---
title: "A student evaluating a solid for use in an oxygen-generating device heats a pure sample of \\(\\text{NaClO}_3\\text{(s)}\\) in a reaction tube. During heating, the solid becomes a colorless liquid and then releases a colorless gas. The gas is collected after the initial air in the apparatus has been displaced. Which observation would provide the most definitive evidence that the sample underwent a chemical change rather than only a phase change?"
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url: "https://nerd-notes.com/ubq/119433/"
date_modified: "2026-08-19T12:40:18+00:00"
---

# A student evaluating a solid for use in an oxygen-generating device heats a pure sample of \(\text{NaClO}_3\text{(s)}\) in a reaction tube. During heating, the solid becomes a colorless liquid and then releases a colorless gas. The gas is collected after the initial air in the apparatus has been displaced. Which observation would provide the most definitive evidence that the sample underwent a chemical change rather than only a phase change?

A student evaluating a solid for use in an oxygen-generating device heats a pure sample of \(\text{NaClO}_3\text{(s)}\) in a reaction tube. During heating, the solid becomes a colorless liquid and then releases a colorless gas. The gas is collected after the initial air in the apparatus has been displaced. Which observation would provide the most definitive evidence that the sample underwent a chemical change rather than only a phase change?

- **A.** The temperature remains constant for two minutes while the visible solid becomes a colorless liquid.
- **B.** The gas collected after the air is displaced relights a glowing splint, while a solid residue remains.
- **C.** The colorless liquid becomes a white solid after the reaction tube returns to room temperature.
- **D.** The mass of the reaction tube and its contents is lower after heating than before heating.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119433/*