Chemistry: Distillation Process

Study Notes

Definition: Distillation is the process of vaporizing a liquid, re-condensing it, and collecting it in a container.
Boiling point of mixtures depends on mole fraction of the component present.
In pure substances, temperature remains constant during distillation as long as both vapor and liquid are present.
In miscible liquid mixtures, temperature increases throughout the process because the composition of vapor changes continuously.

Evaporation is a type of vaporization that occurs only on the surface of a liquid.
Theoretically, evaporation means the free escape of vapors from the surface of a liquid below its boiling point.

Temperature: rate of evaporation is directly proportional to temperature.
Surface area: rate of evaporation is directly proportional to the surface area of the content vessel exposed.
Agitation: stirring or agitating the solution prevents decomposition of the preparation at the bottom of the container.
Atmospheric aqueous vapour pressure: rate of evaporation is affected by atmospheric moisture content.
Atmospheric pressure on the liquid under evaporation: rate of evaporation is inversely proportional to atmospheric pressure on the surface of the liquid.

Maximum evaporation is attained at the boiling point of the liquid.
Thermostable preparations can be evaporated at higher temperatures, while thermolabile preparations require low temperatures.
Extremely heat-sensitive substances are evaporated under reduced pressure.
Time required for evaporation is critical, and evaporation should be carried out for a short time at low temperature.