SEPARATIONTECHNIQUESIfasubstancedoesnotdissolveinasolvent,wesaythatitisinsoluble.Forexample,sanddoesnotdissolveinwater–itisinsoluble.Filtrationisamethodforseparatinganinsolublesolidfromaliquid.Whenamixtureofsandandwaterisfiltered:

• thesandstaysbehindinthefilterpaper(itbecomestheresidue)• thewaterpassesthroughthefilterpaper(itbecomesthefiltrate)

1.Abeakercontainingamixtureofinsolublesolidandliquid.Thereisfilterpaperinafilterfunnelaboveanotherbeaker.

2.Pourthemixturethroughthefilterfunnel.

3.Letthewaterdrainandleavetheinsolublesolidtodry.

Eg.SeparatingsandfromSaltwater.Evaporationisusedtoseparateasolublesolidfromaliquid.Forexample,coppersulfateissolubleinwater–itscrystalsdissolveinwatertoformcopper

sulfatesolution.Duringevaporation,thewaterevaporatesawayleavingsolidcoppersulfatecrystalsbehind.

1. 2. AsolutionisplacedinanevaporatingbasinandheatedwithaBunsen

burner.3. Reducethevolumeofthesolutionuntilyougetasaturatedsolution

(concentratedsolution)4. Leavethesampletocooldownandevaporateatroomtemperature5. Filterthecrystalsfromthesolutionandletitdryoverablottingpaper.

Separatingmixturesofliquids

Mixturesofliquidscanbeseparatedaccordingtotheirproperties.Thetechniqueuseddependsonwhethertheliquidsdissolveineachother,andsoaremiscible,oriftheyareimmiscible.

• Fractionaldistillationisatechniqueusedtoseparatemiscibleliquidsaccordingtotheirboilingpoints.

• Simpledistillationistoseparatemixtureoftwomisciblesolvents• Chromatographyisusedtoseparatemixturesofcolouredcompounds.

Separatingthesolventfromasolution–simpledistillation

Simpledistillationisamethodforseparatingthesolventfromasolution.• Forexample,watercanbeseparatedfromsaltsolutionbysimple

distillation.Thismethodworksbecausewaterhasamuchlowerboilingpointthansalt.Whenthesolutionisheated,thewaterevaporates.

• Itisthencooledandcondensedintoaseparatecontainer.Thesaltdoesnotevaporateandsoitstaysbehind.

Everypuresubstancehasitsownparticularmeltingpointandboilingpoint.Onewaytocheckthepurityoftheseparatedliquidistomeasureitsboilingpoint.Forexample,purewaterboilsat100°C.Ifitcontainsanydissolvedsolids,itsboilingpointwillbehigherthanthis.

Separationofliquids

• Liquidscanbedescribedintwoways–1.immiscible-donotmixtogether2.miscible–mixtogether

Theseparationtechniqueusedforeachliquiddependsonthepropertiesoftheliquids.

Immiscibleliquids

• Oilandwatercanbeseparatedusingafunnel• Immisciblemeansthattheliquidsdon'tdissolveineachother–oiland

waterareanexample.• Itispossibletoshakeuptheliquidsandgetthemtomixbuttheysoon

separate.• Separatingimmiscibleliquidsisdonesimplyusingaseparatingfunnel.The

twoliquidsareputintothefunnelandareleftforashorttimetosettleoutandformtwolayers.

• Thetapofthefunnelisopenedandthebottomliquidisallowedtorun.Thetwoliquidsarenowseparate.

Miscibleliquids

• Miscibleliquidsarehardertoseparateastheydissolveineachother.• Miscibleliquidsareoftenseparatedusingfractionaldistillation.• Thisispossibleasmiscibleliquidshavedifferentboilingpoints.

Fractionaldistillationofliquidair

Youneedtobeabletoexplainhownitrogenandoxygenareobtainedfromtheair.

• About78percentoftheairisnitrogenand21percentisoxygen.• Thesetwogasescanbeseparatedbyfractionaldistillationofliquidair.

FractionalDistillationcolumnatanoilrefinery

LiquefyingtheairFractionaldistillation

Airisfilteredtoremovedust,andthencooledinstagesuntilitreaches–200°C.Atthistemperatureitisaliquid.Wesaythattheairhasbeenliquefied.

Here'swhathappensastheairliquefies:

1. Watervapourcondenses,andisremovedusingabsorbentfilters2. Carbondioxidefreezesat–79ºC,andisremoved3. Oxygenliquefiesat–183ºC4. Nitrogenliquefiesat–196ºCTheliquidnitrogenandoxygenarethenseparatedbyfractionaldistillation.

Ex:• Ethanolcanbeseparatedfromamixtureofethanolandwaterbyfractional

distillation.• Thismethodworksbecausetheliquidsinthemixturehavedifferentboiling

points.• Whenthemixtureisheated,oneliquidevaporatesbeforetheother.

• Onewaytocheckthepurityoftheseparatedliquidsistomeasuretheirboilingpoints.

• Forexample,pureethanolboilsat78°Candpurewaterboilsat100°C

Chromatography

• Paperchromatographyisamethodforseparatingdissolvedsubstancesfromoneanother.

• Itisoftenusedwhenthedissolvedsubstancesarecoloured,suchasinks,foodcolouringsandplantdyes.tworksbecausesomeofthecolouredsubstancesdissolveinthesolventusedbetterthanothers,sotheytravelfurtherupthepaper.

Apencillineisdrawn,andspotsofinkorplantdyeareplacedonit.Thereisacontainerofsolvent,suchaswaterorethanol.1

• Apuresubstancewillonlyproduceonespotonthechromatogramduringpaperchromatography.Twosubstanceswillbethesameiftheyproducethesamecolourofspot,andtheirspotstravelthesamedistanceupthepaper.

• Intheexamplebelow,red,blueandyellowarethreepuresubstances.Thesampleontheleftisamixtureofallthree.

Achromatogram,theresultsofachromatographyexperiment

<

• Thecoloursseparateandmoveupthepaperatdifferentrates• Chromatographycanbeusedtoseparatemixturesofcolouredcompounds.• Mixturesthataresuitableforseparationbychromatographyincludeinks,

dyesandcolouringagentsinfood.Method

1. Simplechromatographyiscarriedoutonpaper.2. Aspotofthemixtureisplacednearthebottomofapieceof

chromatographypaperandthepaperisthenplaceduprightinasuitablesolvent,egwater.

3. Asthesolventsoaksupthepaper,itcarriesthemixtureswithit.4. Differentcomponentsofthemixturewillmoveatdifferentrates.5. Thisseparatesthemixtureout.

Rfvalues(Retardationfactor)orRetentionValue

• DifferentchromatogramsandtheseparatedcomponentsofthemixturescanbeidentifiedbycalculatingtheRfvalueusingtheequation:

• TheRfvalueisdefinedastheratioofthedistancemovedbythesolute(i.e.thedyeorpigmentundertest)andthedistancemovedbythethesolvent(knownastheSolventfront)alongthepaper,wherebothdistancesaremeasuredfromthecommonOriginorApplicationBaseline,thatisthepointwherethesampleisinitiallyspottedonthepaper

Rf=distancemovedbythecompound

distancemovedbythesolvent

• TheRfvalueofaparticularcompoundisalwaysthesame-ifthechromatographyhasbeencarriedoutinthesameway.

• Thisallowsindustrytousechromatographytoidentifycompoundsinmixtures

SeparationofMixtures

Inamixture,sincetheconstituentsubstancesdonotlosetheiridentity,theycanbeseparatedeasilybyphysicalmethods,takingadvantageofthedifferencesintheirphysicalproperties.

Fig1:Filtration

MixtureofSolidsandLiquids

SedimentationandDecantation

Sedimentation is the process of separating an insoluble solid from a liquid inwhichitissuspendedbyallowingittosettletothebottomofthecontainer.Ifthisalso involves pouring off of the liquid leaving the solid behind, it iscalleddecantation.

Filtration

Filtrationisusedforseparatinginsolublesolidsfromaliquid.

Whenamixtureofchalkandwaterispouredthroughafilterpaperinafunnel,chalkparticlesremainsasresidueinthefilterpaper,whilethewatergetscollectedinthebeakerbelowasfiltrate.(seeFig.1)

Evaporation

Evaporationisusedforrecoveringdissolvedsolidsubstancesfromsolutionsbyevaporatingthesolvent.Thesolute“dissolvesout”andisleftbehind.

Sugarcanberecoveredfromasugar-watermixturebyevaporation.Thewaterevaporatestoleavethesolutebehind.Coppersulphate,potashalum,potassiumnitrateetc.canalsoberecoveredfromtheiraqueoussolutionsbyevaporation.

Fig2:Distillation

Distillation

Distillationistheprocessofheatingasolutioncontainingsolublesolidstoformvapoursoftheliquidandthencoolingthevapourstogettheliquidback.

Amixtureofcommonsaltandwateristakeninadistillationflaskandheated.Steamrisesupandcomesoutintothecondenser,whichisacoaxialtubewithacentraltubeforvapourtopassthrough,andanoutertubethroughwhichcoldwatercirculatestoformacoldwaterjacket.Steamcondensesinthecentraltubeandcollectsinareceiverasdistillate.(seeFig.2)

Fig3:Sublimationofammoniumchloride.(Source:NCERT,ScienceIX,p.8)

MixtureofSolids

Sublimation

Sublimation is a process in which some solids, on heating, are transformeddirectlytovapourwithoutpassingthroughtheliquidphase.Thistechniquecanbeusedtoseparateamixtureofsolids,oneofwhichcanundergosublimation.Thevapoursarethencooledseparatelytogetthesublimedsolidback,aprocesscalleddeposition.(Fig.3)

Sublimation is used in the separation of substances like ammoniumchloride,iodine,napthalene,camphorandsulphur.

Extraction

Insomecases,onesubstanceinthemixtureissolubleinaparticularliquidsolventwhereas the other(s) is(are) insoluble in it. The process of dissolving out the

solublecomponentfromamixture,andsubsequentlytreatingthesolutiontogetthesolid,iscalledextraction.

Crystallisationisasophisticatedformofevaporationtechniqueinwhichcrystalsofthesoluteareencouragedtodevelopduringtheprocessof“dissolvingout”fromthesolutionasthesolventevaporates.

MagneticSeparation

Thismethodofseparationisexemplifiedbytheseparationofironfilings.

Amixturewithironfilingsasoneofthecomponentscanbeseparatedusingamagnettoattracttheironparticlesawayfromthemixture.

Fig4:Chromatography

Chromatography

Chromatography is an advanced technique of separation in which individualcomponents of a mixture are separated from each other using the property

ofdifferentialmigration(differentratesofflow).Here,amobilephase,carryingthemixture,ispassedthroughaselectivelyadsorbentstationaryphase,whichcanretainthecomponentsofthemixturetodifferentdegrees.(Fig.4)

MixtureofLiquids

FractionalDistillation

Fig5:FractionalDistillation

Fractionaldistillationistheprocessofseparatingtwoormoremiscibleliquidsbya modified distillation process, in which the distillates are collectedasfractionshavingdifferentboilingpoints.Theseparationoftheliquidsbythismethodisbasedonthedifferenceintheirboilingpoints.(Fig.5)

Fractionaldistillationmakesuseofafractionatingcolumnordistillationcolumn,atubewhichprovidesdifferenttemperaturezonesinsideitduringdistillation,thetemperature decreasing from bottom to top. It provides surfaces on whichcondensations(oflessvolatileliquids)andvaporizations(ofmorevolatileliquids)canoccurbeforethevapoursenterthecondenser inordertoconcentratethemorevolatileliquidinthefirstfractionsandthelessvolatilecomponentsinthelaterfractions.

Fractional distillation is very effective is separating mixtures of volatilecomponents,andiswidelyusedinlaboratoriesandindustries.

Crudepetroleumisseparatedbytheprocessoffractionaldistillationintodifferentfractionslikegasoline,lubricatingoil,kerosene,dieseletc.

Fig6:GravitySeparation.(Source:NCERT,ScienceIX,p.20)

GravitySeparation

Ingravityseparation,amixtureoftwoimmiscibleliquidscanbeseparatedusinga separating funnel, the working of which is based on the differences in thedensitiesoftheliquids.Theheavierliquidwhichsettlesbelowisdrainedoutfirstfrombelowthefunnelintoabeaker,andthenthelighterliquidisdrainedoutintoanotherbeaker.