# How is freezing point depression a colligative property?

Aug 6, 2018

Well, what is a $\text{colligative property}$?

#### Explanation:

According to wiki this is a property of a solution that depends on the NUMBER of particles present in solution, i.e. it depends on the concentration of a solution in (typically) an aqueous solution.

And chemists typically investigate THREE such colligative phenomena:

$\text{(i) Vapour pressure diminution and boiling point elevation.}$

$\text{(ii) Freezing point depression.}$

$\text{(iii) Osmotic pressure...}$

Inorganic chemists can typically use the second such property as an aid to assess the solution structure. The solid state structure can usually be assessed unequivocally by an X-ray diffraction experiment. The solid state structure is not automatically the solution structure, and the altered freezing point of a solution with respect to that of the pure solvent can give evidence to the solution structure. Again, the altered freezing point is PROPORTIONAL to the number of particles in solution, i.e. the concentration, the NUMBER of solute particles.

And the observed freezing point depression of solution with respect to that of the pure solvent can thus give evidence of the molecularity in solution: is it a monomer, a dimer, an oligomer?