If you move up the distillation column, the color of the fractions tends to become lighter. Which option best describes this trend?

If you move up the distillation column, the color of the fractions tends to become lighter. Which option best describes this trend?

• A. Become lighter
• B. Become darker
• C. Stay the same
• D. Change randomly

Answer: (A)

Moving up a distillation column shows separation by boiling point: heavier, higher-boiling components stay lower, while lighter, lower-boiling fractions rise to the top. The color of hydrocarbon fractions tends to reflect molecular size and impurities—heavier, more complex molecules and impurities absorb more visible light and look darker, whereas lighter fractions have smaller molecules and fewer impurities and appear lighter or colorless. So, as you go higher, you’re selecting progressively lighter fractions, which explains why the color becomes lighter. A darker color would imply heavier material, staying the same would ignore the systematic separation, and changing randomly wouldn’t fit how distillation works.

Moving up a distillation column shows separation by boiling point: heavier, higher-boiling components stay lower, while lighter, lower-boiling fractions rise to the top. The color of hydrocarbon fractions tends to reflect molecular size and impurities—heavier, more complex molecules and impurities absorb more visible light and look darker, whereas lighter fractions have smaller molecules and fewer impurities and appear lighter or colorless. So, as you go higher, you’re selecting progressively lighter fractions, which explains why the color becomes lighter. A darker color would imply heavier material, staying the same would ignore the systematic separation, and changing randomly wouldn’t fit how distillation works.