chemical monitoring and management notes distro copy

CHEMICALMONITORINGANDMANAGEMENTNOTES–ROHANBARAR2016

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ChemicalMonitoringandManagementNotesSection1Muchoftheworkofchemistsinvolvesmonitoringthereactantsandproductsofreactionsandmanagingreactionconditions

• Outlinetheroleofachemistemployedinanamedindustryorenterprise,identifyingthebranchofchemistryundertakenbythechemistandexplainingachemicalprinciplethatthechemistuses

Ø Name:BurhanGemikonakliØ PlaceofWork:Qenos,BotanyNSWØ BranchofChemistry:AnalyticalChemistryØ TypeofManufacture:

• EtheneàEthane(C2H6àC2H4+H2)(cracking)• EthaneàPolyethylene(nC2H4à(C2H4)n)

Ø JobDescription1. Todeterminethenature(qualitative)andamount(quantitative)ofanyimpuritiesintheethene

andpolyethene2. Tomonitorandanalyseproductionwastebeforedischarging3. Toadjustreactionconditionstomaximiseyieldinthecrackingfurnace

Ø ChemicalPrinciple• ManyindustriesuseGLC(GasLiquidChromatography)orGSC(GasSolidChromatography)for

analyticalpurposes.Theseparationisbasedonthesolubilityofthecompoundinthestationaryphase.

• Ifthestationaryphaseispolarthenthepolarsubstancesinthesampleinjectionwillcomeoutlast,as

theyaremostsoluble.• Thepositionofthepeaksonthegraphidentifieswhichcompoundsarepresentinthesample,while

theheightofthepeaksindicatestheamount.• Forexample,ifamixturecontainingasmallamountofethanol,amoderateamountofethane,anda

largeamountofethanewasusedasthesampleinjection,theresultantgraphwouldidentifyethaneasthefirstcompoundtoexit(highpeak),followedbyethane(moderatepeak)andfinallyethanol(lowpeak).

• Asinglepeakonthegraphindicatesapuresample• Ingassolidchromatography,adsorption(moleculesofasubstancecollectonthesurfaceofanother

substance)isused.Thegasthatneedstobeanalysedispassedintothesampleinjector,andthedifferentcomponentsofthegashavedifferentadsorbingstrengthtothesolid.Somecomponentsadsorbstronglyontothesolid,andsomoveasthesolidmovesthroughthecolumn.Thecomponentsthatdonotadsorbwellarecarriedthroughbyaninertgasandexitthecolumnmuchfaster.

• Identifytheneedforcollaborationbetweenchemistsastheycollectandanalysedata

Ø Collaborationbetweenchemists:• Increasesreliability• Decreasestheoccurrenceoferrors,thusincreasesaccuracy• Conditionscanbeadjustedtomaximisetheefficiencyofanindustrialprocess(e.g.taskdelegation,

etc.)


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• Manychemicalproblemsrequireexpertiseandin-depthknowledgefromawiderangeofchemicalbranches

• EXAMPLE:Polymerchemistsworkandcollaboratewithprocessengineerstoadjustreactionconditionssothatmaximumyieldsofpolymercanbeobtained

• Describeanexampleofachemicalreactionsuchascombustion,wherereactantsformdifferentproductsunder

differentconditionsandthuswouldneedmonitoringØ Thecombustionoffossilfuels,suchasoctane,havetobemonitoredonindustriallevels,asinefficient

molesofoxygencanleadtoincompletecombustion,formingtoxiccarbonmonoxideandcarbonsoot,bothofwhichcandamageandpollutetheenvironment

Ø Incompletecombustionalsodoesnotreleaseasmuchenergyascompletecombustion,makingcompletecombustiondesirablefromaneconomicstandpoint

Ø Carbonmonoxideinhibitshumanbloodfromeffectivelycarryingoxygen,andcancausedeathinhighconcentrations

Ø Sootisalsoamajorhealthrisk,asitistoxicandaestheticallydispleasing• 2C8H18(l)+25O2(g)à16CO2(g)+18H2O(g)(CompleteCombustionofOctane)• C8H18(l)+6O2(g)à5C(s)+3CO(g)+9H2O(g)(IncompleteCombustionofOctane)Ø Thusmonitoringisrequiredtoprovideasufficientair-to-fuelratio,sothatcompletecombustiontakes

placeandtheoutputofrequiredproductsishighandthecreationofunwantedsubstancesislowØ NOTE:Ifthefueltooxygenratioistoolow,oxidesofnitrogencanbeformedinstead,whichisa

respiratoryirritantandcancontributetotheformationofacidrain• N2(g)+O2(g)à2NO(g)• 2NO(g)+O2(g)à2NO2(g)Ø NOTE:Ifthereweresulfurornitrogenimpuritiesintheoctane,combustionwouldleadtotheproduction

ofSO2andNOx.Whenthesedissolveinrainwater,theywillresultintheformationofacidrainwithapH<5.Thiswillresultinanincreaseoftheacidityofwaterwaysandtheburningoftreeleaves.• SO2(g)+H2O(l) H2SO3(aq)• 2H2SO3(aq)+O2(g)à2H2SO4(aq)ßAcidRain

• Gather,processandpresentinformationfromsecondarysourcesabouttheworkofpractisingscientists

identifying:thevarietyofchemicaloccupationsandaspecificchemicaloccupationforamoredetailedstudyØ Chemistswillmonitorandmanageindustrialprocesses.Thishastobedonetoensure:

1. Reactionsproceedefficiently(highyieldandfastproduction)àDevelopmentchemist,Plantchemist2. TherawmaterialsandproductsarepureàAnalyticalchemist,Quality&controlchemist3. TheworkplaceissafeandhealthyàWorkHealth&Safetychemist4. WastesdonotpollutetheenvironmentàEnvironmentalchemist

Ø DifferentTypesofchemicaloccupations• PolymerChemists• NuclearChemists• AgriculturalChemists• PetroleumChemists• Biochemists

• MetallurgicalChemist• PharmaceuticalChemist• Electrochemist• ForensicChemist• EnvironmentalChemist

ChemicalOccupation WorkDone

PharmaceuticalChemist ResearchesanddispensesdrugsformedicinaluseAnalyticalChemist Analysesconcentrationsofchemicalsinwater,food,ores,andmanufacturedproductsand

developspurificationtechniquesBiochemist ResearcheschemicalreactionsinlivingthingsandorganismsIndustrialChemist MonitorsthemanufacturingprocessofchemicalsOrganicChemist Studiesthechemistryofcarboncompounds(Plastics,fibres,syntheticfibres,medicinaldrugs)PolymerChemist Developsnewlongchainmolecules(polymers)suchasplastics,syntheticfibresandadhesivesInorganicChemist Studyofsynthesis,structureandpropertiesformedbymetallicandnon-metallicelementssuch

asnitrogen,sulfur,phosphorusandchlorinePhysicalChemist Useofphysicalandmathematicalmethodstostudythelawsthatgovernnature–ratesof

reactions,structureofcompoundsandthenatureofchemicalbonding


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EnvironmentalChemist Monitorwater/airsamplesforpollutantsusinginstrumentalanalysisandotherprocedures.Analyseandassessenvironmentaldata.AdviseexternalbodiessuchastheEnvironmentalProtectionAgency(EPA)

IndustrialChemist EnsurethatchemicalreactionshavehighyieldandrateofreactionDesignmonitoringproceduresandqualitycontroltestingCheckthatrawmaterialsmeetspecificationsMonitorweatherproductsaresufficientlypureEnsurethateffluentsandsolidwastesfromthefactorydonotexceedallowablelimitsofpollutants

Section2Chemicalprocessesinindustryrequiremonitoringandmanagementtomaximiseproduction

• IdentifyanddescribetheindustrialusesofammoniaAmmoniaisaverystrong,pungentandchokinggasthatissolubleinwater.ItisproducedbytheHaberprocessandisanindustriallyimportantchemicalØ Fertilisers

§ Compoundswhichpromotethegrowthofplants,andthusprovidesignificantcommercialbenefitstotheagriculturalandhorticulturalindustries

§ 80%oftheammoniaproducedbyindustryisusedintheproductionoffertilisers§ 2NH3(g)+H2SO4(aq)à(NH4)2SO4(aq)§ NH3(g)+HNO3(aq)àNH4NO3(aq)§ NH4NO3isalsousedasafertiliserasNitrogenisaplantnutrient,anditisanacidicsaltthatwill

increasetheacidityofsoil(goodforsomeplants,liketomatoes)Ø Explosives

§ UsedinbothTNT(Trinitrotoluene)andDynamite(Trinitroglycerin)§ NH3isoxidisedtoHNO3andusedtomakeexplosives

Trinitrotoluene Trinitroglycerin

Ø Fibres§ Nylon-6àUsedforgears,fittings,andbearings

Ø HouseholdCleaners

§ CloudyAmmonia§ NH3(g)+H2O(l) NH4OH(aq)ßAlkalithatwilldissolveinoilandproteins

Ø CationicDetergents§ Cationicdetergentsareusedinfabricsoftenersandhairconditioners§ Longhydrocarbonchain,followedbyNbondedto3CH3groups,cappedwithaCl-ion

• Identifythatammoniacanbesynthesisedfromitscomponentgases,nitrogenandhydrogen

Ø Ammoniaisproducedindustriallyfromitscomponentgassesinanexothermic,catalyticandreversiblereaction(HaberProcess)


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Ø N2fromtheairisconvertedtonitrogencompounds(nitrogenfixation)bylightningorbythenitrogenfixingbacteriaintheroodnodulesoflegumessuchasbeansandsnowpeas.N2isverystableduetoitsstrongcovalenttriplebond,whichmustbebroken.

Ø IntheHaberprocess,N2isobtainedfromtheatmospherewhileH2isobtainedfrommethanegas(CH4)withaNickelcatalyst

2CH4(g)+O2(g)à2CO2(g)+4H2(g)

TheN2andH2gassescanthenbesenttotheHaberProcess

• Describethatsynthesisofammoniaoccursasareversiblereactionthatwillreachequilibrium

Ø ThesynthesisofammoniaisareversiblereactionthatwillreachequilibriumØ Theforwardreactionisexothermic,andreleases92kJofenergypermoleØ TherateoftheforwardreactionandreversereactionareequalwhenthesystemreachesequilibriumØ TheconcentrationswillremainconstantafterequilibriumisreachedØ ThisreactionissubjecttoLeChatelier’sPrinciple*,andcanbeinfluencedthroughchangesin

concentration,pressure,volumeandtemperature.*Whenanysystematequilibriumissubjectedtochangeintheconcentrationofreactantsandproducts,temperature,volume,orpressure,thenthesystemreadjustsitselftopartiallycounteracttheeffectoftheappliedchangeandanewequilibriumisestablished.

• Identifythereactionofhydrogenwithnitrogenasexothermic

Ø ThereactionbetweennitrogenandhydrogengasisexothermicØ Ø Theenergyabsorbedtobreakthetriplecovalentbondbetweennitrogenandthesinglecovalentbond

betweenhydrogenISLESSTHANtheenergyreleasedinformingthebondsinammonia.Therefore,theforwardreactionisexothermicasheatisreleased.

• Explainwhytherateofreactionisincreasedbyhighertemperatures

Ø Temperature=RateofReactionØ Particleshavehigherkineticenergiesandmoremoleculeshavesufficientenergytoovercomethe

activationenergybarriertobreakthecovalentbondswithindiatomicN2andH2Ø Increasednumberofparticlecollisionsbetweenreactantmoleculesperunitvolumeperunitoftime,

hencegreaterreactionrateØ NOTE:Thereactionrateisincreasedforboththeforwardandreversereaction

• ExplainwhytheyieldofproductintheHaberprocessisreducedathighertemperaturesusingLeChatelier’s

principleØ ByLCP,increasesintemperaturefavourthereverse(backward)endothermicreactionandsothe

equilibriumshiftslefttoreducethisstressandconsumetheexcessheatandhencereducesyieldofammonia

• ExplainwhytheHaberprocessisbasedonadelicatebalancingactinvolvingreactionenergy,reactionrateand

equilibriumØ BalancingactbetweenyieldofNH3andtherateandyieldatwhichNH3canbeformedthatisboth

reasonableandeconomicallyfeasible


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§ Compromisebetweencost,safety,reactionenergy,reactionrateandthepositionofequilibrium(yield)

§ Theconditionsrequiredtomaximisethesefactorsareoftenconflicting§ Catalyst:Themagnetite(Fe3O4)catalystisusedasitprovidesanalternatereactionpathwaywith

aloweractivationenergy,allowingthereactionratetoremainhighdespitemoderatetemperatures(providesasurfaceforthereaction)

§ Temperature:LCPpredictsthatlowertemperatureswillproduceahigheryieldofammoniaatequilibrium,asitisanexothermicreaction.Iftemperatureistoolow,therateofreactionbecomesuneconomicallyslow(collisionsreducethuslowerrateofreaction),thusacompromisetemperatureof450–500degreesisused.

§ Pressure:LCPpredictsthatlowertemperatureswillproduceahigheryieldofammoniaatequilibrium,astherearefewermolesofgasontheproductssidethanthereactantsside.Increasingpressurewillalsoincreasereactionrate.However,havingthepressureveryhighisexpensivetomaintain(duetotherequiredthicknessofthereactionvessel).Safetyfactorswiththeuseofhighpressurevesselsmustalsobeconsidered.Acompromisepressureof200to300atmospheresisused.

§ RemovingAmmonia:Ammoniaisproducedisseparatedfromunreactednitrogenandhydrogenbyliquefyingitunderpressure/cooling.Theunreactednitrogenandhydrogenarethenrecirculatedintothereactionchambertobeusedagain.Thisisdonedespitethecostsofthisprocess,becauseremovingammoniapreventsthereactionreachingequilibrium(Yield=98%)

§ Individualplantsdecideonprofitability:slow(highyield)orfast(loweryield)Ø COMPROMISE:Carriedoutat450degreesCelsiusandat250atmospheresofpressurewithFe3O4catalyst

• Explainthattheuseofacatalystwilllowerthereactiontemperaturerequiredandidentifythecatalyst(s)usedin

theHaberprocessØ Magnetite(Fe3O4)isusedasacatalyst.Theironinmagnetite

providesasurfaceforthegasphasereaction.(Itdoesthisbyadsorbingthereactingmoleculestoitssurface,whichdistortsandweakenstheirbondssotheycanbemoreeasilybroken)

Ø Theheterogeneouscatalysttakespartinthereactionbutdoesnotget‘usedup’.Therefore,onlyasmallamountofmagnetiteisrequiredtoincreasetherateofreactionbyloweringtheactivationenergy(andthusallowingforlowertemperatures).

Ø ItisimportanttonotethatthecatalystdoesNOTreducetheconcentrationoramountofNH3produced–itsimplyincreasestherateoftheforwardandreversereaction.Thismeansthatequilibriumisestablishedfaster.

Ø Thecatalysthasalifeof5–10years

• AnalysetheimpactofincreasedpressureonthesysteminvolvedintheHaberprocessØ (LCP)Whenpressureisincreasedbyloweringthevolume,theequilibriumwillshifttothesidewithless

gasmolecules.Therefore,theyieldofNH3willincrease.Ø Haberprocessiscarriedoutat250atmospheres(25,000kPa)Ø NOTE:Ifpressureisincreasedbyaddinganinertgasthereisnochangeinconcentrationsortothe

reactionØ NOTE:Whenthepressureisincreased,therateofreactionofboththeforwardandbackwardreaction

increase.Thisisbecausethegreaterconcentrationofgasparticlesincreasesthefrequencyofsuccessfulcollisions.

• ExplainwhymonitoringofthereactionvesselusedintheHaberprocessiscrucialanddiscussthemonitoring

requiredØ Whythereactionvesselhastobemonitored/maintained:

§ TheNitrogentoHydrogenratiomustbe1:3toavoidthebuild-upofonereactant§ Temperatureis450degreesandpressureis250atmospherestogetaneconomicalyieldof

ammonia§ Nooxygenispresentashydrogenisaflammablegaswhichwillexplodeundersuchconditions


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§ Carbonmonoxideandsulfurcompoundswill‘poison’thecatalyst§ Nobuild-upofargon(fromatmosphere)whichwillincreasethepressureunnecessarilyand

decreasetheefficiencyoftheprocess§ Highpressurereactionsaredangerousandcancausedamageandharm,thusthereaction

pressuremustconstantlybemonitoredØ ConstantremovalofNH3byliquefyingammoniaproductasitforms(equilibriumshiftstosidewithless

concentration–right)

• GatherandprocessinformationfromsecondarysourcestodescribetheconditionsunderwhichHaberdevelopedtheindustrialsynthesisofammoniaandevaluateitssignificanceatthattimeinworldhistory

Ø HaberwasaGermanscientistwhoinventedtheprocessin1908Ø Thisprocessallowedforthesynthesisofammoniafromitsgaseouscomponentsofhydrogenand

nitrogengas(450–500degrees,250atmospheres,magnetitecatalyst)Ø WiththehelpofCarlBosch(chemicalengineer),Haberwasabletoimplementtheprocessonan

industrialscaleby1913Ø Thiswasaturbulenttimeinworldhistory(1914wasWWI).ThealliesblockedGermanports,thus

preventingaccesstonitratesfromChile(theyreliedonimportstomakeexplosivesandfertilisers).Ø ThecommercialapplicationoftheHaberprocesswasabletoproduce200tonnesofammoniaby1914

eachday,whichwasusedtohelpGermany’swareffortsandfortheproductionoffertiliserØ Advantages

§ Germanycouldnowproducefertiliserstoincreasecropoutputandincreaseitscapacitytofeeditspopulation.Itcouldalsoproducesignificantamountsofexplosivesforthewar.

§ Itwasalsoaverysignificantscientificdevelopmentwhichshowedtheimpactofscienceongreatersociety

Ø Disadvantages

§ Itraisedsevereethicalandmoralissuesrelatingtotheuseofscience,asitresultedintheproductionofexplosiveswhichkilledpeopleanddestroyedthenaturalenvironment

§ Fertilisersfromammoniahavealsobeenoverused.Asaresult,theywashoutofsoilsandgointowaterways,endangeringmarinelife.

Ø Assessment:Overallverysignificantatthetimeitwasdeveloped,andstillissignificanttoday.Hasimpactedtheglobalnitrogencycle,pollutesgroundwaterandincreasesthelevelofatmosphericnitrogendioxide.Immensevalueinfosteringincreaseinglobalfoodandchemicalproduction,despiteitsnegativeimpactsonincreasingthefeasibilityofproducingexplosiveweaponry.

Section3Manufacturedproducts,includingfood,drugsandhouseholdchemicals,areanalysedtodetermineorensuretheirchemicalcomposition

• Deducetheionspresentinasamplefromtheresultsoftestsand

• Performfirst-handinvestigationstocarryoutarangeoftests,includingflametests,toidentifythefollowingions:phosphate,sulfate,carbonate,chloride,barium,calcium,lead,copper,ironØ Mostindustrialprocesshaveimpuritiesinionicform.

§ Qualitativetestsarecarriedouttoidentifytheionspresent(Flametests,precipitation,colourchangeofsolution)

§ Quantitativetestsdeterminehowmuchofeachionispresent(Atomicabsorptionspectroscopy)Ø FlameTest

1. CleanthenichromewirebyholdingittotheblueBunsenflameuntilthereisnoothercolour.2. Dipthewireinthesampleinconcentratedhydrochloricacid.(Chloridesaltsarethemostvolatile,

andwillproducethemostvisibleresults)3. HoldthenichromewiretotheblueBunsenflame1/3fromthebase,whichisthehottestpartofthe

flame4. Observeandrecordthecolourofthemetalioninanappropriatelytitledenclosedtable§ Theelectronswillabsorbtheheathenergyfromtheflame,andjumptoahigherenergylevel.The

electron,however,cannotremaininthisstateindefinitely.Whentheelectronfallsbackdownto

Solubilityrulesareessentialforthissection!!!


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groundstate(moststablestate),theextraenergyisre-releasedaslight.Ifthewavelengthoflightiswithinthevisiblespectrum,itcanbeobservedintheformofacolouredflame.

§ Onlycationscanbeidentifiedbytheflametest

Ø Reactions§ Pb2+(aq)+2Cl-(aq) PbCl2(s)ßPrimarytestwithHCl§ Pb2+(aq)+2I-(aq) PbI2(s)ßConfirmationtestwithNaI§ Ca2+(aq)+SO4

2-(aq) CaSO4(s)ßPrimarytestwithH2SO4

§ Ba2+(aq)+SO42-(aq) BaSO4(s)ßPrimarytestwithH2SO4

§ Fe2+(aq)+2OH-(aq) Fe(OH)2(s)ßPrimarytestwithNaOH

§ Fe3+(aq)+3OH-(aq) Fe(OH)3(s)ßPrimarytestwithNaOH

§ Cu2+(aq)+2OH-(aq) Cu(OH)2(s)ßPrimarytestwithNaOH

NaI

AddH2SO4

WhitepptNoppt.AddNaOH

AddingNaFwillproducewhitepptwithCabutnopptwithBa

AddingCutoNH3solutionàprecipitatedissolvestogiveadeepbluesolution

Allprecipitationreactionsareequilibrium

ß

SCN-


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Ø TestsforAnions

• Describetheuseofatomicabsorptionspectroscopy(AAS)indetectingconcentrationsofmetalionsinsolutionsandassessitsimpactonscientificunderstandingoftheeffectsoftraceelements


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Ø AASwasinventedinthe1950sbySirAlanWalsh(anAustralianscientist)atCSIROØ ThismethodisusedtodetermineconcentrationsofCATIONS(NOANIONS)atconcentrationslowerthan

1ppmØ Principle

o Thelightabsorbedbyatomsorionsinsolutionisdirectlyproportionaltotheconcentrationoftheions(asabsorptionincreases,concentrationincreases)

o Whenheatisabsorbed,electronsareexcitedandmoveuptoahigherenergystate.Whentheelectronmovesbackintoitsoriginalgroundstate,itreleasestheenergyaslight.Thisemittedlightisdifferentforeachcation,duetothecation’suniqueelectronconfiguration.

o Eachelementhasitsown‘spectrum’,whichcanbeusedtoidentifyit(similartoafingerprint)Ø EmissionLineSpectrumàColouredlinesonablackplateØ AbsorptionLineSpectrumàBlacklinesonacolouredplateØ Components

o LightSource:HollowCathodelampoftheelementthatisbeingtestede.g.Iftestingforcopper,acopperhollowcathodelampisused

o Flame/Nebuliser:Vaporisesthecationsinthesampleo Monochromator/Prism:Onewavelength/colourisselectedtopreventinterferencebyotheratomso PhotomultiplierTube:Detectstransmittedlightintermsofintensityo DigitalReading:Convertsthetransmittedlightintotheabsorbanceasadecimalo InitialLight–TransmittedLight=Absorption

Ø Method1. Preparea200ppmstandardsolutioncontainingthecationtobetestedfor.(similartohowstandard

solutionsfortitrationsareprepared)o Dissolvemassintosmallquantityofdistilledwater,usevolumetricflask,topwithdistilled

water2. Prepareaseriesofdilutedsamplesoftheiontobetested(e.g.100ppm,50ppm,25ppm)3. MeasuretheabsorbanceofeachofthestandardsolitonsusingAASinordertodrawacalibration

curve(alwayslinear,passesthroughorigin)4. Measuretheabsorbanceoftheunknownsolution5. Determinetheconcentrationoftheioninthesolutionusingthecalibrationcurve(ALWAYSLINEAR,

ALWAYSPASSESTHROUGH/MEETSTHEORIGIN(0,0))

Advantages Disadvantages§ Extremelysensitive(measuresconcentrationsas

lowas1ppb)§ Specificduetothehollowcathodelampwhich

emitslightofaspecificwavelength§ Nopriorpreparationofthesamplerequired

§ Onlycationscanbetested§ Veryexpensive(e.g.adifferentcathodelampis

neededforeachcation)§ Onlyoneioncanbetestedforatatime(time

consuming,impracticalinsomesituations)§ TrainedtechnicianrequiredtooperateAAS

Ø TraceElementAnalysis

o Traceelementsarethosethatarerequiredbylivingorganismsinverylowconcentrations(1-100ppm)fortheproperfunctioningofenzymesincells(Highconcentrationsareharmful)

o E.g.Zn(essentialforaminoacidmetabolismandenergyproduction),Co,Ni,Cu,Mo,Seo BeforeAAS,thepresenceandamountofthesetraceelementscouldnotbedetermined.Now,blood,

urineandtissuesamplesaretestedfortheamountoftraceelementspresent.Iftherearedeficiencies,thesecanbeidentifiedandtreated.

Ø Summaryo Introducechemicalprincipleso Discussmethod,includingcomponentso DiscussAdvantagesanddisadvantageso Discusstraceelementso Provideassessmentofthetechnology


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• Gather,processandpresentinformationtodescribeandexplainevidencefortheneedtomonitorlevelsofoneoftheaboveionsinsubstancesusedinsocietyØ Pb2+(Lead)Ø Toxic,heavymetal–releasedasinorganicionsororganicleadØ Enterorganismsviaingestion,inhalation,absorptionthroughskinentersfoodchainandaccumulatesinbody

(difficulttoexcrete)Ø Effects

§ Organdamagebydisruptingenzymesystems§ Intellectualretardation,neurologicaldamage–inchildren–learningdisabilities,impairedhearing–

hyperactivity,ADD§ Inhibitsformationofhaemoglobin(oxygencarryingmoleculeinblood)

Ø PastUses§ White,yellow,redpaint,leadedfuels,manufacturedtoys

Ø Monitoring§ Monitoringinhighwayareas,soil,atmosphere,urbanareas,water§ Stringentstandards(concentrationsinpaints(0.25%)andunleadedpetrol)§ Problemse.g.whenusedinmining,therefiningoflead(slagwastes,fumes,dust)andlead,acid

batteries

• Identifydata,plan,selectequipmentandperformfirsthandinvestigationstomeasurethesulfatecontentoflawnfertiliserandexplainthechemistryinvolved

and• Analyseinformationtoevaluatethereliabilityoftheresultsoftheaboveinvestigationandtoproposesolutionsto

problemsencounteredintheprocedureØ GravimetricAnalysisofSO4

2-byprecipitatingasBaSO4Ø Method:

1. Weigh0.2goffertiliseranddissolveindistilledwater.Filtertoremoveanyinsolublesubstancessuchassand.

2. Acidifythesolutionwith0.5mLofconcentratedHClandgentlyboil.(Willremovecarbonate,whichwouldotherwiseprecipitateasBaCO3)

3. 5%w/vBaCl2isaddeddropwisewithaburetteuntilnomoreprecipitateforms.Avoidexcess,asextrabariumionswillsticktotheprecipitate,increasingweight.

4. CheckthesupernatantforfurtherprecipitationbyallowingthesolidtosettleandaddingadropofBaCl2totheclearsolution.Ifthereisnocloudinessasaresult,precipitationiscomplete.

5. Thebeakerwiththeprecipitateisleftonahotplateforanhourtosettle.ThepowderyBaSO4willclumptogethermakingiteasytofilter.Heatencouragesrecombinationofions.(oppositeofdissociation)

6. FiltertheBaSO4solidusingaweighedsinteredglassfunnel(superiortofilterpaper).Thisisaveryslowprocess,soavacuumpumpcanbeusedtospeedupthisprocess.

7. Washtheprecipitatewithsmallamountsofwater3times(toremoveanybariumionsstickingtotheprecipitate).Thenrisewithsmallamountsofalcohol3times(toremovewater).

8. Drytheprecipitateinanovenat105degreesCelsiusuntilcompletelydry.Coolinadesiccatorandweigh.Continuethisprocessuntiltheweightisconstant.

Ø Safety1. Bariumchlorideistoxicifingested,henceitisimportanttowashhandsthoroughlyafterthe

experiment2. ConcentratedHydrochloricacidisverycorrosiveandcausesseveredamagetotheeyes,skinand

clothes.Wearsafetygogglesandgloves(ifpossible)3. Experimentinvolvestheuseofahotplate,whichcanburnskin.Becarefulwhenhandlingequipment

Ø Results§ DeterminemassofBaSO4§ DividethismassbythemolarmassofBaSO4todeterminethenumberofmoles§ In233.37gramsofBaSO4(1mole),thereare96gofSO4

-§ Multiply(96/233.37)withthemassofBaSO4todeterminethemassofSO4

-§ TofindthepercentageSO4,dividethemassofSO4bythemassoftheoriginalsampleoffertiliser


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Ø Reliability§ Thereliabilityofresultsintheaboveproceduredependupon:

• Onlysulfateionsinthefertiliserbeingprecipitatedbybariumions.• Allofthebariumsulfateprecipitatebeingcollectedbythefilterpaper.

§ Thereliabilityofresultsintheprocedurecanbeimprovedby:• Usingafineanalyticalgradequantitativefilterpaperratherthanaqualitativefilterpaper.• Repeatingtheexperimentseveraltimesandcomparingtheresultsobtainedeachtime.

§ Problems,otherthanreliabilityproblems,thatcouldpossiblybeencounteredduringtheprocedure,andpossiblesolutions,includethefollowing:

Problem Solution

Weighing:Somemassmaybeunaccountedforduetoerrorsincollectionandweighing

WashdownthebeakerwhentransferringtothefiltertoensureallBaSO4istransferred.Filterpapershouldbedriedinanoveninsteadofair,asmoisturecouldstillbepresentandcontaminantsadded.Useaverypreciseelectronicscale.

IncompletePrecipitation:BaSO4formsinanequilibrium,andthusproductionofprecipitatemaynotreachequilibrium

AddexcessBaCl2toshifttheequilibriumtotherightuntilnomoreadditionalwhiteprecipitateforms.CoolthemixtureafteraddingBaCl2inice-watertogreatlyreducethesolubilityofBaSO4.Donotusegreatvolumesofwaterandsolutions,asBaSO4ismoresolubleindilutesolutions.

Presenceofcontaminantions:Phosphateandcarbonatespresentmayreactwithbariumtoformexcessprecipitate

AdditionofHCldissolvestheseprecipitates

Smallsizeofprecipitatecrystals:BaSO4formsveryfinecrystals,whicheasilygothroughnormalfilterpaper,andevensinteredglasscrucibles.

HeatingthesolutionbeforeaddingBaSO4andconstantlystirringincreasestheenergyofthesolution,whichincreasesthenumberofcollisions,thuslargerparticlesareformed.AddingBaCl2slowlyallowstheBaSO4crystalstogrow,andthusbecomelarger.Addingacoagulatingagentsuchasagarsolutioncausesthecrystalstocoagulate.

Filterpapertakesalongperiodoftimetodry DrythefilterpaperinanovenFiltrationtakesalongperiodoftime Useaweighedsinteredglasscrucible

• Gather,processandpresentinformationtointerpretsecondarydatafromAASmeasurementsandevaluatethe

effectivenessofthisinpollutioncontrolADVANTAGESØ AASisextremelyeffectiveinpollutioncontrolofmetalsàaccuratelycalculateconcentrationsofpollutants

eveninlowconcentrations.Thishasgivenusabroaderunderstandingoftheenvironmentandhelpsusimprovethehealthandsafetyofecosystemsandthepublic

§ AASwasusedinBangladeshtodeterminearsenicconcentrationsofgroundwater.ThisallowsthepublictoavoiddrinkinggroundwaterwithhighconcentrationsofArsenic,whichcancausehardpatchesontheskin,skincancer,lungcancer,kidneyandbladdercancerandgangrene.

§ Leadisanothertoxicheavymetalswhichcandamagethebrain,kidneysandreproductivesystembydisruptingenzymesystemmediatedbyothermetalssuchascalcium,ironandzinc.

2PbS+O2à2PbO+2SO22PBO+Cà2Pb+CO2

TheseequationsshowhowleadmayaccumulateinworkersØ AASisarelativelycheapmethod(followingtheinitialstart-upcosts)ofregularlyanalysingwaterwaysandair

qualitytoensurethatthelevelofpollutionisatanacceptablelevel,allowingthemaintenanceofthehealthofthepopulation

Ø AASishighlyspecificandfastforeachsampleanalysed,asthesamplecanbeanalysedwithouthavingtobephysicallyseparated

Ø Thus,AASprovidesaquickandeasywayofroutinelymonitoring/detectingsuchharmfulheavymetalsinsuchworkplaces,toensurethattheyareinconcentrationsbelowwhatisrecommendedbytheappropriatehealthauthorities


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DISADVANTAGESØ AASisonlyusefulfortestingtheconcentrationofmetalpollutants,asitcannotbeusedtodeterminethe

concentrationofnon-metalpollutantsØ Althoughinexpensivetooperate,theinitialcostofsettinguptheAASdeviceishigh,andthusmakesthem

unaffordableforsomepollutionmonitoringagenciesØ Itcanonlybeusedtotestforonemetalatatime.Alsoforeachnewmetaltested,anewhollowcathode

lampwiththespecificmetalhastobesetupàtimeconsumingandexpensiveØ DestructiveanalysisàSampletestedcannotbereusedorreanalysedØ Water:Heavymetalssuchaslead,magnesiumandcalciumformindustrialwasteØ Soil:Lead,Mercury,Cadmium,NickelfromleachingofbatteriesandrubbishdumpØ Air:LeadfromleadedpetrolanddemolitionofoldbuildingswithleadedpaintØ Food:Leadinfruitsgrowninorchardsnearhighways.Mercurybioaccumulationinfish.Ø Mining:Testformetalsinorestodeterminewhetheritiseconomicalornottomineacertainregion

§ Assessment:AAShashadaverypositiveimpactonourabilitytocontrolpollution.WithAAS,wehavetheabilitytoaccuratelyandreliablyanalysesubstancesfordangerouscationsthatwouldotherwisegoundetected.Thishasallowedustotakebettercareofsocietyandtheenvironment.

Section4Humanactivityhascausedchangesinthecompositionandthestructureoftheatmosphere.Chemistsmonitorthesechangessothatfurtherdamagecanbelimited.• Describethecompositionandlayeredstructureoftheatmosphere

Ø Theatmosphereisalayerofgassesabout200to300kmthicksurroundingtheEarth

Ø Troposphere(0-15km)

§ Asthealtitudeincreases,temperaturedecreases§ ThehotaironthesurfaceoftheEarthwillriseduetoconvection,andthecoldairwillcomedown§ Duetothisdisturbance,gassesarewellmixedandweathereventsarefrequent§ Pollutantsaredilutedinthislayerduetotheconstantmovementofgasses

Ø Stratosphere(15-50km)§ Asaltitudeincreases,temperatureincreases§ Hotairremainsontopandcoldairremainsatthebottom(nomixingofgasses)§ Ozonelayerispresentatanaltitudeofabout20km

Ø AtmosphericComposition§ 90%ofgassesareconcentratewithinthetroposphere


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(Approximatevaluesfromthistableneedtobeknown)

§ Gassesofverylowconcentrationsaregiveninppm(partspermillion)• Identifythemainpollutantsfoundintheloweratmosphereandtheirsources

Pollutant Source ImpactLead • Leadedpetrolincars

• Demolishingoldbuildingswithleadedpaint

• MiningFumes

Directpoisonthataffectsthecentralnervoussystem(causesmentalretardation)

NitrogenOxides • Internalcombustionengines• Burningfossilfuelscontaining

nitrogenimpurities• Burningvegetation

Contributestoacidrainandphotochemicalsmog

SulfurDioxide • Burningfossilfuelscontainingsulfur• Smeltingmetalsulfidesinmetal

extraction• ProductionofH2SO4

Contributestotheformationofacidrain

Methane • Bacterialdecompositionoforganicmatter

• Naturalgasseepage

Contributestophotochemicalsmogandthegreenhouseeffect(climatechange)

Hydrocarbons • Vehiclesusingpetrol Contributestophotochemicalsmogandperoxyacetylnitrates(PANs)

CarbonMonoxide • Incompletecombustionofhydrocarbons

• Forestfires• Slowcombustionstores

Combineswithhaemoglobinfasterthanoxygengas,therebyreducingtheoxygencarryingabilityofblood

CarbonDioxide • ForestFires• Vehicles

Contributestoglobalwarmingandclimatechange

Chlorofluorocarbons(CFCs)

• Refrigerators• AirConditioners• AerosolCans

Destroystheozonelayer,allowingshortwavelengthUVradiationtocomedowntotheEarth’ssurfaceandcauseskincancer,sunburnandeyecataracts

Ozone • InternalcombustionenginesN2+O2à2NO2NO+O2à2NO2NO2à(sunlight)NO+O(bothradicals)O(radical)+O2àO3

Photochemicalsmog

Particulates • Sootfromincompletecombustion• Dust• Asbestos

Causesrepositorydifficulties,carcinogenicanddirtiestheenvironment

• DescribeozoneasamoleculeabletoactbothasanupperatmosphereUVradiationshieldandaloweratmosphere

pollutantØ IntheTroposphere

§ Ozoneisaseriouspollutantinthetroposphere,existingatconcentrationsaround0.02ppmincleanair§ Asshowninthetable,ozoneisformedinthetropospherebyinternalcombustionengines


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§ Ozone(photochemicalsmog)isaverystrongoxidantandwilloxidisesofttissueineyesandthroat,disruptsnormalbiochemicalreactions

§ Ozone,inhigherconcentrations,cancausebreathingproblems,aggravationofrespiratoryproblems,headaches,fatigueanddeath(inhighconcentrations)

§ Thus,Ozoneisaseriousandtoxicpollutantinthe‘loweratmosphere’(troposphere)Ø IntheStratosphere

§ Ozoneexistsatmuchhigherconcentrationsinthestratospherenaturally,ataround2to8ppm§ Ozonehasaveryimportantroleinthestratosphere,inwhichitisresponsibleforabsorbingdangerousUVB

radiationfromthesunthatwouldotherwisecauseseriousdamagetolifeonEarth(cancers,burnsandeyecataracts)

§ FormationofOzone• O2(g)à(UVonarrow)2O-

(g)• O2(g)+O-

(g)àO3(g)+heat§ ActionofOzone

• O3(g)à(UVonarrow)O2(g)+O-(g)

• O3(g)+O-(g)à2O2(g)+heat

§ UVradiationisconvertedtoheatenergy+harmlessO2-nootheratmosphericmoleculeshavetheabilitytoabsorbsolarradiationinUVrange

§ Stratospheregetswarmaslightenergyisconstantlyconvertedtoheatenergy§ HenceOzonehasanimportantroleintheStratosphere,inwhichitactsasa‘UVradiationshield’

• Describetheformationofacoordinatecovalentbond

Ø Whenthetwoelectronsthataresharedtoformacovalentbondcomefromasingleatom,thebondisknownasacoordinatecovalentbond

• DemonstratetheformationofcoordinatecovalentbondsusingLewiselectrondotstructures

Ø Covalentbondwherebothofthesharedelectronsforthebondcomefromthesameatom–morereactiveo Bondsareindistinguishablefromregularcovalentbondswhenformed

Ø E.g.NH4+,H3O+andCO

Ø Bondcomesfromlonepairsofoneatom

Ø Inordertodrawacompoundcontainingcoordinatecovalentbonds

§ Numberofelectronsneeded=numberofatoms*8§ Numberofelectronspresent=numberofelectronsatomspresentcurrentlyhave§ Numberofsharedelectrons=needed–present§ Numberofbonds=numberofsharedelectrons/2§ Positionbondsappropriatelytosatisfyallatoms(octet)

Ø Coordinatecovalentbondsaredenotedwitharrows• ComparethepropertiesoftheoxygenallotropesO2andO3andaccountforthemonthebasisofmolecularstructure

andbondingØ Allotrope:Differentphysicalformofthesameelement.Ø Oxygenhas2allotropes:Ozoneandoxygen


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Ozone OxygenGas

Ø ChemicalProperties§ Dependonthestrengthofthecovalentbonds.Thestrongdoublebondinoxygengasishardtobreak

butthesinglebondinO3(coordinatecovalent)isbrokeneasily(998kJ/Molvs107kJ/Mol)§ Ozoneismorereactivethanoxygen§ Bothareoxidisingagents(ozoneisstronger)

Ø PhysicalProperties O2 O3 REASON

GaseousColour Colourless Paleblue -LiquidColour Paleblue Deepblue -SolidColour Paleblue Black-violet -

BP/MP Lower(-183oand-219oC)

Higher(-111oand-193oC)

O3isslightlypolarduetoitsasymmetricelectrondensityanditsbentshape-greaterintermolecularforces

DensityasGas Lower Higher PresenceofadditionalOatominozoneSolubilityinwater Sparingly

soluble(9ppm)MoresolublethanO2

O2isnon-polar,butO3isbentandthuspolar

Reactivity Highlyreactivewithmanymetalsandnon-metals

Veryhighlyreactive,attacksdoublebondsonalkenes

CoordinatecovalentbondinO3isextremelyreactiveIntermediatesingleanddoublebondscreatingO-(anoxidant)

Odour Odourless Pungent Ø Ozonehasaslightpolarityduetothebentstructure.Therefore,therearedipole-dipoleforcesbetweenozone

moleculeswhicharestrongerthantheweakdispersionforcesinoxygengas.Thisresultsinhighermeltingandboilingpoints,aswellassolubilityinwaterascomparedtooxygengas.

• Comparethepropertiesofthegaseousformsofoxygenandtheoxygenfreeradical

Ø FreeRadical:Aneutralspeciesatomwithanunpairedelectron.OxygenfreeradicalsarepresentintheupperatmosphereduetotheeffectsofradiationsuchasUVlightProperty GasesForms(O2,O3) FreeRadicalReactivity Lessreactive(fulloutervalence

shell)Veryreactive(unpaired)

OxidationAbility Lower Higher(unpairedelectron,hightendencytotakeelectronstocompletevalenceshell)

• Identifytheoriginsofchlorofluorocarbons(CFCs)andhalonsintheatmosphere

Ø Chlorofluorocarbons(CFCs)arecompoundscontainingCarbon,ChlorineandFluorineONLY(NoH)Ø HalonsarecompoundscontainingCarbon,Bromine,Fluorine(mayormaynotcontainCl)(NoH)Ø Duringthe1930s,CFCs(and,toalesserextent,halons)replacedammonia(NH3)asthegasinrefrigeratorsandair

conditionersØ CFCswerecheaper,non-toxic,non-flammableeasilycompressibleØ SuchusesofCFCsreleasedmillionsoftonnesofCFCgassesintotheatmosphereoveraperiodofoverhalfa

century,introducingCFCsandHalonsintotheatmosphereØ NamingCFCs

§ ListC,HandF(inthatorder)andsubtract90§ E.g.Cl-CFCl-CF2-Cl=203-90=CFC113(asthereare2carbons,0hydrogensand3fluorines)


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Ø NamingHalons§ ListC,F,Cl,Bre.g.1211

Ø CFC-11wasusedinrefrigeratorsandairconditioners(CCl3F)• Identifyandnameexamplesofisomers(excludinggeometricalandoptical)ofhaloalkanesuptoeightcarbonatoms

Ø Isomer:Samemolecularformulabutdifferentstructures§ IsotopeàAtoms,AllotropeàElement,IsomeràCompounds

Ø Haloalkanes:AlkaneswithhalogensF,Cl,BrandIfunctionalgroupsØ Naming

1. Longestcarbonchainsasyouwouldforalkanes2. Positionofdoublebond(ifpresent)takesprecedenceoverhalogenbutnamedafter3. AddfunctionalgroupprefixesF:fluoro-Cl:chloro-Br:bromoI:Iodo-4. Numberaccordinglowestnumberedlocant(ifmorethan1typeisonsidetostartoncountingfromtheside

thatyoubegintocountfromfirstalphabetically)5. Usedi,trietc.forwritingnumberofhalogenatoms6. Order(ifmorethan1differenttypeofhalogenatom)alphabetically–i.e.chloro,fluoro

Ø E.g.1,1dibromo2-chlorohexane• DiscusstheproblemsassociatedwiththeuseofCFCsandassesstheeffectivenessofstepstakentoalleviatethese

problemsØ CFCsareextremelystableandinsolubleinwater.Therefore,theydonotcomedownfromtheatmospherewith

rainwaterorotherweatherevents,andremaininthetropospherefordecades.Ø Slowly,overmanyyears,CFCsmigratetowardstheStratosphereuntiltheyfinallyreachtheOzonelayerØ TheUVradiationpresentintheozonelayerbreakstheCarbon-ChlorinebondintheCFCandachlorinefree

radicalisformedCCl3F(g)à(UVonArrow)CCl2F•+Cl•

Ø Thischlorinefreeradicalthenattacksozone,formingahypochloritefreeradicalandoxygengas.Thehypochloritefreeradicalthenreactswithanoxygenfreeradical,formingoxygengasandreformingtheoriginalchlorinefreeradical.

Cl•+O3(g)àClO•+O2(g)

ClO•+O•àO2(g)+Cl•Ø Thisprocesscanbedescribedasa‘chainreaction’aschlorineisnotdestroyedintheprocess(canbethoughtof

asahomogenouscatalyst).Theonlywaythiscanbestoppedisifchlorinereactswithmethane.Typically,asingleCFCcompoundcandestroyaround1000ozonemolecules.

Ø Themassdestructionofozoneinthestratosphereleadstothethinningoftheozonelayer.Theseareknownasozone‘holes’(notactualholes,justareasoflowerconcentrationofozone)

Ø Justa1%reductionintheozonelayerincreasesthechanceofskincancerby8%Ø IftheUVBradiationisincreasedby2%ithastheabilitytokillsurfaceplanktonanddisruptthefoodchainØ HalonsaremoredestructivethanCFCsastheC-Brbondbreaksmorereadily.Thebrominefreeradicaldestroys

ozoneinasimilarprocesstochlorine.Ø In1987,theMontrealProtocolbannedtheuseofCFCsandothercompoundsindevelopedcountries

§ StopusingHalonsby1994§ StopmanufacturingCFCsby1996§ PhaseoutHCFCsbythe21stcentury(2020)§ Allowlessdevelopedcountriessomegraceperiodandprovidefinancialsupport

Ø Replacements§ HCFCs

• HaveC-Hbondswitharedecomposablebyradicals–butsignificantamountstillreachesupperatmosphere

• LessharmfulthanCFCsdespitestillhavingClatoms• Temporarysubstitutewithplantstophaseoutby2020(notideal)

§ HFCs• ContainnoCl/BratomsandC-Fbondisstrong–noFfreeradicalsproduced• Donotcontributetoozonedepletion• Moreexpensive;R-124aisusedrefrigerantinAus.


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Ø Itispredictedthatby2050theozonelayerwillberepairednaturallyØ Equations

§ CCl2F2(g)à(UVBRadiationontopofarrow)CClF2(g)(radical)+Cl(g)(radical)§ Cl(g)(radical)+O3(g)àOCl(g)(radical)+O2(g)§ OCl(g)(radical)+O(g)(radical)àCl(g)(radical)+O2(g)

Ø Reactionsthatwillstopthechainreaction§ CH4(g)+Cl(g)(radical)àCH3(g)(radical)+HCl(g)§ NO2(g)+OCl(g)(radical)àClONO2§ Cl•+Cl•àCl2(g)

• Analysetheinformationavailablethatindicateschangesinatmosphericozoneconcentrations,describethechanges

observedandexplainhowthisinformationwasobtainedØ HighozonedepletionoverAntarcticacouldbedueto

§ TheicecrystalsintheaircatalysingthereactionbetweenHClandClONO2intheair§ HCl+ClONO2à(icecrystalsontopofarrow)Cl2+HNO3§ Cl2à(sunlightontopofarrow)2Cl(radical)§ ByOctober,theozonelayeroverAntarcticaisextremelythin,butispartiallyrepairedbylate

DecemberØ OzoneconcentrationismeasuredinDobsonUnitsØ InstrumentstoCollectData

§ DobsonSpectrophotometer(1960s)• Groundbasedinstrumentsforlongtermdataàspecificareaonly

o MeasurestheintensityoffourstandardwavelengthsofUVradiationreflectedbacktoground(2absorbedbyozone,2not)

o Ratiobetweentwointensitiesdeterminedtocalculatetotalozoneo Comparingthevalues.Thegreaterthedifference,thegreatertheozone(good-to

absorbUV)• LIDAR

o Relyonscatteringoflaserlightbyozoneo Fire2beams(oneabsorbedbyozone–308nmandonenot–351nm)o Comparevalues–profileofozoneconcentration(conc.vs.altitude)measuredo Differenceinlaserlightintensity/wavelengthssimilarlyshowspresenceofO3(which

isgoodifitishigher)• TOMS(TotalOzoneMappingSpectrometers)(1980s)

o Satellite,balloonorgroundbased–unitisDobsonUnitàdailyglobalcoverageo MeasuresintensityofawavelengthofUVradiationabsorbedbyozone–compares

tointensityofwavelengthnotabsorbedo Satellite(atalt.aboveozonelayer)observesincomingUVlightat6diff.wavelengths

+observesUVlightbackscatteredbyozoneandcomparesintensityofincomingradiationwithbackscatteredradiationtoformaprofile

o Comparesthedifferentvalueshavingpassedthrough• OMI(OzoneMeasuringInstrument)(current)

o ImprovementofTOMSwithsmallerpixelsizebutlargerviewingangleàallowtomaintaindailyglobalcoveragebutwithmoredetail

o Lookbetweencloudsattroposphere• PresentinformationfromsecondarysourcestowritetheequationstoshowthereactionsinvolvingCFCsandozoneto

demonstratetheremovalofozonefromtheatmosphere(CoveredEarlier)

• Gather,processandpresentinformationfromsecondarysourcesincludingsimulations,molecularmodelkitsor

pictorialrepresentationstomodelisomersofhaloalkanes(Self-Explanatory)


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• PresentinformationfromsecondarysourcestoidentifyalternativechemicalsusedtoreplaceCFCsandevaluatetheeffectivenessoftheiruseasareplacementforCFCs

1. Hydrochlorofluorocarbons(HCFCs)§ Thesehavecarbonhydrogenbindswhichbreakinthetropospherebeforethecompoundcandiffuseto

thestratosphere.Ozonedepletion,however,isstillpossibleasitalsocontainschlorine.2. Hydrofluorocarbons(HFCs)

§ Thesehavenochlorineatoms.Thecarbon-fluorinebondisextremelystronganddoesnotbreakinthepresenceofUVlight.Therefore,nofluorinefreeradicalsaregeneratedthatcanharmtheozonelater.

§ 1,1,1,2-TetrafluoethaneisthegasusedinairconditionersandrefrigeratorsCompoundType OzoneDepletionPotential(ODP)

Halon 10CFC 1HCFC 0.1HFC 0

Section5Humanactivityalsoimpactsonwaterways.Chemicalmonitoringandmanagementassistsinprovidingsafewaterforhumanuseandtoprotectthehabitatsofotherorganisms.• Identifythatwaterqualitycanbedeterminedbyconsidering:concentrationsofcommonions,totaldissolvedsolids,

hardness,turbidity,acidity,dissolvedoxygenandbiochemicaloxygendemand§ ConcentrationsofCommonIons(generallymeasuredinppm).§ Totaldissolvedsolids(TDS):Ameasurethemassofsolidsdissolvedinaunitvolumeofwater(generally

measuredinppm).§ Hardness:Ameasureoftheconcentrationofcalciumandmagnesiumions.§ Turbidity:Ameasureoftheamountofcolloidalsuspendedmatter,whichtranslatesintoadegreeof

cloudinessortransparency(measuredinrelativeunitscallednephelometricturbidityunits,orNTUs).§ Acidity:Ameasureoftheconcentrationofhydrogenions(measuredinpH).§ Dissolvedoxygen(DO):Ameasureoftheconcentrationofoxygen(generallymeasuredinppm).§ Biochemicaloxygendemand(BOD):Ameasureoftheconcentrationofdissolvedoxygenthatisneededfor

thecompletebreakdownoftheorganicmatterinasamplebyaerobicbacteria(generallymeasuredinppm).Goodqualitydrinkingwaterisknownaspotablewater.Itshouldhavethefollowingproperties.

§ Completelyclearandcolourless§ Odourless§ PleasantTaste§ Lowsaltcontent§ Nopathogens§ Notoxicmaterials/substances

Testscanbecarriedouttodeterminewaterqualitybymeasuringthe:

§ Concentrationofcommonionso QualitativeTests

§ FlameTest(C)§ PrecipitationTest(C&A)§ LineSpectrum(Emissionorabsorption)(C)

o QuantitativeTests§ Titrations(C&A)

• TheconcentrationofchlorinecanbedeterminedthroughtitrationwithHNO3,alongwithK2CrO4(yellow)indicator.Thecolourchangesfromyellowtobrickredwhentheendpointhasbeenreached.RedAg2CrO4precipitateswhenthereisnomorechlorine.(PrecipitationTitration)

• Chlorinecanalsobedeterminedbyreactionwithexcesssilvernitrate§ Gravimetry(C&A)§ AAS(AtomicAbsorptionSpectroscopy)(C)§ IonSensitiveElectrode(A)


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• SimilartopHmeters• Measurevoltagedifferenceandconvertresulttochlorineorfluorineconcentration

o Example:GravimetricAnalysisofChlorine§ WeightaknownamountofwateràEvaporateàConcentratedSampleàAcidifywith

HNO3andaddAgNO3àAgClPrecipitateàFilterandDryàWeigh

§ TotalDissolvedSolids(TDS)o QuantitativeTests

§ GravimetricAnalysis• Filterthewatersampletoremoveinsolublesubstances• Weigh• Evaporatetodrynessinapreviouslyweighedevaporatingbasin• Coolandweigh• Provideresultsinppm

§ MeasurementofconductivityconvertedtoTDSinppm

§ Hardnesso HardnessisduetoCa2+andMg2+ionsbeingpresentinthewatero QualitativeàCheckifsoaplathersinwater,orifitformsaninsolublescumo QuantitativeàEDTAComplexometryTitration,AAS

§ Add25.0mLofwaterintoaflask§ Add2mLofNH3/NH4ClbasicbuffersolutionàWillmaintainpHwhenEDTAmakessolution

acidic§ Add3dropsofEriochromeBlackTindicator§ Titratewith0.020mol/LEDTAuntilthereisachangeincolour(redàblue)§ Repeattitrationuntil3readingswithin0.1mLofeachother§ Ca2+IndicatorComplex(Red)+EDTAà[CaEDTA]2-+Indicator(Blue)

• HardnessisreportedasCaCO3ppmevenifitisduetoMagnesium• nCaCO3=nCa=nEDTA(as1:1ratio)=CEDTA*VEDTA=0.01*VolumeofEDTAusedin

Litres.• Dividethisresultby25,multiplyby1000(1litre),then100(mmCaCO3,then1000).

ThiswillgiveareadingofCaCO3inmgin1000mL(ppm).§ If<75ppmthenlow§ If15-150ppmthenmoderate§ If150-300pmmthenhard§ If300-500ppmthenveryhard§ If>500thensaline

o Therearetwotypesofhardness§ Temporary:IfthereisdissolvedCO2,boilingwillremoveCaasCaCO3§ Permanent:NeedtoaddwashingsodaNa2CO3whichremovesCaasCaCO3

§ Turbidity

o Cloudinessorlackoftransparencyisknownasturbidityo Suspendedsolids,suchasclay,resultinturbidityo QualitativeTests

§ SecchiDisks:Insertdiskintowateruntilthecrossatthebasecannotbeseen.Thelengthofthestringiscompared.

§ TurbidityTube:Addwaterintotubeuntilthecrossatthebaseofthetubecannotbeseen.o Quantitative

§ TurbidityismeasuredinNTU(NephelometricTurbidityUnits)§ TurbidityMeter

• Lightispassedthroughasampleofthewater,andtheresultantlighttransmittedismeasured.ThelighttransmittedisinverselyproportionaltotheturbidityinNTU.

• Nephelometer:Lightispassedthroughasampleofwater.Theresultantscatteringoflightismeasured.ThescatteringoflightisproportionaltotheturbidityinNTU.


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§ 1-5NTUispotable§ Lessthan25NTUissuitableforwaterlife

§ Acidity

o Themaincauseofacidityisacidraino MiningcanalsocauseacidityasFeSgetsoxidisedtoSO4

2-àH2SO4.LowpHwilldissolvetoxicmetalsionssuchasaluminium,whichwillbetakenupbyplantsandaquaticlife.

o PotablewatershouldhaveapHof6.5-8.5o Itisnormalforwatertoappearacidicathighertemperatures,astheforwardreactionoftheself-

ionisationofwaterequilibriumisexothermic.Thiscausesgreaterconcentrationsofhydroniumandhydroxide.SincepHmetersonlymeasurehydronium,thewaterappearsacidicathighertemperatures.

o QualitativeàIndicatorso QuantitativeàCalibratedpHmeter+thermometertomeasuretemperature(astempaffectspH)

§ DissolvedOxygen

o OxygendiffusesfromtheairintothewaterandwaterplantsproduceO2inphotosynthesiso Movingwater(e.g.rapids)havemoreDOduetothegreatersurfaceareao DOismeasuredinppm

§ 6-8ppmUnpolluted§ 4-6ppmPolluted§ 2-4SeverelyPolluted§ <2DeadWater

• Atlowerthan5ppm,aquaticlifeisinseverestresso DOdependson

§ Temperature(O2(g) O2(aq)+heat)(LCP)(ThermalPollution)§ AtmosphericPressure:Aspressureincreases,equilibriumshiftsforward,increasingDO

(LCP)§ Presenceofsalt:Assaltconcentrationincreases,DOdecreasesassaltismoresolublein

waterthannon-polaroxygen§ BiologicalOxygenDemand(BOD):AsBODincreases,DOdecreases.

o QualitativeTests:Methyleneblueindicatorturnsblueofthereisoxygeninthewatero QuantitativeTests

§ CalibratedDOmeter§ WinklerTitration

• O2(aq)+2Mn2+(aq)+4OH-(aq)à2MnO(OH)2(s)

• MnO(OH)2(s)+8H+(aq)à2Mn4+(aq)+6H2O(l)

• 2Mn4+(aq)+4I-(aq)à2Mn2+(aq)+2I2(aq)• 2I2(aq)+4S2O3

2-(aq)à4I-(aq)+2S4O6

2-(aq)

• 1:4ratiobetweenoxygengasandthiosulfate• Method

o A250.0reagentbottleisfilledwithwaterandstopperedunderwatertopreventanyairbubblesentering

o Add5mLofMnSO4/NaOH/KIandallowtheprecipitatetosettleo Add1mLofconcentratedH2SO4andmixtodissolvetheprecipitateo Transfer100mLintoatitrationflaskandtitratewith0.025Msodium

thiosulfateNa2S2O3inaburetteusingstarchastheindicator(BlueàColourless)

o Repeat• Results

o nO2=nNa2S2O3/4(as1:4ratio)=0.025*volumeofNa2S2O3used/4o nO2*32(molarmass)*1000(mg)*1000/100(1L)=oxygeninmg/L

(ppm)


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§ BiochemicalOxygenDemand(BOD)o Ameasureoftheorganicmatterinasampleofwaterthatisbrokendownbybacteria(lowerthe

bottle)o ThestandardisBOD-5:Thisistheamountofoxygen(ppm)thatis1Lofwaterwillreactwithat20

degreesCelsiusinthedark(preventphotosynthesis)in5dayso MethodBOD-5

§ Filltwo250.0mLreagentbottleswithwaterandstopperunderwater§ DOofonebottleismeasuredimmediatelyusingtheWinklerTitration§ Theotherbottleisleftinadarkplaceat20degreesCelsiusfor5days,thenDOismeasured

bytheWinklerTitrationo Results

§ SubtractsecondresultfromfirstresulttoobtainBODinppm§ IfBOD>3ppm,thenthewaterispolluted

o BODinvariouslocations§ Cleanriverwater=1-3ppm§ DomesticSewage=350ppm§ Abattoirwaste=2600ppm§ Paperpulpmills=25000ppm

• Identifyfactorsthataffecttheconcentrationsofarangeofionsinsolutioninnaturalbodiesofwatersuchasrivers

andoceansØ Rain

§ CO32-fromdissolvedCO2

§ Na+,Cl-,SO42-fromseaspray

§ Whenrainwaterrunsalongtheground,itcanpickupNO3-,PO4

3-,Mg2+§ Iftherainwaterisacidic,toxicheavymetalslikealuminiumcandissolve

Ø HumanActivity§ Landclearing§ Growingcropsandpasture,fertiliserrunoff,etc.

Ø EffluentDischarge§ Rawortreatedsewage§ Stormwaterrunoff§ Industrialeffluente.g.Pb2+,Cd2+,Cr2+,Cu2+,Zn2+

Ø Leachingfromrubbishdumps§ Ni2+,Cd2+,Pb2+,Hg2+fromdiscardedbatteriescanleachintowaterwayswithrainwater

• Describeandassesstheeffectivenessofmethodsusedtopurifyandsanitisemasswatersupplies

Ø SCREENINGPriortoleavingdamsiteandagainonenteringthetreatmentplants,waterisscreenedtoremovemacro-objectsandscreenablesolids.Freshwaterpassesthroughfinescreenstoremovesolidobjectslikefish,logsandleaves.

Ø AERATIONAerationistheintimateexposureofwaterandair.Whenairismixedwithwater,someimpuritiesinthewater,suchasironandmanganese,becomeoxidized.Onceoxidized,thesechemicalsfalloutofsolutionandbecomesuspendedinthewater.Aerationwillremovetastesandodoursfromwateriftheproblemiscausedbyrelativelyvolatilegasesandorganiccompounds.

Ø COAGULATION/FLOCCULATIONDuringcoagulation,liquidaluminiumsulfate(alumAl2(SO4)3)(orsometimesFeCl3,whichformsFe(OH)3)isaddedtountreatedwater.Whenmixedwiththewater,thiscausesthetinyparticlesofdirtinthewatertosticktogetherorcoagulate.Next,groupsofdirtparticlessticktogethertoformlarger,heavierparticlescalledflocswhichareeasiertoremovebysettlingorfiltration.

Al3+(aq)+H2O(l)àAl(OH)3(s)


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Ø SEDIMENTATIONAsthewaterandtheflocparticlesprogressthroughthetreatmentprocess,theymoveintosedimentationbasinswherethewatermovesslowly,causingtheheavyflocparticlestosettletothebottom.Flocwhichcollectsonthebottomofthebasiniscalledsludge,andispipedtodryinglagoons.

Ø FILTRATIONTheflocculatedstreamisthensentunderpressuretoafilterwhereitpassesthroughabedcomprisedofcrushedanthracite,sandandgravel.Remainingsuspendedsolidsareremovedgivingastreamoflowturbidity.

Ø CHLORINATIONWaterisdisinfectedbeforeitentersthedistributionsystemtoensurethatanydisease-causingbacteria,viruses,andparasitesaredestroyed.Residualconcentrationscanbemaintainedtoguardagainstpossiblebiologicalcontaminationinthewaterdistributionsystem.

Ø FLUORIDATIONFluorideisaddedtothewaterunderthedirectionofNSWHealthtohelppreventtoothdecay.Drinkingwatermustcontainonemilligramoffluorideforeachlitreofwater.

Ø pHADJUSTMENTSLimeisaddedtothefilteredwatertoadjustthepHandstabilisethenaturallysoftwaterinordertominimisecorrosioninthedistributionsystem,andwithincustomers’plumbing.

§ EffectivenessofWaterTreatment

o Advantages§ Flocculation

• Remove99.9%ofbacteria+99%ofviruses• Someorganicmatterfromsoil/vegetationremoved

§ SandFiltration• Removesahighproportionofparticulatematterinlargevolumes(notefficientforsmall

particulates)§ Chlorination

• Removesmostmicro-organismsfromwaterandrelativelylowcosto Disadvantages

§ Cleconomicallyeffective(limitedagainstsomeprotozoansthatformcystsinwater)(somesuchasGiardiaorCryptosporidiumcanstillsurvive)

§ Membranefiltrationanddisinfectionwithozonearemoreeffectivealternatives(butmoreexpensive)

§ HardwatercannotbesoftenedbythewaterpurificationmethodinNSW.Todothis,ionexchangetubesmustbeused(ormicroscopicmembranefilters).

o Effectiveifaccompaniedbypropercatchmentmanagement(combinationofflocculation,sandfiltration,chlorination)

• Describethedesignandcompositionofmicroscopicmembranefiltersandexplainhowtheypurifycontaminated

waterØ Composition

§ Thinsheetsofpolypropylene,polysulfoneorpolytetrafluoroethylenewithtinyholes

Ø Design

§ Rolledintothintubes.Largenumberoftubesarebundledintoafilter.§ Waterrunacrossthesurface(notat)topreventclogging

• Usegravity,vacuum,pressurepumpstoforceliquidthroughmembranewhereparticulatesarecollected

§ Sheet• Foldedbypleating/windinginspiralaroundacore• Housedinanouterplasticcontainertoformacartridge–inserted/removedeasilyinto

filtrationline

ßPolypropyleneStructure


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• Canbebackflushedandreused§ Capillary

• Composedofhollowfibres• Waterrunsalongoutsideofcapillariesandcleanwaterpenetratesporestoinsideofeach

capillary• Manycapillariesbundledtogethertoformamicro-filtrationunitwithlargesurfacearea

§ Filterspurifywaterbyremoveparticulates/microorganismsetc.toimprovewaterqualityØ Watergoesthroughtheholesbutparticlessuchasbacteriacannotpassthroughthesheets.Thefiltercanbe

clearedbypassingcompressedairintheoppositedirectiontowhichthewaterwouldnormallyflowin.Thebacteriacanthenbedislodged.

Ø Ifthesheetsarecoatedwithdeoxycholicacid,heavymetalionscanalsoberemoved(calciumandmagnesium).Usedinindustrywheresoftdrinksandbottledwaterareproduced.

Ø Microfiltration§ 100–1000nmporesize§ Bundlesofhollowpolymerthreads§ Removefinesilt,colloids,rangeofmicrobes(but

fewviruses)Ø Ultrafiltration

§ 5–50nmporesize§ Polymers(e.g.Polysulfoneandcelluloseacetate)

–ionsremovedonlyifmembraneshavespecialsurfactantcoating

§ Removesallmicrobesincl.viruses+largerorganicmolecules

Ø Nanofiltration§ 0.5–5nmporesize§ Polymers(e.g.polyamideorcelluloseacetate)§ Removesallorganicmolecules>300FW+some

saltscontainingdivalentandtrivalentionsØ Advantages

§ Filterverysmallparticles§ Thin,soliquidsflowrapidly§ Reasonablestrong;canbecleanedandreused

Ø Disadvantages§ Expensive;sometimescloggedwithsewerage

• Performfirst-handinvestigationstousequalitativeandquantitativeteststoanalyseandcomparethequalityofwater

samples(Coveredin3.5.1)

• Gather,processandpresentinformationontherangeandchemistryofthetestsusedto:identifyheavymetalpollutionofwaterandmonitorpossibleeutrophicationofwaterways

Ø Phosphates(PO43-)§ Phosphatesareusedindetergentsandfabricsoftenersastheyarecapableoftyingupcalcium,

magnesium,ironandmanganeseions,therebyimprovingoverallwashingperformance.Phosphatesalsoaidinkillinggerms.

§ Phosphatescancontributetoanoversupplyofphosphate(eutrophication)inwaterwaysandcauseanimbalanceoftheaquaticecosystem.Excessivealgalgrowth(sometimesintheformofalgalblooms)canoccurwiththeadditionofavailablephosphatestothefreshwatersystem.Bloomsofcyanobacteria(blue-greenalgae)mayalsobetoxic.Thistoxicitymaybeacute(shorttermsevere)orchronic(longer-termlow-level),andcanbecarcinogenic.Decomposerorganismsthatrequireoxygenmayincrease,whichcandepletetheamountofoxygendissolvedinthewater.Thiscancauseotheraquaticlife,suchasfishandcrustaceans,todie.Thealgaealsocoverthesurfaceofthewaterway,preventinglightfrompenetratingintothewater.Thispreventsaquaticplantsfromphotosynthesising.


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§ Totalphosphorusisdeterminedusingcolourimetry.BoilthewatersamplewithconcentratedsulfuricacidandconcentratednitricacidtoconvertallphosphatestoPO4

3-.Addammoniummolybdateandascorbicacidtogiveabluesolution.MakeaseriesofPO4

3-standards,measuretheabsorbance,andplotthecalibrationgraph.Determinethe[PO4

3-]inthewatersamplefromthegraph.Ø Nitrates(NO3

-)§ Nitratesalsocontributetotheeutrophicationofwaterwaysandencourageexcessivealgalgrowth§ EnterthewaterwayduetoSewerageandFertiliser§ CanbemeasuredquantitativelythroughKjeldahlmethod

• Thewatersampleisboiledwithconcentratedsulfuricacidtoconvertallnitrogento(NH4)2SO4

• ExcessNaOHisaddedandboiledtoremoveallammoniumasammoniagas• NH4

+(aq)+OH-

(aq)àNH3(g)+H2O(l)• TheunreactedNaOHisbacktitratedwithHCl• HCl(aq)+NaOH(aq)àNaCl(aq)+H2O(l)• ThereactedNaOHiscalculatednNaOH=nNH3=nN

Ø HeavyMetals§ Lead,Mercury,Cadmium,Chromium,Copper,Zinc§ Pollutionofwaterbytransitionmetals(Hg,Cd,As)–enterwaterwaysfromindustrialdischarges,

roadrunoff,landfill,agriculturalrunoff§ HeavymetalsInterferewithenzymesystemsandmetabolisminthebody,Bioaccumulate(buildup

intissue),Biomagnify(concentrationincreasesasheavymetalmovesupfoodchain)andpersistinenvironmentforlongperiodsoftime

§ Canbetestedforusingprecipitationreactions(if>1ppm)andAAS(Atomicabsorptionspectroscopy)§ Othertests:IonSelectiveElectrodes(ISE),FlameAtomicAbsorptionSpectroscopy(FAAS),Graphite

Furnace(GFAAS),X-RayFluorescenceSpectroscopy(XRFS)• Gather,processandpresentinformationonthefeaturesofthelocaltownwatersupplyintermsof:catchmentarea,

possiblesourcesofcontaminationinthiscatchment,chemicaltestsavailabletodeterminelevelsandtypesofcontaminants,physicalandchemicalprocessesusedtopurifywater,chemicaladditivesinthewaterandthereasonsforthepresenceoftheseadditives

(RefertoResearchDocumentforthissection)

chemical monitoring and management notes distro copy

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