Colligative Properties Physical properties that are affected by the concentration of solute.

Colligative Properties Most common examples are freezing point, boiling point, and vapor pressure.

Colligative Properties Freezing point – decreased Boiling point – increased Vapor pressure - decreased

Colligative Properties This makes sense based on kinetic theory. It is harder to freeze with a weird shape in the way. It is harder to boil or have a vapor pressure, because these properties are due to movement of molecules and it is harder to get moving with a weird shape in the way.

Colligative Properties For freezing point and boiling point changes, we will use one of two formulas:

Colligative Properties MW = (grams of solute)(k) (kg of solvent) (T) MW = molecular weight T = change in boiling or freezing point K = a constant that varies depending on the solvent.

Colligative Properties MW = (grams of solute)(k) (kg of solvent) (T) For water: Kf = 1.86 (freezing) Kb = .51 (boiling)

Colligative Properties This formula can also be arranged as follows: Kb = Kf Tb Tf Tb = change in boiling temperature Tf = change in freezing temperature

Colligative Properties The other formula that can be used is T = m (k) (n) T = change in freezing or boiling m = molality of the solution k = freezing or boiling constant n = the number of ions the substance dissociates into when dissolved in water