Georganna Benedetto
Penny Lab
27 Jan. 2016
Penny Lab
Teacher’s Instructions
Brief Description of Activity:
The lesson uses in depth laboratory procedure to familiarize students with the operations of a
laboratory as well as an activity to help students learn about physical properties of elements and
the visual manifestations of physical changes. This is done by having students turning a coppercolored penny to a gold-colored penny by heating a penny in a zinc-NaOH solution and then
heating the penny under a bunsen burner.
Learning Goals:
 Students will test
o the outcome of heating a copper penny in a solution of zinc and sodium hydroxide
o the outcome of placing the heated penny in the flame of a bunsen burner
 Students will observe
o the outcome of heating a copper penny in a solution of zinc and sodium hydroxide
o the outcome of placing the heated penny in the flame of a bunsen burner
o the creation of an alloy
 Students will understand
o the general idea of physical properties of elements
o the specifics of the physical changes that a penny undergoes in solution and when
heat is applied
Recommended Grades: K-8th Grade
Estimated Time Required:
a) Prep Time: 10 mins.
b) Class Time: 40 mins.
Key Concepts and Definitions of Terms:
Physical Property: a property (as color, hardness, boiling point) of matter not involving in its
manifestation a chemical change
Physical Change: changes affecting the form of a chemical substance, but not its chemical
composition. Physical changes are used to separate mixtures into their component compounds,
but can not usually be used to separate compounds into chemical elements or simpler compounds
Alloy: A material made of two or more metals, or of a metal and another material. For example,
brass is an alloy of copper and zinc; steel is an alloy of iron and carbon.
Brass: a metal alloy made of copper and zinc; the proportions of zinc and copper can be varied
to create a range of brasses with varying properties. It is a substitutional alloy: atoms of the two
constituents may replace each other within the same crystal structure.
Chemical Property: the chemical identity of a substance that becomes evident during or after a
chemical reaction that results in the change of the substance’s identity.
Chemical Change: any change that results in the formation of new chemical substances. At the
molecular level, chemical changes involve making or breaking of bonds between atoms.
pg. 1
Georganna Benedetto
Penny Lab
27 Jan. 2016
What Happens and Why:
When a copper penny is heated in a solution of sodium hydroxide mixed with zinc dust, small
amounts of zinc dissolve into the surface of the penny. This causes the penny to look silver since
there is now a layer of zinc over the outside of the penny.
When the silver-colored penny is heated, the outside zinc atoms and inside copper atoms move
around because of the heat excitement. This makes the outer layer of zinc mix with the copper
below, which becomes an alloy called yellow brass. In this new alloy the copper is lightened by
the presence of zinc, making it appear a gold color.
Brass is formed physically. The two metals, zinc and copper, do not react chemically. They use
metallic bonding. Both metals want to get rid of electrons to become more stable. The new
alloy is a mixture of varying composition of zinc and copper atoms.
Materials Needed:
1. Copper penny (made before 1982) (one student)
2. 0.1 g zinc dust (per penny) (0.2 for 2 pennies, 0.3 for 3 pennies, ect)
3. Weighing dish
4. 20 mL of NaOH
5. 2 beakers
6. Hot plate
7. Electronic Balance
8. Tongs
9. Bunsen burner
10. Sparker to light bunsen burner
11. Source of gas
12. Kimwipes
Estimated Cost: $60
Safety Information:
 Sodium hydroxide (NaOH) is corrosive to skin and eyes. Wear gloves when handling.
Additionally, NaOH when heated can cause irritation to the respiratory tract. Only heat
under a hood in a lab.
 Flame from bunsen burner can cause serious injury. Be careful when handling.
pg. 2
Georganna Benedetto
Penny Lab
27 Jan. 2016
General Outline of Procedures:
1. Explain the activity to the students
2. Distribute materials to each student. (1 copper penny per student)
3. Help the students measure 0.1 g (per student) of zinc dust in a weighing dish using an
electric balance (0.2 for 2 students, 0.3 for 3 students, ect).
4. Help the students mix zinc dust with 20 mL of NaOH in a 200 mL beaker
5. Help the students place beaker on hot plate turned to level 6 and heat mixture (for approx.
5 mins. but not until the solution is boiling)
6. Have the students add their pennies to the heated solution and keep on hot plate until
penny turns a silver color (approx. 3-4 mins.) (Note: mix about every minute so that the
zinc dust covers all parts of every penny).
7. Attach the bunsen burner to the gas source with a tube.
8. Turn the gas source on.
9. Use the sparker to start a flame.
10. Adjust the bunsen burner to get a strong, blue flame.
11. Help the first student remove their penny with clean tongs.
12. Help the first student rinse their penny under the faucet with water.
13. Have the student dry both the penny and the tongs with a Chemwipe to prevent the water
to cause burn marks on the penny.
14. Help the first student hold their penny in the flame of bunsen burner using tongs until
penny turns a gold color.
15. Help the first student hold their penny under running water to cool both the penny and the
tongs so that they are safe to touch.
16. Repeat steps 7-11 with the remaining pennies and students.
17. Discuss findings and explain to the students the chemistry behind why the copper penny
changed from silver-colored to gold-colored but stayed still composed of zinc and copper
atoms.
18. Help the students answer discussion questions.
19. Clean-up.
pg. 3
Georganna Benedetto
Penny Lab
27 Jan. 2016
Variations:
A supplementary option for students can be demonstrating a chemical reaction such as baking
soda and vinegar to be placed in contrast to the physical changes that are explored in this
lab. Discussion can revolve around the differences in the physical and chemical properties and
changes viewed in the penny and the baking soda reaction.
Special Notes:
The penny must be from before the year 1982 since these pennies are made of copper.
Additionally, this experiment MUST be performed in an environment equipped with safety hood
and gas lines.
Zinc dust can be expensive. It can be ordered from Sigma-Aldrich at the link below.
https://www.sigmaaldrich.com/catalog/search?term=zinc+dust&interface=All&N=0&mode=mat
ch%20partialmax&lang=en&region=US&focus=product
References:
"Physical and Chemical Properties." Web. 24 Jan. 2016.
<http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/properties.html>.
"Brassing a Penny." ASM International. Web. 24 Jan. 2016.
<http://www.asminternational.org/documents/10192/1942082/brasspenny.pdf/b272fe149bac-4759-a375-c47a5cbbf916>.
"Brass Alloys." About Education. 4 Dec. 2014. Web. 24 Jan. 2016.
<http://chemistry.about.com/od/alloys/a/Brass-Alloys.htm>.
"10 Chemical Change Examples." About Education. 19 Feb. 2015. Web. 24 Jan. 2016.
<http://chemistry.about.com/od/matter/a/10-Chemical-Change-Examples.htm>.
"Physical and Chemical Properties." Chem Team. Web. 24 Jan. 2016.
<http://www.chemteam.info/Matter/PhysicalChemProperties.html>.
Picture Sources:
http://logansblog23.blogspot.com/2015/09/6-alchemy-is-turning-lesser-metal-into.html
http://www.gettyimages.com/detail/video/british-penny-held-by-tweezers-in-flame-of-bunsen-st
ck-video-footage/148463218
http://blog.chembark.com/2012/09/21/the-copper-to-silver-to-gold-alchemy-demo/
pg. 4
Georganna Benedetto
Penny Lab
27 Jan. 2016
Gold Penny
Student Instructions
You are a fearless explorer and have found hidden treasure!
CONGRADULATIONS!! But bad treasure hunters are on your
heels. Can you turn this penny gold to trick them into thinking
they found the treasure after you took it?
1. Gather materials.
2. Measure 0.1 g of zinc dust in a weighing dish.
3. Mix zinc dust with 20 mL of NaOH in a beaker.
4. Place beaker on hot plate turned to level 6 and heat mixture
(for approx. 5 mins. but not until the solution is boiling).
5. Add penny to the heated solution and keep on hot plate
until penny turns a silver color (approx. 3-4 mins.).
6. Remove penny with tongs.
7. Rinse the penny under faucet with water.
8. Hold penny in the flame of bunsen burner using tongs until
penny turns a gold color.
9. Hold tong and penny under running water to cool them
down.
10.
Answer lab questions.
11.
Clean up.
pg. 5
Georganna Benedetto
Penny Lab
27 Jan. 2016
Final Questions
1. What happened to the penny when heated in the NaOH and
zinc dust solution?
2. What happened to the penny when placed in the flame
of the bunsen burner?
3. Were the changes in the penny physical or chemical? Why?
pg. 6