Question to Explore:
How can we use properties of density and a chemical reaction to create our own lava lamp?
- clear bottle or container
- vegetable oil
- food coloring
- alka-seltzer tablets
- flashlight (optional)
- Fill a clear bottle or container 3/4 of the way with vegetable oil.
- Fill the rest of the container with water. The water will sink to the bottom under the oil.
- Add a few drops of food coloring. The food coloring is water-based, so it will also sink and color the water that is now at the bottom of the container.
- Break an alka-seltzer tablet into a few small pieces, and drop them in one at a time.
- Watch your lava lamp erupt into activity! As the reaction slows down, simply add more alka-seltzer.
- Try turning off the lights and shining a flashlight at the bottom of your lava lamp. It should start to glow.
View Science Bob’s step by step instructional video below!
Don’t have alka-seltzer tablets at home? Use the following tutorial to create a lava lamp with baking soda and vinegar!
Follow up Questions:
- Which is denser – water or oil? How do you know?
- Why does alka-seltzer make the lava lamp erupt?
- Does alka-seltzer erupt in your stomach when you take it? Why or why not?
If you don’t have alka seltzer on hand, here is another way to create a homemade lava lamp without using alka-seltzer: https://handsonaswegrow.com/how-make-lava-lamp-without-alka-seltzer/
There are two reasons why the oil and water do not mix. 1. They have different densities (the amount of mass per unit volume). The oil is lighter, causing it to stay on top of the water. 2. The water and food coloring molecules are polar (they have unbalanced electrical charges) and are strongly attracted to one another, while the oil molecules are not polar (they have balanced electrical charges) and do not mix with the water or food coloring.
When you place the Alka-Seltzer tablet in, it sinks straight to the bottom. It sinks through the oil without any chemical reactions occurring. However, as soon as it touches the water, carbon dioxide gas bubbles get released. Because these bubbles are less dense than both the water and the oil, they float to the top. They drag some water droplets to the surface with them and when they reach the surface the gas bubbles pop, causing the water droplets to sink back to the bottom. Here you have your lava lamp effect!
When the Alka-Seltzer tablets are consumed, the chemical reaction will stop and the water droplets will sink back to the bottom. You can keep the reaction going with more Alka-Seltzer tablets.
Do not pour the oil down the sink. This can cause a clog. Instead, keep it in a sealed container or put it in the trash.
Learn more with these resources!
Cool Science Experiment Headquarters has tons of cool, creative and easy experiments to explore density.
Magic School Bus (Ups and Downs Episode)
This episode explores density through a sinking and floating adventure. You can find this episode on Netflix Season 2 Episode 13 or by Googling it.
Fizz, Foam, Splatter and Ooze by Joe Rhatigan
A great book full of fun, family-friendly experiments including 2 more on density!
Featured photo: http://scinight.weebly.com/bubbling-lamps-of-lava.html