The diagram shows four fractions and their outlets on a column, with the temperature marked. Reading the diagram, at which outlet is the temperature lowest?
Question 1 Report
The diagram shows four fractions and their outlets on a column, with the temperature marked. Reading the diagram, at which outlet is the temperature lowest?
Answer Details
The temperature scale on the diagram runs from 40 °C beside the top of the column to 350 °C beside the base, so the column is coolest at the top and hottest at the bottom. The outlet drawn level with the 40 °C label, at the very top, is therefore at the lowest temperature.
This gradient is what makes fractional distillation work. Hot vapour enters at the base and cools as it rises; each fraction condenses at the height where the temperature has dropped to its own boiling point. The smallest, most volatile molecules travel furthest before condensing.
The usual error is to link "top" with "hot" because heat rises. In this column the heat source is at the base and the vapour loses energy as it climbs, so the lower outlets are always the hotter ones.
Download The App On Google Playstore
Everything you need to excel in your exams
