Lava Lamp

Introduction

Experience the hypnotizing lava lamp, with its modified colored bubbles sinking and rising. This activity is interesting because changes in density cause beautiful colors to float or sink. Students will love watching this version of a lava lamp with its colorful blobs floating around! What better way to teach students about chemistry than to show them something that will captivate them?

Concepts

• Density
• Chemical reactions
• Polarity

Materials

Safety Precautions

The materials used in this activity are considered nonhazardous. However, all may cause slight irritation to the skin or eyes. Avoid contact of all chemicals with eyes and skin. Follow all laboratory safety guidelines. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remember to wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The solid products of this reaction may be disposed following Flinn method #26a.

Procedure

1. Obtain a 60 mL square bottle.
2. Fill the bottle half full with water.
3. Add 2 or 3 drops of food dye to the bottle.
4. Add oil to the neck level of bottle.
5. Break an Alka-Seltzer tablet into 4 pieces.
6. Drop one piece of the Alka-Seltzer into the bottle.
7. Observe the lava lamp as it bursts to life!

Student Worksheet PDF

12385_Student1.pdf

Teacher Tips

• Once the reaction stops, you can add more Alka-Seltzer.

Discussion

A lava lamp works because of two different scientific principles, density and polarity. Density is the measurement of how compact a substance is—how much of it fits in a certain amount of space, density = mass/volume. If you measure an equal volume of oil and water, you will find that the water is heavier than the same amount of oil. This is because water molecules are packed more tightly and a cup of water actually has more mass than a cup of oil, assuming the volumes are equal. Because water is denser than oil, it will sink to the bottom when the two are put in the same container.

Oil and water also separate owing to their different polarities. Water molecules are “polar” because they have a lopsided electrical charge. The H atoms retain a partial positive charge and the oxygen atoms retain a partial negative charge. The positive end of the water molecule will connect with the negative end of the other molecules. Oil molecules, however, are nonpolar. They don’t have a positive or negative charge, so they are not strongly attracted to the water molecules. This is why oil and water don’t mix.

Store-bought lava lamps use polar and non-polar liquids like the homemade one here. However in store-bought lamps, the densities of the liquids are much closer together than vegetable oil and water. The denser liquid sinks to the bottom, but the lava lamp light heats it up until it expands and becomes less dense, causing it to rise upward. As it gets farther from the light, it cools down, becoming denser again until it sinks; then the cycle starts all over.

Our homemade lava lamp will use Alka-Seltzer to power the lamp. The Alka-Seltzer reacts with the water to produce carbon dioxide gas bubbles, these stick to the water droplets. Sodium bicarbonate reacts with citric acid from the tablet to form water and carbon dioxide gas. The water/gas combo is less dense than the oil, so they rise to the top of the flask. At the top, the gas bubbles pop and escape into the air, allowing the dense water to sink back to the bottom again.