Procedure

• Set up fractional distillation apparatus. Place the liquid to be distilled in the distilling flask. Ensure that the distilling flask is only two-thirds full. Then, turn on the water on the condenser. Now, start the distillation process. The liquid with the lower boiling point boils first. This becomes a vapor, which is then allowed to cool in the condenser. After the temperature falls below the boiling point, it condenses back into liquid, and this distillate is collected in a separate container. Ensure that the distilling flask is not boiled to dryness; stop when there is still some liquid left in the flask.
  
  

Purpose of Application

• Simple distillation is not enough to completely separate two liquid mixtures. If a mixture of two liquids is distilled, the distillate is sure to contain a majority of one liquid and a small percentage of the second liquid. To separate the distillate of the liquids, further re-distillation is required. The number of re-distillations required depends on the liquids that are to be distilled. Fractional distillation comes into use at this stage.
  
  

Mechanism

• Fractional distillation uses an apparatus called the fractionating column, which separates the liquids completely. For this purpose, the mixture is boiled, and when it turns to vapor, it rises up the fractionating column. The vapor condenses after it reaches a certain point in the column. Then, it again turns to vapor and rises up the column. This process continues till the vapor reaches the top of the column and finally condenses in the condenser. This is the point when you get completely purified liquid.
  
  

Refining of Crude Oil

• One of the primary applications of fractional distillation is the refining of crude oil. Crude oil consists of a complex mixture of hydrocarbons and, hence, its separation has to be done with care. Fractional distillation is used for distillation of crude oil containing only a small amount of volatile fractions in it.
  
  

Advantage

• The main advantage of using fractional distillation for the separation of crude oil is that only a small plant is required for the operation, thus reducing the operating costs. Thus, fractional distillation plays a major role in the process of refining of petroleum.