1. A mixture of benzyl alcohol, benzoic acid and benzene is spotted on a silica

Question

1. A mixture of benzyl alcohol, benzoic acid and benzene is spotted on a silica gel TLC plate and is developed in a mixture of 1:1 dichloromethance-methanol as the solvent. Predict the relative Rf values (retention values) for the three components in the sample (fastest to slowest).

Answer: Benzene, benzyl alcohol and benzoic acid (Highest to Lowest)

2. What would happen to the Rf values of the compounds in question 1 if you were to increase the relative concentration of the methanol in the solvent mixture?

Answer: As a solvent, methanol has a very high polarity. Hence, the more polar the solvent (the developing solvent) the farther the distance at which the solutes will travel. The solutes will have a great attractive to the developing solvent.

3. Which compound will elute first when a mixture of toluene and benzaldehyde is loaded on the silica gel column and hexane is used as the eluent?

Answer: Toluene is polar while benzaldehyde is non-polar. With hexane also being polar, I would assume that toluene would elute first from the mixture. The more polar the solvent... The higher the Rf value and the faster the movement up the TLC plate (The more polar the analyte, the more polar the eluent should be).

Explanation / Answer

1st and 2nd are correct. 3rs answer is also correct only differentiating polar and non polar part is wrong.

3rd answer:

Toluene is non polar while benzaldehyde is polar. With hexane is also non polar

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