WAEC Chemistry 2022 Paper

Concept:Dalton’s law of partial pressures states that the partial pressure of a gas in a mixture equals its mole fraction multiplied by the total pressure.Explanation:At s.t.p., the total pressure of the gaseous mixture is $P_{\text{total}} = 1\,\text{atm}$.For gases at the same temperature and pressure, the volume ratio is equal to the mole ratio.Total volume of the mixture is $100\,\text{cm}^3 + 900\,\text{cm}^3 = 1000\,\text{cm}^3$.Mole fraction of oxygen is $\frac{100}{1000} = 0.1$.Using Dalton’s law: $P_{\mathrm{O_2}} = P_{\text{total}} \times \text{mole fraction of } \mathrm{O_2}$.Therefore, $P_{\mathrm{O_2}} = 1\,\text{atm} \times 0.1 = 0.1\,\text{atm}$.Answer:$0.1\,\text{atm}$ (Option B).