Question textAn example of Thin Layer Chromatography (TLC) results:Solvent used in developing a TLC plate: 50:50 hexane : ethyl acetate.Calculate the Retention factor (Rf) value for each component (ρ-aminobenzoic acid (PABA) and Benzocaine) on the plate. (to 2 significant figures)Please refer to p.46 in the lab manual for more information.[table]
TLC results | Rf (retention factor) ρ-aminobenzoic acid (PABA):Distance travelled: 2.1 cmBenzocaine: Distance travelled: 3.5 cmSolvent front: Distance travelled: 4.1 cm | Rf (PABA)= Answer 1 Question 6
Rf (Benzocaine)= Answer 2 Question 6
[/table]Based on the information above, which compound is less polar? Answer 3 Question 6[select: , Benzocaine, PABA, Neither]

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BlackTom AI · Accepted Answer

The problem provides distances traveled on a TLC plate and asks for Rf values and which compound is less polar.
First, recall the formula for Retention factor: Rf = (Distance traveled by the substance) / (Distance traveled by the solvent front).
For PABA, the distance traveled is 2.1 cm, and the solvent front is 4.1 cm. Computing: Rf(PABA) = 2.1 / 4.1 ≈ 0.512, which rounds to 0.51 to 2 significant figures. This indicates a moderate mobility on the plate.
Next, for Benzocaine, the distance traveled is 3.5 cm with the same solvent front of 4.1 cm. Computing: Rf(Benzocaine) = 3.5 / 4.1 ≈ 0.8537, which rounds to 0.85 to 2 significant figures. This higher Rf means Benzocaine moved farther up the plate than PABA.
To determine which compound is less polar, remember that more nonpolar (less polar) compounds generally travel farther toward the solvent front in normal-phase TLC, giving a higher Rf value. Therefore, the compound with the higher Rf is the less polar.
Comparing the two Rf values: 0.51 (PABA) vs. 0.85 (Benzocaine), Benzocaine has the larger Rf and is thus less polar than PABA.
In summary, the calculated Rf values are: Rf(PABA) ≈ 0.51 and Rf(Benzocaine) ≈ 0.85. Based on these values, Benzocaine is the less polar compound.

MCD4400 - T3 - 2025 Prelab Quiz - Esterification - Benzocaine

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