Distillation
Definition and meaning of Distillation in chemistry.
Distillation is a separation technique that purifies or separates liquids based on differences in their boiling points, by vaporizing the more volatile component and then condensing the vapor in a separate vessel.
In more detail
Because the vapor above a heated liquid mixture is enriched in whichever component has the higher vapor pressure (lower boiling point), collecting and cooling that vapor yields a liquid richer in that component than the original mixture. Simple distillation, using a single vaporization-condensation step, works well when boiling points differ by more than about 25°C or when separating a volatile liquid from a nonvolatile solute. Fractional distillation adds a packed fractionating column that provides many repeated vaporization-condensation cycles, allowing separation of liquids with closer boiling points. Distillation is central to petroleum refining, alcohol production, and purifying solvents in the laboratory.
Key facts
| Field | General Chemistry |
|---|---|
| Physical basis | Difference in boiling points / vapor pressures |
| Common types | Simple, fractional, vacuum, and steam distillation |
| Key apparatus | Distillation flask, fractionating column, condenser, receiving flask |
In a whiskey distillery, a fermented mash containing water and ethanol is heated; because ethanol boils at 78.4°C versus water's 100°C, the vapor is enriched in ethanol, and condensing it produces a spirit with higher alcohol content than the starting mash.
Frequently asked questions
What is the difference between simple and fractional distillation?
Simple distillation uses one vaporization-condensation step and suits liquids with widely different boiling points (or removing a volatile liquid from a nonvolatile solid), while fractional distillation uses a fractionating column to perform many such steps, allowing separation of liquids whose boiling points are close together.
Can distillation separate an azeotropic mixture into pure components?
Not by ordinary distillation alone; an azeotrope boils at constant composition, so its vapor has the same composition as the liquid, and additional techniques (e.g., pressure-swing distillation or adding an entrainer) are needed to break it.