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1、实验一有机物熔点的测定（Experiment1Determinationofmeltingpointoforganicmatter）Experiment1DeterminationofmeltingpointoforganicmatterMeltingpoint(melting,point)meansthetemperatureatwhichasolidphasecoexistswithaliquidatequilibriumatatmosphericpressureat1.Accordingtothisdefinition,t
2、heactualmeasurement,firstheatingamountofsolidpowdersampleincapillary,observingthespecimenfromtheinitialmeltingtemperaturerangetocompleteliquefaction.Thus,theresultingmeltingpointiscalledthepointmelting(capillary).Themeltingpointknowninthegeneralorganicchemistrylitera
3、tureisthemeltingpointofsuchacapillary.Themeltingpointisimportantoneofthephysicalpropertiesofsolidmaterial,andcanbeusedfordetectionandidentificationofthepurityofthecompounds.Whensolidscontainimpurities,theyreducethemeltingpointandincreasetherangeofmelting,i.e.,thetemp
4、eraturerangefromtheinitialmeltingtothecompleteliquefaction.Thedeterminationofmeltingpointisoneofthebasicoperationsinorganicchemistryexperiment.Themeltingpointofcommonlyoccurringsolidorganiccompoundsisshownintable1.1.Table1.1meltingpointsofcommonsolidorganiccompoundsC
5、ompoundmeltingpoint(DEGC)Benzoicacidbenzoicacid122.4Ureaurea132.7Cholesterolcholesterol148.5Salicylicacid157~159salicylicacid(fromThe,Merck,index,11th.ed)Adevicethatmeasuresthemeltingpointusuallyhasthefollowingconditions:Aconvenientheatsourceisneeded,andaBunsenburner
6、oranelectricheaterisgenerallyused.Theheatmediumusedmustbestableduringheatingtocontroltheriseorfallofthesampletemperature.Liquidswithhighthermalstabilityandhighboilingpointareoftenused,suchassiliconeoil,glycerin,orsaladoil,sothattheheatisdispersedevenlywithoutcausingt
7、oomuchtemperaturechange.Thetemperaturearoundthesampleshouldbeuniformsothatthesampletemperatureisconsistentwiththemeasuredtemperature.Thisisusuallydoneinagitatorsorconvection.Adeviceformeasuringtemperatureusuallyusesathermometer,andthelowerpartofthethermometershouldbe
8、ascloseaspossibletothesample.Ifasolidorganiccompoundisveryclosetopure,itsmeltingrangewillbeverynarrow,about0.5~1degreescentigrade.B
