Question

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1. What would happen if you used a water-soluble pen on the chromatography paper to mark your origin line? How would this affect the Re values? 2. A student accidently adds 17 ml of NaCl to their beaker rather than the 7 mL of NaCl they were suppose to add to their beaker. How might this mistake affect their chromatogram? Do you think they would be able to obtain any data? Briefly explain your answer. 10 3. Is it possible for an Rf value to be greater than 1.0? 4. Suppose you wanted to identify the dyes that are in a Sharpie pen. Sharpie pens are water- insoluble. How would you modify today's lab so that you could separate the dyes in a Sharpie pen?

Answer 1

1) If a water soluble pen is used to mark the original points on the chromatogram paper then it will interfere with the sample and will run on the chromatogram by interfering with the original sample spots, therefore pencil is used for marking.

2) Chromatography is used for separation of components, thus increase in the amount of NaCl (solute) added indicates that the solution has become concentrated which means that the amount of solution dropped on the chromatogram sheet for study contains more amount of solute particles per unit volume as compared to the expected one. As a result their will be no effect on the R_f value (because it totally depends upon the distance covered by solute and solvent molecules) and their is nothing to do with the concentration term for determining the R_f value.

3) The R_f value is defined as the ratio of the distance covered by solute to the distance covered by the solvent molecule. It can never be greater than one because a value greater than one is only possible if the solute molecule travels more distance compared to the solvent molecule which is not possible because the solute is dissolved in solvent so the distance covered by it (solvent) will always be maximum.

4) According to the principle like dissolves in like, the water insoluble sharpiro dyes can be separated using chromtography by dissolving them in non-polar solvents like benzene, toulene, etc., this is because they are non-polar in nature and thus are insoluble in polar solvents thereby can be easily dissolved in some polar solvents.