---
title: "A student investigates how each of the following solutes partitions between equal-volume layers of water, \\(\\text{H}_2\\text{O}\\), and hexane, \\(\\text{C}_6\\text{H}_{14}\\), at \\(25^\\circ\\text{C}\\).  | Trial | Solute | |——-|——–| | Acid | Dodecanoic acid, \\(\\text{CH}_3(\\text{CH}_2)_{10}\\text{COOH}\\) | | Salt | Sodium dodecanoate, composed of \\(\\text{Na}^{+}\\) and \\(\\text{CH}_3(\\text{CH}_2)_{10}\\text{COO}^{-}\\) |  The concentrations are low enough that aggregation of the solute particles can be neglected. After each mixture reaches equilibrium, the student defines the distribution ratio as \\[ D=\\dfrac{c_{\\mathrm{water}}}{c_{\\mathrm{hexane}}} \\] where each concentration represents the total dissolved solute in that layer. Compared with \\(D\\) for dodecanoic acid, which prediction for \\(D\\) for sodium dodecanoate is best supported?"
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url: "https://nerd-notes.com/ubq/120069/"
date_modified: "2026-08-21T08:41:11+00:00"
---

# A student investigates how each of the following solutes partitions between equal-volume layers of water, \(\text{H}_2\text{O}\), and hexane, \(\text{C}_6\text{H}_{14}\), at \(25^\circ\text{C}\).

| Trial | Solute |
|——-|——–|
| Acid | Dodecanoic acid, \(\text{CH}_3(\text{CH}_2)_{10}\text{COOH}\) |
| Salt | Sodium dodecanoate, composed of \(\text{Na}^{+}\) and \(\text{CH}_3(\text{CH}_2)_{10}\text{COO}^{-}\) |

The concentrations are low enough that aggregation of the solute particles can be neglected. After each mixture reaches equilibrium, the student defines the distribution ratio as
\[
D=\dfrac{c_{\mathrm{water}}}{c_{\mathrm{hexane}}}
\]
where each concentration represents the total dissolved solute in that layer. Compared with \(D\) for dodecanoic acid, which prediction for \(D\) for sodium dodecanoate is best supported?

A student investigates how each of the following solutes partitions between equal-volume layers of water, \(\text{H}_2\text{O}\), and hexane, \(\text{C}_6\text{H}_{14}\), at \(25^\circ\text{C}\).

| Trial | Solute |
|-------|--------|
| Acid | Dodecanoic acid, \(\text{CH}_3(\text{CH}_2)_{10}\text{COOH}\) |
| Salt | Sodium dodecanoate, composed of \(\text{Na}^{+}\) and \(\text{CH}_3(\text{CH}_2)_{10}\text{COO}^{-}\) |

The concentrations are low enough that aggregation of the solute particles can be neglected. After each mixture reaches equilibrium, the student defines the distribution ratio as
\[
D=\dfrac{c_{\mathrm{water}}}{c_{\mathrm{hexane}}}
\]
where each concentration represents the total dissolved solute in that layer. Compared with \(D\) for dodecanoic acid, which prediction for \(D\) for sodium dodecanoate is best supported?

- **A.** \(D\) decreases substantially because replacing \(\text{COOH}\) with \(\text{COO}^{-}\) removes the acid's ability to donate a hydrogen bond to water.
- **B.** \(D\) remains approximately the same because the common \(\text{CH}_3(\text{CH}_2)_{10}\) chain determines the interactions of both solutes with the solvents.
- **C.** \(D\) increases substantially because water stabilizes \(\text{Na}^{+}\) and \(\text{CH}_3(\text{CH}_2)_{10}\text{COO}^{-}\) through ion-dipole interactions, whereas hexane does not effectively stabilize the ions.
- **D.** \(D\) increases substantially because sodium dodecanoate has a larger molar mass and therefore forms stronger London dispersion forces with water than dodecanoic acid does.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120069/*