Floating Penny (Demonstration)
(Reference: Borgford, C.L., and Summerlin, L.R.  Chemical Activities; American Chemical Society: Washington, D.C., 1988; pp 77-78.)

Metal/acid displacement   :   Activity series

The whole class can do this!

Illustrate the idea of metal displacement reactions

Safety goggles should be worn by instructor and students.  HCl is corrosive; handle with care.

Pre-1982 pennies (# of groups)
Triangular file
Post-1982 pennies (# of groups)
150 mL 6 M HCl
100 mL beaker (# of groups)

1. Use a file to score the pennies- about four 1mm scores
2. Place 1 of each type of penny in beaker
3. Cover with about 20 mL acid
4. Leave this in fume hood until next day, post-1982 penny should be floating and the pre-1982 penny should still be on bottom of beaker
5. Remove pennies and rinse thoroughly

The reason for the differences in the years, is that instead of being pure copper, the post-1982 pennies contain zinc in the center, and this will react with HCl because Zn2+ has a lower reduction potential than H+.

Zn(s)  +  HCl(aq)      H2(g)  +  ZnCl(aq)

Can use pre-1982 pennies; post-1982pennies should be discarded in trash once all of the acid has been rinsed.  The ZnCl solution can be rinsed down drain with lots of water.

Ginger Chateauneuf, 2000.