---
title: "A student constructs a galvanic cell at \\(298\\text{ K}\\) based on the following overall reaction:  \\[ \\text{Zn}(s) + \\text{Cu}^{2+}(aq) \\rightarrow \\text{Zn}^{2+}(aq) + \\text{Cu}(s) \\quad E^\\circ_{\\text{cell}} = +1.10\\text{ V} \\]  Initially, both half-cells contain \\(1.0\\text{ M}\\) aqueous solutions. The student then adds a small amount of solid sodium sulfide, \\(\\text{Na}_2\\text{S}(s)\\), to the anode compartment, which causes a precipitate of \\(\\text{ZnS}(s)\\) to form without significantly changing the volume of the solution.  Which of the following best predicts and justifies the effect of adding \\(\\text{Na}_2\\text{S}(s)\\) on the cell potential, \\(E_{\\text{cell}}\\)?"
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url: "https://nerd-notes.com/ubq/123917/"
date_modified: "2026-09-28T12:32:11+00:00"
---

# A student constructs a galvanic cell at \(298\text{ K}\) based on the following overall reaction:

\[ \text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s) \quad E^\circ_{\text{cell}} = +1.10\text{ V} \]

Initially, both half-cells contain \(1.0\text{ M}\) aqueous solutions. The student then adds a small amount of solid sodium sulfide, \(\text{Na}_2\text{S}(s)\), to the anode compartment, which causes a precipitate of \(\text{ZnS}(s)\) to form without significantly changing the volume of the solution.

Which of the following best predicts and justifies the effect of adding \(\text{Na}_2\text{S}(s)\) on the cell potential, \(E_{\text{cell}}\)?

A student constructs a galvanic cell at \(298\text{ K}\) based on the following overall reaction:

\[ \text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s) \quad E^\circ_{\text{cell}} = +1.10\text{ V} \]

Initially, both half-cells contain \(1.0\text{ M}\) aqueous solutions. The student then adds a small amount of solid sodium sulfide, \(\text{Na}_2\text{S}(s)\), to the anode compartment, which causes a precipitate of \(\text{ZnS}(s)\) to form without significantly changing the volume of the solution.

Which of the following best predicts and justifies the effect of adding \(\text{Na}_2\text{S}(s)\) on the cell potential, \(E_{\text{cell}}\)?

- **A.** \(E_{\text{cell}}\) increases because the precipitation of \(\text{ZnS}(s)\) decreases \([\text{Zn}^{2+}]\), which makes \(Q < 1\) and increases the thermodynamic driving force for the forward reaction.
- **B.** \(E_{\text{cell}}\) increases because the precipitate of \(\text{ZnS}(s)\) coats the electrode, increasing the active surface area and lowering the activation energy of the oxidation half-reaction.
- **C.** \(E_{\text{cell}}\) decreases because removing \(\text{Zn}^{2+}(aq)\) increases the value of \(Q\), shifting the system closer to equilibrium.
- **D.** \(E_{\text{cell}}\) decreases because the precipitation of mobile ions lowers the solution conductivity, which decreases the standard cell potential \(E^\circ_{\text{cell}}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123917/*