What do you mean by Rast method?pls explain ?

Dear Student, Rast method is a technique for determining molecular mass by considering freezing point depression. In this method molecular mass of an unknown solute is calculated by measuring depression of freezing point of pure solvent after addition of solute. depression of freezing point(ΔT) is proportional to the concentration of the solution(molality). so the equation is ΔT α m And then ΔT=kf m Here depression of freezing point(ΔT)is experimentally determined mass of solute and also mass of the solvent is known.Therefore by using the above equation molecular weight of solute can easily determined. In laboratories camphor is used as a solvent. Camphor has high Kf (cryoscopic constant) of 39.7 K/molal. Fixed amount of solute whose molecular mass is to be known is added to fixed amount of camphor and freezing point of mixture is observed. Using that in above equation, molality and then molecular mass can be calculated. Regards