Today's experiment is yet another use for the Kitchen Chemistry favorite, baking soda and vinegar. We've used this reaction before to blow up a baloon, or a variation of it (using citric acid rather than vinegar) to make a "pop" bottle (click here). Today we used the reaction as a type of fire extinguisher - to put out a burning candle.
For kids, the foaming of the reaction is the dramatic part that they like the most, but they also like the "magic" of watching the fire go out on the candle. On air we had three candles at different heights to show that the fire was extinguished as the gas generated in the reaction reaches the flame.
When vinegar reacts with baking soda the gas that is rapidly produced is carbon dioxide. You probably know that we can't survive breathing carbon dioxide and neither can a fire. If the carbon dioxide generated displaces enough oxygen from around the flame it goes out - most commercial fire extinguishers work on the same principle. The idea is essentially to smother the fire. You don't need to worry about suffocating yourself, though, because not that much carbon dioxide is generated.
If you want to do this experiment with your children at home the FIRST thing to remember is that fire is by it's very nature dangerous, so adult supervision is vital. You'll need the following supplies
Put the candle in the jar. We used sand and tape to keep our candles upright on the air. Any kind of holder can work, and allowing the kids some creative problem solving time on how to get the candle to stand up in the jar can be fun (it can be done by melting wax from the candle itself - again with adult supervision). Put roughly 1/4 cup of baking soda in the bottom of the jar. Light the candle. Pour in roughly 1/2 cup of vinegar and watch it foam up. Soon after the initial burst of gas (and depending on how high your candle is above the baking soda/vinegar reaction) the candle will just go out.
If you use different sized candles, as we did on the air, you'll see them go out at different times as the carbon dioxide gas reaches the various heights.
What is Fire? A nice site about the chemistry of combustion (fire).
More on Combustion Another site with more detail about the chemistry of combustion.