ABSTRACT
Usually, this equation is written in terms of the molality of B, mB (see Topic D1). At these low concentrations, xB=mBM, where M is the mass of one mole of the solvent, or the molar mass. The equation then becomes:
Kf is the cryoscopic constant or the freezing point depression constant of the solvent A (not to be confused with an equilibrium constant, see section C). Kf can in principle be calculated from the enthalpy of fusion and the freezing point of pure liquid A, but in practice values have been measured experimentally and tabulated for a range of solvents. This value can be used, along with the measured value of ∆Tf, to determine mB and/or xB for any solute.
