Question

On what basis, paper chromatography separates plant pigments
(A) The non polarity of solvents and pigments
(B) The polarity of paper
(C) The polarity of the pigments
(D) All of the above
(E) None of the above

Answer 1

Hint :Paper chromatography is a technique used to separate the different pigments present in the plant. Pigments are nothing but the chemical compounds which can reflect only a particular wavelength. This technique can differentiate the pigments based on shape, size, charge,solubility and adsorption. Here charge is also referred to as polarity.

Complete Step By Step Answer:
In this experiment, leaves are usually crushed with the help of acetone solution and later a little amount of this paste is applied on a filter paper strip using a capillary tube. The extract is applied in the mid section of the line which is drawn horizontally 2 to 3 cm from the tip. This is then placed in a chromatographic chamber where the ether acetone is used as solvent. We can notice that the solvent passes along the paper scattering various pigments to different distances. The movement of the pigments is attributed to its size, solubility,polarity etc. The acetone which is used here is a polar solvent whereas the ether is slightly polar. When coming to the plant pigments, chlorophyll and xanthophyll are polar and carotenes are non polar. The filter paper is also polar. Polar compounds will interact more with the paper travelling slowly whereas the non polar compounds interact more with the solvent and hence travel quickly. By the above explanation, we can conclude that the pigments separation can be attributed to the polarity of paper and pigments and also to the non polarity of solvents and pigments respectively.
So, the correct answer is D.

Note :
As I mentioned, non polar solvents interact with the solvent and move quickly, carotene being non polar is observed at the top whereas chlorophyll being more polar, is observed at the bottom of the paper. The differences in the polarity is due to unequal sharing of electrons.