The vapour pressure of pure liquid ‘A’ at is — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

We have two equations for vapour pressure. Initial solution: $P_A^\circ X_{A,0} + P_B^\circ(1 - X_{A,0}) = 700 \Rightarrow P_A^\circ(0.6375) + P_B^\circ(0.3625) = 700$. Residue: $P_A^\circ(0.3) + P_B^\circ(0.7) = 600$. Multiplying the residue equation by $\frac{0.3625}{0.7} \approx 0.5178$ and subtracting it from the first equation allows us to isolate $P_A^\circ$. Specifically, $0.3375 P_A^\circ = 272.5$, which yields $P_A^\circ = 807.4 \text{ mm Hg}$. Therefore, correct answer is A.