We have to admit, when we asked the children in our clubs what a lava lamp was last term we got a few blank looks! It seems these mesmerising and luminous lights are somewhat a thing of the 90s but that doesn't mean they are any less fun to make!
You will need:
‣ A plastic bottle/ tall glass
‣ Oil (Sunflower/ Veg for examples)
‣ Water
‣ Food Colouring
‣ Alka-seltzer tablets (always ask an adult for help)
Carefully fill your container roughly 2/3 full with oil
Top up the rest with water - you should find the water will sink to the bottom and sit underneath the oil. This is because water is more dense than oil.
Add your food colouring drop by drop into the mixture.This too should sink as it is water based.
Now it's time to create the reaction. Break up an Alka-Seltzer tablet into small pieces and drop them into the mixture.
Watch as your lava lamp comes to life and begins to bubble! If your reaction slows simply add more tablets.
Why doesn't the oil and water mix?
Oil is non-polar meaning it does not have a positive or negative charge and is therefore not attracted to water which does have polar molecules. Oil is described as hydrophobic which literally means "fear of water" so it repels the water molecules.
Why does the water sink below the oil?
Water has a greater density than oil. This means if you measured out the same volume of oil and water, the water would be heavier as the molecules which make up water are more tightly compact.
How does an ordinary lava lamp work?
Density is impacted by heat. A normal lava lamp uses a light bulb which gets hotter the longer it is switched on. As such the dense liquids at the bottom heat up and become less dense and rise to the top. When they reach the top they begin to cool and sink and the cycle starts again.
What does the Alka-Seltzer do?
When the tablet hits the water it begins to dissolve and produce bubbles of Carbon Dioxide (CO2). These bubble of CO2 stick to the water molecules which changes their density. They are now less dense so rise up through the oil. When the gas bubble pop the water molecules sink back down to the bottom.
Have you had chance to make your own? We'd love to see your creations!