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  The Materials

  For this experiment you will need:

  • A teaspoon
  • One tablespoon of baking soda (sodium bicarbonate)
  • One tablespoon of laundry detergent
  • ¾ of a cup of water
  • ¼ cup of vinegar
  • Several drops of food colouring (optional)
  • A 400–millilitre (12–ounce) drinking glass
  • A waterproof plastic or metal tray

The Foaming Volcano

This experiment uses just a few ordinary household chemicals from your kitchen to turn a glass of coloured liquid into a frothing “volcano” that overflows its container.

Place the drinking glass on the tray, and put the baking soda and detergent into the glass. Add the water and a few drops of optional food colouring. Stir the mixture gently.

Quickly pour the vinegar into the glass. The mixture will foam up and over the top of the glass, covering the tray with a froth of tiny bubbles.

You can also produce a colour change from blue-green to red-orange when the vinegar is added to the mixture, by adding a teaspoon of red cabbage juice instead of the food colouring. We explain how to prepare some red cabbage juice in the “Cabbage Juice Indicator” experiment.

How is the big foamy volcano produced? Baking soda is sodium bicarbonate. Vinegar has acetic acid dissolved in water. Sodium bicarbonate reacts with most acids, and the products of the reaction between the sodium bicarbonate and the acetic acid are sodium acetate, water and carbon dioxide gas.

The gas forms bubbles that are surrounded by the liquid. The detergent makes the bubbles last longer, and the foam is produced. The volume of the carbon dioxide gas trapped in the foam is much greater than the glass, so some of it spills over.