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23 Nov 2019

Using Figure 5.6 and the explanation of how to read Figure 5.9 of your text, if your fractional distillation column is not well packed and only provides 2 theoretical plates (the equivalent of two simple distillations), what would be the boiling point of the distillate of your fractional distillation setup starting with a 0.95 mole fraction of water mixture?

Select one:

a. between 65-70 Â°C

b. between 80-90 Â°C

c. between 70-80 Â°C

d. between 90-100 Â°C

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2.) Refer to one of the BP-Composition curves for Cyclohexane - Toluene above. Starting with a mixture of 15% cyclohexane and 85% toluene, to produce distillate having a purity of greater than 90% cyclohexane, what is the minimum number of theoretical plates that a fractional distillation apparatus would need? Show a sketch of how you determined this.

3.) How many simple distillations would produce the same result in Question 2.)?

A mixture of 10 mL of benzene (MW= 78.11 g/mol, d=0.88 g/mL) and 50 mL of p-xylene (MW=106.17 g/mol, d=0.86 g/mL) is distilled.

Calculate the mole percent of each component, and using these mole percents and the figure below, answer the following questions:

1) What is the initial boiling point of this mixture?

2) What is the composition of the vapor in equilibrium with this liquid? What is the composition of the initial condensate from simple distillation?

3) Instead of simple distillation, you set up a fractional distillation. Assuming three threoretical plates, what is the composition of the first fration collected?

Introduction:

This week you will be learning another important technique in the organic chemistry laboratory â distillation. Distillation uses the difference in boiling point of two miscible liquids and thus separates compounds by exploiting different volatilities. While often used in the chemical laboratory, the process itself is a physical separation that uses phase changes (gas / liquid) to effect either complete or partial separation. In the simplest form distillation consists of 2 phase changes, evaporation followed by one condensation step (simple distillation), whereas fractional distillation repeats the process of evaporation followed by condensation inside a distillation column. Besides the physical separation, distillation also provides you with a measure of purity as you will be able to constantly monitor the boiling point of the distillate and compare it to literature values. To corroborate your results of this weekâs experiment, you will additionally perform gas chromatography of the distillates that you obtain. Gas chromatography allows for the analytical separation of compounds based on their boiling point and will serve in your experiment as a basis for determining the purity of the distillate. You will be given a mixture of 2 alcohols and will perform either a simple or a fractional distillation on it. You will then analyze your distillates using gas chromatography, determine the percent composition and thus the success of your distillation.

Questions for the experiment and the analysis:

1) Using the provided GC sample runs including integrations of each of the alcohol mixtures BEFORE the distillation, determine the percent of each of the alcohols in the sample

2) Obtain and tabulate the results of the other five procedures carried by the class

3) For all six procedures, compare the boiling ranges throughout the distillation, as well as the percent composition of the first and last collected fraction

4) Using this data, determine which distillations were successful in separating the two alcohols and which ones were unsuccessful. Make sure to compare this with the theory of distillation and the performance you should expect for simple vs fractional distillation

5) Based on those results, what factor seemingly determines whether a good separation is possible through distillation?

Lab Results:

Impure Methanol:Propanol

Peak 1: Retention Time (min)= 1.290, Area= 19.56, %Area= 7.25

Peak 2: Retention Time (min)= 2.140, Area= 250.19, %Area=92.75

Impure Methanol:Ethanol

Peak 1: Retention Time (min)= 1.265, Area= -4.83, %Area= 14.00

Peak 2: Retention Time (min)= 1.405, Area= -29.67, %Area= 86.00

Impure Methanol:Butanol

Peak 1: Retention Time (min)= 1.305, Area= 30.79, %Area= 3.41

Peak 2: Retention Time (min)= 3.690, Area= 872.07, %Area= 96.59

5 Procedures Carried by the Class Results:

Student 1:

Methanol:Ethanol- first test tube (simple distillation)

Peak 1: Retention Time (min)= 0.860, Area= 0.89, %Area= 4.42

Peak 2: Retention Time (min)= 1.035, Area= 16.92, %Area= 84.16

Peak 3: Retention Time (min)= 1.110, Area= 2.29, %Area= 11.41

Methanol:Ethanol- last test tube (simple distillation)

Peak 1: Retention Time (min)= 1.195, Area= 198.76, %Area= 100.00

Student 2:

Methanol:Ethanol- first test tube (simple distillation)

Peak 1: Retention Time (min)= 1.755, Area= 12.87, %Area= 100.00

Methanol:Ethanol- last test tube (simple distillation)

Peak 1: Retention Time (min)= 1.615, Area= 44.11, %Area= 100.00

Student 3:

Methanol:Ethanol- first test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.555, Area= 11.11, %Area= 98.84

Peak 2: Retention Time (min)= 1.690, Area= 0.13, %Area= 1.16

Methanol:Ethanol- last test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.496, Area= -0.19, %Area= -1.95

Peak 2: Retention Time (min)= 1.585, Area= 10.07, %Area= 101.95

Student 4:

Methanol:Ethanol- first test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.465, Area= 67.70, %Area= 100.00

Methanol:Ethanol- last test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.710, Area= 196.05, %Area= 100.00

Student 5:

Methanol:Propanol- first test tube (simple distillation)

Peak 1: Retention Time (min)= 1.840, Area= 193.42, %Area= 93.47

Peak 2: Retention Time (min)= 2.425, Area= 13.51, %Area= 6.53

Methanol:Propanol- last test tube (simple distillation)

Peak 1: Retention Time (min)= 2.520, Area= 830.06, %Area= 100.00

Student 6: (My Experiment)

Methanol:Propanol- first test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.640, Area= 105.78, %Area= 94.71

Peak 2: Retention Time (min)= 2.205, Area= 5.90, %Area= 5.29

Methanol:Propanol- last test tube (fractional distillation)

Peak 1: Retention Time (min)= 2.410, Area= 790.25, %Area= 100.00

Student 7:

Methanol:Propanol- first test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.685, Area= 42.94, %Area= 100.00

Methanol:Propanol- last test tube (fractional distillation)

(no peak)

Student 8:

Methanol:Butanol- first test tube (simple distillation)

(no peak)

Methanol:Butanol- last test tube (simple distillation)

(no peak)

Student 9:

Methanol:Butanol- first test tube (simple distillation)

Peak 1: Retention Time (min)= 1.090, Area= 272.21, %Area= 84.34

Peak 2: Retention Time (min)= 2.420, Area= 50.53, %Area= 15.66

Methanol:Butanol- last test tube (simple distillation)

Peak 1: Retention Time (min)= 3.210, Area= 1421.66, %Area= 100.00

Student 10:

Methanol:Butanol- first test tube (fractional distillation)

Peak 1: Retention Time (min)= 1.090, Area= 1.92, %Area= 0.20

Peak 2: Retention Time (min)= 2.070, Area= 2.23, %Area= 0.24

Peak 3: Retention Time (min)= 3.010, Area= 932.02, %Area= 99.56

Methanol:Butanol- last test tube (fractional distillation)

Peak 1: Retention Time (min)= 0.906, Area= 0.25, %Area= 0.13

Peak 2: Retention Time (min)= 1.040, Area= 144.64, %Area= 76.40

Peak 3: Retention Time (min)= 2.435, Area= 44.44, %Area= 23.47

My Boiling Points for Methanol:Propanol (fractional distillation)
1/2 mL of Distillate	test tube 1	tube 2	tube 3	tube 4	tube 5	tube 6	tube 7
0.5	69	74	76	79	81	84	90
1	73	75	77	79	82	85	91
1.5	75	75	78	79	82	86	92
2	74	75	78	80	83	87	92
2.5	74	75	78	81	84	88	93
3	75	75	78.5	81	84	90	74

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