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
At 300 K, the ratio of the molar volume of pure B in vapour phase to its molar volume in liquid phase 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
At 300 K, the ratio of the molar volume of pure B in vapour phase to its molar volume in liquid phase is ____.
Answer: 2000
Solution
First, find the vapor pressure of pure B using Raoult's law:
For 5 molal solution: 1000 g A contains 5 mol B
Moles of A = 1000/50 = 20 mol
Molar volume of B in vapor phase:
Molar volume of B in liquid phase:
Ratio:
For 5 molal solution: 1000 g A contains 5 mol B
Moles of A = 1000/50 = 20 mol
Molar volume of B in vapor phase:
Molar volume of B in liquid phase:
Ratio:
JEE Advanced · 2026 · 17 May 2026 · Paper 2 · Numerical answer