In this weeks meeting, we made our own lava lamps. This is an awesome activity because it visually demonstrates the concepts of density, solubility, and chemical reactions. I strongly recommend this activity!
To start, we gave out an assortment of objects including: rocks, styrofoam, different types of sports balls, wood, and coins. Then, we predicted which items would float in water and tested our hypotheses. After some discussion, it was concluded that, “things that are lighter than water float in water”, which is exactly right! Here, we introduced the word density.
Testing out objects: Does it float or sink?
Next, we passed out the water bottles and filled them with 1/3 water and 2/3 oil using a funnel. This step demonstrated that oil floats on top of water because oil is less dense than water.
Then, we added food coloring. We explained to some of the older girls the word “solubility” and how the food coloring can be dissolved in water, but not oil.
Finally, we added the most exciting ingredient… Alka-seltzer! The chemical reaction between Alka-seltzer and water creates CO2 gas, which allows the water to bubble up through the oil. This creates the “lava lamp” look! If you leave the cap screwed on the bottle, the bottle pressurizes. Although a few girls did this by accident, it demonstrated that the chemical reaction was creating a gas.
For extra flair, we added glitter to our lava lamps. At the end, we also gave out the extra Alka-seltzer tablets, which led to many overflowing bottles! Whoops!
Here is the activity sheet we used: Lava_Lamp_Activity_Sheet