Key concepts
Chemistry
Molecules
Buoyancy
Density
Polarity
Introduction
Have you sever seen a lava lamp? They might look complicated, but you can make your own using common kitchen supplies. Try this activity to find out how!
Background
If you look around your kitchen, there are probably a lot of different liquids, including water, juice, milk and oil. Many of these liquids have different properties that you can see, feel and taste. For example, milk is opaque and white whereas water is transparent and clear, and oil has a “slimy” texture that makes it difficult to clean if you spill it.
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Each liquid also has other properties that might not be so obvious because you can’t “see” them easily. For example, they all have different densities (the amount of mass per unit of volume). Many common household liquids such as juice and milk have a density very close to that of water, so you might not notice a difference. Oil, however, has a lower density than water, meaning it can float on top of water. (It is buoyant.) You can see this if you try putting a few drops of oil in a glass of water—they will float on the surface.
Liquids are all made up of molecules that have different chemical properties. Some molecules are polar, meaning they have unbalanced electrical charges. These molecules tend to mix with one another better than they mix with nonpolar molecules, which have evenly distributed charges. You can observe this if you try mixing different liquids together. For example, it’s very easy to mix together juice and milk or water and food coloring. But if you try mixing water and oil—even if you stir vigorously—the liquids “want” to stay separated.
What can you do with all this information? In this project you’ll use it to make your own lava lamp!
Materials
Clear glass
Tap water
Vegetable or mineral oil
Food coloring
Alka–Seltzer tablets
Flashlight (optional)
Preparation
Prepare a work area where you can easily clean up any spills, such as a kitchen counter.
Procedure
Fill your glass about one quarter full with water.
Add several drops of food coloring.
Fill the rest of the glass with oil (not all the way to the brim).
Break an Alka–Seltzer tablet into four roughly equal-size pieces.
Drop one of the pieces into the glass. What happens?
Wait for the bubbles to stop, then drop in another piece. How long do the bubbles last for each piece?
Extra: Stand a large flashlight on its end, with the light facing up, and place the glass on top. Turn off the lights in the room and turn the flashlight on. Drop in another Alka–Seltzer tablet, and you’ve made a lava lamp!
Extra: Try the activity with different temperatures of water. How does water temperature affect your results?
Extra: Try using half a tablet or even a whole tablet at once. What happens?
Extra: Try pouring some salt into your glass instead of using an Alka–Seltzer tablet. What happens?
Extra: Try reversing the order in which you add substances to the glass. What happens if you pour the oil in first, then add the water and food coloring?
Extra: Review the information in the “background” section. Try making a lava lamp with different liquids you can find in your kitchen. What combinations of liquids work, and which ones don't? Can you figure out why?
Observations and results
When you pour the oil into the glass you should see it does not mix with the water—it forms a separate, clear layer on top. This occurs for two reasons: First, the oil and water are different densities—the oil is lighter, so it stays on top. Second, the water (and food coloring) molecules are polar, so they are strongly attracted to one another. The oil molecules are not polar, so they don’t mix with the water or the food coloring. This is why you’ll get the same result no matter what order you pour substances into the glass—the water and food coloring will always sink to the bottom instead of mixing with the oil.
When you drop an Alka–Seltzer tablet into the glass, it sinks to the bottom. It sinks straight through the oil without any chemical reactions occurring. When it touches the water, however, a chemical reaction occurs that releases carbon dioxide gas bubbles. These bubbles are less dense than the water or the oil, so they float to the top—but they “stick” to the water a bit, dragging some water droplets up toward the surface with them. When they reach the surface, the gas bubbles pop and the water droplets sink back to the bottom—creating a lava lamp effect.
Eventually the Alka–Seltzer tablet will be completely consumed, and the chemical reaction will stop. If you let the glass sit still, all the water droplets will sink back to the bottom. (Remember, they don't want to mix with the oil.) But as long as you have more tablets, you can keep the reaction going!
Cleanup
Do not pour all that oil down the drain! It could cause a serious clog. Ask an adult for help disposing of it. Options may include putting it in a sealed container in the trash or pouring it outside.
If necessary, use towels to clean up any spilled water or oil.
More to explore
Make an Alka–Seltzer—Powered Lava Lamp, from Science Buddies
Make Your Own Lava Lamp, from Science Buddies
Create Underwater Fireworks with Chemistry, from Scientific American
Stacking Liquids, from Scientific American
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
