Lava Lamp

Materials

· Bottle of vegetable oil

· 1/2 oz water (not included)

· 91% isopropyl alcohol (2 vials)

· Food coloring

· Glitter

· Alka-Seltzer tablets (2 packs)

Procedure

1. Add the water to the oil. Then add the vials of food coloring and isopropyl alcohol. These three liquids will sink below the oil, and the food coloring will mix with the water because it is water-based. Why do the liquids sink?

2. Add the glitter. You may need to gently shake the bottle so that it sinks.

3. Break one of the Alka-Seltzer into pieces so that it fits into the bottle. Make a prediction—what will happen when you put it into the bottle? Will it sink or float? Will anything else happen? Why?

4. Now place the Alka-Seltzer into the bottle. Was your prediction correct?

5. Place the lid back onto the bottle. What happens to your lava lamp when you do this? Be sure to open the cap frequently to release pressure.  Why is there pressure in the bottle?

6. Repeat steps 4-5 until you run out of  Alka-Seltzer.  What happens if you use a different amount of Alka-Seltzer?

Science Behind it!

When you add the other liquids to the oil, they sink because they are more dense than the oil—this means that the molecules in the other liquids are more tightly packed than the molecules in the oil, so the other liquids are heavier. The alcohol is less dense than the water but more dense than the oil, so it sits on top of the water and below the oil. The Alka-Seltzer tablets sink to the bottom because they are more dense than water.

When the Alka-Seltzer is dropped in the water, it begins to dissolve, and a chemical reaction occurs. The chemical reaction creates carbon dioxide gas, which creates bubbles in the water and alcohol. The bubbles of carbon dioxide are less dense than oil and water, so the bubbles want to rise to the top, and bring some water with them due to surface tension as well as the fact that water molecules are not attracted to oil molecules, so they do not mix (and therefore the gas stays trapped in the water). When the water reaches the top, the gas bubbles pop and are released into the space at the top of the bottle—the leftover water is more dense than the oil, so it sinks back to the bottom.

Since the chemical reaction is producing gas, and the gas is less dense (the molecules are less tightly packed) than the liquid, it takes up more space. This creates pressure in the bottle as the Alka-Seltzer dissolves, so it is important to release the cap to allow the excess gas to escape!