Turning Copper Pennies Into Silver and Gold Pennies

Post date: Jun 6, 2017 8:09:49 PM

QUESTION: Chem 10 students, will the following single displacement reaction occur? Cu (s) + ZnSO4 (aq) (or ZnCl2) --> CuCl2 (aq) + Zn (s)

ANSWER: The correct answer is actually "no reaction" copper is LOWER than Zinc on the activity series.

So why does it seem from the video above that there IS in fact a reaction?

Answer: When solid zinc is added (in addition to the solid copper and the aqueous zinc sulfate), then the reaction actually proceeds as written above. The KEY to this reaction is the presence of the granular zinc. The granular zinc dissolves to Zn+2 ion (OXIDATION) and this Zn+2 ion then deposits onto the copper surface as metallic zinc (REDUCTION) in an energetically favorable process overall. (For more details, read the "Discussion" section of the Flinn Scientific procedure for this demo.)

This reaction happens on the surface of the copper penny, causing the copper penny to have a layer of solid zinc metal (which gives it the "silvery" apperance). Silver is a completely different element (Ag)!

When this zinc-coated penny is then heated, the following reaction occurs: Zn (s) + Cu (s) ----> ZnCu alloy (this is known as brass)

Link for difference between copper, brass, and bronze (link)

source: https://www.sciencecompany.com/Turn-Copper-Pennies-Into-Silver-and-Gold-Pennies.aspx

Turning Copper Pennies Into Silver and Gold Pennies

When a copper penny is zinc plated it will appear to change from its copper color to silver color. And by using sufficient heat, a zinc plated copper penny can be changed to gold.

This version of Silver and Gold Pennies utilizes zinc sulfate as less caustic than sodium hydroxide and works as well.

Supplies

Supplies needed...

To turn the penny silver...

Silver penny turning

    1. Fill the small 50 mL beaker with 3/4 full tap water. This is your rinsing beaker. Set aside.

    2. Dissolve 30 grams of Zinc Sulfate in 100 mL of water in the 250 mL beaker. A little heat from setting on the hot plate will hasten this dissolve.

    3. Place mossy zinc pieces in the beaker with the zinc sulfate solution, enough pieces to almost cover beaker bottom.

    4. Using tweezers, place two or three cleaned up pennies in step three beaker making sure pennies touch the mossy zinc pieces and are not touching each other.

    5. Bring solution to low boil for about 10 minutes. Your pennies will slowly turn a silver color.

    6. Using tweezers, carefully remove the pennies from the solution, rinse and cool them in small wash beaker then dry them on a paper towel.

    7. Voila! You now have a dandy silver colored penny.

To turn the penny gold...

pennies

    1. Place the silver penny on a hot plate heated to about 570°F (300°C). Watch as the heat diffuses the zinc with the copper to form a brass alloy. This will appear as golden in color.

    2. Once the penny is a brassy/golden color, use tweezers to pick up the penny and transfer it into the wash beaker to rinse and cool.

    3. Once cooled, you have a nice gold colored penny!