Spider Lava Lamp (part 3 of 4 of Spooky Science)

By Nicole Rhodes, Lead Science + Math Tutor at The Community Classroom

This Spider Lava Lamp STEM experiment explores the physical properties of liquids and a slightly different chemical reaction. I used black plastic spiders for a Halloween theme, but it could easily be done with plastic confetti for a visually appealing lava lamp. 

Materials 

• Water
• Oil (e.g., Canola oil or Mineral oil)
• Small plastic spiders
• Alka-Seltzer tablets
• Clear glass jar
• Small flashlight (optional)
• Food coloring (optional)

Instructions

Fill the jar with approximately 1 inch of water and a few drops of food coloring. Fill the rest of the container with clear oil. Add plastic spiders. Notice where the spiders settle inside the jar. Then, break an alka-seltzer tablet into small pieces and add them to the container. Observe the tablets sink through the oil and begin to bubble once they reach the water. You can turn this into a lamp, by placing a small flashlight or headlamp behind the jar; infrared headlamps add an eerie glow!

Why does the oil and water separate? Oil is less dense than water because the molecules in oil are bigger than water molecules. Bigger molecules are harder to pack together, so there are fewer oil molecules in a given space than there would be water molecules. What happens to the spiders as you drop them into the container? Small plastic spiders will typically sink through the oil, because they are about as dense as oil, but float on water. I had a mixture of large and small spiders, so one of my big spiders sank in the water, while the smaller ones hovered on top of the water line. Why are bubbles produced from adding the Alka-Seltzer tablets? Alka-Seltzer contains baking soda (a base) and citric acid–and, as we learned from the volcano experiment, when an acid and base mix, they will perform a chemical reaction! This time, citric acid reacts with baking soda to produce water and carbon dioxide gas bubbles. The chemical reaction is as follows:  

HCO3– (aq) + H+ (aq) → H2O (l) + CO2 (g)

To get rid of the oil, I poured it back into an empty oil container to reuse for another experiment. Be careful not to put it down the drain!

• Find part 1 of our Spooky Science series here (Gooey osmosis)
• Find part 2 of our Spooky Science series here (Apple skull volcanoes)

This experiment will appear on News Channel 22 WWLP’s Mass Appeal on Tuesday, October 24.