Air hole Flame colour Combustion open blue complete closed yellow incomplete The same fuel is burned twice on the Bunsen burner shown, once with the air hol...
Question 1 Report
| Air hole | Flame colour | Combustion |
|---|---|---|
| open | blue | complete |
| closed | yellow | incomplete |
The same fuel is burned twice on the Bunsen burner shown, once with the air hole open and once closed. The table records the flame colour and the gas detected. Which flame produces the poisonous gas carbon monoxide?
Answer Details
The air hole controls how much oxygen mixes with the gas before it burns. With the hole open there is plenty of oxygen, combustion is complete and the flame is blue and hot, giving carbon dioxide and water. With the hole closed the gas burns in a limited supply of oxygen, so combustion is incomplete and the flame is yellow, luminous and cooler.
Incomplete combustion is what produces carbon monoxide, because each carbon atom receives only one oxygen atom instead of two, and it also leaves unburnt carbon particles, which are the glowing soot that makes the flame yellow. The yellow flame with the air hole closed is therefore the one giving off the poisonous gas.
Link the colour to the oxygen supply: yellow and sooty always means too little oxygen.
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