About the Activity
If you look around your home you’ll probably see hand soap, dish soap, and maybe even a bar of soap! In this quick and fun experiment, kids will learn how soap’s key molecules, surfactants, reduce the surface tension in water – and by doing that, they’ll understand the importance of washing their hands with soap to prevent the spread of germs.
Grades: Pre-K - 5
Topic: STEM, Chemistry
Estimated Time: 30 minutes
Brought to you by HughesNet
These simple materials will get you started.
- Small foam or paper plate
- Black pepper
- Liquid dish soap
Follow these steps to create your experiment:
- To see an example of the experiment you’re about to do, check out this instructional video here.
- Now, let’s get started! First, add water to your plate. You will need just enough water to cover the bottom of the plate. Did you know? Surfactants, also called surface-active agents, are substances that lower the surface tension of a liquid.
- Now, sprinkle black pepper across the top of the water. Think of your black pepper as make-believe germs or dirt.Did you know? Surface tension is an effect where liquids shrink to their smallest size, making their surfaces strong, as a result. In this activity step, the pepper floated on top of the water on your plate because of the surface tension.
- Next, stick your bare finger in the center of your pepper. What happens? You will probably notice that your finger is covered with pepper.
- Now, cover your clean finger in the dish soap and then stick that same finger in the center of the pepper plate. What happens? The pepper should dance away from your finger. Did you know? Surfactants, like soap, help to reduce the surface tension of water. This allows water to interact with oil and grease. In this activity step, the surfactants pushed the pepper away from your finger – which is what happens when you use soap to remove germs from your hands.
Bonus Activity (Optional)
Why is “Nesquik” quick?
Surfactants aren’t just in soap, they’re also in other household products. Complete this activity to learn more!
- Place two large drops of water on a plate in separate spots.
- Place a pinch of baking cocoa on one drop and a pinch of Nesquik on the other drop.
- What happens? The baking cocoa bunches up on top of the drop because it does not break the surface tension of the water. However, the Nesquik breaks the surface tension in the water drop.
Conclusion: Nesquik is “quick” because it contains lecithin, a surfactant that breaks the surface tension of a liquid and makes it easy to mix in your milk!
Questions for your kids and teens.
- Why are surfactants a key ingredient in soap and cleansers?
- How do surfactants change the surface tensions of water? How does this help us fight against germs?
- Can you identify other surfactants around your home or in the grocery stores?
Investigate and Explore
Take what you've learned to the next level to learn more and explore the possibilities.
Soap has been around for thousands of years. Before soap, many people just used water, occasionally adding sand, mud, or clay to help remove dirt and grime. Over time, different cultures around the world started to experiment with different soaps, by combining oils or animal fats with ash or lye. During World War I, the traditional materials that were used to make soap were scarce. So, a German scientist by the name of Otto Rohm created a new process to make soaps, using surfactants. This new soap was a more effective cleanser and became the standard for soap around the world.
Over the next century, soaps and cleaning products continued to improve, with different scents, forms, and packaging. The next time you wash your hands, be sure to think of how the bubbles you see are actually the surfactants that are removing all the germs from your hands!
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