IB Chemistry IA idea · Electrochemistry and batteries

IB Chemistry IA idea: does an inert salt improve copper plating?

A supporting electrolyte carries current without taking part; test how much it changes the plating.

Electrochemistry and batteries
SL good
HL ideal
Lab Extended Essay potential
Syllabus: R3.2.8, R3.2.15, R3.2.16, S1.4.1, T2

By Photon Academy · Updated 13 November 2026

These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.

Example research question

To adapt, never to copy

How does the concentration of added sodium sulfate in copper(II) sulfate solution (0, 0.10, 0.20, 0.35 and 0.50 mol dm⁻³) affect the mass of copper deposited (g) at a fixed current and time, and the current efficiency?

Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Chemistry IA guide.

Variables

You change: Concentration of added sodium sulfate in copper(II) sulfate solution, 0 to 0.50 mol dm-3 (5 or more values)
You measure: Mass of copper deposited on the cathode (g) at a fixed current and time, and the current efficiency
You keep the same: Current (constant) and time
Electrode area and spacing
Cathode surface preparation and drying
Copper(II) sulfate concentration

Method

Electroplate copper from copper(II) sulfate solutions with different levels of sodium sulfate at constant current, then rinse, dry and weigh the cathode. Compare the mass gained with that expected from Faraday's laws.

Data analysis

Calculate theoretical mass and current efficiency; graph efficiency against electrolyte concentration; propagate uncertainty; assess deposit quality qualitatively as support.

How it works

You change Sodium sulfate concentration (mol dm⁻³) and measure Current efficiency (%) in Copper plating bath, keeping Current, Plating time, Electrode area the same. Expect a graph of Current efficiency / % against Added Na₂SO₄ concentration / mol dm⁻³: Extra ions may help, then add little.

Make it yours

Vary temperature or stirring, and use a second salt for comparison.

Extended Essay angle

Study how electrolyte controls deposit quality, using microscope images or roughness measures.

Safety

Take care with: mains or high-voltage electricity, hazardous chemicals.

Low voltage only. Copper(II) sulfate is harmful and toxic to aquatic life; collect all waste.

Overused classic: the twist has to carry it.

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