---
title: "A student sets up an electrolytic cell with inert platinum electrodes to electroplate nickel from an aqueous solution of \\(\\text{Ni(NO}_3)_2\\). A power supply delivers a measured constant current of \\(2.00\\text{ A}\\) for \\(1930\\text{ s}\\). Based on Faraday’s law, the theoretical mass of \\(\\text{Ni(s)}\\) deposited on the cathode is \\(1.17\\text{ g}\\), but after thoroughly drying the cathode, the student measures a mass gain of only \\(0.88\\text{ g}\\).  Which of the following observations provides the most direct evidence that the lower-than-predicted mass was caused by a competing reduction reaction at the cathode rather than an ammeter calibration error?"
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url: "https://nerd-notes.com/ubq/123935/"
date_modified: "2026-09-28T12:32:19+00:00"
---

# A student sets up an electrolytic cell with inert platinum electrodes to electroplate nickel from an aqueous solution of \(\text{Ni(NO}_3)_2\). A power supply delivers a measured constant current of \(2.00\text{ A}\) for \(1930\text{ s}\). Based on Faraday’s law, the theoretical mass of \(\text{Ni(s)}\) deposited on the cathode is \(1.17\text{ g}\), but after thoroughly drying the cathode, the student measures a mass gain of only \(0.88\text{ g}\).

Which of the following observations provides the most direct evidence that the lower-than-predicted mass was caused by a competing reduction reaction at the cathode rather than an ammeter calibration error?

A student sets up an electrolytic cell with inert platinum electrodes to electroplate nickel from an aqueous solution of \(\text{Ni(NO}_3)_2\). A power supply delivers a measured constant current of \(2.00\text{ A}\) for \(1930\text{ s}\). Based on Faraday's law, the theoretical mass of \(\text{Ni(s)}\) deposited on the cathode is \(1.17\text{ g}\), but after thoroughly drying the cathode, the student measures a mass gain of only \(0.88\text{ g}\).

Which of the following observations provides the most direct evidence that the lower-than-predicted mass was caused by a competing reduction reaction at the cathode rather than an ammeter calibration error?

- **A.** Observing a decrease in the \(\text{pH}\) of the solution near the cathode, because the reduction of \(\text{H}^+\text{(aq)}\) produces hydronium ions at the electrode surface.
- **B.** Observing the evolution of gas bubbles at the anode, because the oxidation of water occurs only when the current efficiency at the cathode drops below \(100\%\).
- **C.** Measuring a mass increase on the anode, because unreduced \(\text{Ni}^{2+}\text{(aq)}\) cations migrate to the positively charged electrode and deposit as metal.
- **D.** Observing the evolution of gas bubbles at the cathode accompanied by an increase in local \(\text{pH}\), because the reduction of \(\text{H}^+\text{(aq)}\) consumes protons and diverts electrons from \(\text{Ni}^{2+}\text{(aq)}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123935/*