Colligative Properties Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering Adding a nonvolatile solute reduces the relative amount of solvent, which results in fewer molecules becoming vapor <100% solvent 100% solvent

Boiling-Point Elevation Adding solute increases the boiling point of the solvent Ex: adding salt to a pot of water to cook pasta Explained by vapor pressure lowering

Freezing-Point Depression Adding solute lowers the freezing point of the solvent Ex: salt or sand on roads to prevent ice

Measure of the degree of dissociation of a solute in a solvent van’t Hoff factor Measure of the degree of dissociation of a solute in a solvent (i) = actual number of particles in soln after dissociation number of formula units initially dissolved in soln i should be nonelectrolytes 1 NaCl 2 CaCl2 3

Reality: Ion pairs The presence of an ion pair reduces the number of particles in solution, causing a reduction in the colligative properties. Electrolytes containing multicharged ions have a greater tendency to form ion pairs than electrolytes that are made up of singly charged ions. a. b.

Arrange the following solutions in order of decreasing freezing point: 0.10 m Na3PO4, 0.35 m NaCl, 0.20 m MgCl2, 0.15 m glucose, 0.15 m CH3COOH.