Final answer:
Fractional distillation improves the purity of the distillate by separating the components of crude oil based on their boiling points.
Step-by-step explanation:
Fractional distillation improves the purity of the distillate by separating the components of crude oil based on their boiling points. As the crude oil is heated in a tall fractionating column, the lighter components with lower boiling temperatures rise to the top while the heavier components with higher boiling temperatures remain at the bottom. When these vaporized components reach cool zones in the column, they condense and are collected as separate fractions. This process allows for the removal of impurities, such as sulfur and nitrogen, and results in the production of purer distillate fractions of different hydrocarbons, like gasoline, diesel, and kerosene.