If you have ever seen a lava lamp, you know how mesmerizing it is to watch the blobs rise and sink through the liquid. Most lava lamps contain a combination of water and wax. As a solid, wax is heavier than water and will sink to the bottom of the container. When wax melts into a liquid, it is lighter than water and will rise or float on top of the water. A lava lamp works by having a heat source at the bottom of the lamp to melt the wax. The melted wax rises through the water, but then sinks as it cools off and begins to harden again.
In this demonstration, we will re-create the effects of a lava lamp using common household items, with no electricity needed! The “blobiness” effect will wear off during the demonstration, but you can regenerate it whenever you want!
The Experiment
Supplies: A clean 1-liter clear soda bottle, tap water, vegetable oil or baby oil, fizzing tablets (such as Alka Seltzer), and food coloring.
What to do: Pour the water into the bottle until it is about 1/3 full. Use a measuring cup or funnel to slowly pour oil into the bottle until it’s almost full. You may have to wait a few minutes for the oil and water to separate. Add about 10 drops of food coloring to the bottle (red is nice, but any color will look great.) The drops will pass through the oil and then mix with the water below. Break a seltzer tablet in pieces and drop a piece into the bottle. DO NOT PUT THE CAP ON THE BOTTLE. Observe what happens. Continue to add pieces of the seltzer tablet as you see fit. What happened inside the bottle after you added the seltzer tablet pieces?
What is happening: The oil floats on top of the water because it is less dense (see the liquid density experiment for more information). The fizzing tablet contains a mixture of powdered acids and bases that begin to combine as they dissolve in the water (see the carbon dioxide experiment). As the tablet dissolves, it creates carbon dioxide gas. As the gas rises through the oil, it takes some of the water with it. When the gas bubble reaches the surface of the oil, the bubble “pops,” allowing the gas to escape, and the water sinks back down through the oil to the bottom.
Extra: Once your tablet pieces are completely dissolved and the reaction is over, you can store the oil & water mixture with the cap on to save for later. To make more blobs, simply add more tablet pieces!
Links
To see this demonstration in action, head over to BASF’s YouTube page.