"Mixing Oil and Water" Return to list of pracs

Aim: This is to illustrate a how oil based substances and water based substances cannot mix.

Equipment: The equipment includes...  

• large glass.
• vegetable oil..
• water.
• food colouring.

Method: Pour water into a large glass. Then pour vegetable oil slowly on top. Add food colouring slowly and see which layer it mixes with ... the oil or water. If the oil layer is narrow enough you can pour very slowly another layer of water on top (complete with a different colour food colouring!). With a bit of work you can obtain any colours (eg. football team colours) or layer upon layer (oil-water-oil-water-) ...

Background knowledge: Oil and water are different types of molecules. There exists in nature two general types of molecules: oil-like molecules and water-like molecules. Water-like molecules have a positive end and a negative end and are more likely to be able to conduct electricity through it more easily. They can react with each other more easily since a negative end of one water-like molecules attracts the positive end of another water-like molecule.

Oil-like molecules do not have a positive or negative end but are neutral at both ends. Similarly, oil-like molecules react only with other oil-like molecules. This is why oil and water do not mix ... they cannot react with each other very easily. Detergent molecules on the other hand are made up of a very long chain of carbon atoms ... one end has both positive and negative parts (making this end a water-like molecule) and the other end neutral (making it an oil-like molecule). When detergent is mixed with clothing in the wash, the oil-like end can dissolve and wash away the oil-like dirt and the water-like end can dissolve and wash away the water-like dirt. Brilliant hey?