Ethyne is passed through a hot tube containing organo-nickel catalyst to produce

Analysis

The question asks for the product formed when ethyne (acetylene) undergoes a specific reaction involving a hot tube and an organo-nickel catalyst. This is a classic organic chemistry reaction known as cyclic polymerization (or trimerization).

Concept Explanation

Ethyne ($C_2H_2$) is an unsaturated hydrocarbon with a triple bond. When three molecules of ethyne are passed through a hot tube (usually at about 400°C) in the presence of an organo-nickel catalyst, they undergo a process called cyclotrimerization.

In this reaction, the three ethyne molecules link together to form a stable, six-carbon cyclic ring. This process converts the aliphatic hydrocarbon (ethyne) into an aromatic hydrocarbon.

The chemical equation for this reaction is: $3C_2H_2 \xrightarrow{\text{hot tube/catalyst}} C_6H_6$

Step-by-Step Solution

1. Identify the reactants: We have ethyne ($C_2H_2$).
2. Identify the process: Passing ethyne through a hot tube with a catalyst triggers the trimerization of the molecules.
3. Calculate the product: • 3 molecules of $C_2H_2$ contain a total of 6 carbon atoms and 6 hydrogen atoms. • $3 \times (C_2H_2) = C_6H_6$.
4. Name the product: The chemical formula $C_6H_6$ corresponds to benzene, which is the simplest aromatic hydrocarbon.

Conclusion

• Isoprene is a precursor for natural rubber.
• Polythene is formed by the polymerization of ethene ($C_2H_4$).
• Ethanol is an alcohol produced by the hydration of ethene or fermentation.
• Benzene is the result of the cyclic trimerization of ethyne.

Exam Tip

Whenever you see "ethyne" and "hot tube" in a chemistry question, immediately think of benzene. It is a very common JAMB question! Remember: 3 molecules of ethyne = 1 molecule of benzene.