Q47 / 180 · COMEDK 2026 (9 May Shift 1) · Chemistry
Identify the correct statement
- AAt the freezing point of a solution containing a non-volatile solute, the vapour pressure of the liquid solvent becomes less than that of the solid solvent
- BA hypotonic solution is more concentrated with respect to the other solution separated from it by a semi permeable membrane
- Correct answerCIn case of dissociation of solute particles in a solution, the van't Hoff factor is more than unity because the observed molar mass has a lesser value
- DThe molal boiling point elevation constant for a solvent is directly proportional to its enthalpy of vaporisation
Solution
At the freezing point of a solution, the vapour pressure of the liquid solvent in the solution is equal to the vapour pressure of the pure solid solvent. Thus, statement (A) is incorrect.
A hypotonic solution has a lower osmotic pressure and is less concentrated compared to the other solution. Thus, statement (B) is incorrect.
In the case of dissociation of solute particles, the number of particles in the solution increases. The van't Hoff factor $i$ is greater than $1$. Since $i = \dfrac{\text{Normal molar mass}}{\text{Observed molar mass}}$, an $i > 1$ implies that the observed molar mass is less than the normal molar mass. Thus, statement (C) is correct.
The molal boiling point elevation constant is given by $K_b = \dfrac{R T_b^2 M}{1000 \Delta_{vap}H}$. It is inversely proportional to the enthalpy of vaporisation $\Delta_{vap}H$. Thus, statement (D) is incorrect.
Answer: In case of dissociation of solute particles in a solution, the van't Hoff factor is more than unity because the observed molar mass has a lesser value
A hypotonic solution has a lower osmotic pressure and is less concentrated compared to the other solution. Thus, statement (B) is incorrect.
In the case of dissociation of solute particles, the number of particles in the solution increases. The van't Hoff factor $i$ is greater than $1$. Since $i = \dfrac{\text{Normal molar mass}}{\text{Observed molar mass}}$, an $i > 1$ implies that the observed molar mass is less than the normal molar mass. Thus, statement (C) is correct.
The molal boiling point elevation constant is given by $K_b = \dfrac{R T_b^2 M}{1000 \Delta_{vap}H}$. It is inversely proportional to the enthalpy of vaporisation $\Delta_{vap}H$. Thus, statement (D) is incorrect.
Answer: In case of dissociation of solute particles in a solution, the van't Hoff factor is more than unity because the observed molar mass has a lesser value
Hence, the correct answer is option: 'C'.