What is the difference between distillation, distillation under reduced pressure and steam distillation?
Distillation is used to separate volatile liquids from nonvolatile impurities, or liquids having a sufficient difference in their boiling points. The vapours are cooled, condensed, and collected separately.
Distillation under reduced pressure purifies liquids with very high boiling points or those decomposing at or below their boiling points. By reducing the pressure on the surface, the liquid boils at a temperature lower than its normal boiling point.
Steam distillation separates substances that are steam volatile and immiscible with water. The liquid boils when the sum of vapour pressures of the organic liquid () and water () equals atmospheric pressure (), i.e., . This makes the organic liquid vaporise at a lower temperature than its boiling point.
Explanation
The answer differentiates the three techniques based on their principles and applications as described in the textbook. Distillation relies on boiling point differences. Distillation under reduced pressure lowers the external pressure to boil high-boiling or thermally unstable liquids at lower temperatures. Steam distillation uses steam to vaporise immiscible, steam-volatile compounds when the combined vapour pressures reach atmospheric pressure.