JAMB Chemistry 2024 Paper

Concept:The percentage by mass of hydrogen in an alkane is calculated by dividing the total mass of hydrogen in the molecular formula by the molar mass of the compound, then multiplying by $100$.Explanation:The aliphatic alkanes form a homologous series with the general formula $\mathrm{C}_n\mathrm{H}_{2n+2}$.Counting from methane ($n=1$), the first five members are methane, ethane, propane, butane, and pentane.Therefore, the sixth member of the class is hexane, with the molecular formula $\mathrm{C}_6\mathrm{H}_{14}$.The molar mass of $\mathrm{C}_6\mathrm{H}_{14}$ is $(6 \times 12) + (14 \times 1) = 72 + 14 = 86$.The total mass of hydrogen in the compound is $14 \times 1 = 14$.Thus, the percentage of hydrogen is $\frac{14}{86} \times 100 = 16.28\%$.Answer:$16.28\%$ (Option C).