In this activity, you will:

• Distinguish between physical and chemical changes
• Observe and understand the changes that occur to metals when they are submerged in water
• Analyze how bronze corrodes and use evidence to determine what type of change it goes through

• 30 – 60 mins

• Vinegar
• Salt
• Steel wool
• Pennies
• Beakers
• Water
• Printed or digital image of Statue of a Victorious Youth

This activity is about chemical change. A chemical change occurs when a substance transforms into an entirely new substance with different properties.

Examine Before and After Pictures of a Bronze Statue

Look at the two images of the Statue of a Victorious Youth below. The image on the left shows its surface before conservation treatment. The image on the right shows the statue as it appears today, after conservation. As you look, focus specifically on the surface of the bronze itself. Write or discuss your answers to the following questions.

• Describe the texture of the statue’s surface in the “before” image. Be specific with the light and dark spots that you see. Where do you see patches of rough and smooth spots?
• In the “after” image, the green and blue coating on the bronze is not paint and was not applied by anyone. What does that suggest about where it came from?
• What do you think is a possible explanation for the bronze to take on different colors?
• How can you find out whether the color changes on the bronze statue are from a physical change or a chemical change?

Understand Physical vs. Chemical Change

Read these definitions carefully. You will use them throughout the activity.

Physical Change: Physical changes are usually reversible. No new substance is created in a physical change. Examples include cutting paper, melting ice, or bending metal. In other words, matter changes shape or form, but stays the same substance.

Chemical Change: Chemical changes are usually NOT reversible. A new substance is formed in a chemical change. Signs of a chemical change may include a permanent color change, gas bubbles, heat or light produced, or new material appearing on the surface. In other words, matter transforms into one or more new substances with different properties.

Conduct Your Experiment

Set Up Your Experiment

Label three areas in your notebook: Penny A, Penny B, Penny C. Record your starting observations for all three pennies before you do anything to them.

• Color
• Shininess (dull, somewhat shiny, very shiny)
• Surface texture

Test Physical Change

Penny A: Set it aside as your control. Nothing happens to it.

Penny B: Rub with steel wool for 30 seconds

• Record what changes you see immediately
• Can you reverse this change? How would you do it?

Test Chemical Change

Put on safety goggles.

• Mix vinegar and a pinch of salt in a beaker.
• Place Penny C in the solution.
• Record observations at 5, 15, and 30 minutes.
• Remove the penny, rinse with water, and pat dry.
• Can you reverse this change easily? Try rubbing the surface. What happens?

Here’s What Happened to Penny C

Bronze is made of copper and tin. When bronze sits in seawater, copper reacts with oxygen and salt:

• Copper + Oxygen → Copper Oxide (black/brown coating)
• Copper Oxide + Saltwater → Copper Carbonate (green/blue patina)

This is a chemical reaction because:

• New substances form (copper oxide, copper carbonate)
• The color permanently changes
• The properties change (harder, more brittle)
• You can’t simply reverse it

Look at the Statue Again

Now that you learned about chemical change, look again at the two images of the Statue of a Victorious Youth.

On a printed copy of the image or on a digital version, mark and label the following:

• Green or blue areas = copper carbonate forming (chemical change)
• Dark brown or black patches = copper oxide forming (chemical change)
• Rough or flaking areas = corrosion damage (chemical change)
• Cleaned smooth areas = surface physically cleaned (physical change)

Write a Conclusion Based on Your Experiment

Answer the following prompt using complete sentences. Your response should be at least one paragraph.

• Is the corrosion on the Statue of a Victorious Youth a physical or chemical change? Use at least three specific pieces of evidence to support your answer.

To slowly damage something over time, like when metal rusts.