Naphthalene burns with a yellow sooty flame. This is because

Naphthalene burns with a yellow sooty flame. This is because

carbon to hydrogen ratio is low
there is incomplete combustion
there is excess supply of air
of presence of impurities of nitrogen and sulfur
This question was previously asked in
UPSC CDS-1 – 2023
When a substance burns with a yellow, sooty flame, it indicates that combustion is incomplete. Combustion is a chemical process where a substance reacts rapidly with oxygen to produce heat and light. Complete combustion occurs when there is sufficient oxygen, producing primarily carbon dioxide and water. Incomplete combustion occurs when there is insufficient oxygen, leading to the formation of carbon monoxide and/or unburnt carbon particles (soot). The yellow colour of the flame is due to the incandescence (glowing due to heat) of these hot soot particles. Naphthalene (C₁₀H₈) is an aromatic hydrocarbon with a relatively high carbon-to-hydrogen ratio compared to simple alkanes. Compounds with higher carbon content require more oxygen for complete combustion and are more prone to incomplete combustion and soot formation, especially in open air where the oxygen supply may not be perfectly mixed.
– A yellow sooty flame is a characteristic sign of incomplete combustion.
– Incomplete combustion produces soot (unburnt carbon particles) which glow yellow when hot.
– Fuels with a high carbon-to-hydrogen ratio are more likely to produce sooty flames during incomplete combustion.
In contrast, complete combustion typically produces a clean, often blue, flame (as seen in a Bunsen burner with the air hole open or a gas stove flame). Factors affecting the completeness of combustion include the amount of oxygen available, the mixing of fuel and air, and the temperature.
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