COLUMN CHROMATOGGRAPHY 1. When packing the column with the initial sand layer an

Question

COLUMN CHROMATOGGRAPHY

1. When packing the column with the initial sand layer and alumina layer, what technique should you employ to achieve a flat surface paalllel to the bench?

2.While TLC relies on capillary forces for moving the solvent, in column chromatography the eluent percolates by what force?

3. Why should you not let the column run dry during column chromatography?

4. A) In this experiment, you are isolating ferrocene and acetylferrocene on an alumina column. Which will elute from the column first and why?

B) How will you determine if the fractions you collect contain pure compound?

5. When using air-pressure to facilitate the solvent flow through the column, you should start with a very slow flow and gradually increase. Why?

6. If you are conducting a column chromatography experiment with colorless compounds, how would we locate the compounds?

7. Suppose you are given 150mg of an unknown compound mixture that contains three compouds and you are told to separate the compounds using column chromatography. How would you decide which solvent system to use.

Explanation / Answer

1. During packing of the column with the initial sand layer and alumina layer, the column can be packed in two ways either it can be done by solid packing or by the liquid slurry made by an appropriate solvent. In both the ways stationary phase is poured from the top of the column and slightly beaten by rubber pipe to pack it tightly for getting the better result. By this way, we can achieve a flat surface parallel to the bench.

2. In column chromatography, the eluent percolates by the force of gravity which pulls down the solvent used during the column and rate of eluent flow towards gravity will depend on the weight, density, and viscosity of the solvents. While TLC relies on capillary forces for moving the solvent upward against the force of gravity.

3. The column should not run dry during column chromatography because if it will happen the compound will come in contact with air which will affect the stability of the compound in addition with this one more this is there which is related to the stability and uniformity of the column. To provide uniform atmosphere and better separation we should avoid the column from being dry. Drying of the column may cause breaking of the column because of energy difference.

4. A) ferrocene will elute first because it is more nonpolar in comparison with the acetylferrocene.

B) The fractions you collect contain pure compound will be confirmed by the TLC analysis. if in TLC you are getting the single product spot its means compound is pure. Later the purity of the compound may be confirmed by the spectroscopic characterization.

5.

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