Durham Academy
Baking soda is chemically known as sodium bicarbonate and is classified as a base. It reacts with acids, such as hydrochloric acid. Carbon dioxide gas is one of the the products of reaction. When excess acid is added to the baking soda the basic properties of the sodium bicarbonate are neutralized and the pH of the resulting mixture drops below 7. Acid-base indicators are organic dyes that take on specific colors depending on the pH.
Methyl orange used in this demonstration changes from orange to red at a pH around 4. The carbon dioxide released is trapped in the soap bubbles and expands, overflowing the container.