3 questions from 2026
Two volatile liquids \( A \) and \( B \) form an ideal solution. Consider a \( 5 \, \text{molal} \) solution of \( B \) in \( A \) inside a closed container having a total vapour pressure of \( 100 \, \text{mm Hg} \) at \( 300 \, \text{K} \). The vapour pressure of pure \( A \) at \( 300 \, \text{K} \) is \( 105 \, \text{mm Hg} \). Assume that \( A \) and \( B \) behave as ideal gases in the vapour phase.
Given:
The gas constant \( R = 0.08 \, \text{L atm K}^{-1} \text{ mol}^{-1} \)
Molar mass of \( A \) is \( 50 \, \text{g mol}^{-1} \)
Molar mass of \( B \) is \( 57 \, \text{g mol}^{-1} \)
Density of liquid \( B \) at \( 300 \, \text{K} \) is \( 0.5 \, \text{g/mL} \)
\( 1 \, \text{atm} = 760 \, \text{mm Hg} \)
The mole fraction of \( B \) in vapour phase which is in equilibrium with this solution is ________.
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 \( 100 \, \text{mm Hg} \) at \( 300 \, \text{K} \). The vapour pressure of pure \( A \) at \( 300 \, \text{K} \) is \( 105 \, \text{mm Hg} \). Assume that \( A \) and \( B \) behave as ideal gases in the vapour phase.
Given:
The gas constant \( R = 0.08 \, \text{L atm K}^{-1} \text{ mol}^{-1} \)
Molar mass of \( A \) is \( 50 \, \text{g mol}^{-1} \)
Molar mass of \( B \) is \( 57 \, \text{g mol}^{-1} \)
Density of liquid \( B \) at \( 300 \, \text{K} \) is \( 0.5 \, \text{g/mL} \)
\( 1 \, \text{atm} = 760 \, \text{mm Hg} \)
At \( 300 \, \text{K} \), the ratio of the molar volume of pure \( B \) in vapour phase to its molar volume in liquid phase is ________.
In a solvent \( S \), a compound \( B \) is partially dissociated into \( C \) and \( D \) as given below:
\( B \rightleftharpoons 2C + 2D \)
\( B, C \) and \( D \) are non-volatile in nature. The molar mass of \( B \) is \( 10 \) times the molar mass of \( S \). The standard boiling point and the standard enthalpy of vaporization of \( S \) are \( 400 \, \text{K} \) and \( 10R \, \text{J mol}^{-1} \), respectively \( (R \) is the gas constant in \( \text{J K}^{-1} \text{ mol}^{-1}) \). A solution of \( B \) in \( S \) with an initial concentration of \( B \) as \( 0.25\% \) (mass/mass) has a boiling point of \( 408 \, \text{K} \) at \( 1 \) bar pressure. In this solution, the mole percent of \( B \) that has been dissociated is ________.
