The Hollow Penny

Student Laboratory Kit

Materials Included In Kit

Hydrochloric acid solution, 6 M, HCl, 1000 mL
Pre-1982 pennies, 20
Post-1982 pennies, 20

Additional Materials Required

(for each lab group)
Water, 125 mL
Balance
Beaker, 150-mL
Beaker, 250-mL
Graduated cylinder, 50-mL
Paper towels
Tongs
Triangular file

Safety Precautions

Hydrochloric acid solution is corrosive to skin and eyes and is moderately toxic by ingestion and inhalation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. Neutralize and dispose of the hydrochloric acid solution according to Flinn Suggested Disposal Method #24b.

Teacher Tips

This kit contains enough materials for 40 students working in pairs to perform the laboratory activity.
The reaction between the post-1982 penny and the hydrochloric acid solution is rapid. Fizzing due to the generation of hydrogen gas can be violent enough to spatter drops of hydrochloric acid solution out of the beaker. If 150-mL beakers are not available, use larger beakers, not smaller ones, to avoid spattering.
To dry the pennies more quickly, have the students dip the pennies in acetone using tongs. Then fan the pennies in the air to allow the acetone to evaporate.
For a variation on this activity, have students file away the entire copper-ridged edge of the pennies, not just three notches. With this band of copper removed, once the hydrochloric acid solution reacts with the zinc, only the outer foils of copper will remain on the post-1982 penny. Instead of making hollow pennies, copper foils with penny imprints are the result.
Before 1982, pennies contained about 2.95 g copper and 0.15 g zinc. During 1982, however, the manufacturing of pennies changed. There were seven different mintings of pennies in 1982. After 1982, the composition of pennies was changed to contain about 2.46 g of zinc and only 0.06 g of copper. The change in composition was for economic reasons. As of June 1999, copper sold for about 60¢ per pound, while zinc sold for about 45¢ per pound—a savings of about 25%. Current prices of copper and zinc are found in the financial pages of most newspapers and on the internet. Have students find the current prices of copper and zinc and calculate and compare the values of a pre-1982 penny and a post-1982 penny. The U.S. Mint has a nice web page (www.usmint.gov) with information about how coins are made and specifications for each coin. See the answer to Question 13 for an interesting note about the composition of pennies during World War II.
For advanced students, have them calculate the E° for the reactions between Zn and HCl (E° = +0.76V) and Cu and HCl (E° = –0.34V). Have them relate the sign of E° to their observed data. The standard reduction potentials for the half reactions involved are listed. When zinc metal is combined with an acid, the net cell potential is positive. The net cell potential is negative for the reaction between copper metal and an acid. Spontaneous reactions have positive net cell potentials, so the reaction between zinc and an acid will be spontaneous, while the reaction between copper and an acid requires a battery.
{11873_Tips_Reaction_1}
Have students test their hypothesis of what other metal might be in the penny by having them carry out reactions in the lab between hydrochloric acid and copper wire and hydrochloric acid and the metal they chose in Question 6. For example, if a student group proposes that the post-1982 pennies are filled with zinc, give the group a piece of mossy zinc and let them carry out the reaction between mossy zinc and hydrochloric acid. If they observe a reaction, then their hypothesis is a valid hypothesis.

Correlation to Next Generation Science Standards (NGSS)^†

Science & Engineering Practices

Analyzing and interpreting data
Constructing explanations and designing solutions

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter

Crosscutting Concepts

Patterns

Performance Expectations

MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

Sample Data

Observations Table

{11873_Data_Table_1}

Data Table. Pre-1982 Penny

{11873_Data_Table_2}

Data Table. Post-1982 Penny

{11873_Data_Table_3}

Answers to Questions

Calculate the mass of each penny lost, if any, during the experiment. Record these values in the data table.
To calculate the mass lost, subtract the mass of the dry penny after the experiment from the mass of the notched penny before the experiment. See data tables for sample data.
Did each of the pennies lose approximately the same mass during the reaction, or did they lose different amounts of mass?
No. The pre-1982 penny lost only a small amount of mass, while the post-1982 penny lost nearly all of its mass.
Based on your observations, did the copper in each penny react with the hydrochloric acid? How do you know?
No. If the copper on each penny had reacted with the hydrochloric acid it would have dissolved and would not have been present at the end of the experiment. Instead, the copper part of each penny was still present, and the etchings were even unharmed.
Look at the activity series in Table 1 of the Background section. Should copper react with the hydrochloric acid? Hint: Should copper metal be able to replace hydrogen ions? Explain your answer.
No. Copper metal should not be able to replace hydrogen ions because copper appears below hydrogen in the activity series. A metal must appear above another metal to be able to replace it.
Based on your observations, are the two pennies composed of the same metal(s)? Explain.
No. Clearly, both pennies contain copper. But, the post-1982 penny was filled with a metal other than copper, while thepre-1982 penny is filled with mostly copper.
Looking at the activity series in Table 1 of the Background section, propose a metal that could have been used to fill the inside of the post-1982 penny.
Student answers will vary. Any metal that appears above hydrogen in the activity series is a valid choice; however, students should consider the reactivity of the metal they choose. For example, sodium would not be a good choice because it is very water- and air-reactive. The post-1982 penny is actually filled with zinc.
Write the chemical equation for the reaction between copper metal and hydrochloric acid. If no reaction occurs, write NR on the products side.
Cu(s) + HCI(aq) → NR
Write the chemical equation for the reaction between the metal you chose in Question 6 and hydrochloric acid.
Student answers will vary. For example, if a student chose zinc, the reaction is Zn(s) + 2HCI(aq) → ZnCI₂(aq) + H₂(g)
Calculate the % weight of copper in each penny. Record these values in the data tables.
See data tables for sample data. Answers should be calculated using the following formula for % weight.

{11873_Answers_Equation_1}
Calculate the % weight of any other metal(s) in each penny. Record these values in the data tables.
See data tables for sample data. Answers should be calculated using the following formula for % weight.

{11873_Answers_Equation_2}
If the year were rubbed off a penny, how could you determine if the penny was pre-1982 or post-1982 without destroying the penny?
Weigh the penny. Determine if its mass matches that of the pre-1982 penny or the post-1982 penny weighed in this experiment. The masses of the two pennies are different because copper and zinc (or another metal) have different densities.
Why do you think copper pennies are filled with another metal instead of being made of pure copper?
Zinc is less expensive than copper. Any material used to fill the inside of the penny should be cheaper than copper.
Would it be a good idea to make pennies out of the pure metal you chose in Question 6? Why or why not?
No. Money should be made of indestructible materials. If pennies were made of zinc or another metal that can be replaced by acid, they would dissolve when in contact with acids. However, during World War II, pennies were all zinc because copper was needed to make brass shell casings.
Describe an experiment that you could carry out in the lab to determine if the hypothesis you made in Question 6 was a valid hypothesis.
Student answers will vary. A piece of the metal chosen could be placed in hydrochloric acid. The mixture should then be observed to see if any reaction occurs. If no reaction occurs, the metal will look the same before and after the experiment. If a reaction does occur, the metal will dissolve, producing hydrogen gas (fizzing).
If cost were not a factor, what would be the best metal out of which to make coins? Hint: Look at the activity series of the metals in Table 1 of the Background section.
Gold would be the best choice based on the activity series shown in Table 1. It is the least reactive metal, and therefore the most stable.

References

ChemCom, Teacher’s Guide, 3rd ed.; Stanitski, C. L., Ed.; Kendall/Hunt: Dubuque, IA, 1998; pp 48, 173.

Recommended Products

Item No.	Description

Student Pages
© 2018 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission of these student pages is granted only to science teachers who have purchased this product from Flinn Scientific, Inc. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system, without permission in writing from Flinn Scientific, Inc.
Student Pages The Hollow Penny Introduction Pennies are made of copper, aren’t they? The outside is certainly made of copper, but that’s not the whole story. In this lab, the composition of two pennies from different years will be investigated. Concepts Activity series of metals Redox reactions Single-replacement reactions Background Oxidation–reduction, or redox, reactions are reactions in which electrons are transferred from one element to another. A common type of redox reaction is a single replacement reaction. Single replacement reactions involve the replacement of one element in a compound with another element. The general form for single replacement reactions is shown in Equation 1. {11873_Background_Equation_1} Metals are commonly involved in single replacement reactions. Some metals can replace other metals in their compounds, while some metals cannot. In Equation 1, if “A” and “B” are metals, “A” replaces “B” in its compound “BC.” The reaction is not reversible, so “B” cannot replace “A” in the compound “AC.” The ability to replace another metal determines a metal’s reactivity—the better the ability to replace another metal, the more reactive a metal is. The activity series of metals is a scheme that places the metals in order of reactivity (see Table 1). Note: Hydrogen is listed in the activity series even though it is not actually a metal. For the purposes of the activity series, it is considered to behave as a metal. The metals at the top are the most reactive and can therefore replace most other metals. Reactivity decreases as you move down the list, with those at the bottom of the list capable of replacing only a few other metals. A metal can replace another metal if it appears above that metal in the activity series. In Equation 1, “A” must be the more reactive metal (higher up on the activity series and capable of replacing “B”) while “B” is the less active metal (lower on the activity series and not capable of replacing “A”). {11873_Background_Table_1_The activity series of metals} Looking at a specific example, if the two metals are aluminum, Al, and copper, Cu, then in Equation 1 “A” must be aluminum and “B” must be copper since aluminum appears higher up on the activity series than copper and is therefore a more active metal than copper. An example of a reaction involving these two metals is the reaction between aluminum metal and cupric chloride solution (see Equation 2). {11873_Background_Equation_2} In this reaction, aluminum is said to replace copper since the cupric chloride compound becomes aluminum chloride. In redox terms, the cupric ion has been reduced to copper metal while aluminum metal has been oxidized to the aluminum ion. Because copper appears below aluminum on the activity series, it is less reactive than aluminum and cannot replace aluminum in a compound. As a result, the reverse of Equation 2 does not occur spontaneously (see Equation 3). {11873_Background_Equation_3} Materials Water, 125 mL Balance Beaker, 150-mL Beaker, 250-mL Graduated cylinder, 50-mL Hydrochloric acid solution, 6 M, HCl, 40 mL Paper towels Post-1982 penny Pre-1982 penny Tongs Triangular file Safety Precautions Hydrochloric acid solution is corrosive to skin and eyes and is moderately toxic by ingestion and inhalation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Procedure Day 1 Using a triangular file, file three notches in a pre-1982 and a post-1982 penny. See Figure 1. {11873_Procedure_Figure_1} Weigh the notched pre-1982 penny on a balance. Record its weight in the data table. Weigh the notched post-1982 penny on a balance. Record its weight in the data table. Caution: 6 M hydrochloric acid solution is corrosive to skin and eyes. Avoid all contact with skin and eyes. Pour about 40 mL of 6 M hydrochloric acid solution into a 150-mL beaker. Using tongs, place both pennies in the beaker of hydrochloric acid solution so that they are both completely submerged. Observe the reaction between the hydrochloric acid solution and the pennies. Record your observations in the Observations Table. Set the beaker in a safe place as instructed by your teacher and allow the reaction to continue overnight. Day 2 Fill a 250-mL beaker about half-full with water. Using tongs, transfer both pennies from the hydrochloric acid solution to the beaker of water. Still using the tongs, move the pennies through the water to rinse them. Remove each penny from the water and hold each under running water to thoroughly rinse it. Look into the center of each penny through one of the notches. Record your observations in the Observations Table. Dry each penny with a paper towel. Write your name on a clean paper towel. Place the pennies next to your name. Allow them to dry completely overnight. Day 3 Weigh each completely dry penny on a balance. Record the weight of each penny in the data tables. Student Worksheet PDF 11873_Student1.pdf

Student Pages

The Hollow Penny

Introduction

Pennies are made of copper, aren’t they? The outside is certainly made of copper, but that’s not the whole story. In this lab, the composition of two pennies from different years will be investigated.

Concepts

Activity series of metals
Redox reactions
Single-replacement reactions

Background

Oxidation–reduction, or redox, reactions are reactions in which electrons are transferred from one element to another. A common type of redox reaction is a single replacement reaction. Single replacement reactions involve the replacement of one element in a compound with another element. The general form for single replacement reactions is shown in Equation 1.

{11873_Background_Equation_1}

Metals are commonly involved in single replacement reactions. Some metals can replace other metals in their compounds, while some metals cannot. In Equation 1, if “A” and “B” are metals, “A” replaces “B” in its compound “BC.” The reaction is not reversible, so “B” cannot replace “A” in the compound “AC.” The ability to replace another metal determines a metal’s reactivity—the better the ability to replace another metal, the more reactive a metal is. The activity series of metals is a scheme that places the metals in order of reactivity (see Table 1). Note: Hydrogen is listed in the activity series even though it is not actually a metal. For the purposes of the activity series, it is considered to behave as a metal. The metals at the top are the most reactive and can therefore replace most other metals. Reactivity decreases as you move down the list, with those at the bottom of the list capable of replacing only a few other metals. A metal can replace another metal if it appears above that metal in the activity series. In Equation 1, “A” must be the more reactive metal (higher up on the activity series and capable of replacing “B”) while “B” is the less active metal (lower on the activity series and not capable of replacing “A”).

{11873_Background_Table_1_The activity series of metals}

Looking at a specific example, if the two metals are aluminum, Al, and copper, Cu, then in Equation 1 “A” must be aluminum and “B” must be copper since aluminum appears higher up on the activity series than copper and is therefore a more active metal than copper. An example of a reaction involving these two metals is the reaction between aluminum metal and cupric chloride solution (see Equation 2).

{11873_Background_Equation_2}

In this reaction, aluminum is said to replace copper since the cupric chloride compound becomes aluminum chloride. In redox terms, the cupric ion has been reduced to copper metal while aluminum metal has been oxidized to the aluminum ion. Because copper appears below aluminum on the activity series, it is less reactive than aluminum and cannot replace aluminum in a compound. As a result, the reverse of Equation 2 does not occur spontaneously (see Equation 3).

{11873_Background_Equation_3}

Materials

Water, 125 mL
Balance
Beaker, 150-mL
Beaker, 250-mL
Graduated cylinder, 50-mL
Hydrochloric acid solution, 6 M, HCl, 40 mL
Paper towels
Post-1982 penny
Pre-1982 penny
Tongs
Triangular file

Safety Precautions

Hydrochloric acid solution is corrosive to skin and eyes and is moderately toxic by ingestion and inhalation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Day 1

Using a triangular file, file three notches in a pre-1982 and a post-1982 penny. See Figure 1.
{11873_Procedure_Figure_1}
Weigh the notched pre-1982 penny on a balance. Record its weight in the data table.
Weigh the notched post-1982 penny on a balance. Record its weight in the data table.
Caution: 6 M hydrochloric acid solution is corrosive to skin and eyes. Avoid all contact with skin and eyes. Pour about 40 mL of 6 M hydrochloric acid solution into a 150-mL beaker.
Using tongs, place both pennies in the beaker of hydrochloric acid solution so that they are both completely submerged.
Observe the reaction between the hydrochloric acid solution and the pennies. Record your observations in the Observations Table.
Set the beaker in a safe place as instructed by your teacher and allow the reaction to continue overnight.

Day 2

Fill a 250-mL beaker about half-full with water.
Using tongs, transfer both pennies from the hydrochloric acid solution to the beaker of water. Still using the tongs, move the pennies through the water to rinse them.
Remove each penny from the water and hold each under running water to thoroughly rinse it.
Look into the center of each penny through one of the notches. Record your observations in the Observations Table.
Dry each penny with a paper towel. Write your name on a clean paper towel. Place the pennies next to your name. Allow them to dry completely overnight.

Day 3

Weigh each completely dry penny on a balance. Record the weight of each penny in the data tables.

Student Worksheet PDF

11873_Student1.pdf

^†Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.

Teacher Notes

The Hollow Penny

Student Laboratory Kit

Materials Included In Kit

Additional Materials Required

Safety Precautions

Disposal

Teacher Tips

Correlation to Next Generation Science Standards (NGSS)†

Science & Engineering Practices

Disciplinary Core Ideas

Crosscutting Concepts

Performance Expectations

Sample Data

Answers to Questions

References

Recommended Products

Student Pages

The Hollow Penny

Introduction

Concepts

Background

Materials

Safety Precautions

Procedure

Student Worksheet PDF

Correlation to Next Generation Science Standards (NGSS)^†