Distillation

SIMPLE DISTILLATION

Simple Distillation of an Aqueous Solution Containing a Nonvolatile Solute

Reatl pugesl67-172, turcl make a pre-lab write up before entering laboratory to do this experilnent.

The apparatus for sirnple distillation is shown in figure 98

(page 166) of the textbook. Instead of a RB flask, a 50-

mL graduated cylinder is used as the receiver.Assemble the Apparatus with 5O-nrl RB flask as distillingflask and a 50-mL graduated cylinder as the receiver'

Pour 25 mL of the colored solution to be distilled into the

distilling flask and add a few boiling stones into it' Heat

the flask using a heating mantle*. (Do not overheat. Witha little experience the conect setting for proper amount ofheat for the distillation can be determined' Start from a

low setting and gradually increase the heat when

necessary.)

The solution boils and vapors pass rnto the condenser where it will be converted to liquid. Duringdistillation the tenrperature of the vapor should not fluctuate. Supelheating or uneven heating lnay cause

fluctuations in temperature. The distillate collected must be colorless. If not, you have not done the

distillation properly and you must start over. The distillation should be stopped when a few milliliters ofthe solution is still left in the distilling flask.

In youl Laboratory notebook, note the distillation temperature after each two milliliters of the distillate is

collected. Plot a graph of miliiliters of distrllate collected (x-axis) versus temperature (y-axis).

*Refn, to pflges 150-152 to leant to use the lrcating mantles properly.

Simple Distillation of Methanol

Using the same apparatus, distil 25 rnl- of methanol. The distilling flask should be washed ar-rd dried.

Residual water may be present on tllee-way adapter and thelmometer. Therefore, they should also be

dried. The drying can be achieved by rinsing these pieces with a small amount of metiranol. If no heating

mantle is availabie, use steam as a source of heat. Distil the salne way you distilled aqlleous solution inthe previous experiment. Boiling stones must be used in this distillation also.

Wlite down the distillation temperature after each two milliliters of the distillate is collected and plot a

glaph of milliliters of distillate collected (x-axis) versus temperature (y-axis).

Simple Distillation of an Unknown Liquid

This experiment is to detemrine the boiling point of the liquid given. Obtain the liquid for distillationfrom your instructor. Carry out the distillation the same way you carried out the distillation of methanol.

In this experiment also, note the distillation temperature after each two milliliters of the distillate iscollected and plot a graph of milliliters of distillate collected (x-axis) versus temperature (y-axis).

The boiling point of the liquid is the temperature at which the bulk of the liquid distils.From the boihng point, determine the identity of the liquid.

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EXP. 2: COMPARISON OF A SIMPLE DISTILLATION AND FRACTIONALDISTILLATION OF A METHANOL.WATER MIXTURE,.

Read the followins topics in your Lab Manual:"Boilins Stones" ; "Hggting l\4gnt]g"; "Clamps and Clamping" ; "SinqplslDi$illatflgq";'"Fractional Distillation"; and "Theor)' of Distillation"'

Complete a pre-lab write up before coming to the lab to perform this experiment.

Obiective: The objective of this experiment is to carry out a simple distillation and a

fractional distillation of a methanol-water mixture and compare the efficiency of separationobtained by the two methods.

Part I: Simple Distillation of 50-50 (bv volume) Methanol-Water Mixture.

Background:Simple distillation is carried out when the liquid to be purified contains a non-volatile

impurity or another liquid that boils at least 25C highet than the first.

Diagram:The apparatus for simple distillation is shown in Figure 20.1 (page 166) of the Lab Manual.Instead of a round-bottom flask (RB flask), use a 50-mL graduated cylinder as the

'receiving flask'. The modified diagram is shown below.

Procedure:

1. Assemble the apparatus using a 50-mL RB flask as distilling flask and a 50-mL graduated

cylinder as the receiving flask.

2. Pour 25 mLof the 50-50 methanol water mixture into the distilling flask.

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4.

3 . Add a few boiling stones into it. (Use 1 boiling stone if it is big, about 4-6 if it is small).

Note:o At the start of the distilling process, the flask should not be less than one-third full,

and not more than half-filled with the liquid.o Make sure that the bulb of the thermometer is below the side-arm and that'all

joints line up.o Make sure that the joints are tights and the whole setup is secured properly.o Make sure that the water in the condenser is running uphill and that there is a

steady flow of water.

Heat the flask using a Thermowell heating mantle.o If a heating mantle is not available, you may use a Bunsen burner.o Start from a low setting and gradually increase the heat when necessary.

o Do not overheat. With a little experience the correct setting for proper amount ofheat for the distillation can be determined.

o Boiling will start slowly and then rapidly. As the liquid boils, the vapors willcondense on the thermometer and the temperature will go up quickly and then

stabilize. The vapors will pass into the condenser where it will be converted to

liquid.

In your laboratory notebook, note the temperature at which the first drop of distillate is

collected.o The temperature on the thermometer must not fluctuate throughout the distillation

process. Superheating or uneven heating may cause fluctuations in the temperature.

Record the next temperature when 3 mL distillate is collected and thereafter at every mLof distillate collected.

7. Stop the distillation when about 1-2 milliliters of the solution is still left in the distillingflask.

. To stop the distillation, tum down the setting on the Thermowell, and lower theThermowell heating mantle. (If using a Bunsen burner, then turn the flame off.)

8. Plot a graphof milliliters of distillate collected (X-axis) versus temperature (Y-axis).

Data: Simple Distillation of 50-50 (by volume) Methanol-Water Mixture.

Vol. of distillatecollected (mL)Temperature

5.

6.

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Part II: Fractional Distillation of 50-50 (bv volume) Methanol-Water Mixture.

Backsround: Fractional distillation is used to separate liquids that are miscible (soluble ineach other), and boil less than 25Co from each other at a pressure of one atmosphere.

Part of the setup for fractional distillation is shown in Figure 20.10 (page 180) of the LabManual. The setup for fractional distillation is similar to that of the simple distillation, except

for one major difference-the fractionating column. (The fractionating column must not be

confused with the condenser. The fractionating column is wider and has glass projectionsinside at the bottom to hold the column packing-saddles in our case.)

Diagram:

Procedure:

1. Assemble the apparatus using a 50-mL RB flask as distilling flask and a 50-mL graduated

cylinder as the receiving flask. The fractionation column must be loosely, but uniformlypacked with 'saddles', and clamped vertically.

2. Pour 25 mL of the 50-50 methanol water mixture into the distilling flask.

3. Add a few boiling stones into it.(Follow precautions as you would for simple distillation)

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4. Heatthe distillation flask slowly using a Thermowell heating mantle.

fractionating column.o If the heating is too rapid, the column will be 'flooded' and separation of the

components will not be satisfactory. A rapid distillation does not allow equilibrium tobe established between the liquid and the vapor, and little or no fractionation results.

The fficiency of the column increases as the rate of distillation decreases.

o If the column starts to get flooded, turn down the heat.

5. In your laboratory notebook, note the temperature at which the first drop of distillate is

collected.o The temperature on the thermometer must not fluctuate throughout the distillation

process. Superheating or uneven heating may cause fluctuations in the temperature.

6. Record the next temperature when 3 mL distillate is collected and thereafter at every mLof distillate collected.

7. Stop the distillation when about 1-2 milliliters of the solution is still left in the distillingflask.o To stop the distillation, turn down the setting on the Thermowell, and lower the

Thermowell heating mantle. If using a Bunsen burner, then turn the flame off.

8. Plot a graphof milliliters of distillate collected (X-axis) versus temperature (Y-axis) on the

same graph as in part I. (Use the same X and Y axes.)

Data: Fractional Distillation of 50-50 (bv volume) Methanol-Water Mixture.

Vol. of distillatecollected (mL)Temperature

Conclusion: (Compare the two plots and draw your conclusion about the separation ofmixture achieved by simple and by fractional distillation.)

Adapted from "Techniques and Experiments in Oreanic Chemistry" 2nd ed., Leon Gortler and

Robert Tripp, Avery Publishing Group Inc., New Jersey pp.17-22 (1979).

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