Question

What is indicated by sooty flame?

Answer 1

Sooty flame is the flame when an organic compound (hydrocarbons) on burning gives yellow flame and black smoke (soot). This type of flame is observed when a carbon compound is burned partially due to the lack of oxygen present or due to the structure of that compound. Therefore, the soot is basically the unburnt particles of carbon.

Complete answer:
We know that, there are two types of flames, one is clear and non-sooty flame and the other one is sooty flame.
Non-sooty flame is the clean flame and it is observed when no unburnt carbon is left and no black soot is produced. This flame is observed when aliphatic or non-aromatic compounds (hydrocarbons) are completely burnt in presence of oxygen.
While sooty flame is a yellow flame with black particles or smoke which is known as soot. It is observed when the compound being burnt has very high carbon content and due to the lack of oxygen, some amount of carbon is left unburnt and produces soot.
This flame test is used in the laboratory to determine if the given organic compound is aromatic or non-aromatic.
Hence, we can say that sooty flame indicates that the compound is aromatic (has high carbon content) and there is incomplete combustion of carbon.

Note :
Hydrocarbons are organic compounds which mainly consist of carbon and hydrogen atoms. Aromatic compounds are those which consist of at least one aromatic ring (benzene ring) while the aliphatic hydrocarbons are the ones which do not have aromatic ring (benzene ring) in the structure.