For a nonvolatile solute, boiling point elevation ΔTb is given by which expression?

• A. ΔTb = i Kb m
• B. ΔTb = i Kb
• C. ΔTb = Kb m / i
• D. ΔTb = m i / Kb

Answer: (A)

Boiling point elevation is a colligative property, meaning it depends on how many dissolved particles the solute adds to the solvent, not on their identity. In dilute solutions, the rise in boiling temperature is proportional to the molality of the solute, the solvent’s ebullioscopic constant, and the number of particles produced per formula unit of solute, captured by ΔTb = i Kb m. Here, i is the van’t Hoff factor, which equals 1 for non-dissociating solutes and is greater than 1 for electrolytes that dissociate into multiple particles. Kb is a property of the solvent, and m is the molality. This is why the correct expression multiplies i, Kb, and m. The other forms either omit a factor or place i or Kb in the wrong position, which would not reflect the way the boiling point elevation scales with particle number, solvent characteristics, and concentration.