NONINTUITIVE DEMOS AND ACTIVITIESWord文档下载推荐.docx

NONINTUITIVE DEMOS AND ACTIVITIESWord文档下载推荐.docx

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610-642-5231Email:

katzdavid@hslc.org

Chemicaldemonstrationsareaneffectivemeansofpromotingstudentinterest,aswellasameansofpresentingabstractconceptsonaconcretebasis.Studentexcitement,however,isparticularlyarousedwhenanunexpectedeventtakesplace.Sucheventswillsparkquestions,stimulatediscussion,andberememberedlongafterthechemistrycourseisover.

ThereareanumberofdemonstrationsthatproducestartlingchemicaleventsorlonglastingmemoriesthatIuseinclassesandprograms.Someoftheseinclude:

Puttingmarshmallowchickens,bunnies,orchocolatecoveredmarshmallowcookiesinavacuumchamberandloweringthepressure.

Addingequalvolumesofabsoluteethylalcohol（absolute,maybedenatured）andcoloredwater（usefoodcolor）toalongglasstube,leavingasmallairbubbleatoneend,andmixingbyrepeatedlyturningthetubeupsidedownandallowingthebubbletomovetothetop.

Investigatingwhycansofdietsoftdrinksusuallyfloatwhilecansofregularsoftdrinkssinkinwater.

Icecubessinkinaliquidresemblingwater.（ethylalcohol）

Observingaliquidthathasunequallevelsinthesidesofanopenu-tube.

Studyingthedifferencesintypesofrubbermaterialsandhowtheyaffectthebounceofarubberball.Inthisactivity,onestudentisgivenano-bounceball.

Bouncingsoapbubblesoffone’ssleeve.

Eachdemonstrationoractivityusuallyresultsinanumberofquestionsandfurtherinvestigations.Ifproperlypresented,theyaregoodwaystoencourageobservationsandtodevelopcriticalthinkingskills.

ACHEMICALGENIE

2000,1990byDavidA.Katz.Allrightsreserved.

Reproductionpermittedforeducationaluseprovidedoriginalcopyrightisincluded.

1.MATERIALSNEEDED:

hydrogenperoxide,H2O2,30%manganesedioxide,MnO2（ordryyeast）

flask,1000mL（orusea2-LiterPETbottle）rubberstoppertofitflask（orcapforbottle）

tissue（Kleenex,Puffs,etc...）string

2.SAFETYPRECAUTIONS:

Wearsafetygogglesorglasses

30%hydrogenperoxideiscaustictotheskinandeyes.Handlewithcare.Incaseofskincontact,rinsetheaffectedareaswellwithwater.Storeunusedhydrogenperoxideinafreezer.

Manganesedioxideisastrongoxidant,avoidcontactwithorganicmaterial.Inhalationcanleadtoincreasedincidenceofrespiratoryinfectionandeffectsonthecentralnervoussystem.Itisassumedtobeharmfulifsallowed.Avoiddust.Washhandswellafterhandling.

Thisreactiongeneratesheat.UseonlyPyrex-typecontainers.Touchingthecontainermayresultinaburn.

3.DISPOSAL:

Hydrogenperoxidecanbedisposedofdownthedrainwithrunningwater.

Manganesedioxideshouldbedisposedofassolidwasteinanapprovedlandfill.

4.PROCEDURE:

Prepareahead:

Putasmallamountofmanganesedioxide,approximately1/8teaspoon,onapieceoftissuepaper,andtiewithstringtomakeasmallsack.Cutoffexcesspaper.

Placeabout100mLof30%hydrogenperoxideintoa1000mLFlorenceflask.Placethetissuepapersackofmanganesedioxideintotheneckoftheflaskandusearubberstoppertoholdthestringsothatthesackdoesnotfallintotheliquid.Cutoffexcessstring.DONOTSTOPPERTOOTIGHT.

Whenthestopperisremoved,thepapersackcontainingthemanganesedioxidewillfallintothehydrogenperoxidesolutionandachemical“genie”willbeproduced.

5.EXPLANATION:

Thisreactionisthecatalyticdecompositionofhydrogenperoxide:

2H2O2→2H2O+O2

Othercatalyststhatcanbeusedarepotassiumiodide,KI,rawliver,andyeast.

The“genie”thatisobservedisactuallyafogofcondensingwatervapormixedwithoxygengas.Thisparticularreactioncannotbeusedtoshowtheproductionofoxygenbytheglowingsplinttestduetothelargeamountofwatervaporproduced.

6.UTILIZATIONANDVARIATIONS:

Thisisanexcellent“welcome”demonstrationatthestartofthesemesteroratthebeginningofaprogram.Thisdemonstrationshouldberepeatedonasmallerscalewithsome3%or6%hydrogenperoxidetoshowtheproductionofoxygenbytheglowingsplinttest.

Acknowledgement:

TheauthorwishestothankRonPerkins,GreenwichHighSchool,forthisdemonstration.

CONSERVATIONOFVOLUME

2000byDavidA.Katz.Allrightsreserved.

2clearacetatesheets,8½

x11inchesCleartape（Scotchtapeorequivalent）

ricepanortray

Therearenosafetyhazardsintheexperiment.

Therearenodisposalhazardsinthisexperiment.

Rolloneacetatesheetintoacylinder8½

incheshigh.Butttheendsandtapethem.

Rollasecondacetatesheetintoacylinder11incheshigh.Buttheendsandtapethem.

Placethe11-inchcylinderonatray.Fillthecylinderwithrice（uncooked）.Taplightlytosettletherice.

Placethe8½

-inchcylinderaroundthetallcylinder.Asktheclass,Whathappenstothericewhenthetallcylinderisremoved?

.

Removethetallcylinder.

Calculatethevolumeofthetwocylindersusingtheformula:

V=πr2h

where:

V=volumeofcylinder

r=radiusofthecylinder

h=heightofthecylinder（either8½

or11inches）

usethesubstitution:

r=c/2π（c=circumferenceofthecylinder,either8½

TheauthorwishestothankDr.CourtneyWillis,DepartmentofPhysics,UniversityofNorthernColorado,forthisdemonstration.

HOTANDCOLD

2000,1997byDavidA.Katz.Allrightsreserved.

2beakers,600mLDensityboxdemonstration（FlinnScientificno.AP4784）

WaterFoodcolor

Hotplate

Donotheatthewatertoboiling.Itshouldbeverywarm,butnottoohottohandle.

Allmaterialsinthisexperimentcanbedisposedofdownthedrain.

Heatabout500mLofwater,inabeaker,untilitiswarm.

Placeabout500mLofcoldtapwaterintoa600mLbeaker（icewatercanbeused,butisnotnecessary）.

Placefoodcolorineachbeakerofwater.（Suggested:

redforhot,blueforcold）

Simultaneously,pourthewaterfrombothbeakersintodifferentsidesofthewaterdensitybox.

Allowthewatertositforabout30to60seconds.Removetheseparatorfromthebox.

Thedensityofwaterdecreaseswithincreasedtemperature.

Thisdemonstratesthedifferenceindensitybetweenhotandcoldwater.Canbeusedtoexplainwhywaterinalakecanbewarmontopandcoldonthebottom.Alsotoexplainhowwaterinalaketurnsoverwhencooling.

IRONFORBREAKFAST

IronfortifiedbreakfastcerealsuchasTotal,SpecialK,etc...

InstantTotalOatmeal（packets）orothercerealcontainingiron（readthelablel）

water.

magneticstirbar,Tefloncoated,oramagnetpaintedwhite

beaker,2000mLorotherlargecontainer（glassorclearplasticpreferred）

magneticstirrerorwoodspoon

plasticbag（1gallonsize）

Therearenohazardsassociatedwithmaterialsinthisexperiment.

Allmaterialsinthisexperimentcanbedisposedofinthetrashordownthedrain.

A.IroninProcessedCereals

Placeonetotwocupsofanironenrichedbreakfastcereal,suchasTotal,SpecialK,etc...,inaplasticbagandcrushthecereal.

Pourthecerealintoalargebeaker（about2Liter）andadd1to1.5litersofwater.PlaceaTefloncoatedmagneticstirringbar（oramagnetpaintedwhite）intothemixture.Stirthemixtureforabout15minutesusingeitherawoodspoonoramagneticstirrer.

Useastirbarretrieverorpourthesolutionintoalargewastecontainer,takingcarenottopouroutthestirbar,andretrievethestirbar.Examinethestirbar.Whatdoyouobserve?

B.IroninInstantCereal

ObtainapackageofInstantTotalOatmealandaTefloncoatedstirbaroramagnetpainedwhite.

Openthepackageofoatmealandplacethemagnetintothecereal.Stirthecerealwiththemagnetorholdthetopclosedandshakethepackage.Retrievethemagnet.Examinethestirbar.Whatdoyouobserve?

Ironisoftenaddedtofortifiedcerealsintheformofpowderediron（oftenlistedasreducedironintheingredients）.Powderedironiseasytomeasureandhasnostabilityproblemsinthisform.

Uponingestingthecereal,someoftheironisdissolvedinthestomachacidandwillbeabsorbedintothesystemasitpassesthroughtheintestines.Notalltheiron（aswellastheothernutrients）willbeabsorbed.Remember,asingleservingcontainsthedailyadultrequirementofvitaminsandminerals.

IronisaddedtotheInstantOatmealpackagesalongwiththecereal.Itisnotcookedin.

Thisdemonstrationcanbeusedinadiscussionoftheelementsandtheiruseorinadiscussionoffoodandnutrition.

ItissuggestedthattheexperimentusingTotal,orotherbrandofcereal,bedonefirst.TheimpactoftheInstantCreamofWheatisgreateraftertheironhasbeendisc