Colligative properties

Vapor pressure lowering

Raoult's Law: P = XP°, where P = vapor pressure of substance in solution, P° = the vapor pressure of the pure substance and X = its mole fraction

• Mole fraction = moles of solute dissolved in total moles of solution = n_a /n

Boiling point elevation

T_b = k_bm, where m = molality = moles solute/kg solvent, and k_b is a constant specific to the solvent.

• Molality = moles of solute dissolved in 1 kg of solvent.

Freezing point depression

T_f = -k_fm, where m = molality = moles solute/kg solvent, and k_f is a constant specific to the solvent.

• Molality = moles of solute dissolved in 1 kg of solvent.

Osmotic pressure ()

V = nRT; or, dividing both sides by V, = MRT, where M = molarity.

• Molarity = moles of solute dissolved in 1 L of solution.

© R A Paselk

Last modified 15 April 2011