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小说阅读鉴赏技巧Novelreadingappreciationskills
熔沸点的测定(Determinationofmeltingpoint)
ExperimentC-3determinationofmeltingpoint
Objective:
1.Tostudytheprincipleofmeltingpointdetermination,theapplicationandthefactorsaffectingthedeterminationresults.
2、studytheuseofcapillaryandchargingmethod.
WithSarkozytube3,todeterminethemeltingpoint.
Experimentalprinciple:
themeltingpointofasubstanceisthetemperatureatwhichthesolid-liquidtwo-phasevaporpressureisequalatagivenpressure,thatis,thetemperatureatwhichthesolidphasecoexistswiththeliquidphase.Puresolidorganiccompoundsusuallyhaveafixedmeltingpoint,whichisunderacertainpressureandheatedtonearthemeltingpoint,thechangeofsolid-liquidtwo-phasebetweenverysensitive,fromthebeginningtomeltcompletelymelted,thetemperaturechangeisgenerallynotmorethan0.5to1DEGC.Substancescontainingimpuritiestendtohavelowermeltingpointsthanpureones,andthemeltingprocesshasagreatertemperaturechange.Thisisofgreatvalueintheidentificationofpuresolidorganiccompounds,andthepurityofthecompoundscanbequalitativelydeterminedaccordingtothelengthofthemeltingprocess.
Experimentalprocedure:
(1)preparationofmeltingpointtubes
1.drawncapillary.Withthesampleloadedcapillary,anditsdiameteris1~1.2mm,40~50mm[longifSarkozymeltingpointtube,alengthofabout70~75mm].Thebestwearouttubeorpipeforcapillarytubedrawing10mmthinglass.Todrawthecapillarybefore,shouldputthetube(orglasstube)withchromicacidanddistilledwaterwashedanddried,becausecannotbepulledintoacapillarycleaning.
Methods:
handstodrawthecapillaryglasstube,rotaryheatinginstrongoxidizingflame,whichfullyburningsoftdarkcherryred.Theglasstubemovesawayfromtheflame,andthenbegantoslow,fastandelongated,reciprocatingrotatingglasstube,untilpulledintoanouterdiameterof1to1.2mmofthecapillary,trombone,paycloseattentiontothethicknessofthecapillary.Thedrawncapillarytubeiscutattwotimestherequiredlength,andtheendsarefusedattheedgeofthesmallflametoclose(theclosedtubebottomisthin)soasnottoleavedustinstorage.Whentheutilitymodelisused,thecapillarypipeiscutoffinthemiddle,andthentwomeltingpointspipesareformed.
2.loadingofsample
0.1~0.2gdrypowderonthesurfaceofsampledishintoasmallpileofpile,themeltingpointoftheopenendofthetubeinsertedinthesample,takeasmallamountofpowder.Themeltingpointofpipeerectedonthedesktopatafew(meltingpointtubemustfalldirectionperpendiculartothedesktop,ormeltingpointtubesareeasytofracture),thesampleintothebottomofthetube.Repeatthematerialseveraltimes.Themeltingpointofpipefromalengthofabout40~50cmhighglasstubefellintothedish,repeatedseveraltimes,sothatthesampleattheendofthepipetightlytogether.Thesamplemustbeuniformandstrong.Thesampleheightisabout2~3mm.
3.instrumentation
FigureC-3-1,figureC-3-2
Sarkozywillclamptheiron,pourintheliquidbathbathforeasyheatconduction,highlevelsidetubeabout0.5cm.ThethermometerwithanotchedsingleholecorkfixedonSarkozytube.Thenusethethermometermercuryballdippedinasmallamountofbath,willbeinstalledtothemeltingpointofthesampletubecarefullywetting,adhesiononthethermometerside,canalsousethelatextubeismadeofathinshearrubberringisfixedonthethermometerandthecentraltubeinthesamplemeltingpointthermometermercuryball.Therubberringishigherthantheprofitlevelandtherubberbathbath,inordertoavoidcontact.ThethermometerintotheSarkozytubeinthemiddledepthofmercuryballjustatthemidpointofthetwosidesofthepipelineatSarkozyprevail.
Thethermalconductivityofliquidbath,usuallywithconcentratedsulfuricacid,glycerolandliquidparaffin.Whichoptionisselecteddependsontherequiredtemperaturetwo.Ifthetemperatureisbelow140,itisbettertouseliquidparaffinorglycerin.Medicinalliquidparaffincanbeheatedto220degrees,stilldoesnotchangecolor.Theneedtobeheatedto140degreesabove,butalsobyconcentratedsulfuricacid,hotconcentratedsulphuricacidisverycorrosive,ifusedimproperly,concentratedsulfuricacidspilledeasilyhurt.Therefore,whenmeasuringthemeltingpoint,weargoggles.
Thetemperatureexceeds250degrees,andtheconcentratedsulfuricacidgivesoffwhitesmoke,whichhindersthereadingoftemperature.Inthiscase,potassiumsulfatecanbeaddedtotheconcentratedsulfuricacidtoheatittoasaturatedsolution,
Thenthemeasurementsweremade.
Theuseofconcentratedsulfuricacidinahotbath,sometimesduetoorganicmatterfallsintoacidandblack,interferewiththeobservationofthesamplemeltingprocess.Inthiscase,somepotassiumnitratecrystalscanbeaddedtoremoveorganicmatter.
4.determinationmethod
Inordertoaccuratelydeterminethemeltingpoint,theheatingtime,especiallyintheheatingtothemeltingpointclosetothesample,mustmakethetemperatureriseslowlyandevenly.Foreachsample,atleastfortwotimes.Forthefirsttime,thetemperaturecanbeincreasedrapidly,andthetemperaturecanbeincreasedby5degreesperminute.Thusanapproximatemeltingpointcanbeobtained.Thentookahotbathtocooldown,changealoadedsampletubemadeofseconddeterminationofmeltingpoint.
Secondmeltingpointdetermination,atthebeginning(startingfastriseWenkperminuterise10degrees,laterreducedto5DEGC),whenthetemperatureinordertoapproximatethelowmeltingpointofabout10DEGC,thenasmallflame,sothatthetemperatureriseslowlyandevenly(every1DEGC),materialchangesintesttubeobservethemeltingpoint,meltingpointtuberecordhasjustappearedinsmalldropletsofliquidandsampleexactlythetwomeltingtemperaturereadings.Themorepurethematerial,thesmallerthedifferencebetweenthetwotemperatures.Ifthetemperatureistoohigh,therangeofthemeltingpointisnotcorrect.
Whenrecordingthemeltingpoint,thetemperatureatwhichtheinitialmeltingandthefullmeltingarerecorded,suchas123~125degreescentigrade,mustnotberecordedonlyfortheaverageofthetwotemperatures,suchas124degreescentigrade.
Aftertheexperiment,thethermometerisremoved,placedintheasbestosnetmakeitsnaturalcoolingtoroomtemperature,usingwastepapertowipebath,andthenrinsewithwater.Ifthethermometerisremovedfromthehotbathimmediatelyafterwashing,thermometerwillbysuddenrupture.Bathliquidcoolingandthenfellbacktothebottle.
5.calibrationofthermometer
Whenthemeltingpointismeasuredbytheabovemethod,thereisacertaindeviationbetweenthemeltingpointreadingsofthethermometerandthetruemeltingpoint.Thismaybeduetotheerrorofthethermometer.Forexample,thecapillaryholeinageneralthermometerisnotnecessarilyveryuniform,andsometimesthecalibrationisnotveryaccurate.Secondly,therearetwokindsofthermometer,fullimmersionandsemiimmersion.Fullimmersionscalethermometersareevenlyheatedinthemercurythermometerlineundertheconditionofit,andtheheatinginmeasuringthemeltingpointofonlypartofthemercuryline,thusexposingthemercurylinetemperatureisofcourseallheatingislow.Inaddition,afterlong-termuseofthermometer,glassmayalsooccurvolumedeformation,sothatthecalibrationisnotallowed.Inordertocorrectthethermometer,astandardthermometercanbeused,andthemeltingpointofpureorganiccompoundsisusuallyusedasastandardforcorrection.Theerrorcanberemovedbycorrectingthethermometerbythismethod.Thecorrectionaslongasthechoiceofanumberofpurecompoundsofknownpointasthestandard,determinationoftheirmeltingpoint,toobservethemeltingpointandmeltingpointknownasabscissa,thedifferenceofthelongitudinalcoordinate,drawingcurves,atanytemperaturereadingscanbereaddirectlyfromthecurve.
Themeltingpointofastandardsampleisasfollows,andcanbechosenwhencalibrated.
Meltingpoint(temperature)ofsample,meltingpoint(DEGC)
Waterice0urea132
Alphanaphthylamine503,5-twonitrobenzo204205
Twoaniline,53,two,acetophenonetwo,95
Twochlorobenzene,53alphanaphthol96
Benzoicacid,phenylester70,twophenylhydroxyaceticacid150
Naphthalene80salicylicacid159
Twonitrobenzene,90anthracene,216
114phenolphthaleinacetanilide215
Benzoicacid122anthraquinone286
Adipicacid132
Thebestmeasurezerowithamixtureofdistilledwaterandpurewater,distilledwater20mlplacedina15X2.5cmtube,thetubeimmersedinicecolddistilledwaterbathtothepartoftheice,withaglassrodtostirtheicewatermixturewillberemovedfromtheicebathtube,thenthetemperaturegaugeisinsertedintotheicethewater,gentlystirthemixture,afterconstanttemperaturereadings(23min).
Thinkingquestion
1.whatisthemeltingpoint?
Whatisthemeltingprocess?
2.whatisthemeltingprocessofpureandimpurematerials?
3.whatproblemsshouldbepaidattentiontoincapillaryloadingsample?
Whyshouldthe4.Sarkozynozzleoftherubberplugslot?
5.howhighisthesampleheightinthecapillary?
6.whenmeasuringthemeltingpoint,whyshouldasmallfireheating?
7.ifthesampletubeofthefirsttestcanbeusedforsecondmeltingpointmeasurements,why?
8.whatwillhappenifyouencounterthefollowingmeltingpoint?
(1)themeltingpointtubeisnotclean.
(2)thewallofmeltingpointtubeistoothick.
(3)thesampleis