Question

A carbon compound ‘A’ on heating with excess conc. H₂SO₄, forms a compound ‘B’, which on addition of one mole of hydrogen gas in the presence of nickel catalyst forms a compound ‘C’. ‘C’ on combustion in air forms 2 moles of carbon dioxide and 3 moles of water. Identify ‘A’, ‘B’ and ‘C’ and write their structures. Give chemical equations of the reactions involved. Also state the role of concentrated sulphuric acid in the formation of ‘B’ from ‘A’.

Answer 1

A: Ethyl alcohol (CH₃CH₂OH)

Structure of A:

\[\begin{array}{cc}
\ce{H}\phantom{....}\ce{H}\phantom{.......}\\
|\phantom{......}|\phantom{.......}\\
\ce{H - C - C - O - H}\\
|\phantom{......}|\phantom{.......}\\
\ce{H}\phantom{....}\ce{H}\phantom{.......}\\
\end{array}\]

B: Ethene (CH₂ = CH₂)

Structure of B:

\[\begin{array}{cc}
\ce{H}\phantom{....}\ce{H}\\
|\phantom{......}|\\
\ce{H - C = C - H}\\
\end{array}\]

C: Ethane (CH₃ = CH₃)

Structure of C:

\[\begin{array}{cc}
\ce{H}\phantom{....}\ce{H}\\
|\phantom{......}|\\
\ce{H - C - C - H}\\
|\phantom{......}|\\
\ce{H}\phantom{....}\ce{H}\\
\end{array}\]

Reaction:

(i) \[\ce{\underset{(A)}{CH3CH2OH} ->[H2SO4] \underset{(B)}{CH2 = CH2}+ H2O}\]

(ii) \[\ce{\underset{(B)}{CH2 = CH2} ->[Ni/H2] \underset{(C)}{CH3 - CH3}}\]

(iii) \[\ce{CH3 - CH3 + \frac{7}{2}O2 -> 2CO2 + 3H2O}\]

In reaction (i), sulphuric acid serves as a dehydrator, drawing water molecules out of alcohol to create an unsaturated compound.