ACS General Chemistry 2 Practice Exam

Colligative properties depend on the number of dissolved particles, not on their identity. The size of both boiling point elevation and freezing point depression is set by how many solute particles are in solution, which is captured by molality and the van't Hoff factor. The equations ΔTb = i Kb m and ΔTf = i Kf m show this directly: m is the molality (moles of solute per kilogram of solvent), and i accounts for how many particles the solute produces in solution (dissociation or association). For a non-electrolyte, i is about 1; for a salt like NaCl, i is about 2 because it dissociates into two ions, increasing the shifts. Increasing concentration or a higher degree of dissociation makes the changes larger. Time isn’t a factor in the magnitude once equilibrium is reached, and the molar mass of the solute doesn’t directly influence these effects because what matters is particle count, not mass. Solvent polarity can influence how well something dissolves, but after dissolution the shifts depend on the number of particles.