The ‘Golden’ Penny
Teacher Resource/ Demonstration
Ministry Expectations:
Overall Expectations: Investigate, through inquiry, physical and chemical properties
of common elements and simple Compounds
Specific Expectations:
Use appropriate terminology related to chemical reactions, including, but not
limited to: compounds, product, and reactant
Distinguish between elements and compounds
Required Materials
1. Zinc (powdered or granular) (2-4g’s)
2. 3 mol Sodium Hydroxide (25-30ml’s)
3. Evaporating Dish
4. Pre-1982 American Copper Pennies
5. White Vinegar
6. Table Salt
7. Bunsen Burner
8. Crucible Tongs
9. Scoopula
10. Paper Towel
Introduction/Purpose:
One of the goals of the ancient alchemists was to convert base metals into gold.
Although this goal was never attained by chemical methods, the alchemists were able to
perform many color changes to make metals resemble gold. In this experiment you will
produce some color changes to a copper token and demonstrate diffusion in the solid state.
Procedure:
1. In a clean Petri dish, combine white vinegar and table salt. Add Copper pennies
to the mixture and let sit for approximately 3-4 Minutes. Rinse and leave to dry.
2. Add 2-3g’s of either granular or powdered Zinc to an Evaporating Dish. With
approximately 25ml of 3mol Sodium Hydroxide (NaOH), cover the Zinc.
3. Using a Bunsen Burner, heat the contents to a simmer with a ‘cool’ flame. If a
Bunsen Burner is not available, a heat plate set to medium-high heat will work
as well.
4. Once bubbles appear, reduce heat and add the Copper pennies using a pair of
Crucible Tongs.
5. Leave pennies in simmering solution for approximately 2-3 minutes.
6. After the time expires, remove the pennies from the solution using the Crucible
Tongs and quench under water. Dry with a paper towel. Observe the change.
7. Next, with the Crucible Tongs, hold the pennies near the flame from the Bunsen
Burner. Observe the results.
Safety:
1. Avoid skin and eye contact with the Sodium Hydroxide (NaOH). As it is a very
strong base, it is important to wear goggles, gloves and an apron at all times to
prevent injury and potential skin irritation or burning.
2. Instruct students of appropriate procedures in the case of a NaOH spill or
accidental contact. Keep White vinegar nearby in order to treat any potential
contact or spills.
3. While using Bunsen Burner, make sure any long hair or loose clothing is tied
back to prevent injury.
4. Always handle pennies with Crucible Tongs
5. Upon lab completion, rinse hands with White vinegar and wash in cold water.
6. Remind students to follow the safe lab procedures while carrying out lab
observations.
Results:
Reaction 1:
The combination of Sodium Hydroxide and Zinc reacts to produce Sodium Zincate
NaOH + ZnNa2ZnO2 + H2
Once contacted by the Copper from the penny, this is converted to metallic Zinc and results
in a loosely held zinc coating.
Reaction 2:
The second reaction involves the heating of the penny to fuse together the zinc and copper
metals to give an alloy (homogeneous metal mixture) known as brass.
Explanation
In this reaction, Zinc dissolves in the hot concentrated Sodium Hydroxide solution to form
Sodium Zincate, (Na2ZnO2). When the Copper penny is added to the solution, an
electrochemical couple formed by the Copper-Zinc contact causes the Zincate ion to migrate
to the Copper surface where it is broken down and reduced to metallic Zinc by Hydrogen,
forming a coating on the penny. This results in the pennies colour to change from copper to
silver due to a loose coating of Zinc on its surface. When the penny is heated by the flame
from the Bunsen Burner, the Zinc then fuses with the copper to form a layer of the alloy
brass, which results in the penny changing to a gold colour. Brass varies from 60-82% Cu
and from 18-40% Zn.