Making Pennies Into Gold

Key Concepts

• Chemical Alchemy: The process of altering the appearance of metals through chemical reactions.
• Alloy: A mixture of two or more metallic elements (in this case, copper and zinc to form brass).
• Zinc Plating: The process of coating a metal surface with a thin layer of zinc.
• Thermal Diffusion: The process of using heat to fuse two metals together to create an alloy.

The Process of Creating "Gold" Pennies

1. Preparation and Cleaning

The process begins with cleaning the pennies to ensure the surface is free of oxidation or debris. This is achieved by soaking the pennies in a solution of vinegar (acetic acid) and salt (sodium chloride). This step is crucial to ensure the subsequent chemical coating adheres properly to the copper surface.

2. Zinc Coating (The "Silver" Stage)

To achieve the initial transformation, the cleaned pennies are submerged in a mixture of zinc dust and sodium hydroxide (NaOH). When heated in a laboratory setting, the zinc coats the copper penny, giving it a silver-like appearance. At this stage, the penny is essentially a copper core with a zinc-plated exterior.

3. Creating the Brass Alloy (The "Gold" Stage)

The final transformation into a gold-colored coin relies on the properties of alloys.

• The Science: Brass is an alloy composed of copper and zinc.
• Methodology: By applying heat to the zinc-coated penny, the zinc atoms diffuse into the surface layer of the copper. This thermal process fuses the two metals, creating a thin layer of brass on the surface of the penny, which reflects light in a way that mimics the appearance of gold.

Real-World Context and Observations

• Educational Application: This experiment is a staple in high school chemistry curricula, used by teachers to demonstrate chemical reactions, metal properties, and the concept of alloys in an engaging, hands-on manner.
• St. Patrick’s Day Phenomenon: The video notes that these "gold" pennies often enter public circulation around St. Patrick’s Day. While these occurrences are sometimes jokingly attributed to "leprechauns," they are actually the result of students practicing chemistry and sharing their work with the public.
• Safety and Execution: While the demonstration appears simple, it requires controlled laboratory conditions, specifically the use of sodium hydroxide and heat, to safely and effectively achieve the metallic fusion.

Synthesis

The transformation of a standard copper penny into a "gold" coin is a practical demonstration of chemical alchemy. By utilizing a two-step process—first plating the copper with zinc and then applying heat to induce the formation of a brass alloy—students can visually observe the transition of metal properties. This experiment serves as a bridge between theoretical chemistry and tangible, real-world applications, turning a common classroom lesson into a creative, albeit temporary, "gold" coin.