Chapter 2

Molecular Weight Determinations


Molecular weight of the compounds is determined by the determination of colligative properties. The methods are as follows:

  • Ebullioscopic method
  • Cryoscopic method
  • Vapour pressure lowering method
  • Mass spectrometric method
  • Osmometric method

In 1919, Cottrell vapour lift pump made it possible to measure the boiling point which proved useful for the measurement of the molecular weight.


This method is commonly known as the boiling point elevation method. The boiling point is defined as the temperature at which the vapour pressure is equal to the atmospheric pressure. The boiling point depends on the solute dissolved in the solvent. It decreases when a non-volatile solute is present ...

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