Lava Lamp Experiment
Help kids explore mass, density, and polarity with this lava lamp experiment. When we study materials in science, we discuss their characteristics. These three characteristics help us describe, compare, and contrast a substance to other substances.
But don’t shy away from this activity because it sounds technical. Making a lava lamp is just plain fun for all ages. I have had children as young as four and as old as 15 do this experiment. Below the experiment steps are two explanations of what is happening in this activity–one basic explanation and one more advanced.
Also, you may want to pair this activity with studying the properties of water. This post has detailed information about polarity and another experiment using water and oil.
Materials Need for the Lava Lamp Experiment
- Water
- Tall glass or glass jar
- Food coloring
- Cooking Oil
- Effervescent antacid tablets
Lava Lamp Instructions
- In a measuring cup, color 1/2 cup of water with food coloring color of choice. Stir well.
- Fill the glass jar between ½ and 2/3 full with vegetable oil.
- Then, pour in the colored water into the glass jar.
- Break the antacid tablets into about 3 pieces
- Drop in one piece of the antacid seltzer at a time into the jar.
What is Happening in our Lava Lamp Experiment
In this experiment, the vegetable oil and water do not mix because oil is less dense than water. The food coloring dissolves in the water and sinks to the bottom due to its higher density.
When the Alka-Seltzer tablet is added to the jar, the tablet reacts with the water and releases carbon dioxide gas bubbles. Alka-Seltzer contains citric acid and sodium bicarbonate (baking soda), which react with water to form carbon dioxide gas bubbles.
A More Indepth Look at Density ad Mass
Density tells us how tightly packed the molecules are in a substance, basically, how much stuff is squeezed into a certain space. The formula for calculating density is density=(mass x volume)
Density is a measure of how much mass is contained in a given volume. (Remember mass is not the same as weight.) Mass is the amount of matter in an object.
The Mass, Volume, Density Song on YouTube is a fun way of helping your child understand mass, density, and volume. In the song, they help students visualize density (how tightly packed molecules are) by using the example of people on a train or subway and how tightly packed they are in the subway car.
Oil is less dense than water, so it floats on top of the water instead of mixing with it. The molecules in oil are bigger than the molecules in water. Because they’re bigger, they can’t squeeze together as tightly as water molecules do. This means they need more space for the same amount of stuff, which makes them less crowded together and less dense.
Water molecules are snugly packed together, so there’s more mass in the same volume compared to the cooking oil. Since water is denser than oil, when pouring them together into the same container, the water will sink below the oil.
Food coloring is water-based, so it dissolves in the water and sinks to the bottom due to its higher density compared to oil.
When the tablet is dropped into water, the citric acid and sodium bicarbonate in the Alka-Seltzer react together in a process called acid-base reaction. This reaction produces carbon dioxide gas (CO2), water (H2O), and a salt. The chemical equation for this reaction is:
Citric Acid+Sodium Bicarbonate→Carbon Dioxide+Water+Sodium Citrate
These bubbles attach to the colored water and rise to the top due to their buoyancy, creating a lava lamp-like effect.
In addition, water molecules are polar, meaning they have a positive and negative end, while oil molecules are non-polar, so they don’t mix well with polar substances like water. Check out our post on testing the properties of water to learn more about the polar properties of water.
Discussion Questions
After completing the lava lamp experiment, here are a few discussion questions to help students remember and demonstrate their understanding of the activity:
- Why do you think the oil and water do not mix in the bottle?
- What happened when the antacid tablet was added to the bottle?
- How does the bubbling reaction create the lava lamp effect?