Describe the trend in a fractionating column at low temperature.

Describe the trend in a fractionating column at low temperature.

• A. Low temperature= small molecules with low boiling points, volatility increases, flammability increases, number of carbon atoms decreases.
• B. High temperature= large molecules with high boiling points.
• C. Temperature has no effect on volatility.
• D. Medium temperature isolates heavy molecules.

Answer: (A)

In a fractional distillation column, the column is cooler as you go up, so components separate mainly by boiling point along that temperature gradient. At low temperature, only the small molecules with low boiling points will reach the vapor phase and move upward; heavier, higher-boiling compounds stay liquid lower down. So the vapor reaching the top is enriched in these light, low-boiling substances, which are typically more volatile and often have lower molecular weight (fewer carbon atoms). That’s why the trend described—small molecules with low boiling points vaporizing first and rising to the top, with increased volatility and a tendency toward lighter, more flammable compounds—fits the low-temperature region of a fractionating column.

In a fractional distillation column, the column is cooler as you go up, so components separate mainly by boiling point along that temperature gradient. At low temperature, only the small molecules with low boiling points will reach the vapor phase and move upward; heavier, higher-boiling compounds stay liquid lower down. So the vapor reaching the top is enriched in these light, low-boiling substances, which are typically more volatile and often have lower molecular weight (fewer carbon atoms). That’s why the trend described—small molecules with low boiling points vaporizing first and rising to the top, with increased volatility and a tendency toward lighter, more flammable compounds—fits the low-temperature region of a fractionating column.