Interesting online CONFCHEM discussion going on right now on the ChemWiki and
greater STEMWiki Hyperlibary project. Come join the discussion.

ChemWiki: The Dynamic Chemistry Hypertext > Under Construction > Demonstrations > Additional Demos > Cathodic Protection

Cathodic Protection


Chemical Concepts Demonstrated

  • Corrosion
  • Cathodic protection
  • Sacrificial anode


Both dishes contain a solution of HCl, 3% H2O2, and KSCN.
  • The first dish contains an iron nail.
  • The second dish contains an iron nail with one end wrapped in copper wire connected to a piece of zinc metal.


The solution in the dish containing the lone nail turns a pink color, and the intensity of the color increases over time.  In the dish containing the nail/zinc metal connection, a gas is produced on the surface of the metal, but the pink color does not appear.  When the connection between the nail and the zinc metal is severed, the solution begins to turn pink.

Explanations (including important chemical equations)

The pink coloration is due to the formation of Fe(SCN)2+/Fe(SCN)2+ complexes.  This indicates that the iron metal is being oxidized to the Fe3+ ion.  This won't occur in the second dish as long as the nail is connected to the zinc metal strip.   When the two metals are connected, the zinc undergoes oxidation to Zn 2+ at the same time that H + ions are reduced to H2on the surface of the iron nail.



You must to post a comment.
Last modified
10:28, 2 Oct 2013



(not set)
(not set)

Creative Commons License Unless otherwise noted, content in the UC Davis ChemWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at Questions and concerns can be directed toward Prof. Delmar Larsen (, Founder and Director. Terms of Use