"J Burns" wrote in message

On 9/29/14, 6:09 AM, dadiOH wrote:
"J Burns" wrote in message


I looked for a steel item that I was sure wasn't plated. I
tried a rusty screw with a penny. I got bubbles, a black,
water-soluble deposit on the penny, and copper on the screw.

Right. The acid - even though weak - dissolved some copper.
Those copper ions are positive. The acid also dissolved some
iron; those ions are also positive leaving the screw negative.
The copper ions are
more
strongly attracted to the screw than are the iron ions. The
bubbles were hydrogen gas. The black would be an iron salt.

I wonder why the bath wasn't blue. Maybe there was very little
copper in it at any time, or maybe it was in some form besides CU++
ions.

Perhaps it would be if there were more? If a copper compound it
could be blue or green, Copper when burned can produce a flame that
is green (usual), blue, red or colorless depending upon temperature
and whether the flame is anoxidizing or reducing one.

I've read that you can put pennies in a vinegar-salt bath, remove them,
put in an iron item, and pull it out plated. I'll believe that when I
see it!

??? You just did. Separate times for copper and steel is no different
than the two simultaneously.

I wonder if my copper-plated screw is now rustproof.

Yes until the exceedingly thin layer of copper is breached.

--

dadiOH
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