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Separating Cyclohexane and Toluene by Distillation

Separating Cyclohexane and Toluene by Distillation

Aim:

The purpose of this experiment is to separate the miscible liquids, Toluene and Cyclohexane, by the process of fractional distillation and then compare the efficiency of this distillation process to the simple distillation data provided by the lab instructor.

Introduction and Theory:

Distillation is a common laboratory technique utilized to separate miscible liquids by taking advantage of the differences in their boiling points. When the most volatile substance’s boiling point is reached, the once liquid phase enters a gaseous phase and turns into vapor. This vapor then condenses to form the liquid phase once again. Moreover, there are two types of distillation – simple and fractional. These two techniques are very similar, but they do have minor differences. Fractional distillation for example, is assembled with a fractional column which assists in the re-condensation aspect of this process. Essentially, fractional distillation completes several simple distillations in one single apparatus.

In this experiment, the technique of fractional distillation is used to separate toluene and cyclohexane, two miscible liquids. Because cyclohexane is the more volatile substance, with a lower boiling point (80.74°C) than that of toluene (110.6°C), it is the substance that will first accumulate in the receiver – the graduated cylinder containing the distillate. We will then record the temperature as every 5mL of distillate accrues and analyze our results to properly understand the trend and patterns of fractional distillation data. After undergoing this experiment, we are then responsible for comparing the efficiencies of both simple distillation and fractional distillation.

Table of Physical Properties and Hazards:

Compound

Physical Properties

Hazards

Cyclohexane

(C6H12)

Molar mass: 84.16 g/mol

Melting point: 6.47°C

Boiling Point: 80.74°C

Physical state: Liquid

Cyclohexane vapor is irritating to the skin, eyes, and respiratory tract. This chemical is highly flammable and can react with other oxidizing materials. It should be used under a fume hood.

Toluene

(C7H8)

Molar mass: 92.14 g/mol

Melting point: -95°C

Boiling Point: 110.6°C

Physical state: Liquid

High concentrations of toluene exposure can lead to irritation of the eyes and nose, weakness, dizziness, and damage to the central nervous system, etc. It is a highly toxic and flammable chemical and should be utilized under the fume hood at all times.

Water

(H2O)

Molar mass: 18.02 g/mol

Melting point: 0°C

Boiling Point: 100°C

Physical State: Liquid

When heated, water should be handled with extreme care to prevent burns or other injuries. Mixtures with harmful chemicals/ and water can be dangerous and should be handled with care as well.

Procedure and Observations:

Separating Cyclohexane and Toluene by Distillation img1

Picture 1: Labeled picture displaying the equipment used to assemble a fractional distillation apparatus.

At the start of this experiment, the fractional distillation apparatus was constructed in the fume hood.  A pot, a distilling head, a condenser, an adapter, a receiver, and a fractional column placed between the pot and the distilling head were some of the many equipment that were used to build this apparatus. Once the apparatus was made, the condenser was then connected to a water tap with rubber tubing from within the fume hood to ensure the transfer of water – water would enter the condenser at the bottom and exit from the top.

Once the distillation apparatus was assembled, it was time to prepare the homogenous mixture of toluene and cyclohexane. Two boiling chips and 25 mL each of cyclohexane and toluene were placed into the pot. The water was turned on and the distillation apparatus was checked to ensure proper water flow. The mixture of cyclohexane and toluene was then heated to boiling and the condensation line was absorbed as it moved up the fractional column. When condensation reached the top of the column the temperature was reduced so that the condensation line remained slightly below the side arm of the distilling head. The column was then wrapped with aluminum foil to minimize possible temperature fluctuations during this process.

The temperature and heating rate were then adjusted so that a rate no greater than 1 drop per second was produced. The temperature was recorded when the first dropped was collected into the receiver (79°C). It was then recorded after every 5mL of distillate accumulated. The distillation was continued until the temperature reached 110°C. The simple distillation data was provided to the class by the lab instructor. The data for both simple and fractional distillation were graphed and efficiently compared.

Results:

In the experiment, the temperature was recorded after every 5mL, until 45mL of distillate accumulated in the receiver. A simple distillation was completed separately, and the temperature was recorded and provided by the lab instructor. This data, as well as the data collected in the fractional distillation experiment is shown in Table 1. To efficiently compare this data, a graph was constructed. In Graph 1, it is apparent that though the temperatures between simple and fractional distillation are similar, there are noticeable differences. Fractional distillation has a steeper increase from 20mL to 35mL and stabilizes more efficiently from 40mL to 45mL than simple distillation.

Table 1: Table displaying the temperatures (ºC) of both simple and fractional distillation after every 5mL of distillate accumulated in the receiver.

Volume (mL)

Simple Distillation Temperature (ºC)

Fractional Distillation Temperature (ºC)

5

81

79

10

83

81

15

84

83

20

85

85

25

86

88

30

87

93

35

91

103

40

97

105

45

98

105

Separating Cyclohexane and Toluene by Distillation img2

Graph 1: Line graph displaying the temperatures (ºC) of both simple (blue line) and fractional distillation (orange line) after every 5mL of distillate accumulated in the receiver.

Conclusion:

In the final analysis, through the process of fractional distillation, we were able to successful separate toluene and cyclohexane by taking advantage of their differences in boiling points. Because cyclohexane has a lower boiling point (80.74°C) than that of toluene (110.6°C) it was able to evaporate faster and thus collect in the receiver as the distillate. When graphed compared to simple distillation, it can be concluded that fractional distillation is far more efficient and results in better separation of the liquids. This is largely due to the fact that the volatile liquid distills, re-evaporates, and condenses again, leading to multiple distillations within one process. 

References:

“Toluene.” National Center for Biotechnology Information. PubChem Compound Database,

U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/toluene.

“UNITED STATES DEPARTMENT OF LABOR.” Occupational Safety and Health

Administration, www.osha.gov/SLTC/toluene/health_hazards.html.

“CDC - NIOSH Pocket Guide to Chemical Hazards - Cyclohexane.” Centers for Disease Control

and Prevention, Centers for Disease Control and Prevention,

www.cdc.gov/niosh/npg/npgd0163.html

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