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title: "A student investigates two structural isomers with the molecular formula \\(\\text{C}_2\\text{H}_2\\text{Cl}_2\\): *cis*-1,2-dichloroethene and *trans*-1,2-dichloroethene. Chlorine is substantially more electronegative than carbon, creating polar \\(\\text{C}-\\text{Cl}\\) bonds in both molecules. The student hypothesizes that the *cis* isomer possesses a net molecular dipole moment, whereas the *trans* isomer is nonpolar because its individual bond dipoles cancel due to symmetry. Which of the following experimental observations would provide the best evidence to identify an unknown liquid sample as the *cis* isomer rather than the *trans* isomer?"
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url: "https://nerd-notes.com/ubq/121409/"
date_modified: "2026-08-23T05:02:08+00:00"
---

# A student investigates two structural isomers with the molecular formula \(\text{C}_2\text{H}_2\text{Cl}_2\): *cis*-1,2-dichloroethene and *trans*-1,2-dichloroethene. Chlorine is substantially more electronegative than carbon, creating polar \(\text{C}-\text{Cl}\) bonds in both molecules. The student hypothesizes that the *cis* isomer possesses a net molecular dipole moment, whereas the *trans* isomer is nonpolar because its individual bond dipoles cancel due to symmetry. Which of the following experimental observations would provide the best evidence to identify an unknown liquid sample as the *cis* isomer rather than the *trans* isomer?

A student investigates two structural isomers with the molecular formula \(\text{C}_2\text{H}_2\text{Cl}_2\): *cis*-1,2-dichloroethene and *trans*-1,2-dichloroethene. Chlorine is substantially more electronegative than carbon, creating polar \(\text{C}-\text{Cl}\) bonds in both molecules. The student hypothesizes that the *cis* isomer possesses a net molecular dipole moment, whereas the *trans* isomer is nonpolar because its individual bond dipoles cancel due to symmetry. Which of the following experimental observations would provide the best evidence to identify an unknown liquid sample as the *cis* isomer rather than the *trans* isomer?

- **A.** Demonstrating that the sample undergoes complete thermal decomposition into solid carbon, chlorine gas, and hydrogen gas at elevated temperatures.
- **B.** Demonstrating that elemental analysis of the sample yields an empirical formula with a carbon to hydrogen to chlorine mole ratio of \(1:1:1\).
- **C.** Demonstrating that mass spectrometry of the sample produces a parent molecular ion peak corresponding to a molar mass of \(96.9 \text{ g/mol}\).
- **D.** Demonstrating that a thin stream of the liquid sample is deflected when placed in an electric field between two oppositely charged plates.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121409/*