Concept:Vacuum distillation is utilized to lower the boiling point of liquids that might otherwise decompose at their normal, high boiling points by drastically reducing the external pressure.
Formula:$$ P_{\text{external}} \downarrow \implies \text{Boiling Point} \downarrow $$
Solution:- Under normal atmospheric pressure (760 torr), glycerin boils at \( 290^\circ\text{C} \). At this high temperature, it actually begins to chemically decompose.
- By applying a vacuum and reducing the external pressure all the way down to just 50 torr, the vapor pressure of glycerin matches the external pressure much sooner.
- Experimentally (and classically taught in standard textbooks), at 50 torr, the boiling point of glycerin safely drops to \( 210^\circ\text{C} \), allowing it to be distilled without degradation.
Why other options are incorrect:Options A, B, and C represent temperatures
higher than the normal boiling point, which would require an
increase in external pressure, completely contradicting the premise of vacuum distillation.
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