Re: Why iron nail turns copper coated when w/vinegar& pennies

Dear Jocelyn,

This is a question about electrochemistry.  People that study 
electrochemistry want to know how chemicals gain and lose free electrons.

The acid you used, vinegar, contains hydrogen ions.  Water has hydrogen 
ions in it too, but vinegar normally has about 10,000 times more.

When you put copper pennies and iron nails in acid, the hydrogen ions 
which lack an electron take electrons from copper and iron because the 
copper and iron atoms are not strong enough to hold onto some of their 
electrons.  Hydrogen takes two electrons from copper and three from iron.  
If you watch closely, small bubbles will form on the pennies and the 
nails.  These will be bubbles of hydrogen.  The hydrogen ions are turning 
into molecules of two hydrogen atoms and the metal atoms that are solid 
are turning into ions that move into the acid.

The struggle does not end there.  The iron and copper may be weaker than 
hydrogen, but the copper is stronger than iron when it comes to grabbing 
electrons.  The copper will look for iron atoms in the nail and grab their 
electrons.  Since the copper is taking the electrons from the iron at the 
outside surface of the nail, the copper turns back into a solid and you 
can see its characteristic "copper" color.  The iron ions are colorless, 
so you cannot see them, but they are there in the solution along with more 
copper ions.

The reaction will happen faster if the acid is warmer.

Another interesting experiment is to make a stack of pennies and dimes, 
arranged so that the dimes and pennies are mixed, dip the stack in lemon 
juice, and then press small wires connected to a flashlight bulb to either 
end of the stack.  If the dimes are old (have silver in them) and the 
juice is fresh, the bulb will glow, at least a little.

I hope this was a clear answer. If it was not, let me know what you did 
not understand or found confusing.

Dr. Edward Peterson
xpetersonx@aol.com