JAMB Chemistry 2010 Paper

Concept:Boiling point depends on molecular size and intermolecular forces; hydrogen bonding increases the boiling point of alcohols.Explanation:Butane, $\mathrm{C}_4\mathrm{H}_{10}$, has a small molecule with only weak van der Waals forces, so its boiling point is very low, about $-1^\circ\mathrm{C}$.Propanol, $\mathrm{C}_3\mathrm{H}_7\mathrm{OH}$, has a similar molar mass to butane, but it can form hydrogen bonds between its molecules, raising its boiling point to about $97^\circ\mathrm{C}$.Heptane, $\mathrm{C}_7\mathrm{H}_{16}$, has a much higher molar mass, so its intermolecular forces are stronger, giving a boiling point of about $98^\circ\mathrm{C}$.Therefore, the order of increasing boiling points is butane first, then propanol, then heptane.Answer:$\mathrm{C}_4\mathrm{H}_{10} \rightarrow \mathrm{C}_3\mathrm{H}_7\mathrm{OH} \rightarrow \mathrm{C}_7\mathrm{H}_{16}$ — Option D.