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Experiment # 4

Distillation

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Recrystallization

Extraction

Impure

compound

Isolation

Distillation Liquids only

Chromatography Solids or Liquids

Purification

Establishingpurity

Melting point Boiling point

Spectroscopy

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Distillation

Purification of liquids by vaporization and condensation

vaporization condensation

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Purification methods for liquids

Distillation

Simple

distillation

Fractional

distillation

Vacuum

distillation

Steam

distillation

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Simple DistillationSeparating liquids from

a. Non volatile impuritiesb. Another liquid boiling at least 400 C higher than the first.

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Theory of simple distillationDiagram of dependence of vapor pressure on temperature. Blue curve is forpure water, and green curve is for a solution of water and sugar

Vaporpressure(torr)

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Simple DistillationPurpose

Purification of Cyclohexane (b.p. 810C at 760 torr), volatile organic liquid,containing a nonvolatile impurity, Dye

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Simple DistillationSetting Up

1 2 3 4

7 85 6

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Simple Distillation

Dos and Don'ts

Place 10 mL of cyclohexane, 2 drops of dye, stir bar in R.B

flask

Place the heating mantle after adding the liquid to the round bottom

as g. 3

The top of the mercury bulb of the thermometer should be adjacent

to the side arm of the still head. (fig. 5)

Use Keck clips to hold the condenser, vacuum adapter, and receiver

in place ( fig.8)

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Simple Distillation

Begin heating the R.B. flask. As soon as the liquid begins to boil and

the condensing vapors have reached the thermometer bulb, regulate

the heat supply so that distillation continues steadily at a rate of 2-4drops per second

If a drop of liquid cannot be seen suspended from the end of the

thermometer, the rate of distillation is too fast.

As soon as the distillation rate is adjusted and the head temperature is

constant, note and record the temperature

Stop heating when only 2-3 ml of impure cyclohexane remains in

the distillation flask.

Record the volume of distilled cyclohexane that you obtained

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Fractional Distillation

The technique can be used to separate pure liquid components from

a mixture containing two or more volatile substances if their boiling

points are close to each other

It involves multiple simple distillations

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Theory of Fractional Distillation

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Fractional DistillationPurpose

To separate the two volatile components, Cyclohexane ( b.p. 810C),

and Toluene ( b.p. 1100C)

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Fractional DistillationSetting Up

1 32 4

5 6 7

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Fractional DistillationDos and Donts

Place 10 mL of cyclohexane, 20 mL of toluene, stir bar in R.B. flask

When packing the column, be careful not to break off the glass

indentations at the base of the column

Do not pack the column too tightly

The top of the mercury bulb of the thermometer should be adjacent

to the side arm of the still head.

Use Keck clips to hold the column, condenser, vacuum adapter, and

receiver in place

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Fractional Distillation As the mixture is heated, the head temperature will rise to 810C(760

torr), and distillation will begin

faster than one drop of distillate every 1-2 sec

If a drop of liquid cannot be seen suspended from the end of the

thermometer, the rate of distillation is too fast

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Fractional Distillation

Collecting fractions

Collect the first fraction at 810C 30C , label it A

Change to the second receiver and increase the heat, label it B

Collect the last fraction when temperature reaches 1100C, label it C

Results

The temperature range while the distillation is steady ( 1 & 3fractions )

The volume of distillate collected in each receiver

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Fractional Distillation

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Save samples, Waste disposal

Three fractions obtained from fractional distillation should be saved

for the future lab gas chromatography

The cyclohexane obtained from simple distillation should be

disposed of in non halogenated waste container

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