Supplies Needed
  • A glass Jar or clear drinking Glass
  • Oil
  • Salt
  • Food Colouring(Optional)

1. Pour about 3/4 cup of water into the jar.

2. Pour about 1/3 cup of oil into the jar. When everything settles, is the oil on top of the water or underneath it?

3. If you want, add one drop of food colouring to the jar. What Happens? Is the drop in the oil or in the water? Does the colour spread?

4. Add some salt on top of the oil and count slowly to 5. What happens to food colouring? What happens to the salt?

5. Add more salt to keep the action going for as long as you want. 


Science behind the Experiment

Why does the oil float on the water?

Oil floats on water because a drop of oil is lighter than a drop of water of the same size. Another way of saying this is to say that water is denser than oil. Density is a measurement of how much a given volume of something weighs. Things that are less dense than water will float in water. Things that are more dense than water will sink.

Even though oil and water are both liquids, they are what scientist call immiscible liquids. That’s a fancy word that means they don’t mix.

What happens when you put salt?

Salt is heavier than water, so when you pour salt on the oil, it sinks to the bottom of the mixture, carrying a blob of oil with it. In the water, the salt starts to dissolve. As it dissolves, the salt releases the oil, which floats back up to the top of the water.

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