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Industrial Chemistry Notes - AceHSC · 2020-04-12 · INDUSTRIAL CHEMISTRY NOTES – ROHAN BARAR...
Transcript of Industrial Chemistry Notes - AceHSC · 2020-04-12 · INDUSTRIAL CHEMISTRY NOTES – ROHAN BARAR...
INDUSTRIALCHEMISTRYNOTES–ROHANBARAR2016
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IndustrialChemistryNotesSection1Industrialchemistryprocesseshaveenabledscientiststodevelopreplacementsfornaturalproducts
• Discusstheissuesassociatedwithshrinkingworldresourceswithregardtooneidentifiednaturalproductthatisnotafossilfuel,identifyingthereplacementmaterialsusedand/orcurrentresearchinplacetofindareplacementforthenamedmaterial
• Identifydata,gatherandprocessinformationtoidentifyanddiscusstheissuesassociatedwiththeincreasedneedforanaturalresourcethatisnotafossilfuelandevaluatetheprogresscurrentlybeingmadetosolvetheproblemsidentifiedØ Shrinkingworldresourcesaredueto:
§ Increaseindemand§ Inabilityforthenaturalresourcetomeet
demand
§ Depletionofthenaturalresource§ Economiccompetition,increasingprices§ EnvironmentalIssues
Ø Naturalproductsinclude§ NaturalRubber§ Wood§ Wool
§ Ivory§ Soap§ Fertiliser
Theincreasingpopulationoftheworldisleadingtogreaterdemandonallnaturalresources,andastheyarebeingdepleted,syntheticalternativesmuchbefound.Onesuchresourceisrubber.
Ø Naturalrubberisobtainedfromthesapoftherubbertree
(Latex)(Polyisoprene)Ø Anincisionismadeintothebarkofatree,andlatexsap
collectedandrefinedintousablerubberØ Itisapolymerof2-methyl-1,3-butadieneØ Rubberisusedtomanufacturetyres,belting,hoses,tubing,insulators,valvesandfootwearØ Thisisbecauserubberiselastic,tough,impermeable,adhesive,easilymouldableandanelectricalinsulator
Ø Naturalrubbermustundergoprocessingsoitsflexibilityandsolidityarepreservedinallconditionso Softeningbymastication(passingrubberbetweenrollers)o Grindinganddissolvinginasuitablesubstanceforcompoundingwithother
ingredientse.g.fillers,pigments,antioxidants,plasticiserso Sheetingandextrusionintovariousshapeso Vulcanisation(heatingofrubberwithsulfurinordertocrosslinkpolymerswith
sulfur)tomakeitelastic,hard,andlesssusceptibletochemicals(asshownonright).(Crosslinkingcausestherubbertospringbackintoshapewhenstretched)
Ø Limitsofnaturalrubbero Perishwhenexposedtowearo Softwhenwarm,brittlewhencoldo Hastobevulcanised(crosslinkedwithsulfur)
Ø Untilthe1940s,rubbertreesweretheprimarysourceofrubber,especiallytreesintropicalareassuchas
MalayaandBurma.
Twosignificanteventscauseddemandfornaturalrubber• TheCommercialisationoftheAutomobile
o Aftertheautomobilewasinventedtherewashighdemandforrubberforthetyresaswellasvariousothercomponentsofthecar
o Asnaturalrubbercouldnotmeetdemands,syntheticrubberwasdeveloped
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• TheSecondWorldWaro TheconflictofWorldWarIIinterruptednaturalrubbersupplies,andalsocausedanincreasein
demand(formilitaryvehicletyres)o GermanandUSscientistsdevelopedsyntheticpolymerstoreplacerubbero AfterWWII,thedemandforrubbercouldnotbemetbynaturalrubbertreeplantations,andthus
syntheticrubbersdominatedthemarketinsteadØ ThefirstsyntheticrubbertobedevelopedwasNeoprene(Polychloroprene)Ø ThispolymerwasflameretardantandhadsuperiorstrengthtonaturalrubberØ Neopreneisstillinusetodayinavarietyofindustries(CivilEngineering&Aquatics)Ø Neopreneisusefulatelevatedtemperaturesandisusedforheavy-dutyapplicationssuchaswetsuits
Ø Approximately80%oftheworld’srubberproductiontodayisfromsyntheticpolymers,themostcommon
onebeingSBR(styrene-butadienerubber)Ø Thisisacopolymerofbutadieneandstyrene
Styrene Butadiene SBR
Ø Today’smostcommonsyntheticrubberisSBR,madefromtwomonomers:butadiene(B)andstyrene(S)inthepatternBBBSBBBS(Butadiene-Butadiene-Butadiene-Styreneetc.)
Ø SBRhasalowcostanddesirablepropertiesØ Copolymeralsousedtomanufactureballs,shoesandelasticbandsØ Therawmaterialisobtainedfromcrudeoil,whichisnon-renewable.Ifcrudeoilisnotavailable,natural
rubberwillhavetobeusedtomeetthedemandordevelopabiopolymerwiththepropertiesofrubber.
Ø AdvantagesofSyntheticRubberoverNaturalRubbero Betteragingandweatheringo Greaterresistancetooil,solvents,oxygen,ozoneandcertainchemicalso Resilienceoverawidertemperaturerangeo Lesserneedforchemicaltreatmenttoassumefavourableproperties
Ø Assessment:Effective,moreversatilereplacementthatsolvesproblemsofsupplyanddemand.Attemptsto
findnon-petrochemicalalternativesformoresustainableproduction.Syntheticrubberhasbecomecheapertoproducethannaturalrubber.
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Section2Manyindustrialprocessesinvolvemanipulationofequilibriumreactions
• Explaintheeffectofchangingthefollowingfactorsonidentifiedequilibriumreactions:pressure,volume,concentrationandtemperatureLeChatelier’sprinciplestatesthatifasystematequilibriumisdisturbed,itwillmovetopartiallycounteractchangesintheconcentrationofproductsandreactants,volume,pressureandtemperatureØ Pressure
• Totalpressureissumofindividualpressuresofeachcomponentgas(NOLIQUIDSORSOLIDS)• Balancetheequation.Calculatethetotalnumberof‘moles’ofgasoneachsideofthereaction.• Increasingpressurewhenthetotal‘moles’ofreactantgassesislargershiftsequilibriumrighttowards
products(equilibriumtriestodecreasepressure)(andviceversa(decreasingpressure))• Increasingpressurewhenthetotal‘moles’ofproductgassesislargershiftsequilibriumlefttowards
reactants(equilibriumtriestodecreasepressure)(andviceversa(decreasingpressure))Ø Volume
• AnincreaseinvolumeisequivalenttoadecreaseinpressureoAdecreaseinvolumeisequivalenttoanincreaseinpressure(andviceversa)
Ø Concentration• Increasingconcentrationofreactantscausesthereversereactiontobefavoured(producingmore
products)(andviceversa)• Increasingconcentrationofproductscausestheforwardreactiontobefavoured(producingmore
reactants)(andviceversa)Ø Temperature
• EndothermicReaction–Anincreaseintemp.causesequilibriumtoshifttofavourreversereaction• ExothermicReaction–Anincreaseintemp.causesequilibriumtoshifttofavourforwardreaction• Note:Usingparticletheory/kineticenergy,increasingtemp.increasesrateofreactionforboth
• Interprettheequilibriumconstantexpression(nounitsrequired)fromthechemicalequationofequilibrium
reactionsand
• ProcessandpresentinformationfromsecondarysourcestocalculateKfromequilibriumconditionsØ PORKàProductsOverReactantsisK
Ø aA+bB cC+dD,𝐾 = [$]&['](
[)]*[+],(equilibriumconstantexpression)
Ø Whattheexpressionincludes• Allgasses• Allaqueoussolutions• Nosolidsorliquids(solvents)
Ø Theequilibriumconstantforthereversereactionisthereciprocaloftheequilibriumconstantfortheforwardreaction(1/const.)
Ø TheRICEBoxExample: N2 H2 NH3
Ratio 1 3 2Initial 0.5 0.8 0Change -0.075 -0.225 +0.15Equilibrium 0.425 0.575 0.15§ TheRICEboxcanbeusedtocalculatetheequilibriumconstantwhentheconcentration(orpartial
pressure)ofallaqueous/gaseouscomponentsisnotknown§ Writethebalancedequation,andthenfillinthe‘Ratio’rowinthetable§ Fillinallknowninformation(e.g.theinitialconcentrationofcertaincompounds)§ Usetheratiotodeterminethechange(+or–dependingonthesideoftheequation)§ Determinetheequilibriumvalues(I+C=E)andsubintotheequationforK
Ø ValueofKindicateswhereKliesinreaction• K≈1:Equilibriumdoesnotliestronglytoleftorright(middle)• K>104:Equilibriumstronglyfavoursproducts(right)–largevalue
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• K<10-4:Equilibriumstronglyfavoursreactants(left)–smallvalue
• Identifythattemperatureistheonlyfactorthatchangesthevalueoftheequilibriumconstant(K)foragivenequationØ TemperatureistheonlyfactorthatchangesK(equilibriumconstant)
• Kwillincreasewithincreasewithincreasingtemperatureiftheforwardreactionisendothermic• Kwilldecreasewithincreasingtemperatureiftheforwardreactionisexothermic(andviceversafor
both)
• Identifydata,planandperformafirst-handinvestigationtomodelanequilibriumreactionØ Method
1. Filla100mLmeasuringcylinderwithwater.LabelitA.2. Inserta2mLgranulatedpipetteandallowthewatertorise.3. Transferthisvolumeofwatertoanempty100mLmeasuringcylinder.LabelitB.4. Inserta5mLgranulatedpipetteintoBandallowthewatertoriseup.5. TransferthisvolumeofwaterbacktoA.6. MeasurethevolumesofwaterinAandB7. Thisisoncecycle.Continueuntilthevolumesstayconstant.(Willbedifferentvolumes)
Advantages Disadvantages
• Candemonstratehowareversiblereactionreachesequilibriumandthattheconcentrationremainsconstantafterequilibriumisreached
• Canalsoshowadisturbanceinconcentrationwillaffecttheequilibrium
• Clearlyseparatesreactantsandproducts(2measuringcylinders)
• Allowsanalysisoftheequilibriumconstant
• Cannotshowtheeffectoftemperature,volumeandpressureonanequilibriumreaction
• Uses2measuringcylindersinsteadofoneclosedcontainer
• Worksusingvolumesratherthanconcentrationorpartialpressures
• Chooseequipmentandperformafirst-handinvestigationtogatherinformationandqualitativelyanalysean
equilibriumreaction𝐹𝑒/0(23) + 𝑆𝐶𝑁9
(23) [𝐹𝑒 𝑆𝐶𝑁 ];0(23) + ℎ𝑒𝑎𝑡Ø Fe3+isyellow,SCN-iscolourlessØ Method
1. Mix5mLof1MFeCl3with5mLof1MNH4SCNinatesttubetogetabloodredsolution2. Dilutetoget30mLwithdistilledwateranddiluteequallyinto6testtubes3. Carryoutthefollowingtests
TestTube Test Observation Reason1 Add1mLofFeCl3 Darker [Fe3+]increaseforward2 Add1mLNH4SCN Darker [SCN-]increaseforward3 Add1mLNaForNaHPO4 Lighter [Fe3+]decreasereverse4 Heatinawaterbath Lighter Forwardisexothermic,high
tempfavoursreverse5 Coolinicebath Darker Lowtempwillfavourthe
forwardexothermicreaction
6 Control BloodRed N/A
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Section3Sulfuricacidisoneofthemostimportantindustrialchemicals
• OutlinethreeusesofsulfuricacidinindustryØ Theproductionofsulfuricacidisthelargestindustryintheworld
1. Fertiliser§ 85%ofthesulfuricacidproducedisusedtomakesolublefertiliser.§ 2NH3(g)+H2SO4(l)à(NH4)2SO4(s)
2. SteelProcessing§ Usedtoremoverustfromsteelbeforegalvanising(coatingwithtin)orpainting§ Fe2O3(s)+3H2SO4(aq)àFe2(SO4)3(aq)+3H2O(l)
3. CarBatteries§ SulfuricacidisusedastheelectrolyteinLead-Acidcarbatteries
• Describetheprocessesusedtoextractsulfurfrommineraldeposits,identifyingthepropertiesofsulfurwhich
allowitsextractionandanalysingpotentialenvironmentalissuesthatmaybeassociatedwithitsextractionØ InAustralia,themainsourceofsulfurisfromthesmeltingofcopperoreinMt.IsaØ Sulfurcanalsobeextractedfromcrudeoilandnaturalgas
Ø FraschProcess
• TheFraschProcessiscapableofextractingpureelementalsulfurfrommineraldeposits
• Themainmechanismconsistsof3concentric(onewithinanother)pipes.TheorderofthesepipesISIMPORTANT.o Superheatedwater@160°C:Meltsthedepositofsulfur.Outermostpipe.o Compressedair:Buildspressurewhichcausesthemoltensulfurtomove
upthe3rdpipe.InnermostPipe.o MoltenSulfur:Thepipethattakesthemoltensulfurfromthedeposit.
MiddlePipe.
• PropertiesofSulfurthatmakethismethodappropriateo Sulfurhasalowmeltingpointof113°C,meaningthatthesuperheated
watercanmeltito Sulfurhaslowdensity,meaningthatthecompressedaircanpushitupthe
pipeo Sulfurisinsolubleinwater,meaningitreadilyseparatesfromwaterwhen
itexitsthemoltensulfurpipe(nofurtherseparationprocessesrequired)
• EnvironmentalIssueso Sulfurisinertandnon-toxic,soitposesminimalthreattotheenvironmento Ifsulfurisoxidised,itformsSO2,whichisaleadingcauseofacidrain(asdiscussedinAcidic
Environment)o Ifreduced,itformsH2S,whichisatoxicandbad-smellinggaso Thehotwaterusedintheprocesscancausethermalpollution(LowerDissolvedOxygen,etc.)o Waterusedcanbecontaminatedwithothersubstancesfromthesulfurdeposito Theremovalofsulfurfromthegroundcausescavitiesintheground,whichcancollapseinon
themselves(GroundSubsidence).Thesearedifficulttobackfill.
• OutlinethestepsandconditionsnecessaryfortheindustrialproductionofH2SO4fromitsrawmaterials• DescribethereactionconditionsnecessaryfortheproductionofSO2andSO3• ApplytherelationshipbetweenratesofreactionandequilibriumconditionstotheproductionofSO2andSO3• Gather,processandpresentinformationfromsecondarysourcestodescribethestepsandchemistryinvolvedin
theindustrialproductionofH2SO4anduseavailableevidencetoanalysetheprocesstopredictwaysinwhichtheoutputofsulfuricacidcanbemaximisedØ TheindustrialproductionofH2SO4isknownastheContactProcess
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Ø Thereare4stepstothecontactprocess1. CombustionofSulfur
Ø S(l)+2O2(g)àSO2(g)+heatØ MoltensulfurissprayedintothefurnacetoincreasesurfaceareaØ ‘Dry’airisusedwithanoxygenlevelofabout33%
2.ProductionofSO3
Ø 2SO2(g)+O2(g) SO3(g)+heat(ΔH=-99KJ/mol)Ø Therateofreactionisincreasedby
o Increasingreactiontemperature(increasedcollisions,howeverreducesyield(LCP))o Addingporousvanadiumoxide(V2O5)catalyst(increasestherateoftheforwardandreverse
reaction)Ø ByLCP,theyieldisincreasedby
o Moderatereactiontemperatures(400-500°C)o Pressuresofabout1-2atmosphereso IncreasingtheconcentrationofO2o SO3isconstantlyremovedandcooled
Ø Tomaximiseyield,theinitialairusedcontainsabout30%–50%moreoxygenthanisrequiredØ ThisincreasedconcentrationofO2(g)forcesreactiontoright,maximisingyieldØ Thereactioniscarriedoutatabout1.5atm.Sincethereisa1.5:1ratioofgasparticles,thereactionis
alsoforcedtotherighttoreducepressure,maximisingyieldØ Theinitialgasstreamatthebeginningofthisstepisat1000°Caftercombustionofsulfur-thisistoo
hightoproduceeffectiveyieldintheexothermicreactionaboveØ Thegasstreamiscooled(heatexchanged,withheatusedtoliquefysulfurinfirststep,whichreduces
heatreleasedfromprocess)toabout550°CØ Atthislowertemperature,thegasstreampassesoverabedofV2O5catalyst,whichproducesa
relativelyrapid70%conversionofSO2toSO3.Ø Thegasstreamisthenfurthercooledto400°Candpassedoverasecondcatalyticbed,producing
overall97%conversionatthelowertemperatureØ TheremaininggasstreamispassedoverafinalbedofV2O5toproducea99.7%conversion.0.3%SO2
releasedisconsideredacceptable.Ø HighpressuresARENOTUSEDasitisnoteconomictousethemindustrially
3.Formationofoleum
Ø TheproducedSO3isreactedwithexistingsulfuricacidtoproduceoleum(athick,oilyliquid)Ø SO3(g)+H2SO4(l)àH2S2O7(l)Ø TheSO3isnotdirectlyreactedwithwater,asthereactionishighlyexothermicandwouldproducea
highlytoxicvapourofsulfuricacid,whichwouldbeincrediblydangeroustoplantworkers.
4.ProductionofH2SO4Ø H2S2O7(l)+H2O(l)à2H2SO4(l)Ø OleumisaddedtowatertoproducetwomolesofsulfuricacidØ Thisresultantacidis98%pure
EnvironmentalIssues
Ø SomeSO2inevitablyescapes,causingacidrainØ Exitinggasescanbepassedthrougha“scrubber”(containingthestronglyoxidisingCaro’sacid,H2SO5)
toconvertexcessSO2tosulfuricacidØ SpillageofacidsintransportandacidraindecreasespHofwaterwaysØ Thermalpollutioninterfereswithreproductivecyclesandmigratorycyclesofaquaticlifeand
increasestherateofweedgrowth.Italsolowerslevelsofdissolvedoxygenandothergases.
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• Describe,usingexamples,thereactionsofsulfuricacidactingasanoxidisingagentandasadehydratingagent• Performfirst-handinvestigationstoobservethereactionsofsulfuricacidactingasanoxidisingagentandasa
dehydratingagentØ DehydratingAgent
• C2H5OH(l)à(withconc. H;SOJ)C2H4(g)+H2O• CuSO4.5H2O(s)àCuSO4(s)+5H2O(l)(Saltgoesfromblueàwhite)• Esterification(H2SO4isusedasacatalyst)• Concentratedsulfuricacidwilldehydratesugar,leavingasolidcolumnofcarbon.Thesteam
producedinthereactioncausesthesolidcarbontoriseup• ThisexperimentmustbedoneinthefumecupboardasthesteamgeneratedwillcontainH2SO4,
whichishighlydangerous.C12H22O11(s)à12C(s)+11H2O(l)(H2SO4onarrow)
Ø OxidisingAgent
1)OxidisesIodide(colourless)toiodine(purple/brown)o Add2gofKIcrystalsintoatesttubeo AddafewdropsofH2SO4(l)totheKIinafumecupboardo Observethepurplegas(I2)o TestforSO2withfilterpapersoakedinacidifiedK2Cr2O7whichturnsfromorangetogreen(Cr3+)
§ Oxidation:2I-àI2+e-§ Reduction:4H++SO4
2-+2e-àSO2+2H2O(l)§ 4H++SO4
2-+2I-àI2+SO2+2H2O(l)• SO2(g)producedwillreduceacidifiedK2Cr2O7toCr3+whichisgreen• 2KI(s)+2H2SO4(l)àI2(g)+K2SO4(aq)+2H2O(l)2)Oxidisescoppermetal
o Sulfuristheoxidisingagentinconcentratedsulfuricacido Cu(s)+2H2SO4(l)àCuSO4(aq)+SO2(g)+2H2O(l)o S(s)+2H2SO4(l)→3SO2(g)+2H2O(l)o Hydrogenistheoxidisingagentindilutesulfuricacido Zn(s)+H2SO4(aq)àZnSO4(aq)+H2(g)
• Describeandexplaintheexothermicnatureofsulfuricacidionisation
H2SO4(l)+H2O(l)àH3O+(aq)+HSO4
-(aq) ΔH=-90kJ/mol
HSO4-(aq)+H2O(l) H3O(aq)+SO4
2-(aq) (35%ionisation)
Ø BondsBroken:O-HbondsinH2SO4Ø BondsFormed:CoordinatecovalentbondbetweenH2O&H+Ø ReasonsforExothermicNature
o FormationofthebondsthatmakeupH3O+releasevastamountsofenergy–morethanwhatisrequiredtobreakthebondthatheldthehydrogeninH2SO4(netlossofenergy)
o Energy:Form>Break(soenergyreleased,henceexothermic)
• IdentifyanddescribesafetyprecautionsthatmustbetakenwhenusinganddilutingconcentratedsulfuricacidØ SafetyIssues
• Ingestion=causeseriousburnsofmouth,etc.• Inhalation=corrosiveandhighlytoxic–causesevereirritationandburns• Skin=causesevereirritation,burns,charringofskin=flushwithwater,removeclothing• Eyes=causesevereburns,eyedamage=flushwithdirectsteamofwater• Ifspilledonbench=evacuate,isolateandneutralise(NaHCO3);weargogglesandclothingatall
times
Ø ToDiluteH2SO4• Slowlyaddasmallofamountofconc.H2SO4toalargeamountofH2Oàwatercanabsorband
dissipateproducedheat(duetolargeheatcapacity)(NEVERADDWATERTOACID,ALWAYSACIDTOWATER)
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• Ifwaterisaddedtosulfuricacid,theheatgeneratedwillturnthewaterintosteam,resultinginamistofsulfuricacidwhichisverydangerous
• Performwhilestirringandcoolinginfumecupboardwithprotectiveclothing/goggles• SpillscanbeneutralisedusingNaHCO3
Ø Precautionsforuse
• Weargloves• Wearsafetyglasses• Worknearasupplyofrunningwater• HaveasupplyforNa2CO3orNaHCO3nearby• Avoiddribblingtheaciddowntheoutsideofthebottleontothelabelwhenpouring• Useadriptray• Forregularuse,storeinglassbottlesnogreaterthan1litreinvolume
• Useavailableevidencetorelatethepropertiesofsulfuricacidtosafetyprecautionsnecessaryforitstransport
andstorageØ Conc.H2SO4=highmolarity(10M+etc.)=nearlyallmoleculesaremolecular(veryfewions)
• Doesnotattackstealoriron–ionscannotdissociatesodoesnotactasoxidant• H2SO4(l)isstoredandtransportedinsteelcontainersasitdoesnotreactwithsteelandthusthe
containerwillnotbreak• Ensurewateriskeptaway(fullyenclosedcontainers)–subsequentdilutioncancausedissociation
ofionsàcorrosionØ DiluteH2SO4=containsfreeH3O+ions=oxidisemetals
• Dilutesulfuricacid,however,hasH+,andwillreactwithsteeltoformironsulfate(FeSO4)• Cannotbestoredinsteelcontainers–useinertglassorplastictoavoidreactions• Smallcontainersstoredinplastictraysincaseofbreakage• Keepawayfromwood(exothermicdehydrationreaction)
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Section4Theindustrialproductionofsodiumhydroxiderequirestheuseofelectrolysis
• ExplainthedifferencebetweengalvaniccellsandelectrolyticcellsintermsofenergyrequirementsGalvanicCell ElectrolyticCell
Ø ChemicaltoElectricalEnergy(throughredoxandmetaldisplacementreactions)
Ø ProducesanelectriccurrentØ SpontaneousreactionØ Anodeis(-)Cathodeis(+)Ø E0ispositive
Ø ElectricaltoChemicalEnergy(throughredoxandmetaldisplacementreactions)
Ø RequiresinputofelectriccurrentØ Non-spontaneousreaction(forced)Ø Anodeis(+)Cathodeis(-)Ø E0isnegative
Ø GalvanicCellsusuallyconsistoftwohalfcellslinkedbyasaltbridgeandexternalcircuitØ ElectrolyticCellsusuallyconsistofonecontainerandasingleelectrolyte,withthecontainerseparatedhalfway
byamembranewhichonlyallowsionstopassthroughNOTE:VoltageofbatteryneedstobegreaterthanvoltageotherwiseproducedfromtheGalvaniccell(i.e.IfEMF=-1.1VthenVofbatteryneedstobe>1.1Vforelectrolyticcelltowork)
Ø Inbothcells,theanodeisoxidisedandthecathodeisreduced(THUSANOX/REDCATAPPLIESTOBOTH)Ø Electronflowisalwaysfromnegativetopositive
• Outlinethestepsintheindustrialproductionofsodiumhydroxidefromsodiumchloridesolutionanddescribethereactionintermsofnetionicandfullformulaeequations
• Distinguishbetweenthethreeelectrolysismethodsusedtoextractsodiumhydroxide:mercuryprocess,diaphragmprocessandmembraneprocessbydescribingeachprocessandanalysingthetechnicalandenvironmentaldifficultiesinvolvedineachprocessØ Electrolysis:Theprocesswherebyanelectricalcurrentisusedtobringaboutanon-spontaneouschemical
reaction(often,butnotalwaysdecomposition)Ø SodiumHydroxideisanextremelycommerciallysignificantalkali.Itisusedto:
o Makeproductsincludingplastics,soapsrayonandtextileso Revitalizingacidsinpetroleumrefiningo Removalofpainto Etchingaluminiumo Dehorningofcattleo Duringtwostepsofthepapermakingprocesso Usedinrelaxerstohelpstraightenhair
Ø Itisproducedbytheelectrolysisofsalt(brine)andwaterØ NaOHisclassifiedasastrongbaseasitundergoescompleteionisationØ ALL3INDUSTRIALPROCESSESBEGINWITHBRINEPURIFICATIONSTEPS.THISISDONEBYPRECIPITATION.
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o CalciumionsareremovedbyaddingsodiumcarbonateCa2+(aq)+CO3
2-(aq)àCaCO3(s)
o MagnesiumionsareremovedbyaddingsodiumhydroxideMg2+(aq)+2OH-
(aq)àMg(OH)2(s)o Ironionsareremovedbythesodiumcarbonateandsodiumhydroxide
Fe2+(aq)+CO32-(aq)àFeCO3(s)
Fe2+(aq)+2OH-(aq)àFe(OH)2(s)
o SulfateionsareremovedbyaddingcalciumchlorideSO4
2-(aq)+Ca2+(aq)àCaSO4(s)
TheMercuryCellØ Uptotheyear2000,thismethodwasusedinNSWtoproduceNaOH
CHEMISTRYØ Themercurycelliscomprisedoftwotanks,connectedbyflowingmercury,whichiscontinuouslypumped
throughaseriesofpipesØ Purifiedconcentratedbrinesolution(30%NaCl)ispumpedintothefirsttankofthecell,wherethe
chlorineanionsareoxidisedatatitaniumanodeformingchlorinegas–thisgasisthenremovedfromthemercurycellandstoredforotherpossibleuses
2Cl-(aq)àCl2(g)+2e-
Ø Thesodiumionsdissolveintheflowingstreamofmercury(thecathode)toformanamalgamNa+(aq)+e-àNa(s)
Ø Theflowingmercurythenflowsintothesecondtank,whichcontainspurifiedwaterØ ThesodiumintheamalgamreactswiththewaterandverypureNaOHandhydrogengasareformed
Na(Hg)+H2O(l)àNaOH(aq)+H2(g)+Hg(l)Ø ThehydrogengasisremovedfromthemercurycellandstoredforotherpossibleusesØ TheNaOHcanthenbetappedoff,andthemercurycanbepumpedbackintothefirsttank
OVERALL:2NaCl(aq)+2H2O(l)à2NaOH(aq)+Cl2(g)+H2(g)
CONSIDERATIONS
Ø Attheanode,chlorinegasisevolved;itisacorrosive,powerfuloxidisingagent.HenceanINERTanodeoftitaniumplatesisused.
Ø Mercuryisusedasthecathodebecause:o Itisaliquid,andcanbepumpedaroundasystemo Itreadilyformsalloys(amalgams)withmanymetals(e.g.sodium)o Whenusingamercurycathode,sodiumions,notwatermolecules,arepreferentiallyreduced,as
opposedtousingothercathodesØ Thetitaniumplatesareheldveryclosetothemercurysurfacetoallowforverylargecurrentflows;this
promoteselectrolysis(3to4voltsareused,butwithtensofthousandsofamperesofcurrent)Ø Therawmaterials(brineandwater)mustbepurifiedbeforeuseØ Thedepletedbrinemustbecontinuouslyreplacedwithfreshbrine
ENVIRONMENTALIMPACTSØ Althoughthesystemappearstobeclosed,smallmercurylossestotheenvironmentalareinevitable;100-
200gofmercuryisreleasedintotheenvironment(e.g.oceans)foreverytonneofNaOHproduced.Ø MercurycompoundscanbepassedontohumansbybiomagnificationØ Thisisofagreatconcern;mercuryisaheavy-metal,andaneurotoxinØ ThismethodisnotusedinNSWanymoreduetomercurytoxicityconcerns
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TheDiaphragmProcessCHEMISTRY
Ø ThecellconsistsofatitaniumanodeandsteelcathodeØ HassmallerelectricalrequirementscomparedtothemercurycellØ Purifiedsaturatedbrineisenteredintothecell,andthechlorineanionsareoxidisedattheanodetoform
chlorinegas.Thisgasisthensentoutofthecellandcollectedforotheruses.2Cl-(aq)àCl2(g)+2e-
Ø Thesodiumions,however,migratetothecathodebypassingthroughtheasbestosdiaphragmØ Purifiedwaterisenteredintothecellonthesideofthecathode,whereitisreducedtoformhydrogen
gasandhydroxideions.Thishydrogengasisalsosentoutofthecellandstoredforotheruses.2H2O(l)+2e-àH2(g)+2OH-
(aq)
Ø TheremainingNa+andOH-ionsinsolutionmakeuptheNaOH,whichisthensentoutofthecellOVERALL:2NaCl(aq)+2H2O(l)à2NaOH(aq)+Cl2(g)+H2(g)
CONSIDERATIONSØ Again,chlorinegasisevolvedattheanode,andhenceasuitablematerialmustbeused-mustbe
resistanttochemicalattackØ Chlorinemustbeseparatedfromthehydrogen,astheyreactvigorouslytoformcorrosiveHClgasØ Alargesystemofmanysmallcellsisemployed,insteadofonelargecellØ 3.5-5voltsused,withtensofthousandsofamperesofcurrent.Ø Theasbestosissupposedtoactasabarrierforthemovementofions,Ø allowingonlythemovementofNa+ionsintothesteelmesh,andpreventingthemovementofhydroxide
andchlorideions,however,someunwantedionmovementoccurs:o SmallamountsofCl−ionscrosstheasbestos,andreactwiththeNa+(formingsalt,NaCl,whichis
animpurityinthefinalproduct)andalsoreactwiththeOH−(formingthechloriteion,ClO−,astrongoxidant).
o SmallamountsofOH−ionsalsomovebackintothebrine,formingNaOHandClO−inthedepletedbrine.
Ø DuetothenatureofthediaphragmthefinalproductalwayscontainsNaCl,whichisonlypartiallyremovedbycrystallisation.
ENVIRONMENTALIMPACTS
Ø Asbestosfibresarequitedangerous,andinhalationofthesefibrescancausearangeoflungdiseases,suchasasbestosis
Ø Thedepletedbrinecannotbereleasedimmediatelybackintotheenvironment,duetothepresenceofsmallquantitiesofbasicNaOH,andoxidisingClO−ions,whichhavetoberemoved
Ø ClO-ionsharmaquaticorganisms,anddisruptthefoodchain
TheMembraneProcessCHEMISTRY
Ø ThecellconsistsofatitaniumanodeandsteelcathodeØ Asinglecellisdividedintotwohalvesbyanion-exchangepolymermembranemadeof
polytetrafluoroethylene(Teflon).Ø Thismembraneisselectivelypermeable,andallowsthediffusionofwaterandsodiumionsONLY.
Chlorideandhydroxideionscannotpass.(UNLIKEINTHEDIAPHRAGMPROCESS)Ø Inthefirsthalf,brineispumpedin,andwaterinthesecondhalf.
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Ø Onthetitaniumanode,chlorineisproduced,andonthenickelcathode,hydrogenandhydroxideionsareproduced.
o 2Cl-(aq)àCl2(g)+2e-o 2H2O(l)+2e-àH2(g)+2OH-
(aq)o Overallequationalsoidenticaltothatofthediaphragmprocess
Ø Thesodiumionspassthroughthemembrane,andcombinewiththehydroxideions,formingverypureNaOH,whichiscontinuouslyremoved.
Ø Thestructureofthecellisidenticaltothatofthediaphragmprocess,onlythattheasbestosdiaphragmisreplacedwiththepolytetrafluoroethylenemembrane.CONSIDERATIONS
Ø Thiscellsolvestheproblemsofboththemercuryanddiaphragmcellso Therearenotoxicmaterialsused,suchasmercuryorasbestos;averyinertpolymerisusedas
themembrane.o VerypureNaOHisformed,aswiththemercurycell,asthereisnocontaminationoftheproduct
withchlorideions,andthedepletedbrineisjustNaClsolution.o Titaniumisusedasanodeasitwithstandschlorineattack.
Ø Thepolymerhasmanyusefulproperties,suchasitsselectivepermeability,aswellasitsabilitytoresistchemicalattackinastronglybasicsolution
Ø Justaswiththediaphragmcell,alargesystemofmanysmallcellsisemployed,insteadofonelargecello 3.5-5voltsused,withtensofthousandsofamperesofcurrent
ENVIRONMENTALIMPACTSØ Becauseofthenatureofthemembrane,andtheinertelectrodesused,thereareveryfewenvironmental
issuesassociatedwiththiscellØ IssuesincludetheleakageofchlorinegasandNaOHintotheenvironmentØ Excessbrinemustnotbedepositedintowaterways,asthiswillincreasethesalinityandupsetthenatural
balanceØ Ascomparedtothetwoothercells,thiscellproducesveryhighqualityNaOHwithalmostno
environmentalorhealthissuesandconcerns
NON-SPECIFICTECHNICALITIESThelocationoftheplantisatechnicalconsiderationthatmustbeinaccordancewiththeavailabilityofthefollowing:
• Cheapelectricity(asthisisTHEmajorcost)• Theremustbecheapbrineaswellasfreshwatersources• Alocalworkforcewillingtoworkatsuitableexpenditure• Itmustbebuiltawayfromurbanandresidentialareas,duetothelargeamountsofnoiseandheat
thattheplantsemit• Suitablewastedisposalmustbeavailable
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• Identify,planandperformafirsthandinvestigationtoidentifytheproductsoftheelectrolysisofanaqueoussolutionofsodiumchlorideØ Aim:ToinvestigatethechemistryinvolvedinelectrolysingdifferentaqueoussolutionsofsodiumchlorideØ Safety:Wearsafetyglassesandprotectiveclothing.Makesurepowersourceisturnedoffwhenconnecting
anddisconnectingelectrodes.Chlorinegasispoisonoussoworkinafumecupboardandavoidbreathingthevapour.
Ø Equipmentrequired:• HofmannVoltameter• RetortStandandClamp• DCPowerSource(0-12V)• 2Electricalleadswithalligatorclips
• GraphiteORTitaniumelectrodes• 50mlsaturatedsodiumchloridesolution• 5oml0.1mol/Lsodiumchloridesolution• Universalindicator
Ø Procedure(A–Electrolysisofsaturatedsodiumchloridesolutionwithinertelectrodes)1. FilltheHofmannVoltameterwithsodiumchloridesolution.2. Addafewdropsphenolphthaleinindicatortothevoltameter.3. Connecttheelectrodes(graphiteORtitanium)totheDCpowersupplyusingtheelectricalleads
provided.Ensuretheelectrodesareabouthalfcoveredwithsolution.4. Setthepowersupplyto6-8Vandswitchonthepower.Youmayneedtoadjustthepoweroutput.
Electrolysethesolutionfor2-3minutes.5. Observeandrecordanychanges,suchascolouroftheindicatororevolutionofgasateach
electrode.6. Switchoffthepowersupply.7. Holdastripofmoistredlitmuspaperovertheanodecompartmentandopenthevalve.(Thepaper
shouldbebleachedwhitebythechlorinegas)8. Collectthegasatthecathodeinatesttubeandperformthepoptest.(Thegasishydrogen)9. Determinetheanionproducedatthecathodeofthevoltameter(phenolphthaleinwillbepurpledue
totheproductionofhydroxideions).10. Recordallobservationsinaresultstable.
Ø Procedure(B–Electrolysisof0.1mol/Lsodiumchloridesolution)1. Repeatsteps1-7asforpartAusingthedilutesolutionofsodiumchloride
(Insteadoftestingforchlorinegas,testforoxygengasbycollectinginatesttubeandcheckingifthegasisabletorelightaglowingsplint)
Ø Results Observations
Anode CathodePartA ChlorineGas
(BubblingatElectrode)(BleachesmoistredLitmusPaper)
HydrogenGas(BasicpH)(BubblingatElectrode)(PositivetoPopTest)
PartB OxygenGas(AcidicpH)(BubblingatElectrode)
(Reignitesanextinguishedsplint)
HydrogenGas(BasicpH)(BubblingatElectrode)(PositivetoPopTest)
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• AnalyseinformationfromsecondarysourcestopredictandexplainthedifferentproductsoftheelectrolysisofaqueousandmoltensodiumchlorideØ DiluteNaCl(1mol/L)–Na,Cl,H2O
o ANODE:2H2O(l)àO2(g)+4H+(aq)+4e- EOX=-1.23V
o CATHODE:2H2O(l)+2e-àH2(g)+2OH-(aq) ERED=0.83V
o ECELL=-2.06V(NONSPONTANEOUS)v Gasbubblesattheanodewillrekindleaglowingsplitv Gasbubblesatthecathodewilltestpositivetothe‘poptest’v Phenolphthaleinwillturnpinkatthecathodeduetothehydroxideproduced
Ø ConcentratedNaCl(5mol/L)–Na,Cl,H2Oo ANODE:2Cl-(aq)àCl2(g)+2e-o CATHODE:2H2O(l)+2e-àH2(g)+2OH-
(aq)o As[Cl-]ismorethan1mol/Litwillgetoxidisedinsteadofwater.Thedifferenceinvoltageisapprox.
0.1Vo Na+willnotgetreducedatthecathodeasthedifferenceinvoltageisapprox.2V,morethanthatof
waterv Chlorinegasattheanodev Moistredlitmuspaperwillbebleachedwhiteaschorinegasisableachingagentv Hydrogengasandhydroxideatthecathode–sametestsasforthediluteNaCl
Ø MoltenNaCl–Na,Clo ANODE:2Cl-(l)àCl2(g)+2e-o Cathode:Na+(l)+e-àNa(l)o SilveryglobuleswhenaddedtowaterwillreactvigorouslyproducinghydrogengasandNaOH
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Section5Saponificationisanimportantorganicindustrialprocess
• DescribesaponificationastheconversioninbasicsolutionoffatsandoilstoglycerolandsaltsoffattyacidsØ Saponificationistheconversionoffatsandoilstosoapandglycerol
byreactingthefatsandoilswithconcentratedNaOHorKOH(theconversion,inbasicsolution,offatsandoilsintoglycerolandthesaltsoffattyacids)
Ø FatsandoilsaretriglyceridesØ Thenumberofhydrogenatomscanchangeasthelongcarbonchain
canhavedoublebonds(mainlyinoils)orcanbesaturated(mainlyinfats)
Ø Soapisthesodiumsaltoffattyacids
E.G.GlycerylTripalmitate+SodiumHydroxideàGlycerol+SodiumPalmitate
Ø Thesodiumhydroxide(NaOH)splitsthetriglyceride(hydrolysis)alongtheesterbond(–COOC–)Ø The3hydroxylgroups(OH-)attachtotheglyceryl,formingglycerolØ Thefattyacids(carboxylateions)reactwiththeNa+ions,formingthe3“saltsoffattyacids”(inthiscase
sodiumpalmitate)
• Glycerolo Glycerolisatri-alcoholcompoundderivedfrompropane,itcontainsanalcohol
group(ahydroxyl)oneverycarbono UsingIUPACnomenclature,anothernameforglycerolispropane-1,2,3-triolo Widelyusedinthefoodindustryasasweetenerandhumectant(reducesthe
lossofmoisturebyforminghydrogenbondswithwater)andinpharmaceuticalformulations
o UsedinIceCream,skinlotions,mouthwashes,coughmedicines,etc.
• FattyAcidso Fattyacidsarelongcarboxylicacidsthatoccurinfatsandoils.o Therearemanytypesoffattyacids,whichvaryinthenumberofcarbons(12-18)aswellasinthe
degreeofsaturation(doublebonds).o LauricAcid(12-C)
§ CH3-(CH2)10-COOHo LinoleicAcid(18-C)
§ CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH
• FatsandOilso OrganiccompoundsknownasTriglycerides
§ Fatsaresolidandoilsareliquidatroomtemperature.o Atriglycerideisacompoundinwhichall3hydroxylgroupsofaglycerolmoleculehavebeen
ESTERIFIEDwithcarboxylgroupsfromthreefattyacidchains,waterisaby-product.o Threeesterbondsareformed;triglyceridesaretri-esters.o Thenaturalformationoffatsandoilsisanesterificationreaction.
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• Saponification
o Reversaloftheprocessthatformsfatsandoils.o Thereactionbetweenanesterandhydroxideiontoformanalcoholandacarboxylateanion.o Hydrolysisofanesterunderalkalineconditions.o Conversion,inbasicsolution,offatsandoilsintoglycerolandthesaltsoffattyacids.o Saltsoffattyacids,suchassodiumstearate,areSOAPS.o Saponificationisthechemicalprocessofproducingsoaps.
o Sodiumhydroxide(NaOH)splitsthetriglyceride(hydrolysis)alongtheesterbond(-COOC-)
§ The3hydroxylgroups(OH-)attachtotheglycerylformingglycerol.o Thefattyacids(carboxylateions)reactwiththeNa+ions,formingthe3saltsoffattyacids–
sodiumstearate.
• Describetheconditionsunderwhichsaponificationcanbeperformedintheschoollaboratoryandcomparethesewithindustrialpreparationofsoap
• Performafirst-handinvestigationtocarryoutsaponificationandtesttheproductØ Method
1. Mix20mLofoliveoilwith5mLof4mol/LNaOHinabeaker(withboilingchips)2. Gentlyboilonahotplatewithconstantstirring3. AddmoreNaOHuntilsolidparticlesseparate4. Coolandadd10mlofsaturatedNaClsolution(‘saltingout’,asNaClismoresolubleinwaterthan
thesodiumsaltoffattyacids,thesoapwillprecipitate)5. Thesoapisfilteredandwashedwithwatertoremovethesurfacealkali(whichhiscaustic)6. Perfumeandcolourmaybeadded,andthesoapismouldedintoshape
Ø RiskAssessmentIdentify Assess Control
ConcentratedNaOH Caustic–willdissolveproteins Wearsafetyglasses,gloves,alongsleevedlabcoatandenclosedshoes
HotOil Causesburnstotheskinwhenhot+Flammable
UseofahotplateasopposedtoaBunsenflameConstantstirringofmixturepreventsthespittingofhotoil
Ø Comparisonof‘SchoolMethod’with‘IndustrialMethod’School Industry
Usedvegetableoil Choppedupanimalfat4mol/LNaOH 30%w/vNaOHBoil HeatuntilallfatisdissolvedMixwithNaCl NearlysaturatedbrineSoapisfiltered ScoopedoutfromthetopThefiltrateisdiscarded Glycerolseparatedfromtheaqueouslayers.
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• AccountforthecleaningactionofsoapbydescribingitsstructureØ Whenaddedtowater,thesodiumsaltofafattyacid
dissociatestoproduceasodiumcationandanegativelychargedfattyacidanion
Ø Theheadofthesoapion(COO-)ispolar,andthushydrophilic(solubleinwater)
Ø Thetailofthesoapisnonpolar(hydrocarbonchain)andisthusinsolubleinwater(hydrophobic),butsolubleinfatsandoils
Ø Asurfactant(surfaceactingagent)isachemical“wetting-agent”thatlowerstheinterfacialtensionbetweentwoliquids,andhence,allowsthemtomix
Ø SOAPisasurfactant;itallowspolarwaterandnon-polargrease/dirttomixØ Becauseofthis,thesoapionwillformmicellesinwater,wherethepolarheadformshydrogenbonds
withthewater,andthetaildissolvesinoilandgreasedropletsduetoweakdispersionforcesØ Throughtheprocessofagitation,themicellesbecomesuspendedinthewater,forminganemulsionØ Thegreaseandoilcannowbewashedaway,leavingacleansurface
Ø Soapcleansandremovesgrease/dirtfromobjectsbythefollowingsteps:
1. Adirtyobjectisplacedinsoapywater.2. Thesoapimmediatelybeginstoattachtothegrease(thehydrophobictailspenetratethegrease
BUTthehydrophilicheadremainsinthewater)3. Thegreaseisliftedofftheobjectasthesoapsurroundsthegrease.4. Thegreaseiscompletelyliftedofftheobject,andissurroundedbysoap.
Ø Thegreasemoleculeiscompletelyencasedwithinasheathofsoapmoleculeswiththeirhydrophilicheadsincontactwithwater,whilethehydrophobictailscontainthegreasemolecule;thissheathallowsittodissolveinwater.
Ø Asthemixtureisagitated,moregreaseisliftedofthesurfaceofthedirtyobject,andmoregrease/soapparticlesareformed.
Ø Thegrease/soapparticlesarenegativelycharged(duetothenegativeheadofthesoap),andhencetheyrepeleachother,preventingthegreasefromclumpingbacktogether.
Ø Thesewatersolubleparticlesarethensimplywashedoffwithwater:
• Explainthatsoap,waterandoiltogetherformanemulsionwiththesoapactingasanemulsifierØ Anemulsionisastablemixtureof2immiscibleliquids,withtinydropletsofoneliquidevenlydispersed
throughouttheother.Ø Normally,mixturesof2immiscibleliquidsrapidlyseparate(suchasoilandwater);emulsionsare
stabilisedbytheactionofEMULSIFIERS:o Emulsifiersarethesameassurfactants.o Theyreducetheinterfacialtensiontoallowimmiscibleliquidstomix
Ø Intheexampleofawater/oilemulsion,theemulsifierusedissoap;henceasoapyoil/watermixtureconsistsofoilparticlesevenlydispersedthroughoutthewater.
Ø Inthiscase,thereismorewaterthanoil,andhencetheoilisdispersedthroughoutthewater;iftherewasmoreoilthanwater,thewaterwouldbedispersedthroughouttheoil,asisthecasewithbutter
Ø Thenon-polartailsofsoapmoleculesgatheraroundoildroplets,sothatthenegativelychargepolarendsfaceoutwards.
Ø Thiscreatesanegativechargeonthedropletofoilwhichrepelsothernegativelychargessoapandoildroplets,preventingtheformationoflargeclumpsofoil.
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Ø Thisalsoallowswatertointeractwiththeoildroplets.Thusoildropletsaredistributedthroughthewater.
• Distinguishbetweensoapsandsyntheticdetergentsintermsofthestructureofthemolecule,chemical
compositionandeffectinhardwater• Distinguishbetweenanionic,cationicandnon-ionicsyntheticdetergentsintermsofchemicalcompositionand
usesTypeofSurfactant Structure Chemical
CompositionEffectinHardWater
Soapuses Howtheywork
Soap(SodiumStereate)NaCH3(CH2)16COO
C,H,O,Na+ Ca2+/Mg2+formsascumwithfattyacid–doesnotwork.
PersonalHygiene Formsmicellesinwater.Oildissolvesinlonghydrophobictailandanionicheaddissolvesinwater.
Anionic–AlkylBenzeneSulfanoates(3oxygens)
C,H,O,S,Na+,K+ DoesnotprecipitatewithCa2+,Mg2+butdoesnotworkwellinhardwater.
Laundryliquidsandshampoos.Generatelargeamountsoffoam.
Similartosoap,anionicheaddissolvesinwatermakinghydrogenbondsandion-dipoleinteractives.
AlkylSulfanoates(4oxygens)
Non-ionicEthoxylatesmolecules(Noions)
C,H,O WorkswellasMg2+,Ca2+donotreact
Usedinpaintsandfront–loadingwashingmachines.Cosmeticsandpesticides.Wherefoamislessdesirable.
Ethoxygroupsformhydrogenbondswithsurroundingwatermolecules.
Cationic
C,H,N,Cl-
Quartenaryammoniumderivativeswhere3Hhavebeenreplacedwithmethylgroupsandoneisreplacedbyhydrocarbonchain.
WorkswellasCa2+,Mg2+donotreactwithcation.
Fabricsoftenersandhairconditioners.Positiveheadsattachtothenegativehairscales,leavingsmoothfeelandshinypart.
Negativechargeonwetclothesandhairattractthepositivehead.Thefabricorhairiscoatedwithhydrocarbonchainàreducesstatic.
• Gather,processandpresentinformationfromsecondarysourcestoidentifyarangeoffatsandoilsusedforsoap-
makingØ Tallow:Processedanimal-fats(usuallywaste).Itproducescommonsoap.Ø CoconutOil:Pressedoutofdriedcoconuts(copra);itisarelativelypureoil.Thisproducesahardsoap
thatlathersverywell.Ø SheaButter:Thefatderivedfromthefruit(ornut)ortheSheatree.Itproducesasoftsoapthatisvery
moisturisingandgentleonskin.Ø Animalfatsuchascattleandsheep.Ø Vegetableoilssuchascoconut,olive,sunflower.Ø Vegetablefatssuchascocoabutter.
• Performafirst-handinvestigationtogatherinformationanddescribethepropertiesofanamedemulsionand
relatethesepropertiestoitsusesØ NaturalEmulsifiers(surfactants)
o Caseineinmilkkeepsoildropletsdispersedinwater.o Lechitinfromeggyolkkeepsoil/wateremulsioninmayonnaise.
Ø NamedEmulsion:Buttero Smallamountofwaterisdispersedinoil.o Duetothefatinthebutteritcanbespreadonthebreadwithoutthebreadabsorbingthewater.o Duetothewaterinthebutter,watersolublesubstancessuchassaltandfooddyecanbemixed.
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Ø Mayonnaiseo Mayonnaiseisanemulsionofvegetableoilandeggyolks,withtheemulsifierbeingthelecithin
foundnaturallyintheeggyolk.o Otheradditionsmaybemadeforflavour,suchasvinegar,mustardofsalt,butthebasic
compositionofmayonnaiseisoilandeggyolks.o Mayonnaiseismadebyslowlyaddingoiltoaneggyolk,whilewhiskingvigorouslytodispersethe
oil;thelecithinstabilisesthemixture.Ø PropertiesinRelationtoUses:
o MayonnaiseisaverySTABLEemulsion,duetothestrongemulsifyingpropertiesoflecithin.Itdoesnotseparateintoitscomponentliquidsevenwhenstoredforlongperiodsoftime.
o Thispropertyisusefulasitisafoodproduct;itneedstostayinanediblecondition,instorage,forrelativelylongperiodsoftime.
o Mayonnaisealsohasthepropertyofhavingacreamy‘mouth-feel’,andnotfeelingoily.Mostpeoplefindthesensationofeatingpureoilunpleasant,butfindthecreamytasteofmayonnaiseenjoyable.However,mayonnaiseisactuallyonaverage75%oil.Thepropertyoftheemulsionashavingacreamytextureaddstoitsuseasafood.
• Performafirst-handinvestigationtodemonstratetheeffectofsoapasanemulsifierMethod
1. Add2mLofwaterand2mLofoilintotwotesttubes.2. Add2gofsoapintoonetesttube.3. Mixboththetesttubesuntiltheoilisdispersedinwatergivinga
homogenoussolution.4. Leavefor10minutesundisturbedandobserve.
ResultsØ Thesolutionwithoutthesoapseparatedintooilandwater.The
solutionwiththesoapstaysdispersed.
• Solveproblemsanduseavailableevidencetodiscuss,usingexamples,theenvironmentalimpactsoftheuseofsoapsanddetergents
Ø Biodegradability:o Soaphasverylittleenvironmentalimpactbecauseitisveryeasilybrokendownintocarbon
dioxideandwaterduetotheactionofbacteria.o Therearetwotypesofanionicdetergents:detergentswithbranchedchains,anddetergentswith
unbranched(linear)chains:§ Branched-chainanionicdetergentswerethefirstdetergentsformed.Theywerenot
biodegradable,andledtoconsiderableenvironmentalproblems:• Detergentbuiltupinwaterways,andriversanddamswereconstantlycovered
inlayersoffoam• Itwasaestheticallyandenvironmentallyunwanted• Thefoamreducedsunlightenteringthewater,affectingthephotosynthesisof
waterplants.Thisledtoadropindissolvedoxygenlevels.§ Thelineardetergentswerethencreated;thesearemuchmorebiodegradablethanthe
brancheddetergentsandsolvedthefoamproblem.
INDUSTRIALCHEMISTRYNOTES–ROHANBARAR2016
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Ø ExcessLevelsofPhosphates:o Soapsdonotcontainanyphosphateso AnionicdetergentsareaffectedslightlybythepresenceofMg2+andCa2+ionsinhard-watero Substancescalled‘builders’areaddedtodetergentstoincreasetheirefficiencyo Builders(suchassodiumtripolyphosphate:Na5P3O10)reactwiththeionsinhard-water,softening
thewater.Buildersalsoincreasethealkalinityofthewater,whichincreasesthedetergentscleaningpower.
o However,theincreasinglevelofphosphatesinwaterwaysasaresultofphosphatebuildersisamajorenvironmentalproblem.
§ Excessphosphatesinwaterwaysleadtoeutrophication,whichsubsequentlyleadtoalgalblooms
§ Asaresultofthealgalbloom,thebiologicaloxygendemandofthewaterwaywillincrease,leadingtoasubsequentdecreaseindissolvedoxygen
§ Thisdecreaseindissolvedoxygencausesstresstoaquaticlife,asthereisnolongersufficientoxygeninthewatertoadequatelysupporttheseorganisms
§ Thealgaecoverthesurfaceofthewaterway,preventinglightfromenteringintothewaterway.Thispreventsaquaticplantsfromphotosynthesising,causingfurtherdamagetoorganismswithinthewaterway.
o Thiscausesseveredegradationofwaterquality,thepromotionofanaerobicconditionsandthedisturbanceofanaturalecosystem
Ø BiocidalEffectsofCationicDetergentso Cationicdetergentshavemildbiocidalproperties,astheydisruptthecellularprocessesin
bacterialcellso Thus,theirpresenceinwastewaterandseweragecancausethebacteriawhichbreaksdown
wastetobekilled.o Thisoccursathigherconcentrationsonly;lowerconcentrationsofcationicdetergentsdon’t
harmthebacteriawhichbreakthemdown.o Athigherconcentrations,thesebiocidalpropertiescanstartharminglargerorganismsin
waterways.Ø Issuesrelatingtonon-ionicdetergents
o Whendisposedofintowaterways,transformedtoalkylphenolsthroughbiologicaldegradation.Alkylphenolsaretoxicandhavehormone-likeeffectsonmarineandfreshwaterlife.
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Section6TheSolvayprocesshasbeeninusesincethe1860s
• IdentifytherawmaterialsusedintheSolvayprocessandnametheproductsØ Rawmaterialsaresodiumchloride(NaCl-brine),ammonia(NH3)andcalciumcarbonate(CaCO3-limestone)Ø Productsaresodiumcarbonate(Na2CO3)andcalciumchloride(CaCl2-waste)
• Describetheusesofsodiumcarbonate
1. Glassmaking:Na2CO3andsandareusedtomakesodaglass,whichcanbeeasilymoulded2. MakingofsoapsanddetergentsasareplacementforNaOH3. Commonbasefortheneutralisationofacidicspills4. Usedinthesofteningofhardwater,removescalciumandmagnesiumfromwaterascarbonates5. Usedinthemanufacturingofpapertoseparatecellulosefromlignin6. UsedinthemanufactureofNaHCO3bakingsoda7. Usedtoremovesulfurdioxidefromwastegassesinpowerstations
• Identify,givenaflowchart,thesequenceofstepsusedintheSolvayprocessanddescribethechemistryinvolved
inbrinepurification,hydrogencarbonateformation,formationofsodiumcarbonateandammoniarecovery
OVERALLSOLVAYEQUATION:2NaCl(aq)+CaCO3(s)àNa2CO3(s)+CaCl2(aq)
ReactionsSummary:• LimeKiln:CaCO3(s)à(heat)CaO(s)+CO2(g)• Carbonator:CO2(g)+NaCl(aq)+NH3(aq)+H2O(l)àNaHCO3(s)+NH4Cl(aq)• Converter:2NaHCO3(s)à(heatat300°C)Na2CO3(s)+H2O(g)+CO2(g)• Slaker:CaO(s)+H2O(l)àCa(OH)2(aq)• AmmoniaRecoveryUnit:Ca(OH)2(aq)+2NH4Cl(aq)àCaCl2(aq)+2NH3(g)+2H2O(l)
Ø Stages1.BrinePurification(SAMEASPURIFICATIONUSEDINPRODUCTIONOFNaOH)
• Brineisobtainedfromsaltwater(underground),rocksaltdepositsandfromseawater• Thesesourcesoftencontainimpurities,suchasCa,Mg,Feandsmallamountsofheavymetalso Na2CO3isusedtoprecipitateoutcalciumo NaOHisusedtoprecipitateoutmagnesium,ironandtheotherheavymetalso Alltheprecipitatedmetalscanthenbefilteredfromthebrine
Ca2+(aq)+CO32-(aq)àCaCO3(s)
Mg2+(aq)+2OH-(aq)àMg(OH)2(s)
Fe3+(aq)+3OH-(aq)àFe(OH)3(s)
2.DecompositionofCaCO3
• CaCO3isneededintheSolvayprocessinordertoproduceCO2(g)forthecarbonatorCaCO3(s)à(heat)CaO(s)+CO2(g)
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3.HydrogenCarbonateFormationCO2(g)+H2O(l) H2CO3(aq)
H2CO3(aq)+NH3(aq) NH4+(aq)+HCO3
-(aq)
HCO3-(aq)+Na+(aq) NaHCO3(s)
OVERALL:CO2(g)+NaCl(aq)+NH3(aq)+H2O(l)à(at0°C)NaHCO3(s)+NH4Cl(aq)• Whenthisreactionisperformedatlowertemperatures(0°C)thenormallysolubleNaHCO3instead
formsasolidwhichcanbefilteredfromNH4Cl(aq)• NH3willpivottheformationofHCO3
-(asH2CO3isaweakacidandwithalowdegreeofionisationwithoutammonia)
H2CO3(aq)+H2O(l) HCO3-(aq)+H3O+
(aq)(Thisequilibriumliesheavilytowardtheleft,henceusingammoniaisadvantageous)
4.FormationofSodiumCarbonate
• ThesolidNaHCO3isthenfilteredoffandheadedinaconverter2NaHCO3(s)à(heatat300°C)Na2CO3(s)+H2O(g)+CO2(g)
5.AmmoniaRecovery
• Calciumhydroxideisproducedintheslaker,wherecalciumoxidefromthelimekilnisreactedwithwater
• Thiscalciumhydroxideisreactedwithammoniumchloridetoproduceammoniagas,whichisthensenttothecarbonatorwhereitcantakepartinthereactiononceagain
CaCO3(s)à(heat)CaO(s)+CO2(g)
CaO(s)+H2O(l)àCa(OH)2(aq)Ca(OH)2(aq)+2NH4Cl(aq)àCaCl2(aq)+2NH3(g)+2H2O(l)
• DiscussenvironmentalissuesassociatedwiththeSolvayprocessandexplainhowtheseissuesareaddressed
Ø DisposalofwasteCaCl2• Ifcalciumchlorideisdisposeddirectlyintotheocean,itwillincrease[Cl-]andTDS,displacingdissolved
oxygenandcarbondioxidegas(hencewillcausestresstoaquaticlife)• Ifcalciumchlorideisburiedunderground,itmaybeleachedintosurroundingsoil,toxifyingit• Solutions:
o Reusethecalciumchlorideasadryingagentoradditiveforconcreteandbrickso Dilutethecalciumchloridebeforeitisdischargedintotheoceano Evaporatethecalciumchloridetodrynessandburyinspecialisedburialsites
Ø AmmoniaLoss• Ammoniaisatoxicairpollutant• Solutions:
o Carefullymonitorandmanageammoniaconcentrationsintheair.Usespecialisedequipmenttomonitorammonialeakage.
Ø ThermalPollution• Wasteheatcancausethermalpollution,whichresultsinreducedamountsofcarbondioxideandoxygenin
waterways,causingstresstoaquaticlifeanddisruptingthemigratorycyclesoffish• Solutions:
o Ifnearocean,dilutewithcoldwateranddischarge.Ifinland,usecoolingpools.Ø Mining
• Miningofbrineandcalciumcarbonatecancauseearthsubsidence,destructionofhabitatsandthereleaseoftoxicfumes,particulatesanddustintotheatmosphere(causingpollutionandrespiratorydifficulties)
• Solutions:o Backfillingminedareas,usingdustscrubberstoreducetheamountofairpollutantsreleased
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• Performafirst-handinvestigationtoassessriskfactorsandthencarryoutachemicalstepinvolvedintheSolvayprocess,identifyinganydifficultiesassociatedwiththelaboratorymodellingofthestepØ Thedecompositionofsodiumhydrogencarbonate(NaHCO3)that
takesplaceintheconverterØ Results
• Carbondioxidegasproducedcauseslimewatertobubbleandturnmilky
Ø Difficultiesincarryingouttheexperiment• Iftheflameisremoved,thelimewateris‘suckedback’through
thedeliverytubecreatingbothsteamandpressureàCausesglassequipmenttocrackorbreak.Thickpyrexglasstesttubesarethereforeused,andlimewaterisremovedbeforeremovingtheBunsenburner.
• Processinformationtosolveproblemsandquantitativelyanalysetherelativequantitiesofreactantsandproducts
ineachstepoftheprocess(mole,concentration,volume,massyieldproblems,self-explanatory)
• UseavailableevidencetodeterminethecriteriausedtolocateachemicalindustryusingtheSolvayprocessasanexampleØ AvailabilityofRawMaterials
• Theplantmustbelocatednearaminingarea(limestone)ornearthesea(brine).Ideally,theplantshouldalsobelocatedneartransportlinestoallowforeffectiveimportandexportlogistics.
Ø AvailabilityofEnergy&Labour• Theplantshouldbelocatednearapowerdistributionstation,asitischeapertouseanexistingpower
distribution• Theplantshouldbelocatednearapopulationcentretoallowforeasytransportforworkersand
employeesØ LocationofMarkets
• Ideally,theplantshouldbelocatednearapopulationandinproximitytootherindustries(e.g.glassfactory)
• TheplantcouldalsobelocatedneartheseatoallowforseatradeØ DisposalofWaste
• Forthedisposalofcalciumchloride,theplantshouldbelocatednearthesea• Topreventextensivethermalpollution,theplantshouldalsobelocatednearthesea
Ø AmmoniaLeakage• Theplantisbestlocatedawayfrompopulationsduetothetoxicityofammonia
Ø OVERALLTHEPLANTSHOULDBELOCATED:o Outsidethepopulationcentre,butnotinaremoteareaeither(ontheoutskirts)o Neartheseaforasupplyofbrine,awaytodischargewasteandtoavoidthermalpollutiono Neartransportlinesforeffectiveimportandexportlogistics