Colligative Properties

temperature, while molality does not. This makes molality a better measurement when temperature is a factor in the equation.

COLLIGATIVE PROPERTIES

The colligative properties of a solution will depend on the numbers of solvent and solute particles and not on the nature of the particles. They involve the vapor pressure decrease, boiling point elevation, freezing point depression, and osmotic pressure. They are based on the solute concentration and a given constant.

The colligative property of boiling point elevation fits the relationship of this: boiling point elevation equals the solute concentration (molality) multiplied by a constant, in this case, the boiling point constant. The vapor pressure change is based on the mole fraction of the solute and the vapor pressure of the pure solvent. The freezing point depression is based on the molality of the solute and the freezing point constant. The osmotic pressure is based on the molarity of the solute. Note that the freezing point and boiling point changes are based on molality as this is not temperature-dependent.

Boiling points of solutions will all be higher than that of the pure solvent. This difference is proportional to the concentration of the solute particles. The change in boiling point equals the boiling point constant multiplied by the molality of the solute. The boiling point constant is also called the ebullioscopic constant, which is dependent on the properties of the solvent.

The freezing point depression is a greater phenomenon than the boiling point elevation; it is also based on the molality of the solute as well as a constant that varies according to the solvent. Like the boiling point elevation, the change in temperature is the constant multiplied by the molality of the solute. Both the freezing point depression and boiling point elevation can be predicted by the phase diagram changes of a solution versus a solvent.

The boiling point of any substance is reached when the chemical potential of the pure solvent in liquid form reaches that of the chemical potential of the pure vapor. It will be a higher temperature in the solution versus the solvent form. The freezing point is reached when the chemical potential of the pure solvent as a liquid reaches that of the