---
title: "A student constructs a concentration cell at \\(298\\text{ K}\\) using two identical \\(\\text{Cu(s)}\\) electrodes. Compartment 1 contains \\(100\\text{ mL}\\) of \\(0.010\\text{ M }\\text{CuSO}_4\\text{(aq)}\\) and serves as the anode, while compartment 2 contains \\(100\\text{ mL}\\) of \\(1.0\\text{ M }\\text{CuSO}_4\\text{(aq)}\\) and serves as the cathode. The overall spontaneous cell reaction is represented below.  \\[\\text{Cu}^{2+}\\text{(aq, compartment 2)} \\rightarrow \\text{Cu}^{2+}\\text{(aq, compartment 1)}\\quad E_{\\text{cell}} > 0\\text{ V}\\]  The student then adds excess concentrated \\(\\text{NH}_3\\text{(aq)}\\) to compartment 2, causing the solution to turn dark blue due to the formation of the tetraamminecopper(II) complex ion according to the following equilibrium:  \\[\\text{Cu}^{2+}\\text{(aq)} + 4\\text{NH}_3\\text{(aq)} \\rightleftharpoons [\\text{Cu}(\\text{NH}_3)_4]^{2+}\\text{(aq)} \\quad K_f \\gg 1\\]  Which of the following best predicts the effect of adding excess \\(\\text{NH}_3\\text{(aq)}\\) to compartment 2 on the cell potential, \\(E_{\\text{cell}}\\), and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/123923/"
date_modified: "2026-09-28T12:32:14+00:00"
---

# A student constructs a concentration cell at \(298\text{ K}\) using two identical \(\text{Cu(s)}\) electrodes. Compartment 1 contains \(100\text{ mL}\) of \(0.010\text{ M }\text{CuSO}_4\text{(aq)}\) and serves as the anode, while compartment 2 contains \(100\text{ mL}\) of \(1.0\text{ M }\text{CuSO}_4\text{(aq)}\) and serves as the cathode. The overall spontaneous cell reaction is represented below.

\[\text{Cu}^{2+}\text{(aq, compartment 2)} \rightarrow \text{Cu}^{2+}\text{(aq, compartment 1)}\quad E_{\text{cell}} > 0\text{ V}\]

The student then adds excess concentrated \(\text{NH}_3\text{(aq)}\) to compartment 2, causing the solution to turn dark blue due to the formation of the tetraamminecopper(II) complex ion according to the following equilibrium:

\[\text{Cu}^{2+}\text{(aq)} + 4\text{NH}_3\text{(aq)} \rightleftharpoons [\text{Cu}(\text{NH}_3)_4]^{2+}\text{(aq)} \quad K_f \gg 1\]

Which of the following best predicts the effect of adding excess \(\text{NH}_3\text{(aq)}\) to compartment 2 on the cell potential, \(E_{\text{cell}}\), and provides the correct justification?

A student constructs a concentration cell at \(298\text{ K}\) using two identical \(\text{Cu(s)}\) electrodes. Compartment 1 contains \(100\text{ mL}\) of \(0.010\text{ M }\text{CuSO}_4\text{(aq)}\) and serves as the anode, while compartment 2 contains \(100\text{ mL}\) of \(1.0\text{ M }\text{CuSO}_4\text{(aq)}\) and serves as the cathode. The overall spontaneous cell reaction is represented below.

\[\text{Cu}^{2+}\text{(aq, compartment 2)} \rightarrow \text{Cu}^{2+}\text{(aq, compartment 1)}\quad E_{\text{cell}} > 0\text{ V}\]

The student then adds excess concentrated \(\text{NH}_3\text{(aq)}\) to compartment 2, causing the solution to turn dark blue due to the formation of the tetraamminecopper(II) complex ion according to the following equilibrium:

\[\text{Cu}^{2+}\text{(aq)} + 4\text{NH}_3\text{(aq)} \rightleftharpoons [\text{Cu}(\text{NH}_3)_4]^{2+}\text{(aq)} \quad K_f \gg 1\]

Which of the following best predicts the effect of adding excess \(\text{NH}_3\text{(aq)}\) to compartment 2 on the cell potential, \(E_{\text{cell}}\), and provides the correct justification?

- **A.** \(E_{\text{cell}}\) increases because \([\text{Cu}(\text{NH}_3)_4]^{2+}\text{(aq)}\) is a stronger oxidizing agent than free \(\text{Cu}^{2+}\text{(aq)}\), increasing the reduction potential of compartment 2.
- **B.** \(E_{\text{cell}}\) decreases because complex formation drastically reduces \([\text{Cu}^{2+}]\) in compartment 2, causing the reaction quotient \(Q\) to increase such that \(Q > 1\).
- **C.** \(E_{\text{cell}}\) decreases because adding \(\text{NH}_3\text{(aq)}\) increases the total solution volume, which dilutes \(\text{Cu}^{2+}\text{(aq)}\) and \(\text{SO}_4^{2-}\text{(aq)}\) equally without shifting the equilibrium.
- **D.** \(E_{\text{cell}}\) increases because complex formation consumes product ions from the overall cell reaction, driving the forward process and making \(\Delta G\) more negative.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123923/*