17. The Drive To Make Things       Happen   Previous PageNext Page
      Freezing Point Depression

Example. A saturated solution of glutamic acid (an amino acid) in water has 1.50 g of glutamic acid per 100 g of water. The observed freezing point of the solution is -0.189íC. What is the molecular weight of glutamic acid?


Example. A 200-mg sample of cytochrome c (a protein) is dissolved in 10 ml of water. The molecular weight of cytochrome c is 12,400. What is the expected freezing point depression?


The sensitivity of molecular weight measurements can be increased somewhat by choosing solvents with larger kf or kb. Camphor, an organic compound, often is used because it has a kf of 40.0. Using molten camphor as a solvent increases the sensitivity by more than twenty times, but this is practical only if the molecule whose molecular weight is to be found is both soluble in camphor and stable at the camphor melting point of 180° C.


   Page 18 of 56 HomeGlossary