Fizzing and Foaming

With just a few household chemicals you can turn a glass of colored liquid into a froth that overflows its container.

For this experiment you will need:

Place the drinking glass on the tray. Put 15 cm3 baking soda and 15 cm3  laundry detergent to the glass. Add 180 mL of water and a few drops of optional food coloring. Gently stir the mixture to mix the contents of the glass. To display and observe the fizzing and foaming, 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.

To produce a color change when the vinegar is added to the mixture in the glass, you can substitute some red cabbage juice for the optional food coloring. The experiment titled "Exploring Acids and Bases with Red Cabbage" gives instructions on how to prepare some red cabbage juice. With red cabbage juice, the mixture will chage color from blue-green before adding vinegar to red-orange after the vinegar is added. For a different color change, try grape juice.

In this experiment, the fizz is produced by a chemical reaction between baking soda and vinegar. Baking soda and vinegar react, and one of the products of the reaction is carbon dioxide gas. This gas forms bubbles that are surrounded by the liquid. The laundry detergent makes the bubbles last longer, and a foam is produced. The volume of the gas produced and trapped in the foam is much greater than the glass can hold, so some of it spills over the top of the glass.

Baking soda is sodium bicarbonate. Vinegar contains acetic acid dissolved in water. Sodium barcarbonate reacts with most acids. The products of the reaction with vinegar are carbon dioxide gas, sodium acetate, and water.

The reaction of sodium bicarbonate to form carbon dioxide gas is the basis of its use as a levening agent in baking. Cakes are solid foams. The foam is produced when bubbles of carbon dioxide from the reaction of sodium bicarbonate are trapped in the batter. As the cake bakes, the batter dries, and the trapped bubbles of carbon dioxide form the holes in the cake.

For additional information, see CHEMICAL DEMONSTRATIONS: A Handbook for Teachers of Chemistry, Volume 3, by Bassam Z. Shakhashiri, The University of Wisconsin Press, 2537 Daniels Street, Madison, Wisconsin 53704.

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