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Direct Redox Reactions

Introduces reduction/oxidation reactions and shows relative oxidation activity of many metals.

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Preserving the Statue

Preserving the Statue

Credit: Trilok Rangan
Source: http://www.flickr.com/photos/64807146@N00/4268621613
License: CC BY-NC 3.0

As you enter New York Harbor, you pass Liberty Island. On that island is a very large green statue that has come to represent freedom for millions of people. The original copper color has weathered over the years, but the values represented by the statue still remain unchanged.

Amazing But True

  • The Statue of Liberty presents an interesting combination of chemical challenges. The frame is made of iron while the “skin” is copper, giving rise to the possibility of an oxidation-reduction reaction between the two metals. The immediate environment is moist with a significant amount of salt water in the air. A number of electrochemical processes can (and did) occur over the years since its arrival in the U.S. in 1895.
  • Credit: Boston Public Library
    Source: http://www.flickr.com/photos/boston_public_library/9550111150/
    License: CC BY-NC 3.0

    An advertisement from the late 19th century showing the Statue of Liberty in her original copper skin [Figure2]

  • A major problem with the statue has to do with the original construction. The copper skin at places came in direct contact with the iron support beams. To work around the situation, asbestos pads covered with shellac were placed between the iron and copper. However, salt water broke this barrier down and set up a situation of limited electrical conductivity leading to corrosion.
  • After cleaning all the corrosion off, the iron portion was treated with zinc. A quick look at the activity series explains why. Zinc is above iron in the series, meaning that zinc would be more likely to oxidize while iron would remain in the metallic state and not corrode.
  • Watch a video of the history of the Statue of Liberty at the link below: https://www.youtube.com/watch?v=LY8F8QObsTA

Show What You Know

Use the links below to learn more about the Statue of Liberty, then answer the following questions.

  1. Why is the Statue of Liberty green?
  2. What was the main problem identified by the National Park Service?
  3. What was used to blast away the old coatings in order to repair the corrosion seen in 1984?
  4. How was the statue treated to slow down further iron corrosion?
  5. Why were plastic cooling towers used as replacement items when the statue was renovated?

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Image Attributions

  1. [1]^ Credit: Trilok Rangan; Source: http://www.flickr.com/photos/64807146@N00/4268621613; License: CC BY-NC 3.0
  2. [2]^ Credit: Boston Public Library; Source: http://www.flickr.com/photos/boston_public_library/9550111150/; License: CC BY-NC 3.0

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