International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which fraction of crude oil is collected at the highest point during fractional distillation?

1. Bitumen

2. Fuel oil

3. Gasoline

4. Refinery gases

The correct answer is: Refinery gases

During fractional distillation of crude oil, different components are separated based on their boiling points. The component with the lowest boiling point will rise the highest in the fractionating column and is collected at the highest point. Refinery gases, which include gases such as methane, ethane, propane, and butane, have the lowest boiling points among the fractions of crude oil. Consequently, they vaporize and rise to the top of the distillation column, where they are then condensed and collected. In contrast, bitumen, fuel oil, and gasoline have higher boiling points compared to refinery gases. Bitumen is collected at the bottom because it has the highest boiling point and is less volatile, while fuel oil and gasoline are collected at intermediate points in the column, as their boiling points are higher than those of the refinery gases but lower than those of bitumen. This process highlights the principle that during fractional distillation, components are separated based on their volatility, with gases being collected at the highest point due to their lower boiling points.