You will need:
- Plastic drinks bottle
- Cooking oil
- Blue food colouring
- A funnel
Step 1. Fill 1/3 of the bottle with water.
Step 2. Add a few drops of blue food colouring and swish around (remember to put lid back on first!).
Step 3. Fill the rest of the bottle with oil, to the very top. Use a funnel to help here so you don’t spill.
Step 4. Replace the lid, and slowly tilt from side to side. What do you notice?
The oil and the water do not mix, instead layers are formed and it looks like ocean waves are moving in the bottle. The oil sits on top of the water because it is less dense. Some liquids with different densities can mix together, but oil and water can’t. Do you know why not? Well, for liquids to mix, their molecules (the small particles everything is made up from) need to stick together. Water molecules are known as polar molecules so they have a positive end (+) and a negative end (-). Oil molecules are non-polar so they don’t have a positive (+) or a negative (-) end. Polar molecules only stick to other polar molecules and not non-polar molecules. So water and oil molecules cannot stick together, keeping them forever separate.