2016年第42周化學教研成果雙語igcse-iron and aluminium

Ironandaluminium（鐵和鋁Metalsaremalleable-theycanbebentandsh dwithoutbreaking.Thisisbecausetheyconsistoflayersofatomsthatcanslideoveroneanotherwhenthemetalisbent,hammeredorpressed.Metallicbonds（金屬鍵Metalsformgiantstructuresinwhichelectronsintheouterssofthemetalatomsarefreetomove.Themetallicbondistheforceofattractionbetweenthesefreeelectronsandmetalions.Metallicbondsarestrong,sometalscanmaintainaregularstructureandusuallyhavehighmeltingandboilingpoints.（高和高沸點）Metalsaregoodconductorsofelectricityandheat.Thisisbecausethedelocalisedelectrons（電子）canmovethroughoutthemetal.Metalextractionandthereactivityseries（金屬的和活動性Themethodusedtoextractametalfromitsoredependsuponthestabilityofitscompoundintheore,whichinturndependsuponthereactivityofthemetal:Theoxidesofveryreactivemetals,suchasaluminium,formstableoxidesandothercompounds.Alotofenergyisneededtoreducethemtoextractthemetal.Theoxidesoflessreactivemetals,suchasiron,formlessstableoxidesandothercompounds.Relativelylittleenergyisneededtoreducethemtoextractthemetal.So,themethodofextractionofametalfromitsoredependsonthemetal'spositioninthereactivityseries.ReactivityandextractionThetabledisplayssomemetalsindecreasingorderofreactivityandthemethodsusedtoextractthem.(Non-ReductionbycarbonorcarbonReductionbycarbonorcarbonReductionbycarbonorcarbonReductionbycarbonorcarbon(Non-VariouschemicalVariouschemicalVariouschemicalVariouschemicalWecanseefromthetablethatreactivemetals,suchasaluminium,areextractedbyelectrolysis,whilealessreactivemetal,suchasiron,maybeextractedbyreductionwithcarbon.Becausegolditissounreactive,itisfoundasthenativemetalandnotasacompound.Itdoesnotneedtobechemicallyseparated.However,chemicalreactionsmaybeneededtoremoveotherelementsthatmightcontaminatethemetal.Extractingaluminium（鋁的AluminiumisthemostabundantmetalonEarth.Butitisexpensive,largelybecauseoftheamountofelectricityusedintheextractionprocess.Aluminiumoreiscalledbauxite（鋁土礦）Thebauxiteispurifiedtoyieldawhite-aluminiumoxide-fromwhichaluminiumcanbeTheextractionisdonebyelectrolysis.Butthealuminiumoxidemustbemeltedsothaectricitycanpassthroughit.However,aluminiumoxidehasaveryhighmeltingpoint(over2000°C)soitwouldbeexpensivetomeltit.Instead,itisdissolvedinmoltencryolite（溶解在熔融的冰晶石中）-uminiumcompoundwithalowermeltingpointthuminiumoxide.Theuseofmoltencryoliteasasolventreducessomeoftheenergycostsinvolvedinextractingaluminium.Thediagramshowsuminiumoxideelectrolysiscell.Boththenegativeelectrode(cathode)andpositiveelectrode(anode)aremadeofgraphite,aformofcarbon.AluminiumionsreceiveelectronsatthenegativeelectrodeandarereducedtoaluminiumAl3++3e-→Themoltenaluminiumsinkstothebottomofthecell,whereitistapped Oxideionsloseelectronsatthepositiveelectrodesandareoxidisedtooxygengas:2O→O Thisoxygenreactswiththecarbonofthepositiveelectrodes,formingcarbondioxide,sotheygraduallyburnaway.Asaresult,thepositiveelectrodeshavetobereplacedfrequently.Thisaddstothecostoftheprocess.Extractingiron（煉鐵Theblastfurnace（高爐煉鐵Ironisextractedfromironoreinahugecontainercalledablastfurnace.IronoressuchashaematitecontainiroI)oxide,Fe2O3.TheoxygenmustberemovedfromtheiroI)oxideinordertoleavetheironbehind.Reactionsinwhichoxygenisremovedarecalledreductionreactions.Carbonismorereactivethaniron,soitcandisplaceironfromiroI)oxide.Herearetheequationsforthereaction:IroI)oxide+carbon→iron+carbondioxide2Fe2O3(s)+3C(s)→4Fe(l)+3CO2(g)Inthisreaction,theiroI)oxideisreducedtoiron,andthecarbonisoxidisedtocarbondioxide.Intheblastfurnace,itissohotthatcarbonmonoxidecanbeused,inplaceofcarbon,toreducetheiroI)oxide:iroI)oxide+carbonmonoxide→iron+carbondioxideFe2O3(s)+3CO(s)→2Fe(l)+3CO2(g)Rawmaterialsforthereaction（原材料的反應RawIronoreAcompoundthatcontainsBurnsinairtoproduceheat,andreactstoformcarbonmonoxide(neededtoreducetheironoxide)HelpstoremoveacidicimpuritiesfromtheironbyreactingwiththemtoformmoltenslagAllowsthecoketoburn,andsoproducesRemovingThecalciumcarbonateinthelimestonethermally posestoformcalciumoxide.calciumcarbonate→calciumoxide+carbondioxideCaCO3(s)→CaO(s)+Thecalciumoxidethenreactswithsilica(sand)impuritiesinthehaematite,toproduceslag-whichiscalciumsilicate.calciumoxide+silica→calciumsilicateCaO(s)+SiO2(s)→CaSiO3(l)Thisreactionisaneutralisationreaction.Calciumoxideisbasic(asitisametaloxide)andsilicaisacidic(asitisanon-metaloxide).Usesofironandaluminium（鐵、鋁的使用）IronandsteelIronisanelement.Steelisloyofironwithcarbonandsometimesotherelementsinverysmallties.Steelisharderandstrongerthanironandlesslikelytorust.Ironversusaluminiuminthecarindustry（鐵鋁在汽車行業(yè)Ironandaluminiumareusedtobuildcars.Theyarebothmalleable-theycanbebentorpressedintosh .Thetablesummarisessomedifferencesintheirproperties.CorrodesAluminiumhassomeadvantagesoversteel.Sinceithasalowerdensitythanironorsteel,acarbodymadefromaluminiumwillbelighterthanthesamecarbodymadefromsteel.ThisresultsinimprovedfuelAlso,aluminiumdoesnotcorrodeeasilybecauseithasaprotectivelayerofaluminiumoxide.Therefore,acarbodymadefromaluminiumwillcorrodelessthanonemadefromsteel.Itshouldlastlongerasaresult.However,aluminiumismoreexpensivethansteel.Acarmadefromaluminiumislikelytobemoreexpensivethanonemadefromsteel.Otherusesofironandsteel（鋼鐵的其他應用Steeliswidelyusedintheconstructionindustry.Foritisusedfortheframesofmanylargebuildings,andintheconstructionofbridges,becauseitisverystrongitisusedincablesforcranesbecauseitisverystrongundertension(whenitisusedtoreinforceconcretebecauseitexpandsandcontractsatthesameratewhenheatedandcooled,anditaddsstrengthandflexibilitytotheconcrete(whichwouldbebrittlewithoutit)Otherusesofaluminium（鋁的其他應用）Aluminiumhasavarietyofuses.ForitisusedintheaerospaceindustrybecauseofitslowitisusedinthehomeasfoilforwrapandstoringfoodbecauseitsprotectiveoxidelayerpreventsitfromreactingwiththechemicalsinfooditisusedinhighvoltagepowerlinesintheNationalGridbecauseitisagoodconductorofelectricity,anditslowdensitypreventsthewiresfromsaggingtoomuchorbreakingundertheirownweightUsesofironandaluminium（合金loyisamixtureoftwoormoreelements,whereatleastoneelementisametal.Mostalloysaremixturesoftwoormoremetals.Forexample,brassisamixtureofcopperandzinc.Steelisloyofironwithcarbon,butotherelementsmayalsobeaddedtochangeitsproperties.Alloysareusefulbecausethepropertiesofthealloyaredifferentfromthepropertiesoftheelementstheyaremadefrom.Alloyscontainatomsofdifferentsizes.Thesedifferentsizesdistorttheregulararrangementsofatoms.Thismakesitmoredifficultforthelayersto