A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
A mixture of ethyne and air is not used for welding because limiting the supply of air results in incomplete combustion. Air contains limited oxygen which is insufficient for complete burning of ethyne.
Ethyne is an unsaturated carbon compound. When burnt with limited oxygen from air, it produces a yellow flame with lots of black smoke. This results in soot formation and the flame is not suitable for welding purposes.
For welding, a mixture of ethyne and pure oxygen is used because it provides a sufficiently oxygen-rich mixture. This ensures complete combustion and produces a clean blue flame with the high temperature required for welding metals.
Explanation
The textbook context explains that limiting the supply of air results in incomplete combustion, giving a sooty flame. Ethyne is identified as an unsaturated carbon compound (C₂H₂) with triple bonds. The context states that unsaturated carbon compounds give a yellow flame with lots of black smoke. For welding, a high-temperature clean flame is needed, which requires a sufficiently oxygen-rich mixture for complete combustion. Pure oxygen provides this, while air (with limited oxygen content) would cause incomplete combustion and soot formation.