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RAININPipet-LiteXLSPipet-LiteXLS192PipettesIntroductionDr.KlausJürgenWannowius192ChemistryinthecloudsThemechanismresponsibleforproducingacidrainDr.KlausJürgenWannowius193193KlausJürgenWannowiusstudiedchemistryatTUDarmstadtbetween1966–1975.HehasbeeninvolvedinscientificworkwithintheChemistrydepartmentsince1972.Helecturedchemistsonthefoundationcourseonstoichiometryforeightsemesters.Around150scientificpiecesofhomeworkwereproducedbyteachingstudentsunderhissupervision.Thesealladdressedpreparative,analyticalandkineticissues.Inthe1990'sasamemberofSFB233'DynamicsandChemistryofHydrometeors'hewasinvolvedinexplainingreactionsbetweenhydroperoxidesandsubstancesinatmosphericair.Sincethespringof1999Dr.WannowiushasbeenresponsibleforcontactwithschoolswithintheChemistrydepartment.Hehasdesignedanumberofeventsforschoolchildrenofeveryageandaptitudeunderthelogo'CHEMIEFÜRSCHÜLER'(Chemistryforschools)andruntheeventswiththeassistanceofthetechnicaldepartment.HehasbeenheadoftheMerck–TUDarmstadtjuniorlabatTUDarmstadtsinceSeptember2008.Whenmeteorologiststalkofhydrometeors,theyquitesimplymeanraindropsorallformsofprecipitatedwaterintheatmosphere.Cloudsinturnaremixturesofwaterdropsandparticlesandareverypronetoreactions.Forexample,nolessthanahundredchemicalreactionstakeplaceinonedropofwater.Theyoftenproducechangestotheacidityoftheprecipitationandcauseacidrain.Inthe1990'sDr.WannowiuswasamemberofSFB233'DynamicsandChemistryofHydrometeors'andwasinvolvedinexplainingreactionsbetweenhydroperoxidesandsubstancesinatmosphericair.Thepreparationofsolutionsofvariousconcentrationsisakeystageintheprocessdescribedinthispaper.Thisprocessusuallyinvolvesproducingthereactionsolutionsandmixtureswantedbypipettingfrommastersolutions(higherconcentration).Thekeytothisisusingvolume-measuringpipetteswhichareeasytouseandofferhighlevelsofaccuracy.PipettesIntroductionReferencesectionPipettesDispenser524DispenserandvolumeterThepipetteistheinstrumentusedtodispensesmalltoextremelysmallvolumesintheabsenceofconnectionstostoragecontainers.Pipettingisamethodbywhichaspecificvolumeofliquidistransferredfromonecontainertoanotherwithmaximumaccuracyandprecision.Pipettesworkaccordingtothedisplacementprinciple.Whenamovablepistoniscompressed,theaircolumnbelowthepistonispusheddown,whenreleasedtheaircolumnisdrawnup.Theliquidtobepipettedistransportedintheattachedpipettetip.Detailedinformationaboutourpipettesandtipscanbefoundfrompage198onwards.Thepipette525(8rowsby12columns)soastoenablefastoperation.Electronicpipettesareparticularlysuitableforrepetitivetasks,astheyreducelong-termstrainonthehandstoaminimumandcanensureultimateprecision.Air-cushionsystemAir-cushionsystemPistonShaftEjectabletipSampleAircushionDirectdisplacementsystemShaftDisposablecapillarySampleDisposablepistonPlunger™RMnDRM/ReferencesectionρisthemassmandvolumeVquotientofasubstance(massdensity).Sincedensityisdependentontemperature,thetemperaturemustalwaysbespecified.Relativedensityistheratioofthedensityρofasubstancetothereferencedensityρ0ofareferencesubstanceunderconditionsthatmustbespecifiedseparatelyforbothsubstances.MeasuringprincipleDensitymeasurementonMettleRtoleDoDe40,De45andDe51instrumentsisbasedontheelectro-magnetically-inducedoscillationofaU-shapedglasstube.Atransmitterinducesoscillation.theoscillationperiodismeasuredwithasensor.thecompleteforwardandbackwardmotionofavibra-tionisknownasaperiod,itsdurationismeasuredastheoscillationperiodt.thenumberofperiodspersecondisreferredtoasthefrequencyf.eachglasstubeoscillatesatanaturalfrequency.thischangeswhenthetubeisfilledwithagasorliquid.Frequencyisafunctionofmass.Asthemassincreases,thefrequencydecreases,i.e.theoscillationperiodtbecomeslonger.d=ρρ0TimeoscillationperiodtAmplitudef=1T[s–1]theoscillationperiodtiscalculatedaccordingtotheequation:therefore:Vibrationstimulator/vibrationmeterMeasuringtubeofdefinedvolumecapacityρ=Densityofthesampleintheloadcell[g/cm3