Learning Library

# Corrosiveness of Soda

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### Materials:

• 2 cans of cola
• 5 dull pennies
• Food storage container
• White piece of paper
• Camera
• Notebook and paper

### Procedure:

1. Give your pennies a drink! Collect some old, dull and tarnished pennies for this experiment. Find a container that’s large enough that you can lay the pennies side by side.
2. Create a hypothesis, your best guess about what is going to happen. What do you think will happen to the pennies when you leave them in cola bath overnight?
3. Take a picture of your pennies. Line them up in order according to the dates on the penny. Take a photo of them with a piece of white paper as the background.
4. Now your pennies are ready to take a bath. Line them up in the container, and pour the cola over them so that they’re sitting in a cola bath.
5. Before bed, come back to your experiment and flip the pennies over.
6. Good morning! Now it’s time to take another look at your pennies. Take the pennies out of their bath and wash them off. Line them up in the same order you did before you bathed them, and take another photo. Has anything changed?

### Results:

After a day in the cola bath, the pennies will be very shiny.

### Why?

There are lots of stories about the amazing powers of soda and the not-so-amazing effects of soda on your body. Some are true—others are not.

So why can soda, particularly sugary colas, make pennies shiny? It’s all because of a chemical reaction. In a chemical reaction, two different chemicals change each other. Part of the reason the pennies change has to do with the pennies, and part of the reason has to do with the cola.

Pennies are made out of copper, and after a while, copper gets dull. This is because the copper in the pennies reacts with air to create copper oxide. Yes, there are chemical reactions going on all over the place! Copper oxide looks less shiny than plain copper.

If you had to describe the taste of cola, you might describe it as tangy. That's because cola has acid in it – phosphoric acid, to be precise. Most colas have a pH of 2.5-3.5. The scale for pH is a way to determine how acidic something is. It goes from 0 to 14, and everything under 7 is acidic. This means that cola is quite acidic! Vinegar has a pH of 2.5, making it just a little more acidic than some colas.

When the copper oxide (the pennies) and the phosphoric acid (the cola) get together in the bath, the acid reacts with the copper oxide on the pennies and dissolves it. That’s why the pennies get shiny.

What else could you put into the cola bath? If you’d like to try something that’s a little more like your teeth, both limestone landscaping rocks and chalk have a lot of calcium in them. What do you think will happen to them when they sit in a cola bath overnight?

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