6. Suppose you are cleaning out a stockroom with hundreds of bottles of chemical

Question

6. Suppose you are cleaning out a stockroom with hundreds of bottles of chemicals. You find two unlabeled bottles, and when you run both compounds on a TLC plate (same plate, same conditions), they have the same Rf value. Are they the same compound? Explain. (No more than 2–3 sentences)

7. How will the Rf value of a compound be affected if the developing solvent is allowed to run off the top of the TLC plate (i.e., the TLC plate is allowed to remain in the developing chamber after the solvent front has reached the top of the plate)? Explain your answer.

Explanation / Answer

6.If two compounds have same Rf value under same condition ,that doesn't mean that the two compounds are identical.Two compounds may or may not be identical.Rf is a measure of polarity.Many compounds have similar polarity.

7.When the eluent reaches the top of the plate it will start to evaporate.But capillary action will continue to draw up the eluent and the sample.Now in this condition it is not possible to accurately determine the distance traveled by the developing sample.we can measure the distance from origin to top of the plate.So the distance traveled by the developing solvent will be small and distance traveled by the sample will be too large.So the calculated Rf value will be greater than the actual value and it will not be accurate.

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