This lovely, colourful jar experiment is super easy to set up and carry out but looks amazing!
What you’ll need:
A jar or glass
Fill the glass or jar about 3/4 full of warm water
Carefully pour a small layer of oil onto the surface of the water and leave to settle. Note that oil and water don’t mix!
Use a pipette to carefully drop small amounts of food colouring into the jar. You should see the food colouring drop through the oil into the water leaving colourful trails behind.
The Science Bit
Why do oil and water not mix?
Water is a polar molecule – it’s structure means that is has a positive charge one end and a negative charge the other. Water molecules stick together because the positive end of one water molecule is attracted to the negative end of another. The structure of an oil molecule structure is different – it is non polar, which means its charge is more evenly spread out . In fact oil is hydrophobic (water fearing) so it tries to get as far away from water as possible.
Why does oil sit on top of water?
The reason that oil rests on top of the water rather than underneath is because oil is less dense than water.
Why does food colouring not mix with oil?
The food colouring we used was water based and therefore does not mix with the oil, but sinks through the oil into the water below.
Why does the food colouring leave trails?
Since the addition of the colouring makes the food colouring heavier than the water it sinks to the bottom leaving trails (resembling fireworks) as some of the colour diffuses into the water.