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

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BlackTom AI · Accepted Answer

Let’s break down the data given for the TLC results and then interpret what it means for polarity.
First, we calculate the Rf values using the formula: Rf = distance travelled by compound / distance travelled by solvent front.
For ρ-aminobenzoic acid (PABA): distance travelled = 2.1 cm, solvent front = 4.1 cm. So Rf(PABA) = 2.1 / 4.1 ≈ 0.512, which rounds to 0.51 to two significant figures.
For Benzocaine: distance travelled = 3.5 cm, solvent front = 4.1 cm. So Rf(Benzocaine) = 3.5 / 4.1 ≈ 0.854, which rounds to 0.85 to two significant figures.
Now, interpret what the Rf values say about polarity. In TLC with a given solvent system, compounds with higher Rf travel farther up the plate and are generally less polar (they interact less with the polar stationary phase). Conversely, lower Rf values indicate relatively more polar compounds that interact more with the stationary phase and travel less.
Comparing the two compounds, Benzocaine has the higher Rf (0.85) and thus is less polar than PABA, which has an Rf of 0.51.
Answering the multiple-choice prompt about which compound is less polar: Benzocaine is the less polar compound, since its higher Rf indicates weaker interaction with the polar stationary phase under the given solvent system.
Note: If you were to check the logic the other way, PABA with Rf ≈ 0.51 would be more polar than Benzocaine in this TLC setup, and the option stating Benzocaine is less polar is the correct choice.

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