Distillation Formal Lab Report 2k5k5a

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Experiment 3: Distillation of Cyclohexane and Toluene Peter Ickes October 2, 2014

Abstract: In this experiment, a 1:1 solution of cyclohexane and toluene was separated using simple and fractional distillation techniques performed on both macro- and microscale levels. Graphs of temperature vs. volume of distillate collected showed the changes in vapor temperature for each experiment. Early and late samples of the distillate were also taken for each experiment and then analyzed using gas chromatography. These results showed higher purity obtained from fractional distillation when compared with simple distillation.

2 Introduction: Distillation is a laboratory method which can be used to separate liquids from a homogenous mixture based upon their boiling points. The boiling point of a liquid is the temperature at which the vapor pressure of the liquid is equal to the applied pressure from its environment, i.e. the barometric pressure for a given day. Because boiling point is reliant upon atmospheric pressure, there is a positive relationship between the two, though it is not linear. The boiling point at a given pressure can be calculated using the Clausius-Clapeyron equation (1), which is ( )

(

)

(1)

When dealing with a mixture of ideal liquids, their contributions to total vapor pressure of the entire solution may be calculated using Dalton’s law of partial pressures (2). (2) Both P1 and P2 can be calculated using Raoult’s law (3). In this equation, P1 and P2 are the vapor pressures of the pure liquids, respectively, at a specific temperature. N1 and N2 are the mole fractions of each liquid in the mixture. Combing (2) and (3) results in the final equation (4). and

(3) (4)

In a mixture, the substance with the lower boiling point will boil off first. This is called the more volatile liquid. As the procedure continues, the proportion of the two liquids in the distillate will shift from favoring the more volatile liquid to the less volatile. In order to purify a substance, serial distillations may be performed using an early portion of the successive distillates. Distillation involves heating the mixture to its boiling point, then guiding the vapors to a cooling device where they are condensed. This liquid is known as the distillate. Two types of distillation were conducted in this lab. In a simple distillation procedure, a mixture is heated to boiling, the vapors rise, condense, and then are collected. In a fractional distillation, an inert substance is inserted into the column. The vapors condense on this material first and then, as the temperature rises towards the top of the column, they into the gas phase. This boil-condense process is repeated several times, so the final distillate is much more pure than that resulting from the simple distillation procedure. Additionally, in this lab both microscale and macroscale distillations were performed. The difference between these is that microscale is performed on small amounts of mixture (about 5 ml), while macroscale is performed on large volumes. Here, both styles of distillation were performed on a mixture of cyclohexane and toluene. The results were examined by gas chromatography and analysis of change in temperature reliant upon volume of distillate collected. A note should be made here concerning azeotropes, liquid mixtures that do not form ideal solutions. Azeotropes form solutions that have boiling points either higher or lower than their pure liquid substances. An example can be seen in water and ethanol, which together have a

3 boiling point of 78.2° C, while separately, water and ethanol have boiling points of 100° C and 78.3° C, respectively. Procedure Microscale Distillation A microscale simple distillation apparatus was set up as shown in Figure 1. 2 ml each of cyclohexane and toluene were added to a roundbottom boiling flask in addition to a boiling chip. The flask was heated on an aluminum block placed upon the corner of a hot plate. The sample was heated until it began to boil and the distillation rate reach approximately 1 drop every 5 seconds. After the first 3 drops had distilled, the next 3 were collected in a vial for analysis by gas chromatography (GC). The distillation proceeded until approximately 3 ml of condensation was collected. Then, 3 final drops were sampled and sent for GC analysis. The temperature of the vapor was recorded every 2-3 drops over the course of the distillation. After the apparatus had cooled, a fractional column was added. This altered set up is shown in Figure 2. Fresh cyclohexane and toluene were added to the flask along with a new boiling chip. The same procedure as above was then performed with the fractional column in place. The early and late distillate samples were also submitted for GC analysis. A temperature versus time graph of both the simple and fractional distillations plotted on the same axes is shown in Graph 1. Macroscale Distillation A simple distillation apparatus was set up as shown in Figure 3 using a 100 ml round bottom boiling flask. 30 ml each of cyclohexane and toluene were added to the flask with a few boiling chips. This mixture was heated with a heating mantel until the condensation dropped at a regular rate of approximately 1 drop per second. This was collected in a graduated cylinder. After the first 3 drops distilled, the next 3 were collected for GC analysis. The temperature was recorded for every 2 ml of distillate. This experiment was run until 50 ml of distillate had been collected. At this point, 3 final drops were collected in a vial for analysis via GC. Once the apparatus had cooled, a fractional column was added. The cyclohexane and toluene distillate collected from the previous macroscale simple distillation was reused for the following experiment, while new boiling chips were added. The procedure was then conducted according to the same process outlined in the immediately preceding paragraph. Early and late samples were again collected for GC analysis. Again, the procedure was run until approximately 50 ml had been collected. Temperature vs. volume collected results for both simple and fractional macroscale distillations are shown in Graph 2.

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Figure 1. Simple Microscale Distillation Apparatus used to separate 4-mL mixture of 1:1 cyclohexane:toluene.

Figure 2. Fractional Microscale Distillation Apparatus used to separate 4-mL mixture of 1:1 cyclohexane:toluene. Aluminum foil was wrapped around the fractional column.

Figure 3. Simple Macroscale Distillation Apparatus used to separate 60-mL mixture of 1:1 cyclohexane:toluene.

5 Results and Discussion Shown below is Graph 1, a comparison of temperature of the vapor compared to the number of drops collected. As can be seen from the graph, though the simple distillation ended at a slightly higher temperature than the fractional distillation.

Temperature (ºC)

Graph 1: Microscale Distillation 93 91 89 87 85 83 81 79 77 75 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Drops Collected

Moving on to the macroscale distillation, shown in Graph 2, it can be seen that the fractional distillation shows a slightly more radical shift in temperatures during the middle period of the experiment, indicating a radical shift in composition of both the distillate and the stillboiling solution.

Graph 2: Macroscale Distillation Temperature (ºC)

110 105 100 95 90 85 80 75 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Volume Collected (ml) Simple

Fractional

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7 Below, in Table 1, is shown the percentages of each cyclohexane and toluene taken from the early and late samples using GC analysis. The range for the fraction distillation is shown as slightly smaller than the simple distillation. This is indicative of the effects the fractional column has on the process, resulting in a purer distillate at the early and late extremes of the process. Also, it can be seen from this table that the boiling point of cyclohexane is lower than that of toluene. This was confirmed in the literature, which listed the boiling point of cyclohexane as 81º C, whereas the value for toluene is 111º C. Table 1 Simple % Cyclohexane % Toluene

Early 70.84 29.13

Microscale Distillation Fractional Late Early Late 2.16 73.04 4.32 87.81 26.92 95.66

Finally, the GC results from the two macroscale distillations are shown in Table 2 below. This makes it extremely apparent that the fractional column adds greatly to producing a more pure distillate. This is trend is confirmed in both the graphs as well, which show a sharp shift in the temperature when compared to volume of distillate collected, indicating a radical shift in the composition of both the distillate and the liquid left in the flask.

Table 2

% Cyclohexane % Toluene

Macroscale Distillation Simple Fractional Early Late Early Late 73.89 10.03 84.46 3.17 26.06 89.95 15.47 96.81

Conclusion This experiment consisted of distilling a mixture containing equal halves of cyclohexane and toluene, both by macroscale and microscale distillation. In each of these two categories, both simple and fractional distillation was done. After collecting early and late samples during each distillation, it was found in all cases that fractional distillation is more accurate and efficient in separating cyclohexane and toluene. This was the result of the increased surface area provided by the fractional column, which allowed a greater number of liquid-gas phase changes as the vapor itself condensed and re-boiled several times as it moved up the column. Neither the micoscale nor macroscale distillation results indicated whether one was significantly better than the other at separating the two substances.

8 References Macroscale Distillation Apparatus. (2014). Image. Found on: www.ochem-meltingpod.wikispaces.com/Distillation+of+Acetone Microscale Distillation Apparatus. (2013). Image. Found on: www.geocities.ws/dcarrd2000/infroduction.1html Zubrick, J. W. (2008). The organic chem lab survival manual: A student’s guide to techniques. Danvers, MA: John Wiley & Sons, Inc.