Two volatile liquids A and B form an ideal solution. Consider a 5 molal solution of B in A inside a closed container having a total vapour pressure of 100 mm Hg at 300 K. The vapour pressure of pure A at 300 K is 105 mm Hg. Assume that and behave as ideal gases in the vapour phase.
Given:
The gas constant L atm K⁻¹ mol⁻¹
Molar mass of is 50 g mol⁻¹
Molar mass of B is 57 g mol⁻¹
Density of liquid B at 300 K is 0.5 g/mL
1 atm = 760 mm Hg
The mole fraction of B in vapour phase which is in equilibrium with this solution is ____.
Given:
The gas constant L atm K⁻¹ mol⁻¹
Molar mass of is 50 g mol⁻¹
Molar mass of B is 57 g mol⁻¹
Density of liquid B at 300 K is 0.5 g/mL
1 atm = 760 mm Hg
The mole fraction of B in vapour phase which is in equilibrium with this solution is ____.
Answer: 0.16
Solution
From the previous question, we found mm Hg.
Mole fraction of B in solution:
Partial pressure of B in vapor:
Mole fraction of B in vapor phase:
Mole fraction of B in solution:
Partial pressure of B in vapor:
Mole fraction of B in vapor phase:
JEE Advanced · 2026 · 17 May 2026 · Paper 2 · Numerical answer