Lesson eLearning

Describe the industrial preparation of acetylene from calcium carbide, write the balanced chemical equation, list two major uses of acetylene, and explain why acetylene is preferred as a fuel in welding.

hard 5 marks Class 10 · Science · Carbon and its Compounds
Answer
Acetylene is produced by reacting calcium carbide with water vapour (CaC2 + 2H2O → C2H2 + Ca(OH)2); it is used for welding and as a chemical feedstock, and is preferred in welding because its oxy‑acetylene flame reaches about 3300 °C, giving a high‑temperature, focused flame.

Step-by-step solution

  1. State the raw material: calcium carbide () obtained by heating coke with lime at ~2000°C.
  2. Write the preparation reaction with water vapour: ; note it is exothermic and produces acetylene gas.
  3. Mention that the gas is collected and purified for industrial use.
  4. List two major uses: (i) oxy‑acetylene welding and cutting of metals, (ii) as a precursor for synthesis of chemicals such as acetaldehyde and vinyl chloride.
  5. Explain why acetylene is preferred in welding: when burnt with oxygen it gives a very high flame temperature (~3300°C), much higher than flames of other hydrocarbon gases, providing a concentrated, easily controllable, high‑energy flame suitable for cutting and joining metals.
  6. Add that acetylene also has a bright, luminous flame and low ignition energy, which are advantageous in welding operations.
Common mistake: Omitting the water‑vapour step in the preparation or failing to mention the high flame temperature that makes acetylene suitable for welding.

Concept tested: Preparation and uses of acetylene

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