ABSTRACT
We saw that nonvolatile solute molecules lower the vapor pressure of the solvent above the solution. Nonvolatile solutes also raise the boiling point of the solution, lower the melting point of the solution, and give rise to the phenomenon of osmosis. These four effects depend only on the number of solute particles present in the solution, not on their chemical identity. For this reason, such properties are called colligative properties, from the Latin word colligare, meaning “to bind together.” Thus, these properties are all related to each other; once one has been measured, the others can be found by calculation-–they are all “bound together.” This means that a 0.01 molal solution of any (non-dissociating) solute should have the same boiling point, the same freezing point, and the same osmotic pressure as a 0.01 molal solution of any other solute in the same solvent.
