2023年全國碩士研究生考試考研英語一試題真題（含答案詳解+作文范文）_第1頁
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1、46.4.02AOACOfficialMethod948.24LeadinColAdditivesMethodIIFirstAction1948FinalAction(ApplicabletoAllakes.)A.ApparatusSeeFigure948.24.PrecipitationtubeBisfittedwithinletsfadditionoftestptionofH2SfreleaseofH2Stransferofprec

2、ipitatePbStofilterinC(fineposityfrittedglasscoveredwithCeliteothersimilarfilteraid).F20–300gPbca0.5gfilteraidisenoughtoallowrapidfiltrationwithcompleteretentionofprecipitate.FiltermustbethoughlywashedwithHNO3followedbyH2

3、Obefeuse.WashallglasswaresuccessivelywithscouringpowderH2OHNO3againwithH2O.WashprecipitationapparatuswithHNO3H2Obetweendeterminations.B.ReagentsAllreagentsshouldbePbfree.See934.07?A(see9.2.20).AnysourceofH2Smaybeused.Scr

4、ubgasfirstwithH2SO4(11)thenwithH2Obefepassingintosolution.C.Determination(Caution:SeeAppendixBsafetynotesonwetoxidationnitricacidperchlicacidsulfuricacidhydrogensulfide.)Weigh2gtestptioninto500mLKjeldahlflaskadd10mLH2SO4

5、10mLHNO3digestoverlowflameuntilSO3fumesappear.Add5mLptionsHNO3(waitinguntilSO3fumesappearbefeaddingeachsucceedingption)untilallganicmatterisinsolution.Slowlyadd5–10mLmixtureofHNO360–70%HClO4(11)continuedigestionuntilwhit

6、eprecipitatefmedshowsfirstsignsofspattering.Letflaskcoolcautiouslyadd5mLH2OthenfewsNH4OH.VigouslyswirlflaskcoolunderrunningH2O.Add20mLcitricacidsolution947.12A(c)(see46.4.01)adjusttopH3.0–3.4(bromophenolblue)withNH4OH.Ad

7、d1mLCuSO4solution(1mgCumL)transfersolutiontoprecipitationtubeBofsulfidingapparatusFigure948.24.BubbleH2Sthroughsolution3–5minatca2bubblessfilterresultingsuspensionthroughCatrateofca1s.Whenfiltrationiscompleteremovereceiv

8、ercontainingfiltrateattachsuctiontesttube.Add3mLhotHNO3throughseparatAdrawthroughfilterfollowwith2mLhotH2O.Detachfilterpassadditional3mLhotHNO3throughfilterwettingallsides.Againfollowwith2mLhotH2O.Iffilterisstillcoledwit

9、hPbSwashagainwithhotHNO3H2O.WashdissolvedsulfidesintoprecipitationtubeBwettingallsidestotakeupanyresidualPbStheninto50–100mLglassstopperedErlenmeyer.Stoppershakefewsremovestopperboiluntilsolutionclearstoremovelasttraceso

10、fH2StocoagulateanyfreeSpresent.Transfersolutionto250mLseparat.Washflaskwithtwo5mLptionsH2Oaddwashingstomainsolution.Add10mLcitricacidsolution5mL10%KCNsolutionfewsofH2NOH?HClsolution947.12A(f)(see46.4.01)topreventoxidatio

11、nofdithizoneadjustpHto8.5–9.5(thymolblue)withNH4OH.Immediatelyextractwith20ptionsdithizone947.12A(d)(see46.4.01)usingthemedilutesolutionunlessexceptionallylargeamountsofPbarepresent.Shake20–30sletlayersseparatenotecolofC

12、HCl3phase.(Leaddithizonecomplexisredbutcolmaybemaskedbyexcessgreendithizonegivingintermediatehuesofpurplecrimson.ColofCHCl3extractgivesfirstindicationofamountofPbpresentprogressofextractioncanbefollowedbynotingcolofsucce

13、ssiveextracts.)DrainCHCl3layerinto125mLshtstemseparatcontaining25–30mLH2OmadeammoniacalwithoneNH4OH(specificgravity0.90).Continueextractionuntil2successiveextractswithsmallptionsofmedilutedithizonesolutionsshowthenegativ

14、ecol(greennotbluishpurple)combiningextractsinsmallerseparat.ShakeletlayersseparatedrainCHCl3fractionintoanothersmallseparatrepeatwashingprocessasbefe.DrainCHCl3fractionascleanlyaspossibleinto100150mLbeakerpasssmallptiono

15、fdilutedithizonesolutionthroughseparatsinsuccessionsoastowashoutsmallptionsofextractpersistinginaqueousfraction.AddtobeakerevapateCHCl3withgentleheatonsteambath.Takeupdryresiduewith3–4mLHNO3heatbyswirlingoverlowflame.Dil

16、utetoca25mLcontinueheating1–2mintoexpeloxidesofN.AddsmallpieceoflitmuspaperneutralizewithNH4OHdiluteto50mL.Add0.5mLHNO3proceedasin934.07?F(see9.2.20).References:JAOAC31677(1948)32621(1949).?2000AOACINTERNATIONALFigure948

17、.24—Sulfidingapparatus.46.4.02AOACOfficialMethod948.24LeadinColAdditivesMethodIIFirstAction1948FinalAction(ApplicabletoAllakes.)A.ApparatusSeeFigure948.24.PrecipitationtubeBisfittedwithinletsfadditionoftestptionofH2Sfrel

18、easeofH2StransferofprecipitatePbStofilterinC(fineposityfrittedglasscoveredwithCeliteothersimilarfilteraid).F20–300gPbca0.5gfilteraidisenoughtoallowrapidfiltrationwithcompleteretentionofprecipitate.Filtermustbethoughlywas

19、hedwithHNO3followedbyH2Obefeuse.WashallglasswaresuccessivelywithscouringpowderH2OHNO3againwithH2O.WashprecipitationapparatuswithHNO3H2Obetweendeterminations.B.ReagentsAllreagentsshouldbePbfree.See934.07?A(see9.2.20).Anys

20、ourceofH2Smaybeused.ScrubgasfirstwithH2SO4(11)thenwithH2Obefepassingintosolution.C.Determination(Caution:SeeAppendixBsafetynotesonwetoxidationnitricacidperchlicacidsulfuricacidhydrogensulfide.)Weigh2gtestptioninto500mLKj

21、eldahlflaskadd10mLH2SO410mLHNO3digestoverlowflameuntilSO3fumesappear.Add5mLptionsHNO3(waitinguntilSO3fumesappearbefeaddingeachsucceedingption)untilallganicmatterisinsolution.Slowlyadd5–10mLmixtureofHNO360–70%HClO4(11)con

22、tinuedigestionuntilwhiteprecipitatefmedshowsfirstsignsofspattering.Letflaskcoolcautiouslyadd5mLH2OthenfewsNH4OH.VigouslyswirlflaskcoolunderrunningH2O.Add20mLcitricacidsolution947.12A(c)(see46.4.01)adjusttopH3.0–3.4(bromo

23、phenolblue)withNH4OH.Add1mLCuSO4solution(1mgCumL)transfersolutiontoprecipitationtubeBofsulfidingapparatusFigure948.24.BubbleH2Sthroughsolution3–5minatca2bubblessfilterresultingsuspensionthroughCatrateofca1s.Whenfiltratio

24、niscompleteremovereceivercontainingfiltrateattachsuctiontesttube.Add3mLhotHNO3throughseparatAdrawthroughfilterfollowwith2mLhotH2O.Detachfilterpassadditional3mLhotHNO3throughfilterwettingallsides.Againfollowwith2mLhotH2O.

25、IffilterisstillcoledwithPbSwashagainwithhotHNO3H2O.WashdissolvedsulfidesintoprecipitationtubeBwettingallsidestotakeupanyresidualPbStheninto50–100mLglassstopperedErlenmeyer.Stoppershakefewsremovestopperboiluntilsolutioncl

26、earstoremovelasttracesofH2StocoagulateanyfreeSpresent.Transfersolutionto250mLseparat.Washflaskwithtwo5mLptionsH2Oaddwashingstomainsolution.Add10mLcitricacidsolution5mL10%KCNsolutionfewsofH2NOH?HClsolution947.12A(f)(see46

27、.4.01)topreventoxidationofdithizoneadjustpHto8.5–9.5(thymolblue)withNH4OH.Immediatelyextractwith20ptionsdithizone947.12A(d)(see46.4.01)usingthemedilutesolutionunlessexceptionallylargeamountsofPbarepresent.Shake20–30sletl

28、ayersseparatenotecolofCHCl3phase.(Leaddithizonecomplexisredbutcolmaybemaskedbyexcessgreendithizonegivingintermediatehuesofpurplecrimson.ColofCHCl3extractgivesfirstindicationofamountofPbpresentprogressofextractioncanbefol

29、lowedbynotingcolofsuccessiveextracts.)DrainCHCl3layerinto125mLshtstemseparatcontaining25–30mLH2OmadeammoniacalwithoneNH4OH(specificgravity0.90).Continueextractionuntil2successiveextractswithsmallptionsofmedilutedithizone

30、solutionsshowthenegativecol(greennotbluishpurple)combiningextractsinsmallerseparat.ShakeletlayersseparatedrainCHCl3fractionintoanothersmallseparatrepeatwashingprocessasbefe.DrainCHCl3fractionascleanlyaspossibleinto100150

31、mLbeakerpasssmallptionofdilutedithizonesolutionthroughseparatsinsuccessionsoastowashoutsmallptionsofextractpersistinginaqueousfraction.AddtobeakerevapateCHCl3withgentleheatonsteambath.Takeupdryresiduewith3–4mLHNO3heatbys

32、wirlingoverlowflame.Dilutetoca25mLcontinueheating1–2mintoexpeloxidesofN.AddsmallpieceoflitmuspaperneutralizewithNH4OHdiluteto50mL.Add0.5mLHNO3proceedasin934.07?F(see9.2.20).References:JAOAC31677(1948)32621(1949).?2000AOA

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