Facts & Exceptions

Glycerol purification: Purified by vacuum distillation to avoid thermal decomposition.

Aniline purification: Purified by steam distillation because it is steam volatile and immiscible with water.

Kjeldahl's Method exception: Fails for Nitrobenzene, Azobenzene, and Pyridine because their nitrogen cannot be quantitatively converted into $$(\text{NH}_4)_2\text{SO}_4$$

Boiling point vs Impurities: Soluble non-volatile impurities raise the boiling point and lower the melting point of an organic compound.