Question

Which of the following statements are correct?

• A. \( 0.1 \, \text{M} \, \text{KCl} \) solution will have the same osmotic pressure as \( 0.1 \, \text{M} \, \text{glucose} \) solution.
• B. \( 0.1 \, \text{M} \, \text{KCl} \) solution will have the same boiling point as \( 0.1 \, \text{M} \, \text{urea} \) solution.
• C. \( 0.1 \, \text{M} \, \text{glucose} \) and \( 0.1 \, \text{M} \, \text{urea} \) are isotonic.
• D. \( 0.1 \, \text{M} \, \text{MgCl}_2 \) solution will have less relative lowering of vapor pressure than \( 0.1 \, \text{M} \, \text{NaCl} \).

Hint:

In colligative properties, the effect is dependent on the number of particles in the solution, not the nature of the particles. For example, dissociation increases the number of particles in the solution, affecting properties like osmotic pressure, boiling point elevation, and vapor pressure lowering.

Answer 1

The Correct Option is D

Statement 1:
0.1 M KCl solution will have the same osmotic pressure as 0.1 M glucose solution.

Incorrect. Osmotic pressure depends on the number of particles in the solution.
KCl dissociates into two ions: K+ and Cl-, while glucose does not dissociate.
Therefore, 0.1 M KCl will have a higher osmotic pressure than 0.1 M glucose because it produces more particles.
Thus, Statement 1 is incorrect.

Statement 2:
0.1 M KCl solution will have the same boiling point as 0.1 M urea solution.

Incorrect. The boiling point elevation is a colligative property that depends on the number of particles in the solution.
Since KCl dissociates into two ions while urea does not dissociate, the 0.1 M KCl solution will have more particles and, therefore, a higher boiling point.
Thus, Statement 2 is incorrect.

Statement 3:
0.1 M glucose and 0.1 M urea are isotonic.

Correct. For two solutions to be isotonic, they must have the same osmotic pressure.
Since both glucose and urea do not dissociate, they will both produce the same number of particles in solution.
Therefore, their osmotic pressures will be equal, making them isotonic.
Thus, Statement 3 is correct.

Statement 4:
0.1 M MgCl2 solution will have less relative lowering of vapor pressure than 0.1 M NaCl.

Correct. The relative lowering of vapor pressure is given by the equation:
ΔP = (n_solute / n_solvent).
MgCl2 dissociates into three ions (Mg2+ and two Cl-), while NaCl dissociates into two ions (Na+ and Cl-).
Therefore, 0.1 M MgCl2 produces more particles in solution, leading to less relative lowering of vapor pressure.
Thus, Statement 4 is correct.

Conclusion: Based on the above analysis, the correct answer is Option (4):
0.1 M MgCl2 solution will have less relative lowering of vapor pressure than 0.1 M NaCl.