Gravimetric Sulfate Determination Helpful HintsWord文档下载推荐.docx
- 文档编号:21622146
- 上传时间:2023-01-31
- 格式:DOCX
- 页数:16
- 大小:332.97KB
Gravimetric Sulfate Determination Helpful HintsWord文档下载推荐.docx
《Gravimetric Sulfate Determination Helpful HintsWord文档下载推荐.docx》由会员分享,可在线阅读,更多相关《Gravimetric Sulfate Determination Helpful HintsWord文档下载推荐.docx(16页珍藏版)》请在冰豆网上搜索。
ThisWebpageandaccompanyingphotosareinthepublicdomainandmaybecopiedwithoutrestriction.
Thesmallheatingpadsavailableinthelaboratoryarelargeenoughtoholdthethree400mLbeakerstobeusedinthisexperiment,asshowninthephotoattheright.Heatingallthreeinsuchclosequartershasitsdangers,ofcourse,mainlythatoftippingoneoverandlosingonesample!
Soasnottomixupyoursamples,labeleach1,2and3withagraphitepencil.
Noticebelowhowoneofthebeakerscontainingthedissolvedsulfatesampleisplacedbeneathaburetfilledwith5%bariumchloridesolution.Theprecipitateisformedbyaddingthebariumchlorideslowlytothehotsulfatesolution.Theslowadditionassuresthattherelativesupersaturationalwaysremainslowsoastoavoidtheformationofanon-crystallinecolloidalsuspensionofbariumsulfateparticles.Thealuminumfoilseeninthisphotographisnotnecessaryasthetemperatureofthesolutionisnothighenoughtomeltthepaintonthebaseoftheringstand.
Theadditionofbariumchloridesolutioncanalsobedonedropwiseusinganeyedropper(belowright)butyoumustmakesurethattheeyedropperiscleanbeforeyoustart,thatyoudotheadditionusingameasuredamountofbariumchloridesolutionplacedinasmallbeakerandthatyoudon'
tallowanybariumchloridesolutiontocontaminatetherubberbulboftheeyedropper.Usingthismethodallowsyoutoaddthebariumchloridesolutiontothebeakerswhiletheyarecontinuingtobeheatedonthehotpads.
<
BR<
>
Thefiltrationwillbecarriedoutusingglassorplasticfunnelsfittedwithashlessfilterpaper.Ashlessfilterpaperispurecelluloseandwilldecomposeinthepresenceofheatandairtowaterandcarbondioxide.Noresidualnon-volatilesubstancesremain.Ashlessfilterpapercomesintheformofcircleswhichmustbefoldedappropriatelytotrapallofthebariumsulfateprecipitate.Clickheretoseehowtofoldashlessfilterpaper.
Thefunnelrack(belowleft)isusefultoallowyoutocarryoutthefiltrationofallsamplessimultaneously.MakesurethatthefilterpaperyouuseisASHLESS.Erlenmeyerflasksmaybeusedtocatchthefiltrate.Aseachflaskfillsup,examinethefiltratetomakesurethatitisfreeofanyprecipitate.
Ifthefiltratesamplesarecleartheymaybediscarded.Presenceofprecipitatesuggestseitheraholeinyourfilterpaperoroverfillingafunnelsothatprecipitatewasnotcaughtbythefilter.Ineithercase,askyourinstructorabouttheproceduretobefollowed.
Asisoftenthecaseinlaboratorychemistrythereismorethanonecorrectwaytocarryoutaprocedureandthesamecanbesaidfortheincorrectexecutionofaprocedure.Herearefourpicturestoillustratethepoint.Thefirsttwoillustratecorrectwaysofpouringyourfiltrateandsuspendedprecipitateintothefilterinthefunnel.Inthefirstoneontherightnotethatthestudentisusingastirringrodtoprovidearouteforthesolutionintothefilter.Thelipofthebeakerissufficientlyclosetothefiltersothatthefallingsolutionneverspeedsupfastenoughtoformdropletsandendupabovethefilterpaperor,worse,onthelabbench.
Thepictureattheleftshowsthepouringoperationneartheendofthetransfer.Astirringrodisusedagainbutheldinplaceacrossthetopofthebeakerforstability.Thelipofthebeakerisagaincloseenoughtothefunnelnottoletanyofthesolutiongetaway.Theonlycriticismthatmightbeofferedhereisthatthelengthofthefallofsolutionisalittletoogreat.Soastominimizethepossibilityoflossowingtosolutionturbulenceasitfalls,thepathoffalloughttobeshortened.
Thenextpictureontherightshowsastudentsimplypouringhissolutionoutofthebeaker.Immediatelyafterthisphotowastaken,thefallingliquidcurledupontothebeakerowingtothesurfacetensionofwater.Somewaslostonthefilterabovethefilterpaperandsomedribbleddownthesideofthebeaker.Astirringrodoughttobeusedtoprovideagoodpathforthesolutionbeingtransferred.
Thephotoimmediatelytotheleftshowstheuseofastirringrodtoprovideapath,buttherodisatanangleofinclinationtoolowtoprovideagoodpathforthesolution.Thepathoughttobemoreverticalorthereisagoodchancethatsomesolutionwillbelostbydribblingofftherod.Inaddition,thedistanceofthelipofthebeakeristoofarfromthefunnelandthereiseverylikelihoodthatatsomepointsomeoftheliquidtravelingdowntherodwillseparatefromitandbelostfromtheanalysis.
Therecertainlyisnoneedtobeatthissubjecttodeath,butI'
lllaytwomorephotosonyouthenmoveontotherestofthesehelpfulhints.Eventhoughitisslightlyoutoffocus,thephotoontheleftshowsanearlyverticalstirringrod.Thisisaboutasgoodasitisgoingtoget.Thepossibilitythatanyofthesupernatantisgoingtodribbledowntheoutsideofthebeakerunderthelipiskepttoaminimumbythistechnique.PleasebecognizantthattherodDOESNOTTOUCHthefilterpaper.Youmustavoidthatsoasnottomakeholesthroughwhichtheprecipitatemightbelost.Thephotoontherightillustratesthatoneoughttotrytopourpracticallyallofthesupernatantthroughthefilterpaperbeforestartingontheprecipitate.Thatwaythefilterpaperremainsuncloggedbyprecipitateuntiltheveryend.Thestudentisintheprocessoftransferringtheprecipitate.Thiscanbedonebyacombinationoflow-volumewashesfromyourwashbottleandcoaxingtheprecipitateoutwithyourrubberpolicement,asshownhere.
Finally,thesetupontherightshowsafiltratewhichresultedfromleakageeitherthroughoraroundthefilterpaperinthesmallbeaker.TheappropriatetechniquewouldhavebeenforthestudenttofoldanewpieceoffilterpaperandplaceitUNDERthefirstoneandcontinuefiltering,includingarefiltrationofthefiltratewiththeresiduefollowedbywashingasdescribedbelowandthenashingofbothpiecesoffilterpaper.Infactthestudentwashedtheprecipitateoffthefilterpaperbackintothesuspensionyettobefilteredandthrewawaytheoldfilterpaper.Recoveryofthefilterpaperfromthetrashcanisnotrecommendedbecauseofthepossibilityithaspickedupothermaterial,sohehasthechoiceofriskingalowresultifallprecipitatewasnotwashedfromitorstartingover.Inanycase,thefiltrateinthelargerbeakerisappropriatelyclear,sothereisnoapparentleakageofprecipitateintoit.
Hotwaterwashesof15mLeachneedtobetestedwithtwodropsofsilvernitratesolutionforanylingeringchlorideion.Thesethreephotographs,fromlefttorightshowwhatyoumightexpecttoseeasallofthechlorideisleachedfromtheprecipitate.
Foldyourfilterpapersothattheprecipitateistrappedinsideandsothatthefinalshapeissmallenoughtobestuffedintoacleancruciblewhichhasbeenpreviouslyweighed.Itdoesn'
tmatterifthefilterpaperisstilldamp.ItmaybeeasiertofoldandtostuffifitISdamp,butbecarefulnottofolditinamannerwhichcausesthepaperitselftorupturebecauseyoumightlosesomeofyourprecipitate.Noteintheimageontheleftthatthefilterpaperhasbeenstuffedintothecrucibleandheatinghasbegun.Theimageinthemiddleshowsthatastheashingprocessprogressesthefilterpaperblackensandthereisthepossibilityofspontaneouscombustion.Keepyourcruciblecoverreadytoextinguishanyflamewhichmightproducesufficientturbulencetoallowtheescapeoffragmentsoffilterpapercoatedwithprecipitate.Finally,theimageontherightshowsthecruciblejustpriortofinalashing.
Bywayofsomefinalobservations,asthefilterpaperisheatedandlosesitsmoistureandthenbeginstodistilldestructively,turningtocarbonandreleasingtheinevitabletarsfromthethermaldestructionofthecellulose,itisimportanttocoveritsoasnottoallowittoburstintoflamebecausetheturbulencemightallowsomebariumsulfatecakedonittoescapewiththefumes.
Ontheotherhand,coveringthecruciblehasitsperilsaswellasthephotoontheleftshows.Lookcloselyandyoucanseethatthecrucibleisheldinmid-airbecausethetophasstucktotherim.Thedestructivelydistilledtarcancausethecaptosticktothecrucibleallowingbothtobeliftedtogetherbythecoverknob.Don'
tliftsuchapairtoohighbecausethecovermaysuddenlyseparatefromthecruciblecausingbreakageofthecrucible.
Allowthecrucibleandcovertocool,thengentlyprythetwoapart.Therimofthecrucibleandtheroofofthecoverbothwillhavetarandcarbonaceousmaterialcakedonthem.Notetheundersideofthecruciblecapinthephotoattheleft
Bothcanbesubjectedtoheatingandultimatelyloseallofthatresidueasshowninthephotoimmediatelyontheright.Ifthereisanysuspicionthatsomeofthebariumsulfatemayhavedepositedontheroofofthecover,youmayweighitafterheatingitthoroughlytoremoveallofthecarbonaceousmaterial,thenwashit,heatittodrynessandweighitagain.Experiencehasshownthoughthatrarelydoesanybariumsulfatedepositwiththedestructivelydistilledresidueonthecover.
Evenifyouhaveaspeckofblackmaterial,itisgoodtocontinueheatingforawhiletogetridofitifitiscarbonaceousmaterialasshownhereinthephotosattheleftandtheright.
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Gravimetric Sulfate Determination Helpful Hints
![提示](https://static.bdocx.com/images/bang_tan.gif)
链接地址:https://www.bdocx.com/doc/21622146.html