P a g e | 1 Myeeka Hammond June 5, 2017 Distillation Purpose: The purpose of distillation is to purify volatile liquids either by separating them from
nonvolatile materials or from other volatile substances. The main purpose of this experiment is to see which type of distillation is more efficient. Introduction: Distillation is a common method used to determine the boiling point of a solution to purify
volatile liquids by separating them from other nonvolatile liquids or from other volatile liquids. Distillation relies on each compound having different boiling points. The process involves the mixture being heated to its boiling point, cooling the vapor until it reverts to its liquid state, and collecting the condensate. The boiling point if liquid is the temperature at which the vapor pressure is equal to atmospheric pressure. In this lab, both simple distillation and fractional distillation are used to separate a mixture and the results are compared to see which method of distillation is more effective. Simple distillation is used to separate volatile liquids from non-volatile impurities or from another volatile liquid whose boiling point is at least 80°C higher than that of the t he liquid it is being separated from. Fractional distillation is used to separate two volatile liquids with a boiling point difference less than 80°C. Fractional distillation is doing a simple distillation repeatedly, but it is accomplished accomplished automatically in one process. A vertical column is used, packed with an inert material such as glass wool or glass helices, and is inserted between the distilling flask and condenser. Part 1: Simple Distillation Materials:
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Simple distillation apparatus 100 mL heating mantle and rheostat 10 mL of cyclohexane (C6H12) 10 mL of toluene (C6H5-CH3) 100 mL bottom round flask 2-3 boiling chips 2 water tubes 2 10 mL graduated cylinders cylinders Water from the pipe Thermometer
Procedure: After setting up the simple distillation apparatus, we obtained 10 mL of cyclohexane and 10
mL of toluene and placed it in the 100-mL bottom round flask. We then attached the bottom round flask to the apparatus and used a clip to ensure that it would not fall off. To ensure that heat did not leave the bottom round flask we wrapped it in aluminum foil and then waited for the professor to check our
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set-up and give us the ok to start the actual experiment. Once we got the okay we turn on the water to the apparatus and waited for the solution in the flask to start boiling to record the temperature and then waited, again, to get the temperature of the first drop into the graduated cylinder. After that we measured the temperature for every 1 mL of solution that went into to the graduated cylinder, for about 15mL. Part 2: Fractional distillation Materials:
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Fractional distillation apparatus Thermometer 10 mL of cyclohexane (C6H12) 10 mL of toluene (C6H5-CH3) 2-3 boiling chips 100 mL bottom round flask 2 water tubes 2 10 mL graduated cylinders Water from the pipe 100 mL heating mantle and rheostat
Procedure: The first thing that was done for the fractional distillation was setting up the required
apparatus. Once the apparatus was set up we obtained 10 mL of toluene and 10 mL of cyclohexane and placed it in the 100-mL bottom round flask. We then attached the flask to the apparatus and attached the water tubes to the apparatus. Once everything was in place we waited for out professor to give us the okay to being doing the distillation of the two compounds. To begin we turned on t he heating mantle, to a higher number than that of simple distillation, and at the same time turned on the water from the pipe to run through the apparatus. After the heating has begun, we waited to get that first mL of solution to record the first temperature after than we recorded the temperature for each mL of solution that went into the graduated cylinder. Data and observations:
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Simple
Fractional
Distillation
Distillation
1 mL
89
79
2 mL
89
79
3 mL
89
79
4 mL
90
79
5 mL
90
79
6 mL
91
81
7 mL
91.5
82
8 mL
92
89
9 mL
93
91
10 mL
95
106
11 mL
96.5
107
12 mL
98
107
13 mL
100
107
14 mL
100
108
15 mL
100
109
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Volume vs Temperature 110
105
100
E R U T A 95 R E P M E T 90 D A E H
85
80
75 1 mL
2 mL
3 mL
4 mL
5 mL
6 mL
7 mL
8 mL
9 mL 10 mL 11 mL 12 mL 13 mL 14 mL 15 mL
VOLUME Simple Distillation
Fractional Distillation
The literature boiling point of Toluene is 110.6°C and for cyclohexane it is 80.74°C. In the experiment, when we did simple distillation the first substance resulted in a boiling point of 89°C which is far off from the boiling point of either substance that we were testing. For the second liquid that we were trying to distill, the resulting temperature was 100°C. On the other hand, fraction distillation resulted in a closer boiling point to the literature values. For the first boiling point, we achieved 79°C and the second boiling point was 109°C. There are a number reasons that we had the wrong numbers for the simple distillation. The most obvious reason could be that t he thermometer was not positioned incorrectly, resulting in the observed temperature to be incorrect. Another reason is that we could have heated the solution too quickly which will result in a poor separation. On the o ther hand, we could have not heated the solution enough which might have led to the vapor condensing and returning to the distillation flask instead actually distilling into the graduated cylinders. The distillation should occur at a rate of about o ne drops every 20-30 seconds, so enough heat needs to be supplied to achieve that. Another thing that happened when doing the simple distillation, was that we ran out of solution in the bottom round flask to go to the amount of mL that our teacher was requiring. This is most likely due to the liquid boiling in the flask but
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none was being collected in the graduated cylinder. This may be due to a leaking connector, causing some of the vapor to escape or some of the condensation to drip before reaching the open end of the apparatus. Even though the boiling points that we achieved from our experiment were not that off, they still were not the exact numbers. This can be due to several reasons. Because of the longer path the solution has to take in fractional distillation, the distillation might slow down and cause the temperature to fluctuate a little, which means that a little more heat is required to continue. Another reason is that the distillation column might have been packed too tightly with the glass wool, this leads to the column flooding leading to some of the liquid to collect in the column and go all t he way through. These are just a few reasons why our numbers were not exact, but they were a sharp boiling point. Overall conclusion: In this lab, simple distillation and fractional distillation is used to separate the same
mixture. The results of each method of distillation are compared to determine which method of distillation is more effective in separating a mixture. Based on these results simple distillation did not separate the mixture as effectively as fractional distillation. This experiment proves that fractional distillation is more effective in separating a mixture of volatile substances. Post Lab Questions: 1. Was there a difference between the head temperature when the liquid first started t o boil and the temperature when the first portion of distillate was collected? Explain
No, the temperatures are equal as the liquid and gas are in equilibrium at boiling point. So, their temperatures are equal. The temperature change within 2C indicate pure distillate. 2. What would be the effect of having the thermometer above the side arm of the three-way collecting tube?
Then the thermometer will not read the correct equilibrium temperature as the distillate will not condense on the thermometer bulb. 3. If two miscible liquids are each found to boil at exactly the same temperature, could you safely conclude that they are identical? Why?
No, boiling point is a physical property. Same boiling temperature indicates same van der Waal’s force between molecules in the liquid. Other properties like absorption spectra of spectrophotometer, refractive index, density, dipole moment etc. are also required to match. Same boiling point liquids can be separated by chromatography methods as they cannot be separated by distillation. The method is used for separating optical isomers. 4. What is the purpose of the boiling chips?
The purpose of the boiling chip is to prevent bumping.
P a g e | 6 Myeeka Hammond June 5, 2017 Distillation 5. How would the observed temperature be affected if a distillation were performed on the top of a mountain? Explain.
At high altitude of the top of a mountain, the boiling point would be reduced, which will speed up the distillation process because the solution will be able to boil more easily. 6. Why should water enter a condenser at the lowest point and l eave at the highest point?
Water should enter a condenser at the lowest point and leave at the highest point so that it does not get into the boiling flask and contaminate the solution you are trying to distill.
