Gas Candle Detection

Gas Flame Detection

Detect Carbon Dioxide gas with a candle flame. Will the flame get smaller, bigger, snuff out, change colour? How the flame behaves tells you the type of invisible gas present.

Suitable for kids aged 10+ with parental supervision

CAUTIONThis experiment requires use of an open candle flame. Please exercise caution, and only perform under adult supervision. It also requires the use of a knife to cut a candle. This task should only be undertaken by an adult.

You Need:
  • 2-3cm candle piece with wick (have an adult cut the piece using a knife from an ordinary household candle)
  • Aluminium foil patty pan
  • Piece of wire about 40cm in length
  • Chop Stick or similar
  • Scissors
  • Glass jar, preferably with a wide mouth
  • Vinegar
  • Baking soda
  • Matches
  • Small measuring cup to measure 30ml
  • Teaspoon
What to do:
  1. First, prepare the candle holder. Cut a foil patty pan down its side and along its base to the centre point with scissors. Place the candle on the pan, and slide the cut sides over each other to adjust the pan size and have it fit snuggly around the candle.
  2. Make a loop at one end of the wire and place it over the candle and patty pan. Twist it on itself to secure the candle and patty pan tightly (a bit like a lasso).
  3. Twist the other end of the wire around the end of the chop stick a few times. The holder should now look a bit like a fishing rod. With the chop stick as the handle, the wire as the line and the candle as the bait.
  4. Measure out 30mls of vinegar and pour it into the glass jar.
  5. Add one heaped spoon of baking soda. Watch it fizz and bubble. The fizz and bubbles are caused by a gas produced when these two chemicals are mixed (chemical reaction), but we dont know what this invisible gas is.
  6. To find out, have an adult light the candle in the candle holder. You can then lower the lit candle into the jar. How does the flame respond in the presence of this new gas? Some possibilities to think about: oxygen will make the flame grow bigger, nitrogen will result in no change to the flame (approx. 78% of our air is composed of nitrogen), argon will cause the flame to shrink, carbon dioxide will snuff out the flame. So, what gas is made when vinegar and baking soda are mixed?
  7. Have a few tries at lowering the flame into the jar (re-lighting if necessary). A bit of a challenge: can you lower the candle in and pull it out before the flame snuffs out? Eventually the flame stays alight when you lower it into the jar. Why?

Why is it so?

When vinegar and baking soda are mixed a chemical reaction occurs that results in carbon dioxide gas formation. The fizz and bubbles tells you its a gas, but how can you demonstrate that it is, in fact, carbon dioxide gas? Its interesting to think about how scientists work with matter thats invisible like a gas, and this is a good activity to show one way of working and identifying gasses. How the flame responds will indicate the type of gas made. Think about the possibilities - oxygen, argon, nitrogen, carbon dioxide all gasses found in air. The flame snuffs out telling you that indeed the gas in the jar produced by mixing vinegar and baking soda is carbon dioxide. After a while, the flame stops going out because the chemical reaction has finished and no more carbon dioxide gas is being made to put out the candle.