Pepper and Soap Science Experiment

This classic pepper and soap science experiment feels more like a magic trick!

It’s SO fun to do, and kids will be so impressed. However, the science behind this experiment is quite simple. This is all about surface tension!

This science goes well with a study on the properties of matter, especially if you are learning about water’s polarity.

This experiment works well with all ages. Preschoolers and kindergartners will LOVE this, but it’s equally fun for middle school or high school students, and they’ll be able to actually understand what’s going on with the effect of soap on water.

Supplies Needed for the Pepper and Soap Science Experiment:

• A shallow dish
• Water
• Pepper
• Liquid dish soap

First, fill a shallow bowl or dish with water. You really don’t need a lot, so it doesn’t have to be up to the edge or anything.

Then sprinkle pepper onto the water.

Dip your finger in the dish soap, and then put your finger in the center of the pepper water.

The pepper will suddenly rush toward the sides of the bowl! It’s amazing how fast this happens.

Kids may want to use LOTS of pepper because it’s fun to shake the shaker, but this experiment actually works the best if you don’t use a ton. If you use a smaller amount of pepper, it will travel all the way to the edges of the bowl with a larger “clear” space in the middle. This makes it very easy to see what’s happening!

Janie and I wanted to do the experiment a second time, but somehow we completely ran out of pepper! I hadn’t paid attention to how low it was getting. So we tried dried parsley flakes, and they worked very well! This was a really fun variation.

The Science Explanation:

Water molecules attract each other because of the covalent bonds that are present between the hydrogen atoms and oxygen atom. Each molecule of H₂O has a slight negative charge at the oxygen end and a slight positive charge at the hydrogen end. This makes the water molecules act as little magnets that attract each other. It’s like the molecules are holding hands with each other, and they don’t want to let go!

You observe this in action when you see huge drops of water that seem to pile up really high. It’s the reason that you can fit so many drops of water on a penny without it spilling over.

Soap is a surfactant, which means that each molecule has a hydrophilic or “water loving” end and a hydrophobic or “grease loving” end. This property of soap enables to it weaken the bonds between the water molecules. Without much of a bond, the water molecules stop holding hands and spread out.

We saw the dramatic effects of this spreading out in the pepper experiment! The pepper went zooming away from the soap and towards the edge of the bowl.

More Surface Tension Science Experiments:

Drops of Water on a Penny – How many drops of water can you fit on a penny? This is mind-blowing! Then compare with soapy water for a fun experiment.

Make a Fish Swim with Soap – this is another impressive one! Make a little foam fish zoom through the water.

Polarity of Water Science Experiments – here are several awesome experiments that demonstrate the effects of water’s polarity.

Science experiments with water are SO cool!