Colligative Properties Objectives: Be able to list the colligative properties of solutions Identify the variables that change the colligative properties of a solution. Key Terms: colligative property, vapor pressure reduction, boiling point elevation, freezing point depression, osmosis, osmotic pressure

Colligative Properties Solutions have different properties than the solvents that the solutes are dissolved in. – The differences are explained by the colligative properties of the solutions. – The colligative properties depend on the effect that the solutes have on the solvents and not the properties of the solutes themselves.

Vapor Pressure Reduction Vapor pressure of a solution reduces with increasing molar weight(addition of a non-volatile solute – Reduction takes place as the solutes take up space at the surface

Boiling Point Elevation – Due to the vapor pressure reduction more heat is needed to bring vapor pressure equal to atmospheric pressure –D T b = K b x m (K is the constant for the solvent to which solute is added, m is the molality of the final solution)

Freezing Point Depression Addition of a non-volatile solute lowers the freeing point of a solution due to the vapor pressure reduction –D T f = K f x m (K is the constant for the solvent to which solute is added, m is the molality of the final solution)

Osmotic Pressure Osmosis - movement of a solvent through a semi- permeable membrane – As the number of moles of a solute increases in a solution, the osmotic pressure of the solution increases – The movement of the solvent across the membrane will move to the solution with the highest osmotic pressure