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Distillation - Experimental Procedure

Aim

Set up a simple distillation column for an unknown mixture in order to separate into two purer

fractions. The boiling point of the purer fractions will then be measured and used to determine which

organic solvent they are.

Health & Safety

BASIC SAFETY RULES:

a) Do not eat, drink or chew whilst doing the experiment.

b) Keep your face at a safe distance from open flames and heated solutions. Never look into aheated solution from above.

c) Avoid breathing in dust or vapor. When smelling solutions, gently wave the air above the

solution towards your nose with your hand.

d) Wash any spilled solutions from your skin with plenty of water, and notify the instructor.e) Report any accident, no matter how minor, to the instructor/report the nearest health post.

The experiment involves heating liquids to their boiling point by use of a heating mantle. The heatingmantle may reach temperatures of 300

oC and caution must be exercised in handling the heating mantel

and the equipment being heated. Low boiling point solvents may also be used and therefore must be

aware of the effects of rapidly heating such solvents or if solvents come into contact with a hot surface.

Procedure

1. Distillation

You will be given 30 ml of an unknown liquid mixture that is to be purified by simple distillation andfor which the boiling point range is to be determined.

1. Assemble the assigned distillation apparatus (consisting of the distillation flask, refluxassembly, thermometer (up to 150 oC), distillation arm, condenser attached to a water supply

and receiver) on a heating mantle using a heating block, ensuring that the reflux round bottom

flask (50 ml) contains 30 ml of the unknown liquid and a few boiling chips. Collection will bemade in a dry graduated cylinder at the receiver. The round bottom flask must be supported by a

clamp (do not over tighten). Clips must be used to support the remaining connections. The

thermometer must be placed where the bulb is positioned at the distillation arm. Do not seal thesystem closed.

2. Check with the TA or Instructor that the assembly is ready.

3. The condenser is connected to a single water supply. Ensure only a gentle flow of water in the

system rapid flow of water may cause the leads to be ejected from the assembly and flooding.4. Place the distillation flask in contact with the heating mantle ensure heating mantle is below

50 oC cover the reflux assembly in aluminum foil just below the distillation arm.

5. Heat the unknown liquid gradually until the thermometer reaches a temperature around 50oC

then proceed at a slower rate till the vapor condenses and is collected at the receiver. As the

lower boiling point component is distilled, the boiling point of the mixture in the distillation

flask will increase.6. Record the temperature at the first drop collected and for every 2 ml of liquid collected

thereafter.

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7. After 10 ml is collected, remove the cylinder and label Component A. Place another dry

cylinder underneath the receiver.

8. If the distillation flask is approaching dryness, remove the heat source immediately and contactyour TA or Instructor.

9. Collect the next 10 ml, recording the temperature after every 2 ml is collected. Towards the end

of the collection, the thermometer should reach a constant temperature.10.Turn off the heating source. You must ensure the system is cool before touching it.

11.

Once the system has cooled sufficiently, collect the residual liquid in the distillation flask and

label Component B.

2. Boiling point determination

1. Assemble the assigned boiling point apparatus (consisting of a heating flask with a side arm,

thermometer (up to 150oC), and a reflux condenser) on a heating mantle using a heating block,

ensuring that the heating flask contains at least 5 ml of Component A or B and a few boiling

chips. It is advised that you should test the boiling point of Component A first and then B. Thethermometer must be placed above the level of the liquid and not where the bulb contacts the

glassware. Do not seal the system closed.

2.

Check with the TA or Instructor that the assembly is ready.3. The condenser is connected to a single water supply. Ensure only a gentle flow of water in the

system rapid flow of water may cause the leads to be ejected from the assembly and flooding.

4. Place the heating flask in contact with the heating mantle ensure heating mantle is below 50oC.

5. Heat the Component liquid gradually until the system produces condensation on the

thermometer.

6. Record the temperature of the system.7. Turn off the heating source. You must ensure the system is cool before touching it.

8. Repeat for the other Component liquid.

Result processing

Identify the unknowns by their boiling points using the possible boiling points of compounds.

Construct a table like that given below, to record the temperature at the distillation "head" as a functionof volume distilled. You will record your data in report form. Plot distillate temperature (oC) vs. volume

of distillate (ml) collected for the mixture and use the graph to determine the boiling points of the two

compounds in the mixture and identify the compound in the mixture.

Report Form

Volume distilled

(ml) 0 2 4 6 8 10 12 14

Temperature (oC)

Volume distilled

(ml) 16 18 20 22 24 26 28 30

Temperature (oC)

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Observed boiling point of the first compound (A): ____________oC

range

Literature boiling point of the first compound (A): ____________oCrange

Observed boiling point of the second compound (B): ____________oC

rangeLiterature boiling point of the second compound (B): ____________oC

range

Identity of MixtureCompound A is _____________________

(name)Compound B is _____________________

(name)

Identity of Mixture (Group 2)BP for compound A _________oC; Compound A is _____________________

(name)

BP for compound B _________oC; Compound B is _____________________(name)

Post-lab Questions

1. One mole of compound A, with vapor pressure 400 mmHg at 50 oC, mixed with 3 moles of

compound B, with vapor pressure 480 mmHg at 50 oC to form a homogeneous solution. What is

the vapor pressure of mixture at 50 oC?

(1 mark)

2. Why should a distilling flask be filled not less than 1/3 filled or more than 2/3 full?(1 mark)

3. A 50% aqueous solution of ethanol (50 ml total) is distilled and collected in 10ml fractions.

Predict the boiling range of each fraction.(2.5 marks)

fractions vol. collected(ml) temp. oC (predicted)1 102 20

3 30

4 405 50

4. What is the mole fraction of each component if 3.9 g of benzene (C6H6) is dissolved in 4.6 g oftoluene (C7H8)?

(2 marks)

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