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.