Column chromatography is a larger scale of thin layer chromatography.

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Column chromatography is a larger scale of thin layer chromatography. In this case, the dye mixture- a two coloured compound- was added into the column. The separation of the two different colours began as a mobile phase- mixture of 50% ethanol and 50%water- was run through the stationary phase (alumina- Al2O3). The whole separation process depends on the polarity of the stationary phase, the mobile phase and the compounds composing the dye mixture.

The compounds have their own equilibrium between being adsorbed onto the alumina and being soluble in the water-ethanol mixture; the most soluble or least adsorbed compounds travel fast down the column and hence could be separated from the other coloured compound. This could be explained through intermolecular forces; the alumina will form more hydrogen bonds compared to Van der Waals forces with the strongly polar compound. The hydrogen bonds form between the “highly electronegative oxygen atoms in Alumina” and the hydrogen atoms in the compounds. Whereas, the less polar compound will dissolve more in the water-ethanol mixture; and form less hydrogen bonds with the alumina compared to the number of Van der Waals forces that will also form.

The compound which is adsorbed more will not travel as further as the compound with lower polarity. The compound with lower polarity will travel in the mobile phase, further down the column as it spends most of its time dissolved in the water-ethanol mixture than in being adsorbed by the alumina stationary phase.

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 The movement of the compound in the mobile phase through a column is called elution and the water-ethanol mobile phase is named eluent.

When it comes to a point where the least polar compound is separated and the most polar compound is left in the column; it will take a very long period of time to wash the most polar compound out of the column. In order to accomplish this at a faster rate, the mobile phase could be replaced with another eluent which has higher polarity. The greater attraction between a very polar eluent and the coloured compound will ...

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