Soap - how does it get things clean?

Soap - how does it get things clean?

Soapy surprise!

How does soap work?

We showed you how to make a soap sculpture. It looks pretty cool, but do you know how soap works? Try this experiment to find out.

What you need:

  • Jam jar (or other small container) with lid
  • Cooking oil
  • Water
  • Washing up liquid

How to:

  1. Put some cooking oil and water in the jam jar. Screw the lid on tightly and shake.
  2. Let the jar stand for a few minutes. What do you notice? The oil and water should separate into layers.
  3. Add a few drops of washing up liquid to the oil and water and screw the lid on tightly again.
  4. Shake and leave for a few minutes. What do you see?

You should see a cloudy mixture. The oil and water are no longer in separate layers.

What happened?

Washing up liquid is a kind of soap. Normally, oil and water don't mix, so they separate into two different layers. Soap breaks up the oil into smaller drops, which can mix with the water. It works because soap is made up of molecules with two very different ends. One end of soap molecules love water - they are hydrophilic. The other end of soap molecues hate water - they are hydrophobic.

Hydrophobic ends of soap molecule all attach to the oil. Hydrophilic ends stick out into the water. This causes a drop of oil to form:


These drops of oil are suspended in the water. This is how soap cleans your hands - it causes drops of grease and dirt to be pulled off your hands and suspended in water. These drops are washed away when you rinse your hands.