In this demonstration, students witness carbon dioxide being produced by a reaction between two common household chemicals. They then use one of the physical properties of carbon dioxide to extinguish a flame with what looks like magic.
Mixing vinegar (acid) and baking soda (base) creates a chemical reaction. When the two combine they create carbon dioxide (CO2) gas. When baking soda is mixed with an acid such as chocolate, yogurt, buttermilk or honey in muffins or a cake, the same type of chemical reaction occurs. The released bubbles of CO2 fluff up the batter.
When the reaction takes place inside a closed balloon, the CO2 pushes against the walls of the balloon, causing it to expand. This serves as evidence that a gas is being produced inside the balloon.
CO2 is heavier than air. When released from the balloon into a glass, it will collect at the bottom. If this CO2 is "poured" over the flame, it pushes the lighter air out of the way. The flame needs the oxygen in the air to burn, so the carbon dioxide puts out the flame.
One type of fire extinguisher uses carbon dioxide. It pushes oxygen out of the way, putting out the fire. This type of extinguisher leaves no mess behind, as opposed to chemical-, water-, and foam-based extinguishers. Carbon dioxide extinguishers are used in theatres, computer rooms, or other sensitive telecommunication areas.
If you wait too long to "pour" the carbon dioxide gas on the flame, the demonstration will not work. One of the properties of gas is that it will diffuse evenly in the space that surrounds it. This is why we do not live in a layer of CO2 where the life expectancy would be 2.5 minutes!
Because CO2 is colourless, you cannot see it being poured. However, it is possible to see how CO2 sinks and can be poured when working with dry ice (frozen CO2) because the cold CO2 causes water in the air to form mist. Hence working with dry ice could be a nice follow-up to this activity.
