This project tests the effectiveness of different acidic solutions (like lemon juice, vinegar, and ketchup) in cleaning the tarnish off of old pennies. It's a quick and satisfying experiment that demonstrates a real-world chemical reaction.
If dull pennies are soaked in acidic solutions, then they will become shiny because the acid will dissolve the copper oxide tarnish that has formed on their surface.
As an Amazon Associate, this site earns from qualifying purchases.
Label your cups: 'Vinegar', 'Lemon Juice', 'Ketchup', 'Soapy Water', and 'Water' (control).
Pour each liquid into its corresponding cup.
Place 2-3 dull pennies in each cup, making sure they are completely submerged.
Let the pennies soak for 10-15 minutes.
Remove the pennies from the solutions and rinse them with water.
Place the pennies on a paper towel to dry.
Compare the shininess of the pennies from each solution to each other and to pennies that were not soaked.
Record your observations and rank the solutions from most effective to least effective.
The acidic solutions—vinegar, lemon juice, and ketchup (which contains vinegar)—will be the most effective at cleaning the pennies. The pennies in these solutions will become bright and shiny. The soapy water and plain water will have little to no effect. This is because the acid reacts with the dull copper oxide on the penny's surface, dissolving it and revealing the shiny copper underneath.
The type of liquid the pennies are soaked in.
The shininess of the pennies after soaking.
The amount of time the pennies are soaked, the initial condition of the pennies, and the temperature.
Do not taste any of the liquids. Wash your hands after the experiment. The liquids can be safely poured down the drain.
Display your 'before' and 'after' pennies for each solution.
Create a chart that ranks the cleaning power of each liquid.
Explain the chemical reaction: Copper Oxide + Acid -> Copper Salt + Water. The copper salt is washed away, leaving the shiny copper.
Pennies are made mostly of copper. The copper on the surface of the penny reacts with oxygen in the air over time to form a new substance called copper oxide. This copper oxide is what makes the pennies look dull and brown or green.
Ketchup contains vinegar (acetic acid) and tomatoes (which contain citric acid). These acids are what do the cleaning, just like the plain vinegar and lemon juice. The thick consistency of ketchup helps it stick to the penny's surface.
If you soak a penny in vinegar (especially with salt added) and then let it dry without rinsing, it might turn green! This is because the acid removes the protective oxide layer, and the copper then reacts with the air and leftover acid to form a green-blue compound called malachite.
