---
title: "A student tests an electrochemical cell designed to recover copper from a waste solution. One half-cell contains a \\(\\text{Zn(s)}\\) electrode in \\(1.0 \\, \\text{M}\\) \\(\\text{Zn}^{2+}\\text{(aq)}\\), and the other contains a \\(\\text{Cu(s)}\\) electrode in \\(1.0 \\, \\text{M}\\) \\(\\text{Cu}^{2+}\\text{(aq)}\\). The half-cells are connected by a \\(\\text{KNO}_3\\) salt bridge, and no external power source is used. The student proposes that the following half-reaction occurs spontaneously at the zinc electrode.  \\[ \\text{Zn(s)} \\rightarrow \\text{Zn}^{2+}\\text{(aq)} + 2e^- \\]  Which observation would provide the most direct experimental evidence that the proposed oxidation half-reaction occurs spontaneously at the zinc electrode?"
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url: "https://nerd-notes.com/ubq/119504/"
date_modified: "2026-08-21T17:20:11+00:00"
---

# A student tests an electrochemical cell designed to recover copper from a waste solution. One half-cell contains a \(\text{Zn(s)}\) electrode in \(1.0 \, \text{M}\) \(\text{Zn}^{2+}\text{(aq)}\), and the other contains a \(\text{Cu(s)}\) electrode in \(1.0 \, \text{M}\) \(\text{Cu}^{2+}\text{(aq)}\). The half-cells are connected by a \(\text{KNO}_3\) salt bridge, and no external power source is used. The student proposes that the following half-reaction occurs spontaneously at the zinc electrode.

\[
\text{Zn(s)} \rightarrow \text{Zn}^{2+}\text{(aq)} + 2e^-
\]

Which observation would provide the most direct experimental evidence that the proposed oxidation half-reaction occurs spontaneously at the zinc electrode?

A student tests an electrochemical cell designed to recover copper from a waste solution. One half-cell contains a \(\text{Zn(s)}\) electrode in \(1.0 \, \text{M}\) \(\text{Zn}^{2+}\text{(aq)}\), and the other contains a \(\text{Cu(s)}\) electrode in \(1.0 \, \text{M}\) \(\text{Cu}^{2+}\text{(aq)}\). The half-cells are connected by a \(\text{KNO}_3\) salt bridge, and no external power source is used. The student proposes that the following half-reaction occurs spontaneously at the zinc electrode.

\[
\text{Zn(s)} \rightarrow \text{Zn}^{2+}\text{(aq)} + 2e^-
\]

Which observation would provide the most direct experimental evidence that the proposed oxidation half-reaction occurs spontaneously at the zinc electrode?

- **A.** With the circuit open, the voltmeter reads \(+1.10 \, \text{V}\) when its positive lead is connected to the \(\text{Cu(s)}\) electrode.
- **B.** After the circuit is closed, the \(\text{Cu(s)}\) electrode gains mass while \([\text{Cu}^{2+}]\) decreases and electrons enter that electrode through the wire.
- **C.** After the circuit is closed, \(\text{NO}_3^-\text{(aq)}\) ions migrate toward the zinc half-cell while electrical current passes through the external circuit.
- **D.** After the circuit is closed with no external power source, the \(\text{Zn}(s)\) electrode loses mass, \([\text{Zn}^{2+}]\) increases, and electrons flow away from that electrode.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119504/*