Chromatography question

[khalil]

 Somebody please help me with this question

From previous results, a student knows the R(f) values for 2 dyes that she wishes to investigate are 0.72 and 0.80.
It is proposed that the dyes be run on the same peice of paper and, for various reasons, that the spots should have  a seperation of at least 1 cm at the end of the procedure.
What is the minumum height of the chromatography paper that she should use in the experiment.

thanks

[shinny]

Well you know that the minimum height of the paper is equal to the minimum distance travelled by the solvent front, as the solvent front isn't allowed to 'fall off' the edge of the paper. Also, because the values are given by , then the distance between the two components will be % of the length of the paper. For this to be equal to at least 1cm, then 1cm=8%. Therefore, the paper must be at least 12.5 cm long. Then of course, you have to account for the length that is submerged by the solvent and the little 'run up' space, but I don't recall there being any standard height for that, so I'll assume that the question doesn't take that into account.

[khalil]

thanks man i can alwys rely on u