A mixture of ethyne and air is not used for welding whereas oxygen and ethyne mixture is preferred.

Question

Give reason why:

(i) A mixture of ethyne and air is not used for welding whereas oxygen and ethyne mixture is preferred. 

(ii) Carbon does not form C⁴⁺ and C^4– ions.

Answer 1

(i) When a mixture of air and ethyne (C₂H₂) is used, incomplete combustion takes place and as a result a sooty flame is obtained, which is not effective for welding. 

If ethyne is burned with oxygen, complete combustion takes place and gives a clean flame which is ideal for welding. This welding is also known as oxy-acetylene welding.

(ii) Carbon has 4 valence electrons. The two given situations can be analysed separately.

To form C⁴⁺ cation, it has to lose 4 electrons, but an enormous amount of energy is required to remove the electrons, because of the strong nuclear force of attraction. 

To form ^C4- anion, it has to gain 4 electrons, but it would be difficult for the nucleus with 6 protons to hold onto 10 electrons. In brief, the anion formed would not be stable.