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Chem 334

Figure 1 Figure 2. Chem 334. Expt. #3 Simple and Fractional Distillation ; Analysis of Distillation Fractions by GC. What factors affect the boiling point of a compound?. Experiment #3 compounds. EA = ethyl acetate CH 3 CO 2 CH 2 CH 3

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Chem 334

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  1. Figure 1 Figure 2 Chem 334 Expt. #3 Simple and Fractional Distillation; Analysis of Distillation Fractions by GC

  2. What factors affect the boiling point of a compound?

  3. Experiment #3 compounds EA = ethyl acetateCH3CO2CH2CH3 EP = ethyl propionateCH3CH2CO2CH2CH3 b.p. = 77oC b.p. = 99oC

  4. Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate?

  5. See Techniques 2 and 3 Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate?

  6. Boiling Point - Composition for a Liquid-Liquid Mixture Raoult’s Law “mixture of two liquids will have a b.p. that is between the b.ps. of the pure liquids” PX = PoXNX where PX is the partial pressure of X PoX is vapor pressure of pure X NX is the mole fraction of X in mixture (Exception: Azeotropes)

  7. Assume a mixture of x moles of EA and y moles of EP What would be the mole ratio? What would be the mole fraction of EA in the mixture?

  8. Boiling Point - Composition for EA - EP mixture Total vapor pressure of mixture “Ptotal” is the sum of the partial pressures due to EA and EP. Ptotal = PEA + PEP If “Ptotal” is equal to the external pressure, boiling occurs.

  9. Your experiment: We will do two distillations: A simple distillation and a fractional distillation. Work in teams of two: One student sets up the simple distillation and the other student sets up the fractional distillation glassware.

  10. Table for Simple (Fractional) Distillation Temp oC # drops Record your data: Temp. & # drops 1 4 8 12 70 etc. Also collect data for Fractional Distillation

  11. Simple Distillation Set-up Thermometer position collect the 1st two drops here, in a receiving vial. Label! * Add boiling chip Figure 1

  12. Continue recording your data

  13. Fractional Distillation Set-up Micro-column & steel sponge Do not “stuff” the column too tightly Be careful not to cut your hand with the steel sponge when packing the column. * Figure 2

  14. Simple & Fractional Distillation Plot Both Curves on one Graph Temperature Plot both S1 and F1 curves on the same graph 98 oC oC oC oC 0 4 8 12 16 20 24 28 …………………..etc. Volume of distillate (# drops)

  15. Part C. Analysis of Distillation Fractions by GC HP 5890 Gas Chromatograph

  16. Flow Diagram for a Capillary GC Sample Injector Carrier Gas GC Detector vent Open Tubular Capillary Column

  17. Gas Chromatography • A separation method for volatile compounds • A chromatography method:Stationary phase and moving phase • Separation is based on • physical & chemical properties of each compound • different interaction with the stationary phase • A true microscale method!

  18. Each peak (in a good separation) represents one compound. Retention time Injection point

  19. Each peak (in a good separation) represents one compound. The area under each peak corresponds to moles of the compound

  20. Gas chromatogram of a 50:50 (v:v) EA/EP mixture In diethyl ether EA EP Remember: Diethyl ether ≠ Petroleum ether !!!

  21. Next time: • Gas chromatography (conclusion) • Steam distillation: Isolation of eugenol from cloves

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