---
title: "A student performs four separate lab procedures at \\(25^\\circ\\text{C}\\) and atmospheric pressure, recording the initial conditions and final observations in the table below.  | Procedure | Initial system | Manipulation | Final observation | | :— | :— | :— | :— | | 1 | \\(10\\text{ mL}\\) of colorless \\(\\text{KI(aq)}\\) | Added \\(10\\text{ mL}\\) of colorless \\(\\text{Pb(NO}_3)_2\\text{(aq)}\\) | Immediate formation of a bright yellow solid | | 2 | \\(50\\text{ mL}\\) of colorless \\(\\text{H}_2\\text{O(l)}\\) | Added \\(2.0\\text{ g}\\) of white \\(\\text{C}_{12}\\text{H}_{22}\\text{O}_{11}\\text{(s)}\\) with stirring | Solid disappears to form a clear, colorless liquid | | 3 | \\(10\\text{ mL}\\) of dark blue \\(\\text{CuSO}_4\\text{(aq)}\\) | Added \\(40\\text{ mL}\\) of colorless \\(\\text{H}_2\\text{O(l)}\\) with stirring | Mixture becomes a uniform pale blue liquid | | 4 | \\(25\\text{ mL}\\) of colorless \\(\\text{H}_2\\text{O(l)}\\) | Heated from \\(25^\\circ\\text{C}\\) to \\(100^\\circ\\text{C}\\) | Bubbles form and liquid vaporizes as steam |  Based on the observations recorded in the table, which procedure provides the best evidence that a chemical reaction occurred, and why?"
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url: "https://nerd-notes.com/ubq/119668/"
date_modified: "2026-08-21T08:11:59+00:00"
---

# A student performs four separate lab procedures at \(25^\circ\text{C}\) and atmospheric pressure, recording the initial conditions and final observations in the table below.

| Procedure | Initial system | Manipulation | Final observation |
| :— | :— | :— | :— |
| 1 | \(10\text{ mL}\) of colorless \(\text{KI(aq)}\) | Added \(10\text{ mL}\) of colorless \(\text{Pb(NO}_3)_2\text{(aq)}\) | Immediate formation of a bright yellow solid |
| 2 | \(50\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) | Added \(2.0\text{ g}\) of white \(\text{C}_{12}\text{H}_{22}\text{O}_{11}\text{(s)}\) with stirring | Solid disappears to form a clear, colorless liquid |
| 3 | \(10\text{ mL}\) of dark blue \(\text{CuSO}_4\text{(aq)}\) | Added \(40\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) with stirring | Mixture becomes a uniform pale blue liquid |
| 4 | \(25\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) | Heated from \(25^\circ\text{C}\) to \(100^\circ\text{C}\) | Bubbles form and liquid vaporizes as steam |

Based on the observations recorded in the table, which procedure provides the best evidence that a chemical reaction occurred, and why?

A student performs four separate lab procedures at \(25^\circ\text{C}\) and atmospheric pressure, recording the initial conditions and final observations in the table below.

| Procedure | Initial system | Manipulation | Final observation |
| :--- | :--- | :--- | :--- |
| 1 | \(10\text{ mL}\) of colorless \(\text{KI(aq)}\) | Added \(10\text{ mL}\) of colorless \(\text{Pb(NO}_3)_2\text{(aq)}\) | Immediate formation of a bright yellow solid |
| 2 | \(50\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) | Added \(2.0\text{ g}\) of white \(\text{C}_{12}\text{H}_{22}\text{O}_{11}\text{(s)}\) with stirring | Solid disappears to form a clear, colorless liquid |
| 3 | \(10\text{ mL}\) of dark blue \(\text{CuSO}_4\text{(aq)}\) | Added \(40\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) with stirring | Mixture becomes a uniform pale blue liquid |
| 4 | \(25\text{ mL}\) of colorless \(\text{H}_2\text{O(l)}\) | Heated from \(25^\circ\text{C}\) to \(100^\circ\text{C}\) | Bubbles form and liquid vaporizes as steam |

Based on the observations recorded in the table, which procedure provides the best evidence that a chemical reaction occurred, and why?

- **A.** Procedure \(1\), because the formation of an insoluble solid with a distinct color indicates the production of a new substance with new chemical bonds.
- **B.** Procedure \(2\), because the dissolving of the solid indicates that covalent bonds within the sucrose molecules were broken.
- **C.** Procedure \(3\), because the change in color intensity indicates that \(\text{Cu}^{2+}\) ions were chemically converted into a different species.
- **D.** Procedure \(4\), because the production of vapor bubbles indicates that intramolecular \(\text{O}-\text{H}\) bonds were broken.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119668/*