What you'll need:
- Small soft drink bottle
- Food colouring
- 2 tablespoons of cooking oil
- Dish washing liquid or detergent
- Add a few drops of food colouring to the water.
- Pour about 2 tablespoons of the coloured water along with the 2 tablespoons of cooking oil into the small soft drink bottle.
- Screw the lid on tight and shake the bottle as hard as you can.
- Put the bottle back down and have a look, it may have seemed as though the liquids were mixing together but the oil will float back to the top.
While water often mixes with other liquids to form solutions, oil and water does not. Water molecules are strongly attracted to each other, this is the same for oil, because they are more attracted to their own molecules they just don't mix together. They separate and the oil floats above the water because it has a lower density.
If you really think oil and water belong together then try adding some dish washing liquid or detergent. Detergent is attracted to both water and oil helping them all join together and form something called an emulsion. This is extra handy when washing those greasy dishes, the detergent takes the oil and grime off the plates and into the water, yay!