Experiment 4: Distillation Timothy Hudson David C. Carandang, Monroe D. Orlina Group 4, Chem 31.1, AB1, Ms. Arlou Angeles May 9, 2013 I.
Abstract Distillation is a purification technique in which compounds with different boiling points can be separated by controlled heating. An important concept involved in distillation is Raoult ’s Law. This means that the vapor pressure of an ideal solution is directly dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution. In this experiment, the objectives were to separate components of a mixture using both simple distillation and fractional distillation and to be able to explain the principles behind the processes involved. In simple distillation, 5 ml distilled water, 2 ml ethanol and a boiling chip were added to a distillation tube. Next, the distillation set-up was assembled. The sample was heated and the rate of heating was adjust so that the rate of distillation would be 3 drops per minute. The same was done with fractional distillation except that the set-up included a fractionating column. Both results show a more linear distillation graph. This was the exact exact opposite of the theoretical results. This might happened because of different factors like inconsistent inconsistent data gathering. New concepts like azeotropes were also explained. In conlusion, not all the objectives were achieved. However, the principles behind distillation which is more important was explained. explained. II.
Keywords distillation, azeotropes, fractionating column, boiling point, Raoult’s Law
III.
Introduction Distillation is a purification technique in which compounds with different boiling points can be separated by controlled heating. Vapors from a sufficiently heated sample can be condensed and collected, purer than the initial mixture. The liquid which has not vaporized is called the residue, and the liquid which is collected in the receiver is called the distillate. An im portant concept involved in distillation is Raoult’s Law. This means that the vapor pressure of an ideal solution is directly dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution. In this experiment, the objectives were to separate components of a mixture using both simple distillation and fractional distillation and to be able to explain the principles behind the processes involved. IV. Experimental Experiments were done to show the separation of components of a mixture using simple distillation and fractional distillation. In simple distillation, 5 ml distilled water, 2 ml ethanol and a boiling chip were added to a distillation tube. Next, the distillation set-up was assembled. The sample was heated and the rate of heating was adjust so that the rate of distillation would be 3 drops per minute. After that, temperature was recorded for every 0.1 ml distillate. The first distillate ranged from 74-82oC. Another receiver was used used to continue the process until 0.4 ml remained in the distillation tube. A distillation curve was then constructed and the number of components in the distillate, the respective boiling points of each and the approximate volume % of the lowest-boiling component were determined.
In fractional distillation, same procedures were done except that the set-up had a fractionating column attached. Figure 2: Set-up for Fractional Distillation
Figure 1: Set-up for Simple Distillation
CHEM 31.1, Distillation
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V.
Results
Figure 3: Graph showing results from simple distillation.
SIMPLE DISTILLATION 120 100 e r u 80 t a r e 60 p m 40 e T 20 0 1
4
7 10 13 16 19 22 25 28 31 34 37 40
Drops
Table 1: Data of first and second distillate of simple distillation
because it directly condenses. The theoretical graph should be diagonal but the experimental graph was almost linear. Fractional distillation usually employed with separation of complex mixtures at small boiling point difference. It is essentially simple distillation but there is a fractionating column in which the liquid reevaporates making the distillate purer. In our set-up, our fractionating column is made up of glass beads. The fractionating column is designed to increase the surface area of contact thus it promotes recondensation and re-evaporation. In our experiment, our graph is almost linear which is theoretically wrong. The theoretical graph of a fractional distillation set-up is that it should be really steep because the rate of distillation is slow which also means that the temperature rises slow and the amount of distillate increases during that steep slope. Figure 5: Graph showing theoretical slopes of simple and fractional distillation.
Figure 4: Graph showing results from fractional distillation
FRACTIONAL DISTILLATION 100 e r u t a r e p m e T
95 90 85 80 75 70 1 2 3 4 5 6 7 8 9 101112131415161718
Drops
Table 2: Data of first and second distillate of fractional distillation
VI.
Discussion Simple distillation is usually used only to separate liquids whose boiling points differ greatly. In the process, all the hot vapors are immediately channeled into a condenser. Therefore, the distillate won’t be as pure. In our experiment, the first distillate was at 84oC. Also, our second distillate was at 84 o C. However, this shouldn’t be the case. In this experiment, the temperature should constantly rise CHEM 31.1, Distillation
In the mixture of ethanol and water, it doesn ’t always conform to Raoult ’s Law. At 78.1oC, the distillate will always contain 95.5% ethanol and 4.5% water. This type of behavior wherein two or more liquids in such a way that its components cannot be altered by simple distillation is called an azeotrope. This happens because, when an azeotrope is boiled, the vapor has the same proportions of constituents as the unboiled mixture. There are two types of azeotropes. First is positive azeotropes. Positive azeotropes have high pressure and minimum boiling point. This can be seen in Figure 6. Figure 6: Positive Azeotropes
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The other one are negative azeotropes. They have low pressure and maximum boiling point. This can be seen in Figure 7. Figure 7: Negative Azeotropes
inconsistent in our data gathering, the sourc e of heat was difficult to control or the thermometer might not be correctly calibrated. Even with all those dilemma, we were still able to succeed in the second objective which was to learn and explain the concepts behind the process. We would like to recommend that there should be better equipment for this experiment. Also, we believe that we should also do steam distillation for the sake of more learning. Overall, the experiment is a success theoretically but not in actuality. VIII. References Ault, A. Techniques and Experiments for Organic Chemistry. (1987). Wells Avenue, Newton Massachusetts Brown, et. al., Chemistry: the Central Science. (2012). Singapore: Pearson Education Asia Pte Ltd Chang, R. (2010). Chemistry 10th ed. New York: The McGraw-Hill Companies, Inc. Feiser, L.F. Organic Experiments. (1975). D.C. Heath and Company Laboratory Manual in Organic Chemistry. (2010). UPM: CAS, DPSM.
I hereby certify that I have given substantial contribution to this report. Our ethanol-water mixture is a positive azeotrope. Figure 8: Ethanol-water azeotrope graph.
Timothy Hudson David C. Carandang
Monroe D. Orlina
To add to the discussion, the boiling point of ethanol is about 78 oC and the boiling point of water is about 100 oC. They separate because at that temperatures, they evaporate and condense which means that the distillate will be essentially purer. Simple distillation gives a less pure distillate than fractional distillation. Ethanol and water can be 100% purified by other means and not simple and fractional distillation. This can be done by dehydrogenation or adding a new azoetrope mixture for water to evaporate. VII. Conclusions and Recommendations Distillation is a purification technique in which compounds with different boiling points can be separated by controlled heating. In conclusion, the first part of the experiment was a bit of a failure because of different factors. We were not able to successfully distill the solution because we were CHEM 31.1, Distillation
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