If the boiling points of two compounds differ by 80oC at atmospheric pressure, w

Question

If the boiling points of two compounds differ by 80oC at atmospheric pressure, what will be the effect on the relationship by decreasing the pressure to 1mm (no number, just a general process)?

2. What will happen to the efficiency of a distillation if the distilling flask is more than half full? Nearly empty?

3. An HPLC was run on your two fractions from your distillation. What was general type of column used? Why did the mesitylene elute last?

4. Sometimes molecular ions do not appear on a Mass Spec. Give one reason why this might happen.

Explanation / Answer

Boiling point means the temperature at which vapour pressure of the liquid becomes equal to the atmospheric pressure.

If the atmospheric pressure is decreased, then vapour pressure will also be lowered to boil the liquid (as it will become equal to atmospheric pressure soon). It implies, less heat is required. That is, boiling point will decrease for the liquid on lowering the atmospheric pressure.

Hence, boiling point for both the liquids will decrease on decreasing atmospheric pressure.

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