A manufacturer operates an electrolytic cell to coat identical brass fasteners with a…
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A manufacturer operates an electrolytic cell to coat identical brass fasteners with a thin layer of zinc for corrosion resistance. During a quality-control review, two operating parameters are altered independently while all other conditions are held constant.
• Scenario 1: The current delivered to the cell is doubled while plating time remains fixed.
• Scenario 2: The plating time is doubled while current remains fixed.
Assume that temperature, electrolyte composition, stirring rate, and electrode geometry are unchanged, and that the zinc layer forms uniformly over the entire surface of each fastener.
(a) For each scenario, qualitatively predict whether the final zinc coating thickness on a single fastener will increase, decrease, or remain unchanged relative to the original operating conditions. Provide a brief explanation based on the relationships among electric charge passed, moles of electrons transferred, moles of zinc deposited, and geometric considerations.
(b) Compare the mass of zinc deposited in Scenario 1 with the mass deposited in Scenario 2. Explain any similarities or differences in terms of fundamental electrochemical principles.
(c) Suppose that in Scenario 1 the desired coating thickness is exceeded, leading to wasted material. Describe TWO practical adjustments (other than changing current or time) the operator could implement to bring the thickness back to specification, and justify how each adjustment would achieve the goal without compromising coating uniformity.