JAMB Chemistry 2019 Paper

Concept:Find the empirical formula from percentage composition, then multiply it by a whole number $n$ using the given molar mass.Explanation:Convert each percentage to moles by dividing by the relative atomic mass.Carbon: $\frac{40.0}{12} \approx 3.33$ molHydrogen: $\frac{6.7}{1} = 6.7$ molOxygen: $\frac{53.3}{16} \approx 3.33$ molDivide each mole value by the smallest value, $3.33$.$C: \frac{3.33}{3.33} = 1$$H: \frac{6.7}{3.33} \approx 2$$O: \frac{3.33}{3.33} = 1$So the empirical formula is $\mathrm{CH}_2\mathrm{O}$.Its empirical molar mass is $12 + 2(1) + 16 = 30$.Given molar mass is $180$, so $n = \frac{180}{30} = 6$.Therefore, molecular formula is $(\mathrm{CH}_2\mathrm{O})_6 = \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$.Answer:$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$ (Option C).