In boiling point elevation, which statement identifies a factor that increases ΔTb for a nonvolatile solute?

• A. Increasing molality
• B. Increasing Tb°
• C. Increasing Kb
• D. Decreasing i

Answer: (C)

Boiling point elevation is a colligative property described by ΔTb = i × Kb × m, where m is the molality of the solute, i is the van’t Hoff factor (how many particles the solute produces in solution), and Kb is the ebullioscopic constant of the solvent. The larger the product i × Kb × m, the larger the elevation of the boiling point.

Among the factors listed, increasing Kb directly makes the solvent more sensitive to dissolved particles—the same amount of solute particles will cause a bigger rise in boiling point if the solvent has a larger ebullioscopic constant. That means raising Kb increases ΔTb for a nonvolatile solute.

Increasing molality would also raise ΔTb, since ΔTb is proportional to m, but the solvent-specific factor that governs how strong that effect is across any solute is Kb. Decreasing i would reduce ΔTb, and Tb° is just the pure solvent’s boiling point baseline, not the amount by which the boiling point is elevated.