Colligative Properties of Solutions

Chemistry Honors

How do you get from this…

…to this?

Add an ionic compound!

Colligative Properties

• Properties that depend only on the number of solute particles and not on their identity.

Some Colligative Properties are:

• Boiling point elevation

• Freezing Point depression

• Vapor pressure lowering

Effects of solute on properties of water

• The particles of solute are surrounded by and are attracted to particles of solvent.

• Now the solvent particles have less kinetic energy.

• The presence of solute particles interferes with crystalline lattice formation of solid ice.

Ionic vs Molecular Solutes

• Ionic solutes produce two or more ion particles in solution.

• They affect the colligative properties proportionately more than molecular solutes (that do not ionize).

• The effect is proportional to the number of particles of the solute in the solution.

How many particles do each of the following give upon solvation?

• NaCl- 2 particles Na+1 and Cl-1

• CaCl2- 3 particles, 1 Ca and 2 Cl-1 ions

• Glucose- one particle only, one molecule of glucose (glucose is covalent compound not an ionic compound)