Question

An organic compound A on heating with concentrated H₂SO₄ forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Answer 1

When ethanol (compound A) is heated with concentrated sulphuric acid, it forms ethene and water,

\[\ce{\underset{(ethanol)}{C2H5OH}\overset{Conc. H2SO4}{->}\underset{(ethene)}{CH2 = CH2} + H2O}\]

Hence, compound B is ethene. When hydrogen is added to ethene in the presence of nickel catalyst, it forms saturated compound ethane. 

\[\begin{array}{cc}
\ce{H}\phantom{....}\ce{H}\phantom{..............}\ce{H}\phantom{....}\ce{H}\\
|\phantom{....}|\phantom{................}|\phantom{....}|\\
\ce{H - C = C - H \overset{Ni}{->}H - C - C - H}\\
\phantom{.....................}|\phantom{....}|\\
\ce{(Ethene)\phantom{.............}\ce{H}\phantom{...}\ce{H}}\\
\phantom{......................}\ce{(Ethene)}\\
\end{array}\]

Hence, compound C is ethane. On combustion, ethane forms carbon dioxide and water.

\[\ce{C2H6 + 3 1/2O2 -> 2CO2 + 3H2O}\]