Question

‘‘A compound $\text{'}\mathrm{X}\text{'}$on combustion gives a yellow flame with lots of smoke".What inference would you draw from this statement?

Answer 1

• Unsaturated hydrocarbons like ethyne (C₂H₂) produce a yellow flame when burnt in oxygen (O₂) due to incomplete combustion in air.
• The percentage of carbon (C) is comparatively higher than that of alkanes and so does not get completely oxidized in air.

These are defined as the reactions that occur in the absence of sufficient oxygen because of which substances are unable to burn completely. Such reactions leave soot in the container due to this process along with the formation of carbon monoxide (CO) which is an air pollutant.

(1) The saturated hydrocarbons (alkanes) generally burn in air with a blue,non-sooty flame.

(2) The unsaturated hydrocarbons (alkenes and alkynes) burn in the air with a yellow, sooty flame (producing black smoke).

(3) Burning of unsaturated hydrocarbons in pure oxygen will result in complete burning to produce a blue flame (without any smoke at all).