Lab: Percent Composition of a Penny

Percent Composition of a Penny
Background Information:
Post-1983 pennies have a copper jacket and a zinc core. We hope to determine the
percent composition of these two metals. This will be done by reacting the zinc with
hydrochloric acid to form zinc ions in a single replacement reaction. The acid reacts with the
zinc but not copper. The reaction of zinc metal with the hydrochloric acid (HCl) produces zinc
chloride and hydrogen gas.
Safety:
Wear your safety goggles and apron
If you spill Hydrochloric acid on yourself, rinse with water
Procedure:
DAY I
1. Take a post-1983 penny and, using a triangular file, etch an “X” on one side of the penny.
Also etch a notch on the edge of the penny in the four positions shown in the diagram.
2. Mass and record the mass of the penny.
3. Using a graduated cylinder, measure 60.0 mL of 3.0 M HCl and pour it into your 100mL
beaker.
4. Place the penny in the HCl solution etch side up and record observations for 3-5 minutes.
5. Place the beaker in your lab drawer.
6. Answer question #1 for tomorrow. Read and prepare a data table for Day II.
DAY II
1. Using your forceps, carefully remove the fragile copper jacket that is left from the penny.
Rinse it gently in distilled water.
2. Dry the penny in acetone solution. Swirl the penny in the solution.
3. Pour the acid solution from your beaker into the waste container at the center table. Rinse
and dry your beaker.
4. Take a magic marker and write your lab drawer number on the side of your 50 mL beaker.
5. Place the penny in the beaker and put the beaker on the appropriate shelf of the drying
oven.
DAY III
1. Mass and record the mass of the dry copper jacket.
2. Complete the questions and calculations for tomorrow.

Questions Answer in complete sentences
SHOW ALL MATH FOR CREDIT! INCLUDE UNITS & SIG FIGS IN ALL ANSWERS!
1. Write the balanced equation for the reaction. Include (states) .
2. Calculate the mass of zinc found in the penny.
3. Calculate the mass of copper in the penny.
4. Calculate the percent zinc and the percent copper in a penny.
5. Record the class average for percent zinc.
6. List at least four sources of error and how they would specifically affect your results.
7. Examine the ingredients of a cola soda such as Coke or Pepsi. Could you safely store a
cola soda like Coke or Pepsi in a zinc container? In a copper container? Explain your
answer based on the ingredients.
8. a) Using your balanced equation from #1, determine the number of moles of HCl needed
to react with 2.00 g of zinc metal.
b) How many moles of zinc chloride are produced?
c) How many gram of hydrogen gas are produced?
d) What is happening to the potential energy of the system? How do you know?
9. a) Using your balanced eqation from #1, which element is oxidized in the reaction?
Explain.
b) Which element is reduced? Explain.