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1、Infrared Spectroscopy(IR)Lab,Infrared Spectroscopy Identification of UnknownThe use of selected physical properties and Infrared Spectroscopy to determine the identity of an unknown compound.Text MaterialsSlayden pp.33-44Pavia pp.851 885(Infrared Spectroscopy)pp.941-959(Mass Spectrometry)pp.719-729(
2、Simple Distillation)Solomons Sec.2.16;9.12-9.14Lecture Slides(Dr.Schornick Web Site)URL:http:/classweb.gmu.edu/jschorni/irlecture.ppt,2/22/2023,1,Infrared Spectroscopy(IR)Lab,Elements of the Experiment1st WeekLecture on Theory of:Infrared SpectroscopyMass SpectroscopyUltraviolet/Visible Spectroscopy
3、2nd WeekDetermination of Unknown Physical PropertiesIR Spectrum of UnknownSpectroscopy Problem Set:Will be E-Mailed by InstructorDue Date to be Determined,2/22/2023,2,Infrared Spectroscopy(IR)Lab,Physical Properties of Spectroscopy UnknownBoiling Point&Purification via Simple DistillationPhysical De
4、scription of Purified UnknownSolubility Relative to WaterDensity Relative to WaterRefractive Index(Corrected for Temperature)Infrared Spectrum AnalysisAnalysis of Results&identification of UnknownUnknown List Slayden Manual,Appendix 3,p.125-127Verify physical properties with appropriate literature c
5、itation(Merck,CRC,etc.).The literature citation for a compound must include the item number,if applicable,and page number,2/22/2023,3,Infrared Spectroscopy(IR)Lab,Simple Distillation BackgroundNote:The Distillation process(Simple and Fractional)will be formally introduced in a later experimentSimple
6、 Distillation will be introduced here as part of the Spectroscopy experiment to purify the sample and determine its Boiling PointDistillation,like Spectroscopy,Melting Point,Refractive Index,etc.is one of the tools we introduce you to in the Organic I&II coursesBoiling point and purification of a sa
7、mple by Simple Distillation is one of several physical properties solubility&density relative to water,refractive index,melting point that you will determine routinely on sample unknowns,2/22/2023,4,Infrared Spectroscopy(IR)Lab,Simple Distillation Background(Cont)Single Vaporization/Condensation cyc
8、le of a liquid sampleThe Distillate for a mixture is always impure at any temperature range between the range of boiling points of the components Therefore,it is impossible to completely separate the components in a mixture with simple distillation.Relatively pure substances can be obtained from a m
9、ixture with Simple Distillation,if the boiling points of the components differ by a large amount(100oC)Redistilling the distillate from multiple sequential vaporization-condensation cycles would produce increasingly pure substances,but this is a very tedious process.,2/22/2023,5,Infrared Spectroscop
10、y(IR)Lab,Simple Distillation Background(Cont)Samples of unknown organic compounds that students receive in Organic Lab are generally pure,but may contain some impurities that could produce ambiguous results when determining the chemical or physical properties of the compoundSimple Distillation is us
11、ed to purify the sample by separating the pure compound that comes over in a narrow temperature range corresponding to its boiling point from the impurities that have boiling points lower than or higher than the compound,2/22/2023,6,Infrared Spectroscopy(IR)Lab,Simple Distillation Basics StepsSet up
12、 Simple Distillation apparatus(next slide)Heat sample and collect-in a waste beaker-all distillate that comes over while the temperature continues to rise.Usually this involves only a small amount,if any,of the distillate.When the temperature stabilizes over a narrow temperature range collect the di
13、stillate in a small clean container.The bulk of the sample will be collected here.Stop collecting sample when the temperature begins to rise again,i.e.,any sample remaining at this point would consist of impurities with boiling points above that of your unknown sample.,2/22/2023,7,Infrared Spectrosc
14、opy(IR)Lab,Typical Distillation Setup,2/22/2023,8,Infrared Spectroscopy(IR)Lab,Simple Distillation ProcedureSet up Simple Distillation apparatusUse 25 mL or 50 mL Distillation flaskPlace a Corundum or Teflon boiling chip in the flaskStart gentle water flow through condenserPut a waste receiving cont
15、ainer(small beaker)into an ice water bath especially for low boiling liquids.Begin heating sampleNote:The sample may appear to be boiling,but the actual boiling point is not reached until the temperature of the boiling liquid and the vapor surrounding the thermometer bulb reach equilibrium.At this p
16、oint the vapor will start to condense in the condenser,2/22/2023,9,Infrared Spectroscopy(IR)Lab,Simple Distillation-ProcedureNote the temperature when the distillate begins to drip into the waste receiving containerContinue to collect distillate in the waste container until the temperature begins to
17、 level offRemove the waster container and begin collecting the distillate in a small clean Erlenmeyer flaskNote the temperature when you start to collect the purified sampleContinue to collect the sample until the temperature begins to rise again(it may not change before the all of the sample has co
18、me over)Note the temperature just before the temperature begins to changeThe first and last temperatures recorded in the narrow boiling range represent the boiling point range of your sample,2/22/2023,10,Infrared Spectroscopy(IR)Lab,Solubility&Density Relative to WaterPlace about 2 mL Distilled Wate
19、r in a medium test tubeAdd 4-5 drops of the solid or purified liquid unknownShake test tube firmlyObserve solubility of Sample in Distilled WaterIf sample is insoluble,observe whether sample:Floats on top of waterFloats in the middle of the waterSinks to the bottom of the test tube,2/22/2023,11,Infr
20、ared Spectroscopy(IR)Lab,Refractive IndexClean prisms of ABBE Refractometer with tissues&Methyl Alcohol BE GENTLE!Do not touch prism with fingers or other hard objects,use tissuesPlace 3-4 drops of sample on Prism.Close Prism and raise lamp in front of Prism Portal.Flip switch on left side to turn o
21、n light.Use large dial on right to bring light/dark image into view.If image cannot be found,flip switch on left down and use large dial on right to bring the Scale into view around 1.4000,2/22/2023,12,Infrared Spectroscopy(IR)Lab,Refractive Index(Cont)Release switch on left and use large dial on ri
22、ght to bring light/dark image into viewSharpen line of demarcation using Drum dial on front of instrument.Use Eyepiece to sharpen Cross-HairsAlign the line of demarcation with the Cross-HairsFlip switch on left down and read value to 4 decimal placesEx.1.5523,2/22/2023,13,Infrared Spectroscopy(IR)La
23、b,The following equation adjusts the raw Refractive Index value to 20oC:ND20=NDRm Temp+(Rm Temp 20)*0.00045 Ex:For an observed value of 1.5523 at 16oC,the correction is:ND20=1.5523+(16 20)*0.00045=1.5523+(-4)*0.00045=1.5505,2/22/2023,14,Refractive Index(Cont),Infrared Spectroscopy(IR)Lab,Infrared Sp
24、ectroscopyLiquid Samples1 to 2 drops of liquid sample are placed between two single crystals of sodium chloride(Salt Plates)Note:NaCl plates are water soluble keep dry Solid Samples Soluble in AcetoneDissolve sample in acetoneEvaporate on Salt PlateSolid Samples Not Soluble in AcetoneMake Potassium
25、Bromide(KBR)pelletPut Salt Plate sandwich in Plate HolderPlace Plate Holder into Beam Slot of IR Spectrometer,2/22/2023,15,Infrared Spectroscopy(IR)Lab,Infrared Spectroscopy ContConfirm with instructor that“Background”has been scanned in.Select Memory location(X,Y,or Z)Press“SCAN”buttonVerify No.of
26、Scans is“4”;if not,notify instructorPress“Execute”(last(far right)“soft”buttonIf spectrum absorptions bottom out,remove Salt Plate holder and reload Salt Plate with less sample.Rerun Scan/Execute againPush“Plot”to produce chartRemove Cell Holder and disassembleClean Salt Plate with acetone and dry with ChemWipePlace Salt Plate in desiccator,2/22/2023,16,
