Chapter 15, Problem 1Q

Interpretation Introduction

Interpretation:

The reason for the low mobility of chlorophylls on column chromatography is to be determined.

Concept introduction:

Column chromatography is a technique in analytical chemistry that is used to separate a single compound from a mixture of components.

Answer to Problem 1Q

Chlorophylls are polar compounds. Therefore, chlorophylls tend to attach with the silica in the column which are also polar. Carotene are less polar compounds which easily elute through the column.

Explanation of Solution

In column chromatography, a long column is used that is packed with a polar compound such as silica or alumina. This compound acts as the stationary phase of the process.Silica (or alumina) is a polar compound. Usually, polar compound interact with other polar compounds due to attractions between them. When sample is passed which contains both silica and alumina through this column, chlorophyll tends to retain in the column while carotene elutes first. This is mainly because chlorophyll is a polar compound that retains in the column. Carotene is a less polar compound that elutes from the column.

The $R_f$ value in chromatography is the ratio between the distance moved by the solute and distance moved by the solvent. The $R_f$ value for chlorophyll is lower than the $R_f$ value of carotene because the movement of chlorophyll is very little compared to carotene.

Conclusion

Chlorophyll is a polar compound while carotene is a less polar compound. In the presence of a polar stationary phase, chlorophyll moves slower than carotene because chlorophyll attracts to the polar stationary phase.