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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


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.


%(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


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.


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.


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.)


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.


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.


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).


Onceallthegroupshavesummarisedtheirobservationsormeasurements,a‘scribe’tocollectalltheresultsfromeachofthegroupssothatyoucancollateasummaryoftheentireclass’sresults.


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.


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?


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)


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


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>.


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.


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.


PartE3:Extension2-TestingourscientificquestionRemembertotakephotosthroughoutyourexperimenttoaddtoyourscientificposter.

Whathappened?Recordyourobservationsormeasurements:

There were no significant differences between the tests usingcarbonatedwateranddemineralisedwater.


Onceallthegroupshavesummarisedtheirobservationsormeasurements,a‘scribe’tocollectalltheresultsfromeachofthegroupssothatyoucancollateasummaryoftheentireclass’sresults.


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.


• 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).