JAMB Chemistry 2024 Paper

Concept:Vapour density is the ratio of the mass of a given volume of gas to the mass of the same volume of hydrogen. It is also equal to half of the molar mass of the gas.Explanation:At s.t.p., $1$ mole of any gas occupies $22.4\ \mathrm{dm}^3$.The gas occupies $5.6\ \mathrm{dm}^3$, which is $\frac{5.6}{22.4} = \frac{1}{4}$ of a mole.So, $11.0\ \mathrm{g}$ represents $\frac{1}{4}$ mole of the gas.Therefore, the molar mass is:$$M = 11.0\ \mathrm{g} \times 4 = 44\ \mathrm{g\ mol}^{-1}$$Vapour density is calculated using:$$\text{Vapour density} = \frac{\text{Molar mass}}{2}$$$$= \frac{44}{2} = 22$$Answer:The vapour density of the gas is $22$.Correct option: A.