Question

Product B of the reaction is:
\[{\text{Ca}}{{\text{C}}_{\text{2}}}\xrightarrow{{{{\text{H}}_{\text{2}}}{\text{O}}}}{\text{A}}\xrightarrow{{{\text{Red hot Cu tube}}}}{\text{B}}\]. (A) Toluene
(B) ethyl benzene
(C) Benzene
(D) Butyne

Answer 1

Hint: \[Ca{C_2}\] is a chemical formula for Calcium carbide. Calcium carbide is a colourless substance. It is present in the solid state. It is mainly used in the preparation of industrial gas called acetylene.

Complete Solution :
- Calcium carbide is a colourless solid. It will undergo hydrolysis to produce compound A which is Acetylene. Acetylene is also known as ethyne. This reaction is an exothermic reaction and it will produce a by-product called slaked lime. Calcium hydroxide is another name for slaked lime. This reaction was first discovered by Friedrich Wohler in the year 1862. Carbide is used for the preparation of the industrial gas called acetylene.
- The reaction of hydrolysis of carbide is given below:
\[{\text{Ca}}{{\text{C}}_{\text{2}}}\xrightarrow{{{\text{2}}{{\text{H}}_{\text{2}}}{\text{O}}}}{C_2}{H_2} + Ca{(OH)_2}\]

- When the acetylene gas is passed into the red hot tube of Cu at around 500K, it will undergo cyclic polymerisation to produce compound B which is benzene. This process is also known as Trimerisation. Reaction requires three moles of acetylene molecules.
The reaction of Trimerisation of acetylene is given below:
\[{\text{3CH}} \equiv {\text{CH}}\xrightarrow[{{\text{500K}}}]{{{\text{red hot Cu tube}}}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}\]
Therefore, in the above reaction the product B will be Benzene, \[{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}\].
So, the correct answer is “Option C”.

Additional Information.
General characteristics of Acetylene
- Acetylene is an organic chemical compound with chemical formula of \[CH \equiv CH\].
- It is unstable in pure form.
- the carbon atoms in acetylene have \[s{p^3}\] hybridisation and thus have a linear structure.
- It is used as an industrial gas for various purposes.
- It is used in portable gas lamps.
So, the correct answer is “Option C”.

Note: Not only from acetylene, benzene can also be prepared from chemical compounds and by other processes. It can be prepared by
- decarboxylation of sodium benzoate.
- Heating of phenol with zinc.
- preparation from sulphonic acid.
- Reduction of benzene diazonium chloride.