How does the colour of the crude oil fractions change as you go down the distillation column?

How does the colour of the crude oil fractions change as you go down the distillation column?

• A. Get darker
• B. Get lighter
• C. Stay the same
• D. Change to bright colors

Answer: (A)

As you go down the distillation column, the fractions become heavier, with larger and more complex hydrocarbon molecules and more impurities. These bigger molecules absorb more visible light, so the liquid looks darker. Lighter, top fractions contain smaller, simpler molecules that are more transparent, often pale or colourless, while the heavy bottom fractions and residues appear dark brown to black. So the colour getting darker reflects increasing molecular size and impurity content as you move deeper into the column.

As you go down the distillation column, the fractions become heavier, with larger and more complex hydrocarbon molecules and more impurities. These bigger molecules absorb more visible light, so the liquid looks darker. Lighter, top fractions contain smaller, simpler molecules that are more transparent, often pale or colourless, while the heavy bottom fractions and residues appear dark brown to black. So the colour getting darker reflects increasing molecular size and impurity content as you move deeper into the column.