---
title: "A student conducts an experiment to determine the molar mass of an unknown pure volatile liquid using the vapor density method. A sample of the liquid is completely vaporized in a closed container, and the temperature, pressure, volume, and mass of the vapor are recorded across three separate trials at \\(300\\text{ K}\\).  | Trial | Pressure (\\(\\text{atm}\\)) | Volume (\\(\\text{L}\\)) | Temperature (\\(\\text{K}\\)) | Mass of vapor (\\(\\text{g}\\)) | | :—: | :—: | :—: | :—: | :—: | | 1 | \\(1.00\\) | \\(0.246\\) | \\(300\\) | \\(0.88\\) | | 2 | \\(0.50\\) | \\(0.492\\) | \\(300\\) | \\(0.88\\) | | 3 | \\(0.75\\) | \\(0.246\\) | \\(300\\) | \\(0.66\\) |  The student consults the following reference table of candidate volatile liquids:  | Candidate liquid | Molecular formula | Molar mass (\\(\\text{g/mol}\\)) | | :— | :— | :— | | Ethanol | \\(\\text{C}_2\\text{H}_6\\text{O}\\) | \\(46\\) | | Acetone | \\(\\text{C}_3\\text{H}_6\\text{O}\\) | \\(58\\) | | Diethyl ether | \\(\\text{C}_4\\text{H}_{10}\\text{O}\\) | \\(74\\) | | Ethyl acetate | \\(\\text{C}_4\\text{H}_8\\text{O}_2\\) | \\(88\\) |  Based on the experimental data, which of the candidate liquids is the unknown, and which statement provides the correct justification?"
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url: "https://nerd-notes.com/ubq/123720/"
date_modified: "2026-09-28T12:02:09+00:00"
---

# A student conducts an experiment to determine the molar mass of an unknown pure volatile liquid using the vapor density method. A sample of the liquid is completely vaporized in a closed container, and the temperature, pressure, volume, and mass of the vapor are recorded across three separate trials at \(300\text{ K}\).

| Trial | Pressure (\(\text{atm}\)) | Volume (\(\text{L}\)) | Temperature (\(\text{K}\)) | Mass of vapor (\(\text{g}\)) |
| :—: | :—: | :—: | :—: | :—: |
| 1 | \(1.00\) | \(0.246\) | \(300\) | \(0.88\) |
| 2 | \(0.50\) | \(0.492\) | \(300\) | \(0.88\) |
| 3 | \(0.75\) | \(0.246\) | \(300\) | \(0.66\) |

The student consults the following reference table of candidate volatile liquids:

| Candidate liquid | Molecular formula | Molar mass (\(\text{g/mol}\)) |
| :— | :— | :— |
| Ethanol | \(\text{C}_2\text{H}_6\text{O}\) | \(46\) |
| Acetone | \(\text{C}_3\text{H}_6\text{O}\) | \(58\) |
| Diethyl ether | \(\text{C}_4\text{H}_{10}\text{O}\) | \(74\) |
| Ethyl acetate | \(\text{C}_4\text{H}_8\text{O}_2\) | \(88\) |

Based on the experimental data, which of the candidate liquids is the unknown, and which statement provides the correct justification?

A student conducts an experiment to determine the molar mass of an unknown pure volatile liquid using the vapor density method. A sample of the liquid is completely vaporized in a closed container, and the temperature, pressure, volume, and mass of the vapor are recorded across three separate trials at \(300\text{ K}\).

| Trial | Pressure (\(\text{atm}\)) | Volume (\(\text{L}\)) | Temperature (\(\text{K}\)) | Mass of vapor (\(\text{g}\)) |
| :---: | :---: | :---: | :---: | :---: |
| 1 | \(1.00\) | \(0.246\) | \(300\) | \(0.88\) |
| 2 | \(0.50\) | \(0.492\) | \(300\) | \(0.88\) |
| 3 | \(0.75\) | \(0.246\) | \(300\) | \(0.66\) |

The student consults the following reference table of candidate volatile liquids:

| Candidate liquid | Molecular formula | Molar mass (\(\text{g/mol}\)) |
| :--- | :--- | :--- |
| Ethanol | \(\text{C}_2\text{H}_6\text{O}\) | \(46\) |
| Acetone | \(\text{C}_3\text{H}_6\text{O}\) | \(58\) |
| Diethyl ether | \(\text{C}_4\text{H}_{10}\text{O}\) | \(74\) |
| Ethyl acetate | \(\text{C}_4\text{H}_8\text{O}_2\) | \(88\) |

Based on the experimental data, which of the candidate liquids is the unknown, and which statement provides the correct justification?

- **A.** Ethanol, because applying the standard molar volume of \(22.4\text{ L/mol}\) to the volume of Trial 1 gives an estimated molar mass of \(46\text{ g/mol}\).
- **B.** Acetone, because using the Celsius temperature of \(27^\circ\text{C}\) in place of Kelvin in the ideal gas equation yields an estimated molar mass of \(58\text{ g/mol}\).
- **C.** Diethyl ether, because dividing the average mass of the three trials by the product of average pressure and average volume yields a molar mass of \(74\text{ g/mol}\).
- **D.** Ethyl acetate, because applying \(M = \dfrac{mRT}{PV}\) to each trial consistently yields a molar mass of \(88\text{ g/mol}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123720/*