corrosion: all at sea - deakin university
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Page|29 SampleAnswers–Corrosion:AllatSea–AustralasianCorrosionAssociationFoundation
S A M P L E A N S W E R S
Corrosion:AllatSea
IntroductionTheoceanisoneofthemostnaturalcorrosiveenvironments,madeupofdissolvedminerals(mainlysodiumchloride)andcarbondioxidefromtheatmosphere.
Residentslivingnearcoastalareasmayneedtoreplacemetalobjectsregularlyifleftoutsideforprolongedperiodsduetocorrosion(e.g.cars,bikes,gardentools,BBQ’s,golfclubs).Familiesorbusinessesthatrelyonboatsand/orotherleisurewatercraft(e.g.jetskis,yachts,ships)withmetallicparts,mustdeterorprotectagainsttheeffectsofcorrosion
Photo:DrIanMacLeod,HeritageConservationSolutions.Photographusedwithpermission
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Atsomelocations,marinearchaeologistsfindmetalartefactsandshipwreckswithseverecorrosionduetotheprolongedtimespentsubmergedintheocean,whileatothersitesthereareartefactsandshipwreckswithalmostnocorrosion.Whyisthereadifferenceintheextentofcorrosion?
Inthisactivity,youwillsimulateandtestwhichenvironmentalconditionsinfluencetheratecorrosionofdifferentmetalsanddescribetheobservedchanges.
KeyideasCorrosion–Theprocessofdestructionordeteriorationofametallicmaterialasaresultofchemicalreactionswiththesurroundingenvironment.
Metal-Asubstancethatusually(1)canconductelectricity,(2)canconductheat,(2)hasshininess(lustre),andcanbedeformedwhenstruckwithahammerorotherhardobject(malleability).Whenmetalsreact,theytendtoloseelectronstoformpositiveions(cations).
Chemicalcomposition–Therelativeamountsofdifferentelementsorsubstancesthatarepresentinasample.
Alloy-Asolidmixtureoftwoormoremetals.Somealloyscanincludenon-metalcomponents.Steelisanalloythatconsistsofironwithsmallamountsofcarbon.Stainlesssteelisanalloythatconsistsofironwithsmallamountsofcarbonandabout18%chromium.18-caratgoldinjewelleryisanalloyof75%gold,7.5%silverand7.5%copper.Bronzeandpewterareothercommonalloys.
Reactivityseries–Arankingoflistingofmetalsfromthemostreactivetotheleastreactive.
Solution-Amixtureoftwoormoresubstancesthatishomogeneous.Homogeneousmeansthatthesolutionisevenlymixedandhasthesameappearanceandcompositioneverywhereinthemixture.Itispossibletohavegassolutions,liquidsolutions,andsolidsolutions.Inthislaboratorylearningactivity,solutionwillrefertowater-basedliquidsolutions.
Concentration-Theratiooftheamountofasoluteinasolventortotalsolution.Therearemanywaysofmeasuringandexpressingconcentration.Inthislaboratorylearningactivity,theconcentrationwillbeexpressedasthepercentagemassperunitvolume.
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%(m/v)-Percentagemasspervolume(%m/v)isonemethodofmeasuringconcentration,definedasthemassofthesoluteper100mLofsolution
concentration (%m/v)=mass of dissolved substance (g)
volume of solution (mL)×100%
Dissolve-Theprocessinwhichthesoluteinteractswiththesolventtoformasolution.Thisonlyappliestomixturesinwhichthesolutewasoriginallyinadifferentgas/liquid/solidstatesfromthesolvent.
Solute–Asubstancewhichisdissolvedinasolventtoformasolution.
Solvent–Thelargestcomponentofaliquidoragas,inwhichanothersubstance(thesolute)isdissolvedtoformasolution.
Investigation-Ascientificprocessofansweringaquestion,exploringanideaorsolvingaproblemthatrequiresactivitiessuchasplanningacourseofaction,collectingdata,interpretingdata,reachingaconclusionandcommunicatingtheseactivities
Variable-Somethingthatcanchange.
Dependentvariable-Variablethatchangesinresponsetochangesintheindependentvariableandthatisobservedormeasured.
Independentvariable-Variablethatisdeliberatelychanged.
Controlledvariables-Variablesthatarekeptconstant.
Fairtest-Whentestingdifferentmaterialsallthevariablesexcepttheonebeingtestedneedtobekeptthesame.
Equipmentandmaterials• Plasticorglassbeakers• Cookingsalt• Plasticspoonsorglassstirringrods• Demineralisedwater• Paperclips,hairpins(or‘bobbypins’),metalwashers,
aluminiumfoil(1cmstrips),ironnails,galvanisednails,etc.• Plastictweezersortongs• 100mLmeasuringcylinder• Stickylabelsormarkerpens• Safetyglasses/gogglesandgloves
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Optional• Metalcoins• Stainlesssteelcutlery• Additionalmetalsamples• Carbonatedmineralwaterorsodawater• Softdrink• Hotwaterbath• Thermometer• Scissors• Steelwool• Emerypaperorsandpaper• Electronicbalanceorscales• Timerorstopwatch
Hazards• Nails,aluminiumfoilpieces,emerypaperandsteelwoolmay
causecutsand/orlacerationstoskinifnothandledcorrectly.• Waterthatisusedincorrosionexperimentsmaycontained
dissolvedions,andshouldnotbeconsumed.• Useofakettletoboilwatermustbesituatedawayfromwet
areasandmustbeingoodcondition(i.e.nofrayedchordsorexposedwires).Thereisdangerofburnsfromahotapplianceand/orhotwaterorsteam.
LessonplanorganisationLessons1and2:RecallofconceptslearnedfromYears7and8onsolutions,solvents,solutes,concentration,reactivityseriesofmetalsandchemicalreactionsinvolvingformationofrust/corrosion.
%(m/v)-Percentagemasspervolume(%m/v)isonemethodofmeasuringconcentration,definedasthemassofthesoluteper100mLofsolution
concentration (%m/v)=mass of dissolved substance (g)
volume of solution (mL)×100%
Lesson3:Plantheinquiryandsetuptheinvestigation.
Lesson4:Checktheresultsoftheinvestigationandanalysetheresults.
Lessons5and6:Completepresentationoftheinvestigationasalaboratoryreport,scientificposter,multimedia,orotherformat.
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PartA1:InvestigationInstructionsYouwillworkingroupsofapproximatelyfourstudents.Eachgroupisassignedtwometalseach,sothateachpairofstudentsworkswiththesamemetal.
Inyourgroups,designanexperiment,usingtheprovidedequipment,thatwilldetermineifametalundergoescorrosion.
Suggestedprocedureforpreparationofsolutions:
• Toprepareasolutionofconcentrationof5%(m/v)ofsaltindemineralisedwater,weigh5gofsaltintoadrybeakerandaddapproximately80-90mLdemineralisedwater.Dissolvethesaltbeforetoppingupwithdemineralisedwatertothe100-mLmark.
• Thisprocedurecanbeadaptedtomakesolutionswithotherconcentrationsofsaltindemineralisedwater.
• Thisprocedurecanbeadaptedtomakesolutionswithotherconcentrationsofsaltinothertypesofwater.
PartA2:ScientificquestionsSuggestoneortwoscientificquestionsthatyoucouldaskusingyourexperimentalequipmentandmaterials:
Possiblescientificquestionsinclude:• Howcancorrosionbedetected?• Howcanafairtestbeensured?• Aresomemetalscorrodedmoreeasily?Aresomemoreresistant
tocorrosion?• Iscorrosionmorepronouncedinhotterwater?• Iscorrosionmorepronouncedinsaltywater?• Iscorrosionmorepronouncedindifferenttypesofwater?
Carbonatedwater?Softdrink?Tankwater?Borewater?
Somescientificquestionswillbemoresuitableforinvestigationinaclassroomsetting.Yourteacherwillleadadiscussiontodecidewhichscientificquestionswillbeinvestigated.Yourgroupwillthendecidehowtoinvestigatethatquestion.
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Thescientificquestionthatmygroupwillinvestigateis:
NOTETOTEACHERS:Dependingonthemetal,itispossibletovisuallyobservetheeffectofcorrosionoverafewhours.ItisrecommendedthatLessons3and4arenotadoubleperiod.
Possiblescientificquestionsinclude:• Aresomemetalscorrodedmoreeasily?Aresomemoreresistant
tocorrosion?• Iscorrosionmorepronouncedinsaltywater?
Ourhypothesisis:
Ourindependentvariableis:
Thisdependsonthescientificquestion.Foreachtest,possibleindependentvariablesincludesaltcontent,timeofexposuretowater,temperature,theratiooftheexposedsurfaceareaofthemetaltoitsvolume(ormass),etc.
Ourdependentvariableis:
Theobviousobservable(dependent)variableistheextentofcorrosion.
(Atyears9and10,thereisnoeasymethodofquantifyingtheextentofcorrosion.)
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Ourcontrolledvariablesare:
Controlledvariablesarethevariablesthatarekeptfixed.Controlledvariablesincludethesizeandshapeofthemetalpieces.Anypossibleindependentvariablethatisnotvariedisacontrolledvariable.
Wewillusethefollowingexperimentalprocedure.(Ifappropriate,makeadrawingofyourproposal.)
Apossibleexperimentalprocedureis:
• Prepareacontrolconsistingofabeakerofdemineralisedwater.• Prepareasetofbeakerswithconditionsthatvaryoneormore
independentvariables.Controlledvariablesincludethesizeandshapeofthemetalpieces.Anypossibleindependentvariablethatisnotvariedisacontrolledvariable.
• Forexample,tomakeasaltsolutionof10%m/vofsaltinwater,weigh10gofsaltintoadrybeakerandfillapproximately80mLwater.Dissolvethesalt,thenfillto100mLwithmark.
• Moststudentswillnothavethisnextstep.Rubthemetalsampleswithametalfile,sandpaperorsimilarabrasivesurface/material.Whatdoesthisachieve?
• Placethemetalsample(s)intothevariouswatersamples.• Waitanappropriatetimeinterval.Itissuggestedthatatimeinterval
of1-2daysbetweenlessons3and4isgood.Anearlierversionofthislaboratorylearningactivityincorrectlysuggestedthatitmightbepossibletousethemassofthesolidtomonitortheextentofcorrosion.Furthertestshavefoundthatthechangeinmassisinsignificant.
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Arethereanysafetyissuestoconsider?
• Nails, aluminium foil pieces, emery paper and steel wool maycausecutsand/orlacerationstoskinifnothandledcorrectly.
• Water that is used in corrosion experiments may containeddissolvedions,andshouldnotbeconsumed.
• Use of a kettle to boilwatermust be situated away fromwetareas andmust be in good condition (i.e. no frayed chords orexposedwires). There is danger of burns fromahot applianceand/orhotwaterorsteam.
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PartA3:TestingourscientificquestionGetapprovalfromyourteacherofyourplans(PartA2)beforestartingPartA3.
Remembertotakephotosthroughoutyourexperimenttoaddtoyourscientificposter.
Whathappened?Recordyourobservationsormeasurements:
Tests usingPaslode Bright Nails from Bunnings had easily observablecorrosion after a few hours, even with deionised or demineralisedwater.Thewater turnsanorangeycolour that is characteristicof rust(ironoxide)andorangeflecksarevisibleonthesurfaceofthenails.
Tests using Pinnacle “yellow zinc” washers with deionised ordemineralisedwater produced small bubbles of gas on the surface ofthewashers.Therewerevisiblechangestothesewashers.
Therewaslessvisiblechangetowasherswhichhadmostofthe“yellowzinc” coating removedby theuseof ametal file before the test (twoleft-hand-mostwashers).
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Onceallthegroupshavesummarisedtheirobservationsormeasurements,a‘scribe’tocollectalltheresultsfromeachofthegroupssothatyoucancollateasummaryoftheentireclass’sresults.
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PartB:Analysisofresults
PartC:Drawingconclusions(discussionprompts)Whatwasthepurposeofusingdemineralisedwaterinsteadoftapwaterinthisexperiment?
Demineralisedwaterhasverylowconcentrationsofcommonionsthatcause hardness of tap, bore and mineral water. Any corrosion thatoccursindemineralisedwater,indicatesthatthiscorrosionisnotduetoionslikeMg2+orCa2+,thatarecommonlyfoundinborewaterandother“hard”waters, andalsonotdue toCl-, that is commonly found in tapwaterinmanytowns.
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Lookingatyourresults,whichmetalswerethemostreactivetothecorrosiveenvironment(s)simulatedinthisactivity?
Of the commonly available metals, aluminium, zinc and iron are themost reactive. The corrosionof iron is theeasiest to seeas there is averyobviouscolourchange.
Lookingatyourresults,whichmetalsweretheleastreactivetothecorrosiveenvironment(s)simulatedinthisactivity?
Most metals are resistant to corrosion because shops and suppliersusually sell alloysandmetalswith surface coatings,bothofwhicharedesignedtominimisecorrosion.Coins,copper,alloy(egstainlesssteel)aregenerallyresistanttocorrosion.
Wasthisafairtest?Aretherevariablesthatyouhavenotcontrolledinyourexperiment?Howmightthesevariablesaffectyourconclusions?
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Usingtheinternet,learnaboutthechemicalcomposition(makeup)ofsomeofthemetalsthatyouhaveusedinthisactivity.
ThePaslodewebsitestatesthatbrightnailsareun-plated,brightironwithnocorrosionprotectivecoating<https://www.paslode.com.au/products/fasteners/104-paslode-nails>.
Usinginternetortextbookresources,writeawordequationforthereactionofoneofthemetalsthatyoutestedfromthisactivity.
iron(s)+oxygen(g)®iron(III)oxide
BBCBitesize(2014)<http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway/chemical_resources/making_carsrev1.shtml>
Usinginternetortextbookresources,writeachemicalequation,describedbytheabovewordequation.
Theactualrustingprocessisquitecomplicatedandinvolvesseveralstepsandwithseveralironspecies.Theironspeciescanhavedifferentforms,dependingontheamountofwaterthatispresent.
Atyear10level,theoverallequationgivenbelowisacceptable.
4Fe(s)+3O2(g)®2Fe2O3(s)
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PartD:Extension1Theoceanisnottheonlycorrosiveenvironment.Usetheinternetoralibrarytoresearchothertypesofcorrosiveenvironmentsandthetypesofcorrosionthatcanoccurwithinthem.
Corrosiondependsonthreefactors:• Ametalthatcanbecorroded(oxidised)• Moisture(tohelpthemovementofions/electrolytesduringthe
corrosionprocess)• Presenceofoxygenofsomeotheroxidisingagent.
Non-marineenvironmentsthathavethesefactorsinclude:• Sea-sideenvironment(onlandbutwithlotsofseaspray)• Inagardenwithlotsofrain• Areasthatusesalttode-iceroads(rarelyusedinAustralia)
Usetheinternetoralibrarytoresearchmaterialsormethodsusedtopreventcorrosionandsuggestwhichone(s)aresuitablefortheenvironment(s)thatyouhavedescribedabove.
Materialsormethodsusedtopreventcorrosioninclude:• Alloyslikestainlesssteel(mainlyiron,butwithsmallamountsof
carbonandabout18%chromium)• Surfacecoatingslikepaint• Surfacecoatings/treatmentslikegalvanisation,whichisalayerof
zinc(whichformsaprotectivelayerofzincoxide)• Usingasacrificialanode,whichattachesapieceofeasily-corroded
metaltothepieceofmetalbeingprotected.Thesacrificialanodeiscorrodedinpreferencetothepieceofmetalbeingprotected.
InJanuary2003,thefamouschairliftatArthur’sSeat,ontheMorningtonPeninsula(southofMelbourne)collapsed,injuring
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passengersandleavingsomestrandedforseveralhours(seefootnote2).
Usetheinternetoralibrarytoresearchtheanswerstothefollowingquestions:
• Whattypeofcorrosionwasblamedforthisnear-disaster?• Howdoesthistypeofcorrosionoccur?• Whattypesofpersonnelwereinvolvedintheinvestigationand
managementofthisaccident?• Whathumanfactorswereinvolvedintheincident?• Howcouldthesefactorshavebeenmanaged?• Whateconomiccostsoccurredasaresultoftheaccident?
PartE1:Extension2-InstructionsConsultwithyourteacherifyoushoulddothissecondextension.
Basedonyourresultsandtheclassresults,canyouproposesomeadditionaltestsrelatingtothecorrosionofmetals?TobettercompareyourresultsfromthisPartwithyourearlierinvestigations,itissuggestedthatyouhavesimilarhypothesesandexperimentalprocedures.
2 TheAge(2003).‘ChairliftCollapse18Hurt’Retrieved16thJuly2017from<http://www.theage.com.au/articles/2003/01/03/1041566225573.html>.
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PartE2:Extension2-ScientificquestionsOurhypothesisis:
Apossiblehypothesis is that thepresenceofdissolvedcarbondioxidewill displace oxygen, and that the absence of oxygen is expected todecreasetheextentofcorrosioncomparedtodemineralisedwater.
Ourindependentvariableis:
Thisdependsonthescientificquestion.Foreachtest,possibleindependentvariablesincludesaltcontent,temperature,theratiooftheexposedsurfaceareaofthemetaltoitsvolume(ormass),etc.
Ourdependentvariableis:
Again,itissuggestedthattheextentofcorrosionbemonitoredvisually.
Ourcontrolledvariablesare:
Controlledvariablesarethevariablesthatarekeptfixed.Controlledvariablesincludethesizeandshapeofthemetalpieces.Anypossibleindependentvariablethatisnotvariedisacontrolledvariable.
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Wewillusethefollowingexperimentalprocedure.(Ifappropriate,makeadrawingofyourproposal.)
Ideally this procedure should be very similar as the procedure withdemineralisedwater,sothatthetestsforthetwotypesofwatercanbecompared. However, some students might think of ways to improvetheirprocedure,andhencetheprocedureheremightbedifferentfromtheprocedurewithdemineralisedwater.
Arethereanysafetyissuestoconsider?
Theseshouldbesimilartosafetyissuesforthetestswithdemineralisedwater.
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PartE3:Extension2-TestingourscientificquestionRemembertotakephotosthroughoutyourexperimenttoaddtoyourscientificposter.
Whathappened?Recordyourobservationsormeasurements:
There were no significant differences between the tests usingcarbonatedwateranddemineralisedwater.
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Onceallthegroupshavesummarisedtheirobservationsormeasurements,a‘scribe’tocollectalltheresultsfromeachofthegroupssothatyoucancollateasummaryoftheentireclass’sresults.
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PartE4:Extension2-Analysisofresults
PartF:Scientificposter5. Completeintroduction:
• One-totwo-paragraphoverviewofthereasonforcompletingtheinvestigation,thescientificcontextandanexplanationoftherelevantscientifictheory.
• Allsourcesneedtobeacknowledged.
6. Completethediscussionsection:
• Discussyourscientificquestioninthissection.POEisoftenausefulguideistohelpwhatyouputinthissection:
a. Predict.Yourscientificquestion,hypothesisandpredictionofwhatwillhappen.
b. Observe.Whatyouobservedormeasured.
c. Explain.Didyourobservationsormeasurementsagreewithyourexpectationsandprediction?Canyouexplainwhy?
• Discusstheimplicationsofyourresults.
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• Werethereanylimitationstoyourinvestigation?
7. Completetheconclusionsection:
• Stateyourmainresultfromyourinvestigation.
• Statewhetherthissupportsorrefutesyourhypothesis.
8. CompleteReferencesandAcknowledgements.
AcknowledgementsThecontributionsofLindaLawrie,JessicaSawandIanBentley,totherefinementofthislaboratorylearningactivityaregratefullyacknowledged.
• PhotographofshipwreckhasbeenusedandredistributedbypermissionofDrIanMacLeod,HeritageConservationSolutions.
• PhotographsofcorrosionexperimentshavebeenusedandredistributedbypermissionofJessicaSawandKieranLim.
CopyrightandCreativeCommonsExceptinglogos,trademarksorotherthird-partycontentasindicated,thisresourceisdistributedunderaCreativeCommons‘Attribution-NonCommercial-ShareAlike’4.0InternationalLicense.Themoralrightsoftheauthors,CarolynDrenenandKieranLim,havebeenassertedundertheAustralianCopyrightAct1968(Cth).
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