Colligative Properties

Colligative and Non-Colligative Properties

As you know, solutions are a mixture of solute and solvent. When the two are mixed together, the solution contains different properties than that of the solute and solvent individually. These properties are defined as either colligative or non-colligative. Colligative properties depend on the amount of dissolved particles in a solution. The identity of the particles in the solution does not make a difference. Non-colligative properties depend on the actually identity of the dissolved solute that was added to the solvent.

The best way to compare the difference between colligative and non-colligative properties is to compare a solution of sugar and salt. A 1.0 M sugar solution and 0.5 M salt solution will contain about the same amount of dissolved particles. Why do they have the same amount of particles? Upon dissolving, each sodium chlorine ion creates two particles; the sodium ion and chlorine ion. Since the same amount of particles is present, both solutions will have the same colligative properties. These solutions share the same freezing point, boiling point, and vapor pressure. What properties are different? Well, the non-colligative properties are affected. These solutions will differ in taste, viscosity, surface tension, and solubility.

Raoult’s Law, Boiling Point Elevation, and Freezing Point Depression

Why does the boiling point and freezing point change when a solute is added? French chemist Francois Raoult discovered that the addition of a solute to a solution affects the vapor pressure. If the vapor pressure is affected, so is the boiling point and freezing point. View this presentation to learn about Raoult’s law, boiling point elevation, and freezing point depression.

View a printable version of the interactivity.

 

Colligative Properties Review

Now that you have investigated colligative properties of solutions, complete this non-graded activity to check your knowledge. Read each statement and decide whether it is True or False. Then, click SUBMIT to check your response. Click on the interactivity thumbnail, and then click NEXT to get started.