Five Minute Science: The Separating Oil Experiment

Blog Post created by teachontarioteam on Jul 23, 2015

Welcome to Five Minute Science where we offer up cool science experiments you and your kids can do together using everyday household items, in about five minutes!


This week you get to separate oil from water and learn some science too, from the experts at Let's Talk Science.



To show how oil and water don’t mix.


Be sure to ask your child what he or she thinks might happen before you do the experiment – what result is expected when you pour cooking oil into a glass of coloured water?





The Experiment


Oil and Water Before_644X362-450x253.jpg

  1. Cooking Oil
  2. Water
  3. Food colouring
  4. A clear glass
  5. A spoon


  1. Fill the clear glass about half full of water.
  2. Add food colouring to water and stir using the spoon.
  3. Slowly pour cooking oil into the glass with water.



Explaining the Science:

What happened when you poured cooking oil into the glass of coloured water? Did you see the oil rise to the top of the glass, forming its own layer? Why do you think that happened?


The scientific explanation is that oil and water are liquids that don’t mix due to their molecular structure. Water molecules are attracted to each other, while oil molecules are attracted to each other. Water molecules are not attracted to oil molecules and oil molecules are not attracted to water molecules, so when the cooking oil is poured into a glass of water, the oil and water molecules separate from each other.


But why does the oil float to the top, instead of the water? That's because the cooking oil has a lower density than the water, in other words it's lighter, so it floats to the top. This is the same reason why a blow-up toy floats in a pool – the air in the toy is less dense than the water.


Curriculum Connection:

This experiment is simple, safe and appropriate for any age. In the Ontario Science and Technology curriculum, Properties of Liquids and Solids is taught in grade 2.


Extra Credit!
  • What happens when you add other liquids like vinegar or carbonated water to the oil and water? Do they mix, float on top, or sink to the bottom? Why?
  • What happens when you add food colouring to the cooking oil first, and then add water? Why?