Exploding fire science experiments are wonderful features at live science museum shows. These experiments "wow" the crowd and help to show something about science, but they are not safe unless the building is set up correctly. This fire science experiment is not exploding, but is great for teaching kids about the science of fire.
- Clear glass jar
- Antacid tablets (must contain sodium bicarbonate)
- Disposable cup
- Table knife or fork
- Small piece of wax-based clay
FIRE SCIENCE EXPERIMENT STEPS
Step 1: Remove the label and completely dry the inside of a clear glass jar. A spaghetti sauce jar works well.
Step 2: *An adult must handle the antacid tablets or an adult must provide close supervision while the kids help with the antacid tablets.* Take an antacid tablet out the package and place it in the bottom of a dry cup. Using the table knife or fork, chop up the antacid tablet into smaller pieces.
Using the table knife or fork, break the antacid tablets into smaller pieces in the bottom of a dry cup.
Step 3: Place a ball of clay on the bottom of the candle. Now press the unlit candle and clay into the bottom of the jar, inside the jar. Using tongs or long needle-nose pliers helps to grip the candle to press it against the glass at the bottom of the jar.
Step 4: Pour the broken antacid tablet pieces around the unlit candle.
Antacid pieces in the bottom of the jar surrounding the candle
Step 5: *An adult must handle lighting the candle.* Light the candle by turning the jar upside down. The flame from the match rises which is why holding the jar upside down helps allow the candle to be lit inside the jar. Turn the jar over and set it on the counter.
Have an adult carefully light the candle
Step 6: Tip the jar slightly and carefully pour the water in the jar around the candle, without pouring it over the flame.
Quickly, but carefully pour the water around the lit candle, but do not extinguish the flame
Step 7: Observe the reaction taking place within the mixture of water and tablet pieces.
The sodium bicarbonate reacts with water resulting in CO2 gas. The bubbles in the jar is the result of CO2 gas being produced.
Step 8: Watch the candle for the next minute or two. The candle will start to crackle, then eventually burn out.
As C02 gas is produced from the chemical reaction, other gases inside the jar are pushed out.
The bubbles you saw as soon as the water was added to the antacid pieces was carbon dioxide gas being released. Antacid contains sodium bicarbonate (NaHCO3), which is also known as baking soda. Sodium bicarbonate is a weak base. When antacid is combined with water it reacts quickly, resulting in the release of sodium, water and carbon dioxide. Using smashed up pieces of the antacid helps speed up the reaction.
The second interesting thing that happened in this experiment was what happened to the fire. The lit candle in this experiment was using oxygen to continue to burn. When the carbon dioxide is released it starts to mix with the oxygen-rich air in the jar. Carbon dioxide gas is heavier than oxygen but this is not why the flame is extinguished. As more and more carbon dioxide gas is released by the antacid reaction there just is not enough oxygen left in the jar for the fire to continue. At first, the flame may crackle, but then finally it will stop burning.
Did you know that there are carbon dioxide fire extinguishers? CO2 (carbon dioxide) fire extinguishers work by moving the oxygen away from the location of the fire, extinguishing the flames. Now that we have seen the results of the fire experiment we know why these types of fire extinguishers work well.