How does viscosity change as you go down the distillation column?

• A. More viscous
• B. Less viscous
• C. Remains the same
• D. Becomes gaseous

Answer: (A)

Viscosity is about how easily a liquid flows. In a distillation column, you separate liquids by boiling point, so heavier, long-chain molecules with higher boiling points settle toward the bottom. These big molecules interact more strongly and move past one another less easily, making the liquid more difficult to flow. Even though the bottom is hotter (which would tend to lower viscosity), the dominance of these heavy, long-chain molecules means the liquids become more viscous as you go down. The top contains light, short-chain fractions that flow readily, so they are less viscous. In short, the liquid becomes more viscous as you go down the column.