Electroplating, Purifying Copper and Fuel Cells
Three applications of electrochemistry. The first two use active (non-inert) electrodes, which behave very differently from the graphite ones.
1. Electroplating
ELECTROPLATING coats an object with a thin layer of metal using electrolysis.
Why: to improve appearance, to prevent corrosion, or to give a cheaper metal the properties of an expensive one.
The set-up — three rules:
1. The OBJECT to be plated is the CATHODE (negative) — metal ions are attracted to it and deposited there. 2. The ANODE is made of the PLATING METAL — it dissolves to replenish the solution. 3. The ELECTROLYTE contains ions of the PLATING METAL.
Example — silver-plating a spoon:
- Cathode: the spoon
- Anode: pure silver
- Electrolyte: silver nitrate solution
Half-equations:
Cathode: Ag⁺ + e⁻ → Ag (silver deposited on the spoon) Anode: Ag → Ag⁺ + e⁻ (silver dissolves into solution)
The object is always the CATHODE. Positive metal ions are attracted to the negative electrode — get this the wrong way round and nothing plates.
The anode DISSOLVES and gets lighter; the cathode gets HEAVIER. The concentration of the electrolyte stays constant, because ions are replaced as fast as they are removed.
For a good, even coating: use a low current over a longer time, and make sure the object is clean.
2. Purifying copper
The same principle, applied industrially.
Anode: IMPURE copper. Cathode: PURE copper. Electrolyte: copper(II) sulfate solution.
What happens:
- At the anode, impure copper dissolves: Cu → Cu²⁺ + 2e⁻
- At the cathode, pure copper is deposited: Cu²⁺ + 2e⁻ → Cu
- The impurities fall to the bottom as ANODE SLUDGE (often containing valuable silver and gold)
The anode LOSES mass and the cathode GAINS mass — by the same amount if the current is efficient. This is a favourite exam calculation.
The electrolyte’s concentration does not change, because copper dissolves at the anode as fast as it deposits at the cathode.
3. Active vs inert electrodes
| Inert (graphite, platinum) | Active (copper, silver) | |
|---|---|---|
| Takes part? | no | yes — dissolves at the anode |
| Anode product | a non-metal (O₂, Cl₂) | the metal dissolves |
| Used for | ordinary electrolysis | electroplating, purification |
With inert electrodes, oxygen is released at the anode; with a copper anode, the copper dissolves instead. Recognising which type of electrode you have is the first step in any electroplating question.
4. Simple cells
A simple cell produces electricity from two different metals in an electrolyte.
The bigger the DIFFERENCE in reactivity between the two metals, the LARGER the voltage.
The MORE reactive metal is the NEGATIVE electrode — it loses electrons more readily, and those electrons flow through the wire to the less reactive metal.
Example: magnesium and copper give a larger voltage than zinc and copper, because magnesium and copper are further apart in the reactivity series.
5. Hydrogen–oxygen fuel cells
A FUEL CELL produces electricity directly from the reaction of a fuel with oxygen, without combustion.
The overall reaction: 2H₂ + O₂ → 2H₂O The only product is WATER.
How it works: hydrogen is supplied to one electrode and oxygen to the other. Hydrogen is oxidised, releasing electrons that flow through the external circuit, and they combine with oxygen and hydrogen ions to form water.
Advantages:
- The only product is water — no CO₂, no pollutants at the point of use
- More efficient than a combustion engine, because energy is not lost as heat
- No moving parts, so quiet and reliable
- Does not run down like a battery — it keeps working while fuel is supplied
Disadvantages:
- Hydrogen is difficult and dangerous to STORE and TRANSPORT — it is a highly flammable gas
- Hydrogen is usually manufactured using fossil fuels, so the CO₂ is produced elsewhere
- Expensive catalysts (platinum) are needed
- Limited refuelling infrastructure
The strongest exam answer notes that “no CO₂ at the point of use” is not the same as “no CO₂ overall” — it depends how the hydrogen was made.
6. Mistakes that cost marks
Making the object the anode in electroplating.
Using an inert anode where an active one is needed.
Saying the electrolyte concentration changes in electroplating or copper purification.
Getting the mass changes backwards — anode loses, cathode gains.
Putting electrons on the wrong side of a half-equation.
Saying the less reactive metal is negative in a simple cell.
Saying a fuel cell produces no CO₂ at all, without the qualification.
Forgetting the storage problem for hydrogen.
Frequently asked questions
Which electrode is the object being plated? The cathode (negative).
What is the anode made of? The plating metal, which dissolves.
Why doesn’t the electrolyte run out? The anode dissolves to replace the ions removed at the cathode.
How is copper purified? Impure copper anode, pure copper cathode, copper sulfate electrolyte — impurities fall as anode sludge.
What happens to the electrode masses? The anode loses mass; the cathode gains it.
What is an active electrode? One that takes part in the reaction — such as a copper anode that dissolves.
What makes a simple cell’s voltage larger? A bigger difference in reactivity between the two metals.
Which metal is the negative electrode? The more reactive one.
What is the only product of a hydrogen fuel cell? Water.
What is the main disadvantage of fuel cells? Storing and transporting hydrogen safely — and the CO₂ produced in making the hydrogen.
Quick revision checklist
- I know the object is the cathode in electroplating
- I know the anode is the plating metal
- I know the electrolyte contains the plating metal’s ions
- I can write both half-equations
- I know why the electrolyte concentration is constant
- I can describe copper purification and the anode sludge
- I know which electrode gains and which loses mass
- I can distinguish active from inert electrodes
- I know reactivity difference determines a simple cell’s voltage
- I know the fuel cell equation and that water is the only product
- I can give advantages and disadvantages, including the hydrogen-storage problem
These notes cover electroplating, copper purification and fuel cells in the Cambridge IGCSE Chemistry (0620) syllabus and are written for Grade 9–11 / Year 10–11 students. They are based on teaching patterns observed across a large set of one-to-one IGCSE Chemistry lessons. These were among the less-covered subtopics in that set, so the page follows the syllabus closely rather than being padded. Always check the current syllabus for your own exam series.
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