COLLIGATIVE PROPERTIES

Colligative Property A colligative property is a property of

solutions that depends only upon the number of solute particles, not upon their identity.

Types of colligative properties• freezing-point depression• Boiling-point elevation

Connecting to Your World Cooking instructions often

call for the addition of a small amount of salt to the cooking water. Dissolved salt elevates the boiling point of water. You will learn how to calculate the amount the boiling point of the cooking water rises.

Remember the formula for molality

Q:How are freezing-point depression and boiling-point elevation related to molality?

A:The magnitudes of the freezing-point depression (ΔTf) and the boiling-point elevation (Δ Tb) of a solution are directly proportional to the molal concentration (m)

Freezing Point Depression The freezing point of a solution is lower than the

freezing point of the pure solvent The difference in temperature between the freezing

point of a solution and the freezing point of the pure solvent is called the freezing-point depression.

The constant, Kf, is the molal freezing-point depression constant

Freezing Point Depression

Freezing Point Depression

Boiling Point Elevation The boiling point of a solution is higher than the

boiling point of the pure solvent.• The difference in temperature between the boiling

point of a solution and the boiling point of the pure solvent is the boiling-point elevation.

The constant, Kb, is the molal boiling-point elevation constant

Boiling Point Elevation

Boiling Point Elevation