Question

Why a mixture of ethyne and air is not used for welding?

Answer 1

Welding - Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion.
A mixture of ethyne and air is not used for welding because-

1. When Ethyne is burnt in the air, incomplete burning takes place and produces a sooty flame because of the limited supply of oxygen present in the air. $$\begin{gathered} 2{\mathrm{C}}_2{\mathrm{H}}_2+\mathrm{Air}\to 4\mathrm{CO}+2{\mathrm{H}}_2\mathrm{O}+\mathrm{Sooty}\mathrm{flame} \\ \left(\mathrm{Ethyne}\right)\left(\mathrm{Carbon}\mathrm{monooxide}\right)\left(\mathrm{Water}\right) \end{gathered}$$
2. If Ethyne is burnt in oxygen, it gives a clean flame with a high temperature (3000°C) due to the complete combustion of ethyne $$\begin{gathered} 2{\mathrm{C}}_2{\mathrm{H}}_2+5{\mathrm{O}}_2\to 4{\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}+\mathrm{Heat} \\ \left(\mathrm{Ethyne}\right)\left(\mathrm{Oxygen}\right)\left(\mathrm{Carbon}\mathrm{dioxide}\right)\left(\mathrm{Water}\right) \end{gathered}$$
3. Hence, this oxyacetylene flame is used for welding, and it is not possible to attain such a high temperature with air.
4. Therefore, a mixture of Ethylene and air is not suitable for welding.

Hence, due to the low temperature attain by the mixture of ethylene and air, it is not used for weilding which requires high temperature.