Soap is good at cleaning because it acts as an emulsifier, enabling one liquid to disperse into another immiscible liquid. While oil (which attracts dirt) doesn’t naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.
It’s easy to demonstrate the action of an emulsifer. All you need are two immiscible liquids and a little dishwashing detergent or soap.
Emulsifier Demo Materials
- oil or kerosene
- dishwashing detergent or soap
- flask or clear glass
If you like, you can add food coloring to this demonstration. It will color the water and not the oil or kerosene. You don’t need to add coloring to tell the water and oil apart, though. Some oils are naturally colored. Or, if you use kerosene, it’s often tinted so people can identify it on sight.
Perform the Demonstration
- Add some oil or kerosene together with some water in a flask. Swirl the contents around to try to mix them. What happens?
- Add a squirt of dishwashing liquid. Swirl or shake the flask to mix the ingredients. How has the layer of kerosene or oil been changed?
What could be easier, right?
Pepper and Water Emulsifier Trick
This video shows another fun way to illustrate emulsification. If you sprinkle pepper on a dish of water and touch your finger to the surface of the liquid, you get a wet finger but no reaction from the pepper. Next, if you put a drop of liquid dishwashing soap on the tip of your finger and touch the surface of the water, the pepper seems to scatter away.