WAEC Chemistry 2022 Paper

Concept:The empirical formula is found by converting the masses of each element to moles and then simplifying their ratio to whole numbers.Explanation:Given mass of $M = 60 \, \text{g}$ and molar mass of $M = 120 \, \text{g/mol}$.Moles of $M = \frac{60}{120} = 0.5 \text{ mol}$.Given mass of oxygen $= 24 \, \text{g}$ and $O = 16 \, \text{g/mol}$.Moles of $O = \frac{24}{16} = 1.5 \text{ mol}$.Now divide each mole value by the smallest value, $0.5$.Ratio of $M = \frac{0.5}{0.5} = 1$.Ratio of $O = \frac{1.5}{0.5} = 3$.So the simplest whole-number ratio is $M : O = 1 : 3$.Answer:The empirical formula is $\mathrm{MO}_3$.Correct option: C. $\mathrm{MO}_{3}$.