Simple Distillation Lecture Notes

Introduction

Raoult's Law
- Predicts vapor pressure of a liquid in a mixture:
  - Vapor Pressure = Pure Vapor Pressure × Mole Fraction
Dalton's Law
- Total pressure in a system = Sum of vapor pressures of each component.
- Applicable regardless of component identity.
Ideal Gas Law
- Commonly expressed as: PV = nRT
- Rearranged to: PV/nT = R.
- Allows understanding of pressure and moles relationship in a system.
- Mole fraction of compound A = Partial Pressure of A / Total Pressure.

Example of a binary mixture (50 mole % benzene and toluene).
At boiling point:
- Toluene: Pure vapor pressure = 300 Torr → Partial = 150 Torr (0.5 mole fraction).
- Benzene: Pure vapor pressure = 1200 Torr → Partial = 600 Torr.
Result: Vapor above the liquid is 80 mole % benzene, indicating concentration increase.

Components of a Simple Still:
- Boiling Flask: Heat source.
- Three-Way Condenser (Still Head): Diverts vapor to cooler environment for recondensation.
- West Condenser: Long narrow tube with a water jacket for cooling.
- Vacuum Adapter:
  - Diverts condensed liquid to receiving flask.
  - Open to atmosphere, preventing a closed system.
- Receiving Flask: Collected liquid kept cool.

Mixture heated in boiling flask starts forming vapor (80% benzene, 20% toluene).
Vapor diverted into West condenser, where it is cooled and collected in receiving flask.
Over time, receiving flask accumulates an enriched benzene sample (80 mole %).

Tool for predicting efficiency of simple distillation.
Plot Structure: Temperature vs. mole percent of one component (benzene).
Example:
- Start with 50% benzene → Vapor composition becomes 80%.
Plotting Points:
- Connect points to create a curve representing system behavior.
- Enables quick composition determination of distillate.