thermal expansion of sea water—an experiment海水热膨胀实验

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1、STEMThermalExpansionofSeaWater—anExperiment(teachersguide—suggestedanswersinreditalics)BackgroundEachwatermoleculeincludesoneoxygenatomandtwohydrogenatomsthatshareelectronsincovalentbonds.Becauseoxygenatomshaveahigherelectronaffinitythanhydrogenatoms,theelectronsthatmo

2、vebackandforthbetweenthetwohydrogenatomsandtheoxygenatomspendmoretimeontheoxygenatomthanonthehydrogenatoms.Asaresult,theoxygenendsofwatermoleculeshaveaslightlynegativechargeandthehydrogenendshaveaslightlypositivecharge.Therefore,watermoleculesarereferredtoaspolarmolecu

3、les.Negativelychargedoxygenendsofwatermoleculesareattractedtohydrogenendsofdifferentwatermolecules.Theattractionbetweenwatermoleculesiscalledahydrogenbond.Hydrogenbondsaremucheasiertobreakthancovalentbondswithinwatermolecules.Evenso,hydrogenbondsareresponsibleformanyof

4、theunusualcharacteristicsofwater.Watermoleculeslosekineticenergyasthetemperaturedecreasestothefreezingpoint.Thehydrogenbondbetweenwatermoleculesorganizesiceintoahexagonalsolidstructure.Icehasafairlyopen(orlowdensity)structure.Whenicemelts,icestructureswillcollapseandth

5、ehydrogenbondsbetweenwatermoleculeswillpullthewatermoleculesclosertogetheruntilwaterreachesatemperatureof4ºCelsius.Thatisthetemperaturewherewaterhasitsgreatestdensity.Asthetemperatureofliquidwaterrisesabove4ºCelsius,thekineticenergyofthewatermoleculescontinuestoriseand

6、thehydrogenbondsbetweenwatermoleculesarenotabletopreventthewatermoleculesfrommovingapart.Asaresult,abodyofwillexpandasitstemperaturerisesabove4ºCelsius.Supplies·25mlGraduatedcylinderthatcanwithstandheat.Graduationsshouldbe0.5mlor0.2ml·Refrigeratedwater(~15ºC)·Corkwitha

7、holeinitthatfitssnuglyinthecylinder·Thermometer(fitssnuglyintothehole)·Potholders·GraphpaperorgraphingprogramFig.2.ExperimentSetupwww.umassk12.net/ipyASTEMEDProgramattheUniversityofMassachusetts,fundedbytheNationalScienceFoundationandsupportedbytheClimateSystemResearch

8、CenterinconjunctionwiththeInternationalPolarYearSTEMProcedurePerformthefollowingexperimentandrecordyourresultsinadata