WAEC Chemistry 2010 Paper

Concept:The empirical formula is the simplest whole-number ratio of atoms present in a compound, calculated from percentage composition by mass.Explanation:Assume a $100\,g$ sample of the compound.Then the given percentages become masses in grams.Calculate moles of each element using its atomic mass.Carbon: $\frac{40.0}{12.0} = 3.33$ molHydrogen: $\frac{6.7}{1.0} = 6.7$ molOxygen: $\frac{53.3}{16.0} = 3.33$ molDivide each mole value by the smallest value, $3.33$ mol.Carbon: $\frac{3.33}{3.33} = 1$Hydrogen: $\frac{6.7}{3.33} \approx 2$Oxygen: $\frac{3.33}{3.33} = 1$The simplest whole-number ratio is C:H:O $= 1:2:1$.Therefore, the empirical formula is $\mathrm{CH_2O}$.Answer:$\mathrm{CH_2O}$ (Option C)