How to Make a Baking Soda Volcano | The Classic STEM Eruption

A baking soda volcano works by mixing baking soda with vinegar to create carbon dioxide gas, producing a safe, foamy eruption that mimics real lava.

This is the classic science fair project that uses nothing more than household ingredients to create an impressive chemical reaction. The process pairs a base (baking soda) with an acid (vinegar) to release carbon dioxide gas, which pushes the colored soapy mixture up and over the mouth of the container. The result is a bubbly, non-toxic lava flow that kids love and teachers trust for demonstrating acid-base reactions in real time.

What You Need For The Reaction

The magic happens with just four main ingredients, plus something to build the mountain around. Standard quantities from the ARM & HAMMER official STEM guide call for 2–4 tablespoons of baking soda and ½–1 cup of white vinegar. A squirt of dish soap creates the thick foam, and red food coloring turns it into convincing lava. Warm water helps the reaction speed up—cold ingredients slow it down noticeably.

Skip the glass containers here. Use a plastic water bottle or cup taped to a cookie sheet, because the foam travels fast and needs a wide, easy-to-clean base underneath.

Building The Volcano Structure

Tape a plastic bottle to the center of a baking sheet first—if the bottle tips, the lava spills sideways instead of flowing down the mountain. Shape a cone of play-doh, clay, or papier-mâché around the bottle, keeping the top opening clear so you can pour ingredients in later. Once the structure is dry, paint it to look like a real volcano with browns, grays, and a little green at the base.

The Eruption Sequence: Step by Step

The most reliable approach combines the two: prep the liquid mixture first, then add the dry ingredient, so you aren’t scrambling mid-eruption.

• Prepare the liquid blend in a separate cup: mix vinegar, a generous squirt of dish soap, a few drops of warm water, and red food coloring.
• Add the baking soda to the bottle inside your volcano. Two to three tablespoons is the sweet spot—more than that causes the foam to overflow the cone before it can flow down the mountain.
• Pour the vinegar mixture in quickly. The reaction is immediate: the foam rises, bubbles over the top, and runs down the sides like slow-motion lava. If you want a longer show, pour the vinegar in steadily rather than all at once.

The reaction is repeatable. Once the foam stops, add more baking soda and more vinegar to trigger another eruption. A pre-made volcano kit simplifies the mess by providing a reusable mold and the right proportions, which is helpful when running the experiment with a classroom or younger kids.

Getting The Best Results

The most common mistake is leaving out the dish soap—without it, you get a clear fizzy liquid instead of the thick foam that looks like lava. Another frequent issue is using cold vinegar or cold water, which slows the gas production enough that the eruption looks weak. Warm water mixed with the baking soda helps the reaction start fast and produce dense foam.

If the bottle isn’t taped securely to the base board, the whole structure can tip over when the reaction starts shaking it, dumping the lava before it has a chance to flow. And if you fill the bottle too high with baking soda, the foam never reaches a nice slow cascade—it just belches up and spills everywhere at once.

The reaction is completely non-toxic. It produces carbon dioxide and water, and the foam washes off most surfaces with plain water. Red food coloring can stain fabric and porous stone, though, so use washable paint on the volcano’s outer surface and keep the experiment on a cookie sheet or take it outside.