Here is another fun science experiment to try in our ‘Home Science for Kids Series’.
So here goes… here is how to make a lava lamp with home ingredients to demonstrate density.
A tall jar, glass or an empty pop bottle
Vegetable oil (if you have some used oil this will work, just sieve it to remove any bits)
Some food colouring
Alka Seltzer (or 2/3 bicarbonate of soda and 1/3 citric acid)
Pour water into your lava lamp container to about ¼ full.
Add the vegetable oil until the lava lamp container is almost full.
Add some drops of food colouring and watch what happens as they fall through the oil and meet the water.
Now it’s the fun part – add the Alka Seltzer (break it into quarters) or a teaspoonful of bicarbonate of soda and citric acid mix and see what happens.
Try again using tonic water instead of tap water. See what is different when you add the food colouring.
How about trying with 2 different food colours? What happens now?
What happens with warm not cold water?
The science behind this experiment is all about density, just like in our last experiment.
Everything is made up of molecules. If these molecules are packed tightly together in an object, then that object is dense. If the molecules are further away from each other, then that object is less dense. This is the same for a liquid.
The oil floats on the water because oil is less dense than water. The reason the oil and water do not mix is because of intermolecular polarity. Water molecules have a small positive charge at one end and a small negative charge at the other end. This means that water molecules are attracted to other water molecules and they bond together forming drops. Oil molecules are non-polar and have no charge and are attracted to other oil molecules. The two different molecules don’t bond to each other, that is why they stay in their separate layers.
When you added the Alka Seltzer it sank to the bottom where it dissolved. This made a gas; Carbon Dioxide. When the gas bubbles rose through the oil, they took trapped bits of coloured water with them. When they reached the top, the gas escaped, and the water went back down to the bottom.
You can store the lava lamp with a top on it; just make sure all of the gas has released first before sealing it!