ORGO LAB 8 - Weekly lab 8 PDF

Preview

Summary

Weekly lab 8...

Description

Expt 9.2; Column Chromatography of the fulorene-fluorenone mixture

Rebecca Gotthelf CHE210L Section A 11/9/17

I.

Abstract The objective of this experiment was to take a mixture and filtrate it to get crude fulorene and fluorenone to use and separate through column chromatography. The objective was met, as different fractions were collected, and then tested on chromatography paper to compare with the known samples of fluorene and flurenone, combine, dry, collect, and find a percent recovery. Overall, after the fractions, there was a 12% fluorene recovery, and 57% fluorenone recovery. II.

Introduction

1. Briefly describe the process of column chromatography. Why is it called “adsorption” chromatography. Make it clear in the discussion what the stationary and mobile phases are (CAREFUL, not were) in this lab and how they work together to effect separation. Column chromatography allows the isolation of the desired compounds from a mixture. It’s called absorption chromatography because the stationary phase is a solid absorbent, and that is what is placed in a column. The mobile phase is the liquid that is put at the top and then flow down the column, and in this lab, the mobile phase is solvent, and the absorbent phase is the alumina. When the mixture is loaded into the column, the molecules bind to the alumina, and the mobile phase molecules with interact with the liquid solvent, and go down the column. The polarity of the solvent will determine the speed and quality of separation. 2. Predict the order of elution of a mixture of cyclohexane (an alkane), butyl acetate (an ester), benzoic acid (a carboxylic acid), methyl t-butyl ether (an ether), and cyclohexanol (an alcohol) from an alumina column. 1. The cyclohexane 2. Methyl t-butyl ether 3. Butyl acetate 4. Cyclohexanol 5. Benzoic acid 3. What would be the expected result in this experiment if only 2% MTBE/ligroin (as opposed to 2% MTBE/ligroin followed by 100% MTBE) were used as the eluent in this experiment? Explain your answer. Separation would be extremely slow and not a lot of separation would occur, due to ligroin having low polarity, it would have a low solvent power. 4. Why are laboratory workers cautioned not to allow the liquid level in chromatography columns to drop below the top of the adsorbent? When the liquid level in chromatography columns drop below the top of the absorbent there will be cracks that form in the adsorbent, this would lead for the chromatography column to decrease its ability to properly perform the separation of the compounds in the mixture.

III. Experimental Section Procedure and Modifications: The procedure was taken from Williamson, pages 194-196, with modifications to the procedure. The modifications will be attached to the back of the lab report.

Reaction and Theoretical Yield Calculation:

Fluorene:

Fluorenone:

IV.

Results and Discussion:

Data: Initial mass (g) Collected mass (g) Fluorene .051g .006g 9-fluorenone .051g .029g Mass of alumina: 4.07g Mass of sand: .52g Mass of fluorine/9-fluorenone mixture: .051g Rf values: Slide Fluorenone Fluorene 2 3 6

Percent recovery 12% 57%

Rf value 1/5.2 2.5/5.2 2.5/5.2 2.5/5.2 1.5/5.2

Analysis: In this lab, fluorene and fluorenone were separated utilizing column chromatography. The fluorene and fluorenone mixture filtered through the column, and were put in different fractional vials, which were then tested on a tlc slate. Fluorene is less polar than fluorenone and is therefore the first product and is calculated in the first few fractions. The separation

was a success because after testing the knowns on the tlc slate, and then testing each separate fraction, the Rf values were nearly identical. This indicates that the mixture was successfully separated and was pure. V.

Works Cited: 1. Williamson, Kenneth L; Minard, Robert D. ; Masters, Katherine M. Macroscale and Microscale Organic Experiments, 6th ed., chapter 10, pages 194-196; Houghton Mifflin Co.: New York, 2013....