Lab #5 Penny Sandwiches
Step 1 Using the file or coarse sandpaper, completely remove the copper coating from the edge of both pennies. Pour the lemon juice into one container. Position one penny in the container so that it is standing on its edge against the side of the container. Pour the vinegar into the second container and similarly position the second penny. Observe the pennies for 4 or 5 minutes. (a) What do you see? (b) What is occurring? [Note: Don't necessarily look for a "big" change all of sudden but rather a subtle process at first] (c) What is the identity of the observed substance?
a) I see bubbles in both containers.
b) A chemical process which causes the bubbles.
c) Hydrogen gas.
Step 2 (a) Observe the pennies over the course of 1 week and describe any difference(s) in their behavior. (b) What accounts for the difference(s)? (c) What specific process is occurring in each container? (d) How do you know when the processes are complete? (e) Use your observations to rank the three elements hydrogen, copper, and zinc from most to least reactive.
a) Bubbles stop in the lemon juice first but are still forming in the vinegar. I notice the zinc interior is dissolving and the copper coating is left.
b) There is more acid in the lemon juice than in the vinegar.
c) The reaction of zinc with an acid.
d) The reactions are complete when the bubbles stop forming.
e) Zinc, Hydrogen, Copper
What is the chemistry-based reason for this peculiar construction of a penny?
Zinc is too reactive to for the coin to be totally made out of zinc. The copper is not as reactive and is a protective coating.