Chemistry · Ch 3 — Some Analytical Techniques
Fractional Distillation
Fractional Distillation
When Simple Distillation Isn't Enough
If the boiling points of two liquids in a mixture are not appreciably different, simple distillation cannot separate them cleanly. For such mixtures, fractional distillation is used instead, employing a special assembly in which the distillation flask is fitted with a fractionating column positioned between the flask and the condenser, so that rising vapours must pass through the column before reaching the condenser.
Why the Column Works …
What this figure shows. The same basic distillation setup as simple distillation (round-bottom flask, thermometer, side arm, water-jacketed condenser, receiver, heat source), but with a vertical fractionating column inserted into the neck of the distillation flask, between the flask and the point where the thermometer/side-arm assembly leads to the condenser, so that all rising vapour must pass up through the column before it can reach the condenser. Note: the source textbook's running paragraph refers to this figure as 'Fig. 2.5(a)', while the figure itself is captioned 'Fig. 3.5(a)' — an apparent chapter-number slip in the original printed book (thi …
What this figure shows. Captioned in the plural ('Fractionating Columns'), implying more than one design of the column referred to in the running text is pictured side by side; the source text describes only the column's function (a tall column providing a large surface area over which ascending vapour and descending condensed liquid exchange heat and composition) and does not itself describe the individual column shapes shown, so this description is limited to that functional role, disclosed here as a lower-confidence reading of the figure's exact visual conten …