小说阅读鉴赏技巧Novel reading appreciation skillsWord下载.docx

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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