Question

What is the principle of paper chromatography( also thin layer chromatography) when a more polar solvent is added, the one with higher Rf value is more polar or less polar?

Answer 1

less polar i read somewhere dunno d reason but the point is higher the Rf less it ll be polar and vice versa ok

Answer 2

that's what my book has written but my classmate has different interpretation which seems to be quite sensible

Answer 3

can u tell me ur doubt

Answer 4

so one of the interpretations is that the pigment is absorbed by the solvent, so it would not travel for long distance. If the solvent is more polar, the one with smaller Rf value would be more polar pigment.

The second interpretation is that the pigment is absorbed by the solvent,as the solvent travels on the paper, the pigment would also follow the solvent and move up. For more polar solvent , the pigment with higher Rf would be more polar

Very confusing :S

Answer 5

i can also give u a guess but not sure but i ll put my view too..

Answer 6

as we know pigments absorbed by solvent and when the solvent moves it recieves diff freequencies of light by moving so i dont get point to say more polar more Rf

Answer 7

so more polar, less Rf?

Answer 8

yea keep this thing in ur mind :)

Answer 9

then how to determine the solvent is more polar? if i use ethanol + water as the solvent what should it be?

Answer 10

no idea sorry i m erching m1 here who know di to clear all ur doubts

Answer 11

hmm.. thanks..

Answer 12

Paper chromatography is an analytical chemistry technique for separating and identifying mixtures that are or can be colored, especially pigments. This can also be used in secondary or primary colors in ink experiments. This method has been largely replaced by thin layer chromatography, however it is still a powerful teaching tool. Two-way paper chromatography, also called two-dimensional chromatography, involves using two solvents and rotating the paper 90° in between. This is useful for separating complex mixtures of similar compounds, for example, amino acids......

Paper chromatography is one method for testing the purity of compounds and identifying substances. Paper chromatography is a useful technique because it is relatively quick and requires small quantities of material. Separations in paper chromatography involve the same principles as those in thin layer chromatography. In paper chromatography, like thin layer chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate readily according to how strongly they adsorb on the stationary phase versus how readily they dissolve in the mobile phase.
When a colored chemical sample is placed on a filter paper, the colors separate from the sample by placing one end of the paper in a solvent. The solvent diffuses up the paper, dissolving the various molecules in the sample according to the polarities of the molecules and the solvent. If the sample contains more than one color, that means it must have more than one kind of molecule. Because of the different chemical structures of each kind of molecule, the chances are very high that each molecule will have at least a slightly different polarity, giving each molecule a different solubility in the solvent. The unequal solubilities cause the various color molecules to leave solution at different places as the solvent continues to move up the paper. The more soluble a molecule is, the higher it will migrate up the paper. If a chemical is very nonpolar it will not dissolve at all in a very polar solvent. This is the same for a very polar chemical and a very nonpolar solvent....

Answer 13

we dont need the definition u have to clear the doubts which was raised above

Answer 14

Check this.
http://en.wikipedia.org/wiki/Paper_chromatography

Answer 15

doubts are raised only when definitions are not cleared...

Answer 16

Do u want some videos?

Answer 17

of what?

Answer 18

I mean paper chromatography?

Answer 19

ok well its better u guys convinced @Callisto as i have to go .. thnx to all of u :)

Answer 20

Welcome, but how to refer someone in response?

Answer 21

Hi @aadarsh - you use the '@' symbol and a list of people you've fanned should appear. Even if you haven't fanned them, if you type their username they will receive a ping, just like what @heena did here.

Great work on this by all of you btw, thanks for making OpenStudy a great place!

Answer 22

@cshalvey r u a professor?

Answer 23

Hi @vishal kothari - no, just a lowly OpenStudy employee ;).

Answer 24

kk

Answer 25

yeah got it. Cheers cshlavey!!!!! Tahnks a lot.

Answer 26

sorry, but can you guys explain it in a simpler way? Is more polar pigment have large Rf value for more polar solvent (given that the stationary phase is water, mobile phase is ethanol + water) ?
can you explain in the following steps:
yes / no --> principle
Second question, how can we determine what solvent to use each time? Thanks and sorry for bothering

Answer 27

u still didnt get dats bad well i ll ask ur doubt to my sir hope ll not get mey again den.. but need time ok

Answer 28

Waiting for the response of Heena didi!!!!!!!

Answer 29

well.. i get my answer.... my teacher said the paper was first 'dipped' to cellulose. Hence it contains a layer of water as the stationary phase. When the paper is added to the solvent+pigment, the more water-soluble pigment will be absorbed by the stationary phase. Then, as the less water soluble solvent moves up, the less water-soluble pigment also moves up. So the larger the Rf value, the less polar the solvent is. Hmm.. I hope you understand what I've said..

Answer 30

yup :) actaully my sir said till yet i didnt taught u so wait till dat time :'(

Answer 31

So is my teacher correct?

Answer 32

i dunno my teacher said u have to wait means approx 4mnths :(

Answer 33

by then my exam ends lol. Thanks anyway!

Answer 34

sorry (: