Why does soap repel pepper

Instead of splashing or flattening, the water will form small, hemispherical droplets on the paper. These water droplets can hold their shapes because water molecules are more attracted to one another than they are to the wax paper. The strength of that attraction helps hold a water droplet together. Get ready to make a splash! Observations and results During this activity you tested five different household products to see how they affected the movement of pepper flakes in water.

Pepper is hydrophobic, which means water is not attracted to it. Therefore, unlike salt or sugar pepper will not dissolve in water. The pepper is able to float on the surface because water molecules like to cling to one another. They arrange themselves in a way that creates surface tension on the top of the water. This tension keeps the pepper flakes floating on top instead of sinking to the bottom of the bowl.

You should have observed a change in the behavior of the pepper flakes when you added different household products. Adding three of the products—the dishwashing liquid, glass cleaner and toothpaste—to the water should all have caused the pepper flakes to instantly dart away from the toothpick. Before we break down why this happens can you think of anything that dishwashing liquid, glass cleaner and toothpaste have in common?

And that important trait helps explain why the pepper was chased away by each of those three products. Soaps and cleaners are designed to break down the surface tension of water. This helps make them good cleaning tools. When you add the dishwashing liquid, toothpaste or glass cleaner to the water it breaks up the surface tension. The water molecules, however, want to stick together and maintain that tension, so they move away from the soap, carrying the pepper with them!

Clean up Discard any remaining liquid down the drain and throw away any used toothpicks. This activity brought to you in partnership with Science Buddies. Already a subscriber? Sign in. Thanks for reading Scientific American.

Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Materials Ground black pepper—at least five teaspoons A shallow bowl or aluminum pie tin Something light in color works best.

Liquid dishwashing soap Cooking oil Milk Toothpaste Glass cleaner Water Five toothpicks An adult helper Paper Pencil or pen Access to a sink Preparation Use your paper and pencil to create a table with two columns and six rows. Gather your materials on a surface that can withstand spills. This activity uses household chemicals that, if handled incorrectly, can be dangerous.

Please have an adult help you! Procedure Fill your bowl or pan two thirds full of water. Sprinkle one teaspoon of black pepper over the water. Observe the behavior of the pepper. Does the pepper sink or float? Does it spread out or clump together? What else do you notice about the pepper? Carefully dip the end of your toothpick into the cooking oil. It's great fun to do with children as a simple science experiment with dramatic effects, or you could perform it as a party trick.

When you have everything you need, go ahead and follow the instructions or watch the video for a visual demonstration and full instructions. Take your plate or bowl, I like to use a white one to give good contrast with the black pepper and pour on a pool of water approximately 1cm deep or more. Sprinkle over a dusting of ground black pepper all over the pool of water.

You should find the pepper sits on the surface of the water. This is because water has a high surface tension, meaning the water molecules have a strong attraction to each other and they like to stick together. Water has a higher surface tension then most liquids, this is the reason you're able to slightly overfill a glass with water, and why some insects are able to sit on the surface of pond water.

As the pepper is so light, it sits on the surface of the water rather the sinking to the bottom. The pepper is also hydrophobic which means water is not attracted to it, and as such the pepper does not dissolve into the water, it just remains resting on the surface. Try dipping your finger tip into the water. You should see it has no real effect on the pepper. You may find some of the pepper sticks to your finger, but nothing else really happens.

Then dip that finger into the center of the water. You should find the pepper immediately scatters and darts away from your finger, towards the edge of the water. The result is quite impressive to watch and can be seen in the video at the start of this Instructable. I found that the demonstration works even better if you reduce the amount of pepper you use, because it's able to move further before it bunches up, so the effect is even more impressive. So whats happening here?