Maybe this will help you...is this the cryoscpic question...all about molality...P-Chem see Atkins text:
When working with boiling point elevations or freezing point depressions of solutions, it is convenient to express the solute concentration in terms of its molality m defined by the relation:
For this unit of concentration, the boiling point elevation, Tb - Tºb or DTb, and the freezing point depression, Tºf - Tf or DTf, in ºC at low concentrations are given by the equations:
DTb = kbm DTf = kfm
where kb and kf are characteristic of the solvent used. For water, kb = 0.52 and kf = 1.86. For benzene, kb = 2.53 and kf = 5.10.
One of the main uses of the colligative properties of solutions is in connection with the determination of the molar masses of unknown substances. If we dissolve a known amount of solute in a given amount of solvent and measure DTb or DTf of the solution produced, and if we know the appropriate k for the solvent, we can find the molality and hence the molar mass, MM, of the solute. In the case of the freezing point depression, the reaction would be: