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National Chemistry Week - Experiments - Falling Spheres

The Aim:

to make spheres of coloured water float between a layer of water and oil

What you will need:

  • 60 mL (1/4 cup) of liquid cooking oil (Crisco oil works well.)
  • 60 mL (1/4 cup) of water
  • 1 glass jar (baby food size)
  • blue, red or green food colouring
  • eyedropper
  • pencil

What to do:

  1. Pour the water into the jar first.

  2. Very slowly add the liquid oil so that the oil sits on top.

  3. Using the eyedropper, add about five drops of food colouring to the jar.

  4. Use a pencil to push the drops of food colouring down to the surface of the water.

  5. Encourage observations.

[IMAGE OF SPHERES GOING THROUGH OIL]

You could also try this using vinegar in place of the water layer, and powdered baking soda in place of the coloured water drops. Spectacular!

After the spheres have all dissolved, cap the jar and shake it vigorously. Set the jar down and observe what happens. The denser water will sink to the bottom. The centre is a mix of oil and water This is heavier than oil but lighter than water. The top layer is the oil with some trapped water in it that will eventually settle out.

Two separate layers form. The balls of food colouring will float just beneath the surface of the oil. Some of the spheres will sink and as they touch the water they will immediately break apart and dissolve. Oil and water are immiscible, therefore, they will separate into layers. Since this oil is lighter than water it sits on top. This is due to a density difference. The food colouring is water-based and will not dissolve in oil. When the coloured balls hit the water they will dissolve in it.

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