The theoretical vapour pressures of two pure liquids A and B, that form an ideal binary solution, ar — Solutions and Colligative Properties Chemistry Question
Question
The theoretical vapour pressures of two pure liquids A and B, that form an ideal binary solution, are $100\text{ torr}$ and $900\text{ torr}$ respectively at a constant temperature T. If a liquid mixture is prepared with exactly $1\text{ mole}$ of A and $1\text{ mole}$ of B, what will be the equilibrium total vapour pressure of the mixture?
Answer: B
💡 Solution & Explanation
The mixture consists of 1 mole of A and 1 mole of B, meaning total moles = 2. Therefore, $X_A = 1/2 = 0.5$ and $X_B = 1/2 = 0.5$. According to Raoult's law for ideal solutions, $P_{total} = P_A^0 X_A + P_B^0 X_B = (100 \times 0.5) + (900 \times 0.5) = 50 + 450 = 500\text{ torr}$.
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