Have you ever wondered how fire extinguishers work? The science is simpler than you might think. At the heart of many fire extinguishers is a compound that we encounter every day: carbon dioxide (CO2). In this fire extinguisher experiment, a chemical reaction between baking soda and vinegar produces carbon dioxide gas that puts out a candle flame. But how? Let’s explore.
Understanding Fire Extinguishers
Fire requires three elements to exist: heat, fuel, and oxygen. They form what is known as the fire triangle. If you remove any one of these components, the fire goes out. Carbon dioxide extinguishers work by removing oxygen from the equation, replacing it with CO2.
While carbon dioxide contains oxygen in its chemical formula, the chemical bonds connecting it to carbon aren’t broken by the relatively low energy of a fire. So, its oxygen is unavailable for combustion. Also, carbon dioxide is more dense than air and sinks. This helps blanket the fire, preventing fresh oxygen from reaching it. Carbon dioxide from a fire extinguisher also cools the fire dramatically because the gas chills as it converts from high pressure in the canister to an unpressurized gas.
Fire Extinguisher Experiment Materials
You only need a few simple materials for making a DIY fire extinguisher:
- Baking Soda (Sodium Bicarbonate – NaHCO3)
- Vinegar (Acetic Acid – CH3COOH)
- A tall container (a pitcher or cup)
- A small candle
- Matches or a lighter
Perform the Fire Extinguisher Experiment
Safety First! Make sure to perform this experiment in a well-ventilated area and under adult supervision if you’re a minor.
- Mix a couple of tablespoons of baking soda with an equal amount of vinegar in a cup or other container. You don’t need exact measurements. The chemical reaction produces fizzing. It’s also an endothermic reaction, meaning it pulls heat from its surroundings and feels cold. This is the same reaction that makes “lava” in the chemical volcano project, except in that project, dishwashing soap traps the gas and makes lasting bubbles.
- Light a small candle or tea light.
- Tilt the cup over the candle flame. You want the invisible carbon dioxide gas flowing out of the container, not the liquid.
- The flames goes out.
Congratulations, you’ve just made a homemade carbon dioxide fire extinguisher!
The Chemical Reaction
The bubbling reaction you see is the chemical reaction between the baking soda (NaHCO3) and vinegar (CH3COOH). This reaction produces carbon dioxide (CO2), water (H2O), and sodium acetate or washing soda (CH3COONa). The equation for the reaction is as follows:
NaHCO3 + CH3COOH → CO2 + H2O + CH3COONa
How the Fire Extinguisher Experiment Works
Carbon dioxide is denser than air and does not support combustion. When you tip the container over the flame, the carbon dioxide flows down and pushes away the oxygen-rich air that the candle flame needs to keep burning. So, the flame goes out.
Here are some questions an instructor could ask students that stimulate further thought:
- Why is it important that carbon dioxide is denser than air in this experiment?
- Could other acids be used instead of vinegar in this reaction? If so, which ones and why?
- How does the temperature change during the reaction? How might this help in extinguishing a fire?
- In the chemical reaction equation, which compound is the limiting reactant and why?
- What other household items could produce carbon dioxide, and how could they be used safely in a similar experiment?
- Why is it important to not use this homemade fire extinguisher in case of a real fire?
Remember to always conduct experiments safely and responsibly. The point of this experiment is not to encourage the use of DIY fire extinguishers in emergencies, but rather to show how chemistry is a part of our everyday lives, even in the devices we use to keep ourselves safe.
Disclaimer: This experiment is meant for educational purposes only. A homemade fire extinguisher should not be used as a substitute for a professionally made, certified fire extinguisher in the event of a real fire. Always prioritize safety first and when in doubt, contact your local fire department.
- Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
- Lackner, Maximilian; Winter, Franz; Agarwal, Avinash K., eds. (2010). Handbook of Combustion. Wiley-VCH. ISBN 978-3-527-32449-1.
- Thieme, Christian (2000). “Sodium Carbonates”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_299 ISBN 978-3527306732.