1. Assign the relative Rf values you would expect for the standard compounds (ib

Question

1. Assign the relative Rf values you would expect for the standard compounds (ibuprofen, acetaminophen, aspirin, and caffeine) if they were all run on the same TLC plate in an appropriate solvent. Rank from higest to lowest.

Consider the image of the three TLC plates above. These TLC plates show the same compounds (A and B) run in three different solvents (Mixture 1, Mixture 2. and Mixture 3). The baseline is shown as a red line, and the solvent front as a blue line. Complete the sentences below based on the images of these TLC plates. The best solvent mixture for separating a mixture of A and B would be is too polar, and the compounds do not to be separated efficiently. is not polar enough, and the compounds do not to be separated efficiently.

Explanation / Answer

1)

we know that

higher the polarity of the compunds , higher the values

so

the ranking for the Rf values of the compounds is

higher Ibuprofen > Aspirin > Acetaminophen > Caffeine lower

2)

if the Rf value is in between 0.3 and 0.7 , then it is a good solvent mixture

looking at the three given mixtures

the Rf value of mixture 1 is in between 0.3 and 0.7

the Rf values of mixture2 is close to 0.9

the Rf values of mixture 3 is close to 0.1

So

the best solvent mixture for separating A and B would be mixture 1

now

we know that

more the polarity, larger the rf value , larger the distance it travels

So

solvent mixture 2 travels a larger distance and reaches the solvent front

So solvent mixture 2 is too polar and the compounds do not interact with the solvent enough

also

solvent mixture 3 does not travel and remains at the baseline

So solvent mixture 3 is not polar enough and the compunds do not interact with the plate enough

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