Determination of molecular mass of dissolved substance
Chemijos laboratorinis darbas. Determination of molecular mass of dissolved substance by cryoscopic method. The aim and objectives To determine the molecular mass of dissolved substance by cryoscopic method. Theory. Chemicals Unknown solute, distilled water. Equipment test tube, chemical glass, mixing stick, thermometer, cork, pipette. Procedure. Results. Conclusion. After measuring the freezing points of pure solvent and solution with an unknown substance and doing the calculations we have discovered the molar mass of substance is 186 g/mol.
The change in the freezing point and the boiling point varies directly as the molal concentration of solution. Molality () is a solution concentration expressed as the number of moles of a solute per kilogram of a solvent. One molal (1m) solution contains one mole of a solute in each 1 kilogram of a solvent.
The equation relating to freezing point depression to molality is:
The proportionality constant in this equation is called the the molal freezing point (cryoscopic) constant. Its magnitude depends upon the nature of the solvent. The cryoscopic constant for water is