CBSE Class 10 Science 2017 · Paper 31/1 · Question 7

Structural formula of ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$: $$\begin{array}{ccccccccc}& & \text{H}& & \text{H}& & & & \\ & & |& & |& & & & \\ \text{H}& -& \text{C}& -& \text{C}& -& \text{O}& -& \text{H}\\ & & |& & |& & & & \\ & & \text{H}& & \text{H}& & & & \end{array}$$ When ethanol is heated with excess concentrated sulphuric acid at $443$ K it is dehydrated: each molecule loses one molecule of water, and ethene, an unsaturated hydrocarbon, is formed. $${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{443\text{K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$$ Role of conc. ${\text{H}}_2{\text{SO}}_4$: it acts as a dehydrating agent — it removes water from ethanol.