JEE Main · 2022 · 28 Jul 2022 · Shift 2 · Solutions

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A gaseous mixture of two substances A and B, under a total pressure of 0.8 atm is in equilibrium with an ideal liquid solution. The mole fraction of substance A is 0.5 in the vapour phase and 0.2 in the liquid phase. The vapour pressure of pure liquid A is _____ atm. (Nearest integer)

Answer: 2

Solution

In the vapor phase, yₐ = 0.5, so partial pressure Pₐ = 0.5 × 0.8 = 0.4 atm. For an ideal solution, Raoult's law gives Pₐ = P°ₐ × xₐ, where xₐ = 0.2 (mole fraction in liquid). Therefore P°ₐ = Pₐ/xₐ = 0.4/0.2 = 2 atm.

JEE Main · 2022 · 28 Jul 2022 · Shift 2 · Integer answer

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