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Ted Mooney, P.E. RET
Pine Beach, NJ

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Zinc coating of coins

Hi there:

Could someone please help me maintain credibility with my daughter?

We got a science fair project off the internet that involves boiling sodium hydroxide solution, adding zinc filings then adding a penny. The penny turns silver then, when cleaned and heated with a propane torch, turns golden. We tried this over the weekend and it actually works!

My daughter is asking me to provide the theory behind this. Could someone please help!

Michael Longland
CH2M HILL Canada Limited - Toronto, Ontario, Canada

I did this experiment in chemistry class a few days ago and I think what your daughter is looking for is that the penny is still a penny is't just being stripped of this chemical make-up. Pennies made before 1982 were made up of 97% copper and 3% of zinc. Now they are made of 97.6% copper and no zinc. So when you dip it in that solution it's eating away at the copper and just changing the chemical property.

Ashley C.
- Wickliffe, Ohio

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