Boiling-point elevation (colligative property): Compared with the pure solvent, the boiling point of a solution containing a nonvolatile solute is

Introduction / Context:Solutions containing a nonvolatile solute display colligative effects such as boiling-point elevation and freezing-point depression. These depend on solute particle number rather than chemical identity, provided the solute does not dissociate or associate unusually. Boiling-point elevation is routinely used in chemical engineering (e.g., evaporators) and physical chemistry.

Given Data / Assumptions:

• Nonvolatile solute; solvent is volatile.
• Ambient pressure is fixed (e.g., 1 bar) when comparing boiling points.
• Solution is ideal or sufficiently dilute to apply colligative behavior.

Concept / Approach:Adding a nonvolatile solute lowers the solvent’s vapor pressure at a given temperature (Raoult’s law), so to reach the external pressure required for boiling, the solution must be heated to a higher temperature. The elevation ΔTb = Kb * m * i (where Kb is ebullioscopic constant, m is molality, and i is van’t Hoff factor) quantifies the effect.

Step-by-Step Solution:

Verification / Alternative check:Measured ebullioscopic constants (e.g., water Kb ≈ 0.512 K·kg/mol) predict positive ΔTb for real solutions, confirming the qualitative result.

Why Other Options Are Wrong:

• Less / Same: contradict the basic colligative behavior.
• 'Either more or less': for nonvolatile solutes, the direction is consistently elevation.
• 'Undefined unless pressure is specified': pressure is assumed fixed during comparison.

Common Pitfalls:Confusing nonvolatile with volatile solutes; ignoring dissociation (i) which changes magnitude but not direction for electrolytes.

Final Answer:More