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.47 in the lab manual for more information. [table]
TLC results | Rf (retention factor) ρ-aminobenzoic acid (PABA):Distance travelled: 2.1 cm Benzocaine: Distance travelled: 3.5 cm Solvent 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? Multiple choice 1 Question 61. PABA2. Benzocaine3. NeitherMark 1.00 out of 1.00

Question

BlackTom AI · Accepted Answer

First, I will restate the problem details to establish the data we’re working with: distances travelled by the compounds are PABA = 2.1 cm, Benzocaine = 3.5 cm, and the solvent front distance = 4.1 cm. The TLC formula for the retention factor is Rf = (Distance travelled by the compound) / (Distance travelled by the solvent front).

Option-wise, there are no listed answer choices in the provided data, but the general question asks which compound is less polar based on the given TLC data. With TLC, a higher Rf value indicates less polarity (it travels farther with the solvent front, implying weaker interactions with the stationary phase).

Calculating Rf values:
- For ρ-aminobenzoic acid (PABA): Rf = 2.1 cm / 4.1 cm ≈ 0.512, which rounds to 0.51 to two significant figures.
- For Benzocaine: Rf = 3.5 cm / 4.1 cm ≈ 0.854, which rounds to 0.85 to two significant figures.

Comparing the two Rf values, Benzocaine has the higher Rf (0.85) than PABA (0.51). Since a higher Rf corresponds to lower polarity in this TLC setup, Benzocaine is the less polar compound.

If we were to map these to the implied multiple-choice options you described, the correct choice would be the one identifying Benzocaine as the less polar compound. The other option would be PABA, which, having the lower Rf, is comparatively more polar under these conditions. The “Neither” option would be incorrect since one compound clearly shows a higher Rf.

Summary of the key points:
- PABA Rf ≈ 0.51; Benzocaine Rf ≈ 0.85.
- Higher Rf → less polar under the given solvent system.
- Therefore, Benzocaine is the less polar compound in this context.

CHM1052 - MUM S2 2025 CHM1052 Ex 3 - Fischer esterification (Benzocaine) - Pre-lab exercise

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