Question

The gaseous mixture used for welding of metals is

• A. \(C_2H_4,\ O_2\)
• B. \(C_4H_{10},\ O_2\)
• C. \(C_2H_2,\ N_2\)
• D. \(C_2H_2,\ O_2\)

Hint:

Oxy-acetylene flame is widely used in welding because acetylene burns in oxygen to produce a very high temperature flame suitable for melting metals.

Answer 1

The Correct Option is D

Step 1: Identify the gas mixture used for metal welding.
Metal welding requires temperatures above 3000 K. The standard industrial process uses acetylene ($C_2H_2$) burned in pure oxygen ($O_2$), known as oxy-acetylene welding.
Step 2: Write the combustion reaction of acetylene in oxygen.
\[ 2C_2H_2 + 5O_2 \rightarrow 4CO_2 + 2H_2O + \text{heat} \] This produces a flame temperature of approximately $3000^\circ C$ to $3500^\circ C$.
Step 3: Explain why acetylene is preferred for welding.
Acetylene has a high calorific value and produces the hottest commercially available gas flame when burned in oxygen. No other common hydrocarbon achieves the same flame temperature.
Step 4: Evaluate and eliminate incorrect options.
$C_2H_4 + O_2$: ethylene burns cooler, insufficient for welding. $C_4H_{10} + O_2$: butane cannot achieve required temperatures. $C_2H_2 + N_2$: nitrogen is inert and cannot support combustion.
Step 5: Confirm $C_2H_2$ and $O_2$ as the answer.
The oxy-acetylene mixture is the industry-standard for metal cutting and welding worldwide.
Step 6: State the final answer.
\[ \boxed{C_2H_2 \text{ and } O_2} \]