Question

Light a Bunsen burner and adjust the air hole at the base to get different types of flames/ presence of smoke. When do you get a yellow, sooty flame? When do you get a blue flame?

Answer 1

Hint: When a substance burns in the air. It can burn completely or can be incomplete. Blue light corresponds to the high-temperature zone of the burner. The yellow light corresponds to the low-temperature zone of the burner.

Complete answer
Saturated compounds when burns in presence of oxygen give clear flame or blue flame due to complete combustion. The burning of the unsaturated compound in presence of air produces a yellow flame with lots of black smoke.

The saturated hydrocarbon can also produce a sooty flame. This black smoke produced by the combustion of unsaturated hydrocarbons gets deposited on the metal surface. Which blocks holes of the metal surface on which the compound burns so the air supply gets blocked. Thus the saturated compounds also produce sooty flame due to an insufficient supply of air. The insufficient supply of air causes the incompletely burning of saturated hydrocarbons.

Therefore, when we light a Bunsen burner and adjust the air hole at the base to get different types of flames/ presence of smoke we get a yellow, sooty flame if the holes of the burner are blocked and the substance does not get sufficient oxygen supply and we get a blue flame if the holes of the burner are opened and the substance getting sufficient oxygen supply.

Note: The burning of saturated or unsaturated hydrocarbons in presence of oxygen is known as combustion. The combustion of a hydrocarbon produces carbon dioxide, water, heat, and light. When a substance gets burned in presence of oxygen-rich air, the blue flame is observed and when the substance gets burned in presence of oxygen-deficient air, the yellow flame is observed. Complete combustion gives blue flame and incomplete combustion gives yellow flame.