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topic 7838

Project on NaCl



I am doing a science project and I need a little help.

We submerged pennies, a screw, and half a nail in NaCl. I need to know what were the bubbles on the screw and what caused the change on the nail? After we took the pennies out we rinsed half of them and half we did not rinse. Why did the rinsed pennies look normal after one day? Why did the green color appear on the unrinsed pennies?

April Carter
AOL - Lake Charles, Louisiana


This experiment has nothing to do with whether the metal has been shaped into a penny, a screw, or a nail; it has to do with what kind of metal those items are made of.

Cutting a nail in half should probably expose steel on the inside, and the skin is probably zinc. But you didn't tell us what you saw as "the change on the nail". Did it turn black, white, blue, coppery-colored? Did it rust, gas up, disappear?

There is no guessing what the screw is made of: you would need to tell us. Without knowing what the screw was made of, I don't know how we can tell you meaningfully what the gas bubbles were, and why they developed there instead of elsewhere.

Pennies have a copper skin. If you rinse the penny, it should not discolor and it didn't. If you leave the saltwater on the penny, it will dissolve some of the copper, and this dissolved copper will dry on to the penny. Dissolved copper, i.e., copper ions, are blue.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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