Fire vs. Fizz: Using carbon dioxide to extinguish a flame

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Do you have a fire extinguisher at home? There are different types of fire extinguishers for different types of fires, but some of the most common substances in fire extinguishers are either water, dry chemicals, wet chemicals or carbon dioxide.

But why, oh why, do they use carbon dioxide in a fire extinguisher? I’m glad you asked!

The Fire vs. Fizz experiment demonstrates how carbon dioxide can effectively suffocate a flame by displacing the oxygen the flame needs to burn. We use a classic chemical reaction to create carbon dioxide. We also see if we can reignite the flame!

Are you ready to become a fireman and see what puts out a flame? Let’s get to it!

How to make the Fire VS Fizz science experiment

Supplies you will need

For this experiment, you’ll need:

• Lighter
• Vinegar
• Baking soda
• Candle (candle height should be shorter than the bowl)
• Glass bowl

Before you start

Please watch fingers around the flame.

Instructions

Here is how to do this experiment with your child:

Step 1: Attach the candle to the glass dish

Using your lighter, melt some of the wax on the bottom of the candle and quickly push the melted wax and candle into the middle portion of the bottom of the glass bowl.

The candle should stay upright once the melted wax dries.

Step 2: Add baking soda to the bowl

Sprinkle some baking soda on the bottom of the bowl, covering the bottom.

Step 3: Light the candle

Before you start the chemical reaction, go ahead and light your candle. If you try to light it after the chemical reaction takes place, it might not ignite.

Step 4: Add vinegar to the baking soda in the bowl and observe

The baking soda and vinegar mixture will begin to froth, releasing carbon dioxide gas. That gas should extinguish your candle, even though no liquid touched it!

Carbon dioxide is filling the bottom of the glass bowl and, since the flame is below the top of the bowl, the flame is smothered by the carbon dioxide. That cuts off the fire’s oxygen supply (more on that below), causing it to extinguish.

Step 5: Try lighting the candle again

It’s impossible!

The STEM behind the Fire VS Fizz science experiment

This experiment teaches:

• Chemical reactions
• Carbon dioxide as a fire extinguisher
• Safety

How it works

This experiment works by using carbon dioxide to starve the flame of the candle, effectively extinguishing it.

When we mix vinegar and baking soda (a chemical reaction), carbon dioxide is released inside the bowl. Carbon dioxide is heavier than oxygen and tends to settle at the bottom of the container it is in. As it accumulates at the bottom of the bowl, it displaces the oxygen.

Fire needs oxygen to continue burning. With less oxygen available, the flame’s ability to keep burning is reduced and the flame is extinguished.

Essentially, carbon dioxide acts as a blanket, smothering the flame by preventing it from accessing the oxygen it needs to continue burning.

As long as the carbon dioxide stays in the bowl, the flame cannot be reignited!

Chemical reactions

A chemical reaction is, in a nutshell, when you transform one substance (the reactant) into another substance (the product).

When you bake a cake, you’re starting a series of chemical reactions. The flour, sugar, eggs, and baking soda (or powder) interact with each other under heat.

The baking soda reacts with the acidic ingredients (like the buttermilk or vinegar) to produce carbon dioxide gas, which causes the cake to rise. The proteins in the eggs and flour denature (change their structure) due to the heat, creating a firm texture. The sugars caramelize, giving the cake a golden-brown color and a sweet flavor.

So we use chemical reactions even when cooking!

This experiment utilizes one of the classic experiment chemical reactions: vinegar and baking soda.

Vinegar (an acid) and baking soda (a base), when mixed, create water, sodium acetate, water, and carbon dioxide.

The carbon dioxide gas is the fizzing and bubbling that you see in the chemical reaction.

Carbon dioxide as a fire extinguisher

Carbon dioxide is a popular choice for extinguishing fires, especially in confined spaces and for Class B fires (involving flammable liquids and gases).

Since carbon dioxide is heavier than air, it sinks and tends to accumulate in low-lying areas. As the carbon dioxide accumulates, it pushes oxygen out of the space, effectively reducing the oxygen concentration. That’s important because fires need oxygen to continue burning.

As the cloud of carbon dioxide expands, it begins to cool the fire, which helps reduce the temperature below the ignition point.

By reducing oxygen and cooling the fire, the carbon dioxide gas starves the flames, which prevents them from spreading or reigniting.

Safety

Even though carbon dioxide is not harmful in small concentrations like this, it’s still important to talk to your child about exercising safety when handling chemical reactions.

It’s a great opportunity to talk about safety equipment and measures, like wearing goggles and performing chemical reaction experiments in well-ventilated areas.

More experiments about chemical reactions to try out with your child

• Fizz, Pop, Inflate: The magical balloon experiment with a chemical reaction
• Rev Up with Engineering Fun: Build a Chemical Reaction Car!
• Homemade Lava Lamps: Chemistry in action!