How can freezing point depression determine purity?
If the freezing point depression constant is known you can calculate the molal concentration of solute from a measured freezing point depression, assuming the concentration is dilute enough to be considered an ideal solution.
For water, the freezing point depression constant is
If an aqueous solution has a measured freezing point of
then the molal concentration of solute is given by
Freezing point depression does not depend on which solute is present, only on the total concentration of dissolved species. If the solute is dissociated (e.g.