A student used TLC the Lab to identify the presence of acetaminophen, acetylsali
ID: 977912 • Letter: A
Question
A student used TLC the Lab to identify the presence of acetaminophen, acetylsalicylic acids and caffeine in a sample. He correctly spotted each substance separately on the TLC He was able to see the different retention factor of each compound on the TLC but he realized that he has forgotten to label the spots on his plate After researching the chemical structures of the compounds he learned that acetaminophen has a Rf of 0.7 acetylsalicylic acid has a Rt of 0.2? and Caffeine has a Rt 0 4 From this information, student can conclude that on the TLC.Explanation / Answer
On TLC plate Retention Factor is defined as,
Rf = (Distance travelled by compound)/(Distance travelled by solvent front)
Here, the distance travelled by solvent front is constant (Denominator constant) hence Rf value will be more for the higher value of distance travelled by compound.
We are having Rf values as,
Rf (Acetominophene) = 0.7
Rf(Caffeine) = 0.4
Rf(Acetylsalicylic acid) = 0.2
It means of above compounds increasing order of the distance travelled by compound
On TLC will be,
Acetyl salicylic acid (Rf = 0.2) < Caffeine (Rf = 0.4) < Acetominophene (Rf= 0.7)
Hence on TLC plate shown,
Spot 1 = Acetyl salicylic acid.
Spot 2 = Caffeine
Spot 3 = Acetominophene
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