2019 O Level Chem P1 Q8 — Macromolecules / Substances and Bonding Solution

Answer: B (methane and nylon). Work out each substance from its description.

X is a gas at room temperature and pressure that burns to give carbon dioxide and water, so X is a hydrocarbon that is gaseous at r.t.p. Methane, CH₄, is a gas, whereas octane, C₈H₁₈, is a liquid (boiling point about 126 °C), so X must be methane.

Y is a macromolecule whose small units are joined by amide linkages. An amide (–CONH–) linkage is the hallmark of a polyamide. Nylon is a polyamide, formed by condensation polymerisation between a diamine and a dicarboxylic acid. Terylene, by contrast, is a polyester with ester (–COO–) linkages, so it is ruled out. The pair that fits is methane and nylon, which is row B. The common trap is to confuse the amide linkage of nylon with the ester linkage of Terylene.