Halloween Density Jar

This is a super simple, fun Halloween density investigation that is perfect for introducing the concept of liquids having different densities and for practising making and testing predictions. All you need to do is set up an easy density jar with oil and water and try to find a spooky object for each layer.

Halloween Density Jar

What you need

Empty bottle or jar

Water

Oil – we used very cheap vegetable oil.

Halloween objects to test - we used plastic spiders, eyeball bouncy balls and decorative foil ghosts

Method

Half-fill the container with water, then add some oil. The oil should float on top of the water layer.

Carefully drop the small objects into the jar and watch what happens. Try to find something to float on each layer.

See this post for a full explanation about density.

Why do oil and water not mix?

This is because water is a polar molecule – its structure means that it has a positive charge at one end and a negative charge at the other. Water molecules stick together because the positive end of one water molecule is attracted to the negative end of another water molecule.

An oil molecule has a different structure, it is non polar meaning that its charge is evenly spread out, so oil molecules are not attracted to water molecules. Oil is hydrophobic and tries to get as far away from water as possible.

If you liked this activity, we've got lots more Halloween Science and Halloween STEM Challenges you might like!