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

Which of the following is a characteristic of refinery gases?

1. They have the highest boiling point

2. They are the most viscous fraction

3. They are gaseous at room temperature

4. They contain large hydrocarbons

The correct answer is: They are gaseous at room temperature

Refinery gases are primarily composed of small hydrocarbons, such as methane, ethane, propane, and butane. One of their defining characteristics is that they are gaseous at room temperature. This is due to their relatively low molecular weights and low boiling points, which allow them to exist in the gaseous state at ordinary temperatures. In the context of the other options, refinery gases do not have the highest boiling point, as they are lighter fractions within the crude oil spectrum. They also do not represent the most viscous fraction; viscosity typically increases with molecular size and complexity, meaning that larger hydrocarbons, which are found in heavier fractions, will be more viscous. Finally, refinery gases contain predominantly small hydrocarbons rather than large ones, contrasting with heavier fractions that contain larger hydrocarbon chains. This understanding of refinery gases is essential in petroleum processing and the applications of different hydrocarbon fractions.