Download Phenomenon: Oxidation of Iron

Phenomenon:OxidationofIron
Thissimpledemonstrationcanbeusedasa
phenomenonduringaunitonchemicalweatheringof
rockstoactivatestudentthinkingabouthowchemical
reactionsmaychangerocksattheEarth’ssurface.
Oxidationisachemicalreactionwhereanelement
lossesoneormoreelectronsandresultsinan
increaseinitsoxidationstate(ex.Fe2+→Fe3+).For
example,ironrustformswhenironisoxidized
(formingironoxide).Thetopimageshowsthe
oxidationofironnailsformingrust.Theoxidationof
ironandtheformationofironoxidesisresponsible
fortherustyredcolorcommonlyfoundin
sedimentaryrockssuchasthesandstoneinthe
secondimage.Somemineralsinrocks(suchasolivine,
pyroxeneandmagnetite)containironandoxidizein
thepresenceofoxygenfromtheatmosphereand
waterattheEarth’ssurface.Theoxidationofironis
acceleratedinthepresenceofacidandsalt.
Inthisdemonstration,soakapieceoffinesteelwool
invinegarandapinchofsaltforafewminutes.
NationalParkServicePhoto
Shakeofftheexcessvinegarandinsertthesteelwool
intoanErlenmeyerflask(1000mlflaskworkswell).Putaballoonontopoftheflasktosealthe
steelwoolinsidetheflask(bottomleftfigure).Afteraboutanhour,theballoonwillbedrawn
downintotheflaskastheoxygenintheair
reactswiththeironinthesteelwoolto
formironoxide(bottomrightfigure).This
activitydemonstratesthatironreactswith
oxygenintheatmospheretoformiron
oxide.Likewise,iron-bearingmineralsin
theEarth’scrustmayreactwithoxygento
formironoxide.Aftertheexperiment,the
steelwoolcanberemovedfromtheflask.
Itwillbenoticeablyrustyinappearance
duetotheoxidationofironandthe
formationofironoxide.