Fun Science: Rainbow in a jar

Everyone loves rainbows. Even on a wet and miserable rainy day with a bit of sunshine a rainbow can easily brighten up your day and put you in a good mood. This experiment allows you to create your own rainbow in a jar using simple household ingredients.

Rainbow in a jar

You will need:

  • A tall, see-through container (a jam jar will work well)
  • Golden syrup
  • Washing up liquid (blue or green)
  • Oil
  • Water
  • Food colouring

Method:

  • Add the golden syrup to the jar, trying not to let it touch the sides of the jar. It may be easier to use a squeezy bottle as this will create less mess.
  • Next, add the washing up liquid to the jar, squeezing it down the side of the jar so that it settles on top of the golden syrup.
  • Now you need to add colouring to the water (any colour is fine as long as it stands out against the washing up liquid). Then add the coloured water to the jar, again pouring it down the side of the jar so that it doesn’t mix.
  • Next you will need to add the oil to the jar, being careful to let it settle on the top of the water.

 

The Science Bit:

So what keeps all these layers all separated from each other? It’s how dense, or heavy, each liquid is. The honey is heaviest, and sits nicely on the bottom. The washing up liquid is not quite as dense as the golden syrup, but is more dense than the oil, and so on.

Layering them from most dense to least dense from the bottom to the top ensures that the rainbow maintains its distinct lines.

What if you had added the layers in the reverse order? Would you still see a rainbow? Try it.

What if you changed the colours around but added each liquid in the original order?

What happens if you mix your rainbow in a jar with a spoon?