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Column chromatography lab ...

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XYZ Name Title of experiment: Column Chromatography. Completion of experiment: June 17, 2019

Date  report submitted: June 24, 2019

Objective:- To separate a mixture of ferrocene and acetylferrocene by column chromatography followed by the recrystallization of individual components . Introduction:- Column chromatography is one of the most useful methods for the separation and purification of both solids and liquids when carrying out small-scale experiments. In the present experiment it is typical: a reaction is carried out, it does not go to completion, and so column chromatography is used to separate the product from starting material, reagents, and byproducts. The theory of column chromatography is analogous to that of thin layer chromatography. The most common adsorbents—silica gel and alumina—are the same ones used in TLC. The sample is dissolved in a small quantity of solvent (the eluent) and applied to the top of the column. The eluent, instead of rising by capillary action up a thin layer, flows down through the column filled with the adsorbent. Just as in TLC, there is an equilibrium established between the solute adsorbed on the silica gel or alumina and the eluting solvent flowing down through the column. Under some conditions the solute may be partitioning between an absorbed solvent and the elution solvent; the partition coefficient, just as in the extraction process, determines the efficiency of separation in chromatography. The partition coefficient is determined by the solubility of the solute in the two phases, as was discussed in the extraction experiment. Three mutual interactions must be considered in column chromatography: the polarity of the sample, the polarity of the eluting solvent, and the activity of the adsorbent. Materials:Name of compounds

Molecular weight

MP/BP (℃)

Density (g/mL)

Alumina

101.96 g/mol

BP= 2977

3.95

Ferrocene

186.04 g/mol

MP=172-174

1.11

Acetylferrocene

228.08 g/ mol

MP= 85-86

1.014

Procedure:- A microscale column was used for measuring quantities of alumina and hexane. Alumina was filled upto about ¾ length of the column and evacuated in a clean 30-mL beaker.This beaker was covered when not in use to avoid air contamination. The beaker was washed right away using acetone and dumped into organic waste. Any beakers or flasks used for this mixture were cleaned in the same way. The column was filled with hexane up to half its length and the apparatus was assembled as described by the lab manual (page no. 194). Small amounts of powdered alumina were added to the column through a funnel while gently tapping the sides of the column with a pencil. The column was packed until the packing settles to a minimum height. The solvent was allowed to drain to about 5 mm above the top surface of the absorbent. A protective layer of sand was added to the top. In a small beaker, a dry slurry of 90 mg of a 50:50 mixture of acetylferrocene and ferrocene absorbed onto 300 mg of alumina was prepared. This mixture was transferred to the top of the column using a plastic funnel. Hexane was added to the top of the column and the valve was opened for eluting the two compounds. The first to be eluted, ferrocene, was seen as a yellow band and collected in 10-mL erlenmeyer flask. The elution was observed as the orange band in the column started moving towards the bottom through the alumina. Drops of ferrocene left behind at the tip of the stopcock were washed off with hexane. Clear, eluent drops were collected in a separate 30- mL beaker. Without allowing the column to run dry, a 50:50 mixture of hexane and t-butyl methyl ether (MTBE) was added to the top of the column. As soon as orange drops were observed, they were collected in a tared,10-mL beaker. Orange drops signified the presence of acetylferrocene, the second substance to be eluted. The elution was observed as the orange layer stopped moving and eventually the adsorbent started turning clearer. Drops of acetylferrocene left at the tip of the stopcock were washed off with hexane and MTBE mixture. Two solutions were obtained one containing ferrocene (yellow solution) and the other containing acetylferrocene (orange solution). Solvents were evaporated from the solutions by blowing a gentle stream of air using a pasteur pipette. After the solvents were completely evaporated, two powders (orange and yellow) were obtained. These powders were dissolved in minimal amount of hot hexane and allowed to cool to room temperature.The solutes were recrystallized by placing the beakers in a container

filled with ice. The crystals were filtered out using vacuum filtration and the beakers were rinsed with ice-cold hexane. The crystals were then weighed and identified using their melting points. Results:Name Of the Compound.

Ferrocene

Acetylferrocene

Trial 1

Trial 2

Trial 1

Trial 2

Grams Used

0.0471g

0.05g

0.0471g

0.05g

Mass of the flask

23.929g

23.75g

28.393g

28.23 g

Mass of the flask and compound

23.976g

23.793g

28.457g

28.26 g

Mass of the compound

0.047g

0.043

0.064g

0.03g

% recovery

99.7%

86%

135%

60%

Grams Used Of a Mixture For trail 1 =0.0943g Since it was a 50:50 mixture Grams used for A= Total /2=0.0471 Mass of the Compound = Mass of the flask and compound - Mass of the flask = 23.976g - 23.929g= 0.0471g % recovery = (Grams obtained / Grams Used) * 100 = (0.0470/0.0471)*100 = 99.7% Discussion: In this lab column chromatography technique was used to separate the pure compound from impurity of mixture based on their polarity or solubility. The mass of the pure ferrocene was found to be 0.047g and 0.043g respectively in trail 1 and 2. The mass of pure acetylferrocene was found to be 0.064g and 0.03g. The calculated percent yield for the acetylferrocene in trial 1 was 135%, which is statistically impossible because this means that matter was somehow created. Reasoning for the high yield could be that the products were not dried properly following filtration or that there were impurities in the product because it was not filtered for

long enough. Those impurities added weight to the product and caused the unrealistically high yield. Conclusion: The purpose of this experiment was to use the technique of column chromatography to find the mass of the pure Solid Compound from a 50:50 mixture. The percent yield for Ferrocene was 99.7% and 86% while the percent Yield for acetylferrocene was 135% and 60%. There was a high percent yield for acetylferrocene was due to sources of error....