Re: Physics & Chemistry

["Frank M. Lanzafame" <flanzafame@eckert.acadcomp.monroecc.edu>]

> 	Yes the temperature of solution well be a bit higher.  
> Possibly more interesting is to compare the rates at which a 
> stressed and an unstressed spring dissolve.  A more common variant of
> this is an acid etch of a piece of metal of which part of it is more
> stress the the rest of it.  It beleive that I have heard that the
> stressed part dissolves slightly faster.
> roger haar   U of AZ

There is a classic demonstration of corrosion as an electrochemical process in 
which a piece of iron is placed in a petri dish with an agar (gelatin) and KCl 
mixture.  It demonstrates that oxidation and reduction occur in distinctly 
different regions.  Reduction of oxygen is demonstrated with phenolphthalein 
which turns pink in the presence of OH- produced.  Oxidation is shown with a 
blue complex of iron ferri (or ferro I forget which) cyanide.  The 
oxidation takes place preferentially in an oxygen poor region.  

Further, it can be shown that oxidation of iron takes place preferentially at 
sites where the iron has been stressed.  This can be as simple as a bend in an 
iron nail.


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  :-)   Frank M. Lanzafame           Department of Chemistry  :-) 
  :-)   Monroe Community College     1000 East Henrietta Rd.  :-) 
  :-)   Rochester, NY   14623        (716)  292-2396          :-) 
  :-)   Internet:  flanzafame@eckert.acadcomp.monroecc.edu    :-) 
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