1_which of the following solvents ,hexane,methylene chloride,acetone, or methano

Question

1_which of the following solvents ,hexane,methylene chloride,acetone, or methanol will give the best separation on a TLC plate of a mixure composed of the following :

a) benzophenone and benohydrol

b) iodobenzene and 4-ehtyltoluene

2- consider the follwoing errors that could occur when running TLC. Identify the couse of the problem and tell what should be done to correct the problem.

a) A two- component mixture containing 2-octene and 1,3-dimethylbenzene gave only one spot with an Rf value of 0.97. the solvent is acetone.

b) A mixture was placed on a TLC plate , but when the LTC plate was developed the solvent front had run off the top of the plate .

3- A colored mixtre was added to the top of a chromatography column. solvent was added immediately and the entire volume in the reservoir turned orange. No separation could be obtained. What went wrong ?

4- How might you monitor the progress of a column chromatography when the sample is colorless? suggest 2 methods..

Explanation / Answer

1. a) methylene chloride

b) hexane

2. a) Reason= more polar solvent will move all spot together and will give poor separation.

Correction= use less polar solvent methylene dichloride or use mixture of Hexane, Ethyl acetate

b) problem= if the TLC plate developed beyond Solvent front means Rf value will never be accurate.

Correction = Elute TLC plate 3/4 th of its total length.

3. Reason =Before packing into chromatographic column material must be made slurry and it should be completely dried.

Correction= dry the slurry completely and keep a cotton over it after added it in column

4. If the column in colourless use UV lamp to visualise spots.

Use staining solutions such as Ninhydrin, KMnO4 etc..

.

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