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