Fractional Distillation lecture(2)

# Fractional Distillation lecture(2) - Fractional...

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Fractional Distillation EXP. 3B [pp. 55-67; 132-135] CHE-231 Organic Chemistry University of Kentucky

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• Distillation is a technique used for separating a mixture of liquids. • The separation is based upon the differences in their boiling points (and thus the vapor pressure). • Boiling point and vapor pressure are inversely proportional (the higher the boiling point, the lower the vapor pressure and vice versa). Background
• An effective distillation requires that the components of the solution have significantly different boiling points (preferably between 30-40°C). • Example Background continued Toluene (BP 111°C) CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Hexane (BP 69°C)

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• During the process, a liquid is heated to its boiling point and the vapors generated are condensed by cooling and collected in a receiving vessel, or they return to the boiling mixture. • A theoretical plate represents one vaporization/ condensation cycle. • If two cycles occur, the distillation has two theoretical plates. Background continued
Macro-Scale Simple Distillation Setup

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Simple Distillation curve Temperature Volume
Added column provides larger surface area for multiple simple distillations Fractional Distillation Setup orgchem.colorado. e du/. ../fractdist.html

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Temperature Volume Fractional Distillation curve
X axis = mole fraction of hexane Y axis = Temperature Curve X = Liquid Composition Curve Y = Vapor Composition When mole fraction of hexane is 1.0, the liquid will boil at ~ 69°C When mole fraction of toluene is 1.0, the liquid will boil at ~ 111°C Point m A n on the graph = mole fraction of hexane and toluene is 0.5 (liquid composition 50% each), the liquid will boil at ~ 80.8 °C. The corresponding vapor composition (Point m B n ) will be 77% hexane, 23% toluene Phase diagram

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Al Block Only one thermometer is used which is inside the Hickman still head. Use Al block instead
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Fractional Distillation lecture(2) - Fractional...

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