Activity

Lava Lamp Challenge

Oil, water, and a fizzing tablet turn a plastic bottle into a lava lamp with blobs that rise and sink on their own.

Ages: 7–13
Duration: 60 minutes

What kids build

A working lava lamp in a bottle, plus notes on how water temperature changes the size and speed of the blobs.

Materials we bring

Clear plastic bottle or tall glass, about 16 oz
Vegetable oil, enough to fill about three quarters of the bottle
Water, enough to fill about a quarter of the bottle
Food coloring
Fizzing antacid tablets (Alka-Seltzer type), 2 to 3 per team
Tray or towel for spills
Optional flashlight for the glow
Optional second bottle for a warm versus cold water test

How we run it

01 Set up tables with materials for each team, with a tray or towel under every bottle.
02 Tell kids they are chemists today and their mission is to build a lava lamp that makes the biggest, longest-lasting blobs.
03 Fill the bottle about a quarter full with water.
04 Slowly pour in vegetable oil until the bottle is about three quarters full. Wait and watch the oil and water settle into two layers. Ask kids why the oil floats instead of mixing in.
05 Add 8 to 10 drops of food coloring. The drops fall through the oil without mixing and only color the water at the bottom.
06 Break a fizzing tablet into 2 or 3 smaller pieces and drop one piece into the bottle.
07 Watch the colored blobs rise up through the oil and sink back down. The tablet makes gas bubbles that carry colored water up, and the water drops once the gas escapes at the top.
08 Add another tablet piece each time the bubbling slows down. Leave the bottle open so the gas can escape.
09 Turn off the lights and shine a flashlight up through the bottom of the bottle.
10 Draw or describe your blobs. How big are they, and how fast do they move?
11 Compare teams. Which setup gave the best lava lamp effect, and why?

Kids layer water and vegetable oil in a bottle, color the water, and drop in pieces of a fizzing tablet. The tablet makes carbon dioxide bubbles that lift blobs of colored water through the oil, and the blobs sink again once the gas escapes. A warm versus cold bottle shows how temperature changes the speed of a reaction.

Real-world connection

Why oil spills float

Oil is less dense than water, so it floats on top. It also never mixes in, because water molecules are polar and oil molecules are not. That is why an oil spill spreads across the top of the ocean and why salad dressing separates into layers in the fridge. The fizz comes from carbon dioxide, the same gas that bubbles in soda and in baking soda volcanoes.

Go deeper

Extension ideas

Warm versus cold water

Build two bottles that are the same except for the water temperature. Drop in the same size tablet piece and compare how big and fast the blobs are and how long the bubbling lasts.

More tablet at once

Try dropping in two or three pieces at the same time. Does the lava lamp get wilder or just finish sooner?

When we have run this

Scheduled and past visits

Past

OCT 7 2026

Wednesday, October 7
Completed

Sewell Mill Library and Cultural Center

Kids layered water and vegetable oil in a bottle, colored the water, and dropped in pieces of a fizzing tablet to make blobs that rise and sink like a real lava lamp. Along the way they saw why oil floats on water and never mixes in.

Bring this to your space

Want the Lava Lamp Challenge at your library or school?

Tell us your space, your age range, and rough timing. We will come to you. Materials are on us.

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