Watching a lava lamp’s coloured bubbles rise and sink involves more science than meets the eye! The different densities and polarities of the various components of a lava lamp show a fantastic phenomenon that you can recreate at home. Let’s do just that!
Materials
- Clear, empty water bottle
- Vegetable oil (enough to fill your bottle 3/4 full)
- Water
- Food colouring
- Alka-Seltzer tablets
Procedure
- Fill your water bottle ¾ full with vegetable oil. Make a prediction: what do you think will happen when adding water to the oil? Will they mix? If not, what will the mixture look like?
- Fill the rest of the water bottle with water. STEM Q For You: What happened to the water? The water should have sunk to the bottom of the container. Make a prediction! What do you think will happen when food colouring is added to this mix? Will it sink or rise?
- Add a few drops of food colouring into the container. STEM Q for you: What happened to the food colouring? It should have sunk to the bottom and mixed with the water.
- Make sure your bottle is sitting on a plate or cookie sheet with edges. Break an Alka-Seltzer tablet into a few small pieces and drop them into your water bottle one at a time. STEM Q For You: What happened to the mixture after adding the Alka-Seltzer tablet? The lava lamp should have erupted and created bubbles that floated throughout the mixture! As the reaction slows down and the bubbles pop, add more Alka-Seltzer to continue the reaction.
The STEM Behind the Fun
What is density?
Density is a measure of how compact a substance is or how much of it fits in a certain amount of space.
How did density affect the mixture of oil and water?
You observed that the water sunk to the bottom of the bottle, making it the “heavier” or denser substance. This is because water molecules are packed more tightly in comparison to oil molecules. Therefore, a cup of water actually has more mass than a cup of oil.
What is polarity?
Polarity prevents the oil and water from mixing together. It is a way of separating types of molecules into 2 groups, “polar” and “non-polar”.
What does it mean if a molecule is “polar” or “non-polar”?
In chemistry, a polar bond is a bond between two atoms that carries a charge, with one positive end and one negative end of the molecule. A non-polar bond does not carry a charge.
How did polarity affect the mixture of oil and water?
Water molecules are “polar” and have two positively charged hydrogen ends and one negatively charged oxygen end. These positive ends of the molecule will connect to negative ends of another molecule, letting them attach to other polar molecules. Oil particles are non-polar with no negative or positive charge, so they are not attracted to water molecules at all, preventing the mixture of the two substances.
What role did Alka-Seltzer play in the lava lamp?
The Alka-Seltzer reacts with water to produce carbon dioxide gas bubbles. These stick to the water droplets and form a molecule that is less dense than oil so it will rise to the top of the bottle. When they reach the top, the gas bubbles pop and escape into the air, allowing the dense water to sink back to the bottom again.
How does heat affect density in a real lava lamp?
Light and heat can change the density of a liquid in a lava lamp. Heat makes a substance less dense, causing it to float upward and away from the heat source at the bottom of the lamp. As it gets further from the light, it cools down and sinks again, starting the cycle all over!
Try This!
What other fluids are denser than water? How do various substances and temperatures layer within a mixture? Try building a density column using different temperatures of water.
