In a solvent S, a compound B is partially dissociated into C and D as given below:
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 are 400 K and J mol⁻¹, respectively ( is the gas constant in J K⁻¹ 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 K at 1 bar pressure. In this solution, the mole percent of B that has been dissociated is ____.
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 are 400 K and J mol⁻¹, respectively ( is the gas constant in J K⁻¹ 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 K at 1 bar pressure. In this solution, the mole percent of B that has been dissociated is ____.
Answer: 33.17
Solution
For the dissociation: ,
Van't Hoff factor:
For 0.25% (w/w) solution: 100 g solution contains 0.25 g B and 99.75 g S
Molality =
Ebullioscopic constant:
Elevation in boiling point: K
Van't Hoff factor:
For 0.25% (w/w) solution: 100 g solution contains 0.25 g B and 99.75 g S
Molality =
Ebullioscopic constant:
Elevation in boiling point: K
JEE Advanced · 2026 · 17 May 2026 · Paper 2 · Numerical answer