Gas welding safety and gas generation: The statement ‘‘Low-pressure acetylene for welding is produced at the job site by the chemical reaction between water and calcium carbonate’’ is — choose the correct assessment based on standard carbide generators and chemistry.

Introduction / Context:

Acetylene (C₂H₂) is a common fuel gas in oxy–acetylene welding. Historically, portable generators produced acetylene on site. Knowing the correct reactants is vital for both safety and exam accuracy.

Given Data / Assumptions:

• ‘‘Low-pressure acetylene’’ refers to generator-produced gas (legacy practice).
• Question cites water reacting with calcium carbonate.
• Standard generator chemistry should be applied.

Concept / Approach:

The canonical reaction in acetylene generators is between water and calcium carbide (CaC₂): CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂. Calcium carbonate (CaCO₃) does not yield acetylene upon contact with water; it is limestone and would require acid to evolve CO₂, not C₂H₂. Therefore, the statement is incorrect.

Step-by-Step Solution:

Verification / Alternative check:

Industrial practice has largely shifted to dissolved acetylene in cylinders (acetone/DMF), but where on-site generation is used, the reagent remains CaC₂, confirming the correction.

Why Other Options Are Wrong:

• Correct / Conditionally correct / Lab-grade / Cylinder-based: all contradict the fundamental chemistry; cylinders contain dissolved acetylene, not generated from CaCO₃ on site.

Common Pitfalls:

• Confusing carbide with carbonate due to similar names.
• Assuming any calcium compound with water can produce acetylene—only CaC₂ does.

Final Answer:

Incorrect