Demonstration 2

Floating Pennies

Removal of Zinc from Pennies

Objective: The different reactivities of copper and zinc to hydrochloric acid will be used to separate the two metals in a post-1983 penny. The percent of zinc and of copper can be calculated as well as the economic value of each.

Time: This activity must be performed over a period of two days. Only a few minutes of student time are required each day.

Materials and Supplies:

one penny (newer than 1983)

20 ml 6 M HCl

100 ml beaker

triangular file

centigram balance

forceps or tongs

acetone (optional)

General Safety Guidelines:


  1. Use a triangular file to make four 1 mm deep scores in the penny's edge at 90 ° apart.

  2. Determine the mass of the penny on a balance and give this value to the students.

  3. Place the penny in a 100ml beaker and add 20ml of 6M HCl.

  4. Place this beaker in the fume hood or other safe area overnight.

  5. The penny should be floating the next day. Decant the HCl off into the sink, flushing with plenty of water, add about 50ml of tap water to the beaker containing the penny to rinse it off, pour the water off, and tip the penny out onto a paper towel. Leave the penny on the towel to dry a few minutes.

  6. When the penny is dry, determine the mass again. Report this value to the students.

  7. Determine the mass of a pre-1982 penny and report this value to the students also.

Video Clip

Questions and Calculations:

1. From the masses of the penny before and after the reaction, calculate the mass of zinc in the penny.

2. Calculate the percentage of zinc and the percentage of copper in the penny.

3. From a newspaper look up the prices of copper and zinc at the present time. Note the units. If the units are dollars per ounce, convert the value to dollars per gram. (1 pound = 454 grams)

4. From the mass of zinc and the current market value of zinc, calculate the value of zinc in the penny. Do the same for the copper in the penny.

5. Determine the value of the copper in the pre-1982 penny.

Why do you think our government switched to a copper-clad zinc penny?

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