Expert: Dr. Henry Boyter, Jr. - 6/21/2004

Question
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Followup To
Question -
-My chemistry book says; "At the start of descending paper chromatography why must the spot of the dye be below the solvent (water) level" Please explain that if the spot of dye is below the water level than wont it dissolve in water to escape chromatography?Is it that i am understanding the statement below water level to be inside the water wrongly.Please explain where i am wrong.Or tell me what does below the solvent level in descending paper chromatography really means.Iam confused please tell me.Answer all my questions please.------------------------
Followup To
Question -In descending paper chromatography,the chromatogram is held vertically,and the spot of dye is drooped on the top of the chromatogram.-But at the beginning of the experiment,why must the spot of the dye be below than the water(solvent) level?your answer was perhaps more relevant to the ascending paper chromatography method in which the dye spot is above the solvent level so the dye should not dissolve in it and escape separation.Please answer my question related to descending paper chromatography method. THANKING YOU AGAIN.-----------------------
Followup To
Question - Sir, you did not understand the question.I asked why should the spot of dye be lower than water level in this case its likely to dissolve in water.Please answer it for God sake.
I have searched this question for many days. Still i could not get the answer."During descending paper chromatography why should the spot of the dye to be separated be lower than the water (solvent) level?
Answer -
So the dye doesn't dissove in the solvent instead of moving down the paper.
Answer -
That is the answer.  Maybe your use of the term descending paper chromatography is different than mine.  Describe the process in detail.
Answer -
It is still the same answer.  You want the spot to run down the paper so the mobile phase has to start above the spot.  If not, the spot will dissolve in the mobile phase and spread out in all four directions giving you movement in all four directions.

Answer
Last try.

The water is added to the top of a vertical piece of paper (several ways of doing this).  The spot is below the level of the water because the water runs DOWN the paper, so the spot has to be in front of the solvent front as it proceeds down the paper.