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topic 29019

Corrode pennies



2004

I'm doing a Science Fair project on the question...In what liquid does a penny corrode faster? And for my hypothesis I have been looking at the ingredients to all my liquids(Coke, Dr.Pepper, Cranberry Juice, Water, Orange Juice, and chlorine water, vinegar w/ water, vinegar)...but I don't know what half the stuff is! And what would make the penny corrode! Please help!

Lizzy [last name deleted for privacy by Editor]
student - Santee, California, U.S


2004

Lizzy,

I hope you have done some homework on what you do not know by now. Vinegar is mainly a dilute acetic acid. Chlorine water would normally be bleach is some water. In absolutes, chlorine water would be hydrochloric acid, which you do not want to mess around with! Orange juice will have mainly citric acid, but will have trace amounts of other organic acids. I do not know off the top of my head what Cranberry juice would have for a main acid, but would probably have some ascorbic acid which is vitamin C. Read the can for coke and DR Pepper. The main acid will be phosphoric, but will probably have one or two others in lesser amounts.

Copper dissolves in strong acids, but you do not have any strong acids, so you will get a slow conversion of the copper to copper ions which will react with some of the assorted anions to give you a nasty looking corrosion product. Note that new pennies have a zinc core. This is amphoteric, meaning it will dissolve in an acid or a base. Weak acids will do this, so look for the center of the copper sandwich to form white zinc corrosion products. Cut a penny in half to expose more of the zinc and compare the corrosion rates. You can do the rest of your homework with a dictionary and google. If all else fails, check out a chemistry book for the reactions.

James Watts
- Navarre, Florida


May 9, 2011

Lizzy,
Coke definitely does not dissolve a penny! I am doing the same experiment, which dissolves a penny faster, bleach or Coca-Cola? well I have discovered that bleach corrodes (eats away) at the penny strongly over a period of 5 days. There is so much acid that the penny is not able to withstand the pressure. I hope this helps you on your experiment!

Eddie [last name deleted for privacy by Editor]
- Midland Texas United States of America
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