Kids, can you guess what carbon dioxide gas will do to the flame from a candle? Here is how to check your guess. You will need a wide-mouth bottle or jar (or a 250 ml beaker), 3-4 teaspoons of baking soda, 1/4 cup vinegar, a birthday candle, a square of cardboard that will fit inside the jar, matches, and tongs.

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

Light the candle and drip some wax onto the cardboard square. Blow out the candle and position it in the hot wax until it stands alone. Place the candle on its base inside the jar. Spread the baking soda around the base of the candle. Light the candle again, using tongs to hold the match. Carefully pour the vinegar down the side of the jar. What do you see happening?

The reaction between vinegar (weak acetic acid solution in water, HC₂H₃O₂ ) and baking soda (sodium bicarbonate, NaHCO₃ ) produces carbon dioxide gas (CO₂ ). The candle cannot continue to burn in a carbon dioxide atmosphere because fires needs oxygen to burn, so the flame is extinguished! This activity is a variation of the common baking soda-vinegar volcano.

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
June 1994