Carbon Dioxide Flame Extinguisher
Gaseous carbon dioxide is poured into a clear walled vessel containing four lit tea candles suspended at varying heights. The candles are extinguished one at a time from the lowest to the highest.
Illustrate the concept of carbon dioxide not being able to support combustion, as well as showing that carbon dioxide is denser than air.
Solid carbon dioxide (dry ice) sublimes at a temperature of -78.5 °C. At this temperature, it has a density of 1.56 g/L. The density of oxygen at 25 °C is 1.31 g/L. As the more dense carbon dioxide is poured into a vessel containing four lit candles suspended at varying heights, the candles are extinguished one at a time from the bottom up.
Prepare a clear plastic tank by placing four jars and/or beakers of varying capacities inverted so that you have a cascading array. Place a tea candle on the bottom of each beaker/jar. Place a number of pieces of dry ice in a plastic pitcher and allow them to stand for ca. ten minutes in order to allow it to fill with carbon dioxide gas. Have a barbecue lighter ready to ignite the candles.
Light the candles and slowly pour the carbon dioxide gas into the containment vessel. Point out that the heavy gas can be poured much like a liquid, but it cannot be seen. The candles will extinguish one by one from the bottom up.
Handle dry ice with protective gloves. Keep flammables away from open flames. Never place dry ice in a sealed container. Wear appropriate eye protection.
Allow excess dry ice to sublime. All other materials may be reused.