How to make a Lava Lamp

What is Polarity?

You probably noticed that oil and water don’t mix. And the reason is a property called polarity.

A molecule is polar when its electrons are shared unevenly, creating a slightly positive end and a slightly negative end. This usually happens when the atoms have different electronegativities and the molecule's shape does not cancel out those differences. Electronegativity is a very important chemical property that describes how strongly an atom attracts shared electrons in a chemical bond. Nonpolar molecules contain atoms with similar electronegativities or have a symmetrical shape that balances the charge.

But how is polarity connected to the fact that water and oil don’t mix? Well, water is a polar molecule (hydrogen and oxygen form polar bonds) and oil is a nonpolar molecule (consisting of hydrogen and carbon which are of similar electronegativity).

Polar and nonpolar molecules just aren't attracted to each other. Because water molecules are so strongly attracted to other water molecules, they crowd out the oil molecules, keeping the two groups separated.

Materials needed for the Homemade Lava Lamp

• Empty bottle. Glass bottle or plastic bottle will serve the purpose. The only important thing is that the bottle is transparent. As for size, we recommend at least a 1-liter bottle so we can observe the effect better. But an even bigger bottle will be good for our activity.
• Water. 1 quarter liter (250 mL) of water will be enough if we use a 1-liter bottle. If you are using a bigger bottle, make sure 1 quarter is filled with water.
• Kitchen or cooking oil. We will need to fill 3 quarters of the bottle with oil. So if we are using a 1-liter bottle, we need 7.5 deciliters (750 mL) of cooking oil. Any liquid oil will do the trick. We can also use baby oil as an alternative to cooking oil.
• Food colors. For added effect, you can add a few drops of food coloring. You can buy them in most supermarkets and we recommend adding a couple of drops of red color for a real lava effect.
• Fizzing tablet or officially known as Effervescent tablet. This will be the trigger for our lava bubbles. Fizzing tablets are easiest to come by as vitamin or food supplement tablets and you can find them in most supermarkets as, for example, magnesium tablets.
• Kitchen funnel. Funnel is not mandatory but it will make pouring water and oil in our empty bottle much easier.

Instructions on doing the Lava Lamp Science Experiment

If you would like to see how we made our lava lamp, you can watch the video at the beginning of the article. And for step-by-step instructions continue reading below.

1. Pour water into the bottle. Here we can use the funnel to make our job easier. Make sure 1 quarter of the bottle is filled with water.
2. Pour oil into the bottle. Now add the oil to fill the bottle to the top if you used a 1-liter bottle (leave few centimeters of space to avoid accidental spills). In any case, add 3 times more oil than the amount of water you added.
3. Add food colors. Now we can add a few drops of food colors to our bottle to make the final effect more spectacular. As mentioned in the materials section, adding red color will make a great lava effect.
4. Drop the fizzing tablet into the bottle. And to start our lava lamp, all we need to do is add a fizzing tablet. If you used a 1-liter bottle, even half a fizzing tablet will make a great lava lamp. You can add the whole tablet for a longer and stronger effect. You can experiment with different amounts of fizzing tablets. Good thing is that you can repeat the process indefinitely as long as you have fizzing tablets. When one is used, just drop another one for the lava lamp to continue to work.
5. Enjoy the show and mesmerizing lava bubbles effect!

The Science behind the Lava Lamp Experiment

Okay, now we know why water and oil don't mix, but how do those "lava bubbles" work? When we drop food coloring into the bottle, it doesn't mix with oil molecules, but it does with water molecules. How come? Again, it is all about polarity. Most liquid food colorings are water-based, so they mix easily with water but not with oil. We can conclude that “Like dissolves like.”.

So polar molecules will mix with other polar molecules, and nonpolar molecules will mix with other nonpolar molecules. So if you remember that water is a polar molecule, anything that we can dissolve in it (like salt or sugar) must also be a polar molecule! Anything that dissolves in oil is nonpolar.

Polarity explains why they don't mix, but it doesn't explain why oil ends up on top. For that we need a different concept: density. Density tells us how much matter is packed into a certain amount of space. Oil is less dense than water, so it floats on top instead of sinking.

About Fizzing Tablets

Fizzing tablets contain baking soda and citric acid. The citric acid and baking soda in the tablet are ionic/polar compounds. They cannot dissolve or react in the nonpolar oil. When they mix with water, they make carbon dioxide which we see as bubbles in the water. The gas bubbles are less dense than the surrounding liquid, so they rise toward the surface. As it rises, it picks up some colored water. When the bubble escapes at the surface, the gas disappears into the air, but the colored water it was carrying doesn't go with it. That little droplet of colored water is still denser than oil, so it can't just sit on top or blend into the oil layer above it. Gravity pulls it back down, and since oil and water still don't mix, the droplet sinks straight through the oil until it reunites with the water layer at the bottom.

What will you learn by making your own Lava Lamp?

• Chemistry knowledge. Learning about polar and nonpolar molecules, different liquids and chemical properties of fizzing tablets will improve our knowledge of chemistry.
• Measuring and ratios. Since we need to add different ratios of water and oil in the bottle, we will learn about ratios and practice measuring.
• What is polarity. By doing this activity, we will demonstrate how polarity works and how it enables us to achieve the lava lamp effect.
• Recognize an acid-base reaction. By observing the fizzing tablet in the water, we observe the acid-base reaction and chemical process of creating carbon dioxide.
• How to conduct an experiment. Planning and gathering materials, preparing an experiment, observing the processes, and making conclusions will help us develop knowledge on how to properly conduct an experiment.

Frequently Asked Questions

We hope you enjoyed this activity and that you are still enjoying your lava lamp. If you would like some more similar fun science experiments, we have some great recommendations:

• If you want another great activity to demonstrate polarity and you want to expand your knowledge, be sure to check the How to make colorful milk polarity experiment article.
• And for more chemical processes and learning about diffusion, we recommend checking How to demonstrate diffusion with hot and cold water activity.
• Another great chemistry experiment we recommend, if you want to learn about oxygen and oxidation, is Apple Oxidation Experiment.
• And last but not least, you can create your own volcano and make it erupt by doing Homemade Volcano activity with vinegar and baking soda.

Happy experimenting!