Tuesday 10 September 2013

Fireworks in a glass jar!

Admittedly this is not actually fireworks but it looks like fireworks and it involves science!

What you will need:
  • A tall glass or a transparent plastic cup or an empty clear jar
  • Oil
  • Water
  • Food Colouring
  • Salt
What to do:

Fill your glass 3/4 with water and then put about 2 cm of oil on top.

Carefully and gently add drops of food colouring onto the surface of the oil.  (You can use as many different colours as you like.)

Now for the magic.  Sprinkle salt over the top and watch your own mini firework display!

Time to investigate -

Experiments you could try:

How long will the effect go on if you keep adding salt?

Try adding different substances like sand, flour, sugar or talcum powder.  Does it have the same effect?

Try using different food oils - does it give the same effect?

Does the shape and size of the glass make a difference?

How does it work?
First of all, the oil floats on top of the water because water is denser (to find out about density click herethan the water. Since the salt is denser than the oil it sinks down into the water.  When the salt sinks it takes some of the oil with it but when the salt dissolves the oil goes back up because it becomes less dense and takes some oil with it, but then the salt dissolves making the oil go back to it's original density and because the oil by itself is less dense the oil floats back to the top!

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