Beacon Lesson Plan Library

Changes in the Copper Penny

Patricia Davison

Description

This is a unique and fun way to introduce the difference between a physical change in a substance and a chemical change. The student studies the volume, density, altering shape, and chemistry of a copper penny.

Objectives

The student knows the difference between a physical change in a substance (e.g., altering the shape, form, volume, or density) and a chemical change (i.e., producing new substances with different characteristics).

Materials

-Copper pennies dated before and after 1982
-Digital scales and balances
-Calipers
-Centimeter rulers
-Exacto knife
-1 L hydrochloric acid
-Dropper
-Pencils
-Baking soda
-Water
-Data Tables (see Associated File)
-Table of Densities (see Associated File)

Preparations

1. Gather materials for activity and assign homework for students to bring in pre 1982 and post 1982 pennies.
2. Make copies of Data Tables and Table of Densities (see Associated File).
3. Make copies of Periodic Tables references available.
4. Prepare 1 L hydrochloric acid, some for dropping on pennies as a teacher demonstration and some for overnight soaking of the pennies.
5. On day 3 place pennies in a paste of baking soda and water prior to returning the pennies to the students.

Procedures

NOTE: Remind students of all safety precautions when using chemicals.

DAY 1

1. Ask students if they know the chemical composition of a copper penny. List and discuss their answers.

2. Divide students into groups of 3 according to the dates of pennies they brought in.

3. Discuss centimeters and the difference between weight and mass and density. Students should take notes for future reference.

4. Students use scales and balances to get linear measurements and masses of their pennies.

5. Students record measurements and draw a comparison of class data on the board.

DAY 2

1. Students discuss the difference between a physical change and chemical change through a mini-lecture and demo by the teacher.

2. Teacher Demo: Physical change (Use sandpaper and scratch surface of the two dated pennies) and chemical change (Use HCl drops on pennies).

3. Students record observations on Data Tables (see Associated File). Compare group data with class and close with discussion.

4. Students give pennies to teacher for overnight soaking in concentrated HCl.

5. Use an exacto knife to cut 2 lines on each side of pennies. Then place in HCl for overnight soaking.

DAY 3
(Note: Place pennies in a paste of baking soda and water before returning them today. Once they have stopped bubbling, they are ready for students to handle.)

1. Students make observations and record results.

2. Students re-mass their pennies and record results. Observe students' work and give feedback where appropriate.

3. Students brainstorm on observed changes.

4. Students reference the Table of Densities (see Associated File).

5. If density measurements are correct, students will conclude that the metal in copper pennies dated post 1982 is zinc, based on its density match. If the wrong conclusion is reached, students need to re-check their math and/or measurements.

Assessments

Use observation of students and completed Data Tables (see Associated File) to formatively assess the students' ability to:
-Use real world objects to investigate measuring mass and volume.
-Use real world objects to calculate density and study chemical changes in matter.
-Know the difference between a physical change and a chemical change in substances.
(If a student does not perform well, pair him/her with a successful peer or give individual teacher instruction.)

Extensions

This lesson can be extended by being tied into an economics and math lesson. Students can research the costs of metals in the daily newspapers and coin books comparing the cost of copper and zinc in today's market. Students can be assessed by completing the Cost of Producing Pennies table (see Associated File). Students will be able to see that the percentage of copper in pennies prior to 1982 is more than after 1982 showing that the value of pennies after 1982 is less.

Attached Files

This file contains Data Tables and a Table of Densities.     File Extension: pdf

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