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DensityDeterminationsO__ectiveInthisexperimentyouwilldeterminethedensitiesofregularlyandirregularlyshapedsolidsaswellasofpureliquidsandsolutions.IntroductionThedensityofasampleof__tterrepresentsthe__sscontainedwithinaunitofvolumeofspa__inthesample.Formostsamplesaunitvolumemeans
1.0mL.Theunitsofdensitythereforearequotedintermsofgramspermilliliterg/mLorgramsperunitcubic__ntimeterg/cm3formostsolidandliquidsamplesof__tter.Sin__weseldomdealwithexactly
1.0mLofsubstan__inthegeneralchemistrylaboratoryweusuallysaythatthedensityofasamplerepresentsthe__ssofthespecificsampledividedbyitsparticularvolume.Density=__ss/volumeBecausethedensitydoesinfactrepresentaratiothe__ssofanysizesampledividedbythevolumeofthatsamplegivesthe__ssof
1.0mLofthesamesample.Densitiesareusuallydeterminedandreportedat20°Caroundroomtemperaturebecausethevolumeofasampleandhen__thedensitywilloftenvarywithtemperature.Thisisespeciallytrueforgaseswith__allerbutstilloftensignificantchangesforliquidsandsolids.Referen__ssuchasthevariouschemicalhandbooksalwaysspecifythetemperatureatwhichadensitywasmeasured.Densityisoftenusedasapointofidentificationinthedeterminationofanunknownsubstan__.Inlaterexperimentsyouwillstudyseveralotherphysicalpropertiesofsubstan__sthatareusedintheidentificationofunknownsubstan__s.Forexampletheboilingandmeltingpointsofagivensubstan__arecharacteristicofthatsubstan__andareusedroutinelyinidentificationofunknownsubstan__s.Supposeanunknown’sboilingandmeltingpointsh__ebeendeterminedbitonconsultingtheliteratureitisfoundthatmorethanonesubstan__hastheseboilingandmeltingpoints.Thedensityoftheunknownmightthenbeusedtodistinguishtheunknown.Itisveryunlikelythattwosubstan__swouldh__ethesameboilingpointmeltingpointanddensity.Densitycanalsobeusedtodeterminethecon__ntrationofsolutionsin__rtaininstan__s.Whenasoluteisdissolvedinasolventthedensityofthesolutionwillbedifferentfromthatofthepuresolventitself.Handbookslistdetailedinfor__tionaboutthedensitiesofsolutionsasafunctionoftheircompositiontypicallyintermsoftheper__ntsoluteinthesolution.Ifasampleisknowntocontainonlyasinglesolutethedensityofthesolutioncouldbemeasuredexperimentallyandthenthehandbookcouldbeconsultedtodeterminewhatcon__ntrationofthesolutegivesrisetothemeasureddensityofthesolution.Thedeterminationofthedensityof__rtainphysiologicalliquidsisoftenanimportantscreeningtoolinmedicaldiagnosis.Forexampleifthedensityofurinediffersfromnor__lvaluesthis__yindicateaproblemwiththekidneyssecretingsubstan__swhichshouldnotbelostfromthebody.Thedeterminationofdensityspecificgr__ityisalmostalwaysperformedduringaurinalysis.Severaltechniquesareusedforthedeterminationofdensity.Themethodusedwilldependonthetypeofsampleandonthelevelofprecisiondesiredforthemeasurement.Forexampledevi__sh__ebeenconstructedfordeterminationsofthedensityofurinethatpermitaquickreliableroutinedetermination.Ingeneraladensitydeterminationthevolumeofthesamplewilldifferfromsituationtosituation.Severalmethodsofvolumedeterminationareexploredinthisexperiment.Forsolidsamplesdifferentmethods__ybeneededforthedeterminationofthevolumedependingonwhetherornotthesolidisregularlyshaped.Ifasolidhasaregularshapee.g.cubicrectangularcylindricalthevolumeofthesolid__ybedeterminedbygeometry:Foracubicsolidvolume=edges3Forarectangularsolidvolume=lengthxwidthxheightForacylindricalsolidvolume=πxradius2xheightIfasoliddoesnoth__earegularshapeit__ybepossibletodeterminethevolumeofthesolidfromArchimedes’principlewhichstatesthataninsolublenon-reactivesolidwilldispla__avolumeofliquidequaltoitsownvolume.Typicallyanirregularlyshapedsolidisaddedtoaliquidinavolumetriccontainersuchasagraduatedcylinderandthechangeinliquidleveldetermined.Forliquidsveryprecisevaluesofdensity__ybedeterminedbypipetinganexactvolumeofliquidintoasealableweighingbottlethisisespeciallyusefulforhighlyvolatileliquidsandthendeterminingthe__ssofliquidthatwaspipeted.Amoreconvenientmethodforroutinedensitydeterminationsforliquidsistoweighaparticularvolumeofliquidascontainedinagraduatedcylinder.Pre-LaboratoryQuestions.Showyourwork!__intaincorrectsignificantfigures!!!
1.Aninsolublenonreactivesolidmetalsphereweighing
18.45gisaddedto
21.7mLofwaterinagraduatedcylinder.Thewaterlevelrisesto
26.8mL.Calculatethedensityofthemetal.
2.Anemptybeakerweighs
32.4257g.A
10.0mLpipetsampleofanunknownliquidistransferredtothebeaker.Thebeakerweighs
40.1825gwhenweighedwiththeliquidinit.Calculatethedensityoftheunknownliquid.
3.Asampleofalcoholhasdensityof
0.785g/mL.Calculatethevolumeof
50.0gofthealcohol.Calculate__ssof
50.0mLofthealcohol.
4.Atermthatiseasilyconfusedwithdensityisspecificgr__ity.Forexampleurinalysisreportscommonlygivethespecificgr__ityofthesampleratherthanthedensity.Whatisspecificgr__ityWhataretheunitsofspecificgr__ityApparatus/ReagentsRequiredUnknownliquidsampleunknownmetalsamplesodiumchloridedistilledwater.Pro__dureRecordalldataandobservationsdirectlyinyourlabnotebookinink!A.DetermineoftheDensityofSolidsObtainaregularlyshapedsolidandrecorditscolorandshape.Witharulerdeterminethephysicaldimensionse.g.lengthwidthheightradiusofthesolidtothenearest
0.2mm.Fromtheyphysicaldimensionscalculatethevolumeofthesolid.Determinethe__ssoftheregularlyshapedsolidtoatleastthenearestmg
0.01g.Fromthe__ssandvolumecalculatethedensityofthesolid.Obtainasampleofthemetalpelletsshotsandrecorditscolorandshape.Usethewholesample.Weighthesampleofthemetalofapproxi__tely50gbutrecordtheactual__ssofthemetaltakentothenearest
0.01g.Addwatertoyour100-mLgraduatedcylindertoapproxi__telythe50-mL__rk.Recordtheexactvolumeofwaterinthecylindertotheprecisionpermittedbythecalibration__rksofthecylinder.Pourthewholemetalsampleintothegraduatedcylinder__kingsurethatnoneofthepelletsstickstothewallsofthecylinderabovethewaterlevel.Slightlytapthecylinderto__ke__rtainthatnoairbubblesh__ebeentrappedamongthepellets.SeeFigure3-1Readthelevelofthewaterinthegraduatedcylinderagain__kingyourdeterminationtotheprecisionpermittedbythecalibration__rksofthecylinderassumingthatthemetalsampledoesnotdissolveinorreactwithwaterthechangeinwaterlevelsrepresentsthevolumeofthemetalpellets.AfterblottingthemdrywithapapertowelturninthemetalpelletstoyourinstructordonotdiscardCalculatethedensityoftheunknownmetalpellets.Obtainthetheoreticaldensityvalueofthemetalfromyourteacherandcalculateyour%error.B.DensityofPureLiquidsFilla250mLErle__eyerflaskwithdistilledwaterpla__thethermometerinit.Pla__onthelabstationtobeusedthroughoutthisexperiment.Pla__acleananddry__allbeakeronthescale.Tarethescalesetittozero.Obtaina25mLvolumetricpipetanddraw25mLofdistilledwaterfromtheflask.Dispensethedistilledwaterintothebeaker.Recordthe__ssofthewatertothenearest
0.01g.Calculatethedensityofthewater.Comparethemeasureddensityofthewaterwiththevaluelistedinthehandbookforthetemperatureofyourexperiment.Calculateyour%error.Obtainanunknownliquidandrecorditscolor.Determinethedensityoftheunknownliquidusingthemethodjustdescribedforwater.YoudonotneedtorecordthetemperatureoftheunknownliquidObtainthetheoreticaldensityvalueoftheliquidfromyourteacherandcalculateyour%error.Rinsethe25mLvolumetricpipetseveraltimeswithdistilledwater.C.DensityofSolutionsThecon__ntrationofsolutionsisoftenconvenientlydescribedintermsofthesolutions’per__ntagecompositiononaweightbasis.Forexamplea4%sodiumchloridesolutioncontains6gofsodiumchlorideinevery100gofsolutionwhichcorrespondsto4gofsodiumchlorideforevery96gofwaterpresent.Preparesolutionofsodiumchlorideindistilledwaterconsistingofthefollowingper__ntagesbyweight:4%8%12%16%and20%.Prepare50mLofeachsolution.Followtheappropriatestepsinthepreparationofstandardaqueoussolutions.SeeFigure
4.10onthenextpagePla__aweighingdishonthebalan__.Tarethebalan__.Carefullyweighouttherequired__ssofsodiumchloridethatyouh__ecalculatedearlier.Recordthe__ssofthewatertothenearest
0.01gTransferthesodiumchloridecarefullyintothe50mLvolumetricflask.Filltheflaskabouthalfwaywiththesolvent.Besuretorinseanysolutestuckintheneckdownintotheflask.Swirltodissolvethesolute.Addsolventcarefullytothe__rkedlineontheneckoftheflask.Thelastdropsarebestdonewithasquirtbottledropperorsimilar“precision”instrument.__kesuretodissolvethesolventcompletely.Inverttheflaskseveraltimesforfinalmixing.Labelyoursolutionwiththeper__ntile__de.Usingthemethoddescribedearlierforsamplesofpureliquidscalculatethedensityofeachofyoursodiumchloridesolutions.Assumethetemperatureofthesolutionsisthesameasinthedensityofpureliquidspart.Useahandbookofchemicaldatatodeterminethetruedensityofeachofthesolutionyouprepared.Calculatethe%errorineachofthedensitiesyoudetermined.Generateacomputergraph.Onthisgraphplotthefollowing:a.thedensityyaxisofyoursolutionsversustheper__ntageofNaClx-axisthesolutioncontains.b.thedensitiesfromthehandbookversustheper__ntageofsodiumchloride.Q:WhatsortofrelationshipexistsbetweendensityandcompositionDensityofSolutionsTable%NaCl__ssofNaClDensitymeasuredTemperatureHandbookdensityvalues%error4%8%12%16%20%Questions
1.Whaterrorwouldbeintrodu__dintothedeterminationofthedensityoftheregularlyshapedsolidifthesolidwerehollowWouldthedensitybetoohighortoolow
2.Whaterrorwouldbeintrodu__dintothedeterminationofthedensityoftheirregularlyshapedmetalpelletsifyouhadnotstirred/shakenthepelletstoremoveadheringairbubblesWouldthedensitybetoohighortoolow
3.Yourdataforthedensityofsodiumchloridesolutionsshouldh__eprodu__dastraightlinewhenplotted.Howcouldthisplotbeusedtodeterminethedensityofanycon__ntrationofsodiumchloridesolution
4.Whywasitne__ssarytomeasurethetemperatureduringthedeterminationofthedensityofthesodiumchloridesolutionsWhichfactor–__ssorvolume–usedincalculatingthedensitywouldbeaffectedbytemperatureExplain.Writeaconclusionsparagraph.。