Phenomenon:OxidationofIronThissimpledemonstrationcanbeusedasaphenomenonduringaunitonchemicalweatheringofrockstoactivatestudentthinkingabouthowchemicalreactionsmaychangerocksattheEarth’ssurface.Oxidationisachemicalreactionwhereanelementlossesoneormoreelectronsandresultsinanincreaseinitsoxidationstate(ex.Fe2+→Fe3+).Forexample,ironrustformswhenironisoxidized(formingironoxide).Thetopimageshowstheoxidationofironnailsformingrust.Theoxidationofironandtheformationofironoxidesisresponsiblefortherustyredcolorcommonlyfoundinsedimentaryrockssuchasthesandstoneinthesecondimage.Somemineralsinrocks(suchasolivine,pyroxeneandmagnetite)containironandoxidizeinthepresenceofoxygenfromtheatmosphereandwaterattheEarth’ssurface.Theoxidationofironisacceleratedinthepresenceofacidandsalt.Inthisdemonstration,soakapieceoffinesteelwoolinvinegarandapinchofsaltforafewminutes.ShakeofftheexcessvinegarandinsertthesteelwoolintoanErlenmeyerflask(1000mlflaskworkswell).Putaballoonontopoftheflasktosealthesteelwoolinsidetheflask(bottomleftfigure).Afteraboutanhour,theballoonwillbedrawn

downintotheflaskastheoxygenintheairreactswiththeironinthesteelwooltoformironoxide(bottomrightfigure).Thisactivitydemonstratesthatironreactswithoxygenintheatmospheretoformironoxide.Likewise,iron-bearingmineralsintheEarth’scrustmayreactwithoxygentoformironoxide.Aftertheexperiment,thesteelwoolcanberemovedfromtheflask.Itwillbenoticeablyrustyinappearanceduetotheoxidationofironandtheformationofironoxide.

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