How does fractional distillation differ from simple distillation?

Fractional distillation differs from simple distillation in its ability to separate mixtures with close boiling points.

In simple distillation, a mixture is heated to change the most volatile component from a liquid into a gas. This gas is then cooled and condensed back into a liquid, which is collected in a separate container. This method is effective when the components of the mixture have significantly different boiling points. For example, if you wanted to separate water and ethanol, simple distillation would be a suitable method because ethanol boils at 78.37°C while water boils at 100°C.

However, when the components of a mixture have boiling points that are close together, simple distillation is not effective. This is where fractional distillation comes in. Fractional distillation uses a fractionating column, which is a long, narrow piece of equipment that creates a temperature gradient. The column is hottest at the bottom and coolest at the top. As the mixture is heated, the vapours rise up the column. The vapours of the component with the higher boiling point condense on the lower, hotter part of the column, while the vapours of the component with the lower boiling point condense on the upper, cooler part of the column.

This process allows for a more precise separation of the components. For example, fractional distillation is used in the petroleum industry to separate the various components of crude oil, which all have very close boiling points.

In summary, while both simple and fractional distillation are techniques used to separate mixtures, fractional distillation is used when the components have close boiling points, and simple distillation is used when the boiling points are significantly different.