Distillation

What are the results of the following procedural errors: -Heating the solution too quickly -Opening a cold sample vial -Not capping a vial tightly -Having the oven temperature too hot on the GC -Having an air bubble in the syringe when injecting your GC sample

1. Heat too quickly: won't allow vapor-liquid equilibration within fractionating column.Less volatile (higher bp) must condense to liquid and more volatile (MeOAC less bp) must turn to vapor 2. Opening a cold sample vial: condensation on the outside of the vial will add to the weight 3. Not capping a vial tightly: loss of vapors so lower weight 4. Having the oven temperature too hot on the GC: decrease in retention time and compound may not separate 5. Having an air bubble in the syringe: shifting retention times and irregular peaks

Four factors that influence GC retention?

1. boiling point of compound (can't change) 2. column length (can't change) 3. carrier gas flow rate (easy to modify) 4. oven temperature (easy to modify)

Use the phase diagram on slide 9 to answer the following questions. What liquid composition will provide a solution that will boil at 75 °C?

30% A, 70% B

What is the minimum difference in boiling points needed in order to cleanly separate a mixture of two liquids by simple distillation?

70 degrees Celsius is needed to separate w/ simple distillation

Explain why there is a difference (if any) between the boiling point of pure methyl acetate and the boiling points you recorded for the distillates you collected in the simple and the fractional distillations.

A. The "pure" methyl acetate could actually contain impurities from compound B. If the compound was heated too quickly a poor vapor-liquid equilibrium exists. Therefore, even though the pot/distillate has pure methyl acetate in liquid form, the vapors surrounding are from compound B

What two factors determine the vapor composition above a liquid mixture at any given temperature?

First factor - external pressure Second factor - sample purity

Define the term "azeotrope".

Mixture that distills at a constant temperature with constant composition.

If you distilled a mixture which was made from 17 moles of MeOAc and 34 moles of EtOAc, would it boil at 62 C? Why or why not?

The mixture of MeOAc and EtOAc in the molar ratio 1:2 forms an azeotropic mixture, i.e. it boils at a constant temperature of 62C under normal atmospheric pressure without any change in composition. So it will boil.

Why should you not clean your glassware with water immediately before conducting your distillation?

The water could vaporize when heated and disrupt the purity of your compound.