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Density of Gas (Melissa Savage)

Putting out the Flame

Using A Mystery Gas to Put Out a Candle

  • Light a candle in a small beaker
  • In another beaker mix vinegar and baking soda
  • Without pouring out the liquid, pour the carbon dioxide gas from the vinegar/baking soda beaker onto the small beaker with the candle
  • The candle will go out

Describing the Chemical Reaction between Baking Soda and Vinegar

Baking soda, a pure chemical called sodium bicarbonate, has the chemical formula:


When dissolved in water baking soda separates into sodium (Na+) and bicarbonate ions (HCO3- ):

NaHCO3 ---> Na+(aq) + HCO3-(aq)

Vinegar, a weak (5%) solution of acetic acid in water, partially dissociates into hydrogen ( H+) and acetate ions (CH3COO-):

CH3COOH <--> H+(aq) + CH3COO-(aq)

The reaction between baking soda and vinegar is actually two reactions, an acid base reaction followed by a decomposition reaction.

When the two ingredients are mixed, hydrogen ions ( H+) from the vinegar react with the bicarbonate ions (HCO3- ) from the baking soda to form a new chemical called carbonic acid (H2CO3).

H+ + HCO3- ---> H2CO3

The carbonic acid thus formed then immediately decomposes into carbon dioxide gas (CO2)and water (H2O).

H2CO3 ---> H2O + CO2

It's this carbon dioxide gas that you see bubbling and foaming as soon as you mix baking soda and vinegar together.

Using the molecular structures of only the components involved, the chemical reaction can be written:

baking soda and vinegar reaction

The overall reaction however, is often written as follows:

NaHCO3 (aq) + CH3COOH (aq) ----> CO2 (g) + H2O (l) + CH3COONa (aq)


Lake Nyos

Mount Nyiragongo- Carbon Dioxide

Mammoth Lake

                          Before                                                                     After


  1. What is the atomic weight of Carbon Dioxide?
  2. What is the atomic weight of Nitrogen and Oxygen?
  3. Why does the candle go out?
  4. Why does the lighter go out again when trying to relight the candle?
  5. How much vinegar and baking soda do you have to mix to fill a 500ml beaker with carbon dioxide?


This activity shows the existence of an invisible substance that put out the fire.  When vinegar is poured into the dissolved baking soda, carbon dioxide is released.  The carbon dioxide fills the beaker, pushing out the oxygen and extinguishing the flame.