The Skittles rainbow or an exploration of density

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The Skittles rainbow or an exploration of density

I love colour, somehow it just makes my whole day feel better when I have bright things going on around me. That means that this experiment has the added benefit of making me cheerful at the same time as letting the kids explore science!

This is definitely one of the easier experiments that we do at our place. But easy does not equal boring. Everyone in our family from Ethan who is three to my father who is a lot older than that, enjoys watching the effect of this experiment. It’s almost hypnotising. I do also think that the fact that my kids usually sneak a couple of Skittles to eat as we do this experiment aids the frequency with which it’s requested!

Anyhow enough with the introductions, let’s jump into this colourful experiment.

Materials

  1. A white plate (paper, plastic or crockery are all fine)
  2. A packet of Skittles
  3. A cup or jug
  4. Warm water

Method

  1. Place the Skittles in a circle around the inside rim of the plate. For the most appealing results, alternate colours. Make sure that the Skittles are all the same distance from the centre.
  2. Use the cup or jug to pour warm water into the centre of the plate. Keep pouring until the water just reaches each Skittle.
  3. Watch your beautiful Skittles rainbow appear.

The science

The colour coating on the outside of the Skittles is soluble in water. When the water touches the coating, it dissolves making a solution. If the water touches each of the Skittles at the same time, the solution created by each Skittle has the same density as the solution next to it. This means that the solutions don’t mix but travel in parallel, moving into the water that is less dense towards the middle of the plate.

Once all of the water is the same density the colours tend to mix eventually.

Rainbow coloured water made by Skittles on a plate

Things to try

If you are keen to extend this activity a bit, you could try the following variations:

  1. Set out 2 of plates that are same size and made of the same materials. Set the experiment up as above but use warm water on one plate and iced water on the other. Time how long it takes each plate to complete the rainbow.
  2. Use other liquids such as white vinegar and soda water.

If you and your kids had fun with this experiment you might enjoy these others from our blog:

A Skittles density tower

Colourful walking water

Magic rainbow milk


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