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Corrosion

Corrosion. What Causes It and What Prevents It ?. What is Corrosion ?. Corrosion is an electrochemical reaction. The corrosion of metals is an example of an oxidation-reduction reaction, or also referred to as a “re- dox reaction.”. What is a re- dox reaction?.

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Corrosion

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  1. Corrosion What Causes It and What Prevents It ?

  2. What is Corrosion ? • Corrosion is an electrochemical reaction. • The corrosion of metals is an example of an oxidation-reduction reaction, or also referred to as a “re-dox reaction.”

  3. What is a re-dox reaction? • An oxidation-reduction reaction is a chemical reaction where the oxidation number of atoms involved change. • Oxidation describes the loss of electrons by a molecule, atom or ion . • Reduction describes the gain of electrons by a molecule, atom or ion.

  4. Redox reactions cause the rusting and corrosion of certain metals • The key reaction in the rusting of iron is the reduction of oxygen: • O2 + 4 e- + 2 H2O → 4 OH- • Electrons for this reaction are supplied by the oxidation of iron in the reaction: • Fe → Fe2+ + 2 e− • These reactions occur in the presence of water, with this reaction being crucial to corrosion: • 4 Fe2+ + O2 → 4 Fe3+ + 2 O 2− + 4 e− • Certain environments can accelerate the reactions involved.

  5. How do we prevent rust? • We cannot totally prevent rust from occurring completely. • One thing we can do is sacrifice a substitute metal in place of the iron (or other metal) we wish to protect. • The redox reaction will affect the most reactive metal it comes in contact with. • We can connect more reactive metals to the one we wish to save. • Another method is to “paint” the iron with a layer of more reactive metal to be reacted with.

  6. Why do we care? • Prevention of rust to certain metals is important for a few reasons ……… The Kinzua Bridge after it collapsed The collapsed Silver Bridge, picture taken as seen from the Ohio side of the river An oil tanker carrying thousands of gallons of oil

  7. Today’s Lab • Part 1: Testing environments • Looking to see what environments accelerate corrosion. • Part 2: Testing metals that protect iron from corrosion • Looking to see what metals are more reactive than iron.

  8. Safety • Goggles at ALL times • We are dealing with strong acids and strong bases, so care must be taken when handling. • Gloves when handling chemicals.

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