdryiceblockuntilthetwopiecesfittogetherwithoutagap.3. Storethedryiceinaninsulatedcontaineruntilthetimeforthepresentationofthedemonstration.

Demonstration

1. Removetheindentedpieceofdryicefromthecontainerandplaceitonatowel.2. Fillthecavitywithmagnesiumturnings.3. Makesurethatnocombustiblematerialsareneartheapparatus.4. Thenextstepsarebestdonewithapartner.Lightthemagnesiumturnings.Thiswilltake15secondsorso,since

oxygenhasbeendepletedfromtheairaroundtheturningsandthemagnesiumisquitecold.5. Whileonepersonislightingthemagnesium,theotherpersonshouldbereadytoplacetheotherpieceofdryiceover

theburningmagnesium.Thisneedstobedonequicklyinordertominimizethereactionofmagnesiumwithmolecularoxygen,whichisafasterandmoreexothermicreaction.

6. Oncetheotherpieceofdryiceisinplace,stepback,dimthelightsandwatchthedryiceglowbrilliantlywhite!7. Oncethereactionhasceasedtoglow(3-5minutes),removethetoppieceofdryiceandshowthewhiteMgO.Using

thetongs,theshelloftheMgOballcanbecrackedopentorevealablackpowderwhichiselementalcarbon.HazardsWorkinawell-ventilatedarea.Donotlookdirectlyatburningmagnesium.Thereactionwillreleasesomefineparticlesofmagnesiumandmagnesiumoxideintotheair.Thiscanbeharmfulifinhaledinlargequantities.Neitheracarbondioxidenorawaterfireextinguisherwillputoutamagnesiumfire.Shouldafireresult,thebestthingtodoistoletitburnoutonitsown,provideditisnotgrowingoutofcontrol.Inthatcasecallthefiredepartment.DiscussionThewhite,flakymaterialisMgOwhiletheblackresidueismostlycarbonwithtracesofMg3N2.Thereactionisbrokendownintoelementarystepsasshownbelow.Theenergiesassociatedwitheachstepweretakenfromoneoftwosources,steps1-6[3]andsteps7-9[2].

ElementaryStep Associatedenergy(kJ)1. 2[Mg(s)®Mg(l)] 2[132]2. 2[Mg(l)®Mg(g)] 2[9.037]3. 2[Mg(g)®Mg1+(g)+e-] 2[737.3]4. 2[Mg1+(g)®Mg2+(g)+e-] 2[1,449.8]5. CO2(g)®C(s)+O2(g) 392.06. O2(g)®2O(g) 497.317. 2[O(g)+e-®O1-(g)] 2[-141]

8. 2[O1-(g)+e-®O2-(g)] 2[878]9. 2[Mg2+(g)+O2-(g)®MgO(s) 2[-3916]NetReaction: 2Mg(s)+CO2(g)®2MgO(s)+C(s) netenergy:-812

Thedominantthermodynamictermthatgivesrisetotheexothermicityofthereactionisthelatticeenergy,step9.Becauseofthestabilityofmagnesiumoxide,carbondioxideyieldsitsoxygentomagnesiumtoformthisproduct.Magnesiumwillreactwithotheroxides.Thekeyfactorishowmuchenergyisrequiredtodecomposetheoxideasillustratedinstep5.Sand(SiO2)andwater(H2O)willbothreactwithmagnesiumundertheproperconditions.Unlikethealkalimetals,magnesiumdoesnotreactviolentlywithwateratroomtemperature.Thereasonforthisdifferenceisthatalayerofinsolublemagnesiumoxideformsaroundthemagnesiumwhichseparatestheremainderofthemagnesiumfromthewater.Withsodiumandpotassium,theheatofthereactionisenoughtomelttheremainingmetal,thusincreasingtheaccessiblesurfaceareawhichvigorouslyacceleratesthereaction.Thebottomlineisthatmagnesiumwilltakeoxygenfromnearlyanysourcetoformtheremarkablystablecompound,magnesiumoxide.References

1. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.1,p.90-92.2. Zumdahl,S.S.;Zumdahl,S.A.,Chemistry,5thed.;HoughtonMifflin:Boston,2000.3. HandbookofChemistryandPhysics,54thed.;CRCPress,Cleveland,OH,1973-1974.

SugarDehydrationWithoutSulfuricAcidEquipment60mLsyringewithnozzlecutoff,scrapmetalheatshield,mortarandpestle,pipettewithbulb,matchorbutanelighter,aluminumfoiland100mLbeaker.ReagentsTablesugar,potassiumchlorate,95%ethanol.Presentation

1. Weighout15goftablesugar(sucrose)and4gofpotassiumchlorate.2. Placethesugarandpotassiumchlorateinthemortarandlightlygrinduntilyouproduceafinepowderandthetwo

componentsaremixedthoroughly.3. Pulltheplungerbackintothesyringeuntilitreachesthe20mLmark.4. Pourthepowdermixtureintothesyringetoadepthofapproximately0.5cm,addenoughethanoltothoroughlywet

thepowder.Tapthesyringeplungerdownonasolidsurfacetoremoveairbubbles.5. Repeatstep4untilthesyringeisfull.6. Covertheopenendofthesyringewiththescrapmetal.Invertthesyringeandplacethescrapmetalonafirmsurface.

Depresstheplungertofurthercompressthemixture.7. Liftthesyringeoffofthescrapmetalandextrudethemixturefromthesyringe.Youshouldendupwithacolumn

approximately2-3cmhighrestingonthescrapmetal.Ifyouarenotgoingtousethedemonstrationwithinafewminutes,youshouldcoveritwithasmallbeakertominimizetheethanolevaporation.

8. Placethemixtureonasurfaceandremoveanycombustiblematerialbackabouttwofeet.Layingdownsomealuminumfoilwillmakeanyeventualcleanupeasier.

9. Removethebeakerifthereisone,addanotherdropperfullofethanoltothemixtureandlightitwiththematchorbutanelighter.

HazardsPotassiumchlorateisastrongoxidizingagent.Caution,therearewarningsthatpotassiumchlorateshouldnotbeexposedtoheat,shockorfrictionandthatdoingsomayleadtofireorexplosion,especiallyifthereareoxidizablecontaminantspresentsuchassugar.Thisdemonstrationhasbeenperformedrepeatedlywithoutexperiencinganysuchproblemsassociatedwiththelightgrindingthatiscalledfor,butsuchpossibilitiesshouldalwaysbetakenintoaccount.Thereisasmallamountofsmokeandflameassociatedwiththesereactions.Aroomwithevenmoderatelydecentventilationwillhavenoproblemdealingwiththeamountsproduced.Theheatshieldwillgetquitewarmfromthereactionsandmaycauseburnsifhandledtoosoonuponcompletionofthedemonstration.DiscussionThisdemonstrationconsistsofthreereactions,eachsucceedingreactionisdependentuponthepreviousreactionforitsactivationenergy.Allofthereactionsareexothermic.

CH3CH2OH(l)+3O2(g) 2CO2(g)+3H2O(g)+1236kJ 1

C12H22O11(s)+8KClO3(s) 12CO2(g)+11H2O(g)+8KCl(s)+2029kJ 2

C12H22O11(s) 12C(s)+11H2O(g)+429kJ 3

Theenergiesthatareshownforthethreereactionsarebasedupontheassumptionsthatthewaterandcarbonbeingformedareinthegaseousandgraphiteformsrespectively.Thereisevidencethattheseassumptionsarenotentirelyaccurate(2,3).Fromreaction2,wecanseethatpotassiumchloratereactswiththesugar,butthereisonlyenoughpotassiumchloratetoreactwithapproximately16%oftheavailablesugar.Thisallowstheremaining84%ofthesugartoreactaccordingtoreaction3,drivenbytheenergyreleaseofreaction2.Thegasesthatareproducedduringthesereactionsleavethesolidcarbonriddledwithgaspockets,producingalight,airycarboncolumn.References

1. ToddP.SilversteinandYiZhangJ.Chem.Educ.1998,Vol.75,p.748-749.2. Shakhashiri,B.Z.ChemicalDemonstrations,AHandbookforTeachersofChemistry,UniversityofWisconsinPress:

Madison,WI,1983;Vol.1,pp.77-78.3. Dahn,J.R.;Zheng,T.;Liu,Y.;Xue,J.S.Science1995,270,590-593.

GasesRelativeDiffusionRatesofGasesEquipmentSpeciallyconstructeddiffusionratetube,laserpointer,ringstand,clamps,cottonswabs(2),smallrubberbands(2).ReagentsConcentratedHClandNH3solutions.Presentation

1. Clamptheglasstubetotheringstandsothatitisexactlyhorizontal.2. Screwthetwoplugs,thesmalloneholdingthelaserpointerandthelargerone,intotheappropriatethreadsonthe

glasstube.3. Adjusttheclamporrubberbandsuntilthelaserpointercomesonandstayson.4. Adjustthelaserpointerorientationuntilittravelsthelengthoftheglasstubeandstrikesnearthecenterofthelarge

plug.5. Placeasmallrubberbandontheshaftofeachswab.Adjustthepositionoftherubberbandssothattheheadofthe

swabrestsjustabovethemaintube,sothattheheadsdon'tinterfereinthelaserbeampath.6. PlaceseveraldropsofconcentratedHClononeofthecottonswabs.PlaceseveraldropsofconcentratedNH3onthe

secondcottonswab.7. Placeoneswabintoeachoftheaccesstubeslocatedneartheendsofthemaintube.Allowtheswabstogodowntothe

pointthattherubberbandontheshaftstopsthetravel.8. Dimtheroomlights.9. Afterabout3-4minutes,thesolidammoniumchlorideparticleswillbegintoformandtheywillscatterthelaserlight.

Thiswillproduceaveryvisibleredspotinthemaintubewheretheparticleshaveformed.10. Youmaymeasuretherelativedistancesfromtheparticleformationtotheswablocation.Theresultswillconform

reasonablywelltoGraham'slaw,oryoumaysimplypointoutthattheparticlesformedclosertotheHClswabthantotheammoniaswabbecauseammoniaislighterandtravelsfaster.

HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Concentratedaqueousammoniacancauseburnsandisirritatingtotheskin,eyes,andrespiratorysystem.Thelightfromlaserpointersmaycauseeyedamageifshowndirectlyintotheeye.DiscussionThereactionweareexaminingisthefollowing:NH3(g)+HCl(g)®NH4Cl(s)Thetwogasesarereleasedatoppositeendsofanenclosedglasstube.Whenthegasesmeet,theyformammoniumchloride.Theammoniumchlorideisformedasafinelydividedwhitepowder,someofwhichremainssuspendedintheairandsomeofwhichdepositsontheglasssurface.Graham'slawtellsusthattherateofdiffusionofagasisinverselyproportionaltothesquarerootofthemolecularm

massofthegas. and

GiventhemolecularmassesofHCl(36.5g/mol)andNH3(17.0g/mol),wecalculatearelativerateof Thissaysthatinagivenamountoftime,NH3shouldtravel1.46timesasfarasHCl.Inpractice,weseethevalueofabout1.27.Thereasonforthisisthatthegasesareactuallydiffusingthroughathirdgas(air).Thereareadditionalcollisionsthatretardtheprogressofthefastergas,NH3toagreaterdegreethantheslowergas,HCl.Ifagreenlaserpointerisavailable,thescatteredlightismuchmoredramaticthanwiththeredlaserpointers.

ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.59-62.

TheCollapsingCanEquipmentWater,1-5galloncanfittedwitharubberstopperorvalve,ringstand,largeironringorlargeclamp,Bunsenburnerandglovesforhandlinghotcan.Alternatively:Aluminumsodacan,tongs,anda2-literbeakerfilledwithicewater,wirescreenfortheburnerorhotplate.Presentation

1. Addwatertothecantoadepthofapproximately1cm.2. Heatthewaterinthecanuntilsteamissuescontinuallyfromthecan.Caution,theburnerflamecanquicklyburna

holeinthealuminumcan.Fora5galloncan,thesteamshouldbeallowedtoissueforaminimumof5minutes.3. TurnofftheBunsenburnerandquicklystopperthecanorclosethevalve.ORRemovethealuminumcanfromthe

heatwiththetongsandquicklyinvertitinthebeakeroficewater.4. Youmayspeedthecoolingofthegalloncansbysprayingthemwithcoldwater.

HazardsThehotcan,waterandespeciallythesteamcancausesevereburns.DiscussionTheboilingwaterdisplacesairleavingtheinteriorofthecanfilledalmostentirelywithwatervaporatatmosphericpressure.Asthecancools,theinteriorpressureequalsthevaporpressureofwateratthattemperature.At25°Cthevaporpressureofwaterisapproximately20mmHg,thepressuredifferentialisapproximately14lbs/in2orforarectangularcanwhosedimensionsare4"x10"x8"thetotalpressureexertedonthesurfaceofthecanis:[2x(4x10)+2x(4x8)+2x(8x10)]x14=4.2x103lbsorapproximately2tons.ReferencesAlyeaandDutton,p.23(10-1).

NitricAcidActsUponCopperEquipment1literroundbottomedflask,corkring,1holestoppertofitroundbottomedflask,900glassbendtofitintostopper,approximately60cmofTygontubingtofittheglassbend,2literorlargerclearcontainer(beaker,flask,bucket,aquarium,etc.,2pre1983U.S.penniesor6gramsofcopper,longglassstirrod,alightboximprovesthevisibilitytremendouslyReagents50mLofconcentratednitricacid,approximately2litersoftapwater,1-2mLof0.1%phenolphthaleinsolution,6MorstrongerammoniasolutionPreparation

1. Fillthelargecontainernearlyfullwithtapwater.2. Add1-2mLofthephenolphthaleinsolutiontothelargecontainerandstir.3. Addammoniasolutiondropwisewithstirringuntilthesolutionisdistinctlypink,butnotanyexcess.4. Inserttheglassbendintothestopperandintothetubing.5. Placethetubingintothecontaineruntilitisnearthebottom.

Presentation1. Placeallofthecomponentsonalightboxifoneisavailable.2. Placetheroundbottomedflaskonthecorkring,tiltitandgentlyallowthepenniestoslidetothebottomoftheflask.

Placetheflaskupright.3. Carefullyaddthe50mLofnitricacidtotheroundbottomedflask.4. Quicklyplacethestopperfirmlyintotheroundbottomedflask.

HazardsNitricacidisacorrosivechemicalwithanumberofadverseeffects:EffectsofExposure:TARGETORGANS:EYES,SKIN,MUCOUSMEMBRANESOFTHERESPIRATORYTRACT,TEETH.THISMATERIALISCORROSIVETOANYBODYTISSUESITCONTACTS.DENTALEROSIONISALSOREPORTED.ACUTEEFFECTS-IRRITATIONAND/ORCORROSIVEBURNSOFSKIN,EYES,ANDUPPERRESPIRATORYTRACT(URT),DELAYEDPULMONARYEDEMA,PNEUMONITIS,BRONCHITIS,ANDDENTALEROSION.Nitrogendioxideisatoxiccompound,donotinhaleit.INHALATION:PULMONARYTRACTIRRITATION,THROATIRRITATION,TIGHTNESSINCHEST,HEADACHE,NAUSEA,&GRADUALLOSSOFSTRENGTH.SKIN/EYES:CORROSIVEACTION.Thisdemonstrationpresentsseveralveryinterestingchemicalandphysicalphenomena.Thefirstreactionisanoxidationreductionreactionwherecopperisoxidizedfromthezerostatetoa+2stateandthenitrogenisreducedfromthe+5stateinnitratetothe+2stateinnitrogenmonoxide.Itmaybepointedoutthatotherstrongacidssuchashydrochloricandsulfuricdonotreactwithcopper.Thered-browngasthatappearsintheroundbottomedflaskiscausedbythesamecompoundresponsibleforthered-brownhazethathangsovercertaincities,nitrogendioxide.Thenitrogenmonoxidereactswithatmosphericoxygentoproducenitrogendioxideasshowninthesecondreaction.Thereisacid-basechemistrygoingon.Thenitrogendioxidethatisproducedintheroundbottomedflaskisbubbledthroughwaterthathasbeenmadebasicviatheadditionofammoniaandtheconditionmadevisiblebythepresenceofphenolphthalein.Asthenitrogendioxidebubblesthroughthebasicsolution,thepinkcolordisappears.Thisshowsthatthesolutionisnolongerbasic,buthasbecomeacidic.Thenitrogendioxidehasbeenconvertedtonitricacidandnitrousacidasshowninthethirdreaction.Thisisthesamereactionbywhichnitrogenoxidepollutantsmakeacidrain.Thereactionbetweenthecopperandthenitricacidisexothermic.Thecontentsoftheround-bottomedflaskincludingthegasareatanelevatedtemperature.Thereactioncomestoanendwhenthelastofthecopperisusedup.Thismakesthecoppertheyieldlimitingreagent.Whenthereactionceases,thebubblesofgasstop.Asthecontentsoftheround-bottomedflaskcool,thegaspressuredecreasesintheroundbottomedflask.Thisillustratesthepressure-temperaturerelationshipofgases.Asthepressureintheroundbottomedflaskdecreases,thegasinthetubingisdrawnbackintotheflaskandwaterfromtheErlenmeyerflaskisalsodrawnthroughthetubing.Thisisafairlyslowprocesssincetheflaskcoolsslowly.Nitrogendioxideissolubleinwaterandiscontinuouslydissolvinginthewaterfromthelargecontainer.Sincetheinterfacebetweenthenitrogenoxideandthewaterisconfinedtothecrosssectionalareaofthetubing,thedissolutionproceedsslowly.Whenthewaterfromthelargecontainerfinallyisdrawnallthewaythroughthetubingandenterstheround-bottomedflask,theinterfacebecomemuchlargerandtherateofdissolutionincreasesdramatically.Withinamatterofsecondsnearlytheentireround-bottomedflaskisfilledwithwaterfromthelargecontainer.ThesolutionnowintheroundbottomedflasktakesonthecharacteristicbluecoloroftheCu(H2O)n2+(nistypically4,)whichillustratessomecomplexionchemistry.

3Cu(s)+2NO3-(aq)+8H+(aq) 3Cu2+(aq)+4H2O(l)+2NO(g)

2NO(g)+O2(g) 2NO2(g)

2NO2(g)+H2O(l) H+(aq)+NO3-(aq)+HNO2(aq)

3HNO2(aq) H+(aq)+NO3-(aq)+2NO(g)+H2O(l)TheprocedureusedinthisdemonstrationislooselybaseduponapamphletauthoredbyLang,ShowalterandShulfer1.ThechemistryisdescribedinabookbyShakhashiri2.References

1. C.MarvinLang,DonaldL.Showalter,GaryJ.Shulfer,"YESVIRGINIA,...LEARNINGCHEMISTRYCANBEFUN!",UniversityofWisconsin-StevensPoint,1992,p.2-3.

2. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.165-166.

ElectronsandAtomMagneticSusceptibilityEquipment5kilogaussmagnet,ringstandwithwoodoraluminumrodclampedontop,threadwithloopatendaffixedtorod,smalltesttubeswithhookineachstopperforstringattachment.Additionally,adigitalbalancewithaminimumaccuracyof0.1gandahookbelowthepanmaybeused.ReagentsSiO2,KNO3,Na2SO4,CoCl2,NiSO4,NiCl2,MnO2,Fe2O3,Fe3O4,NH4VO3,KMnO4,K2Cr2O7,Cu,Co(NH3)6Cl3,Na3FeF6,Cr2O3,(NH4)2SO4·FeSO4,Ironnails,Co(NH3)4Cl2Cl.Presentation

1. Removekeeperfrommagnet.Forcekeeperdownwiththumbs,allowingtheheavydisktofollowthemagnet’sinnersurfacesuntilthekeepercanberemoved.

2. Hangthesamplesonthethread.Adjustthelengthandheightsothesampleislevelwiththepolesofthemagnet.Movethemagnetalongthedesk.Thesampletubewillfollowthemagnetornot.Describeatomicarchitectureofsample,notecolor,guessweatherpara-ordiamagnetic,covalentorionicbonding.

3. Alternatively,suspendthetubedirectlyfromthebalancehook(outofmagneticfield)andzerothebalance.4. Suspendthetubefromthreadsothatitisinthemagneticfield.5. Noteifanychangeinthebalancereadingoccurs.

HazardsRemovewristwatch.Theironnailsmaysmashagainstthemagnetandbreakthetesttube.DiscussionParamagneticmaterialscontainunpairedelectrons.ReferencesTutorialVideoTapeIIIfoundinLearningResourcesCentersinWalterLibraryandSt.PaulLibrary.

IonsandMoleculesExtractionEquipment250or500-mLseparatoryfunnel,four100-mLbeakers,overheadprojector,ringstandwithironring.ReagentsAbout500mLofwatersaturatedwithiodineandabout300mLofchloroformorcyclohexane.Presentation

1. Halffilltheseparatoryfunnelwiththewater/iodinesolution.Becertainthestopcockisclosedfirst!2. Dispense~20mLofthewater/iodinesolutionintoa100mLbeaker.3. Placethebeakerontheoverheadprojector,sothatitmaybeseenthatsomeofthelightisabsorbedbythesolution.4. Add75-100mLofchloroformorcyclohexanetotheseparatoryfunnel.Stoppertheseparatoryfunnel.5. Holdthestopperinplaceandinverttheseparatoryfunnel2-3timesfairlyquickly.6. Righttheseparatoryfunnelandloosenthestoppertoventsomeofthepressurethathasbuiltup.7. Replacethestopper,andholditasyouinvertseveralmoretimes.Theorganiclayershouldbedistinctlypurple.8. Continuetoinvertuntilthecolorofthechloroformlayerbecomesconstant.9. Drainthechloroformlayerintoacontainer.

Repeatsteps2-9forasmanytimesasyoucareto.Theamountsstatedhereareforaseriesof3extractions.HazardsVaporofiodineisasevereirritantandlachrymator.Solutionsofiodineirritateskin.Contactsmaycauseskinburns.Chloroformmayirritateeyesandskin(withnoseriousdamage).Chloroformisasuspectedcarcinogenandteratogen.Therefore,avoidcontactswithiodineandchloroform;theyshouldbehandledwithcare.Excessiveinhalationofcyclohexaneisirritatingtotheupperrespiratorytract.Repeatedcontactwiththeskincancausedermatitis.DiscussionIodineisanon-polarmoleculethishasaweakinteractionwiththehydrogenbondedwatermolecules.Theenergyassociatedwiththeiodine/waterinteractionsisnotenoughtocompensateforthelostenergyofthewater/waterinteractions.Thisultimatelymeansthatnotmuchiodinewilldissolveinwater.Ifasolventwithweakersolvent/solventinteractionsthanwaterwereintroducedtothissystem,iodinewouldfinditeasiertodisrupttheseinteractionsandinsertitself(dissolve)betweenthe

solventmolecules,cyclohexaneorchloroformaresuchsolvents.Theyhavenohydrogenbondingandareonlyveryslightlypolar.Energywise,itismorefavorablefortheiodinetodissolveinthenon-polarsolventthaninthewater,soitexistspreferentially(butnottotally,anequilibriumwillexist)inthenon-polarsolvent.Thereleaseofenergyastheiodineswitchessolventsispartiallyresponsiblefortheinitialbuildupofpressureintheseparatoryfunnel.Thissameargumentexplainswhythenon-polarsolventdoesnotdissolveinthewater,sotwolayersareproducedwhenthetwosolventsareaddedtogether.Thetransferofiodinefromthewatertothechloroformisanequilibriumprocess.Thiscanbeseenintheseriesofbeakersoftheiodine/waterthatweredispensedfromtheseparatoryfunnel.Aftereachextractionofiodinewithchloroform,theamountofiodineremaininginthewaterbecamelessandless.Theseriesofbeakersbecomeslessandlesscoloredastheiodineresponsibleforthecolorisremoved.Whydotheextractioninaseriesofsmalladditionsinsteadofonelargeaddition?Assumethattheiodinedistributesitselfbetweenthewaterandchloroformlayerinaratioof1:9respectively.Thismeansthatoneextractionwillremove90%oftheoriginaliodinefromthewater,leaving10%behind.Asecondextractionremoves90%oftheremainingiodinefromthewater.Intermsoftheoriginalamountofiodinethatwouldbe:

(0.10)(0.90)=0.090or9%Thisleaves0.10-0.090=0.010or1%oftheoriginaliodineinthewaterand0.990or99.0%oftheoriginaliodineisinthetwochloroformextractions.Thisiscertainlybetterthanthe90%gainedfromoneextraction.Thiscouldgoonandondependinguponyourpatienceandhowmuchchloroformyoucanlayyourhandson.Threeextractionswouldleaveonly0.0010or0.1%oftheoriginaliodineinthewater.Theprocessofextractionsreachesitsultimatepracticallimitsinatechniqueknownaschromatography.Thisatechniquewherethenumberofextractionshasgrownhuge(100’softhousandsinsomecases)andthesizeofthesolventfractionshasshrunktoessentiallyashellofafewsolventmoleculessurroundingasolutemolecule(iodineinthiscase).References

1. AlyeaandDutton,p.223.2. TutorialVideoTapeIXfoundinLearningResourcesCentersinSt.PaulLibrary.TutorialVideoTapeXIIIalsofoundin

theLearningResourcesCenters

TyndallEffect(lightscattering)(bluesky-redsunset)EquipmentOne1-litertallformbeaker,longstirringrod,overheadprojector,maskforoverheadwithaholecutinthecenter(thehole'sdiametershouldbeslighlysmallerthanthebeaker'sdiameter).ReagentsOneliterof0.025MHClsolution,6mLofsaturatedsodiumthiosulfatesolution(Na2S2O3).Presentation

1. Placethemaskontheoverhead,centertheholeontheprojector.2. AddtheHClsolutiontothebeaker,placethebeakerovertheholeinthemask.3. Focustheprojector,sothereisabrightspotonthescreen.4. Add6mLofthethiosulfatesolutiontothebeakerandstir.Removethestirringrodandobservethebeakerandthe

spotonthescreen.HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Sodiumthiosulfatemaybeharmfulifswallowedorinhaled,maycauseirritationtoskin,eyesandrespiratorytract.DiscussionThefirstsignsofturbidityoccurinthebeakerinapproximately1to1.5minutes.Thecontentsofthebeakerwillbecomesmoreturbidastimegoeson.Thebeakerwillbegintoglowandwillglowmorebrighlyastheturbidityincreases.Thespotonthescreenwilldarkenandtakeonareddish-orangetint.Eventually,thespotwilldarkencompletely(inapproximately4.5minutes).Theseeffectsresultfromthelightbeingscatteredbycolloidalparticlesofsulfur.thesesulfurparticlesaregeneratedviathefollowingreaction:

S2O32-(aq)+H+(aq)®S(colloidal)+HSO3-(aq)Alittletimeisrequiredtoproducecolloidalparticlesofsufficientsizetonoticablyscatter,soyougettoseethegradualincreaseofthescatteringeffect.Scatteringintensityisproportionaltothefourthpowerofthefrequencyofthelightbeingscattered.Thismeansthatbluelighthasamoreintensescatteringthanredlight.Asthebluelightisscattered,thebeakertakesonabluishglowandthespotoflightreachingthescreenhastheblueremovedfromitandbecomesmorereddish.When

thereareenoughcolloidalparticlesinthesolution,nolightgetsthroughandthespotonthescreendarkenstoblack.Asimilareffectcanbeseeninthesky.Particlesintheatmospherescatterthebluewavelengthandweseeabluesky.Atsunriseandsunsetthesunlighttravelsthroughthemaximumamountofatmospheretoreachyoureye,duringthisjourney,thegreatestamountsofbluewavelengthsarescatteredandthelightthatreachesyoureyeiscorrespondinglyricherintheredwavelengths.Ifthenumberofscatteringparticlesisincreasedfromsourcessuchasforestfiresorvolcaniceruptions,yougetspectacularlyredsunrisesandsunsets.References

• B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.3,p.353-357

Liquids&SolidsTheFranklinFlaskEquipmentFranklinflask,boilingchip,ringstandplusironring,thermometerortemperatureprobe,stopper,burnerorhotplate,thermalglovesortowel.ReagentsWater,crushedice.Presentation

1. Partiallyfilltheflaskwithwaterandaddaboilingchip.2. Heatofthewateruntilboilingvigorously.3. Withdrawtheflaskfromtheheatusingthermalglovesoratowel.4. Whennomoresteamissuesfromtheflask,insertthestopperwiththethermometerortemperatureprobeintothe

flaskfirmly.TestsecurityofstopperbyinvertingtheflaskOVERTHESINK.Ifsecure,invertflaskonringstand.5. Placecrushediceintheconcavebottom.Waterwillboiluntiliceismelted.Keepreplenishingtheiceuntilthewater

hasfallentowithin15-20°Cofroomtemperature.

HazardsTheflaskandthehotwatercancauseburns.Tryingtoseatthestoppertoofirmlymaycausetheneckoftheflasktobreak.DiscussionThepressureinsidetheflaskequalsthevaporpressureofthewateratanygiventemperature.Thecoldsurfacecondensessomeofthewatervaporandreducesthepressurebelowtheequilibriumvaporpressureofwater.Thewaterboilstoreestablishequilibrium.Thehottestwatermoleculesenterthevaporphase.Thislowerstheflask'stemperatureviaevaporativecooling.ReferencesAlyeaandDutton,p.60(4-4s).

SolutionsandSaltsBeer’sLawEquipmentPlasticwellplatewithsixwells,dropper,smallglassstirrod,overheadprojector.ReagentsKMnO4solutionofsufficientconcentrationtobecompletelyopaque.Presentation

1. Place5mLofDIwaterinwells1-3,place10mLofDIwaterinwells4-6.Placewelltrayonoverheadprojector.2. UsingtheKMnO4solution,add1droptowell1,2dropstowell2and4dropstowell3.Stirthewells.3. UsingtheKMnO4solution,add2dropstowell4,4dropstowell5and8dropstowell6.Stirthewells.

HazardsPotassiumpermanganateisastrongoxidizer.Dustcausessevererespiratoryirritation.Eithersolidorsolutionscauseburnsofskin.DiscussionItshouldbenotedthattheKMnO4concentrationsinwells1,2,and3areequaltotheKMnO4concentrationsinwells4,5,and6respectively.Thisisnotarigorousexperimentalormathematicalproof,butdoesconveytheessenceofBeer’slaw.Inwells1-3,theonlyparameterthatischangingistheconcentrationoftheKMnO4.Theconcentrationinwell3istwicethatofwell2whichistwicethatofwell1.ItmaybereasonablysaidthattheamountoflightabsorbedortheabsorbanceAofthesolutionisproportionaltotheconcentrationCoftheabsorbingspecies.

AaCIfthewellsonthetwodifferentrowsarecompared,itappearsthattheabsorbanceofwell4matchesthatofwell2andthat5matches6.TheKMnO4concentrationinwell4ishalftheKMnO4concentrationinwell2.Theonlydifferenceisthatthepathlengthbofwell4isdoublethatofwell2.Itmaybereasonablysaidthattheabsorbanceofthesolutionisproportionaltothepathlength.

AabMathematically,somethingthatisproportionaltotwoindependentquantitiesisproportionaltotheirproduct.

AabCWecanchangetheproportionalitytoanequalitybytheadditionofaproportionalityconstant.InthecaseofBeer’slawthatproportionalityconstantiscalledthemolarabsorbtivitye.

A=ebC

AcidsBasesandBufferAlka-SeltzerBufferEquipmentOne6wellplate,smallstirrod,smallrinsebeaker.Reagents50-60mLofDIwater,Alka-Seltzertablet,universalindicatorandsolutionsof1MHCland1MNaOH.Presentation

1. Add20-25dropsofuniversalindicatortotheDIwater.2. PourequalamountsoftheDIwaterw/indicatorintoeachofthesixwells,approximately10mL.3. BreaktheAlka-Seltzertabletandchoosetwopiecesofapproximatelyequalmassinthe0.15-0.20grange.4. AddoneAlka-Seltzerpiecetowell3andtheothertowell6andstir.5. Addonedropof1MHCltowell1andonedropof1MNaOHtowell4andstir.6. AddHCltowell3in5dropintervalswithstirringuntilthecolorinwell3matchesthecolorinwell1.Thiswilltake

approximately25drops.7. AddNaOHtowell6in5dropintervalswithstirringuntilthecolorinwell6matchesthecolorinwell3.Thiswilltake

approximately25drops.HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.DiscussionAnAlka-Seltzertabletcontains1.9g(0.022mole)ofsodiumbicarbonateand1.0g(0.005mole)ofcitricacid.Keepinmindweareusingfractionsofthis.Whenthetabletisaddedtowater,thecitricacidreactswiththebicarbonate,producingcitrateandcarbondioxidegas.

3HCO3-(aq)+H3C3H5O7(aq)®C3H5O73-(aq)+3CO2(g)+3H2O(l)Thebalancedreactionandthestartingamountsofsodiumbicarbonateshowthatthereisanexcessofthebicarbonateion.ThisexcessisresponsibleforthebufferingeffectoftheAlka-Seltzer.Thebicarbonatecanreactwithexcessacid,

HCO3-(aq)+H+(aq)®CO2(g)+H2O(l)Orthebicarbonatecanreactwithexcessbase.

HCO3-(aq)+OH-(aq)®CO32-(aq)+H2O(l)ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.3,p.186-187.

DisappearingColorEquipment1Lor500mLFlorenceflask,stopper.Reagents1:3ethanol:watersolutionwiththymolphthaleinindicator.Presentation

1. Thesolutionshouldbeadarkblue,ifitisnotblue,add1MNaOHuntilitis.Thistypicallyrequires1-1.5mLperliterofsolution.

2. FillaFlorenceflaskapproximately1/2to1/3fullofthesolutionandstopperthesolution.3. Havestudentsunstoppertheflask,whispersomecommandtothesolution,restoppertheflaskandgiveitagentle

swirl.4. Havethestudentpasstheflasktothenextstudent.5. Repeatsteps3and4untilsolutionturnscolorless.6. Returnthesolutiontothestoragebottleforuseatalaterdate.

HazardsSolidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.Ethylalcoholisflammable.DiscussionWhenthissolutionisexposedtoasourceofCO2,thepHwilldecreaseandchangethethymolphthaleinindicatortoitsacidicformwhichiscolorless.Theethanolkeepsthethymolphthaleininsolution.Thefollowingreactionsillustratewhatisoccurringintheflask.ReferencesL.R.Summerlin,J.L.Ealy,ChemicalDemonstrations,ASourcebookforTeachers,WashingtonD.C.,AmericanChemicalSociety,SecondEdition,1988,Vol.1,p.59.

RedCabbageAcidBaseIndicatorEquipmentBlender,knife,wiremesh,enough250mLbeakersforeveryproposedsample+3,10-mLgraduatedcylinder,glassstirrods.ApHmetermaybeusedtoconfirmthecolorobservations.ReagentsHeadofredcabbage,DIwater,0.5MsolutionsofHClandNaOH,assortedhouseholdproductssuchasmilk,soap,aspirin,vinegar,etc.Avoidbleachunlessyourarepreparedtotalkaboutoxidation.PresentationProcedure:

1. Cuthalfaheadofredcabbageinto1-inchcubes,placeinblender,covercabbagewithDIwater,andblendthoroughly.2. Pourthejuiceintoa250-mLbeaker,usingawiremeshtoremovethemajorityofanyremainingsolids.

Presentation:

1. Add5mLofcabbagejuicetobeakersof0.5MHClandNaOHtoprovidecolorreferencepoints.2. Add5mLofthecabbagejuicetoeachsample.3. Liquidsamples:Pour125mLintoa250-mLbeaker,addcabbagejuiceandmix.4. Solidsamples:Add~1teaspoonofsolidtoa250mLbeaker,add125mLofDIwater,cabbagejuice,andmix.5. YoumayuseapHmetertodeterminethepHvaluesofallofthesamples.

HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.DiscussionRedcabbageandotherplants(beets,blueberries,radishes,andmanymore)containaclassofcompoundscalledanthocyanins.Anthocyaninshavedifferentcolorsthatdependuponthenumbersofremovableprotonsthatremainattached

tothemolecule.Anthocyaninsareweakacids.Whenweakacidshavedifferentcolorsdependinguponthenumberofprotonsthatremainwiththemolecule,wecallthemacid-baseindicators.Someofthemorecommonacid-baseindicatorsarephenolphthaleinandlitmus(neitherofwhichareanthocyanins).IfweweretorepresentananthocyaninmoleculeandtworemovableprotonsasH2Antho,theequilibriashowingthelossofitsprotonswouldbe:

H2Antho H++HAntho-HAntho- H++Antho2-

IfH2AnthowereredandHAntho-wereblueandAntho2-wereyellow,wemightseearedcoloratlowpH,blueatmediumpH,andyellowathighpH.AswechangefromlowtohighpHwegofromalarge[H+]tomoderate[H+]andfinallytolow[H+].Asthe[H+]changes,wegraduallyconvertamongthethreeformsoftheanthocyamin.Thecolorsthatwouldbeseenwouldbe:

[H+] colorveryhigh redhigh mixtureofredandbluemoderate blue

low mixtureofblueandyellow

verylow yellow

ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.3,p.50-57(procedureE).



Presentation

5. Placeallofthecomponentsonalightboxifoneisavailable.6. Placetheroundbottomedflaskonthecorkring,tiltitandgentlyallowthepenniestoslidetothebottomoftheflask.


HazardsNitricacidisacorrosivechemicalwithanumberofadverseeffects:EffectsofExposure:TARGETORGANS:EYES,SKIN,MUCOUSMEMBRANESOFTHERESPIRATORYTRACT,TEETH.THISMATERIALISCORROSIVETOANYBODYTISSUESITCONTACTS.DENTALEROSIONISALSOREPORTED.ACUTEEFFECTS-IRRITATIONAND/ORCORROSIVEBURNSOFSKIN,EYES,ANDUPPERRESPIRATORYTRACT(URT),DELAYEDPULMONARYEDEMA,PNEUMONITIS,BRONCHITIS,ANDDENTALEROSION.Nitrogendioxideisatoxiccompound,donotinhaleit.INHALATION:PULMONARYTRACTIRRITATION,THROATIRRITATION,TIGHTNESSINCHEST,HEADACHE,NAUSEA,&GRADUALLOSSOFSTRENGTH.SKIN/EYES:CORROSIVEACTION.DiscussionThisdemonstrationpresentsseveralveryinterestingchemicalandphysicalphenomena.Thefirstreactionisanoxidationreductionreactionwherecopperisoxidizedfromthezerostatetoa+2stateandthenitrogenisreducedfromthe+5stateinnitratetothe+2stateinnitrogenmonoxide.Itmaybepointedoutthatotherstrongacidssuchashydrochloricandsulfuricdonotreactwithcopper.

Thered-browngasthatappearsintheroundbottomedflaskiscausedbythesamecompoundresponsibleforthered-brownhazethathangsovercertaincities,nitrogendioxide.Thenitrogenmonoxidereactswithatmosphericoxygentoproducenitrogendioxideasshowninthesecondreaction.Thereisacid-basechemistrygoingon.Thenitrogendioxidethatisproducedintheroundbottomedflaskisbubbledthroughwaterthathasbeenmadebasicviatheadditionofammoniaandtheconditionmadevisiblebythepresenceofphenolphthalein.Asthenitrogendioxidebubblesthroughthebasicsolution,thepinkcolordisappears.Thisshowsthatthesolutionisnolongerbasic,buthasbecomeacidic.Thenitrogendioxidehasbeenconvertedtonitricacidandnitrousacidasshowninthethirdreaction.Thisisthesamereactionbywhichnitrogenoxidepollutantsmakeacidrain.Thereactionbetweenthecopperandthenitricacidisexothermic.Thecontentsoftheround-bottomedflaskincludingthegasareatanelevatedtemperature.Thereactioncomestoanendwhenthelastofthecopperisusedup.Thismakesthecoppertheyieldlimitingreagent.Whenthereactionceases,thebubblesofgasstop.Asthecontentsoftheround-bottomedflaskcool,thegaspressuredecreasesintheroundbottomedflask.Thisillustratesthepressure-temperaturerelationshipofgases.Asthepressureintheroundbottomedflaskdecreases,thegasinthetubingisdrawnbackintotheflaskandwaterfromtheErlenmeyerflaskisalsodrawnthroughthetubing.Thisisafairlyslowprocesssincetheflaskcoolsslowly.Nitrogendioxideissolubleinwaterandiscontinuouslydissolvinginthewaterfromthelargecontainer.Sincetheinterfacebetweenthenitrogenoxideandthewaterisconfinedtothecrosssectionalareaofthetubing,thedissolutionproceedsslowly.Whenthewaterfromthelargecontainerfinallyisdrawnallthewaythroughthetubingandenterstheround-bottomedflask,theinterfacebecomemuchlargerandtherateofdissolutionincreasesdramatically.Withinamatterofsecondsnearlytheentireround-bottomedflaskisfilledwithwaterfromthelargecontainer.ThesolutionnowintheroundbottomedflasktakesonthecharacteristicbluecoloroftheCu(H2O)n2+(nistypically4,)whichillustratessomecomplexionchemistry.




3HNO2(aq) H+(aq)+NO3-(aq)+2NO(g)+H2O(l)TheprocedureusedinthisdemonstrationislooselybaseduponapamphletauthoredbyLang,ShowalterandShulfer1.ThechemistryisdescribedinabookbyShakhashiri2.References

3. C.MarvinLang,DonaldL.Showalter,GaryJ.Shulfer,"YESVIRGINIA,...LEARNINGCHEMISTRYCANBEFUN!",UniversityofWisconsin-StevensPoint,1992,p.2-3.

4. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.165-166.

ElectrochemistryElectrolysisofWaterEquipmentHoffmanapparatus,platinumelectrodes,AC-DCrectifier,100DC"housecurrent".ReagentsDilutesulfuricacid.Presentation

1. Filltubewithdilutesulfuricacid.Becertaineachofthesidetubesiscompletelyfilledwiththesolution.2. Connecttheterminalstothecurrent.Thepowersupplyshouldbesetanywherebetween6-12volts,dependingupon

howfastyouwishtheelectrolysistoproceed.3. Allowreactiontooccur.Thehydrogentubewillfillattwicetherateoftheoxygentube.

HazardsBecausesulfuricacidisbothastrongacidandapowerfuldehydratingagent,itmustbehandledwithgreatcare.Thedilutionofconcentratedsulfuricacidisahighlyexothermicprocessandreleasessufficientheattocauseburns.Therefore,whenpreparingdilutesolutionsfromtheconcentratedacid,alwaysaddtheacidtothewater,slowly,withstirringandcooling

thereceivingbeaker.Hydrogenandoxygengaseswillbeproducedincloseproximitytooneanother.Thisisanexplosivecombinationandanysparkcouldsetoffthisreaction.DiscussionTherearetwoelectrochemicalreactionstakingplace:oxidationisoccurringattheanodeandreductionisoccurringatthecathode.

Cathode:2H2O(l)+2e-®H2(g)+2OH-Anode:2H2O(l)®O2(g)+4H+(aq)+4e-

Tokeepthenumbersofelectronsbalanced,thecathodereactionmusttakeplace,twiceasmuchastheanodereaction.Ifthecathodereactionismultipliedby2andthetworeactionsareaddedtogetherweget:

6H2O(l)+4e-®2H2(g)+O2(g)+4H+(aq)+4OH-(aq)+4e-IfwecombinetheH+andOH-toformH2Oandcancelspeciesthatappearonbothsidesofthearrow,wegettheoverallnetreaction:

Net:2H2O(l)®2H2(g)+O2(g)

Sinceequalmolesofgasesatequalpressuresoccupyequalvolumes,thefactthatthevolumeofhydrogenistwicethatoftheoxygenconfirmsthattherearetwiceasmanymolesofhydrogenasoxygenbeingproduced.ReferencesAlyeaandDutton,p.222.

HClCannonEquipmentOne250-mLErlenmeyerflask,a#6stopperwith3holes,twographiteelectrodesofadiametertofitthestopperholesandalengthtoreachnearlytothebottomoftheflask,powersupplycapableofapproximately6voltsand2amperes,100-mLclearplasticgraduatedcylinder,withendspoutcutoff,2-holestoppertofitthegraduatedcylinder,corktofitthegraduatedcylinder,plastictubingandglassbendstochannelgasesandacameraflaskorsomeothersourceofintensewhitelight.Optional:redandbluefilters.Reagents250mLof6MHCl,250mLof6MNaOHPresentation








HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.Thecorkispropelledwithsufficientforcetocauseinjuryifsomeoneishitatblankrange.Thecylindermayshatterifthecorkisseatedtoofirmly.Thecylinderweakenswitheverydemonstrationandwillusuallyburstafter3-4uses.Thedemonstratorshouldwearsometypeofhearingprotectionandtheaudienceshouldbecautionedtocovertheirears.

DiscussionCl2+light(500nm)®2Cl•(initiation)Cl•+H2®HCl+H•(propagation)H•+Cl2®HCl+Cl•(propagation)2Cl•®Cl2(possibletermination)H•+O2®HOO•(possibletermination)Cl•+O2®ClO2•(possibletermination)radical+containerwall(possibletermination)


FuelCellsandElectrolysisEquipmentSolarModule,PEM-Electrolyserwithstoragecylinders,2overflowpipesforstoragecylinders,PEMFuelCell,LoadMeasurementBox,2redcables,2blackcables,4siliconetubes,3tubingstoppers,stopwatch,lampwith100Wattbulb(maximum),alignmentdiagram.Foracompletepictureoftheapparatus,seeFig.1.ReagentsDistilledordeionizedwaterPresentationThiskitcanperformseveralfunctions:A.Thesolarmoduleconvertslightintocurrent

1. Placethesolarmoduleonthealignmentdiagramsothatitisdirectlyovertheshadedregionofthecircle,facingthelamp.

2. Placethelamponthealignmentdiagramsothattheedgeofthebulbisovertheedgeofthebulbdiagram.3. Turnonthelamp.4. Tomeasurethecurrentorvoltageofthepowergenerated,connectthesolarmoduletotheappropriateinputsonthe

loadmeasurementboxusingbananaclips(optional).B.Thecurrentsplitswaterintohydrogenandoxygenintheelectrolyser

1. Connecttheoverflowpipestothegasstoragecylinders.2. FilltheO2andH2gasstoragecylinderstothe0mLmarkwithdistilledwater.3. Connectthesolarmoduletotheelectrolyserwiththebananaclips.

C.Thehydrogenandoxygenarefedintothefuelcell,wheretheyareconverteddirectlyintoelectricalcurrent.

1. Connecttheelectrolysertotheappropriatefuelcellgasinletsusingthetwolongsiliconetubes(thegasinletsofthefuelcellarelocatedabovetheoutlets).

2. Connecttheshortsiliconetubestothegasoutletsofthefuelcell(locateddirectlybelowthegasinlets).Bothofthesetubesshouldbepluggedontheotherend.

3. Beforerunningthefuelcell,oneshouldcollect5-10mLofH2inthehydrogenstoragecylinder.4. Toinitiateacurrent,unplugthehydrogenoutlettubebrieflytoallowhydrogentogettothefuelcell.Thiscanbe

monitoredbywatchingthebubblesinthesiliconetube.D.Thecurrentdrivestheelectricmotororthebulb.

1. Connectthefuelcelltothecurrentinputoftheloadmeasurementboxusingbananaclips.2. Anadditionalsetofbananaclipscanbeusedtomeasurethevoltageproducedbythefuelcell.3. Ohm'sLawcanbedemonstratedbyvaryingtheresistanceandcomparingthecurrentandvoltage.4. Turntheloadto"lamp"toseethelamplightup.Itisveryfaintbuttakenoteoftheefficiencyoftheprocess.A100

wattbulbcanbarelylighta12mWbulbafterthepowerhasbeenconvertedthroughthesevariousprocesses.5. Turntheloadto"motor"toseethemotorspin.Thisismuchmorevisible.6. Thefuelcellwillrunaslongasthe100Wlampremainsontoproducehydrogenorthereishydrogenremainingin

thestoragetube.Tostopthefuelcell,simplyremoveitshydrogensupply.HazardsSincehydrogengasisproducedinthedemonstration,openflamesandsparksshouldbekeptaway.Thelampgeneratesalotofheatandcouldoverheatthesystemifitisplacedtooclosetothesolarmodule.Thelampandsolarmoduleshouldbehandledcarefullyastheycouldresultinskinburns.Discussion

Thechemicalreactionsinvolvedintheseprocessesarethedecomposition,viaelectrolysis,andreformation,viafuelcell,ofwater:

2H2O(l)®2H2(g)+O2(g)2H2(g)+O2(g)®2H2O(l)

Thefuelcellworkslikeabattery-thedifferenceisthatthefuelcellisconstantlysuppliedwithnewfuel(H2).Attheanode,hydrogengasislysedandionizedtoprotonsandelectrons(seeFig2.).Theseprotonspassthroughthepolymerelectrolytemembrane(nafion,seeFig2.)untiltheyfindoxygenandultimatelyformwater.Thisisthecathodereaction.

Figure2Theelectronsproducedattheanodeareunabletopassthroughthepolymerelectrolyte.Insteadtheygetpushedupoutofthecellintoacircuitthatultimatelyconnectstothecathode.Thecurrentofthiscircuitcanbeusedtopoweramotororalightbulb.Thecatalystsusedinhydrogenfuelcellsareusuallyamixtureofplatinumandruthenium.PlatinumprovidesasurfacetowhichH2(g)canbind.ThisbindingweakenstheH-Hbondsothatlysingandionizationcaneasilyoccur(seeFig.2).Asimilarprocesshappensatthecathode,facilitatingthejoiningofoxygen,electrons,andprotonstoformwater.Theexpenseoftheplatinumcatalystisonereasonwhyfuelcellsarenotyetuniversalinautomobiles.Anotherdrawbackisthatthesecatalystsarepoisonedovertimeandeventuallylosetheiractivity.Thepoisoningistheresultofsulfur,carbonmonoxide,andothercontaminantscoatingthecatalyticsurface.Thesolarmodule'smaximumvoltageis2.4Vwhileitsmaximumgeneratedcurrentis200mA.Theelectrolyserrunson1.5Vandacurrentofupto500mA.ItcanproduceH2atamaximumrateof3.5mL/min.Thefuelcellrunson0.7Vandcanproduceacurrentof1000mA.Thefuelcellkitcomeswithmultiplemanualsforvariousexperimentstoexploredifferentaspectsoftheprocesses.CalculationscanbemadetoverifyOhm'slaw,Avogadro'snumber,andthestoichiometryofwater.Feelfreetosearchthroughthemfortheexperimentbestsuitedforyoursituation.References

1. Editors:TedListerandHenrikColell,EnergythroughHydrogen,researchnotes,HeliocentrisEnergiesysteme,GmbH,Berlin,Germany,2000

2. OperatingInstructions:SolarHydrogenTechnologyScienceKit

Copper-ZincGalvanicCellEquipmentTwo250-mLtallformbeakers,stripofzinc,stripofcopper,twoclampstoholdmetalstrips,saltbridgefilledwith3%agarand1MKClorKNO3,voltmeterorcomputerinterface.Reagents250mLof1.0MCuSO4and250mLof1.0MZnSO4.Presentation

1. Pouroneofthesolutionsintoabeakerandtheothersolutionintotheotherbeaker.2. ClampthecopperstripintothebeakercontainingtheCuSO4solutionanddotheequivalentwiththezincstrip.3. Connectthetwobeakerswiththesaltbridge.Itiscriticalthatthesaltbridgereachbeneaththesurfaceofboth

solutionsandthattherearenoairbubblesanywherethroughoutthebridge.4. Connectoneleadfromthevoltmetertoeachofthemetalstrips.Youshouldgetareadingnear1.10V.

Note:Inordertopreservethesaltbridge,aftercompletingthedemonstration,removethesaltbridgefromthebeakers,rinsewithDIwaterandreturnittoitsstoragecontainer.HazardsCopperCompoundscanbetoxiciftakeninternally,anddustfromcoppercompoundscanirritatemucousmembranes.DiscussionThestandardreductionpotentialsforthetwohalf-cellsaregivenbelow.

ThereactionwiththemorepositiveE°proceedsasitiswritten(Itisthecathodicreactionandthecopperstripisthecathode.).Thereactionwiththelesspositive(morenegative)E°willbeforcedtoproceedintheoppositedirectionasitiswritten(Itistheanodicreactionandthezincstripistheanode.).ChangingthedirectionofareactionchangesthesignofE°forthereaction.AddthetworeactionaccordingtothewaytheywillbereactingandsumtheappropriateE°valuetoproducetheoverallcellreactionandthecellpotential.

Physically,thissaysthatthecopperstripwillgetheavierascopperionsarereducedanddepositedonitssurfaceandthezincstripwillbegettinglighteraszincatomsareoxidizedandleavethesurfaceandenterthesolution.Ascanbeseeninthephoto,ourexperimentalcellis20mVlowerthanthepredicted1.10V.Thereareanumberoffactorsthatcanaccountforthis.Themostlikelyfactorsarethatthesolutionsarenotat1molarconcentrationandthattherearepotentialdropsduetoresistancetoelectricalconductivityinthesaltbridgeandthesolutions.ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1992,Vol.4,p.189.

PlatingCopperontoIronEquipmentPieceofiron(strip,rod,etc.),250-mLbeaker.ReagentsJustaboutanyCu2+containingsolutionataconcentrationof0.1-1.0M.Presentation

1. Pour50-150mLoftheCu2+solutionintothebeaker.2. DipthepieceofironintotheCu2+solution.Thecopperwillbeginplatingtheironimmediatelyandwithinsecondsthe

coppercoatingwillbequitevisible.

HazardsSolutionsofCu2+irritateeyesandmayirritateskin.DiscussionThestandardreductionpotentialsforthetwohalf-cellsaregivenbelow.

ThereactionwiththemorepositiveE°proceedsasitiswritten(Itisthecathodicreaction.).Thereactionwiththelesspositive(morenegative)E°willbeforcedtoproceedintheoppositedirectionasitiswritten(Itistheanodicreaction.).ChangingthedirectionofareactionchangesthesignofE°forthereaction.AddthetworeactionaccordingtothewaytheywillbereactingandsumtheappropriateE°valuestoproducetheoverallcellreactionandthecellpotential.

Physically,thissaysthattheCu2+concentrationwilldecreaseascopperionsarereducedanddepositedonthesurfaceoftheironandtheironstripwillbegettinglighterasironatomsareoxidizedandleavethesurfaceandenterthesolution.Ifallowedtocontinue,thesolutionwouldlosethebluecolorfromtheCu2+andbecomeapalegreenfromtheFe2+.

TearinganAluminumCaninHalfEquipmentYouwillneedanaluminumcan,andacontainerlargeenoughtositthecanin.ReagentsApproximately400-500mLof1MCuCl2.Presentation

1. Rinsethealuminumcan.2. Scoretheinsideofthecanabouthalfwayupcompletelyaroundthecircumferenceofthecan.Thisremovestheplastic

liningandexposesthebarealuminum.3. Placethecanintheprotectivecontainer.4. PourenoughCu2+solutionintothecansothatthesolutionlevelisabovethescoremark.5. Waitapproximately1-3minutes.6. Pourthesolutionoutofthecan.7. Gripeachendofthecanandsimultaneouslytwistandpull.Thecanwilltearaparteasilyalongthescore.

Youcanplayatrickbyusingascoredcanandanunscoredcanandchoosingtwovolunteersfromtheaudience(oneclearlystrongerthantheother).Afterfinishingstep6,givetheunscoredcantothestrongervolunteer.Theweakervolunteerwilltearaparttheircanwithease.

HazardsSolutionsofCuCl2irritateeyesandmayirritateskin.DiscussionThestandardreductionpotentialsforthetwohalf-cellsaregivenbelow.

ThereactionwiththemorepositiveE°proceedsasitiswritten(Itisthecathodicreaction.).Thereactionwiththelesspositive(morenegative)E°willbeforcedtoproceedintheoppositedirectionasitiswritten(Itistheanodicreaction.).ChangingthedirectionofareactionchangesthesignofE°forthereaction.AddthetworeactionaccordingtothewaytheywillbereactingandsumtheappropriateE°valuetoproducetheoverallcellreactionandthecellpotential.

Thisreactioncanonlytakeplaceoncethealuminummetalisexposedfrombehindtheprotectiveplasticcoating.ReferencesLeeR.Summerlin,JamesL.Ealy,ChemicalDemonstrations,ASourcebookforTeachers,WashingtonD.C.,AmericanChemicalSociety,SecondEdition,1988,Vol.1,p.152-153.

IronCorrosionEquipmentPetridish,ironwireornail.ReagentsAgar,potassiumchloride,potassiumferricyanide(K3Fe(CN)6),phenolphthaleinsolution,6MHNO3.PresentationSolutionpreparation:Thismakes60mLofsolution,whichissufficienttomakeuptwopetridishes.Thesolutionwillbe1%w/wagar,0.3MKCl.

1. Add0.6gofagar,1.3gKCl,2-3mLof0.1MK3Fe(CN)6,20dropsof0.01%phenolphthaleinsolutionand60mLofDIwatertoa150-mLbeaker.

2. Heatgentlywithstirringuntileverythingisdissolved.3. Pourthesolutionintothepetridishesuntilthelevelisapproximatelyhalffull.4. Placealidonthepetridishandallowittocool.Aslongasthedishesremaincoveredandthesolutiondoesn’tdryout,

thesemaybestoreduntilneeded.Demonstration:

1. Cleananironnailorpieceofwirebybrieflydippingitin6MHNO3.2. Aftercleaning,cutalengthofwire~5cminlength.Besuretocutbothendsfreshly.3. Pushtheirondownintotheagarsolution,approximatelyinthecenterofthedish.4. Observewhattheironandagarsolutionlooklike.Thismaybedoneusinganoverheadprojectorforlargerclasses.5. Thecolorsdevelopovertime.Typicallytheyarequitedistinctafter9minutes.Examinetheironandagarsolution

afterthecolorshavedeveloped.

HazardsContactswithsolidpotassiumchlorideorwithitssolutionsmayleadtoanallergicskinreaction,dustmaycausethroatirritation.Concentratednitricacidisbothastrongacidandapowerfuloxidizingagent.Contactwithcombustiblematerialscancausefires.Contactwiththeskincanresultinsevereburns.Thevaporirritatestherespiratorysystem,eyes,andothermucousmembranes,andtherefore,concentratednitricacidshouldbehandledonlyinawell-ventilatedarea.Potassium

ferricyanidemaycauseeyeandskinirritation,causesdigestiveandrespiratorytractirritation.Itmaybeharmfulifswallowedorabsorbedthroughtheskin.DiscussionThepieceofironappearsuniformonthelargescale,butattheatomiclevelitisquiteirregular.Regionsoftheironwhichhavebeensubjectedtointensestress,likethestampedheadandpointofthenail,ortheshearedendsofthewire,containatomsthathaveahigherenergythanthereunstressedneighbors.Theseregionsloseelectronsorundergooxidationslightlymorereadilythantheunstressedregions.Thereactionisshownbelow.

Fe(s) Fe2+(aq)+2e-Theseelectronsarereadilytakenupduringthereductionofwater,accordingtothereactionbelow.

2H2O(l)+2e- 2OH-(aq)+H2(g)alternatively

2H2O(l)+O2(g)+4e- 4OH-(aq)Ifwecankeepwaterandoxygenawayfromourironsurfaces,wecanminimizetheamountofcorrosionthatcanoccur,sinceoxidationcannotoccurwithoutreduction.Thisiswhywepaintandwaxourcars.Thecolorsarecreatedfromtwoadditionalreactionsasshownbelow.PhenolphthaleinisaweakacidandwillbedenotedasHPh.

HPh(aq)+OH-(aq) Ph-(aq)+H2O(l)colorlesspink

WherevertherearesignificantquantitiesofOH-theregionwillturnpink.

H2O(l)+K+(aq)+Fe2+(aq)+Fe(CN)63-(aq)®KFe[Fe(CN)6]·H2O(s)paleyellowblue

ThislastcompoundiscallvariouslyTurnbull’sblueorPrussianblue.Itissomewhatunusualinthatitisamixedvalencecompoundcontainingironinboththe+2and+3oxidationstates.TheagarsolutionwillturnblueinanyregionwithasupplyofFe2+.ReferencesLeeR.Summerlin,ChristyL.Borgford,andJulieL.Ealy,ChemicalDemonstrations,ASourcebookforTeachers,WashingtonD.C.,AmericanChemicalSociety,SecondEdition,1988,Vol.2,p.191-192.



Presentation

9. Placeallofthecomponentsonalightboxifoneisavailable.10. Placetheroundbottomedflaskonthecorkring,tiltitandgentlyallowthepenniestoslidetothebottomoftheflask.


HazardsNitricacidisacorrosivechemicalwithanumberofadverseeffects:EffectsofExposure:TARGETORGANS:EYES,SKIN,MUCOUSMEMBRANESOFTHERESPIRATORYTRACT,TEETH.THISMATERIALISCORROSIVETOANYBODYTISSUESITCONTACTS.DENTALEROSIONISALSOREPORTED.ACUTEEFFECTS-IRRITATIONAND/ORCORROSIVEBURNSOFSKIN,EYES,ANDUPPERRESPIRATORYTRACT(URT),DELAYEDPULMONARYEDEMA,PNEUMONITIS,BRONCHITIS,ANDDENTALEROSION.Nitrogendioxideisatoxiccompound,donotinhaleit.INHALATION:PULMONARYTRACTIRRITATION,THROAT

IRRITATION,TIGHTNESSINCHEST,HEADACHE,NAUSEA,&GRADUALLOSSOFSTRENGTH.SKIN/EYES:CORROSIVEACTION.DiscussionThisdemonstrationpresentsseveralveryinterestingchemicalandphysicalphenomena.Thefirstreactionisanoxidationreductionreactionwherecopperisoxidizedfromthezerostatetoa+2stateandthenitrogenisreducedfromthe+5stateinnitratetothe+2stateinnitrogenmonoxide.Itmaybepointedoutthatotherstrongacidssuchashydrochloricandsulfuricdonotreactwithcopper.Thered-browngasthatappearsintheroundbottomedflaskiscausedbythesamecompoundresponsibleforthered-brownhazethathangsovercertaincities,nitrogendioxide.Thenitrogenmonoxidereactswithatmosphericoxygentoproducenitrogendioxideasshowninthesecondreaction.Thereisacid-basechemistrygoingon.Thenitrogendioxidethatisproducedintheroundbottomedflaskisbubbledthroughwaterthathasbeenmadebasicviatheadditionofammoniaandtheconditionmadevisiblebythepresenceofphenolphthalein.Asthenitrogendioxidebubblesthroughthebasicsolution,thepinkcolordisappears.Thisshowsthatthesolutionisnolongerbasic,buthasbecomeacidic.Thenitrogendioxidehasbeenconvertedtonitricacidandnitrousacidasshowninthethirdreaction.Thisisthesamereactionbywhichnitrogenoxidepollutantsmakeacidrain.Thereactionbetweenthecopperandthenitricacidisexothermic.Thecontentsoftheround-bottomedflaskincludingthegasareatanelevatedtemperature.Thereactioncomestoanendwhenthelastofthecopperisusedup.Thismakesthecoppertheyieldlimitingreagent.Whenthereactionceases,thebubblesofgasstop.Asthecontentsoftheround-bottomedflaskcool,thegaspressuredecreasesintheroundbottomedflask.Thisillustratesthepressure-temperaturerelationshipofgases.Asthepressureintheroundbottomedflaskdecreases,thegasinthetubingisdrawnbackintotheflaskandwaterfromtheErlenmeyerflaskisalsodrawnthroughthetubing.Thisisafairlyslowprocesssincetheflaskcoolsslowly.Nitrogendioxideissolubleinwaterandiscontinuouslydissolvinginthewaterfromthelargecontainer.Sincetheinterfacebetweenthenitrogenoxideandthewaterisconfinedtothecrosssectionalareaofthetubing,thedissolutionproceedsslowly.Whenthewaterfromthelargecontainerfinallyisdrawnallthewaythroughthetubingandenterstheround-bottomedflask,theinterfacebecomemuchlargerandtherateofdissolutionincreasesdramatically.Withinamatterofsecondsnearlytheentireround-bottomedflaskisfilledwithwaterfromthelargecontainer.ThesolutionnowintheroundbottomedflasktakesonthecharacteristicbluecoloroftheCu(H2O)n2+(nistypically4,)whichillustratessomecomplexionchemistry.




3HNO2(aq) H+(aq)+NO3-(aq)+2NO(g)+H2O(l)TheprocedureusedinthisdemonstrationislooselybaseduponapamphletauthoredbyLang,ShowalterandShulfer1.ThechemistryisdescribedinabookbyShakhashiri2.References1. C.MarvinLang,DonaldL.Showalter,GaryJ.Shulfer,"YESVIRGINIA,...LEARNINGCHEMISTRYCANBEFUN!",Universityof

Wisconsin-StevensPoint,1992,p.2-3.2. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.165-166.

KineticsCatalysisCatalyticOxidationofAmmonia

Equipment250-mLErlenmyerflask,rubberstopperforflask,barbecuelighter,rodtosupportwireacrossthetopoftheflask,coiledplatinumwire.Thecoilshouldbeapproximately7mmindiameterandlooseenoughthattheadjacentcoilssonottouch.Reagents25-75mLofconcentratedaqueousammoniasolution.Presentation

1. Pourtheammoniasolutionintotheflaskandstopperit.2. Attachwiretoitssupport.3. Adjustthelengthsothattheendoftheplatinumis1-3cmabovethesurfaceoftheammoniasolution.4. Unstoppertheflask.5. Heattheendoftheplatinumwireuntilitbeginstoglowred.6. Quickly,putthewiredownintotheflask.7. Thewirewillglowbrightly.8. Thewiremayberemovedfromtheflaskanditwillceasetoglow.9. Ifthewireisreturnedtotheflaskbeforeitgetstoocool,itwillagainglowbrightly.Thismayberepeatedmanytimes.

HazardsConcentratedaqueousammoniacancauseburnsandisirritatingtotheskin,eyes,andrespiratorytract.Nitrogendioxideisanextremelytoxicgas.Itisirritatingtotherespiratorytract.DiscussionAmmoniaiscatalyticallyoxidizedattheplatinumsurfaceaccordingtothefollowingreaction.

5NH3(g)+5O2(g)®4NO(g)+6H2O(g)Thereactionisexothermicandaswrittenreleases920kJofenergy.Asecondreactionproceedsautomaticallyfromthefirstreaction.

2NO(g)+O2(g)®2NO2(g)Thesecondreactionisalsoexothermicandaswrittenreleases112kJofenergy.ThesetworeactionstakentogethermakeuptwothirdsoftheOstwaldprocessforthesynthesisofnitricacid.IftheNO2(g)wereputintocontactwithliquidwater,nitricacidandNO(g)wouldbeproduced.Theinitialheatingofthewirewiththelighterprovidestheactvationenergyforthereaction.Oncethereactionbegins,thereleasedenergywillprovidemorethanenoughactivationenergyforsubsequentreactionstooccur.Aninterestingvariationofthisdemonstrationistosubstituteathincopperwire,approximately0.2mmindiameterfortheplatimunwire(2).Theheatfromthereactionissufficienttomeltthecopperwire.Themoltencopperwillspatterandmakeaspectaculareffect.Additionally,someofthecopperwilloxidizeandturntheammoniasolutionbluebyformingacomplexionbetweentheCu2+ionandtheammonia[Cu(NH3)4]2+.Thisvariationdoesnotworkasconsistentlywellastheplatinumversiondoes.References

1. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.214-2152. Gilbert,Alyea,Dutton,Dreisbach,TestedDemonstrationsinChemistry,PublishedbyarrangementwiththeJournalof

ChemicalEducation,1994,Vol.I,p.I-35

PlatinumCatalyzedReactionofHydrogenandOxygenEquipmentDisposableglasspipet,rubberhose3-6feetlongtofitpipetandregulator,ringstand,ironring,wiremesh.ReagentsTankofhydrogengaswithregulatorand0.5%platinized1/8inchaluminapelletsPresentation

1. Poundasmallindentationintothecenterofthewiremeshlargeenoughtocontain2-3ofthealuminapettets.Theroundedendofaballpeenhammerworkswellforthis.Withouttheindentation,thehydrogenstreamwillblowthepelletsoffofthescreen.

2. Attachtheironringtotheringstand.Theheightisnotcritical.Placethewiremeshontheringandplace2-3pelletsintheindentation.

3. Attachtherubberhosetothepipetandtheregulatoroutlet.4. Openthehydrogencylinderandadjusttheoutletpressuretoapproximately10psi.5. Dimthelights.

6. Holdthepipetapproximately6-10cmfromthepelletsandallowthehydrogemstreamtoflowoverthepellets.Note:Holdthepipettoocloseandalloftheoxygenwillbedisplacedfromaroundthepellets,holdthepipettoofarawayandthehydrogenconcentrationwillbetoodilutearoundthepellets,eitherwaytherewillbenoreaction.

7. Thepelletswillbegintoglowredhotiftheexothermicreactionbetweenhydrogenandoxygenbeginstooccur.Youmayusetheglowtojudgehowtoadjustthehydrogenstream.Adjustyourpositionformaximumglow.Whenthisisachieved,thehydrogemstreamwilligniteshortlythereafter.

8. Displaytheflametotheaudience.Closingtheoutletvalveontheregulatorwillcausetheflametogoout.Repeatifdesired.

9. Closethecylindervalve.

HazardsHydrogenisanexplosivegas,useinawellventilatedroomanddonotallowquantitiesofunreactedhydrogentobuildup.Theflameproducedinthisdemonstrationisveryhotandcanbeupto25cmlong.Donotallowtheflametocomenearanyoneoranycombustibles.DiscussionThecombinationofhydrogenandoxygentoformwaterisanexothermicprocess.Despitethisfact,hydrogenandoxygenwillnotreactautomaticallywhenmixedtogether.Thereasonforthisistheratherlargeactivationenergyneededtobeginthereaction.Themechanismisverycomplex(2-4).Howeverwedoknowthatitisafreeradicalmechanismandthatoneoftheinitiationstepsis:

H2(g)®2H•(g)Breakingthebondbetweenthetwohydrogenatomsrequires432kJ/mole.Thisenergyistypicallyinitiallyprovidedbyasparkoraflame.Afterthereactionbegins,theenergyproducedfromitwillprovidethenecessaryenergytocontinuebreakingapartthehydrogenmolecules.Acatalystprovidesanalternativemechanismthathasaloweractivationenergy,thisallowsthereactiontoproceedwithouttherequirementoftheinitialadditionofenergyviaaflameorspark.Hydrogenmoleculeswilladsorbtotheplatinumsurface.Theenergyoftheinteractionbetweenthehydrogenatomsandtheplatinumsurfacecontributestothebreakingofthebondbetweenthehydrogenatoms.Theseparatehydrogenatomsarethenfreetoreactatthesurfaceorleavethesurfaceandparticipateinthewaterformingsteps.References

1. Developedinhouse.2. Eggers,D.F.,Jr.;Gregory,N.W.;Halsey,G.D.,Jr.;Rabinovitch,B.S.PhysicalChemistry,Wilely:NewYork,1954,p.475.3. Nicholas,John.ChemicalKinetics,Halsted:1976,p.143Pannetier,G.;Souchay,P.ChemicalKinetics,Elsevier:New

York,1967,p.211.

GenieinaBottleEquipment2litersodabottle(orothercontainer-beaker,flask,etc),goggles,spatula,mortarandpestleReagents30%hydrogenperoxide,manganesedioxide,it'scatalyticeffectisgreatestifitisfreshlygroundwithin24hoursofuse.Presentation

1. Pour50-100mLof30%hydrogenperoxideinto2literbottle(enoughtocoverthe"dimples")orcontainer.2. Addapea-sizedamountofmanganesedioxidetobottleorcontainer.3. Gaseousoxygenwillbeemittedfromthebottle.Thereactionisexothermic;thesodabottlewillgethotandshrink

slightly.

Hazards30%hydrogenperoxideisastrongoxidizingagent;contactwitheyesandskinshouldbeavoided.Incaseofcontact,flushwithwaterforatleast15minutes.Getmedicalattentionifeyesareaffected.Alsoavoidcontactofhydrogenperoxideandcombustiblematerials.30%hydrogenperoxidemustbestoredinitsoriginalcontainer.DiscussionOxygenisacolorless,odorlessgasatroomtemperatureandatmosphericpressure.ThediscoveryofoxygenistypicallyattributedtoJosephPriestly.However,itwasLavoisierwhofirstrealizedthisgaswasauniquecomponentofair.Hereoxygenisformedfromthedecompositionofhydrogenperoxide.Hydrogenperoxideisnotaverystablecompoundanditsdecompositioncanbeinducedbymanymeans.Lightwilldecomposeit,whichiswhyitissoldinbrownbottlesindrugstores.Thesurfaceofmanganesedioxideprovidesaparticularlyfavorableenvironmenttocatalyzethedecomposition,thoughthemechanismissomewhatpoorlyunderstood.

2H2O2(aq) O2(g)+2H2O(l)

The"genieinthebottle"effectisfinelydividedwaterdropletspropelledfromthebottlebytheoxygenformedviathedecompositionofhydrogenperoxide.ReferencesB.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.137-141

CatalyticDecompositionofHydrogenPeroxidebyIodide"Elephant'sToothpaste"EquipmentLargegraduatedcylinder(500mL)or2litersodabottle,goggles,plastictrayorsheetReagents30%hydrogenperoxide,dishwashingdetergent,saturatedsolutionofpotassiumiodide-OR-solidpotassiumiodidePresentation

1. Placegraduatedcylinderorsodabottleinaplastictrayoronalargesheetofplastic.2. Pour~50mLof30%hydrogenperoxideintothecylinderorbottle.3. Addasquirtofdishwashingdetergent;agitateslightly.4. Add~10mLofpotassiumiodidesolutionOR1/4spoonfulofsolidpotassiumiodide.(Note:Thereactionismuch

fasterwiththeKIsolution.)Stepbackquicklyafteraddingthepotassiumiodide.Hazards30%hydrogenperoxideisastrongoxidizingagent;contactwitheyesandskinshouldbeavoided.Incaseofcontact,flushwithwaterforatleast15minutes.Getmedicalattentionifeyesareaffected.Alsoavoidcontactofhydrogenperoxideandcombustiblematerials.30%hydrogenperoxidemustbestoredinitsoriginalcontainer.DiscussionOxygenisacolorless,odorlessgasatroomtemperatureandatmosphericpressure.Itisformedherebythecatalyticdecompositionofhydrogenperoxidebytheiodideion.H2O2(aq)+I-(aq) OI-(aq)+H2O(l)Step1H2O2(aq)+OI-(aq) I-(aq)+H2O(l)+O2(g)Step22H2O2(aq) 2H2O(l)+O2(g)OverallThefirststepistheratelimitingstepofthereaction.Theoxygenthatisproducedcausesthedishwashingdetergenttofoam;thefoamwillshootoutofthecontainer!Notethattheiodidedoesnotappearintheoverallreaction.Theoverallreactionisexothermic;theheatproducedisenoughtoslightlyshrinktheplasticofthetwoliterbottle.Foraninterestingtwist,putasmallamountoffoodcoloring(~5-10drops)inastripalongthewallofthesodabottleorgraduatedcylinder(moredramaticifdonewithgraduatedcylinder.Theresultingfoamwillhaveastrongerresemblancetotoothpaste.ReferencesL.R.SummerlinandJ.L.Ealy,Jr.ChemicalDemonstrations,ASourcebookforTeachers,WashingtonD.C.,1985,p.71.

EquilibriumEquilibriumBetweenNO2andN2O4EquipmentOneortwosealedborosilicateglasstube(s)filledwithnitrogendioxidegas,twotallform1literbeakers,hotplate,tapwater,ice.ReagentsNonePresentation

1. Filloneofthebeakerswithtapwaterandplaceonhotplate,heatuntilboiling.2. Fillthesecondbeakerwithamixtureoficeandtapwater.3. Displaythesealedtube(s)containingnitrogendioxide.Awhitebackgroundmakesthemmuchmorevisible.4. Ifyouhavetwotubes,placeoneineachbeaker.Therewillbesignificantchangesinhowdarkthebrowncolorisin

eachtube(coldtubegetslighter,hottubegetsdarker).

5. Ifyouareworkingwithasingletube,notethecoloratroomtemperatureandthenplacethetubeineitherofthepreparedbaths.Notethenewcolorofthetube.

6. Removethetubefromthebaththatitisinandplaceitintheotherbath.Notethenewcoloroftube.

HazardsTheborosilicatetubescaneasilywithstandthetemperatureextremesofthesetwobaths,careshouldbetakensoasnottodamagethetubesandallowthenitrogendioxidetoescape.Nitrogendioxideisanextremelytoxicgas.Itisirritatingtotherespiratorytract.DiscussionTheequilibriumillustratedinthisdemonstrationisbetweennitrogendioxide(NO2)anddinitrogentetroxide(N2O4).Thechemicalequationisshownbelow.

2NO2(g) N2O4(g)PhysicalConstantsofCompoundsofInterest[2]

Compound Physicalstate meltingpoint(oC) boilingpoint(oC)NO2 browngasinequil.withN2O4 undefined seeN2O4N2O4 colorlessliquidinequil.withNO2 -9.3 21.15N2O3 blueliquidorsolid -101.1 decomposes~3HNO3 colorlessliquid -41.6 83

Nitrogendioxideisadarkreddishbrowngasanddinitrogentetroxideisacolorlessgas.Whentheequilibriumisshiftedtotheleft,aswritten,theamountofnitrogendioxideincreases,theamountofdinitrogentetroxidedecreasesandthecolorofthetubedarkens.Whentheequilibriumisshiftedtotheright,aswritten,theamountofnitrogendioxidedecreases,theamountofdinitrogentetroxideincreasesandthecolorofthetubelightens.Therearetwofairlyeasywaystoshifttheequilibrium,thefirstmakesuseoftheexothermicityofthereaction.Aswritten,thereactionreleasesreleases58kJofenergy(DHo=-58kJ).Sinceenergyisreleased,addingmoreenergyviaheatingshifttheequilibriumtotheleftandremovingenergyviacoolingwillshifttheequilibriumtotheright.Thesecondmethodutilizeschangesinpressuretoshifttheequilibrium.Thiswillbecoveredinanotherdemonstration.

IfthetubescontainedpureNO2,allthatwouldbeseeninthisdemonstrationwouldbevaryingshadesofbrown,butifthelastimageisexaminedclosely,ablue/geenliquidcanbeseeinthebottomofthecoldtube.Thiscomesaboutbecausethereisatleastatraceofwaterinthetubesandthisleadstothefollowingreaction.

2N2O4(l)+H2O(l) 2N2O3(l)+2HNO3(l)

FromthetableweseethatN2O3isablueliquidundertheseconditions.PureHNO3iscolorless,butifitiscontaminatedwithNO2itbecomesyellow.Theyellowandbluecomponentsofthisreactionproducetheblue/greenliquidthatisseen.Ithasnotbeenshowninthisdemonstration,butifthetubeiscooledbelowthemeltingpointofN2O4,Theliquidwillloseitsgreencomponentandbecometotallyblue.Thereasonforthisisasfollows.Inthesolidphase,themixtureofNO2andN2O4becomesexclusivelyN2O4.ThismeansthereisnolongeranyNO2tocolortheHNO3yellow.Withouttheyellowcomponenttheliquidbecomescompletelyblue.PlacingthetubeinsomepowdereddryiceisaconvenientwaytoseethisphenomenonReferences

1. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1989,Vol.2,p.180-1832. Electronicversion,CRCHandbookofChemistryandPhysics,81sted.

OrganicReactionsRelativeReactivitiesofPrimary,SecondaryandTertiaryAlcohols

I.LucasTestEquipmentThreesmallscrewtopvials,pipettesw/bulbs,overheadprojector.Reagents1-butanol,2-butanol,2-methyl-2-propanol,Lucasreagent(16ganhydrouszincchloridedissolvedin10mLconcentratedhydrochloricacid).Presentation

1. Add5dropsofanalcoholtoavial.2. Repeatsteponewiththeothertwoalcoholsandseparatevials.

3. AddthreesqueezesoftheLucasreagenttotheprimaryalcoholvial,screwthelidon,shakevigorously,andlaythevialonitssideonthecenteroftheoverheadprojector.

4. Repeatstep2forthesecondaryalcoholandthenthetertiaryalcohol.HazardsVaporsofthesethreealcoholsaremildlyirritatingtoeyes,nose,throat,andaretoxicuponinhalation.Liquidcontactwitheyesisirritatingandmayproduceburns.Repeatedcontactwithskinmaydry(defat)andcrackskin.Hydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.

DiscussionThetertiaryalcoholwillreactimmediatelytoproduceaninsolublealkylhalide.Thismakesthecontentsofthevialcloudyandthevialwillappearblackonthescreen.Thesecondaryalcoholreactsmoreslowlytoproducethecorrespondingalkylhalide.Thetimevariesfromapproximately1-3minutesdependinguponthetemperature.Thescreenimagewillinitiallyappearclear,butwillgraduallydarkentoblack.Theprimaryalcoholwillnotreact,soitsscreenimageisclearandremainsso.ReferencesPavia,Lampman,Kriz,IntroductiontoOrganicLaboratoryTechniques,2ndedition,SaundersCollegepub.,1982,p.427.

II.ChromicAcidTestEquipmentThree50mLbeakersw/stirrods,pipettesw/bulbs,overheadprojector.Reagents1-butanol,2-butanol,2-methyl-2-propanol,chromicacid(1gchromium(VI)oxidedissolvedin1mLofconcentratedsulfuricacidandthisdilutedwith3mLofDIwater).Presentation

1. Addenoughofthethreealcoholstoseparatebeakerstocoverthebottoms.2. Placethebeakersontheoverheadprojector.3. Add~2dropsofthechromicacidsolution(enoughtogivethemixtureadefiniteyellowcolor)toabeakerandstirthe

contents.4. Repeatstepthreefortheothertwobeakers.

HazardsVaporsofthesethreealcoholsaremildlyirritatingtoeyes,nose,throat,andaretoxicuponinhalation.Liquidcontactwitheyesisirritatingandmayproduceburns.Repeatedcontactwithskinmaydry(defat)andcrackskin.Becausesulfuricacidisbothastrongacidandapowerfuldehydratingagent,itmustbehandledwithgreatcare.Thedilutionofconcentratedsulfuricacidisahighlyexothermicprocessandreleasessufficientheattocauseburns.Therefore,whenpreparingdilutesolutionsfromtheconcentratedacid,alwaysaddtheacidtothewater,slowly,withstirringandcoolingthereceivingbeaker.Bothchromicoxide(VI)andchromicacidarepowerfuloxidizingagentsandsuspectedhumancarcinogens.Contactwithsolidchromicanhydridemayresultinsevereburnsofeyeswithpossiblepermanentvisionloss.Skincontactwithsolidchromicanhydrideorwithconcentratedsolutionsofchromicacidcausesburnswithpotentialformajorskindamage.DiscussionPrimaryandsecondaryalcoholswillbeoxidizedtocarboxylicacidsandketonesrespectively.Thetertiaryalcoholwillnotreact.Whenthealcoholisoxidized,theCr6+(yellow/orange)isreducedtoCr3+(blue/green).Thereforetheappearanceofabluegreencolorisindicativeofaprimaryorsecondaryalcohol.Thebeakersthathavereactionstakeplacemaybecomeopaquefromavarietyofprecipitates.Thecolorscanstillbeviewedfromtheside.ReferencesPavia,Lampman,Kriz,IntroductiontoOrganicLaboratoryTechniques,2ndedition,SaundersCollegepub.,1982,p.427.

BreathalyzerEquipmentEvaporatingdish,glasswool,disposablepipets,2mmdiameterglassrodapproximately10-15cmlong,hotplate,smallspatula,smallfunnelandshortlengthofrubbertubing(~2cm).Ifthisistobeviewedinalargeclassroom,avideocameraisalmostessential.ReagentsConcentratedsulfuricacid,saturatedpotassiumdichromatesolution,20%sodiumsilicatesolution,ethanolPreparation

1. Add5mLof20%sodiumsilicatesolutiontoanevaporatingdish.Theseamountswillprovideenoughtreatedsilicageltomake6trials.

2. Addsaturatedpotassiumdichromatesolutiondropwiseuntilyougetanintenseyellowcolor.

3. Addconcentratedsulfuricaciddropwiseuntilthesolutiongelsandturnsorange.4. Gentlywarmtheevaporatingdishtodryoutthesilicagel.5. Stirandscrapethegeluntilitisfairlydryandabouttheconsistencyofcoarsesand.6. Addconcentratedsulfuricaciddropwisetoreturnalittlemoisturetothesilicagel.Note:Toodryandthereactionwill

notoccur,toowetandyoucannotfillthepipet.7. Pushalooseplugofglasswoolintotheconstrictedendofadisposablepipet.8. Attachasmallfunneltothelargeendofthepipetwithashortlengthofrubbertubing.9. Addthesilicageltothepipet,taplightlytolooselypackthegel.Note:Youwantaloosepackingwithoutlarge

channelsorvoids,butnotsotightthatthegaswon'teasilypassthroughthepipet.10. Placealooseglasswoolplugontopofthegeltoholditinplace.11. Sealtheendsofthepipetuntilreadyforuse.Thepipetmaybestoredindefinitelysolongasthepipetiskeptsealedso

thatnomoistureistransferredandnocontaminationprematurelyreducesthedichromate.Presentation

1. Clampthepipethorizontallytoaringstandandremovethesealsfromtheendsofthepipet.2. Takeacleanoneholerubberstoppersize6-8andplaceaballoonlipoverthelargeendofthestopper.3. Addapproximately2-5dropsofethanoltotheballoonthroughthestopperhole.Themoredropsthatareadded,the

fasterandmorecompletethereactionwillbe.4. Inflatetheballoon,pinchtheneckoftheballoonandcarefullyinsertthelargeendofthepipetintotheholeofthe

stopperjustfarenoughsothatthestopperwillremainconnectedtothepipet.5. Releasetheballoonneck,sothattheairandethanolvaporcanpassthroughthepipet.6. Ifyoudon'twanttoperformthesestepsinclass,youcanperformsteps2-4beforeclassandclamptheneckofthe

balloonshut.Releasetheclampwhenyouarereadytoperformthedemonstration.

HazardsSulfuricacid:Thissubstanceisasevereeyeirritantandcouldcausepermanentdamagetoyoureyesandblindness.Thissubstanceiscorrosive.Contactwiththeskincouldcausepermanentinjury(includingscarring)totheaffectedarea.Ingestionmaycausesevereirritationorulcerationofthedigestivetract,whichmayresultinnausea,vomiting,diarrhea,andinseverecases,collapse,shockanddeath.Thissubstanceisextremelyirritatingifinhaled.Inhalationoftheaerosolormistofthismaterialmaycauseseriousadverseeffectsincludingacutelungdamageanddeath.Potassiumdichromate:Causeseyeburns.Maycausechemicalconjunctivitisandcornealdamage.Maybefatalifabsorbedthroughtheskin.Causesskinburns.Maycauseskinsensitization,anallergicreaction,whichbecomesevidentuponre-exposuretothismaterial.Chromeulcers,penetratinglesionsoftheskin,occurchieflyonthehandandforearmwheretherehasbeenabreakintheepidermis.Maybefatalifswallowed.Maycausesevereandpermanentdamagetothedigestivetract.Causesgastrointestinaltractburns.Maycauseasthmaticattacksduetoallergicsensitizationoftherespiratorytract.Maycauseulcerationandperforationofthenasalseptumifinhaledinexcessivequantities.Causeschemicalburnstotherespiratorytract.Aspirationmayleadtopulmonaryedema.Sodiumsilicate:Mayresultinirritationtoeyes,skin,lungsandgastrointestinaltract.Ethanol:Vaporsmaybeirritatingtotheeyes,noseandthroat.Inhalationmaycauseheadache,nausea,vomiting,dizziness,drowsiness,irritationtotherespiratorytractandlossodconsciousness.Thevaporsarehighlyflammable,keepawayfromopenflames.DiscussionThisdemonstrationillustratestheoxidationofethanolbydichromate(orange)underacidicconditionstoproduceacetaldehyde,seefirstreactionbelow.Thedichromatethenoxidizestheacetaldehydeunderacidicconditionstoaceticacid,seesecondreactionbelow.Asthedichromateisoxidizingthevariousreactants,itisinturnbeingreducedtoCr3+,,whichisgreen.Theanimationshowsapipetfilledwithabrightorangemixtureofsilicagelimpregnatedwithpotassiumdichromateandsulfuricacid.Asthereactionproceeds,thecolorchangestogreencausedbythepresenceofCr3+intheformofthesparinglysolublechromium(III)sulfatesalt.Thisparticularanimationutilized2dropsofethanoladdedtotheballoonandthereactiontakesplaceoveraperiodof5minutes.Addingmoredropswouldhavecausedthechangestooccurinamuchshorterperiodoftime.Ifapersoniscloseenoughtothisdemonstration,theodorsofacetaldehydeandaceticacidmaybedetectedexitingthepipet.Alsothetubegetsslightlywarm.Thisisprobablyacombinationoftheexothermicityofthechemicalreactionsandtheproducedwaterdilutingtheconcentratedsulfuricacidheldinthesilicagel.Thisreactionwillworkonanyprimaryalcohol.Thereactionswouldbethesamewithappropriatesubstitutionsoftheinitialalcoholandtheresultingaldehydeandcarboxylicacid.Thisreactionwillconvertasecondaryalcoholtoaketoneandthereactionwillnotproceedasthedichromateisincabableofoxidizingtheresultingketone.Noreactionwilloccurforatertiaryalcohol.Thesereactionsorlackofreactionareusedinorganicchemistrytoidentifytheparticulartypeofalcoholasapreliminarystepinitsidentification.Thistypeofalcoholdetectionwasoncecommonlyusedbylawenforecementagencies.Ithasbeenreplacedwithotherdetectionmethodsutilizinginfraredspectroscopy,chromatographyandamperometric

detection.Thereareseveralreasonsthatthismethodhasbeenphasedoutovertheyears;onebeingthetoxicityofchromiumcompoundsandanotherbeingthebetteraccuracyandprecisionofthenewermethods.

3CH3CH2OH(aq)+K2Cr2O7(aq)+4H2SO4(aq) 3CH3CHO(aq)+Cr2(SO4)3(s)+K2SO4(aq)+7H2O(l)

3CH3CHO(aq)+K2Cr2O7(aq)+4H2SO4(aq) 3CH3CO2H(aq)+Cr2(SO4)3(s)+K2SO4(aq)+4H2O(l)Theinitialideaforthisdemonstrationwasfoundinaninternetarticle1,severalmodificationsweremadetoachievemorereproducibleresults.Thechemistrymentionedherewastakenfromanorganiclaboratorymanual2,andwasexpandedupon.References

1. http://chem.lapeer.org/Chem1Docs/Breathalyzer.html2. Pavia,Lampman,Kriz,IntroductiontoOrganicLaboratoryTechniques,2ndedition,SaundersCollegepub.,1982,p.427.

SugarDehydrationWithoutSulfuricAcidEquipment60mLsyringewithnozzlecutoff,scrapmetalheatshield,mortarandpestle,pipettewithbulb,matchorbutanelighter,aluminumfoiland100mLbeaker.ReagentsTablesugar,potassiumchlorate,95%ethanol.Presentation

10. Weighout15goftablesugar(sucrose)and4gofpotassiumchlorate.11. Placethesugarandpotassiumchlorateinthemortarandlightlygrinduntilyouproduceafinepowderandthetwo

componentsaremixedthoroughly.12. Pulltheplungerbackintothesyringeuntilitreachesthe20mLmark.13. Pourthepowdermixtureintothesyringetoadepthofapproximately0.5cm,addenoughethanoltothoroughlywet

thepowder.Tapthesyringeplungerdownonasolidsurfacetoremoveairbubbles.14. Repeatstep4untilthesyringeisfull.15. Covertheopenendofthesyringewiththescrapmetal.Invertthesyringeandplacethescrapmetalonafirmsurface.

Depresstheplungertofurthercompressthemixture.16. Liftthesyringeoffofthescrapmetalandextrudethemixturefromthesyringe.Youshouldendupwithacolumn

approximately2-3cmhighrestingonthescrapmetal.Ifyouarenotgoingtousethedemonstrationwithinafewminutes,youshouldcoveritwithasmallbeakertominimizetheethanolevaporation.

17. Placethemixtureonasurfaceandremoveanycombustiblematerialbackabouttwofeet.Layingdownsomealuminumfoilwillmakeanyeventualcleanupeasier.

18. Removethebeakerifthereisone,addanotherdropperfullofethanoltothemixtureandlightitwiththematchorbutanelighter.

HazardsPotassiumchlorateisastrongoxidizingagent.Caution,therearewarningsthatpotassiumchlorateshouldnotbeexposedtoheat,shockorfrictionandthatdoingsomayleadtofireorexplosion,especiallyifthereareoxidizablecontaminantspresentsuchassugar.Thisdemonstrationhasbeenperformedrepeatedlywithoutexperiencinganysuchproblemsassociatedwiththelightgrindingthatiscalledfor,butsuchpossibilitiesshouldalwaysbetakenintoaccount.Thereisasmallamountofsmokeandflameassociatedwiththesereactions.Aroomwithevenmoderatelydecentventilationwillhavenoproblemdealingwiththeamountsproduced.Theheatshieldwillgetquitewarmfromthereactionsandmaycauseburnsifhandledtoosoonuponcompletionofthedemonstration.DiscussionThisdemonstrationconsistsofthreereactions,eachsucceedingreactionisdependentuponthepreviousreactionforitsactivationenergy.Allofthereactionsareexothermic.

CH3CH2OH(l)+3O2(g) 2CO2(g)+3H2O(g)+1236kJ 1

C12H22O11(s)+8KClO3(s) 12CO2(g)+11H2O(g)+8KCl(s)+2029kJ 2

C12H22O11(s) 12C(s)+11H2O(g)+429kJ 3Theenergiesthatareshownforthethreereactionsarebasedupontheassumptionsthatthewaterandcarbonbeingformedareinthegaseousandgraphiteformsrespectively.Thereisevidencethattheseassumptionsarenotentirelyaccurate(2,3).Fromreaction2,wecanseethatpotassiumchloratereactswiththesugar,butthereisonlyenoughpotassiumchloratetoreactwithapproximately16%oftheavailablesugar.Thisallowstheremaining84%ofthesugartoreactaccordingtoreaction

3,drivenbytheenergyreleaseofreaction2.Thegasesthatareproducedduringthesereactionsleavethesolidcarbonriddledwithgaspockets,producingalight,airycarboncolumn.References

4. ToddP.SilversteinandYiZhangJ.Chem.Educ.1998,Vol.75,p.748-749.5. Shakhashiri,B.Z.ChemicalDemonstrations,AHandbookforTeachersofChemistry,UniversityofWisconsinPress:

Madison,WI,1983;Vol.1,pp.77-78.6. Dahn,J.R.;Zheng,T.;Liu,Y.;Xue,J.S.Science1995,270,590-593.

Diels-AlderReactionEquipmentvideocamera,13X100mmtesttubes(3)Reagents0.05Msolutionofanthraceneintoluene(178mg/20mL),0.05Msolutionoffuranintoluene(72.7mg/20mL),0.01Msolution4-phenyl-1,2,3-triazolin-3,5-dione(N-PTD)intoluene(35mg/20mL)Presentation

1. Add1mLofN-PTDsolutiontoeachofthethreetesttubes.ThefirsttubeisonlyusedtoshowthecoloroftheN-PTDbeforereactionwithadiene.

2. Tothesecondtesttubeadd15dropsofanthracenesolution.3. Tothethirdtesttubeadd15dropsoffuransolution.4. Drawthesolutionsintesttubes2and3intoapipetinordertomixthecontents.

DiscussionTheDiels-Alderreactionwasdiscoveredin1928byGermanchemistsOttoDielsandKurtAlder,whoreceivedtheNobelPrizeinchemistryin1950fortheirworktowardsunderstandingthis4+2cycloaddition.TheDiels-Alderreactioncontinuestobeawidelyusedreactioninmodernorganicsynthesisbecauseinonesteptwocarbon-carbonbondsaremadeinastereoselectiveway.IntheDiels-Alderreaction,analkeneoranalkynereactwithaconjugateddienetoformanunsaturatedsix-memberedring.Forthisdemonstration,acolorlessdiene(furan(1)oranthracene(2))isreactedwithareddieneophile(4-phenyl-1,2,3-triazolin-3,5-dione(N-PTD)(3))andacolorlessadductisformed.

Referenceshttp://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/p2_cyclo_add-e.htm(asseenonJune20,2003)

ProductionandCombustionofAcetyleneEquipmentCarbideminer'slamp,butanelighter.ReagentsCalciumcarbide,water

Preparation1. Addapproximately10gramsofsolidcalciumcarbidetothebottomchamberofthelamp.2. Securelyscrewthetwopartsofthelamptogether.3. Filltheupperchamberofthelampwithwater.

Presentation1. Turnthewaterdropcontrolleverlocatedonthetopofthelampapproximately3clicksinaclockwisedirection.2. Waitapproximately10secondstoallowtheacetyleneconcentrationtobuiltupandtoflushtheoxygenoutofthe

lamp.3. Lightthebutanelighterandbringitnearthegasoutletnozzlelocatedinthecenterofthereflector.Theacetylene

shouldigniteandaflamewillprojectfromthenozzle.4. Adjustthewaterdropleverclockwisetomaketheflamelargerorcounter-clockwisetomaketheflamesmaller.

Dimmingtheroomlightwillshowjusthowpowerfulasourceofilluminationthislampcanbe.5. Toturnthelampoff,returnthewaterdroplevertoitsoriginalposition.Theflamewillbecomesmallerandeventually

gooutasthesupplyofacetyleneisexhausted.

HazardsCalciumcarbideproducesflammableacetyleneuponcontactwithwater.Thecalciumcarbidemaycontainacontaminantresultinginthereleaseofthetoxicgasphosphineoncontactwithwater.Inhalation:Cough,Labouredbreathing,Shortnessofbreath,Sorethroat.Skin:Redness,Skinburns,Pain.Eyes:Redness,Pain,Blurredvision,Severedeepburns.Ingestion:Labouredbreathing.Shockorcollapse(furtherseeInhalation).DiscussionThereactionbetweencalciumcarbideandwatertoformacetyleneidshownbelow:

CaC2(s)+2H2O(l) Ca(OH)2(aq)+C2H2(g)Thecombustionofacetyleneisillustratedbythefollowingreaction.

2C2H2(g)+5O2(g) 4CO2(g)+2H2O(g)Theresultingflameisaveryluminousyellow..ReferencesDevelopedinhouse.

ExtractionofDNAEquipmentBlender,beaker(100mL),strainer,testtubes(upto10largetubesandstoppersiftubesaretobepassedaroundclass),stirsticksandtesttuberackReagentsDNAsource(splitpeasworkbest),salt,water,liquiddetergent,meattenderizer,alcohol(70%isopropylalcoholor95%ethylalcoholworkwell)Presentation

1. Measure~100mL(1/2cup)DNAsource(splitpeas),pinchofsalt(~1mLor1/8tsp),and~200mLofwater(doubletheamountoftheDNAsource)intoblender.Blendonhighfor15-20sec.

2. Pourthe"peasoup"throughastrainerintoabeaker.Howmuch"soup"doyouhave?Addavolumeofdetergentequalto1/6ofthe"peasoup"volume.Mixslightlyandletsitfor5-10minutes.(Thisisveryimportant-donotmoveontoStep3withoutwaiting.)

3. Poursoapy"peasoup"intotesttubes;filleach~1/3full.Addapinchofmeattenderizertoeachtesttube.MixVERYgently(oryouwillbreakuptheDNA).4.Tiltthetesttubeatanangleof~45°.Pourthealcoholgentlydownthesideofeachtesttubeuntiltubeareabout2/3full.Twolayersshouldform.TheDNAwillriseintothetoplayer(alcohollayer).TheDNAcanberemovedwithastirstick(sometimes).

DiscussionToextractDNA,youmustremoveitfromthecellsoftheDNAsourcesuchasthesplitpeas.Blendingthepeaswithsomesaltandwaterbreaksthecellsapart.However,theDNAisstillsafelycontainedinthecellbecauseofthecellandnuclearmembranes.Thesecellmembranesaremadeupoflipids(likegrease),whichhaveapolarheadandanon-polartail.Thedetergentalsoconsistsofpolarheadsandnon-polartails.ThemoleculesindetergentareabletopullapartthecellandnuclearmembraneswhichleavetheDNAinthe"peasoup".TheDNAinthe"peasoup"isstillcoveredandprotectedbytheproteinsfromthecell.Themeattenderizer(orpineapplejuiceorcontactlenssolution)containenzymeswhichareabletocutaparttheseproteinstoleavetheDNAalone.Alcoholislessdensethanwaterandthereforefloatsabovethe"peasoup".Theproteins,lipids,andDNAallneedtodecidewhichsolutiontheyprefer.TheproteinsandlipidspreferthewaterandtheDNAprefersthe

alcohol.TheDNAthereforemovesintothealcohollayer.TheDNAformedtendstobestringyandclumpedtogether.Youcantrytoremoveitfromthetesttubeswithastirstickbutitisoftendifficulttodoso.SomeinterestingDNAfacts:EachcellofyourbodycontainssixfeetofDNA!Ourbodiescontainabout100trillioncells-thatmeanswehavemorethanabillionmilesofDNAwithinourbodies!Tofitthisintoyourcells,theDNAispackedefficientlybytwistingtightlyandclumpingtogether.Somedemotips:ThisdemonstrationworksforavarietyofDNAsources,detergents,andtenderizers.IfyoudonotseeDNAforming,itmaybeduetothetypeofDNAsource(seediscussionbelow)orthetimingintheprocedure.Itisveryimportanttowaitthe5-10minutesinStep2orthecellandnuclearmembraneswillremainintact,notallowingtheDNAtobeextracted.IfyoudonotseeanyDNAimmediately,wait30-60minutes....theDNAwillusuallyextractintothealcohollayerwithtime.DifferentDNAsourceswillyieldDNAatdifferentrates.Frozenpeasdonotmakeagoodsubsitituteforsplitpeasduetothelargeamountofwatercontainedinthepeas.ExtractingDNAfromonionsworkswell,butthecolorofthesolutionisnotasnice.RedcabbageisnotagoodDNAsourceasthesolutionistoodarkandtheDNAisextractedratherslowly.TrytoexperimentwithothersourcesofDNA!

PolymersNylonRopeTrickEquipmentRingstandwithroller,4ouncejarwithlid,glassrodwithhookedend.ReagentsSolution"A"(0.5Mhexamethylenediamine(H2N(CH2)6NH2,alsocalled1,6-diaminohexane)and0.5Msodiumhydroxideinwater),Solution"B"(0.2Msebacoylchloride(ClOC(CH2)8COCl)inhexane).PresentationPreparation

1. Makesolution"A"byplacingabottleofhexamethylenediamineinwarmwatertomeltit(m.p.39-40°C).Dispense6.0gofthehexamethylenediamineintoabottle.Add2.0gofsodiumhydroxideandadd100mLofDIwatertothebottle.Capthebottletightlyandshaketodissolveandmix.

2. Makesolution"B"bydispensing2.0g(1.6mL)ofsebacoylchlorideintoabottle,add100mLofhexanetothebottle.Capthebottletightlyandshaketomix.

Demonstration

1. Add25-50mLofsolution"A"tothejar.2. Placetheglassrodinthecenterofthejarwiththehookdown.3. Carefullypourthesamevolumeofsolution"B"assolution"A"downtheglassrod,soasnottodisturbtheinterface

betweenthetwosolutions.4. Aftersolution"B"hasbeenadded,pulltheglassrodoutofthejar.Thehookwillsnagthenylonthathasformedatthe

interfaceofthetwosolutions.5. Wrapthestrandofnylonaroundtherollerandwindthenylonstrandontotherollerwithasteadypace.6. Whenyouaredonewindingthenylon,closethejartominimizethehexanefumes.

HazardsSebacoylchlorideiscorrosiveandreactswithwater,soitcausessevereburnstoeveryareaofcontact.Itisharmfulifswallowed,inhaledorabsorbedthroughskin.1,6-diaminohexaneiscorrosive.Itcausesburnestoanyareaofcontact.Itisharmfulifswallowed,inhaledorabsorbedthroughskin.1,6-diaminohexaneisextremelydestructivetotheupperrespiratorytract,eyesandskin.Itiscombustibleeitherasliquidorasvapor.Solidsodiumhydroxideanditsconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.Overexposuretovaporsofhexaneisirritatingtotherespiratorytract.Contactwithliquidisirritatingtoskinandtoeyes.DiscussionTheword"nylon"isusedtorepresentsyntheticpolyamides.Thevariousnylonsaredescribedbyanumberingsystemthatindicatesthenumberofcarbonatomsinthemonomerchains.Nylonsfromdiaminesanddibasicacidsaredesignatedbytwonumbers,thefirstrepresentingthediamineandthesecondthedibasicacid[2].Thenylonformedinthisdemonstrationwouldbe6-10nylon.

nH2N(CH2)6NH2+nClCO(CH2)8COCl®[-NH(CH2)6NH-CO(CH2)8CO-]n+2nHClReferences

1. B.Z.Shakhashiri,ChemicalDemonstrations,AHandbookforTeachersofChemistry,Wisconsin,1983,Vol.1,p.213-215.2. Ravve,OrganicChemistryofMacromolecules,MarcelDekker:NewYork,1967,ch.15.

LightHClCannonEquipmentOne250-mLErlenmeyerflask,a#6stopperwith3holes,twographiteelectrodesofadiametertofitthestopperholesandalengthtoreachnearlytothebottomoftheflask,powersupplycapableofapproximately6voltsand2amperes,100-mLclearplasticgraduatedcylinder,withendspoutcutoff,2-holestoppertofitthegraduatedcylinder,corktofitthegraduatedcylinder,plastictubingandglassbendstochannelgasesandacameraflaskorsomeothersourceofintensewhitelight.Optional:redandbluefilters.Reagents250mLof6MHCl,250mLof6MNaOHPresentation








HazardsHydrochloricacidcanirritatetheskin.Hydrochloricacidvaporsareextremelyirritatingtotheeyesandrespiratorysystem.Therefore,itshouldbehandledonlyinwell-ventilatedarea.Solidsodiumhydroxideandconcentratedsolutionscancausesevereburnstoeyes,skin,andmucousmembranes.Thecorkispropelledwithsufficientforcetocauseinjuryifsomeoneishitatblankrange.Thecylindermayshatterifthecorkisseatedtoofirmly.Thecylinderweakenswitheverydemonstrationandwillusuallyburstafter3-4uses.Thedemonstratorshouldwearsometypeofhearingprotectionandtheaudienceshouldbecautionedtocovertheirears.Discussion

Cl2+light(500nm)®2Cl•(initiation)Cl•+H2®HCl+H•(propagation)H•+Cl2®HCl+Cl•(propagation)2Cl•®Cl2(possibletermination)H•+O2®HOO•(possibletermination)Cl•+O2®ClO2•(possibletermination)radical+containerwall(possibletermination)


Beer’sLawEquipmentPlasticwellplatewithsixwells,dropper,smallglassstirrod,overheadprojector.ReagentsKMnO4solutionofsufficientconcentrationtobecompletelyopaque.Presentation

1. Place5mLofDIwaterinwells1-3,place10mLofDIwaterinwells4-6.Placewelltrayonoverheadprojector.

2. UsingtheKMnO4solution,add1droptowell1,2dropstowell2and4dropstowell3.Stirthewells.3. UsingtheKMnO4solution,add2dropstowell4,4dropstowell5and8dropstowell6.Stirthewells.

HazardsPotassiumpermanganateisastrongoxidizer.Dustcausessevererespiratoryirritation.Eithersolidorsolutionscauseburnsofskin.DiscussionItshouldbenotedthattheKMnO4concentrationsinwells1,2,and3areequaltotheKMnO4concentrationsinwells4,5,and6respectively.Thisisnotarigorousexperimentalormathematicalproof,butdoesconveytheessenceofBeer’slaw.Inwells1-3,theonlyparameterthatischangingistheconcentrationoftheKMnO4.Theconcentrationinwell3istwicethatofwell2whichistwicethatofwell1.ItmaybereasonablysaidthattheamountoflightabsorbedortheabsorbanceAofthesolutionisproportionaltotheconcentrationCoftheabsorbingspecies.

AaCIfthewellsonthetwodifferentrowsarecompared,itappearsthattheabsorbanceofwell4matchesthatofwell2andthat5matches6.TheKMnO4concentrationinwell4ishalftheKMnO4concentrationinwell2.Theonlydifferenceisthatthepathlengthbofwell4isdoublethatofwell2.Itmaybereasonablysaidthattheabsorbanceofthesolutionisproportionaltothepathlength.

AabMathematically,somethingthatisproportionaltotwoindependentquantitiesisproportionaltotheirproduct.

AabCWecanchangetheproportionalitytoanequalitybytheadditionofaproportionalityconstant.InthecaseofBeer’slawthatproportionalityconstantiscalledthemolarabsorbtivitye.

A=ebC

LaboratoryTechniquesSeparationofFoodDyesViaColumnChromatographyEquipment10-mLsyringeswithluerlocktip(6)(Thedemonstrationmaybeperformedwithonlyonesyringe,butitismuchmoretimeconsuming.),6-wellmicroplate,andanoverheadprojectorReagentsSep-Pak®C18cartridge,grapeflavoredKool-Aid®orgrapesoda,70%isopropylalcoholsolution(minimum20mL),25%isopropylalcoholsolution(minimum10mL),5%isopropylalcoholsolution(minimum10mL),deionizedwaterPresentationPreparation

1. Usegrapesodaasitcomesormakea0.3gKool-Aidper100mLDIwatersolution(minimum20mL).2. Labelthesyringesasfollows:"grape#1","grape","DIwater","70%isopropylalcohol","25%isopropylalcohol#3",

"5%isopropylalcohol#2".3. Filleachofthesyringeswith10mLoftheappropriatesolution.4. Pretreatthecolumnbyinsertingthe"70%isopropylalcohol"syringefirmlyintotheendofthecolumnandpushing

thesolutionthroughthecolumn.Note:Alwaysconnecttothelongendofthecolumn.5. Dothesamethingwiththe"DIwater"syringe.6. Afterthedemonstration,repeatsteps4and5andthecolumnmaybereusedindefinitely.

Demonstration

1. Placethemicroplateontheoverheadprojector.2. Injectthecontentsofthe"grape"syringeintooneofthewells,notethepurplecolor.3. Insertthe"grape#1"syringefirmlyintotheendofthecolumnandinjectthecontentsintoanemptywell,notethat

theeluentiscolorless.Youmayalsonotethatthecolumnnowhasapurplecolor.4. Insertthe"5%isopropylalcohol#2"syringefirmlyintotheendofthecolumnandinjectthecontentsintoanempty

well,notethattheeluenthasaredcolor.Youmayalsonotethatthecolumnnowhasabluecolor.5. Insertthe"25%isopropylalcohol#3"syringefirmlyintotheendofthecolumnandinjectthecontentsintoanempty

well,notethattheeluenthasabluecolor.Youmayalsonotethatthecolumnisnowcolorlessornearlyso.HazardsIsopropylalcoholisflammableandshouldbekeptawayfromignitionsources,alsoEXPOSURETOHIGHVAPOURCONCENTRATIONSMAYCAUSEEYEIRRITATION.EXPOSURETOHIGHVAPOURCONCENTRATIONSMAYCAUSERESPIRATORYTRACTIRRITATION,HEADACHE,DIZZINESS,NAUSEA,INCOORDINATION,DROWSINESSANDLOSSOF

CONSCIOUSNESS.ALTHOUGHINGESTIONISUNLIKELY,LIQUIDWOULDIRRITATEUPPERDIGESTIVETRACTIFSWALLOWED.INGESTIONOFTHISPRODUCTMAYCAUSEHEADACHE,DIZZINESS,FATIQUEANDCENTRALNERVOUSSYSTEMDEPRESSION.DiscussionTheingredientslistedontheKool-Aidpackageare:citricacid,claciumphosphate,salt,maltodextrin,modifiedcornstarch,artificialflavo,ascorbicacid,FD&Cred40andFD&Cblue1.Thelasttwoingredientsaretheinterestingcomponentsforthisdemonstration.Thiscombinationofredandbluedyesgivesthegrapedrinkitscharacteristicpurplecolor.Thesearerelativelynon-polarmolecules,evenallowingforsomechargeseparationfromthepartialionizationofthesodiumions.Red40isasomewhatmorepolarmoleculethanisblue1.Thiscanbeexplainedbythesizesofthemolecules.Eachmoleculewillhaveasimilaramountofchargefromionization,butsinceblue1isalargermoleculetheresultingchargewillbespreadoutoveralargermolecule.ThecontentsoftheSep-Pakcolumn(stationaryphase)areverynon-polar.Ifthedyemoleculesaredissolvedinarelativelypolarsolvent(mobilephase)suchaswaterandtheresultingsolutionisforcedthroughthecolumn,Thedyemoleculeswillpreferentiallyassociatewiththestationaryphase.Thisresultsinacolorlessliquid(eluent)exitingthecolumnandthecolumntakesonthepurplecolorfromthedyes.Ifwedecreasethepolarityofthemobilephase,itshouldbepossibletocausethedyemoleculestoleavethestationaryphaseandthusremovethemfromthecolumn.A5%isopropylalcoholand95%watermobilephasewillremovethered40dyefromthestationaryphaseandtheresultingeluentwillberedfromthedyeandthecolumnwillappearbluefromblue1thatremainsonthecolumn.Aslighlylesspolarmobilephaseconsistingof25%isopropylalcoholand75%waterwillremovetheblue1dyefromthestationaryphaseandtheresultingeluentwillbebluefromthedyeandthecolumnwillappearwhiteorcolorless.Theremaybesomeslightbluecolorifallofthedyehasnotbeenremoved.Themorepolarmolecule,red40isremovedwiththemorepolarmobilephaseandthelesspolarmoleculemblue1,isremovedwiththelesspolarmobilephase.References

1. Vonderbrink,S.A.,LaboratoryExperimentsforAdvancedPlacementChemistry,FlinnScientific:Batavia,IL,1995,pp149-153.

2. Bidlingmeyer,B.A.,Warren,F.V.,J.Chem.Educ.,1984,61,716-720.

ExtractionEquipment250or500-mLseparatoryfunnel,four100-mLbeakers,overheadprojector,ringstandwithironring.ReagentsAbout500mLofwatersaturatedwithiodineandabout300mLofchloroformorcyclohexane.Presentation

1. Halffilltheseparatoryfunnelwiththewater/iodinesolution.Becertainthestopcockisclosedfirst!2. Dispense~20mLofthewater/iodinesolutionintoa100mLbeaker.3. Placethebeakerontheoverheadprojector,sothatitmaybeseenthatsomeofthelightisabsorbedbythesolution.4. Add75-100mLofchloroformorcyclohexanetotheseparatoryfunnel.Stoppertheseparatoryfunnel.5. Holdthestopperinplaceandinverttheseparatoryfunnel2-3timesfairlyquickly.6. Righttheseparatoryfunnelandloosenthestoppertoventsomeofthepressurethathasbuiltup.7. Replacethestopper,andholditasyouinvertseveralmoretimes.Theorganiclayershouldbedistinctlypurple.8. Continuetoinvertuntilthecolorofthechloroformlayerbecomesconstant.9. Drainthechloroformlayerintoacontainer.10. Repeatsteps2-9forasmanytimesasyoucareto.Theamountsstatedhereareforaseriesof3extractions.

HazardsVaporofiodineisasevereirritantandlachrymator.Solutionsofiodineirritateskin.Contactsmaycauseskinburns.Chloroformmayirritateeyesandskin(withnoseriousdamage).Chloroformisasuspectedcarcinogenandteratogen.Therefore,avoidcontactswithiodineandchloroform;theyshouldbehandledwithcare.Excessiveinhalationofcyclohexaneisirritatingtotheupperrespiratorytract.Repeatedcontactwiththeskincancausedermatitis.Discussion

Iodineisanon-polarmoleculethishasaweakinteractionwiththehydrogenbondedwatermolecules.Theenergyassociatedwiththeiodine/waterinteractionsisnotenoughtocompensateforthelostenergyofthewater/waterinteractions.Thisultimatelymeansthatnotmuchiodinewilldissolveinwater.Ifasolventwithweakersolvent/solventinteractionsthanwaterwereintroducedtothissystem,iodinewouldfinditeasiertodisrupttheseinteractionsandinsertitself(dissolve)betweenthesolventmolecules,cyclohexaneorchloroformaresuchsolvents.Theyhavenohydrogenbondingandareonlyveryslightlypolar.Energywise,itismorefavorablefortheiodinetodissolveinthenon-polarsolventthaninthewater,soitexistspreferentially(butnottotally,anequilibriumwillexist)inthenon-polarsolvent.Thereleaseofenergyastheiodineswitchessolventsispartiallyresponsiblefortheinitialbuildupofpressureintheseparatoryfunnel.Thissameargumentexplainswhythenon-polarsolventdoesnotdissolveinthewater,sotwolayersareproducedwhenthetwosolventsareaddedtogether.Thetransferofiodinefromthewatertothechloroformisanequilibriumprocess.Thiscanbeseenintheseriesofbeakersoftheiodine/waterthatweredispensedfromtheseparatoryfunnel.Aftereachextractionofiodinewithchloroform,theamountofiodineremaininginthewaterbecamelessandless.Theseriesofbeakersbecomeslessandlesscoloredastheiodineresponsibleforthecolorisremoved.Whydotheextractioninaseriesofsmalladditionsinsteadofonelargeaddition?Assumethattheiodinedistributesitselfbetweenthewaterandchloroformlayerinaratioof1:9respectively.Thismeansthatoneextractionwillremove90%oftheoriginaliodinefromthewater,leaving10%behind.Asecondextractionremoves90%oftheremainingiodinefromthewater.Intermsoftheoriginalamountofiodinethatwouldbe:

(0.10)(0.90)=0.090or9%

Thisleaves0.10-0.090=0.010or1%oftheoriginaliodineinthewaterand0.990or99.0%oftheoriginaliodineisinthetwochloroformextractions.Thisiscertainlybetterthanthe90%gainedfromoneextraction.Thiscouldgoonandondependinguponyourpatienceandhowmuchchloroformyoucanlayyourhandson.Threeextractionswouldleaveonly0.0010or0.1%oftheoriginaliodineinthewater.Theprocessofextractionsreachesitsultimatepracticallimitsinatechniqueknownaschromatography.Thisatechniquewherethenumberofextractionshasgrownhuge(100’softhousandsinsomecases)andthesizeofthesolventfractionshasshrunktoessentiallyashellofafewsolventmoleculessurroundingasolutemolecule(iodineinthiscase).References

1. AlyeaandDutton,p.223.2. TutorialVideoTapeIXfoundinLearningResourcesCentersinSt.PaulLibrary.TutorialVideoTapeXIIIalsofoundin

theLearningResourcesCenters.

BiochemistryExtractionofDNAEquipmentBlender,beaker(100mL),strainer,testtubes(upto10largetubesandstoppersiftubesaretobepassedaroundclass),stirsticksandtesttuberackReagentsDNAsource(splitpeasworkbest),salt,water,liquiddetergent,meattenderizer,alcohol(70%isopropylalcoholor95%ethylalcoholworkwell)Presentation

1. Measure~100mL(1/2cup)DNAsource(splitpeas),pinchofsalt(~1mLor1/8tsp),and~200mLofwater(doubletheamountoftheDNAsource)intoblender.Blendonhighfor15-20sec.

2. Pourthe"peasoup"throughastrainerintoabeaker.Howmuch"soup"doyouhave?Addavolumeofdetergentequalto1/6ofthe"peasoup"volume.Mixslightlyandletsitfor5-10minutes.(Thisisveryimportant-donotmoveontoStep3withoutwaiting.)

3. Poursoapy"peasoup"intotesttubes;filleach~1/3full.Addapinchofmeattenderizertoeachtesttube.MixVERYgently(oryouwillbreakuptheDNA).4.Tiltthetesttubeatanangleof~45°.Pourthealcoholgentlydownthesideofeachtesttubeuntiltubeareabout2/3full.Twolayersshouldform.TheDNAwillriseintothetoplayer(alcohollayer).TheDNAcanberemovedwithastirstick(sometimes).

DiscussionToextractDNA,youmustremoveitfromthecellsoftheDNAsourcesuchasthesplitpeas.Blendingthepeaswithsomesaltandwaterbreaksthecellsapart.However,theDNAisstillsafelycontainedinthecellbecauseofthecellandnuclearmembranes.Thesecellmembranesaremadeupoflipids(likegrease),whichhaveapolarheadandanon-polartail.Thedetergentalsoconsistsofpolarheadsandnon-polartails.Themoleculesindetergentareabletopullapartthecellandnuclear

membraneswhichleavetheDNAinthe"peasoup".TheDNAinthe"peasoup"isstillcoveredandprotectedbytheproteinsfromthecell.Themeattenderizer(orpineapplejuiceorcontactlenssolution)containenzymeswhichareabletocutaparttheseproteinstoleavetheDNAalone.Alcoholislessdensethanwaterandthereforefloatsabovethe"peasoup".Theproteins,lipids,andDNAallneedtodecidewhichsolutiontheyprefer.TheproteinsandlipidspreferthewaterandtheDNAprefersthealcohol.TheDNAthereforemovesintothealcohollayer.TheDNAformedtendstobestringyandclumpedtogether.Youcantrytoremoveitfromthetesttubeswithastirstickbutitisoftendifficulttodoso.SomeinterestingDNAfacts:EachcellofyourbodycontainssixfeetofDNA!Ourbodiescontainabout100trillioncells-thatmeanswehavemorethanabillionmilesofDNAwithinourbodies!Tofitthisintoyourcells,theDNAispackedefficientlybytwistingtightlyandclumpingtogether.Somedemotips:ThisdemonstrationworksforavarietyofDNAsources,detergents,andtenderizers.IfyoudonotseeDNAforming,itmaybeduetothetypeofDNAsource(seediscussionbelow)orthetimingintheprocedure.Itisveryimportanttowaitthe5-10minutesinStep2orthecellandnuclearmembraneswillremainintact,notallowingtheDNAtobeextracted.IfyoudonotseeanyDNAimmediately,wait30-60minutes....theDNAwillusuallyextractintothealcohollayerwithtime.DifferentDNAsourceswillyieldDNAatdifferentrates.Frozenpeasdonotmakeagoodsubsitituteforsplitpeasduetothelargeamountofwatercontainedinthepeas.ExtractingDNAfromonionsworkswell,butthecolorofthesolutionisnotasnice.RedcabbageisnotagoodDNAsourceasthesolutionistoodarkandtheDNAisextractedratherslowly.TrytoexperimentwithothersourcesofDNA!

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Compounds & Elements - Department of ChemistryCompounds & Elements Electrolysis of Water Equipment Hoffman apparatus, platinum electrodes, AC-DC rectifier, 100 DC "house current"