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Electrochemistry Test Notes.docx

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York University
CHEM 1000
Michael Hempstead

Electrochemistry Corrosion  Corrosion is an electrochemical process in which metal reacts with its environment to form an oxide or other compound  We live in an oxidizing environment where corrosion of a metal occurs  Corrosion of iron is a problem more than corrosion of aluminum because of the nature formed on the surface of the metal  4Al + 3O2 - 2Al2O3  Aluminum oxide adheres tightly to the surface of the metal  Iron compounds flake off exposing new iron to be corroded  Corrosion of iron is a complex process affected by other substances than oxygen  First oxidation of iron starts on a surface with oxygen and water  Fe - Fe ^2+ + 2e-  Iron ions diffuse through water through a surface metal  The electrons are picked up by oxygen molecules dissolved in water on the surface at a point away from the original oxidation site  1/2O2 + H2O + 2e- - 2OH-  Combo of iron (II) ions and hydroxide ions form a low-solubility precipitate of iron(II) hydroxide which is further oxidized by oxygen and water to form iron (III) hydroxide, yellow-brown solid  The red-brown rust is from dehydrated iron(III) hydroxide to form iron(III) hydroxide and hydrated iron (III) oxide  Certain conditions are needed to start rusting  Because iron can be corroded by other substances, this explains why acid rain corrodes iron more than natural rain  Ships rust in seawater than in freshwater  Chloride ions from salt blocks the protective oxide coatings protecting the metal which exposes more metal to be corroded  Electrolytes like sodium chloride conduct electricity and improve charge transfer accelerating the rusting process  Rusting of iron can be accelerated by acidic solutions,
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