---
title: "A student uses thin-layer chromatography to compare three neutral analytes, \\(P\\), \\(Q\\), and \\(R\\), that are similar in size and differ primarily in molecular polarity. Separate plates coated with a polar silica-gel stationary phase are developed using the mobile phases shown in the table. Development is stopped at different times, so the solvent-front distances differ.  | Mobile phase | Dielectric constant, \\(\\varepsilon_r\\) | Solvent-front distance \\((\\text{cm})\\) | Distance traveled by \\(P\\) \\((\\text{cm})\\) | Distance traveled by \\(Q\\) \\((\\text{cm})\\) | Distance traveled by \\(R\\) \\((\\text{cm})\\) | |—|—:|—:|—:|—:|—:| | Hexane, \\(\\text{C}_6\\text{H}_{14}\\) | \\(1.9\\) | \\(8.0\\) | \\(6.4\\) | \\(3.2\\) | \\(1.6\\) | | Ethyl acetate, \\(\\text{CH}_3\\text{COOCH}_2\\text{CH}_3\\) | \\(6.0\\) | \\(5.0\\) | \\(4.5\\) | \\(3.5\\) | \\(2.0\\) |  The retention factor is defined as \\[ R_f=\\dfrac{\\text{distance traveled by analyte}}{\\text{distance traveled by solvent front}} \\]  Which choice best identifies the most polar analyte and explains the effect of replacing hexane with ethyl acetate?"
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url: "https://nerd-notes.com/ubq/120042/"
date_modified: "2026-08-21T08:40:55+00:00"
---

# A student uses thin-layer chromatography to compare three neutral analytes, \(P\), \(Q\), and \(R\), that are similar in size and differ primarily in molecular polarity. Separate plates coated with a polar silica-gel stationary phase are developed using the mobile phases shown in the table. Development is stopped at different times, so the solvent-front distances differ.

| Mobile phase | Dielectric constant, \(\varepsilon_r\) | Solvent-front distance \((\text{cm})\) | Distance traveled by \(P\) \((\text{cm})\) | Distance traveled by \(Q\) \((\text{cm})\) | Distance traveled by \(R\) \((\text{cm})\) |
|—|—:|—:|—:|—:|—:|
| Hexane, \(\text{C}_6\text{H}_{14}\) | \(1.9\) | \(8.0\) | \(6.4\) | \(3.2\) | \(1.6\) |
| Ethyl acetate, \(\text{CH}_3\text{COOCH}_2\text{CH}_3\) | \(6.0\) | \(5.0\) | \(4.5\) | \(3.5\) | \(2.0\) |

The retention factor is defined as
\[
R_f=\dfrac{\text{distance traveled by analyte}}{\text{distance traveled by solvent front}}
\]

Which choice best identifies the most polar analyte and explains the effect of replacing hexane with ethyl acetate?

A student uses thin-layer chromatography to compare three neutral analytes, \(P\), \(Q\), and \(R\), that are similar in size and differ primarily in molecular polarity. Separate plates coated with a polar silica-gel stationary phase are developed using the mobile phases shown in the table. Development is stopped at different times, so the solvent-front distances differ.

| Mobile phase | Dielectric constant, \(\varepsilon_r\) | Solvent-front distance \((\text{cm})\) | Distance traveled by \(P\) \((\text{cm})\) | Distance traveled by \(Q\) \((\text{cm})\) | Distance traveled by \(R\) \((\text{cm})\) |
|---|---:|---:|---:|---:|---:|
| Hexane, \(\text{C}_6\text{H}_{14}\) | \(1.9\) | \(8.0\) | \(6.4\) | \(3.2\) | \(1.6\) |
| Ethyl acetate, \(\text{CH}_3\text{COOCH}_2\text{CH}_3\) | \(6.0\) | \(5.0\) | \(4.5\) | \(3.5\) | \(2.0\) |

The retention factor is defined as
\[
R_f=\dfrac{\text{distance traveled by analyte}}{\text{distance traveled by solvent front}}
\]

Which choice best identifies the most polar analyte and explains the effect of replacing hexane with ethyl acetate?

- **A.** Analyte \(R\) is the most polar because the higher-\(\varepsilon_r\) mobile phase strengthens the attraction between \(R\) and the polar stationary phase, causing its \(R_f\) to increase.
- **B.** Analyte \(R\) is the most polar because it has the smallest \(R_f\) in both mobile phases, and ethyl acetate competes more strongly than hexane for interactions with the polar stationary phase, increasing the \(R_f\) values of all the analytes.
- **C.** Analyte \(Q\) is the most polar because its \(R_f\) increases by \(0.30\), the largest change caused by increasing \(\varepsilon_r\).
- **D.** Analyte \(P\) is the most polar because it has the largest \(R_f\) in both mobile phases, indicating the strongest attraction to each mobile phase.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120042/*