ChemistryICSE Class 10 · Electrolysis

Electroplating and Electrorefining: Nickel, Silver and Copper (ICSE Class 10)

Updated 15 October 2026 · Fact-checked

Electroplating coats an article with a thin layer of another metal by electrolysis. The article is the cathode, the plating metal is the anode, and the electrolyte contains ions of the plating metal. Electrorefining purifies copper: impure copper is the anode, pure copper the cathode, acidified copper sulphate the electrolyte.

Notice the plating metal is the anode and dissolves, while Ni²⁺ ions travel to the iron cathode and deposit, so the solution stays the same.

Illustration drawn for QuestionBuddy.

Understand Electroplating and Electrorefining

Both processes are electrolysis with an active anode: the anode is made of the metal being deposited, so it dissolves as fast as metal is deposited on the cathode, and the concentration of metal ions in the electrolyte stays constant.

Electroplating is the process of depositing a thin, even layer of a superior metal on an article by electrolysis. It is done to protect the article from corrosion (nickel or chromium on iron) and to give it an attractive, shiny finish (silver on cutlery, gold on jewellery).

Three rules fix the set-up:
1. Article to be plated = cathode. Metal ions are reduced and deposited at the cathode: $N i^{2 +} + 2 e^{-} \to N i$ .
2. Plating metal = anode. It is oxidised and dissolves, replacing the ions used up: $N i - 2 e^{-} \to N i^{2 +}$ .
3. Electrolyte = a solution containing ions of the plating metal. For nickel: nickel sulphate solution. For silver: sodium argentocyanide, Na[Ag(CN)₂].

Conditions for a good coat. The article must be clean and free of grease and rust, or the deposit will not stick. A direct current is used: with alternating current the electrodes swap polarity many times a second, so metal deposited in one half-cycle would dissolve in the next. A low current for a longer time gives a smooth, even, firmly adhering layer; a high current gives a rough, loose deposit that peels.

Why sodium argentocyanide for silver? In silver nitrate solution, silver ions are deposited too quickly and the coat is uneven and flaky. Sodium argentocyanide releases Ag⁺ ions slowly and steadily, so silver deposits evenly and adheres well.

Electrorefining of copper. Copper from the furnace contains impurities. In electrolytic refining the impure copper is the anode (a thick block), a thin sheet of pure copper is the cathode, and the electrolyte is acidified copper(II) sulphate solution. At the anode copper atoms lose electrons and go into solution ( $C u - 2 e^{-} \to C u^{2 +}$ ); at the cathode an equal number of Cu²⁺ ions gain electrons and deposit as pure copper ( $C u^{2 +} + 2 e^{-} \to C u$ ). Soluble impurities stay in the solution; insoluble impurities, including precious metals such as silver and gold, collect below the anode as anode mud. The anode becomes thinner, the cathode thicker, and the blue colour of the solution does not fade.

Plating versus refining. In plating the cathode is a different object that receives a thin coat; in refining the cathode is the same metal and grows thick, and the aim is purity, not appearance.

Electroplating and Electrorefining: formulas and key facts

Nickel plating: cathode (article): $N i^{2 +} + 2 e^{-} \to N i$
Nickel plating: anode (pure nickel): $N i - 2 e^{-} \to N i^{2 +}$
Silver plating: cathode and anode: $A g^{+} + e^{-} \to A g; A g - e^{-} \to A g^{+}$
Electrorefining of copper: $Anode: C u - 2 e^{-} \to C u^{2 +}; Cathode: C u^{2 +} + 2 e^{-} \to C u$
Set-up for nickel plating: Electrolyte nickel sulphate solution
Cathode the article (iron key, cup)
Anode block of pure nickel
Current direct, low, for a long time
Set-up for silver plating: Electrolyte sodium argentocyanide solution
Cathode the article (spoon, bangle)
Anode block of pure silver
Current direct, low, for a long time
Set-up for refining copper: Electrolyte acidified copper(II) sulphate solution
Cathode thin sheet of pure copper
Anode thick block of impure copper
Impurities soluble ones stay in solution; insoluble ones form anode mud

Electrolyte	nickel sulphate solution
Cathode	the article (iron key, cup)
Anode	block of pure nickel
Current	direct, low, for a long time

Electrolyte	sodium argentocyanide solution
Cathode	the article (spoon, bangle)
Anode	block of pure silver
Current	direct, low, for a long time

Electrolyte	acidified copper(II) sulphate solution
Cathode	thin sheet of pure copper
Anode	thick block of impure copper
Impurities	soluble ones stay in solution; insoluble ones form anode mud

How to solve Electroplating and Electrorefining questions

Electroplating and refining questions follow a fixed pattern: name the electrolyte and electrodes, write the two electrode equations, give observations and a reason. Answer in that order.

1Decide which object receives the metal: it is always the cathode.
2The anode is a block of the pure metal being deposited (impure copper in refining).
3Name an electrolyte that contains ions of that metal: NiSO₄ for nickel, Na[Ag(CN)₂] for silver, acidified CuSO₄ for copper.
4Write the cathode equation as metal ions gaining electrons, and the anode equation as metal atoms losing electrons, with the right charge on the ion (Ni²⁺, Ag⁺, Cu²⁺).
5State the observations: cathode gains a coat or grows thicker; anode becomes thinner; colour or concentration of the electrolyte stays the same.
6Add the conditions if asked: clean article, direct current, low current for a long time.

Electroplating and Electrorefining in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Designing a silver-plating cell

Suppose a small jewellery workshop wants to give a copper bangle a thin, shiny silver coat that will not peel.

Describe the cell it should set up: electrolyte, cathode, anode, the electrode reactions and two conditions for a good coat.

Try it first, then show the solutionSolution

The bangle receives silver, so it is the cathode; a block of pure silver is the anode.
Electrolyte: sodium argentocyanide solution, which releases Ag⁺ ions slowly and steadily.
Cathode: $A g^{+} + e^{-} \to A g$ ; anode: $A g - e^{-} \to A g^{+}$ .
Clean and degrease the bangle; pass a low direct current for a longer time.

Answer: Bangle as cathode, pure silver anode, sodium argentocyanide electrolyte, clean surface and a low direct current for a long time.

Memory hook: The thing you want to coat goes to the cathode: 'Cathode Collects the Coat'.

Tricks to remember Electroplating and Electrorefining

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cathode Collects the Coat
The article, which collects the metal coat, is always the cathode. The donor metal is the anode.
Use it when: Placing the article and the plating metal correctly.
Low and slow
Low current, long time, direct current: 'Low and slow, never AC'.
Use it when: Conditions for good electroplating.
Mud under the anode
In refining, rubbish falls off the impure anode and sits under it as anode mud.
Use it when: Where the impurities go.

Electroplating and Electrorefining: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Electrolyte for silver plating · 1 mark · MCQBoard level

The electrolyte used for silver plating a steel spoon is:
(a) silver nitrate
(b) sodium argentocyanide
(c) silver chloride
(d) sodium chloride

Try it first, then show the solutionSolution

The electrolyte must contain silver ions and release them slowly for an even coat.
Silver chloride is insoluble; silver nitrate deposits too quickly.

Answer: (b) sodium argentocyanide.

Example 2: Nickel plating an iron key · 2 marks · Short answerBoard level

An iron key is to be electroplated with nickel. Name (a) the electrolyte, (b) the cathode, (c) the anode.

Try it first, then show the solutionSolution

(a) Nickel sulphate solution (contains Ni²⁺ ions).
(b) The iron key (the article to be plated).
(c) A block of pure nickel.

Answer: (a) Nickel sulphate solution (b) the iron key (c) pure nickel.

Example 3: Reactions and observations in nickel plating · 3 marks · Short answerHarder board level

For the nickel plating of an iron key: (a) write the reaction at each electrode, (b) state what is observed at each electrode, (c) explain why the concentration of Ni²⁺ ions in the electrolyte does not change.

Try it first, then show the solutionSolution

(a) Cathode: $N i^{2 +} + 2 e^{-} \to N i$ . Anode: $N i - 2 e^{-} \to N i^{2 +}$ .
(b) A greyish-white layer of nickel forms on the key; the nickel anode gradually becomes thinner.
(c) Each Ni²⁺ ion removed at the cathode is replaced by one formed at the anode.

Answer: (a) As above. (b) Key coated with nickel; anode wears away. (c) Ions removed at the cathode are replaced at the same rate from the anode.

Example 4: Refining copper · 4 marks · Long answerHarder board level

Copper is purified by electrolysis. State (a) the electrolyte, (b) the material of the anode and of the cathode, (c) the reaction at each electrode, (d) what happens to the impurities.

Try it first, then show the solutionSolution

(a) Acidified copper(II) sulphate solution.
(b) Anode: thick block of impure copper. Cathode: thin sheet of pure copper.
(c) Anode: $C u - 2 e^{-} \to C u^{2 +}$ . Cathode: $C u^{2 +} + 2 e^{-} \to C u$ .
(d) Soluble impurities remain in solution; insoluble impurities settle below the anode as anode mud.

Answer: Acidified CuSO₄; impure copper anode, pure copper cathode; copper dissolves at the anode and deposits at the cathode; impurities stay in solution or form anode mud.

Example 5: Spot the errors · 4 marks · Long answerHOTS / competency

A student tries to silver-plate a brass medal. She uses silver nitrate solution, connects the medal to the positive terminal and a silver rod to the negative terminal, uses an AC supply and passes a large current for two minutes. Identify four mistakes and correct each one.

Try it first, then show the solutionSolution

Medal at the positive terminal makes it the anode: it should be the cathode (negative terminal); the silver rod should be the anode.
AC reverses polarity, so any silver deposited would dissolve again: use direct current.
A large current for a short time gives a rough, flaky deposit: use a low current for a longer time.
Silver nitrate releases Ag⁺ too quickly for an even coat: use sodium argentocyanide solution.

Answer: Medal must be the cathode and silver the anode; use DC; use a low current for a long time; use sodium argentocyanide instead of silver nitrate.

Example 6: Inert anode in a plating bath · 3 marks · Short answerHOTS / competency

In a nickel-plating bath the nickel anode is replaced by a platinum anode. Nickel sulphate is still the electrolyte. (a) What is now formed at the anode? (b) What happens to the concentration of Ni²⁺ ions and to the solution over time? (c) Why does plating eventually stop?

Try it first, then show the solutionSolution

(a) Platinum is inert, so an anion is discharged: OH⁻ (in preference to SO₄²⁻) gives oxygen, $4 O H^{-} - 4 e^{-} \to 2 H_{2} O + O_{2}$ .
(b) Ni²⁺ ions are removed at the cathode but not replaced, so their concentration falls; H⁺ and SO₄²⁻ are left behind and the solution becomes acidic.
(c) When the Ni²⁺ ions are used up there is nothing left to deposit.

Answer: (a) Oxygen. (b) Ni²⁺ concentration falls and the solution turns acidic. (c) Ni²⁺ ions run out because the anode no longer replaces them.

Where students lose marks in Electroplating and Electrorefining

The slips examiners see most often, and what to write instead.

Mistake: Naming the cathode without the reason
In 2024 (Q2(i)) examiners noted that candidates said the article goes at the cathode but did not say that Ni²⁺ ions are reduced and deposited there.
Do this: Write: 'The article is the cathode because Ni²⁺ ions gain electrons there and nickel is deposited on it.'
Usually costs: 1 mark.
Mistake: Reversed or wrongly charged electrode equation
Examiners reported the cathode equation written in reverse (Ni → Ni²⁺) or with the wrong valency (2024 Q2(i)).
Wrong working
Cathode: Ni → Ni²⁺ + 2e⁻
Right working
Cathode: Ni²⁺ + 2e⁻ → Ni
Do this: At the cathode ions gain electrons; at the anode atoms lose electrons. Nickel ion is Ni²⁺, silver ion Ag⁺.
Usually costs: 1 mark per equation.
Mistake: Wrong plating conditions
Candidates wrote 'large current' or 'no change at the anode' (2024 Q2(i)).
Do this: Low current for a long time, direct current; the anode gradually dissolves.
Usually costs: 1 mark.
Mistake: Wrong silver anode reaction
In 2025 (Q2(iii)) examiners found candidates unsure of the anode reaction, Ag → Ag⁺ + e⁻.
Do this: The anode metal itself is oxidised: one silver atom loses one electron.
Usually costs: 1 mark.

Exam tips

Learn the three set-ups (nickel plating, silver plating, copper refining) as tables; Section B questions often give a diagram and ask you to label it.
Always write ionic electrode equations with the electrons shown; the examiner accepts $N i - 2 e^{-} \to N i^{2 +}$ or $N i \to N i^{2 +} + 2 e^{-}$ .
When asked for an observation, describe what you would see (coat on the article, anode thinner, colour unchanged), not just the equation.
Electrorefining is listed for reference in Metallurgy, but its equations are required in Electrolysis.

Practice questions on Electroplating and Electrorefining

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
In the electrorefining of copper, the impure copper is made:
(a) the cathode
(b) the anode
(c) the electrolyte
(d) both electrodes
Hint
Which electrode dissolves?
Answer
(b) the anode.
Q2 · 1 mark · Very short answerBoard level
Define electroplating.
Hint
Thin layer, by electrolysis.
Answer
Electroplating is the process of depositing a thin layer of a superior metal on an article by electrolysis.
Q3 · 1 mark · Very short answerBoard level
Why must an article be cleaned and degreased before it is electroplated?
Hint
Think about how well the coat sticks.
Answer
Grease, dirt or rust prevent the metal from depositing evenly and sticking firmly; the coat would be patchy and would peel.
Q4 · 2 marks · Short answerHarder board level
Why is a low current passed for a longer time during electroplating?
Hint
Compare the deposit from a high current.
Answer
A low current deposits metal slowly, giving a smooth, uniform and firmly adhering coat. A high current deposits metal quickly as a rough, loose layer that peels off.
Q5 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Sodium argentocyanide is used instead of silver nitrate for silver plating.
Reason (R): Sodium argentocyanide releases silver ions slowly and steadily.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Fast deposition gives an uneven coat.
Answer
(a).
Q6 · 2 marks · Short answerHarder board level
In silver plating, write the reaction at the anode and name the electrode that loses mass.
Hint
The anode is a silver block.
Answer
$A g - e^{-} \to A g^{+}$ (or $A g \to A g^{+} + e^{-}$ ). The silver anode loses mass.
Q7 · 3 marks · Short answerHarder board level
Give three differences between electroplating with nickel and electrorefining of copper.
Hint
Purpose, nature of the cathode, what the anode is.
Answer
(1) Purpose: plating gives a protective or decorative coat; refining purifies a metal. (2) Cathode: in plating, the article (a different metal); in refining, a thin sheet of pure copper. (3) Anode: in plating, pure nickel; in refining, impure copper, which leaves anode mud. (Also: electrolyte NiSO₄ versus acidified CuSO₄.)
Q8 · 2 marks · Short answerHOTS / competency
Suppose a nickel-plated iron cup gets a deep scratch and rust appears only along the scratch after a few weeks. Explain why the rest of the cup does not rust and why the scratch does.
Hint
What does the nickel layer do?
Answer
The nickel coat keeps air and moisture away from the iron underneath, so the coated surface does not rust. The scratch removes the coat, exposing iron to air and moisture, so iron rusts there.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Electrolyte for nickel plating?Show answer
Nickel sulphate solution.
2.Which electrode is the article in electroplating?Show answer
The cathode.
3.What is anode mud?Show answer
Insoluble impurities that collect below the impure copper anode during refining.
4.Why is AC not used for electroplating?Show answer
It reverses the electrodes, so the deposited metal would dissolve again.
5.Electrolyte in the refining of copper?Show answer
Acidified copper(II) sulphate solution.
6.Two reasons for electroplating?Show answer
To prevent corrosion and to give an attractive finish.

Electroplating and Electrorefining: frequently asked questions

Why is the article made the cathode in electroplating?

Metal ions in the electrolyte are positive, so they move to the cathode, gain electrons and are deposited as metal on whatever is at the cathode.

Why does the electrolyte concentration stay constant in electroplating?

The anode is made of the plating metal and dissolves, producing ions at the same rate as they are deposited at the cathode.

Why is silver nitrate not used for silver plating?

It deposits silver too quickly, giving an uneven, loosely held coat. Sodium argentocyanide supplies Ag⁺ ions slowly, so the coat is even and firm.

What happens to the impurities during electrorefining of copper?

Soluble impurities stay in the solution; insoluble ones, including precious metals, settle under the anode as anode mud.