3. If the TLC plate development had stopped before the solvent front reached the top of…

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3. If the TLC plate development had stopped before the solvent front reached the top of…

3. If the TLC plate development had stopped before the solvent front reached the top of the TLC plate (i.e. maybe it reached the middle of the TLC plate when it was stopped, instead):

a) Would the Rf values have been affected? If so, how? If not, why not? Give a numerical example to support your answer.

b) Would the size of the spots have been affected? If so, how? If not, why not? (Hint: think about the diffusion of the spot on the TLC plate as it spends more time on the stationary phase. For example, what happens over time if you put a small drop of food coloring in water?)

4. What are the highest and lowest possible Rf values on a TLC plate?

5. Leaks from underground tanks spread gasoline and additives into the water supply chromatographically. The water carries them away as it moves through the soil. Among gasoline and the additives MTBE and ethanol, which would spread fastest? Which would spread slowest? Explain your answer in terms of intermolecular forces.

CH3(CH2)6CH3-Octane (one component of gasoline)

CH3CH2OH-Ethanol

CH3OC(CH3)3- MTBE

6. When a TLC separation is performed, it is typically done in sealed and a liner is sometimes used to help keep the air inside the TLC chamber saturated with the mobile phase solvent. If a TLC chamber is not saturated with the solvent in the air, how do you think the speed of development would have been affected? (Hint: how volatile is methylene chloride? Do you think it would say on the TLC plate if it was open to the air?)

7. If the distances had been measured in inches instead of mm:

a) Would the Rf values have been affected?

b) If so, how? If not, why not? Give a numerical example to support your answer.

8. If the solvent was allowed to reach the top of the TLC plate and not stpped until well after this happened:

a) Would the Rf values have been affected?

b) If so, how? If not, why not? (Hint: would the solvent keep traveling up the TLC plate? How does that affect the distance traveled of the compounds being separated?)

9. Does Rf have units? If so, what? If not, why not?

10. a) Ethyl acetate rises slower on a silica plate than methylene chloride. Explain why in terms of polarity.

b) How fast would water rise compared to ethyl acetate and methylene chloride.

11. A spot and its solvent front rise 1.3 cm and 6.4 cm, respectively.

a) What is the Rf value of the spot?

b) If the solvent front had risen 7.9 cm, how far would the spot have risen?

c) If the spot had risen 6.0 cm, how far would the solvent front have risen?

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