WAEC Chemistry 2013 Paper

Concept:The empirical formula is found from the mole ratio of the elements present in the compound.Explanation:The hydrocarbon contains only carbon and hydrogen.So, percentage of hydrogen $= 100\% - 92.3\% = 7.7\%$.Now, find the moles of each element in $100$ g of the compound.Moles of carbon $= \frac{92.3}{12.0} = 7.69$Moles of hydrogen $= \frac{7.7}{1.00} = 7.7$To get the simplest ratio, divide both by the smaller value, $7.7$.$C : H = \frac{7.69}{7.7} : \frac{7.7}{7.7} \approx 1 : 1$Hence, the empirical formula is $\mathrm{CH}$.Answer:$\mathrm{CH}$ (Option A)