Dehydration and Gas Chromatography PDF

Preview

Summary

Lab...

Description

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

Purpose The purpose of this lab is to use fractional distillation, extraction, and gas Chromatography to separate a mixture minimizing mechanical losses although it is not possible to yield the entire components.

Introduction By definition, the word chromatography means the graphing of color. It was originated back in 1903 by a Russian botanist, who extracted color from green leaves and washed his extraction with petroleum ether and other compounds. All the pigments became separated as it was put in a chalk-filled tube and distinct color was observed. Currently, chromatography is still being used but mostly for colorless compounds as it allows them to be separated even if the quantity is small; and it is also the first technique for separation and analysis. There are two phases in the most common form of chromatography: mobile and nonmobile. Just like the name said, the mobile phase is usually liquid, or gas and the stationary phase is usually solid or liquid. Using the theory of migration, it is the passage of a substance from one phase to another back and forth. It is expressed by the distribution of ratio K, defined as followed: K=

ts tm

Where ts express the time spent in stationary phase and tm expresses the time spent in mobile phase. Thin Layer Chromatography (TLC), column chromatography, High Performance Liquid Chromatography (HPLC), Gas-liquid Chromatography (GC), ion exchange - are different type of Chromatography that are widely used and are a physical method of separation. In organic chemistry, TLC, GC, HPLC and Column chromatography are thus far the most practiced and important techniques. TLC and Column chromatography are known as adsorption chromatography and GC is known as Gas chromatography. The type of chromatography that is performed on substances is based on how the volatility of the substance can be separated. If the mixture of the substances is non-volatile, the first two techniques, TLC and Column chromatography are used. On the other hand, if it is volatile, the gas chromatography is used. Gas Chromatography, also known as vapor chromatography, is a useful method that can not only be applied to chemistry but other science. Although it is somewhat similar to both TLC

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

and Column Chromatography, there are some differences such as the fact that the stationary phase in GC is composed of a nonvolatile liquid or solid for example silicone or hydrocarbon grease, which can be used as a coat on an non moving powdered support material for example a crushed firebrick or diatomaceous earth. Another difference is that the mobile phase also is an inert gas; usually nitrogen or helium. The absorption of the compounds at the stationary phase and the relative vapor pressure are two things that determine how soluble the components in the mixture are in the moving gas phase. In Gas Chromatography, the polarity or non-polarity of the elements in the mobile phase are not a factor in the separation of the mixture but temperature on the other hand is. To use GC in a lab, the compounds that are being used need to have a vapor pressure less than 1 mm and a temperature no more than 300 ℃ giving that both compounds are still stable. Gas Chromatography is considered being more effective way to separate a mixture than distillation because anything that can be distilled at a pressure as low as 0.01 mm can also be done by gas Chromatography. Even if a mixture has compounds with two different boiling point can be separated using GC. It can also be used to separate a very small or a very large sample size. In Gas chromatography, the component is heated where it is vaporized and carried through the column where later it is turned into liquid to be collected later. The retention time of an experiment is the time before the peak happen. In this lab, gas chromatography will be used to figure out if the compound has a specific pressure and other properties that makes them separable while dehydration will help figuring out the experimental losses and some error that might have occurred previously.

Mechanism:

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

Procedure For this experiment, the materials that were used were: 

Fractional Distillation Apparatus



Column



Heating mantle



2-methylcyclohexane



Flasks



Boiling chips



10ml 2-methylcyclohexanol



Calcium chloride



3mL Phosphoric acid



NaOH

To start the experiment

-

Reactant was combined in a round bottom flask.

-

About 10 mL of 2-methylcyclohexane and 3 mL of 85% of Phosphoric acid was added into that flask.

-

Boiling chips was added, and everything was sealed and secured

-

The mixture was slowly heated up until it until it started to boil

-

The vapor started to fill up the column and everything will be collected into the other flask

-

The collected substance was added to a separated funnel

-

The flask was wash with some water and added to the separated funnel

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

-

More water was then added to the separated funnel

-

The funnel was shacked for 20 second

-

Layer were formed: organic and inorganic. Organic layer was on the bottom and Organic on top

-

The PH of the component was checked to make sure that it is not acidic

-

The solution was than washed with 2 ml of NaOH to make sure that all acidic remaining were washed away.

-

The bottom layer was then taken out.

-

Calcium Chloride was added to a flask

-

The purified compound on the flannel was added to that flask and shacked.

-

The liquid was then poured out in a different flask and weighted.

-

Sample was then run through the gas Chromatography.

Table of Physical Constants

C7H14O

Meltin g point (℃) 114.1855 -9.5℃

Boiling Density point (℃) 0.93 165166 ℃

Phosphoric acid

H3PO4

97.9

42℃

158 ℃

1.99g/cm3

Soluble in water and Alcohol

Sodium Hydroxide

NaOH

39.97

318 ℃

1388 ℃

2.12 g/cm3

Soluble in water, ethanol, methanol

Water

H2O

18.01

0℃

100℃

997 kg/m3

Soluble in ethanol, methanol, acetone

Calcium Chloride

CaCl2

110.98

772℃

1935 ℃

2.15g/cm3

Soluble in water, Acetic acid

1methylcyclohexene

C7H12

96.17

105.9 ℃

0.811g/mL Soluble in 25℃ water

3methylcyclohexene

C7H12

96.17

Name

Chemica l formula

2methylcyclohexanol

MW g/mol

Solubility

Poor solubility in water

0.811g/mL Soluble in 25℃ water 105.9 ℃

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

Results

Figure 1: this picture shows the results of the Chromatogram showing two peaks one of each component that was in the mixture.

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

Calculations

Figure 2: this picture contains all the calculations: area of both peaks and the percentage for each of them.

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

Discussion In this lab, gas chromatography and dehydration were applied as a way to separate a mixture and it was successful. As shown in picture 1, the two substances had the same peak which implies that there was the same amount of compounds of each of them in the lab but also that they share somewhat similar properties. Although they have some similarities, peak B was favored in GC which makes it the major product while peak a was the minor. In calculations, both areas, peaks and yield were calculated as a way to explain what happened in the experiment. It was found that our experiment was successful. The total of the peak for both peaks is equal to 100%, which suggested that our experiment was perfect, and it is somehow impossible to have a perfect experiment. Therefore, there might have been some calculations errors based on the height and the width, which means that the area might be wrong. Some sources of error for this experiment could be impurities from unclean glass; inaccurate measurement or readings of the substance collected, which means that it could be more or less than what we actually have noted.

Post Lab question 1- Why is it necessary to wash the crude methylcyclohexenes with aqueous sodium bicarbonate solution? -

One reason to wash the crude methylcyclohexene with aqueous sodium bicarbonate is to take out any acidic remaining or any byproducts

2- List the manipulations where mechanical loss of product could have occurred. -

Mechanical loss could have occurred when the components were transferred from one flask to another; or at the beginning when the component was being collected and filtered.

3- Identities of the components in a mixture may be determined by a technique called Spiking. Suppose you had run a gas chromatogram on your product and had then deliberately added a drop of a known sample of 3-methylcyclohexene to a drop of your product. What would you expect the new chromatogram to show you? -

Gas Chromatography will not say what kind of mixture it is but only the amount. If for example in this lab we have two peaks and let’s say that they are a 10:1 ratio. After adding the drops of 3-methylcyclohexene we run it and the new ration is 3:1, which is less than 10:1, it can be concluded that 3-methylcyclohexene was the minor component.

Erma Despierre

CHM2210L Dehydration and Gas Chromatography

10/26/2020

On the other hand, if it is more than 10:1 ratio. Let’s say that it is 20:1 or 30:1 then it can be concluded that 3-methylcyclohexene was the major product in the main sample. So, the new chromatogram will show which one is the major or which one is the minor. 4- Do you consider this a good preparative procedure for making 3-methylcyclohexene? Why? -

I do not consider this to be a good preparative procedure for making 3methylcyclohexene because it would probably make more than one product if it was to do through the dehydration process and the products would be less and high substitute alkene. 3-methylcyclohexane is the minor product that was formed.

Work Cited Keller, Leonard. Organic Chemistry I &II Forth Edition. Miami, 2014. PubChem Docs. n.d. October 2020. https://pubchemblog.ncbi.nlm.nih.gov/....